Trajectory Tracking For An Omnidirectional Mobile Robot With Friction Compensation

Omnidirectional mobile robot is a holonomic robot with high maneuverability,which is suitable for working in narrow space and widely used in many fields.In the process of going forward for an omnidirectional mobile robot,the direction of friction force is opposite to the robot,which hinders the movement of the robot and decreases the control effect of trajectory tracking.Thus,the friction compensation problem becomes a key to improve control precision.This thesis aims to solve the trajectory tracking control with friction compensation for an omnidirectional mobile robot and design controllers with strong robustness based on active disturbance rejection controller(ADRC).The main contents of this thesis are as follows:Firstly,based on the experimental platform of the omnidirectional mobile robot,the force of the robot is analyzed and the dynamic equation of the omnidirectional mobile robot in the mobile coordinate system is obtained.Then the dynamics model of the omnidirectional mobile robot with friction model in the world coordinate is set up by coordinate transformation and the characteristics of the model are analyzed.Secondly,an ADRC with friction compensation for omnidirectional mobile robot is designed.The controller consists of trajectory tracking and friction compensation.The friction compensation is estimated by the extended state observer.In order to improve the accuracy of friction estimation,the known part of the model is added to the observer.In order to reduce the impact of the complex nonlinear friction on the system,the controller gain increases with the decrease of the robot's speed in the trajectory tracking part.Subsequently,the stability analysis shows that the control system is bounded input bounded output stable.Finally,the effectiveness and robustness of the controller are verified by simulation and experiment.Thirdly,to solve the dependence of the model predictive control on the accuracy of the friction model,a model predictive controller with friction compensation is designed combined with the traditional model predictive controller and ADRC.The friction is estimated by the extended state observer and used as constraint of model predictive controller.The voltage is obtained by solving the optimization problem.The stability analysis shows that the control system is bounded input bounded output stable.Finally,the robustness and practicability of the controller are verified by simulation and experimental results respectively.Finally,a summary of this paper and the future work are proposed.