High performance twisted and coiled soft actuator with spandex fiber for artificial muscles

This paper reports the twisted and coiled soft actuator (abbreviated with STCA) with spandex fiber. The STCA exhibits higher actuation strain at lower temperature than the previous nylon twisted and coiled soft actuators (abbreviated with NTCAs). While NTCAs are fabricated using a twist-insertion process until coils are formed, a new method is developed to fabricate the STCA using the ultra-stretch of spandex, whereby the STCA is twisted again after the coil has been formed. A 6-gear-twist-insertion device that increases the stability and the fabrication speed is developed to fabricate the STCA. The superior performance exhibited by the STCA is due to the 14% contraction strain of the bare spandex (bare nylon: 4%) and the low spring constant of 0.0115 N mm−1. The maximum tensile actuation strain of STCA was 45% at 130 °C, and the maximum specific work was 1.523 kJ kg−1 at 130 °C. STCA could repeatedly actuate 100 times with a strain change of less than 0.4%.