Discrete Pneumatic-Tendon-Coupled Actuators with Interconnected Air Circuit for Untethered Soft Robots

Abstract

Untethered soft robots (USRs) based on single-actuation methods face inherent limitations due to restricted energy resources, which adversely affect their performance. Pneumatic-tendon-coupled actuators (PTCAs) offer an effective approach for USRs by combining the compliance and variable stiffness of pneumatic actuation with the precision and rapid motion control of tendon-driven actuation. However, current PTCA-based USRs are limited in versatility and efficiency when executing complex tasks. This research introduces discrete pneumatic-tendon-coupled actuators with interconnected air circuit (DPTCAs-IAC) to address these limitations through two major design approaches: 1) multiple discrete DPTCAs with integrated micro pump, providing additional degrees of freedom and independent motion control while regulating internal pressure without significantly adding weight; and 2) interconnecting multiple DPTCAs through air circuits to facilitate gas flow and enhance efficiency. Theoretical modeling and experimental tests conducted on single DPTCA and DPTCAs-IAC show that the IAC effectively reduces actuation torque and that opposite-direction movements consume less energy compared to same-direction movements. An untethered soft robotic gripper and an untethered quadruped robot with soft legs based on DPTCAs-IAC are developed. Both demonstrate excellent controllability, compact system integration, and multifunctionality, highlighting the potential of DPTCAs-IAC in advancing the development of complex untethered soft robots.