A New Design for a Rotatory Joint Actuator Made with a Shape Memory Alloy Contractile Wire

Presented in this paper is a new design approach for a bias force type of shape memory alloy (SMA) rotatory joint actuator, which uses an SMA contractile wire as an actuating element. A quasi-static analysis is assumed and a coefficient of variation of bias stress, fi, is introduced to give a quantitative expression of a variation of bias stress in terms of a working stress range of the SMA wire. The effects of this coefficient on the load efficiency and the bias spring's parameters of a bias force SMA rotatory joint actuator are described. The use of this coefficient,B leads to a simple design procedure. An example design case is carried out by using this design procedure to demonstrate its usefulness. This paper does not cover an analysis of thermal response history of a designed actuator. The design approach described in this paper will provide a practical and convenient method for use in design of bias force SMA rotatory joint actuators for design requirements of maximum loads and maximum displacements.