Trajectory Tracking Control Of Wheeled Robot Subject To Input Constraints

Wheeled mobile robots are widely used in various fields of daily life and industrial production due to their simple structure and flexibility.All kinds of complex tasks of wheeled mobile robots are based on motion control.As an important branch of motion control,trajectory tracking has attracted more and more scholars’ attention.In practical application scenarios,due to the consideration of safety factors and the restriction of motor characteristics,the input saturation constraint of mobile robot is inevitable.If the input saturation constraint is ignored when designing the controller,the tracking performance of the system will be degraded,even worse,the system will become unstable.In this thesis,the trajectory tracking control problem of wheeled mobile robot with input saturation constraints is studied in view of the fact that the center of mass of the wheeled mobile robot does not coincide with the center of the axis of the driving wheels.(1)The trajectory tracking control problem of the wheeled mobile robot subject to the torque saturation constraint is studied.Firstly,based on the kinematic trajectory tracking error model of mobile robots,a new Lyapunov function is designed,and based on this function,a new kinematic controller is obtained to achieve accurate tracking of the reference trajectory.Secondly,Based on the dynamic model of the mobile robot,a dynamic controller is designed,and the parameter selection conditions satisfying the torque saturation constraint are given,which achieve asymptotic tracking of velocity.Then,The stability of the entire system is proved by Lyapunov stability theory.Finally,some numerical examples are given to show the effectiveness of the proposed control method.(2)The trajectory tracking control problem under velocity constraint and torque saturation is investigated.Firstly,For the kinematic trajectory tracking error model of mobile robots,a novel kinematic controller based on a first-order filter is designed,which effectively reduces the difficulty of adjusting control parameters while guaranteeing the convergence of tracking error.Secondly,A bounded dynamic controller including trajectory tracking error is designed,which realizes the accurate tracking of the actual velocity of the mobile robot to the output velocity of the kinematic controller,and guarantees the stability of the entire double closed-loop control system.Then,Combining with the velocity tracking error,the kinematic controller,and the dynamic controller,a less conservative control parameter tuning condition is given,guaranteeing that both the velocity constraint and the torque saturation constraint are satisfied simultaneously.Finally,the simulation results show that the proposed control method has better tracking performance and less conservation.(3)The trajectory tracking control problem of mobile robots with torque saturation constraints and external disturbances is studied.Firstly,Based on the trajectory tracking error model of mobile robot,a new kinematic controller is designed to accurately track the reference trajectory.Secondly,the Radial Basis Function(RBF)neural network is used to approximate the external disturbance in the dynamic model,and adaptive feedback terms are used to compensate for the approximation error of the neural network.Then,a dynamic controller is designed based on the non-singular terminal sliding surface.The Anti-Windup auxiliary dynamic system is proposed,and the velocity errors are guaranteed to converge to zero in finite time.Finally,the effectiveness of the proposed method is verified by some numerical simulations.