Study On Global Modification Method For High Precision Plane Optical Component

Plane optical component is one of the important parts of the optical system. Nowadays the optical system is developing towards the direction of large scale and high accuracy, which puts forward higher requirement for both quantity and quality of optical component. On the one hand, the rapidly increasing quantity of the optical component including the plane optical component needed by the optical system requires high machining efficiency. On the other hand, the surface accuracy of optical component needs to be higher in order to achieve higher image quality. At present the current processing technologies are hard to meet the needs of these two aspects at the same time, so how to improve the machining efficiency of plane optical component and ensure high surface quality is one of the research problems need to be solved.Lightweight design of space mirror raises the wide application of ceramic materials. In order to overcome the defects of ceramic material, the ceramic substrate needs to be conducted with surface modification technology and the operating requirement is achieved by processing the modified layer. The thickness of modified layer is one of the main factors deciding the manufacturing cost of the mirror. Therefore, reducing the total material removal amount on the basis of meeting the requirement can reduce the modified layer thickness and largely reduce the mirror manufacturing cost.In this paper, based on the above application background, a new processing method for global modification is put forward on the basis of the traditional chemical mechanical polishing process. The basic principle and theoretical foundation is expounded, the processing system is established by theoretical analysis and the test verification is also conducted. The main work is as follows:(1) Based on the basic principle of traditional chemical mechanical polishing, the new processing method for global modification is proposed by removing annular region on polishing pad which is concentric with the pad. By this means the contact between the workpiece surface and the annular region can be avoided and the distribution features of the material removal rate is changed to achieve the global modification. The principle of the method is expounded.(2) A prediction model of the material removal rate distribution features along radial direction of the workpiece is established and the corresponding GUI program is written by MATLAB software to analyze of the surface material removal rate distribution trends in different modification conditions (annular region location and width) and polishing parameters (polishing pressure, rotating speed, eccentricity, etc.).(3) The effect of workpiece surface profile on the material removal rate distribution is studied, and the distribution rule on workpiece surface and change rule with the surface profile of the Preston coefficient are analyzed based on the measured material removal rate distribution and contact pressure analyzed based on the actual surface profile, and the accurately predictability of the material removal rate is also studied.(4) A special device is designed for global modification processing of glass wafer with a diameter of 100 mm and two groups of global modification processing test respectively with and without oscillating are conducted. The test results show that the two ways of modification processing can significantly improve workpiece surface profile accuracy. It is found that the latter modification way can obtain smoother surface profile along the radial direction, meanwhile beyond the edge of polishing pad can get higher correcting ability of the edge effect and lower total material removal amount in the modification processing.