Testing coiled nylon threads as artificial muscles for exoskeletons

Abstract

The popularity of robotic exoskeletons in rehabilitation is on the rise. However, high cost and bulkiness are two limitations that hinder their popularity and everyday use. Our overarching goal is to develop a low-cost lightweight exoskeleton for stroke rehabilitation. Researchers have developed a method to transform fishing lines into artificial muscles. The goal of this project was to manufacture muscle fibers and test their mechanical properties, specifically the maximum force they can withstand before failing. Two types of fishing line (53 and 111 N) were coiled using a hand drill and weights of 170g and 240g, respectively. We then used a tensile machine to measure the force at failure for ten fibers of each type to assess the consistency of our manufacturing method. The line rated for 53 N failed at an average force of 6 N (standard deviation: 1 N). As expected, the line rated for 111 N failed at a higher average force of 10 N (standard deviation: 2 N). One of the main results is the rather large standard deviations computed, which ideally will be minimized by a more reliable manufacturing process that will ensure constant coiling speed and line tension. We were able to manufacture muscle fibers from fishing lines and quantified the maximum amount of force they can withstand before failure. Current work focus on understanding the failure mechanisms and building a rig to ensure better manufacturing consistency. Future work will focus on testing additional potentially stronger materials and develop the system to control the fiber contraction. This study represents the first critical step towards designing large artificial muscles. These muscles have the potential to replace the heavy energy-consuming electrical and pneumatic actuators currently used in exoskeletons.