Design And Simulation Of The Control System For An Autonomous Mobile Manipulator

Nowadays,the mobile manipulator has attracted the attention of many researchers because of its flexible operating capacity,wide applicable range and powerful features.However the complex structure,the highly coupling dynamics and the presence of external disturbance increase the difficulty to design a controller for an autonomous mobile manipulator.In the last few years,a good number of researches have been oriented to develop strategies for solving the motion problem of the mobile manipulator.But the problems of the stability and robustness of the mobile manipulator system have not been solved well.Therefore,the control system of the mobile manipulator is designed in this paper,which leads to the better stability and good performance of the mobile manipulator.Firstly,the mechanical structure of the mobile manipulator with the characteristic of two inverted pendulum is analyzed to get the motion characteristic of the manipulator around the equilibrium point.Then the kinetic model of the mobile manipulator is determined by using the principle of energy conversation.Furthermore,the mathematical model of the mobile manipulator is obtained based on the Lagrangian modeling method.Finally,the linear mathematical model of the mobile manipulator with time delay is obtained considering the influence of measurement uncertainties.In terms of the resultant model,a low order controller is designed based on D-partition method and an extended Hermite-Bielher theorem to achieve the stability of the mobile manipulator.For the PD controller,two design methods of the stable region are proposed based on D-partition method and an extended Hermite-Bielher theorem.Firstly,the stable region of the proportional control parameter is obtained.By sweeping the resultant stable region of the proportional control parameter,then the derivative control parameters corresponding todifferent proportional control parameters is obtained based on the extended Hermite-Bielher theorem.Due to the large computation of the proposed method,another method that can determine the stable region of the PD controller is presented based on D-partition method.The end-effector of the mobile manipulator is ensured to be stable as long as the control parameter is selected in the stable region.The stable region of the PID controller parameters is obtained by using the extended Hermite-Bielher theorem.The control parameters are optimized according to H infinity performance index.The optimized PID control parameters can ensure the stability of the end-effector of the mobile manipulator in a short time and the system has good performance.In practical application,the presence of external disturbance affects the performance of the autonomous mobile manipulator.In order to ensure the stability of the mobile manipulator against external disturbance,the control method is extended to the two-degree-of-freedom controller.The proposed two-degree-of-freedom controller is based on disturbance observer and the designed low order controller.The controllers consist of the inner-loop controller and the outer-loop controller.The main objective of the inner-loop controller is to reject the perturbation of the external environment and improve the robustness of the parameter variation and compensate the uncertainty of the mobile manipulator system.The main objective of the outer-loop controller is to achieve the trajectory tracking of the end-effector.Through the cooperation of these two kinds of controllers,the mobile manipulator is ensured to be stable and has a good robustness.In this paper,the design method of the mobile manipulator system with the characteristic of two inverted pendulum is proposed,which provides a theoretical basis for the control of the stability of the mobile manipulator with different functions in practical application.