A Research On The System For Measuring The Diameter And Sphericity Of The Ball Based On Pneumatic Measurement

In this paper, the subject we studied is from the Fifteen Key Metrology Project of Military Industry in National Defense: the high accurate measurement system for measuring the diameter and sphericity of the ball. We mainly research the principle of the spherical surface measurement system base on pneumatic measurement and design the air circuit and framework of the system. After referring to the related data, the Authors did a large number of experimentation studies to complete the design and research of the system hardware.Through theoretical research and practical experiments, we deeply study pneumatic measurement system for measuring the diameter and sphericity of the ball, using the micro-diameter nozzle and high differential pressure. In the conditions that the working pressure is 0.4MPa, the main nozzle diameter is 0.4mm and the diameter of measurement of nozzle is 0.4mm, we got that the linear range of measurement reached 82um, the sensitivity was 42.9mv/um, the resolution of the measurement was 0.1 um, and measurement uncertainty of the diameter is (0.5 + D/100)um and the measurement uncertainty of sphericity is (0.4 + D/200)um , thereinto, Dis the diameter of the workpiece to be tested. So the system can rapidly, accurately and stably access the parameters of the ball which is less than 30um in manufacturing tolerance and has a diameter ranging between 6mm and 100mm. By computer, the system completes the measurement of spherical surface through data collection, data processing automatically, linear range identification and error analysis.In addition, in this paper, the main factors caused by pressure fluctuations which influence air source quality of the air compressor for pneumatic measurement was analyzed with emphasis, a mathematic model of the air route of pneumatic measurement is established, the throttle chamber composed of pneumatic resistance and pneumatic capacity in stability design of air source is introduced, which has a low pass air route characteristic. Through the error analysis, elimination methods of pressure fluctuations affecting the air source quality are presented and a stable air source system for pneumatic measurement is designed and established, Finally the demand of pneumatic measurement of high accuracy to air source quality is reached. The method for measuring the spherical surface with a diameter ranging between 6mm to 100mm and 30um in tolerance is shown with an in-depth study, and a useful test to extend the application of high accuracy micro-nozzle pneumatic measurement system is attempted, which will provide the foundations of theory and practice about research and application of online high accuracy measurement on industrial fields.