Toru Tsumugiwa

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.

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.

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.

Compliance measurement for the Mitsubishi PA-10 robot

In this study, we measure the compliance characteristics of the 7-degree-of-freedom (DOF) vertical multiarticulated Mitsubishi PA-10 robot. To determine the compliance characteristics of the robot, numerical values of joint compliance are identified by a partial simultaneous measurement method using a force/torque sensor and a 3-D measurement system. The identified compliance is derived from an extended 10-DOF link model that comprises three additional virtual joints and seven actual joints. The virtual joints, which can be handled in the same manner as the actual joints, can be used for more accurate identification. The modeling error derived from link flexibility may be compensated by introducing the extended link model with additional virtual joints. To investigate the accuracy of the compliances identified with the extended link model, verification experiments were conducted. The results show that precise compliance characteristics are obtained from the extended link model. Finally, we reveal the compliance model of the Mitsubishi PA-10 robot, which comprises the numerical values of the joint compliance and a simple kinematic modeling. Graphical Abstract

Object inherent dynamics based motion control in human-robot cooperative task system

In this paper we address a robot motion control scheme for a human-robot cooperative task. From the viewpoint of improving the operative efficiency of the cooperative task, we designed a novel robot control system, in which inherent dynamics of the target task and the object is conserved. The proposed control scheme differs widely from an ordinary impedance control scheme in that the inherent dynamics of the target task and the object is substituted by impedance characteristics. Under the proposed control scheme, the dynamics of the target task and that of the robot motion are uncoupled and independent. The proposed control system enables the human operator to carry out the cooperative task intuitively by only considering the inherent dynamics of the target task and the object. To confirm the effectiveness of the proposed control system, an experiment base on a peg insertion task involving human-robot cooperation is carried out. The experimental results show that the proposed control scheme is effective for cooperative tasks requiring precision.

Grasp and Transport Control of a Chopsticks-Type Robot

In this paper, a method for changing the control mode based on position and force errors called the SCOME method is applied to a two-fingered robot hand composed of elastic joints. This robot is called a chopsticks-type robot and a cylindrical object is grasped and transported by the robot. First, we propose a control strategy for the robot based on a desired value of position and force for grasping and transporting an unknown object. Second, we explain the SCOME method, in which the control mode is selected on the basis of the point on the characteristic curve of position vs. force where the target value of work required to obtain the desired position and force is satisfied. Next, a grasp and transport control experiment is conducted using the robot to manipulate various objects made of different materials and with various outer diameters. The experimental results illustrate the validity of the chopsticks-type robot.