Iterative and Feedback Control for Hysteresis Compensation in SMA

This paper investigates the design of an iteration-based controller combined with feedback control to address the positioning error caused by hysteresis in a shape memory alloy (SMA) actuator. Without compensation, the positioning error due to hysteresis can be excessively large (greater than 20%), therefore limiting the performance of SMAs in positioning applications. An iterative controller based on the Preisach hysteresis model is used to compensate for the hysteresis. However, one of the major challenges with SMA at or near the phase-transition zones, from martensite to austenite and vice versa, is the output response is shown to be sensitive to small changes in the input. In practice, an iterative controller provides limited performance due to lack of robustness. It is demonstrated that combining a simple feedback controller with an iterative controller provides the needed robustness to enable high-precision tracking. Experimental results are presented that show maximum tracking error of 0.15% of the total displacement range—this value is approximately the noise level of the sensor measurement.