Soft robots are particularly suitable for in-pipe inspection, where locomotion must be achieved within confined, curved, and geometrically constrained environments without damaging the pipe wall. In this context, structural compliance is not only a safety feature but also a functional design principle, enabling the robot to adapt to the pipe geometry, maintain distributed contact, and generate locomotion through controlled anchoring and extension–contraction cycles. This study presents the design, fabrication, and experimental validation of an earthworm-inspired soft pneumatic robot for in-pipe inspection. The robot uses inflatable anchoring elements for alternating radial anchoring and pneumatic bellows actuators for extension–contraction cycles, enabling locomotion while maintaining stable contact with the pipe wall. A laboratory-scale prototype was fabricated using additive manufacturing and evaluated with a dedicated pneumatic and control system. Experiments were conducted to determine locomotion performance, operating pressures, actuation timing, friction characteristics, bend negotiation, and load capacity. The optimal anchoring pressure was only 0.1 bar, demonstrating that reliable contact with the pipe wall can be achieved at a very low pneumatic pressure. The robot achieved average locomotion speeds of 21.07 mm/s in horizontal and 20.59 mm/s in vertical PVC pipes, successfully traversed a 90° pipe bend, and demonstrated a maximum vertical load capacity of 1.2 kg. These results demonstrate the feasibility of the proposed biomimetic soft robotic concept for in-pipe inspection and provide a basis for future development toward autonomous operation and industrially relevant testing.
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