METHOD OF CALCULATING A FINISHED LENS

Abstract

A finished lens with a predetermined shape, including one front face, one back face and a perimeter corresponding to the shape, including a prescription part on the lens that together with the front face fulfills prescription data of a wearer and a peripheral part on the lens, the prescription part being delimited by a thickness curve and the peripheral part extending from the thickness curve towards an outer edge of the lens, the thickness curve corresponding to a value of thickness less than or equal to a predetermined thickness requirement.

Claims

1. A computer implemented method of calculating a finished lens with a predetermined shape, comprising one front face, one back face and a perimeter corresponding to said shape, comprising the following steps: providing a lens blank having a convex front face and a concave back face; determining, free of frame shape data into which the lens is to be mounted, a prescription part on the lens that together with the front face fulfills prescription data of a wearer and a peripheral part on the lens by determining a first curvature profile of a back surface to be machined on the back face of the lens blank, and by determining a thickness curve corresponding to a value of thickness less than or equal to a predetermined thickness requirement, the prescription part being delimited by the thickness curve and the peripheral part extending from the thickness curve towards an outer edge of the lens.

2. A computer implemented method of calculating a finished lens, with a predetermined shape, comprising one front face, one back face and a perimeter corresponding to said shape, comprising the following additional steps: providing a minimum edge thickness for the finished lens; determining a first curvature profile of a back surface to be machined on the back face of a lens blank; determining whether a thickness of outer edge of a peripheral part of that lens blank machined on the back face with the first curvature profile at the peripheral part will be less than the minimum edge thickness; and if the thickness of outer edge of the peripheral part will be less than the minimum edge thickness, determining a new curvature profile of the peripheral part of the back surface to be machined wherein the thickness in the peripheral part is greater or equal to the minimum edge thickness in order to avoid sharp edge, the finished lens comprising a prescription part being delimited by a thickness curve and the peripheral part extending from the thickness curve towards an outer edge of the lens, the thickness curve corresponding to a value of thickness less than or equal to a predetermined thickness requirement.

3. The method pursuant to claim 1, wherein the predetermined thickness requirement corresponds to an edge thickness of the lens cut provided during an ordering of the finished lens.

4. The method pursuant to claim 1, wherein the thickness curve is an isothickness curve.

5. The method pursuant to claim 1, wherein a local or global safety margin is applied to the thickness curve in order to define the thickness curve delimiting the prescription part and the peripheral part of the lens.

6. The method pursuant to claim 2, wherein the minimum edge thickness is preferably greater than or equal to 0.4 mm.

7. The method pursuant to claim 2, wherein the step of determining a new curvature profile of the peripheral part of the back surface to be machined is based on an interpolation method of soundly distributed points.

8. The method pursuant to claim 2, further comprising a step of optimization of the position and/or the size of sharp edges zones at the peripheral part of the back surface of the back face of the lens wherein the curvature profile have to be modified.

9. The method pursuant to claim 8, further comprising the following steps: determining a cribbed diameter D.sub.cribb of the finished lens; and determining the best position for the cribbing diameter in order to minimize overlapping areas between said cribbing diameter and a predetermined thickness curve and/or to minimize the curvature of the back surface in the peripheral part.

10. The method pursuant to claim 1, further comprising a step of optimizing the orientation of the finished lens during a varnish coating step.

11. A method for manufacturing an optical lens comprising a step of engraving manufacturing marks in the peripheral part of the finished lens determined by using the method of claim 1.

12. The method pursuant to claim 11, further comprising a step of optimizing the cosmetic control step.

13. A non-transitory computer-readable medium comprising program code for carrying out the steps of the method according to claim 1.

14. A non-transitory computer-readable medium comprising program code for carrying out the steps of the method according to claim 2.

15. A finished lens with a predetermined shape, comprising one front face, one back face and a perimeter corresponding to said shape, comprising a prescription part on the lens that together with the front face fulfills prescription data of a wearer and a peripheral part on the lens, the prescription part being delimited by a thickness curve and the peripheral part extending from the thickness curve towards an outer edge of the lens, the thickness curve corresponding to a value of thickness less than or equal to a predetermined thickness requirement.

Description

[0065] We give hereafter a detailed description of embodiments of a method pursuant to the invention, by referring to the following pictures:

[0066] FIGS. 1A and 1B are respectively a front view and a perspective view of an finished lens having a sharp edge,

[0067] FIGS. 2A and 2B are respectively a front view and a perspective view of an finished lens having a non-sharp edge,

[0068] FIG. 3 is a front view of an finished lens having a sharp edge and showing a central area delimiting the perimeter of a useful part of the optical lens intended to be mounted on a frame,

[0069] FIG. 4 is a front view of a finished lens showing iso-thickness distribution through the lens,

[0070] FIGS. 5A and 5B are front views of a finished lens showing respectively an example of a chosen iso-thickness curve and said chosen iso-thickness curve included the useful part of the optical lens intended to be mounted on a frame,

[0071] FIGS. 6A, 6B, 6C and 6D are four front views of a finished lens illustrating four steps of an embodiment of interpolation method included in a method pursuant to the invention,

[0072] FIG. 7 is a diagram giving the thickness of the finished lens versus a sector of a diameter of said lens showing a sharp edge,

[0073] FIG. 8 is the diagram of FIG. 7 after a correction and showing an outer edge of the finished lens with a minimal thickness.

[0074] Referring to FIGS. 2A, 2B, 7 and 8, a method pursuant to the invention aims to provide a finished lens 1 with a predetermined shape with an outer edge 15 which is not sharp but having a minimal edge thickness. Such a finished lens 1 has a rear face (or a concave face) and a front face (or a convex face) and its thickness decreases from a central area to a outer edge 15. The predetermined shape of the finished lens (1) may to be chosen among an elliptical shape, a circular shape and any optimized shape.

[0075] The finished lens 1 must integrally comprise a useful part 5 which is intended to be mounted on a predetermined frame

[0076] According to a method pursuant to the invention, the method comprises the following steps: [0077] Obtaining prescription data of a wearer S1, [0078] Providing a lens blank having a convex front face and a concave back face S2, [0079] Selecting S5 a thickness curve corresponding to a value of thickness less than or equal to a predetermined thickness requirement, this curve defining: [0080] an outer perimeter of a prescription part 13 of the back surface to be machined on the back face of the finished lens 1 that together with the front surface of the front face of the lens blank fulfills the prescription data of the wearer and [0081] a peripheral part 14 on the back surface to be machined on the back face of the lens blank extended from the thickness curve towards the outer edge 15 of the finished lens 1

[0082] In addition, in one embodiment, the method comprises the following steps: [0083] Providing a minimum edge thickness for the finished lens 1 S3, [0084] Determining a first curvature profile of a back surface to be machined on the back face of the lens blank S4, [0085] Determining S6 whether a thickness of the outer edge 15 of the peripheral part 14 will be less than the minimum edge thickness if the back surface of the lens blank is manufactured to have the first curvature profile at the peripheral part 14 [0086] If the thickness of the outer edge 15 of the peripheral part 14 will be less than the minimum edge thickness and thus the outer edge 15 is sharp, determining an optimised curvature profile of the peripheral part 14 of the back surface to be machined wherein the thickness in the peripheral part 14 is greater or equal the minimum edge thickness so as to obtain the outer edge 15 having a minimal thickness and which is preferably no longer sharp.

[0087] In step S3, the minimum edge thickness Te.sub.min is provided. The minimum edge thickness Te.sub.min is the minimum edge thickness requested at the outer edge 15 of the finished lens 1 to be produced from the lens blank. The value of the minimum edge thickness Te.sub.min is preferably chosen to avoid any sharp edge at the outer edge 15 of the finished lens 1 and provide finished lens with predetermined shape.

[0088] Preferably, the minimum edge thickness Te.sub.min is greater than or equal to 0.4 mm.

[0089] In step S5, the thickness curve 12 corresponding to a value of thickness less than or equal a predetermined thickness requirement Tr is determined and in the back surface of the back face of the lens the prescription part 13 and the peripheral part 14 are defined.

[0090] In one embodiment of the invention, the predetermined thickness requirement Tr may be the value of the outer edge thickness of the lens cut. This data may be provided during ordering of the optical lens.

[0091] Preferably, the predetermined thickness requirement Tr is greater than or equal to 0.8 mm.

[0092] In order to define the thickness curve 12, the method pursuant to the invention comprises a thickness determining step wherein the thickness of the lens 1 which back surface is to be machined at several points is determined.

[0093] The thickness is defined by the front and back surface and the distance between the faces at a given point of these surfaces.

[0094] The values of thickness may be determined by any known method in any convenient coordinate system by any known lab management system.

[0095] In one embodiment of the invention, in a first substep, a map of iso-thickness curves 7, 8, 9 in the finished lens 1 is established. Indeed, by knowing the geometry of the finished lens 1 and, in particular, the back surface of the back face to be machined it is possible to establish a cartography of the iso-thickness curves 7, 8, 9 in said lens 1. The distribution of thickness in the lenses is illustrated in FIG. 4. The greatest thickness of the finished lens 1 is located in a central area 10 of said lens 1, while the thinnest thickness of said lens 1 is located in a peripheral area 11, the thickness decreasing from said central area 10 to said peripheral edge 11.

[0096] In a second substep, a iso-thickness curve 12 as illustrated in FIG. 5A corresponding to a given thickness is chosen.

[0097] In one embodiment, the iso-thickness curve 12 is chosen so as to correspond to a value which is less than or equal to the predetermined thickness requirement Tr that correspond to the minimal thickness required on the edge of the lens cut.

[0098] In another embodiment, the chosen iso-thickness curve 12 is defined based on an adjustable value depending on the type of frame intended to receive the the cut lens.

[0099] Referring to FIG. 5B, this suitable iso-thickness curve 12 delimits the prescription part 13 which must include the useful part 5 of the optical lens 1 intended to be mounted on a predetermined frame and the peripheral part 14 that extend toward the outer edge 15 of the finished lens 1.

[0100] On the example illustrated on FIG. 5B, the chosen suitable iso-thickness curve 12 surrounds the useful part 5 of the optical lens 1, by keeping a minimal distance with said useful part 5.

[0101] The inventors have identified that when using thickness curves based on thickness required on the edge of the cut lens or type of frame data, the useful part 5 of the lens is always included in the prescription part 13 of the finished lens 1.

[0102] According to the invention, the useful part data 5 and/or frame shape data defining the contour of the spectacle frame are not used to define the prescription part 13 and the peripheral part 14 of the back surface of the back face of the finished lens. This means that the determination of the two different parts is free of frame shape data into which the finished lens 1 when cut is to be mounted.

[0103] In one embodiment not illustrated, a safety margin may be provided to the thickness curve 12. In this case, the thickness curve 12 selected to define the outer perimeter of the prescription part 14 is modified locally or globally to include in its contour points wherein the thickness is less than the thickness requirement Tr. The advantage is to ensure that the useful part 5 of the cut lens is not distorted in the frame contour.

[0104] In a next step, the algorithm determines if a thickness of the outer edge 15 of the peripheral part 14 is less than the minimum edge thickness Te.sub.min when the back surface of the lens blank is manufactured with the first curvature profile.

[0105] If the algorithm detects that the outer edge 15 of the peripheral part 14 will be less than the minimum edge thickness Te.sub.min and thus is too thin and thus is sharp, as illustrated on the example of FIG. 7, a step to determine an optimised curvature profile of the peripheral part 14 of the back surface to be machined is performed by said algorithm. In this step, the thickness in the peripheral part 14 is modified to be greater or equal to the minimum edge thickness Te.sub.min so as to obtain an outer edge 15 with a minimal predetermined thickness, as illustrated on the example of FIG. 8.

[0106] This minimal thickness can be for example 0.4 mm.

[0107] On the diagram of FIG. 8, the algorithm calculates a new machining profile or optimised curvature profile of the back surface of the back face of the finished lens 1 as illustrated by the curve 18 replacing the initial profile illustrated by the doted curve 17. In this way, the outer edge 15 has a minimal thickness and is no longer sharp. The initial profile materialized by the curve 17 shows an outer sharp edge 15 delimiting a recess 3, and the new machining profile allows to compensate this recess 3 by extending the diameter of the finished lens 1 in order to give a predetermined shape to said lens, for example circular. Consequently, the outer edge 15 which was initially sharp is displaced so as to increase the optical lens sizes, explaining the difference of outer edge 15 locations between FIG. 7 and FIG. 8.

[0108] To determine the optimised curvature profile of the peripheral part 14 of the back surface to be machined wherein the thickness of the peripheral part 14 should be greater or equal the minimum edge thickness Te.sub.min, several methods of surface optimization or adjustment may be used under the given conditions.

[0109] The method may be any known interpolation method.

[0110] In one embodiment, the interpolation method uses a first set of points internal to the thickness curve 12 wherein the minimum edge thickness Te.sub.min is satisfied and a second set of points at the outer edge of the peripheral part of the finished lens wherein the minimum edge thickness Te.sub.min is not satisfied to optimize the thickness of the second points to provide an optimised curvature profile of the peripheral part 14 of the back surface to be machined.

[0111] In one example, the method of determining an optimised curvature profile of the peripheral part for the back surface to be machined comprises the following steps: [0112] Sampling a first set of points 20 which are internal to the chosen iso-thickness curve 12 and which define a portion with a thickness greater or equal to the minimum edge thickness Te.sub.min as illustrated in FIG. 6A, [0113] In one alternative as the one illustrated in FIG. 6A, the first set of points is defined not only in the edge of the isothickness curve but also in all the surface which outer perimeter is the iso-thickness curve 12. [0114] Sampling a second set of points 21 which are different from the first points 20 wherein the minimum edge thickness Te.sub.min is not satisfied and which are distributed on the outer edge 15 of the peripheral part 14 as illustrated in FIG. 6B, [0115] optimize the altitude of the second points 21 so that the thickness corresponding to said second points 21 is greater than or equal to the minimal thickness Te.sub.min, [0116] Calculate an optimized curvature profile of the peripheral part of the back surface constituted by sampled points on the interpolating for the points out of the iso-thickness line 12 and the sampled points on the initial back surface when the latest are inside or on the chosen iso-thickness line 12.

[0117] In one example, the second set of points may be equally distributed as illustrated in FIG. 6B.

[0118] In another embodiment, the method provides a step of sampling a third set of points 22 that described a contour having a predetermined diameter which is larger than the diameter of the finished lens 1, so as to link the interpolated back surface to the initial back surface as illustrated in FIG. 6C and a step of calculate the interpolating of these points 22 as illustrated in FIG. 6D.

[0119] In another embodiment, the determination of the optimized curvature profile of the back surface of the back face of the finished lens 1 can be weighed to take into account a manufacturing requirement function thanks to the minimum edge thickness. The latter function may define manufacturing constraints linked to the manufacturing processes used and/or related cutting tools with the authorized maximum curvature they can provide to a surface.

[0120] In addition, one or several cutting steps during the machining of the back surface of the back face of the lens 1 may be provided to define the optimized curvature profile of the back surface of the back face of the lens.

[0121] The method may further comprise a step of optimization of the zones at the peripheral part of the back face of the lens wherein the curvature profile have to be modified, called sharp edge zones, when sharp edge is identified.

[0122] This optimization may at least include the optimisation of the position and/or orientation and/or the size of the sharp edge zones at the peripheral part of the back face of the lens 1.

[0123] The optimization of the sharp edge zones of the peripheral part 14 comprises the following sub steps: [0124] Determining a cribbed diameter D.sub.cribb of the finished lens, [0125] Determining the best position for the cribbing diameter in order to minimize the overlapping areas between said cribbing diameter and a predetermined thickness curve and/or to minimize the curvature of the back surface in the peripheral part.

[0126] The determination of the cribbed diameter D.sub.cribb may be made by any known method.

[0127] The predetermined thickness curve may be preferably greater than or equal to 0.4 mm.

[0128] To determine the best position for the cribbing diameter, the position and/or the size of the cribbed diameter Dcribb compared to the predetermined thickness curve may be optimised.

[0129] In one embodiment, the best position of the cribbed diameter D.sub.cribb is defined by iterative solutions in an appropriate coordination system.

[0130] In another embodiment, the method includes a step of optimizing the orientation of the finished lens in a varnish basket during a varnish coating step based on the definition of the peripheral part and prescription part delimited by the chosen thickness curve 12.

[0131] The optimization of the orientation of the finished lens in a varnish basket comprises the following sub steps: [0132] Determining the location of the handling means of the varnish basket, e.g clips elements, in order to put the handling means in the peripheral part 14. [0133] Determining the best position for the lens in order to maximize the distance between the thickness curve 12 and the handling means.

[0134] The determination of the best position may be made by any known method.

[0135] To determine the best position, the orientation of the lens may be optimised to move away the handling means from the thickness curve 12.

[0136] When the best position is defined, varnish basket orientation visible marking in the peripheral part of the lens may be defined and engraved to drive the operator during the loading of the basket.

[0137] In another embodiment, the location of the drop may further be optimized to be put in the peripheral part of the lens.

[0138] Another embodiment concerns a method for manufacturing an optical lens comprising a step of edging the finished lens determined by using the method as disclosed above.

[0139] In addition, the manufacturing method may include a step of engraving manufacturing marks in the peripheral part of the lens. Those engraving marks could be helpful during the manufacturing process or useful for the eye care professional to give him/her information about the lens. However as these marks will be cut out of the lens during the edging of the lens, they are not intended for the wearer.

[0140] In another embodiment, the manufacturing method may include a step of optimizing the cosmetic control of the lenses.

[0141] During the cosmetic control step, the location of a cosmetic default in the lens is determined and if the default is detected in the peripheral part of the lens as defined according to the methods of the invention, the lens is not rejected as having a cosmetic default since this peripheral part will be suppressed during the edging of the lens to be mounted in a frame.