Experimental characterization of thermally-activated artificial muscles based on coiled nylon fishing lines

Abstract

The discovery of an innovative class of thermally activated actuators based on twisted polymeric fibres has opened new horizons toward the development of effective devices that can be easily manufactured using inexpensive materials such as fishing lines or sewing threads. These new devices show large deformations when heated together with promising performance in terms of energy and power densities. With the aim of providing information and data useful for the future engineering applications, we present the results of a thermo-mechanical characterization conducted on a specific type of twisted polymeric fibre (i.e. nylon-made coiled actuators) that is considered particularly promising. A custom experimental test-bench and procedure have been developed and employed to run isothermal and isometric tensile tests on a set of specimens that are fabricated with a simple and repeatable process. The results of the experiments highlight some important issues related to the response of these actuators such as hysteresis, repeatability, predictability and stored elastic energy

Stretchable artificial muscles from coiled polymer fibers

“…Above a certain pre-load level the contraction strains remain constant since the full contraction can be achieved without coil-coil contact. Isometric actuation tests [19] have shown that the force generated increases linearly with temperature and the force -temperature coefficient increases only slightly with increasing pre-loading. The near independence of actuator strain and stress generated of polymer coil muscles on pre-load is unusual, as most artificial muscles show a decreasing actuation response with an increase in pre-…”

“…Actuation studies reported to date for polymer coil muscles have only considered the isotonic (∆F A =0) [14] or isometric (∆L A =0) [19] actuation behaviors. These studies have investigated the effect of pre-stretch on the isotonic actuation strain (Fig.…”

Self-Sensing of Deflection, Force, and Temperature for Joule-Heated Twisted and Coiled Polymer Muscles via Electrical Impedance

“…Although a number of methods exist [4], [5], [16], [20], the simplest application oriented method is Joule heating with a resistance wire. Wrapping the resistance wire around the polymer, as illustrated in Fig.…”

“…Training of the muscle is usually seen as repeating the actuation cycle in the setup a number of times before performing the actual experiment [5], [20], [21]. We let muscles undergo a number of cycles of heating and cooling, from room temperature to the maximum actuation temperature, in the intended setup.…”

“…It is a thermally activated actuator in the form of a coil made of a twisted polymer fiber such as a nylon fishing line. Despite low speed and efficiency, this actuator is capable of high strain, high power-and work density [5] and production is inexpensive [4].…”