Earthworm-inspired MASH (Multi-material, Adaptive Strain-limiting, Hybrid) Actuators for Soft Robots

Abstract This research presents a new class of versatile multi-material hybrid actuators, powered by pneumatics and electrostatic adhesion (EA) based adaptive strain-limiting layers. Soft pneumatic actuators with strain-limiting layers as the mainstream actuation for soft robotics have been developed for decades. However, due to their permanent strain-limiting layers, those actuators possess fewer motion patterns. Inspired by the longitudinal muscles of the earthworm, we present a concept of an adaptive strain-limiting layer with the ability to vary its length, stiffness and position. By integrating two flexible EA brakes into a soft pneumatic actuator as adaptive strain-limiting layers, the actuator can achieve multiple motion patterns including extension, contraction and bilateral bending, with permutations amongst these motions. The EA-based strain-limiting layer can increase the original actuator length by up to 86%, and the baseline actuator stiffness by up to 605%. To demonstrate its potential in locomotion and manipulation, we developed an earthworm-inspired crawling robot possessing great terrain adaptability and a versatile soft robotic gripper based on this hybrid actuator concept.