Hierarchical fuzzy control based on spatial posture for a support-tracked type in-pipe robot

Autonomous movement is important for the in-pipe robot. Because of the complex environment of the pipe, traditional control methods such as proportional-integral-derivative (PID) can not be used to implement autonomous movement for the support-tracked type in-pipe robot. A hierarchical fuzzy controller is proposed in this paper, which consists of fuzzy steering control and fuzzy posture control. The fuzzy steering control is utilized to control the robot's turning movement in the elbow pipe, while the fuzzy posture control is used to adjust the posture of the robot in the straight pipe. The robot's posture will periodically coincide after every 120 degrees, when the robot rotates around its central axis. The symmetry is helpful to reduce the 12 x 7 x 7 three-dimensional fuzzy posture control rule table to five 7 x 7 two-dimensional fuzzy rule tables. A support-tracked in-pipe robot prototype is developed to verify the performance of the hierarchical fuzzy controller. Simulation and experimental results show that the robot with the controller could successfully pass the 45 degrees and 90 degrees elbows with a smaller change of posture compared to the case without the controller. As the robot with the controller could pass the elbow without obvious posture change, the proposed controller can be utilized to implement autonomous movement of an in-pipe robot.