Synergistically configured shape memory alloy for variable stiffness translational actuation

Abstract

The structural composition of two elastic elements, shape memory alloy wire (active actuating element) and spring (the passive bias), offers variable stiffness actuation. Based on this principle, a variable stiffness linear actuator is conceptually designed and developed. It is electromechanical by nature, that is, it is electrically activated and creates translational/linear motion. The variable stiffness linear actuator engages shape memory alloy wire(s) along with a passive compression spring to work synergistically. The biasing element offers recovery force to the shape memory alloy wire as well as compliance to the whole structure. The synergistic configuration exhibits an aiding force, thereby allowing an actuation with large displacement and a wide range of stiffness. The actuator mechanism is implemented through parallel action and further proposes two different modes of operation: pull mode (i.e. the disc moving along a fixed shaft) and push mode (i.e. linear reciprocating motion of the pushrod). The shape memory alloy configured actuator mechanism is analysed theoretically; the working model of the variable stiffness linear actuator is developed and investigated experimentally. The results apprise that the variable stiffness linear actuator is capable of offering large displacement and in reproducing the stiffness profile for active compliance control applications.