Unmanned Ground Vehicle Control Method Based On Wheel-road Friction Compensation Mechanism

Unmanned ground vehicle is a ground mobile platform of autonomous driving or remote control operation, which can be used one time or more times, can carry a certain number of load, and can run according to a preset path and perform some tasks. As the unmanned ground vehicle has the characteristics of automatic control and highly intelligent, therefore, it often can reach the place where vehicle is difficult to reach, or which is very dangerous for human, and can complete the work that human can't finish directly. In short, unmanned ground vehicle has attracted more and more attention.The dynamics equation of unmanned ground vehicle possesses the characteristics of nonlinearity, strong coupling, nonholonomic constraints etc. In order to facilitate the study of motion control and trajectory tracking of system, it is necessary to establish the dynamics equation of system. Firstly, nonlinear dynamics model is established by Euler Lagrange energy method, and the nonholonomic constraints are eliminated by reduced order processing, so as to lay a foundation for the subsequent controller design. On above basis, considering wheel friction interference that effects on the vehicle tire, action mechanism of friction can be analyzed, the unmanned ground vehicle ground friction model with wheel-road friction interference can be established. Further, we can take the wheel dynamic sliding effect into account, and analyzes its influence on the wheel longitudinal force, then the unmanned ground vehicle wheel-road friction model with the dynamic sliding effect.Secondly, the trajectory tracking control method based on terminal sliding mode control is proposed for the motion control and trajectory tracking of the unmanned ground vehicle. The double closed loop control strategy is used to establish the control system structure:in the outer loop, we design the posture error controller to achieve arbitrary reference trajectory tracking under the inertial coordinate system. In the inner loop, we design the controller using the terminal sliding mode control strategy to realize speed tracking.Thirdly, the online identification and compensation mechanism of wheel ground friction based on the adaptive law are proposed for the wheel ground friction disturbance in the ground friction model of an unmanned ground vehicle. The adaptive law of the global interference and the adaptive law of the parameters interference are designed respectively by using the gradient descent method, and we can design terminal sliding mode controller of the system under the adaptive friction compensation mechanism.Finally, aiming at the dynamic slip interference of unmanned ground vehicle wheel-road friction model, the online identification and compensation mechanism of the RBF neural network of radial sliding friction can be designed. The universal approximation characteristics of RBF neural network can be used to approximate this uncertain wheel-road friction, and we can design the terminal sliding mode controller under the RBF neural network sliding friction identification and compensation mechanism.By using the Lyapunov stability theorem, the stability of the system with the proposed control strategies can be proved theoretically, and numerical simulations are carried out to demonstrate the feasibility and availability of the proposed controllers by MATLAB software. This study can significantly improve the unmanned ground vehicles in complex unstructured environment adaptability, and has double values of theoretical research and practical application.