Details of a Researcher - ISHIGAMI Genya

Papers - ISHIGAMI Genya

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Evaluating and advancing scaling methods for reliable wheel mobility prediction in low-gravity environments

Omura T., Ishigami G.

Journal of Terramechanics 122 2026.04

ISSN 00224898

Predicting wheel mobility in low-gravity environments through Earth-based gravity tests offers a practical alternative to expensive parabolic flights and computationally intensive numerical simulations. However, an optimal scaling method for varying wheel speeds remains unidentified. This study systematically evaluated three scaling methods — Granular Scaling Laws (GSL), reduced-weight tests, and equal-mass tests — using Discrete Element Method simulations at three wheel angular velocities (π/10, π, and 2π rad/s). The methods were assessed based on their accuracy in predicting horizontal velocity, slip ratio, sinkage, and power consumption under free-driving conditions. GSL maintained errors below 5% across all conditions, while the equal-mass test showed velocity-dependent degradation with errors reaching 234% at high speeds. The reduced-weight test underestimated sinkage by over 100%, risking vehicle immobilization. An analytical framework employing an inertial number was developed to quantify soil flow characteristics, facilitating a comprehensive comparative analysis of the scaling methods. This analysis revealed that the equal-mass test inadequately captured dynamic flow phenomena, accounting for its velocity-dependent degradation. Conversely, GSL accurately reproduced soil flow characteristics under all conditions, enabling precise mobility predictions over a broad velocity range. These findings establish GSL as the most accurate and practical scaling approach for extraterrestrial rover mobility design and analysis.

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Deep probabilistic traversability with test-time adaptation for uncertainty-aware planetary rover navigation

Endo, M., Taniai, T., Ishigami, G.

SCIENTIFIC REPORTS 16 ( 1 ) 2026.02

ISSN 2045-2322

Traversability assessment of deformable terrain is vital for safe rover navigation on planetary surfaces. Machine learning (ML) is a powerful tool for traversability prediction but faces predictive uncertainty. This uncertainty leads to prediction errors, increasing the risk of wheel slips and immobilization for planetary rovers. To address this issue, we integrate principal approaches to uncertainty handling -- quantification, exploitation, and adaptation -- into a single learning and planning framework for rover navigation. The key concept is \emph{deep probabilistic traversability}, forming the basis of an end-to-end probabilistic ML model that predicts slip distributions directly from rover traverse observations. This probabilistic model quantifies uncertainties in slip prediction and exploits them as traversability costs in path planning. Its end-to-end nature also allows adaptation of pre-trained models with in-situ traverse experience to reduce uncertainties. We perform extensive simulations in synthetic environments that pose representative uncertainties in planetary analog terrains. Experimental results show that our method achieves more robust path planning under novel environmental conditions than existing approaches.

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Exhaustive evaluation of microgravity landing dynamics for small body exploration

Otsuki M., Baba M., Imada T., Yamato M., Ohashi T., Takahashi M., Himeno T., Maeda T., Ozaki S., Ishigami G., Kobayashi T., Kitazono K.

Acta Astronautica (Elsevier BV) 238 1 - 12 2026.01

ISSN 00945765

Landing dynamics play a crucial role in the success of planetary missions, particularly in low-gravity environments, and determining optimal landing sites continues to be challenging. This paper reports a method for landing safety evaluation based on spacecraft dynamics for landings on the surface layer of small bodies in the Martian moons exploration project. Unlike conventional short-duration contact explorations, spacecraft designed for the exploration of Martian moons will remain on the surface of Phobos for several hours post landing. Owing to low gravitational forces, small bodies exhibit an inadequate restoring force, which can result in overturning and rebounding of the spacecraft; moreover, the gravitational forces on Martian moons are several tens of times greater than that on other small bodies, such as Ryugu and Itokawa, necessitating a consideration of the impact acceleration during landing. In this study, a distinctive model was constructed based on low-gravity experimental results, with the capacity to replicate the flexibility of the spacecraft structure, tank sloshing, shock absorption, and interaction with the surface layer. Subsequently, we confirmed the unique behaviors of the spacecraft during its landing simulation on authentic terrain, and candidate landing areas were evaluated based on nine safety criteria. This evaluation process entailed the identification of safe landing areas, yielding a 20% reduction in the number of safe landing sites compared with that based exclusively on terrain.

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Slope-aware Adaptive Gaussian Process Sampling for Robotic Information Gathering on Rough Terrain

Tazaki M., Ishigami G.

2026 IEEE SICE International Symposium on System Integration Sii 2026 1619 - 1625 2026

Wheeled robots are increasingly utilized for environmental exploration and data collection in environments inaccessible to humans, such as the lunar surface. While adaptive sampling methods like the Upper Confidence Bound (UCB) can balance the trade-off between exploration and measurement data exploitation to model Regions of Interest (ROI), they do not explicitly incorporate robot traversability into the trade-off. Consequently, when faced with multiple scientifically promising locations, the UCB may select paths for the robot that are costly in terms of travel time, leading to time-inefficient surveys, particularly in sloped terrain. To address this limitation, we propose the Slope-aware Upper Confidence Bound (SaUCB), a novel acquisition function that integrates a traversability score based on terrain slope directly into the decision-making process. This allows the robot to explicitly balance exploration, exploitation, and traversal time. Through an extensive simulation study in realistic geological features of lunar terrain models, we demonstrate that the proposed approach generates significantly more time-efficient survey paths. Our method also demonstrates an improved trade-off between investigation time and modeling accuracy within the ROI compared to conventional approaches.

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Maneuverability Ellipsoid for Analyzing Sampling Space of Model Predictive Path-Integral Control for 4WIDS Robot Navigation

Ueda R., Ishigami G.

2026 IEEE SICE International Symposium on System Integration Sii 2026 545 - 552 2026

Four-wheel independent drive and steering (4WIDS) robot possesses high maneuverability, with exploiting its stemming 8-DoF (Degrees of Freedom) control inputs, for navigation itself in complex, obstacle-rich environments. In such scenarios, Model Predictive Path Integral (MPPI) control, a sampling-based approach to model predictive control, has emerged as a powerful technique. While MPPI can effectively handle nonlinear dynamics and non-differentiable cost functions, it confronts the fundamental challenge of curse of dimensionality, where the number of required samples grows exponentially with the dimension of the control space. Although dimensionality reduction of the control space is a known countermeasure for suppressing the computational burden of MPPI, a systematic analysis for rationally designing the reduced space remains as an open issue. This research therefore addresses this issue by first proposing a novel metric, Maneuverability Ellipsoid of the 4WIDS, to quantify the robot's maneuvering capability with regard to the multiple DoFs of the robot control inputs. Based on this ellipsoid, we numerically analyze a sampling method for selecting variables that contribute higher maneuverability in the MPPI framework. The robot maneuverability index is also proposed that is quantified by the size and shape of the manipulability ellipsoid. Through simulations, we demonstrate that this index significantly correlates with the success rate of robot navigation.

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Energy-Efficient Objects Collection with Tethered Mobile Robots Twins with Dynamic Grouping of Scattered Objects

Nakamura H., Nagai H., Ishigami G.

2026 IEEE SICE International Symposium on System Integration Sii 2026 1579 - 1586 2026

This paper addresses an energy-efficient object collection problem using two mobile robots twins, equipped with a flexible tool such as a net or tether. This problem is subject to a routing problem for a collection sequence that minimizes total energy consumption of both robots for collecting scattered, multiple objects. To this end, we propose a dynamic programming-based route planning method, where the robot state is defined by energy consumption and its position. As the flexible tool allows the robots to collect a number of objects all at once, we implement a grouping circle of the tool, the radius of which depends on the number of the collected objects. The method incorporates a load-dependent velocity model as well as the load-dependent radius of object grouping circles to realistically reflect robot dynamics during the cooperative collection and transportation of the objects. Simulations were conducted under various scenarios with different object distributions, start positions of the robots, and the maximum velocities of the robots. The simulation results demonstrate that the proposed method reduces both energy consumption and travel time compared to baseline methods.

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Granular Scaling Laws for accurate prediction of wheel mobility on slopes in low-gravity environments

Takuya Omura, Genya Ishigami

Journal of Terramechanics (Elsevier BV) 120 101085 - 101085 2025.10

ISSN 00224898

This study proposes an enhanced Granular Scaling Law (GSL) for accurately predicting wheel mobility on sloped terrain in low-gravity environments. First, wheel driving simulations were conducted using the Discrete Element Method (DEM) with a lunar regolith simulant under Earth's gravity. The GSL was then applied to convert simulation data obtained under various slope angles and wheel angular velocities into corresponding predictions for lunar gravity. These GSL-based predictions were validated against additional DEM simulations conducted directly under lunar gravity. The comparison revealed that the enhanced GSL accurately predicts four key mobility parameters: wheel horizontal velocity, slip ratio, sinkage, and power consumption, with a mean square percentage error of less than 5%. Notably, the study confirmed that GSL remains effective even in transient states and high-speed driving conditions, where wheel-soil interactions become particularly complex. This comprehensive verification, covering slopes up to ±10∘ and slip ratios ranging from negative to approximately 0.9, demonstrates that the enhanced GSL serves as a highly effective predictive method. It provides a practical framework for exploration rover design and mission planning in low-gravity environments, where precise consideration of wheel-soil interactions is critical.

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DEM-based analysis and optimization of an excavation bucket drum for in-situ resource utilization

Nakano T., Omura T., Galati R., Ishigami G.

Journal of Terramechanics 120 2025.10

ISSN 00224898

The bucket drum, a cylindrical rotating mechanism that efficiently excavates and collects lunar regolith, is essential for in-situ resource utilization (ISRU). While bucket drums offer advantages in energy efficiency and adaptability to low-gravity conditions, optimizing their shape and motion remains an open issue. Therefore, this paper aims to find an optimal design of the bucket drum using the discrete element method (DEM). We focus on five key design parameters were analyzed: two related to bucket shape (scoop throat length and scoop inlet number) and three related to motion (bucket vertical force, horizontal velocity, and angular velocity). These parameters were evaluated based on two performance indices: sand fill ratio and excavation power consumption. By solving the multi-objective problem of maximizing fill ratio while minimizing power consumption, an optimal design of the bucket drum was identified. Subsequently, a bucket drum with the optimal shape was 3D-printed, and the optimal motion of the bucket drum was applied using the soil excavation test apparatus. The test results qualitatively matched the results derived from the DEM analysis. This highlights the validity of the relationship between the design parameters and two performance indices, contributing to the advancement of ISRU excavation technologies.

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Mechanical properties of loose soil during dynamic penetration of landing pad under microgravity

Otsuki M., Maeda T., Ozaki S., Ishigami G., Kobayashi T.

Journal of Terramechanics 120 2025.10

ISSN 00224898

The safety of lunar and planetary exploration is contingent upon a preliminary assessment of the interaction between loose soils composed of regolith that covers a celestial surface and the landing gear of spacecraft, which should be designed in accordance with the findings of the assessment. However, given the issues associated with replicating the surface layer of celestial bodies on Earth, the verification of the gear design can be challenging. Conducting a real-size low-gravity test in the design verification process of a large spacecraft remains cumbersome and resource intensive. As such, drawing valuable knowledge from scale model tests is the only available solution. This paper presents the results and findings of a dynamic penetration test conducted on a scaled landing pad under microgravity using a drop tower. The experimental findings demonstrate that the results of the dynamic penetration of the pad into the regolith simulant are not necessarily indicative of the worst-case scenario of low-gravity conditions and that they are equivalent to the results obtained in the gravitational environment of the earth. This finding suggests that design verification may be feasible through tests using a full-scale spacecraft model.

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Orbital magnetic moments in FeCr2S4 studied by x-ray magnetic circular dichroism

V. K. Verma, J. Patra, V. R. Singh, Y. Nonaka, G. Shibata, K. Ishigami, A. Tanaka, K. Ohgushi, Y. Tokura, T. Koide, A. Fujimori

2025.08

We have investigated the element specific magnetic characteristics of single-crystal FeCr2S4 using x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). We have found that the Fe L2,3-edge XAS spectra do not exhibit clear multiplet structures, indicating strong hybridization between the Fe 3d and S 3p orbitals, leading to delocalized rather than localized electronic states. The Fe 3d and Cr 3d spin moments are antiferromagnetically coupled, consistent with the Goodenough-Kanamori rule. The orbital magnetic moments of Fe and Cr are determined to be -0.23 and -0.017 μB/ion, respectively. The large orbital magnetic moment of Fe is due to the d6 configuration under the relatively weak tetrahedra crystal field at the Fe site, and the delocalized Fe electrons maintain the orbital degree of freedom in spite of their itinerant nature. To understand phenomena such as the gigantic Kerr rotation, it is essential to consider not only the orbital degrees of freedom but also the role of spin-orbit coupling, which induces a finite orbital magnetic moment through t2 and e level hybridization under the tetrahedral crystal field. This finite orbital moment serves as a direct indicator of spin-orbit interaction strength and links element-specific orbital magnetism to the large Kerr rotation. On the other hand, the octahedral crystal-field splitting of the Cr 3d level is large enough to result in the quenching of the orbital moment of the Cr ion in FeCr2S4.

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Design and Development of Jamming-based Stiffness-Adjustable Wheel on Soft Terrain

Suthisomboon, T., Bonardi, S., Ishigami. G.,

Journal of Terramechanics (PERGAMON-ELSEVIER SCIENCE LTD) 117 101014 (11pages) 2025

Research paper (scientific journal), Joint Work, Lead author, Corresponding author, Accepted, ISSN 00224898

Traversing soft terrain poses a major challenge for planetary wheeled rovers, and various studies have demonstrated ways to enhance rover mobility by transforming the wheel structure or adjusting the wheel's stiffness, which results in a change in wheel contact area on the terrain. This paper presents a novel idea using the jamming mechanism for modulating the wheel's stiffness. The developed wheel consists of the core body, wheel outer rim, inner flexure, and cable tension mechanism. The jamming mechanism is realized by adjusting the cable tension inserted between the outer rim of the wheel. The wheel stiffness measuement test confirms that the wheel with low stiffness can reduce its stiffness for 75% of the high stiffness configuration. The wheel's traversability on soft terrain are also evaluated based on slip ratio and current consumption. The results demonstrate that the lower-stiffness configuration outperforms the higher-stiffness wheel under various conditions. These findings, being consistent with previous works on flexible wheels, highlight the potential benefits of the jamming-based stiffness-adjustable wheel for rough terrain traverse with various payload conditions.

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Simultaneous Planning of Path-and-Rendezvous PointsUsing Bidirectional Informed RRT* for UAV-UGV Coordination

Tazaki Minori, Ishigami Genya

Journal of the Robotics Society of Japan (The Robotics Society of Japan) 43 ( 8 ) 811 - 814 2025

ISSN 02891824

Cooperative exploration by unmanned aerial vehicles (UAVs) and unmanned ground vehicles (UGVs) is efficient for long-duration surveys and wider exploration areas. We propose a rendezvous point determination and path planning method that reduces the travel distance between survey points in a UAV-UGV cooperative system, in which the UAV can recharge itself by landing on the UGV. In this study, Bidirectional Informed Rapidly-exploring Random Tree* that selectively extends paths for UAV and UGV in a specific direction is developed. Simulation study in three different terrains confirms that this method can reduce the travel distance by 5–7% compared to existing methods.

DRPA-MPPI: Dynamic Repulsive Potential Augmented MPPI for Reactive Navigation in Unstructured Environments

Fuke T., Endo M., Honda K., Ishigami G.

IEEE International Conference on Automation Science and Engineering 961 - 968 2025

ISSN 21618070

Reactive mobile robot navigation in unstructured environments is challenging when robots encounter unexpected obstacles that invalidate previously planned trajectories. Model predictive path integral control (MPPI) enables reactive planning, but still suffers from limited prediction horizons that lead to local minima traps near obstacles. Current solutions rely on heuristic cost design or scenario-specific pre-training, which often limits their adaptability to new environments. We introduce dynamic repulsive potential augmented MPPI (DRPA-MPPI), which dynamically detects potential entrapments on the predicted trajectories. Upon detecting local minima, DRPA-MPPI automatically switches between standard goal-oriented optimization and a modified cost function that generates repulsive forces away from local minima. Comprehensive testing in simulated obstacle-rich environments confirms DRPA-MPPI's superior navigation performance and safety compared to conventional methods with less computational burden.

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Drawbar pull experiment and analysis of grousered-track unit on sandy terrain

Azuma R., Maeda T., Horie K., Miyai S., Sugimura S., Ishigami G.

Proceedings of the 55th Conference of the Istvs Istvs 2025 52 - 57 2025

Tracked vehicles are commonly used on construction sites because of their high vehicle stability and traversability with large ground contact area. Grousers attached to the track shoe enhance vehicle stability and traversability, mitigating the risk of slipping on rough terrain. While many past studies investigated the mechanical effect of a single grouser shoe, experimental test of an entire grousered-track unit remains limited due to non-uniform stress distribution of the track unit on the ground. In this study, we developed an experimental apparatus with a grousered-track unit and conducted drawbar pull experiment on sandy terrain. We measured the slip ratio and sinkage of the track unit with various traction load corresponding to the drawbar pull of the track unit. The relationship between the drawbar pull coefficient, which is the ratio of the drawbar pull to the vertical load of the track, and the slip ratio was examined. The experiments confirmed that the slip ratio remains constant when the drawbar pull coefficient is approximately 0.4 or lower. Within this range, the track unit maintains small sinkage and a stable driving state. However, when the drawbar pull coefficient exceeds approximately 0.45, the slip ratio sharply increases as larger traction load cases the track unit to an unstable driving state by repeating the move-and-stop motion. This trend was observed regardless of the varied vertical load. These findings suggest that the relationship of the slip-drawbar pull coefficient and the threshold for stable/unstable driving state are useful for evaluating the traversability of the grousered-track unit.

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Physics-Based Torque Prediction Model for Excavating Drums on Granular Soil

Galati R., Nakano T., Ishigami G., Reina G.

Journal of Field Robotics 43 ( 3 ) 2237 - 2253 2025

ISSN 15564959

Accurate torque prediction for excavating drums is critical for the design and autonomous control of planetary rovers operating in loose, unstructured regolith. Existing terramechanics models may fail to capture the full dynamics of rotating excavation drums. In this paper, we present a unified, physics-based torque prediction model with two novel dynamic effects: a longitudinal, velocity-sensitive bulldozing resistance term that grows logarithmically with forward speed, and a regolith-accumulation torque that evolves as the drum buckets fill. We validate our approach on a custom four-wheel holonomic rover excavating Silica Sand No. 5 across multiple test sequences spanning different angular and translational velocities. The model achieves a normalized RMSE generally below 12%, an MAE under 0.15 Nm, and (Formula presented.), in nearly all cases, accurately reproducing the temporal evolution toward steady-state torque plateaus. Its modular structure and reliance on minimal empirical tuning make it suitable for real-time torque estimation in future autonomous planetary missions.

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Development of Bucket Drum Excavation System with Reaction Force Control for In-Situ Resource Utilization

Nakano T., Omura T., Ishigami G.

2025 International Conference on Space Robotics Isparo 2025 490 - 497 2025

This paper presents the development and experimental evaluation of a bucket drum excavation system for InSitu Resource Utilization (ISRU). A custom-designed bucket drum, equipped with a vertical lift mechanism for reaction force control during excavation, has been developed and mounted on a mobile robotic platform. Experiments under varying target reaction force conditions demonstrated the controller's suitability and effectiveness. Additionally, excavation performance was compared under two scenarios: when the robot was stationary and while it was in motion. Results showed that the excavation by bucket drum in robot motion was more energy efficient since the bucket drum can excavate fresh and uncompacted soil. These findings highlight the potential of reaction force control for the bucket drum mounted on mobile robotic platforms.

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Design, Development, and Motion Analysis of Robotic Arm for Rover Rescue from Sand Traps

Hanaoka Nahoko, Ishigami Genya

Journal of the Robotics Society of Japan (The Robotics Society of Japan) 43 ( 7 ) 699 - 702 2025

ISSN 02891824

The construction of lunar infrastructure is crucial for future human activities. Unmanned vehicles, such as rovers, serve as key mobility systems for construction tasks but face the risk of becoming trapped by sand and immobilized on uneven terrains. This paper focuses on a scenario where a rover being stuck is rescued by another rover via a robotic manipulator. We design and prototype a two-link robotic manipulator and conduct dynamic simulation along with experimental demonstrations. The experimental result are generally consistent with simulation results, particularly in terms of identifying the energy-efficient configurations of the manipulator for effective rescue operations.

Non-contact seesaw-type force sensor for evaluation of force characteristics of soft actuators

SATO Soya, HOKIGUCHI Shigetora, ASAI Makoto, ISHIGAMI Genya, TAKAHASHI Hidetoshi

The Proceedings of JSME annual Conference on Robotics and Mechatronics (Robomec) (The Japan Society of Mechanical Engineers) 2025 ( 0 ) 1A2-R05 2025

Soft actuators are constrained in their deformation when subjected to loads, so their performance needs to be evaluated similarly to that of conventional motors. In this study, we propose a seesaw-type force sensor consisting of a beam with multiple load points having different spring constants and a laser displacement meter. The relationship between force and displacement is evaluated by applying force from a soft actuator and measuring the displacement. The load points of the fabricated seesaw-type beams had spring constants ranging from 1.2 N/m to 15.9 N/m. The soft actuators were ionic polymer-metal composite (IPMC) actuators with a size of 5 mm × 25 mm and a thickness of 190 μm. In the experiment with the IPMC actuator, the force was high and the displacement was small at 5.3 mN and 0.3 mm where the spring constant was large, and the opposite trend was observed at 2.3 mN and 1.9 mm where the spring constant was small.

Towards Local Minima-free Robotic Navigation: Model Predictive Path Integral Control via Repulsive Potential Augmentation

Fuke T., Endo M., Honda K., Ishigami G.

2025 IEEE SICE International Symposium on System Integration Sii 2025 1112 - 1117 2025

Model-based control is a crucial component of robotic navigation. However, it often struggles with entrapment in local minima due to its inherent nature as a finite, myopic optimization procedure. Previous studies have addressed this issue but sacrificed either solution quality due to their reactive nature or computational efficiency in generating explicit paths for proactive guidance. To this end, we propose a motion planning method that proactively avoids local minima without any guidance from global paths. The key idea is repulsive potential augmentation, integrating high-level directional information into the Model Predictive Path Integral control as a single repulsive term through an artificial potential field. We evaluate our method through theoretical analysis and simulations in environments with obstacles that induce local minima. Results show that our method guarantees the avoidance of local minima and outperforms existing methods in terms of global optimality without decreasing computational efficiency.

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Slope-aware Maximum Uncertainty Sampling for Time-efficient Robotic Mapping on Rough Terrain

Tazaki M., Ishigami G.

2025 International Conference on Space Robotics Isparo 2025 64 - 71 2025

Robotic information gathering methods combining Gaussian Process (GP) regression and Bayesian Optimization (BO) are effective for mapping of soil mechanical properties in uncertain or unknown extraterrestrial terrain. However, standard applications of such methods often model robot traversability as a simple go/no-go constraint, without fully incorporating it as a variable cost that impacts overall efficiency. This limitation is critical on rough terrains like the lunar surface, where traversability heavily influences the trade-off between survey time and modeling accuracy. To address this gap, we propose a comprehensive approach for slope-aware robotic information gathering. The core of this approach is a novel adaptive sampling method, Slope-aware Maximum Uncertainty Sampling (SaMUS), which features a new BO acquisition function that explicitly incorporates terrain slope to balance uncertainty reduction with path traversability. We demonstrate the effectiveness of our method through an extensive simulation study in two environment types: controlled basic terrains for qualitative analysis and realistic lunar terrains for evaluating the performance of the proposed method. The results show that the proposed approach generates significantly more time-efficient survey paths by strategically avoiding highslope regions. Quantitative analysis on the realistic terrains further demonstrates that our method achieves a better tradeoff between survey time and modeling accuracy, particularly on flat and steep terrains. Finally, we provide practical guidelines for selecting optimal parameters based on terrain class and operational time constraints.

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Slip estimation model for traversability-based motion planning of cargo rover on extraterrestrial surface

Nishishita T., Ishigami G.

Frontiers in Robotics and AI 12 2025

ISSN 2296-9144

As part of the robotics technologies required for In-situ resource utilization (ISRU), the development of cargo rovers for transporting resources is needed. However, these cargo rovers have unique technical challenges that differ from conventional exploration rovers, including the need to traverse rough terrains with their varying mass due to transporting payloads. Moreover, research addressing these challenges has been limited, and the relevant technologies have not been fully established. To address these challenges, this paper proposes a parametric model for estimating wheel slippage. The model is formulated as a function of four input parameters: slope angle, rover heading angle, payload mass, and wheel angular velocity, and is applicable to resource-transporting rovers with varying mass. Additionally, the use of a parametric model reduces computational load, which offers advantages for onboard implementation. The proposed estimation model was quantitatively evaluated by comparing datasets obtained from multi-body dynamics analysis. This paper also introduces a new traversability assessment model which incorporates the proposed slip estimation model. We demonstrated the proposed model by integrating it into a sampling based motion planning. The simulation result of the motion planning show that the planner with our model can generate safer motions and enables the rover to reach the target regardless of the cargo payload.

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Snap and Jump: How Elastic Shells Pop Out

Takara Abe, Isamu Hashiguchi, Yukitake Nakahara, Shunsuke Kobayashi, Ryuichi Tarumi, Hidetoshi Takahashi, Genya Ishigami, Tomohiko G. Sano

2024.10

Grip, walk, crawl, and jump. Soft robots are integrated functional structures composed of compliant mechanisms, whose activity spans various industrial applications such as surgery, healthcare, surveillance, and even planetary exploration. One of their promising mobility mechanism is snap-buckling; the instability mode of flexible structures passing from one equilibrium state to another can instantaneously generate large power for its motion. Predicting their performance with even simple geometry requires disentangling material, geometric nonlinearity, and contact, thereby still being a challenging problem to date. Here, we study the jumping dynamics of hemispherical elastic shells driven by snap-buckling, as a model system of soft jumping mechanisms, combining experiments, simulations, and analytical theory. We find that the contact transition dynamics trigger the jumping phenomenon upon snap-buckling by constructing the analytical predictions with shell elasticity in excellent agreement with both experiments and simulations. Despite the simple geometry of the shell, its dynamical performance primarily relies on a complex interplay between elasticity, geometry, and contact friction. By elucidating the dynamics of the building blocks of soft robots that undergo large deformations, we can build their predictive experimental and numerical framework. Our research paves the way for designing soft robots suitable for the required loading conditions or structural requirements without empirical methods.

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Tangle- and Contact-free Path Planning for a Tethered Mobile Robot using Deep Reinforcement Learning

Shimada, R., and Ishigami, G.,

Frontiers in Robotics and AI (Frontiers in Robotics and AI) 11 1388634 (13 pages) 2024.09

Research paper (scientific journal), Joint Work, Lead author, Corresponding author, Accepted, ISSN 2296-9144

This paper presents a tangle- and contact-free path planning (TCFPP) for a mobile robot attached to a base station with a finite-length cable. This type of robot, called a tethered mobile robot, can endure long-time exploration with a continuous power supply and stable communication via its cable. However, the robot faces potential hazards that endanger its operation such as cable snagging on and cable entanglement with obstacles and the robot. To address these challenges, our approach incorporates homotopy-aware path planning into deep reinforcement learning. The proposed reward design in the learning problem penalizes the cable-obstacle and cable-robot contacts and encourages the robot to follow the homotopy-aware path toward a goal. We consider two distinct scenarios for the initial cable configuration: 1) the robot pulls the cable sequentially from the base while heading for the goal, and 2) the robot moves to the goal starting from a state where the cable has already been partially deployed. The proposed method is compared with naive approaches in terms of contact avoidance and path similarity. Simulation results revealed that the robot can successfully find a contact-minimized path under the guidance of the reference path in both scenarios.

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Acoustic Odometry for Wheeled Robots on Loose Sandy Terrain

Andreu Gimenez Bolinches and Genya Ishigami

Proceedings of 13th International Workshop on Robot Motion and Control (RoMoCo2024) 255-260 - 260 2024.07

Research paper (international conference proceedings), Joint Work, Last author, Accepted, ISSN 2575-5579

This work proposes a system capable of estimating the longitudinal velocity of a wheeled robot on loose sandy terrain using only acoustic sensors. These will likely be present anyway in many future ground mobile robots for human-robot interaction purposes. The proposed system consists of an audio feature extraction module, based on gammatone filterbanks, and a prediction module, based on a convolutional neural network. The proposed system has been tested in a single wheel test bed with a wheel driving up to speeds of 0.07 m/s in a wide range of wheel slippage resulting in an average drift of 5 mm/s. A qualitative evaluation of the proposed system against other sources of odometry shows that acoustic and visual methods vulnerabilities do not overlap, which indicates that a system based on acoustic sensors can be a feasible auxiliary source of odometry. The system is able to make a prediction from a single audio frame with a duration of 15 ms in only 2 ms on a user-level commercially available CPU.

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Parameter study and identification of DEM modeling for varied sand moisture content based on bulldozing experiment

Sato N., Ishigami G.

Journal of Terramechanics (Journal of Terramechanics) 113-114 100971 (15 pages) 2024.06

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 00224898

The discrete element method (DEM) has been widely used to simulate varied sand particles interacting with earthmoving machines. However, past research using DEM barely addressed accurate verification and validation for different sand moisture content. Therefore, the main purpose of this paper is to reveal the range of key parameters of an adhesive force model used in the DEM simulation corresponding to the specific sand moisture content. We considered the bulldozing phenomenon to be typical earthmoving work and performed the bulldozing experiments under different sand moisture levels to investigate the bulldozing force variations. Subsequently, the DEM simulation with an adhesive force model calculated the bulldozing force corresponding to the experimental results. The values for two adhesive parameters, i.e., a scaling magnitude and the maximum adhesive distance between particles, were adjusted such that the maximum bulldozing force calculated in the DEM coincides with that of the experiments under different moisture contents. The experimental verification of the DEM revealed the relationship curves between these two key parameters corresponding to the different moisture content. The relationship obtained in this paper implies that the DEM simulation carefully adjusting the adhesive force parameters can reproduce machine interaction on moist sand environments accurately.

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BenchNav: Simulation Platform for Benchmarking Off-road Navigation Algorithms with Probabilistic Traversability

Masafumi Endo, Kohei Honda, Genya Ishigami

2024.05

As robotic navigation techniques in perception and planning advance, mobile robots increasingly venture into off-road environments involving complex traversability. However, selecting suitable planning methods remains a challenge due to their algorithmic diversity, as each offers unique benefits. To aid in algorithm design, we introduce BenchNav, an open-source PyTorch-based simulation platform for benchmarking off-road navigation with uncertain traversability. Built upon Gymnasium, BenchNav provides three key features: 1) a data generation pipeline for preparing synthetic natural environments, 2) built-in machine learning models for traversability prediction, and 3) consistent execution of path and motion planning across different algorithms. We show BenchNav's versatility through simulation examples in off-road environments, employing three representative planning algorithms from different domains. https://github.com/masafumiendo/benchnav

Perception-and-Energy-aware Motion Planning for UAV using Learning-based Model under Heteroscedastic Uncertainty

Reiya Takemura and Genya Ishigami

Proceedings of the 2024 IEEE International Conference on Robotics and Automation (ICRA 2024) pp. 10103-10109 - 10109 2024.05

Research paper (international conference proceedings), Joint Work, Last author, Accepted, ISSN 10504729

Global navigation satellite systems (GNSS) denied environments/conditions require unmanned aerial vehicles (UAVs) to energy-efficiently and reliably fly. To this end, this study presents perception-and-energy-aware motion planning for UAVs in GNSS-denied environments. The proposed planner solves the trajectory planning problem by optimizing a cost function consisting of two indices: the total energy consumption of a UAV and the perception quality of light detection and ranging (LiDAR) sensor mounted on the UAV. Before online navigation, a high-fidelity simulator acquires a flight dataset to learn energy consumption for the UAV and heteroscedastic uncertainty associated with LiDAR measurements, both as functions of the horizontal velocity of the UAV. The learned models enable the online planner to estimate energy consumption and perception quality, reducing UAV battery usage and localization errors. Simulation experiments in a photorealistic environment confirm that the proposed planner can address the trade-off between energy efficiency and perception quality under heteroscedastic uncertainty. The open-source code is released at https://gitlab.com/ReI08/perception-energy-planner.

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Accurate Rover Mobility Analysis Using HILS-DRFT with Real-Time Parameter Tuning Approach

Takahiro Fuke, Sora Ishikawa and Genya Ishigami

Proceedings of the 21st International and 12th Asia-Pacific Regional Conference of the International Society for Terrain-Vehicle Systems 2024.01

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Granular Flow in Reduced Gravity: Analysis and Insights from Centrifuge Experiments at the International Space Station

Takuya Omura and Genya Ishigami

Proceedings of the 21st International and 12th Asia-Pacific Regional Conference of the International Society for Terrain-Vehicle Systems 2024.01

Research paper (international conference proceedings), Joint Work, Last author, Accepted

DEM-Based Analysis and Optimization of Excavation Bucket Drum for In-Situ Resource Utilization

Tomoyasu Nakano, Takuya Omura and Genya Ishigami

Proceedings of the 21st International and 12th Asia-Pacific Regional Conference of the International Society for Terrain-Vehicle Systems 2024.01

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Collaborative Robot Systems for Lunar Landing Pad Construction

Kenji Nagaoka, Genya Ishigami, Munetaka Ueno, Keiji Nagatani

Proc. of the AROB-ISBC-SWARM 2024 pp. 985-986 2024.01

Research paper (international conference proceedings), Joint Work, Accepted

Task force report on study cycles construction for henceforward International Space Exploration sciences

NAMIKI Noriyuki, ISHIGAMI Genya, SAKURAI Masato, INATOMI Yuko, KOBAYASHI Taizo, TERADA Naoki, MIYAMOTO Hideaki, YAMAGISHI Akihiko, YAMADA Toru

Space Utilization Research, Vol. 38 2023: Proceedings of The Thirty-eighth Space Utilization Symposium (宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS)) 2024.01

CiNii Research

車輪ロボットの移動性能を可視化する可操縦性楕円体の提案

Ryo Ueda, Genya Ishigami

Journal of the Robotics Society of Japan (The Robotics Society of Japan) 2024

Research paper (scientific journal), Joint Work, Last author, Accepted

車輪ロボットの移動性能を可視化する可操縦性楕円体の提案

Yuki Goto, Genya Ishigami

Journal of the Robotics Society of Japan (The Robotics Society of Japan) 2024

Research paper (scientific journal), Joint Work, Last author, Accepted

Modeling of slip rate-dependent traversability for path planning of wheeled mobile robot in sandy terrain

Sakayori G., Ishigami G.

Frontiers in Robotics and AI (Frontiers in Robotics and AI) 11 1320261 (16 pages) 2024

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 2296-9144

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DEM-based Analysis for Interaction Mechanics of Tracked Vehicle on Soils Containing Water

Yanagawa Hiroki, Ishigami Genya

Journal of the Robotics Society of Japan (The Robotics Society of Japan) 42 ( 4 ) 406 - 409 2024

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 02891824

Tracked vehicles has been widely used in unstructured environments such as on uneven/deformable terrains. The mobility of the track unit consisting of interconnected metal plates is the key to enhance the safety of the vehicle. This study focuses on the track and soil interaction, particularly the wetted soil. The Distinct Element Method is applied for analyzing the interaction stress between the track and soil with varied moisture content and slip ratio. The analysis revealed that the significant stress is generated to the leading edge of the track unit and the stress distribution shifts toward the rear region of the track in moist soil.

2919 | Accurate Rover Mobility Analysis Using HILS-DRFT with Real-Time Parameter Tuning Approach

Fuke T., Ishikawa S., Ishigami G.

Proceedings of the 21st International and 12th Asia Pacific Regional Conference of the Istvs 99 - 103 2024

Offroad mobility in extraterrestrial exploration can be significantly degraded by vehicle slippage on soft terrain covered with fine powdery sand known as regolith. Comprehensive design analysis and verification of the rover's mobility have been widely investigated using numerical and experimental approaches. Numerical simulations for the mobility analysis require accurate modeling of the contact forces between the wheel and sand. While several wheel-sand interaction models have been proposed based on the Bekker-Wong-Reece theory, the Dynamic Resistive Force Theory (DRFT) proposed in the early 2020s is a notable approach for its low computational cost and adaptability to quasi-dynamic motion. The scaling factor used in DRFT is the only parameter for representing sand-dependent parameters, and its value needs to be empirically tuned to achieve accurate and reliable mobility analysis. Therefore, the authors have integrated a single-wheel test bed into a closed-loop Hardware-In-the-Loop Simulation (HILS) associated with DRFT. This HILS-DRFT experimentally observes the characteristics of the wheel sinking phenomenon in the wheel test bed, and then, the value of the scaling factor is tuned in real-time by the difference between the observed wheel sinkage and the DRFT simulation. This real-time parameter tuning method accurately reproduces wheel mobility, particularly in its transient states, which were previously unachievable with DRFT alone. The proposed HILS-DRFT with the real-time tuning method will contribute to the efficient and reliable development of rovers.

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9295 | Granular Scaling Laws for Accurate Prediction of Wheel Mobility on Slopes in Low-gravity Environments

Omura T., Ishigami G.

Proceedings of the 21st International and 12th Asia Pacific Regional Conference of the Istvs 310 - 316 2024

Analyzing the mobility of wheeled rovers on loose sand in low-gravity environments remains a significant challenge. Among several experimental techniques, such as parabolic flight and reduced-weight tests, granular scaling laws (GSL) have recently been proposed to predict wheel mobility under low-gravity conditions via earth-gravity tests. Although the GSL accurately predicts wheel mobility on flat terrain in low-gravity environments, its capability to predict wheel mobility on slopes in such environments still needs to be verified. This study developed a GSL and investigated its accuracy in predicting wheel mobility on slopes in low-gravity environments. The discrete element method (DEM) was utilized to test wheel mobility at various slope angles under Earth's gravity. Subsequently, by applying a multiple scaling function, the GSL converted the results from the Earth-gravity tests to predict wheel mobility under lunar gravity. The GSL-based predictions were compared with DEM simulations conducted under lunar gravity conditions. The results indicated that the wheel mobility under lunar gravity predicted by the GSL closely corresponded to that calculated via the DEM. These findings indicate that the GSL can accurately predict wheeled-rover mobility on slopes in low-gravity environments.

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4213 | DEM-Based Analysis and Optimization of an Excavation Bucket Drum for In-Situ Resource Utilization

Nakano T., Omura T., Ishigami G.

Proceedings of the 21st International and 12th Asia Pacific Regional Conference of the Istvs 151 - 157 2024

Lunar infrastructure construction involves leveling of the lunar surface and collecting lunar regolith as a building material. RASSOR 2.0 developed by NASA is one of the typical robotic vehicles as a lunar excavator. It features cylindrical rotating bucket drums for collecting regolith, positioning it as a pivotal tool for future lunar in-situ resource utilization and infrastructure development. However, the optimization of the bucket drum's shape and its motion remain as open issue. Therefore, this study aims to find an optimal design of the bucket drum through numerical simulation using the discrete element method (DEM). We introduce five key design parameters of the bucket drum: two of them are related to the bucket shape (scoop throat length, scoop inlet number) and the rest of them are to motion (bucket vertical force, horizontal velocity, and angular velocity). These five parameters were examined in accordance with two performance indices: the sand fill ratio in the drum and the power consumption of the excavation. Solving the multi-objective problem of increasing the fill ratio and reducing power consumption, we found an optimal bucket drum shape and motion. Subsequently, a bucket drum reflecting the optimal shape was fabricated, and the optimal motion was tested. The test results qualitatively matched with the results derived from the DEM analysis. This outcome highlights the validity of the relationship between the design parameters and two performance indices.

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Granular flow experiment using artificial gravity generator at International Space Station

S. Ozaki, G. Ishigami, M. Otsuki, H. Miyamoto, K. Wada, Y. Watanabe, T. Nishino, H. Kojima, K. Soda, Y. Nakao, M. Sutoh, T. Maeda, T. Kobayashi

npj Microgravity (npj Microgravity) 9 ( 1 ) 61 (13 pages) 2023.12

Research paper (scientific journal), Joint Work, Accepted

Studying the gravity-dependent characteristics of regolith, fine-grained granular media covering extra-terrestrial bodies is essential for the reliable design and analysis of landers and rovers for space exploration. In this study, we propose an experimental approach to examine a granular flow under stable artificial gravity conditions for a long duration generated by a centrifuge at the International Space Station. We also perform a discrete element simulation of the granular flow in both artificial and natural gravity environments. The simulation results verify that the granular flows in artificial and natural gravity are consistent. Further, regression analysis of the experimental results reveals that the mass flow rate of granular flow quantitatively follows a well-known physics-based law with some deviations under low-gravity conditions, implying that the bulk density of the granular media decreases with gravity. This insight also indicates that the bulk density considered in simulation studies of space probes under low-gravity conditions needs to be tuned for their reliable design and analysis.

Path Planning Method for Soil Investigation using Mobile Robot

Arai Kohei, Ishigami Genya

Journal of the Robotics Society of Japan (The Robotics Society of Japan) 41 ( 9 ) 813 - 816 2023.11

Research paper (scientific journal), Last author, Accepted, ISSN 02891824

A lunar landing base is a key infrastructure for mass transportation from Earth to the Moon and for sustainable activities on the Moon in the future. Unmanned robots are expected to survey the soil stiffness of multiple points for securely constructing the landing infrastructure. There is a trade-off between the time or energy required for the survey, the number of survey points, and the completeness of the survey. This paper proposes a path planning for robotic soil investigation that determines the location and the number of additional survey points. The proposed method aims to obtain completeness of information related to the soil stiffness as well as to reduce the survey time. The simulation study reveals that the method achieves obtaining a certain level of completeness while it reduces the time required for the survey.

Experimental analysis on jumping mechanism using snap-through buckling of an elastic strip

Shuhei Shimizu, Takara Abe, Tomohiko G. Sano, Genya Ishigami

IUTAM Symposium on Nonlinear dynamics for design of mechanical systems across different length/time scales PS08, (2 pages) 2023.09

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Jumping mechanism of elastic shells on rigid or granular substrates

Takara Abe, Shuhei Shimizu, Genya Ishigami, Tomohiko G. Sano

IUTAM Symposium on Nonlinear dynamics for design of mechanical systems across different length/time scales PS07, (2 pages) 2023.09

Research paper (international conference proceedings), Joint Work, Accepted

UV laser etching process: enhancing bending performance in ionic polymer-metal composites (IPMC)

N. Furusawa, K. Soda, N. Matsuhisa, G. Ishigami, J. Ogawa, M. Asai and H. Takahashi

Proc. of the 14th Japan-China-Korea Joint Conference on MEMS/NEMS 2023 2023-P-022 (2 pages) 2023.09

Research paper (international conference proceedings), Joint Work

Path Planning with Cable-obstacles Avoidance for a Tethered Mobile Robot in Unstructured Environments

Ryuki Shimada and Genya Ishigami

Proceedings of the 34th International Symposium on Space Technology and Science (ISTS 2023) 2023-k-04, (8 pages) 2023.08

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Energy-and-perception-aware planning and navigation framework for unmanned aerial vehicles

Takemura R., Aoki N., Ishigami G.

Advances in Mechanical Engineering (Advances in Mechanical Engineering) 15 ( 4 ) 1 - 17 2023.04

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 16878132

This paper presents an energy and perception aware framework for path planning and navigation of unmanned aerial vehicles (UAVs) in GNSS-denied and spatiotemporal wind environments. The proposed framework mainly consists of the global and local path planning methods that respectively consider the energy consumption of an UAV and perception quality of a light detection and ranging (LiDAR) sensor mounted on the UAV. The energy consumption is estimated based on the aerodynamic model that calculates drag and lift forces on the UAV. The global planner then uses the total energy consumption in the spatiotemporal wind as the cost function to find an energy-efficient path as a set of waypoints. The local path planning navigates the UAV between the waypoints with maintaining the perception quality. The perception quality is quantified based on how well the LiDAR sensor scans feature points around the UAV that highly correlates with the navigation accuracy. Numerical simulation study for each of the global and local path planners validates their usefulness. Further, the overall framework is entirely verified in a long-range flight scenario of the photorealistic environments developed in the Gazebo simulation.

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Autonomous tracking and landing of an unmanned aerial vehicle on a ground vehicle in rough terrain

Aoki N., Ishigami G.

Advanced Robotics (Advanced Robotics) 37 ( 5 ) 344 - 355 2023

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 01691864

Collaborative exploration using unmanned aerial vehicles (UAVs) and unmanned ground vehicles (UGVs) has become increasingly popular in academia over the past decade. This study addresses the task of autonomously landing a UAV on a ground vehicle in rough terrain, which is fundamental, yet challenging, for UAV-UGV collaborative exploration. The method proposed in this paper estimates the relative pose and velocity between UAV and UGV and uses model predictive control for UAV trajectory planning while considering the field of view of camera onboard the UAV. Through a simulation study, we confirmed that the proposed method enables a UAV to accurately track the UGV traversing in rough terrain, and to land on it with 100% success rate at the UGV velocity of 1.0 m/s and still 50% at 3.0 m/s.

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LSTM-based Prediction of Excavating Resistive Force Using Bucket Trajectory Shape

Hashizume Kosuke, Aizawa Masanori, Ooi Takeshi, Ishigami Genya

Journal of the Robotics Society of Japan (The Robotics Society of Japan) 41 ( 1 ) 102 - 105 2023

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 02891824

Unmanned construction machine has become a promising technology in the civil engineering field. The machine is still less efficient, especially in excavating soil, than the manned construction because the unmanned machine works carefully to avoid potential hazards due to unpredicted soil deformation as well as excavation force. This research aims to predict time-series resistive force of bucket during soil excavation based on the Recurrent Neural Network. First, we experimentally obtain excavating resistive force for various excavation trajectories. In the experiment, a bucket follows pre-determined trajectories with four different elliptical arcs, and the resistive force acting on the bucket is measured. The prediction model of the resistive force is then elaborated by indexing the bucket trajectories. The model validation confirms that the aspect ratio of the ellipse of the trajectories is an effective index for accurately predicting the excavating resistive force.

Hardware-in-the-loop Simulation for Real-time Autonomous Tracking and Landing of an Unmanned Aerial Vehicle

Aoki N., Ishigami G.

2023 IEEE/SICE International Symposium on System Integration, SII 2023 (2023 IEEE/SICE International Symposium on System Integration, SII 2023) 2023

Research paper (international conference proceedings), Joint Work, Last author, Accepted, ISSN 2474-2317

Collaborative exploration using unmanned aerial vehicles (UAVs) and unmanned ground vehicles (UGVs) has become increasingly popular in the past decade. This study addresses real-time autonomous tracking and landing of a UAV on a moving ground vehicle, which is fundamental for the UAV-UGV collaborative exploration. The method proposed in this study estimates the relative pose and velocity between a UAV and UGV, and uses model predictive control for UAV trajectory planning while considering the field of view of the camera onboard the UAV. We elaborate the hardware-in-the-loop simulator (HITL) with a physical companion computer, and confirm that the proposed method enables a UAV to land on a UGV traversing on rough terrain based on online computations in the HITL. Additionally, we present statistical analysis of the simulation results of typical and computationally demanding scenarios to elucidate the computational cost on the real machine.

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Uncertainty-Aware Trajectory Planning: Using Uncertainty Quantification and Propagation in Traversability Prediction of Planetary Rovers

Reiya Takemura, Genya Ishigami

IEEE Robotics & Automation Magazine (Institute of Electrical and Electronics Engineers (IEEE)) 31 ( 2 ) 2 - 12 2023

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 10709932

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Risk-aware Path Planning via Probabilistic Fusion of Traversability Prediction for Planetary Rovers on Heterogeneous Terrains

Endo M., Taniai T., Yonetani R., Ishigami G.

Proceedings - IEEE International Conference on Robotics and Automation (Proceedings - IEEE International Conference on Robotics and Automation) 2023-May 11852 - 11858 2023

Research paper (international conference proceedings), Joint Work, Last author, Accepted, ISSN 10504729

Machine learning (ML) plays a crucial role in assessing traversability for autonomous rover operations on deformable terrains but suffers from inevitable prediction errors. Especially for heterogeneous terrains where the geological features vary from place to place, erroneous traversability prediction can become more apparent, increasing the risk of unrecoverable rover's wheel slip and immobilization. In this work, we propose a new path planning algorithm that explicitly accounts for such erroneous prediction. The key idea is the probabilistic fusion of distinctive ML models for terrain type classification and slip prediction into a single distribution. This gives us a multimodal slip distribution accounting for heterogeneous terrains and further allows statistical risk assessment to be applied to derive risk-aware traversing costs for path planning. Extensive simulation experiments have demonstrated that the proposed method is able to generate more feasible paths on heterogeneous terrains compared to existing methods.

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Experimental Validation of Traction Control of Compaction Roller Towed by Small Mobile Robot

Sasaki Yuto, Ishigami Genya

Journal of the Robotics Society of Japan (The Robotics Society of Japan) 41 ( 8 ) 732 - 735 2023

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 02891824

Constructing lunar infrastructures including landing pad and habitable base is essential for enhancing lunar exploration and utilization in the future. The lunar surface regolith, fine-grained loose soil, needs to be compacted and consolidated enough for securely constructing the infrastructures. In this paper, we present a traction control of compaction roller towed by a small mobile robot. The control method aims to minimize the relative drawbar pull between the small mobile robot and the compaction roller. We also manufactured two different shapes of compaction rollers and verified the relationship between the roller shape and control performance. The experimental results show that the proposed traction control effectively minimizes the relative drawbar pull for the spiral-shaped roller while it becomes unstable for the cylindrical-shaped roller because of the roller excites soil bulldozing or excavation during its rolling.

Computationally efficient and sub-optimal trajectory planning framework based on trajectory-quality growth rate analysis

Takemura R., Ishigami G.

Frontiers in Robotics and AI (Frontiers in Robotics and AI) 9 994437 (15 pages) 2022.10

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 2296-9144

A planetary exploration rover has been used for scientific missions or as a precursor for a future manned mission. The rover’s autonomous system is managed by a space-qualified, radiation-hardened onboard computer; hence, the processing performance for such a computer is strictly limited, owing to the limitation to power supply. Generally, a computationally efficient algorithm in the autonomous system is favorable. This study, therefore, presents a computationally efficient and sub-optimal trajectory planning framework for the rover. The framework exploits an incremental search algorithm, which can generate more optimal solutions as the number of iterations increases. Such an incremental search is subjected to the trade-off between trajectory optimality and computational burden. Therefore, we introduce the trajectory-quality growth rate (TQGR) to statistically analyze the relationship between trajectory optimality and computational cost. This analysis is conducted in several types of terrain, and the planning stop criterion is estimated. Furthermore, the relation between terrain features and the stop criterion is modeled offline by a machine learning technique. Then, using the criterion predicted by the model, the proposed framework appropriately interrupts the incremental search in online motion planning, resulting in a sub-optimal trajectory with less computational burden. Trajectory planning simulation in various real terrain data validates that the proposed framework can, on average, reduce the computational cost by 47.6% while maintaining 63.8% of trajectory optimality. Furthermore, the simulation result shows the proposed framework still performs well even though the planning stop criterion is not adequately predicted.

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Active Traversability Learning via Risk-Aware Information Gathering for Planetary Exploration Rovers

Endo M., Ishigami G.

IEEE Robotics and Automation Letters (IEEE Robotics and Automation Letters) 7 ( 4 ) 11855 - 11862 2022.10

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 2377-3766

Traversability prediction enables safe and efficient autonomous rover operation on deformable planetary surfaces. Revealing spatial distribution from terrain geometry to rover slip behavior is key to assessing prospective traversability, but is hindered by insufficient in situ measurements on hazardous states due to conservative rover traverses. To achieve a more accurate prediction, this letter proposes a framework that actively learns latent traversability by exploring informative terrain under the constraints of stochastic rover slip. With a Gaussian process (GP) modeling the spatial distribution, we devise an iterative two-stage framework that gradually refines the model estimation, combining risk-aware informative path planning and GP updates by taking in situ measurements. The path planning stage employs our designed sampling-based algorithm to generate informative trajectories with fault-tolerant risk inference, while the GP is cautiously updated with traverse data to avoid rover immobilization. Chance constraint formulation is exploited in the framework to infer the stochastic reachability of informative regions. Through GP estimates reducing uncertainty, the algorithm incrementally reaches informative yet hazardous states along feasible trajectories. Simulation studies in rough terrain environments demonstrate that the proposed framework gathers informative traverse data while averting rover stuck situations to estimate the latent traversability model.

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Active Traversability Learning via Risk-aware Information Gathering for Planetary Exploration Rovers

Masafumi Endo and Genya Ishigami

Proceedings of 2022 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2022) pp. 11855-11862 2022.09

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Cr doping-induced ferromagnetism in the spin-glass Cd1-xMnxTe studied by x-ray magnetic circular dichroism

V. K. Verma, S. Sakamoto, K. Ishikawa, V. R. Singh, K. Ishigami, G. Shibata, T. Kadono, T. Koide, S. Kuroda, A. Fujimori

2022.04

The prototypical diluted magnetic semiconductor Cd1-xMnxTe is a spin glass (x<0.6) or an antiferromagnet (x>0.6), but becomes ferromagnetic upon doping with a small amount of Cr atoms substituting for Mn. In order to investigate the origin of the ferromagnetism in Cd1-x-yMnxCryTe, we have studied its element specific magnetic properties by x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) at the Cr and Mn L2,3 edges. Thin films were grown by molecular beam epitaxy with a fixed Mn content of x = 0.2 and varying Cr content in the range of y = 0 - 0.04. Measured XAS and XMCD spectra indicate that both Cr and Mn atoms are divalent and that the ferromagnetic or superparamagnetic components of Cr and Mn are aligned in the same directions. The magnetization of Mn increases with increasing Cr content. These results can be explained if ferromagnetic interaction exists between neighboring Mn and Cr ions although interaction between Mn atoms is largely antiferromagnetic. We conclude that each ferromagnetic or superparamagnetic cluster consists of ferromagnetically coupled several Cr and a much larger number of Mn ions.

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Energy-Efficient Path Planning for UAV Using Spatiotemporal Wind Model

Aoki Nobuaki, Ishigami Genya

Journal of the Robotics Society of Japan (The Robotics Society of Japan) 40 ( 3 ) 255 - 258 2022

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 0289-1824

Unmanned aerial vehicles (UAVs) have been deployed in various applications. The UAVs are limited in their flight duration owing to the payload, battery capacity, or wind effects. To address the issue, we propose an energy-efficient path planning method for UAVs that explicitly considers spatiotemporal wind speed. The proposed method exploits the wind-based energy consumption model as the cost function and also implements a variable-resolution grid in the graph search. The simulation study with 648 scenarios confirms the validity of the proposed method. Further, the statistical analysis of the simulation results summarizes the impact of wind and freight mass on UAV path plannings.

Human-Following Control in Furrow For Agricultural Support Robot

Yorozu A., Ishigami G., Takahashi M.

Proceedings of the 16th International Conference on Intelligent Autonomous Systems (Lecture Notes in Networks and Systems) 412 LNNS 155 - 164 2022

Research paper (international conference proceedings), Joint Work, Accepted, ISSN 23673370

In Japan, the reduction in agricultural work population and increase in abandoned cultivated land are major social issues. To overcome these issues, we have proposed a small agricultural robot that supports the transportation of harvested crops while it follows the user. To move in the furrowed field, ridges and furrows where the robot can move must be detected using robot-mounted sensors and follow the ridge while avoiding the ridges and crop rows. However, when the robot follows the user ahead of it, it has difficulty detecting the ridges because of occlusion by the user. In addition, the robot requires to follow the user and move in and out of furrows of different widths in the farm field. To achieve smooth and safe harvesting support in the field with different width furrows, we propose a method for ridge detection and tracking by measuring the furrow width and interpolation using an RGB-D camera and a method for human-following control while avoiding ridges according to the ridge observation state using fuzzy set theory. To verify the proposed methods, experiments in the farm are carried out.

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Development of Hardware-in-the-loop Simulator for Rough Terrain Mobile Robotand Its Application to Real-time Tuning of Wheel Dynamics Model

Ishikawa Sora, Ishigami Genya

Journal of the Robotics Society of Japan (The Robotics Society of Japan) 40 ( 6 ) 542 - 545 2022

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 02891824

Robotic mobility analysis in rough terrain is essential for mission success on robots deployed on planetary surfaces, construction, or disaster sites. A Hardware-in-the-loop Simulation (HILS) is known as an accurate and feasible method for dynamic analysis. The HILS is the hybrid approach that considers the contact dynamics of a robot in an actual environment and calculates the robot vehicle dynamics in a numerical simulation. We developed a HILS for wheeled mobile robot in loose terrain using a single wheel test bed. The HILS is verified under several traction load conditions. Further, the HILS is coupled with a wheel contact model based on the Dynamic Resistive Force Theory (DRFT). This HILS-DRFT can simultaneously simulate multiple wheels of the mobile robot. To improve the reliability of the DRFT, we implemented a real-time tuning process for the scaling factor used in the DRFT based on the wheel sinkage. The HILS-DRFT with the real-time tuning accurately reproduces the driving force of the actual vehicle.

Perception-aware Receding Horizon Path Planning for UAVs with LiDAR-based SLAM

Takemura R., Ishigami G.

IEEE International Conference on Multisensor Fusion and Integration for Intelligent Systems (IEEE International Conference on Multisensor Fusion and Integration for Intelligent Systems) 2022-September 2022

Research paper (international conference proceedings), Joint Work, Last author, Accepted

This paper presents a perception-aware path planning framework for unmanned aerial vehicles (UAVs) that explicitly considers perception quality of a light detection and ranging (LiDAR) sensor. The perception quality is quantified based on how scattered feature points are in LiDAR-based simultaneous localization and mapping, which can improve the accuracy of pose estimation of UAVs. In the planning step of a UAV, the proposed framework selects the best path based on the perception quality from a library of candidate paths generated by the rapidly-exploring random trees algorithm. Consequently, the UAV can autonomously fly to a destination in a receding horizon manner. Several simulation trials of the photorealistic environments confirm that our proposed path planner reduces pose estimation error by approximately 85 % on average as compared with a purely-reactive path planner.

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Experimental Analysis and Numerical Modeling of Bulldozing Force with Varied Soil Moisture Content

Naohiro Sato, Genya Ishigami

11th Asia-Pacific Regional Conference of the International Society of Terrain Vehicle Systems - 2022

Last author, Accepted

CiNii Research

Development of Underwater Soft Robot Inspired by Flatworm using IPMC and Silicone Rubber

SODA Keinosuke, MATSUHISA Naoji, ISHIGAMI Genya, TAKAHASHI Hidetoshi, FURUSAWA Norihiro, OGAWA Jun

The Proceedings of JSME annual Conference on Robotics and Mechatronics (Robomec) (The Japan Society of Mechanical Engineers) 2022 ( 0 ) 2A1-G07 2022

Biomimetic soft robots followed by marine creatures morphology and propulsion mechanics expected to possess high adaptability and maneuverability in underwater world where conventional rigid robots are hardly utilized. Our research group aims to develop an underwater soft robot inspired by marine flatworms which shows a unique and well-organized swimming behavior. Among several types of soft actuators for realizing both robotic softness and flexibility, we focus on an ionic polymer–metal composite (IPMC) as a membranous actuator. This paper mainly introduces a manufacturing process of the IPMC and experimental tests of different types of the IPMC actuators. We found that mean electric resistance of the IPMC increases as decreasing the voltage induced to the IPMC, regardless of the size of the IPMC. The relationship between the voltage and resistance of the IPMC may be correlated with the capacitor component of a simplified RC circuit model of IPMC.

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Development of Underwater Soft Robot Inspired by Flatworm using IPMC and Silicone Rubber

OGAWA Jun, TAKAHASHI Hidetoshi, MATSUHISA Naoji, SODA Keinosuke, FURUSAWA Norihiro, ISHIGAMI Genya

The Proceedings of JSME annual Conference on Robotics and Mechatronics (Robomec) (The Japan Society of Mechanical Engineers) 2022 ( 0 ) 2A1-G07 2022

IPMCとシリコーンゴムを用いたヒラムシ型水中ソフトロボットの開発

ロボティクス・メカトロニクス講演会講演概要集 2022

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ヒラムシのひだの羽ばたき位相差を持つ羽ばたき機

ロボティクス・メカトロニクス講演会講演概要集 2022

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Ornithopter with flapping phase difference of flatworm

FURUSAWA Norihiro, SODA Keinosuke, ISHIGAMI Genya, TAKAHASHI Hidetoshi

The Proceedings of JSME annual Conference on Robotics and Mechatronics (Robomec) (The Japan Society of Mechanical Engineers) 2022 ( 0 ) 2A1-F10 2022

This paper describes a swimming robot that imitates a flatworm. The model was made with a length of 20 cm, which is about twice the size of a flatworm. As for the folds, they were reproduced by flat wing waves that mimicked the flatworm using a single motor and a phase-shifting slider-crank mechanism. In this way, the phase speed of the folds can be freely changed by changing the phase difference of the crank. The performance of the fabricated robot was evaluated using a high-speed camera and tracking software. For the flapping amplitude, the ornithopter showed no significant errors other than misalignment of parts.

Ornithopter with flapping phase difference of flatworm

FURUSAWA Norihiro, SODA Keinosuke, ISHIGAMI Genya, TAKAHASHI Hidetoshi

The Proceedings of JSME annual Conference on Robotics and Mechatronics (Robomec) (The Japan Society of Mechanical Engineers) 2022 ( 0 ) 2A1-F10 2022

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Special issue on Advanced Construction Robot System PREFACE

Ohno, K; Osumi, H; Ishigami, G; Nagatani, K

ADVANCED ROBOTICS 35 ( 23 ) 1375 - 1375 2021.12

ISSN 0169-1864

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CNN-Based Terrain Classification with Moisture Content Using RGB-IR Images

Goto Tomoya, Ishigami Genya

Journal of Robotics and Mechatronics (Fuji Technology Press Ltd.) 33 ( 6 ) 1294 - 1302 2021.12

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 09153942

Unmanned mobile robots in rough terrains are a key technology for achieving smart agriculture and smart construction. The mobility performance of robots highly depends on the moisture content of soil, and past few studies have focused on terrain classification using moisture content. In this study, we demonstrate a convolutional neural network-based terrain classification method using RGB-infrared (IR) images. The method first classifies soil types and then categorizes the moisture content of the terrain. A three-step image preprocessing for RGB-IR images is also integrated into the method that is applicable to an actual environment. An experimental study of the terrain classification confirmed that the proposed method achieved an accuracy of more than 99% in classifying the soil type. Furthermore, the classification accuracy of the moisture content was approximately 69% for pumice and 100% for dark soil. The proposed method can be useful for different scenarios, such as small-scale agriculture with mobile robots, smart agriculture for monitoring the moisture content, and earthworks in small areas.

Simulation Analysis on Steering Characteristics for Vehicle Design of Manned Pressurized Lunar Rover

Naho Yashiro, Genya Ishigami

Proceedings of 20th ISTVS International and 9th Americas Regional Conference (The Japan Society of Mechanical Engineers) 2020 ( 0 ) 002 (11 pages) - B13 2021.09

Research paper (international conference proceedings), Joint Work, Last author, Accepted

This paper describes a steering maneuverability analysis for a manned pressurized lunar rover. To improve steering maneuverability, this paper focused on vehicle design parameters and inputs, such as tread, wheelbase, center of gravity position, and steering angle. The work on this paper first built a simulation model, which used parameters of the moon, and next analyzed cornering characteristics by changing vehicle design parameters. The analysis performed in this paper shows influence of each parameter and input to the motion. Simulation results showed the tread, center of gravity position and steering angle gives impact to steering maneuverability. The paper also discusses and proposes about allowable vehicle design parameters.

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Spatio-temporal prediction of soil deformation in bucket excavation using machine learning

Saku Yuki, Aizawa Masanori, Ooi Takeshi, Ishigami Genya

ADVANCED ROBOTICS (Advanced Robotics) 35 ( 23 ) 1404 - 1417 2021.06

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 0169-1864

This paper proposes a prediction model for three-dimensional spatio-temporal soil deformation in bucket excavation. The prediction model for soil deformation (PMSD) consists of two machine learning processes: the long short-term memory (LSTM) and convolutional autoencoder (Conv-AE). These processes use datasets obtained from an experimental apparatus for bucket excavation developed in this work. The apparatus equips multiple depth cameras that precisely capture time-series data of soil deformation in bucket excavation. The LSTM, an extension of a recurrent neural network, successively predicts three-dimensional soil deformation. The Conv-AE is incorporated to both ends of the LSTM in order to quasi-reversibly compress and reconstruct the datasets so that the computational burden of the LSTM is relaxed. Qualitative and quantitative evaluations of the PMSD confirm the feasibility of time-series prediction of three-dimensional soil deformation. The Conv-AE shows sufficient accuracy equivalent to the measurement accuracy of the depth camera. The prediction accuracy of the PMSD is about 10 mm in most of the cases.

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Visualization and analysis of wheel camber angle effect for slope traversability using an in-wheel camera

Matsumura R, Ishigami G

Journal of Terramechanics (Journal of Terramechanics) 93 1 - 10 2021.02

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 00224898

This paper visualizes and analyzes an effect of a wheel camber angle for the slope traversability in sandy terrain. An in-wheel camera developed in this work captures the wheel-soil contact phenomenon generated beneath the wheel through a transparent section of the wheel surface. The images taken by the camera are then analyzed using the particle image velocimetry. The soil flows with various wheel camber angles are analyzed with regard to the soil failure observed on the slope surface. The analysis reveals that the slope failure and soil accumulation in front of the wheel significantly affect the wheel forces and distributions of the wheel sinkage in the wheel width direction. Further, the side force of the wheel in traversing a slope decreases as the slip ratio increases because the shear stress in the slope downward direction decreases owing to the slope failure.

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Experimental study on wheel-soil interaction mechanics using in-wheel sensor and particle image velocimetry Part I: Analysis and modeling of normal stress of lightweight wheeled vehicles

Tsubaki H, Ishigami G

Journal of Terramechanics (Journal of Terramechanics) 93 23 - 39 2021.02

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 00224898

This study aims to develop a wheel-soil interaction model for a lightweight wheeled vehicle by measuring the normal stress distribution beneath the wheel. The main contribution of this work is to clarify the wheel-soil interaction using a wheel testbed that equips multiple sensory systems. An in-wheel sensor accurately measures the normal stress distribution as well as the contact angles of the wheel. Particle image velocimetry with a standard off-the-shelf camera analyzes soil flow beneath the wheel. The proposed model for the normal stress distribution is formulated based on these experimental data and takes into account the following phenomena for the lightweight vehicles that have not been considered in the classical model: (1) the normal stress distribution takes the form of a Gaussian curve; (2) the normal stress distribution concentrates in the front region of the wheel contact patch; (3) the distribution is divided into two areas with the boundary determined by the maximum normal stress angle; and (4) the maximum normal stress exponentially decreases as the slip ratio increases. Then, the proposed model is experimentally validated. Furthermore, a simulation study for the wheel driving characteristics using the proposed model confirms the accuracy of the proposed model.

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Spatio-Temporal Prediction of Soil Deformation using Machine Learning

Saku Yuki, Aizawa Masanori, Ooi Takeshi, Ishigami Genya

Journal of the Robotics Society of Japan (The Robotics Society of Japan) 39 ( 4 ) 367 - 370 2021

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 0289-1824

Unmanned construction machine working in dangerous environments such as construction sites and disaster areas has been developed. However, it is still necessary to improve its work efficiency especially during bulldozing and excavating soil. This research aims to develop a method for predicting soil deformation using machine learning. The feasibility of the proposed method is verified in a scenario where a simple bulldozing blade excavates soil. In the experiment, soil deformation at a front part of the blade is captured by multiple stereoscopic cameras. The camera provides depth data that are then converted to height field data. This dataset is fed to machine learning using Recurrent Neural Network (RNN) because soil deformation is continuous phenomena depending on time variation. The learned model for predicting soil deformation is confirmed in varied intrusion depth of the bulldozing blade.

Energy-aware trajectory planning for planetary rovers

Sakayori G, Ishigami G

Advanced Robotics (Advanced Robotics) 35 ( 21-22 ) 1302 - 1316 2021

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 01691864

Planetary rovers are becoming indispensable for exploration activities and science missions. The rover used in such mission is often limited in its operation time owing to power and computational resources of the rover. In this paper, a trajectory planning method for a planetary rover is proposed that considers vehicle dynamics, and energy management of the rover. The vehicle dynamics is approximated from a dynamic simulation of the rover, which can estimate the power consumption in accordance with terrain traversability of the rover. The power generation of the solar array panel mounted on the rover is also taken into account. The simulation study confirmed the usefulness of the proposed method, especially in scenarios where slopes could be observed, and one result indicated that the energy margin could be improved by 4.1 kJ, 13.9 (Formula presented.) at maximum.

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EXPERIMENTAL MEASUREMENT OF SOIL-TRACK CONTACT STRESS IN STEERING MOTION ON LOOSE SAND

Shomura T., Ishibashi S., Ishigami G.

Proceedings of the 20th International and 9th Americas Conference of the International Society for Terrain-Vehicle Systems, ISTVS 2021 (Proceedings of the 20th International and 9th Americas Conference of the International Society for Terrain-Vehicle Systems, ISTVS 2021) 2021

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Modeling the dynamic interaction of construction machines on loose terrain is essential for accurately predicting the vehicle's motion and for reliably conducting its operation. The track system is often exploited as the mobility for the construction machine the track shows high trafficability on loose terrain. Track-terrain interaction mechanics has been well investigated in the past, while that in steering motion of the track remains an open issue. Therefore, this research aims to clarify the interaction mechanics of the steering track on loose sand using the following experimental apparatus: an in-track sensor and a track-steering testbed. The in-track sensor possesses multiple small three-axis sensors on the track shoes. Each track shoe has multiple holes for the sensor such that the sensing position is selectable along with the track direction. This in-track sensor can measure the contact stress distribution generated between the track and loose sand. The steering testbed emulates a pivot turning of a tracked vehicle by offsetting the track at an arbitrary distance from the center of rotation of the steering testbed. The experiments using these two apparatuses reveal that the shear stress beneath the track shows a different tendency in its steering motion: the maximum shear stress of the towed track is generated at the center of the contact region while that of the driving track is at the front region. These observations can contribute to a better understanding of the steering motion of a construction machine on loose terrain.

Wide-range routing method for lunar exploration rovers using multi-objective optimization

Reina Nakanishi, Genya Ishigami

Advanced Robotics (Robotics Society of Japan) 35 ( 21-22 ) 1317 - 1331 2021

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 01691864

This paper presents a wide-range routing method for multiple rovers deployed for a lunar polar exploration mission. In the mission scenario considered in this paper, multiple exploration points are divided into several sets of points to be assigned to multiple rovers. Subsequently, routes between the exploration points are generated for each rover. This assignment and routing problems are well known as the multiple Traveling Salesman Problem (mTSP). The scenario aims to minimize two objective functions: the sum and standard deviation of operation time among the multiple rovers. This problem is then subject to the multi-objective mTSP (MOmTSP). Therefore, the proposed method is composed of a three-step procedure for solving the MOmTSP. First, the k-means algorithm divides an exploration area into several regions for the number of rovers. Subsequently, a routing algorithm with the space-filling curve and 2-opt algorithm determines the order of exploration points in each region. A local path planner then generates a feasible path between two exploration points. The simulation results using the proposed method with 80 cases are statistically analyzed. We confirm that the proposed method solves the multiple optimization problems by finding the routes that can equalize the rover's operation time and minimize their deviations.

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Traversability-based Trajectory Planning with Quasi-Dynamic Vehicle Model in Loose Soil

Takemura R., Ishigami G.

Proceedings of the 2021 IEEE International Conference on Intelligent Robots and Systems (IEEE International Conference on Intelligent Robots and Systems) 8411 - 8417 2021

Research paper (international conference proceedings), Joint Work, Last author, Accepted, ISSN 21530858

This paper presents a framework for trajectory planning that explicitly considers robotic traversability based on a quasi-dynamic vehicle model of a mobile robot in loose soil. The quasi-dynamic model estimates the slip effect due to wheel-terrain interaction forces regardless of solving complicated multibody dynamics. Therefore, our proposed model is computationally efficient for quantifying how the robot safely traverses each trajectory segment generated by a planning algorithm. The trajectory planning in our framework exploits a sampling-based incremental search algorithm, i.e., Closed-Loop Rapidly-Exploring Random Trees (CL-RRT). In the tree extension process of the CL-RRT, the traversability assessment based on the quasi-dynamic vehicle model excludes the trajectory segment associated with a hazardous wheel slip ratio. As a result, a trajectory generated from the proposed framework is safely traversable for the robot even in high slip terrain. Simulation results show that the proposed vehicle model can run 57K times faster than the dynamic model and predict the robot motion 3 times more accurately than the kinematic model. Multiple trials of the trajectory planning simulation show that our proposed framework incorporated with the quasi-dynamic model reduces a wheel slip ratio by about 40 % as compared with the kinematic model.

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TOWARDS MODIFIED DYNAMIC RESISTIVE FORCE THEORY FOR A FAST-ROTATING WHEEL ON LOOSE SAND

Tanabe Y., Ishigami G.

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Newly proposed missions to the Moon/Mars often require vehicles to operate at high speed for time-efficient surface explorations. Among wheel-terrain interaction models in the past being applicable for quasi-static locomotion, a granular Resistive Force Theory (RFT) is increasingly employed alternatively for its simplicity and applicability. The RFT has also been extended to the Dynamic RFT (DRFT), which considers the rate-dependent effects often seen in the high-speed locomotion. In this research, first, we validate the DRFT through single-wheel experiments. The results suggest that the original DRFT underestimates the influence of wheel rut and that the granular flow beneath the wheel may decrease the wheel traction force. We then propose an empirically modified DRFT (m-DRFT), which considers an appropriate evaluation of the wheel rut depth and a simplified model for the granular flow. The comparison with the experimental results confirms that the m-DRFT accurately predicts the wheel drawbar pull in relatively low slip conditions while the original DRFT overestimates it. Moreover, the m-DRFT reproduces the temporal oscillations of the drawbar pull generated by the wheel grousers. These results imply that the m-DRFT is applicable for transient locomotion state or even fast-rotating wheel where estimating the sequential changes of wheel forces becomes essential.

TOWARDS HIGH-FIDELITY ANALYSIS ON WHEELED MOBILE ROBOT ON SOFT TERRAIN USING HARDWARE-IN-THE-LOOP SIMULATOR

Ishikawa S., Ishigami G.

Research paper (international conference proceedings), Joint Work, Last author, Accepted

This paper introduces a Hardware-In-the-Loop Simulation (HILS) framework for a wheeled mobile robot traveling on sandy terrain. The HILS is a hybrid method that incorporates an experimental approach into a numerical simulation. The HILS in our work employs a single-wheel testbed for the experimental setup where the traction force of the wheel on soft soil under various slip conditions is measured. The dynamics of the robot vehicle in response to the wheel traction force is calculated by a simple dynamics model based on Newton’s equation of motion. A key technique of the HILS developed in this work is the damping coefficient implemented in the dynamics model. To verify the fidelity and stability of the HILS, wheel driving tests with the HILS are conducted in the following process: first, a wheel driving data (wheel translational velocity, wheel traction force, and wheel slip) with various input parameters (damping coefficient and wheel angular velocity) is experimentally measured only using the wheel testbed. Subsequently, another wheel driving data is measured while the HILS calculates the dynamic response of the wheel in accordance with the corresponding external forces. The validity of the HILS is compared based on the difference between the actual and calculated wheel driving data. In this process, the value of the damping coefficient is determined such that the dynamic response well matches with the actual driving data. Furthermore, wheel driving data with external disturbances to the wheel is experimentally simulated using the HILS.

Granular flow experiment using artificial gravity generator on International Space Station

Ozaki, S. and Ishigami, G. and Otsuki, M. and Miyamoto, H. and Wada, K. and Watanabe, Y. and Nishino, T. and Kojima, H. and Soda, K. and Nakao, Y. and Sutoh, M. and Maeda, T. and Kobayashi, T.

ResearchSquare 2021

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特集「古今未曽有の日本の月/火星地下世界探査 (UZUME)計画」小型探査プローブ搭載の複数広角カメラを用いた縦孔側壁の3次元再構成特集「古今未曽有の日本の月/火星地下世界探査 (UZUME)計画」小型探査プローブ搭載の複数広角カメラを用いた縦孔側壁の3次元再構成

Enokida N., Miyauchi T., Ishigami G.

Planetary People - The Japanese Society for Planetary Sciences (The Japanese Society for Planetary Sciences) 29 ( 4 ) 208 2020.12

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 0918-273X

（要旨） 本論文では，月縦孔降下中の探査プローブが撮像した複数の時系列画像を用いて，月縦孔側壁形状を3次元再構成することを目的とする．3次元再構成では，Simultaneous Localization and Mapping (SLAM) の技術を援用し，探査プローブの自由落下運動条件をSLAM の各処理過程に組み込むことによって，カメラの回転に頑強なSLAM へと改良した．提案SLAM のシミュレーション検証において，3次元再構成の精度向上を確認した．さらに，探査プローブ搭載カメラの性能の違いによる3次元再構成への影響の検証も実施し，本研究で得られた検証結果から，ミッションシナリオと探査プローブの運動要件，カメラ性能に関する議論を行った．

Experimental study on wheel-soil interaction mechanics using in-wheel sensor and particle image velocimetry part II. Analysis and modeling of shear stress of lightweight wheeled vehicle

Horiko S, Ishigami G

Journal of Terramechanics (Journal of Terramechanics) 91 243 - 256 2020.10

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 00224898

Wheeled vehicle mobility on loose sand is highly subject to shear deformation of sand around the wheel because the shear stress generates traction force of the wheel. The main contribution of this paper is to improve a shear stress model for a lightweight wheeled vehicle on dry sand. This work exploits two experimental approaches, an in-wheel sensor and a particle image velocimetry that precisely measure the shear stress and shear deformation generated at the interaction boundary. Further, the paper improves a shear stress model. The model proposed in this paper considers a force chain generated inside the granular media, boundary friction between the wheel surface and sand, and velocity dependency of the friction. The proposed model is experimentally validated, and its usefulness is confirmed through numerical simulation of the wheel traction force. The simulation result confirmed that the proposed model calculated the traction force with an accuracy about 70%, whereas the conventional one overestimated the force, and its accuracy was 13% at the best.

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サイバスロン電動車いすシリーズ日本2019

石上玄也

日本ロボット学会誌 (The Robotics Society of Japan) 38 ( 2 ) 151 - 154 2020.03

Lead author, Accepted, ISSN 0289-1824

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Vision-based measurement of spatio-temporal deformation of excavated soil for the estimation of bucket resistive force

Tsuchiya K, Ishigami G

Journal of Terramechanics (Journal of Terramechanics) 90 11 - 21 2020

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 00224898

© 2020 ISTVS This paper reports a vision-based technique of measuring the spatio-temporal deformation of excavated soil for estimating the bucket resistive force. The proposed measurement technique uses two depth cameras to determine three-dimensional soil-surface displacement. The technique consists of the following two processes: the first is related to image correlation between the two cameras, and the second involves data filtering and smoothing for generating soil deformation as a continuously curved surface. The proposed technique delivers measurement accuracy to the nearest centimeter. Typical experimental results of the three-dimensional measurement of soil deformation using the proposed technique are presented in the paper. Further, this study updates an interaction model for the resistive-force estimation while a bucket excavates soil. The model introduces a correction variable that changes with the bucket wrist angle by exploiting the experimental measurement of soil deformation. The model estimates the resistive force with an error of less than one quarter of the maximum force. These updates also exhibit the effectiveness of the proposed technique.

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Path planning method taking into account the deviation of the vehicle on rough terrain

TAJIMA Ryo, ISHIGAMI Genya

The Proceedings of JSME annual Conference on Robotics and Mechatronics (Robomec) (The Japan Society of Mechanical Engineers) 2020 ( 0 ) 2P1 - B14 2020

In recent years, the effectiveness of autonomous robots on planet surfaces and in crisis situations have been recognized. During planetary exploration missions, it is crucial to plan a route where the planetary rovers can reach its destination safely. However, when these rovers are traversing on the trail, the estimated driving force does not always match that in the real world. This can result in the rovers deviating from its planned course. This paper proposes a new cost function that takes the rover deviation into account and evaluates this method using multi-point path planning simulations. A grid-based path planning method is used with Dijkstra 's algorithm as it 's foundation.

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ロボットシミュレータ開発

金広文男, 中岡慎一郎, 杉原知道, 石上玄也, 尾崎伸吾

日本ロボット学会誌 (The Robotics Society of Japan) 37 ( 9 ) 835 - 838 2019.11

Lead author, Accepted, ISSN 0289-1824

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Resistive Force Estimation for Bucket Excavation Using Machine Learning

Kenji Tsuchiya Genya Ishigami

Proceedings of the 15th Europian-African Regional Conference of the International Society of Terrain Vehicle Systems (ISTVS2019) 9 pages 2019.09

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Slip Estimation Using Machine Learning of Wheel Trace Patterns for Mobile Robot on Loose Soil

Yuki Saku, Genya Ishigami

Proceedings of the 15th Europian-African Regional Conference of the International Society of Terrain Vehicle Systems (ISTVS2019) 9 pages 2019.09

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Ridge-tracking for Strawberry Harvesting Support Robot According to Farmer's Behavior

Ayanori Yorozu, Genya Ishigami, Masaki Takahashi

Proceedings of the 12th Conference on Field and Service Robotics (FSR2019) #32 (11 pages) 2019.08

Research paper (international conference proceedings), Joint Work, Accepted

Dynamic Simulation of Sky Crane Landing System for Mars Exploration Rover

Kotaro Hirota, Genya Ishigami

Proceedings of the 32nd International Symposium on Space Technology and Science (ISTS 2019) k-55 (5 pages) 2019.06

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Current Status of UZUME Mission

Junichi Haruyama, Isao Kawano, Toshihiko Nishibori, Takahiro Iwata, Yukio Yamamoto, Masato Sakurai, Masatsugu Otsuki, Genya Ishigami

Proceedings of the 32nd International Symposium on Space Technology and Science (ISTS 2019) k-06 (6 pages) 2019.06

Research paper (international conference proceedings), Joint Work, Accepted

Routing Method for Wide-Range Exploration of Multiple Rovers in Rough Terrain

Reina Nakanishi, Genya Ishigami

Proceedings of the 32nd International Symposium on Space Technology and Science (ISTS 2019) k-09 (6 pages) 2019.06

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Routing Problem of Multiple Mobile Robots with Human Workers for Pickup and Dispatch Tasks in Warehouse

Ono Y, Ishigami G

Proceedings of the 2019 IEEE/SICE International Symposium on System Integration, SII 2019 (Proceedings of the 2019 IEEE/SICE International Symposium on System Integration, SII 2019) 176 - 181 2019.04

Research paper (international conference proceedings), Joint Work, Last author, Accepted

© 2019 IEEE. This paper presents a routing problem of multiple mobile robots collaborating with human workers in a ware-house. In a scenario considered in this paper, the warehouse stores several different of heavy items on multiple stock locations. The human worker pick items up from corresponding stock location, puts them on one of the mobile robot carriers, and then visits another stock location. The multiple mobile robots deployed in the warehouse visit stock locations by following specified routes, carry several items for the worker, and deliver them to a dispatch area in the warehouse. Here, an appropriate number of robots, the maximum speed of each robot, and the load capacity of each robot should be quantitatively analyzed while the routing problem of the multiple robots with the human worker in the warehouse is considered. The research in this paper develops a simulation framework in which the worker and the robots cooperatively performs the pickup and dispatch tasks. An algorithm of the routing problem in the framework is addressed based on the Mixed-integer linear programming, which calculates the order of the picking points for each robot. Simulation studies for an actual warehouse are performed with different conditions between the number of robots, speed, and load capacity. The simulation framework calculates a task time which indicates how long the robots and worker need to complete one shipping list. The task time also quantitatively indicate how large the multiple robots reduce the work load of the human worker.

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Simulator for disaster response robotics

Kanehiro F., Nakaoka S., Sugihara T., Wakisaka N., Ishigami G., Ozaki S., Tadokoro S.

Springer Tracts in Advanced Robotics (Springer Tracts in Advanced Robotics) 128 453 - 477 2019

Research paper (scientific journal), Joint Work, Accepted, ISSN 16107438

© Springer Nature Switzerland AG 2019. This chapter presents a simulator for disaster response robots based on the Choreonoid framework. Two physics engines and a graphics engine were developed and integrated into the framework. One physics engine enables robust contact-force computation among rigid bodies based on volumetric intersection and a relaxed constraint, whereas the other enables accurate and computationally efficient computation of machine–terrain interaction mechanics based on macro and microscopic approaches. The graphics engine allows simulating natural phenomena, such as rain, fire, and smoke, based on a particle system to resemble tough scenarios at disaster sites. In addition, wide-angle vision sensors, such as omnidirectional cameras and LIDAR sensors, can be simulated using multiple rendering screens. Overall, the simulator provides a tool for the efficient and safe development of disaster response robots.

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Dual-arm construction robot with remote-control function

Yoshinada H., Kurashiki K., Kondo D., Nagatani K., Kiribayashi S., Fuchida M., Tanaka M., Yamashita A., Asama H., Shibata T., Okutomi M., Sasaki Y., Yokokohji Y., Konyo M., Nagano H., Kanehiro F., Sugihara T., Ishigami G., Ozaki S., Suzumori K., Ide T., Yamamoto A., Hioki K., Oomichi T., Ashizawa S., Tadakuma K., Takamori T., Kimura T., Murphy R., Tadokoro S.

Springer Tracts in Advanced Robotics (Springer Tracts in Advanced Robotics) 128 195 - 264 2019

Research paper (scientific journal), Joint Work, Accepted, ISSN 16107438

© Springer Nature Switzerland AG 2019. In disaster areas, operating heavy construction equipment remotely and autonomously is necessary, but conventional remote-controlled heavy equipment has problems such as insufficient operability, limited mobility on slopes and stairs, and low work efficiency because of difficult remote control. As part of the ImPACT-TRC Program, a group of Japanese researchers attempts to solve these problems by developing a construction robot for disaster relief tasks with a new mechanism and new control methods. This chapter presents the overview of construction robot and the details of main elemental technologies making up the robot. Section 5.1 describes the basic configuration of the robot and the teleoperation system. Section 5.2 is a tether powered drone which provides extra visual information. Sections 5.4 and 5.3 are force and tactile feedback for skillful teleoperation. Section 5.5 is visual information feedback which consists of an arbitrary viewpoint visualization system and a visible and LWIR camera system to observe surrounding of the robot in a dark night scene and/or a very foggy scene. These functions can dramatically increase construction eq

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Development of In-track Sensor System for Three Dimensional Measurement of Pressure Distribution on Loose Soil

Satoshi Ishibashi, Genya Ishigami

Proceedings of the Joint 10th Asia-Pacific Conference of the International Society for Terrain-Vehicle Systems 1-2 (11 pages) 2018.07

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Experimental Analysis of Camber Angle Effect on Slope Traversability of Wheeled Mobile Robot

Ryota Matsumura, Genya Ishigami

Proceedings of the Joint 10th Asia-Pacific Conference of the International Society for Terrain-Vehicle Systems 5-1 (8 pages) 2018.07

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Experimental Analysis of Bucket-soil Interaction Mechanics using Sensor-embedded Bucket Test Apparatus

Kenji Tsuchiya, Genya Ishigami

Proceedings of the Joint 10th Asia-Pacific Conference of the International Society for Terrain-Vehicle Systems 8-4 (11 pages) 2018.07

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Experimental Analysis on Landing Dynamics of Martian Moon Spacecraft based on Similarity Law

Daiki Yamaguchi, Genya Ishigami

Proceedings of the 14th International Symposium on Artificial Intelligence, Robotics and Automation in Space (i-SAIRAS 2018) 3a-4 (8 pages) 2018.06

Research paper (international conference proceedings), Joint Work, Last author

Simulation Study on Landing Behavior of Spacecraft in Microgravity Environment based on Multibody Dynamics Model

Haruhi Katsumata, Genya Ishigami

Proceedings of the 14th International Symposium on Artificial Intelligence, Robotics and Automation in Space (i-SAIRAS 2018) 3a-3 (7 pages) 2018.06

Research paper (international conference proceedings), Joint Work, Last author

Strategic Deployment and Rerouting Methods for Wide-range Surface Exploration using Multiple Rovers

Reina Nakanishi, Genya Ishigami

Proceedings of the 14th International Symposium on Artificial Intelligence, Robotics and Automation in Space (i-SAIRAS 2018) 6c-a (5 pages) 2018.06

Research paper (international conference proceedings), Joint Work, Last author

Computationally Efficient Mapping for a Mobile Robot with a Downsampling Method for the Iterative Closest Point

Deguchi Shodai, Ishigami Genya

Journal of Robotics and Mechatronics (Journal of Robotics and Mechatronics) 29 ( 6 ) 65 - 75 2018.02

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 09153942

© 2018, Fuji Technology Press. All rights reserved. This paper proposes a computationally efficient method for generating a three-dimensional environment map and estimating robot position. The proposed method assumes that a laser range finder mounted on a mobile robot can be used to provide a set of point cloud data of an environment around the mobile robot. The proposed method then extracts typical feature points from the point cloud data using an intensity image taken by the laser range finder. Subsequently, feature points extracted from two or more different sets of point cloud data are correlated by the iterative closest point algorithm that matches the points between the sets, creating a large map of the environment as well as estimating robot location in the map. The proposed method maintains an accuracy of the mapping while reducing the computational cost by downsampling the points used for the iterative closest point. An experimental demonstration using a mobile robot test bed confirms the usefulness of the proposed method.

Strategy Optimization for Energy Efficient Extraterrestrial Drilling Using Combined Power Map

Pan, Siyi and Ishigami Genya

IEEE Robotics and Automation Letters 2 ( 4 ) 1980 - 1987 2017.10

Research paper (scientific journal), Joint Work, Last author, Accepted

Extraterrestrial drilling is an important sampling method for understanding the formation of another celestial body and finding traces of life beyond earth. Currently, such tasks mainly rely on remotely controlled space robots. Because of limited energy available for space robots, it is highly demanded to improve the energy efficiency in the extraterrestrial drilling tasks. In this paper, we propose an algorithm called combined power map (CPM) method that can optimize extraterrestrial drilling strategies in order to improve energy efficiency. The algorithm comprehensively considers the effect of sampling positions, robot positions, and robotic arm configurations on drilling energy consumption and has the ability to manage the energy efficiency gain and corresponding risks. Simulations show that the CPM method can significantly reduce the drilling energy consumption and effectively limit accompanying risks.

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Development and performance evaluation of planar travel distance sensors for mobile robots in sandy terrain

Yanagisawa Arata, Ishigami Genya

Journal of Robotics and Mechatronics (Fuji Technology Press) 29 ( 5 ) 887 - 894 2017.10

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 0915-3942

A planar travel distance sensor (two-dimensional sen-sor) was developed for a mobile robot in sandy terrain. The sensor system uses an optical flow device integrated into a small module with a simple configuration. The system achieves a high sampling rate on the order of milliseconds as well as precise measurement on a sub-millimeter order. Its performance was evaluated experimentally for measurement accuracy and repeatability, velocity response, robustness at varied heights with respect to terrain, and terrain surface characteristics. The experimental results confirm that the two-dimensional sensor system is accurate, having an error of distance traveled of less than a few percent, and that it possesses a wide dynamic range for the robot’s traveling velocity. This paper also discusses the applicability of the two-dimensional sensor for practical scenarios on the basis of the experimental findings.

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Traversability-based RRT∗ for planetary rover path planning in rough terrain with LIDAR point cloud data

Takemura Reiya, Ishigami Genya

Journal of Robotics and Mechatronics (Fuji Technology Press) 29 ( 5 ) 838 - 846 2017.10

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 0915-3942

Sampling-based search algorithms such as Rapidly-Exploring Random Trees (RRT) have been utilized for mobile robot path planning and motion planning in high dimensional continuous spaces. This paper presents a path planning method for a planetary exploration rover in rough terrain. The proposed method exploits the framework of a sampling-based search, the optimal RRT (RRT∗) algorithm. The terrain geometry used for planning is composed of point cloud data close to continuous space captured by a light detection and ranging (LIDAR) sensor. During the path planning phase, the proposed RRT∗ algorithm directly samples a point (node) from the LI-DAR point cloud data. The path planner then considers the rough terrain traversability of the rover during the tree expansion process of RRT∗. This process improves conventional RRT∗ in that the generated path is safe and feasible for the rover in rough terrain. In this paper, simulation study on the proposed path planning algorithm in various real terrain data confirms its usefulness.

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Wheel slip classification method for mobile robot in sandy terrain using in-wheel sensor

Omura Takuya, Ishigami Genya

Journal of Robotics and Mechatronics (Fuji Technology Press) 29 ( 5 ) 902 - 910 2017.10

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 0915-3942

This paper proposes a method that can estimate and classify the magnitude of wheel slippage for a mobile robot in sandy terrains. The proposed method exploits a sensor suite, called an in-wheel sensor, which measures the normal force and contact angle at the wheel-sand interaction boundary. An experimental test using the in-wheel sensor reveals that the maximum normal force and exit angle of the wheel explicitly vary with the magnitude of the wheel slippage. These characteristics are then fed into a machine learning algorithm, which classifies the wheel slippage into three categories: non-stuck wheel, quasi-stuck wheel, and stuck wheel. The usefulness of the proposed method for slip classification is experimentally evaluated using a four-wheel-drive test bed rover.

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Modeling of Bucket-soil Interaction Mechanics based on Improved Resistive Force Theory

Ryota Yoneyama, Takuya Omura, Genya Ishigami

Proceedings of the 19th International & 14th European-African Regional Conference of the International Society of Terrain Vehicle Systems SES-09-1 (12 pages) 2017.09

Research paper (international conference proceedings), Joint Work, Last author, Accepted

A high-fidelity simulator for a construction machine particularly contributes to an unmanned construction system since the simulator efficiently manages and schedules tasks required for the machines in a systematic way. Besides, the simulator also provides a virtual reality as a training platform for an operator for tele-operated unmanned construction machine. The simulator is generally subject to a well-known trade-off between computational burden and simulation accuracy. Therefore, the main scope of this research is to establish an accurate and computationally efficient simulator for an excavator, and particularly this paper focuses on an interaction model of an excavator bucket. An accurate excavation mechanics is of a key issue to characterize dynamic motion of the excavator. The model developed in this paper basically exploits the Resistive Force Theory with considering soil surcharge while excavating. The proposed model is experimentally validated in different types of excavation motion using a bucket experimental apparatus.

Slip Estimation and Classification Using In-wheel Sensor for Mobile Robot in Sandy Terrain

Takuya Omura, Genya Ishigami

Proceedings of the 19th International & 14th European-African Regional Conference of the International Society of Terrain Vehicle Systems SES-09-2 (10 pages) 2017.09

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Sandy terrain often traps wheeled vehicle or mobile robot with immobilizing wheel stuck. The wheel stuck phenomenon is highly related to wheel slippage and soil failure. Therefore, wheel slip detection and estimation is particularly important for avoiding the wheel stuck phenomenon. This paper proposes a method that can estimate and classify a magnitude of wheel slip using an in-wheel sensor system. The in-wheel sensor captures wheel-terrain interaction characteristics such as contact angles and normal force around the wheel. The proposed method basically estimates a wheel slip by comparing the measured data from the in-wheel sensor with a look-up table generated by a machine learning algorithm. Training data for the machine learning is a variety of experimental data set given from the in-wheel sensor. The look-up table developed in this work distinguishes the magnitude of wheel slippage into three categories: non-stuck wheel, quasi-stuck wheel, and stuck wheel. Experimental demonstration of the proposed method achieves the slip estimation with an accuracy of 90 % or more. Moreover, it is found that tracking the interaction characteristics in a spatiotemporal manner can predict an immobilizing wheel slip or even wheel stuck, resulting in a decrease of mobility hazard.

LDM (Life Detection Microscope): In situ Imaging of Living Cells on Surface of Mars

Akihiko YAMAGISHI, Takehiko SATOH, Keigo ENYA, Atsuo MIYAKAWA, Yoshitaka YOSHIMURA, Hajime HONDA, Eiichi IMAI, Satoshi SASAKI, Genya ISHIGAMI, Kazuhisa FUJITA, Hideaki MIYAMOTO

Transactions of the Japan Society for Aeronautical and Space Sciences, Aerospace Technology Japan (Japan Society for Aeronautical and Space Sciences) 14 ( ists30 ) Pk_117 - Pk_124 2017.02

Research paper (scientific journal), Joint Work, Accepted

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Automated Dust Devil Detection on Mars

Kazunori OGOHARA, Daiki YASUNAGA, Genya ISHIGAMI

Transactions of the Japan Society for Aeronautical and Space Sciences, Aerospace Technology Japan 14 ( ists30 ) Pk_131 - Pk_136 2017.02

Research paper (scientific journal), Joint Work, Accepted

A system for automated dust devil detection on Mars is developed based on images taken by the navigation camera aboard the Mars Exploration Rover, Spirit. This system enables us to pick up dust devils from the large number of images without checking each image visually and affords us a powerful tool for searching for dust devils and revealing their statistical properties for scientific studies. From an engineering point of view, the volume of dust devil image data to be downlinked to Earth for dust devil studies can also be drastically reduced by automated detection of dust devils because we can trim dust devil regions on the images onboard. A simple performance test using images taken on a particular sol shows that this system can detect almost all of the dust devils though also includes some false positives. Precision and recall are 0.85 and 0.81, respectively, which are comparable with or more effective than those in previous studies.

Energy Efficient Slope Traversability Planning for Mobile Robot in Loose Soil

Go Sakayori, Genya Ishigami

Proceedings of the 2017 IEEE International Conference on Mechatronics 99-104 - 104 2017.02

Research paper (international conference proceedings), Joint Work, Last author, Accepted

This paper proposes an energy-efficient trajectory planning method for a wheeled robot in slope ascending scenario. This method basically exploits a power consumption model of the robot which is obtained from the following two phases: first, the values of the robot power consumption in different slope angle, robot velocity, and robot heading angle are numerically calculated using a dynamic simulation of the robot taking into account of an accurate wheel-soil interaction mechanics; and subsequently, an approximated model for the robot power consumption is elaborated by neural network. Using the power consumption model an energy-efficient trajectory for a slope traversal case can be generated. Here, a bezier curve is used to provide a smooth trajectory designed with an appropriate arrival time as well as the control points for the curve. The numerical simulation result of the trajectory planning based on the proposed method gives several insights for a feasible trajectory for slope ascending scenario.

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Gyro-based odometry associated with steering characteristics for wheeled mobile robot in rough terrain

Nagata Takuma, Ishigami Genya

Advanced Robotics (TAYLOR & FRANCIS LTD) 30 ( 23 ) 1495 - 1508 2016.12

Research paper (scientific journal), Joint Work, Accepted, ISSN 0169-1864

Mobile robot used for planetary exploration performs several scientific missions over long distance travel and needs to have a high degree of autonomous mobility system because the communication delay from the Earth impedes its direct teleoperation. Localization of a mobile robot is of particular importance on the autonomous mobility. Classical localization methods such as wheel/visual odometry have been widely investigated and demonstrated, but they possess a well-known trade-off between computational cost and localization accuracy. This paper proposes an accurate gyro-based odometry method for a wheeled mobile robot in rough terrain. The robot in rough terrain is often subject to large wheel slip or vehicle sideslip related with its steering maneuver, and those slips degrade the localization accuracy. The basic approach of the proposed method is to exploit odometry data for the robot distance traveled as well as gyroscope data for the robot heading calculation; however each data-set is weighted in accordance with steering characteristics of a robot in rough terrain. The usefulness of the proposed method is examined through field experiments using a wheeled mobile robot testbed in Martian analog site. The experimental result confirms that the proposed method accurately estimates the robot trajectory.

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Experimental Investigation of Stuck Wheel Characteristics in Loose Sand

Takuya Ohmura, Genya Ishigami

Proceedings of the 8th Americas Regional Conference of the International Society for Terrain-Vehicle Systems #56 (9 pages) 2016.09

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Modeling of Wheel-soil Interaction Mechanisms based on Accurate Measurement of Pressure Distribution for Lightweight Vehicle

Hiroki Tsubaki, Genya Ishigami

Proceedings of the 8th Americas Regional Conference of the International Society for Terrain-Vehicle Systems #39 (11 pages) 2016.09

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Power Consumption Model for Slope Traversal of Wheeled Robot based on Dynamic Simulation

Go Sakayori, Genya Ishigami

Proceedings of the 8th Americas Regional Conference of the International Society for Terrain-Vehicle Systems #79 (11 pages) 2016.09

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Experimental Evaluation of Gyro-based Odometry Focusing on Steering Characteristics of Wheeled Mobile Robot in Rough Terrain

Takuma Nagata, Genya Ishigami

Proceedings of the 13th International Symposium on Artificial Intelligence, Robotics and Automation in Space (i-SAIRAS 2016) 8b-4 2016.06

Research paper (international conference proceedings), Joint Work, Last author

Experimental Evaluation of Voltage Control Methods in Electrical Power System for Planetary Rover

Takahiro Akutsu, Genya Ishigami

Proceedings of the 13th International Symposium on Artificial Intelligence, Robotics and Automation in Space (i-SAIRAS 2016) 8a-4 2016.06

Research paper (international conference proceedings), Joint Work, Last author

Modeling of LiDAR Measurement Uncertainty for Rover Path Planning

Koki Tanaka, Genya Ishigami

Proceedings of the 13th International Symposium on Artificial Intelligence, Robotics and Automation in Space (i-SAIRAS 2016) 5c-2 2016.06

Research paper (international conference proceedings), Joint Work, Last author

Power-synchronized Path Planning for Mobile Robot in Rough Terrain

Go Sakayori, Genya Ishigami

Proceedings of the 13th International Symposium on Artificial Intelligence, Robotics and Automation in Space (i-SAIRAS 2016) 5c-4 2016.06

Research paper (international conference proceedings), Joint Work, Last author

Modeling and control of robots on rough terrain

Keiji Nagatani, Genya Ishigami, Yoshito Okada

Springer Handbook of Robotics (Springer International Publishing) 1267 - 1284 2016.01

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Mission Concepts of Unprecedented Zipangu Underworld of the Moon Exploration (UZUME) Project

Junichi HARUYAMA, Isao KAWANO, Takashi KUBOTA, Masatsugu OTSUKI, Hiroki KATO, Toshihiko NISHIBORI, Takahiro IWATA, Yukio YAMAMOTO, Yoshiaki ISHIHARA, Aiko NAGAMATSU, Kazuhito SHIMADA, Toshiaki HASENAKA, Tomokatsu MOROTA, Masaki N. NISHINO, Ko HASHIZUME, Kazuto SAIKI, Motomaro SHIRA, Goro KOMATSU, Nobuyuki HASEBE, Hisayoshi SHIMIZU, Hideaki MIYAMOTO, Kensei KOBAYASHI, Shinichi YOKOBORI, Tatsuhiro MICHIKAMI, Satoru YAMAMOTO, Yasuhiro YOKOTA, Hitoshi ARISUMI, Genya ISHIGAMI, Katsushi FURUTANI, Yuichi MICHIKAWA

TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN (Japan Society for Aeronautical and Space Sciences) 14 ( ists30 ) Pk_147 - Pk_150 2016

Research paper (scientific journal), Joint Work, Accepted

We are planning to explore the caverns through the skylight holes on the Moon and Mars. The holes and their associated subsurface caverns are among the most important future exploration targets. The importance of the lunar and Martian holes and their associated caverns is categorized from two aspects: (1) fresh materials are easily observed and sampled there, and (2) the subsurface caverns provide a safe, quiet environment. The expectation of lunar and Martian hole and cavern exploration is increasing in Japan. We name the project as UZUME (Unprecedented Zipangu (Japan) Underworld of the Moon Exploration) whose name is after a Japanese mythology. The ultimate purpose of the UZUME project is to investigate how to expand human activity and survival in space and on extraterrestrial bodies.

Excavation model of soil sampling device based on particle image velocimetry

Mori, Daiki, Ishigami, Genya

JOURNAL OF TERRAMECHANICS (PERGAMON-ELSEVIER SCIENCE LTD) 62 19 - 29 2015.12

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 0022-4898

This work aims to establish an energy-efficient strategy for sampling Martian subsurface soil for future extraterrestrial-life exploration missions. To this end, requirements for a robotic arm are carefully examined and an end-effector shape suitable for subsurface soil sampling is determined. A soil tool interaction model is formulated based soil-flow measured by particle image velocimetry (PIV). The proposed model calculates the resistance forces and torque generated during the sampling procedure and is validated through a comparison of experimental data obtained from the force sensor and numerical data calculated from the proposed model. Results indicate that the proposed model provides an accurate estimation of the force generated during soil sampling. Furthermore, the interaction model is capable of estimating the robotic arm's energy consumption and calculating the most efficient tool size to use. (C) 2015 ISTVS. Published by Elsevier Ltd. All rights reserved.

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Development of in-wheel sensor system for accurate measurement of wheel terrain interaction characteristics

Shirai, Takayuki, Ishigami, Genya

JOURNAL OF TERRAMECHANICS (PERGAMON-ELSEVIER SCIENCE LTD) 62 51 - 61 2015.12

Research paper (scientific journal), Joint Work, Last author, Accepted, ISSN 0022-4898

Planetary rovers need high mobility on a rough terrain such as sandy soil, because such a terrain often impedes the rover mobility and causes significant wheel slip. Therefore, the accurate estimation of wheel soil interaction characteristics is an important issue. Recent studies related to wheel soil interaction mechanics have revealed that the classical wheel model has not adequately addressed the actual interaction characteristics observed through experiments. This article proposes an in-wheel sensor system equipped with two sensory devices on the wheel surface: force sensors that directly measure the force distribution between the wheel and soil and light sensors that accurately detect the wheel soil surface boundary line. This sensor design enables the accurate measurement of wheel terrain interaction characteristics such as wheel force distribution, wheel soil contact angles, and wheel sinkage when the powered wheel runs on loose sand. In this article, the development of the in-wheel sensor system is introduced along with its system diagram and sensor modules. The usefulness of the in-wheel sensor system is then experimentally evaluated via a single wheel test bench. The experimental results confirm that explicit differences can be observed between the classical wheel model and practical data measured by the in-wheel sensor system. (C) 2015 ISTVS. Published by Elsevier Ltd. All rights reserved.

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Design and Development of Built-in-Clutch Joint for Single-Drive and Multi-Degrees of Freedom Manipulator

Saki Morita. Daiki Mori, and Genya Ishigami

The 6th International Conference on Advanced Mechatronics 2A1-11 2015.12

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Design, Development, and Mobility Evaluation of an Omnidirectional Mobile Robot for Rough Terrain

Ishigami, Genya, Iagnemma, Karl, Overholt, Jim, Hudas, Greg

JOURNAL OF FIELD ROBOTICS (WILEY-BLACKWELL) 32 ( 6 ) 880 - 896 2015.09

Research paper (scientific journal), Joint Work, Lead author, Corresponding author, Accepted, ISSN 1556-4959

Omnidirectional vehicles have been widely applied in several areas, but most of them are designed for the case of motion on flat, smooth terrain, and are not feasible for outdoor usage. This paper presents the design and development of an omnidirectional mobile robot that possesses high mobility in rough terrain. The omnidirectional robot consists of a main body with four sets of mobility modules, called an active split offset caster (ASOC). The ASOC module has independently driven dual wheels that produce arbitrary planar translational velocity, enabling the robot to achieve its omnidirectional motion. Each module is connected to the main body via a parallel link with shock absorbers, allowing the robot to conform to uneven terrain. In this paper, the design and development of the ASOC-driven omnidirectional mobile robot for rough terrain are described. A control scheme that considers the kinematics of the omnidirectional mobile robot is presented. The mobility of the robot is also evaluated experimentally based on a metric called the ASOC mobility index. The mobility evaluation test clarifies a design tradeoff between terrain adaptability and omnidirectional mobility due to the shock absorbers. In addition, an odometry improvement technique that can reduce position estimation error due to wheel slippage is proposed. Experimental odometry tests confirmed that the proposed technique is able to improve the odometry accuracy for sharp-turning maneuvers.

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Generalized Force-and-Energy Manipulability for Design and Control of Redundant Robotic Arm

Daiki Mori, Genya Ishigami

Proceedings of the 2015 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2015) 2015-December pp. 1131-1136 - 1136 2015.09

Research paper (international conference proceedings), Joint Work, Last author, Accepted, ISSN 21530858

There is a possibility of remaining indication of microorganisms on Martian subsurface and therefore, a robotic arm mounted on an exploration robot is required to dig to a certain depth and collect appropriate sample to be analyzed. However, the environment on the surface of Mars is harsh and most of all, limited power is available from the solar panel. In this paper, FEMI (Force-and-Energy Manipulability Index) is proposed to evaluate a feasible arm configuration for low energy consumption in its soil sampling operation. FEMI is calculated by the combination of an energy manipulability of an arm and an external force generated at an end effector of the arm. The FEMI derives the most feasible configuration on the joint angles of the arm for each sampling point. The usefulness of the FEMI is confirmed through a numerical simulation of a robotic arm. The simulation also presents that the FEMI can be used to obtain mechanical parameters of the arm such as link length and motor power, that are optimally-designed for a certain mission.

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Automated Dust Devil Detection on Mars

Kazunori Ogohara, Daiki Yasunaga1, Genya Ishigami

Proceedings of the 30th International Symposium on Space Technology and Science (ISTS 2015) k-44 2015.07

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Design and Development of Navigation/Geological Cameras for a Mars Rover

Takehiko Satoh, Hideaki Miyamoto, Takafumi Niihara, Genya Ishigami

Proceedings of the 30th International Symposium on Space Technology and Science (ISTS 2015) k-41 2015.07

Research paper (international conference proceedings), Joint Work, Accepted

LDM (Life Detection Microscope): In situ imaging of living cells on surface of Mars

Akihiko Yamagishi, Takehiko Satoh, Keigo Enya, Atsuo Miyakawa, YoshimuraYoshitaka, Hajime Honda, Eiichi Imai, Satoshi Sasaki, Genya Ishigami, Hirohide Demura, Kazuhisa Fujita, Hideaki Miyamoto

Proceedings of the 30th International Symposium on Space Technology and Science (ISTS 2015) k-40 2015.07

Research paper (international conference proceedings), Joint Work, Accepted

Preliminary Thermal Design of a Mars Rover Mission "MELOS"

Ryuta Hatakenaka, Kazuhisa Fujita, Taku Nonomura, Moto Takai, Hiroyuki Toyota, Takehiko Satoh, Hiroyuki Sugita, Genya Ishigami, Akihiko Yamagishi, Hideaki Miyamoto, Kazuhiro Umetani

Proceedings of the 45th International Conference on Environmental Systems ICES-2015-247 2015.07

Research paper (international conference proceedings), Joint Work

Mission Scope Definition and Preliminarily Design Study of Mars Surface Exploration Rover

Genya Ishigami, Kazuhisa Fujita, Ryuta Hatakenaka, Hiroyuki Toyota, Takehiko Sato, Moto Takai, Taku Nonomura

Proceedings of the 30th International Symposium on Space Technology and Science (ISTS 2015) k-39 2015.07

Research paper (international conference proceedings), Joint Work, Lead author, Corresponding author, Accepted

Mission Concepts of Unprecedented Zipangu Underworld of the Moon Exploration (UZUME) Project

Junichi Haruyama, Isao Kawano, Takashi Kubota, Masatsugu Otsuki, Hiroki Kato, Toshihiko Nishibori, Takahiro Iwata, Yukio Yamamoto, Yoshiaki Ishihara, Aiko Nagamatsu, Kazuto Shimada, Toshiaki Hasenaka, Tomokatsu Morota, Masaki N. Nishino, Ko Hashizume, Kazuto Saiki, Motomaro Shirao, Goro Komatsu, Nobuyuki Hasebe, Hisayoshi Shimizu, Hideaki Miyamoto, Kensei Kobayashi, Shinichi Yokobori, Tatsuhiro Michikami, Satoru Yamamoto, Yasuhiro. Yokota, Hitoshi Arisumi, Genya Ishigami, Katsusi Furutani, Yuichi Michikawa

Proceedings of the 30th International Symposium on Space Technology and Science (ISTS 2015) k-29 2015.07

Research paper (international conference proceedings), Joint Work, Accepted

Japan’s Mars Rover Mission - System Design and Development Status

Kazuhisa Fujita, Genya Ishigami, Ryuta Hatakenaka, Moto Takai, Hiroyuki Toyota, Naoko Ogawa, Misuzu Haruki, Hiroshi Takeuchi, Taku Nonomura, Kazuhiko Yamada, Hiroki Takayanagi, Takashi Ozawa, Shingo Matsuyama, Akira Oyama, Akihiko Yamagishi, Shingo Kameda, Hirdy Miyamoto, Takehiko Satoh

Proceedings of the 30th International Symposium on Space Technology and Science (ISTS 2015) 2015.07

Research paper (international conference proceedings), Joint Work, Accepted

車輪走行実験による沈下過渡状態におけるせん断変形モデル有効性の評価

水上憲明, 石上玄也, 吉光徹雄, 久保田孝

日本機械学会論文集 (日本機械学会) 81 ( 825 ) 14 - 00514-14-00514 2015.01

Research paper (scientific journal), Joint Work, Accepted, ISSN 2187-9761

Soft soils cover on planetary surfaces, so the wheels for exploration rovers easily slip. Understanding an interaction between a wheel and soft soils is important for a traction control to improve rover traversability. The interaction between the wheel and soft soils has been studied in a field of terramechanics. Since the classical terramechanics-based wheel model considers only a static state of a wheel sinkage, the wheel model is not applicable to the wheel sinkage and slip. Thus the dynamic normal stress model and shear deformation model were proposed to deal with the problems of the wheel sinkage and the slip. The dynamic normal stress model was proposed by considering the wheel sinking velocity and a variation of soil state for solving the problem of wheel sinkage. And the shear deformation model was proposed by considering the shear characteristics for solving the problem of wheel slip. The shear deformation model was formulated by the shear test. The simulation verified the validity of the dynamic normal stress model and the shear deformation model in the transient state. In this paper, a single wheel experiments was performed to evaluate the shear deformation model by comparing the simulation results and the experimental results. Then the characteristics of the wheel sinkage and slip and the effectiveness of the model were confirmed.

Accurate Measurement of Multidirectional Interaction Mechanisms between Wheel Stress and Soil Deformation using In-wheel Sensor and PIV techniques

Hiroki Tsubaki, Takayuki Shirai, Genya Ishigami

Proceedings of the 13th European Conference of the International Society for Terrain-Vehicle Systems 97-109 2015.01

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Towards Terrain Classification Method based on Force-sinkage Characteristics measured with In-wheel Sensor System

Takayuki Shirai, Hiroki Tsubaki, and Genya Ishigami

Proceedings of the 13th European Conference of the International Society for Terrain-Vehicle Systems 282-289 2015.01

Research paper (international conference proceedings), Joint Work, Last author, Accepted

Japan's mars rover mission for edl demonstration and life search

Kazuhisa Fujita, Genya Ishigami, Takehiko Satoh, Akihiko Yamagishi, Hirdy Miyamoto

Proceedings of the International Astronautical Congress, IAC 2 1061 - 1068 2015

Research paper (international conference proceedings), Joint Work, ISSN 0074-1795

A Martian rover mission is currently entertained in Japan Aerospace Exploration Agency (JAXA) for launch in 2020s. The primary scopes of this mission are to demonstrate the entry-descent-landing and surface exploration technologies on Mars, to search for signs of live organisms, and to determine when the ocean is lost in the past Martian history. In order to cut down the mission cost and the development risk, the spacecraft is designed as a compact medium-class spacecraft whose total wet mass at Earth departure is approximately 900 kg. The spacecraft system consists of the cruise module and the atmospheric entry module which is subdivided into a forebody and an aftbody aeroshell, a landing module, and a rover, in a typical reference mission design under consideration. The current status of research and development is briefly presented as well.

Accurate Estimation of Wheel Pressure-Sinkage Traits on Sandy Terrain using In-wheel Sensor System

Takayuki Shirai, Genya Ishigami

Proceedings of the 12th International Symposium on Artificial Intelligence, Robotics and Automation in Space (i-SAIRAS 2014) 8a-2 2014.06

Research paper (international conference proceedings), Joint Work, Last author

Current Status and Prospects of Terramechanics-based Simulation Techniques for Planetary Rover Locomotion

Taizo Kobayashi, Genya Ishigami, Shingo Ozaki, Masataku Sutoh

Proceedings of the 12th International Symposium on Artificial Intelligence, Robotics and Automation in Space (i-SAIRAS 2014) 11b-3 2014.06

Research paper (international conference proceedings), Joint Work

Light-Independent Feature Detection using Intensity Data of Laser Range Finder

Kentaro Kimura, Genya Ishigami

Proceedings of the 12th International Symposium on Artificial Intelligence, Robotics and Automation in Space (i-SAIRAS 2014) 11a-3 2014.06

Research paper (international conference proceedings), Joint Work, Last author

Towards Space-hardened, Small-lightweight Laser Range Imager for Planetary Exploration Rover

Genya Ishigami, Takahide Mizuno

Proceedings of the 12th International Symposium on Artificial Intelligence, Robotics and Automation in Space (i-SAIRAS 2014) 11a-2 2014.06

Research paper (international conference proceedings), Joint Work, Lead author, Corresponding author

Soil Interaction Model of Hemispherical Sampling Device based on PIV Analysis

Daiki Mori, Genya Ishigami

Proceedings of the 12th International Symposium on Artificial Intelligence, Robotics and Automation in Space (i-SAIRAS 2014) 9a-2 2014.06

Research paper (international conference proceedings), Joint Work

JAXAの探査ローバ開発の現状

大槻真嗣, 若林幸子, 石上玄也, 須藤真琢

日本ロボット学会誌 32 ( 5 ) 408-411 2014.06

Accepted, ISSN 0289-1824

Conceptual Design Study of Mars EDL System with a Compact Rover

Kazuhisa Fujita, Genya Ishigami, Naoko Ogawa, Akira Oyama, Kazuhiko Yamada, Takashi Kubota, Akihiko Yamagishi, Hirdy Miyamoto, and Takehiko Satoh

Proceedings of the AIAA Science and Technology Forum and Exposition 2014 1739890 2014.01

Research paper (international conference proceedings), Joint Work

Design, development, and mobility test of an omnidirectional mobile robot for rough Terrain

Genya Ishigami, Elvine Pineda, Jim Overholt, Greg Hudas, Karl Iagnemma

Springer Tracts in Advanced Robotics 92 599 - 611 2014

Research paper (international conference proceedings), Joint Work, Lead author, Corresponding author, Accepted, ISSN 1610-7438

Omnidirectional vehicles have been widely applied in several areas, but most of them are designed for the case of motion on flat, smooth terrain, and are not feasible for outdoor usage. This paper presents an omnidirectional mobile robot that possesses highmobility in rough terrain. The omnidirectional robot employs four sets of mobility modules, called active split offset caster (ASOC). The ASOCmodule has two independently-driven wheels that produce arbitrary planar translational velocity, enabling the robot to achieve its omnidirectional mobility. Each module is connected to the main body of the robot via a parallel link with shock absorbers. In this paper, a design and development of the ASOC-driven omnidirectional mobile robot for rough terrain are described. Also, a control scheme that considers a kinematics of the omnidirectional mobile robot is presented. The omnidirectional mobility of the robot regardless of ifs heading direction is experimentally evaluated based on ametric called omnidirectional mobility index. © Springer-Verlag Berlin Heidelberg 2014.

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Path planning and navigation framework for a planetary exploration rover using a laser range finder

Genya Ishigami, Masatsugu Otsuki, Takashi Kubota

Springer Tracts in Advanced Robotics 92 431 - 447 2014

Research paper (international conference proceedings), Joint Work, Lead author, Corresponding author, Accepted, ISSN 1610-7438

This chapter presents a path planning and navigation framework for a planetary exploration rover and its experimental tests at a Lunar/Martian analog site. The framework developed in this work employs a laser range finder (LRF) for terrain feature mapping. The path planning algorithm generates a feasible path based on a cost function consisting of terrain inclination, terrain roughness, and path length. A set of navigation commands for the rover is then computed from the generated path. The rover executes those navigation commands to reach a desired goal. In this paper, a terrain mapping technique that uses a LRF is described along with an introduction to a cylindrical coordinate digital elevation map (C2DEM). The gird-based path planning algorithm is also presented. Field experiments regarding the path planning and navigation that evaluate the feasibility of the framework developed in this work are reported. © Springer-Verlag Berlin Heidelberg 2014.

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Particle Filter based 3D Position Tracking for Terrain Rovers using Laser Point Clouds

Peshala G. Jayasekara, Genya Ishigami, Takashi Kubota

2014 IEEE/RSJ INTERNATIONAL CONFERENCE ON INTELLIGENT ROBOTS AND SYSTEMS (IROS 2014) (IEEE) 2369 - 2374 2014

Research paper (international conference proceedings), Joint Work, Accepted, ISSN 2153-0858

Difficult conditions on outdoor terrains make outdoor autonomy for rovers, a challenging task. The conventional wheel odometry method uses orientation measurements to assume a momentary plane to apply wheel encoder readings. On uneven terrains, this method often gives poor results for position tracking, and therefore rarely used. To improve the conventional odometry motion model, immediate terrain data can be used. This paper proposes a novel state variable extension (SVE) method to establish a connection between state space variables of a terrain rover by combining terrain point clouds with rover kinematics. The simulation results show that when the 2D state variables (x, y, yaw) are known, the 2D state can be extended to its 3D state (x, y, z, roll, pitch, yaw) with minimal error. The proposed SVE method is employed in a particle filter to determine the 2D state variables, which in turn results in achieving the full 3D position tracking of the rover.

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Terrain adaptive detector selection for visual odometry in natural scenes

Kyohei Otsu, Masatsugu Otsuki, Genya Ishigami, Takashi Kubota

Advanced Robotics 27 ( 18 ) 1465-1476 - 1476 2013.10

Research paper (scientific journal), Joint Work, Accepted, ISSN 01691864

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Range-Dependent Terrain Mapping and Multi-path Planning using Cylindrical Coordinates for Planetary Exploration Rover

Genya Ishigami, Masatsugu Otsuki, Takashi Kubota

Journal of Field Robotics (WILEY-BLACKWELL) 30 ( 4 ) 536-551 - 551 2013.07

Research paper (scientific journal), Joint Work, Lead author, Corresponding author, Accepted, ISSN 1556-4959

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Case Study of Trajectory Design for Synergetic Mars Exploration by Orbiter and Lander

Naoko Ogawa, Kazuhisa Fujita, Takashi Kubota, Genya Ishigami, Akira Oyama, Kazuhiko Yamada, and Takehiko Satoh

Proceedings of the 29th International Symposium on Space Technology and Science (ISTS 2013) k-66p 2013.06

Research paper (international conference proceedings), Joint Work, Accepted

Feasibility Study of a Small, Lightweight Rover for Mars Surface Exploration

Genya Ishigami, Takashi Kubota, Kazuhisa Fujita, Naoko Ogawa, Takehiko Sato

Proceedings of the 29th International Symposium on Space Technology and Science (ISTS 2013) k-12 2013.06

Research paper (international conference proceedings), Joint Work, Lead author, Corresponding author, Accepted

Design Study of Mars EDL Demonstrator for MELOS mission

Kazuhisa Fujita, Genya Ishigami, Naoko Ogawa, Akira Oyama, Kazuhiko Yamada, Takashi Kubota, Hirdy Miyamoto, and Takehiko Satoh

Proceedings of the 29th International Symposium on Space Technology and Science (ISTS 2013) k-11 2013.06

Research paper (international conference proceedings), Joint Work, Accepted

MELOS Life Search Plan: Search for Microbes on the Mars Surface with Special Interest in Methane-oxidizing Bacteria

Akihiko Yamagishi, Yoshitaka Yoshimura, Hajime Honda, Aatsuo Miyakawa, Takehiko Satoh, Gennya Ishigami, Junichi Haruyama, Kensei Kobayashi, Takeshi Naganuma, Sho Sasaki, Hideaki Miyamoto

Proceedings of the 29th International Symposium on Space Technology and Science (ISTS 2013) (THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES) 12 ( 29 ) k-13 - Tk_48 2013.06

Research paper (international conference proceedings), Joint Work, Accepted, ISSN 1884-0485

Our project aims to search for methane-oxidizing microbes on the Mars surface. The project is in preparation under the scheme of the MELOS working group. Martian soil will be sampled from a depth of about 5 - 10 cm below the surface, where organisms are expected to be protected from the harsh hyper-oxidative environment of the Mars surface. The soils will be stained with a cocktail of fluorescent reagents, and examined by fluorescence microscopy. A combination of fluorescent dyes has been selected to identify life forms in samples. A combination of dyes will be used to detect membranes surrounding the "cell". A substrate dye that emits fluorescence upon cleavage by a catalytic reaction will be used to detect the catalytic activity of the "cell". This combination will also be useful for detecting pre-biotic organic material as well as remnants of ancient Martian life. Hydrolysis of the polymers in the "cell" followed by HPLC for amino acid analysis will be effective for examining whether Martian life is identical to or different from terrestrial life. The number and type of the amino acids as well as their chirality will be analyzed to distinguish whether the polymers are contaminants from Earth.

Preliminary Design Study of EDL System for Japan's Mars Rover Mission

Kazuhisa Fujita, Genya Ishigami, Naoko Ogawa, Akira Oyama, Kazuhiko Yamada, Takashi Kubota, Hirdy Miyamoto, and Takehiko Satoh

Proceedings of the 4th International Atmospheric reentry Association Days 2013.04

Research paper (international conference proceedings), Joint Work

An examination of feature detection for real-time visual odometry in untextured natural terrain

Kyohei Otsu, Masatsugu Otsuki, Genya Ishigami, Takashi Kubota

Advances in Intelligent Systems and Computing (Springer Verlag) 208 405 - 414 2013

Research paper (international conference proceedings), Joint Work, Accepted, ISSN 2194-5357

Estimating the position of a robot is an essential requirement for autonomous mobile robots. Visual Odometry is a promising localization method in slippery natural terrain, which drastically degrades the accuracy of Wheel Odometry, while relying neither on other infrastructure nor any prior knowledge. Visual Odometry, however, suffers from the instability of feature extraction from the untextured natural terrain. To date, a number of feature detectors have been proposed for stable feature detection. This paper compares commonly used detectors in terms of robustness, localization accuracy and computational efficiency, and points out their trade-off problems among those criteria. To solve the problem, a hybrid algorithm is proposed which dynamically switches between multiple detectors according to the texture of terrain. Validity of the algorithm is proved by the simulation using dataset at volcanic areas in Japan. © 2013 Springer-Verlag.

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Proposal for the Mars life search equipments : Search for cells, aminoacids and methane

山岸明彦, 吉村義隆, 長沼毅, 宮川厚夫, 出村裕英, 豊田岐聡, 本多元, 小林憲正, 三田肇, 大野宗佑, 石丸亮, 小林喬郎, 戸野倉賢一, 石上玄也, 佐々木晶, 宮本英昭

Planetary People (Journal of the Japanese Society for Planetary Sciences) (The Japanese Society for Planetary Sciences) 21 ( 2 ) 276 - 282 2012.09

Research paper (scientific journal), Joint Work, Accepted, ISSN 0918-273X

CiNii Research

火星生命探査機器群提案 -- 細胞，アミノ酸，メタン検出を目的とした --

山岸明彦, 吉村義隆, 長沼毅, 宮川厚夫, 出村裕英, 豊田岐聡, 本多元, 小林憲正, 三田肇, 大野宗祐, 石丸亮, 小林喬郎, 戸野倉賢一, 石上玄也, 佐々木晶, 宮本英昭

日本惑星科学会誌 (The Japanese Society for Planetary Sciences) 21 ( 3 ) 276-282 - 282 2012.09

Research paper (scientific journal), Joint Work, Accepted, ISSN 0918-273X

CiNii Research

Advanced Visual Odometry for Planetary Exploration Rover,

Kyohei Otsu, Masatsugu Otsuki, Genya Ishigami, Takashi Kubota

Proceedings of the 11th International Symposium on Artificial Intelligence, Robotics and Automation in Space (i-SAIRAS 2012) 9a-2 2012.09

Research paper (international conference proceedings), Joint Work

LIDAR-based Terrain Mapping and Navigation for Planetary Exploration Rover,

Genya Ishigami, Masatsugu Otsuki, Takashi Kubota

Proceedings of the 11th International Symposium on Artificial Intelligence, Robotics and Automation in Space (i-SAIRAS 2012) 4c-4 2012.09

Research paper (international conference proceedings), Joint Work, Lead author, Corresponding author

Testing and Validation of Autonomous Navigation for Planetary Exploration Rover, Cuatro, using Opensource Simulation Tools,

Peshala G. Jayasekara, Genya Ishigami, Takashi Kubota

Proceedings of the 11th International Symposium on Artificial Intelligence, Robotics and Automation in Space (i-SAIRAS 2012) 9c-4 2012.09

Research paper (international conference proceedings), Joint Work

Motion Control with Modification ofAcceleration for planetary Rover on soft Terrain,

Masatsugu Otsuki, Genya Ishigami, Shinichiro Narita, Sachiko Wakabayashi

Proceedings of the 11th International Symposium on Artificial Intelligence, Robotics and Automation in Space (i-SAIRAS 2012) 11a-2 2012.09

Research paper (international conference proceedings), Joint Work

Design, Development, and Mobility test of an Omnidirectional Mobile Robot for Rough Terrain,

Genya Ishigami, Elvine Pineda, Jim Overholt, Greg Hudas, Karl Iagnemma

Proceedings of the 8th International Conference on Field and Service Robotics (FSR 2012) No. 48 2012.07

Research paper (international conference proceedings), Joint Work, Lead author, Corresponding author, Accepted

自立移動ロボットによる火山地域の探査活動

大槻真嗣, 石上玄也, 嶋田貴信, 久保田孝, 作田真理子, オリチロンアン, 大津恭平, 清水拓

日本惑星科学会誌 21 ( 2 ) 111-120 2012.06

Research paper (scientific journal), Joint Work, Accepted, ISSN 0918-273X

Multi-material Anisotropic Friction Wheels for Omnidirectional Ground Vehicles

Genya Ishigami, Jim Overholt, Karl Iagnemma

Journal of Robotics and Mechatronics (Fuji Technology Press) 24 ( 1 ) 261-267 - 267 2012.02

Research paper (scientific journal), Joint Work, Lead author, Corresponding author, Accepted, ISSN 1883-8049

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Field Robotics Technology for Secure System and Exploration from the Earth to the Space,

Takashi Kubota, Masatsugu Otsuki, Genya Ishigami, Takanobu Shimada

Proceedings of the Global COE Symposium on Secure-Life Electronics pp. 3--18 2012.01

Research paper (international conference proceedings), Joint Work

Load Distribution Control of a Six-Wheeled Robotic Vehicle in Rough Terrain

Taizo Kobayashi, Genya Ishigami, Keiji Nagatani, Kazuyoshi Tateyama

Proceedings of 17th International Conference of the International Society for Terrain-Vehicle Systems (ISTVS 2011) Track 2-4 - 575 2011.09

Research paper (international conference proceedings), Joint Work, Accepted

In future lunar/planetary exploration missions, wheeled rovers will be promising robots to perform wide-area explorations. Wheeled robots, however, are prone to slip in soft and uneven terrain, and therefore, securing the mobility performance is a critical problem. This paper first describes a simple soil-wheel interaction model which enables slipratio estimation from a combination of wheel load and traction. Second, a drive control method for maintaining vehicle mobility is discussed and a six-wheeled robot which implements the control system was developed. The robot has six wheels and six vertical suspensions with built-in linear actuators. Load cells are installed between each wheel and suspension to monitor the wheel load, and the positions of wheels are individually controlled by moving the suspensions up and/or down so as to keep the desired wheel loads. In this study, a simple algorithm for distributing equivalent load to every wheel was implemented in the control system. Experiments were performed and the effectiveness of the drive control method was examined.

Development of Electrical Power Systems for Test-bed Rovers Aiming to Planetary Surface Exploration,

Takanobu Shimada, Masatsugu Otsuki, Hiroyuki Toyota, Genya Ishigami, Takashi Kubota

Proceedings of the 9th European Space Power Conference Ref. 2104158 2011.06

Research paper (international conference proceedings), Joint Work

Experimental Study on Mobility and Navigation for Exploration Rover in Natural Rough Terrain,

Masatsugu Otsuki, Genya Ishigami, Takanobu Shimada, Shogo Takanashi, Orchlon Ann, Takashi Kubota

Proceedings of the 28th International Symposium on Space Technology and Science (ISTS 2011) d-87p 2011.06

Research paper (international conference proceedings), Joint Work, Accepted

Modeling of Flexible and Rigid Wheels for Exploration Rover on Rough Terrain

Genya Ishigami, Masatsugu Otsuki, Takashi Kubota, Karl Iagnemma

Proceedings of the 28th International Symposium on Space Technology and Science (ISTS 2011) d-30 2011.06

Research paper (international conference proceedings), Joint Work, Lead author, Corresponding author, Accepted

Performance Analysis and Odometry Improvement of an Omnidirectional Mobile Robot for Outdoor Terrain

Genya Ishigami, Elvine Pineda, Jim Overholt, Greg Hudas, Karl Iagnemma

2011 IEEE/RSJ INTERNATIONAL CONFERENCE ON INTELLIGENT ROBOTS AND SYSTEMS (IEEE) 4091 - 4096 2011

Research paper (international conference proceedings), Joint Work, Lead author, Accepted, ISSN 2153-0858

In this paper an omnidirectional mobile robot that possesses high mobility in rough terrain is presented. The omnidirectional robot has four active split offset caster (ASOC) modules, enabling the robot to move in any planar direction. It also possesses passive suspension articulation, allowing the robot to conform to uneven terrain. The agility of the robot is experimentally evaluated in various configurations. In addition, an odometry method that mitigates position estimation error due to wheel slippage is proposed. A key aspect of the proposed method is to utilize sensory data of wheel velocity, and turning rate around each ASOC pivot shaft, along with kinematic constraints of the robot configuration. Experimental odometry tests with different maneuvers in rough terrain are presented that confirm the utility of the proposed method.

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Path Planning and Evaluation for Planetary Rovers Based on Dynamic Mobility Index

Genya Ishigami, Keiji Nagatani, Kazuya Yoshida

2011 IEEE/RSJ INTERNATIONAL CONFERENCE ON INTELLIGENT ROBOTS AND SYSTEMS (IEEE) 601 - 606 2011

Research paper (international conference proceedings), Joint Work, Lead author, Accepted, ISSN 2153-0858

Planetary exploration rovers are required to (semi-) autonomously navigate itself on rough terrain. In such scenario, a feasible path to be followed must be accurately planned, allowing the rover to safely traverse without any mobility hazards. In this paper, a path planning and evaluation strategy that explicitly considers dynamic mobility of the rover is presented. The proposed strategy consists of the following three steps. First, various paths on a given terrain map are generated with varying weighting factors for path planning algorithm. Each path is then examined through complete dynamic simulations of the rover in which the rover travels along with the path. The simulation result provides a metric for robotic mobility. The metric, termed a dynamic mobility index, consists of stability of the rover, wheel slippage, elapsed time, and energy consumption. All of the paths generated are quantitatively evaluated based on the dynamic mobility index, and then, the most feasible path between them is obtained. Demonstrations for the path planning and evaluation are presented in this paper that confirms the validity of the proposed strategy.

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Multi-material Anisotropic Friction Wheels for Omnidirectional Ground Vehicles,

Genya Ishigami, Jim Overholt, Karl Iagnemma

Proceedings of the 5th International Conference on Advanced Mechatronics pp. 658--662 2010.10

Research paper (international conference proceedings), Joint Work, Lead author, Corresponding author, Accepted

Statistical Mobility Prediction for Planetary Surface Exploration Rovers in Uncertain Terrain

Genya Ishigami, Gaurav Kewlani, Karl Iagnemma

2010 IEEE INTERNATIONAL CONFERENCE ON ROBOTICS AND AUTOMATION (ICRA) 16 ( 4 ) 588 - 593 2010.08

Accepted, ISSN 10504729

Planetary surface exploration rovers must accurately and efficiently predict their mobility on natural, rough terrain. Most approaches to mobility prediction assume precise a priori knowledge of terrain physical parameters, however in practical scenarios knowledge of terrain parameters contains significant uncertainty. In this paper, a statistical method for mobility prediction that incorporates terrain uncertainty is presented. The proposed method consists of two techniques: a wheeled vehicle model for calculating vehicle dynamic motion and wheel-terrain interaction forces, and a stochastic response surface method (SRSM) for modeling of uncertainty. The proposed method generates a predicted motion path of the rover with confidence ellipses indicating the probable rover position due to uncertainty in terrain physical parameters. Rover orientations and wheel slippage are also predicted. The computational efficiency of SRSM as compared to conventional Monte Carlo methods is shown via numerical simulations. Experimental results of rover travel over sloped terrain in two different uncertain terrains are presented that confirms the utility of the proposed mobility prediction method. ©2010 IEEE.

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Development of a Visual Odometry System for a Wheeled Robot on Loose Soil Using a Telecentric Camera

Keiji Nagatani, Ayako Ikeda, Genya Ishigami, Kazuya Yoshida, Isaku Nagai

Advanced Robotics (TAYLOR & FRANCIS LTD) 24 ( 8-9 ) 1149-1167 - 1167 2010.05

Research paper (scientific journal), Joint Work, Accepted, ISSN 0169-1864

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Statistical Mobility Prediction for Planetary Surface Exploration Rovers in Uncertain Terrain,

Genya Ishigami, Gaurav Kewlani, Karl Iagnemma

Proceedings of the 2010 IEEE International Conference on Robotics and Automation (ICRA 2010) pp. 588--593 2010.05

Research paper (international conference proceedings), Joint Work, Lead author, Corresponding author, Accepted

Odometry Correction Using Visual Slip-Angle Estimation for Planetary Rovers

Giulio Reina, Genya Ishigami, Keiji Nagatani, Kazuya Yoshida

Advanced Robotics (VSP BV) 24 ( 3 ) 359-385 - 385 2010.02

Research paper (scientific journal), Joint Work, Accepted, ISSN 0169-1864

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Design and Analysis of a Soft Mobile Robot Composed of Multiple Thermally Activated Joints Driven by a Single Actuator

Nadia Cheng, Genya Ishigami, Stephan Hawthorne, Hao Chen, Malik Hansen, Maria Telleria, Robert Playter, Karl Iagnemma

2010 IEEE INTERNATIONAL CONFERENCE ON ROBOTICS AND AUTOMATION (ICRA) (IEEE) 5207 - 5212 2010

Research paper (international conference proceedings), Joint Work, Accepted, ISSN 1050-4729

Soft robotic systems have applications in industrial, medical, and security applications. Many applications require these robots to be small and lightweight. One challenge in developing a soft robotic system is to drive multiple degrees-of-freedom (DOF) with few actuators, thereby reducing system size and weight. This paper presents the analysis and design of an inchworm-like mobile robot that consists of multiple, independent thermally activated joints but is driven by a single actuator. To realize control of this under-actuated system, a solder-based locking mechanism has been developed to selectively activate individual joints without requiring additional actuators. The design and performance analysis of a prototype mobile robot that is capable of inchworm-like translational and steering motion is described. The design of novel "feet" with anisotropic friction properties is also described.

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Predictable Mobility A Statistical Approach for Planetary Surface Exploration Rovers in Uncertain Terrain

Genya Ishigami, Gaurav Kewlani, Karl Iagnemma

IEEE ROBOTICS & AUTOMATION MAGAZINE (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC) 16 ( 4 ) 61 - 70 2009.12

Research paper (scientific journal), Joint Work, Lead author, Corresponding author, Accepted, ISSN 1070-9932

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Slope Traversal Controls for Planetary Exploration Rover on Sandy Terrain

Genya Ishigami, Keiji Nagatani, Kazuya Yoshida

Journal of Field Robotics (WILEY-BLACKWELL) 26 ( 3 ) 264-286 - 286 2009.03

Research paper (scientific journal), Joint Work, Lead author, Corresponding author, Accepted, ISSN 1556-4959

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Stochastic Mobility-based Path Planning in Uncertain Environments

Gaurav Kewlani, Genya Ishigami, Karl Iagnemma

2009 IEEE-RSJ INTERNATIONAL CONFERENCE ON INTELLIGENT ROBOTS AND SYSTEMS (IEEE) 1183 - 1189 2009

Research paper (international conference proceedings), Joint Work, Accepted

The ability of mobile robots to generate feasible trajectories online is an important requirement for their autonomous operation in unstructured environments. Many path generation techniques focus on generation of time- or distance-optimal paths while obeying dynamic constraints, and often assume precise knowledge of robot and/or environmental (i.e. terrain) properties. In uneven terrain, it is essential that the robot mobility over the terrain be explicitly considered in the planning process. Further, since significant uncertainty is often associated with robot and/or terrain parameter knowledge, this should also be accounted for in a path generation algorithm. Here, extensions to the rapidly exploring random tree (RRT) algorithm are presented that explicitly consider robot mobility and robot parameter uncertainty based on the stochastic response surface method (SRSM). Simulation results suggest that the proposed approach can be used for generating safe paths on uncertain, uneven terrain.

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Action Planner of Hybrid Leg-Wheel Robots for Lunar and Planetary Exploration.

Eric Rohmer, Giulio Reina, Genya Ishigami, Keiji Nagatani, Kazuya Yoshida

Proceedings of the 2008 IEEE/RSJ International Conference on Intelligent Robots and Systems 3902 - 3907 2008.10

Research paper (international conference proceedings), Joint Work, Accepted

In this paper, we propose an action planning algorithm and its evaluation method based on dynamic simulation for a novel type of hybrid leg-wheel rover for planetary exploration. Hybrid leg-wheel robots are recently receiving a growing interest from the space community to explore planets, since they offer an appropriate solution to gain improved speed and mobility on unstructured terrain. However, in order to fully reach the hybrid mechanism's potential, it is necessary to establish an optimal way to define when to use one over the other locomotion mode, depending on the soil conditions and topology. Even though this step is crucial, little attention has been devoted to this topic by the robotic community. The switching of motion mode, that is either wheel or leg are the actions to be planned, that we are considering in this paper. We aim at generating the safest and the least energy demanding path to reach a point of scientific interest. In order to define the optimal path with the set of switching actions required for the robot to follow it, the authors developed an action planning algorithm and a path evaluation method based on a four steps approach. First, an optimal candidate path on a rough terrain is generated based on topology and specifications' criteria functions. Then switching actions are defined along this path depending on the hybrid robot's performances in each motion mode. The next step is a dynamic simulation of the robot controlled to follow the path. Finally, the path is evaluated based on the energy profile spent by the actuators and calculated by the simulation. Demonstrations for the proposed technique are addressed along with a discussion on characteristics of the candidate path and the energy profile of the robot. ©2008 IEEE.

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Trafficability Analysis for Lunar/Planetary Exploration Rover Using Thrust-Cornering Characteristic Diagram Proc. of IEEE/RSJInt

Genya Ishigami, Keiji Nagatani, Kazuya Yoshida

Conference on Intelligent Robots and Systems 2228 - 2233 2008.09

Research paper (international conference proceedings), Joint Work, Lead author, Corresponding author, Accepted

In this paper, a trafficability analysis for the exploration rover is described. A rover traveling on loose terrain often experiences its slippages (wheel slips or vehicle sideslip), and in particular, these slips become larger when the rover traverses on sandy slopes. The authors have investigated traction mechanics of a rigid wheel of the rover on loose terrain with paying attention to slipping behaviors of the wheel. In this paper, based on our previous works regarding the wheel-terrain mechanics, we propose a Thrust-Cornering Characteristic Diagram for trafficability analyses of the rover. The thrust-cornering characteristic diagram consists of various characteristics curves of wheel forces, namely thrust and cornering forces, with various wheel slippage conditions. This diagram provides quantitative criteria for slope traversing capability of the rover on arbitrary angles of slope. The usefulness of the proposed diagram for the trafficability analysis is confirmed through slope traversal experiments using a four-wheel test bed. Further, a steering maneuver control for slope traversing situation is discussed based on the diagram. ©2008 IEEE.

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Slope Traversal Experiments with Slip Compensation Control for Lunar/Planetary Exploration Rover

Genya Ishigami, Keiji Nagatani, Kazuya Yoshida

IEEE International Conference on Robotics and Automation 2295 - 2300 2008.09

Accepted, ISSN 10504729

This paper presents slope traversal experiments with slip compensation control for lunar/planetary exploration rovers. On loose soil, wheels of the rover easily slip even when the rover travels with relatively low velocity. Because of the slip, following an arbitrary path on loose soil becomes a difficult task for the rover, and also, the slip will increase when the rover traverses a slope. To cope with the slip issue, the authors previously proposed path following control strategy taking wheel slippages into account. Through numerical simulations in the previous work, it has been confirmed that the proposed control effectively compensates and reduces the slip motions of the rover, and then, the rover can follow a given path. In order to confirm the usefulness of the proposed control for practical application, slope traversal experiments using a four-wheeled rover test bed are addressed in this paper. The control performance of the slip compensation is compared to that of no slip control based on motion traces of the rover in side slope traversal case. Further, the effectiveness of the proposed control is verified by quantitative evaluations of distance and orientation errors. ©2008 IEEE.

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Sensing Position Planning for Lunar Exploration Rovers2008

Andres Mora, Genya Ishigami, Keiji Nagatani, Kazuya Yoshida

IEEE International Conference on Mechatronics and Automation TA3-3 732 - 737 2008.08

Research paper (international conference proceedings), Joint Work, Accepted

In this paper, the authors present a novel criterion for path planning based on the visibility index caused by obstacles detected through laser range sensors when exploring lunar craters. The proposed path planning algorithm calculates an index based on terrain roughness, path length and occlusion, and determines the areas where obstacles may limit the visibility of the area where the rover must go next. The derivation of the visibility index is explained in detail and the algorithm steps are described throughly. Simulations were carried out in order to test the proposed algorithm and a results are presented. © 2008 IEEE.

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Slope Traversal Experiments with Slip Compensation Control for Lunar/Planetary Exploration Rover,

Genya Ishigami, Keiji Nagatani, Kazuya Yoshida

Proceedings of the 2008 IEEE International Conference on Robotics and Automation (ICRA 2008) pp. 2295--2300 2008.05

Research paper (international conference proceedings), Joint Work, Lead author, Corresponding author, Accepted

Terramechanics-based Analysis and Control for Lunar/Planetary Exploration Robots

Genya Ishigami

東北大学大学院工学研究科航空宇宙工学専攻博士学位論文 2008.02

Doctoral thesis, Single Work, Lead author, Last author, Corresponding author, Accepted

Vision-based Estimation of Slip Angle for Mobile Robots and Planetary Rovers

Giulio Reina, Genya Ishigami, Keiji Nagatani, Kazuya Yoshida

IEEE International Conference on Robotics and Automation 2295 - 2300 2008

Research paper (international conference proceedings), Joint Work, Accepted, ISSN 10504729

For a mobile robot it is critical to detect and compensate for slippage, especially when driving in rough terrain environments. Due to its highly unpredictable nature, drift largely affects the accuracy of localization and control systems, even leading, in extreme cases, to the danger of vehicle entrapment with consequent mission failure. This paper presents a novel method for lateral slip estimation based on visually observing the trace produced by the wheels of the robot, during traverse of soft, deformable terrain, as that expected for lunar and planetary rovers. The proposed algorithm uses a robust Hough transform enhanced by fuzzy reasoning to estimate the angle of inclination of the wheel trace with respect to the vehicle reference frame. Any deviation of the wheel trace from the planned path of the robot suggests occurrence of sideslip that can be detected, and more interestingly, measured. This allows one to estimate the actual heading angle of the robot, usually referred to as the slip angle. The details of the various steps of the visual algorithm are presented and the results of experimental tests performed in the field with an allterrain rover are shown, proving the method to be effective and robust. ©2008 IEEE.

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Path Planning for Planetary Exploration Rovers and Its Evaluation Based on Wheel Slip

Genya Ishigami, Keiji Nagatani, Kazuya Yoshida

Proceedings of the International Conference on Robotics and Automation 2361 - 2366 2007.04

Research paper (international conference proceedings), Joint Work, Lead author, Corresponding author, Accepted, ISSN 10504729

In this paper, a path planning and its evaluation method is described with taking into account wheel slip dynamics of lunar/planetary exploration rovers. The surface of the planetary body is largely covered with powdery soil. On such loose soil, the wheel slippage which will make the rover get stuck must be concerned. Since the slippage dynamically depends on the posture/velocity of vehicle, soil characteristics, and wheel-soil interactions, it becomes difficult issues to incorporate the wheel slip dynamics as a criterion into path-planning algorithms. To tackle the slippage problem, the authors develop the path-planning algorithm and the path-evaluation method based on the following approach. First, a path on a rough terrain is generated with the terrain-based criteria function. Subsequently, the dynamics simulation of a rover is carried out in which the rover is controlled to follow the candidate path. Finally, the path is properly evaluated based on the slip motion profiles calculated by the simulation. Demonstrations for the proposed technique are addressed along with a discussion on characteristics of the candidate path and the slip motion profile of the rover. © 2007 IEEE.

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Terramechanics-Based Model for Steering Maneuver of Planetary Exploration Rovers on Loose Soil

Genya Ishigami, Akiko Miwa, Keiji Nagatani, Kazuya Yoshida

Journal of Field Robotics (JOHN WILEY & SONS INC) 24 ( 3 ) 233--250 - 250 2007.03

Research paper (scientific journal), Joint Work, Lead author, Corresponding author, Accepted, ISSN 1556-4959

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Path Following Control with Slip Compensation on Loose Soil for Exploration Rover

Genya Ishigami, Keiji Nagatani, Kazuya Yoshida

Proceedings of the 2006 IEEE/RSJ International Conference on Intelligent Robots and Systems 5552 - 5557 2006.10

Research paper (international conference proceedings), Joint Work, Lead author, Corresponding author, Accepted

In this paper, a path following control strategy for lunar/planetary exploration rovers is described, taking into account slip motion of the rover. It is determined that the slip motion of each wheel of the rover must be increased and cannot be neglected when the rover travels on loose soil. Because of slip, following an arbitrary path on loose soil is a difficult task. In order to improve this situation, the authors have developed a path following algorithm with slip compensation. In this algorithm, both steering and driving maneuvers of the rover are derived not only to follow an arbitrary path, but also simultaneously compensate for the slip. The performance of the path following strategy is confirmed through numerical simulation using the wheel-and-vehicle model elaborated in our previous research. The slip motion of the wheel is also addressed, based on a terramechanics approach. The proposed path following algorithm shows better performance than traditional control without slip compensation in the simulation. © 2006 IEEE.

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Terramechanics-Based Analysis on Slope Traversability for a Planetary Exploration Rover

Ishigami, G., Miwa, A., Nagatani, K., and Yoshida, K.,

Proceedings of the 25th International Symposium on Space Technology and Science (ISTS 2006) pp. 1025--1030 2006.06

Research paper (international conference proceedings), Joint Work, Lead author, Corresponding author, Accepted

Terramechanics-based analysis and traction control of a lunar/planetary rover

Kazuya Yoshida, Toshinobu Watanabe, Noriyuki Mizuno, Genya Ishigami

FIELD AND SERVICE ROBOTICS: RECENT ADVANCES IN RESEARCH AND APPLICATIONS (SPRINGER-VERLAG BERLIN) 24 225 - 234 2006

Research paper (international conference proceedings), Joint Work, Accepted, ISSN 1610-7438

This paper presents analysis of traction mechanics and control of a lunar/planetary rover based on the models obtained from terramechanics. A case study has been conducted for a rover test bed to negotiate a slope of loose soil such as regolith that covers most of lunar surface. The tire traction force is modeled as a function of the vertical load and slip ratio of the wheel. Bekker's terramechanic formulae are employed to derive an improved practical model that calculates net traction force, referred to as Drawbar Pull, with a reasonable precision. Experiments are carried out in two phases. First, the physical behavior of a wheel on loose soil is observed using a single-wheel test bed, then the empirical parameters of the tire and soil are identified. Second, the slope climbing capability is studied by using a rover test bed that has independently driven four wheels. The traction margin and slip margin are defined to be used in a traction control. In the slope experiment, it turned out that the climbing capability was saturated at 14 degrees due to the lack of enough driving torque in wheels. But theoretical investigation suggests that this is not the limitation of terrain trafficability and climbing capability can be improved by increased driving torque and proper load distribution.

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Steering Trajectory Analysis of Planetary Exploration Rovers Based on All-Wheel Dynamics Model

Genya Ishigami, Akiko Miwa, Kazuya Yoshida

The 8th Int. symposium on Artificial Intelligence, Robotics and Automation in Space SP-603 ( 603 ) 1 - 8 2005.09

Research paper (international conference proceedings), Joint Work, Lead author, Corresponding author, ISSN 03796566

This paper describes a steering trajectory analysis for planetary exploration rovers. Analysis of the steering trajectory is an important issue in order to plan and control the motion maneuvers of a planetary rover. Since a rover might easily slip and skid on loose soil, it is difficult to estimate and analyze the motion of the rover or the behavior of its wheels. The authors developed a model that respects the dynamics of each wheel's slip and skid behavior in order to deal with the steering trajectory of the rover. The developed model is called All-Wheel Dynamics Model. In the all-wheel dynamics model, the behavior of each wheel on loose soil is modeled based on terramechanics. The steering trajectory of the rover is obtained by a numerical simulation using the wheel-and-vehicle dynamics model. The proposed model is able to correspond to the experimental results with reasonable precision.

Steering Characteristics of a Rigid Wheel for Exploration on Loose Soil

Kazuya Yoshida, Genya Ishigami

Proceedings of 2004 IEEE/RSJ International Conference on Intelligent Robots and Systems 4 3995 - 4000 2005

Research paper (international conference proceedings), Joint Work, Accepted

In this paper, steering characteristics of a rigid wheel (tire) on loose soil is investigated. Based on terra-mechanic analysis, the lateral force characteristics of a driving wheel is modeled as a function of slip ratio and slip angle. The model suggests that the lateral force decreases according to the increment of the slip ratio and increases according to the increment of the slip angle. Such characteristics are confirmed and evaluated by experiments using simulated lunar-surface soil, called Lunar Regolith Simulant. The proposed model is validated with the experimental results in reasonable precision. A model that properly predicts the lateral force will be useful for future practical issues, such as controlling the steering motion of a vehicle for following a desired trajectory in the operational phase, and also to compare the feasibility and/or stability of candidate steering maneuvers in the motion planning phase.

Steering characteristics of an exploration rover on loose soil based on all-wheel dynamics model

G Ishigami, K Yoshida

2005 IEEE/RSJ INTERNATIONAL CONFERENCE ON INTELLIGENT ROBOTS AND SYSTEMS, VOLS 1-4 (IEEE) 2041 - 2046 2005

Research paper (international conference proceedings), Joint Work, Lead author, Accepted

In this paper, steering characteristics of an exploration rover on loose soil is studied. Analysis of the steering characteristics is a key to plan and control the motion trajectory of a rover. Traditionally, such analysis has been made based on a model called "bicycle model" In that model, a four-wheel car-like vehicle is approximated by a two-wheel bicycle-like vehicle with the fore-wheels and the rear-wheels paired. However, the bicycle model does not show a good performance when a vehicle travels off-road. In order to analyze the steering characteristics of a vehicle on loose soil, the authors develop a model that respects the dynamics of each wheel's slip and skid behavior. The developed model is called All-Wheel Dynamics Model. In the all-wheel dynamics model, the behavior of each wheel on loose soil is modeled based on terramechanics. The motion trajectory of the vehicle is obtained by numerical simulation using the wheel-and-vehicle dynamics model. The validity of the proposed model is examined by the experiments of a wheel and a vehicle using simulated lunar-surface soil. The experimental results show that the proposed model provides a better approximation than the traditional bicycle model.

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Long Range Navigation on Desert by a Dual-Wheel Micro Rover

Genya ISHIGAMI, Noriyuki MIZUNO, Akiko MIWA, Kazuya YOSHIDA

The 24th International Symposium on Space Technology and Science, Miyazaki, Japan 1 - 6 2004

Research paper (international conference proceedings), Joint Work, Lead author, Corresponding author, Accepted

Terramechanics-Based Analysis for Slope Climbing Capability of a Lunar/Planetary Rover

K.Yoshida, N.Mizuno, G.Ishigami, A.Miwa

The 24th International Symposium on Space Technology aned Science,2004 k-6, (6 pages) 2004

Research paper (international conference proceedings), Joint Work, Accepted

Slip, Traction Control, and Navigation of a Lunar Rover

Yoshida, K., Watanabe, T., Mizuno, N., and Ishigami, G.,

Proceedings of the 7th International Symposium on Artificial Intelligence, Robotics and Automation in Space (i-SAIRAS 2003) AS21 2003.06

Research paper (international conference proceedings), Joint Work, Last author

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