Hysteresis with lonely stroke in artificial muscles: Characterization, modeling, and inverse compensation

Abstract

Artificial muscles are inherently compliant actuators that exhibit high power density and impressive stroke and force outputs. They have found numerous applications in advanced mechatronic and robotic systems. Termed as lonely stroke, the first quasi-static input–output cycle of artificial muscles is inconsistent with subsequent cycles that are repeatable and exhibit hysteresis. The lonely stroke not only affects the behavior of artificial muscles, but also presents coupling with the subsequent repeatable hysteresis cycles. While lonely stroke has been reported in a number of artificial muscles, existing studies lack systematic experimental characterization procedure. Furthermore, no models or compensation schemes have been proposed. In this work, we propose the first study to systematically characterize, model, and compensate for the hysteresis with lonely stroke property in artificial muscles. The experimental procedure to characterize the hysteresis with lonely stroke behavior is presented. A modeling approach is developed through the expansion of the input range of the Preisach operator, a widely adopted hysteresis model, to physically infeasible region. The effects of such expansion on the model accuracy and computational cost are studied. An iterative algorithm is proposed to compensate for the hysteresis with lonely stroke by approximately inverting the proposed expanded Preisach operator. The effectiveness of the proposed scheme is validated by comprehensive simulation and experimental results. While this study primarily considers super-coiled polymer (SCP) actuators, the proposed model is also validated for several popular artificial muscles.