Memory alloy actuator

The phase change in shape memory alloys (SMA) is highly nonlinear, and the development of advanced position ing applications for SMA actuators benefits from the availability of good models of this behaviour. One phenomenological model for SMA transformation kinetics is Madill’s model, which has recently been extended to include the effect of time varying stress. This extension allows for the modelling of stress disturbances and the simulation and prediction of stress-strain behaviour. In this work, we couple the phase kinetics of the extended model with a series-based mechanical model which includes both shape memory and superelastic behaviour. This coupled model is inverted and used to investigate different control architectures for sine tracking and stress disturbance rejection for an SMA actuator with constant load. Open-loop model-inverse feedforward control is compared with simple PI feedback and the combination of feedforward plus feedback. The results show in particular that using complicated inverse models does not always bring the expected increase in perfor mance, and that other limitations of SMA actuators can negate the benefit of model-inverse feedforward.