Investigation of functional characteristics of a synergistically configured parallel-type shape memory alloy variable stiffness actuator

Abstract

Variable stiffness actuator is the essential element for force control and motion generation of most mechanical systems that are used for soft robotic, biomimetic and biomedical applications. Mechanical systems when integrated with smart materials enable controlled variation of stiffness in addition to control of force and displacement, thus exhibiting superior characteristics. Active compliant/variable stiffness actuator using shape memory alloy allows simple and compact design, exhibits comparable actuator efficiency and offers directional controllable actuation, self-sensing and a wide range of variable stiffness. The functional characteristics of a synergistically operated translational/linear compliant variable stiffness actuator, configured synergistically with shape memory alloy wire(s) and passive compression spring, are determined experimentally under no load without control to offer translational actuation. Repetitive actuation is made possible through electrical activation (direct Joule heating) of shape memory alloy wire(s) and the aiding force (the restoring (bias) force) of the passive spring. Actuation with variable stiffness is obtained from the inherent stiffness variation of shape memory alloy during its phase transformation, along with the fixed stiffness of the passive compliant element. The scope of improving the range of stiffness through varied forms and connections of the elements is recognized, while retaining the basic structure without compromising its simplicity.