Precise tracking control of shape memory alloy actuator systems using hyperbolic tangential sliding mode control with time delay estimation

This paper focuses on a simple and robust tracking control method based on a hyperbolic tangential sliding mode control (SMC) and time delay estimation (TDE) for a shape memory alloy (SMA) actuator. The TDE is used to compensate for hysteresis and other nonlinearities in the SMA dynamics, and the hyperbolic tangential SMC is used to specify nonlinear error dynamics which slides without exceeding the velocity limitation. The implementation process of the proposed control is easy by virtue of its model-free nature and transparent structure. The precise and robust tracking performance of the proposed control is verified by experiments on a bias-type SMA actuator system. Through the experiment, small tracking errors are observed throughout a significantly wide range of speed for a desired trajectory, and successfully maintained on the order of 10−2° against an external disturbance.