Accurate force control and motion disturbance rejection for shape memory alloy actuators

This paper presents simulation and experimental results for closed-loop force control of single-wire Shape Memory Alloy (SMA) actuators. The simulation uses a model derived from the frequency response analysis of SMA. Although the large-scale response has hysteresis and nonlinearities, small-signal frequency response analysis is possible on SMA wires, with detectable force response at frequencies up to 100 Hz. The model has been demonstrated to accurately predict closed-loop behaviour. A high performance force control system using PID control is also demonstrated. Results show fast convergence, and excellent setpoint and tracking accuracy with practically no sign of limit cycles. Experimental results in this paper are the first to have demonstrated stable and accurate response with good rejection of large motion disturbances.