Soft Rod-Like Robot Crawling: Overcoming Tube Boundaries for Enhanced Navigation

This paper presents a motion control strategy for a magnetically actuated rod-like soft robot, enabling it to transition from free space into a tube and overcome structural boundaries. Although soft robots have shown promise in navigating constrained environments, initiating entry into narrow channels and transitioning across sudden changes in geometry, such as the boundary between open space and a confined tube, remains a significant challenge. To address this limitation, we introduce a crawling-based transition mechanism that allows the soft robot to actively engage with the tube entrance, facilitating smooth entry without relying on external guiding structures. We developed a modeling framework to analyze the propulsion dynamics, considering elastic energy storage, frictional interaction, and magnetic actuation. Experiments confirmed that propulsion efficiency depends on the stored elastic energy and how it is released. Our results suggest that controlled oscillatory actuation enables the robot to overcome boundary constraints, which could be an available approach for navigation in confined environments. This work advances magnetically driven soft robotic locomotion, with potential applications in minimally invasive procedures and targeted drug delivery.