Research On Nonlinear Robust Control Of Wheeled Mobile Robots Under Nonholonomic Constraints

With the vigorous development of modern society,human beings' requirements for themselves' quality of life are constantly improving,It has become a trend in contemporary society,which requires the continuous upgrading of modern material production models,and the use of robots to improve the efficiency and quality of social production.Wheeled mobile robots have excellent maneuverability,simple electrical structure,strong load capacity,and low energy loss.Hence,they are widely used in many technological fields,such as logistics and cargo handling,military blasting insurance,household indoor services,factory inspections and Welding industrial accessories,etc.Because of this,usually,there is no uniform standard for the workplace environment of wheeled mobile robots.Furthermore,uncertain external interference often affects the stability of the mobile robot's operation,and may even lead to unpredictable losses in severe cases.Therefore,it is of great practical significance to study how to overcome external interference and improve the robustness of wheeled mobile robots in practical applications.This paper considers the two practical situations of wheeled mobile robots with uncertain load and saturation constraints of the actuators,and separately researches how to achieve robust trajectory tracking in these two situations.In addition,the actual trajectory tracking experiments are carried out to investigate the problem of robust trajectory tracking.The theoretical results have been verified.The main research contents of this paper are as follows.When the load of the wheeled mobile robot is uncertain,a robust trajectory tracking controller is designed based on the dual closed-loop control framework.In the outer loop,a smooth nonlinear kinematics controller is designed to generate a virtual velocity that can realize trajectory tracking.In the inner loop,a nonlinear speed error feedback controller is designed to control the wheeled mobile robot to track the virtual speed generated by the kinematics controller,thereby indirectly realizing trajectory tracking.In addition,the influence of the mobile robot's uncertain load is regarded as part of the total disturbance,and an extended state observer based on a nonlinear function is designed to estimate the total disturbance in real time,which is used to compensate the control input to improve the robustness of the system.When the actuator of the wheeled mobile robot has saturation constraints,a saturation control strategy for trajectory tracking is proposed based on the double closed-loop structure.In the outer loop,a kinematic controller with speed saturation constraints is designed based on Backstepping technology,in which a sign function is used to improve the response speed and robustness of the control system.In the inner loop,an extended state observer is used to enhance the robustness of the system,and an integral sliding mode saturation controller is designed for the saturation constraint of the actuator to quickly respond to the speed target generated by the kinematics controller.At the same time,the robust performance of the system is enhanced.