Design and Characterization of Twisted and Coiled Polymers and Their Applications as Soft Actuators

Abstract

This study is an experimental investigation of twisted and coiled polymer actuators, focusing on characterization of the effects of design and operating parameters on the actuator performance. Using nylon-6 monofilaments, a custom fabrication and testing setup was designed to enable control of the operating conditions, precursor fiber diameter, actuator spring index, motor speed, training conditions, coil bias angle, pre-stretch of the precursor fiber, and pre-stretch of the actuator. Isotonic, isometric, and eccentric contraction tests were performed to evaluate each parameter’s effects on actuator stroke, force, and range in variable stiffness. Results demonstrate that optimal actuator performance is influenced by the operating conditions, selection of precursor fiber diameter, spring index, coil bias angle, training conditions, and the magnitude of pre-stretch in the precursor fiber and fully coiled actuator. This comprehensive experimental evaluation aims to assist in the optimization of twisted and coiled polymer actuators tailored to specific stroke, force, and variable stiffness performance requirements.

Keywords

• Actuators
• artificial muscles
• smart materials
• soft robotics
• twisted coiled polymer actuators
• variable stiffness