Modeling of shape memory alloy actuator and tracking control system with the model

There has been great demand for shape memory alloy (SMA) actuators within the field of micro-machines. However, the thermomechanical behavior of SMA actuators is too complicated to accurately predict their response. Moreover the tracking control accuracy of SMA actuators is limited due to the inherent hysteresis nonlinearity. The paper presents a model of an SMA actuator for use in mechanical design and a control system for compensating the hysteresis. First, the model based on constitutive laws developed by Brinson et al. (1996) and our proposed hysteresis model is demonstrated. Next, we propose a control system composed of a proportional integral derivative (PID) feedback loop and a feedforward loop. In the feedforward loop, the desired control input corresponding to the desired displacement is obtained from a static SMA model derived by modifying the classic Preisach hysteresis model. We also propose a method for identifying parameters of the hysteresis model. This methods demands only measurement of the major loop. Application of the control system to our developed SMA actuator shows that the tracking control performance is improved.