Position control of SMA actuator based on inverse empirical model and SMC-RBF compensation

Due to the nonlinear saturated hysteretic behavior of SMA during the phase transformation, it is not easy to achieve accurate position tracking control by establishing an effective controller for the SMA actuator system. In this paper, an accurate position control method based on inverse empirical hysteresis model with simple structure and SMC-RBF compensation is proposed. The inverse empirical hysteresis model which shows the hysteresis effect of SMA wire for both heating and cooling processes is used to calculate a proper input voltage according to the desired position. Then, a compensation control part based on SMC-RBF is added to the closed-loop control system to estimate the difference between empirical hysteresis model and exact hysteresis effect, unknown dynamics, as well as disturbances, which can also minimize the requirement for an accurate inverse hysteresis model. Since the major part of input voltage for SMA actuator is calculated from inverse empirical hysteresis model, the proposed method shows faster response speed than the case in which only SMC-RBF is used. In addition, the position tracking results demonstrate that the proposed method has better tracking capability for trajectory with high frequency as well as less overshoot/undershoot than PID controller. Consequently, this proposed method with simple structure should be a viable alternative for position control of SMA actuators.