Continuous and highly efficient production of twisted monofilaments for twisted coiled polymer actuators

Twisted, coiled polymer actuators (TCPAs) are a recently developed type of thermal actuator that have several key advantages such as low cost, light weight, low hysteresis, high contractility, and high energy density. These features make them a promising option for soft robotics or prosthetics. However, with the state-of-the-art manufacturing process the final TCPAs are relatively short (approx. 10 cm) due to the finite length of the fiber before twisting and the shortening of the fiber upon coiling. Even with a highly automated production process their length renders them unusable for scalable textile processes like weaving, knitting, or braiding. In this work a continuous twisting process based on a plying machine is presented that allows to produce quasi-endless highly twisted fibers. Depending on the direction of twisting and coiling the TCPAs expand or contract. For a twist density of 1000 twists/m, the manufactured TCPAs contract 50 % between 25 and 100 deg C. Furthermore, the twisted fibers can be plied together with an additional wire to form twist-stable yarns. The metal wire can be used to heat the TCPA or it can function as a resistive or inductive sensor. These yarns can then easily be processed with textile technologies like braiding or knitting.