Extraction of Processing Annulus for Large Aspheric Mirror
Numerical control gadget is a computer controlled optical surfacing(CCOS)technology commonly used in large aspheric mirror grinding and polishing nowadays.In engineering practice,when the surface shape is refined to a certain preci-sion,the residual error of the surface shape is often annular,which is quite different from the adjacent parts residual.In order to improve the machining efficiency,these annuluses can be individually corrected by small lapping tools.So the position and width of the zones need to be extracted.This thesis proposes a method suitable for large aspheric mirrors,which maps the height of the surface residual to the color space to become an image,then uses K-Means clustering to segment the image,selects the target interval,and obtains the annulus to be processed.At this time,the width information of the annulus can be calculated to determine the size of the lapping tool;On the other hand,the skeleton is extracted to get the position information of the target annulus,and then generate the processing path available for the machine tool.This method is applied to the aspheric primary mirror of a 1.6 meter telescope,and the annulus is extracted to guide the surface processing.The RMS value primary mirror shape is better than1/40wavelength after multiple machining and auxiliary smooth polishing iteration.
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