HIGH-FREQUENCY SMA ACTUATION BASED ON MICRO-WIRE BUNDLING

Shape memory alloys (SMA) gained prominence in a wide variety of applications, due to their unique properties, such as light-weight, high energy density and low cost. The shape memory effect allows SMA to restore their shape when heated, after deformation at lower temperatures. The actuation cycles of SMA-wires show analogy to contraction and relaxation of muscles, so that so-called antagonistic actuator configurations are becoming popular not only for bio-inspired applications. The thermal activation of SMA leads to a limitation in the actuation frequency, basically due to time-consuming cooling process, so currently considered frequencies are typically below 10 Hz. The thermal conductivity can be enhanced by increasing surface-to-volume ratio, i.e., using thinner SMA wires. A Muscle-joint-structure developed by S.-M. Kirsch, F. Welsch, S. Seelecke and P. Motzki (2023), which uses a bundle of 25µm-thick SMA wires was able to reach frequencies up to 66 Hz during repeated rotational movement. One motivation for the development of these high frequency lightweight joint geometries are typical wing flapping motions in nature and their reproduction in drone robotic systems, which range from 10-20 Hz for bats to several hundred Hertz for insects. This presentation focuses on optimization of this system in terms of electronics, mechanics and control to maximize the actuation frequency beyond 100 Hz, maintaining necessary strokes and rotational angles for the creation of lift forces.