Distortion of removal function based on the local asphericity of aspheric surface and the viscoelasticity of polishing tool in computer-controlled optical surfacing

Abstract

In the process of large aspheric optical surfaces fabrication, the distortion of the removal function is a big problem that affects the producing efficiency and accuracy, due to the misfit between the tool and the aspheric surface in the contact region. Consequently, this paper aims to find out the influence factors and the distortion rule of aspheric removal function in the computer-controlled optical surfacing. Firstly, based on the analysis of the sub-aperture polishing technology for the large aspheric optical surfaces, the local asphericity of aspheric surface and the viscoelasticity of polishing tool are supposed to be the main sources. After that, a method to calculate the local asphericity considering the misfit between the tool and the aspheric surface is proposed based on the least square method, and the viscoelasticity of the polishing tool is obtained through viscoelastic experiment. Subsequently, combining the results of the local asphericity of aspheric surface and the viscoelasticity of polishing tool, the prediction of the distortion rule of aspheric removal function is presented. Finally, the comparative experiment is carried out, and the removal function on different regions of the aspheric surface is obtained. The experimental result indicated that the distortion of the removal function is consistent with the theoretical result. Through this study, the distortion rule of aspheric removal function in the computer-controlled optical surfacing with pitch tool is finally mastered, which provides a theoretical guidance for the computer-controlled optical surfacing process optimization.

Polishing trajectory planning method for optimal removal of full surface

“…Because the width of the polishing path is much smaller than the radius of the small tool head and the workpiece, the relationship between the amount of material removed and the overlap length between the paths is nearly linear. Figure 5 shows the relationship between Dh 1 (r) and s i based on equation (5). When 0 \ s i \ 2a, as s i increases, Dh 1 (r) decrease, that is, the amount of material removed decreases with the increase of track spacing.…”

“…Computer Controlled Optical Surfacing, referred to as CCOS, is based on the surface inspection results to quantitatively simulate the polishing machining allowance, 4 and use computer technology to control the small tool head to move on the surface of the workpiece with a preset trajectory. This technology determines the parameters such as polishing pressure, feed speed and residence time distribution, 5 and use numerical control (NC) servo technology to accurately remove optical workpieces, thereby correcting surface errors and improving accuracy. Computer quantifiable control algorithms and NC machine tools have higher accuracy and repeatability, which significantly improves the surface convergence rate and processing efficiency.…”