Papers by Keyword: Asphere

Abstract: This paper describes the application of loose-abrasive processes to the manufacture of 1.4 meter, off-axis aspheric, hexagonal mirror-segments. These are prototypes for the 39 m European Extremely Large Telescope (E-ELT). The application of active forces to correct the overall form of segments in the telescope, means that the overall form-accuracy achieved in polishing can be less critical than for a non-active mirror. However, it is a requirement that the base-radii and conic constants of mirror-segments are very closely matched, so that the combined image is not degraded. This means that abrasive processes have to operate with respect to an absolute rather than relative datum. Furthermore, there are stringent requirements on mid-spatial frequency defects on segment surfaces, and on edge-roll. These control stray-light, and ultimately detectability of faint astronomical targets. We describe the CNC abrasive techniques we have developed in response. We then demonstrate the success of the approach, which represents the first time ever that segments have been processed entirely in the hexagonal shape:- a milestone in loose-abrasive processing. Finally, we address up-scale for the unprecedented number of segments required for the E-ELT build-phase.

Abstract: This paper introduces the affecting factors of tool clamping error of the axis direction in aspheric manufacturing process, and analyses the effects of tool clamping errors of the wheel along X and Y directions on processing area and contour error curve in depth in the aspheric manufacture parallel grinding, and calculates the relationship between tool clamping error of axis direction and aspheric shape error, and applies the theory in the machining process. The experiments show that the processing time decreases by 60% with satisfactory precision. The surface accuracy of 0.15 μm (0.237λ) of PV value and 0.023 μm (0.036λ) of RMS value can be achieved for 51.5 mm diameter aspheric surfaces. The theoretical analyses and error compensation methods are validated through the experiments, and the results show that the rapid process of aspheric surfaces can be realized.

Abstract: The grafting polymerization reaction of Hemp fibers and acrylonitrile was studied in this paper, discussed hyperchromatic solution of Hemp fibers. The morphology, structure and chemical composition of Hemp fiber after and before grafting polymerization treatment were analyzed through SEM, XRD and FTIR. Results showed that grafting percentage and dyeing percentage were all enhanced because of grafting polymerization treatment on Hemp fiber.

Abstract: Magnetorheological finishing (MRF) is a novel precision optical machining technology. Owing to its flexible finishing process, MRF can eliminate subsurface damage, smooth rms micro roughness and correct surface figure errors. The finishing process can be easily controlled by a computer. Through proper designing of numerical control, sphere and asphere optics can be machined by magnetorheological finishing with high quality. Optical sphere is machined using dwell time algorithm and surface shape 2 pt. PV has been improved from 0.17um to 0.07um.

Abstract: Recent developments in next generation disc technology, cameras in mobile phones, zoom-lenses for small digital cameras and camcorders, digital SLRs, and television cameras have amplified the demand for affordable optical systems with outstanding image quality, a combination that can only be achieved using aspheric surfaces. The metrology of aspheric surfaces is a classical problem, but solutions so far have not fulfilled all demands for system cost, TACT (Total Average Cycle Time), minimized tooling, measurement uncertainty, spatial resolution, robustness in a production environment and many more. Zygo Corp. presents here a new method [1,2] for measurement of rotationally symmetrical aspheric surfaces using a new commercial system, which has the potential to fulfill these industry requirements. During measurement, the surface is scanned along its symmetry axis in a Fizeau cavity with a spherical reference surface. The coordinates x,y,z at the (moving) zone of normal incidence are derived from simultaneous phase-measurements at the apex and zone. Phase-shifting Fizeau interferometry and displacement interferometry are combined in the new commercial system to realize this new method. Aspheric departure from a best-fitsphere approaching 800 microns can be measured, and absolute measurement is possible with an absolutely calibrated transmission sphere. A custom parabolic artifact is measured with conventional null Fizeau interferometry and by the new commercial system. Data is reported for each technique along with a difference map achieved by fiducialized data subtract where 32.0 nm peak-to-valley (PV) and 3.6 nm R.M.S. are achieved.

Abstract: ASPHERO5 is a funded German research project (project prime: Schneider OpticalMachines) with the goal of economic fabrication of high precision aspheres. The research is concentrated on the classical process chain consisting of grinding and polishing. The characterization of the incoming and outgoing surface quality is one issue to characterize the improvements. The variation of the local removal rate related to local curvature is one of the limiting factors of the polishing process. In this paper we report on first results characterizing the surface quality with a PSD (Power Spectral Density) algorithm and analyzing the local removal rates for the polishing step. In our research, two types of aspheres with 30 and 60 mm diameter were polished with a spinning tool process. The final deviation between simulation and experiment was less than 10 percent. That’s the starting point for further investigations within the project.