Abstract:
An optical-grade surfacing tool includes: a rigid holder ( 60 ); an elastically compressible interface ( 12 ) secured to the rigid holder ( 60 ); and a flexible pad ( 13 ) that can be applied against a surface to be machined ( 71 ) and secured to the interface ( 12 ) opposite the rigid holder ( 60 ). The pad ( 13 ) is carried by an elastically extensible membrane ( 14 ) including: a central plate ( 15 ); and a plurality of straps ( 18 ) each radially protruding from the periphery of the plate ( 15 ) and each having a distal portion engaged with a fastening element ( 38 ), each strap ( 18 ) rotating about the side surface ( 28 ) of the interface ( 12 ) and extending up to the fastening element, each strap ( 18 ) being taut.

Description:
FIELD OF THE INVENTION 
     The invention relates to optical grade surfacing, for surfaces such as a face of an ophthalmic lens, a camera lens, an instrument for observing distant objects or a semiconductor substrate. 
     Surfacing means any operation aiming to modify the state of a previously worked surface. It is a question in particular of polishing, grinding or fine grinding operations aiming to modify (reduce or increase) the roughness of the surface and/or to reduce undulation thereof. 
     TECHNOLOGICAL BACKGROUND 
     There is already known, in particular from French patent application 2 834 662, to which corresponds US patent application 2005/0101235, French patent application 2 857 610, to which corresponds US patent application 2006/0154581, and French patent application 2 900 356, to which corresponds international application WO 2007/128894, a tool for surfacing an optical surface, the tool including: a rigid support having a transverse end surface; an elastically compressible interface attached to the rigid support, including a central part that is in line with to said end surface of the rigid support and a peripheral part that is transversely beyond said end surface of the rigid support, having a first transverse end surface, a second transverse end surface and a lateral surface extending from the periphery of the first end surface to the periphery of the second end surface, said first end surface being pressed against and covering said end surface of the rigid support; and a flexible pad adapted to be pressed against a surface to be worked, attached to the interface on the opposite side to the rigid support, including a central part that is in line with said end surface of the rigid support and a peripheral part that is transversely beyond said end surface of the rigid support. 
     To reduce the roughness of the optical surface, the tool is brought into contact with the optical surface and a sufficient pressure of the tool is maintained on it so that, by deformation of the interface, the pad espouses the shape of the optical surface. 
     While spraying the optical surface with a fluid, it is driven in rotation relative to the tool (or vice-versa) and is swept by the tool. 
     The optical surface is generally driven in rotation, friction between it and the tool being sufficient to entrain the tool so that it rotates with it. 
     The surfacing operation necessitates an abrasive that can be contained in the pad or in the fluid. 
     During surfacing, the interface, which is elastically compressible, compensates the curvature difference between the end surface of the tool support and the optical surface. 
     The results achieved by these tools are generally satisfactory, but it is sometimes difficult to avoid certain defects of appearance, namely the orange skin effect and the sheeplike effect. 
     To remedy these appearance defects, a flexible pad having a diameter larger than that of the interface so that the pad has an annular portion projecting transversely beyond the interface has already been proposed. 
     The resulting tool achieves an improvement in surface appearance, but in some circumstances such appearance defects remain. 
     OBJECT OF THE INVENTION 
     The invention aims to provide a surfacing tool of particularly high performance in terms of minimizing appearance defects, in particular but not exclusively for surfaces to be worked that are concave. 
     To this end it proposes an optical grade surfacing tool including: a rigid support having a transverse end surface; an elastically compressible interface attached to the rigid support, including a central part that is in line with said end surface of the rigid support and a peripheral part that is transversely beyond said end surface of the rigid support, having a first transverse end surface, a second transverse end surface and a lateral surface extending from the periphery of the first end surface to the periphery of the second end surface, said first end surface being pressed against and covering said end surface of the rigid support; and a flexible pad adapted to be pressed against a surface to be worked, attached to the interface on the opposite side to the rigid support, including a central part that is in line with said end surface of the rigid support and a peripheral part that is transversely beyond said end surface of the rigid support; characterized in that said pad is carried by an elastically stretchy membrane, said membrane including:
         a central plateau having a first transverse end surface to which said pad is stuck and a second transverse end surface pressed against and covering said second transverse end surface of said interface; and   a plurality of straps each projecting radially from the periphery of said plateau and each having a distal part interengaged with an attachment means situated in line with the first end surface of the interface, each of said straps passing around said lateral surface of the interface and then extending as far as said attachment means, each strap being taut.       

     The membrane of the tool of the invention both keeps the pad taut and surrounds the periphery of the interface. 
     This enables the tool of the invention to offer particularly high performance, notably in terms of maintaining contact with the surface to be worked, including when the latter has strong variations of altitude, for example when it is one face of a spectacle lens for correcting the vision of a wearer suffering from presbyopia, myopia and astigmatism. 
     Thanks to its performance in terms of maintaining contact with the surface to be worked, the tool of the invention makes it possible to obtain a particularly high quality of surfacing, in particular but not exclusively for concave surfaces. 
     According to preferred features of implementing the membrane of the tool of the invention:
         an opening is formed in the distal part of each of said straps in order to engage that distal part over a projecting element forming said attachment means;   said opening is oblong;   said projecting element is part of said rigid support;   said projecting element is part of a flange around said rigid support;   said central plateau and said straps of said membrane are made in one piece; and/or   the second end surface of said central plateau is stuck to said second end surface of said interface.       

     According to other features preferred because of the increased performance that they provide:
         the tool further includes a deformable ring disposed between said peripheral part of the interface and said straps;   said rigid support is part of a base including a flexible collar around said support, said elastically compressible interface being pressed against and covering an end surface of said collar located on the same side as said end surface; and/or   said base includes a rigid core having a transverse end surface and a flexible backing plate pressed against and covering said end surface, said rigid support being formed by said rigid core and a central part of said backing plate located in line with said transverse end surface of the core, said collar being formed by a peripheral part of said backing plate extending transversely beyond said end surface of said rigid core.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The description of the invention continues now with the detailed description of embodiments of the invention given hereinafter by way of nonlimiting illustration and with reference to the appended drawings. In the drawings: 
         FIG. 1  is a plan view of a surfacing tool of the invention; 
         FIG. 2  is a top view of the combination of the tensioning membrane and the pad, shown flat; 
         FIG. 3  is a view in section taken along the line III-III in  FIG. 1 ; 
         FIG. 4  is a view similar to  FIG. 3 , showing how the tool is deformed in contact with a concave surface to be worked; and 
         FIG. 5  is a partial view in section showing a variant of strap attachment means. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The tool  10  shown in the drawings includes a base  11 , an elastically compressible interface  12  attached to the base  11 , a flexible pad  13  attached to the interface  12  on the opposite side to the base  11 , a membrane  14  for tensioning the pad  13  and a deformable ring  16  disposed between the peripheral part of the interface  12  and the straps  18  of the membrane  14 . 
     With the exception of the membrane  14 , the general shape of the tool  10  is that of a circular cylinder and the tool has an axis X of symmetry that defines a longitudinal direction. 
     The base  11  includes a rigid core  20  and a flexible backing plate  21 . On the side seen at the bottom in  FIG. 3 , the base  11  has a transverse end surface  25 . 
     In the absence of stress, i.e. in a position that is not represented because the tensioning membrane  14  acts on the backing plate  21  including in the rest position shown in  FIGS. 1 and 3 , the end surface  25  is plane. 
     The interface  12  has a first end surface  26 , a second end surface  27  and a lateral surface  28  extending from the periphery of the surface  26  to the periphery of the surface  27 . 
     In the absence of stress, i.e. in a position that is not shown, as explained above, the interface  12  has the general shape of a disk. 
     By the surface  26 , the interface  12  is pressed against and covers the surface  25  of the base  11 . 
     The attachment of the base  11  and the interface  12  to each other is effected here by sticking them together over the whole of the surfaces  25  and  26 . 
     The base  11  includes a cavity  30  opening onto the opposite side to the end surface  25  and extending in the longitudinal direction partway through the thickness of the base  11 . 
     The cavity  30  is disposed centrally and is adapted for mounting the tool  10  on the head of the spindle of a surfacing machine. 
     The cavity  30  has a part-spherical portion  31  with the overall shape of three quarters of a sphere and a cylindrical portion  32  extending between the portion  31  and the opening of the cavity  30 . 
     The spindle head adapted to be received into the cavity  30  includes a part-spherical end conformed like the portion  31  and a cylindrical portion of smaller diameter than the portion  32 . 
     The base  11  and the spindle of the machine simply clip together, the material around the cylindrical portion  31  being deformable so that the spherical part of the head of the spindle can be housed in the portion  32 . 
     When the spindle head is engaged in the cavity  30 , the tool  10  cooperates with the spindle in the manner of a ball joint. 
     The cavity  30  is produced in the rigid core  20 , which is described in more detail next. 
     The core  20  includes a body  35  and a head  36 . 
     The body  35  includes an annular flange  37  and a threaded stud  38  projecting from the flange  37  on the side seen at the top in  FIG. 2 , the stud  38  being at the center of the flange  37 . 
     The cavity  30  is produced in the stud  38 . 
     The end surface  40  of the body  35  that is seen at the bottom in  FIG. 3  is flat and continuous, the respective end surfaces of the flange  37  and the stud  38  being flush with each other. 
     Here the flange  37  is in practice of metal, for example steel, and the stud  38  is in practice of relatively rigid plastic material molded onto the flange  37 . The stiffness of the stud  38  is chosen so that it cannot be deformed at the level of the surface  40  but can be deformed at the level of the cylindrical portion  32  to enable clipping of the spindle head into the cavity  30 . 
     On its external lateral surface projecting from the flange  37 , the stud  38  has a thread enabling it to cooperate with the threaded bore at the center of the head  36 , which cooperates with the body  35  in the manner of a nut. 
     Here the head  36  has in practice a generally annular shape with the same outside diameter as the flange  37  and with two lateral cutaway portions  41  to expose two parallel flat faces  42  parallel to the axial or longitudinal direction X in order to enable the head  36  to be tightened and loosened relative to the flange  37  using a conventional wrench designed for turning nuts. 
     Here the backing plate  21  is formed by a flexible disk  51 . 
     In the absence of stress the disk  51  is generally circular with a diameter similar to that of the interface  12 . 
     The disk  51  is concentric with the remainder of the tool, and in particular concentric with the interface  12  and the core  20 . 
     Here the disk  51  has a thickness similar to that of the membrane  14 . 
     The disk  51  is attached to the core  20  by sticking its transverse end surface, seen at the top in  FIG. 3 , to the whole of the surface  40 . 
     The transverse end surface of the disk  51  seen at the bottom in  FIG. 3  forms the transverse end surface  25  of the base  11 . 
     Given the stiffness of the end surface  40  of the core  20  and the incompressibility of the disk  51  in the axial or longitudinal direction X, or in any event its very low compressibility compared to the compressibility of the interface  12 , the central portion  51   a  of the disk  51  located in line with the end surface  40  can be considered rigid because it cannot bend like the peripheral portion  51   b  which is transversely beyond the surface  40 . 
     Thus the base  11  includes:
         a rigid support  60  formed by the core  20  and the central part  51   a  of the disk  51 , this rigid support having a transverse end surface corresponding to the central part  25   a  of the surface  25  situated in line with the end surface  40 ; and   a flexible collar  61  formed by the peripheral part  51   b  of the disk  51 , this collar surrounding the rigid support  60 , the elastically compressible interface  12  being pressed against and covering the end surface  25   b  of the collar  61  and the end surface  25   a  of the rigid support  60 .       

     It will be noted that the elastically compressible interface  12  includes a central part  12   a  that is in line with the transverse end surface  40  or  25   a  and a peripheral part  12   b  that is transversely beyond the transverse end surface  40  or  25   a.    
     In the absence of stress, the pad  13  has the general shape of a disk of slightly greater diameter than the interface  12 . The thickness of the pad  13  is significantly less than the thickness of the interface  12 . 
     The membrane  14  is produced in an elastically stretchy material significantly thinner than the interface  12 . 
     As seen more particularly in  FIG. 2 , the membrane  14  includes a central plateau  15  and a plurality of identical straps  18 , here six straps, projecting radially from the periphery of the plateau  15 . 
     In  FIG. 1 , the membrane  14  is shown in bold line as when placed on the rest of the tool  10 , while one of the straps  18  is shown in chain-dotted line as when flat. In  FIG. 2 , the pad  13  and the membrane  14  are shown as when flat. 
     In the absence of stress, the plateau  15  has the general shape of a disk of similar diameter to the interface  12 . 
     The central plateau  15  has, on the side seen at the bottom in  FIG. 3  (this side is not visible in  FIG. 2 ), a transverse end surface  22  and, on the side that is seen at the top in  FIG. 3  (this side is visible in  FIG. 2 ), a transverse end surface  23 . 
     Here the pad  13  is pressed against and covers the end surface  22  and is stuck to the membrane  14  over the whole of the surface  22 . 
     On the side opposite the pad  13 , the plateau  15  is pressed against and covers the end surface  27  of the interface  12 . Here the plateau  15  is attached to the interface  12  by sticking its end surface  23  to the whole of the end surface  27  of the interface  12 . 
     Each of the straps  18  has a distal part in which an opening  19  is formed, here an oblong opening. 
     Alternatively, the openings  19  are conformed differently, for example being circular. 
     Here the straps  18  have the shape of a band the width of which is greater at the central plateau  15  end than at the distal portion end, the width decreasing regularly over the length of the straps. 
     Here the central plateau  15  and the straps  18  are made in one piece from a disk of material from which the initial gaps between the straps have been cut out. 
     In the tool  10 , each of the straps  18  turns around the lateral surface  28  of the interface  12  and around the deformable ring  16  and then extends as far as the pin  38  that is engaged in the opening  19 , the pin  38  thus forming means for attaching the distal part of each strap  18  in line with the end surface  26  of the interface  12 . 
     The respective distal parts of the straps  18  are stacked and gripped between the body  35  and the head  36  of the core  20 . 
     When it is interengaged in this way with the pin  38 , each of the straps  18  is taut, its arrangement being determined accordingly, in particular the location of the opening  19 . 
     Fitting the straps  18  to the pin  38  thus tensions the central plateau  15  of the membrane  14  and thus tensions the pad  13  that is stuck to the plateau  15 . 
     This tensioning enables the pad  13  to work under improved conditions and in particular eliminates or greatly reduces the risk of creases appearing on the pad  13  during surfacing. 
     Thanks to the plateau  15  of the membrane  14 , the pad  13  also benefits from increased strength, which makes it possible to use an especially thin pad  13 . 
     The arrangement of the straps  18  is such here that, because of the effect of the tensioning produced by the straps  18 , the interface  12  adopts a conformation in which its peripheral part  12   b  is raised so that the surface  70  of the pad  13  intended to come into contact with the surface to be worked is slightly convex. 
     It will be noted that tensioning the pad  13  by means of the membrane  14  has the benefit of making possible easy adjustment of the tension, simply by varying the location of the opening  19  in the straps  18 , thus offering excellent repeatability from one tool to another. 
     It will also be noted that it is possible to provide a plurality of orifices like the orifice  19  on the straps  18  in order, with the same membrane such as the membrane  14 , to offer a plurality of tensions in the pad such as the pad  13 . 
     It will further be noted that surrounding the lateral surface  28  of the interface  12  with the straps  18  provides a belting effect that is favorable to the behavior of the tool  10  during deformations, in particular because it opposes shearing of the interface  12  at its periphery. 
     When the tool  10  is pressed against a concave surface to be worked, such as the surface  71  shown in  FIG. 4 , the elastically compressible interface  12  is deformed to allow the surface  70  to espouse the surface  71 . 
     It is seen that the interface  12  is strongly compressed in the central part  12   a.    
     To effect surfacing, the lens  72  of which the surface  71  is part is mounted on a rotary support (not shown) and the tool  10  is pressed against the surface  71  with sufficient force for the pad  13  to espouse its shape. 
     Here the tool  10  is free to rotate while however being off-center relative to the optical surface  71 . 
     The friction between the surface  71  to be worked and the pad  13  is sufficient to entrain the tool  10  in rotation about the axis X of symmetry and in the same direction as the lens  72 . 
     The optical surface  71  is sprayed with a spray fluid that is either non-abrasive or abrasive according to whether the pad  13  exercises this function itself or not. 
     In order to sweep the whole of the optical surface  71 , the tool  10  is moved during surfacing along a radial trajectory, the point of intersection of the axis X of the tool  10  with the optical surface  71  effecting a to-and-fro movement between two return points. 
     During surfacing, the fact that the membrane  14  offers both tensioning of the pad  13  and belting of the periphery of the interface  12  means that the tool offers particularly good performance in terms of remaining in contact with the surface  71  to be worked, including when the latter surface features large variations in altitude, for example if it is one face of an eyeglass lens for correcting the vision of a wearer suffering from presbyopia, myopia and astigmatism. 
     The beneficial effect of belting the peripheral portion of the interface  12  by means of the straps  18 , notably in respect of the uniformity of the pressure exerted on the surface to be worked such as the surface  71 , is reinforced by the presence of the deformable ring  16 , which itself, because it is continuous, also achieves some uniformization of the forces. 
     It will be noted that the presence of the collar  61  is also favorable to uniform distribution of the pressure exerted on the surface to be worked. 
       FIG. 5  shows a variant of the tool  10  in which the attachment means providing a grip on the distal parts of the straps  18  are not formed by the pin  38  of the core  20  but by studs projecting from the collar  61 . 
     In this variant, the disk  51  is replaced by a disk  51 ′ having in an intermediate position between the core  20  and the ring  16  a domed head stud  55  projecting from the side that is seen on the top in  FIG. 3 , i.e. the side opposite the interface  12 . 
     In this variant, the straps  18  are shorter so that they can produce the required tension by engagement of their opening  19  over the corresponding stud  55 . 
     Here the disk  51 ′ and the stud  55  are molded in one piece, but it is of course possible to attach the stud  55  or the like by gluing or by any other fixing means. 
     In variants that are not shown, the attachment means of the straps such as the straps  18 , while remaining in line with the end surface  26  of the interface  12 , are different from the pin  38  and the studs  55 , for example, for some straps at least, a portion of the spindle on which the tool is mounted; studs similar to the studs  55  arranged at the periphery of a core such as the core  20  or a rigid support such as the support  60 ; or attachment means that are not part of a core or rigid support, for example hooks at locations similar to those of the studs  55 . 
     In the tool  10 , the attachment between the assembly formed by the pad  13  and the membrane  14  and the rest of the tool involves sticking the central plateau  15  to the interface  12 . This prevents the plateau  15  slipping relative to the interface  12 . 
     Alternatively, in configurations in which the risk of slipping is low, the attachment between the assembly formed by the pad such as the pad  13  and the membrane such as the membrane  14  is effected only by the straps such as the strap  18 . 
     In some circumstances it is also possible to effect the attachment of the core such as the core  20  or the rigid support such as the support  60  to the rest of the tool only by the straps such as the strap  18 . 
     In the tool  10  shown, the diameter of the pad  13  is stuck than the diameter of the plateau  15 . Alternatively, the diameter of the pad  13  is different, for example identical to or even slightly less than the diameter of the plateau  15 . 
     In the tool  10  shown, the pad  13  is stuck directly to the plateau  15 . Alternatively, an intermediate disk is disposed between the pad  13  and the plateau  15 . 
     In a variant of the tool  10  that is not shown, adapted to work a surface of more pronounced concavity than the surface  71 , the end surface like the end surface  40  or  25   a  is not flat but instead convex and/or the interface like the interface  12  has an initial conformation curved in corresponding fashion and is of uniform thickness. 
     In other variants that are not shown, the disk  51  has a thickness significantly different from that of the membrane  14 ; a supplementary disk, of smaller diameter than the disk  51  and of greater diameter than the flange  37 , is disposed between the flange  37  and the disk  51 ; the rigid support  60  and the collar  61  are replaced by a rigid support and a collar arranged differently, for example as described in French patent application 2 900 356, to which international application WO 2007/128894 corresponds, or there is no such collar. 
     Numerous other variants are possible as a function of circumstances and in this respect it is pointed out that the invention is not limited to the examples described and shown.