EP1107849B1 - Method for producing a multifocal correction lens, and system for implementing same - Google Patents

Abstract

The invention concerns a method for producing multifocal correction lenses from semi-finished lenses (1) having at least a first positioning marker M, associated with a correction A called distant vision correction, and a second positioning marker M' associated with a correction B called near vision correction. The method comprises a step which consists in a surface grinding of the semi-finished lens (1) on an internal surface of said lens. The latter is inclined at a specific angle (beta), for example using a wedge, so as to induce a prism of prismatic deviation such that the distant vision and the near vision optical centres are brought together and merge. The invention also concerns a system controlled by a data processing device, for example a micro-computer (8), for automatically carrying out the surface grinding step using a recorded programme and parameters input (80) by an operator.

Description

The present invention relates to the realization of corrective lenses with multiple focal points, in particular intended for the manufacture of optical glasses for glasses for improvement of human vision when correction necessary varies according to the distance from the object observed. Phone is the case of correction of presbyopia, which leads to known manner, mainly to double glasses or triple focus (so-called bi-focal or tri-focal lenses), or at lenses with progressively variable focal length from one point to the other of the lens (commonly called progressive lenses). The invention relates in particular to a method of production of such glasses, as well as on a delivery system implementing such a method, namely in particular a system automated production of a corrective lens, controlled by a program information processing system checked in.

Under the prior art to the invention, it is interesting to recall the patent documents US 2 310 925 for dual focus lenses (for far vision and close vision respectively) or three focal points, US 2,869,455 describing the invention of so-called progressive glass, US 5,430,504 for manufacturing technology in the case of a so-called merged glass, where the jump between two zones at different homes is dimmed. These documents explain widely the methods of manufacturing hearth glasses multiple and the machining which is carried out on the front face, or external face, convex convex. It is by this surface that we introduce the different radii of curvature chosen in function of the desired powers, which result in variations in the thickness of the glass, the radius of curvature of the concave face being generally uniform. We assume while the glass is made up entirely in one transparent, mineral or organic material.

The glasses obtained for their unsightly nature linked to strong variations thick. Another group of methods overcomes the use of a single material, having the same index of refraction in all areas of optical glass. We then provides two refractive index materials different and we incorporate, by fusion, a lens small diameter auxiliary in the material of a larger diameter main lens. This again, incorporation takes place on the front of the main lens. The main lens is used to obtain correction in far vision, and the auxiliary lens add an additional correction to get the correction in close vision. The two corrections are obtained essentially by the relative values of refractive indices, without requiring a difference in radius of curvature. The overall power variation is easy to make progressive from one point to another of the glass by playing on the thickness of the layers of different indices.

The glasses thus produced are not necessarily free of drawbacks. In particular, the passage of vision far to near vision leads to image jumps that are disruptive to the user and are unknown to avoid. To try to mitigate this kind of inconvenience, we may prefer triple focus glasses, but then prejudice to aesthetics, because we come back to variations notable thickness. Typical correction ranges in focal lengths are 0.3m to 0.5m for vision close, from 0.5 m to 1 m for intermediate vision, and from 2 m to infinity for distant vision.

In practice, current industrial conditions involve the manufacture of semi-finished glasses various usual corrections, which are updated opticians and that they only have to adapt in positioning of the main center of curvature to each individual. In addition, they tend to favor aesthetics by using a variation of index rather than of thickness (more possibly a gradual variation power by surfacing), without taking into account the fact that the angular difference between the orientation of the gaze far vision and the orientation of the gaze in near vision varies from individual to individual. More generally, nothing is made to provide the user with optimal comfort.

Consequently, the invention aims mainly at improve the visual comfort suitable for everyone without harming as much to the aesthetics sought. It also aims, what doing, to respect the best conditions of industrial feasibility, in particular by proceeding from semi-finished glasses such as those currently available and using materials that are convenient to use at low cost.

To do this, the invention essentially proposes, in a process for manufacturing corrective lenses of the vision presenting an addition of power for the correction of near vision compared to vision of far, to perform mechanical machining of an internal face of each glass, in reduction of its thickness, which adds a prismatic deviation, calculated as a function of a distance individual between a vision application center of away and a near vision application center, for bring the near vision correction center back to closer to the near vision application center.

In practice, we proceed by starting advantageously of semi-finished glasses in which the said addition is achieved at least in large part by variation of the refractive index of the transparent material constituting said glass at an external face thereof, and the complementary machining according to the invention is then produced by facing the opposite internal face.

For the most common hearth glasses multiples, preferably with gradual variation of the power, the prismatic deviation to be ensured is variable between 0.5 and 1.5 diopters. At its simplest, it is applied single, centered along the axis of displacement look between distance vision and near vision. She is then obtained all the more easily, by interposing a appropriately sized shim between the lens semi-finished and its support to cause a shift of the spherical milling axis on the inside of the glass.

To further improve the implementation conditions work and industrial practice of the invention it will often advantageous to admit that gap information between distant vision and near vision centers to take into account is the same for all individuals asking for the same addition value in vision correction up close for a distance vision correction value determined.

According to a preferred embodiment in industrial application, the subject of the invention is in particular a method for producing a corrective glass with multiple focal points, in particular for glasses, from a semi-finished glass with determined optical characteristics, said semi-finished lens comprising a first concave curved face and a second convex curved face, and being provided with at least a first positioning mark M , associated with a correction A , called far vision correction, and a second positioning mark M ' , associated with an additive correction B , called close vision correction, both located on said convex face and constituted by points, characterized in that it comprises at least one step of surfacing by removing material over a determined depth of l 'one of said faces using abrasive machining means moving in translation along a first axis, in that said surfacing step comprises the presentati on said semi-finished glass in front of the machining means, so that a second axis, orthogonal to a plane tangent to the point constituting said first positioning mark M is inclined at a determined angle relative to said first axis, by so as to induce in the semi-finished glass a prism aligned with the line segment MM ', whose apex angle is a function of said inclination angle, and in that the prismatic deviation in diopters Δ' of said induced prism obeys the following relation: Δ '= ( MM '× AT ) + Y × ( A + B ) with MM 'the distance in centimeters separating said points M and M', A and B said corrections, expressed in diopters, and y the distance in centimeters separating point M ' from the optical center in close view of said corrective lens.

A system for implementing the method according to the invention is defined in claim 9.

• la figure 1 illustre le principe de l'addition par variation d'indice dans un verre correcteur bi-focal classique ;
• les figures 2A et 2B illustrent un exemple de verre semi-fini, à partir duquel le verre correcteur définitif suivant l'invention est réalisé, en vues de face et de côté respectivement ;
• les figures 3A et 3B illustrent deux verres correcteurs, pour oeil droit et pour oeil gauche respectivement ;
• la figure 4 illustre schématiquement une étape préliminaire au surfaçage d'un verre semi-fini, consistant à fixer celui-ci sur un support ;
• la figure 5 illustre un verre correcteur progressif et les différents références optiques qui le caractérisent ;
• les figures 6A et 6B illustrent schématiquement des exemples de verres correcteurs double foyer, sans et avec prisme de déviation respectivement ;
• les figures 7A illustrent schématiquement, en vue de face, un verre double foyer et un verre triple foyer, destinés à la correction de l'oeil droit ;
• les figures 8A et 8B illustrent schématiquement des dispositifs de surfaçage, selon deux variantes de réalisation d'un système suivant l'invention ;
• et la figure 9 illustre schématiquement un système automatisé de surfaçage piloté par un système de traitement de l'information à programme enregistré.

The invention will be better understood and other characteristics and advantages will appear on reading the description which follows and the appended figures, among which:

• FIG. 1 illustrates the principle of addition by variation of index in a conventional bi-focal corrective lens;
• FIGS. 2A and 2B illustrate an example of semi-finished glass, from which the final corrective glass according to the invention is produced, in front and side views respectively;
• FIGS. 3A and 3B illustrate two corrective lenses, for the right eye and for the left eye respectively;
• Figure 4 schematically illustrates a preliminary step in the surfacing of a semi-finished glass, consisting of fixing it on a support;
• FIG. 5 illustrates a progressive corrective lens and the various optical references which characterize it;
• FIGS. 6A and 6B schematically illustrate examples of corrective bifocal lenses, without and with deflection prism respectively;
• FIGS. 7A schematically illustrate, in front view, a double focal lens and a triple focal lens, intended for the correction of the right eye;
• FIGS. 8A and 8B schematically illustrate surfacing devices, according to two alternative embodiments of a system according to the invention;
• and FIG. 9 schematically illustrates an automated surfacing system controlled by an information processing system with a recorded program.

The problem encountered at the origin of this invention is understandable by considering a corrective lens of the vision of a presbyopic individual, realized in the form a bifocal lens as shown schematically by Figure 1, and the positions of optical centers.

This lens L is assumed to be composed of two lenses: a main lens L ₁ whose optical characteristics are defined for distant vision and an auxiliary lens L ₂ , of smaller size and of different index, attached to the front face of the lens L ₁ (external face on a pair of glasses), which introduces a necessary additive correction in close vision.

The optical centers of the two lenses are not confused, but offset in the vertical direction 0Y here, supposed to correspond to the direction of movement of the gaze when the user switches from a distant vision (in principle in the center of the finished lens) to a close vision (in principle directed downwards), and vice versa. In this way, point marks M and M ′ are distinguished on the surface of the glass, respectively in correspondence with the optical centers of the two lenses L ₁ and L ₂ . The point M materializes what is called the center of application of far vision, and the point M ' the center of application of near vision. Note that in the case of a progressive lens, it is not possible to isolate physically separate lenses. M is then defined as being the center from which the progression starts and M ' the center of end of progression.

In practice, industrially produced semi-finished glasses usually consist of circular lenses 1, as shown diagrammatically in FIGS. 2A and 2B, in front and side view, respectively. The difference in level from the main lens to the auxiliary lens is not visually sensitive. The front or external face, fe , appears convex curved according to an appropriate radius of curvature, and the internal surface, fi , has a concave curvature parallel to the external face. On its surface, the external face fe shows various marks, intended to guide the production of the final corrective glass, by surface machining in reduction of thickness according to a process which will be detailed below. One finds there in particular the point M, the point M ', the latter surrounded by a small circle, an axis l _H said to be horizontal because perpendicular to the imaginary line joining the points M and M ', and an additional mark distinguishing the semi glasses -finishes intended for a right eye or a left eye (for example an " R " for the right eye, as illustrated in FIG. 2A).

In reality, the movement of the pupil from one eye of the wearer moving his gaze to pass from one vision to the other, for example from distant vision to close vision, is normally not strictly vertical. In FIGS. 3A and 3B, there is shown diagrammatically corrective lenses, referenced L _D and L _G , intended respectively for the right eye and the left eye of a spectacle wearer. The references M _D , M _G , M ' _D and M' _G have the same meaning as the references M and M ', but they are associated with the right eye and the left eye respectively. The corrective lenses L _D and L _{G show} orthonormal axes XY centered on the points M _D and M _G respectively. We note that if we project the centers of the pupils of the right eye and the left eye on the vertical axes Y, respectively in P _D and P _G , the line segments M _D -M ' _D of a part, and M _G -M ' _G on the other hand, are inclined with respect to the vertical axes Y and in the opposite direction. The line segment M _D -M ' _D forms with the vertical axis M _D Y an angle -α _D , in the trigonometric direction, and the line segment M _G -M' _G forms with the vertical axis M _G Y an angle + α _G in the opposite direction. Usually α _D and α _G have the same absolute value, on the order of 7 to 8 degrees.

If we refer again to Figure 1, we notice a point O ', materializing what we can call the optical center of correction in close vision, by analogy with a point O (not shown because assumed to be confused with the point M ) constituting the optical center for correction in far vision, specific to the main lens. As a result of the usual manufacturing conditions for glasses, the position of point O 'is located intermediate between M and M'. However, for the close-up vision to be of good quality, it is desirable, in accordance with what the invention allows, for the points M 'and O ' to be combined, or at least very close to each other, so that the gaze remains centered on the optical center of the correction zone used.

According to the laws of optics, the distance MO ' is linked to the distance MM ' in accordance with the relation: MO '= MM '× B A + B in which A represents the correction of distant vision along the axis MM ′ and B represents the additive correction for close-up vision, these corrections being expressed in diopters. By convention, the positive meaning of the vectors is from top to bottom. It is clear from this relationship that the value MO 'is normally not zero. The greater the correction in far vision, the more O 'deviates from M '. This results in deformations in close vision, which causes inconvenience to the user which can go as far as nausea. This drawback can be remedied, in particular with regard to progressive lenses, by creating an induced prism effect, as will now be described.

As already indicated, a corrective lens is produced by machining a semi-finished glass (see Figures 2A and 2B), advantageously chosen from a standard range, by depending on the amplitude of the corrections to be obtained. Glass semi-finished 1, as shown diagrammatically in FIG. 4, is arranged on a support 2 comprising a body main 20, substantially cylindrical, surmounted by a annular ring 21, forming receptacle for the face external (convex in the example in Figure 4). Glass semi-finished 1 is blocked by gluing using metal fuse.

Positioning is carried out using the marks on the surface of the external face fe (see FIG. 2A). To do this also, the cylindrical body 20 and the annular ring 21 may include a channel 22 which pierces them right through, of axis A _H. The point M can therefore be seen from the front and from the back and positioned at the center of the opening of the channel 22.

According to an additional arrangement, a wedge-shaped wedge 3 is inserted between the external face fe and the crown 21, the role of which is to induce in the glass finally obtained a prismatic optical deviation. As a result, the axis A ′ _H , orthogonal to the plane tangent to the surface of the external face fe at M , forms an angle β with the axis A _H. It should be noted here that in practice, the wedge 3 is not a solid object. It is preferably materialized by three points of which it is possible to control adjustable displacements to modify the orientation and the angle of the prism.

To obtain the final corrective lens, a surface treatment of the internal face (concave) is then carried out. The glass 1 and support 2 assembly is presented to a machine tool (not shown), the support being locked in a receiving member and moving a priori along the axis A _H. Due to the fact that the glass 1 is inclined relative to this axis A _H , the desired prism is reproduced, during the machining operation, with an apex angle which is a function of that of the block, but in the opposite direction.

According to the invention, the value of the added prism is calculated so that the position of O ′ is optimized. In this way, in addition to good compatibility with the technological means currently available in the optical industry, it ensures instant and comfortable close reading whatever the correction in far vision and the necessary addition, for the glasses. progressive in particular. All research effort is avoided, the reading application center being immediately in its ideal position. The distortions in close vision are very attenuated and the intermediate visions instantaneous. The transition from distant vision to intermediate and / or close vision takes place without image jump, whatever the type of corrective lens, with double or triple focus or with progressively variable corrective power.

In the case of progressive lenses, we can admit that the angle of rotation of the eye in angular displacement of the gaze is substantially constant, in a typical range from 37 to 38 degrees. This allows to adopt forms of bet particularly advantageous implementation of the invention. This is how we will now describe, in a more detailed, the implementation of the method according to the invention with reference to FIG. 5, which represents, in front view, an example of a progressive type corrective lens.

• M : centre à partir duquel démarre la progression, qui sera également appelé centre bloqueur, car il sert de référence pour le positionnement du verre semi-fini (voir figure 4) ;
• M' : fin de progression ;
• O : centre optique en vision lointaine ;
• O': par analogie, centre optique en vision rapprochée du verre semi-fini (en réalité une combinaison des visions rapprochée et lointaine) ;
• O" : centre optique, toujours en vision rapprochée, mais tenant compte de la présence d'un prisme induit suivant l'axe MM' caractéristique de l'invention ;
• A : correction en vision lointaine selon l'axe de référence MM' ;
• B : valeur de la correction additionnelle (vision rapprochée) ;
• Δ' : déviation prismatique ajoutée au verre correcteur, exprimée en dioptries ;
• α : angle que forme l'axe MM' et un axe vertical Y d'un référentiel orthonormé XY.

The main characteristic marks of this glass L have been reported in this figure 5 among:

• M : center from which the progression starts, which will also be called the blocking center, because it serves as a reference for the positioning of the semi-finished lens (see Figure 4);
• M ': end of progression;
• O : optical center in distant vision;
• O ': by analogy, optical center in close-up vision of the semi-finished glass (in reality a combination of close-up and distant vision);
• O ": optical center, still in close-up vision, but taking into account the presence of an induced prism along the axis MM 'characteristic of the invention;
• A: correction in far vision along the reference axis MM ';
• B : value of the additional correction (close-up vision);
• Δ ': prismatic deviation added to the corrective lens, expressed in diopters;
• α: angle formed by the axis MM 'and a vertical axis Y of an orthonormal reference frame XY .

In a normally surfaced glass, that is to say without prismatic correction, the points O and M are merged and the position of O 'is given by the relation (1). However, for the close-up vision to be of good quality, it is necessary in accordance with the invention that the points M 'and O ' are, if not confused, at least very close to each other. To obtain this result, it is planned to add a vertical prism to the glass during the surfacing step. The prism must be on the lower base, i.e. positive, for a lens associated with a positive A correction, and on the upper base, i.e. negative, for a lens associated with a negative A correction . A special case arises when A = 0. In this limiting case, there is no need for an additional prism.

To fix the ideas, FIGS. 6A and 6B schematically illustrate examples of corrective bifocal lenses, L _DF and L ' _DF , respectively without vertical prism and with vertical prism. For purposes of illustration, the scales are not respected, in order to better highlight the prismatic configuration of the corrective lens L ' _DF of FIG. 6B.

When we introduce a vertical prism, the point O 'becomes O ", taking into account this introduction. If we refer to the relation (1), so that O " and M' are confused, it is necessary that the following relation is satisfied: MO "= MM '

The laws of optics, which translate the prismatic deviation of any prism by the relation: Δ = D xd in which D is the power in diopters and d the distance in centimeters, make it possible to express the prismatic deviation Δ of the corrective lens of the invention (for example L'DF of FIG. 6B), as a function of MM ', B and A, so that the points O "and M ' are merged.

We obtain the following relation: Δ ' = MM '× AT

In this case, by expressing the optical powers in diopters and the distances in millimeters, we observe that the position of O becomes: MO = 10 Δ ' AT = 10 × MM '× AT 10 × AT from where : MO = MM '

It follows that the optical centers O and O " are merged. This can thus ensure that there is no longer any jump or displacement of the image. The visual comfort is also optimized by the fact that M 'and O "are merged and that there is therefore no more distortion of the image in close vision.

However, in the forms of implementation preferred of the invention for healthy practice. industrial, we just act by machining in reduction glass thickness on the inner side, so on the basic power of the glass for distant vision, without touch the addition zone for close vision such as that it appears by variation of index of the material opposite glass, and thus add a prism effect unique remaining the same over the entire extent of the glass. Of more, the calculation of the prismatic deviation thus induced can be further simplified by admitting that the gap between near vision application center and center application of far vision on glass is the same for all individuals requesting the same correction (distant vision and addition for close vision) by a same type of multifocal or progressive lens.

Supposing that one wishes to move O "by a distance y with respect to M ', in a vertical direction, or more precisely along the axis MM ' (FIG. 5), it is necessary to provide a prism Δ ', of which the power is given by the following relation: Δ '= ( MM '× AT ) + Y × ( AT + B ) A and B being expressed in diopters, and the distances in centimeters. If y is sufficiently weak, we obtain results very close to those obtained when relation (4) is verified. The relation (7) is therefore the most general relation, the relation (4) being strictly verified when y = 0.

To fix the ideas, we will now detail the application of the method according to the invention to three cases individuals: glasses with bi-focal lenses, tri-focal lenses or progressive lenses.

FIG. 7A schematically illustrates, in front view, a bifocal lens 4 intended for the correction of the right eye. It comprises two distinct areas: the main lens 40 and a small area 41, called the "patch", constituting the near vision area. Also shown in this Figure 7A, the points M and M ', located in the areas 40 and 41, respectively.

If we call A _OD and A _OG the corrections to be made for the right eye and the left eye respectively, the inclination α of the axes MM 'being assumed to be + 8 degrees and - 8 degrees relative to the vertical, A _OD and A _OG conventionally obey the following two relationships (the angles being expressed in degrees and A _OD and A _OG in diopters): AT OD = SPH + CYL cos (γ - 8) and AT OG = SPH + CYL cos (γ + 8) formulas in which γ is the angle of the axis of astigmatism, SPH the value of the sphere of the corrective lens, and CYL the value of the astigmatism of the corrective lens.

In this case, and according to the method of the invention, the prism to be added is typically given by the relation: Δ '= AT for a distance MM 'usually equal to 10 mm.

FIG. 7B schematically illustrates, in front view, a triple focal lens 5 intended for the correction of the right eye. It comprises three distinct zones: the main lens 50 and two superimposed zones of small dimensions 51 and 52, intended to provide intermediate vision and close vision, respectively. As previously, in this FIG. 7B, the points M and M ′ , located in the zones 50 and 52, are shown respectively.

In the case of tri-focal lenses, the distance separating M from M 'is, on average, typically 16 mm. The relation (10) therefore becomes: Δ = 16 AT 10

The method of the invention applies equally well to progressive lenses. It is even the preferred case of application of the invention, since the advantages obtained in improving visual comfort for an appreciated aesthetic while respecting industrial feasibility are particularly sensitive to it. The prismatic deviation that is added to the traditional semi-finished glass, calculated as a function of the distance MM '(translating the individual angular difference between near vision and far vision) and the addition of power between far vision and near vision has the consequence, by bringing O '(near vision optical center) closer to M ' as the invention requires, by contrast, moving the optical center 0 away from point M. However, in practice this has only a perfectly negligible impact on visual comfort, which is explained by the extent of the visual fields due to the fact that in the vast majority of presbyopes, correction in near vision (3 diopters per example) is much stronger than the distance vision correction (0.5 to 1 diopter in the opposite direction).

Such glasses have already been shown in Figures 3A and 3B. Referring by way of example to Figure 3A (correction for the right eye), we made appear in P _D the projection of the center of the pupil on the glass. The distance between P _D and M _D is, on average, 2 mm. The distances between M _D and M ' _D and P _D M' _D are 14.5 and 16.5 mm respectively. M ' _D is shifted 2 mm inwards. The distance between the points P _D and M ' _D of 16.5 mm corresponds to a vertical angle of rotation of the eye to pass from distant vision to close vision of the order of 37 to 38 degrees. Naturally, the same values are found for the corrective lens intended for the left eye (FIG. 3B: LG ).

The axis M _D M ' _D is substantially vertical, as for bi-focal and tri-focal lenses, but with a slightly stronger angle of deviation from the vertical, typically 12 degrees. The formulas (8) and (9) then become: AT OD = SPH + CYL cos (γ - 12) and : AT OG = SPH + CYL cos (γ + 12)

The ideal value for Δ 'is typically given by the following relation (29 = 2 x 14.5 mm): Δ '= 29 AT 20

For an offset M ' O ' = y (in mm), the value of the prism Δ 'is given by the following relation: Δ '= 29 AT + 2 there ( AT + B ) 20

We will now describe in more detail the complete process for producing corrective lenses according to the invention. As has been recalled, the glasses are made from semi-finished glasses sold by various companies. The manufacture of these glasses does not enter not directly within the scope of the invention. The stage of surfacing the glass to obtain characteristics consistent with the expected result, in particular so that the relation (4) is satisfied, remains entirely compatible with the technologies used in the known art, which is a definite advantage.

According to a first method in accordance with what has been described with reference to FIG. 4, to which we will again refer, we position the semi-finished glass 1 (see FIG. 2A and 2B) on a support 2, comprising a body 22 and an annular ring 21 for receiving the semi-finished glass 1. The positioning is carried out, as indicated by means of visible marks on the convex surface (FIG. 2A: fe ) of the semi-finished glass 1. For obtain the desired prismatic deflection value Δ ', a prismatic insert 3 (prism Δ) is introduced between the semi-finished glass 1 and the support 2, according to this embodiment.

For bi-focal and tri-focal lenses, the value of the prism Δ is identical to the value Δ '. The value of this prism therefore obeys relations (10) or (11), depending on whether it it is a bi-focal lens or a tri-focal lens.

On the other hand, for progressive lenses, the prism induced on the glass Δ 'is different from the prism shown physically by the hold Δ. In cases where no one wishes not be satisfied with an approximation corresponding to the cases the most common of presbyopic individuals, so it's necessary to make corrections so that, given dimensions of the inserted shim (Figure 4: 3), Δ ' satisfy the relation (15) above. Practice shows that it is not advisable to establish a mathematical formula describing the aforementioned fixes by a correlation between the dimensions of the shim and the induced prism, and that it is better to proceed by experimental calibration to determine this correlation.

The first step is to determine a value of prismatic shim, assuming that Δ = Δ ', shim value which can be called "coarse". Physically, the angle at apex of the prismatic wedge is equal to the angle at the apex a prism equivalent to Δ '. To get the final result expected, it is necessary to make corrections, when a second step. To determine these fixes, proceed experimentally, for example by performing comparisons on prototypes made with different addition values B and a set of prismatic shims predetermined, for Δ> 0 and Δ <0. It is recalled that if the value of the prism is Δ = 0, there is no need addition. On the other hand, obtain a shim for Δ <0, is equivalent to inserting a shim in the positive direction and two identical shims in the negative direction. This operating mode simplifies the calibration process. The contribution of fixes above allows to refine the result and to converge the prismatic correction value finally obtained towards the desired value, i.e. that satisfying the relation (14).

Once these preliminary operations have been carried out, the final corrective glass can be obtained by a process surfacing fully compatible with those used in known art.

Figure 8A illustrates one of the commonly used methods. A machine tool 6, known as a surface generator, is used. This comprises a cutter, 60, the abrasive front face 62 of which advantageously has a diameter substantially equal to or greater than that of the semi-finished glass 1 (conventionally circular) and of radius of curvature equal to that of its convex face fe . The body 20 of the support 2 of the semi-finished glass 1 is locked in jaws 63, or any similar member, of a fixed support (not shown), mechanically coupled to the machine tool 6. The cutter 60 is placed at the end of a rotary axis 61, the axis of symmetry of which coincides with the axis of symmetry A _H of the support 2. When the cutter advances in translation along this axis A _H , it will attack the concave face fi of the glass 1 As it is inclined at an angle β relative to the axis A _H , the surfacing process results in a withdrawal of material, on the one hand, but also in the creation of a prism in the glass. in the opposite direction to the wedge 3. The attack on the glass 1 continues until a predetermined corrective glass thickness is obtained, this in a manner well known in itself.

For example, the cutter 60 is made of material diamond and rotates at a typical speed of 4500 revolutions / minute.

The following operation consists, in a manner known per se, of performing a smoothing and polishing of the two surfaces, fe and fi , possibly but not necessarily returned to the normal position, that is to say the glass not inclined, and identically for these two surfaces. These operations do not make any significant modification to the correction values obtained during the surfacing step. It is also possible to carry out surface treatments of the glasses, on their external face fe, such as an anti-reflective treatment.

Finally, in a manner also known per se, we cut the glass according to a predetermined template. He is not in necessary effect that the final glasses are circular. The corrective lenses, right and left, are cut to the shape of the spectacle frame which must to receive.

According to the surfacing process which has just been described, we introduce a physical prismatic wedge which induce a reverse prism in the glass of value strictly identical for bi-focal or tri-focal lenses, or of approximate value for progressive lenses. The same effect can be obtained without introducing a prism. In effect, if the semi-finished glass has a coincident axis of symmetry with that of support 2 and if the milling axis is inclined with respect to this axis, we get the same effect as previously.

Figure 8B schematically illustrates this milling process. The shaft 61 supporting the cutter body 60 rotates around an axis A " _H forming an angle β with the axis A _H. The device of FIG. 8A is therefore perfectly dual to the device of FIG. 8B. of course it is a relative inclination of the axes A _H and A " _H , the latter possibly remaining horizontal. It may indeed be easier to appropriately tilt the support holder 63 than the rotary shaft 61 of the machine tool 6. It is also possible to combine the two methods.

Finally, another known method consists in calibrating the semi-finished glass using three points integral with the support, and at least one of which is of different length of the other two. It follows that the semi-finished glass is carried by a tripod and presented in strawberry tilted, as before. If the three points are of equal length, we can implement a variant similar to the variant of FIG. 8B.

Other methods are also known, in particular a process using a small cutter and sweeping the entire surface of the semi-finished glass. Usually, this process gives less precise results and the strawberry wears out very quickly.

In a preferred embodiment, the steps machining of semi-finished glass and making a prism of predetermined value (i.e. satisfying one of the relations (4) or (7), in general, and one of the relations (10), (11), (14) or (15), in particular, depending on the type of corrective lens to be obtained) can be made fully automatic.

Figure 9 schematically illustrates a system complete authorizing such automation.

The shaft 61 cutter holder 60 is driven by a first rotary motor 64. The support 66 of this motor is mechanically coupled to a second rotary motor 68, for example by means of a set of gears comprising a screw end or a rack 67 (or any similar device) driving the support 66 along a horizontal axis A _H. It is also possible to use a stepping motor, instead of the rack and pinion gear 67 and the rotary motor 68. Finally, there is provided a slide device fixed on a flat support (not shown), or a similar device. , so as to guide the horizontal translation of the motor 64 and to support it.

In the embodiment described in FIG. 9, the semi-finished glass, of axis of symmetry A ′ _H , is made integral with a support, here referenced 2 ′. The support 2 'is itself carried by a motorized positioning device. It is positioned in space so that the point M is on the horizontal axis A _H (horizontal axis and axis of symmetry of the shaft 61) and that the axis of symmetry A ' _H of the semi-glass finite 1 form an angle of predetermined value β. This angle β is such that one will obtain the value of induced prism Δ 'satisfying one of the abovementioned relations. So that these last two requirements can be satisfied simultaneously, it is necessary that the support 2 'has two degrees of freedom: possibility of rotation about a horizontal axis, orthogonal to the axis A _H , to obtain the angle d 'tilt β, and translation along the axis A' _H to be able to place the point M on the axis A _H.

The different motorized components are controlled by a program information processing system recorded 8, including, for example, a microcomputer with general use with one or more specific cards (not shown), provided with input-output ports to which are connected, by connections specialized or standard (parallel, series), the different motorized parts.

In FIG. 9, the processing system of the information is a microcomputer 8 provided with standard peripherals, including a screen display 81, a keyboard 80, and a reader floppy disk 82. The main ones have also been represented connections between the microcomputer 8, on the one hand, and the motorized parts, 7, 64 and 68, on the other hand.

Link l ₁ transmits instructions to the member 7 controlling the positioning of the support 2 'in rotation and in translation. The latter is associated with one or more conventional sensors, in particular of position (not shown), for example of an opto-electronic type. These sensors allow, among other things, to determine the position in space of the semi-finished glass 1. To do this, knowing the exact position of the horizontal axis A _H which is fixed, we can use the reference marks ( see Figure 2A) worn on the surface fe of the semi-finished glass 1. One can in particular carry out an otic reading of the position in space of these marks, or marks.

Whatever the method used, an additional link l ₂ transmits the results of the measurements made to the microcomputer. In return, the latter can therefore, via the connection l ₁ , control in real time the movement of the semi-finished glass 1, so that the aforementioned positioning requirements are satisfied and block it in the position reached, so to be presented to the strawberry 60 with the desired β inclination. Naturally, the links l ₁ and l ₂ can be merged into a single bidirectional link.

The microcomputer 8 controls the operation of the motor 64 by the link 1. It can be instructions for a simple on-off control or instructions also controlling the speed of rotation of the motor 64.

Finally, the microcomputer 8 controls the forward and backward translation of the cutter 60, along the axis A _H , this by means of the motor 68 and the worm screw 67 acting on the base 66 of the motor 64 (in the example described). To do this, provision is made for a connection l ₅ transmitting the forward or reverse operating instructions to the motor 68. It is also necessary to provide a position sensor (not shown) transmitting data relating to the position reached at all times by the cutter 60. It may be an electromechanical transducer or an opto-electronic transducer: coded wheel, etc., coupled to the worm screw 67.

If the motor 68 is of the stepping type, there are generally digital data representing the position of the actuator acting on the base 66 of the motor 64. Such data are directly usable by the microcomputer 8, without that an analog-to-digital conversion is required. A link l ₄ conveys the position measurement signals of the cutter 60 along the axis A _H. As before, the unidirectional links, l ₄ and l ₅ , can be merged into a single bidirectional link.

It should be clear that the connections, l ₁ , l ₃ and l ₄ , for controlling the motorized members, 7, 64 and 68, do not normally carry electrical power signals, but that they act on electromechanical switches ( relays, etc.) and / or electronic (semiconductor switches, etc.) disposed between conventional electrical and / or fluid supply circuits (not shown) and these motorized members.

The microcomputer 8 records, in the memory of mass (hard drive, not shown) of which it is usually provided with data and instructions program for the production of corrective lenses, especially for the surfacing machining step. In a way more particular still, in accordance with the characteristic main of the invention it records the data and instructions for obtaining an induced prism in the glass corresponding to relation (4), so general, and to either specific relationship (10), (11) or (14), more specifically, depending on the type of corrective lens to obtain (bi-focal, tri-focal or progressive).

In the case of progressive lenses, since the induced prism obtained, of value Δ ', cannot be directly derived from the value of the angle β, it is also useful to record a database gathering the results of experiments on a range of prototypes manufactured with various values of β angles and B additions. These data are used to introduce the aforementioned fixes.

The data and program instructions can be entered initially by hand using the keyboard 80, or better still by reading a DK diskette (diskette drive 82) or any other magnetic or optical medium, provided that the microcomputer 8 is provided with an appropriate reader. You can still enter the data and instructions in the microcomputer by download, via a modem. This provision is particularly advantageous if the place of manufacture of corrective lenses is in a store dependent on a chain. The programs and the application data can then be developed centrally and be available in real time, by simple query of a central database made available to all members, either for the production of corrective lenses proper , either to initialize or update a local database.

It is easy to understand that the control program registered and / or the data associated with it may be easily modified or updated, for example to take into account the availability of new types of glasses semi-finished, or simply to correct errors in the program or improve performance. Of such modifications are also necessary when change machine tool or when replacing some components of the machining chain. This characteristic adds to the flexibility of the process.

In operational operating mode, an operator enters the parameters necessary for carrying out the surfacing step of the corrective lens to be produced, taking into account all the parameters associated with this step: characteristics of the basic semi-finished lens, type of corrective lens and values of the corrections to be obtained ( A , B ), angular deviation β to obtain the prism Δ ', possibly the corrective parameters for the progressive lenses (or at least the indication that such corrections must be introduced, the program then automatically introducing). The data and instructions entered are displayed on the screen 81, in text and / or graphic form. As an example, the program can display a menu in the form of questions which the operator must answer to fully define the corrective lens he wishes to make. In response, the program can display on screen 81 the characteristics or the model of the semi-finished glass to be used if these data were not entered in the previous step.

The operator then launches the actual surfacing step, which takes place automatically under the control of the recorded program that he has configured in the previous step. This surfacing step is carried out in the manner previously described, by bidirectional exchanges of data and / or instructions, via the various links, l ₁ to l ₅ , between the microcomputer 8, the motorized members, 7, 64 and 68 , which it controls, and the sensors, in particular of position, associated with these motorized members.

Naturally, other types of support can be used for semi-finished glass 1, for example a support of the tri-point type. It is only necessary that the axes of symmetry of the semi-finished glass 1 and of the cutter 60 form a determined angle β, so as to induce a prism in the glass which verifies the relation (4), which allows the points to be confused. M ', O ' and O ", or to get closer when the relation (7) is verified).

The process is also compatible with the production of astigmatism corrective lenses, in playing on relations (8) and (9), or (12) and (13).

In light of the foregoing description, it is clear that the invention achieves the goals that it has set.

The production method, comprising a step of surfacing, allows to obtain multi corrective lenses hearths, in particular double hearth, triple hearth and progressive, and brings many benefits. These corrective lenses do not do not exhibit, in particular, the unpleasant phenomenon of jumping image when switching from one vision mode to another (vision distant near vision, for example). The distortions in close vision are imperceptible. They offer great reading comfort and adaptation Instant.

The production process remains compatible with known art technologies and allows use like base material, commonly semi-finished glasses commercially available and selected from a range standard.

Finally, in a preferred embodiment, it allows a great automation of the process, by the use of computerized means.

It should be clear, however, that the invention is not not limited to only examples of achievements explicitly described, in particular in relation to FIGS. 5 to 9. In particular, for the surfacing step, it can be done use of various technologies, only some of which have been detailed.

Claims (10)

1. Method for producing vision correction lenses from semi-finished lenses having a power addition for near-vision correction with respect to distant-vision correction, characterised in that mechanical machining that adds a prismatic deviation is performed on an internal face of each lens, through reducing the thickness thereof, and this prismatic deviation is calculated, based on an individual distance MM ' between a distant-vision application centre M and a near-vision application centre M', in order, to bring back the optical correction centre in near-vision O' as close as possible to the near-vision application centre M'.
2. Method according to claim 1 for producing, in particular for presbyopia glasses, a potentially progressive, multi-focal correction lens from a semi-finished lens (1) with determined optical characteristics, by varying the index and/or thickness, characterised in that, said semi-finished lens (1) comprising a first concave face (fi) and a second convex face (fe) and including at least a first positioning marker M associated with a so-called distant-vision correction A that materialises said distant-vision application centre, and a second positioning marker M', associated with a so-called near-vision additive correction B that materialises said near-vision application centre, said method includes at least a surfacing step wherein material is removed to a determined depth from one of said faces, preferably said internal face (fi), using abrasion machining means (60) which are translated along a first axis (AH, A"H), said surfacing step including presenting said semi-finished lens (1) in front of said machining means (60) such that a second axis (A'H) orthogonal to a tangent plane at the point constituting said first positioning marker M is inclined at a determined angle (β) with respect to said first axis (AH, A"H), so as to induce into the semi-finished lens a prism aligned on the rectilinear segment MM ' having an apex angle which is a function of said angle of inclination (β), and in that the prismatic deviation Δ', in diopters, of said induced prism complies with the equation: Δ' = ( MM ' x A)+ Y x (A + B) in which MM ' is the distance in centimetres between said points M and M', A and B are said corrections expressed in diopters, and Y is the distance in centimetres between the point M' and the optical near-vision centre of said correction lens (4, 5).
3. Method according to claim 1 or 2, characterised in that corrections are made which are equivalent to an angle of inclination α of an axis comprising said points M and M' with respect to the vertical and in that, for the right eye and for the left eye respectively, said angle α is assumed to be +8 degrees and -8 degrees.
4. Method according to either of claims 1 or 2, characterised in that said semi-finished lens (1) is selected in a standard range for determining said distant-vision correction A, in that it consists of a substantially circular-shaped glass block having determined optical characteristics, with said block being inscribed between two faces having identical radii of curvature, of which one is a convex, so-called external face (fe) and the other is a concave, so-called internal face (fi), and in that the surfacing step consists in removing material to a determined depth from said concave face (fi), with the semi-finished lens (1) being presented to said machining means (60) at an angle of inclination (β).
5. Method according to any one of claims 1 to 3, characterised in that it comprises a preliminary step consisting of securing said semi-finished lens (1) on a support (2) having an axis of symmetry, placing between said support (2) and said semi-finished lens (1) a prismatic shim (3) with an apex angle equal to said angle of inclination (β), but in a direction opposite to said induced vertical prism to be produced, so as to obtain a same inclination of this semi-finished lens (1) with respect to said axis of symmetry, and placing said support (2) in front of said machining means (60) with said axis of symmetry being coincident with said translation axis (AH).
6. Method according to any one of claims 1 to 3, characterised in that it includes a preliminary step consisting of securing said semi-finished lens (1) on a support (2) having an axis of symmetry (AH) such that this axis of symmetry (AH) is coincident with said second axis (A'H), and placing said support (2) in front of said machining means (60) so that said axis of symmetry (AH) forms an angle equal to said angle of inclination (β) with said translation axis (A"H).
7. Method according to any one of claims 1 to 5, characterised in that, when said correction lens to be produced (4) is of the bifocal type, the method comprises a step of selecting a value for the angle of inclination (β) corresponding to an apex angle of the induced prism such that the prismatic correction thereof complies with the following equation: Δ' = A wherein A is said distant-vision correction expressed in diopters.
8. Method according to any one of claims 1 to 5, characterised in that, when said correction lens to be produced is of the trifocal type (5), the method comprises a step of selecting a value for the angle of inclination corresponding to an apex angle of the induced prism such that the prismatic correction of said prism complies with the following equation: Δ' = 16A 10 wherein A is said distant-vision correction expressed in diopters.
9. Method according to any one of claims 1 to 5, characterised in that, when said correction lens to be produced is of the so-called progressive type (L), the method comprises a first step of selecting a so-called rough angle of inclination value (β) equal to the apex angle of a prismatic correction prism that complies with the equation: Δ' = 29A 20 wherein A is said distant-vision correction expressed in diopters, and a second step of correcting said rough angle value with the aid of experimental data so that said prismatic deviation of the prism induced into the lens will converge towards said equation Δ' = 29A 20 wherein said experimental data is obtained from comparative measurements of a series of progressive lens prototypes with determined prismatic corrections and additive corrections.
10. System for producing a multi-focal correction lens, in particular for glasses, for carrying out the method according to any one of the preceding claims, characterised in that it comprises a support for said semi-finished lens (1) with motorised inclination means (7) for slanting said support with respect to a horizontal axis (AH), machining means (6) comprising an abrasive milling cutter (60) for said concave face (fi) of the semi-finished lens (1), and a rotary motor (64) driving said abrasive milling cutter (60) at a determined angular speed, and motorised means (66-68) for translating said milling cutter (60) along said horizontal axis (AH) so as to perform said surfacing step removing material to a determined depth from said concave face (fi), in that said system also comprises position sensors for measuring the spatial instantaneous positions of said motorised inclination means (7), said abrasive milling cutter (60) and said translating motorised means (66-68) for displacing said abrasive milling cutter (60), and a data processing system with a recorded program (8), comprising at least means (80, 82) for inputting and collecting of data by an operator and of instructions for programming and storing these data, and in that said data processing system (8) controls said motorised inclination means (7), said rotary motor (64) and said translating motorised means (66-68) for displacing said abrasive cutter (60), based in particular on said measurements taken by said position sensors and on parameters collected via said data inputting.and collecting means (80) by an operator, so as to present said semi-finished lens (1) to said machining means (60) at said angle of inclination (β), based on said corrections to be made.

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