METHOD OF CALCULATING A FINISHED LENS

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.

The invention relates to a method of calculating a finished lens and the related systems and lenses.

An optical lens concerned by such a method has one concave face and one convex face and an outer perimeter, where the outer perimeter has a thickness within a preestablished range.

An optical lens is generally manufactured from a semi-finished lens blank. A semi-finished lens blank generally has two opposing major surfaces at least one of which is unfinished. The unfinished surface is typically the surface corresponding to the back surface of the optical lens which, in use, is orientated towards the eye of a wearer. The unfinished surface of the semi-finished lens blank is machined according to the wearer's prescription to provide the required back surface of the optical lens. Prior to machining of the back surface, the diameter of the blank typically is reduced by cutting to a shape e. g. round or ellipsoidal, which cutting process is known as cribbing.

An optical lens having finished back and front surfaces is often referred to as an uncut optical lens or finished lens. The finished lens is then edged according to a shape of a frame on which the optical lens is to be mounted in order to obtain an edged or cut lens.

Referring toFIGS.1A,1B and3, by machining the unfinished back surface of the semi-finished lens blank so that it fulfills a particular preestablished prescription, there may be problems with the thickness of the outer perimeter2of the finished lens. Indeed, it is possible that the thickness may be excessively fine, and even that it may be null or negative, which means that the outer perimeter2of the finished lens, once it has been machined, is no longer circular, has recesses3and result in formation of local sharp edge4at the outer perimeter of the finished lens.

Sharp edge4is disadvantageous in that it is prone to cracking or chipping resulting in one or both of contamination of subsequent cleaning or coating steps of the manufacturing process and an unusable finished lens.

Additionally, the sharp edge4damages the polishing tools during the polishing step of the manufacturing process.

Additionally, the sharp edge4makes the finished lens harder to handle either manually or by machine and is likely to cause injuries to a person who would handle said finished lens.

Finally, finished lenses with sharp edges4are more likely to exhibit coating defects such as for example some anti reflective coating not correctly coated on the finished lens and be rejected as unacceptable from a cosmetic basis.

Indeed, the suppression of such sharp edges4is interesting for the following reasons:Avoiding to damage some tools such as, for example, polishing tools on the sharp parts of the finished lens,Allowing the automation of the manufacturing method by reducing the shapes diversity of the finished lens to be handled,Facilitating the handling of the finished lens,Reducing the edge fragility,Improving the esthetic of the finished lens to be delivered.

Known solutions are related to a method tending to remove the sharp edge of a finished lens by knowing the shape of the frame on which the optical lens is intended to be mounted. The finished lens has a thickness within a pre-established range, a central useful area that fulfils a particular pre-established ophthalmic prescription, which defines a machined surface, and which has a useful perimeter that coincides with the perimeter of a particular pre-established frame, and an outer transition area that joins the useful perimeter of central useful area to outer perimeter.

More globally, during the lens manufacturing process, marking of lens handling clips in the useful part of the lenses may appear as well as drop of varnish in the useful part of the lenses.

In addition, lenses may be rejected for defaults that only appear in the non useful part of the lenses that will be finally edged.

There is a need to optimise cosmetic control rejection and varnish coating process during the manufacturing of lenses.

Furthermore, a method pursuant to the invention allows to avoid the presence of sharp edge in a finished lens, free of the constraints to use the shape of the frame on which the optical lens is intended to be mounted, while guaranteeing to the cribbed finished lens a shape whose geometry is mastered.

A first object of the invention is 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.

The principle of this method pursuant to the invention lies in the determination of thickness curves in the finished lens, then in a choice of a suitable thickness curve determining a prescription part and a peripheral non useful part of the lens without using the frame shape intended to receive the useful part of the optical lens, the prescription part surrounding the useful part of the optical lens intended to be mounted on a frame.

The term “useful part” refers to the lens part which will be machined in the optical lens and which will have the final suitable shape to be mounted on a frame.

According to a possible characteristic of the invention, the method further includes a step of optimizing the orientation of the finished lens during a varnish coating step.

According to a possible characteristic of the invention, varnish basket orientation markings in the peripheral part of the lenses are defined.

A second object of the invention is 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.

A third object of the invention is 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,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 the lens blank,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 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 lensDetermining whether a thickness of the outer edge of the 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 if the back surface of the back face of the lens blank is manufactured using the first curvature profile at the peripheral partIf 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 the minimum edge thickness in order to avoid sharp edge.

The principle of a method pursuant to the invention lies in the determination of thickness curves in the finished lens, then in a choice of a suitable thickness curve surrounding the useful part of the optical lens intended to be mounted on a frame, and finally in a determination of an optimized curvature profile at the peripheral part of the back surface to be machined situated around the prescription part delimited by said thickness curve, if the algorithm detects the presence of a potential sharp edge.

The choice of the thickness curve is made, without using the frame shape data intended to receive the useful part of the optical lens.

A method pursuant to the invention presents the advantage to manufacture optical lenses without any sharp edge and without exactly knowing the frame on which the finished lenses are intended to be mounted or without using this last information.

According to a possible characteristic of the invention, the predetermined thickness requirement corresponds to an edge thickness of the lens cut provided during an ordering of the finished lens.

According to a possible characteristic of the invention, the thickness curve is an isothickness curve.

According to a possible characteristic of the invention, 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.

According to a possible characteristic of the invention, the minimal edge thickness is preferably greater than or equal to 0.4 mm. With such a thickness value we can estimate that the outer edge of the lens is no longer sharp.

According to a possible characteristic of the invention, the predetermined shape of the optical lens is to be chosen among an elliptical shape, a circular shape or an optimized shape. These kinds of shape aim to facilitate for example the handling of lenses or the coating processes to avoid coating defects on the lenses.

According to a possible characteristic of the invention the determination of the new curvature profile of the peripheral part of the back surface to be machined is weighed to take into account a manufacturing requirement function.

According to a possible characteristic of the invention, 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.

According to a possible characteristic of the invention, the step of determining a new curvature profile of the peripheral part of the back surface to be machined comprises the following steps:Sampling of a first set of points which are internal to the chosen thickness curve,Sampling of a second set of points which are different from the first points and which are situated on the outer edge,Change of the altitude of the second points so that the thickness corresponding to said second points is greater than or equal to the minimal predetermined thickness,Calculation of a back surface constituted by sampled points on the interpolating for the points out of the thickness curve and the sampled points on the initial surface when the latest are inside or on the chosen thickness curve.

According to a possible characteristic of the invention, the method comprises a step of optimization of the position and/or orientation and/or the size of identified 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.

According to a possible characteristic of the invention, the method comprises the following steps:Determining a cribbed diameter Dcribbof the finished lens,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.

Another object of the invention is a method for manufacturing an optical lens comprising a step of edging the finished lens determined by using the methods as disclosed above.

According to a possible characteristic of the invention, the method further includes a step of engraving manufacturing marks in the peripheral part of the lens.

According to a possible characteristic of the invention, the method further includes a step of optimizing a lens cosmetic control step.

According to a possible characteristic of the invention, 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, the lens is not rejected as having a cosmetic default.

Another object of the invention is a computer program product comprising program code for carrying out the steps of a method as disclosed above, when the computer program product is run on a data processing device.

Another object of the invention is a computer-readable medium carrying one or more sequences of instructions of the computer program product.

Another object of the invention is 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. Such finished lens may be preferably obtained by a computer implemented method according to the invention.

Referring toFIGS.2A,2B,7and8, a method pursuant to the invention aims to provide a finished lens1with a predetermined shape with an outer edge15which is not sharp but having a minimal edge thickness. Such a finished lens1has 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 edge15. The predetermined shape of the finished lens (1) may to be chosen among an elliptical shape, a circular shape and any optimized shape.

The finished lens1must integrally comprise a useful part5which is intended to be mounted on a predetermined frame

According to a method pursuant to the invention, the method comprises the following steps:Obtaining prescription data of a wearer S1,Providing a lens blank having a convex front face and a concave back face S2,Selecting S5a thickness curve corresponding to a value of thickness less than or equal to a predetermined thickness requirement, this curve defining:an outer perimeter of a prescription part13of the back surface to be machined on the back face of the finished lens1that together with the front surface of the front face of the lens blank fulfills the prescription data of the wearer anda peripheral part14on the back surface to be machined on the back face of the lens blank extended from the thickness curve towards the outer edge15of the finished lens1

In addition, in one embodiment, the method comprises the following steps:Providing a minimum edge thickness for the finished lens1S3,Determining a first curvature profile of a back surface to be machined on the back face of the lens blank S4,Determining S6whether a thickness of the outer edge15of the peripheral part14will 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 part14If the thickness of the outer edge15of the peripheral part14will be less than the minimum edge thickness and thus the outer edge15is sharp, determining an optimised curvature profile of the peripheral part14of the back surface to be machined wherein the thickness in the peripheral part14is greater or equal the minimum edge thickness so as to obtain the outer edge15having a minimal thickness and which is preferably no longer sharp.

In step S3, the minimum edge thickness Teminis provided. The minimum edge thickness Teminis the minimum edge thickness requested at the outer edge15of the finished lens1to be produced from the lens blank. The value of the minimum edge thickness Teminis preferably chosen to avoid any sharp edge at the outer edge15of the finished lens1and provide finished lens with predetermined shape.

Preferably, the minimum edge thickness Teminis greater than or equal to 0.4 mm.

In step S5, the thickness curve12corresponding 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 part13and the peripheral part14are defined.

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.

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

In order to define the thickness curve12, the method pursuant to the invention comprises a thickness determining step wherein the thickness of the lens1which back surface is to be machined at several points is determined.

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

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

In one embodiment of the invention, in a first substep, a map of iso-thickness curves7,8,9in the finished lens1is established. Indeed, by knowing the geometry of the finished lens1and, in particular, the back surface of the back face to be machined it is possible to establish a cartography of the iso-thickness curves7,8,9in said lens1. The distribution of thickness in the lenses is illustrated inFIG.4. The greatest thickness of the finished lens1is located in a central area10of said lens1, while the thinnest thickness of said lens1is located in a peripheral area11, the thickness decreasing from said central area10to said peripheral edge11.

In a second substep, a iso-thickness curve12as illustrated inFIG.5Acorresponding to a given thickness is chosen.

In one embodiment, the iso-thickness curve12is 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.

In another embodiment, the chosen iso-thickness curve12is defined based on an adjustable value depending on the type of frame intended to receive the the cut lens.

Referring toFIG.5B, this suitable iso-thickness curve12delimits the prescription part13which must include the useful part5of the optical lens1intended to be mounted on a predetermined frame and the peripheral part14that extend toward the outer edge15of the finished lens1.

On the example illustrated onFIG.5B, the chosen suitable iso-thickness curve12surrounds the useful part5of the optical lens1, by keeping a minimal distance with said useful part5.

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 part5of the lens is always included in the prescription part13of the finished lens1.

According to the invention, the useful part data5and/or frame shape data defining the contour of the spectacle frame are not used to define the prescription part13and the peripheral part14of 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 lens1when cut is to be mounted.

In one embodiment not illustrated, a safety margin may be provided to the thickness curve12. In this case, the thickness curve12selected to define the outer perimeter of the prescription part14is 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 part5of the cut lens is not distorted in the frame contour.

In a next step, the algorithm determines if a thickness of the outer edge15of the peripheral part14is less than the minimum edge thickness Teminwhen the back surface of the lens blank is manufactured with the first curvature profile.

If the algorithm detects that the outer edge15of the peripheral part14will be less than the minimum edge thickness Teminand thus is too thin and thus is sharp, as illustrated on the example ofFIG.7, a step to determine an optimised curvature profile of the peripheral part14of the back surface to be machined is performed by said algorithm. In this step, the thickness in the peripheral part14is modified to be greater or equal to the minimum edge thickness Teminso as to obtain an outer edge15with a minimal predetermined thickness, as illustrated on the example ofFIG.8.

This minimal thickness can be for example 0.4 mm.

On the diagram ofFIG.8, the algorithm calculates a new machining profile or optimised curvature profile of the back surface of the back face of the finished lens1as illustrated by the curve18replacing the initial profile illustrated by the doted curve17. In this way, the outer edge15has a minimal thickness and is no longer sharp. The initial profile materialized by the curve17shows an outer sharp edge15delimiting a recess3, and the new machining profile allows to compensate this recess3by extending the diameter of the finished lens1in order to give a predetermined shape to said lens, for example circular. Consequently, the outer edge15which was initially sharp is displaced so as to increase the optical lens sizes, explaining the difference of outer edge15locations betweenFIG.7andFIG.8.

To determine the optimised curvature profile of the peripheral part14of the back surface to be machined wherein the thickness of the peripheral part14should be greater or equal the minimum edge thickness Temin, several methods of surface optimization or adjustment may be used under the given conditions.

The method may be any known interpolation method.

In one embodiment, the interpolation method uses a first set of points internal to the thickness curve12wherein the minimum edge thickness Teminis satisfied and a second set of points at the outer edge of the peripheral part of the finished lens wherein the minimum edge thickness Teminis not satisfied to optimize the thickness of the second points to provide an optimised curvature profile of the peripheral part14of the back surface to be machined.

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:Sampling a first set of points20which are internal to the chosen iso-thickness curve12and which define a portion with a thickness greater or equal to the minimum edge thickness Teminas illustrated inFIG.6A,In one alternative as the one illustrated inFIG.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 curve12.Sampling a second set of points21which are different from the first points20wherein the minimum edge thickness Teminis not satisfied and which are distributed on the outer edge15of the peripheral part14as illustrated inFIG.6B,optimize the altitude of the second points21so that the thickness corresponding to said second points21is greater than or equal to the minimal thickness Temin,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 line12and the sampled points on the initial back surface when the latest are inside or on the chosen iso-thickness line12.

In one example, the second set of points may be equally distributed as illustrated inFIG.6B.

In another embodiment, the method provides a step of sampling a third set of points22that described a contour having a predetermined diameter which is larger than the diameter of the finished lens1, so as to link the interpolated back surface to the initial back surface as illustrated inFIG.6Cand a step of calculate the interpolating of these points22as illustrated inFIG.6D.

In another embodiment, the determination of the optimized curvature profile of the back surface of the back face of the finished lens1can 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.

In addition, one or several cutting steps during the machining of the back surface of the back face of the lens1may be provided to define the optimized curvature profile of the back surface of the back face of the lens.

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.

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 lens1.

The optimization of the sharp edge zones of the peripheral part14comprises the following sub steps:Determining a cribbed diameter Dcribbof the finished lens,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.

The determination of the cribbed diameter Dcribbmay be made by any known method.

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

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.

In one embodiment, the best position of the cribbed diameter Dcribbis defined by iterative solutions in an appropriate coordination system.

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 curve12.

The optimization of the orientation of the finished lens in a varnish basket comprises the following sub steps: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 part14.Determining the best position for the lens in order to maximize the distance between the thickness curve12and the handling means.

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

To determine the best position, the orientation of the lens may be optimised to move away the handling means from the thickness curve12.

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.

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

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.

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.

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

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.