A model extended temperature and strain controller modulated with PWM for precision position control of shape memory alloy actuators

This paper presents a novel control strategy for precision position control of Shape Memory Alloy (SMA) actuators by using a combination of large and small signal controllers. The large signal controller, responsible for coarse positioning, is an NPID temperature controller that gets its desired temperature value online from a computationally efficient stress-strain and phase kinetics SMA model that accounts for time varying stresses. The small signal controller, responsible for fine positioning, is an NPID position (strain) controller. The control signals are modulated with PWM to generate a series of current pulses that heat the SMA. The control strategy is tested on an SMA wire, first, with various constant loads and then with varying loads. The results show robust and precise tracking control with exceptional disturbance rejection.