Computer Controlled Polishing Process Research Articles

Toward the fabrication of a 5-μm-resolution Wolter microscope for the National Ignition Facility (invited).

Advancements in computer-controlled polishing, metrology, and replication have led to an x-ray mirror fabrication process that is capable of producing high-resolution Wolter microscopes. We present the fabrication and test of a nickel-cobalt replicated full-shell x-ray mirror that was electroformed from a finely figured and polished mandrel. This mandrel was designed for an 8-m source-to-detector-distance microscope, with 10× magnification, and was optimized to reduce shell distortions that occur within 20mm of the shell ends. This, in combination with an improved replication tooling design and refined bath parameters informed by a detailed COMSOL Multiphysics® model, has led to reductions in replication errors in the mirrors. Mandrel surface fabrication was improved by implementing a computer-controlled polishing process that corrected the low-frequency mandrel figure error and achieved <2.0nm RMS convergence error. X-ray tests performed on a pair of mirror shells replicated from the mandrel have demonstrated <10 μm full-width at half-maximum (FWHM) spatial resolution. Here, we discuss the development process, highlight results from metrology and x-ray testing, and define a path for achieving a program goal of 5 μm FWHM resolution.

Development and theoretical analysis of novel center-inlet computer-controlled polishing process for high-efficiency polishing of optical surfaces

Although traditional computer-controlled optical surfacing (CCOS) technology has been successfully developed for polishing large aspheric optics, the polishing process continues to pose several challenges, including polishing tool wear and uneven distribution of polishing particles in contact areas. To improve the efficiency and stability of the polishing process, we present a novel center-inlet computer-controlled polishing (CCCP) process and tool for high-efficiency polishing of large-diameter aspheric optics. Compared with traditional CCOS, the most distinctive feature of CCCP is that the polishing slurry is supplied by the central hole of the polishing tool to improve its utilization efficiency. Moreover, a flexible coupling is used to connect the tool and motorized spindle to keep the tool in parallel with the work surface during the polishing process. The experimental apparatus and optimization design of the CCCP tool were first constructed based on CCOS. Then, the material removal mechanisms were explained by a series of theoretical and experimental studies. Results indicated that CCCP can improve the wear resistance of the polishing pad and make fuller and more even abrasive grain supply compared with traditional CCOS. The innovative theoretical model was verified and used for optimizing the epicyclic tool motion in CCCP. The experiments indicated that CCCP can produce a higher material removal rate and a better surface state than can CCOS.

Utilisation of time-variant influence functions in the computer controlled polishing

In the computer controlled polishing, a polishing tool moves in a well-defined manner across the workpiece surface in order to individually remove the surface error-profile. The commonly used technique to calculate the moving of the polishing tool is the dwell time method. Based on a constant (time-invariant) removal characteristic of the polishing tool (influence function) the amount of material to be removed is controlled via the dwell time. The longer the polishing tool is in contact with a particular area of the workpiece, the more material is removed at this position. Mathematical basics to calculate dwell time-profiles are shown, and a new approach considering time-variant influence functions for the computer controlled polishing is introduced. The results point out that time-variant influence functions may contribute to further decrease the process time, and thus to make a computer controlled polishing process more efficient. The reduction of the process time was observed to approximately 35% using a combination of the dwell time method with time-variant influence functions.

Correlation between influence-function quality and predictability of a computer-controlled polishing process

A mathematical method has been developed to analyze influence functions that are used in a computer-controlled polishing process. The influence function itself is usually generated by some kind of calibration where the exact procedure is dependent on the process used. The method is able to determine asymmetries in an influence function. Application of this method yields a value that may be used to judge the quality of an influence function. That quality is also an indicator of the variance of the evolving surface error profile, since a close relationship between it and the polishing process exists. On the basis of an ideal, theoretical process, a model to handle and quantify the result of a real polishing process is described. Practical application of this model demonstrates the effect of influence-function quality on the polishing result. Based on this model, the predictability of the polishing result is evaluated. This initiative to judge influence functions by their quality is an important contribution to the development of computer-controlled polishing. Due to improved process reliability, the reject rate will decrease, and the result will be more economic manufacture.

Dwell time algorithm for computer-controlled polishing of small axis-symmetrical aspherical lens mold

SAMSUNG Electronics Co.Opto-Mechatronics LabDigital Media R&D Center416 Maetan-3Dong, Paldal-GuSuwon City, Kyungki-DoKorea 442-742E-mail: hocheol@samsung.comMinyang YangKorea Advanced Institute of Science andTechnologyDepartment of Mechanical Engineering373-1 Kusong-dong, Yusong-guTaejonKorea 305-701E-mail: myyang@kaist.ac.krAbstract. We describe a dwell time algorithm for the polishing of smallaxis-symmetrical aspherical surfaces. The dwell time distribution of thescanning polishing tool on the rotating workpiece is calculated to reducethe residual surface error. The dwell time at each discrete grid is calcu-lated as an integer multiple of the workpiece rotation period, which isalso useful for the spatially varying case in the local polishing area. Aspherical polyurethane tool with abrasives is adopted for a computer-controlled polishing process. A linear algebraic equation of removaldepth, removal matrix, and dwell time is derived by convolution of theremoval depth at the dwell positions. The nonnegative least-squaresmethod gives a solution to minimize residual error. Parametric effectssuch as the dwell grid interval are simulated. Finally, an experiment fortool mark removal is performed and the dwell time algorithm is evaluatedto be valid.

Modeling the computer-controlled polishing process

Modeling the computer-controlled polishing process