FR2832511A1 - Method of polishing optical surface for astronomical use involves attaching surface to high stability substrate prior to final machining and polishing - Google Patents

Abstract

The method of polishing an optical surface for astronomical use involves supporting the surface on a substrate of low density material with a high resistance to compression and flexing to allow the machining and polishing of the thin surface layer to produce a high precision optical surface. the substrate can be of expanded plastic cast onto the back of the surface

Description

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System and method for manufacturing light elements with a surface polishable up to high precision optical quality.

 1 a-Scope of the invention: This invention relates to the design and manufacture of light elements from a hybrid structure associating traditional hard materials in a polishable thin layer with a solid support in light and rigid composite materials. This can be applied to optical and radio components as well as to architectural or mechanical surfaces and can be suitable for both terrestrial and spatial environment.

 1 b-The state of the prior art: Optics: Solid glass or ceramic mirrors are heavy and difficult to produce.

 Traditional thermally stable materials are expensive and the production of mechanical supports eliminating their localized stress is complex. Lightening techniques, such as milling the back side of mirrors, are complex and expensive.

Radio: Today's large satellite dishes are most often made of sandwich or metal structures of the bent sheet type on a trellis sensitive to corrosion and having a strong wind resistance. The weight of the whole can reach considerable values (300t for a diameter of 32m).

 These require a high surface finish, associated with good dimensional stability.

Mechanical: The guiding surfaces of the machines are preferably made using massive pieces of machined metal which transmit vibrations and generate resonances which limit the precision of machining.

 The proposed system replaces it with Insoles or guide rules made of hard and thin material fixed on a low-mass composite beam, which also has good thermal stability and absorbs vibrations.

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Architecture: Glazed facade cladding is currently carried out using thick glass panels held above insulation by metal frames. These are heavy and dangerous in the event of a fall or fire. Their replacement by the proposed composite structure allows the creation of light glass of large dimensions as well as light and supported glazed facade elements over their entire surface thus avoiding the fall of heavy and sharp pieces. These composite materials also have good properties in terms of thermal and sound insulation.

Aerospace imagery The current mirrors are massive and lightened by machining the rear face. It is complex and expensive technology. The proposed composite mirrors would allow a significant weight gain.

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 1 c - Detailed description: This description describes the principle of the invention and its implementation and is in no way limited to the examples below.

The present invention is characterized in that a hard material, dense or not, in a thin layer, which can be brought to a surface state of high precision, is supported by a rigid substrate of low density whose high characteristics in compression allow the working of the thin surface layer as if it had the inertia corresponding to a solid part; in particular machining and polishing operations.

Examples: 1-Spherical or parabolic mirror for telescope:
The mirror consists of a thermoformed meniscus made of thin glass (a few mm) supported by a composite substrate of expanded or syntactic resin foam. Such a mirror is very light and rigid. The thin glass layer which constitutes the reflecting optical layer can be polished as if it were a solid glass mirror thanks to the rigidity and the compressive strength of the support. The resin support is cast on the back of the mirror so as to ensure a good mechanical connection and is optionally reinforced with carbon or fiberglass or kevlar elements to increase its bending rigidity for large diameters. Such a mirror does not need a suspension cell since the optical layer of glass supported over its entire surface is not subjected to mechanical stress. The fixing of the composite mirror block can be simply carried out by integrating inserts in the resin support without transmitting stress in the optical layer.

Examples: 2-Architectural panels:
These panels consist of a thin glass plate bonded to an expanded or syntactic resin plate comprising mechanical fixing inserts. This technique is also applicable to other mineral coatings of the marble or granite type in thin plates (a few mm).

 The rigidity being given by the composite support, a layer of thin glass is sufficient (only a few mm) since the coating and support functions are dissociated and provided by separate elements: glass for the coating and resin for the support.

 The resin is insensitive to moisture and fixes the glass over its entire surface.

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 2-Diagrams: 1/5-General principle 2/5-Hybrid glass or ceramic system and composite support 3/5-Integral composite system 4/5-Architectural panels 5/5-Mechanical guiding elements

Claims (6)

 3-Claims: 1-Process allowing the production of hard surfaces in thin layers characterized in that the surfaces are supported by a solid low density substrate having a high resistance to compression and to bending so as to allow machining and polishing the surface thin layer to obtain high precision optical quality required by professional astronomical or radio applications. 2-According to claim 1 process characterized in that the substrate is a rigid substrate of low density of the expanded or syntactic resin type cast or glued to the back of the surface so as to ensure good mechanical bonding. 3-A method according to claim 2 characterized in that for a large surface, the support is reinforced by carbon or fiberglass or kevlar elements to increase its flexural rigidity. 4-A method according to claims 2 and 3 characterized in that the support comprises mechanical fixing inserts 5-A method according to claim 1 characterized in that the surface produced is a very light and rigid spherical or aspherical mirror for a telescope. 6-A method according to claim 1 characterized in that the surface produced is a rigid and lightweight architectural insulating coating panel with glass surface. 7-A method according to claim 1 characterized in that the surface produced is a thin and light reflecting glass of large dimension supported by a light and rigid substrate described in claim 2.