Comparison of position control algorithms of embedded shape memory alloy actuators

This paper presents a comparison of the algorithms for control of shape memory alloy (SMA) actuators. An adaptive airfoil is a case of smart composites which utilize embedded SMA actuators. The airfoil is deformed by the SMA actuators which are heated with electric current. The controller adjusts the electric current of the actuators to reach the desired shape of the airfoil. The aim of this study was to investigate the feasibility of proportional-integral-derivative (PID) control of embedded SMA actuators. In previous studies model-based controllers were found to be efficient but thorough comparison with PID control has not been done before. In this paper an anti-windup compensated (AWC) PI controller was compared to an experimental model-based controller and a neural network controller. The performances of the controllers were evaluated in step response tests and a set value ramp tracking. The control experiments were performed at room temperature and during the tests a fan improved cooling of the airfoil. Robustness of the controllers was determined by changing the airflow around the airfoil when the set value was kept constant. The control tests demonstrated the benefits of the AWC PI controller and that the other nonlinearities in the system are not as critical as the power limitation. This result indicates that a SMA actuator can be controlled successfully with PID if the power limiter is appropriately compensated.