Non-contact On-line Measurement Of The Micro-topography Of Ultra-precision Machined Surface

As it is known, the quality of machined surface is one of the important factors that determine its functional character. While in the increasing application of ultra-precision machining technology, the surface quality of machined parts becomes more significant. So the measurement of micro-profile of ultra-precision machining surface is an important task in modern science and technology. In recent ten years, some researchers in the world have made a lot of studies on the measuring methods of ultra-precision machining surface, and have produced some new principles of measurement.After presenting the development of ultra-precision machined surface measuring techniques, the author has analyzed some typical kinds of measuring methods in detail, and has pointed out their characteristics and limitations respectively. Based on theoretical studies, a non-contact on-line measuring system is designed and made, which is mainly applied in measuring the micro-profile and roughness of the ultra-precision machined surface on diamond turning lathe, and the desired measured subject is KDP crystal or non-spherical lens. Besides, the theory of stabilized frequency is expounded, and the analysis of the circuit is made at length. In the phase measurement, AD8302 chip is introduced, which promotes the phase accuracy and simplifies the system structure. Finally, we have analyzed the vertical and lateral resolution of the system, and have compared its measuring result withZYGO and Taly-6 profilometers using the same sample. It has shown that this system can accomplish the on-line nanometer measurement.In this paper, a new on-line measuring profile system is presented, which has a light source of a stabilized He-Ne laser with two longitudinal modes. Based on the principle of differential interferometer, the measurement and reference arms of this profilometer are designed as coaxial. So the vertical micro-displacement cannot introduce errors into optical-distance, and the mechanical vibration and air turbulence has very small effect on the instrument performance. Furthermore, the polarization features of two longitudinal laser is applied to design the optional divided structure with birefringence crystal, thus the noise caused by reflected light back to laser is successfully avoided. Parts of non-coaxial light paths are designed to pass through the crystal, to reduce the disturbance from the environment. In summary, this system has very high resolution and anti-interference feature. Under the circumstance when vibration amplitudes reach 300nm, the profilometer still has sub-nanometer level resolution. The on-line version of the profilometer can be put on the kniferest of a diamond lathe to measure the micro-profile of ultra-precision machining surfaces. The vertical resolution and the lateral resolution are better than 0.2 nm and 0.5 μm, respectively.This online measuring system adopts computer technique to collect and process data. Thus it can measure surface roughness parameters in common use and draw the profile of measured surface. Also, this system can solve the measuring problem of ultra-precision machining surface without damnification and pollution. The operation of the system is convenient, the measuring accuracy is high, and the repetition is fine. In addition, the system, which can be easily made and don't need special measuring environment, has favorable universality and cost performance.