Constrained force control of shape memory alloy actuators

Experimental results are presented to show that SMA actuators are able to control forces both rapidly and precisely. An antagonistic pair of constrained actuators is shown to be capable of rapidly changing the set-point throughout a ±7.00 N range. Although the system entered into a limit cycle at the set-point, the limit cycle magnitude was small. The peak to peak amplitude of the limit cycles was only 0.07 N with a worst case average offset of 0.016 N at high force rates up to 75 N.s^-1. Simulation results also indicate that accuracy could be improved with an increased sampling rate. The SMA actuator pair was also shown to be capable of accurate tracking. The maximum tracking error for a f=0.500 Kz, 2.00 N sine wave was 0.04 N. For the 2 Hz tracking, the maximum error was approximately equal to the boundary layer width which was set at 0.30 N