A Tensegrity-Based Inchworm-Like Robot for Crawling in Pipes With Varying Diameters

Most current in-pipe robots are usually designed for pipes of a specific size. In this letter, we propose a novel inchworm-like in-pipe robot based on the concept of tensegrity for moving in pipes with varying diameters. Firstly, a tensegrity-based robotic module capable of two kinds of shape change is designed. One kind is extension in the axial direction accompanied by contraction in the radial direction, which is the basis for the wave-like crawling movement of the in-pipe robot. The other kind is expansion in the radial direction while keeping changeless in the axial direction, enabling the module adaptable to pipes with different diameters. Then, the geometrical equilibrium configuration of the tensegrity module is determined, followed by kinematic analysis using force density method. By cascading three modules, the in-pipe crawling robot is developed. Finally, a series of experiments are performed to test the shape changeability and friction force of the tensegrity module, and the mobility, load capacity, and adaptability of the in-pipe robot. The results validate that the robot can crawl in horizontal pipes, vertical pipes, and elbow pipes under the control of a simple actuation sequence. Furthermore, the robot has the abilities to adapt to pipes with different diameters varying from 100 mm to 180 mm. It is suggested that the usage of tensegrity structures brings about higher adaptability, flexibility, and mobility to the in-pipe crawling robot.