Proposal of a Feedback Control System for a Thermally Driven High-Power-Density Actuator

Shape memory alloy (SMA) actuators can generate force via the phase transition of the SMA, related to its temperature variations. The amount of force and the response duration length are approximately proportional to the SMA’s volume and mass. The higher-power actuator, which consists of a single SMA tube, has mechanical simplicity and high reliability; however, it has a relatively long driving duration, and actuation timing uncertainties caused by the environmental temperature variations. Because of its huge heat capacity, the environment temperature variations affect the actuator’s temperature, the phase transformation uncertainties, and force generation profiles, resulting in differences in the actuation timing that are tens of seconds. This paper proposes a suitable feedback control system consisting of two methods. One is the construction of a physical model for SMA tube thermomechanical coupling response that has suitable complexity for the real-time control system design by the limited application condition. The other is a reference trajectory generation and tracking method by using the model predictive control method with a constructed physical model, resulting in a possible drive timing uncertainty reduction. The effectiveness of the proposed methods was verified by specific test piece system identification and control simulations performed both numerically and experimentally. In addition, the effectiveness of the online control system itself was confirmed by comparing the results of a traditional control system using the proportional integral derivative method. The result indicates the potential of the possible application system for SMA actuators.