Amplitude-Modulating Switching Feedback for Position Control of Shape Memory Alloy Actuators

In this paper we discuss a novel shape memory alloy (SMA) actuator for minimally invasive robotic surgery (MIRS). Initial characterizations of this actuator reveal that it is well-suited for MIRS, capable of generating relatively large forces (up to 500 mN) over substantial distances (up to 500mum). We focus our attention on the position control of two actuators in an antagonistic configuration. In particular, we report our developments toward a switching control architecture that minimizes energy consumption and heating of the actuators, in an attempt to extend their useful life. A variable switching control architecture drives a pair of SMA actuators, alternately turning "on" one actuator based on the sign of the position error signal. While such control is robust to model and environment uncertainties, large current amplitudes may increase temperatures excessively and result in limit cycle behavior. To counter these effects, the amplitudes are modulated over distinct error regions. The resulting amplitude-modulating switching control algorithm allows for smooth and robust position control without knowledge of underlying models of the SMA actuator