A study on impedance control using passive elements for human-assist system

This paper considers a power assist system of fingers as an example of human-assist system and describes impedance control of it. The assist system is required not only to assist the movement of fingers but also to be strictly stable. Impedance control based on position control is often used for the assist devices because the control system is simpler than that of the devices based on force control. But if the impedance parameters are made to be small in order to get good maneuverability, the system becomes unstable because of the delay of the position control system especially when the assisted tool touches high stiffness environment such as a wall. So, an impedance control method based on position control with passive elements is proposed. Then it is shown that the system controlled by the proposed method with very low impedance parameters is stable even if the system touches a high stiffness environment.