A closed-loop position control scheme for SMA-actuated joints

Abstract

We present the design and implementation of a closed-loop control scheme for revolute joints actuated by SMA spring actuators in an antagonistic configuration. The proposed scheme employs a feedforward term, obtained as the inverse of the modified Prandtl-Ishlinskii (MPI) model of the system's response, in conjunction with angular position feedback from a joint potentiometer, to compensate for the hysteresis and asymmetries, and achieve fast and effective tracking of a reference angular position. Experimental results indicate the efficacy of the proposed scheme, and a series of prototypes demonstrate its applicability in the development of small-scale SMA-actuated robots.