Sliding mode-based control of thin Shape Memory Alloy actuators using a spatial hysteresis approximation

Shape Memory Alloy (SMA) actuators rely their operation on a thermally driven phase change. The SMA's stroke position control problem thus involves the material temperature in a direct or indirect way. In thin SMA actuators, deviations between the actual and the estimation of the temperature profile can affect the performance of model-based control. In this work, an intermediary strategy, between a model-free and a model-based one, is proposed, where local approximations to the hysteretic trajectories are used in place of a complete hysteresis description. The localized trajectory is then spatially shifted to encapsulate the hysteretic behavior. A sliding mode based controller is constructed by this implementation exhibiting accurate tracking behavior. The advantages against existing model-free controllers are further investigated over a multi-rate control scheme. The results show that efficient tracking position control can be reached even at very low output feedback frequencies.