Normal-Force Control for an In-Pipe Robot According to the Inclination of Pipelines

To move freely, in-pipe robots must be able to adapt to the various geometric changes of pipes. Previously, we described an in-pipe robot that can adapt to changes in diameter and curvature of center curves. This robot is able to estimate the forces exerted on the inner surface of the pipes and balance its posture inside the pipe using angular sensors attached to its rotational joints. In this paper, a method is proposed to estimate the relative attitude between the robot's main body and the pipe using the angular sensors attached to a pantograph mechanism. The use of angular sensors makes the structure of the robot simpler and more effective than the use of force or vision sensors because the normal forces and attitude can be estimated from measured angle information. This geometric estimation of attitude relative to the pipes enables the robot to recognize the inclination of the pipes. The PAROYS-II robot can control its normal force according to the variation in pipe inclination. Thus, the proposed method could reduce power consumption and stress on the robot's parts. The algorithm has been validated by multiple experiments.