Peristaltic Soft Robot for Long-distance Pipe Inspection with an Endoskeletal Structure for Propulsion and Traction Amplification

This study proposed a peristaltic motion-type inspection robot equipped with a "linear antagonistic mechanism using artificial muscles with an endoskeletal structure" to amplify propulsion and traction. We sought to develop an in-pipe inspection robot for long, narrow, and complex pipes requiring large propulsion, traction, and flexibility. In a previous study, we proposed a linear antagonistic mechanism allowing the inspection robot to generate both high propulsion and traction along with flexibility in narrow pipes. The proposed mechanism consisted of two extension actuators and a gripping actuator sandwiched between these extension actuators. The large extension force by the extension actuators is distributed to both propulsion and traction. However, owing to the piston-shaped configuration of the extension actuators, the generated force decreased in a manner dependent on the cross-sectional area within narrow pipelines. Therefore, the in-pipe inspection robot took time to move in long-distance, small-diameter pipes with multiple bends. This paper describes a "linear antagonistic mechanism using artificial muscles with an endoskeletal structure" that amplifies propulsion and traction by inserting a tension spring (skeleton) inside the contraction actuators (artificial muscles) and utilizing the action force generated by the actuator and transmitted by the tension spring. In this study, the developed robot with an endoskeleton exhibited maximum propulsion of 60.2 N, surpassing its non-endoskeleton counterpart by a factor of 1.61. Furthermore, the robot equipped with the endoskeleton passed through an elbow pipe 1.29 times faster than that without the endoskeleton, reducing the time from 741 to 576 s. The function value that compares the propulsion and traction considering the effects of the applied pressure and pipe diameter required for long-distance inspection was more than 1.13 times that of the previous study. In addition, the non-dimensionalized traction was 1.55 times greater than that of any other pipe inspection robot, and the propulsion was large enough to pass through a bending pipe. This result indicates the feasibility of the developed robot for inspecting long, narrow, and complex pipes.