Use of antagonistic shape memory alloy wires in load positioning applications

This paper is concerned with the analysis of an actuation system for load positioning applications based on a pair of antagonistic shape memory alloy wires. In this system, the restoring force required to stretch a wire in martensitic phase can be actively controlled by modulating the power provided to its antagonistic element. For the generation of controlled repeatable motions, this is an undoubted advantage over a configuration based on a single wire, where the restoring force is generated by a passive element such as a constant load or a spring. In order to ease the comprehension of the actuation principle based on antagonistic shape memory wires, this paper reports at first the derivation of a lumped parameter mathematical model of the actuation system. Then, the behaviour predicted by the model is used to support the analysis of the experimental results obtained with a special test bench consisting of two antagonistic NiTi wires driving a low-friction slider mounted on a linear guide.