ADRC-based Position/Force Control Of An Omnidirectional Mobile Manipulator

The mobile manipulator plays an increasingly important role in manufacturing industries.It is of great practical significance to study the position/force control of the mobile manipulator.In practical applications,the position/force control of mobile manipulators is affected by many factors,like inaccurate model parameters,the external force disturbance and uncertain external environmental factors.Therefore,the accurate control of the position / force of the mobile manipulator is a difficult problem.In this paper,we deal with the position / force control of the omnidirectional mobile manipulator.Firstly,the kinematic and dynamic relationship of the omnidirectional mobile manipulator are analyzed.D-H representation is used to obtain the kinematic relationship between the joint variables and the end position.The Lagrange equation is used to analyze the dynamics.Then an integrated dynamic model is established.Secondly,aiming at the uncertainties of model parameters and external disturbance in the position/force control of the omnidirectional mobile manipulator,a passivity-based Active Disturbances Rejection Control(ADRC)algorithm is proposed.The control algorithm consists of two parts: passivity-based controller and the improved linear extended state observer.The passivity-based controller makes use of passivity characteristics of the omnidirectional mobile manipulator and reshapes the energy function to design the controller from the energy perspective,which can also guarantee the stability of the system.Compared with the traditional linear extended state observer,the proposed linear extended state observer is improved in the aspects of integral saturation and adjusting speed.It estimates the total disturbances of the system and adjusts the control signal in real time to compensate the disturbance,which can improve the robustness of the system observably.The effectiveness of the passivity-based ADRC algorithm is verified by simulation results.Finally,aiming at the uncertain working environment in the position / force control of the omnidirectional mobile manipulator,an ADRC algorithm based on the parameter adaptive impedance control is proposed in this thesis.The performance function of the control system is first defined,and the adaptive algorithm of the impedance parameters is designed according to the gradient direction of the energy function and the betterment process.Therefore,the impedance parameters can adapt to the changes of the external environment.Then,the parameter adaptive impedance controller of the omnidirectional mobile manipulator in joint space is designed according to the impedance model,and the disturbance estimated by the improved extended state observer is compensated in the controller.The simulation results show that the proposed method can achieve accurate position/force control of omnidirectional mobile manipulator in the uncertain external environment.