Testing of Coiled Nylon Actuators for Use in Spastic Hand Exoskeletons

Natural muscles have many favorable characteristics including their high power-to-weight ratio, efficient energy conversion and fast actuation times. These factors become important criteria for judging artificial actuation methods. Unfortunately, traditional systems such as pneumatic and electromagnetic motors have yet to attain similar characteristics. In recent years, a new category of actuators has been developed from highly twisted and coiled low-cost nylon fibers. These muscles are capable of providing a powerful stroke per cycle with a reversible contraction. In this paper, twisted and coiled polymer (TCP) actuators with two different commercially available nylon fibers: Shieldex conductive yarn 117/17 and 235/34 are fabricated and tested, then implemented into a low profile, hand exoskeleton. Maintaining quality control on muscle fabrication proved to be challenging and the use of nylon as muscle actuators for exoskeletons would require much more research and better measurements of critical parameters before providing a consistent solution.