Zeeko (United Kingdom)

This paper builds on previous reported work describing the marriage of robots and CNC polishing machines, both for the pre-processing of parts, and to automate operations hitherto manually conducted on the CNC platforms. This paper reviews strategies for metrology, then takes the work a stage forward by reporting the use of a robot to automate the exchange of a part between CNC machine and metrology station, the probing of the part, and the capture of interferometer data. This constitutes an important step towards realization of an automated manufacturing cell.

Shape Adaptive Grinding (SAG) is novel process for rapid finishing of ceramic freeform optics. In this paper, we report results from an investigation into the brittle-ductile transition observable on ceramic materials such as silicon carbide.

Shape Adaptive Grinding (SAG) is a novel finishing process capable of achieving optical surface finish on silicon carbide. In this paper, we report on the application of SAG to grinding of an aspheric optic.

We report on the first-ever demonstration of grinding and polishing full-size, off-axis aspheric, mirror segments as prototypes for an extremely large telescope, processed entirely in the final hexagonal shape. We first describe the overall strategy for controlling form and mid spatial frequencies, at levels in the vicinity of <10nm RMS surface. This relies first on direct CNC grinding of the base-form of these 1.4m segments, using the Cranfield BoX™ machine. The segments are then mounted on a custom designed (Optic Glyndwr Optoelectronic Engineering Group) three segment hydraulic support, and CNC polished on a Zeeko IRP 1600 machine using a variety of custom tooling. We overview the fullaperture and sub-aperture metrology techniques used to close the process-loop and certify quality, all of which operate with the segment in-situ on the IRP1600. We then focus on the pristine edge-definition achieved by the combination of tool-lift and smoothing operations; results never previously demonstrated on full-size pre-cut hexagonal segments. Finally, the paper discusses the feasibility of scaling the process to deliver 931 segments in seven years, as required for the E-ELT project.

Ultra-precision diamond turning can deliver very accurate form, often less than 100nm P-V. A possible manufacturing method for thin Wolter type-1 mirrors in hard X-ray space telescopes thus involves generating electroless nickel plated mandrels by diamond turning, before coating them with a reflective film and substrate. However, the surface texture after turning falls far short from the requirements of X-ray and EUV applications. The machining marks need to be removed, with hand polishing still widely employed. There is thus a compelling need for automated finishing of turned dies. A two step finishing method is presented that combines fluid jet and precessed bonnet polishing on a common 7-axis CNC platform. This method is capable of finishing diamond turned electroless nickel plated dies down to 0.28nm rms roughness, while deterministically improving form error down to 30nm P-V. The fluid jet polishing process, which consists of pressurizing water and abrasive particles for delivery through a nozzle, has been specially optimized with a newly designed slurry delivery unit and computer simulations, to remove diamond turning marks without introducing another waviness signature. The precessed bonnet polishing method, which consists of an inflated membrane rotated at an angle from the local normal to the surface and controlled by geometrical position relative to the work-piece, is subsequently employed with a novel control algorithm to deliver scratch-free surface roughness down to 0.28 nm rms. The combination of these two deterministic processes to finish aspheric and freeform dies promises to unlock new frontiers in X-ray and EUV optics fabrication.

Segment-edges for extremely large telescopes are critical for observations requiring high contrast and SNR, e.g. detecting exo-planets. In parallel, industrial requirements for edge-control are emerging in several applications. This paper reports on a new approach, where edges are controlled throughout polishing of the entire surface of a part, which has been pre-machined to its final external dimensions. The method deploys compliant bonnets delivering influence functions of variable diameter, complemented by small pitch tools sized to accommodate aspheric mis-fit. We describe results on witness hexagons in preparation for full size prototype segments for the European Extremely Large Telescope, and comment on wider applications of the technology.

The physical characterization of exoplanets will require to take spectra at several orbital positions. For that purpose, a direct imaging capability is necessary. Direct imaging requires an efficient stellar suppression mechanism, associated with an ultrasmooth telescope. We show that before future large space missions (interferometer, 4-8 m class coronograph, external occulter or Fresnel imager), direct imaging of giant planets and close-by super-Earth are at the cross-road of a high scientific interest and a reasonable feasibility. The scientific interest lies in the fact that super-Earths share common geophysical attributes with Earths. They already begin to be detected by radial velocity (RV) and, together with giant planets, they have a larger area than Earths, making them detectable with a 1.5-2 m class telescope in reflected light. We propose such a (space) telescope be a first step before large direct imaging missions.

This paper describes a major advance in the post-treatment of diamond-turned surfaces to remove repetitive micro-structure; a result which could have a major beneficial impact on fabrication of Walter-type X-ray mandrels, and metal mirrors. Diamond-turning is highly deterministic and versatile in producing axially-symmetric forms, and through fast-tool servos, non-axially symmetric, free-form and micro-structured surfaces. However, the fine turning marks left in the metal surface limit performance. In this paper, we describe how fluid-jet polishing under CNC control can be used to eliminate these structures, without significantly degrading the surface roughness or form produced by the prior turning operation.

Abstract We describe and summarize the optical challenges for future instrumentation for Extremely Large Telescopes (ELTs). Knowing the complex instrumental requirements is crucial for the successful design of 30–60 m aperture telescopes. After all, the success of ELTs will heavily rely on its instrumentation and this, in turn, will depend on the ability to produce large and ultra‐precise optical components like light‐weight mirrors, aspheric lenses, segmented filters, and large gratings. New materials and manufacturing processes are currently under study, both at research institutes and in industry. In the present paper, we report on its progress with particular emphasize on volume‐phase‐holographic gratings, photochromic materials, sintered silicon‐carbide mirrors, ion‐beam figuring, ultra‐precision surfaces, and free‐form optics. All are promising technologies opening new degrees of freedom to optical designers. New optronic‐mechanical systems will enable efficient use of the very large focal planes. We also provide exploratory descriptions of “old” and “new” optical technologies together with suggestions to instrument designers to overcome some of the challenges placed by ELT instrumentation. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)