Development Of Mechanical System For Microspheres' Sphericity Measurement

In the field of nano technology,microspheres are often used as the tip-ball of a measuring system.With the development of machining precision and the miniaturization of the critical dimension of precision device,the microsphere in a measuring system is required to be as small as possible.For a micro-nano coordinate measuring machine(CMM),probing balls with diameters below a few hundred microns are needed,and their sphericity have to be qualified within tens of nanometers level or even higher.However,there is no mature technology yet to measure the sphericity of microspheres,which needs further exploration.A new sphericity measurement method with high precision is proposed in this thesis,which is aimed at microspheres with diameters in the range of tens microns to sub millimeter.And based on this method,a sphericity measuring system is developed,the performance of the system structure is then tested primarily.Except for the high precision measurement on Sphericity of microspheres,this system can also be applied to three-dimensional(3D)measurement for other similar micro objects.In the sphericity measuring system,two scanning probe styluses,which are comprised of tungsten probe with large length-to-diameter ratio and quartz tuning fork,were placed on the circle contour of the measured microsphere symmetrically,and used to scan the circle contour of microsphere.By using differential measurement,the influence of spindle radial motion error during the microspheres 3D measurement can be eliminated.And then,the multi-dimensional and multi-directional scanning measurement of the microspheres can be realized through the rotating structure.The 3D profile parameters of the spherical surface are then obtained,and the critical dimensions of the microspheres can be got.The overall structure of the system includes scanning probe styluses,clamping and driven structure of scanning probe styluses and the measured microsphere,the rotating structure,and visual guided alignment structure.In this thesis,the construction and commissioning of the sphericity measuring system are elaborated.Furthermore,the performance of the system is tested by experiment,such as the quality factor of scanning probe stylus,the precision of the nano positioning table,and the coarse alignment accuracy of the scanning probe styluses.According to the experimental results,the resonant characteristics of the scanning probe styluses in the measuring system are proven to be qualified.The kinematic resolution of the scanning probe styluses and the measured microspheres are 0.5nm,0.5nm,0.9nm,respectively.The coarse alignment accuracy of the scanning probe styluses based on the visual guided alignment structure is reached up to micron level,and can be further improved.The experimental results verify the validity of the sphericity measuring system.