EP0123891B1 - 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
EP0123891B1
EP0123891B1 EP84103309A EP84103309A EP0123891B1 EP 0123891 B1 EP0123891 B1 EP 0123891B1 EP 84103309 A EP84103309 A EP 84103309A EP 84103309 A EP84103309 A EP 84103309A EP 0123891 B1 EP0123891 B1 EP 0123891B1
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Prior art keywords
axis
lens
plate
grinding member
radius
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EP84103309A
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German (de)
French (fr)
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EP0123891A3 (en
EP0123891A2 (en
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Claude-Michel Juvet
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Comadur SA
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Comadur SA
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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 round converging lens and included in the thickness of a plate of a transparent mineral material.
  • US-A 3,905,163 describes a method for machining lenses in the thickness of the plate.
  • each lens is formed by first digging a groove which surrounds the part of the plate intended to comprise it, then machining the lens by successive grindings, to rough it, form it, then polish it.
  • the lenses thus produced are large, which is not the case for example when the plate is a watch glass.
  • the object of the present invention is to remedy this drawback.
  • the oscillating movement is controlled in synchronism with the rotation movement of the plate around the second axis, thanks to a cam secured to the support of the plate, which cooperates with a finger secured to the frame of the machine. .
  • This oscillating movement is to move the grinding wheel relative to the center of the plate, to define the outline of the converging lens, the shape of which is advantageously non-circular.
  • the grinding wheel must have a diameter sufficient to sweep the entire surface to be machined at each revolution of the plate.
  • the method is not intended to form a converging lens included in the thickness of a plate. In addition, it does not achieve the goal defined above.
  • 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 makes it possible to drive it in rotation, 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 a max , the diameters D and d and the radius of curvature R can be expressed by the formula: This relation is used to define the maximum amplitude of the oscillating movement 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 a max is between 5 and 20 ° approximately.
  • this maximum amplitude is equivalent to an oscillation such that a varies from + Qmax to -a max '
  • the oscillation must have a minimum amplitude, between a max and a mln , a min being equal to a max minus the difference of the angles associated with half of the arc embraced by the lens and the arc kissed by the millstone.
  • 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, the maximum value a max of which is obtained when the spindle 28 is at its maximum oscillation (FIG. 3b).
  • 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 however 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 form 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 amax.
  • the parts 20a and 20b can be produced independently of the body of the grinding wheel, and then fixed to the latter by conventional connecting means. Thanks to the fact that the angle a max is important, the central area of the concave torus portion 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)

Description

La présente invention concerne un procédé pour former une lentille convergente ronde et comprise dans l'épaisseur d'une plaque d'un matériau minéral transparent.The present invention relates to a method for forming a round converging lens and included in the thickness of 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.

C'est pourquoi il est souhaitable d'utiliser des verres en matériau minéral, munis d'une lentille convergente comprise dans leur épaisseur.This is why it is desirable to use glasses of mineral material, provided with a converging lens included in their thickness.

Le brevet US-A 3.905.163 décrit un procédé permettant d'usiner des lentilles dans l'épaisseur de la plaque. Dans ce brevet, chaque lentille est formée en commençant par creuser une gorge qui entoure la partie de la plaque destinée à la comporter, puis à usiner la lentille par meulages successifs, pour l'ébaucher, la former, puis la polir. Tout laisse supposer que les lentilles ainsi réalisées sont de grande dimension, ce qui n'est pas le cas par exemple lorsque la plaque est un verre de montre.US-A 3,905,163 describes a method for machining lenses in the thickness of the plate. In this patent, each lens is formed by first digging a groove which surrounds the part of the plate intended to comprise it, then machining the lens by successive grindings, to rough it, form it, then polish it. Everything suggests that the lenses thus produced are large, which is not the case for example when the plate is a watch glass.

Or, on a constaté que, dans ce procédé, la meule s'use rapidement à sa périphérie, ce qui modifie la courbure de la lentille, spécialement lorsque cette dernière est petite.However, it has been found that, in this process, the grinding wheel quickly wears at its periphery, which modifies the curvature of the lens, especially when the latter is small.

Le but de la présente invention est de remédier à cet inconvénient.The object of the present invention is to remedy this drawback.

Ce but est atteint grâce aux caractéristiques particulières que présente le procédé de la revendication 1.This object is achieved thanks to the particular characteristics which the process of claim 1 exhibits.

Il était certes connu par le brevet US―A―1.491.383 d'usiner une plaque en matériau minéral transparent, de manière qu'elle comporte une lentille convergente dans sa partie centrale, au moyen d'un procédé voisin de celui de la revendication 1. Dans ce procédé, la périphérie de la plaque est amincie en effectuant simultanément une rotation de la plaque autour d'un premier axe perpendiculaire à la zone comportant la lentille convergente, et passant par le centre de cette zone, un meulage de la périphérie, au moyen d'une meule tournant autour d'un deuxième axe, et un mouvement oscillant de la plaque autour d'un troisième axe, perpendiculaire au plan contenant les premier et deuxième, axes et coupant le premier axe. Il faut relever que dans ce cas, le mouvement oscillant est commandé en synchronisme avec le mouvement de rotation de la plaque autour du deuxième axe, grâce à une came solidaire du support de la plaque, qui coopère avec un doigt solidaire du bâti de la machine.It was certainly known from US patent ― A ― 1,491,383 to machine a plate of transparent mineral material, so that it has a converging lens in its central part, by a process similar to that of claim 1. In this method, the periphery of the plate is thinned by simultaneously rotating the plate around a first axis perpendicular to the zone comprising the converging lens, and passing through the center of this zone, grinding the periphery , by means of a grinding wheel rotating around a second axis, and an oscillating movement of the plate around a third axis, perpendicular to the plane containing the first and second axes and intersecting the first axis. It should be noted that in this case, the oscillating movement is controlled in synchronism with the rotation movement of the plate around the second axis, thanks to a cam secured to the support of the plate, which cooperates with a finger secured to the frame of the machine. .

Ce mouvement oscillant a pour but de déplacer la meule par rapport au centre de la plaque, pour définir le contour de la lentille convergente, dont la forme est avantageusement non circulaire.The purpose of this oscillating movement is to move the grinding wheel relative to the center of the plate, to define the outline of the converging lens, the shape of which is advantageously non-circular.

Dans ces conditions, il va de soi que la meule doit avoir un diamètre suffisant pour balayer toute la surface à usiner à chaque tour de la plaque.Under these conditions, it goes without saying that the grinding wheel must have a diameter sufficient to sweep the entire surface to be machined at each revolution of the plate.

Le procédé n'est pas destiné à former une lentille convergente comprise dans l'épaisseur d'une plaque. De plus, il ne permet pas d'attein- dre le but défini ci-dessus.The method is not intended to form a converging lens included in the thickness of a plate. In addition, it does not achieve the goal defined above.

Dans le procédé selon l'invention, 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'au- toaffûtage de la meule. Si, par contre, l'arc embrassé par la partie active de la meule est inférieur à la motié 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.In the method according to the invention, when the arc embraced by the active part of the grinding wheel exceeds half of the arc of the lens, the only function of the oscillating movement is to ensure 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 the 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:
  • FIG. 1 represents a device allowing the implementation of this method;
  • FIGS. 2, 3 and 4 show in vertical section three different arrangements of a part of the device shown in FIG. 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'entraîner 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 makes it possible to drive it in rotation, 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 le 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 amax, les diamètres D et d et le rayon de courbure R peut être exprimée par la formule:

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 amax est compris entre 5 et 20° environ.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 a max , the diameters D and d and the radius of curvature R can be expressed by the formula:
Figure imgb0001
 This relation is used to define the maximum amplitude of the oscillating movement 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 a 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 a varie de +Qmax à -amax' 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 amax et amln, amin étant égal à amax 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 a varies from + Qmax to -a max ' When the arc embraced by the active part of the grinding wheel is less than half the arc embraced by the lens, the oscillation must have a minimum amplitude, between a max and a mln , a min being equal to a max minus the difference of the angles associated with half of the arc embraced by the lens and the arc kissed by the millstone.

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 t'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 amax 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
La valeur de (d-e) est typiquement comprise entre D/3 et 2D/3, ce qui fait que l'angle amax est, ici aussi, compris entre 5° et 20°.In the second variant of the method according to the invention, represented 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, the maximum value a max of which 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). Tilting 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
 The value of (de) is typically between D / 3 and 2D / 3, so that the angle a 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 amax 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 a 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 however 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 amin (figure 4a), tel que la meule soit en contact avec la partie centrale de la lentille, et amax (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 a 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 amax 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 form 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 amax. In this case, the parts 20a and 20b can be produced independently of the body of the grinding wheel, and then fixed to the latter by conventional connecting means. Thanks to the fact that the angle a max is important, the central area of the concave torus portion 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.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. A method of forming a round convergent lens within the thickness of a plate of transparent mineral material, characterised in that it simultaneously involves:
-rotating said plate about a first axis which is perpendicular to the region where said lens is to be formed and which extends through the centre of said region;
-grinding said region with a grinding member having an operative portion which has a diameter less than the diameter of the lens and which rotates about a second axis;
-oscillating the plate or the grinding member about a third axis perpendicular to the plane containing the first and second axes, intersecting said first axis and located at a distance from said region equal to the radius of curvature required for the lens; and
-independently controlling the drive means for rotating the plate about the first axis and the means for oscillating the plate or the grinding member about the third axis.
2. A method according to claim 1, characterised in that the second axis intersects the third axis and in that the operative portion of said grinding member defines a round concave surface having a radius equal to the radius of curvature of the lens.
3. A method according to claim 1, characterised in that the second and third axes are spaced a constant distance apart from each other by a constant value not equal to zero and in that the operative portion of the grinding member is shaped as a portion of a concave torus whose generating axis coincides with said second axis, and whose generating circle has a radius equal to the radius of curvature of the lens, the distance between the generating axis and the centre of the generating circle being equal to the distance between the second and third axes.
4. A method according to claim 3, characterised in that the diameter d of the grinding member, the diameter D of the lens and the maximum angle amax formed by the first and second axes fit the inequality: D cos amax≥d.
5. A method according to claim 4, wherein said grinding member has a body of cylindrical shape, characterised in that said body is connected to the operative portion of the grinding member by a frustum of a cone whose narrow portion adjoins said body, the angle at the apex of said cone being 2 amaxo
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
CH1800/83A CH651773A5 (en) 1983-03-31 1983-03-31 PROCESS FOR FORMING A CONVERGENT LENS IN A PLATE OF TRANSPARENT MINERAL MATERIAL.
CH1800/83 1983-03-31

Publications (3)

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

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EP84103309A Expired EP0123891B1 (en) 1983-03-31 1984-03-26 Method of shaping a convergent lens in a plate made of a transparent mineral material

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US (1) US4584799A (en)
EP (1) EP0123891B1 (en)
JP (1) JPS59187449A (en)
CH (1) CH651773A5 (en)
DE (1) DE3471270D1 (en)
SG (1) SG38991G (en)

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Also Published As

Publication number Publication date
US4584799A (en) 1986-04-29
EP0123891A3 (en) 1986-02-05
DE3471270D1 (en) 1988-06-23
JPS59187449A (en) 1984-10-24
EP0123891A2 (en) 1984-11-07
SG38991G (en) 1991-07-26
CH651773A5 (en) 1985-10-15

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