Research On A New Spool-valve Overlap Pneumatic Measuring System

The spool valve is a throttling actuator using a sharp-edged square holeformed by the two mating edges of the mating sleeve and spool. It is widely usedin many hydraulic control components because of the high linearity of itscontrolled output flow. The overlap value is the axial assembly mating dimensionbetween those edges. This is the comprehensive indicator of spool valve, so itsaccuracy is of great importance to the control system. The manufacturingprecision of this valve is limited by its measurement accuracy currently. Sincehydraulic control components are becoming more widely used and have an higherprecision, it’s necessary to develop automatic and intelligent measuring system.Pressure type pneumatic measurement is a kind of non-contact measurement withfast response and high resolution. It’s very convenient and self-cleaning whichmakes it very suitable for the measurement of sophisticated structures. What’smore, the technology for converting pressure to electricity has been welldeveloped, which is an advantage over the flow type used in pneumatic system.In this thesis, research on a new valve overlap pneumatic measurementsystem has been done using a theoretical analysis of pressure type pneumaticmeasuring. The principle of the whole measurement system was demonstratedand the math mathematical model of this system was built to define themeasurement objects, as well as the reference of the physical model developedon AMEsim platform. Then, the relationship between source pressure, structureof the air circuit and the pressure response were displayed. Finally, theparameters of the system were optimized.The error transfer path of this measuring system was deduced. Error modelscaused by supply pressure fluctuation were demonstrated, including the model ofpressure display error in chamber, the model of transfer function error and t hecalculation errors of the unilateral fitting and overlap.A new measurement system was developed with considering precision anddurability. The hardware of this system was designed, including the optimaldesign of the air circuit, design and strength check of mechanical parts as well as the control subsystem. In addition, the control software was programmed onLabVIEW to meet the automation requirement.The last part of this thesis is the experiments. Firstly, essential calibrationexperiments were made. Then, the precision of the new system was tested byseveral experiments, including a comparison test. The properties of the pressureconstant control circuit were also tested, on basis of which, the optimal designwas applied in the air circuit. Results show that this new system has higheraccuracy and better repeatability than existing one. The air circuit has animportant contribution to the stability of measurement.