Low-Profile Polymer Actuator Fabrication for Spastic Hand Exoskeletons

Abstract

Spasticity is a neurological impairment that presents itself in the form of a continuous muscle contraction, with the key motor deficit being impaired hand function. Hand exoskeleton technologies play a vital role in the therapeutic rehabilitation of this condition. The optimal design of these devices is currently a challenge due to the limited availability of actuation devices that are light weight, portable, and aesthetically pleasing. Natural muscles have many favourable characteristics, such as their high power-to-weight ratio, efficient energy conversion, and fast actuation times. Unfortunately, traditional systems such as pneumatics muscles and electromagnetic motors have yet to attain similar properties. These traditional actuators exhibit hysteretic performance, high manufacturing cost, low stroke, and limited cycle life. In recent years a new category of actuators has been developed from highly twisted and coiled low-cost nylon fibres such as fishing line and conductive sewing thread. These muscles produce a high specific work per cycle with a reversible contraction. This thesis develops and tests these twisted and coiled polymer (TCP) actuators using various nylon and polyethylene polymers in order to establish a foundation for their implementation as a novel actuation device in a spastic hand exoskeleton. An initial comprehensive experimental evaluation of several nylon fibres is completed by attempting to reproduce the work of previous researchers. Subsequently, the information obtained is taken and adapted to the development of UHMWPE TCPs and other types of nylon monofilament. This thesis characterizes the contractility and force output of these novel actuation devices.