Study On Control Of Difunctional Pneumatic Valve Positioner Based On The Switch Valves

Pneumatic control system has been widely used in the production of industrialautomation. The pneumatic valve positioner based on the switch valve studied inthis paper is an important part of the instruments and devices which are used in theprocess control of the industrial automatic production. Compared with the systemcontrolled via proportional/servo valve, this system is cheaper, has betterperformance to resist contamination and is easier to maintain, etc. Due to gascompressibility, low stiffness and friction nonlinearity, it is difficult for the switchvalve pneumatic control system to get stable response process and precisepositioning performance. To achieve good position control of the pneumaticpositioning system based on the on-off valve, which meets the requirements ofcertain position indicators, what this paper aims at is to do some related research onthe control of pneumatic valve positioner, analyzed re lated features of the system,and explored the way of working principle and control strategy of the controlsystem. Specific research contents are as follows:First, this paper set up the structural model of the double-acting pneumaticvalve positioner based on switch valve by the use of switch valves with two two-way, then did some theory analysis including the building of the system’s flowcontinuity equation, energy equation, and kinematic equation, analyzed the reasonof the phenomenon of "crawling" in the pneumatic system, and mainly analyzedflow equation of the switch valve’s port, kinematics equation and movementcharacteristics of the valve’s core.Secondly, analyzed the working principle of switch valve controlled by thePWM. On the basis, explored static and steady state response characteristics of thePWM on-off va lve pneumatic control system by using of pneumatic system modelbuilt by the AMESim, and did some correlation analysis based on the staticcharacteristic curve obtained. Explored the on-off valve control systemcharacteristic curve of the steady-state output pressure and pressure fluctuationunder the driving of three different conduction modes by the system’s AMESimmodel, which are double side with one-way drive signal, double side with in phaseand reverse phase drive signals。Moreover, according to the research on the PWM switch valve pneumaticsystem’s characteristics, explored the control features of the system in threedifferent conducting ways mentioned above respectively, by whic h analyzed that themode of driving in phase PWM has obvious advantages in easing the crawling phenomenon and ripple problem, then explored the effects of the system’sparameters on the pneumatic system with the drive way of in phase PWM, such asinitial pressure, pipe length, external load, etc, and sought the optimum parametersof the system which is under control. Simulation results showed that the positioningtime was less than5s, the steady state error was not higher than0.5%, and thesystem had good steady state characteristics.At last, built the test bench of pneumatic valve positione r controlled by theswitch valve which used the MATLAB/xPC Target toolbox for real-time control anddata acquisition, and the ATMEGA64SCM as the controller of the systemprogrammed by the C language, then tested the simulation’s results above. Theexperiment results showed that experiment results and the system simulation resultshad a good agreement, and met the practical requirements of performance indicators.