Earthworm-Inspired Soft Robot Design Based on Non-Uniform Poisson's Ratio Structure

The mechanism by which earthworms achieve efficient peristaltic locomotion, characterized by the coordinated thinning/lengthening and thickening/shortening of their body segments, has long been a classic subject of study in biomimetic robots. Inspired by earthworm peristalsis, this study proposes a cylindrical soft robot with a non-uniform Poisson's ratio. Its negative and positive Poisson's ratio regions mimic the anchoring function of the earthworm's longitudinal muscles and the propulsive extension function of circular muscles, respectively. A single-motor-driven two-regions robot was first developed, achieving forward locomotion in horizontal pipes, but a momentary loss of wall contact prevented vertical climbing. To overcome this, a four-region robot was designed. Applying a quarter-cycle phase difference between two serially connected units ensures continuous wall contact. This enhances horizontal speed and stability and, via waveform optimization, enables anti-gravity climbing in vertical pipes. The robot also adapts to different pipe diameters by adjusting driving parameters, demonstrating good environmental adaptability. This work provides a novel, simple, and controllable solution for soft robots, demonstrating broad application prospects in the field of pipeline inspection.