In the selection of CNC complex parts processing, the best way, of course, is through a variety of ways to compare, so as to select the best quality CNC. Optical aspheric surface testing technology should be able to quickly judge the surface error in the process of mirror processing, give further correction instructions by random feedback, and solve the final inspection of parts.
At present, the most widely used method of aspheric surface measurement is light wave interferometry, which has higher measurement accuracy and better spatial resolution. It can measure the whole surface quickly, and the highest resolution can reach sub nanometer level. But for different optical aspheric surfaces, the corresponding optical template must be prepared to measure. The structure of this measurement system is usually very complex.
Aspheric surface can be measured by holographic interferometry, but a hologram must be made whether standard aspheric surface or CGH is used, and there must be corresponding holograms for aspheric surface with different equations. But up to now, the domestic technology of making hologram is only limited to some traditional technology, and the hologram for ultra precision measurement of aspheric surface basically depends on imports, which greatly limits the testing and processing of optical aspheric parts. At present, it costs about US $10000 to import a hologram for ultra precision measurement of aspheric surface, and we need to tell each other the equation of aspheric surface. For the model task, it involves confidentiality and other issues. Especially for some pre research or in research projects and unformed projects, due to the large variety and quantity of aspheric surfaces involved, the cost is very considerable, so it is urgent to develop the hologram for aspheric surface measurement.
At present, the most advanced technology abroad is to use computer generated hologram ram for aspheric surface measurement and laser writing system to make hologram, which not only greatly reduces the production cost, but also shortens the production cycle. The most typical prototype is the laser plotter clws300 laser engraving system developed by Stuttgart University in Germany. The diameter of laser recording point is 0.5 μ m, the positioning accuracy of radial coordinate is 0.08 μ m (RMS), and the positioning accuracy of angular direction is 0.1s “(RMS).
The high precision laser engraving system mainly includes the following aspects
Optical part: including laser, acousto-optic modulator, auto focusing system and the overall design and layout of optical path, etc;
Mechanical part: high precision air bearing, high precision motion guide rail, vibration isolation platform, etc;
Electric control part: motion and positioning control of high-precision mechanical system, laser, modulator and automatic focusing control, including coordination control of mechanical and optical systems
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