The Study Of Sphericity On-site Measurement Based On Precision Spherical Grinding Machine

Ball valves are used widely in industrial production. The core of ball valve is a sphere, the sphere rotate around the stem to make the valve to be opened and closed. Valve sealing performance is the primary indicator to evaluate the performance and reliability of valves. This set the strict request to shape accuracy and the surface quality of the valve core. At present, manual test with micrometer is the main method to measure sphericity of the valve core, this affect the sphericity examination efficiency enormously. And no one do the research about on-site measurement of sphericity. Using the advanced sensor technology and the computer technology to survey the sphericity of valve core on-site is the necessary of improving survey efficiency, also is the technological development tendency.Precision spherical grinding machine is a special machine to manufacture the valve core. Spherical form accuracy and surface roughness are affected by the spindle rotation error of spherical grinding machine. A measurement system was designed using the simple-point method. The system consists of the high accuracy standard ball, high accuracy non-contact displacement transducer and encoder. The rotation error measuring principle was introduced. The measuring error occurred in the process of measuring and the elimination methods were analyzed. The rotation error data was measured and analyzed automatically in the experiment. The least squares method was used to evaluated the error data and high precision measurement of the rotation error was finally achieved. The results of the study have important reference value to the spherical surface processing and the sphericity measurement.In order to improve the survey efficiency, a new method of on-site measuring sphericity is proposed based on high-precision sphere grinding machine. The measuring basis and the automatic measuring instruments are built based on the sphere grinding machine. The radius variation as well as corresponding longitude and latitude values of the measuring points evenly distributed over sphere are measured. The mathematical models of the spherical center coordinate and the least square radius are established based on the least square method. The least square sphere is then fitted by the measured values. The measured sphere and the least square sphere are compared by comparison charts and the sphericity value is on-site achieved through calculation. The feasibility of the proposed method is analyzed by comparing the measurement result with that measured by traditional measuring method. Finally, analyzed influence to the sphericity measurement caused by the rotation error of the grinder.