Abstract: Soft in-pipe robot has good adaptability in tubular circumstances, while its rigidity is insufficient, which affects the traction performance. This paper proposes a novel worm-like in-pipe robot with a rigid and soft structure, which not only has strong traction ability but also flexible mobility in the shaped pipes. Imitating the structure features of the earthworm, the bionic in-pipe robot structure is designed including two soft anchor parts and one rigid telescopic part. The soft-supporting mechanism is the key factor for the in-pipe robot excellent performance, whose mathematical model is established and the mechanical characteristics are analyzed, which is used to optimize the structural parameters. The prototype is developed and the motion control strategy is planned. Various performances of the in-pipe robot are tested, such as the traction ability, moving velocity and adaptability. For comparative analysis, different operating scenarios are built including the horizontal pipe, the inclined pipe, the vertical pipe and other unstructured pipes. The experiment results show that the in-pipe robot is suitable for many kinds of pipe applications, the average traction is about 6.8N, the moving velocity is in the range of 9.5 to 12.7 mm/s.

Key words: In-pipe robot , · Bionic design , · Rigid and soft structure , · Mechanical characteristics