Research On Movement Control Method Of Nonholonomic Wheeled Mobile Robot

In the theoretical study of the movement control of the wheeled mobile robot(WMR), it is supposed that WMR's wheels are pure rolling without slipping. So WMR's movement is under restrictions. This ideal constraint is one kind of nonholonomic constraint in nature. This makes WMR becomes the typical example of the nonholonomic System. Therefore it has crucial practical value and theoretical significance to study nonholonomic system represented by WMR.In the basis of referring to and summarizing extensive literature, this text study deeply WMR's problem of movement control comprising trajectory tracking and point stabilization. The main research contents of papers have the following respects:Sliding mode variable structure control theory is studying for application in WMR's movement control, two control methods are proposed.Firstly, a sliding mode control method of nonholonomic WMR based on it's kinematics mode in two-dimensional polar coordinate is proposed. In polar coordinate, two sliding surfaces are selected according to the position and direction and eliminate the posture constraint of the WMR. Based the two sliding surfaces two controllers are designed, they are respectively position controller and direction controller. One is to guarantee the asymptotic position tracking even with the direction error when the position-tracking errors exist or the reference trajectories are moving. The other is to guarantee the asymptotic direction tracking when the position-tracking errors are sufficiently small and the reference trajectory does not move. By combining two controllers together, both asymptotic posture stabilization and trajectory tracking are achieved for reference trajectories at global regions except the arbitrary small region around the origin. Constraints on the desired linear and angular velocities as well as the posture of the WMR are eliminated. After analyzing the stability of controllers, their performance is proved by simulation.Then, the problems on robust stabilization and tracking of WMR are studied. Through defining a global reversible conversion, the kinetic model of WMR is transformed into a facilitate extended Heisenberg system form. On the basis of two cases of uncertainty factors existing, two robust integral sliding mode controllers are designed based on the form. One is the controller based on first order integral sliding mode, it eliminates affect of matching uncertainty to system. Next, extending idea of integral sliding mode, a second order integral sliding mode controller is designed. It eliminates affect of matching and mismatching uncertainty factors to system. The problems on trajectory tracking and posture stabilization of WMR with form of extend Heisenberg system that has drifting uncertainty factors is solved. A integral sliding mode is eminently emphasized, it can keep away from some control singular points presented to reaching stage of tradition sliding mode control.The inherent ability of mode predictive control (MPC) to handle constrained systems makes it a promising technique for the control of nonholonomic mobile robots. A first-state contractive model predictive control method is proposed aim at solving the problem on trajectory tracking and posture stabilization of nonholonomic WMR. The exponential stability of proposed MPC strategy is guaranteed through adding a first-state contractive restraint. Different from controllers in the other literatures, the proposed FSC-MPC also has ability of simultaneous tracking and stabilization. Simulation results indicate that FSC-MPC controller can obtain satisfactory system response.A global output-feedback controller is presented that solves both tracking and stabilization simultaneously for WMR at the torque level. The quadratic velocity terms in the WMR dynamics are removed by coordinate change. The observer of system is designed to build anew status in the system so that it can satisfy the condition that practical control input of system must be force or moment in the practical application. The controller is designed according to two steps, and it's synthesizing is based on coordinate transformation, Lyapunov direct method, and backstepping technical. After analyzing stability of two subsystem, the presented controller's effectiveness is proved by simulation.