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.

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.

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.

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.

This paper presents a novel strategy of adjusting impedance parameters of a robot's 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 robot's 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.

Static characteristics of the human finger are investigated using a mechanical planar model of the finger. They are represented by mapping a tendon force vector to a manipulating force vector of the fingertip. Force manipulability of the fingertip is defined as a force manipulability set obtained from the mapping under the condition that the norm of the tendon force vector is not more than a unit value. The shapes of the sets are geometrically obtained and graphically represented in the simulation results. The simulation visually demonstrates the static characteristics of the finger.

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 Whitney's 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 Whitney's 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.

In a peg-in-hole task, the task-performable areas are graphically evaluated using gray scales from the manipulability and a DMA (dexterity measure for assembly) in the reachable areas of a manipulator. The DMA is represented as relation between a unit value of joint angular errors to be allowable in the task and a unit value of joint angular errors of the manipulator. The DMA consists of a DMGC (dexterity measure for geometric conditions) and a DMFC (dexterity measure for force conditions). These measures relate to task conditions including both compliance of an RCC (remote center compliance) and compliance of the manipulator joints. The task conditions are represented as the physics models. The manipulability measure is used to check the neighborhoods of the mechanical singularities of the manipulator. A graphic representation enables us to understand easily the relations between the task and the kinematics of the manipulator, since it integrates the DMA and the manipulability measure in the reachable areas.