Design equations for binary shape memory actuators under arbitrary external forces

This article presents the design equations for an on-off shape memory alloy actuator working against an external system of arbitrary constant forces. A binary shape memory alloy actuator is considered where a cursor is moved against both conservative and dissipative forces, which may be different during the push or pull phase. Three cases are analysed and differentiated in the way the bias force is applied to the primary shape memory alloy spring: using a constant force, a conventional spring or a second shape memory alloy spring. Closed-form dimensionless design equations are developed, which form the basis of a step-by-step procedure for an optimal design of the whole actuator.