Research On Trajectory Tracking Control Of Four-wheel Skidding Steering Robots

Wheeled mobile robots have flexible and stable motion performance,they have broad application prospects in society.In recent years,more and more attention has been paid to the research of mobile robots.This thesis mainly studies the trajectory tracking problem of four-wheel skid steering robots.Firstly,a nonholonomic constraint equation for a four-wheel skid steering robot is established,and the derivation of the error equation for lateral velocity is analyzed.The back-stepping and back-stepping sliding-mode trajectory tracking control laws are designed respectively based on the kinematics model of the mobile robot.By constructing Lyapunov functions,the global stability of the system under two control laws is proved,and the tracking effectiveness is compared and analyzed based on the tracking results of circular and S-shaped trajectories.Then,a skidding coefficient with step change is designed to simulate the movement of the mobile robot on the actual road surface.Aiming at the phenomenon that the pose maintaining ability declines under the condition of the fluctuation of the slippage coefficient in the conventional back-stepping control,a new tracking error equation is established,the controller output is corrected by estimating the wheel slip coefficient in real time using the estimated function.The control stability of the control system under the fluctuation of the object model parameters is improved and the effectiveness of the control algorithm is proved by the simulation results.Considering that the lateral velocity is large and can not be neglected when the mobile robot has a large lateral deflection in the steering motion,the sliding mode tracking control with three switching surfaces is designed according to the trajectory tracking error equation after the lateral velocity is added.Finally,an adaptive sliding mode control algorithm is designed to solve the instability of the control system when the model parameters are changed.The effectiveness of the control algorithm is verified by the simulation of the experiments.