Modelling of Wire-on-Drum Shape Memory Actuators for Linear and Rotary Motion

The paper presents the analytical model of a linear/rotary solid-state actuator formed by a shape memory wire wound over a cylindrical drum. The model assumes a bilinear stress-strain behaviour of the wire in the martensitic state (low temperature) and a linear elastic response in the austenitic state (high temperature). Based on simple equilibrium conditions, the model calculates the stress and strain distributions in the wire subjected to a constant backup force and to frictional sliding forces at the contact with the drum. Closed-form expressions are supplied for the stroke produced by whatever actuator geometry. The model shows that large strokes (up to one half of the drum diameter) are achieved if the frictional coefficient is kept below 0.01. Rolling-contact architectures or sonic-pulse excitation of the drum are discussed as technical solutions to obtain such low friction values.