An investigation on the stiffness variation in a synergistically configured SMA actuator

This paper presents the study of stiffness variation in a linear/translational actuator which is a synergistic configuration of a passive compression spring with shape memory alloy (SMA) wire(s). The synergistic SMA based actuator uses an aiding force to create repetitive motion, to be capable of producing increased displacement. The range of stiffness of the actuator relies on two controlling factors i.e., the number of SMA wires and the energy storing capacity of the spring. Increase in the number of SMA wires offers simultaneous improvement of force and stiffness. The above is analyzed theoretically and verified through experiments. The tracking performance of the actuator is obtained through simulation with stiffness feedback for PID control action, using the data acquired from real time experiments.