Reseach On Inversion-based Tracking Control Of Mobile Robots

In order to meet the requirements of the wide application of mobile robots in defense, industry, aerospace, exploration and other fields, all the countries with advanced science and technology have increased the investment in the study on mobile robots. The trajectory tracking control is the critical technology for mobile robots to take their mission. Trajectory tracking refers to looking for a control law of input, enabling mobile robot to track the planned trajectory, moving to the goal posture. However, the mobile robot is a nonlinear system with several nonholonomic constraints. Moreover, the mobile robots are limited by uncertainties and external disturbance. Therefore, the robust trajectory tracking control of the nonholonomic mobile robots is facing enormous challenges.In this paper, a robust trajectory tracking control approach is studied and designed for nonholonomic mobile robots with uncertainties and external disturbance, by using inversion-based control technology. The main work and innovations are listed as follows:1. A kind of two-degree-freedom control system based on disturbance observer(DOB) is proposed. First, the maximum tracking errors of the unit feedback control system and the two degree and two-degree-freedom control system in the uncertainty is computed, and the tracking performances of the two are discussed. Second, DOB-based two-degree-freedom control approach is proposed. The proposed approach combines DOB and two-degree-freedom control system. Finally, stability, tracking performance and disturbance rejection ability of the DOB-based two-degree-freedom control approach are discussed. Theoretical analysis shows that this proposed approach can improve the tracking performance and disturbance rejection ability.2. The nonholonomic constraint of mobile robots is studied firstly. Then the kinematics model, the dynamics model and the motor-driving model of mobile robot are established.3. An inversion-based torque control law is proposed for the dynamics model of mobile robots with uncertainties and external disturbance. The proposed control law, which is developed with the help of backstepping technique, can compensate the external disturbances and the equivalent disturbance caused by uncertainties online. Asymptotic stability of the trajectory-tracking system is guaranteed by Lyapunov theory and Barbalat lemma. Simulation results show that the proposed control law can enable mobile robots to track the desired trajectory effectively, and be superior to Computed-Torque method in tracking performance and disturbance rejection ability.4. A robust trajectory tracking controller, which takes the voltages of the motors as the control input signals, is designed for the motor-driving model of mobile robot with uncertainties and external disturbance. In proposed controller, the DOB-based two-degree-freedom control approach is introduced to improve the tracking performance and disturbance rejection performance. Asymptotic stability is proved by using Lyapunov method and the Barbalat lemma. Simulation results show that the trajectory tracking control system adopting the DOB-based two-degree-freedom control system shows a better performance than that adopting the two-degree-freedom control system.