Abstract:
A translucent synthetic material article such as an ophthalmic lens comprises a plurality of well-shaped cells, some of which have at least one upstanding projection on their bottom walls. The projection have a height between 1/5 and 1/1 the cell depth and are upwardly tapering and wedge-shaped. The plurality of cells are arranged in rows and columns to define a matrix. When the translucent article is illuminated, the well-shaped cells with upstanding projections display enhanced contrast compared with such cells without upstanding projections, thereby producing an identification marking or the like.

Description:
BACKGROUND OF THE INVENTION 
     The present invention concerns marking any translucent synthetic material object, i.e. applying a symbol to that object for identifying and/or tracing it. 
     The symbol can include, for example, a serial number, a reference number or any other inscription relating to the characteristics of the object concerned, the treatment it has undergone or that it is to undergo. 
     The present invention is more particularly, although not necessary exclusively, directed to the situation in which the object is an ophthalmic lens. 
     To assure the identification and/or the tracing, i.e. the “traceability”, of an ophthalmic lens, whether it is a mineral glass ophthalmic lens or an organic material (synthetic material) ophthalmic lens, and thereby to enable its characteristics to be determined at any time by a simple reading process, it is necessary to apply to it a symbol including all the required information, in encoded form or otherwise. 
     In the case of a mineral glass ophthalmic lens, or more generally any object made from such glass, for example the molding shells used to mold synthetic material ophthalmic lenses, it has been proposed to use an etching process, in particular a laser etching process. 
     This is the case, for example, in published French patent application N°2 732 917 (application N°95 04314 filed Apr. 11, 1995). 
     In the above French patent application, it is proposed to cause the beam from a YAG laser to interfere with a layer of a particular material, in this instance a cement capable of reacting with the glass, applied to the surface of the object to be treated beforehand for this purpose. 
     This has the advantage of combining the resulting etching with a coloration which, by increasing the contrast of the etching, facilitates and renders more accurate subsequent reading of the symbol obtained in this way. 
     In the case of marking mineral glass objects, it is therefore satisfactory. 
     However, although they may be acceptable for mineral glass objects to be used many times, for example molding shells for molding synthetic material ophthalmic lenses, the costs inherent in the use of a cement of this kind are less acceptable for synthetic material objects which are not re-used, for example the ophthalmic lenses themselves, because they represent an unnecessary increase in the overall cost of such items. 
     Moreover, no such cement is necessary in this case, an appropriate choice of its wavelength enabling the laser beam to react directly with the synthetic material. 
     BRIEF SUMMARY OF THE INVENTION 
     A general object of the present invention is an arrangement which advantageously achieves sufficient contrast of the symbol obtained for subsequent reading of the symbol to be reliable, despite the absence of cement. 
     To be more precise, the present invention consists firstly in a method of marking a translucent synthetic material object, for example a synthetic material ophthalmic lens, it being understood that this material is then not only translucent but also transparent, and that the object concerned can be bare, varnished or coated with any material, for example an anti-reflection material. 
     The method in accordance with the invention is generally characterized in that said object is etched in the form of cells and each etched cell is in the form of a well and has at least one projection upstanding on the bottom of said well. 
     Trials have confirmed that, with a projection of this kind, each etched cell appears on reading as an area sufficiently dark to be identified as actually being an etched cell. 
     The reason for this is probably that the projection leads to local diffusion and/or refraction of light enabling the required identification of an etched cell as such by contrast with a non-etched cell. 
     When, in a preferred embodiment, the etching is assured in a manner known in itself using a laser, each etched cell is made, for example, by using the laser to execute at least two shots offset relative to each other. 
     As also confirmed by trials, the offset between the shots provides a very simple way to obtain the required projection. 
     Because of this offset, the shots resemble scanning with a small amplitude which conditions the width finally obtained for the etched cell formed in this way. 
     In practise three laser shots forming two projections for each etched cell constitute, in accordance with the invention, a good compromise between fast execution of the symbol required and sufficient definition of the latter for subsequent reading. 
     The present invention further consists in any translucent synthetic material object, and in particular any ophthalmic lens, provided with a symbol of the above kind. 
     Trials show that subsequent reading of this symbol can advantageously be reliable, even after the application to any such object of a layer of any thin and transparent material, such as a varnish or an anti-reflection material. 
     The present invention further consists in a symbol reader enabling such reading to be effected in a simple manner. 
     The symbol reader is generally characterized in that it includes a CCD camera and an illuminating device adapted to generate a beam the transverse dimension of which is between one and three times that of the symbol to be read. 
     For example, this illuminating device is an illuminating strip disposed transversely to the optical axis of the system. 
     To read the symbol on a translucent synthetic material object it is sufficient to dispose the symbol on the object between the CCD camera and the illuminating strip. 
     No calibration or supplementary adjustment is necessary. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various aspects of the invention, their features and their advantages will emerge from the following description given by way of example with reference to the accompanying diagrammatic drawings. 
     FIG. 1 is a sectional elevation view showing the marking in accordance with the invention of a translucent synthetic material object; 
     FIG. 2 is a partial plan view of this object, at the location of the symbol that it carries after such marking, to a larger scale and in the direction of the arrow II in FIG. 1; 
     FIG. 3 shows the detail III from FIG. 2 to a still larger scale; 
     FIG. 4 is a partial sectional view of the object marked in this way taken along the line IV—IV in FIG.  3  and to a still larger scale; 
     FIG. 5 is a sectional elevation view, similar to FIG. 1, of a symbol reader in accordance with the invention; 
     FIG. 6 is an example of etching measured by means of a roughness meter. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The figures show, by way of example, the situation in which the object  10  to be marked is an ophthalmic lens, to be more precise an unprocessed ophthalmic lens, i.e. a circular contour blank to be trimmed to fit it to an eyeglass frame. 
     The object  10  therefore has two main faces  11 A,  11 B, one of which is concave and the other convex, and an edge  12 , in practise a flat edge. 
     In the case of a correcting ophthalmic lens, at least one of the main faces  11 A,  11 B is spherical, aspherical, toroidal, progressive or multifocal. 
     This is usually the convex face  11 B intended to form its front face. 
     Be this as it may, the object  10  to be marked, which can be bare, varnished or coated with any material, for example an anti-reflection material, is made from a translucent synthetic material and, more precisely, in this case of an ophthalmic lens, a transparent synthetic material. 
     This synthetic material can be any synthetic material that can be used to manufacture an ophthalmic lens, for example, such as those sold under the trade names “ORMA” and “ORMEX” or those described in French patent N°2 699 541, for example. 
     As previously stated, the aim is to apply at least one localized symbol  13  to the object  10  for identifying it and/or tracing it. 
     In the embodiment shown, there is only one symbol  13 . 
     This symbol  13  is preferably, but not necessarily exclusively, applied to the concave main face  11 A of the object  10 , near the edge  12  of the latter, in a part of the object  10  that will be removed when it is trimmed and/or its surface is machined. 
     To form the symbol  13  the object  10  is etched in a cellular manner known in itself. 
     In other words, the symbol  13  comprises at least one etched cell  14  and is in practise made up of a plurality of etched cells  14  recessed into the surface of the object  10  which alternate individually or in groups with non-etched (i.e. still smooth) cells  15  on the object  10 . 
     For better individualization relative to the non-etched cells  15 , the etched cells  14  are shaded in FIG.  3 . 
     Furthermore, to simplify the drawing, FIG. 3 shows the etched cells  14  as having a square contour when seen in plan view. 
     It goes without saying that this contour can be different, however, for example rectangular. 
     Be this as it may, the etched cells  14  preferably all have the same contour, as is the case in the embodiment shown. 
     The non-etched cells  15  themselves all have the same contour, which is the same as that of the etched cells  14 . 
     In the embodiment shown, and in a manner that is known in itself, the etched cells  14  are divided into lines L and columns C constituting a matrix type symbol. 
     As shown diagrammatically in FIG. 1, the etching necessary to mark the object  10  is assured, in a manner that is known in itself, by means of a laser  16  the beam  18  from which forms a focused or unfocused spot on the main face  11 A of the object  10 , using a galvanometer head  19  enabling deviation at will along the outline of the symbol  13  to be obtained. 
     The corresponding arrangements are well known in themselves and will not be described here, not being relevant to the present invention. 
     Suffice to say that, in practise, the laser  16  is a CO 2  type laser, for example, having a wavelength equal to 10 μm, and that it preferably operates continuously, under the control of a computer, its beam being interrupted on command by means of an electromagnetic shutter. 
     In accordance with the invention, each etched cell  14  is in the form of a well  20  as shown diagrammatically in FIG.  4  and has at least one upstanding projection  22  on the bottom  21  of the well  20 . 
     Although this is not obligatory, the maximum amplitude H of the projection  22  above the bottom  21  of the well  20  is preferably a fraction of the depth P of the well  20  having a value between a value equal to one fifth of the depth P and a value equal to the depth P, the depth P being measured from the main face  11 A concerned of the object  10 . 
     In other words          P   5     &lt;   H   &lt;   P                          
     Although this is not obligatory, the maximum amplitude H of the projection or projections  22  upstanding from the bottom  21  of the well  20  is preferably equal to at least two fifths of the depth P of the latter. 
     Although this is not obligatory, the wells  20  formed by the various etched cells  14  preferably have substantially the same depth P. 
     In the embodiment shown, each of the wells  20  formed by an etched cell  14  has upstanding on its bottom  21  two projections  22  offset relative to each other. 
     The two projections  22  have substantially the same maximum amplitude H. 
     Although this is not obligatory, the projections  22  are preferably in the form of spikes, as shown here. 
     In other words, they are generally wedge-shaped and taper from the bottom  21  of the well  20  to their apex  23 , which forms a sharp edge. 
     At their apex  23 , the projections  22  divide the internal volume of the well  20  transversely into three substantially equal parts, as shown in FIG.  4 . 
     In accordance with the invention, to obtain projections  22  on the bottom  21  of the well  20  formed by each etched cell  14 , the etched cell  14  is made by executing at least two shots of the laser  16  offset relative to each other. 
     Obviously, two such shots produce one projection  22 . 
     In the case where, as shown, two projections  22  are upstanding from the bottom  21  of the well  20  formed by each etched cell  14 , an etched cell  14  of this kind is therefore obtained by executing with the laser  16  three successive shots offset relative to each other. 
     For aligned etched cells  14  the corresponding line L is preferably scanned a number of times equal to the number of shots to be effected using the laser  16  and, from one scan to the next, the shots are offset by the same amount for each of the etched cells  14  to be produced. 
     As previously indicated, each etched cell  14  is itself the result of scanning with a small amplitude by offsetting the shots which produce it. 
     Let D 1  be the transverse dimension at the surface of each etched cell  14  and therefore of each non-etched cell  15 . 
     This transverse dimension D 1  is preferably at least equal to 0.1 mm. 
     For example, it is in the order 0.35 mm. 
     If, under these conditions, the symbol  13  includes a number of lines L between  15  and  25  and an equal number of columns C, for example, this number being in the order of  19 , for example, the transverse dimension D 2  of the symbol  13  is in the range 1.5 mm to 25 mm, for example around 6 mm. 
     A symbol reader  25  of the type shown in FIG. 5 can be used for subsequent reading of the symbol  13 . 
     In accordance with the invention, the symbol reader  25  includes a CCD camera  26  and an illuminating device  27  adapted to generate at least one beam F the transverse dimension D 3  of which is between one and five times that D 2  of the symbol  13  to be read, which is favorable to obtaining good contrast. 
     In the embodiment shown, the illuminating device  27  includes, by way of non-limiting example, one or more light sources  28 , in this instance several of them, each generating a beam F and being placed on a line transverse to the overall optical axis. 
     The CCD camera  26  is well known in itself and will not be described here, not being relevant to the present invention. 
     Suffice to say that it is a charge-coupled device including an array made up of a plurality of receiving cells. 
     The light sources  28  can be light-emitting diodes, for example. 
     As shown here, for example, five light sources  28  can be provided, regularly arranged on either side of the overall optical axis. 
     In the embodiment shown, there is a support plane  29  against which the object  10  has to be applied, and which can be an apertured plate, for example, between the CCD camera  26  and the illuminating device  27  and a frosted glass  30  between the support plane  29  and the illuminating device  27 . 
     In practise the transverse dimension D 3  of a beam F from the illuminating device  27  is that at the level of this frosted glass  30 . 
     In use, the light sources  28  are turned on one after the other. 
     The central light source  28 , which is on the overall optical axis, illuminates the object  10  in an area of the latter that does not generate any prism effect. 
     The light sources  28  farthest from the axis of the CCD camera  26  compensate to a greater or lesser degree the prism deviation that can be caused by the object  10  at the location of the symbol  13 . 
     Each halo of light projected onto the frosted glass  30  by a light source  28  acts as a diffusive source. 
     On reading the symbol  13 , and as mentioned above, the etched cells  14  show dark in a manner that is highly contrasted to the non-etched cells  15 . 
     Thus reading is particularly reliable. 
     The FIG. 6 diagram corresponds to a reading taken by means of a roughness meter along a column C of the symbol  13 . 
     The projections  22  are clearly apparent. 
     They are clearly much more than mere roughness of the surface. 
     Particularly satisfactory results have been obtained with symbols  13  in which each etched cell  14  forms a well  20  having a depth P at least equal to 25 μm, with a maximal amplitude H of the projection or projections  22  on the bottom  21  of the well  20  in the range 5 μm to 25 μm. 
     Of course, the numerical values given above are given by way of example only and cannot in any way be regarded as limiting on the present invention. 
     More generally, the present invention is not limited to the embodiments and uses described and shown, but encompasses any variant execution. 
     In the case of the symbol reader in particular, other embodiments of the illuminating device used are feasible. For example, the latter can use optical fibers or an extensive light source behind a mobile diaphragm.