Optimal Design of a Novel High Authority SMA Actuator

Statically determinate structures with truss elements have simple mechanisms, light weight, and high rigidity. Based on the flexural truss structure, a high authority actuator comprising a triangular truss core, a facesheet, and actuation elements is proposed. It is clamped at one end and free at the other. The actuation element comprises a one-way shape memory alloy ( SMA ) wire and a helical spring. The elements are activated by heating, and recovered by the force supplied from the compressed spring and/or the external force once the SMA wire is cooled. A design that integrates this basic unit into a high authority flexural system has been analyzed. The actuation force and strain of SMA actuation elements are obtained by solving a coupled problem that combines a thermomechanical constitutive model of SMAs, heat conduction equation, and the spring response. An optimization procedure has been devised and used to determine the preferred designs by determining the minimum weight. The design is subjected to multiple linear/nonlinear constraints: (i) the specified minimum authority (product of end displacement and dead weight to be lifted); (ii) the upper limit for the power consumption; (iii) no structural failures such as face/core yielding and face/core buckling; and (iv) the requirements for the optimal design of the compression spring.