Adaptive motion control of mobile robots.

Abstract

In this thesis, three topics related to mobile robot motion control are discussed. A hybrid opto-electronic processor is developed to provide the absolute robot motion information. A cross-coupling controller is used to coordinate the motion of different control loops. An adaptive motion controller is used to compensate for the external motion errors. A method that determines the absolute position of a mobile robot with a hybrid opto-electronic processor has been developed. Position estimates are based on an analysis of circular landmarks that are detected by a TV camera attached to a mobile robot. For robust operation, the parameters of the landmark image are extracted at high speeds using an optical Hough Transform processor. The coordinates of the mobile robot are then computed. Different sources of position estimation errors have also been analyzed, and consequent algorithms to improve the navigation performance of the mobile robot have been developed and evaluated by both computer simulation and experiments to provide good performance. Cross-coupling control is used to coordinate the motion of different drive loops, which results in only small position and orientation errors. The cross-coupling controller has excellent disturbance rejection and, therefore, is advantageous when the robot is not loaded symmetrically or travels at high speed. The cross-coupling controller is analyzed and experiments are conducted to evaluate its performance. The experimental results show accuracy improvements over conventional controllers, especially in compensating for orientation error caused by the internal error sources. A model reference adaptive motion controller is designed and built for a differential-drive mobile robot. The controller uses absolute robot motion information to modify the control parameters in real time and, in turn, to compensate for the motion errors. The cross-coupling control method is used to compensate for the internal errors that can be detected by the wheel encoders. The adaptive controller provides compensation for the external errors. The adaptive controller is analyzed, and the stability and convergence are discussed. Both computer simulation and experiments are conducted to evaluate the control system. The results show significant improvements over the conventional controller.