A shape memory alloy spring-based actuator with stiffness and position controllability

In this paper, a one-degree-of-freedom actuator that is based on shape memory alloy (SMA) springs is developed and tested. The use of SMA springs allows a larger actuation workspace and controllable stiffness than SMA wires. It is shown that the actuator demonstrates a good positioning accuracy in addition to a higher level of stiffness control. A strategy based on the variable structure control method is implemented for simultaneous displacement and stiffness control. It is shown that the actuator’s position is always kept within a boundary layer defined around the desired position while a preferred stiffness is also obtained in the actuator. Such an actuator could be used to develop flexible mechanical systems which need to adapt to environmental changes in the form of external loading variation.