Precision Control of SMA Actuators with a Real Time Model-Based Controller and Extended VSC

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 course 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 extended variable structure controller that uses an asymmetrical boundary layer to prevent over-heating of the wire and whose control signals adapt to the dynamic load on the wire. 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 within 0.03% strain with exceptional disturbance rejection.