Papers - NOZAKI, Takahiro

ANEMONE: a framework for three-dimensional simulations of solid-state electroaerodynamic propulsion systems

H Shibata, S Shimizu, T Nozaki

Computer Physics Communications, 109749 315 2025.10

ISSN  00104655

　View Summary

Solid-state electro-aerodynamic propulsion systems are devices that utilize atmospheric pressure corona discharge and have been actively researched in recent years as a means of achieving silent drones. However, these systems contain multiple, widely disparate time and spatial scales. Therefore, the governing equations of the systems, a three-component plasma fluid model that considers the presence of electrons, positive ions, and negative ions, constitute a stiff non-linear system of partial differential equations, challenging to solve. Here, we have developed an ANEMONE simulator capable of numerically estimating the corona inception voltage and energy conversion efficiency in three-dimensional solid-state electro-aerodynamic propulsion systems. Specifically, on the basis of the governing equations, we adopted the method of characteristics and the perturbation method to obtain the sub-problems. Furthermore, we have successfully obtained the integral equations, making the sub-problems easier to solve. Finally, we validated the prediction results based on the theoretical results in a previous study. Remarkably, ANEMONE is the first simulator in the world which predicted the two representative performance (i.e., the corona inception voltage and energy conversion efficiency) of fully three-dimensional propulsion systems. Program summary: Program Title: ANEMONE CPC Library link to program files: https://doi.org/10.17632/2sxsg2pmyp.1 Licensing provisions: MIT Programming language: C++ Nature of problem: Solid-state electro-aerodynamic propulsion system [1] ionizes the ambient air and can propel silent drones. For the rapid-prototyping of the system, it is important to utilize numerical simulation, but the spatial and temporal scales of the system are diverse; hence, the corresponding governing equations (e.g. the three-component plasma fluid model which can simultaneously consider electrons, positive and negative ions) are too stiff to solve. For example, the overall spatial scale of the system is the order of meters, while the scale of the electrodes is the order of micrometers. Moreover, the ions move between electrodes in the order of milliseconds, while the Maxwell dielectric relaxation time scale is in the order of nanoseconds. Solution method: For the issue of the spatial scales, we adopt a three-dimensional hierarchical Cartesian grid method together with the adaptive mesh refinement method. Moreover, this leads fully automatic mesh generation and ensures the grid convergence. For the issue of the temporal scales, we adopt the perturbation method [2] combined with the method of characteristics. This can decompose the original problem into many subproblems easy to solve. References: [1] Haofeng Xu, et al., Flight of an aeroplane with solid-state propulsion, Nature 563 (7732) (2018) 532–535. [2] Hisaichi Shibata, et al., Performance prediction of electrohydrodynamic thrusters by the perturbation method, Phys. Plasmas 23 (5) (2016).

• Access to Document (DOI)

On the integral form of a three-component plasma fluid model

H Shibata, T Nozaki

Physics of Plasmas 32 (6) 32 ( 6 )  2025.06

ISSN  1070664X

　View Summary

Solid-state propulsion is a near-silent plasma thruster that can be mounted on drones. It generates thrust by inducing corona discharge between asymmetric electrodes, which ionizes the surrounding air and accelerates it as a plasma jet. For rapid societal implementation, numerical analysis is crucial and numerous studies have addressed this aspect. However, high-thrust solid-state propulsion systems, such as MSD (multistage ducted thrusters), exhibit complex plasma flows in which both positive and negative corona discharges occur simultaneously. Therefore, MSD analysis requires the adoption of a plasma three-component model that simultaneously accounts for electrons, positive ions, and negative ions. However, because this model involves phenomena with disparate time and spatial scales, it requires substantial computational costs. In this study, different from previous research, we attempt to reduce computational cost and enhance numerical stability by first transforming the partial differential equations representing the three-component model into ordinary differential equations using the method of characteristics and then expressing those in integral form through manual calculation. The derived integral solution was validated by comparing it with experimental results from negative corona discharge within a coaxial cylinder electrode and point-to-plate electrodes and negative corona discharge around a single-stage thruster, confirming that the simulation's predictive accuracy is reliable.

• Access to Document (DOI)

Thrust Control with Switching in Electrodynamic Propulsion Systems with Corona Discharge

S Yashita, H Katagiri, T Kitamura, T Nozaki

2025 IEEE International Conference on Mechatronics (ICM), 1-6  2025

ISSN  2837-1143

　View Summary

Electroaerodynamics (EAD) is one phenomenon that manipulates gas with high voltage. Corona discharge is a typical example and is known to produce thrust quietly without moving parts. Therefore, it is expected to be utilized in various ways, such as a thrust source of drones. As thrust with corona discharge depends on the applied voltage, it is necessary to manipulate the applied voltage for thrust control. However, large-scale systems require several tens of kV, and there is little adequate research on these systems. Thus, an adequate switching method is essential, and it is also crucial to elucidate the effect of switching on thrust. Hence, this study conducted thrust control with corona discharge and analyzed the influence of switching on thrust. Specifically, a resistor is connected in series to the electrode, and a switching element is connected in parallel with the resistor. The proposed method stabilizes and limits the voltage applied to the switching element and effectively controls the thrust and the voltage applied to the electrode. Two experiments were conducted to reveal the electrical characteristics of the electrode in corona discharge and confirm the effectiveness of the proposal. The first experiment showed the potential of switching for the electrode with corona discharge on the collector side. Moreover, the second experiment demonstrated that the proposed switching method worked properly, and thrust can be controlled by changing the duty ratio of switching. The achievements of this study are expected to control levitation systems EAD, such as corona discharge, and realize stable control.

• Access to Document (DOI)

Positioning Control for Voice Coil Motor Using Unbalanced Multilevel Inverter Topology

G Takei, H Obara, R Haneda, T Nozaki

2025 IEEE International Conference on Mechatronics (ICM), 1-6  2025

ISSN  2837-1143

　View Summary

This article proposes a new multi-level inverter (MLI) based on flying capacitor inverter (FCI), with focused on high-precision positioning control for a voice coil motor (VCM). Multi-level inverters (MLIs) have the characteristic that increasing the number of output voltage levels reduces the output voltage error. However, as the number of levels increases, the number of circuit elements increases, and the circuit becomes more complex. In addition, the output voltage amplitude for each level is constant in conventional inverters. As a result, such as high-precision positioning control of VCM, designing an appropriate inverter for a reference wave that contains a large amount of low-voltage components increases the number of circuit elements. Therefore, this paper proposes a MLI with two unbalanced dc-input voltages, referred to as unbalanced MLIs (UMLIs) hereinafter. This topology uses two different dc-input voltages, and it is possible to reduce the output voltage level in extremely low-voltage range compared to other voltage levels. Simulation results when the high-precision positioning control of the VCM confirm that the proposed UMLIs improves the control performance compared to the conventional FCIs with equal number of output voltage levels and uniform level widths.

• Access to Document (DOI)

Investigation of Relationship between Electrode Integration Method and Force-to-Volume Ratio in Force Generation System Using Corona Discharge

H Katagiri, S Yashita, T Kitamura, T Nozaki

2025 IEEE International Conference on Mechatronics (ICM), 1-6  2025

ISSN  2837-1143

　View Summary

A force generation mechanism utilizing corona discharge has the advantages of being lightweight, compact, and having no moving parts. The general structure of an electrode used to generate corona discharge is a wire on the high-voltage side and a flat plate on the ground side. To gain greater force generated by corona discharge, it is necessary to install and integrate a large number of electrodes. However, if a large number of electrodes are integrated, the required volume will increase. Therefore, a method of integrating the electrodes to increase the force-to-volume ratio is needed. Therefore, this paper comprehensively examines the two-dimensional arrangement of electrodes on the ground side and investigates the relationship with the force-to-volume ratio. Specifically, the force-to-volume ratio was investigated when the ground side was made of hollow hexagons, squares, or triangles compared to the wire-plate electrode. Also, since it is known that the force is more significant when needles are used on the high-voltage side rather than wires, the high-voltage side was made into a needle for electrodes with hollow polygons. The experimental results show that the force-to-volume ratios of the needle-hollow polygon electrodes were larger when the applied voltage was low, around 20 kV, and that of the wire-plate electrode was larger when the applied voltage was higher than 30 kV. These results show the relationship between the method of integrating the electrodes and the force-to-volume ratio, which was unknown in corona discharge. They can be used as a reference in the design of actuators.

• Access to Document (DOI)

Performance prediction of fully three-dimensional solid-state propulsion systems by eigenvalue problem decomposition

H Shibata, T Nozaki

arXiv e-prints, arXiv: 2503.17910  2025

Control Stiffness-Based Motion Reproduction for Environmental Impedance Variation

A Takakura, T Nozaki

2025 IEEE International Conference on Mechatronics (ICM), 1-6  2025

ISSN  2837-1143

　View Summary

Motion generation technology contributes to the automation of the robots, especially in the industrial field. Imitation learning and motion reproduction system (MRS) are one of the motion generation methods that widely applied. However, machine learning-based methods require a large amount of data and are weak against extrapolation. Although MRS has merit in terms of the data number, it is weak regarding environmental variation. In particular, the environmental impedance variation have occurred, both position and force tracking are impossible. As several conventional studies have been done to reduce only position or force tracking errors, they can not adapt force or position priority tasks, respectively. Therefore, this paper proposes a novel compensation law based on designed control stiffness using the hybrid angle. The validity of this proposal is confirmed by simulation. This paper contributes to the MRS expansion of the environmental impedance variation with consideration of the task's priority physical value.

• Access to Document (DOI)

ANEMONE: a fully three-dimensional solid-state electro-aerodynamic propulsion system simulator

H Shibata, S Shimizu, T Nozaki

arXiv preprint arXiv:2503.17910  2025

Consideration of Micro-Macro 4-channel Bilateral Control Scheme Using Piezoelectric Actuator

S Kozu, T Nozaki

2025 IEEE International Conference on Mechatronics (ICM), 1-6  2025

ISSN  2837-1143

　View Summary

In micro-manipulations such as cell manipulation, if the operator can feel the tactile sensation of the object, those operations are expected to be more efficient. Scale bilateral control, in which micro-manipulation is performed remotely and position and force information is transmitted bidirectionally between the two systems, could be one of the solutions for tactile transmission. In this control, the use of a linear motor as a human-operating system and a stacked piezoelectric actuator as a micro-manipulating system has been proposed. In this context, a linear motor is an inertial system, and a piezoelectric actuator is a stiff system. However, the control scheme and theory of bilateral control have been established only for inertial systems. In previous studies, piezoelectric actuators were modeled as inertial systems, and the construction of bilateral control systems according to the scheme of inertial systems was attempted. This paper attempts to construct bilateral control by modeling piezoelectric actuators as a second-order linear system close to the actuator's physical properties. Experiments revealed that the proposed bilateral control scheme performs well as the conventional scheme. This study contributes to constructing bilateral control between two systems with different structures.

• Access to Document (DOI)

Force/Tactile Sensation for Contact Task

K Ohnishi, T Nozaki, Y Saito, H Asai, T Kitamura

Emotional Engineering, Vol. 10: Emotional Engineering as a Culture for 22nd …  2025

Development of a Support Vector Machine-based Automated Facial Le Fort I Osteotomy Robot

K Niwa, K Yane, Y Saito, K Hashikawa, T Nozaki

 2025

Simultaneous two-axis position estimation of receiver coil using different radii of transmitter coils in WPT

Y Tomioka, T Nozaki

IECON 2024-50th Annual Conference of the IEEE Industrial Electronics Society …  2024

ISSN  21624704

　View Summary

Wireless power transmission (WPT) is a major technology and is mainly used in transmitting power to small electronic devices. WPT is also expected to be used for larger, higher-power devices such as EVs. One of the problems with the use of WPT is the loss of efficiency due to the misalignment of the transmitter and receiver coils. Previous studies focus on circuital methods to prevent efficiency loss such as impedance matching or frequency tuning. However, these methods do not solve the coil misalignment itself. The purpose of this paper is to propose a two-axis position estimation method in order to eliminate the misalignment. The two axes mean the parallel and vertical directions of the coils. Knowing coil position information in two axes will contribute significantly to position adjustment between coils, compared to the case of only one axis position information. This paper also verified the accuracy of the proposed method experimentally.

• Access to Document (DOI)

Robot command upgrade by integration of position and force information from multiple motion reproduction results

K Yane, T Nozaki

IECON 2024-50th Annual Conference of the IEEE Industrial Electronics Society …  2024

ISSN  21624704

　View Summary

Motion reproduction is a motion generation method in robotics characterized by the small amount of required data and its adaptability to environmental variations. However, completing the task is difficult when the environmental position variation is significant. Therefore, the proposed method generates motion data that is adaptive to environmental fluctuations by performing motion reproduction, with data integrating the position and velocity responses when motion reproduction is performed and the original force response. In simulations, it successfully made contact with the environment even when the distance to the environment was varied. In other words, the proposed method can create motions such that the task succeeded using the failed reproduction data.

• Access to Document (DOI)

Probing Signal Injection for Compatible Realization of Operationality and Impedance Identification

A Takakura, K Yane, T Nozaki

IECON 2024-50th Annual Conference of the IEEE Industrial Electronics Society …  2024

ISSN  21624704

　View Summary

Environmental recognition has an important role in tele-operation. It contributes to the stabilization of complex interactions of robots with the environment. Previous studies have focused on the vision-based method. However, subject dynamics, expressed as stiffness or viscosity, can not be obtained from visual information. One method to determine this is to apply a probing signal to the system and satisfy persistent excitation (PE). However, it comes with the disadvantage of deteriorating operationality for the vibration. Thus, this paper proposed a probing signal compensation method for a 4ch bilateral control system by using a band-pass filter (BPF). Therefore, dynamics identification was accomplished with sufficient PE derived from the probing signal. While on the leader device, oscillations were suppressed and operationality was guaranteed. The proposal contributes to compatible environmental recognition and operationality indemnification for tele-operation systems.

• Access to Document (DOI)

Experimental Validation of Admittance-based Bilateral Teleoperation Preventing Position Drift Using Position-controlled Industrial Manipulators

I Kotani, T Nozaki

IECON 2024-50th Annual Conference of the IEEE Industrial Electronics Society …  2024

ISSN  21624704

　View Summary

Bilateral teleoperation is a key technology that enables to perform contact-rich tasks remotely. Bilateral teleoperation using commercial industrial manipulators has practical advantages, however, industrial manipulators have low backdrivability and no torque control, so admittance-based force control is required. 2ch admittance-based bilateral teleoperation has been proposed that is compatible with industrial manipulators. However, the conventional 2ch admittance-based type does not take into account the discrepancy of admittance control period and communication period between the leader and the follower that bring out position drift. In this paper, 4ch admittance-based bilateral teleoperation that prevents position drift is proposed, and a comparison between three constructs of admittance-based teleoperation using position-controlled industrial manipulator is conducted through experiments using commercial industrial manipulators Yaskawa GP7 and HC10DTP.

• Access to Document (DOI)

Control for 2-DOF electroaerodynamic levitation systems considering discharge characteristics

S Yashita, H Katagiri, K Yane, T Kitamura, H Tsubata, T Nozaki

IECON 2024-50th Annual Conference of the IEEE Industrial Electronics Society …  2024

ISSN  21624704

　View Summary

Electroaerodynamics (EAD) is a phenomenon that generates a gas motion by applying high voltage between electrodes. One method of creating thrust with EAD is the use of the corona discharge, which is a self-sustaining discharge. Since it does not require any moving parts, the corona discharge produces thrust robustly and quietly. Therefore, this thrust system is expected to be utilized as the thrust source for drones. However, since the relationship between thrust and applied voltage is nonlinear, dealing with this problem in control is indispensable. Although some studies have been conducted on control methods with the corona discharge, few have been performed on multidegrees of freedom (DOF) control based on theoretical modeling, which is essential for achieving attitude control during flight. Thus, this paper proposes a control system based on theoretical modeling to realize 2-DOF height and angle control. This study utilizes the idea of differential mode and voltage range limitations and introduces a disturbance observer (DOB) to construct a control system. Two simulations are conducted to verify the effectiveness of the proposal. The first simulation shows that the proposal can follow the command value with small errors, indicating the possibility of multi-DOF control. The second simulation revealed that the proposal significantly suppressed attitude change under disturbance and contributed to improved responsiveness.

• Access to Document (DOI)

Vertical Adjustment Method with Mechanical Power Factor Feedback

T Shimada, K Yane, I Kotani, S Kozu, T Nozaki

2024 IEEE 33rd International Symposium on Industrial Electronics (ISIE), 1-6  2024

ISSN  21635137

　View Summary

There are some dangerous situations under tunnel construction. Since humans fill small halls on the surface of a tunnel with explosives by their hands, they always work with risks of injury or death due to accidents of unexpected explosions or collapses of tunnels. In order to proceed with construction, remote control robots that take the place of their work have been developed. Although they made construction safer for humans, the operation of remote control robots is difficult. This paper proposes a method to adjust the angle vertically by using mechanical power factor feedback. When the robot's arm hits the target object, it estimates an angle deviation by mechanical power. The mechanical power factor is an analogy to power factor in electronics, which is proposed to estimate an angle deviation easily instead of using an angle sensor. It makes it possible not only to evaluate a performance of robots but also estimate an angle deviation for the vertical adjustment. Thus, the proposal has advantages in terms of focusing on the mechanical power factor. By conducting simulations, the results of the estimation of angle deviation were verified.

• Access to Document (DOI)

Realization of Scaled Admittance Bilateral Control with Different Inertias Using Piezoelectric Actuator

S Kozu, I Kotani, K Seki, N Motoi, T Nozaki

2024 IEEE International Conference on Advanced Intelligent Mechatronics (AIM …    1103 - 1108 2024

ISSN  21596247

　View Summary

In micro-manipulations such as cell manipulation, it is desirable for the operator to feel the haptic sensation of the object. Bilateral control can remotely transmit position and force information between leader and follower systems. In this control, the use of a linear motor as a leader and a stacked piezoelectric actuator as a follower has been proposed to achieve micro-scale operation. There is a lot that needs to be clarified about bilateral control when the structure differs between leader and follower systems. In conventional scaled 4channel (4ch) bilateral control, a theory of oblique coordinate control has been proposed that considers differences in the inertia of leader and follower systems. However, when a piezoelectric actuator is used, the control scheme differs from using two linear motors with different inertias because the structures of the leader and follower systems are entirely different. Another method is scaled admittance bilateral control. However, the control design when structures and inertias of the two systems are different has not yet been clarified. In this paper, a scaled admittance bilateral control using a piezoelectric actuator and a linear motor is constructed. Experiments confirm that the realized scaled admittance bilateral control has the equivalent position and force tracking performances as the conventional scaled 4ch bilateral control using a piezoelectric actuator. Furthermore, the designed scaled admittance bilateral control is more robust to fluctuations in the nominal inertia of the piezoelectric actuator than the conventional scaled 4 ch bilateral control.

• Access to Document (DOI)

Motion Reproduction of Loading Explosive with Compensation for Variations in Position and Direction of Hole by Image Processing

M Horikoshi, I Kotani, T Nozaki

2024 IEEE International Conference on Advanced Intelligent Mechatronics (AIM …    1151 - 1156 2024

ISSN  21596247

　View Summary

Mountain tunnel excavation has two problems, which are a shortage of skilled engineers and frequent industrial accidents. Automation of mountain tunnel excavation is progressing to solve these problems. However, loading explosives in mountain tunnel excavation is difficult to automate because this task requires a sense of force. Motion reproduction is an expected method to automate the process of loading explosives that takes the sense of force into account. It uses bilateral control to save and reproduce motions and has the advantage of being able to reproduce forces and teach human skills to manipulators. On the other hand, motion reproduction cannot succeed in saved tasks when the relative position of the loading hole and manipulator or the direction of the loading hole changes from the saving phase. Therefore, this paper proposes a method to compensate for variations in relative position and direction by image processing based on depth information in motion reproduction for automation of loading explosives. Experiments showed the effectiveness of the proposed method through the successful reproduction of the insertion motion despite variations in relative position and direction.

• Access to Document (DOI)

Effect of Coil Size on Efficiency of Wireless Power Transfer with Magnetic Field Resonant by Halbach Array

T Oba, Y Tomioka, T Nozaki

2024 IEEE International Conference on Advanced Intelligent Mechatronics (AIM …    1050 - 1055 2024

ISSN  21596247

　View Summary

In recent years, wireless power transfer (WPT) has become popular from the viewpoint of easy charging. Among them, magnetic field resonance WPT is being researched and developed due to its high efficiency. However, there are magnetic fluxes that cannot be used for power supply and are leaking out in magnetic field resonance WPT. Therefore, this paper applies a special magnet arrangement, a Halbach array, for transmission coils. The Halbach array transmission coils can concentrate the magnetic fluxes on one side. This feature allows the magnetic fluxes to be concentrated to increase the amount of magnetic fluxes chained to the receiving coil. It has a significant effect on efficiency. Since the size of the transmission and receiving coils also affects efficiency, this paper changes the size of the coils and analyzes its effect on efficiency. The efficiency of the Halbach array transmission coils will be confirmed by comparison with conventional transmission coils.

• Access to Document (DOI)

Automatic Explosives Loading System Based on Motion Reproduction Adapting to Changes in Unevenness and Hole Orientation

M Horikoshi, I Kotani, K Yane, A Watanabe, T Nozaki

IEEJ Journal of Industry Applications, 24005263 14 ( 2 ) 196 - 204 2024

ISSN  21871094

　View Summary

Automation of loading explosives in mountain tunnel excavation is being promoted to solve the shortage of skilled technicians and the high incidence of industrial accidents. Loading explosives requires human-specific skills such as appropriate force, sensation, and adaptation to environmental changes, which have not been considered in previous studies. In this study, force-aware automation was realized that can adapt to environmental changes based on motion reproduction. Motion reproduction uses bilateral control to record and reproduce movements, and has the advantage of reproducing forces and teaching human skills to manipulators. Meanwhile, if the 3D relative position of a loading hole and a 6-DOF manipulator or the orientation or the unevenness of the loading hole changes from the recording mode, the recorded task will not be successful. Therefore, a method is proposed herein for detecting the 3D relative position, orientation, and unevenness of a loading hole, besides a method of motion reproduction with compensation for these changes to realize an automatic explosives loading system. The orientation is detected from the area of the ellipse extracted via image processing. Experiments confirmed that changes from the recording mode could be compensated for during reproducing so that recorded insertion motion could be successfully reproduced, even if the position and orientation changed.

• Access to Document (DOI)

Motion Generation in Hybrid Control Converted from Human Motion Data

K Yane, T Nozaki

2024 IEEE 18th International Conference on Advanced Motion Control (AMC), 1-6  2024

Modeling of Device Using Corona Discharge Considering Voltage Range Limitation and Delay

S Yashita, H Katagiri, T Kitamura, T Nozaki

2024 IEEE 18th International Conference on Advanced Motion Control (AMC), 1-6  2024

Data generation device and data generation system

Y Saito, K Ohnishi, T Nozaki

US Patent 12,123,796  2024

Verification of Anode Position and Generated Force Vector of EHD at Wire-cylinder Electrode

T Kitamura, H Katagiri, S Yashita, Y Saito, H Asai, K Ohnishi, T Nozaki

2023 IEEE 32nd International Symposium on Industrial Electronics (ISIE), 1-6 2023-June 2023

　View Summary

Electrohydrodynamics (EHD) is a thrust force produced when high voltage is applied to two electrodes, and actuators using EHD are expected to reduce equipment size and the effects of friction. However, the EHD effect of multiple anode electrodes has yet to be verified and should be considered when fabricating a multi-degree-of-freedom actuator using EHD. This paper examines the relationship between the applied voltage and the generated EHD to verify the effect of multiple anode electrodes on the EHD. Experiments were conducted using a device with two anode electrodes at right angles and another with two parallel electrodes. The results showed that the two anode electrodes placed at right angles interfered with each other, and the generated forces were not superposed. The direction of the generated force was approximately 45 deg. When the electrodes were placed horizontally, it was confirmed that the generated forces were superposed, indicating that the arrangement, not the number of anode electrodes, was the cause of the interference.

• Access to Document (DOI)

Preliminary Study of Object Recognition by Converting Physical Responses to Images in Two Dimensions

K Yane, T Nozaki

2023 IEEE International Conference on Mechatronics (ICM), 1-6  2023

　View Summary

The use of robots is desired as a replacement for human labor. However, it is difficult for robots to respond flexibly to changes in objects and environments and perform tasks. Recently, many systems have been proposed that can flexibly respond to changes by generating robot motions using machine learning. Many machine learning methods use a camera to acquire environmental information, and feature extraction is performed using images acquired from the camera using CNN (Convolutional Neural Network), CAE (Convolutional Auto Encoder), or other methods. Many methods estimate the input values in the next step by inputting the image features, position data and reaction force data acquired from the robot together into the RNN (Recurrent Neural Network), etc. However, in most cases, the relationship between the image and robot data is learned without explicitly stating it. Therefore, in this paper, the data acquired from the robot is converted to images and used in combination with images from the camera to make the interaction between the robot and the environment explicit and to improve the estimation accuracy of NNs. In simulations, the proposed method was used to perform the task of discriminating the target of motion, and the high estimation accuracy was confirmed. In the future, we plan to use this method as input data for motion generation to generate motion according to the object.

• Access to Document (DOI)

Estimation of Coil Position Using Receiving Voltage for Wireless Power Transfer with Magnetic Field Resonance

Y Tomioka, T Nozaki

IECON 2023-49th Annual Conference of the IEEE Industrial Electronics Society …  2023

ISSN  21624704

　View Summary

Wireless power transfer (WPT) is a widely used technology today, and one challenge is to prevent the reduction of efficiency due to misalignment between the receiver and the transmitter. One solution is to reduce the misalignment by positioning the receiver at the position that maximizes efficiency, but this requires estimating the positional relationship between the devices. This paper aims to estimate the distance between coils by the receiving voltage value using a magnetic field resonance-type WPT device based on the modelings of mutual inductance from previous studies. Modeling of mutual inductance is performed for the coaxial and non-coaxial coil cases, and a theory is derived for estimating the coil positions from the received voltages. Accuracy is evaluated by comparing experimental data of receiving voltage and distance between coils with theoretical values.

• Access to Document (DOI)

Effect of Electrode's Shape and Application Voltage on Thrust Generated by Corona Discharge

H Katagiri, S Yashita, T Kitamura, Y Inada, Y Kazoe, T Nozaki

IECON 2023-49th Annual Conference of the IEEE Industrial Electronics Society …  2023

ISSN  21624704

　View Summary

A method to generate wind based on electrohy-drodynamics (EHD) using corona discharge has been applied to various thrust-producing devices. However, the relationship between electrode structure and wind-induced thrust is still unclear, and electrode design guidelines have not yet been established. Therefore, this paper aims to formulate the relationship between the thrust and electrodes' configuration by taking continuous data from experiments. Experiments were conducted to investigate the change in thrust when the gap between electrodes was varied continuously, and when changing the shape of electrodes, after a preliminary experiment on the relationship between voltage polarity and thrust. Experiments revealed that thrust increased as the gap decreased at the same voltage, thrust began to be generated at a lower voltage when the emitter electrode was needles than when it was a wire. From these experimental results, it was demonstrated that the thrust was expressed as a linear equation of voltage, that there is an inverse proportion-like relationship between the gap and thrust, and that the corona discharge inception voltage became lower when needles were used as the emitter electrode, where the voltage applied, instead of a wire. These findings and considerations will greatly help to establish guidelines for designing devices using this method, which generates thrust without any moving parts.

• Access to Document (DOI)

Development of Optical Proximity/Biaxial Force Sensor and Application to Contact Movement

T Baba, T Murakami, HI Krebs, T Nozaki

2023 IEEE 32nd International Symposium on Industrial Electronics (ISIE), 1-6 2023-June 2023

　View Summary

Proximity sensors measure the distance to an object and detect contact. Hence, proximity sensors are typically mounted and used in end-effectors. There might be situations where it is necessary to acquire information on not only distance and contact; but also the normal force and shear force. The conventional proximity/biaxial force sensor utilizes beam deflection but brittle material and interference limit its performance. Here we present a novel proximity/decoupled biaxial force sensor made of sturdy materials, springs, and photo reflectors. We demonstrate this sensor's performance and advantage of the proposed sensor in teleoperation and during a task requiring rubbing an object.

• Access to Document (DOI)

Development of Optical Distance, Normal Force, Shear Force Sensor

T Baba, T Murakami, HI Krebs, T Nozaki

IEEJ Journal of Industry Applications 12 (5), 894-900 12 ( 5 ) 894 - 900 2023

ISSN  21871094

　View Summary

Proximity and tactile sensors have been widely used to control robots. However, each of these sensors has its own shortcomings. Visual sensors have blind spots, whereas tactile sensors cannot acquire information when non-contact. To overcome these problems, this study develops an optical sensor that can measure the distance and two-axis forces using a beam structure and photo reflectors. The sensor is inexpensive owing to its simple structure. Moreover, the sensor is demonstrated to have sufficient accuracy for both the distance and force measurements at 0.2, 0.5, and 1.0 Hz. Additionally, the usefulness of the sensor is confirmed based on reduced impact control at the time of contact and force control.

• Access to Document (DOI)

Development of Automatically Controlled Facial Osteotomy Robot using Force Information-For Safe Le Fort I Osteotomy

K Niwa, K Yane, Y Kido, T Kitamura, T Nozaki

2023 IEEE 32nd International Symposium on Industrial Electronics (ISIE), 1-6 2023-June 2023

　View Summary

The development of automatically controlled medical robots (ACMR) has certain limitations. Due to their rigidity, if they are used in surgery, it would be extremely difficult to protect the patient's soft blood vessels and nerves. Hence, ACMR have not been put into practical use. The main purpose of this research is to address the limitations in order to develop the world's first ACMR that has a successful practical application within surgery. The first surgical procedure we aim to apply the ACMR to is Le Fort I osteotomy in maxillofacial surgery. While performing Le Fort I osteotomy, the robots must avoid damage to the descending palatine artery, which can cause fatal bleeding. We succeeded in automatically stopping the osteotomy immediately before the artery without the need to acquire model numerical information in advance, that is, with a model-free detection. The proposed method for auto-stopping is to identify the osteotomy reaction force obtained by the reaction force observer using the concept of the Z-score.

• Access to Document (DOI)

Attitude control method based on differential mode voltage considering start voltage of corona discharge

S Yashita, H Katagiri, T Kitamura, K Yane, Y Inada, Y Kazoe, T Nozaki

IECON 2023-49th Annual Conference of the IEEE Industrial Electronics Society …  2023

ISSN  21624704

　View Summary

A corona discharge is a kind of self-sustaining discharge that is generated by applying high voltage to asymmetric electrodes. The thrust by the corona discharge is expected as a new actuator since it has no moving parts, is quiet, and is robust. However, the relationship between the applied voltage and the thrust is highly nonlinear, which means that this problem must be solved by control. Furthermore, a control system that compensates for disturbances such as wind and modeling errors is also required. Therefore, this paper proposes a control system with a voltage range limitation that takes into account the characteristics of corona discharges and the disturbance observer to improve disturbance suppression characteristics. Two experiments were conducted to confirm the effectiveness of the proposed method. The first experiment shows that the proposed method improves the response speed by 70.0% in step response. The second experiment indicates that the proposed method enhances the response speed by 60.0% in disturbance response and suppresses angle change by 42.3%. Through experiments, it is confirmed that the proposed method succeeded in attitude control on the centimeter order and improved control performance.

• Access to Document (DOI)

Angle Control Using Corona Discharge Considering Voltage Range Limitations

S Yashita, H Katagiri, T Kitamura, Y Inada, Y Kazoe, T Nozaki

2023 IEEE 32nd International Symposium on Industrial Electronics (ISIE), 1-6 2023-June 2023

　View Summary

A corona discharge is a type of self-sustaining discharge, which is often observed between pin-to-plate electrodes under high-voltage application. Force generation using the corona discharge has no moving parts and is robust; therefore it can be used as a new actuator. However, the relationship between the input voltage and output force caused by the corona discharge is highly nonlinear, so it is essential to deal with this issue through control. In particular, it is important to consider the two types of limitations induced by the corona discharge. First, the corona discharge has a lower voltage limit at which the discharge is initiated, thus without the consideration of the corona inception voltage, the response speed deteriorates, and the overshoot increases. Second, excessive applied voltage causes spark discharge, which causes safety problems. Therefore, this paper proposes voltage reference generation and an angle control method based on differential mode voltage that considers the aforementioned voltage range limitations. Simulations confirm that the proposed method improves the response speed by 13.2% and suppresses the overshoot by 28.0% when torque disturbances are added while the applied voltage fit within the desired range.

• Access to Document (DOI)

Admittance separation method for admittance-based bilateral control

I Kotani, T Nozaki

IECON 2023-49th Annual Conference of the IEEE Industrial Electronics Society …  2023

ISSN  21624704

　View Summary

Admittance-based bilateral control is reported to have the same performance as 4ch bilateral control with only force communication. However, admittance-based bilateral control was easy to vibrate when in contact with the hard environment. Previous studies did not assume the contact vibration. Damping injection is one of the effective methods to suppress the vibration, however it generates the extra operational force proportional to velocity. Thus the operability deteriorates. To suppress the contact vibration, this paper proposed admittance separation method. This method used different admittance values for position control and acceleration feedforward. Making a smaller values of admittance for position control is effective in suppressing vibration when in contact with the environment. Moreover, the extra operational force is inertial force, so it is generated only at the beginning of the movement. Thus proposal has advantages in terms of operability. The validity of the proposal was confirmed by simulation of contact with the environment.

• Access to Document (DOI)

Control system, control method, and storage medium

T Nozaki

US Patent App. 18/014,116  2023

Development of an optical sensor capable of measuring distance, tilt, and contact force

T Nozaki, HI Krebs

IEEE Transactions on Industrial Electronics 69 (5), 4938-4945 (IEEE Transactions on Industrial Electronics)  69 ( 5 ) 4938 - 4945 2022.05

ISSN  02780046

　View Summary

Depth, proximity, and tactile sensors are often used in robotic object manipulation. The three types of sensors are combined to address each sensor limitation: Depth use is limited by blind spots and measurable range, proximity sensor is limited to millimetric distances, and the tactile sensor requires direct contact with the object. Here we present a novel sensor that can simultaneously measure millimetric distance and surface tilt, as well as contact force. We demonstrated the advantage of this novel sensor during a contact task. There, we implemented an admittance control and succeeded in achieving smooth transition from zero- to infinite-impedance contact condition and vice-versa. This novel sensor affords the realization of advanced interactions between robot and objects and contrary to previous approaches - limited by distance, blind spots, and impact force during initial contact - demonstrated good performance at all times with smooth and continuous measurements during contact.

• Access to Document (DOI)

Work in the time of Covid-19: actuators and sensors for rehabilitation robotics

R Chaichaowarat, S Nishimura, T Nozaki, HI Krebs

IEEJ Journal of Industry Applications 11 (2), 256-265 (IEEJ Journal of Industry Applications)  11 ( 2 ) 256 - 265 2022

ISSN  21871094

　View Summary

This paper reports on our work conducted during 2020 in the development of actuation and sensing techniques and devices. In gait rehabilitation, active body weight support systems are often needed to guarantee the safety of patients. These support systems are required to operate at two distinct operation points: A high-force operating mode to hold a patient and prevent falls and, conversely, a "transparent mode"that reduces the mechanical impedance of high-force actuators to enable patients, even those who are weak or paralyzed, to easily express movement. However, the ability to deliver high forces and easily manipulate robots is a key challenge in improving the force-based interaction control. Force feedback is an effective approach to reduce the inertia and friction of robots, but stability is paramount particularly when interacting with humans. By modeling the environment as a second-order spring-mass-damper system and considering the phase response, we derived the control parameter gains required to guarantee a stable human-robot interaction. The design of actuators with intrinsically adjustable mechanical properties is a complementary strategy. For instance, the stiffness of actuators can be modulated by adjusting the unsupported length of a cantilever leaf spring. To model the spring stiffness under deflection, an ideal cantilever support model cannot be assumed for a conventional design of a slider with dual roller pairs, particularly with a soft spring. We proposed a beam deflection model considering the non-zero slopes at the contact points between the rollers and spring. The spring parameters were determined to attain the desired range of stiffness with a short traveling distance of the adjuster. For a single degree-offreedom (DOF) linear motion, we investigated a macro-mini actuation concept using an electrorheological-fluid brake. Balancing these conflicting requirements between the driving force generated from the non-backdrivable high-force unit and the low-inertia and low-friction unit was achieved by controlling the electrical field affecting the fluid yield stress between the rotor and stator electrodes of the brake. One of the limitations of the feedback control scheme was noisy force sensors. We discuss our novel proximity and force sensor using optical techniques and conclude with a description of low-profile 3-DOF flat motor.

• Access to Document (DOI)

Recognition of environmental impedance configuration by neural network using time-series contact state response

K Yane, T Nozaki

2022 IEEE 17th International Conference on Advanced Motion Control (AMC …    426 - 431 2022

ISSN  1943-6572

• Access to Document (DOI)

Performance improvement of bilateral teleoperation with hydraulic actuator by friction compensation

Y Saito, H Asai, T Kitamura, W Iida, T Nozaki, K Ohnishi

2022 IEEE 17th International Conference on Advanced Motion Control (AMC …    250 - 255 2022

ISSN  1943-6572

• Access to Document (DOI)

Object Detection in Motion Reproduction System with Segmentation Algorithm

X Sun, T Nozaki, K Ohnishi, T Murakami

2022 IEEE 17th International Conference on Advanced Motion Control (AMC), 42-47    42 - 47 2022

ISSN  1943-6572

• Access to Document (DOI)

Motion Generation Based on Physical Property Estimation in Motion Copy System

T Kitamura, X Sun, Y Saito, H Asai, T Nozaki, K Ohnishi

2022 IEEE 17th International Conference on Advanced Motion Control (AMC), 62-67    62 - 67 2022

ISSN  1943-6572

• Access to Document (DOI)

Model-Free Detection of Penetration and Automatic Stop Control in Dental Implant Surgery Based on Differential Value of Torque

Y Kido, H Kawana, S Asoda, T Nozaki, T Murakami

2022 IEEE 17th International Conference on Advanced Motion Control (AMC …    144 - 149 2022

ISSN  1943-6572

• Access to Document (DOI)

Improvement and Analysis of Position and Speed Estimator in Low Speed Range for IPMSM Based on Disturbance Observer

R Nakatsuka, T Nozaki

2022 IEEE 17th International Conference on Advanced Motion Control (AMC …    225 - 230 2022

ISSN  1943-6572

• Access to Document (DOI)

Force Control at Arbitrary Position of Manipulator Based on Estimated Contact State by Force/Torque Sensor Installed at Base Frame

H Handa, T Nozaki

2022 IEEE 17th International Conference on Advanced Motion Control (AMC …    420 - 425 2022

ISSN  1943-6572

• Access to Document (DOI)

Experimental Verification of a Novel Continuously Variable Transmission with Electro-Hydrostatic Actuator

H Asai, K Sugihara, T Kitamura, Y Saito, K Ohnishi, T Nozaki

2022 IEEE 17th International Conference on Advanced Motion Control (AMC), 30-35    30 - 35 2022

ISSN  1943-6572

• Access to Document (DOI)

Delay Time of Human Motion Generation in Response to Changing Periods in Force Tracking Task

K Yane, HI Krebs, T Nozaki

2022 9th IEEE RAS/EMBS International Conference for Biomedical Robotics and … 2022-August 2022

ISSN  21551774

　View Summary

It is important to understand how humans gen-erate tracking forces when considering the increase of human- robot interactions. Previous research has mostly focused on po-sitional target tasks. A recent study was conducted to investigate the basic characteristics of the force tracking task. That study suggested predictive compensatory behavior in humans during fast rhythmic movements. In this paper, we investigated the relationship between the frequency of rhythmic force generation and predictive compensation in humans. Here we conducted experiments using four square waves with different periods as target values with four healthy young subjects. Subjects were instructed to control the force exerted at the tip of their fingers during a force pursuit tracking task. The results suggest the following: the faster the tracking period, the faster the delay time converges to a steady value; the relationship between the motion period and the rate of convergence is not linear; individual differences in delay time are large when the force generation is transitioning from slow to very fast, which corresponds to the rhythmic task; when the period is extremely short (the period is 1 sec), the ascent and descent force characteristics are different.

• Access to Document (DOI)

Position/force controller, and position/force control method and storage medium

K Ohnishi, T Nozaki, T Mizoguchi

US Patent App. 17/429,240  2022

Position and Speed Estimation in Low Speed Range for IPMSM Based on Disturbance Observer

R Nakatsuka, T Nozaki

IECON 2021–47th Annual Conference of the IEEE Industrial Electronics Society … (IECON Proceedings (Industrial Electronics Conference))  2021-October 2021.10

ISSN  1553-572X

　View Summary

Interior Permanent Magnet Synchronous Motors (IPMSM) are an important component for a robotic application because of its high torque property. In order to drive IPMSM with high efficiency, feedback control with rotor position sensors is utilized. However, since those sensors make the instrument size large and the cost high, many researches on sensorless control which is feedback control without position sensors have been conducted. Especially for low-speed range, sensorless control with the use of additional high-frequency signals to detect rotor position has been proposed although these signals might cause rotor vibration or low efficiency. This paper proposes a novel position estimation method based on disturbance observer which detect position estimation error. The estimation method achieves detection of rotor position at low speed since rotor saliency and current derivative are utilized. This method differs from conventional observer-based methods in that the disturbance observer not only estimates the phase, but also estimates the term proportional to the axial error and applies a compensation voltage for it. This method also avoids to use any additional signals such as high-frequency voltage for the estimation. The effectiveness of the proposal was confirmed by simulations.

• Access to Document (DOI)

Stability and Robustness of the Disturbance Observer-Based Motion Control Systems in Discrete-Time Domain

Sariyildiz E., Hangai S., Uzunovic T., Nozaki T., Ohnishi K.

IEEE/ASME Transactions on Mechatronics (IEEE/ASME Transactions on Mechatronics)  26 ( 4 ) 2139 - 2150 2021.08

ISSN  10834435

　View Summary

This article analyses the robust stability and performance of the disturbance observer (DOb) based digital motion control systems in the discrete-time domain. It is shown that the phase margin and the robustness of the digital motion controller can be directly adjusted by tuning the nominal plant model and the bandwidth of the observer. However, they have the upper and lower bounds due to robust stability and performance constraints as well as the noise sensitivity. The constraints on the design parameters of the DOb change when the digital motion controller is synthesized by measuring different states of a servosystem. For example, the bandwidth of the DOb is limited by the noise sensitivity and waterbed effect when the velocity and position measurements are employed in the digital robust motion controller synthesis. The robustness constraint due to the waterbed effect is removed when the DOb is implemented by acceleration measurement. The design constraints on the nominal plant model and the bandwidth of the observer are analytically derived by employing the generalized Bode integral theorem in discrete time. The proposed design constraints allow one to systematically synthesize a high-performance DOb-based digital robust motion controller. The experimental results are given to verify the proposed analysis and synthesis methods.

• Access to Document (DOI)

Identification of contact position and force estimation on manipulator using force sensor implemented on base frame

H Handa, T Nozaki, T Murakami

IEEJ Journal of Industry Applications 10 (3), 324-330 (IEEJ Journal of Industry Applications)  10 ( 3 ) 324 - 330 2021.05

ISSN  21871094

　View Summary

Sensing is essential in human cooperative robots to realize safe and powerful operations against contact with the surrounding environment. Contact sensing has been studied for manipulators to avoid accidents caused by collisions between humans and robots. Conventional research has demonstrated that contact sensing requires many sensors or has a limited measurable range. In the conventional research without sensors, modeling systems, such as frictional force and plant parameters, have been used to estimate the contact force. However, a high reduction ratio mechanism for achieving powerful operations hinders accurate force estimation. This study proposes a method to estimate the contact force and contact position on a manipulator with a high reduction ratio mechanism by installing only one force/torque sensor on the base frame of the manipulator. By using the proposed method, the contact force and contact position can be detected regardless of the location where the contact force is applied. Furthermore, when the contact force is applied in a location where the contact position cannot be accurately estimated, an estimated disturbance or a link motion is used to determine the contact position. The effectiveness of the proposed method is validated through experiments.

• Access to Document (DOI)

Haptic Data Prediction and Extrapolation for Communication Traffic Reduction of Four-Channel Bilateral Control System

Hangai S., Nozaki T.

IEEE Transactions on Industrial Informatics (IEEE Transactions on Industrial Informatics)  17 ( 4 ) 2611 - 2620 2021.04

ISSN  15513203

　View Summary

© 2005-2012 IEEE. Robotic teleoperation with a bilateral control system has attracted attention owing to its haptic transmission performance. However, conventional bilateral control systems require broadband communication to transmit the vivid haptic sensation. This problem limits the application range of the bilateral control systems. The communication traffic can be reduced by predicting and extrapolating the incoming data. However, in the conventional prediction-based methods, only one type (e.g., position, velocity, or force) of data is transmitted per one direction because of the difficulty of predicting multiple independent data. The novelty of this article is the realization of the prediction-based traffic reduction in the four-channel bilateral control system that transmits accurate haptic sensation by communicating both position and force data. By equivalently transforming this control scheme in the structure of impedance control, the transmit data are summed up to one data, equilibrium force. The equilibrium force is not only transmitted but extrapolated on the receiver side. As a result, the communication frequency becomes low without degrading haptic transmission performance. The validity of the proposed method was confirmed through experiments and succeeded to reduce the communication data size to less than 3.0%. The proposed method helps to realize a high-performance bilateral control system on band-limited networks.

• Access to Document (DOI)

Association of periodontal disease with atherosclerosis in 70-year-old Japanese older adults

Kitamura Masahiro, Ikebe Kazunori, Kamide Kei, Gondo Yasuyuki, Yamashita Motozo, Takedachi Masahide, Nozaki Takenori, Fujihara Chiharu, Yamada Satoru, Kashiwagi Yoichiro, Miki Koji, Iwayama Tomoaki, Hatta Kodai, Mihara Yusuke, Kurushima Yuko, Takeshita Hajime, Kabayama Mai, Oguro Ryousuke, Kawai Tatsuo, Akasaka Hiroshi, Takeya Yasushi, Yamamoto Koichi, Sugimoto Ken, Ishizaki Tatsuro, Arai Yasumichi, Masui Yukie, Takahashi Ryutaro, Rakugi Hiromi, Maeda Yoshinobu, Murakami Shinya

ODONTOLOGY 109 ( 2 ) 506 - 513 2021.04

ISSN  1618-1247

• Access to Document (DOI)

Admittance control-based bilateral control system considering position error

S Kimura, T Nozaki, T Murakami

2021 IEEE International Conference on Mechatronics (ICM), 1-6 (2021 IEEE International Conference on Mechatronics, ICM 2021)   2021.03

　View Summary

This paper proposes a bilateral control system implementing an admittance control system. Bilateral control system realizes teleoperation of a remote robot with a sense of touch. We focus on an admittance-based bilateral control system, which needs only two communication channels and has almost the same control performance as an acceleration-based bilateral control system, which is one of the highest transparent teleoperation systems. However, the conventional admittance-based system assumes an ideal communication situation where there is no communication time delay and no packet loss and has possible to increase position error as time goes on in practical use. The proposed admittance-based system achieves the same control performance as the conventional structure without increasing position error even if there is a communication delay. The validity of the proposed system is confirmed through simulations and experiments.

• Access to Document (DOI)

Development of neural network-based explicit force control with disturbance observer

T Okano, T Nozaki, T Murakami

IEEJ Journal of Industry Applications 10 (2), 153-164 (IEEJ Journal of Industry Applications)  10 ( 2 ) 153 - 164 2021.03

ISSN  21871094

　View Summary

Human support robots are in high demand and the performance enhancement through force control has been extensively studied. However, the design of the force controller and selection of appropriate gains are sometimes difficult because they are affected by the conditions of motion such as environmental impedance or model uncertainties. This study discusses force control with a disturbance observer and applies a neural network (NN) into its controller; the NN works as both the feedback and feedforward components. The contribution of this study is to show the development method of force control using disturbance observer and a NN, which enhances the performance of force control from the perspective of both feedback and feedforward components. The structure of the controller and composition of the NN were selected through simulation results; moreover, the compensator based on NN was designed in a frequency range higher than the cutoff frequency of the observer with a small number of hidden layers. Moreover, this study discusses a training method of weights in real time. Simulations and experiments were performed for showing the effectiveness of the proposal.

• Access to Document (DOI)

Discrete-time analysis and synthesis of disturbance observer-based robust force control systems

E Sariyildiz, S Hangai, T Uzunovic, T Nozaki

IEEE Access 9, 148911-148924 (IEEE Access)  9   148911 - 148924 2021

ISSN  2169-3536

　View Summary

This paper analyses Disturbance Observer- (DOb-) based robust force control systems in the discrete-time domain. The robust force controller is implemented using velocity and acceleration measurements. A DOb is employed in an inner-loop to achieve robustness, and another DOb, viz. Reaction Force Observer (RFOb), is employed in an outer-loop to estimate interaction forces and improve the performance of force control. First, the inner-loop is analysed. It is shown that the DOb works as a phaselead/lag compensator tuned by the nominal design parameters in the inner-loop. The phase margin of the inner-loop controller and the bandwidth of the velocity-based (i.e., conventional) DOb are constrained not only by noise-sensitivity but also by the waterbed effect. This explains why we observe unstable responses as the bandwidth of the conventional DOb increases in practice. To eliminate the design constraint due to the waterbed effect, this paper proposes an acceleration-based DOb. Then, the robust force controller is analysed. It is shown that the design parameters of the RFOb have a notable effect on the stability of the robust force control system. For example, the robust force controller has a non-minimum phase zero (zeros) when the RFOb is not properly tuned. This may cause severe stability and performance problems when conducting force control applications. By using the stability and robustness analyses, this paper proposes new design tools which enable one to synthesize a high-performance robust force control system. Simulations and experiments are presented to validate the proposed analysis and synthesis methods.

• Access to Document (DOI)

Development of a microsurgery‐assisted robot for high‐precision thread traction and tension control, and confirmation of its applicability

S Hangai, T Nozaki, T Soma, H Miyashita, S Asoda, M Yazawa, K Sato, ...

The International Journal of Medical Robotics and Computer Assisted Surgery …  2021

Perception of Approaching Objects in Bilateral Control Using Proximity Sensor

T Nozaki, T Karato, T Murakami, HI Krebs

The Proceedings of The 9th IIAE International Conference on Industrial …  2021

Development of a Novel Hydrostatic Continuously Variable Transmission with Fast Path Switching

K Sugihara, T Nozaki, T Murakami

Proceedings of the 9th IIAE International Conference on Industrial …  2021

Characteristics of Human Behavior in Force Modulation while Performing Force Tracking Tasks

Nozaki T., Krebs H.I.

Proceedings of the IEEE RAS and EMBS International Conference on Biomedical Robotics and Biomechatronics (Proceedings of the IEEE RAS and EMBS International Conference on Biomedical Robotics and Biomechatronics)  2020-November   240 - 245 2020.11

ISSN  9781728159072

　View Summary

© 2020 IEEE. In designing a human-computer interface, it is vital to understand the principle behind motion generation in humans. Previous research has mostly focused on kinematics and not kinetics. In this paper, we present the characteristics of human behavior while performing force tracking tasks. Here we present a preliminary study in which three type of measurements were conducted with three healthy young adult male subjects to characterize force modulation (discrete, rhythmic, and target transition). Subjects were instructed to control the force exerted to the load cell during a force pursuit tracking task. The visually-guided discrete attempt investigated human behavior when the target changed discretely (every 5 seconds). The rhythmic attempt investigated human behavior when the target changed continuously and periodically (every 1 second). The target transition required subjects to alter the behavior of the input force. The results suggest the following: the differential value of the force generated by a human is sufficiently large, while the response speed is based on visual information; humans can predict future reference to a small degree and attempt to improve or correct their force; and the rule of superimposition comes into effect with regard to the differential value of force.

• Access to Document (DOI)

Online Motion Modification by Operator in Motion Reproduction System

Sun X., Nozaki T., Ohnishi K., Murakami T.

IECON Proceedings (Industrial Electronics Conference) (IECON Proceedings (Industrial Electronics Conference))  2020-October   668 - 673 2020.10

ISSN  9781728154145

　View Summary

© 2020 IEEE. This paper proposes a novel online motion modification method in motion reproduction system. Motion reproduction is used to reproduce human motion saved through bilateral control. Bilateral control is a teleoperation which can transmit both position and force. Human judgement is needed for compensating the saved motion when the environment is different. However, conventional motion reproduction system only relies on saved motion or environment in slave side. Therefore operators in master side cannot modify the motion after motion has been saved. Instead of just reproducing the motion data, the proposed method adds master system at motion reproduction phase so that an operator can modify the motion. If the master system is simply added to motion reproduction system, the operator's motion and saved motion will interfere each other. Therefore, we propose to use weightings to suppress the interference. Simulated results validates the effectiveness of the proposal.

• Access to Document (DOI)

An Approach to Evaluation Index-Based Gain Scheduling for Acceleration-Based Four-Channel Bilateral Control

精密工学会誌  2020.09

• Access to Document (DOI)

Visualization of important human motion feature using convolutional neural network

Fukui M., Kokubun G., Nozaki T.

Proceedings of the IEEE International Conference on Industrial Technology (Proceedings of the IEEE International Conference on Industrial Technology)  2020-February   406 - 411 2020.02

ISSN  9781728157542

　View Summary

© 2020 IEEE. Human motion feature extraction is necessary for robot motion generation. In particular, feature extraction methods related to non-periodic motion should be proposed. Recently, the number of the human motion recognition studies utilizing Convolutional Neural Network (CNN) is increasing due to the brilliant ability of extracting and identifying features. CNN has the same or better discrimination ability than humans so that the features extracted by CNN are thought to be useful for human motion understanding. However, since the internal structure of CNN is like a black box, it is difficult to understand the extracted features. In order to understand the features, some visualization methods which are utilized in the image field are applied in this paper. Furthermore, the many conventional studies utilizing the gradient are not preferred for visualizing CNN which recognizes human motion because human motion is sensitive for the object which treated. That is, the gradient method does not work because the value varies greatly depending on the environment even in the same motion. Therefore, new visualizing method without using the gradient is proposed in this paper. The proposed method visualizes CNN focusing part by following the neuron in CNN. Since this method does not require the gradient, the stable and accurate visualization can be performed. The effectiveness is shown by experiments.

• Access to Document (DOI)

Extended T-type boost inverter for capacitance reduction

Sugimoto T., Nozaki T., Murakami T.

Proceedings of the IEEE International Conference on Industrial Technology (Proceedings of the IEEE International Conference on Industrial Technology)  2020-February   474 - 479 2020.02

ISSN  9781728157542

　View Summary

© 2020 IEEE. In these days, multilevel inverters are focused thanks to their advantages, such as small voltage stress, low electromagnetic interferences, and harmonics reduction. Generally, renewable energy sources output a low DC voltage. From the viewpoint of efficiency, a single-stage conversion system which can directly change the lower DC-link voltage to higher AC voltage is required. Some single-stage conversion systems have been proposed before. However, these systems have large energy storage such as an inductor and a capacitor. This paper proposes a multilevel boost inverter stepping up the AC output peak voltage at any boost ratio by changing the number of switched capacitors. To reduce the capacitance, the proposed inverter has multiple conduction patterns when the output voltage is boosted. This characteristic distributes the discharging time to multiple capacitors. This inverter can set any maximum boost ratio and apply to the multiphase applications. The operation principle and the boost ability with multiple boost ratios were confirmed by simulations and experiments. The capacitance reduction was also confirmed by simulations.

• Access to Document (DOI)

Independent Drive of Multiple AC Motors Using Amplitude Modulation

Yamada Y., Nozaki T., Murakami T.

Proceedings of the IEEE International Conference on Industrial Technology (Proceedings of the IEEE International Conference on Industrial Technology)  2020-February   181 - 186 2020.02

ISSN  9781728157542

　View Summary

© 2020 IEEE. With the recent development of electric drive technology, systems with multiple electric motors are increasingly used in various applications. Among them, methods of driving multiple electric motors by using only one power source is studied. This multi-motor drive system contributes to the reduction of the number of power supplies and electric parts. Because of these characteristics, the system is effective in reducing the weight and the size of whole system. Therefore, this paper proposes a circuit that can control motors by frequency separation using the principle of amplitude modulation. As a result, it is possible to drive a plurality of motors independently and simultaneously with only one power supply. The simulations of multiple motor drives by the proposed circuit was conducted.

• Access to Document (DOI)

Measurement of joint moments using wearable sensors

Fukutoku K., Nozaki T., Murakami T.

IEEJ Journal of Industry Applications (IEEJ Journal of Industry Applications)  9 ( 2 ) 125 - 131 2020

ISSN  21871094

　View Summary

© 2020 The Institute of Electrical Engineers of Japan. Advanced rehabilitation requires a measurement system that quantitatively analyzes the actions of each individual. Joint moment is an indice used to quantitatively evaluate an individual's actions. Conventionally, force plates and highspeed cameras have been used to analyze joint moments. However, these devices need to be fixed in a laboratory, which limits the measurable motions and measurement range. Further, these sensors are expensive. Hence, it is difficult to use them in medical or nursing care facilities. Therefore, this study aimed to estimate joint moments using inexpensive and wearable sensors. This paper proposes a practical joint moments estimation system using inertial measurement units, which is a wearable sensor. The proposed method uses wearable sensors to measure continuous motion without limitation. It is also cheaper than conventional systems. The effectiveness of the proposed system was verified by comparison with the method using force sensors.

• Access to Document (DOI)

Development of a microsurgery-assisted robot for high-precision thread traction and tension control, and confirmation of its applicability

Hangai S., Nozaki T., Soma T., Miyashita H., Asoda S., Yazawa M., Sato K., Kawana H., Ohnishi K., Kobayashi E.

International Journal of Medical Robotics and Computer Assisted Surgery (International Journal of Medical Robotics and Computer Assisted Surgery)  17 ( 2 ) e2205 2020

ISSN  14785951

　View Summary

© 2020 The Authors. The International Journal of Medical Robotics and Computer Assisted Surgery published by John Wiley & Sons Ltd. Background: Microsurgery requires high skills for suturing using fragile threads, often within narrow surgical fields. Precise tension is required for good healing and to avoid the risk of thread breakage. Methods: To meet the demands, we developed a novel assist robot utilizing high-precision sensorless haptic technology. The robot adopts a cable-driven mechanism to maintain a distance from the surgical area and enhances compatibility with surgical equipment such as microscopes. The robot performance was verified through in vitro and in vivo experiments using a rat model. Results: The realization of precise tension control was confirmed in both experiments. In particular, in the in vivo experiments, the developed robot succeeded to produce a knot with an accurate tension of 0.66% error. Conclusions: The developed robot can realize to control traction force precisely. This technology might open up the window for a full assist robot for microsurgery with haptic feeling.

• Access to Document (DOI)

Impedance Field-based Teleoperation with Data Holders for Reducing Data Traffic in Haptic Transmission and Its Analysis of Performance and Stability

Hangai S., Nozaki T.

IEEE Access (IEEE Access)  9   6334 - 6343 2020

ISSN  2169-3536

　View Summary

CCBY In order to realize a vivid tactile transmission in a teleoperation system, it is necessary to send and receive a lot of motion information such as position, speed, and force with extreme high frequency. In addition, in the actual use, many systems are connected to each other through a network. Against this backdrop, the explosive increase in communication traffic becomes a serious problem. The difficulty of this problem is that there exist complicated exchanges of motion information among the systems and they affect each other. Therefore, this paper proposes a novel configuration of a teleoperation system that consists of the conversion technique of transmitted and received information into a single physical quantity (equilibrium force) and the reconstruction technique of discrete data (ZOH: zero-order hold/FOH: first-order hold). The analyses and experiments revealed that 1) FOH is superior to ZOH in terms of operational force 2) FOH and ZOH are about the same performance in terms of reproducibility 3) FOH tends to be more unstable when the packet transmission period increases.

• Access to Document (DOI)

A Method to Make a Robot Understand What was a Target Object in Motion Copying System

Sun Xiaobai, Nozaki Takahiro, Murakami Toshiyuki, Ohnishi Kouhei

2020 IEEE 16TH INTERNATIONAL WORKSHOP ON ADVANCED MOTION CONTROL (AMC)    241 - 246 2020

ISSN  1943-6572

Observer Structure Considering Reluctance Torque of IPMSM for Noise Resistance

Yamada Y., Nozaki T., Murakami T.

IECON Proceedings (Industrial Electronics Conference) (IECON Proceedings (Industrial Electronics Conference))  2019-October   461 - 466 2019.10

ISSN  9781728148786

　View Summary

© 2019 IEEE. In this paper, Disturbance OBserver (DOB) and Reaction Torque OBserver (RTOB) considering reluctance torque is proposed. By changing the structure of DOB when performing Maximum Torque Per Amplitude Control (MTPAC), a high torque and a robust control system is designed. Specifically, a control system resistant to noise is designed by considering the reluctance torque in the torque constant part. The proposed method is effective in situations where noise is large, as in position sensorless control. Due to the noise resistance, the vibration of the current or torque is reduced. Also, by considering the reluctance torque, the estimated value of the reaction torque can be estimated accurately. Therefore the performance of the force control is improved. The effectiveness of the proposed method is confirmed by simulation.

• Access to Document (DOI)

A Controller Design Method of Bilateral Teleoperation for Velocity Control Driver

Saito Y., Shimmyo S., Nozaki T., Ohnishi K.

IECON Proceedings (Industrial Electronics Conference) (IECON Proceedings (Industrial Electronics Conference))  2019-October   3585 - 3590 2019.10

ISSN  9781728148786

　View Summary

© 2019 IEEE. Bilateral control can realize haptic feedback required for securing safety and diversity in teleoperation by robots. Since conventional approaches are based on a servo controller which has high-performance current control or torque control, there is a barrier for advancing into society. The objective of this paper is to propose a design method of the bilateral controller using velocity control driver to achieve haptic feedback. The velocity control driver such as an inverter is widely used in the industrial fields. In the proposed method, a reaction force observer modified for velocity control driver is used to estimate environmental reaction force. The control system is constructed by applying the concept of hybrid control which controls velocity and force independently, and the concept of modal space which separates motions into functions is also applied. Furthermore, the proposed bilateral controller is designed based on the ideal conditions of operationality and reproducibility. The validity of the proposal is verified through a simulation and an experiment. The obtained results show that the proposed controller successfully achieves the teleoperation with haptic feedback using velocity control driver.

• Access to Document (DOI)

Extended T-Type Boost Inverter Using Switched Capacitors

Sugimoto T., Nozaki T., Murakami T.

IECON Proceedings (Industrial Electronics Conference) (IECON Proceedings (Industrial Electronics Conference))  2019-October   1756 - 1761 2019.10

ISSN  9781728148786

　View Summary

© 2019 IEEE. Recently, for renewable energy applications, multilevel inverters are an attractive option due to their advantages, such as harmonics reduction, low electromagnetic interferences, and small voltage stress. Additionally, lower DC-link voltage should be converted to higher AC voltage, which needs an inverter and a DC-DC boost converter or a transformer. However, the two-stage conversion reduces efficiency and reliability in renewable energy applications. Hence, a single-stage conversion system which can directly change the lower DC-link voltage to higher AC voltage is required. Some single-stage conversion systems have been proposed before. However, the maximum boost ratio and the level of these systems are constant, which limits applications. This paper proposes a multilevel boost inverter stepping up the AC output peak voltage at any boost ratio by changing the number of switched capacitors. The operation principle and the boost ability with multiple boost ratios are confirmed by simulations.

• Access to Document (DOI)

Continuously Variable Transmission by High-speed Path Switching of Linear Electro-hydrostatic Actuator

Sugihara K., Nozaki T., Murakami T.

IECON Proceedings (Industrial Electronics Conference) (IECON Proceedings (Industrial Electronics Conference))  2019-October   3603 - 3608 2019.10

ISSN  9781728148786

　View Summary

© 2019 IEEE. In robotic systems, reduction drives are utilized to increase actuators' force. Actuators with a constant reduction ratio can not achieve characteristics of both high velocity driving and high force driving. In order to perform various tasks, high force drive and high velocity drive are required for robotic actuators since required driving characteristics are different among tasks. Therefore, a mechanism which can change a reduction ratio continuously is needed. This paper proposes a mechanism that can change a reduction ratio with a linear electro-hydrostatic actuator (EHA). The proposed mechanism switches between two discrete reduction ratios by switching two oil paths with solenoid valves. Furthermore, this paper realizes a continuously variable reduction ratio by switching the solenoid valves quickly. This paper confirms that the reduction ratio changes continuously and widely by simulations.

• Access to Document (DOI)

Bandwidth Expansion of Bilateral Teleoperation Based on Synergy of Observer Gain and Velocity Feedback Gain

Shimmyo S., Saito Y., Nozaki T., Ohnishi K.

IECON Proceedings (Industrial Electronics Conference) (IECON Proceedings (Industrial Electronics Conference))  2019-October   3597 - 3602 2019.10

ISSN  9781728148786

　View Summary

© 2019 IEEE. Bilateral control is getting much attention as a key technology in teleoperation. A reproducibility is one of the performance indices of bilateral teleoperation, and four-channel acceleration-based bilateral control (4ch ABC) which has a high reproducibility with wide bandwidth enables operators to feel environmental impedance, clearly. Both position control and force control are required for the 4ch ABC, and a PD controller and a P controller are often utilized with a disturbance observer (DOB) and a reaction force observer (RFOB). This paper discusses how operators can feel environmental impedance with wide bandwidth in the 4ch ABC. A damping ratio of a PD controller has been, conventionally, set about 1 by imitating a traditional design principle of servo control. This paper theoretically reveals that a velocity feedback gain of a PD controller affects a bandwidth of reproducibility as a synergy with observer gains of a DOB, and a PD controller using a high velocity feedback gain is introduced. The validity of the theoretical analysis is confirmed by simulations and experimental results.

• Access to Document (DOI)

Power-based restoration of haptic teleoperation from communication blackout

Hangai S., Nozaki T.

IEEE International Conference on Industrial Informatics (INDIN) (IEEE International Conference on Industrial Informatics (INDIN))  2019-July   583 - 588 2019.07

ISSN  9781728129273

　View Summary

© 2019 IEEE. Recently, network-based control systems attract a lot of attentions. One of the applications of such control systems is haptic transmission using a bilateral control system. In order to construct the bilateral control system over the time delayed-network, many researchers have proposed many methods and succeeded to improve the stability and performance of the system. By assuring the system's passivity, some of conventional methods have succeeded to stabilize the system even when the communication blackout occurs. However, the passivity-based methods are conservative and deteriorate the performance. In this paper, the mode shifting method is proposed to deal with the communication blackout without considering the system's passivity. In the proposed method, the bilateral controller is shifted to a local controller when the communication blackout occurs. By shifting to the local controller, the system is not destabilized by the blackout. Moreover, when the communication recovers, the bilateral controller is gradually restored to regulate the robot's output power. Owing to the power regulation, the robots never damage environmental objects during and after the communication blackout. Therefore, the proposed method realizes stable and safe control even under the blackout. The validity of the proposed method is confirmed by simulations and a experiment.

• Access to Document (DOI)

Sensorless Bilateral Control Using Hall ICs

Akutsu S., Nozaki T., Murakami T.

Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019 (Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019)     243 - 248 2019.05

ISSN  9781538669594

　View Summary

© 2019 IEEE. Sensorless bilateral control has been studied to improve fault-tolerance of teleoperation without using torque sensors, position sensors, and other mechanical sensors. However, sensorless control often has less control accuracy due to model errors, parameter variations, and other unexpected factors. Feedback control with some position sensors is practically required for teleoperation. Therefore, this study aims at sensorless bilateral control using Hall ICs. A proposed bilateral control does not necessarily require disturbance observers unlike a conventional method originally using high-resolution sensors. Owing to this advantage, low-resolution sensors are applicable to the proposed bilateral control. Experiments showed that the proposed method succeeded bilateral control using Hall ICs without mechanical sensors, although the conventional control did not work using the low-resolution sensors. Therefore, the proposed method will be able to enhance fault-tolerance of teleoperation systems.

• Access to Document (DOI)

Symmetric Operational Force Compensator for Bilateral Teleoperation under Time Delay Based on Power Flow Direction

Shimmyo S., Saito Y., Nozaki T., Ohnishi K.

Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019 (Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019)     700 - 705 2019.05

ISSN  9781538669594

　View Summary

© 2019 IEEE. This paper proposes an operational force reduction method for four-channel bilateral teleoperation under time delay. The four-channel bilateral control is an attractive way to realize a remote control with haptic sensation. In general, the haptic sensation deteriorates under the time delay in the four-channel bilateral teleoperation, e.g., operationality of the teleoperation, stability of the system, and other performances. To improve the operationality in free motion, a communication disturbance observer and a three-channel bilateral control have been proposed. Although the operational force in the free motion is reduced by these methods, the system becomes asymmetric. This means that the performance of the remote control from the slave side deteriorates in these methods. To overcome this problem, a novel symmetric compensator by using variable compliance control is proposed. A feedback gain is varied based on a power flow direction. The validity of the proposed method is confirmed by experimental results.

• Access to Document (DOI)

A Decentralized Force Controller Synthesis for Compliant Robots Driven by Series Elastic Actuators

Sariyildiz E., Mutlu R., Nozaki T., Murakami T.

Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019 (Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019)     661 - 666 2019.05

ISSN  9781538669594

　View Summary

© 2019 IEEE. This paper deals with the decentralized force control problem of compliant robots driven by Series Elastic Actuators (SEAs). The decentralized force control problem of a compliant robot manipulator is transformed into the robust position control problem of a servo system by using Hooke's law and lumping the nonlinear dynamics and unknown disturbances of the robot manipulator into a fictitious disturbance variable. In order to precisely follow the reference force trajectories at joint space, i.e., the position trajectories of the servo systems, the robust controller is synthesized by using Disturbance Observer (DOb) and Sliding Mode Control (SMC). Although the robust force controller can be synthesized by using only SMC, the force control signal may suffer from high control signal chattering as the force reference input is increased. In addition to improving the robustness of force control, DOb significantly suppresses the discontinuous control signal chattering by allowing to decrease the SMC gain. When the proposed decentralized robust force controller is implemented, the compliant robot can precisely track desired force trajectories and safely contact to different environments. The validity of the proposed force controller is verified by giving the simulation results of a redundant robot manipulator.

• Access to Document (DOI)

Grasping Point Estimation Based on Stored Motion and Depth Data in Motion Reproduction System

Sun X., Nozaki T., Murakami T., Ohnishi K.

Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019 (Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019)     471 - 476 2019.05

ISSN  9781538669594

　View Summary

© 2019 IEEE. Most countries are running shortage of working force due to the aging population and reduction in the birthrate. Robot manipulators are expected to replace human work. However, it it still difficult for manipulators to do simple tasks such as fruit harvesting, foods cooking or toy assembling. A problem for robotic automation arise in the difficulty in teaching how much force manipulators should use for a task execution. Motion reproduction system, which uses bilateral control to store motion data, is one of a method to teach manipulators motion including position and force. The problem concerning motion reproduction system is that the motion reproducing fails if environment is changed between motion saving phase and motion reproducing phase. Motion reproduction system which can understand and adapt to environment is required. Vision sensor can sense environment. Computer vision is mainly focus on how to classify objects. Vision information is seldom combined with motion control especially force motion. Therefore, I propose a motion reproduction system in which reproduced motion is decided based on several motions and collected depth data. Convolutional Neural Network(CNN) was used to estimate a motion command from a depth image. Saved force data was used to generate labels for training. The label decision is different from conventional Machine learning alzorithm.

• Access to Document (DOI)

Development of Three-Axis Seating Posture Holding Assist Chair and Proposed Variable Compliance Control

Togashi N., Shimono T., Nozaki T., Shibata T., Aoyama Y., Kitahashi Y.

Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019 (Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019)     455 - 460 2019.05

ISSN  9781538669594

　View Summary

© 2019 IEEE. This paper introduces the development of the seating posture holding assist chair and proposes the variable compliance control method. The children with cerebral palsy (CP) cannot control the seating posture themselves. In order to support their life, a wheelchair for holding the seating posture is used. However, the seating posture is holding forcibly. As a result, they get stressed and press their back to wheelchair. From the backgrounds, the seating posture holding assist chair is developed in our research. This chair has three-degrees rotational axis in reclining, twist of hip, and neck. Furthermore, the variable compliance control for holding seating posture is proposed. By experiment of reclining control, the proposed control method is verified.

• Access to Document (DOI)

Automatically-Tuned Damping Injection for Stable Bilateral Control under Time Delay

Hangai S., Nozaki T.

Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019 (Proceedings - 2019 IEEE International Conference on Mechatronics, ICM 2019)     667 - 672 2019.05

ISSN  9781538669594

　View Summary

© 2019 IEEE. Bilateral control is one of the methods to realize a teleoperation with force feedback. However, communication time delay seriously deteriorates operationality and stability of bilateral control. Although 3-channel bilateral control has been proposed to improve operationality, the system becomes unstable in contact motion. Damping injection is an effective method to stabilize the contact motion by producing viscous force. However, this method produces large operational force and deteriorates operationality. Many researchers tried to inject damping without deteriorating operationality. However, their methods are affected by several situations/factors such as delay time or operator's motion speed. As a result, their methods require a redesigning procedure in order to deal with such situations/factors. In this paper, automatically-tuned damping injection is proposed to stabilize the contact motion in 3-channel bilateral control. In the proposed method, damping gain is automatically determined by monitoring the Lyapunov stability of the force control. The effectiveness of the proposed method is verified by experiments.

• Access to Document (DOI)

Design of bilateral control based on equivalent circuit model

Akutsu S., Nozaki T., Murakami T.

Proceedings of the IEEE International Conference on Industrial Technology (Proceedings of the IEEE International Conference on Industrial Technology)  2019-February   1351 - 1356 2019.02

ISSN  9781538663769

　View Summary

© 2019 IEEE. Haptic teleoperation has been studied as an attractive technology for a long time. Although the haptic teleoperation has been already realized by conventional methods, their physical meanings are remained vague and unclear. This paper explains bilateral control for the haptic teleoperation using an equivalent circuit model. Owing to the circuit model, which takes into account characteristics of electrical actuators, a control strategy and its physical meanings are clearly illustrated. Torque (force) control and position (velocity) control for the haptic teleoperation can be designed independently because of mode decomposition. Feedback controller design for each control is based on analyses of sensitivity derived from the equivalent circuit. The control strategy derived from the equivalent circuit have been confirmed by experiments and resulted in the haptic teleoperation.

• Access to Document (DOI)

Impedance Field Expression of Bilateral Control for Reducing Data Traffic in Haptic Transmission

Nozaki T., Shimizu S., Murakami T., Oboe R.

IEEE Transactions on Industrial Electronics (IEEE Transactions on Industrial Electronics)  66 ( 2 ) 1142 - 1150 2019.02

ISSN  02780046

　View Summary

© 1982-2012 IEEE. It is expected that bilateral control will find broad applications such as mobile robot exploration and operations in extreme environments. However, the transmission of vivid haptic sensation requires a rapid data-transfer rate of haptic data due to the short sampling period and high-frequency communication. The objective of this paper is aimed at the traffic reduction of haptic data by exploiting an impedance field equivalence of a standard bilateral control. The proposed approach theoretically clarifies the equivalence of the standard bilateral control and impedance control in terms of haptic transmission. Based on this equivalence, the same performance of a standard bilateral control can be achieved by only communicating the force information that determines the equilibrium position of the impedance control. The validity of the proposed approach is confirmed through both simulations and experiments. The obtained results show that the proposed approach successfully reduced the amount of communicated haptic data without any disadvantages compared with the standard acceleration-based bilateral system. This paper shows novel interpretation that haptic transmission is realized by controlling the equilibrium force, which contributes reducing data traffic in haptic transmission and understanding motion generation.

• Access to Document (DOI)

Multilevel inverter topology using current path change for zero current switching

Sugimoto T., Nozaki T., Murakami T.

IEEJ Journal of Industry Applications (IEEJ Journal of Industry Applications)  8 ( 2 ) 250 - 255 2019

ISSN  21871094

　View Summary

© 2019 The Institute of Electrical Engineers of Japan. In motor drive applications, a high switching frequency is required to mitigate current harmonics, which cause a copper loss. However, the high switching frequency makes the switching loss large. Hence, some switching loss reduction techniques have been studied in the past. These techniques have some problems. This paper proposes a multilevel inverter topology for switching loss reduction. Because of provision of multiple current paths, the proposed inverter realizes the zero current switching. Consequently, a loss of the whole system including an inverter and motor can be reduced with a higher switching frequency. The switching loss of the proposed inverter is smaller than that of the conventional one. It was verified that the proposed inverter has some advantages at high switching frequency, through calculations.

• Access to Document (DOI)

Haptics-Led Innovation for Coming Society

K. Ohnishi and T. Nozaki and Y. Saito and T. Shimono and T. Mizoguchi

2019 IEEE International Electron Devices Meeting (IEDM) ({IEEE})   2019

ISSN  2380-9248

• Access to Document (DOI)

Selective wireless power transfer via magnetic resonant coupling by using variable impedance circuit

Nakagawa T., Sugimoto T., Nozaki T., Murakami T.

Proceedings: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society (Proceedings: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society)     4834 - 4839 2018.12

ISSN  9781509066841

　View Summary

© 2018 IEEE. Recently, Wireless Power Transfer (WPT) via Magnetic Resonant Coupling is especially focused around the world. Since a space will have a lot of devices in the future, WPT considering multiple devices will be required. It is important to consider not only power transfer efficiency but also power distribution when power is wirelessly transferred to multiple devices. The amount of received power in a receiver depends on the impedance of the receiver and the ratio of power distribution has the relation to the impedance. Conventional WPT system requires a few controllable repeaters and the large size of the receiver. In this paper, a variable impedance circuit for power distribution is proposed. Using the proposed circuit controllable by DC voltage, the problem for the conventional system is solved. In the future when WPT is popular, the circuit realizes electrically controllable power distribution.

• Access to Document (DOI)

Position and torque sensorless motion transmission using parameter identification based on least mean squares method

Akutsu S., Nozaki T., Murakami T.

Proceedings: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society (Proceedings: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society)     5098 - 5103 2018.12

ISSN  9781509066841

　View Summary

© 2018 IEEE. Motion transmission is a technology which is expected to be used for teleoperation systems. Sensorless control can improve fault tolerance of teleoperation robots exposed to harsh environments. However, sensorless control methods are generally sensitive to parameter errors of an actuator. A previously proposed sensorless motion transmission method especially requires the accurate value of resistance. Therefore, this work aims to identify resistance of two direct current motors used as a master slave system. Taking account of the master slave system of which common mode and differential mode correspond respectively to torque transmission and velocity synchronization, a least mean squares method jointly using a voltage injection is newly applied to the differential mode. Simulation results validated the proposed identification method and indicated that the sensorless motion transmission succeeded using the identified resistance value. The proposed novel method will improve the usefulness of sensorless motion transmission by adaptability to parameter errors.

• Access to Document (DOI)

Multilevel inverter topology for switching loss reduction

Sugimoto T., Nozaki T., Murakami T.

Proceedings: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society (Proceedings: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society)     1345 - 1350 2018.12

ISSN  9781509066841

　View Summary

© 2018 IEEE. In motor drive application, a high switching frequency is required in order to mitigate current harmonics which cause a copper loss. However, the high switching frequency makes the switching loss large. Hence, some switching loss reduction techniques have been studied before. However, they requires complicated circuits. This paper proposes a multilevel inverter topology for a switching loss reduction. By changing current paths, the proposed inverter realizes the zero current switching. It was experimentally verified that the proposed inverter realizes the zero current switching by a foundation circuit.

• Access to Document (DOI)

Design of a multi-stage stiffness enhancing unit for a soft robotic finger and its robust motion control

Mutlu R., Sariyildiz E., Nozaki T., Alici G.

Proceedings: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society (Proceedings: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society)     5074 - 5079 2018.12

ISSN  9781509066841

　View Summary

© 2018 IEEE. Conventional robotics have always pursued methods to bring robots near human. Human robot interaction (HRI) has gained great momentum to realize freeing robots with various control methods to ensure their safe operations with human presence. Soft robotics, alternatively, focuses on building robots mainly made of low elastic moduli materials, which may not be capable of harming humans due to nature of the materials they are made of, nevertheless, requires stiffness augmentation to be able to transmit relatively higher forces. In this study, we designed and fabricated an underactuated soft robotic finger using fused deposition modelling type 3D printing with a thermoplastic elastomer material. Robotic finger is actuated with a tendon-cable attached to a linear servo-actuator while secondary linear servo-actuator is used to control position of a stiffness-enhancement unit made of bistable metal strips. In order to verify stiffness enhancement, we perform precise position control and estimate external disturbances. Experimental results suggest that estimated external disturbances (i.e. stiffness of soft robotic finger) change under the same position conditions (finger flexion) thanks to precise robust motion controller.

• Access to Document (DOI)

Fiber suspended micro force transmission system using scaling bilateral control

Hangai S., Nozaki T., Ohnishi K.

Proceedings: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society (Proceedings: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society)     4575 - 4580 2018.12

ISSN  9781509066841

　View Summary

© 2018 IEEE. In this paper, friction-reduced scaling bilateral control system for micro force transmission is proposed. Recently, demand for micro manipulation is drastically increasing in the fields of medical or biological science. In order to support micro manipulation, many researchers are trying to apply force feedback to the manipulation. One of the methods is bilateral control with Reaction Force Observer(RFOB). Bilateral control system is composed of a master robot and slave robot. Slave robot tracks master robot's motion and transmits reaction force to operator at master side. In the conventional bilateral control system, if reaction force is smaller than frictional force of machine structure, operator cannot distinguish the slight reaction force at hand. In this paper, actuator is supported by fiber to reduce the frictional force. Furthermore, disturbance arisen by fiber tension is modeled, and compensated. Experiments are conducted to validate the proposal.

• Access to Document (DOI)

Design of iterative learning control for force control considering environmental impedance

Fukui M., Akutsu S., Okano T., Nozaki T., Murakami T.

Proceedings: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society (Proceedings: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society)     4569 - 4574 2018.12

ISSN  9781509066841

　View Summary

© 2018 IEEE. In this paper, a new approach for high-precise force control in repeated tasks is proposed. In the general force control, the feedback control tends to be used for a matching the output force to the desired force safely. However, when the feedback control is used, the input of the plant does not change until the error is observed. The characteristic makes reactivity bad. In the position control, the model-based feedforward control is often used to solve this problem. However, the model-based feedforward control cannot be used in force control due to the difficulty of making the accurate model. The main reason of this problem is the uncertainty of the environmental impedance. Owing to the uncertainty, the model-based feedforward control cannot work properly. To solve this problem, Iterative Learning Control (ILC) is used in this paper. ILC does not require the accurate model, and it is able to match the output force to the desired one through repeated trials. However, the convergence condition in force control has not been analyzed until now. In this paper, by taking account of the environmental impedance of the object, a new convergence restriction is proposed. Under the proposed condition, the force control in repeated tasks becomes more precise. The procedure was demonstrated on simulations.

• Access to Document (DOI)

Design and Evaluation of a Remote Actuated Finger Exoskeleton Using Motion-Copying System for Tendon Rehabilitation

Lemerle S., Nozaki T., Ohnishi K.

IEEE Transactions on Industrial Informatics (IEEE Transactions on Industrial Informatics)  14 ( 11 ) 5167 - 5177 2018.11

ISSN  15513203

　View Summary

© 2017 IEEE. Hand recovery process is a major issue in the rehabilitation field as hands are vital to perform most daily activities. This paper presents the design and evaluation of a one actuated degree-of-freedom exoskeleton finger using flexible actuator to assist patients in rehabilitation process and more specifically in tendon recovery protocols. The control strategy based on the motion-copying system is used to be able to take advantages of the sensation of the patient. The wearability and adaptability of the device are improved, compared to other specific devices, mainly by the use of remote actuation and light-weight materials. Evaluation of the device in terms of wearability, adaptability, repeatability and accuracy of the position estimation are conducted. All these criteria are confirmed. The next step is to test the device in actual recovery protocols to evaluate its efficiency.

• Access to Document (DOI)

Human motion analysis and its application to walking stabilization with COG and ZMP

Kim S., Hirota K., Nozaki T., Murakami T.

IEEE Transactions on Industrial Informatics (IEEE Transactions on Industrial Informatics)  14 ( 11 ) 5178 - 5186 2018.11

ISSN  15513203

　View Summary

© 2005-2012 IEEE. A stability index has been generally used in a gait system of formulaic structure. In this standardized structure, a human model has a center of gravity (COG), while a robot device has a zero moment point (ZMP) with COG as the stability standard in the walking motion. In the gait system of wearable type, the stability of human model is closely related with the robot device, in other words, the COG and ZMP are located in the limited domain of human motion and robot task. In this paper, the human and device are designed individually and the knee joint of human is unconstrained from the device work to allow the human reliance. The stability index that includes the COG and ZMP is defined. The validation of this index is guaranteed through a few tests to describe a correlation between the stability index and the human model condition. Based on the validity of the stability index, the experiment for the walking stabilization is implemented with the ZMP estimation by reaction torque observer.

• Access to Document (DOI)

A Stability Analysis for the Acceleration-Based Robust Position Control of Robot Manipulators via Disturbance Observer

Sariyildiz E., Sekiguchi H., Nozaki T., Ugurlu B., Ohnishi K.

IEEE/ASME Transactions on Mechatronics (IEEE/ASME Transactions on Mechatronics)  23 ( 5 ) 2369 - 2378 2018.10

ISSN  10834435

　View Summary

© 1996-2012 IEEE. This paper proposes a new nonlinear stability analysis for the acceleration-based robust position control of robot manipulators by using disturbance observer (DOb). It is shown that if the nominal inertia matrix is properly tuned in the design of a DOb, then the position error asymptotically goes to zero in regulation control and is uniformly ultimately bounded in trajectory-tracking control. As the bandwidth of a DOb and the nominal inertia matrix are increased, the bound of error shrinks, i.e., the robust stability and performance of the position control system are improved. However, neither the bandwidth of the DOb nor the nominal inertia matrix can be freely increased due to practical design constraints, e.g., the robust position controller becomes more noise-sensitive when they are increased. The proposed stability analysis provides insights into the dynamic behavior of DOb-based robust motion control systems. It is theoretically and experimentally proved that nondiagonal elements of the nominal inertia matrix are useful in improving the stability and in adjusting the tradeoff between robustness and noise sensitivity. The validity of the proposal is verified by simulation and experimental results.

• Access to Document (DOI)

Improvement of supporting robot for lower limb and evaluation of output force in vertical direction

Inamura N., Shimono T., Mizoguchi T., Nozaki T., Ishii S., Ohnishi K.

IEEE/ASME International Conference on Advanced Intelligent Mechatronics, AIM (IEEE/ASME International Conference on Advanced Intelligent Mechatronics, AIM)  2018-July   1240 - 1245 2018.08

ISSN  9781538618547

　View Summary

© 2018 IEEE. There are many falling accidents of elderly people. The main reason of these accidents is that their muscle of lower limb weaken with aging. The purpose of this research is to provide them an assisting robot that can support their weight. As the robot consists of belt and rotational motor, adjusting to subject and subject's posture is easy. Thanks to the structure, hip and knee joints' extensor torques are generated by the belt pulling up when the motor rotates. We also created an evaluation apparatus that simulates human lower limb with pulleys and links to conduct an experiment. In this paper, we consider when to assist during stance phase of walking, and the experiment was conducted in order to confirm whether the apparatus follows the motion equations. Experimental results show that there are some error between calculated force and measured force. This error may be resulted from friction between belt and pulleys.

• Access to Document (DOI)

Artificial Replacement of Human Sensation Using Haptic Transplant Technology

Fukushima S., Sekiguchi H., Saito Y., Iida W., Nozaki T., Ohnishi K.

IEEE Transactions on Industrial Electronics (IEEE Transactions on Industrial Electronics)  65 ( 5 ) 3985 - 3994 2018.05

ISSN  02780046

　View Summary

© 2018 IEEE. This study proposes a novel prosthetic hand that can artificially replace human sensation using haptic transplant technology. Conventional motorized prostheses are unable to precisely control the grasping force of the hand due to the lack of force sensation. In this paper, a haptic prosthetic hand is developed that allows for intuitive operation and precise force adjustment. These functions are realized by artificially transplanting the tactile sensation of a healthy part of the user's body to the amputated part of their body. The haptic transplant technology transmits the force sensation of the prosthesis to the master interface attached to the amputee's healthy part of body using bilateral control without a force sensor. Furthermore, variable compliance control is proposed for flexible adaptation to the shape of the object being grasped. The effectiveness of the proposed system was experimentally verified by comparing the controllability of the proposed system with that of a myoelectric prosthesis. In summary, an artificial replacement for human sensation was developed, and the intuitive operability and flexibility of the proposed system were confirmed.

• Access to Document (DOI)

Translation and inclination control for Intelligent Tension Pole based on mode decoupling method

Hanaoka R., Nozaki T., Murakami T.

IEEJ Journal of Industry Applications (IEEJ Journal of Industry Applications)  7 ( 2 ) 158 - 165 2018

ISSN  21871094

　View Summary

© 2018 The Institute of Electrical Engineers of Japan. An aging society is a serious problem in many developed countries. Due to this issue, there has been a significant increase in the demand for assist devices that can support human motion. This paper proposes a novel assist device, Intelligent Tension Pole (ITP), to assist in indoor activities of daily living (ADL), and it is expected to provide support for achieving self-reliance, space saving, and stability. The structure and control system of this assist device are presented. This novel assist device is based on a movable handrail, and therefore wheels are added to the lower and upper ends of the tension pole. In addition, a ball screw, which enables the ITP to move while stretching to the floor and ceiling at any time using force control, is added. In order to improve user comfort and reduce the risk of falling down of the ITP, translation and inclination controls of the ITP are applied to the wheel control. These controls are controlled independently by the mode decoupling method. Experiments are conducted to verify the effectiveness of the proposed device and its control system.

• Access to Document (DOI)

Position and torque sensorless motion transmission using voltage compensation

Akutsu S., Nozaki T., Sekiguchi H., Murakami T.

IEEJ Journal of Industry Applications (IEEJ Journal of Industry Applications)  7 ( 2 ) 150 - 157 2018

ISSN  21871094

　View Summary

© 2018 The Institute of Electrical Engineers of Japan. This paper aims to realize position and torque sensorless motion transmission between a generator and a motor. The proposed voltage compensation method requires only one current sensor on the generator side. Since the motor side is completely sensorless, this system is suitable for operation under harsh environments. Comparative analyses indicate that the proposed method satisfies the conditions for the transmission of an actual tactile sensation. Simulations and experiments confirmed that motion transmission is realized using the proposed method.

• Access to Document (DOI)

Telexistence and Real Haptics

Takahiro Nozaki and Satoshi Hangai

Journal of the Robotics Society of Japan (The Robotics Society of Japan)  36 ( 10 ) 668 - 672 2018

ISSN  0289-1824

• Access to Document (DOI)