Fast manufacturing of E-ELT mirror segments using CNC polishing

Gray, Caroline; Baker, Ian P.; Davies, Gary; Evans, RA; Field, N. L.; Fox-Leonard, Tony; Messelink, Wilhelmus A. C. M.; Mitchell, John B.; Rees, Philippa; Waine, S.; Walker, David D.; Yu, Guoyu

doi:10.1117/12.2023475

Cited by 11 publications

(3 citation statements)

References 9 publications

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“…However, it needs a high-precision reference sphere, which is costly and complex. Comley et al [1] and Gray et al [11] reported the profile data of E-ELT segments (1.4 m size) measured with an off-machine Leitz CMM. Su and co-workers investigated a swing arm profilometer for in situ measurement of aspherics.…”

Section: Introductionmentioning

confidence: 99%

Developing on-machine 3D profile measurement for deterministic fabrication of aspheric mirrors

Dong¹,

Cheng²,

Ye³

et al. 2014

Appl. Opt.

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Three-dimensional profile measurement is perceived as an indispensable process for deterministic fabrication of aspheric mirrors. In this work, we develop on-machine 3D profile measurement on a subaperture polishing machine, namely, JR-1800. The influences of mechanical errors, misalignments, output stability, temperature variation, and natural vibration are investigated in detail by calibration, mechanical alignment, and finite-element analysis. Two quantitative methods are presented for aligning the turntable, length gauge, and workpiece into together. An error compensation model is also developed for further eliminating misalignments. For feasibility validation, two prototypical workpieces are measured by JR-1800 and an interferometer. The results indicate that JR-1800 has an RMS repeatability of ~λ/30 (λ=632.8 nm). The data provided by the two systems are highly coincident. Direct subtractions of the results from the two systems indicate that the RMS deviations for both segments are less than 0.07 μm.

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Section: Introductionmentioning

confidence: 99%

Developing on-machine 3D profile measurement for deterministic fabrication of aspheric mirrors

Dong¹,

Cheng²,

Ye³

et al. 2014

Appl. Opt.

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“…We have previously reported [4] on successful completion, at the National Facility for Ultra Precision Surfaces, of a 1.4 m Master Spherical Segment (R = 84 m), which is used as a comparator to assert segment-matching and absolute radius-ofcurvature. We have also described completion of three 1.4 m across-corners, hexagonal, off-axis aspheric mirror segments, with formal acceptance [5]. CNC grinding was performed using the BOX™machine [6] at Cranfield University.…”

Section: Introductionmentioning

confidence: 99%

Robotic automation in computer controlled polishing

Walker

Bibby

et al. 2016

J. Eur. Opt. Soc.-Rapid Publ.

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We first present a Case Study-the manufacture of 1.4 m prototype mirror-segments for the European Extremely Large Telescope, undertaken by the National Facility for Ultra Precision Surfaces, at the OpTIC facility operated by Glyndŵr University. Scale-up to serial-manufacture demands delivery of a 1.4 m off-axis aspheric hexagonal segment with surface precision < 10 nm RMS everyfour days, compared with a typical year or more for an one-off part. This requires a radically-new approach to large optics fabrication, which will inevitably propagate into wider industrial optics. We report on how these ambitious requirements have stimulated an investigation into the synergy between robots and computer numerically controlled ('CNC') polishing machines for optical fabrication. The objective was not to assess which is superior. Rather, it was to understand for the first time their complementary properties, leading us to operate them together as a unit, integrated in hardware and software. Three key areas are reported. First is the novel use of robots to automate currently-manual operations on CNC polishing machines, to improve work-throughput, mitigate risk of damage to parts, and reduce dependence on highly-skilled staff. Second is the use of robots to pre-process surfaces prior to CNC polishing, to reduce total process time. The third draws the threads together, describing our vision of the automated manufacturing cell, where the operator interacts at cell rather than machine level. This promises to deliver a step-change in end-to-end manufacturing times and costs, compared with either platform used on its own or, indeed, the state-of-the-art used elsewhere.

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“…For this reason, we report on a new approach [5]. Ultra-precision bound-abrasive CNC machining of the off-axis asphere, and then smoothing, polishing and form-correction, are all performed on the blank in its final hexagonal state.…”

Section: Introductionmentioning

confidence: 99%

Advanced Abrasive Processes for Manufacturing Prototype Mirror Segments for the World’s Largest Telescope

Walker

Davies

Fox-Leonard

et al. 2014

AMR

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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 anabsoluterather thanrelativedatum. 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.

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Fast manufacturing of E-ELT mirror segments using CNC polishing

Cited by 11 publications

References 9 publications

Developing on-machine 3D profile measurement for deterministic fabrication of aspheric mirrors

Developing on-machine 3D profile measurement for deterministic fabrication of aspheric mirrors

Robotic automation in computer controlled polishing

Advanced Abrasive Processes for Manufacturing Prototype Mirror Segments for the World’s Largest Telescope

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