Monitoring of the glazing state of the pitch polishing lap by an image texture analysis method in full-aperture continuous polishing.

Full-aperture continuous polishing using a pitch lap is one of the key processes in finishing large flat optical elements. The pitch lap has relief lines cutting into the surface to increase its surface roughness and to improve the polishing results. During polishing, the pitch lap surface is glazed due to the transverse rheologic flow and creep of the pitch lap by the element and conditioner, which has significant influence on the polishing results. In this study, an image texture analysis method is proposed to monitor the glazing state of the pitch lap. The images of the pitch lap surface are captured online, and the image textures are analyzed with the gray level co-occurrence matrix (GLCM) method. The experiments revealed that the GLCM eigenvalues of the surface image are strongly correlative with the glazing state of the pitch lap, which has a linear impact on the material removal rate and material removal uniformity. To the best of our knowledge, this study provides a novel and useful method to monitor the surface glazing state of the pitch lap.