A Maxwell-Slip Based Hysteresis Model for Nonlinear Stiffness Compliant Actuators

Hysteresis nonlinearity is a common issue in nonlinear stiffness compliant actuators. In this type of actuators, the hysteresis effect is obvious and the associated torque curve is nonlinear. Although many mathematical models have been developed for describing hysteresis, they are usually developed with black-box modeling and the model parameters are difficult to tune to match the experimental data well among inputs with different amplitudes. This paper presents a novel hysteresis modeling method for a nonlinear stiffness compliant actuator of which the shapes of the associate torque curves vary with amplitudes. In this method, a concept called "virtual deformation" is adopted to transform the nonlinearity curve into a polyline-based model. Then, a modified Maxwell-Slip model is developed to estimate the output torque of the actuator according to the virtual deformation. Experiments of the proposed hysteresis modeling method applied in a nonlinear stiffness compliant actuator have been conducted and the results showed that the root-mean-square-error (RMSE) of the estimated torque was reduced by 18.6% and the computation cost was reduced to less than one sixteenth using our proposed hysteresis model compared with Nonlienar Backlash Model (NBM).