Design equations for binary shape memory actuators under dissipative forces

Abstract

An analytical procedure to design binary shape memory actuators is described. A generic actuator is considered where a cursor is moved against dissipative forces using an elastic system containing a primary shape memory spring and a bias (backup) element. Three typical cases are analysed and differentiated in the way the bias force is applied to the primary shape memory spring, using a constant force, a conventional spring, or a second shape memory spring. Dimensionless, closed-form relationships are developed, which form the basis of a step-by-step procedure for an optimal design of the whole actuator (primary active spring and bias element). Specific formulas regarding the detailed design of the shape memory elements of the actuator in the form of straight wires and wire helical springs are also presented.