WO2007065981A2

WO2007065981A2 - Grinder auto-calibration method

Info

Publication number: WO2007065981A2
Application number: PCT/FR2006/002457
Authority: WO
Inventors: Michel Nauche
Original assignee: Essilor International (Compagnie Generale D'optique)
Priority date: 2005-12-05
Filing date: 2006-11-03
Publication date: 2007-06-14
Also published as: FR2894170B1; WO2007065981A3; FR2894170A1

Abstract

The invention relates to a method for auto-calibrating a device for trimming ophthalmic lenses. The inventive method comprises the following steps which are performed after an ophthalmic lens (L1) has been trimmed using the trimming device, namely: a measurement is taken of the length (RHO) of at least one radius of the lens; the aforementioned length measurement is compared to the expected length (RHOo) of said radius; the result of the comparison is stored in a history containing the results of each comparison for lenses trimmed successively by the trimming device; and at least one set function is calculated for the subsequent trimming of another lens, said calculation taking account of the comparison results associated with several lenses in the history.

Description

SELF-CALIBRATION METHOD OF A GRINDER

TECHNICAL FIELD TO WHICH THE INVENTION RELATES

The present invention relates generally to a method of self-calibration of an ophthalmic lens trimming device which is carried out regularly in order to always have a reliable spatial reference making it possible to precisely shape the ophthalmic lenses.

It finds an advantageous application in the calibration of a trimming device comprising a beveling wheel.

TECHNOLOGICAL BACKGROUND

The technical part of the optician's profession consists in mounting a pair of ophthalmic lenses on a frame selected by a wearer. This assembly is broken down into five main operations:

- the acquisition of the geometric data of the bezels of the circles of the frame selected by the wearer,

the centering of each lens which consists in determining the position which each lens will occupy on the frame so as to be suitably centered opposite the pupil of the wearer's eye so that it exercises the optical function properly which it was designed,

- the probing of each lens which consists in determining the coordinates of points on each of the faces of the lens characterizing the geometry of its contour after trimming, then

- the creation of a clipping instruction (in the form of a so-called ray restitution function) which defines the desired spatial position of the contour on the lens to be clipped taking into account the geometric data read from the corresponding bezel, parameters of defined centering and probing of the lens, and finally,

- the trimming of each lens which consists in machining or cutting its contour to the desired shape, taking into account the defined trimming instruction, with possibly, at the end of machining, the beveling which consists in carrying out on the edge of the lens , by means of a beveling wheel, a bevel intended to hold the lens in the bezel that the frame has.

In order to simplify the work of the optician, it is desirable that the machining is precise enough so that the lens fits exactly and without forcing into the bezel of the frame chosen by the wearer. This precision in fact makes it possible to avoid the optician being forced to carry out the trimming and beveling of the lens several times for its mounting on its frame.

In order to achieve sufficient precision during machining, it is necessary to know the exact position of the various elements of the trimming device, in particular that of the beveling wheel, relative to the support means of the ophthalmic lens. With this in mind, the optician is currently calibrating the trimming device regularly in order to have a precise reference of these various parameters. This reference then defines a calibration constant which is integrated into the restitution function.

The Applicant has found that, despite the care taken in calibrating as it is carried out today, there remain nesting imperfections which cause difficulties in mounting the lenses on their frame which may possibly require a resumption of their machining, or even the disposal of the ophthalmic lens.

OBJECT OF THE INVENTION

The present invention relates to a method of self-calibration of the grinder making it possible to improve the fitting precision of the lenses in their frame.

More particularly, according to the invention, there is proposed a method of self-calibration of an ophthalmic lens trimming device comprising, for at least one sampling of the ophthalmic lenses successively trimmed by the trimming device for their mounting on the frames. associated with them, after the trimming of each ophthalmic lens, a measurement of the length of at least one ray of this lens, a comparison of this length with the expected length for this ray, a storage of the result of this comparison in a history containing the results of each comparison of lenses successively trimmed by the trimming device, and a calculation of at least one setpoint function for a subsequent trimming of another lens, this calculation taking into account the comparison results associated with several lenses from this history.

Thus, according to the invention, the self-calibration method is implemented following the trimming of a lens intended to be mounted on a frame chosen by a wearer, which makes it possible to measure imperfections directly on the latter. from the previous clipping by comparing the lens shape obtained with the desired lens shape according to the setpoint function. The lens used for this calibration measurement is not specifically dedicated to this calibration operation, but consists of one of the lenses cut out in the context of the normal operation of the device, with a view to incorporating it into a pair of glasses. There is thus no loss of time due to the progress of an additional calibration process. In addition, the device self-calibrates continuously and systematically (for all cutout lenses, at regular intervals) or easily programmable, so that it remains precise throughout its life.

A new reference function is thus deduced therefrom for the next lens to be traced, aiming to attenuate the imperfections detected on the lens or lenses previously cut out. Continuous monitoring of the various parameters of the clipping device then makes it possible to clipping each lens with increased precision.

This continuous monitoring is currently becoming crucial since the shape and granularity of the new grinding stones are subject to rapid change. In fact, in order to reduce the time required to machine an ophthalmic lens, the forces exerted by a grinding wheel on a lens are greater than before.

On the one hand, when the shape of the grinding wheel changes, the length of each restored ray of the lens also changes; it is therefore important to take into account the evolution of the shape of the grinding wheel.

On the other hand, when the grain of the wheel is no longer new but is polished, it is more difficult to remove material removed from the lens; consequently, the force exerted by the grinding wheel on the lens is greater, consequently resulting in greater bending of the lens, which modifies the length of the returned radius. It is therefore important to take into account the evolution of the bending of the lenses in order to machine them correctly.

Furthermore, the creation of a history allows the clipping device to take advantage of the clipping previously carried out on other lenses (with a view to mounting them on frames chosen by different wearers) in order to refine the value of its constant d 'calibration. Such learning thus makes it possible to predict what value of the machining constant will allow a future lens to be correctly trimmed from its first machining. According to an advantageous characteristic of the invention, the measurement of the length of radius of the lens is carried out while the lens is still blocked on a support by means of which it has been cut out and from which said lens has not been separate.

The lens is thus measured directly on the trimming device.

This therefore prevents any loss of frame of reference, the lens being measured in the same frame of reference as that in which it has been cropped, without the geometric errors of repositioning the lens in a new measurement frame of reference which would inevitably result from a follow-up unlocking a re-blocking of the lens.

According to another advantageous characteristic of the self-calibration method according to the invention, for each of the lenses successively cut out, an indicator of a category of material to which this lens belongs is stored in the history, and, to calculate the subsequent trimming setpoint function of the other lens, said material category indicator is taken into account. Advantageously then, to calculate the function of subsequent trimming setpoint of the other lens, the comparison results associated with several lenses belonging to the same material category from this history are taken into account, excluding the associated comparison results. lenses belonging to a different category of material.

Thus, the method takes into account the fact that the bending of a lens during its machining depends not only on the state of the grinding wheel but also on the material of the lens. Indeed, a lens made of a moderately rigid material such as polycarbonate is more subjected to bending than a lens made of a very rigid material such as mineral glass. The memorization of an indicator therefore makes it possible to take into account, for the calculation of the calibration constant, only the results of the comparisons associated with lenses belonging to the same category of material.

Advantageously, the clipping instruction being defined in the form of a ray restitution function giving, for each ray of the lens, the length of this ray, the result of the comparison constitutes a calibration constant integrated into said function. restitution and independent of the considered radius. In general, it can be considered that the difference between the actual length after trimming and the expected length is the same whatever the radius considered on the lens, or varies only slightly or in specific cases. Thus, the determination of a simple calibration constant makes it possible to simplify the taking into account of the calibration by the trimming device.

Advantageously then, the taking into account of the comparison results associated with several lenses of the history is carried out by averaging at least the last two calibration constants of the history and by integrating the result of this average in the function of restitution of rays of a subsequent clipping of the other lens.

Advantageously otherwise, the taking into account of the comparison results associated with several lenses of the history is carried out by an asymptotic evaluation based on at least the last two calibration calibration constants of the history and by integrating the result of this evaluation in the ray restitution function of a subsequent trimming of the other lens.

Advantageously still, the taking into account of the results of comparison associated with several lenses of the history is carried out by a logarithmic evaluation based on at least the last three constants of calibration of the history and by integrating the result of this evaluation in the ray restitution function of a subsequent trimming of the other lens.

According to another advantageous characteristic of the invention, when the difference between the length of one of the rays of the ophthalmic lens and the expected length for this ray is greater than or equal to 0.02 mm, the rays are touched up of the lens.

Thus, when, during a calibration, a too large difference is detected between the expected length of one of the spokes of the lens and its actual length, the lens is again trimmed since the latter cannot be nested directly in the circle of the frame chosen by the future wearer. Calibration therefore allows the optician to avoid the tedious operation of correctly reinstalling the lens on the trimming device and trimming it a second time after realizing that it does not fit correctly in its circle of mount. DETAILED DESCRIPTION OF AN EXAMPLE OF EMBODIMENT

The description which follows with reference to the appended drawings given by way of nonlimiting examples will make it clear what the invention consists of and how it can be implemented.

In the accompanying drawings:

- Figure 1 is a general schematic perspective view of a clipping device;

- Figure 2 is a perspective view of the clipping device of Figure 1 comprising means for controlling the size of an ophthalmic lens; - Figure 3 is a partial perspective view of the clipping device of Figure 1 showing, from another angle and on a larger scale, the control means of Figure 2; and

- Figure 4 is a detail view in partial section of a beveled lens. contact of the control means of figure 2.

The beveling device according to the invention can be produced in the form of any cutting or material removal machine adapted to modify the contour of the ophthalmic lens to create a bevel adaptable to a bezel of a circle of a frame selected by a carrier.

In the example shown diagrammatically in FIG. 1, the trimming device comprises, in a manner known per se, an automatic grinder 10, commonly known as digital. The grinder 10 comprises in particular an electronic and computer system comprising control means capable of controlling its different degrees of freedom. This electronic and computer system also includes calculation software adapted to carry out the various deductions specific to the method according to the invention and a buffer memory. Is set up in this buffer memory, for each lens to be beveled, a clipping instruction function defined in the form of a restitution function giving, for each ray of a lens, the length that this ray must have so that the lens can correctly fit into the frame chosen by the wearer. This restitution function includes in particular a calibration constant independent of the shape of the ophthalmic lens L1 to be trimmed and of the frame for which this lens is intended. This constant, on the other hand, allows changes in characteristics to be taken into account. mechanical and geometric aspects of the grinder 10. The present method aims to determine this calibration constant.

The electronic and computer system also includes a history, here in the form of a digital register (database), in which are listed the calibration constants measured by the device on the lenses previously cut out (for their mounting on frames chosen by different wearers) as well as a representative indicator of their material category (for example flexible, semi-rigid and rigid). This indicator is supplied to the electronic and computer system by the user when trimming each lens.

The grinder 10 comprises, in this case, a rocker 11, which is mounted freely pivoting about a first axis A1, in practice a horizontal axis, on a frame 1. This pivoting is controlled, as we will see in more detail thereafter.

For immobilizing and driving in rotation an ophthalmic lens such as L1 to be machined, the grinder is equipped with support means constituted by two support and rotation drive shafts 12, 13. These two shafts 12, 13 are aligned with each other along a second axis A2, called the locking axis, parallel to the first axis A1. The two shafts 12, 13 are driven in rotation synchronously by a motor (not shown), via a common drive mechanism (not shown) on board the rocker 11. This common synchronous drive mechanism for rotation is of the type current, known in itself.

Alternatively, provision could also be made to drive the two shafts by two separate motors synchronized mechanically or electronically.

The rotation ROT of the shafts 12, 13 is controlled by a central electronic and computer system (not shown) such as an integrated microcomputer or a set of dedicated integrated circuits (ASIC).

Each of the shafts 12, 13 has a free end which faces the other and which is equipped with a blocking nose 62, 63. The two blocking noses 62, 63 are generally of revolution around the axis A2 and each have an application face 64, 65 generally transverse, arranged to bear against the corresponding face of the ophthalmic lens L1. The shaft 13 is movable in translation along the blocking axis A2, opposite the other shaft 12, to achieve the axial compression tightening of the lens L1 between the two blocking noses 62, 63. The shaft 13 is controlled for this axial translation by a drive motor via an actuating mechanism (not shown) controlled by the central electronic and computer system. The other shaft 12 is fixed in translation along the blocking axis A2.

The clipping device comprises, on the other hand, a train of grinding stones comprising at least one beveling grinding wheel 14, which is set in rotation on a third axis parallel to the first axis A1, called the axis of revolution A3, and which is also duly driven in rotation by a motor not shown. This beveling wheel 14 is generally cylindrical around the axis A3 and carries a bevel groove 14A of general V-shaped profile and an opening angle C1 approximately equal to 120 degrees. For simplicity, the axes A1, A2 and A3 have only been shown schematically in broken lines in Figure 1 which illustrates the general principle of constitution of a grinder, incidentally known in itself. A more detailed and specific embodiment of the invention is illustrated by FIGS. 2 and 3.

In practice, as shown in FIG. 2, the grinder 10 comprises a train of several grinding wheels mounted coaxially on the axis of revolution A3, for roughing, finishing of the projection of the ophthalmic lens 12 to be machined and beveling. These different wheels are each adapted to the material of the cut lens and to the type of operation performed.

The wheel train is attached to a common shaft of axis A3 ensuring their rotational drive during the overhanging and beveling operation. This common shaft, which is not visible in the figures, is controlled in rotation by an electric motor 20 controlled by the electronic and computer system.

The wheel train is also movable in translation along the A3 axis and is controlled in this translation by a controlled motorization. Concretely, the whole set of grinding wheels, its shaft and its motor is carried by a carriage 21 which is itself mounted on slides 22 integral with the frame 1 to slide along the axis of revolution A3. The translational movement of the grinding wheel carriage 21 is called “transfer” and is noted TRA in FIGS. 2. This transfer is controlled by a motorized drive mechanism (not shown), such as a screw and nut or rack system, controlled by the central electronic and computer system.

To allow dynamic adjustment of the distance between the axis A3 of the beveling wheel 14 and the axis A2 of the lens during beveling, use is made of the pivoting capacity of the lever 11 around the axis A1. This pivoting in fact causes a displacement, here substantially vertical, of the lens L1 sandwiched between the shafts 12, 13 which brings the lens closer or further away from the grinding wheels 14. This mobility, which makes it possible to restore the desired form of beveling and programmed in a system electronic and computer, is called restitution and is noted RES in the figures. This RES restitution mobility is controlled by the central electronic and IT system.

In the example schematically illustrated in FIG. 1, the grinder 10 comprises, for this restitution, a link 16, which, articulated to the chassis 1 around the same first axis A1 as the rocker 11 at one of its ends, is articulated , at the other of its ends, along a fourth axis A4 parallel to the first axis A1, to a nut 17 movably mounted along a fifth axis A5, commonly known as the restitution axis, perpendicular to the first axis A1, with, intervening between this link 16 and the rocker 11, a contact sensor 18. This contact sensor 18 is, for example, constituted by a Hall effect cell or a simple electrical contact.

As shown diagrammatically in FIG. 1, the nut 17 is a threaded nut in screw connection with a threaded rod 15 which, aligned along the fifth axis A5, is rotated by a restitution motor 19. This motor 19 is controlled by the central electronic and computer system. We noted T the pivot angle of the rocker 11 around the axis A1 relative to the horizontal. This angle T is associated with the vertical translation, denoted R, of the nut 17 along the axis A5. When, duly clamped between the two shafts 12, 13, the ophthalmic lens L1 to be machined is brought into contact with the grinding wheel 14, it is the object of an effective removal of material until the rocker 11 comes to abut against the link 16 following a support which, being made at the level of the contact sensor 18, is duly detected by the latter.

Here, a strain gauge associated with the lever is provided to measure the advance machining force applied to the lens. In this way, the grinding advance force applied to the lens is continuously measured during machining. It is then possible optionally to control the progression of the nut 17, and therefore of the lever 11, not by means of the link system 16 - contact sensor 18, but so that this advance force remains below a value of maximum setpoint. This set value is, for each lens, adapted to the material and to the shape of this lens.

Anyway, for the machining of the ophthalmic lens L1 along a given contour, it suffices, therefore, on the one hand, to consequently move the nut 17 along the fifth axis A5, under the control of the motor 19, to control the restitution movement and, on the other hand, to jointly pivot the support shafts 12, 13 around the second axis A2, in practice under the control of the motor which controls them. The transverse restitution movement RES of the rocker 11 and the rotational movement ROT of the shafts 12, 13 of the lens are controlled in coordination by an electronic and computer system (not shown), duly programmed for this purpose, so that all the points of the contour of the ophthalmic lens L1 are successively reduced to the correct diameter.

The grinder illustrated in FIG. 2 further comprises a finishing module 25 which embeds chamfering and creasing grinders 30, 31 mounted on a common axis 32 and which is movable according to a degree of mobility, in a direction substantially transverse to the axis A2 of the shafts 12, 13 for holding the lens as well as to the axis A5 of the RES reproduction. This degree of mobility is called retraction and is noted ESC in the figures.

This finishing module 25 also has a drill 35 adapted to make holes in the ophthalmic lens when it is intended to be mounted on a frame of the pierced type. This drill 35 has a drill adapted to pivot around a drilling axis A6. It further comprises a base 34 able to pivot about an axis A7 orthogonal to the drilling axis A6. This mobility makes it possible to correctly orient the drill relative to the lens during its drilling. Furthermore, this base 34 is provided with a finger 38 whose end 39 is spherical and is adapted to be inserted in a cam track 51 defined by two side walls 54, 57 belonging to a plate 50 which is integral with the frame 1 of the grinder. The front face 58 of this plate 50 is vertical and is disposed opposite the finger 38 of the drill 53. Thus, when the finger 38 is inserted in the cam path 51, the drill 35 is precisely guided and oriented around axis A7 for drilling the ophthalmic lens. In this case, the retraction consists of a pivoting of the finishing module 25 around the axis A3. Concretely, the module 25 is carried by a lever 26 secured to a tubular sleeve 27 mounted on the carriage 21 to pivot around the axis A3. To control its pivoting, the sleeve 27 is provided, at its end opposite to the lever 26, with a toothed wheel 28 which meshes with a pinion (not visible in the figures) equipping the shaft with an electric motor 29 integral with the carriage 21.

We observe, in summary, that the degrees of mobility available on such a clipping grinder are:

the rotation of the lens making it possible to rotate the lens about its axis of maintenance, which is generally normal to the general plane of the lens,

- restitution, consisting of a transverse relative mobility of the lens (that is to say in the general plane of the lens) relative to the grinding wheels, making it possible to reproduce the different rays describing the outline of the desired shape of the lens ,

- the transfer, consisting of an axial relative mobility of the lens (that is to say perpendicular to the general plane of the lens) relative to the grinding wheels, making it possible to position vis-à-vis the lens and the clipping grinding wheel chosen.

- The retraction, consisting of a relative transverse mobility, in a direction distinct from that of the restitution, of the finishing module relative to the lens, making it possible to put in the position of use and to store the finishing module.

In this context, the general aim of the invention is to integrate a calibration function with this grinder. To this end, the module 25 is provided with a reference rod 70.

This reference rod 70 is integrated into the finishing module 25 so that it has the same degrees of freedom as those of the module 25.

The integration of the calibration function within a beveling machine however implies that the reference rod 70 is suitably positioned opposite the ophthalmic lens to be palpated. We want to achieve this positioning by optimizing the use of already existing degrees of machining mobility and above all by avoiding creating additional degrees of mobility and / or control mechanisms dedicated to calibration. This positioning is thus achieved by means of two pre-existing degrees of mobility, independently of the calibration function, which are the retraction ESC on the one hand and the transfer TRA on the other.

Thus, for the implementation of the calibration function, the module 25 is pivotally controlled around the axis A3 (ESC retraction) to adopt two main angular positions, including:

an inactive position (shown in FIGS. 2 and 3) in which the module 25 is distant from the shafts 12, 13 for holding the ophthalmic lens L1 and in which it is stored under a protective cover (not shown) when it is not used, thus freeing up the space necessary for machining the lens on the grinding wheels 14 without risk of conflict,

an active position (represented in FIG. 4) in which the reference rod 70 is positioned between the shafts 12, 13 for holding the lens and the beveling wheel 14, substantially vertical to the axis A2 or, more generally, on or near the trajectory (in this case cylindrical) of the axis A2 of the lens in its useful travel for restitution RES, as will be described in detail later.

The inactive position is not in itself the subject of the present invention and will therefore not be described in more detail. The relative positioning of the ophthalmic lens L1 on the reference rod 70 will also be described later.

The reference rod 70 is oriented on the upper face of the module 25 when the latter is in the active position so that in this position, the ophthalmic lens L1 enclosed in the shafts 12, 13 can come into contact with the reference rod 70. This upper face is not planar but has a generally cylindrical shape around the axis of revolution A3 so that when the ophthalmic lens L1 is in contact with the reference rod 70 which is itself in the active position, whatever the angular position of retraction of the module 25, the distance between the locking axis A2 and the axis of revolution A3 is constant.

The reference rod 70 has several measurement profiles arranged on different zones making it possible to calibrate the beveling device.

A first zone has a first receiving groove 71 of general V-shaped profile arranged transversely to the axis of revolution A3. This throat reception has an opening angle C2 less than the opening angle C1 of the bevel groove 14A of the grinding wheel 14. This opening angle C2 is approximately 105 degrees. The mouth width of this groove corresponds to a first characteristic width of support LC1. Here, the first characteristic support width is approximately 1.8 millimeters.

A second zone has a second receiving groove 72 parallel to the first receiving groove 71 and also having a general V-shaped profile. Its opening angle C3 is here the same as that of the first receiving groove 71 but its mouth width is less than that of the first receiving groove 71. Its mouth width corresponds to a second characteristic width of support (LC2). Here, the second characteristic support width is approximately 1.5 millimeters.

A third zone has a rib 73 of rectangular profile, the edges 73A of which are chamfered according to a rounded profile. This rib 73 is arranged parallel to the two receiving grooves 71, 72. It has a width of 0.5 millimeter and a height of about 1 millimeter. It is particularly suitable for making grooving depth measurements on ophthalmic lenses having not a bevel but a groove. It can however be used to take a profile of the bevel profile of an ophthalmic lens in order to check the wear of the bevel groove 14A of the grinding wheel 14.

The reference rod 70 is offset in height relative to the module 25 so that it laterally has two shoulders 74 whose edges 74A form arcs of a circle. These edges 74A are also chamfered according to a rounded profile. It is therefore also possible to make a reading of the profile of the bevel of an ophthalmic lens by bringing the bevel of the ophthalmic lens L1 into contact with one or other of the edges 74A formed by these shoulders 74 or with the edges 73A rib 73.

The grooves 71, 72, the edges 73A, 74A of the rib 73 and the shoulders 74 have circular lateral profiles centered on the axis A3 of retraction.

The use of the reception grooves 71, 72 of the reference rod 70 during the calibration of the trimming device makes it possible to refine the precision of the measurements so that the fitting of the lens on its bezel is done correctly. In fact, ideally, the beveling of the ophthalmic lens L1 is carried out so that the lens, once cut out, fits perfectly into the bezel of the circle of the spectacle frame chosen by the wearer. This beveling is carried out by means of the ray restitution function which associates a length with each ray of the lens.

With a view to nesting, the “interesting” length of each ray is consequently the length separating the optical center of the lens, arranged on the locking axis A2, from the points of the bevel in contact with the bezel. However, the points of the bevel in contact with the bezel are not the points forming the top of the bevel, nor points of the base of the bevel, but rather points which are located on each face of the bevel. In section on a lens, as shown in FIG. 4, these two points intended to be in contact with the bezel of the frame 10 are arranged opposite on each face of the bevel and are separated by a distance equal to the width at the opening of the bezel. The first characteristic width of support LC1 being calculated to be equal on average to the opening widths of the bezel bezels, these two points are separated by a distance corresponding approximately to the width LC1. Thus, the first receiving groove 71 of the reference rod simulates an interlocking of the lens in its frame. Consequently, when the bevel of the ophthalmic lens L1 is disposed in the first receiving groove 71 of the reference rod 70, the distance separating the blocking axis A2 from the ophthalmic lens L1 corresponds to this "interesting" length. The use of the first receiving groove 71 of the reference rod 70 thus makes it possible to dispense with any additional calculation intended to take into account the distance separating these two points from the top of the bevel.

The calibration operation itself is broken down into five main stages.

During a first step, which can be called beveling step, the user has an ophthalmic lens L1 not cut out between the two shafts 12,13. The shaft 13, movable in translation along the blocking axis A2, is controlled in translation in order to firmly enclose the ophthalmic lens L1 between the application faces 64,65 of the blocking noses 62,63. When the ophthalmic lens L1 is correctly maintained, the electronic and computer system controls the transfer mobility TRA in order to precisely position the bevel groove 14A of the grinding wheel 14 facing the edge of the non-contoured ophthalmic lens L1 and of maintaining it in this position. It then controls the restitution mobility RES in order to position the edge of the lens on the bevelling groove 14. The grinding wheel 14 is then rotated in order to produce a bevel over the entire periphery of the ophthalmic lens L1, such so that the lens is cropped according to the desired contour corresponding to the rendering function provided for the cropping of this lens L1, so that it is mountable on the spectacle frame chosen by the wearer. The system then blocks the rotation of the shafts 12, 13.

The electronic and computer system then controls the restitution mobility RES in order to move the ophthalmic lens L1 away from the beveling wheel 14 and then the retraction mobility ESC to bring the module 25 into the active position.

During a second step, which can be called the positioning step, the electronic and computer system pilot, as illustrated in FIG. 4, the mobility of restitution RES and that of transfer TRA to bring the bevel of the ophthalmic lens L1 against one end, for example the left end, of the reference rod 70. When the strain gauge associated with the rocker detects a force signifying the contacting of the lens against the reference rod 70, the torque of the motor inducing the RES return movement is decreased. The electronic system then controls the transfer TRA of the module 25 so that the reference rod 70 slides continuously or by successive jumps along the bevel of the lens. During this translation, the torque of the motor driving the restitution movement RES is kept constantly low but not zero so that the bevel of the ophthalmic lens L1 enters and leaves each of the measurement grooves 71, 72 of the reference rod 70 At the end of this step, the module 25 is brought back by the electronic and computer system to the inactive position.

Alternatively, it is possible to provide for the reference rod 70 to have self-centering mobility, free with elastic return, in a direction parallel to the axis A3. This mobility then allows a self-axial adjustment of the reference rod 70 when it is disposed against the bevel of the ophthalmic lens L1 so that the latter does not deform in bending during contact of the reference rod 70 against the bevel of the lens. In this case, the bevel of the ophthalmic lens L1 is directly placed opposite the receiving groove 71, before bringing the lens into contact with the rod 70. The freedom of axial movement (in the direction of the axis of revolution A3) of the reference rod 70 allows the centering of the receiving groove 71 on the bevel of the lens, the latter sliding on the lateral face of the groove with which it is in contact until it is exactly opposite from the bottom of the receiving groove 71. Consequently, this mobility allows complete penetration of the bevel into the groove 71 with bringing the edges of this groove into contact with the sides of the bevel.

During a third step, which can be called the measurement step, this first standard position of the blocking axis A2 is measured with respect to the reference rod 70. The software integrated into the electronic and computer system compares the values of the distances recorded between the blocking axis A2 and the axis of revolution A3 around which the reference rod 70 pivots. It thus marks in particular the position of the blocking axis A2 relative to the axis of revolution A3 in which the two flanks of the bevel of the ophthalmic lens L1 were in contact with the two edges of the first receiving groove 71. This position corresponds in fact to a position in which the distance between the blocking axis A2 and l 'axis of revolution A3 is minimal. The raised position in which the bevel is placed in the first receiving groove 71 is called the standard position.

The electronic and computer system then again controls the various mobilities of the trimming device to replace the ophthalmic lens L1 in the standard position. When it is in this position, it controls the rotational mobility so that the entire outline of the lens is palpated by the first receiving groove 71. It thus measures, for each radius R, the length RHO of this radius separating the blocking axis A2 from the upper face of the reference rod 70.

During a fourth step, which can be called comparison step, the software of the electronic and computer system compares for a given radius R the length RHO of this radius with the length RHOo expected for this radius R (i.e. - say that calculated by the ray restitution function). The difference between the length RHO of this radius and its expected length RHOo corresponds to the clipping error. This difference then provides the value of the calibration constant associated with the beveled ophthalmic lens L1. The electronic and computer system then completes the digital register by integrating the value of this calibration constant as well as the indicator associated with the material of the clipped ophthalmic lens L1. The calculation software simultaneously calculates the difference between the length RHO of the radius R of the ophthalmic lens L1 and the expected length RHOo of this radius.

If the actual length obtained RHO is greater than or equal to the expected length RHOo by more than 0.02 millimeters, the electronic and computer system again proceeds to the step of trimming the ophthalmic lens

L1 having previously integrated into the ray restitution function of this lens the calibration constant which has been calculated.

On the other hand, if the actual length RHO obtained of radius R is less than the expected length RHOo by more than 0.02 millimeters, the ophthalmic lens L1 is discarded.

Otherwise, more often than not, if the difference between the expected length RHOo and the actual length obtained RHO is less than 0.02 millimeters, it is considered that the trimming of the lens is correct (suitable for mounting on its frame circle

10) and the electronic and computer system proceeds directly to a fifth step.

During this fifth and last step, the electronic and computer system calculates a new ray restitution function associated with the next lens L2 to be cropped (this lens having the same indicator).

For this, the software first calculates a new calibration constant by reading the last ten calibration constants contained in the digital register, by averaging it, then by integrating the result of this average in the restitution function. of the next lens L2 (instead of its calibration constant).

As a variant, the calculation software can read the last ten calibration constants contained in the digital register, determine the approximate linear function of these calibration constants, deduce therefrom a new calibration constant and integrate the latter into the function of return of rays from the next lens L2.

In another variant, the calculation software can read all the calibration constants contained in the digital register, calculate the equation of the approximate logarithmic function of these calibration constants, by deduce a new calibration constant and integrate the latter into the restitution function and deduce from this function the ray restitution function of the next lens L2.

The present invention is in no way limited to the embodiments described and shown, but a person skilled in the art will know how to make any variant which conforms to his spirit.

Claims

1. Method for self-calibration of an ophthalmic lens trimming device comprising, for at least one sampling of the ophthalmic lenses successively trimmed by the trimming device with a view to their mounting on the frames associated with them, after trimming of each ophthalmic lens (L1):

- a measurement of the length (RHO) of at least one radius (R) of this lens

<L1),

- a comparison of this length (RHO) with the expected length (RHOo) for this radius (R),

a storage of the result of this comparison in a history containing the results of each comparison of lenses (L1) successively cut out by the trimming device, and

- A calculation of at least one setpoint function for a subsequent trimming of another lens (L2), this calculation taking into account the comparison results associated with several lenses (L1) from this history.

2. Self-calibration method according to the preceding claim, in which the measurement of the length (RHO) of the radius (R) of the lens (L1) is carried out while the lens is still locked on a support by means of which it was cut and from which said lens (L1) was not separated.

3. Self-calibration method according to one of the preceding claims, in which, for each of the lenses (L1) successively cut out, an indicator is stored in the history of a category of material to which this lens (L1) belongs. ), and, to calculate the subsequent trimming setpoint function of the other lens (L2), said material category indicator is taken into account.

4. Self-calibration method according to the preceding claim, in which, to calculate the subsequent trimming setpoint function of the other lens (L2), account is taken of the comparison results associated with several lenses (L1) belonging to the same material category from this history, excluding the comparison results associated with lenses belonging to a different material category.

5. Self-calibration method according to one of the preceding claims, in which the clipping instruction is defined in the form of a ray restitution function giving, for each ray (R) of the lens (L1) , the expected length (RHOo) of this radius (R), the result of the comparison constitutes a calibration constant integrated into said restitution function and independent of the radius (R) considered.

6. Self-calibration method according to the preceding claim, in which the taking into account of the comparison results associated with several lenses (L1) of the history is carried out by averaging at least the last two calibration constants of the history and by integrating the result of this average into the ray restitution function of a subsequent clipping of the other lens (L2).

7. Self-calibration method according to claim 5, in which the taking into account of the comparison results associated with several lenses (L1) of the history is carried out by an asymptotic evaluation based on at least the last two constants of calibration of the history and integrating the result of this evaluation into the function of restoring rays of a subsequent trimming of the other lens (L2).

8. Self-calibration method according to claim 5, in which the taking into account of the comparison results associated with several lenses (L1) of the history is carried out by a logarithmic evaluation based on at least the last three constants of calibration of the history and integrating the result of this evaluation into the function of restoring rays of a subsequent trimming of the other lens (L2).

9. Self-calibration method according to one of the preceding claims, in which, when the difference between the length (RHO) of the radius (R) of the ophthalmic lens (L1) and the expected length (RHOo) of this radius is greater than or equal to 0.02 mm, the lens rays (L1) are touched up.