Design of Shape Memory Alloy Actuator with High Strain and Variable Structure Control

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ABSTRACT A novel Shape Memory Alloy (SMA) actuator consisting of a number of thin NiTi fibers woven in a counter rotating helical pattern around supporting disks is first described. This structure can be viewed as a parallel mechanism used to accomplish a highly efficient 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 first 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 simplifies amplifier construction. Experimental performance results in the time domain are discussed. 1 Introduction With the continued miniaturization of robotic systems comes the need for powerful, compact, lightweight actuators. Conventional techniques such as electri...

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