The Study On Active Disturbance Rejection Control Of Pneumatic Variable Load Friction And Wear Testing Machine

Friction and wear testing machine as a powerful tool for material performance research has been widely used in various fields.Pneumatic variable load friction and wear testing machine as one of them,using pneumatic loading technology to control its loading pressure through the compressed air.However,due to the strong nonlinearity,strong coupling,uncertainty,the mathematical model of the pneumatic loading system is not accurate,which affects the pressure output control accuracy and hinders its application.In this paper,the pressure control of the friction load test machine is taken as the research core,and the system mathematical model is established based on the principle analysis.Considering the system disturbance,the controllers with high control precision and simple structure are designed to realize the real-time tracking control of the output pressure.The concrete contents and achievements are as follows:Firstly,the structure and working principle of the pneumatic variable load friction and wear testing machine are introduced.Considering the nonlinear factors such as the vibration lagging of electrical proportional valve and the cylinder hysteresis,the load disturbance in the testing machine,on the basis of reasonable assumptions,the mathematical models of them are established,and the state equation of the system model is given further.Secondly,based on the coupling term,the unmodeled part and the disturbance term of the system state equation,an Active Disturbance Rejection Controller is designed which does not depend on the exact mathematical model.The method combines the uncertainty terms for the total disturbance estimated and compensated by Extended State Observer.Compared with the PID controller,the simulation results confirm the effectiveness and disturbance rejection of the designed controller,and improve the control quality of the system.At the same time,taking into account the variation of the system disturbance amplitude,combined with the advantages of Linear Active Disturbance Rejection Controller and Nonlinear Active Disturbance Rejection Controller the Linear/Nonlinear Active Disturbance Rejection Switching Controller with wide interference range,high tracking precision and fast convergence is designed.The convergence analysis of the switched state observer is carried out.The simulation results show that it can effectively solve the problem of the disturbance amplitude change in the pressure tracking control of the pneumatic load friction and wear test machine,and improving the control quality of the system.Finally,based on the working principle of the pneumatic variable load friction and wear testing machine,the measurement and control system test platform is designed.And the digital programs of the controllers are carried out by using VC++ language.The different load signal pneumatic variable load friction and wear test machine pressure tracking control test study are completed under the conditions of no load and loading respectively.The experimental results show that the Active Disturbance Rejection Controller is sufficient to meet the control requirements of the system under normal conditions,but the Linear and Nonlinear Active Disturbance Rejection Switching Controller has higher control precision when the disturbance amplitude is large and the frequency is high.