Comparison of mold designs for SMA-based twisting soft actuator

Abstract

The design of SMA-based soft actuators is often limited by the design of the molds used, and these limitations are even more pronounced for actuators with complex shape memory alloy (SMA) wire positioning such as SMA-based twisting soft actuators. This paper aims at developing new mold designs to enable new design possibilities for the fabrication of pure-twisting smart soft composite (SSC) actuators. The basic design of the actuator uses two SMA wires embedded in a polymeric matrix at opposite eccentricity and crossing the matrix in opposite directions. This positioning induces a twisting motion to the matrix during actuation, but current mold designs impose many limitations on the design of the actuator. In this work, two molds design strategies are proposed that enable three distinct approaches to improve the performance of this actuator: interference fit fastening molds and using intermediate elements to reorient the SMA wires. These solutions enable the design of I-shaped cross-sections, composite cross-sections and square-helix positioning of the SMA wires within the matrix. A base actuator size is used to compare the performance of the different strategies then three actuators using combined solutions are manufactured and tested. Results show that the improved mold design can significantly increase the performance of this type of actuator.