The Research Of Restraining Middle And High Spatial Frequency Errors Based On Controllable Compliant Tool

The modern optical engineering owns some significant extreme features, which is large scale scientific project to make extreme scale or extreme functional system under extreme technical conditions and background. China is currently facing some typical extreme optical research project tasks, such as large telescope systems, nano-scale lithography systems and high-power laser systems. These optical systems make strict requires not only for a larger aperture and relative aperture of optical component, but also for the surface quality. Many optical systems even make specific demands on middle and high spatial frequency errors except for the traditional PV(Peak-Valley) and RMS(Root Mean Square) values. This program will make use of smoothing effect of polishing lap and controllable compliant polishing(magnetorheological finishing) to realize controllability of smoothing effect and eliminate middle and spatial frequency errors. First, the mechanisms and the relationships between controllable compliant and smoothing effect will be researched. Second, two models named smoothing spectral function and smoothing efficiency function will be established to evaluate the smoothing ability of controllable compliant polishing lap and research the smoothing effect quantitatively. Last, the smoothing ability of controllable compliant polishing lap for different spatial frequency errors will be researched based on the mechanism and models developed before. And then this program will focus on the process research of eliminating middle and high spatial frequency errors by using controllable smoothing effect.1. First, the background and the significance for the extreme optical fabrication project of restraining mid-high spatial frequency errors. Then, the domestic and overseas development status about the restrain technologies and evaluate method for mid-high spatial frequency errors will be investigated and classified. Based on the investigation and survey, the smoothing technology of polishing tool for mid-high spatial frequency errors is discussed. And the key problems and technological difficulties of smoothing technology are analysed. Finally, the technical scheme of restraining mid-high spatial frequency errors based on controllable compliant tool is proposed.2. Based on the classical sandwich structure semi-flexible tool and the rigid conformal tool proposed by Arizona University, the structure model of controllable compliance tool will be proposed. Before the controllable compliance microscopic mechanism and macroscopic mechanical properties are analyzed, the magnetorheological(MR) materials will be well investigated. The controllable compliance model will be established from microscopic mechanism to macroscopic mechanical properties. The original basis of the whole thesis can be established.3. The magnetorheological(MR) fluid and an Nd Fe B magnet are used in our experiment to make a controllable complaint polishing tool in principle. The cross section magnetic field distributions of Nb Fe B magnet at different distance are measured to determine the magnetic field ranges that can be applied on the MR fluid. The tool influence function and polishing roughness of controllable complaint polishing tool. The interaction force between MR fluid and Nd Fe B magnet is measured by a tension sensor to validate the controllability of rigidity.4. Based on the mathematical model coherence between filtering and material removal process of CCOS, a method named Smoothing Spectral Function is proposed to quantitatively evaluate different spatial frequency errors correction ability of CCOS process. By calculating the smoothing spectral function curve,the correction ability of CCOS process for different spatial frequency errors can be expressed as a non-dimensional and normalized spectral curve. The correctness of Smoothing Spectral Function is validated by the surface data of a 600 mm zerodur plate mirror that is polished by rigid conformal polishing tool.5. Based on the Smoothing Spectral Function of CCOS process,the theory deduction is conducted further. Two different forms Smoothing Spectral Functions of Tool Influence Function(TIF) are obtained from the two different kinds of mathematical deduction. The Smoothing Spectral Functions of TIF describes the correction ability of TIF for different spatial frequency errors. The correctness of two different forms Smoothing Spectral Function are validated by the experimental data.6. The smoothing efficiency function is introduced first, which will be established based on the parametric smoothing model proposed by Dae Wook Kim of Arizona University. A smoothing experiment is conducted using controllable compliant tool to validate the smoothing efficiency function.