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.