Actuation precision control of SMA actuators used for shape control of inflatable SAR antenna

Shape memory alloy (SMA) actuators have found a wide range of applications due to their unique properties such as high force, long stroke, small size, light weight, silent operation, etc. However, their poor stability and controllability make them a challenge to achieve accurate actuation. This paper presents a simple control strategy based on the idea of adjusting the SMA wire temperature as fast as possible. This strategy is simple, stable, and requires no hysteresis model or thermal model. This strategy is tested with displacement output, and the effects of updating rate and input current on control accuracy are also discussed. Tests are also performed in a thermal vacuum chamber, and the results indicate that the required current for effectively activating SMA actuator is smaller than that in air environment. This control strategy is then used for adjusting boundary tensions of a small membrane synthetic aperture radar (SAR) antenna model. Results show that, under this control strategy, SMA wire actuators can exert desired tensions with very good accuracy.