Abstract:
An optical-grade surfacing tool ( 101 ) is provided with a resilient return element ( 115 ) including a plurality of resiliently flexible strips ( 118 ) that transversely project from a rigid central mounting ( 104 ), each strip ( 118 ) having a distal portion ( 144 ) that engages by bearing directly upon a petal ( 134 ) of a flexible flange ( 131 ) that surrounds the rigid mounting ( 104 ). The distal portion is curved along a round loop such that the end ( 145 ) of each the strip ( 118 ) is rotated toward the rigid mounting ( 104 ).

Description:
FIELD OF THE INVENTION 
     The invention relates to optical quality surfacing, for surfaces such as a face of an ophthalmic lens or lens of a camera or instrument adapted for the observation of remote objects or such as a face of a semiconductor substrate. 
     By surfacing is meant any step aiming to modify the state of a surface that has already been formed. It refers in particular to steps of polishing, grinding, or frosting aiming to modify (reduce or increase) the roughness of the surface and/or to reduce the unevenness thereof. 
     TECHNOLOGICAL BACKGROUND 
     Already known, in particular from French patent application 2 834 662 to which corresponds the U.S. patent application 2005/0101235, from French patent application 2 857 610 to which corresponds to the U.S. patent application 2006/0154581 and from French patent application 2 900 356 to which corresponds the U.S. patent 2008/0171502, is a tool for surfacing an optical surface, comprising: a rigid support having a transverse end surface; an elastically compressible interface connected to the rigid support, comprising a part referred to as central which is located in line with said end surface of the rigid support and a part referred to as peripheral which is located transversely beyond said end surface of the rigid support; a flexible buffer adapted to be applied against a surface to work, connected to the interface on the opposite side to the rigid support, comprising a part referred to as central which is located in line with said end surface of the rigid support and a part referred to as peripheral which is located transversely beyond said end surface of the rigid support; as well as elastic return means disposed between said rigid support and the peripheral part of said interface, the combination of said peripheral part of the buffer, of said peripheral part of the interface and of the elastic return means forming a means for stabilizing the tool during the surfacing, said tool being adapted to perform surfacing for the most part at the central part of the buffer. 
     To reduce the roughness of the optical surface, the tool is brought into contact therewith by maintaining a sufficient tool pressure thereon for the buffer to conform to the optical surface, by deformation of the interface. 
     While irrigating the optical surface with a fluid, it is rotationally driven relative to the tool or (vice-versa) and is swept using that tool. 
     Generally, the optical surface is rotationally driven, its rubbing against the tool being sufficient to rotationally drive the tool conjointly. 
     The surfacing step requires an abrasive which may be contained in the buffer or in the fluid. 
     During the surfacing, the elastically compressible interface makes it possible to compensate for the difference in curvature between the end surface of the support for the tool and the optical surface. 
     An example embodiment of the tool proposed by French patent application 2 834 662, to which corresponds U.S. patent application 2005/0101235, is described below with reference to  FIGS. 1 to 3  of the accompanying drawings, in which
           FIG. 1  is an exploded perspective view of that tool and an ophthalmic lens having an optical surface to be surfaced;     FIG. 2  is a cross-section view of that tool when assembled, during the surfacing of the optical surface of the lens of  FIG. 1 ; and     FIG. 3  is a diagrammatic view from above representing that ophthalmic lens during surfacing using that tool, which tool is represented during the sweeping of the optical surface in two positions one of which is illustrated in dashed line.       

     In  FIG. 1  there is represented a tool  1  for the surfacing of an optical surface  2 , in this case one of the faces of an ophthalmic lens  3 . In  FIG. 1 , as in  FIG. 2 , the optical surface  2  concerned is represented as being concave, but it could equally well be convex. 
     The tool  1  is formed by the stacking of at least three parts, i.e. a rigid part  4 , an elastically compressible part  5 , and a flexible part  6 , which, in what is to follow, will respectively be called support, interface and buffer. 
     As can be seen in particular in  FIG. 1 , the support  4  comprises two jaws, i.e. a lower jaw  7  and an upper jaw  8  which are adapted to be superposed while fitting into each other via a pin  9  projecting from one face  10  of the faces of the upper jaw  8  and adapted to be received in a complementary hole  11  formed, facing it, in a face  12  of the lower jaw  7 . 
     As may be seen in  FIG. 1 , the support  4  is of cylindrical general shape with rotational symmetry and has an axis of symmetry denoted X, which defines direction referred to as longitudinal. 
     The normal to the optical surface  2  at the point of intersection of the axis of symmetry X of the tool  1  with the latter is denoted n. 
     The lower jaw  7  has, remote from its face  12  in which the hole  11  is made, a substantially transversely extending end surface  13 , against which is applied the interface  5 , covering it. 
     The buffer  6  is applied against the interface  5  from the other side thereof relative to the support  4 . 
     To be more precise, the buffer  6  at least in part covers the interface  5  on the opposite side to and in line with the end surface  13 . 
     The rubbing of the buffer  6  against the optical surface  2  will, by means of an abrasive contained in the irrigating fluid or incorporated in the buffer  6  itself, provide superficial removal of material from the optical surface  2  for modification of the surface state, as will be seen below. 
     The buffer comprises a central part  6   a  which is located in line with the end surface  13 , and comprises a peripheral part  14  which is located transversely beyond the end surface  13 . 
     This peripheral part  14  is connected to the support  4  via elastic return means  15 . 
     The peripheral part  14  extends in continuity with the central part  6   a  while being, at rest, substantially coplanar therewith. 
     In the example illustrated in  FIGS. 1 and 2 , the buffer  6  is in one piece, the peripheral part  14  being connected to the central part  6   a  such that they in fact form a single component. 
     In an embodiment represented in thick line in  FIG. 1 , the buffer  6  has the form of a flower, and thus comprises a plurality of petals  14   b  which, projecting transversely from the central part  6   a , form the peripheral part  14  of the buffer  6  and which each extends transversely beyond the end surface  13 . 
     In a variant represented in chain line in  FIG. 1 , the peripheral part  14  takes the form of a crown  14   a  which surrounds the central part  6   a    
     In this case, in the absence of stress, and when it is in one piece, the buffer  6  takes the form of a disk of material of small thickness compared with its diameter, as represented in  FIG. 1 , the peripheral part  14 ,  14   a  thereby forming a collar with respect to the end surface  13 . 
     The return means  15 , which will be described later, may be directly interposed between the support  4  and the peripheral part  14  of the buffer  6 , that is to say, in practice, the collar  14   a  or the petals  14   b    
     The interface  5  comprises not only a central part  5   a  which is located in line with the end surface  13 , but also a peripheral part  16  which is located transversely beyond the end surface  13 . 
     This peripheral part  16  follows on from the central part  5   a , and, for example, in the absence of stress, takes the form of a crown which surrounds the central part  5   a , and which is in fact interposed between the peripheral part  14  of the buffer  6  and the return means  15 . 
     As can be seen in  FIGS. 1 and 2 , the interface  5  is in one piece, its central part  5   a  and peripheral part  16  in fact being connected to form together a single component, the peripheral part  16  forming a collar with respect to the end surface  13 . 
     Thus, in the absence of stress, the one-piece interface  5  takes for example the form of a disk of material of small thickness compared with its transverse dimension (that is to say its diameter). 
     When the interface  5  and the buffer  6  are both one-piece components, they have comparable transverse dimensions. In particular, when they each take the form of a disk of material, for convenience of manufacture they will preferably be chosen of the same diameter. However, it is equally possible to use a buffer having a diameter different from that of the interface, in particular a greater diameter in order to attenuate the edge effects of the tool on the worked surface. 
     Moreover, for reasons which will become apparent hereinafter, a deformable ring  17  is provided interposed between the peripheral part  16  of the interface  5  and the return means  15 . 
     In practice, that ring  17  is fastened to the peripheral part  16  on the other side thereof to the buffer  6 , i.e. on the same side as the support  4 , so that the latter is surrounded by the ring  17 . 
     The ring  17  is preferably of circular longitudinal section, but could equally be of a section of more complex shape, in particular oblong, polygonal, rectangular or square. Moreover, it is placed on the peripheral part  16  concentrically with the support  4 . 
     The return means  15  are described next. 
     They comprise at least one elastically flexible strip  18  which projects transversely from the support  4 , is connected rigidly to the support  4  at a first end  18   a , and is connected to the peripheral part  14  of the buffer  6  by a second end  18   b , referred to as free end, which is an opposite end to the first end  18   a.    
     In this way, under the effect of a force exerted longitudinally on the peripheral part  14  opposite that strip  18 , the latter deforms while exerting on the peripheral part  14  an opposite reaction to said force. 
     In practice, the return means  15  comprise a plurality of such strips  18 , distributed uniformly around the periphery of the support  4 , to act on the whole of the peripheral part  14  of the buffer  6 . 
     The return means  15  in fact take the form of a star-shaped part  19  rigidly fastened to the support  4 . 
     This star-shaped component  19  has a central part  20  from which project a plurality of branches  18  each forming an elastically flexible strip extending radially in a transverse plane. 
     To fasten the star-shaped component  19  to the support  4 , its central part  20  is, in practice, clamped between the jaws  7 ,  8  of the support  4 , its centering being provided by means of a hole  21  through its center through which the pin  9  on the top jaw  8  passes, the assembly being held by fastening means such as screws which, passing through the top jaw  8  and the central part  20  of the star-shaped component  19 , engage in the lower jaw  7 . 
     When, in a previously described embodiment, the one-piece buffer  6  comprises a plurality of petals  14   b , the same number of branches  18  are provided on the star-shaped component  19  as there are petals  14   b , the star-shaped component  19  being oriented so that each branch  18  is in line with a petal  14   b . Accordingly, if the buffer  6  comprises seven petals  14   b , the star-shaped component  19  comprises seven branches  18 , each able to provide the elastic return for one petal  14   b.    
     The ring  17  is fastened to the interface  5 , it being possible for this fastening to be provided by any means, bonding being however preferred, in particular on account of its simplicity. 
     In the embodiment represented, the diameters of the interface  5 , of the buffer  6  and of the star-shaped component  19  are at least twice that of the diameter of the support  4 . 
     Moreover, in the case of surfacing an ophthalmic lens, the diameters of the interface  5  and the buffer  6  are chosen to be substantially equal to the diameter of the lens  3 , so that the diameter of the support  4  is considerably less than the diameter of the lens  3 . 
     The use of the tool  1  is illustrated in  FIGS. 2 and 3 . 
     In this case this is for surfacing or grinding an aspheric convex face  2  of an ophthalmic lens. 
     The lens  3  is mounted on a rotary support (not shown) by means of which it is rotationally driven about a fixed axis Y. 
     The tool  1  is applied against the face  2  with a sufficient force for the buffer  6  to conform to its shape. Here the tool  1  is free to rotate while nevertheless being off-center compared to the optical surface  2 . Forced rotational driving of the tool, by means provided for that purpose, may however be provided. 
     The relative rubbing between the optical surface  2  and the buffer  6  is sufficient to rotationally drive the tool  1  in the same direction as that of the lens  3 , about an axis substantially coincident with the axis X of symmetry of the support  4 . 
     The optical surface  2  is irrigated with an irrigation fluid which is abrasive or non-abrasive depending upon whether or not the buffer itself has that function. 
     To sweep the whole of the optical surface  2 , the tool  1  is moved during surfacing along a radial trajectory, the point of intersection of the rotational axis X of the tool  1  with the optical surface  2  moving to and fro between two turn-back points, namely an outer turn-back point A and an inner turn-back point B, both these points being at a distance from the rotational axis Y of the lens  3 . 
     Thanks to the compressibility of the central part  5   a  of the interface  5 , the central part  6   a  of the buffer  6  deforms to conform to the shape of the optical surface  2 . 
     Thanks to deformation of the flexible strips  18 , the peripheral part  14  of the buffer  6  deforms to conform to the shape of the optical surface  2 . 
     Given the rigidity of the support  4 , material is mostly removed in line with the end surface  13 , i.e. material is essentially removed by the central part  6   a  of the buffer  6 . 
     The peripheral parts  14  of the buffer  6  and  16  of the interface  5  have an essentially stabilizing role, thanks to the increased lift or seating of the tool  1  relative to a conventional tool whose buffer and interface would be limited to the central parts  5   a ,  6   a , and also thanks to the return means  15 , which maintain permanent contact between the peripheral part  14  of the buffer  6  and the optical surface  2 . 
     The deformable ring  17  enables smoothing of the stress distribution exerted on the peripheral rim of the interface  5  and thus on the buffer  6  by the strips  18 . 
     It follows that, regardless of the location of the tool  1  on the optical surface  2 , and regardless of its rotational speed, its rotational axis X is always colinear or substantially colinear with the normal  n  to the optical surface  2 , so that the orientation of the tool  1  is optimized at all times. 
     In the embodiment illustrated in  FIGS. 1 and 2 , the end surface  13  of the support  4  is plane. 
     The tool is thus adapted for surfacing a certain range of optical surfaces  2  with different curvatures. 
     To modify the adaptability of the tool  1 , it is possible to bias the return means  15  by twisting the flexible strips  18  so that they are already flexed at rest, in one direction or the other. 
     If at rest the strips  18  are straight or flexed away from the end surface  13 , the tool  1  is intended for concave optical surfaces  2 , whereas if at rest the strips  18  are bent toward the end surface  13 , the tool  1  is intended for convex optical surfaces  2 . 
     In a first variant which is not illustrated, the end surface  13  of the support  4  is convex, the tool  1  thus being intended for optical surfaces  2  having a more pronounced concavity. 
     In a second variant which is not illustrated, the end surface  13  of the support  4  is on the contrary concave, the tool  1  thus being intended for optical surfaces  2  having a more pronounced convexity. 
     Of course, it is possible to combine the concave or convex embodiment of the end surface  13  with biasing of the return means  15 , as described above. 
     French patent application 2 857 610, to which corresponds U.S. patent application 2006/0154581, proposes that the elastic retain means, rather than being in the form of a star-shaped component such as component  19  illustrated in  FIGS. 1 and 2 , should have a continuous peripheral part bearingly cooperating with the peripheral part of the buffer such as buffer  6 , directly or via only the interface such as interface  5  (no deformable ring such as  17  being provided), the elastic return means comprising, in addition to the continuous peripheral part, a flat or curved collar rigidly fastened, inside, to the support such as support  4 , that collar being formed by a pierced or unpierced wall. 
     The continuous character of the peripheral part of this return means makes it possible to increase the evenness of the surfacing performed by the tool. 
     French patent application 900 356, to which corresponds U.S. patent application 2008/0171502, proposes that the rigid support should belong to a base comprising a flexible collar surrounding the rigid support with the elastically compressible interface covering an end surface of the collar situated on the same side as the end surface of the rigid support. 
     By virtue of the collar, the contact area between the interface and the rest of the tool is particularly large, which ensures a uniform distribution of the pressure applied on the surface to work and thereby makes it possible to perform surfacing steps giving a high quality finish. 
     SUBJECT OF THE INVENTION 
     The invention aims to provide a surfacing tool providing particularly good performance with regard to minimizing defects of finish. 
     To that end the invention provides an optical quality surfacing tool, comprising: a base comprising a flexible collar and a rigid support surrounded by said collar, which collar is subdivided into petals, said rigid support having a transverse end surface; an elastically compressible interface connected to the base, comprising a part referred to as central which is located in line with said end surface of the rigid support and a part referred to as peripheral which is located transversely beyond said end surface of the rigid support, said elastically compressible interface being applied against and covering an end surface of said collar situated on the same side as the end surface of the rigid support; a flexible buffer adapted to be applied against a surface to work, connected to the interface on the opposite side to the rigid support, comprising a part referred to as central which is located in line with said end surface of the rigid support and a part referred to as peripheral which is located transversely beyond said end surface of the rigid support; as well as elastic return means disposed between said rigid support and the peripheral part of said interface, the combination of said peripheral part of the buffer, of said peripheral part of the interface and of the elastic return means forming a means for stabilizing the tool during the surfacing, said tool being adapted to perform surfacing for the most part at the central part of the buffer, characterized in that said elastic return means comprise a plurality of elastically flexible strips which project transversely from the rigid support, each strip having a distal portion in direct bearing cooperation with a said petal; said distal portion being curved in a rounded curl such that the end of each said strip is turned towards said rigid support. 
     The strips and the petals thus cooperate so as to exert a force on the interface which is particularly favorable both with regard to the general form of the tool and with regard to its capacity to deform to follow the variations in altitude of the surface to work, including when it has great variations in altitude as is the case for one of the faces of a spectacles lens provided to correct the version of a presbyopic, myopic and astigmatic wearer. 
     In particular, the form of the distal portions of the strips provides flexible, progressive and continuous give (damping) with regard to the deformations. 
     According to preferred features, each elastic strip is an individual strip mounted onto said rigid support. 
     The assembly of the strips to the rigid support is admittedly more complex than if the strips were to form part of a star-shaped component, but given the existence of the curved distal portion of each strip, the individual or distinct character of the strips is particularly advantageous, on account of the convenience and simplicity of producing the strips that it gives. 
     According to other preferred features, each elastic strip is permanently mounted onto said rigid support. 
     Alternatively, according to other preferred features, said rigid support and each elastic strip are arranged in order for each elastic strip to be mounted onto said rigid support in demountable and remountable manner. 
     Preferably, said rigid support comprises for each strip a cavity having a retaining recess while each strip comprises a U-shaped portion adapted to be accommodated in a said cavity of the support, with one branch of said U-shaped portion comprising a nose adapted to enter said recess. 
     Preferably, for each strip the tool comprises a wedge of elastically compressible material which forcibly inserts between the branches of the U-shaped portion. 
     Preferably, each said wedge has a distal portion which is rounded like the base of the U-shaped portion and a proximal portion which has a tab projecting between two shoulders. 
     Preferably, at the location of the opening of each cavity the tool comprises a rib on the opposite side to that at which said recess is formed. 
     Preferably, said rib has a central passage for a tab for extracting said strip out of said cavity. 
     According to other preferred features, there are more said petals than said strips. 
     Preferably, there are twice as many petals as strips. 
     According to other preferred features, said end surface of the collar is flush with said end surface of said support. 
     According to other preferred features, said rigid support comprises a cavity for receiving the head of a surfacing machine arbor. 
     According to other preferred features, said base is a one-piece plastics molding. 
     According to other preferred features, each strip is of spring steel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure of the invention will now be continued with the detailed description of embodiments, given below by way of non-limiting example, with reference to  FIGS. 4  and following the accompanying drawings. In the drawings: 
         FIG. 1  is an exploded perspective view of that tool and an ophthalmic lens having an optical surface to be surfaced; 
         FIG. 2  is a cross-section view of that tool when assembled, during the surfacing of the optical surface of the lens of  FIG. 1 ; 
         FIG. 3  is a diagrammatic view from above representing that ophthalmic lens during surfacing using that tool, which tool is represented during the sweeping of the optical surface in two positions one of which is illustrated in dashed line; 
         FIG. 4  is a view from above of a part of the tool in accordance with the invention, and more particularly of the base and of the strips; 
         FIG. 5  is the section view in elevation on V-V of  FIG. 4 ; 
         FIG. 6  is a diagrammatic cross-section view of another portion of the tool according to the invention, comprising the elastically compressible interface and the flexible buffer; 
         FIGS. 7 and 8  are similar views to  FIGS. 4 and 5  showing a variant of the base and of the strips; 
         FIG. 9 , which is enlarged relative to  FIG. 8 , is an elevation view of one of the strips comprised by the tool, in the position that it takes at rest, that is to say in the absence of external stresses; 
         FIG. 10  is the view on X-X of  FIG. 9 ; and 
         FIGS. 11 and 12 , which are enlarged relative to  FIG. 8 , are views respectively in elevation and in plan view of the holding shim provided for each strip. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     In what follows, the same numerical references as for the tool  1  have been used for the tool in accordance with the invention, but increased by  100 . 
     In general terms, the tool  101  is arranged like the tool  1 , with:
         a rigid support  104  having a transverse end surface  113 ;   an elastically compressible interface  105  ( FIG. 6 ) which is applied against and which covers the end surface  113 ;   a flexible buffer  106  ( FIG. 6 ) adapted to be applied against the optical surface such as  2  of a lens such as  3  and which is applied against and which covers at least partly the interface  105  on the opposite side to and in line with the end surface  113 , the buffer  106  comprising a central part which is located in line with the end surface  113  and a peripheral part which is located transversely beyond the end surface  113 ; and   elastic return means  115 , here formed by a set of elastically flexible strips  118 , connecting the peripheral part of the buffer  106  to the support  104 , the combination of the peripheral part of the buffer  106  and of the return means forming a means for stabilizing the tool  101  during surfacing, the tool  101  being adapted to perform surfacing which is for the most part located at the central portion of the buffer  106 .       

     The support  104  belongs to a base  130  which has a flexible peripheral part  131  located transversely beyond the centrally disposed rigid support  104 . 
     The peripheral part  131  overall forms a flexible collar having an outer diameter (greater diameter) similar to the outer diameter of the interface  105  and of the buffer  106 . 
     The inner diameter (smaller diameter) of the flexible collar  131  corresponds to the outer diameter of the support  104 , the collar  131  projecting from the lateral wall of the support  104 . 
     In the example illustrated in  FIGS. 4 to 6 , the support  104  and the flexible peripheral collar  131  are a one-piece plastics molding, the support  104  being massive at least in the neighborhood of the surface  113  in order to have the required rigidity whereas the collar  131  has a small wall thickness in order to be flexible. 
     In the preferred example illustrated in  FIGS. 4 to 6 , the collar  131  has fourteen radially oriented slots  133  distributed with equal angular spacing, such that the collar  131  is subdivided into fourteen petals  134  the general form of each of which being that of a truncated angular sector. 
     The subdivision of the collar  131  into petals enables that collar to be flexible in order to conform to different curves of surfaces to polish. 
     The end surface  113  of the support  104  is flush with the surface  132  of the collar  131  on the same side. 
     The fact that the support  104  and the collar  131  are formed from a single piece makes it possible to reduce the edge marking effects of the end surface  113  on the surface to work, such that the tool  101  enables surfacing steps to be carried out with a high quality of aspect. 
     On account of the difference in thickness between the collar  131  and the support  104 , there is a shoulder  135 , on the opposite side to the surfaces  132  and  113 , at the junction between the collar  131  and the support  104 . 
     Overall, of the support  104  has the outline of a hat with a proximal portion  137  of smaller outer diameter than the distal portion  136  to which the end surface  113  and the shoulder  135  belong. 
     The proximal portion  137  serves to connect the support  104 , and more generally the base  130 , to the arbor of the surfacing machine enabling the tool  101  to cooperate with an optical surface such as  2  in the manner explained above with reference to  FIGS. 2 and 3 . 
     The proximal portion  137  has a cavity  140  for receiving the arbor head. The general shape of the cavity  140  is that of three-quarters of a sphere. 
     The arbor head provided for being received in the cavity  140  comprises an end similarly formed in the shape of a portion of a sphere 
     The assembly between the proximal part  137  and the arbor of the machine is made by simple snap engagement, the thickness of the part  137  being sufficiently small. 
     When the arbor head is engaged in the cavity  140 , ball-joint cooperation of the tool  101  relative to the arbor is provided. 
     It should be noted that the center of the cavity  140  is particularly close to the end surface  113 , which enables the tool  101  to orientate itself optimally relative to the surface such as  2  with which the tool  101  has to cooperate. 
     The elastic return means  115  will now be described in detail. 
     These comprise a plurality of elastically flexible strips  118 , of which there are seven here, distributed with equal angular spacing, which project transversely from the support  104  until they come to bear on the collar flexible  131 , on the same side as the portion  137 . 
     In practice, each strip  118  is rigidly connected to the support  104  by screws  141  which press its proximal portion  142 , which is flat, onto an annular surface  143  of the support  104  situated between the portion  137  and the shoulder  135 . 
     The strips  118  are angularly disposed in order to for each to be centered relative to the associated petal  134 . 
     It will be noted that the length of the strips  118  is such that they each extend transversely beyond the collar  131 . 
     The strips  118  each have a distal portion  144  curved towards the associated petal  134  in a rounded curl such that the end  145  of the strip  118  is turned towards the support  104 , the contact zone between the strip  118  and petal  134  being situated back from the end  145 . 
     Thanks to this conformation, each strip  118  is free to slide on the associated petal  134  when they deform, since it is by a relatively flat zone that each strip  118  is in contact with the associated petal  134 , over a relatively flat terminal portion of that petal  134 . 
     It will be noted that if the conformation of the terminal portion  144  had been such that the end  145  was turned towards the strip  118 , and thus if it had been by the end  145  that the strip  118  bore on the petal  134 , the sliding would occur under less good conditions due to the small zone of contact provided by the end  145 . 
     In practice, here, each strip  118  is first of all inclined away from the associated petal  134  then curves towards the associated petal  134  over approximately one half turn. 
     It will be noted that, as can be seen in  FIG. 5 , the contact zone is in the neighborhood of the periphery of the collar  134 . 
     The conformation of the strips  118  and of the petals  134  is such that in the absence of external stress (situation illustrated in  FIG. 5 ) the assembly formed by the surfaces  113  and  132  is concave. 
     As indicated above, the diameter of the interface  105  and of the buffer  106  corresponds to the outer diameter of the collar  131 . 
     The connection between the interface  105  and the base  130  is formed thanks to a double sided adhesive  150  disposed between the interface  105  and the surfaces  113  and  132  of the base  130 . 
     In the illustrated example, the elastically compressible interface  105  is of foam of thickness of the order of 9 mm with a brilliant skin situated on the same side as the buffer  106 . 
     A polyester (PET) film  151 , for example of thickness 23 microns, is heat-welded on the opposite side to the skin, that is to say on the same side as the double sided adhesive  150 . 
     The link between the elastically compressible interface  105  and the flexible buffer  106  is made thanks to a layer  152  of bonding mastic, here a layer 0.5 mm thick. 
     Still in the example illustrated in  FIG. 6 , the flexible buffer  106  has a thickness of the order of  1  mm and the double sided adhesive  150  has a thickness of the order of 0.32 mm. 
     The diameter of the interface  105  and of the buffer  106  is of the order of 55 mm. 
     The base  130  is a one-piece injection molding of plastics material. 
     In the example illustrated, the base  130 , which must be both rigid in the neighborhood of the end surface  113  and flexible at the collar  131  and at the proximal part  137  to enable the snap engagements, while giving good wear resistance for the cooperation with the arbor head, is of polypropylene (PP) or of high density polyethylene (for example HDPE 1000). 
     The base thus has good wear resistance for the cooperation with the arbor head and enables easy bonding with the interface  105 . 
     The end surface  113  of the support  104  is shaped as a portion of a sphere having a radius of curvature of the order of 70 mm. 
     When the base  130  is at rest, that is to say in the absence of external forces, the surface  132  of the collar  131  which, as stated above, is flush with the surface  113 , is shaped with the same curvature. 
     Thanks to the collar  131 , the contact area between the interface  105  and the rest of the tool, which is the base  130  in this case, is particularly great since it is formed both by the surface  113  and by the surface  132 . 
     This ensures a uniform distribution of the pressure exerted on the surface to work, such as the surface  2  of the lens  3 . 
     The risk of marking the surface to work by the ridge-shaped edge of the end surface  13 , as with the prior tool of  FIGS. 1 to 3 , is in particular avoided. 
     This more generally enables the tool  101  to perform surfacing steps having particularly high aspect qualities. 
     Moreover, the fact of having available both surface  113  and surface  132  facilitates the bonding of the interface  105  with the rigid support  104 . When the tool  101  is applied against a convex surface to work such as the surface  2  shown in  FIGS. 1 to 3 , the elastically compressible interface  105  is strongly compressed at the location of the central part and the force exerted by the strips  118  is useful for forcing the peripheral part of the buffer  106  to remain in contact with the surface such as  2 . 
     During the surfacing, the fact that the strips  118  exert a force on the petals  134  directed towards the interface  105  at the location of the periphery thereof, enables the tool  101  to give particularly good performance in relation to maintaining the contact with the surface to work such as 2, including when the latter has considerable variations in altitude, for example if it is a face of a spectacles lens for correcting the vision of a presbyopic, myopic and astigmatic wearer. 
     The conformation of the terminal part  144  has the advantage, thanks to its rounded character, of providing flexible, progressive and continuous damping, favorable to the performance of the tool  101 . 
     It will be noted that it would have been possible to form the distal portion  144  not rounded but with a fold which would play the role of a hinge between two flat portions. Such a conformation would give less good performance since with such a hinge, the progressive and continuous character of the damping would be lost. 
     A variant  130 ′ of the base  130  will now be described with reference to  FIGS. 7 and 8 . The same numerical references have been used for similar parts, but with an exponent symbol ′. 
     The base  130 ′ is arranged like the base  130  but whereas each elastic strip  118  is mounted on permanently to the support  104  (here, the screws  141  cannot be removed), the rigid support  104 ′ and each elastic strip  118 ′ are arranged such that each elastic strip  118 ′ can be mounted on to said rigid support  104 ′ demountably and remountably. 
     The interchangeable character which the strips then have is particularly advantageous for considerations of maintenance and/or fine adjustments of the behavior of the tool. 
     In practice, the support  104 ′ comprises for each strip  118 ′ a cavity  146  having a retaining recess  147  while each strip comprises a U-shaped portion  148  adapted to be accommodated in a cavity  146  of the support  104 ′, with one branch of the U-shaped portion  148  comprising a nose  149  adapted to enter the recess  147 . 
     In addition to the recess  147 , to retain each strip  118 ′ a rib  160  is provided at the opening of each cavity  146 , the rib  160  being on the opposite side to that where the recess  147  is provided. 
     At its center, the rib  160  has a passage into which comes into place a tab  155  (see especially  FIGS. 9 and 10 ) projecting from the opposite branch  156  of the U-shaped portion  148  to the branch comprising the nose  149 . 
     As can be seen in  FIG. 10 , the tab  155  projects between two shoulders  157  of the portion  156 . It is the shoulders  157  which bear on the rib  160 . The tab  155  serves to extract the strip  118 ′ from the housing  146 . 
     As shown by  FIG. 9 , it will be noted that at rest (in the absence of external stresses) the U-shaped portion  148  forms an angle at the vertex A which is greater than when the portion  148  is in place in the housing  146 . 
     Still in order to retain each strip  118 ′ in a cavity  146 , a wedge  161  of elastically compressible material is also provided here, which forcibly inserts between the branches of the U-shaped portion  148 . 
     The wedge  161  has a distal portion  162  which is rounded like the base of the U-shaped portion  148  and a proximal portion  163  which has a tab  164  projecting between two shoulders  165 . 
     The shoulders  165  serve as a stop against the rib  160 . The tab  164  comes into place in the passage of the center of the rib  160 . The tab  164  serves to extract the wedge  161 . 
     In the illustrated examples, there are twice the number of petals  134  or  134 ′ as strips  118  or  118 ′ since this provides here an excellent deformation capacity for following a surface such as the surface  2 . In variants not illustrated, according to circumstances, there are also a greater number of petals than strips but with a different ratio for example two strips for three petals, or even there are as many petals as strips. 
     In variants not illustrated of the embodiment with strips that cannot be demounted or which are permanently mounted on the rigid support (embodiment illustrated in  FIGS. 4 and 5 ), the strips are fastened other than by screws, for example by bonding, riveting, overmolding or even thanks to the presence of an overmolded clamping insert. 
     In variants not illustrated of the embodiment with demountable and remountable strips (embodiment illustrated in  FIGS. 7 to 11 ), the fastening is made with removable screws, the housings for the strips are formed by overmolded inserts (composite base), the support is in two snap-engaged parts, for example with a metal part (part cooperating with the arbor). 
     In still another variant not illustrated, the elastic return means formed by individual strips are replaced by one or more star-shaped parts. 
     In variants not illustrated, the base of the tool according to the invention comprises a number of petals different from fourteen, for example six or sixteen and slots delimiting the petals have different shapes, for example with undulations. 
     In still other variants not illustrated, the conformation of the support  104  is different, for example in two parts forming jaws as in the prior tool illustrated in  FIGS. 1 to 3 . 
     In still other variants of the tool according to the invention, the parts other than the base are arranged differently, for example as illustrated in  FIGS. 1 to 3 . 
     Numerous other variants are possible according to circumstances, and in this connection it is to be recalled that the invention is not limited to the examples described and represented.