Modelling, simulation and characterization of a linear shape memory actuator with compliant bow-like architecture

The design of shape memory alloy actuators typically compromises between force and stroke, the two properties being inversely proportional to one another for any given shape memory alloy element. This article presents a bow-like compliant actuator aimed at improving the specific performance of shape memory wires on both accounts. Conceptually, the actuator is formed by two straight elastic beams mutually hinged at the ends with a pre-stretched shape memory alloy wire in between. Heating of the alloy shortens the wire, which in turn makes the beams to buckle outwards in a symmetric double-arched configuration. The transverse displacement of the beams amplifies the contraction of the wire while producing a favourable output force. This article develops a simple, though accurate, analytical model of the actuator upon which a step-by-step design procedure is built. The theoretical findings are compared with the outcome of a finite element simulation for a case study and with the test data gathered from a physical prototype actuator.