FR2770308A1 - Monolithic isostatic mounting for fragile component - Google Patents

Abstract

The mounting (10) forms a rigid base (12) which can be fixed to a supporting structure, at least three equally-spaced filters (14) providing a rigid connection in two directions and flexibility in the four other degrees of freedom, and one or more feet (16) to receive the fragile component, set on the ends of the filters. Each filter comprises a main vane (18) at a tangent to the mounting's cylindrical surface, and two secondary vanes (20) in planes perpendicular to the main vanes.

Description

MONOLITHIC ISOSTATIC MOUNTING DEVICE
OF A FRAGILE ORGAN, SUCH AS A MIRROR.

DESCRIPTION
Technical area
The invention relates to a device designed to ensure the isostatic mounting of a fragile member, such as a mirror, on a support structure.

 The expression "isostatic mounting" means that the mounting is carried out in such a way that the fragile member undergoes practically no stress liable to cause its elastic deformation.

 Such a device can be used in the case where a fragile organ must be positioned precisely and invariantly, even when differential expansions can occur between the fragile organ and its supporting structure, in such a way that significant efforts are made. can be absorbed without introducing stresses liable to damage the fragile organ.

 The device according to the invention is particularly suitable for mounting a fragile member such as a mirror on a spacecraft (satellite, space probe, space telescope, etc.). In this application, the optical axis of the mirror as well as its focus and its focal distance must be invariable, despite the mechanical and thermal stresses undergone by the spacecraft.

State of the art
As illustrated in particular by the documents
FR-A-2 503 387, FR-A-2 534 663 and FR-A-2 724 236, the isostatic mounting of a fragile organ, such as a mirror, on a supporting structure is usually carried out by means of three separate identical devices, regularly distributed around a cylindrical surface centered on the optical axis of the mirror. Each of these devices comprises a main flexible blade, oriented tangentially to the cylindrical surface, and a deformable member connecting the flexible blade to the mirror.

Depending on the case, the deformable member is constituted by a cross-section beam in the form of an X, T, Y or V, or by an assembly of flexible strips forming between them an X or a V.

 In the mirror mounting systems thus produced, each of the three devices connecting the mirror to the support structure constitutes an independent filter element. Each of the flexible blades has a rigidity, in the circumferential and axial directions, which ensures the desired positioning of the mirror. The flexing of the flexible blades and that of the deformable member ensures the filtering function, by absorbing the major part of the deformations of the supporting structure capable of causing deformations of the fragile organ.

 Existing isostatic mounting devices generally have satisfactory filtering and stability characteristics when the fragile members that they support are of limited mass. On the other hand, the mounting of fragile members exceeding certain dimensions inevitably leads to overall filtering performance lower than that which it is desired to obtain.

 Furthermore, the accuracy of the relative positioning of the filter elements remains limited. In addition, deformations can be generated in these elements during their integration on the supporting structure.

 In a comparable manner, constraints can be introduced into the fragile member, during the integration of the parts to which this member is fixed on the filter elements.

 The stability performance of the assembly can also be reduced by micro-sliding which occurs in the connections during the various integration stages.

 Finally, the integration steps, as well as the controls associated with them, increase assembly times, risks and costs.

Statement of the invention
The subject of the invention is precisely an isostatic mounting device for a fragile member such as a mirror, the monolithic design of which enables it to eliminate the drawbacks of existing devices, and in particular to improve filtering and stability performance by compared to these.

According to the invention, this result is obtained by means of an isostatic device for mounting a fragile member, such as a mirror, on a support structure, this device being characterized in that it comprises a single piece monolithic, in which are formed
- a rigid base capable of being fixed on the
supporting structure
- at least three filter elements, one of which
first end is connected to the base
rigid, these filter elements being
regularly distributed around a surface
cylindrical, ensuring a rigid connection in
two directions, oriented parallel to a
axis of the cylindrical surface and
perpendicular to this axis, and ensuring a
flexible bond according to the other four degrees
of freedom ; and
- at least one shoe capable of receiving the organ
fragile, this pad being connected to a second
end of the filter elements.

 In a monolithic device thus produced, the rigidity of the base makes it possible to significantly reduce the deformations transmitted to the filter elements. Thus, for the same overall filtering performance, the rigidity of these elements can be increased compared to the devices of the prior art, which allows the mounting of heavier fragile members.

 Furthermore, due to the fact that the device is made in one piece, the location accuracy between the filter elements is improved. For the same reason, the drawbacks arising from the integration of the filter elements on the supporting structure (deformations, introduction of stresses in the fragile member, integration time, micro-sliding, etc.) and the integration of the parts carrying the fragile member on the filter elements (stresses, micro-slippages, integration time, etc.) are eliminated. This is also of economic interest in the production of the device (one piece) and due to the simplification of the integration phases.

 In a preferred embodiment of the invention, each filter element comprises a main blade oriented tangentially to the cylindrical surface, and two concurrent secondary blades each having a mean plane perpendicular to a mean plane of the main blade.

 In this case, the two secondary blades of each of the filter elements are arranged symmetrically with respect to a plane oriented radially relative to the cylindrical surface.

 The three filter elements are identical and the first and second ends of the filter elements are located in two planes parallel to each other and perpendicular to the axis of the cylindrical surface. This axis coincides with the optical axis of the fragile organ, when the latter is an optical organ, such as a mirror.

 Advantageously, the first end of each of the filter elements is adjacent to the main blade and the second end is adjacent to a zone of convergence of the two secondary blades.

 Depending on the case, each filter element can support an independent pad at its second end or the three filter elements can be connected to a single pad in the shape of a crown.

 In the first case, each shoe has a flat surface for bonding the fragile member. This surface can be oriented tangentially to the cylindrical surface and turned towards the axis thereof.

All the gluing surfaces of the pads can also be located in the same plane perpendicular to the axis of the cylindrical surface.

 In the second case, the single shoe in the form of a crown can have internally three flat surfaces for bonding the fragile member, located near the second ends of the filter elements, and oriented tangentially to the cylindrical surface. The single shoe in the form of a crown may also have a planar surface for bonding the fragile member, situated in a plane perpendicular to the axis of the cylindrical surface.

Brief description of the drawings
We will now describe, by way of nonlimiting examples, different embodiments of the invention, with reference to the accompanying drawings, in which
- Figure 1 is a perspective view which
represents a monolithic device of
isostatic mounting of a fragile organ, according to
a first embodiment of the invention;
- Figure 2 is a perspective view
comparable to Figure 1, which represents a
isostatic device for mounting an organ
fragile according to a second embodiment
of the invention;
- Figure 3 is a perspective view
comparable to Figures 1 and 2, which represents
an isostatic mounting device for a
fragile organ, according to a third form of
realization of the invention; and
- Figure 4 is a perspective view
comparable to Figures 1 to 3, which represents a
isostatic device for mounting an organ
fragile, according to a fourth form of
realization of the invention.

Detailed description of preferred embodiments
We will first describe, with reference to Figure 1, a first embodiment of an isostatic mounting device of a fragile member, according to the invention.

 This device is formed of a single piece 10, monolithic, made of a material chosen to meet the required requirements of stability, filtering and mechanical strength. This material can in particular be Invar (registered trademark), titanium, steel, aluminum or maraging.

 The monolithic part 10 is obtained from a machined block, for example by electroerosion. This machining process can possibly be combined with more conventional processes such as milling and turning.

 In the embodiment illustrated in FIG. 1, the monolithic part 10 constituting the isostatic mounting device according to the invention comprises a rigid base 12, three filter elements 14 and three pads 16.

 The rigid base 12 serves as an interface between the monolithic part 10 and the support structure (not shown) on which it is desired to mount the rigid member, such as a mirror (not shown). The rigid base is fixed to the support structure by any suitable means such as screws or bolts (not shown) passing through holes (not shown) formed in the base 12.

 Each of the filter elements 14 is approximately in the form of an elongated element, a first end of which is connected to the rigid base 12, constituting with the latter a single piece, as has already been observed. The relative positioning between the filter elements 14 is thus fixed by construction, and the rigidity of the base 12 makes it possible to significantly reduce the deformations applied to the first ends of the filter elements 14, connected to this base.

 More specifically, in the embodiment illustrated in Figure 1, the rigid base 12 is in the form of a relatively thick flat plate, having a top view in the form of a triangle whose angles are rounded or cut. The filter elements 14 protrude on the same face of this plate, in each of the three angles, perpendicular to the faces of the plate constituting the rigid base 12. The filter elements 14 are thus regularly distributed around a cylindrical surface centered on an axis perpendicular to the faces of the plate constituting the base 12. It should be noted that this axis coincides with the optical axis of the fragile member intended to be mounted on the device, when this member is an optical element such as a mirror.

 It will be observed that the shape of the plate constituting the rigid base 12 can be substantially different from that which has just been described, provided that a satisfactory rigid connection is made between the filter elements 14 and that the monolithic part 10 can be fixed. on the supporting structure. In particular, when the device is intended to be installed on a spacecraft, the plate forming the base 12 can be partially hollowed out, in order to reduce the overall mass of the device.

 As illustrated in FIG. 1, the three filter elements 14 are preferably completely identical to each other and their first ends, connected to the rigid base 12, are located in the same plane, perpendicular to the axis of the abovementioned cylindrical surface. In the example described, this plane coincides with the face of the base 12, on which the filter elements are installed.

 The second ends of the filter elements 14 are also located in the same plane, parallel to that which contains their first ends.

 The use of three filter elements explains the approximately triangular shape of the plate constituting the rigid base 12. Alternatively, a number of filter elements 14 greater than three may however be used. The shape of the plate constituting the base 12 is then modified accordingly.

 Each of the filter elements 14 comprises a main blade 18 and two secondary blades 20 which are concurrent.

 Each main blade 18 is rectangular, thin and planar, and its mean plane is oriented tangentially to the aforementioned cylindrical surface. One of the edges of each main blade is connected directly to the rigid base 12, so that this edge coincides with the first end of the corresponding filter element 14. The opposite edge of each of the main blades 18 is thickened, so as to support, at each of its ends, a first end of one of the two secondary blades 20 of the corresponding filter element 14. The opposite ends of the two secondary blades 20 are connected together to form a second end of the filter element 14, this second end supporting one of the pads 16 in the embodiment of FIG. 1.

 More precisely, the two secondary blades 20 of each filter element 14 are rectangular, thin and flat, and their mean plane is perpendicular to the mean plane of the main blade 18 of the corresponding filter element. Furthermore, the bisector plane of the mean planes of the two secondary blades 20 is oriented radially with respect to the above-mentioned cylindrical surface, that is to say perpendicular to the plane of the face of the rigid base 12 on which the filter elements 14 are installed. In other words, the two secondary blades 20 of the same filter element 14 are arranged symmetrically with respect to a plane passing through the axis of the cylindrical surface.

 Furthermore, the rectangular plates forming the secondary blades 20 have a relatively large length relative to their width, and this width is identical to that of the thickened edge of the main blade 18, on which the secondary blades are connected. The thickened edge of the main blade 18 thus forms, with the two secondary blades 20, a hollow triangle, approximately equilateral, of uniform thickness.

 In the embodiment shown in Figure 1, each of the filter elements 14 supports an independent pad 16 at its second end. The pads 16 constitute interface parts, designed to receive the fragile member (not shown). Generally, the fragile member is fixed to the pads 16 by gluing. To this end, each of the pads 16 has a flat surface 22 for bonding this fragile member. In the case of FIG. 1, all the bonding surfaces 22 are situated in the same plane, perpendicular to the axis of the above-mentioned cylindrical surface.

 When operational, each filter element 14 provides a rigid connection between the fragile member glued to the pads 16 and the support structure to which the base 12 is fixed, in a direction of translation oriented perpendicular to the axis of the surface. cylindrical as well as in a direction oriented parallel to this axis. On the other hand, the connection has a certain flexibility according to the other four degrees of freedom (that is to say in translation in a direction perpendicular to the two aforementioned directions and in rotation around the axes materializing these three directions) due to the flexibility main blades 18 and secondary blades 20 of the filter elements 14. By combination of these three elements 14, the holding device illustrated in FIG. 1 provides rigid isostatic support according to the six degrees of freedom. This satisfies, on the one hand, the requirements for holding and stability of the fragile organ and, on the other hand, the desire to ensure effective filtering of deformations between the support structure and the fragile organ.

 Furthermore, in accordance with the invention, the production in a single piece of the rigid base 12, of the filter elements 14 and of the pads 16 makes it possible to improve the filtering and stability performance of the device, compared with the devices of prior art. Thus, the rigidity of the base 12 makes it possible to significantly reduce the deformations transmitted to the first ends of the filter elements 14. For the same overall filtering performance, the rigidity of these elements can thus be increased, which allows mounting heavier fragile organs, compared to the devices of the prior art.

 In space applications, the orientation of the mounting device according to the invention is indifferent. In terrestrial applications, the axis of the cylindrical surface is preferably oriented vertically as illustrated in the figures. The filter elements 14 then protrude upwards on the rigid base 12, and support the pads 16 at their upper end.

 The embodiments which will now be described with reference to Figures 2, 3 and 4 differ essentially from the first embodiment illustrated in Figure 1 by the structure of the interface by which the fragile member is bonded to the device. The monolithic character of the part 10 forming the device as well as the structure of the base 12 and of the elements 14 are moreover similar to those which have been described previously with reference to FIG. 1.

 In the embodiment of FIG. 2, instead of each supporting an independent shoe, the three filter elements 14 are connected to a single shoe 16 in the form of a crown, at their second end. More specifically, the shoe 16 in the form of a crown then has a single flat surface 22 used for bonding the fragile member. This single planar surface 22 is located in a plane perpendicular to the axis of the cylindrical surface around which the filter elements 14 are distributed. Furthermore, it is located on the face of the pad 16 in the form of a crown opposite to that on which the filter elements 14 are connected.

 In the embodiment of Figure 3, there is an arrangement comparable to that of Figure 1, that is to say that each of the filter elements 14 supports a pad 16 independent at its second end. This embodiment differs from that of FIG. 1, however, by the fact that the flat surfaces 22, which are provided on each of the pads 16 to ensure bonding of the fragile member, are oriented tangentially to the cylindrical surface, and turned towards the axis of this surface, that is to say towards the interior of the device.

 Unlike the embodiments previously described with reference to Figures 1 and 2, this embodiment of Figure 3 is intended to allow the attachment of the fragile member by its periphery. This arrangement can in particular be used in the case where the fragile member can be mounted by means of a foot.

 The embodiment of FIG. 4 relates to an assembly of the fragile element by its periphery, comparable to that of FIG. 3, in the case where the three filter elements 14 are connected to a sole pad 16 in the form of a crown, as in the embodiment of Figure 2. In this case, the single shoe 16 in the form of a crown has internally three flat surfaces 22, located near the second ends of the filter elements 14. These flat surfaces 22 allow fixing, by bonding , of the fragile organ, for example by means of a foot. They are oriented tangentially to the cylindrical surface around which the filter elements 14 are distributed.

 The single pad 16 in the form of a crown can then have a substantially uniform thickness over its entire circumference, as in the embodiment of FIG. 2 or, preferably, a reduced thickness between the zones in which the recovery surfaces are formed 22 , in order to lighten the device and allow, by adapting the flexibility of the reduced area, to limit the differential expansion between the device and the fragile member, as shown in FIG. 4. This latter arrangement is particularly suitable for space applications.

Claims (12)

 1. Isostatic mounting device of a fragile member, such as a mirror, on a support structure, this device being characterized in that it comprises a single monolithic part (10), in which are formed  - a rigid base (12) capable of being fixed on the  supporting structure  - at least three filter elements (14), one of which  first end is connected to the base  rigid, the filter elements being  regularly distributed around a surface  cylindrical, ensuring a rigid connection in  two directions, oriented parallel to a  axis of the cylindrical surface and  perpendicular to this axis, and ensuring a  flexible bond according to the other four degrees  of freedom ; and  - at least one shoe (16) capable of receiving the organ  fragile, this pad being connected to a second  end of the filter elements (14).  2. Device according to claim 1, in which each filtering element (14) comprises a main blade (18) oriented tangentially to the cylindrical surface, and two concurrent secondary blades (20) each having a mean plane perpendicular to a mean plane of the main blade (18).  3. Device according to claim 2, wherein the two secondary blades (20) of each of the filter elements (14) are arranged symmetrically with respect to a plane oriented radially relative to said cylindrical surface.  4. Device according to any one of claims 2 and 3, wherein the first end of each of the filter elements (14) is adjacent to the main blade (18) and the second end is adjacent to a zone of convergence of the two blades secondary (20).  5. Device according to any one of the preceding claims, in which each filter element (14) supports an independent pad (16) at its second end.  6. Device according to claim 5, wherein each shoe (16) has a surface (22) for bonding the fragile member, oriented tangentially to said cylindrical surface and turned towards the axis thereof (Figure 3).  7. Device according to claim 5, in which each shoe (16) has a surface (22) for bonding the fragile member, the surfaces for bonding the shoes all being located in the same plane perpendicular to the axis of said surface. cylindrical (figure 1).  8. Device according to any one of claims 1 to 4, in which the three filter elements (14) are connected to a single shoe (16) in the form of a crown, at their second end.  9. Device according to claim 8, in which the single shoe (16) in the form of a crown has internally three surfaces (22) for bonding the fragile member, located near the second ends of the filter elements, oriented tangentially to said surface. cylindrical (figure 4).  10. Device according to claim 8, in which the single shoe (16) in the form of a crown has a surface (22) for bonding the fragile member, situated in a plane perpendicular to the axis of said cylindrical surface (FIG. 2 ).  11. Device according to any one of the preceding claims, in which the three filter elements are identical.  12. Device according to any one of the preceding claims, in which the first and second ends of the filter elements (14) are located in two planes parallel to each other and perpendicular to the axis of said cylindrical surface.