Tracking Control of an Antagonistic Shape Memory Alloy Actuator Pair

Shape memory alloy actuators exhibit significant nonlinearities in their stress-strain-temperature characteristics which makes them difficult to control. This brief presents a control scheme for trajectory tracking using torque control of shape memory alloy (SMA) actuators connected to a rotary load in an antagonistic configuration. Despite possessing interesting properties such as large force to mass ratio, possibility of miniaturization, light weight, and quiet actuation, SMA exhibits undesirable characteristics that should be taken into account when utilizing them as actuators. The undesirable characteristics include hysteresis, nonlinear temperature dependencies, and slow response. By considering the nonlinear behavior and thermal characteristics of SMA, an inversion-based control scheme with time-varying gains is developed in this brief. The proposed controller does not depend on characteristics of SMA wire and only an approximate model is sufficient. The controller performance is further evaluated on an experimental setup.