An earthworm-inspired soft robot with perceptive artificial skin.

The bodies of earthworms are composed of repeating deformable structural units, called metameres, that generate the peristaltic body motions required for limbless underground burrowing and above-ground crawling. Metameres are actuated by circular and longitudinal muscles that are activated synchronously by the animals' nervous systems. A significant number of the neural-motor feedback loops function with sensory input gathered by the animals' highly sensitive skins, which are embedded with light, pressure and chemical receptors. In this paper, adopting the basic mechanisms employed by earthworms, we propose a new type of pneumatically-driven soft robot that can travel inside pipes by mimicking the motions and replicating the functionalities of a single metamere. Furthermore, we introduce a sensing scheme for feedback control that mimics the mechanical sensory capabilities of an earthworm's skin, which was developed upon stretchable liquid circuits capable of measuring strain and detecting pressure variations. The suitability of the proposed approach is demonstrated through several controlled locomotion experiments, employing two different robotic prototypes.