Papers - Murakami, Toshiyuki

Wide-Bandwidth Estimation of Cross-Coupling Factors for Advanced Position-Sensorless Control of IPMSM

Shimamoto, K; Murakami, T

IEEJ JOURNAL OF INDUSTRY APPLICATIONS 14 ( 1 ) 111 - 119 2025

ISSN  2187-1094

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Vibration Suppression and Disturbance Rejection Based on Equivalent Mass and Stiffness Matrices

Ito J., Murakami T.

2025 IEEE International Conference on Mechatronics, ICM 2025  2025

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This paper proposes vibration suppression and disturbance rejection methods for multi-degrees-of-freedom (MDOF) manipulators with flexible joints in the workspace. The proposed methods utilize an equivalent mass matrix (EMM) and equivalent stiffness matrix (ESM) that represent the mass and stiffness in the workspace, respectively. In conventional methods, variations of EMM and ESM can degrade vibration suppression and disturbance rejection performances. Therefore, the proposed methods employ a workspace observer (WOB), resonance ratio control, and load-side workspace observer (LWOB). The WOB and resonance ratio control fix the EMM to constant values and realize stable vibration suppression. The LWOB improves ro-bustness by compensating for disturbances. The stability analyses reveal the parameter conditions. The simulation results show that the proposed methods suppress vibrations and disturbances in the workspace.

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A Remote Control Method for Transport Two-Wheeled Mobile Robot

Kuwata M., Murakami T.

2025 IEEE International Conference on Mechatronics, ICM 2025  2025

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This paper investigates the deployment of transport Two-Wheeled Mobile Robots (TWMRs) within warehouse environments. TWMRs have superior maneuverability and a smaller footprint compared to conventional steering-type Autonomous Mobile Robots (AMRs). This feature makes TWMRs well-suited for narrow spaces and high-reach tasks. Despite these advantages, TWMRs are inherently unstable, necessitating sophisticated control systems to maintain balance. In this study, we propose a control system that enables remote operation of the TWMR, allowing the operator to adjust the pitch angle command. The TWMR is equipped with various control mechanisms, including Disturbance Observer (DOB), PD controller and Lyapunov controller. These components work in conjunction to stabilize the TWMR and enhance the translational position tracking performance. Simulation results demonstrated the effectiveness of our approach, showing that the proposed system successfully stabilized the TWMR and reduced pitch angle variations, especially under load conditions. It also suggested the potential of integrating human control ability with advanced control systems for improved TWMR performance.

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A PID-backstepping Hybrid Position and Attitude Control of a Bi-copter AUV with a Moving Mass

Muto K., Murakami T., Simetti E.

2025 IEEE International Conference on Mechatronics, ICM 2025  2025

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This research aims to design a bi-copter AUV and evaluate its feasibility. Autonomous Underwater Vehicles (AUVs) that sail independently without cables and human operators are in the spotlight as an alternative to human divers. To miniaturize AUVs to operate in narrow spaces, we propose an AUV with two thrusters and two pitch angle servo motors: a 'bi-copter' AUV. The bi-copter is expected to be power efficient, and have high turning performance. However, precise and robust control performance is required to overcome its underactuated characteristics and disturbances. To enhance pitch motion stability, a Pitch Motion Compensator (PMC) with a Pitch Angle Disturbance Observer (PADO) is implemented and controls the position of a moving mass inside the AUV body. We propose a PID-Backstepping Hybrid (PBH) control composed of the PID position controller and the backstepping attitude (roll and yaw motion) controller for the position and attitude control. In addition, We propose the yaw angle reference value calculation methodology to control the y position indirectly. Our proposed method is evaluated by the simulations using MATLAB/Simulink and Simscape including wave disturbance and its feasibility is confirmed.

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Topology Optimization for Motor Slot with Heat Generation Rate Depending on Winding Occupancy

Katsuno, A; Murakami, T

IEEJ JOURNAL OF INDUSTRY APPLICATIONS 13 ( 4 ) 453 - 462 2024

ISSN  2187-1094

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Experimental Study of Tracked Vehicle Velocity Using Estimated Disturbance and Machine Learning for Application to Environments Different from Those in Training

Kuwahara H., Murakami T.

IEEJ Journal of Industry Applications (IEEJ Journal of Industry Applications)  13 ( 2 ) 146 - 154 2024

ISSN  21871094

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This study examines the training policies and environmental robustness of a neural network used in velocity estimation for a tracked vehicle with slippage. In the proposed method, the velocity is estimated by a neural network whose input is an estimated disturbance to the driving axle that includes slippage information. First, we experimentally clarify the proposed method’s scope of applicability and effectiveness under different environmental conditions in training and estimation. Subsequently, we experimentally confirm that the estimated disturbance is robust to environmental changes and complementary to environmental information. Finally, the neural network trained on a flat surface is validated in combination with gravity compensation for acceleration to apply it to driving on a slope.

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A Robust Constrained Control of Upper-Limb Exoskeleton for Isometric Rehabilitation Exercises

Pavia M., Murakami T.

IEEE International Symposium on Industrial Electronics  2024

ISSN  21635137

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The research field of muscle rehabilitation and strength recovery is constantly evolving with new techniques and assistive devices being proposed every year. In particular, the need of specialised structures and clinicians, the cost of the rehabilitation and the rising numbers of patients among injured athletes and elderly people, are making rehabilitation robotics a cost-effective alternative. In the last years, researchers have mainly focused on proposing assistive devices to be used during the rehabilitation or new techniques, in order to make the whole process more effective. Nonetheless, the accessibility and the cost of most of the treatments, still leaves a lot of room to improve for a more inclusive access. Besides giving the freedom to the patient to carry out the rehabilitation at home, it is crucial to properly choose the exercise according to the muscles which need to be trained and the condition of the subject. Especially for injured athletes and for the elderly, isometric exercises and static strength training are a good solution to prevent stressing the joints and moving the damaged muscles. Hence, this paper aims to introduce a new musculoskeletal-specific design framework for upper-limb isometric exercises, after having evaluated with a Hexagon Distribution (HD) the muscle condition of the subject. In addition, a 2-DOF wearable and lightweight exoskeleton is introduced to maintain the correct posture of the arm while performing the task. Finally a randomized controlled trial (RCT) is conducted with a cohort of different groups to show the effectiveness of the proposed method.

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Robust Position Control System of MDOF Manipulator with Flexible Joints

Ito J., Murakami T.

IEEE International Symposium on Industrial Electronics  2024

ISSN  21635137

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This paper proposes a disturbance rejection method for a multi-degrees of freedom (MDOF) manipulator with flexible joints. Mechanical transmitters in joints have low stiffness and the arms of the manipulator vibrate during a fast motion. A motor/arm-side encoder that detects motor and arm angles directly is useful for precise position control. In this paper, the MDOF manipulator has motor/arm-side encoders. The system with flexible joints has motor dynamics between the input and torsional reaction torque. It deteriorates disturbance rejection by acceleration control. The proposed method comprises a torque controller compensating for motor dynamics and a filter improving disturbance rejection. The proposed method enables position control that maintains vibration suppression and improves robustness by utilizing both the motor and arm angle. The validity of the proposed method was confirmed by simulations.

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Disturbance Rejection Improvement in Robust Motion Control of Series Elastic Actuator

Ito J., Murakami T.

Proceedings of the IEEE RAS and EMBS International Conference on Biomedical Robotics and Biomechatronics    1599 - 1604 2024

ISSN  21551774

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Contact safety and high control performance are important for human assistive collaborative robots and wearable technology. A series elastic actuator (SEA) has a spring inserted between the motor and the load, which has high compliance. A motor/load-side encoder that acquires motor and load angles enables precise control. SEA with a motor/load-side encoder is appropriate for a human assistive system. However, resonant poles due to the low stiffness of SEA cause resonant vibration and low robustness. Human assistive systems need to achieve control that is precise and robust to disturbances from humans and the environment. This paper proposes a novel control system design that achieves vibration suppression and high robustness. The proposed method consists of torsion torque control and an inverse system filter. By dividing the suppression of resonant pole effects and improving robustness into different controllers, the proposed method makes it easier to design appropriate gains for human assistive systems than conventional methods. The validity of the proposed method and the effect of stiffness error were verified by simulations of position and force control.

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Position-and-Torque-Sensorless Admittance Control with State Estimation Considering dq-axis Cross-Coupling Factors

Shimamoto K., Murakami T.

IFAC-PapersOnLine (IFAC-PapersOnLine)  56 ( 2 ) 6075 - 6080 2023.07

ISSN  2405-8963

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This paper presents a position estimation compensation method considering dq-axis cross-coupling factors of Interior Permanent Magnet Synchronous Motors (IPMSMs) inductance for position-and-torque-sensorless admittance control. The cross-coupling factors are from dq-axis mutual inductance and deteriorate control and position estimation performance in control methods without the model. Since dq-axis cross-coupling factors of inductance vary with the rotor position and the current, measurement and estimation of the values are difficult. The proposed method estimates the cross-coupling factors and position estimation errors using dq-axis current variation from the injected voltage. In addition, the proposed method compensates the estimated position based on a voltage equation, including the dq-axis cross-coupling factors, by adding the estimated error. As a result, the vibration of current, velocity, and estimated reaction torque were reduced, and the performance of a position-and-torque-sensorless admittance control system was improved. The experimental results show the proposed method's validity and response by the sensorless admittance control.

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Assistance Torque Control Based on Musculoskeletal Hexagon Output Distribution for Upper Limb Exoskeleton

Morishita H., Murakami T.

Proceedings - 2023 IEEE International Conference on Mechatronics, ICM 2023 (Proceedings - 2023 IEEE International Conference on Mechatronics, ICM 2023)   2023

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Upper limb exoskeletons are a current focus of technology for rehabilitation and assistance. Although the exoskeletons are actively researched and various applications are being explored, it poses many challenges because of their robot-human fusion of dynamics. In particular, control strategy is one of main problems to solve. Important points of the exoskeleton control are safety, usability, and prevention of insufficient/excessive assistance. Control of physical HumanRobot Interaction (pHRI) without electromyographic (EMG) measurements is one of solutions for the first and the second points. However, the exoskeletons assist based on only payload information in conventional researches and they have disadvantages in third point. Since ease of output of muscles is affected by the limb posture, assistance should be determined based on both payload and musculoskeletal information of each user. Hence, this paper aims to realize musculoskeletal model-based assistance considering ease of output of muscles. For this aim, hexagon distribution (HD)-based assistance torque calculator is proposed. HD expresses human output characteristics of a hand tip by modeling muscles of an upper limb including bi-articular muscles as 6 muscle groups. In proposed control strategy, first, the maximum human output is derived by HD. Second, it is judged whether assistance is sufficient or insufficient. Finally, assistance torque is adjusted in the case of insufficient assistance. To verify effectiveness of the proposed method, an experiment is conducted. As a result, it is confirmed that the proposed method can assist users based on their musculoskeletal characteristics.

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Determination of the Optimal Number of Phases of a Multiphase Bidirectional Chopper Considering AC Loss in Inductor

Nakamura Takayuki, Murakami Toshiyuki

IEEE ACCESS 11   55814 - 55823 2023

ISSN  2169-3536

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Force Sensorless Hybrid Position/Force Control with Equivalent Mass Matrices Switching for Decoupled Rubbing Motion

Shimamoto K., Murakami T.

IEEJ Journal of Industry Applications (IEEJ Journal of Industry Applications)  12 ( 2 ) 107 - 116 2023

ISSN  21871094

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This paper presents a force sensorless workspace hybrid position/force control method with equivalent mass matrices switching for rubbing motion. The equivalent mass matrices express an interference between control axes. Since the determinant of the matrix computed from the design values of robots becomes near zero around the singular configuration of robots, the utilized matrices are often arbitrarily designed. However, inappropriate matrices conditions deteriorate control performance and could cause vibration during rubbing motion. This study reveals suitable equivalent mass matrices for rubbing motion depending on the velocity of the force control axes. Moreover, a hybrid controller with equivalent mass matrices switching depending on the expected velocity of the force control axes in tasks is proposed. The validity of the proposed hybrid controller is demonstrated by the experimental response of rubbing motion with a parallel link type direct-drive four-link manipulator.

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Posture Stabilization Control Compensating Variation of Body Center of Gravity in Underactuated System

Yajima H., Ishizaki K., Miyata Y., Nawa M., Kato N., Murakami T.

Proceedings - 2023 IEEE International Conference on Mechatronics, ICM 2023 (Proceedings - 2023 IEEE International Conference on Mechatronics, ICM 2023)   2023

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With the recent decreasing birthrate and aging population, cooperative robots are attracting attention for a new workforce. As cooperative robot, robots with a small footprint and high center of gravity, like humans, can be considered more suited. Robots with these features are generally unstable, and posture stabilization control becomes important when the center of gravity is shifted due to holding objects or other factors. Therefore, in this study, we select a two-wheeled robot as the target robot and carrying luggage as the target motion, and establish the posture stabilization. Many studies about two-wheeled transport robots do not adequately consider the shift in the center of gravity, which may lead to rapid acceleration and negatively affect position tracking performance. The purpose of this paper is to compensate the shift in the center of gravity of the vehicle, and can perform transport operations in a steady state. To achieve this purpose, we propose to apply Repulsive compliance control(RCC) to a two-wheeled transport robot. Several experiments show its effectiveness.

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Development of Optical Distance, Normal Force, Shear Force Sensor

Baba T., Murakami T., Krebs H.I., Nozaki T.

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

ISSN  21871094

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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.

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

Baba T., Murakami T., Krebs H.I., Nozaki T.

IEEE International Symposium on Industrial Electronics (IEEE International Symposium on Industrial Electronics)  2023-June 2023

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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.

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Individual Pitch Control of Wind Turbine System by Estimating Wind Speed Using Pitching Moment

Yamada M., Murakami T.

IEEJ Journal of Industry Applications (IEEJ Journal of Industry Applications)  12 ( 5 ) 1008 - 1014 2023

ISSN  21871094

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Wind energy conversion systems (WECS) have become increasingly common in recent years as a result of global warming. WECS needs to release the wind through pitch control during high winds. In this study, a novel method for individual pitch control (IPC) via pitching moment estimation is designed. The conventional IPC method considers the blade load, without keeping the rotor speed at the rated value. This study proposes the application of a reaction force observer (RFOB) to the pitch actuators to estimate the pitching moment of each blade. Using the pitching moment information, we estimate the wind speed for each blade, enabling IPC to simultaneously achieve load reduction and maintain the rotor speed at the rated value. The effectiveness of the proposed method is verified via simulations and experiments.

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Lumped Parameter Thermal Model of Heat-Generating General Geometry in Cylindrical Coordinate System

Katsuno, A; Murakami, T

IEEE ACCESS 11   139249 - 139259 2023

ISSN  2169-3536

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Model-Based Pitch Angle Compensation for Center of Gravity Variation in Underactuated System with an Arm

Kanazawa H., Ishizaki K., Miyata Y., Nawa M., Kato N., Murakami T.

IEEE International Symposium on Industrial Electronics (IEEE International Symposium on Industrial Electronics)  2023-June 2023

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Two-wheeled robots are expected to be used at sites where humans work together. The subject of this paper is a two-wheeled robot with an arm, which can take out loads from shelves in the same manner as a human. When the center of gravity (CoG) of the two-wheeled robot shifts back and forth due to placing a load on the arm, the wheel position control performance deteriorates. A possible method to compensate for the shift in the CoG is to use repulsive compliance control (RCC). However, RCC has the disadvantages that the parameters must be adjusted experimentally and the CoG compensation is slow because the pitch angle is determined dynamically. To address these disadvantages, this paper proposes a method that uses model-based CoG compensation and position control for pitch angle. The model-based controller design simplifies parameter setting and achieves fast CoG compensation by statically determining the desired pitch angle. The validity of the proposed method is confirmed through experiments. The obtained results show that the performance of wheel position control is improved when the load is placed on the arm.

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Position-and-Force-Sensorless Control Considering Equivalent Mass Matrix and Cross-Coupling Factors

Shimamoto K., Murakami T.

IECON Proceedings (Industrial Electronics Conference) (IECON Proceedings (Industrial Electronics Conference))   2023

ISSN  21624704

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This paper presents a hybrid position/force control with equivalent mass matrices for position-and-force-sensorless manipulators and the evaluation of the control system. Position and force estimation methods in the controller are cascaded to estimate the position and force according to the respective characteristics of the electrical and mechanical systems. The proposed controller is designed to reduce vibration of the force control axes' motion from the cross-coupling factors of the dq-axis inductance, which cause position estimation error, and the cross-coupling effects among control axes from equivalent mass matrices, which expresses the relationship between the workspace force and acceleration. The position estimation based on the voltage equation, including the cross-coupling factors, derives compensation terms of the estimation error. The cross-coupling effects between position and force control axes in the equivalent mass matrices are designed to suppress the undesired force response vibrations. The experimental results show that the proposed system kept contact with an object during the rubbing motion by a 4-degree-of-freedom manipulator without position and force sensors. The utilized equivalent mass matrix reduced the force vibration caused by the vibration of the position estimation.

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