Evaluation of efficient and lifetime optimised SMA actuation strategies

Abstract:
Shape memory alloys (SMA) are typically actuated using Ohmic heating. Quasi-static and low-speed actuations are mostly a result of applied high currents at minimum times. This not-optimised actuation often causes local overheating of the material, and a too fast actuation can cause high stresses. This results in several problems such as the loss of the shape memory effect and even accelerated mechanical damage. To overcome the mentioned negative effects on the SMA wire and to increase its lifetime, the applied actuation energy must be controlled precisely, and critical temperatures and stresses must be avoided. This can be realised by dynamic and precise actuation strategies. In this paper, several actuation strategies are determined and evaluated. The procedure of determination is presented, and critical characteristics are shown. To get the necessary insights concerning the actuation high-speed IR imaging, power, displacement, and force measurements are needed. Finally, the selected strategies are evaluated in degradation examination to define the impact on the wire lifetime and the shape memory effect. The results show that energy savings are possible, and the strategies could be used in all SMA based actuators.