Research On Vacuum Pressure Servo Control System Based On High Speed On-off Valve

High-speed on-off valves are increasingly favored by pneumatic control researchers because of their low cost,fast switching speed,strong anti-pollution capability and high repeatability.In order to explore the new control structure of the vacuum servo control system,expand the research methods,and improve the dynamic performance,this paper uses highspeed on-off valve instead of proportional/servo valve as the control component of the negative pressure servo control system.Conventional linear controllers do not achieve the desired control effects due to the discontinuous output of the high-speed on-off valve’s mass flow,the asymmetry of the system’s charging and discharging units,the pumping capability,and the nonlinearity of the system’s own uncertainty.Therefore,this paper carries out research on the vacuum pressure servo control system based on high-speed on-off valve.The main research contents are as follows:1)The PWM(Pulse Width Modulation)dynamic characteristics of the high-speed on-off valve are analyzed.Based on the simulation analysis,the correspondence between the duty cycle of the PWM signal and the average gas mass flow rate of the high-speed onoff valve is obtained.For the nonlinear region existing in the corresponding relationship,the mass flow output linear compensation method is adopted,so that the average gas mass flow rate is approximately positively correlated with the PWM signal duty ratio.2)The mathematical model of the vacuum servo control system is established.Through simulation and experimental analysis,it is found that the charging and discharging units of the system have the asymmetry of charging and pumping capacity.The asymmetric structure of the vacuum servo control system is designed,which makes the charging and discharging capacity of the charging and discharging unit of the system basically symmetrical.At the same time,the asymmetry compensation algorithm is designed to further eliminate the asymmetry effect of the system.3)Due to the uncertainty nonlinearity and parameter uncertainty in the actual modeling process of the vacuum servo control system,two kinds of nonlinear controllers are designed in this paper:(1)Sliding mode variable structure controller on system parameters perturbation is not sensitive,and it has good adaptability to system uncertainty nonlinearity.(2)The adaptive backstepping controller uses its own robustness to suppress the nonlinearity of the system uncertainty,and combines the advantages of the adaptive law online parameter update to improve the control performance of the system.4)The experimental platform of the vacuum pressure servo control system was built,and the experimental design of the nonlinear controller was carried out.The experimental results show that the tracking effect of the adaptive backstepping controller is better than that of the sliding mode variable structure controller,and the stable control effect and dynamic tracking performance can be achieved in the set tracking pressure range.The asymmetry compensation algorithm further eliminates the influence of the asymmetry of the system and improves the control precision of the system.