EP1871572B1 - Method of machining a face of an ophthalmic lens that is prism-ballasted at the centre - Google Patents

Abstract

The invention relates to a method of machining a face (3) of an ophthalmic lens (1) with a main machining step in which the position of a machining tool (8) is synchronised with the angular position of the ophthalmic lens (1) which is rotated around an axis of rotation (4) that is transverse to the face (3), in order to provide the face with a machined surface that is asymmetrical in relation to the axis of rotation (4) of the ophthalmic lens (1); and a complementary machining step in which a recess (22) is machined around the axis of rotation (4) of the lens (1).

Description

The invention relates to the field of manufacturing ophthalmic lenses intended to be inserted into a spectacle frame adapted to correct the view of a wearer.

It relates more particularly to a method of machining a face of such an ophthalmic lens.

The manufacture of an ophthalmic lens generally comprises a first phase during which is produced by molding and / or machining a blank having an edge delimited by a front face and a rear face, and a second phase during which the blank is cut off, that is to say that its edge is machined to move to a shape suitable for insertion into a given spectacle frame.

During the first phase, correction properties corresponding to the prescription of the future wearer are conferred on the ophthalmic lens by the shape and the relative dispositions of the front and rear faces (the rear face being that which is turned towards the wearer's eye). corrective glasses).

Some ophthalmic lenses, in particular so-called "progressive" lenses correcting presbyopia, have an asymmetrical front face or rear face with respect to the longitudinal axis of the cylinder formed by the edge of the uncut lens.

When a face of the lens is symmetrical relative to this longitudinal axis, this face can be machined on the blank by the implementation of a conventional turning method, the blank being rotated about said axis while a machining tool comes into contact with the lens to machine this symmetrical face.

On the other hand, when an asymmetric face is to be produced, conventional turning methods can no longer be used in that they only allow machining symmetrical shapes relative to the axis of rotation of the workpiece.

One solution for machining asymmetric surfaces is to implement a milling process in which a rotary milling tool, movable relative to the blank, machines the asymmetric face. These milling methods applied to the field of ophthalmic lenses generally provide a quality of finishing inferior to that afforded by a turning process.

Another solution allows the implementation of a turning process for machining on the blank an asymmetrical face. This is a process in which the ophthalmic lens is rotated about the longitudinal axis traversing the faces of the lens while a machining tool is synchronized with the angular position of the ophthalmic lens in such a way that to follow the asymmetrical shape that it must machine on the lens.

The documents EP 1 449 616 and GB 2,058,619 describe such a method for machining an asymmetrical face on a lens rotated by a turning device.

The object of the invention is to improve this type of process.

For this purpose, the invention provides a method of machining by turning a face of an ophthalmic lens according to claim 1.

Such a machining method makes it possible to erect a centrally prismatic surface on a lens driven in rotation by minimizing or even eliminating the residual volume of material responsible for a reverse machining phenomenon.

Indeed, during a machining operation of a centrally prismed face where the position of a machining tool is synchronized with the angular position of the ophthalmic lens driven in rotation, the surface to be machined is asymmetrical around of the axis of rotation of the lens, that is to say that the normal to the surface at the point of intersection with the axis of rotation of the lens forms an angle with said axis of rotation. When the machining tool approaches the axis of rotation of the part during its work, a portion of the material to be removed requires that a portion of the tool continues its progression beyond the axis of rotation of the room.

This residual volume, which is called "nipple", is therefore removed by forcing the tool to work intermittently backwards, that is to say with a direction of relative movement between the lens and the tool that is at the opposite of the direction of work for which the tool was intended.

Insofar as the method according to the invention makes it possible to minimize or even eliminate the mentioned pin, the tool is constantly or almost constantly in nominal use. This use is called "nominal" in that it is that provided by the manufacturer of the tool. The use of the tool in the direction provided for in its specifications makes it possible to avoid premature wear of the tool or occasional damage.

According to a preferred feature, said recess defines a portion of said asymmetrical surface.

Said complementary machining step may also be carried out by means of the machining tool, or else by means of a tool distinct from the machining tool.

According to another preferred feature, said complementary machining step is performed without synchronizing the position of a tool for machining the recess with the angular position of the ophthalmic lens rotated.

Moreover, the machining of the recess can be achieved by moving a tool towards the axis of rotation of the ophthalmic lens. The advance of said tool can be stopped when the center of the tool is positioned on the axis of rotation of the ophthalmic lens.

The recess may include an edge passing through the axis of rotation of the ophthalmic lens.

According to a preferred characteristic, a residual volume of material is adapted to be machined downwards by the machining tool during the main machining step, this residual volume being substantially centered with respect to the axis of rotation of the ophthalmic lens. This residual volume can be machined during the main machining step or, conversely, the main machining step can be stopped before machining said residual volume.

• les figures 1 et 2 représentent une lentille ophtalmique progressive, respectivement vue de profil et vue de dessus, qui peut être obtenue grâce à un procédé selon l'invention ;
• la figure 3 est une vue en perspective représentent schématiquement un outil d'usinage adapté à coopérer en tournage avec une pièce cylindrique prismée entraînée en rotation ;
• les figures 4 et 5 représentent l'outil d'usinage de la figure 3, respectivement vu de profil et vu de face ;
• les figures 6 et 7 représentent schématiquement deux modes de travail de l'outil des figures 4 et 5, respectivement un mode nominal et un mode à rebours ;
• la figure 8 représente schématiquement l'outil d'usinage et la surface prismée de la figure 3 ;
• la figure 9 montre une phase d'usinage de la surface prismée par l'outil ;
• la figure 10 montre la même phase d'usinage que la figure 9, après que la pièce prismée ait subi une rotation de 180° ;
• la figure 11 représente schématiquement et simultanément les vues des figures 9 et 10 ;
• les figures 12 à 17 montrent chronologiquement l'étape complémentaire d'usinage d'un évidement du procédé d'usinage selon l'invention ;
• les figures 18 à 22 montrent chronologiquement l'étape du procédé d'usinage selon l'invention qui suit ladite étape complémentaire des figures 12 à 17 ;
• la figure 23 montre le volume résiduel de matière qui est usiné avec l'outil travaillant à rebours ;
• les figures 24 à 27 montrent chronologiquement une opération d'usinage de la surface prismée par l'outil sans usinage préalable d'un évidement ;
• la figure 28 représente le volume résiduel de matière à usiner avec l'outil fonctionnant à rebours, dans le cas de l'opération d'usinage des figures 24 à 27.

Other features and advantages of the invention appear in the light of the description which follows in a preferred embodiment given by way of non-limiting example, description made with reference to the accompanying drawings in which:

• the Figures 1 and 2 represent a progressive ophthalmic lens, respectively seen in profile and seen from above, which can be obtained by means of a method according to the invention;
• the figure 3 is a perspective view schematically show a machining tool adapted to cooperate in turning with a cylindrical part prismée rotated;
• the Figures 4 and 5 represent the machining tool of the figure 3 , respectively seen in profile and seen from the front;
• the Figures 6 and 7 schematically represent two working modes of the tool of the Figures 4 and 5 , respectively a nominal mode and a countdown mode;
• the figure 8 schematically represents the machining tool and the prismed surface of the figure 3 ;
• the figure 9 shows a machining phase of the surface prismed by the tool;
• the figure 10 shows the same machining phase as the figure 9 after the prism piece has been rotated 180 °;
• the figure 11 schematically and simultaneously represents the views of figures 9 and 10 ;
• the Figures 12 to 17 show chronologically the complementary step of machining a recess of the machining method according to the invention;
• the Figures 18 to 22 show chronologically the step of the machining method according to the invention which follows said complementary step of Figures 12 to 17 ;
• the figure 23 shows the residual volume of material that is machined with the tool working backwards;
• the Figures 24 to 27 show chronologically a machining operation of the surface prismed by the tool without prior machining of a recess;
• the figure 28 represents the residual volume of material to be machined with the tool running backwards, in the case of the machining operation of the Figures 24 to 27 .

The Figures 1 and 2 report the shape of a progressive ophthalmic lens 1. The top view of the figure 2 shows that this lens 1 has a circular contour. This circular contour will then be machined to match the contour of the eyeglass frame chosen.

The figure 1 shows the typical profile of such a progressive lens 1. This lens 1 has a rear face 2 whose curvature is regular, and a front face 3 whose curvature strongly increases in a particular area of the lens 1.

The lens 1 therefore has no rotational symmetry with respect to a longitudinal axis 4 passing through the center of the circular contour of the lens 1.

To obtain such a lens 1, it is common to start from a cylinder of raw material, the rear face 2 having possibly been premolded, and to proceed with a machining of the front face 3 from the blank 5 diagrammatically dotted on the figure 1 .

Due to the asymmetry of the front face 3 of the lens 1 relative to the axis 4, this face 3 can be obtained by turning only by synchronizing the position of a machining tool with the angular position of the ophthalmic lens rotated about the axis 4.

In order to simplify the description of the method according to the invention, turning operations will be described with reference to the schematized example to the figure 3 and machining a blank 5 '(hereinafter referred to as "blank 5'") having a prismed surface 6.

More specifically, the operations which will be described as an example thereafter aim to mechanically remove a layer of material 7 of constant thickness from the prismed surface 6 of the blank 5 'during turning operations using a tool 8 associated with a tool holder 9.

The crude 5 'is rotated in the direction 10 about an axis 4' while the tool 8 is movable in the direction 11 parallel to the axis 4 'and in the direction 12 transverse to the axis 4 .

A not shown turning device is adapted to drive the stock 5 'in rotation in the direction 10 and to synchronize the position of the tool 8 in the direction 11 with this rotation, as explained below.

The normal 13 to the prismed surface 6 does not extend along the axis 4 ', which is a consequence of the asymmetry of this surface 6 with respect to the axis 4'.

Although, for the sake of clarity of the description, the operations that will be described later aim to remove a layer 7 of constant thickness of a crude 5 'in the configuration of the figure 3 these operations can be applied to any surface whose normal to the center is distinct from the longitudinal axis of the part, and in particular to the progressive ophthalmic lens of Figures 1 and 2 .

The machining tool 8 shown in figure 3 is shown in detail at Figures 4 and 5 , respectively of profile and face.

This tool 8 has a generally circular shape and has a working face 14 forming a cutting edge with a lateral bevel 15 connecting the working face 14 to a rear face 16 having a smaller diameter than the working face 14.

This tool 8 is held in a tool holder 9, in accordance with the figure 3 by a screw (not shown) fixing the center 17 of the tool 8 to the tool holder 9, or by any means for rigidly binding the tool 8 to the tool holder 9 so that the cutting edge is available on at least a portion of the circumference of the tool 8 for machining the stock 5 '.

The tool 8 may be made of polycrystalline diamond, monocrystalline diamond, or any other material suitable for producing a turning tool.

The Figures 6 and 7 show the turning tool 8 respectively in a so-called "nominal" cut configuration and in a so-called "reverse" cut configuration.

The figure 6 shows that, in the nominal cutting configuration, the rough 5 'to be machined is rotated in the direction 18 and the tool 8 is positioned so that its cutting edge attacks the layer 7 to be removed by its working face 14 This is the configuration for which such a tool 8 has been provided.

The figure 7 , on the other hand, shows tool 8 in the same position as that of figure 6 , while the crude 5 'is rotated in the direction 18' which is the reverse of the direction 18 of the figure 6 . The tool 8 works here in reverse, that is to say that the layer 7 of material to be removed is attacked by the bevel 15 and not by the working face 14. In this configuration, these chips 19 'are still products and the layer 7 of material is effectively removed but it is an improper use of the tool 8 may cause premature wear, or even immediate damage to the cutting edge of the tool 8.

During machining, the tool 8 must therefore be used to the maximum in its nominal configuration rather than in its backward configuration.

The figure 8 is a schematic view showing the elements of the figure 3 , namely the tool 8 (here without its tool holder 9 to simplify the drawing), the surface 6 of the blank 5 'and the layer 7 of material to be machined schematically between the solid line and the dotted line.

The prismed surface 6 is rotated around the axis 4 '.

The turning technique used here for machining the layer 7 of the stock 5 'with the tool 8 makes it possible, in accordance with the figure 9 , to approach the tool 8 of the crude 5 ', which is rotated, to proceed to the machining of the layer 7 at a machining line 20 from which the chips are formed.

The figure 10 also shows the machining of the layer 7 by the tool 8 while the crude 5 'has rotated 180 ° relative to its position of the figure 9 , during his continuous training in rotation. This figure 10 shows that the tool 8, to continue the machining of the layer 7 at the machining line 20, has moved parallel to the axis of rotation 4 'of a distance depending on the asymmetry from the surface 6.

This machining technique allows the tool 8 to be permanently in contact with the layer 7 of material to be machined (although it is asymmetric) driven in rotation, and this thanks to the synchronization of the position of the tool 8 with the angular position of the crude 5 '.

The operations performed according to this machining technique will subsequently be described with reference to a representation in accordance with the figure 11 in which the observer is placed in the frame of the rough 5 ', which is considered immobile, while it is the tool 8 which is considered to be rotatable about the axis 4' in the direction 21. This representation, although equivalent to that of figures 9 and 10 in terms of the relative movements of the tool 8 with respect to the stock 5 ', makes it possible to use drawings such as that of the figure 11 in which are conventionally represented two tools each corresponding to a position of the tool for each half-turn of the crude 5 '. The elements appearing for each of these positions of the tool 8 are identified by a suffix A in the position to the left of the axis 4 'and by a suffix B in the position to the right of the axis 4', in the figures .

The figure 11 combines, according to the said representation, the figures 9 and 10 .

In all the figures, the machining line is represented in bold when the tool 8 is working in nominal mode (example figure 11 ), and is represented in hatched lines when the tool 8 is working backwards (example figure 21 )

The process according to the invention will now be described with reference to Figures 12 to 23 using the representation of the figure 11 .

With reference to the figure 12 , a first step consists of machining a recess around the axis of rotation 4 'of the crude 5'. Tool 8 is at this effect used first in conventional turning, that is to say without synchronizing the position of the tool 8 with the angular position of the crude 5 '.

The tool 8 is thus approached to the surface 6 along the axis 4 '.

With reference to the figure 13 , the tool 8 enters the raw material 5 'while the center 17 of the tool 8 is at a distance from the axis 4' substantially equal to the radius of the tool 8. The penetration of the tool 8 in the raw material 5 'is carried out according to a height adapted to the thickness of the layer 7 of material to be removed (see the position 8B of the tool 8), that is to say the desired depth of pass.

This penetration into the material of the tool 8 being performed according to a conventional turning operation applied to a prismed surface 6, the tool 8 comes to perform the machining operation (position 8B) and is sometimes placed at the distance from surface 6 (position 8A).

With reference to the figure 14 , the tool 8 is then moved in the direction of the axis of rotation 4 'while following a machining height adapted to the thickness of the layer 7 so as to form the recess 22 as and when its displacement.

The recess 22 is then continued until the tool 8 arrives in the central position, that is to say that its center 17 comes to be positioned on the axis 4 '(see figures 15 and 16 ).

The figure 17 shows the recess 22 produced by the operation of Figures 12 to 16 .

Once the recess 22 has been made, actual machining operations are carried out in accordance with the Figures 18 to 22 . These machining operations are now performed according to the turning technique, described above, during which the position of the tool 8 is synchronized with the angular position of the blank 5 '.

The figure 18 shows the penetration of the tool 8 in the raw material 5 'following the layer 7 of material to be machined.

The figure 19 shows the progression of the tool 8 towards the axis 4 '.

From the figure 20 the tool 8, in its position 8A, enters a reverse machining zone. Indeed, the tool in its 8A position layer 7 in nominal mode along a machining line 23 and also processes back the layer 7 along a machining line 24 located on the other side of the axis 4 '.

The figure 21 shows the progression of the tool 8 which finishes machining the layer 7 only countdown until the tool 8 arrives at the position of the figure 22 in which the machining of the layer 7 is completed.

The figure 23 shows the residual volume of material of the layer 7 which remains to be machined before the tool 8 begins to work backwards, that is to say just after the position of the figure 19 .

The residual volume represented at figure 23 is the volume that will be machined back by tool 8.

où R est égal au rayon de l'outil 8 et r est égal à la distance séparant le sommet de ce volume résiduel de l'un de ses bords (voir figure 23).The height f of this residual volume 25 is such that: $$\mathit{f}=\mathit{R}-\sqrt{{\mathit{R}}^2-{\mathit{<figure-callout\; id="2"\; label="r"\; filenames="imgf0001.png"\; state="\{\{state\}\}">r</figure-callout>}}^2}$$

where R is equal to the radius of the tool 8 and r is equal to the distance separating the vertex of this residual volume from one of its edges (see figure 23 ).

Alternatively, it is possible to stop the machining in the position of the figure 19 then to eliminate the residual volume 25 for example by polishing. The tool 8 never goes backwards.

Note that even if this variant is not implemented and that the residual volume 25 is machined in accordance with Figures 20 to 22 the backward work of the tool 8 is limited to this residual volume 25 much less than the total volume of the layer 7 to be machined.

By way of comparison, a machining operation under similar conditions will now be described but without carrying out a preliminary recess.

The Figures 24 to 27 show such an operation.

The figure 24 shows the machining by a tool 26 of a layer 27 of material to be machined on a stock 28. This machining is performed by synchronizing the position of the tool 26 with the angular position of the stock 28.

This figure 24 is the last position of the tool 26 before the beginning of a work in progress since a portion of the machining line 26, at its position 26A, will pass on the other side of the axis 29 of gross turnover 28.

The figure 25 shows indeed that the tool 26 works in nominal machining in its position 26B according to a machining line 30 while it works, at its position 26A, firstly in nominal machining according to a machining line 31 on one side of the axis 29 and, on the other hand, in reverse machining along a machining line 32 on the other side of the axis 29.

Machining continues in this way in accordance with Figures 26 and 27 until complete removal of layer 27.

The figure 28 shows the residual volume 33 of the layer 27 which, from the position of the figure 24 , is machined with the tool 26 working backwards.

The height of the pass f of the residual volume 33 corresponds to the pass depth defining the layer 7 and is much greater than the height f of the residual volume of the process according to the invention (see FIG. figure 23 ).

The method according to the invention therefore allows a significant reduction of the machined volume down when using such a turning technique where the position of a tool is synchronized with the angular position of the rough to be machined.

The difference between the residual volume of the process according to the invention and the residual volume 33 is such that, thanks to the method according to the invention, the machining tool works very little in reverse.

Since the residual volume 25 is also considerably smaller than the residual volume 33, this residual volume 25 may alternatively be left as it is or polished during an additional operation. The machining tool therefore does not work at all backwards according to this variant.

Alternative embodiments of the method can be envisaged without departing from the scope of the invention. In particular, although the operations of Figures 3 to 22 have been described with reference to the machining of a layer 7 of workpiece of regular thickness on a prismed flat surface 6, the method according to the invention naturally applies to the production of an ophthalmic lens in accordance with Figures 1 and 2 by removing a layer of irregularly thick material from a blank 5.

Claims (12)

1. Method of machining by turning a face (3) of an ophthalmic lens (1), which includes a main machining step during which the position of a machining tool (8) is synchronised with the angular position of the ophthalmic lens (1) driven in rotation about a rotation axis (4) transverse to said face (3) so as to machine on said face a surface that is asymmetrical with respect to the rotation axis (4) of the ophthalmic lens (1), this method being characterised in that it includes a complementary step of machining a recess (22) around the rotation axis (4) of the ophthalmic lens (1) and in that the tool for machining the recess (22) is in contact with the ophthalmic lens (1) during only an angular portion of the rotation of the ophthalmic lens (1).
2. Machining method according to claim 1, characterised in that said complementary machining step is performed before said main machining step.
3. Method according to either of claims 1 and 2, characterised in that said recess (22) defines a portion of said asymmetrical surface.
4. Method according to one of claims 1 to 3, characterised in that said complementary machining step is performed using the machining tool (8).
5. Method according to one of claims 1 to 3, characterised in that said complementary machining step is performed using a tool other than the machining tool (8).
6. Method according to one of claims 1 to 5, characterised in that said complementary machining step is performed without synchronising the position of a tool for machining the recess (22) with the angular position of the ophthalmic lens (1) driven in rotation.
7. Method according to claim 6, characterised in that the machining of the recess (22) is effected by moving a tool in the direction of the rotation axis of the ophthalmic lens (1).
8. Method according to claim 7, characterised in that the forward movement of said tool is stopped when the center of the tool is positioned on the rotation axis of the ophthalmic lens (1).
9. Method according to one of claims 1 to 8, characterised in that the recess (22) has an edge passing through the rotation axis of the ophthalmic lens (1).
10. Method according to one of claims 1 to 9, characterised in that a residual volume of material is adapted to be machined in the inverse mode by the machining tool (8) during the main machining step, this residual volume being substantially centered relative to the rotation axis of the ophthalmic lens (1).
11. Method according to claim 10, characterised in that said residual volume is machined during the main machining step.
12. Method according to claim 10, characterised in that the main machining step is stopped before machining said residual volume.

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