論文 - 村上　俊之

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年

ISSN  21871094

　概要を見る

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年

　概要を見る

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年

ISSN  21871094

　概要を見る

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年

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年

　概要を見る

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年

ISSN  21624704

　概要を見る

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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Underactuated Control for Two-Wheeled Mobile Robot with an Arm Using Torque Constraint Conditions and Disturbance Observer

Ito J., Murakami T.

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

　概要を見る

This paper presents an underactuated control system for a two-wheeled mobile robot (TWMR). TWMR is expected to use as an autonomous mobile robot (AMR) that works in human-collaborative spaces. TWMR has a smaller footprint and higher center of gravity (CoG), than typical AMRs. Furthermore, in this study, TWMR has an arm. Therefore, TWMR is superior in handling loads in human-presence spaces. However, TWMR is the underactuated system in the body's translational position and tilting angle. In addition, TWMR is affected by disturbances caused by loads. As a robust underactuated control system, the cascade PI/PD and synthesized pitch angle disturbance observer (SPADO) are considered. The cascade PI/PD results in significant translational position error and oscillatory responses. To cope with this problem, a proposed method minimizes both errors of the translational position and tilting angle within torque constraints. The proposed method utilizes the predictive functional control (PFC) for the underactuated control considering constraints. SPADO improves the accuracy of an internal model of PFC. The validity of the proposed method was confirmed compared with the cascade PI/PD through the simulation.

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A Method of Predicting Posture-related Pain Using Biomechanical Parameters for Patients with Lumbar Spinal Disc Herniation

Hatsushiro A., Tawaki Y., Murakami T.

Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS （Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS）  2023年

ISSN  1557170X

　概要を見る

Lumbar spinal disc herniation is a disease in which the protruding nucleus pulposus presses on the nerve due to actions that place loads on the disc, causing pain in the lower back and lower limbs. About 80% of treatments of disc herniation are conservative treatments, and although it is necessary to live with pain for a long time, there have been no studies that clearly define the relationship between pain and biomechanical parameters. In this study, we proposed a method of identifying biomechanical parameters that predict posture-related pain in patients with lumbar spinal disc herniation. The pain values were quantitatively evaluated by the Numerical Rating Scale (NRS) and the biomechanical parameters were analyzed by OpenSim. Lasso regression was performed to narrow down the biomechanical parameters that were related to pain and derive the mathematical model of the relationship. Therefore, many of the parameters of the obtained mathematical model were related to the lumbar spine and were consistent with areas that be related to lumbar spinal disc herniation.

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Identification of unknown object properties based on tactile motion sequence using 2-finger gripper robot

Thompson J., Kasun Prasanga D., Murakami T.

Precision Engineering （Precision Engineering）  74   347 - 357 2022年03月

ISSN  01416359

　概要を見る

The purpose of service robots is to work and handle a wide range of objects in a human environment. Therefore, they must have the ability to grasp unknown objects with the appropriate force, by dynamically identifying their stiffness, mass, and surface-interaction properties. To ensure the successful grasping of unknown objects, it is significant to estimate the object response properties. In this paper, the cognitive functions to efficiently perform such operations with only tactile motion data and supervised learning using limited data, have been demonstrated. The study uses pinch-grasping performed by a 2-fingered robot experimental setup with a pre-designed motion sequence, over 7 different objects having a wide range of properties to capture the motion data. The proposed approach avails pre-processed motion data to train neural networks for accurately predicting object response properties for 3 unseen test objects. We have done a comparative study among three neural network architectures CNN, LSTM, and CNN-LSTM and we found that novel CNN-LSTM outperforms the other two models in terms of accuracy. The CNN-LSTM regression model achieves 0.98 and 0.97 of R2 value for the prediction of stiffness and mass, respectively and the CNN classification model achieves 94% of accuracy for the surface interaction classification.

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Cognitive Grasping and Manipulation of Unknown Object with Control Grip Force using Cyber Physical System Approach

Thompson J., Murakami T.

IEEJ Journal of Industry Applications （IEEJ Journal of Industry Applications）  11 （ 6 ） 744 - 751 2022年

ISSN  21871094

　概要を見る

Service robots working in human environments must have the ability to grasp a wide variety of unseen objects with appropriate grip force without knowing their properties and its response to action in a human environment. This research uses a novel Cyber Physical System framework to estimate and apply minimum grasping force for unknown objects under a task motion using only tactile motion data captured from sensor-less acceleration-based controlled common gripper. The goal is to use this novel framework for developing functions for position-controlled robots to perform real-time cognitive grasping and enable quick implementation across multiple robots. This paper uses soft sensing inputs from the earlier research to characterize unknown object properties like stiffness, mass and surface interaction and show how a data-based analytics algorithm learns a wide range of object properties and slip status along with task action dynamics features, to propose the grasping action with minimum applied force. We validated that the minimum grasping force is able to hold the object firmly during any task motion. In order to improve the learning, the paper proposes a part of the framework to use virtual simulation to gather more learning data and show results that compare well between simulated results with experimental data. We use the simulated data to train Reinforcement Learning approach and show that small variation in object width can be learnt to identify optimum gripping position.

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Comparison of Filtering Methods in Measuring Human ZMP Using Kinect Sensor

Nagasawa T., Tawaki Y., Murakami T.

IECON Proceedings (Industrial Electronics Conference) （IECON Proceedings (Industrial Electronics Conference)）  2022-October 2022年

　概要を見る

This paper aims to verify the detection accuracy of Zero Moment Point (ZMP) measurements of the human body using the Kinect sensor. In this paper, ZMP is measured based on a multi-link model of the human body. ZMP calculation algorithms using a Low Pass Filter (LPF) and Savitzky-Golay (SG) filter were constructed to investigate filtering methods that can measure ZMP with high accuracy and small lag. The accuracy and responsiveness of these filters were evaluated through experiments measuring ZMP during human walking. Experimental results show that the detection error in ZMP is dominated by the differential noise in the acceleration calculation, and applying the filter only to measured acceleration values increases responsiveness with the same accuracy as when applied to ZMP. We also found that the SG filter is superior to LPF in noise suppression and responsiveness of ZMP measurements, though it occurs overshoot in measurements.

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Evaluation of Mathematical Models for Postural Sway Based on Reproducibility of SDA Parameters

Sakae K., Tawaki Y., Murakami T.

IECON Proceedings (Industrial Electronics Conference) （IECON Proceedings (Industrial Electronics Conference)）  2022-October 2022年

　概要を見る

Evaluation of the falling risk is significant for older people not to fall and become in need of care. The static posturography test is adopted to evaluate the lack of balance ability that causes the falling. This test measures the center of pressure (COP) of humans and evaluates it by analyzing the data. There are three main analysis methods: descriptive statistics, stabilogram diffusion analysis (SDA), and mathematical modeling. Descriptive statistics and SDA represent only statistical values without the mechanism of the posture control system. However, mathematical modeling evaluates the system from the model coefficients containing physical meanings, and we focus on it. The stochastic differential equation of stiffness, viscosity, and stochastic terms are introduced to the mathematical model for the static posturography test. The COP trajectory reproducibility of the model is evaluated using SDA. SDA is a time-based analysis suitable for evaluating the dynamic posture control system. In the experiment, we compare the SDA parameters between older and younger subjects and evaluate the reproducibility of the model using the SDA parameters. As a result, we confirm that the SDA parameters can classify based on age to a certain extent, and the model has higher reproducibility than the conventional model against SDA.

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An Approach of Load-Side Disturbance Rejection Control for Series Elastic Actuators

Hiraoka Atsushi, Murakami Toshiyuki

2022 IEEE 17TH INTERNATIONAL CONFERENCE ON ADVANCED MOTION CONTROL (AMC)    18 - 23 2022年

ISSN  1943-6572

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Classification of Older and Fall-Experienced Subjects by Postural Sway Data Using Mass Spring Damper Model

Tawaki Y., Nishimura T., Murakami T.

IEEE Transactions on Neural Systems and Rehabilitation Engineering （IEEE Transactions on Neural Systems and Rehabilitation Engineering）  30   40 - 49 2022年

ISSN  15344320

　概要を見る

The quiet standing test is used to detect diseases of the postural control system. The descriptive statistics of the center of pressure (COP) of older people during the test tend to be larger than those of healthy young people, but they cannot indicate structural problems in postural control. COP trajectories can be mathematically modeled with structural parameters such as viscosity, stiffness, and stochastic terms; however, the classification accuracy of older and fall-experienced people using such parameters has not been sufficiently verified. In this study, six structural parameters of a mass-spring-damper (MSD) model were estimated using two datasets, in which a total of 212 subjects performed quiet standing tests under four conditions. The estimated parameters were used for classification with a random forest algorithm to examine the differences in classification accuracy compared to seven conventional descriptive statistics methods. For the classification of older subjects, the classification accuracy of the MSD parameter method was the highest in foam condition, with positive likelihood ratios approximately 8.0. For the classification of fall-experienced subjects, the positive likelihood ratio of the MSD parameter method was 5.0, which is better than conventional descriptive statistics. Various MSD parameters revealed that aging and changing the floor surface and visual conditions cause oscillations in the COP behavior. While the MSD parameters were confirmed to help classify older subjects more accurately than the conventional descriptive statistics, there was room for further improvement in the classification accuracy of fall-experienced subjects.

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Position and Cross-Coupling Factors Estimation for Sliding Mode Current Control based Position-Sensorless Control of IPMSM

Shimamoto K., Murakami T.

IEEE Access （IEEE Access）  2022年

　概要を見る

This paper presents a control method with an estimation method of cross-coupling factors of Interior Permanent Magnet Synchronous Motors (IPMSM) inductance for position-sensorless servo drive systems. The cross-coupling factors are from dq-axis mutual inductance. Conventionally, the cross-coupling factors have been ignored in the IPMSM model and deteriorate control performance. That has caused decreasing robustness and velocity vibration in the low-speed range. Since the cross-coupling factors vary with the rotor position and the current, it is hard to measure them. Therefore, the proposed method utilizes a high-frequency voltage injection method to estimate the cross-coupling factors online. In addition, the proposed current control method utilizes a sliding mode control and voltage disturbance observer based on the voltage equation, including the dq-axis mutual inductance model. The estimated cross-coupling factors are reflected in the proposed current controller instantaneously. Experimental results show that the proposed method considering cross-coupling factors increases the robustness to the disturbance force and reduces the velocity vibration.

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Performance Evaluation of Force Control and Reaction Force Estimation in Force Sensorless Hybrid Control for Workspace Based Controller

Shimamoto Keita, Murakami Toshiyuki

2022 IEEE 17TH INTERNATIONAL CONFERENCE ON ADVANCED MOTION CONTROL (AMC)    231 - 236 2022年

ISSN  1943-6572

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Velocity and Attitude Control of Quadcopter with Suspended-payload using Disturbance Observer with Payload Inclination Suppression

Sugaya Taketo, Murakami Toshiyuki

2022 IEEE 17TH INTERNATIONAL CONFERENCE ON ADVANCED MOTION CONTROL (AMC)    414 - 419 2022年

ISSN  1943-6572

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Position Control Considering Slip Motion of Tracked Vehicle Using Driving Force Distribution and Lateral Disturbance Suppression

Kuwahara H., Murakami T.

IEEE Access （IEEE Access）  10   20571 - 20580 2022年

ISSN  2169-3536

　概要を見る

Complex slippage and nonholonomic constraints can disturb the precise movement of tracked vehicles. In this study, a position control system using driving force control and virtual-turning velocity control (VTVC) was established for a tracked vehicle. Slippage in the translational direction can be suppressed by controlling the driving force of the crawlers, estimated using the vehicle velocity. However, the driving forces interfere with each other in a turning motion. Therefore, a driving force distribution method was developed using the instantaneous turning center of a vehicle to decouple the forces. This distribution induced slippage in the direction of turning. In addition, a virtual reference was derived from the vehicle velocity and lateral disturbance, which described the effects of the nonholonomic constraints and skidding of the tracked vehicle. Next, a VTVC method was developed to suppress the lateral disturbance by controlling the turning velocity to follow the virtual reference. The experimental results confirm that the proposed approach ensures high-performance position tracking and adequate slippage of the tracked vehicle.

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Estimation of Jacobian Matrix without accelerometer on Omni-directional Mobile Walker

Ominato Kentaro, Murakami Toshiyuki

2022 IEEE 17TH INTERNATIONAL CONFERENCE ON ADVANCED MOTION CONTROL (AMC)    329 - 334 2022年

ISSN  1943-6572

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Frequency Characteristics of Power Transformer for Isolated DC-DC Converter

Nakamura T., Murakami T.

IEEE Access （IEEE Access）  10   11633 - 11641 2022年

ISSN  2169-3536

　概要を見る

The operational frequency of a transformer is an important factor in the configuration of an isolated DC-DC converter. However, discussions of this frequency are inadequate. This study focuses on the frequency characteristics of the transformers. The frequency characteristics of the impedance and loss of the transformer were obtained to explain their fundamental attributes. When a transformer is employed in a power electronic transformer (PET), the waveform of the voltage is rectangular. The loss under this waveform was obtained in order to observe its characteristics. Furthermore, the problems with the isolated DC-DC converter are explained. The natural frequency, composed of leakage inductance and equivalent-parallel capacitance, determines the performance of the isolated DC-DC converter. When the operational frequency of the isolated DC-DC converter is below its natural frequency, the loss increases under the no-load or light-load conditions. This increase in the loss is caused by the current, which contains the natural frequency of the transformer owing to the ringing.

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