Novel CNC polishing process for control of form and texture on aspheric surfaces

Walker, David D.; Beaucamp, Anthony; Brooks, D.; Freeman, R. R.; King, Andrew; McCavana, Gerry; Morton, R.; Riley, David R.; Simms, J.

doi:10.1117/12.451322

Cited by 42 publications

(16 citation statements)

References 2 publications

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“…The polishing process is being performed by the Zeeko firm (UK), using a IRP600 machine, a CNC polishing systems, controlled on 7-axis, that uses a patented process for the shells polishing, named "Bonnet polishing" [7]. The Zeeko IRP Serie machines have the capability of machining shells with diameter up to 1100 m and height up to 440 mm, as required for WFXT telescope.…”

Section: Ii-c Figuring and Polishing Resultsmentioning

confidence: 99%

Design and development by direct polishing of the WFXT thin polynomial mirror shells

Proserpio

Campana

Citterio

et al. 2017

International Conference on Space Optics — ICSO 2010

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The Wide Field X-ray Telescope (WFXT) is a medium class mission proposed to address key questions about cosmic origins and physics of the cosmos through an unprecedented survey of the sky in the soft X-ray band (0.2-6 keV) [1], [2]. In order to get the desired angular resolution of 10 arcsec (5 arcsec goal) on the entire 1 degrees Field Of View (FOV), the design of the optical system is based on nested grazing-incidence polynomial profiles mirrors, and assumes a focal plane curvature and plate scale corrections among the shells. This design guarantees an increased angular resolution also at large off-axis positions with respect to the usually adopted Wolter I configuration. In order to meet the requirements in terms of mass and effective area (less than 1200 kg, 6000 cm 2 @ 1 keV), the nested shells are thin and made of quartz glass. The telescope assembly is composed by three identical modules of 78 nested shells each, with diameter up to 1.1 m, length in the range of 200-440 mm and thickness of less than 2.2 mm. At this regard, a deterministic direct polishing method is under investigation to manufacture the WFXT thin grazing-incidence mirrors made of quartz. The direct polishing method has already been used for past missions (as Einstein, Rosat, Chandra) but based on much thicker shells (10 mm ore more). The technological challenge for WFXT is to apply the same approach but for 510 times thinner shells. The proposed approach is based on two main steps: first, quartz glass tubes available on the market are ground to conical profiles; second the pre-shaped shells are polished to the required polynomial profiles using a CNC polishing machine. In this paper, preliminary results on the direct grinding and polishing of prototypes shells made by quartz glass with low thickness, representative of the WFXT optical design, are presented.

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Section: Ii-c Figuring and Polishing Resultsmentioning

confidence: 99%

Design and development by direct polishing of the WFXT thin polynomial mirror shells

Proserpio

Campana

Citterio

et al. 2017

International Conference on Space Optics — ICSO 2010

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“…to determine the texture of a precision-ground surface using the Wyko RST500 2. to establish the viability of measuring the form of the precision-ground surface using the 1R3. 3. to scale the Zeeko polishing process from the 190mm maximum dimension used to date, to 500mm 4. to measure and extrapolate removal rates 5. to achieve a form accuracy on the order of lOOnm peak-to-valley over 95% of the surface area in both the axially-symmetric and off-axis cases 6. to establish the machine and process parameters necessary to manufacture 1-2 metre segments 2.2.…”

Section: Objectivesmentioning

confidence: 99%

Manufacture of segments for extremely large telescopes: a new perspective

Walker

Shore

2004

SPIE Proceedings

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We consider the production-route for aspheric segments for extremely large telescopes. The classical stressed-mirror polishing route followed by ion-figuring is introduced, leading to consideration of a new route combining precision aspheric grinding with computer-controlled polishing. We present estimates of process times in the polishing and grinding phases, based on scaling previous experimental results, and outline the next stage of the process development project. We are optimistic that the new route will be capable of faster processing with reduced risk, and will free the telescope and enclosure designers from the dimensional constraints imposed by segment asphericity.

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“…[1][2][3][4][5][6][7] To realize an individual, error-dependent polishing run, knowledge of the surface error profile is essential. The error profile is defined as the difference between a desired surface, for example a sphere, and the real surface of the actual work piece.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2006

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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.

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Novel CNC polishing process for control of form and texture on aspheric surfaces

Cited by 42 publications

References 2 publications

Design and development by direct polishing of the WFXT thin polynomial mirror shells

Design and development by direct polishing of the WFXT thin polynomial mirror shells

Manufacture of segments for extremely large telescopes: a new perspective

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

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