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

Abstract

This paper presents a novel variable impedance control method for a human-robot cooperative task. There is a possibility that an impedance control system based on a positioning control of a robot with time delay of the robot and a human operator becomes unstable, when stiffness of a human arm or body is increased in the human-robot cooperative task. A proposed variable impedance controller varies a 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 was performed. Experimental results illustrate that the proposed control method is effective for the human-robot cooperative task.