Details of a Researcher - Murakami, Toshiyuki

Papers - Murakami, Toshiyuki

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Disturbance observer for DC motor based on Savitzky-Golay filters and application to bilateral control

Hazaz M., Murakami T.

IEEJ Journal of Industry Applications (IEEJ Journal of Industry Applications) 10 ( 2 ) 227 - 235 2021.03

ISSN 21871094

This paper describes the implementation of a disturbance observer-based controller after Savitzky-Golay filters. The cutoff frequency is a bottleneck for the conventional disturbance observers in DC motors with position measurement. The measurement noise limits the cutoff frequency of the pseudo-derivative in the design of the conventional disturbance observers. This study proposes an implementation of a disturbance observer based on Savitzky-Golay filters to improve the performance in noisy conditions with respect to the cutoff frequency of the time derivative. The proposed method was verified through various numerical simulations and experiments, thereby demonstrating its applications in bilateral control.

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

Okano T., Nozaki T., Murakami T.

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

ISSN 21871094

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.

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Identification of Contact Position and Force Estimation on Manipulator Using Force Sensor Implemented on Base Frame

Handa Hinako, Nozaki Takahiro, Murakami Toshiyuki

IEEJ JOURNAL OF INDUSTRY APPLICATIONS (IEEJ Journal of Industry Applications) 10 ( 3 ) 324 - 330 2021

ISSN 2187-1094

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.

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A Robust Hybrid Position/Force Control Considering Motor Torque Saturation

Ohhira T., Yokota K., Tatsumi S., Murakami T.

IEEE Access (IEEE Access) 9 34515 - 34528 2021

ISSN 2169-3536

This paper proposes a robust hybrid position/force control (HPFC) system for multi-degree of freedom manipulators (MDoFMs) with torque constraints on each joint. General HPFC systems can control the interactive contact forces and positions of manipulators in various environments. In HPFC systems, to improve the control performance for MDoFMs, motor torque saturation should be considered. Thus, a robust HPFC system that considers torque constraints by predictive functional control (PFC) is proposed in this paper. The proposed method simultaneously handles the response characteristics and torque constraints of actuators by using PFC as joint space position controllers. Additionally, the robustness of actuators against external forces is enhanced, and the model parameter errors are compensated by the disturbance observer technique. Moreover, implicit force control law and inverse kinematics are introduced for the workspace position/force control to implement the joint space position controllers. Consequently, the stability and robustness of the actuators are considered, and suitable position/force control can be performed even if the torque is saturated. The validity of the proposed method is tested with three planar manipulator joints with a uniaxial force sensor.

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Variable forgetting factor-based adaptive Kalman filter with disturbance estimation considering observation noise reduction

Ohhira T., Shimada A., Murakami T.

IEEE Access (IEEE Access) 9 100747 - 100756 2021

ISSN 2169-3536

This paper addresses the influence reduction of quantization and observation noises in a disturbance observer (DOB) technique. DOB is a disturbance estimation method that makes control systems robust. However, in implementing low-resolution sensors, disturbance estimates from DOB are considerably influenced by observation and quantization noises. In this paper, a novel DOB design method for simultaneous estimation of state and unknown disturbances, including the reduction of noise influences, is proposed. The proposed method is divided into two components. The first component is a Kalman filter (KF)-based DOB for simultaneous estimation of state and unknown disturbances. To improve the estimation performance through the KF-based DOB, a forgetting factor-based adaptive KF (FAKF) was employed. The second component is an adaptive law for the forgetting factor in the FAKF. The adaptive law is used for balancing the estimation accuracy and observation noise reduction. Simulation results involving various types of noise environments demonstrate the effectiveness of the proposed method.

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Linear Langevin-Based Models Providing Predictive Descriptive Statistics for Postural Sway

Tawaki Y., Nishimura T., Murakami T.

IEEE Access (IEEE Access) 9 114485 - 114494 2021

ISSN 2169-3536

Elderly and disabled people frequently experience falls that may require early assessment and training. The quiet standing test provides descriptive statistics such as the center of pressure (COP) sway data, which can be used to analyze the decline in balance ability. Generally, higher descriptive statistics indicate lower balance ability. Stochastic models can model COP trajectories, and such equation parameters were previously used to assess the balance of patients. However, the model equation is a hypothesis and should be verified. In this study, we evaluated whether stochastic models can predict the descriptive statistics of observed COP trajectories. We estimated the model parameters by fitting postural sway data from 49 individuals in four linear stochastic models, and the prediction accuracy was verified by comparing the observed descriptive statistics with the predicted COP trajectories. We observed that the prediction accuracy of the models with stiffness was much higher than those with viscosity only, and the models with the center of mass (COM) had higher prediction accuracy than COP-only models. Therefore, we identified that coefficients from Langevin-based models contained descriptive statistics about a subject's COP trajectory, which suggested that these coefficients can be used to effectively assess balance issues.

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Tracked Vehicle Velocity Estimation by Disturbance Observer and Machine Learning, and its Application to Driving Force Control for Slippage Suppression

Kuwahara H., Murakami T.

IEEJ Journal of Industry Applications (IEEJ Journal of Industry Applications) 11 ( 1 ) 69 - 75 2021

ISSN 21871094

Tracked vehicles generally involve slippage owing to the interaction between the road and track surfaces, which renders accurate motion control difficult. This paper proposes a velocity estimation method for a tracked vehicle with slippage, and its application to driving force control. In this method, the disturbance estimated by a disturbance observer was used as information related to slippage, and a neural network was constructed for velocity estimation. In addition, a driving force observer was designed using the estimated velocity. The driving control of the tracked vehicle to suppress slippage was achieved by using the feedback of the estimated driving force. The proposed method was evaluated experimentally through the velocity estimation performance and slip suppression performance tests.

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Hybrid Position-Force-Posture-Moment Control Based on Euler Angle/Quaternion Feedback

Nakamura Y., Murakami T.

2020 21st International Conference on Research and Education in Mechatronics, REM 2020 (2020 21st International Conference on Research and Education in Mechatronics, REM 2020) 2020.12

ISSN 9781728162249

This paper proposes the robust system to control the position, force, posture, and moment of the multi-link manipulators. Disturbance Observer (DOB) has been researched as an effective method for the robust motion control, however the rotational components such as posture and moment had not been considered in conventional studies. This paper expands the existing DOB-based translational position control to the position-posture control in 6 Degrees-of-Freedom workspace using Euler angle/Quaternion which are the representative methods to describe the posture. Furthermore, the position-force-posture-moment hybrid control is proposed based on the position-posture control. Through the numerical simulation, the effectiveness of the proposed method was confirmed.

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Monitoring of Gait Features during Outdoor Walking by Simple Foot Mounted IMU System

Tawaki Y., Nishimura T., Murakami T.

IECON Proceedings (Industrial Electronics Conference) (IECON Proceedings (Industrial Electronics Conference)) 2020-October 3413 - 3418 2020.10

ISSN 9781728154145

The world population is ageing. In the aged society, grasping the body condition of the elderly is helpful to choose appropriate rehabilitation. This research focuses on the outdoor walking analysis by use of the simple foot mounted IMU system. The walking feature values are estimated by the algorithm, and they are combined with the GPS data obtained by smartphone to compare the feature values of frail elderly and healthy subject. The differences of walking feature values that are calculated by this system show the usefulness of developed system. The developed system is simple, but useful to grasp the gait features changing of the user.

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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

© 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.

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Bilateral Control under Time Delay by Using Adjustment of Equilibrium Acceleration

Takenouchi T., Murakami T.

IECON Proceedings (Industrial Electronics Conference) (IECON Proceedings (Industrial Electronics Conference)) 2020-October 118 - 123 2020.10

ISSN 9781728154145

© 2020 IEEE. This paper aims to lower the operational force for bilateral control under time delay while guaranteeing stability. Bilateral teleoperation system enables humans to work in remote places. However, time delay on network impairs the stability and the performance. The conventional method has trade-off problem between stability and operationality. This paper introduces the concept of equilibrium acceleration, which includes both position and force information, and proposes a method to detect vibration based on the difference of equilibrium acceleration. As a result, the algorithm can be considered simply, and it is possible to stabilize only during vibration and improve the operationality in free motion. Since this paper does not focus on frequency, but vibration, damping control works only during vibration and the operational force can be reduced compared to the conventional method. The effectiveness of the proposed method is verified by simulations and experiments.

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A Standing-up Assist Control Method Considering Movement Speed

Hiraoka A., Murakami T.

IECON Proceedings (Industrial Electronics Conference) (IECON Proceedings (Industrial Electronics Conference)) 2020-October 71 - 76 2020.10

ISSN 9781728154145

© 2020 IEEE. With the rapid aging population, the need for standing-up assist device has grown because standing-up movement is essential for independent living. The standing-up assist controller needs to accomplish high trajectory-following without high rigidity. Therefore, compliant force coordinate transformation control (CFCT) is applied to the controller. This control method induces user to model trajectory effortlessly. Moreover, this paper proposes the algorithm which considers the differences of standing-up movement speed. The proposed algorithm enables the assist device to support the user regardless of the difference of movement speed. The controller is evaluated through experiments.

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A Stabilization Control in Two-Wheeled Walker with Passive Mechanism for Walking Support

Ominato K., Murakami T.

IECON Proceedings (Industrial Electronics Conference) (IECON Proceedings (Industrial Electronics Conference)) 2020-October 65 - 70 2020.10

ISSN 9781728154145

© 2020 IEEE. The aim of this study was to stabilize the posture of a two-wheeled walker in a torque saturated situation during turning. A two-wheeled walker increases the torque of one of the wheels during a turn, which may result in the torque saturation. There was a problem that the posture stability could not be maintained due to this torque saturation. Therefore, this paper proposes to generate a torque reference value in a torque saturation situation when a two-wheeled walker is turning. The simulation in the proposed method was compared with the case without considering the torque saturation. The simulation results showed that both the posture stability and the turning performance were improved. This indicates that the generation of the torque reference value considering the torque saturation is effective. And, we also propose a method to make the two-wheel walker stand still.

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An approach to human walking analysis based on balance, symmetry and stability using COG, ZMP and CP

Kim S., Murakami T.

Applied Sciences (Switzerland) (Applied Sciences (Switzerland)) 10 ( 20 ) 1 - 17 2020.10

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. The parameters of walking have been studied from the viewpoints of joint rotation and translation of body. The balance and symmetry of walking are indispensable features to understand for healthy walking, while also being a personal characteristic. However, quantification has not been easy to carry out in the case of the conventional gait parameters COG (center of gravity) and ZMP (zero moment point). In this approach, the CP (crossing point) is proposed to quantify the concept of symmetry and balance by comparing it to the COG and ZMP. The CP is estimated based on the intersection between the hip line and the ankle line. While the hip line is fixed on the upper body where the COG is, the ankle line is altered depending on the each footfall, where the ZMP is. Therefore, the values of COG, ZMP, and CP have similar or different tendencies in terms of whether balanced walking results in symmetry or not. The validity of this is verified by carrying out a simulation with robot walking, and an experiment using human walking. Through additional experiments, it was noticed that the CP was able to improve the role of COG and ZMP in terms of not only stability, but also its relationship with the movement range of the lower limbs.

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A multi-sensory dataset for the activities of daily living

Ruzzon Marco, Carfi Alessandro, Ishikawa Takahiro, Mastrogiovanni Fulvio, Murakami Toshiyuki

DATA IN BRIEF 32 2020.10

ISSN 2352-3409

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An approach to evaluation index-based gain scheduling for acceleration-based four-channel bilateral control

Okano T., Nozakt T., Murakami T.

Seimitsu Kogaku Kaishi/Journal of the Japan Society for Precision Engineering (Seimitsu Kogaku Kaishi/Journal of the Japan Society for Precision Engineering) 86 ( 9 ) 720 - 730 2020.09

ISSN 09120289

© 2020 Japan Society for Precision Engineering. All rights reserved. Teleoperation is one of the technologies for supporting operators, and its development is strongly demanded. Acceleration-based four-channel Bilateral Control (ABC) is known as a method of teleoperation and achieves highly precise impedance transmission. The gain scheduling for bilateral contrai has basically been focused on the stability by the model-based approach. However, describing the contact motion and precise identification of some nonlinear terms are sometimes highly difficult. Moreover, the gain parameters between the master and slave tend to be set the same although the transfer function of them are different. Therefore, this paper considers the gain setting from the perspective of precise impedance transmission and proposes the evaluation index-based gain scheduling for A B C by using the experimental data. This paper also discusses the designing of gradient-descent algorithm for an actual gain setting by taking the obtained knowledge from evaluation index-based gain scheduling into consideration. The effectiveness of proposed gain scheduling and gain tuning methods were verified through experiments.

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An Approach to Architecture Design of Bilateral Control System based on a Layer Structure

Tanida K., Okano T., Murakami T., Ohnishi K.

IEEJ Journal of Industry Applications (IEEJ Journal of Industry Applications) 9 ( 4 ) 318 - 330 2020.07

ISSN 21871094

©2020 The Institute of Electrical Engineers of Japan. A bilateral control system aims at realizing a fine haptic transmission between a human operator and a remote environment object. Such a system is expected to realize multiple requirements in practical applications, and the architecture design based on a layer structure has to be considered. This paper treats a surgery robot system as an example, and its system has two requirements: "large workspace"and "fine haptic sensation". Using the conventional bilateral control system to realize these requirements simultaneously is difficult because mechanical and control designs are separately discussed. At the same time, a system that has multiple requirements such as a fine/coarse system is often designed only using position information. This study proposed to consider not only mechanical/control design but also the position/force information simultaneously from the perspective of an architecture design. The proposed architecture decomposes the functions into each motor/robot by defining roles and combining each role in the layer structure. The advantage of the proposal is that a complex system can be designed as a entire by combining multiple sub-functions that can be simply designed. As a result, the surgery robot system is designed by considering its requirements, and the experiments are carried out to verify if the requirements are satisfied. Â

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An approach to success-based data compression considering position/force task

Okano T., Murakami T.

Proceedings of the IEEE International Conference on Industrial Technology (Proceedings of the IEEE International Conference on Industrial Technology) 2020-February 363 - 368 2020.02

ISSN 9781728157542

© 2020 IEEE. The number of robots has been increasing and they would widely conduct activities in a variety of situations. The amounts of motion data distribution would also become larger and larger: therefore, the amounts of each motion data are expected to be compressed. The compression of motion data has been widely discussed, but this study focuses on the success-based approach and considering a position/force task. Since the purpose of machine automation is to conduct some tasks, the data can be compressed in the extent that the task is safely and successfully completed. The sampling time of command loading is changed for reducing the amount of motion data. The algorithm for investigating the required sampling times in each motion period and each degrees-of-freedom is developed and applied, and the appropriate values were experimentally obtained. The data compression of motion commands was confirmed as well as the task success based on its compressed motion command.

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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

© 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.

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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

© 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.

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