Control of Thermally Activated Nylon Actuators

Developed recently at the University of Texas at Dallas, super-coiled nylon actuators provide high strength to weight ratios at a low cost in the form of thermally activated linear actuators made from nylon fishing line. These actuators are created using motors to insert twist until the fishing line forms a helical coil, then annealed to allow space for contraction. To control these actuators, a temperature sensor circuit was designed to measure the heat within the coil, and a power control circuit was used in conjunction with a nichrome wire coil to modulate temperature and by extension the contraction of the muscle. The contractile and elastic properties of these muscles make them ideal for vibrational tensegrity robots, which are held together using springs or other tensile elements and are controlled using asymmetric motors. In typical models, the springs act as passive elements, transmitting vibrations between the strut elements to cause the rapid change in shape of the system. The overall goal of this project aims to turn the springs into active elements using super-coiled nylon fishing line as a thermally actuated linear actuator and variable tension spring, for the purposes of active control of tensegrity shape and control of vibrational propagation. Further research will focus on mathematical modeling of the contraction and force produced by the actuators as a function of temperature, so that they can be integrated into tensegrity robots using the control systems previously designed.