Fixed Time Trajectory Tracking Control For Wheeled Mobile Robot With Nonholonomic Constraints

In recent years, with the constant updates and broad applications of computer technology and sensor technology, robot technology has been greatly promoted. At present, robots have been widely used in our life to deal with some of the heavy or dangerous work. In the practical applications, the efficiency of motion control algorithm plays a vital role for the robot to complete the tasks assigned by human beings accurately and quickly. In this paper, the fixed time trajectory tracking controller is designed for nonholonomic mobile robot in the respect of kinematic model and dynamic model respectively. The main works of this paper are as follows:Firstly, for the tracking problem of mobile robot, a fixed time trajectory tracking controller is designed based on the kinematic model. By the cascaded control method, the error dynamics of mobile robot are divided into a first-order subsystem and a second-order subsystem. Then the fixed time control method is used to design the fixed time tracking controller for angular velocity and linear speed. Hence, the mobile robot can track the desired trajectory completely in a fixed time and the settling time is independent of the system initial conditions.Secondly, considering the problem of a mobile robot with parameter uncertainties and external disturbances, a new fixed time tracking torque controller is proposed. Based on the dynamic and kinematics model of mobile robot, the adaptive neural network is used to approximate the uncertain terms and external disturbances in the system, and then the fixed time tracking torque controller is designed so that the mobile robot can achieve the tracking of the reference trajectory completely.Finally, a novel fixed time disturbance observer is designed in view of the uncertainties and external disturbances in the dynamic model of mobile robot. The disturbance observer can estimate the uncertain terms and external disturbances in the fixed time, and the estimated time is independent on the initial estimation error. Based on the observer, a fixed time trajectory tracking torque controller is designed, under which the tracking error can converge to zero in a fixed time so that the mobile robot can achieve the tracking of the reference trajectory.