Design of Shape Memory Alloy Actuator with High Strain andVariable Structure

A novel Shape Memory Alloy (SMA) actuator consisting of a number of thin NiTi bers woven in a counter rotating helical pattern around supporting disks is rst described. This structure can be viewed as a parallel mechanism used to accomplish a highly ee-cient transformation between force and displacement. The actuator overcomes the main mechanical drawback of shape memory alloys, that being limited strain. Two variable structure controllers are applied to a pair of antagonist actuators. The rst involves a switching control input creating a sliding mode in conjunction with a linear control activated within a boundary layer in the vicinity of the set point. The second involves a multi-stage switching control that simpliies ampliier construction. Experimental performance results in the time domain are discussed.