POSITIONING ROTATORY MICRO-ACTUATOR BASED ON SHAPE MEMORY WIRES

An innovative rotational device based on SMA wires with strongly reduced axial dimension and a constant high torque, has been developed. Thanks to its coin-like shape, Micro-SMA motor can be easily placed almost everywhere. Furthermore this actuator has very large torque at reasonable speed, showing thus higher work capabilities than any existing EM actuator with the same overall dimensions. In this paper the conceptual design of the Micro-SMA motor is illustrated, with a specific attention dedicated to the selection of the best functional principle, the modelling of the motor and its functional and size optimisation processes. The final solution is made of a single shape memory wire, locked along a circumference and actuated step by step by a proper power control strategy. A finite element code has been used to eliminate stress peaks on the structure and on the SMA wire. A numerical simulation has been made in order to analyse the temperature behaviour and thus optimise the power control in order not to overheat the system. A fully working prototype has been developed in order to verify the expected behaviour and to test the functional parameters. Further optimisation of the control strategy has been made on the prototype