Modeling and Inverse Compensation of the Quasi-static Voltage-Strain Lonely Stroke and Hysteresis in Supercoiled Polymer Artificial Muscles

Abstract

Supercoiled polymer (SCP) actuator is a recently developed thermally-driven artificial muscle that has shown large strain, high power density, and strong promise in robotics and intelligent systems. Termed as lonely stroke, the first cycle of SCP actuators is inconsistent with subsequent cycles that are repeatable and exhibit hysteresis. The lonely stroke not only affects SCP actuators' performances, but also presents coupling with hysteresis. It is thus crucial to capture the lonely stroke and hysteresis of SCP actuators to fully unleash their potential. However, the existing modeling and control strategies of SCP actuators fail to consider the lonely stroke nonlinearity. In this study, a modeling strategy is proposed to capture the quasi-static voltage-strain lonely stroke and hysteresis in SCP actuators. This is realized by expanding the input range of the Preisach operator, a widely used hysteresis model, to physically infeasible region to account for the lonely stroke. An iterative algorithm is proposed to compensate for the lonely stroke and hysteresis by approximately inverting the proposed model. For comparison purposes, a conventional Preisach operator and a polynomial model are considered. The modeling and control performance of the proposed approach is evaluated in experiments, and the superiority of the proposed scheme is demonstrated.