Ryuichi Yokogawa

Variable impedance control based on estimation of human arm stiffness for human-robot cooperative calligraphic task

This paper presents a novel variable impedance control method for a human-robot cooperative task. An impedance control system based on a positioning control of a robot with time delay of the robot and a human operator can become unstable when the stiffness of a human arm or body is increased in the human-robot cooperative task. The proposed variable impedance controller varies the viscosity coefficient of the robot in proportion to an estimated value of the stiffness of the tip of the human arm. A method of a proposed variable impedance control makes the human-robot cooperative system stable and the cooperative task easy. In order to confirm the usefulness of the proposed control method a cooperative calligraphic task, that is writing a Kanji character with a writing brush, is performed. Experimental results illustrate that the proposed control method is effective for the human-robot cooperative task.

Variable impedance control with virtual stiffness for human-robot cooperative peg-in-hole task

This paper presents a novel variable impedance control for a human-robot cooperative task. Cooperative positioning tasks cannot be performed easily using a conventional position based impedance controller. The proposed controller has a virtual stiffness term in order to make the cooperative positioning task easy and precise. It generates a virtual force in the positioning task using the virtual stiffness term. The virtual force helps the human operator to perform the positioning task easily. In order to confirm the usefulness of the proposed control, a cooperative peg-in-hole task was performed. Experimental results illustrate that the proposed control is effective for the human-robot cooperative task.

Variable impedance control with regard to working process for man-machine cooperation-work system

This paper presents a novel strategy of adjusting impedance parameters of a robots end effector in a man-machine cooperation-work. In the proposed strategy, the impedance parameters are settled with regard to a working process of a human operator that is identified using a passivity index and an extreme value of force applied by the human operator. This approach enables to perform the cooperation-work with a robot easily. In order to confirm the usefulness of the strategy, the cooperation-work to which the robots end effector is moved in the horizontal plane was performed. It is shown that the proposed strategy gives the manipulator a better characteristic than the invariable impedance control and the conventional variable impedance control. Furthermore, by a subjective evaluation test performed to subjects, the proposed control strategy is evaluated better than the other ones. Experimental results illustrate that the proposed control strategy for the robot is suitable for the cooperation-work.

Measurement of Distribution of Maximum Index-Fingertip Force in all Directions at Fingertip in Flexion/Extension Plane

The purpose of the present study is to investigate whether distribution patterns of the maximum fingertip force in all directions from 0 deg to 360 deg around the index fingertip are the same among subjects. Distributions of the maximum index fingertip force were measured at four finger postures for five subjects (healthy males, ages 21 to 25). It became apparent that distribution patterns of the fingertip force were very similar among subjects, through the application of an analysis of variance (level of significance: 5%) to the measurement results. In the production of the maximum fingertip force, Valero-Cuevas et al. [1998, 2000] reported that patterns of control signals for driving muscle forces were common among subjects. The results of the present study indicate that patterns of maximum fingertip force are also similar among subjects. Therefore, the possibility is high that the static transfer characteristic for index fingers from input (i.e., control signals to muscles) to output (ie., the maximum fingertip force) is also common among subjects.

Stability analysis for impedance control of robot for human-robot cooperative task system

This paper presents stability analysis for an impedance control of a specific robot system in a human-robot cooperative task system. In the stability analysis, we consider these conditions such as an impedance characteristic of the robot, time delay of a human operator and a control of the robot, a compliance of structure of the robot, and an environment stiffness respectively. The stability analysis simulation reveals that these conditions have significant influence on the stability of the system. In order to investigate the usefulness of the stability analysis simulation, a verification experiment using a Mitsubishi PA-10 robot arm was carried out. Experimental results illustrate that the investigated stability analysis is useful and effective to simulate and reveal the stability of the human-robot cooperative task system.

Manipulabilities of the index finger and thumb in three tip-pinch postures

Tip-pinch, in which the tips of the index finger and thumb pick up and hold a very fine object, plays an important role in the function of the hand. The objective of this study was to investigate how human subjects affect manipulabilities of the tips of the index finger and thumb within the flexion/extension plane of the finger in three different tip-pinch postures. The index finger and thumb of twenty male subjects, were modeled as linkages, based on measurement results obtained using two three-dimensional position measurement devices. The manipulabilities of the index finger and thumb were investigated in three tip-pinch postures, using three criteria indicating the form and posture of the manipulability ellipse of the linkage model. There were no significant differences (p > 0.05, ANOVA) in each criterion of each digit across the subjects, except for two criteria of the thumb. The manipulabilities of the index finger and thumb were separately similar across all subjects in tip-pinch postures. It was found that the manipulability for the cooperation of the index finger and thumb of all the subjects in tip-pinch depended on the posture of the index finger, but not on the posture of the thumb. In two-dimensional tip-pinch, it was possible that the index finger worked actively while the thumb worked passively to support the manipulation of the index finger.

Switching control of position/torque control for human-robot cooperative task - human-robot cooperative carrying and peg-in-hole task

This paper presents a novel control method for a human-robot cooperative task. There is a problem that a cooperative fitting task, i.e., peg-in-hole task, could not be performed precisely using a conventional impedance control. A proposed controller changes a control mode according to the task. An impedance control based on a position control is used in a carrying task and a torque control with compensation for its dead weight and friction is used in the fitting task. In order to confirm the usefulness of the proposed control, a human-robot cooperative carrying and peg-in-hole task was performed. Experimental results illustrate that the proposed control is effective for the human-robot cooperative task.

Measurement method for compliance of vertical-multi-articulated robot application to 7-DOF robot PA-10

This paper presents a measurement method and its results for a compliance of a vertical-multi-articulated robot. In order to calculate the compliance of a robot, a stiffness of each joint of the robot is required. In this paper, a stiffness of each joint of the robot is measured by using a force/torque sensor and a 3-D motion and position measurement system OPTOTRAK 3020. The proposed measurement method is applied for a 7-DOF robot PA-10 made by MITSUBISHI heavy industries. At first, an 11-DOF link model with 4-virtual joints, i.e., the link model includes virtual 4-DOF, is proposed. Then, a compliance matrix is obtained using a measured joint stiffness matrix of the PA-10 and a Jacobian matrix of a proposed 11-DOF link model. In order to investigate accuracy of the measured joint stiffness, and to confirm effectiveness of the measurement method for the joint stiffness and the proposed link model, experiments measuring the compliance of the PA-10 are conducted. In the experiments, the proposed 11-DOF link model is compared with a 7-DOF link model. Experimental results illustrate that the measured joint stiffness are accurate, and the measurement method and the proposed link model are effective for calculating the compliance of the PA-10.

Variable impedance control with virtual stiffness for human-robot cooperative task (human-robot cooperative peg-in-hole task)

This paper presents a novel variable impedance control for a human-robot cooperative task. A proposed control has a virtual stiffness term that makes the cooperative positioning task easy and precise. Virtual force helps a human operator to perform the positioning task precisely. A cooperative peg-in-hole task experiment was performed. Results illustrate that the proposed control is effective for the cooperative task.

Evaluation of task-performance of a manipulator for a peg-in-hole task

The paper deals with kinematic evaluation of task-performance of a manipulator for a peg-in-hole task. First, a condition of the manipulator for avoidance of jamming on the chamfer of a hole is derived. Secondly, strict conditions for the peg-in-hole task are obtained by adding the condition to Whitneys conditions. Thirdly, a suitability measure of the manipulator for avoidance of jamming on the chamfer (MAJC) is proposed. Finally, it is shown that successful assembly should be guaranteed from not only Whitneys conditions but also the condition for avoidance of jamming on the chamfer and that task-performance of a manipulator should be evaluated on the base of not only a dexterity measure for assembly (DMA) but also the MAJC.