Research On Technology Of Measuring Diameters Of Precise Small Holes With The Method Of Pneumatic Plug Gauge

In manufacture of precise parts, long and thin holes whose diameter is about threemillimeter always need to be measured in scene. As common plug gauge will scratchthe inner surface of the holes, this article adopts pneumatic measurement. Pneumaticmeasurement has many merits like contact less, high precision, high stability and so on.Traditional pneumatic measurement refers to buoy pneumatic gauge, but owing to thelimit of mechanism of the instrument, this kind of apparatus doesn't apply extensivelyin the field of automation measurement. This thesis adopts pressure pneumaticmeasurement, applies microcomputer as controlling chip, connects with the fastestchanging sensor technology and realizes automation measurement of long and thinholes. Data processing and analysis, display and print measurement result and otherdigital function can be realized conveniently.For achieving long and thin holes'precise measurement, this thesis further studythe principle, method, software and hardware of pneumatic measurement for detectingsmall holes'diameter.Firstly, based on the theory of nozzle flapper mechanism, this thesis has built amathematic model of pneumatic plug gauge measurement system. In order to optimizethe values of measurement air circuit and obtain a reasonable transformation ratio anda linear measurement scope, the method of combination of theory and practice hasbeen adopted.Secondly, in the direction of the pneumatic plug gauge mathematic model, thesystem which is used for measuring diameter of small holes has been developed.Measurement system uses differential pressure gas circuit for reduce influence of airsupply fluctuation. Hardware designs mainly include signal amplification circuit, A/Dcircuit, measurement fixture and peripheral interface circuit of microcomputer.Software designs include measurement and standardization. The segment ofmeasurement can display measurement result in real time and print out themeasurement results, measurement time and date. The function of standardizationconsists of data input, data processing and standardization results storing.Finally, the experiment results verify the rationality of the measurement system.Experiment indicates that the accuracy of the measurement system can satisfy actualrequirement. After error analysis for the measurement system, the influence of every tolerance factor to measurement accuracy is quantized. Total error of the measurementsystem is 0.781 m according to root mean square method and less than 1 m.The pneumatic plug gauge digital readout meter not only has simple mechanismand convenient operation, but realizes automation and digitization in measuring longand thin holes'diameter. So this instrument has a good perspective.