Simultaneous Locomotion with Stiffness Perception of an Earthworm-Like Robot in a Soft Tubular Environment

Robots are frequently employed for navigation and detection tasks within tubular environments. However, when operating in soft tubular environments, they face significant challenges. The inherent instability of these structures can impede a robot's locomotion, and their soft tissues might be damaged by the interaction with robots. This study proposes a real-time stiffness perception system in soft tubular environments (e.g., colonic lumen) based on the earthworm-like movement to realize locomotion and detection simultaneously. The proposed soft robot features a central actuator (CA) for axial elongation and contraction, along with two auxiliary anchoring actuators positioned at the front and rear ends (FAA and RAA) to prevent backward slippage during locomotion. Notably, FAA is equipped with a perception mechanism capable of detecting the stiffness of the tubular environment through its interaction during inflation. The analytical modeling for CA's axial elongation, as well as the interaction between FAA and the surrounding tubular environment, has been developed and validated through experimental studies. Furthermore, the overall evaluation is conducted in two distinct tubes with: (1) uniform wall thickness but varied elastic moduli and (2) uniform elastic modulus but varied wall thicknesses. The successful locomotion and accurate perception confirm the capability and efficiency of the robot. In conclusion, the proposed robot system exhibits promising applications for locomotion and simultaneous stiffness detection in medical diagnostics and other fields where simultaneous locomotion and stiffness detection are crucial.