GB2295029A - Adhesive joint between optical element e.g. mirror and support - Google Patents

Adhesive joint between optical element e.g. mirror and support Download PDF

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Publication number
GB2295029A
GB2295029A GB9522774A GB9522774A GB2295029A GB 2295029 A GB2295029 A GB 2295029A GB 9522774 A GB9522774 A GB 9522774A GB 9522774 A GB9522774 A GB 9522774A GB 2295029 A GB2295029 A GB 2295029A
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GB
Grant status
Application
Patent type
Prior art keywords
mirror
support
adhesive
mechanical
volume
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB9522774A
Other versions
GB9522774D0 (en )
Inventor
Franck Normand
Pascal Saunier
Patrick Verrecchia
Vincent Vilbois
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Thales SA
Original Assignee
Thales SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date

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Classifications

    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B7/00Mountings, adjusting means, or light-tight connections, for optical elements
    • G02B7/18Mountings, adjusting means, or light-tight connections, for optical elements for prisms; for mirrors
    • G02B7/182Mountings, adjusting means, or light-tight connections, for optical elements for prisms; for mirrors for mirrors
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B7/00Mountings, adjusting means, or light-tight connections, for optical elements
    • G02B7/008Mountings, adjusting means, or light-tight connections, for optical elements with means for compensating for changes in temperature or for controlling the temperature; thermal stabilisation

Abstract

A mechanical support 2 holds a mirror 1 which is preformed on the face 9 opposite its reflecting face 8 in order to define a bonding space of determined solid volume between the support 2 and the mirror 1. The space thus formed is filled by an adhesive joint 11 whose volume expansion coefficient is determined so that the differential thermal volume variation between the solid volume and the volume of adhesive is substantially zero. Adhesive injection orifice 10i and fixation lugs 7i are shown. <IMAGE>

Description

TITLE OF THE INVENTION "A DEVICE FOR FIXING AN OPTICAL ELEMENT IN PARTICULAR A MIRROR" The invention relates to a device for fixing an optical element, in particular a mirror, on any structure.

In the field of optics, the performance of precision optics such as a lens, a dioptric element or a mirror are directly connected with the surface condition of the working surface as well as with the thermal and mechanical stresses, to which they are subjected, from the environment.

The prior art teaches solutions which solve either the problem of mechanical stresses or the problem of thermal stresses, but rarely both problems simultaneously.

In addition, by adding a third constraint, that of small bulk of the fixing device, no solution allows these three constraints to be combined efficiently in a single device.

The object of the invention is to overcome the abovementioned drawbacks.

To this end, according to this invention there is prided a device for fixing an optical element, in particular a mirror, on any structure, including, in order to retain the optical performance of the mirror in view of the thermal and mechanical stresses from the environment of the mirror, a mechanical support holding the mirror which is preformed on the face opposite its reflecting surface in order to define a bonding space of determined solid volume between the support and the mirror, the space thus formed being filled by an adhesive joint whose volume expansion coefficient is determined so that the differential thermal volume variation between the solid volume and the volume of adhesive is substantially zero.

The main advantage of the invention is that it decouples the assembly function from the optical function, by producing a mirror fixation in a small bulk, limiting both the thermal and mechanical stresses while retaining its planarity characteristics in a wide temperature range. The fixation furthermore has a stiffness which is determined so as to limit the rotations of the mirror in a severe mechanical environment (vibrations, constant accelerations, etc.).

Other advantages and characteristics of the invention will emerge more clearly on reading the following description, given with reference to the appended figures, in which: - Figures 1 to 3 respectively represent prior-art mirror fixation devices, - Figure 4 represents an embodiment of the fixation device according to the invention, - Figure 5 represents a section of the device along the section axis AA in Figure 4, and - Figure 6 represents a detail of the sectional view in Figure 5, corresponding to a lug for fixing the support of the device In these various figures, equivalent elements are designated by the same references.

The devices in Figures 1 and 2 are based on the same principle: a mirror 1 is clamped elastically at three points on its external periphery between a support 2 on which it is placed and clamps 3i, 4i by means of screws Si.

In the device in Figure 1, the clamps 3i are elastic and the mirror 1 rests on three blocks or studs forming an integral part of the support 2.

In the device in Figure 2, the three clamps 4i are rigid and an elastic wedge 6 is interposed between the mirror 1 and the support 2.

In the device in Figure 3, the mirror 1 is preformed in its base to be fixed by screws 5i to the support 2. The mirror 1 and the support 2 are made from the same material and they consequently have the same coefficient of expansion. The surface opposite the working surface of the mirror 1 is preformed in the form of thin lugs 7i used to fix the mirror 1 on the support 2 and to solve the mechanical stress problem.

These three devices do not fulfil one of the main constraints of the invention, which is for the mechanical mirror/support interface to be circumscribed by the surface of the mirror, and with a small thickness.

Furthermore, as regards the device in Figure 3, it is not always possible to make the mirror 1 from the same material as the support 2, because incompatibility problems then appear for a certain number of properties such as the grain size, stress relaxation, capacity for polishing, optical treatments, etc.

In addition, an additional drawback in the latter device is due to the bimetal effect resulting from a nonhomogeneous deformation of the two parts of the assembly.

An embodiment of a device according to the invention is illustrated in Figure 4.

The mirror 1 in Figure 4 has a working surface 8, corresponding to the reflecting face of the mirror 1, and a face 9 opposite the working face, which is preformed to have a central cylindrical foot of determined diameter circumscribed by the bulk of the mirror 1, this diameter corresponding, to within tolerances, to the internal diameter of a ring-shaped mechanical support 2 whose bulk is inscribed within the bulk of the mirror 1.

Various materials can be used to make the support 2 for fixing the mirror 1. However, since the material best suited for making the mirror 1 is glass, chosen for its capacity for polishing and its dimensional stability, a material matched to the stability of glass, that is to say with a coefficient of expansion close to that of glass, is preferred. The mirror 1 is fixed on the support 2 by bonding. The cylindrical foot allows bending via its edge, i.e. via its lateral surface. The adhesive is injected, for example, via an injection orifice 10i arranged radially in the thickness of the support ring 2.

Advantageously, bonding is produced over as large as possible a surface area, with an adhesive joint thickness that is as small as possible and matched so that the expansion difference between the mirror 1 and the support 2 is compensated for by the expansion of the adhesive. This bonding thus guarantees satisfactory stiffness of the mirror 1/support 2 assembly. A flexible adhesive is preferably used in order to limit the transmissions of either thermal or mechanical stresses between the support 2 and the mirror 1.

Figure 5 illustrates a sectional view of the device in Figure 4 along the axis AA.

In this figure, the working face 8 of the mirror 1 is identified by a light ray being reflected from it.

This sectional view demonstrates the adhesive injection lOi.

A detail of this figure, bounded by a dotted and dashed line, is illustrated in Figure 6.

This detail demonstrates a foot 7i for fixing the support 2.

In view of the small thickness of the adhesive joint 11, the stiffness of the fixation lugs 7i is matched so that the deformations (for example: those due to the planarity defect of the support 2 or of the structure) are not communicated to the bonding zone.

Because of this, the mechanical solution illustrated in Figure 6 defines a very rigid linkage in the bonding zone and a less rigid linkage with the fixation lugs 7i.

Thus, the mirror 1/support 2 assembly can be fixed directly by screwing on any structure. Angular adjustment of the mirror 1 can be obtained by retreating the mounting plane (by rectifying or lapping).

In summary, the approach to be adopted for implementing a device according to the invention is as follows: - determination of the minimum thickness of the adhesive joint 11 as a function of the viscosity of the adhesive, - determination of the maximum bonding diameter, and - choice of the glass as a function of its coefficient of expansion.

The parameters necessary for dimensioning the device according to the invention satisfy the following equations: Let V, be the solid volume defined as the space contained between the external diameter of the cylindri cal foot 9 of the mirror 1 and the internal diameter of the support ring 2. This space also corresponds to the maximum volume available for the bonding. The volume V, is expressed by the following formula: V, = hs(r22 - rl2) (1) where h corresponds to the height of the space thus defined, i.e. to the maximum thickness of the adhesive joint 11, rl to the radius of the cylindrical foot 9 of the mirror 1, and r2 to the internal radius of the support 2.

The variation in the volume V, as a function of temperature 8 is expressed by the following formula: <img class="EMIRef" id="026951127-00060001" />

On the basis of the assumption that the deformation figure of the space taken locally between the respective diameters at the cylindrical foot 9 of the mirror 1 and at the support 2 is a trapezium, this trapezium including a first base corresponding to the product of h by the coefficient al of linear expansion of the mirror 1, and a second base corresponding to the product of h by the coefficient a2 of linear expansion of the support 2, the mean thickness of the adhesive joint 11 is then defined by h (a1+a2) , and the variation in 2 solid volume V, is then expressed by the following formula: <img class="EMIRef" id="026951127-00060002" />

The variation in the adhesive volume 11 is expressed by the following formula:: AVc = sh(r2' - rl')3a3A6 (5) where 3a3 corresponds to the volume expansion coefficient of the adhesive 11.

Equating the two volumes #Vc and tV" i.e. of the formulae (4) and (5), makes it possible to determine the coefficient of linear expansion of the mirror 1, i.e. al: AVc = AV, (6) <img class="EMIRef" id="026951127-00070001" />

whence <img class="EMIRef" id="026951127-00070002" />

Thus, by way of a numerical application with R1 = 25 mm and r, = 25.1 mm, the coefficient al of the mirror 1 is equal to 5.8 10-s/R. The adhesive thickness 11 is therefore of the order of 0.1 mm. This coefficient of expansion corresponds to that of a glass frequently used for mirror production.

The invention is not limited to fixing an optical element, but may be extended, without departing from the scope of the invention, to any part that needs to have a mechanical stability close to 10'-6 metres/K.

Claims (8)

1. A device for fixing an optical element, in particular a mirror , on any structure, including in order to retain the optical performance of the mirror in view of the thermal and mechanical stresses from the environment of the mirror , a mechanical support holding the mirror which is preformed on the face opposite its reflecting face in order to define a bonding space of determined solid volume (V,) between the support and the mirror the space thus formed being filled by an adhesive joint whose volume expansion coefficient (3a3) is determined so that the differential thermal volume variation between the solid volume (V,) and the volume of adhesive is substantially zero.
2. A device according to Claim 1, wherein the thickness of the adhesive joint is minimized in order to maximize the mechanical stiffness of the support /mirror assembly while taking into account the viscosity of the adhesive
3. A device according to Claim 2, wherein the adhesive is a flexible adhesive so as to limit the thermal and/or mechanical stress transmissions.
4. A device according to any one of Claims 1 to 3, wherein in order to take into account the small thickness of the adhesive joint , the mechanical linkage of the support onto the structure has a lower stiffness than the mechanical linkage of the support with the mirror in the bonding zone.
5. A device according to any one of Claims 1 to 4, wherein the rear face of the mirror has an axisymmetric surface and in that the support matches this surface as closely as possible.
6. A device according to any one of Claims 1 to 5, wherein the mechanical linkage of the support onto the structure has at least three feet distributed equally on the external perimeter of the support
7. A device according to any one of Claims 1 to 6, wherein the bulk of the mechanical support is less than the bulk of the mirror which it holds, the support not extending beyond the reflecting surface of the mirror
8. A device for fixing an optical element, in particular a mirror, on any structure, substantially as described hereinbefore with reference to the accompanying drawings and as shown in Figures 4 to 6 of those drawings.
GB9522774A 1994-11-10 1995-11-07 Adhesive joint between optical element e.g. mirror and support Withdrawn GB2295029A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
FR9413548A FR2726915B1 (en) 1994-11-10 1994-11-10 Device for fastening an optical element including a mirror

Publications (2)

Publication Number Publication Date
GB9522774D0 true GB9522774D0 (en) 1996-01-10
GB2295029A true true GB2295029A (en) 1996-05-15

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
GB9522774A Withdrawn GB2295029A (en) 1994-11-10 1995-11-07 Adhesive joint between optical element e.g. mirror and support

Country Status (2)

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FR (1) FR2726915B1 (en)
GB (1) GB2295029A (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001022128A1 (en) * 1999-09-17 2001-03-29 Corning Incorporated Controlled stress thermal compensation for filters
EP2009474A1 (en) * 2007-06-27 2008-12-31 Samsung Electronics Co., Ltd. Optical member coupling device and optical scanning apparatus
CN103018878A (en) * 2012-12-21 2013-04-03 中国科学院长春光学精密机械与物理研究所 Reflector supporting structure with temperature compensation function

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20160041361A1 (en) * 2014-08-06 2016-02-11 Sandia Corporation Mounting apparatus

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4037944A (en) * 1976-01-23 1977-07-26 Systron Donner Corporation Low stress optical mounting structure and method
US4723833A (en) * 1984-07-23 1988-02-09 Olympus Optical Company Limited Lens mounting assembly and process
US4895430A (en) * 1988-03-14 1990-01-23 The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration Thermal compensating mount

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5084123A (en) * 1990-07-02 1992-01-28 Hughes Aircraft Company Temperature stable optical bonding method and apparatus
FR2680880B1 (en) * 1991-08-30 1993-11-19 Etudes Realisa Electroniques Device for fixing a mirror on a support structure.

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4037944A (en) * 1976-01-23 1977-07-26 Systron Donner Corporation Low stress optical mounting structure and method
US4723833A (en) * 1984-07-23 1988-02-09 Olympus Optical Company Limited Lens mounting assembly and process
US4895430A (en) * 1988-03-14 1990-01-23 The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration Thermal compensating mount

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001022128A1 (en) * 1999-09-17 2001-03-29 Corning Incorporated Controlled stress thermal compensation for filters
US6304383B1 (en) 1999-09-17 2001-10-16 Corning Incorporated Controlled stress thermal compensation for filters
EP2009474A1 (en) * 2007-06-27 2008-12-31 Samsung Electronics Co., Ltd. Optical member coupling device and optical scanning apparatus
US7719561B2 (en) 2007-06-27 2010-05-18 Samsung Electronics Co., Ltd. Optical member coupling device and optical scanning apparatus
KR101474769B1 (en) * 2007-06-27 2014-12-19 삼성전자 주식회사 Attaching device and the optical scanning device of the optical member
CN103018878A (en) * 2012-12-21 2013-04-03 中国科学院长春光学精密机械与物理研究所 Reflector supporting structure with temperature compensation function

Also Published As

Publication number Publication date Type
FR2726915B1 (en) 1996-12-06 grant
GB9522774D0 (en) 1996-01-10 application
FR2726915A1 (en) 1996-05-15 application

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