In view of the problem of projection distortion in the result of aberration-free point test of off-axis paraboloid mirror, this paper analyzes its formation principle, puts forward a transformation method from the detection coordinate system to the processing coordinate system, according to the mathematical relationship between the two, reconstructs the surface shape of the detection result, realizes the transformation of projection distortion image, and analyzes the error of the transformation result by using the fucial function. It is proved that this method is feasible by using the reconstructed surface results to guide the NC Polishing.
Based on the theoretical model of small-tool polishing, this paper studied the influence of polishing parameters on the results of computer controlled optical surfacing. We compared different parameters of the removal function and the tool path and analyzed the residual mid-spatial frequency errors in the polishing process. The simulation results indicated that raster path combined with Gaussian removal function, contributing to high accuracy of PSD1 RMS, but leading to serious peaks of 1D PSD1 curves in some frequency points. In contrast, pseudo-random path combined with flat-topped removal function, resulting in lower accuracy of PSD1 RMS, but could effectively restrain the amplitude of the 1D PSD1 curves. Finally, experimental study was carried out on both of the 610 mm × 440 mm K9 material transmission mirror and 430 mm × 430 mm fused silica plane window, the RMS value of PSD1 converged from 3.72 nm to 1.61 nm, and decreased from 2.30 nm to 1.37 nm, respectively, which demonstrated the correctness of the model.
In order to improve the stability of the removal function for aspheric surface and realizes its machining. A polishing tool based on non-Newtonian fluid (silly putty) is designed. The influence of shear stress of silly putty in polishing tools on the pressure distribution on the aspheric surface is analyzed. According Preston equation, the removal function of non- Newtonian fluid polishing tool is optimized theoretically based on its surface pressure distribution with the polishing tool executing a planetary motion of the polishing tool. The influence of the structure, materials and driving mode of polishing tool on the removal function shape was analyzed. Then, the polishing tool was improved and the marks on the removal spot were removed. The effect of filling rat io of silly putty and process parameters on removal function was studied by experiments. A method of obtaining stable removal function based on non-Newtonian fluid polishing tools is presented.
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