Efficient Pneumatic Twisted-and-Coiled Actuators Through Dual Enforced Anisotropy

The Cavatappi muscle is a novel soft actuator offering many desirable attributes, such as large linear contraction with negligible radial expansion, compliance, and low cost. However, it has a low energy efficiency (9% ) and requires high-pressure inputs (over 240 psi), limiting its effectiveness in robotics applications. This work proposes a fiber-reinforced pneumatic twisted-and-coiled actuator (FR-PTCA) that addresses these shortcomings by introducing a fiber reinforcement to increase the tube anisotropy. The FR-PTCA has higher energy efficiency (over 19% ) and lower pressure actuation compared to the Cavatappi muscle without sacrificing muscle strain (70% strain at 130 psi). In addition, this work also presents an analytical model of the FR-PTCA that can be used for design optimization and model-based control. The potential applications of these novel actuators are demonstrated through a continuum robot driven by the FR-PTCA.