EP1567305B1 - Method for shaping an optical surface - Google Patents

Description

TECHNICAL AREA

The present invention generally relates to the machining of shapes in mineral materials, especially hard materials such as sapphire, corundum or spinel. More particularly, the present invention relates to a method for machining such mineral materials, in particular adapted for shaping an optical surface in a watch crystal.

TECHNOLOGICAL BACKGROUND

A method, according to the preamble of claim 1, for forming an optical surface in the form of a convergent lens comprised in the thickness of a plate of a transparent mineral material is known from the document EP 0 123 891 , in the name of this Depositor. This method essentially consists of rotating the plate around a first axis perpendicular to the area where the lens is to be formed and machining the desired area by means of an abrasive wheel driven in rotation about a second axis distinct from the first axis and intersecting this first axis at the center of curvature of the desired lens. Oscillating movement of the tool or plate about a third axis perpendicular to the plane containing the first and second axes of rotation and remote from the area by a value equal to the desired radius of curvature of the lens is preferably set work, this oscillating movement ensuring a self-sharpening of the grinding wheel.

According to the method summarized above, it will be noted that the rotary tool used for shaping the lens is a substantially cylindrical (or even frustoconical) grinding wheel carrying, at its active end, abrasive material preferably consisting of diamond. It will be readily understood that the cost of this tool is relatively high given the material to be machined (especially in the case of a hard mineral material such as sapphire), the corresponding abrasive material necessarily having to be incorporated on the head of the tool (typically a diamond powder or a carbide-based compound for machining sapphire), and the complexity of the manufacture of this tool. It should also be noted that the life of such a tool is relatively short and that its replacement must be carried out periodically. The aforementioned points therefore weigh significantly on the manufacturing costs of the artifact.

SUMMARY OF THE INVENTION

A simpler solution to implement and more profitable must therefore be sought. The object of the present invention is to propose such a solution, namely a method for machining hard materials, in particular adapted to shaping a lens, or other optical surface, in a watch crystal made of hard mineral material (sapphire , corundum, spinel or the like). The present invention also aims to propose a solution with both a low cost and a great simplicity of implementation.

The present invention relates to a method for forming a deforming optical surface in a transparent mineral material, in particular sapphire, corundum or spinel, employing a rotary tool and whose characteristics are set forth in claim 1.

It will thus be noted that the tool comprises a body terminated with a head comprising an active surface intended to come into contact with an area of the mineral material where it is desired to shape the desired shape, the head of the tool having at least a first slot, preferably several, opening on the active surface to form an opening allowing abrasive particles conveyed to the area to be shaped the desired shape to be lodged on the active surface and form, throughout the opening or openings formed on this active surface, one or more cutting edges contribute to the shaping of the desired shape.

It will thus be understood that the rotary tool is not strictly speaking an abrasive tool for the mineral material in question. On the contrary, the abrasive power of the tool is created jointly by the tool (in particular by the slot or slots on the head of the tool and the corresponding openings on the active surface of the head) and the abrasive particles conveyed on the machining area. Each opening on the active surface formed by the corresponding slot allows the abrasive particles to lodge and accumulate therein to form, on the active surface of the head of the tool, a excrescence with high abrasive power having the function of a cutting edge. The rotary tool itself thus constitutes a matrix for fixing or freezing the abrasive particles in a suitable configuration allowing the abrasion of the mineral material to be shaped.

The head of the tool is advantageously formed of a non-abrasive material for the mineral material considered and having a compromise between hardness and softness in order to maintain and guarantee the shape of the head and, respectively, allow the abrasive particles to implanted. This material may for example be a metal selected from the group consisting of Cu copper, Zn zinc, Sn tin and Fe iron (or a metal alloy comprising at least one of these metals).

The arrangement of the openings of the slots on the active surface of the tool head can follow any suitable geometric arrangement, the simplest being an arrangement of one or more slots of substantially straight geometry. Slits forming diametrical or parallel openings on the active surface of the tool head may be provided in adequate number on the head of the tool.

To obtain better results in terms of surface quality, it is preferable to arrange each slot so that, during a rotation of the tool, the cutting edge thus formed covers a surface of revolution defined only by an outline. external, that is to say a solid surface having no central recess.

A considerable advantage of the present invention lies in the fact that the rotary tool is very simple and very inexpensive to manufacture, particularly because of the type of material that can be used for the manufacture of the tool and because of the absence of any abrasive incorporated on the head of the tool, this abrasive being conveyed directly to the machining area in the form of abrasive particles carried by a fluid or a liquid. As such, an advantageous variant consists in providing at least one slot so that it also plays the role of routing channel abrasive particles.

Thanks to the invention, the costs associated with shaping the desired shape in the mineral material in question can thus be very substantially reduced. This advantage is particularly decisive in the shaping of hard mineral materials, such as sapphire, corundum or spinel, used in particular in the watch industry for the manufacture of watch glass. The present invention is therefore particularly suitable for shaping optical surfaces, or diopters, (especially deforming optical surfaces such as magnifying lenses) in transparent mineral materials having a high hardness, including sapphire.

SUMMARY DESCRIPTION OF THE DRAWINGS

• la figure 1 représente une installation d'usinage adaptée spécifiquement au façonnage d'une surface optique déformante (par exemple une lentille à surface sphérique convexe) dans un matériau minéral dur et transparent, en particulier dans une glace de montre, cette installation utilisant un outil rotatif selon la présente invention ;
• la figure 2 est une vue en perspective de la partie terminale, ou tête, d'un outil rotatif ;
• la figure 3 est une vue de face de la surface active de la tête de l'outil rotatif de la figure 2 ;
• la figure 4 est une vue en coupe de l'outil rotatif, prise selon la ligne A-A dans la figure 3 ; et
• la figure 5 est un exemple de mise en oeuvre de l'outil rotatif selon l'invention pour l'usinage d'une lentille sphérique convexe à pourtour circulaire dans une plaque de matériau minéral transparent.

Other features and advantages of the present invention will appear more clearly on reading the following detailed description of a preferred embodiment of the invention, given solely by way of non-limiting example and illustrated by the accompanying drawings in which: :

• the figure 1 represents a machining installation specifically adapted to shaping a deforming optical surface (for example a convex spherical surface lens) in a hard and transparent mineral material, in particular in a watch glass, this installation using a rotary tool according to the present invention;
• the figure 2 is a perspective view of the end portion, or head, of a rotary tool;
• the figure 3 is a front view of the active surface of the rotary tool head of the figure 2 ;
• the figure 4 is a sectional view of the rotary tool, taken along the line AA in the figure 3 ; and
• the figure 5 is an example of implementation of the rotary tool according to the invention for machining a circular convex spherical lens around a plate of transparent mineral material.

MODES OF ACHIEVEMENTS

The machining installation illustrated in the figure 1 is essentially similar to the installation shown in the document EP 0 123 891 mentioned above. It comprises a support frame 10 on which are mounted a bracket 12 and a doll 14. The bracket 12 carries a pin 16 at the end of which is a rotary tool 20, of the same axis, designated 42, as the spindle, comprising a substantially cylindrical body terminated by a head 20a intended to come into contact with a zone of the mineral material to be machined. A pulley 18, mounted on the spindle 16, can drive it in rotation about the axis 42 by means of a motor not shown. The bracket 12 further comprises slides 22, 24 and 26 allowing, in a manner quite conventional, the displacement of the tool 20 along three orthogonal axes. More precisely, the slide 22 makes it possible, with the aid of a micrometer screw 23, to move the tool vertically along its axis of rotation, whereas the slides 24 and 26 make it possible, with the aid of the micrometer screws 25 and 27, respectively, to move the tool 20 in a horizontal plane in two perpendicular directions.

The doll 14 carries a pin 28 whose end 28a adjacent to the bracket 12 is, thanks to a bend 28b, offset downwardly relative to the axis of rotation, designated 44, of the pin 28. A table 30 is mounted on a shaft 32 which is perpendicular to the axis 44 of the pin 28 and which pivots in the end 28a. This shaft carries a pulley 34 which drives it in rotation about an axis of rotation, designated 40, by means of a motor not shown in the figure. A posture 36, integral with the table 30, makes it possible to fix a plate 38 of mineral material. This plate 38 may for example be made of a hard and transparent mineral material of the sapphire, corundum or spinel type, such as a watch ice plate that it is desired to provide a lens or other deforming optical surface.

Note that the tool 20 and the setting 36 are both rotated in opposite directions of rotation. In addition, the setting 36 here has a thickness such that the distance between the axis of the pin 28 and the end point of the spherical surface that is desired to shape (located on the axis of rotation 40 of the shaft 32 ) is equal to the radius of curvature, designated R, that must present this spherical surface. Finally, the pin 28 may be associated with unrepresented drive means for printing an oscillating movement of low amplitude or at least adjust its inclination relative to the horizontal plane.

From the above, it will be understood that the installation has several possibilities for driving and positioning the tool 20 and the plate 38. It will be seen later that various operating procedures of the installation can be envisaged, these various procedures all having in common at least the rotation of the tool 20 about its axis of rotation 42. This rotation may, if necessary, be accompanied by a rotation or an oscillating movement of the plate 38 around its axis of rotation 40 and / or an oscillating movement of the plate 38 around the axis of the spindle 28 (this oscillating movement can alternatively be printed with the tool 20 if the stem was fitted 12 adequate means). With regard to details relating to the particular mode of operation consisting of simultaneously rotating the tool 20 and the plate 38, and to impart an oscillating movement to this plate, reference may be made to the method described in the document EP 0 123 891 already mentioned.

In addition to the aforementioned drive and positioning means, it will also be noted that the machining installation comprises means for conveying abrasive particles over the area of the mineral material where the desired shape is to be shaped. These conveying means are schematically illustrated on the figure 1 and essentially comprise a reservoir 50 containing a carrier fluid of abrasive particles (for example a diamond powder suspended in an oil) and a supply conduit 52 for conveying this fluid to the machining zone. Means not shown to adjust the amount of abrasive particles transported to the machining area. It will be understood, in what follows, that the routing of abrasive particles on the machining area and the rotary tool according to the invention together contribute to the shaping of the desired shape in the plate of mineral material.

The Figures 2 to 4 show respectively a perspective view, a front view and a sectional view of the end portion of a rotary tool 20. As can be seen in the Figures 2 to 4 , the body of the rotary tool 20 is terminated by a head 20a comprising an active surface 200 intended to come into contact with the zone of the mineral material where it is desired to shape the desired shape. In this particular example, the active surface 200 of the tool has the shape of a concave spherical cap whose radius of curvature corresponds to the radius of curvature R of the shape to be shaped, in this example a convex spherical optical surface. In this case, the implementation of the tool in the installation illustrated in the figure 1 implies that the axis 40 of the shaft 32, the axis 42 of the pin 16 and the axis 44 of the pin 28 intersect at a point C corresponding to the center of curvature of the convex spherical surface to be shaped in the plate 38 of mineral material (as illustrated in more detail in the figure 5 ).

Note that the active surface 200 of the tool 20 could have a shape other than strictly spherical. Thus, the active surface 200 of the head 20a could take the form of a portion of torus, by analogy with the shape of the wheel considered as a second variant in the document EP 0 123 891 (This particular form then requires a specific adjustment of the installation). In general, the active surface of the tool can take any suitable form. It will be understood in any event that the shaped shape in the mineral material will depend not only on the shape of the active surface of the tool but also on the movement or movements printed on the tool and / or the plate. The shape of the active surface of the head of the tool is not necessarily shaped to the shape of the surface to be shaped.

The head 20a of the tool has at least a first slot opening on the active surface 200 to form an opening. In the example shown in the Figures 2 to 4 , the head 20a of the tool here has a pair of diametrical slots 210, 220, that is to say two substantially rectilinear slots provided in two diametrical planes passing through the axis of rotation 42 of the tool 20. These diametrical slots 210, 220 which run through the end of the head 20a are here arranged substantially perpendicular and consequently form a pair of perpendicular openings corresponding 210a, 220a on the active surface 200 of the tool. It will be noted that the active surface 200 of the rotary tool 20 is subdivided, in this example, into four distinct parts having, here, substantially equal areas.

It will be emphasized that the arrangement as well as the geometry of the slots 210, 220 illustrated in this embodiment are in no way limiting. Only one slot or more than two slots could be provided on the head. In addition, these slots, instead of cutting, could be parallel. Finally, the slots and the corresponding openings on the active surface of the head of the tool may not be rectilinear, this particularly simple geometry being nevertheless the easiest to achieve.

For example, the head of the tool could be provided with a single slot, this slot does not necessarily cover the entire width of the active surface. Note that it is preferable that the slot is configured so that, during a rotation of the tool, the cutting edge formed by the corresponding opening of this slot covers a surface of revolution delimited only by a contour external, that is to say a solid surface without central recess, this configuration being preferable from the point of view of the surface quality of the shaped form. It will be understood that a configuration of diametrical slot, as illustrated in the Figures 2 to 4 , meets this definition.

Note also that the way in which the slots extend in the head of the tool is relatively unimportant. Indeed, the essential lies mainly in the manner in which these slots open on the active surface of the head of the tool. It is indeed through the active surface of the tool, and the supply of abrasive particles on this active surface during machining, that the mineral material can be shaped.

As already mentioned above, each opening on the active surface formed by the corresponding slot allows the abrasive particles to lodge therein and accumulate thereon to form, on the active surface of the head of the tool, a protrusion to a strong abrasive power having the function of a cutting edge, the rotary tool thus constituting a matrix for fixing or freezing the abrasive particles in a suitable configuration for abrasion of the mineral material to be shaped.

The tool 20 may advantageously be made in a non-abrasive material for the mineral material in question, preferably in a material having a compromise between hardness and softness to maintain and guarantee the shape of the head and, respectively, allow the abrasive particles to implant. This material may thus be a metal or a metal alloy comprising at least one metal selected from the group comprising copper Cu, zinc Zn, tin Sn and iron Fe.

As an advantageous variant, it will also be noted that it is possible to configure a slot of the tool so that it also acts as a channel for conveying the abrasive particles onto the machining area. This slot shaped conveyor channel would, in this case, be part of the abrasive particles conveying means and could replace or supplement the supply conduit 52 of the figure 1 .

One embodiment of the invention, for machining a convergent lens (that is to say a convex spherical surface with a circular periphery) will now briefly be presented with reference to FIG. figure 5 .

The tool illustrated in Figures 2 to 4 can be implemented very easily to shape a convergent lens in the thickness of a plate of transparent mineral material. For this purpose, it is appropriate for example to incline the plate 38 by means of the pin 28 of the figure 1 defined angle, designated α, also corresponding to the angle formed by the axis 42 of the tool 20 relative to the axis of rotation 40 of the plate 38 (that is to say the perpendicular to the zone where the lens must be formed and which passes through the center of this zone), the axes 40, 42 passing both through the center of curvature C of the spherical surface to be shaped, designated 380 in the figure 5 . It is then necessary to rotate the tool 20 and the plate 38 around their respective axes 42 and 40 (by means of the pin 16, the shaft 32 and the associated drive means) and to bring the surface active 200 of the head of the tool 20 in contact with the plate 38. In the figure 5 It should be noted that reference numeral 500 generally designates a mixture conveyed to the machining zone containing abrasive particles.

As schematized in the figure 5 , the simultaneous rotation of the tool 20 and the plate 38 around their respective axes of rotation and the adjustment of the angle α between these axes of rotation ensures that the active surface 200 of the tool shapes a portion of convex spherical surface of radius of curvature R having a circular periphery (in other words a convex spherical cap). Since no oscillating movement is printed on the tool or the plate, it will be understood that the diameter of the head of the tool, designated d, must have a minimum value which is greater than half the diameter, designated D, of the lens to be shaped. More specifically, the diameter d of the tool 20, in this particular embodiment, must be at least equal to the diameter D of the desired lens divided by the cosine of the angle α. Note that the angle α is in practice less than 20 °, preferably less than 10 °.

Cette relation (1) est également valable pour le mode de mise en oeuvre précédent à inclinaison fixe.As mentioned in the document EP 0 123 891 , rather than setting a determined inclination of the plate relative to the tool, a movement oscillating about an axis perpendicular to the axes of rotation 42, 40 and passing through the center of curvature C of the lens to be shaped (namely a movement oscillating around the axis 44 of the pin 28 in the figure 1 ) can be printed on the plate 38 (or even the tool). In this case, the maximum angle of inclination of the plate 38 relative to the tool 20, designated α _max , can be expressed by the following formula, which is valid for low amplitude movements (low angles α): $${\mathrm{tan\; \alpha }}_{\max }\approx \left[\mathrm{2}\mathrm{R}\left(\mathrm{D}-\mathrm{d}\right)\right]/\left[\mathrm{4}{\mathrm{R}}^{\mathrm{2}}+\mathrm{D\; d}\right]$$

This relation (1) is also valid for the previous implementation mode with fixed inclination.

Using the tool represented in the Figures 2 to 4 It should be noted that it is possible to shape convex spherical surfaces which do not necessarily have a circular periphery.

So, referring to the figure 5 it is perfectly possible to subject the plate 38 to a repeated movement oscillating about the axis 40, rather than a complete rotation about this axis. By limiting the maximum amplitude of this movement oscillating about the axis 40, for example by subjecting the plate to an angular movement oscillating by about 180 °, it is possible to shape a portion of a spherical cap having a general shape in "C" In the plane of the plate.

Similarly, it is perfectly conceivable not to turn the plate 38 about the axis 40 and to only subject this plate 38 to a movement oscillating about an axis perpendicular to the axis 42 of the tool and passing by the center of curvature C of the spherical surface (for example a movement oscillating about the axis 44 of the spindle 28). In this way, a convex spherical surface of elongate or oblong shape is obtained.

With regard to this last example, it is conceivable to incline further the rotary tool 20 in a plane containing the axis 44 around which the plate 38 oscillates and so that the axis of rotation 42 of the tool 20 cuts the axis 44 at the center of curvature C of the spherical surface to be shaped. This amounts to tilting the tool 20 in the plane of the figure 1 and therefore requires positioning means not shown in the figure to allow this angular adjustment. In this way, a convex spherical surface is also obtained which is elongated but which is inclined in the direction of the width relative to the average plane of the plate 38, instead of a totally symmetrical surface as in the previous example.

In the three aforementioned examples, it will therefore be understood that the rotational movement of the tool 20 about its axis 42 is accompanied by a repeated (or oscillating) relative movement between the tool 20 and the plate 38 to shape a spherical optical surface having a non-circular periphery. More complicated shapes could be obtained by synchronizing several oscillating motions around various axes all passing through the center of curvature of the spherical surface, or non-concordant axes if one wanted to shape a toric surface, for example.

It will be understood in general that various modifications and / or improvements obvious to those skilled in the art can be made to the embodiment described in the present description without departing from the scope of the invention defined by the appended claims. In particular, the active surface of the head of the tool may have a shape other than spherical insofar as it is not desired to subject the tool to a relative movement with respect to the plate of mineral material to be machined. It is thus possible to give the active surface of the tool a non-spherical shape of revolution and to shape a corresponding shape in the mineral material by only rotating the tool (or even by also rotating the plate of material mineral around an axis coincident with the axis of rotation of the tool). The particularly simple spherical shape of the active surface of the head of the tool, as presented above, however, is a particularly simple solution to implement, flexible to use and which allows to shape recesses of various forms in the material.

Finally, it will again be emphasized that the arrangement of the slot (s) on the active surface of the tool head may follow any suitable geometrical arrangement, the simplest of these geometrical arrangements being constituted by one or more essentially rectilinear slots. .

Claims (8)

1. Method for forming an optical surface (380) in a zone of a plate (38) of a transparent mineral material, particularly sapphire, corundum or spinel, wherein a rotating tool (20) comprising a body ending in a head (20a) including an active surface (200) coming into contact with said zone of the mineral material is used,
   wherein said method comprises the simultaneous steps of:

   - setting said tool (20) in rotation about a first axis of rotation (42);

   - putting the active surface (200) of the tool head into contact with the plate (38) in a zone of the mineral material where said optical surface is required to be formed;

   - transporting abrasive particles (500) to said zone; and

   - moving the tool (20) and/or the plate (38) in relation to the other,

   characterized in that said head (20a) of the tool has at least one first slot (210, 220) opening onto said active surface (200) to form therein an aperture (210a, 220a) allowing abrasive particles (500) transported onto said zone to lodge in the active surface (200), wherein said head (20a) is formed of a material that is not abrasive for the mineral material concerned and exhibits a compromise between hardness and softness in order to maintain and guarantee the shape of the head and, respectively, to allow said abrasive particles to be implanted therein, and in that abrasive particles (500) transported onto said zone form, along said aperture (210a, 220a) on the active surface, a cutting edge contributing to forming the required shape.
2. Method according to claim 1, characterised in that said active surface (200) of the head of the tool has essentially the shape of concave spherical surface the radius of curvature of which (R) corresponds to the radius of curvature of the optical surface to be formed, and in that the method further includes a simultaneous operation consisting in setting said plate (38) in rotation about a second axis of rotation (40) which is perpendicular to the zone where said optical surface is required to be formed and passes through the centre of said zone, said first and second axes of rotation (42, 40) passing through the centre of curvature (C) of the convex spherical surface to be formed.
3. Method according to claim 1, characterised in that said active surface (200) of the head of the tool has essentially the shape of concave spherical surface the radius of curvature of which (R) corresponds to the radius of curvature of the optical surface to be formed, and in that the method further includes a simultaneous operation consisting in performing a repeated relative movement of said tool (20) in relation to said plate (38) to form a spherical optical surface having a non circular contour.
4. Method according to claim 3, characterised in that said repeated relative movement is an oscillating movement of said plate (38) or of said tool (20) about an axis (40; 44) distinct from said first axis (42) and intersecting said first axis at the centre of curvature (C) of the convex spherical surface to be formed.
5. Method according to claim 1, characterised in that said head (20a) of the tool has at least one pair of slots (210, 220) forming diametral or parallel apertures (210a, 220a) on said active surface (200).
6. Method according to claim 1, characterised in that said material forming the head (20a) is a metal or metal alloy including at least one metal selected from the group including Cu, Zn, Sn and Fe.
7. Method according to any of the preceding claims, characterised in that at least one of said slots also plays the part of a channel for transporting said abrasive particles to said zone.
8. Method according to any of claims 1 to 6, characterised in that said optical surface (380) is situated in the thickness of the plate (38).

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