Position control considering passive stiffness of rubberless artificial muscle antagonistic drive system

This paper describes position control considering passive stiffness of an antagonistic drive system using a rubberless artificial muscle. The rubberless artificial muscle is a pneumatic actuator similar to a McKibben type artificial muscle. The artificial muscle has a passive compliance characteristic that varies with inner pressure. Therefore, the antagonistic drive system can control the antagonistic position with tuning of passive compliance characteristics. As described in this paper, the system can be either rigid or soft according to the compliance characteristic of the actuator. As described herein, this study confirms the variable stiffness characteristic of the rubberless artificial muscle. Furthermore, a mathematical model is derived to show the relation between the passive stiffness and antagonistic force of the system. This report then explains the contraction displacement linearization system (CDLS), which decides the inner pressure based on the contraction displacement and contraction force. The CDLS performs linearization of the nonlinear characteristics of contraction displacement. The possibility of realizing the antagonistic position control with tuning passive stiffness of the antagonistic drive system was confirmed experimentally.