Abstract:
The invention relates to a deformable system comprising a part of a rectangular block shape, such as a beam, coupled to an actuator enabling the part to be deformed by generating curvature in the length direction, the system being characterized in that said part presents a main portion to be deformed, which main portion carries projections at its ends such that, in longitudinal section, the part presents an elongate U-shape, and in that the actuator presents levers coming to bear against said projections in order to transmit thereto a force suitable for producing deformation of the part.

Description:
FIELD AND BACKGROUND OF THE INVENTION 
   The present invention relates to a deformable system comprising a part in the form of a rectangular block coupled to an actuator enabling it to be deformed to generate curvature in the long direction of the part. 
   Mirrors are already known for use around synchrotrons in which varying curvature makes it possible to change the focus of a beam of X-rays. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a system enabling such a part to be deformed, and is based on the idea of using the part, e.g. a mirror, as a supporting structure. To this end, instead of being in the form of a rectangular parallelepiped, the part is more complex in shape since it has projections at its ends enabling deforming forces to be transmitted to the part. 
   The invention thus provides a deformable system comprising a part generally in the shape of a rectangular block, such as a beam, coupled to an actuator enabling the part to be deformed by generating curvature in its long direction, the system being characterized in that said part, in particular a mirror, presents a main portion to be deformed, the main portion carrying projections at its ends such that, in longitudinal section, the part presents an elongate U-shape, and in that the actuator presents levers each presenting at least one bearing point for acting on said projections in order to transmit a force thereto in such a manner as to deform the part. 
   The device may be characterized in that each lever presents at least one bearing point constituted by at least one rigid plane part, said plane part co-operating with at least one ball for transmitting the force that is to be applied. 
   At least one said ball may be centered by spring blades distributed around its periphery. 
   The device may be characterized in that at least one lever presents a first bearing point disposed in an outside portion of the part, advantageously in line with the central portion and preferably adjacent to the face of the main portion that is opposite from said projections, and a second bearing point spaced apart from the first bearing point towards a free end of said projection and disposed on an inside portion of said projection. 
   The first and/or second bearing point may comprise two of said rigid plane parts. In which case, the first and/or second bearing point may comprise a rocker covering said two rigid plane parts. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other characteristics and advantages of the invention appear on reading the following description given reference to the accompanying drawings, in which: 
       FIG. 1  shows the basic principle of the invention; 
       FIG. 2  is a side view of a device of the invention; 
       FIGS. 3   a  and  3   b  are views from beneath and partially in section on AA and BB showing respectively the configuration of an inside bearing point and of an outside bearing point; 
       FIGS. 4   a  and  4   b  are views on a larger scale showing the longitudinal ends of the  FIG. 2  device,  FIG. 4   c  is a view on a larger scale showing the central portion of  FIG. 2 , and  FIG. 4   d  is an end view of  FIG. 2 ; 
       FIG. 5  shows a preferred embodiment of a ball-centering device; and 
       FIGS. 6 ,  7   a ,  7   b , and  8  show various embodiments of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The part P to be deformed and shown in  FIG. 1  presents a central portion  10  in the shape of a rectangular block to be deformed extending between two main and generally plane surfaces  16  and  17  with two extensions  11  and  12  at its ends, these extensions  11  and  12  preferably extending perpendicularly to the plane of the central portion  10 . The projections  11  and  12  give the part an elongate U-shape when seen in section. These projections are relatively solid so that they deform only negligibly when a force is applied thereto in order to deform the central region  10 . 
   The part P, in particular a mirror, is preferably machined from a single block of material, e.g. of Si, SiO 2 , SiC, Zerodur (trademark in the name of Schott), ULE (trademark in the name of Corning), or any other material of glass or crystal type. 
   The part P is deformed by levers acting on the projections  11  and  12  via bearing points A 1  and B 1  for the projection  11  and bearing points A 2  and B 2  for the projection  12  ( FIG. 1 ). The bearing points A 1  and A 2  are positioned in the inside portions  11 ′ and  12 ′ of the projections  11  and  12 , preferably in the immediate vicinity of their free ends  13  and  14 . The bearing points B 1  and B 2  are disposed on the outside of the part P, advantageously in line with the central portion  10 , and preferably as close as possible to the face  15  to the part P that is opposite from the projections  11  and  12 . 
   In order to curve the main portion  10  of the part P, moment type forces are transmitted to the two ends of the part. To this end, it is appropriate to fix a lever to each end. An actuator  20  such as a hydraulic cylinder ( FIG. 2 ) presenting a cylinder  25  and a rod  26  serves to exert thrust on the levers. 
   The assembly described below allows two levers to be associated with the part P. One of the features of this configuration is that, given that the rectangular block  10  is made of a material that is generally brittle when it constitutes the mirror, it enables large forces to be transmitted thereto by achieving good control over pressures at the points where said forces are applied, and does so without requiring very high precision machining. 
   In addition, the movements induced by temperature variations can take place without slip and without any increase in force (which is important when it is not possible to grease a mechanism due to the conditions under which it works) because of the following: 
   a) the bearing points on the rectangular block are constituted by plane pallets  1  of hard metal which receive the force via balls  5  pressing against the centers of the pellets  1 , which pellets then serve to distribute the pressure delivered by the balls; and 
   b) cylindrical spring blades  7  distributed around the balls keep the balls  5  centered on the plane pellets  1  while allowing small displacements parallel to the bearing plane. 
   Mounting fixed bearing points via spring blades  7  enables them to rock while maintaining a uniform bearing force so as to transmit the pressures and forces from the actuator  20  and distribute them over the bearing zones. 
   It is preferable to use a pair of ball systems  1 ,  5  for each bearing point A 1 , A 2 , B 1 , and B 2 . This disposition is shown in the section views of  FIGS. 3   a  and  3   b.    
   In addition, for the inside bearing points A 1  and A 2  (see  FIG. 3   a ), it is advantageous to use an additional part  6  which covers the two balls  5  via housings  7  and  7 ′ and which presents a region  8  of spherical outline enabling it to rock in co-operation with a plane face  32  of the lever  30 . This additional rocking movement  6  operating like a rocker bar serves to distribute pressure uniformly between the two bearing points provided by the two balls  5 , and thus to obtain deformation that is well-distributed over the width of the main region  10  that is to be curved. It will be understood that the other bearing points B 1  and B 2  do not produce any deformation of the extensions  11  and  12 , but serve above all to act as reference points for the lever, e.g. at the ends of the region  10  (in particular level with the neutral fiber of said region), and can therefore be implemented without a rocking connection  6 . 
   Lateral movement of the part  10  relative to the levers  30  and  40  is prevented by two parts  4  extending from the lever  30  parallel to the longitudinal direction of the part P and bearing simply against the side edges of the region  10  (see  FIGS. 3   b  and  4   a ). 
   Each of the levers  30  and  40  comprises a main arm ( 31 ,  41 ) running along a plane longitudinal end of the part  4  and carrying the outside bearing points B 1  and B 2 , and a plate ( 41 ,  42 ) carrying the inside bearing points A 1  and A 2 . 
   The levers are held pressed against the part  10  firstly by the spring  2  secured to the plate  41  which holds the lever  40  pressed against the parts  1  ( FIG. 3   a ) and by the spring  3  secured to the plate  42  of the lever  40  and which holds it pressed via an end tab  45  (and/or  35 ) of the arm  41  (and/or  31 ). 
   The actuator  20  which is embedded at  21  and  22  between the two levers  30  and  40  acts to urge the two levers  30  and  40  apart, and it can be seen that the assembly is properly referenced in three dimensions. 
   In order to minimize deformation of the part P when it is desired to support the assembly constituted by the part P, the actuator  20 , and the levers  30  and  40 , an isostatic interface is used that is situated in the plane of the neutral fiber FNE of the central region  10  of the part P. 
   This is represented in the drawings by three bearing points  50 :
         two on one of the levers (e.g.  40 , see  FIG. 4   d ); and   one on the other lever (e.g.  30 , see  FIG. 4   a ).       

   The device shown in the drawings enables the assembly to be supported in a position in which the extensions  11  and  12  are directed upwards, but this is merely an example and the design is equally applicable to extensions  11  and  12  that extend downwards. 
   The contacts implemented by the bearing points (or the corresponding center bearing point which is the center of the sphere when using a spherical bead  50 ) are situated in the plane of the neutral fiber FNE of the main portion  10  of the part P, the neutral fiber FNE passing through the middle of the region  10 . 
   In the preferred situation, two balls  50  are thus placed on side arms  52  of one of the levers (e.g.  40 ,  FIG. 4   d ). A hole  51  serving to interface with the other ball  50  is formed on the other lever (e.g.  30 ,  FIG. 4   a ). 
   The positions of the centers  0  of these balls  50  along the length of the region  10  advantageously pass via a plane ZZ′ perpendicular to the long direction and passing via the points  21  and  22  where the actuator  20  bears against the levers  30  and  40 , thus making it possible to ensure that the mass of the actuator does not introduce any moment in the levers  30  and  40 , and thus does not introduce any variation in curvature. 
   In order to limit deformation due to gravity, compensation via bearing points (or retaining means depending on the orientation of the part) can be secured between the actuator  20  and the part P, and they are adjusted to minimize the sag of the part due to gravity. An example application consists in using springs to perform this function, as shown in  FIGS. 2 and 4   c  where there can be seen compensators  27 ,  28 , and  29  between the central portion  10  of the part P and the cylinder  25  or the rod  26  of the actuator  20 , together with compensation springs  27 ′,  28 ′, and  29 ′. 
   In a variant ( FIG. 6 ), the thickness of the region  10  may vary with a relationship that makes it possible, when moments are applied, to obtain a shape other than a shape having a cylindrical profile that is symmetrical about the middle of the length of the mirror: e.g. shape that is elliptical, parabolic, or polynomial in section without any axis of symmetry. 
   In another variant of the invention ( FIGS. 7   a  and  7   b ), the above effect is obtained by modifying the width of the part ( FIG. 7   a ) along its length (a curvilinear rectangular block), using a relationship of the linear type or possessing polynomial terms of higher order. Under such circumstances, symmetry is conserved for the two lateral profiles  10   1  and  10   2  relative to the length of the mirror. 
   In another variant of the invention, the above effect is obtained by changing the lengths of the levers  30  and  40  ( FIG. 8 ). 
   Any combination of these variants is also possible.