EP3470171A1

EP3470171A1 - An improved method of preparing a lens blank for an operation of surfacing thereof

Info

Publication number: EP3470171A1
Application number: EP17306387.6A
Authority: EP
Inventors: Sébastien PIRAUBE; Fred ADOLOFO; Alain Mathieu; Xavier Bultez; Jerome Moine
Original assignee: Essilor International Compagnie Generale dOptique SA
Current assignee: EssilorLuxottica SA
Priority date: 2017-10-13
Filing date: 2017-10-13
Publication date: 2019-04-17
Anticipated expiration: 2037-10-13
Also published as: MX2020003837A; CN111201111B; EP3470171B1; PH12020550199A1; CN111201111A; WO2019072742A1; US20200276684A1

Abstract

A method of preparing a lens blank for a further operation of surfacing to transform the lens blank into a surfaced lens for further transformation into a lens having a lens shape, the operation of surfacing including processing the lens blank so that the surfaced lens exhibits a crib diameter, the method being implemented using a processing module and comprising:
- based on input data (ID) which define the lens shape, defining a temporary crib diameter (D_temp) so that said temporary crib diameter satisfies a set of constraints which includes at least:
- a first constraint whereby the temporary crib diameter (D_temp) is large enough for the surfaced lens having said temporary crib diameter to be suitable to be processed into said lens,
- a second constraint whereby the temporary crib diameter is large enough for the surfaced lens having said temporary crib diameter to include a plurality of reference points defined on the lens blank and which together identify an optical center of the lens,

- choosing the crib diameter as a function of the temporary crib diameter (D_temp), said choosing the crib diameter being configured so that, when a step cribbing configuration is destined to be applied to the operation of surfacing, said crib diameter is chosen among at least one predetermined discrete value (Val₁).

Description

The invention relates to the field of industrial surfacing processes to manufacture ophthalmic lenses.
The invention relates more particularly to a method of optimizing the shape of the periphery that the surfacing of a lens blank destined to be transformed into the final lens is to convey to the lens blank thereafter.
In general, a spectacle lens is specifically manufactured according to every wearer's needs which may take the form of specifications defined in a prescription established by an ophthalmologist.
For the manufacturing of a lens, a lens blank is submitted to various steps to form the desired lens, in particular one of surfacing during which the shape of the lens blank is processed to produce what can be referred to as a surfaced lens so that the latter exhibits desired optical properties.
In practice, such as an operation is often carried out on a semi-finished lens blank whose front surface has previously been processed, the operation of surfacing essentially impacting one of the surfaces of the lens blank, typically the back surface, according to the prescription.
In the context of the invention, the surfacing step includes processing the lens blank to reduce its outer shape to a shape which is typically (although not necessarily) round, exhibiting a chosen diameter, or crib diameter. This operation is usually performed so that the resulting surfaced lens may then be more easily held during following steps, which typically include one during which the lens is immersed in a coating fluid while it is held by a device such as a ring.
Yet, this processing, also known as cribbing, is subject to various constraints, which can easily translate into an extremely varied population of potential crib diameters which result therefrom.
This is undesirable, as this tends to require that the manufacturing process be adjusted to the lens being manufactured, in particular in terms of equipment used to hold the lens which has been cribbed, e.g. for the coating thereof.
The invention seeks to improve this situation.
To this end, the invention relates to a method of preparing a lens blank for a further operation of surfacing of said lens blank configured to transform the lens blank into a surfaced lens at the end thereof for further transformation into a lens having a lens shape and destined to be coupled to a frame, the operation of surfacing including processing the lens blank so that the surfaced lens exhibits a crib diameter, the method being implemented using a processing module and comprising :

based on input data which define the lens shape, defining a temporary crib diameter so that said temporary crib diameter satisfies a set of constraints which includes at least:
a first constraint whereby the temporary crib diameter is large enough for the surfaced lens having said temporary crib diameter to be suitable to be processed into said lens ,
a second constraint whereby the temporary crib diameter is large enough for the surfaced lens having said temporary crib diameter to include a plurality of reference points defined on the lens blank and which together identify an optical center of the lens,
choosing the crib diameter as a function of the temporary crib diameter, said choosing the crib diameter being configured so that, when a step cribbing configuration is destined to be applied to the operation of surfacing, said crib diameter is chosen among at least one predetermined discrete value.

According to an aspect of the invention, the crib diameter is chosen as corresponding to the smallest discrete value which is superior to the temporary crib diameter.
According to an aspect of the invention, the method further comprises, when a surface extension configuration is destined to be applied to the operation of surfacing, generating a surface file to be used during the operation of surfacing for generating the lens shape so that the lens shape is circular with a diameter corresponding to the crib diameter.
According to an aspect of the invention, said one or more predetermined discrete value is formed by a single value.
According to an aspect of the invention, the temporary crib diameter is chosen as the smallest value which satisfies said set of constraints.
According to an aspect of the invention, the set of constraints includes a third constraint according to which the temporary crib diameter is superior or equal to a minimum crib diameter of an apparatus destined to be used to reduce the diameter of the lens blank during the operation of surfacing.
According to an aspect of the invention, for satisfying the first constraint, the temporary crib diameter is taken as superior or equal to a lens shape parameter defined based on twice a maximum radius of the lens shape.
According to an aspect of the invention, the lens shape parameter is taken equal as twice the radius of the lens shape when the generated lens shape is circular.
According to an aspect of the invention, the lens shape parameter is taken equal as twice the sum of the maximum radius and of a margin defined based on a shape of the frame the lens is destined to be coupled to.
According to an aspect of the invention, for satisfying the second constraint, the temporary crib diameter is chosen superior or equal to a reference parameter defined based on twice a distance between a center of the lens shape in a blocking and turning referential of the lens blank during the operation of surfacing and the reference point of the lens blank which is the farthest away from said center.
According to an aspect of the invention, the reference parameter is taken equal to twice the sum of said distance and of a predetermined margin.
The invention also relates to a computer program comprising instructions destined to be executed by a processor for the implementation of the method as defined above.
The invention also relates to a method of surfacing a lens blank configured to transform the lens blank into a surfaced lens at the end thereof for further transformation into a lens having a lens shape and destined to be coupled to a frame, the method comprising:

preparing the lens blank for surfacing using a method of preparing a lens blank as defined above to obtain a crib diameter, and
surfacing the lens blank, said surfacing the lens blank including processing the lens blank so that the surfaced lens exhibits the crib diameter.

The invention also relates to a device for preparing a lens blank for a further operation of surfacing of said lens blank configured to transform the lens blank into a surfaced lens having a lens shape at the end thereof for further transformation into a lens to be coupled to a frame, the operation of surfacing including processing the lens blank so that the surfaced lens exhibits a crib diameter, the device comprising a processing module configured to:

based on input data which define the lens shape, define a temporary crib diameter so that said temporary crib diameter satisfies a set of constraints which includes at least:
a first constraint whereby the temporary crib diameter is large enough for the surfaced lens having said temporary crib diameter to be suitable to be processed into said lens,
a second constraint whereby the temporary crib diameter is large enough for the surfaced lens having said temporary crib diameter to include a plurality of reference points defined on the lens blank and which together identify an optical center of the lens,
choose the crib diameter as a function of the temporary crib diameter, the processing module being configured to choose the crib diameter so that, in response to a step cribbing configuration being destined to be applied to the operation of surfacing, said crib diameter is chosen among at least one predetermined discrete value.

Other features and advantages of the invention will become apparent from the following description provided for indicative and non-limiting purposes, with reference to the accompanying drawings, wherein:

Figure 1 illustrates a lens blank, a surfaced lens and a finished lens;
Figure 2 illustrated a system according to the invention;
Figure 3 illustrates schematically a method of manufacturing a lens according to the invention; and
Figure 4 illustrates steps of a preparation step of the method of Figure 3.

Figure 1 illustrates a lens blank BLA which is used in the context of the invention with a view of manufacturing an ophthalmic lens, or finished lens, LEN designed to exhibit optical properties. In particular, the lens LEN which is obtained advantageously presents eyesight correction properties which address eyesight issues of its intended wearer. The lens LEN is typically designed to be coupled to a frame (now shown) to define spectacles therewith which are to be worn by the wearer.
To obtain the lens LEN, the lens blank BLA which is designed to be processed into the resulting lens is put through a series of operations whose general respective principles are typically known.
One of these operations, on which the invention focuses, is one of surfacing the lens blank to produce a surfaced lens SLE therefrom which is itself to be put through further operations to produce the lens LEN. It should be noted that the surfaced lens LEN advantageously exhibits the target optical properties of the lens LEN.
Advantageously, the lens blank BLA which is used during this step is a semi-finished lens bank. In other words, one of its surfaces has already been processed to a desired shape. Typically, the front surface is thus already processed when the surfacing operation is to take place, only the back surface being then processed. Regardless of whether the lens bank is of the semi-finished type thereafter, the term "lens blank" is to be understood as encompassing configurations in which the lens blank is semi-finished, and configurations in which it is not, although the configurations in which it is are preferred.
As for the details of the operation of surfacing, the step generally revolves around some of the matter of the lens blank being removed therefrom so as to shape the lens blank BLA into the surfaced lens LEN.
In particular, in the sense of the invention, this operation includes a step of cribbing the lens blank BLA, which corresponds to a step during which the external shape of the lens blank is reduced in terms of dimensions to a diameter which is referred to as a crib diameter D_crib.
In effect, the step of cribbing results in the surfaced lens SLE having an external shape which may be circular or not. When it is not round, the term "diameter" is to be understood as referring to the maximal diameter unless specified otherwise.
This external shape is destined to come in contact with a piece of equipment during a further step of the process, typically one of coating the surfaced lens. For instance, the external shape of the surfaced lens is held by a ring used to immerse the surfaced lens in a coating material.
Figure 2 illustrates a system SYS according to the invention, the system SYS being configured to be used during the operation of surfacing in general to shape the lens blank BLA into the surfaced lens SLE.
The system SYS includes a generator GEN which is adapted to be used during the surface per se to remove matter from the lens blank BLA to shape the latter into the surfaced lens SLE. In addition, the system SYS includes an apparatus APP adapted to prepare at least in part the surfacing of the lens blank BLA per se. More specifically, as detailed below, the apparatus APP is configured to determine the crib diameter noted D_crib hereafter, which is applied to the lens blank BLA during the operation of surfacing.
Regarding the generator GEN, it advantageously includes a grinding module GRIN and/or a cutting module CUT which are respectively configured to remove some of the matter of the lens blank BLA to shape the lens blank BLA into the generated lens LEN through grinding, respectively cutting.
For instance, the grinding module and the cutting module are movable relative to a body of the generator by which the lens blank BLA is held.
For instance, to that end, the lens blank BLA is secured to a support which is held by the generator. Advantageously, the lens blank BLA is held in a manner which advantageously allows the lens blank to be moved relative to the body of the generator, typically to rotate relative thereto.
Regarding the apparatus APP, as indicated above, it is configured to prepare the operation of surfacing of the lens blank, and in particular to determine the cribbing diameter to which the lens blank BLA is brought during this operation.
In a general sense, the apparatus APP may be a stand-alone apparatus specifically dedicated to the preparation of the surfacing.
Alternatively, it may be combined with one or more other apparatus destined to be used during the manufacturing of ophthalmic lenses, such as the generator itself.
As illustrated on Figure 2, the apparatus APP is a computer device. It includes a processing module PROC, a memory MEM, a communication interface COM, and a human-machine interface HMI.
The processing module PROC is configured to carry out the method of preparing a lens blank BLA in the sense of the invention, which is detailed hereafter.
The processing module PROC includes one or more processor CPU which is configured to process instructions for the implementation of the method according to the invention.
This processor may be of any known type.
The memory MEM is configured to store computer programs and data which are destined to be processed by the processing module PROC for the operations of the apparatus APP. Typically, it may include one or more programs defining an operating system via which the apparatus performs routine operations. Advantageously, it also includes a computer program PRG comprising instructions destined to be executed by the processing module MOD for the implementation of the method according to the invention detailed below.
As for the data, in the context of the invention, they include input data ID which are configured to describe the shape of the lens LEN, or lens shape, which is to be obtained at the end of the manufacturing process.
It should be noted that this lens shape is to be distinguished from the shape of the surfaced lens SLE, or surfaced lens shape, which is that of the result of the processing of the lens blank BLA through the surfacing of the latter.
On a specific level, the input data ID may advantageously include a model of the lens, i.e. of the manufactured lens. Advantageously, this model is expressed in a blocking/turning referential of the lens, i.e. a referential which uses the center of rotation of the lens blank during the surfacing as its origin and with one or more of its axis corresponding to an axis of rotation of the lens blank during the surfacing.
For instance, the model includes a model of the front surface and back surface of the lens, as well as kinematics between these two surfaces.
Advantageously, the input data ID also include data which describe the lens shape, i.e. the shape of the manufactured lens LEN. For instance, these data include the traced shape of the lens for the wearer.
.Optionally, they also include a diameter information. For instance, this is so when the optical properties of the lens call for a diameter which is considered untypical.
The memory MEM may also contain configuration data CFGD which define preferences for the operation of surfacing which is to occur following the preparation.
The configuration data CFGD advantageously include a frame shape margin M_FS whose value is predetermined. This frame shape margin corresponds to a margin which is provided for the surfaced lens SLE to ensure a good cooperation between the lens LEN and the frame FRA once the lens has been further processed.
The configuration data CFGD advantageously include a step cribbing parameter which defines whether a step cribbing configuration is enabled for the surfacing, whereby the crib diameter D_crib is chosen among at least one predetermined discrete value Val_i. It should be noted that there may be a single discrete value.
The configuration data CFGD advantageously include a list of preferred diameters. For instance, these preferred diameters correspond to the discrete values Val_i among which the crib diameter is chosen.
The configuration data CFGD advantageously include a Minimum Generator Crib Diameter, noted MinGen, which corresponds to a minimum crib diameter that the generator GEN is adapted to provide.
The configuration data CFGD advantageously include a surface extension parameter which describes whether a surface extension configuration is enabled for the surfacing, whereby the surfaced lens has a shape which is purposefully extended to be circular.
The data contained in the memory MEM advantageously also include reference data REFD which define the location of reference points P_REF defined on the lens blank and which together identify an optical center of the lens LEN.
The location of the references points is for instance expressed in a given referential, such as the PRP referential, for Prism Reference Point referential. The Prism Reference Point corresponds to the optical center of the lens. This referential includes three axis passing through the Prism Reference Point, for instance a horizontal axis, a vertical axis, and one passing through the lens and normal to the front surface of the lens. This referential may correspond to the blocking/turning referential.
The reference points P_REF may take the form of circles, such as microcircles.
The human-machine interface HMI is adapted to allow an operator to input data into the apparatus APP and/or to display data for the operator.
The data in question may be any data, in particular that contained in the memory which form all or part of the configuration data CFGD, the input data ID or the reference data REFD.
The human-machine interface HMI may include an input device, such as a keyboard, a mouse, and the like. The input device may also include a screen, optionally combined with the mouse and/or the keyboard to define a touch sensitive screen.
As for the communication interface COM, it is adapted for communication between the apparatus APP and one or more distant device.
Any cable and/or non-cable communication technology may be supported by the communication module COMM.
A method of manufacturing a lens LEN (shown by a dashed line on Figure 1) from a lens blank BLA according to the invention will now be described in reference to the Figures, including Figure 4 .
In reference to Figure 3 , i in a general sense, and as discussed above, the manufacturing includes a step of surfacing a lens blank BLA into a surfaced lens SLE during a step S1.
The process also includes further processing of the surfaced lens SLE into the desired lens LEN during a step S2. This further processing is not the core aspect of the invention, and will therefore not be discussed in more details. In effect, any known technique may be applied to that end.
As for step S 1, it includes the preparation noted PREP of the surfacing of the lens blank BLA, and the surfacing noted SURF of the lens blank BLA per se.
Regarding the preparation PREP, as discussed, its goal, or one of its goals, is the determination of the crib diameter D_crib which is conveyed to the surfaced lens SLE during the surfacing SURF. It is carried out by the apparatus APP, and in particular by the processing module PROC using the memory MEM.
In a general sense, this determination relies on defining a temporary crib diameter D_temp which satisfies a set of constraints, and choosing the crib diameter D_crib based on the temporary crib diameter D_temp so that when the step cribbing configuration is destined to be applied to the operation of surfacing SURF, the crib diameter D_crib is chosen among at least one predetermined discrete value.
The set of constraints includes at least one constraint, and advantageously a plurality of constraints.
Advantageously, it includes a first constraint whereby the temporary crib diameter D_temp is large enough for the surfaced lens SLE having said temporary crib diameter to be suitable to be processed into said lens. In other words, the temporary crib diameter D_temp is chosen so that if the surfaced lens shape were to have this temporary crib diameter, obtaining the lens from the surfaced lens would be possible.
The temporary crib diameter D_temp is determined to verify this first constraint during a step T1.
To that end, the temporary crib diameter D_temp is taken as superior or equal to a lens shape parameter defined based on twice a maximum radius of the lens shape.
In more details, based on the input data ID and the lens shape defined therein, it is determined whether the lens shape is round or not.
If it is, the lens shape parameter, and therefore the temporary crib diameter D_temp, is set to twice the radius of the lens shape, which also corresponds to its maximum radius.
If the lens LEN is not round, the lens shape parameter is set to twice the sum of the maximum radius of the lens shape and of the frame shape margin M_FS. This margin is indeed chosen based on the shape of the frame the lens is destined to be coupled to. Typically, this margin is designed to ensure that the cribbing diameter will not come too close to the final lens shape, thus avoiding any lack of material inside the frame.
The set of constraints advantageously comprises a second constraint whereby the temporary crib diameter D_temp is large enough for the surfaced lens having said temporary crib diameter to include the plurality of reference points P_REF. In other words, the constraint aims to ensure that the reference points are not removed from the lens blank while the latter is cribbed.
The temporary crib diameter D_temp is determined to verify the second constraint during a step T2.
In details, during this step T2, the temporary crib diameter D_temp is chosen superior or equal to a reference parameter defined based on twice a distance between the center of the lens shape in the blocking/turning turning referential of the lens blank during the operation of surfacing and the reference point of the lens blank which is the farthest away from said center. In effect, for each reference point, the distance between this center and the reference point is determined, the obtained distance is summed to a margin distance, and the highest value obtained among the various reference points, noted Rmc for instance, is chosen as the reference parameter. This margin distance is for instance chosen as 1 mm.
Then, it is determined whether the current temporary crib diameter D_temp is inferior to twice the value Rmc.
If so, the temporary crib diameter D_temp is set to twice the value of Rmc.
If not, the current temporary crib diameter D_temp is kept.
Advantageously, the set of constraints includes a third constraint according to which the temporary crib diameter is superior or equal to the minimum generator crib diameter MinGen. In other words, this constraint aims to ensure that the crib diameter is realistic in view of the limitations of the generator GEN.
The temporary crib diameter D_temp is determined so as to verify the third constraint during a step T3.
During this step, it is determined whether the current temporary crib diameter D_temp is inferior to the minimum generator crib diameter MinGen.
If so, the current temporary crib diameter D_temp is set to the minimum generator crib diameter MinGen.
If not, the current temporary crib diameter D_temp is kept.
Indeed, the steps T1 to T3 may be implemented in any order. The temporary crib diameter D_temp is advantageously set to zero prior to the first of these steps. In effect, through these steps, the temporary crib diameter D_temp is advantageously chosen as the smallest value which satisfies the set of constraints.
During a step T4, which preferably takes places after the steps T1 to T3, it is determined whether the step cribbing configuration is enabled for the surfacing SURF. This operation is carried out based on the configuration data CFGD.
In practice, the step cribbing parameter is analyzed to see whether this is the case or not.
If the step cribbing configuration is not enabled for the surfacing SURF, the crib diameter D_crib is chosen based on the current temporary crib diameter D_temp. Advantageously, it is taken equal to the current temporary crib diameter D_temp.
If the step cribbing configuration is enabled, then it is determined whether the preferred diameters contained in the configuration data CFGD comprise at least one preferred diameter which is superior to the current temporary crib diameter D_temp.
If they contain such a diameter, the current temporary crib diameter D_temp is set to a value chosen among these values. Advantageously, it is then taken equal to the smallest preferred diameter which is superior to the current temporary crib diameter D_temp.
If the preferred diameters do not contain a diameter which is superior to the current temporary crib diameter, the current temporary crib diameter D_temp is kept.
The crib diameter D_crib is then chosen based on the temporary crib diameter D_temp. Advantageously, it is taken equal to the temporary crib diameter D_temp.
In effect, at the end of step S4, the crib diameter D_crib has a given value, which forms the final value of the crib diameter.
During an optional step T5, which is preferably implemented after step T4, it is then determined whether the surface extension configuration is enabled for the surfacing SURF.
If so, a surface file is generated. This surface file contains a definition of the shape of the surfaced lens. It is destined to be used during the operation of surfacing SURF for generating the shape of the surfaced lens shape so that the shape of the surfaced lens is circular with a diameter corresponding to the crib diameter. Typically, this surface file is destined to be used as input by the generator to determine the details of the processing of the lens blank BLA.
In other words, when the surface extension is activated, this step includes the generation of instructions destined to the generator GEN so that the shape of the surfaced lens is to be brought to a circular shape having the crib diameter D_crib during the surfacing SURF, whereby this shape can be seen as extended relative to a configuration in which the surface extension configuration is not enabled.
If the surface extension configuration is not enabled, then the process stops.
After this step, whether prior to step T5 or not, the crib diameter D_crib is output by the apparatus for the generator GEN to use as input for the surfacing SURF which takes place thereafter.
The surfacing SURF advantageously uses the crib diameter D_crib to process the lens blank BLA, as well as various other data such as data which reflect those contained in the memory MEM of the apparatus.
This output of the preparation PREP is conveyed through the communication module COM and/or through the human-machine interface HMI, whereby it is then transferred to the generator GEN.
During the surfacing SURF, the lens blank is then processed by the generator GEN, the resulting surfaced lens SLE having the crib diameter D_crib determined during the preparation PREP.
The invention provides several advantages.
Indeed, it greatly helps reducing the variety of dimensions which result from the surfacing of lens blanks in the context of the manufacture of ophthalmic lenses.
In addition, it is easily adaptable to various situations and constraints, which may be imposed by the equipment which is available for the manufacturing.
Moreover, it does not require extensive calculation resources, and may therefore be implemented on various types of computer devices.
It should be noted that the core aspect of the invention has been described as a method of preparing a lens blank. However, it may be seen as a method of surfacing a lens blank to obtain a surfaced lens, or one of cribbing a lens blank with a view to form an ophthalmic lens, wherein the corresponding method includes an initial step of determining the cribbing diameter as detailed above.

Claims

A method of preparing a lens blank (BLA) for a further operation of surfacing of said lens blank configured to transform the lens blank into a surfaced lens (SLE) at the end thereof for further transformation into a lens (LEN) having a lens shape and destined to be coupled to a frame, the operation of surfacing including processing the lens blank (BLA) so that the surfaced lens exhibits a crib diameter (D_crib), the method being implemented using a processing module and comprising :
- based on input data (ID) which define the lens shape, defining a temporary crib diameter (D_temp) so that said temporary crib diameter satisfies a set of constraints which includes at least:

- a first constraint whereby the temporary crib diameter (D_temp) is large enough for the surfaced lens having said temporary crib diameter to be suitable to be processed into said lens (LEN),

- a second constraint whereby the temporary crib diameter is large enough for the surfaced lens having said temporary crib diameter to include a plurality of reference points defined on the lens blank and which together identify an optical center of the lens,

- choosing the crib diameter (D_crib) as a function of the temporary crib diameter (D_temp), said choosing the crib diameter being configured so that, when a step cribbing configuration is destined to be applied to the operation of surfacing, said crib diameter is chosen among at least one predetermined discrete value (Val_i).
The method according to claim 1, wherein the crib diameter (D_crib) is chosen as corresponding to the smallest discrete value which is superior to the temporary crib diameter (D_temp).
The method according to claim 1 or 2, further comprising, when a surface extension configuration is destined to be applied to the operation of surfacing, generating a surface file to be used during the operation of surfacing for generating the lens shape so that the lens shape is circular with a diameter corresponding to the crib diameter (D_crib).
The method according to claims 2 and 3, wherein said one or more predetermined discrete value is formed by a single value.
The method according to any one of the preceding claims, wherein the temporary crib diameter (D_temp) is chosen as the smallest value which satisfies said set of constraints.
The method according to any one of the preceding claims, wherein the set of constraints includes a third constraint according to which the temporary crib diameter is superior or equal to a minimum crib diameter of an apparatus destined to be used to reduce the diameter of the lens blank during the operation of surfacing.
The method according to any one of the preceding claims, wherein, for satisfying the first constraint, the temporary crib diameter is taken as superior or equal to a lens shape parameter defined based on twice a maximum radius of the lens shape.
The method according to any one of the preceding claims, wherein the lens shape parameter is taken equal as twice the radius of the lens shape when the generated lens shape is circular.
The method according to any one of the preceding claims, wherein the lens shape parameter is taken equal as twice the sum of the maximum radius and of a margin defined based on a shape of the frame the lens is destined to be coupled to.
The method according to any one of the preceding claims, wherein for satisfying the second constraint, the temporary crib diameter (D_temp) is chosen superior or equal to a reference parameter defined based on twice a distance between a center of the lens shape in a blocking and turning referential of the lens blank during the operation of surfacing and the reference point of the lens blank which is the farthest away from said center.
The method according to claim 10, wherein the reference parameter is taken equal to twice the sum of said distance and of a predetermined margin.
A computer program comprising instructions destined to be executed by a processor for the implementation of the method according to any one of the preceding claims.
A method of surfacing a lens blank (BLA) configured to transform the lens blank into a surfaced lens (SLE) at the end thereof for further transformation into a lens having a lens shape and destined to be coupled to a frame, the method comprising:
- preparing the lens blank (BLA) for surfacing using a method of preparing a lens blank according to any one of claims 1 to 11 to obtain a crib diameter, and

- surfacing the lens blank, said surfacing the lens blank including processing the lens blank so that the surfaced lens exhibits the crib diameter.
A device for preparing a lens blank (BLA) for a further operation of surfacing of said lens blank configured to transform the lens blank into a surfaced lens (SLE) having a lens shape at the end thereof for further transformation into a lens (LEN) to be coupled to a frame, the operation of surfacing including processing the lens blank so that the surfaced lens (SLE) exhibits a crib diameter, the device comprising a processing module (PROC) configured to:
- based on input data which define the lens shape, define a temporary crib diameter (D_temp) so that said temporary crib diameter (D_crib) satisfies a set of constraints which includes at least:

- a first constraint whereby the temporary crib diameter is large enough for the surfaced lens having said temporary crib diameter to be suitable to be processed into said lens,

- a second constraint whereby the temporary crib diameter is large enough for the surfaced lens having said temporary crib diameter to include a plurality of reference points defined on the lens blank and which together identify an optical center of the lens,

- choose the crib diameter (D_crib) as a function of the temporary crib diameter (D_temp), the processing module being configured to choose the crib diameter so that, in response to a step cribbing configuration being destined to be applied to the operation of surfacing, said crib diameter is chosen among at least one predetermined discrete value.