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EP0123891A2 - Method of shaping a convergent lens in a plate made of a transparent mineral material - Google Patents

Method of shaping a convergent lens in a plate made of a transparent mineral material Download PDF

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Publication number
EP0123891A2
EP0123891A2 EP84103309A EP84103309A EP0123891A2 EP 0123891 A2 EP0123891 A2 EP 0123891A2 EP 84103309 A EP84103309 A EP 84103309A EP 84103309 A EP84103309 A EP 84103309A EP 0123891 A2 EP0123891 A2 EP 0123891A2
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EP
European Patent Office
Prior art keywords
grinding wheel
lens
axis
radius
diameter
Prior art date
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Granted
Application number
EP84103309A
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German (de)
French (fr)
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EP0123891A3 (en
EP0123891B1 (en
Inventor
Claude-Michel Juvet
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Comadur SA
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Comadur SA
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Publication of EP0123891A2 publication Critical patent/EP0123891A2/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B13/00—Machines or devices designed for grinding or polishing optical surfaces on lenses or surfaces of similar shape on other work; Accessories therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B13/00—Machines or devices designed for grinding or polishing optical surfaces on lenses or surfaces of similar shape on other work; Accessories therefor
    • B24B13/04—Machines or devices designed for grinding or polishing optical surfaces on lenses or surfaces of similar shape on other work; Accessories therefor grinding of lenses involving grinding wheels controlled by gearing

Definitions

  • the present invention relates to a method for forming a converging lens in a plate of a transparent mineral material.
  • the object of the invention is to provide a method for manufacturing plates of transparent mineral material provided with a lens, without excess thickness and without risk of delamination.
  • This object is achieved by making the lens by grinding the plate, but this grinding is not carried out using a grinding wheel whose diameter and radius of curvature correspond to the diameter and radius of curvature of the lens because this causes faster wear of the periphery of the grinding wheel than of its central part.
  • the Applicant has in fact surprisingly found that, if a grinding wheel is used whose active part has a diameter less than the diameter of the lens, and that a relative oscillation movement is created between the grinding wheel and the plate, the period between two sharpenings of the grinding wheel is significantly increased.
  • the oscillating movement has the sole function of ensuring the self-sharpening of the grinding wheel. If, on the other hand, the arc embraced by the active part of the grinding wheel is less than half of the arc embraced by the lens, the rotational movement of the plate cannot be sufficient to machine the entire surface of the lens. To guarantee this machining, the oscillation angle must be at least equal to the angle corresponding to the difference between half of the arc embraced by the lens and the arc embraced by the active part of the grinding wheel.
  • the device shown in Figure 1 comprises a support frame 10 on which are mounted a bracket 12 and a headstock 14.
  • the bracket 12 carries a pin 16 at the end of which is fixed a cylindrical grinding wheel 20, of the same axis as the spindle and carrying, at its active end 20a, abrasive material, preferably consisting of diamond powder.
  • a pulley 18, mounted on the spindle 16, makes it possible to drive the latter in rotation by means of a motor not shown.
  • the bracket 12 further comprises slides 22, 24 and 26 allowing, in a completely conventional manner, the movement of the grinding wheel 20 along three orthogonal axes. More specifically, the slide 22 allows, using a micrometric screw 23, to move the grinding wheel vertically along its axis, while the slides 24 and 26 allow, using the micrometric screws 25 and 27 respectively , to move the grinding wheel horizontally in two perpendicular directions.
  • the headstock 14 carries a spindle 28 whose end 28a adjacent to the bracket 12 is, by virtue of an elbow 28b, offset downward relative to the axis of rotation of the spindle.
  • a table 30 is mounted on a shaft 32 which is perpendicular to the axis of the spindle 28 and which pivots in the end 28a. This shaft carries a pulley 34 which allows it to rotate, thanks to a motor not shown in the figure.
  • a fitting 36, integral with the table 30, makes it possible to fix a plate 38, made of transparent mineral material, such as a watch glass, intended to be provided with a lens.
  • the fitting 36 has a thickness such that the distance between the upper face of the plate 38 and the axis of the spindle 28 is equal to the radius of curvature R that the lens should have.
  • the spindle 28 is associated with drive means, not shown, allowing it to impart an oscillating movement of low amplitude.
  • the active part 20a of the grinding wheel has, as shown in FIGS. 2a and 2b, a form of concave spherical cap, of radius equal to the radius of curvature of the lens.
  • the axis 40 of the shaft 32 and the axis 42 of the spindle 16 coincide when the plate 38 is horizontal ( Figure 2a). In the other positions of the plate, these two axes intersect the axis of the spindle 28, shown at 44 and form an angle a whose maximum value ⁇ max corresponds to the extreme positions of the plate.
  • the oscillating movement of the spindle 28 it is possible to increase the time between two sharpenings of the grinding wheel.
  • the oscillation movement is made possible by the fact that the diameter D of the lens is substantially greater than that of the grinding wheel.
  • the d / D ratio is between 1/3 and 2/3.
  • the relationship between the angle ⁇ max , the diameters D and d and the radius of curvature R can be expressed by the formula:
  • This relationship is used to define the maximum amplitude of bone movement cillation of the spindle, which makes it possible to produce, using a grinding wheel of given diameter, a lens of desired diameter and radius of curvature.
  • the angle ⁇ max is between 5 and 20 ° approximately.
  • the axes 40 and 42 of the shaft 32 and of the spindle 16 define a plane, coinciding with the plane of these figures and perpendicular to the axis 44 of spindle 28.
  • the axis 42 of spindle 16 is spaced from axis 44 by a value e.
  • the plate 38 is horizontal (FIG. 3a)
  • the axes of the spindle 16 and of the shaft 32 are parallel.
  • the two axes form an angle a, whose maximum value ⁇ max is obtained when the spindle 28 is at its maximum oscillation (FIG. 3b).
  • (de) is typically between D / 3 and 2D / 3, which means that the angle ⁇ max is, here too, between 5 ° and 20 °.
  • the shape of the end 20a of the grinding wheel is, in this case, a part of a torus whose radius of the generating circle is equal to the radius of curvature R of the lens and whose distance between the generating axis and the center of the circle generator is equal to e.
  • This mode of operation allows the use of a wheel of larger diameter, hence an increase in its service life, due to lower wear.
  • the adjustment of the device is however more delicate.
  • the rules relating to the minimum amplitude of the oscillation are also applicable in this variant, with the difference that for the same diameter, the arc embraced by the active part of the grinding wheel is substantially equal to half of that corresponding to the first variant, because the active part has the shape of a torus part and no longer a sphere cap.
  • connection cone would have a large angle at the top, which would be unsightly.
  • This drawback can be eliminated by using a grinding wheel whose active part 20a, in the shape of a torus part, is connected to the body of the grinding wheel by a truncated cone 20b whose angle at the top is equal to 2 a max .
  • the parts 20a and 20b can be produced independently of the body of the grinding wheel, then fixed to the latter by conventional connecting means. Thanks to the fact that the angle ⁇ max is large, the central zone of the part of the concave torus is prominent and can thus easily be truncated to allow access to the assembly means not shown in the drawing.
  • the oscillation movement is imposed on the table carrying the plate. It goes without saying that if it is the grinding wheel which oscillates, around the same axis 44, the effect obtained is identical.
  • This process lends itself particularly well to the machining of sapphire plates, but also to other materials, such as mineral glass for example.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Grinding And Polishing Of Tertiary Curved Surfaces And Surfaces With Complex Shapes (AREA)
  • Re-Forming, After-Treatment, Cutting And Transporting Of Glass Products (AREA)

Abstract

Procéde pour former une lentille convergente dans une plaque (38) d'un matériau minéral transparent qui consiste à meuler la lentille au moyen d'une meule (20) de diamètre inférieur au diamètre de la lentille et à imprimer un mouvement d'oscillation de la plaque par rapport à la meule. Ce mode de faire permet un auto-afflûtage de la meule.Method for forming a converging lens in a plate (38) of a transparent mineral material which consists in grinding the lens by means of a grinding wheel (20) of diameter smaller than the diameter of the lens and in imparting an oscillation movement of the plate in relation to the grinding wheel. This method allows self-sharpening of the grinding wheel.

Description

La présente invention concerne un procédé pour former une lentille convergente dans une plaque d'un matériau minéral transparent.The present invention relates to a method for forming a converging lens in a plate of a transparent mineral material.

Il est connu d'équiper un verre de montre d'une lentille convergente, en vue de faciliter la lecture du calendrier. Lorsque ce verre est en matériau minéral, la lentille est collée en surépaisseur. Cette solution est toutefois inesthétique et, de plus, un décollement ne peut être entièrement évité. Lorsque le verre est une matière organique, la lentille peut être noyée dans son épaisseur. Malheureusement, ce type de matériau est plus mou, donc plus facilement rayable que les matériaux minéraux, le saphir en particulier, qui confèrent au verre de montre une résistance remarquable à l'abrasion.It is known to equip a watch glass with a converging lens, in order to facilitate the reading of the calendar. When this glass is made of mineral material, the lens is glued in excess thickness. This solution is, however, unsightly and, moreover, detachment cannot be entirely avoided. When glass is an organic material, the lens can be embedded in its thickness. Unfortunately, this type of material is softer and therefore more easily scratched than mineral materials, sapphire in particular, which give watch glass remarkable resistance to abrasion.

Le but de l'invention est de fournir un procédé permettant de fabriquer des plaques en matériau minéral transparent munies d'une lentille, sans surépaisseur et sans risque de décollement.The object of the invention is to provide a method for manufacturing plates of transparent mineral material provided with a lens, without excess thickness and without risk of delamination.

Ce but est atteint en réalisant la lentille par meulage de la plaque, mais ce meulage n'est pas effectué à l'aide d'une meule dont le diamètre et le rayon de courbure correspondent au diamètre et au rayon de courbure de la lentille car cela provoque une usure plus rapide de la périphérie de la meule que de sa partie centrale.This object is achieved by making the lens by grinding the plate, but this grinding is not carried out using a grinding wheel whose diameter and radius of curvature correspond to the diameter and radius of curvature of the lens because this causes faster wear of the periphery of the grinding wheel than of its central part.

Le procédé selon l'invention constiste principalement à effectuer simultanément :

  • - une rotation de la plaque autour d'un premier axe qui est perpendiculaire à la zone où doit être formée la lentille et passe par le centre de cette zone;
  • - un meulage de ladite zone au moyen d'une meule dont la partie active a un diamètre inférieur au diamètre de la lentille et tourne autour d'un deuxième axe contenu dans un plan contenant le premier axe; et
  • - un mouvement oscillant de la meule ou de la plaque autour d'un troisième axe perpendiculaire au plan contenant les premier et deuxième axes et distant de ladite zone d'une valeur égale au rayon de courbure désiré de la lentille.
The method according to the invention mainly consists in simultaneously carrying out:
  • - A rotation of the plate around a first axis which is perpendicular to the area where the lens is to be formed and passes through the center of this area;
  • - grinding of said area by means of a grinding wheel whose active part has a diameter less than the diameter of the lens and rotates around a second axis contained in a plane containing the first axis; and
  • - an oscillating movement of the grinding wheel or the plate around a third axis perpendicular to the plane containing the first and second axes and distant from said zone by a value equal to the desired radius of curvature of the lens.

La demanderesse a en effet constaté de manière surprenante que, si l'on utilise une meule dont la partie active a un diamètre inférieur au diamètre de la lentille, et qu'on crée un mouvement d'oscillation relatif entre la meule et la plaque, la période entre deux affûtages de la meule est augmentée de façon sensible.The Applicant has in fact surprisingly found that, if a grinding wheel is used whose active part has a diameter less than the diameter of the lens, and that a relative oscillation movement is created between the grinding wheel and the plate, the period between two sharpenings of the grinding wheel is significantly increased.

Lorsque l'arc embrassé par la partie active de la meule dépasse la moitié de l'arc de la lentille, le mouvement d'oscillation a pour seule fonction d'assurer l'auto-affûtage de la meule. Si, par contre, l'arc embrassé par la partie active de la meule est inférieur à la moitié de l'arc embrassé par la lentille, le mouvement de rotation de la plaque ne peut suffire à l'usinage de toute la surface de la lentille. Pour garantir cet usinage, il faut que l'angle d'oscillation soit au moins égal à l'angle correspondant à la différence entre la moitié de l'arc embrassé par la lentille et l'arc embrassé par la partie active de la meule.When the arc embraced by the active part of the grinding wheel exceeds half of the arc of the lens, the oscillating movement has the sole function of ensuring the self-sharpening of the grinding wheel. If, on the other hand, the arc embraced by the active part of the grinding wheel is less than half of the arc embraced by the lens, the rotational movement of the plate cannot be sufficient to machine the entire surface of the lens. To guarantee this machining, the oscillation angle must be at least equal to the angle corresponding to the difference between half of the arc embraced by the lens and the arc embraced by the active part of the grinding wheel.

L'invention sera mieux comprise à la lecture de la description qui suit, faite en regard des dessins annexés dans lesquels :

  • - la figure 1 représente un dispositif permettant la mise en oeuvre de ce procédé;
  • - les figures 2, 3 et 4 représentent en coupe verticale trois arrangements différents d'une partie du dispositif représenté à la figure 1.
The invention will be better understood on reading the description which follows, made with reference to the appended drawings in which:
  • - Figure 1 shows a device for the implementation of this method;
  • - Figures 2, 3 and 4 show in vertical section three different arrangements of part of the device shown in Figure 1.

Le dispositif représenté à la figure 1 comprend un bâti-support 10 sur lequel sont montées une potence 12 et une poupée 14. La potence 12 porte une broche 16 à l'extrémité de laquelle est fixée une meule cylindrique 20, de même axe que la broche et portant, à son extrémité active 20a, de la matière abrasive, constituée de préférence par de la poudre de diamant. Une poulie 18, montée sur la broche 16, permet d'entraîner celle-ci en rotation au moyen d'un moteur non représenté. La potence 12 comporte, en outre, des coulisses 22, 24 et 26 permettant, d'une manière tout à fait classique, le déplacement de la meule 20 selon trois axes orthogonaux. De manière plus précise, la coulisse 22 permet, à l'aide d'une vis micrométrique 23, de déplacer la meule verticalement selon son axe, tandis que les coulisses 24 et 26 permettent, à l'aide des vis micrométriques 25 et 27 respectivement, de déplacer la meule horizontalement selon deux directions perpendiculaires.The device shown in Figure 1 comprises a support frame 10 on which are mounted a bracket 12 and a headstock 14. The bracket 12 carries a pin 16 at the end of which is fixed a cylindrical grinding wheel 20, of the same axis as the spindle and carrying, at its active end 20a, abrasive material, preferably consisting of diamond powder. A pulley 18, mounted on the spindle 16, makes it possible to drive the latter in rotation by means of a motor not shown. The bracket 12 further comprises slides 22, 24 and 26 allowing, in a completely conventional manner, the movement of the grinding wheel 20 along three orthogonal axes. More specifically, the slide 22 allows, using a micrometric screw 23, to move the grinding wheel vertically along its axis, while the slides 24 and 26 allow, using the micrometric screws 25 and 27 respectively , to move the grinding wheel horizontally in two perpendicular directions.

La poupée 14 porte une broche 28 dont l'extrémité 28a voisine de la potence 12 est, grâce à un coude 28b, décalée vers le bas par rapport à l'axe de rotation de la broche. Une table 30 est montée sur un arbre 32 qui est perpendiculaire à l'axe de la broche 28 et qui pivote dans l'extrémité 28a. Cet arbre porte une poulie 34 qui permet de l'entrainer en rotation, grâce à un moteur non représenté à la figure. Un posage 36, solidaire de la table 30, permet de fixer une plaque 38, en matériau minéral transparent, telle qu'un verre de montre, destinée à être munie d'une lentille.The headstock 14 carries a spindle 28 whose end 28a adjacent to the bracket 12 is, by virtue of an elbow 28b, offset downward relative to the axis of rotation of the spindle. A table 30 is mounted on a shaft 32 which is perpendicular to the axis of the spindle 28 and which pivots in the end 28a. This shaft carries a pulley 34 which allows it to rotate, thanks to a motor not shown in the figure. A fitting 36, integral with the table 30, makes it possible to fix a plate 38, made of transparent mineral material, such as a watch glass, intended to be provided with a lens.

Il va de soi que la meule 20 et le posage 36 ont des sens de rotation opposés.It goes without saying that the grinding wheel 20 and the setting 36 have opposite directions of rotation.

Le posage 36 a une épaisseur telle que la distance entre la face supérieure de la plaque 38 et l'axe de la broche 28 soit égale au rayon de courbure R que devra avoir la lentille.The fitting 36 has a thickness such that the distance between the upper face of the plate 38 and the axis of the spindle 28 is equal to the radius of curvature R that the lens should have.

La broche 28 est associée à des moyens d'entraînement, non représentés, permettant de lui imprimer un mouvement oscillant de faible amplitude.The spindle 28 is associated with drive means, not shown, allowing it to impart an oscillating movement of low amplitude.

Dans une première variante du procédé selon l'invention, la partie active 20a de la meule a, comme représenté sur les figures 2a et 2b, une forme de calotte sphérique concave, de rayon égal au rayon de courbure de la lentille. En outre, l'axe 40 de l'arbre 32 et l'axe 42 de la broche 16 coïncident lorsque la plaque 38 est horizontale (figure 2a). Dans les autres positions de la plaque, ces deux axes coupent l'axe de la broche 28, représenté en 44 et forment un angle a dont la valeur maximum αmax correspond aux positions extrêmes de la plaque.In a first variant of the method according to the invention, the active part 20a of the grinding wheel has, as shown in FIGS. 2a and 2b, a form of concave spherical cap, of radius equal to the radius of curvature of the lens. In addition, the axis 40 of the shaft 32 and the axis 42 of the spindle 16 coincide when the plate 38 is horizontal (Figure 2a). In the other positions of the plate, these two axes intersect the axis of the spindle 28, shown at 44 and form an angle a whose maximum value α max corresponds to the extreme positions of the plate.

Grâce au mouvement oscillant de la broche 28, il est possible d'augmenter le temps compris entre deux affûtages de la meule. Le mouvement d'oscillation est rendu possible du fait que de diamètre D de la lentille est sensiblement supérieur à celui d de la meule. De façon avantageuse, le rapport d/D est compris entre 1/3 et 2/3. La relation entre l'angle αmax, les diamètres D et d et le rayon de courbure R peut être exprimée par la formule :

Figure imgb0001
Thanks to the oscillating movement of the spindle 28, it is possible to increase the time between two sharpenings of the grinding wheel. The oscillation movement is made possible by the fact that the diameter D of the lens is substantially greater than that of the grinding wheel. Advantageously, the d / D ratio is between 1/3 and 2/3. The relationship between the angle α max , the diameters D and d and the radius of curvature R can be expressed by the formula:
Figure imgb0001

Cette relation sert à définir l'amplitude maximum du mouvement d'oscillation de la broche, qui permet de réaliser, à l'aide d'une meule de diamètre donné, une lentille de diamètre et de rayon de courbure désirés. A titre indicatif, pour une valeur du rayon R de courbure comprise entre une et deux fois le diamètre D de la lentille, et pour un rapport d/D compris entre 1/3 et 2/3, l'angle αmax est compris entre 5 et 20° environ.This relationship is used to define the maximum amplitude of bone movement cillation of the spindle, which makes it possible to produce, using a grinding wheel of given diameter, a lens of desired diameter and radius of curvature. As an indication, for a value of the radius R of curvature between one and twice the diameter D of the lens, and for a ratio d / D between 1/3 and 2/3, the angle α max is between 5 and 20 ° approximately.

La pratique a montré que l'auto-affûtage de la meule est d'autant meilleur que l'amplitude de l'oscillation est grande, pour un diamètre de meule donné. Dans la variante représenté aux figures 2a et 2b, cette amplitude maximum équivaut à une oscillation telle que α varie de +αmax à -αmax. Lorsque l'arc embrassé par la partie active de la meule est inférieur à la moitié de l'arc embrassé par la lentille, l'oscillation doit avoir une amplitude minimum, comprise entre αmax et αmin, αmin étant égal à αmax moins la différence des angles associés à la moitié de l'arc embrassé par la lentille et l'arc embrassé par la meule.Practice has shown that the self-sharpening of the grinding wheel is all the better as the amplitude of the oscillation is large, for a given wheel diameter. In the variant shown in Figures 2a and 2b, this maximum amplitude is equivalent to an oscillation such that α varies from + α max to -α max . When the arc embraced by the active part of the grinding wheel is less than half of the arc embraced by the lens, the oscillation must have a minimum amplitude, between α max and α min , α min being equal to α max minus the difference of the angles associated with half of the arc embraced by the lens and the arc embraced by the grinding wheel.

Dans la deuxième variante du procédé selon l'invention, représentée aux figures 3a et 3b, les axes 40 et 42 de l'arbre 32 et de la broche 16 définissent un plan, coïncidant avec le plan de ces figures et perpendiculaire à l'axe 44 de la broche 28. L'axe 42 de la broche 16 est distant de l'axe 44 d'une valeur e. Lorsque la plaque 38 est horizontale (figure 3a), les axes de la broche 16 et de l'arbre 32 sont parallèles. Dans les autres positions, les deux axes forment un angle a, dont la valeur maximum αmax est obtenue lorsque la broche 28 est au maximum de son oscillation (figure 3b). Celle-ci ne peut se faire que de la position horizontale vers une position inclinée dans laquelle le côté de la lentille opposé à l'axe 42 est surélevé (figure 3b). Un basculement dans l'autre sens aurait pour effet de mettre en contact la meule 20 et le cône de raccordement 46, ce qui détériorerait la meule et altèrerait l'état de surface du cône 46. Dans cette variante, la relation entre les différents paramètres peut être exprimé par la formule :

Figure imgb0002
In the second variant of the method according to the invention, shown in FIGS. 3a and 3b, the axes 40 and 42 of the shaft 32 and of the spindle 16 define a plane, coinciding with the plane of these figures and perpendicular to the axis 44 of spindle 28. The axis 42 of spindle 16 is spaced from axis 44 by a value e. When the plate 38 is horizontal (FIG. 3a), the axes of the spindle 16 and of the shaft 32 are parallel. In the other positions, the two axes form an angle a, whose maximum value α max is obtained when the spindle 28 is at its maximum oscillation (FIG. 3b). This can only be done from the horizontal position to an inclined position in which the side of the lens opposite the axis 42 is raised (Figure 3b). A tilt in the other direction would have the effect of bringing the grinding wheel 20 into contact with the connection cone 46, which would deteriorate the grinding wheel and alter the surface condition of the cone 46. In this variant, the relationship between the different parameters can be expressed by the formula:
Figure imgb0002

La valeur de (d-e) est typiquement comprise entre D/3 et 2D/3, ce qui fait que l'angle αmax est, ici aussi, compris entre 5° et 20°.The value of (de) is typically between D / 3 and 2D / 3, which means that the angle α max is, here too, between 5 ° and 20 °.

Plus la distance e est grande, plus le diamètre de la meule peut être augmenté. Si toutefois la meule a un diamètre trop grand, la forme du cône 46 (figures 3a et 3b) qui entoure la lentille est déformée, dans le sens de l'élargissement, ce qui est préjudiciable à l'esthétique du produit.The greater the distance e, the more the diameter of the grinding wheel can be increased. If, however, the grinding wheel has too large a diameter, the shape of the cone 46 (FIGS. 3a and 3b) which surrounds the lens is deformed, in the direction of widening, which is detrimental to the aesthetics of the product.

Cet inconvénient peut être évité si le diamètre d de la meule, le diamètre D de la lentille, et l'angle αmax répondent à l'inégalité :

Figure imgb0003
This drawback can be avoided if the diameter d of the grinding wheel, the diameter D of the lens, and the angle α max respond to the inequality:
Figure imgb0003

La forme de l'extrémité 20a de la meule est, dans ce cas, une partie de tore dont le rayon du cercle générateur est égal au rayon de courbure R de la lentille et dont la distance entre l'axe générateur et le centre du cercle générateur est égale à e. Ce mode de faire permet d'utiliser une meule de plus grand diamètre, d'où une augmentation de sa durée de vie, à cause d'une usure plus faible. Le réglage du dispositif est toutefois plus délicat.The shape of the end 20a of the grinding wheel is, in this case, a part of a torus whose radius of the generating circle is equal to the radius of curvature R of the lens and whose distance between the generating axis and the center of the circle generator is equal to e. This mode of operation allows the use of a wheel of larger diameter, hence an increase in its service life, due to lower wear. The adjustment of the device is however more delicate.

Les règles relatives à l'amplitude minimum de l'oscillation sont aussi applicable dans cette variante, avec toutefois la différence que pour un même diamètre, l'arc embrassé par la partie active de la meule est sensiblement égale à la moitié de celui correspondant à la première variante, du fait que la partie active a la forme d'une partie de tore et non plus d'une calotte de sphère.The rules relating to the minimum amplitude of the oscillation are also applicable in this variant, with the difference that for the same diameter, the arc embraced by the active part of the grinding wheel is substantially equal to half of that corresponding to the first variant, because the active part has the shape of a torus part and no longer a sphere cap.

La variante représentée aux figures 4a et 4b s'apparente à celle des figures 3a et 3b avec toutefois un angle a qui n'est jamais nul. Ces conditions de travail sont obtenues en faisant osciller la broche 28 entre deux positions extrêmes pour lesquelles les axes 40 et 42 forment des angles αmin (figure 4a), tel que la meule soit en contact avec la partie centrale de la lentille, et a max (figure 4b), tel que la meule soit en contact avec la zone périphérique de la lentille.The variant shown in Figures 4a and 4b is similar to that of Figures 3a and 3b with however an angle a which is never zero. These working conditions are obtained by oscillating the spindle 28 between two extreme positions for which the axes 40 and 42 form angles α min (FIG. 4a), such that the grinding wheel is in contact with the central part of the lens, and a max (Figure 4b), such that the grinding wheel is in contact with the peripheral zone of the lens.

Si dans ce cas, on utilisait une meule similaire à celle des figures 3a et 3b, le cône de raccordement aurait un grand angle au sommet, ce qui serait inesthétique. Cet inconvénient peut être éliminé en utilisant une meule dont la partie active 20a, en forme de partie de tore est reliée au corps de la meule par un tronc de cône 20b dont l'angle au sommet est égal à 2 amax. Dans ce cas, les parties 20a et 20b peuvent être fabriquées indépendament du corps de la meule, puis fixées à celui-ci par des moyens de liaison classiques. Grâce au fait que l'angle αmax est important, la zone centrale de la partie de tore concave est proéminante et peut ainsi facilement être tronquée pour permettre l'accès aux moyens d'assemblage non représentés au dessin.If in this case, a grinding wheel similar to that of FIGS. 3a and 3b was used, the connection cone would have a large angle at the top, which would be unsightly. This drawback can be eliminated by using a grinding wheel whose active part 20a, in the shape of a torus part, is connected to the body of the grinding wheel by a truncated cone 20b whose angle at the top is equal to 2 a max . In that case, the parts 20a and 20b can be produced independently of the body of the grinding wheel, then fixed to the latter by conventional connecting means. Thanks to the fact that the angle α max is large, the central zone of the part of the concave torus is prominent and can thus easily be truncated to allow access to the assembly means not shown in the drawing.

Dans les trois variantes décrites, le mouvement d'oscillation est imposé à la table portant la plaque. Il va de soit que si c'est la meule qui oscille, autour du même axe 44, l'effet obtenu est identique.In the three variants described, the oscillation movement is imposed on the table carrying the plate. It goes without saying that if it is the grinding wheel which oscillates, around the same axis 44, the effect obtained is identical.

Les essais mécaniques effectués avec des plaques réalisées selon ce procédé ont montré que, pour une épaisseur de saphir de 0,6 mm, et pour une épaisseur de lentille égale à 0,2 mm, la résistance mécanique de la plaque n'est nullement affectée.The mechanical tests carried out with plates produced according to this method have shown that, for a thickness of sapphire of 0.6 mm, and for a lens thickness equal to 0.2 mm, the mechanical resistance of the plate is in no way affected. .

Ce procédé se prête particulièrement bien à l'usinage de plaques en saphir, mais aussi à d'autres matériaux, tels que le verre minéral par exemple.This process lends itself particularly well to the machining of sapphire plates, but also to other materials, such as mineral glass for example.

Claims (5)

1. Procédé pour former une lentille convergente dans une plaque d'un matériau minéral transparent, caractérisé en ce qu'il consiste à effectuer simultanément : - une rotation de ladite plaque autour d'un premier axe qui est perpendiculaire à la zone où doit être formée ladite lentille et passe par le centre de cette zone; - un meulage de ladite zone au moyen d'une meule dont la partie active a un diamètre inférieur au diamètre de la lentille et tourne autour d'un deuxième axe; - un mouvement oscillant de la plaque ou de la meule autour d'un troisième axe, perpendiculaire au plan contenant les premier et deuxième axes coupant ledit premier axe et distant de ladite zone d'une valeur égale au rayon de courbure désiré de la lentille. 1. Method for forming a converging lens in a plate of a transparent mineral material, characterized in that it consists in simultaneously carrying out: - A rotation of said plate about a first axis which is perpendicular to the area where said lens is to be formed and passes through the center of this area; - a grinding of said zone by means of a grinding wheel whose active part has a diameter less than the diameter of the lens and rotates around a second axis; - An oscillating movement of the plate or the grinding wheel around a third axis, perpendicular to the plane containing the first and second axes intersecting said first axis and distant from said area by a value equal to the desired radius of curvature of the lens. 2. Procédé selon la revendication 1, caractérisé en ce que le deuxième axe coupe le troisième axe et en ce que la partie active de ladite meule a une forme de calotte sphérique concave, de rayon égal au rayon de courbure de la lentille.2. Method according to claim 1, characterized in that the second axis intersects the third axis and in that the active part of said grinding wheel has the shape of a concave spherical cap, of radius equal to the radius of curvature of the lens. 3. Procédé selon la revendication 1, caractérisé en ce que les deuxième et troisième axes sont éloignés l'un de l'autre d'une valeur constante non nulle et que la partie active de la meule a la forme d'une partie de tore concave, dont l'axe générateur coïncide avec ledit deuxième axe, dont le rayon du cercle générateur est égal au rayon de courbure de la lentille et dont la distance entre l'axe générateur et le centre du cercle générateur est égal à la distance entre les deuxième et troisième axes.3. Method according to claim 1, characterized in that the second and third axes are spaced from each other by a non-zero constant value and that the active part of the grinding wheel has the shape of a torus part concave, the generating axis of which coincides with said second axis, the radius of the generating circle of which is equal to the radius of curvature of the lens and the distance of which between the generating axis and the center of the generating circle is equal to the distance between the second and third axes. 4. Procédé selon la revendication 3, caractérisé en ce que le diamètre d de la meule, le diamètre D de la lentille et l'angle maximum a max que forment les premier et deuxième axes répondent à l'inégalité : D cos αmax ≧ d. 4. Method according to claim 3, characterized in that the diameter d of the grinding wheel, the diameter D of the lens and the maximum angle a max that form the first and second axes respond to the inequality: D cos α max ≧ d. 5. Procédé selon la revendication 4, dans lequel ladite meule comporte un corps de forme cylindrique, caractérisé en ce que ledit corps est relié à la partie active de la meule par un tronc de cône, dont la partie la plus étroite est attenante audit corps, l'angle au sommet dudit cône étant égal à 2 a max 5. Method according to claim 4, wherein said grinding wheel comprises a body of cylindrical shape, characterized in that said body is connected to the active part of the grinding wheel by a truncated cone, the narrowest part of which is adjacent to said body , the angle at the top of said cone being equal to 2 a max
EP84103309A 1983-03-31 1984-03-26 Method of shaping a convergent lens in a plate made of a transparent mineral material Expired EP0123891B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CH1800/83 1983-03-31
CH1800/83A CH651773A5 (en) 1983-03-31 1983-03-31 PROCESS FOR FORMING A CONVERGENT LENS IN A PLATE OF TRANSPARENT MINERAL MATERIAL.

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EP0123891A2 true EP0123891A2 (en) 1984-11-07
EP0123891A3 EP0123891A3 (en) 1986-02-05
EP0123891B1 EP0123891B1 (en) 1988-05-18

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EP (1) EP0123891B1 (en)
JP (1) JPS59187449A (en)
CH (1) CH651773A5 (en)
DE (1) DE3471270D1 (en)
SG (1) SG38991G (en)

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US6406769B1 (en) 1998-04-02 2002-06-18 Comadur S.A. Watch crystal including a lens and manufacturing method for such a lens
KR101277818B1 (en) * 2006-01-25 2013-06-21 구알라 크로져 에스.피.에이. A tamper evident closure for bottles containing valuable drinks
EP1567305B1 (en) * 2002-11-26 2014-04-16 Comadur S.A. Method for shaping an optical surface

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EP0257013B1 (en) * 1986-08-19 1992-01-02 Léon Biebuyck Method and apparatus for mechanically grinding and polishing a surface of a mineral material, especially glass
US6406769B1 (en) 1998-04-02 2002-06-18 Comadur S.A. Watch crystal including a lens and manufacturing method for such a lens
EP1567305B1 (en) * 2002-11-26 2014-04-16 Comadur S.A. Method for shaping an optical surface
KR101277818B1 (en) * 2006-01-25 2013-06-21 구알라 크로져 에스.피.에이. A tamper evident closure for bottles containing valuable drinks

Also Published As

Publication number Publication date
DE3471270D1 (en) 1988-06-23
EP0123891A3 (en) 1986-02-05
JPS59187449A (en) 1984-10-24
US4584799A (en) 1986-04-29
CH651773A5 (en) 1985-10-15
EP0123891B1 (en) 1988-05-18
SG38991G (en) 1991-07-26

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