Automatic T-Branch Travel of an Articulated Wheeled In-Pipe Inspection Robot Using Joint Angle Response to Environmental Changes

This article proposes an automatic T-branch travel method of an articulated wheeled in-pipe inspection robot, AIRo-5.2, using its joint angle response to environmental changes. The robot joints are composed of two passive elastic joints with torsional springs and a single active joint using a polyurethane-based series elastic actuator (SEA). By switching from torque control to angle control of this SEA, the AIRo-5.2 can pass through vertical T-branches. However, the timing needed to switch them has not yet been defined, and thus it was necessary to train the operators. Therefore, a method that uses the middle joint angle change was proposed for automatic T-branch travel. To elucidate the phenomenon of this angle change and to determine the effects of a robot's mechanical parameters, a partial dynamic model was constructed when only the head link contact was released at a T-branch. Finally, the travel performance of our developed in-pipe robot was tested on 10 types of T-branches with different gravity directions. From the experiments, although the probability of completing the course was not 100% in all cases, the effectiveness of our proposed principle and algorithm for automatic T-branch travel was confirmed.