Study On Stable Adaptive Control Of Uncertain Robotic Systems

Robot is not only a great complicated time-varying, highly-coupled, nonlinear systems, but also subjected to various kinds of uncertainties, such as measurement errors, frictions, varying payload, random disturbances, un-modeled dynamics, and so on. So it is very difficult to obtain the integrated and precise dynamics of robot system. It is significance in theory and practicability to the realization of high speed, high precision and great capability robots that modeling and solving the above problems. The design and analysis of controller for robot trajectory tracking is proposed in this thesis. The procedure is based on a series of theories, which include Lyapunov stability theory, adaptive control theory, fuzzy control theory, dynamic surface control, integral variable structure control theory, and so on. The main contents are outlined below:Firstly, a new design scheme for rigid robot manipulators with disturbance is proposed. The proposed approach only requires the feedback of link position states without the velocity information. The design is based on the principle of states observer and the technique of dynamic surface control (DSC). The immeasurable link velocity for the robot model is estimated by an observer. Then, the control law is determined using the states estimates and the DSC. Compared with the existing robot control based on backstepping, the proposed controller is simple. By using of Lyapunov technique, the boundedness and convergence of the observer errors and tracking errors are analyzed, and it is proved that all signals in the closed-loop system are uniformly ultimately bounded. Simulation results show that the control system exhibits good tracking performance.Secondly, a design scheme for rigid-link flexible-joint robot manipulators with unknown dead-zone is proposed. The design is based on the principle of sliding mode control. The approach takes into account the phenomenon and the effect of dead-zone in the operation of robots control. In order to force the system to work in the sliding modes as soon as possible and reduce the adverse effect caused by chattering on real-time control, a new reaching law is presented. Then, the control law is designed by two steps. Simulation results show the effectiveness of the scheme.Lastly, the problem of adaptive fuzzy control for uncertain robot manipulator is discussed. Based on the principle of variable structure control, a novel integral variable structure adaptive fuzzy control strategy with supervisory controller is developed. The fuzzy systems with linear adjustable parameters are used to approximate process unknown functions. With the help of a supervisory controller, the resulting robotic closed-loop system is globally stable in the sense that all signals involved are uniformly bounded. Furthermore, the adaptive compensation term of the optimal approximation error is adopted to reduce the effects of modeling error. Theoretical analysis verifies that tracking error converges to zero. Simulation results demonstrate the effectiveness of the approach.All the strategies suggested in this thesis are proved strictly in theories. And their practicality and validity are verified in simulation. Through the research in this thesis, new ideas are provided for dealing with some practical problems faced by robot manipulators in engineering.