Multi-link Articulated Wheeled In-pipe Robot with Underactuated Twisting Joints

Abstract

This paper presents a multi-link articulated wheeled in-pipe robot that can drive the wheels and roll-joints by only a single actuator mounted in each link. The robot can not only move forward/backward but also move helically in pipes to change its orientation while twisting the body shape. This underactuated motion is generated by a simple miter-geared differential mechanism installed in each joint. Whether the robot moves straight or moves helically depends on the load applied to the wheels and roll-joints. In this study, we assume that this load can be generated by driving the rear wheels and the front wheels of the robot alternatively. To verify the basic performance of our proposed mechanism, experiments in horizontal and vertical straight pipes, as well as a bent pipe, were conducted. We further validated how the different spring stiffnesses influence the underactuation. Thanks to this mechanism, it is not necessary to install an additional actuator for the helical movement (twist of the body shape). Therefore, downsizing and lightweight of the whole robot including cable-savinz can be expected.