Effect of stress on bandwidth of antagonistic shape memory alloy actuators

This article presents the experimental study on the influence of stress generated between the antagonistically connected shape memory alloy wire actuators over its bandwidth of operation. It is a well-known fact that behaviour of shape memory alloy is strongly coupled with temperature, stress and strain. An attempt is made to understand the effect of these factors on its bandwidth from control perspective through frequency response analysis. A phenomenological correlation is presented between the frequency response of antagonistic shape memory alloy and stress acting between the wires under different strains and temperatures. A clear demarcation between influence of temperature and stress over the operating frequency is discussed. Experimental result shows that apart from temperature, operating frequency of antagonistically connected shape memory alloy is also highly influenced by stress acting between the wires at higher temperatures. Also, the effect becomes much more significant under partial transformation strain. The result of the study is extended and demonstrated through tracking control of antagonistic shape memory alloy at a frequency of about 2Hz.