Today, aspherical elements have become an indispensable part of modern high-precision optical assemblies. Several kinds of defects arise during their manufacture. As far as very precise aspherical surfaces are concerned, mid-spatial frequencies are probably the most important issue. This type of imperfection fills the gap between shape (low-spatial frequencies) and microroughness (high-spatial frequencies).
A smaller part of these defects arise during polishing; however, more of them are generated during the grinding process. Due to the interference of different controlling frequencies in the machine and imperfections in the constructional solution of the grinding machine, defects occur on the optical surface, which deform it. The periods of these defects usually lie in an interval of 0.5 to 10 mm, depending on the parameters of the machining process. To prevent the generation of these structures, a comprehensive measurement of the sources and transmission of vibrations was realised using the measuring device VibXpert II. The measurement was made on the grinding machine Optotech MCG 100 CNC. Several simulations of different types of processes were realised and the measurement was also subsequently performed during a real grinding process of aspherical optical surfaces. The data acquired from the measurement of vibrations were mathematically processed in frequency space. The experiment revealed several reasons for these defects.
We focus on the subaperture polishing tool concept development for suppressing midspatial frequencies (MSF) arising from computer numerical control machining of aspherical optical surfaces. The selective effect in the MSF range is achieved by setting the tool viscoelastic properties so that rigidity increases in the frequency-domain generated by the rotational tool movement over the aspheric surface with the MSF while the tool remains flexible in the lower frequency range associated with tool radial direction movement. The mechanism of MSF removal is discussed in detail, including in terms of elasticity module frequency dependences, and is also experimentally verified. In order to monitor and optimize viscoelastic properties, especially in regard to frequency dependences, the dynamic mechanical analysis method has been developed and applied and is presented in the paper as well.
The work deals with the creation of correction data when generating spherical and aspherical surfaces. Generation is performed on the converted 5-axis milling machine, for which it is necessary to generate control programs. In the process of generating surfaces may be formed random errors. Hence the need to measure workpieces, and errors corrected. There is thus solved a measurement of generated surface on coordinate measuring machine Mitutoyo LEGEX 744 and draft methods of data processing by using polynomial of nth order. The measured data are processed by Matlab, specifically CFTool module. This method is further tested and subsequently the experiment evaluated.