Method for shaping ophthalmic products

Abstract

The invention relates to a method for shaping an ophthalmic product (20) using a machining apparatus (200) equipped with a clamping device (202, 203), a machining tool (210) and a force sensor (234) adapted to measure a force related to a force applied to the ophthalmic product (20) by the machining tool. According to the invention, the method comprises: a step of clamping an ophthalmic product in said clamping device; and a step of roughing the ophthalmic product by means of the machining tool in order to bring the initial profile of the ophthalmic product to a final profile of a different shape, in which, during the roughing step:-the value of said force is measured by the force sensor, and-the machining speed is continuously adjusted in order to maintain the measured value equal to the target value.

Description

Technical Field

[0001] The present invention relates generally to the field of eyewear.

[0002] The present invention is applicable to machining equipment including:

[0003] - a clamping device for clamping an ophthalmic product,

[0004] - a machining tool for machining the ophthalmic product, and

[0005] - A force sensor adapted to measure a force related to a force applied by the machining tool to the ophthalmic product.

[0006] The present invention more particularly relates to a method for shaping an ophthalmic lens, the method comprising:

[0007] - a step of clamping an ophthalmic product in said clamping device; and

[0008] - A step of rough machining the ophthalmic product by means of a machining tool in order to bring the initial contour of the ophthalmic product to a final contour of a different shape. Background Art

[0009] The technical part of an optician's work, which consists of fitting a pair of ophthalmic lenses into the spectacle frames chosen by the client, can be divided into four main operations:

[0010] - Obtain the shape of the contour of the rim of the eyeglass frame selected by the customer,

[0011] - centering each ophthalmic lens, consisting in determining the reference system of the lens using the centering marks provided on the lens, and then suitably positioning the contour of the bezel previously acquired in the reference system of the lens, so that the lens, once edged to this contour and then mounted in its frame, is correctly positioned relative to the corresponding eye of the customer and satisfies as best as possible the optical function for which it was designed,

[0012] - blocking each lens, including attaching a blocking accessory to the lens, allowing easy removal of the lens from the centering station and then engaging the lens in the edging station without losing the reference frame, and then

[0013] -Edging each lens involves machining the lens to the previously centered profile.

[0014] Here, the edging operation is of particular interest.

[0015] This operation is usually performed by an edge grinding machine depending on the material of the lens to be edged.

[0016] Various methods are known to do this.

[0017] In a known embodiment, the machining method aims to maintain constant the machining speed (that is to say the speed of the contact point between the lens and the tool). Therefore, the control parameters are calculated before machining the lens, taking into account the material of the lens to be edged.

[0018] In a second known embodiment, when the lens is to be machined in several passes, at each pass the machining depth is calculated according to the average power consumed by the motor in the previous pass, so as to reduce the time required to edge the lens.

[0019] Both methods are based on the assumption that the machining operation is repeatable and that the performance of the tool is constant over time.

[0020] But in reality, this assumption is wrong. As a result, the edge grinding machine cannot be utilized to its fullest potential. Summary of the invention

[0021] In this context, the present invention provides a solution that enables the edge grinding machine to be used to its maximum capabilities in order to optimize productivity.

[0022] More specifically, the invention relates to a method for shaping an ophthalmic product as defined in the introduction, wherein, during a rough machining step, the value of said force is measured by a force sensor and the machining speed is continuously adjusted so as to maintain the measured value equal to a target value - the target value being determined based on the electrical power consumed by the machining equipment.

[0023] Thus, at each moment, the tool is driven in order to machine the ophthalmic product at the maximum possible speed.

[0024] In a preferred embodiment, the target value is maintained at a high level in order to shorten the machining time and, in other words, so that the motor consumption does not exceed a maximum value that would impair the quality of the product.

[0025] Other preferred features of the present invention are as follows:

[0026] - During the roughing step, the machining tool follows a first path that is radial relative to said clamping device until the final contour is reached, and a second path along said final contour.

[0027] The force sensor is adapted to measure a force component which is radial relative to the clamping device.

[0028] - During the rough machining step, a comparison operation is performed to compare the electric power consumed by the machining device with a power threshold, and when the electric power consumed by the machining device is greater than the power threshold, the target value is reduced by a predetermined amount.

[0029] - The comparison operation is performed only when the target value is greater than a predetermined threshold value.

[0030] - The machining speed is determined by means of a proportional-derivative controller.

[0031] The machining speed is determined based on a first difference between the measured value and the target value and a second difference between a measured value measured at a current moment and a measured value measured at a previous moment.

[0032] The final contour is characterized by first points (also named main points), intermediate points are defined between said first points, and during the roughing step, at each sampling instant, the machining device is programmed to:

[0033] ¤Selecting the next point to be reached between the first point and the intermediate point according to the difference between the measured value and the target value, and

[0034] ¤ Controlling the machining tool and the clamping device so that the machining tool reaches the next point in a constant predetermined amount of time from a sampling moment to another sampling moment.

[0035] - The number of the first points is determined according to the maximum machining speed and / or the maximum speed of the machining equipment.

[0036] - The ophthalmic product is an ophthalmic lens or a mold for molding an ophthalmic lens.

[0037] The method comprises, after said rough machining step, a finishing step performed on a portion of the ophthalmic product machined by said machining tool by means of a finishing tool different from said machining tool.

[0038] - During the rough machining step, the ophthalmic product is machined in a single pass by a machining tool around the clamping device. DETAILED DESCRIPTION

[0039] The following description, given by way of non-limiting examples with reference to the accompanying drawings, makes clear what the invention consists of and the manner in which it can be put into practice.

[0040] In the attached picture:

[0041] - Figure 1 is a schematic diagram of a machining apparatus suitable for implementing the method according to the invention,

[0042] - Figure 2 Demonstrated through the Figure 1 Initial and final contours of ophthalmic lenses before and after machining with the equipment

[0043] - Figure 3 shows some points of how the final contour is defined according to the invention, and

[0044] - Figure 4 is a flow chart of a method according to the present invention.

[0045] Figure 1 An apparatus 200 for machining an ophthalmic lens 20 is shown, the apparatus comprising:

[0046] - means 202 , 203 for clamping the ophthalmic lens 20 ;

[0047] at least one tool 210 , 222 , 223 for machining an ophthalmic lens 20 ;

[0048] a force sensor 234 suitable for measuring forces related to the forces applied by the machining tools 210 , 222 , 223 to the ophthalmic lens 20 ; and

[0049] A unit 251 for controlling each machining tool 210 , 222 , 223 relative to the clamping device 202 , 203 .

[0050] The machining device 200 may take the form of any machine for cutting or removing material that is capable of modifying the contour of the ophthalmic lens 20 so as to adapt it to the contour of a corresponding frame of an eyeglass frame selected by the individual.

[0051] exist Figure 1 In the example schematically shown, the machining device 200 consists of an automatic grinding machine 200 (broadly called a digital grinder), as known per se. In this case, this grinding machine comprises:

[0052] - a shaker 201 mounted so as to pivot freely on a support (not shown) about a reference axis A5, in fact a horizontal axis, and supporting an ophthalmic lens 20 to be machined;

[0053] at least one grinding wheel 210 mounted to pivot about a grinding wheel axis A6 parallel to the reference axis A5 and suitably driven in rotation by a motor (not shown);

[0054] A finishing module 220 , which is mounted to rotate about the grinding wheel axis A6 and is equipped with tools 222 , 223 for finishing the ophthalmic lens 20 .

[0055] The pivoting mobility of the rocker 201 about a reference axis is called retraction mobility ESC. It allows the ophthalmic lens 20 to be brought closer to the grinding wheel 210 until the former comes into contact with the latter.

[0056] This shaker 201 is equipped with two shafts 202 , 203 for clamping the ophthalmic lens 20 to be machined and for driving it in rotation, these shafts 202 , 203 corresponding to the aforementioned “clamping means”.

[0057] The two shafts 202 , 203 are aligned with each other along a clamping axis A7 parallel to the axis A5 . The shafts 202 , 203 each have a free end facing each other and equipped with a head for clamping the ophthalmic lens 20 .

[0058] The first of the two axes 202 is fixed against translation along the clamping axis A7 . In contrast, the second of the two axes 203 is movable in translation along the blocking axis A7 in order to allow axial compression clamping of the ophthalmic lens 20 between the two clamping heads.

[0059] exist Figure 1 The grinding machine 200 schematically shown in FIG. 2 comprises only one cylindrical grinding wheel 210 .

[0060] In practice, the grinding machine comprises a set of grinding wheels coaxially mounted on a grinding wheel axis A6 , each grinding wheel being dedicated to a specific shaping operation of the ophthalmic lens 20 to be machined.

[0061] For roughing the lens, a roughing cylindrical grinding wheel is used. This roughing cylindrical grinding wheel is cylindrical, has a diameter greater than 10 cm, and comprises diamonds with a grain size between 100 and 500 microns, and here equal to 300 microns.

[0062] To bevel a lens, which includes machining ribs along the edge face of the lens, a profiled grinding wheel (or "bevel grinding wheel") may be used that contains bevel grooves of dihedral cross-section.

[0063] For polishing the lenses, cylindrical grinding wheels and profile grinding wheels with the same geometry as the two grinding wheels mentioned above are used, these polishing grinding wheels have a particularly small grain size.

[0064] The set of grinding wheels is carried by a slide (not shown) so as to move in translation along the grinding wheel axis A6. The translational movement of the slide carrying the grinding wheels is called "adjustment" TRA.

[0065] It will be understood that what is in question here is the creation of a relative movement between the grinding wheels and the lens and that, as a variant, it is also possible to move the lens axially while the grinding wheels remain stationary.

[0066] Here, the grinding machine 200 further includes a connecting rod 230, one end of which is hinged relative to the bracket so as to pivot about the reference axis A5, and the other end of which is hinged relative to the nut 231 so as to pivot about the axis A8 parallel to the reference axis A5.

[0067] The nut 231 itself is mounted to move in translation along a reconfiguration axis A9 perpendicular to the reference axis A5. The nut 231 is a tapped nut in threaded engagement with a threaded shank 232 driven in rotation by a motor 233 aligned with the reconfiguration axis A9.

[0068] The connecting rod 230 also comprises a force sensor 234 , here consisting of a unidirectional strain gauge, interacting with a stop 204 fixed to the shaker 201 .

[0069] When the ophthalmic lens 20 to be machined is suitably clamped between these two shafts 202, 203, in contact with one of the grinding wheels 210, the aim is to effectively remove material until the stop 204 of the shaker 201 abuts against the connecting rod 230 with a force acting on the strain gauge 234, which is suitably detected and measured by the strain gauge.

[0070] Here, the strain gauge 234 is placed to measure a substantially vertically directed machining force corresponding to the radial component of the force exerted by the ophthalmic lens 20 on the grinding wheel 210 or finishing tool 222 , 223 used.

[0071] In order to machine the ophthalmic lens 20 following a given contour, it is therefore sufficient to move the nut 231 appropriately along the reconstruction axis A9 under the control of the motor 233 to control the reconstruction movement RES and to pivot the support shafts 202, 203 together about the clamping axis A7 on the other hand. The reconstruction movement (and therefore the retraction movement of the shaker 201) and the rotational movement of the shafts 202, 203 are controlled and coordinated by the control unit 251, suitably programmed for this purpose, so that all points of the contour of the ophthalmic lens 20 have the correct diameter in turn.

[0072] According to the invention, this retraction movement is controlled in particular as a function of the machining force measured by the strain gauge 234 in order to maintain it equal to the target value.

[0073] As for the optional finishing module 220 , it has a pivoting mobility around the grinding wheel axis A6 , which mobility is indicated as PIV. This mobility allows it to be brought closer to the ophthalmic lens 20 or moved further away from it.

[0074] The finishing tools 222 , 223 equipped in the finishing module 220 here particularly include a grooved disk 222 suitable for generating grooves along the edge surface of the ophthalmic lens 20 , and a milling cutter 223 suitable for chamfering the sharp edge of the ophthalmic lens 20 .

[0075] These finishing tools 222, 223 are mounted to rotate about a given axis and are driven in rotation by a motor housed in a base 224, which base is itself mounted to pivot on the finishing module 220 about an axis A10 orthogonal to the grinding wheel axis A6. This pivoting mobility of the base 224 about the axis A10, called finishing mobility FIN, allows an optimal orientation of the tools 222, 223 relative to the lens.

[0076] The control unit 251 is an electronic and / or computing unit and specifically allows controlling the following:

[0077] - a motor for driving the translational movement of the second axis 203;

[0078] - a motor for driving the two shafts 202 , 203 in rotation;

[0079] - a motor for driving the slide carrying the grinding wheels in translation with its mobilization mobility TRA;

[0080] - a motor 233 for driving the nut 231 in translational movement with its reconfiguration mobility RES;

[0081] a motor for driving the finishing module 220 in rotation with its pivoting mobility PIV; and

[0082] A motor for driving the base 224 of the finishing tool 222 , 223 in rotation with its finishing mobility FIN.

[0083] Finally, the grinding machine 200 comprises a human-machine interface 252, here comprising a display screen 253, a keyboard 254 and a mouse 255, which are adapted to communicate with the control unit 251. The HMI interface 252 allows the user to input values ​​on the display screen 253, such as the material of the lens, so that the tools of the grinding machine 200 can be appropriately controlled.

[0084] exist Figure 1 In the embodiment of the present invention, the control unit is implemented on a desktop computer connected to the grinder 200. Of course, as a variant, the software part of the grinder can be implemented directly on the electronic circuit of the grinder. The software part of the grinder can also be implemented on a remote computer that communicates with the grinder via a private or public network, for example using an IP (Internet) communication protocol.

[0085] Figure 2A projection of an initial profile 21 of a lens 20 to be machined is shown.

[0086] The figure also shows a projection of the final contour 22 of the lens 20 after machining. This final contour 22 corresponds to the bottom of the bezel of the rim of the spectacle frame selected by the individual, the bezel being suitable for receiving the machined lens.

[0087] Figure 2 Also shown is a "box system" of the final contour 22. As is known, the box system comprises a box 23, which is a rectangle drawn around the projection of the final contour 22, the box having two horizontal sides.

[0088] The center O of the frame 23 is called the frame center. The lens will be blocked between these two axes 202, 203 so that the blocking axis A7 passes through the frame center.

[0089] Before machining the ophthalmic lens 20 , the control unit 251 acquires the geometry of the final contour 22 .

[0090] As will be described in detail below, the final contour 22 takes on a plurality of points P that characterize the shape of the final contour 22. i A set of triplets corresponding to the cylindrical coordinates (r i ,θ i ,z i ) in the form of.

[0091] These coordinates may be obtained from a database accessible to the optician, or by using an imaging device comprising image capture means and image processing means, suitable for processing photographs of sample lenses delivered with the frames, or by feeling the bottom of the bezel of the frame chosen by the individual.

[0092] The lens is then subjected to a centering operation followed by a blocking operation.

[0093] These two operations are well known to those skilled in the art and do not form part of the subject matter of the present invention, so they are only briefly described.

[0094] During the centering operation, the position of the mark or marks etched on the lens is determined and the desired position of the final profile 22 is derived therefrom (so that after the lens has been shaped according to this profile and fitted in the chosen frame, its optical center is correctly positioned relative to the corresponding eye of the spectacle wearer).

[0095] During the blocking operation, the lens is clamped between the shafts 202, 203 of the edge grinder 200 by means of a clamping attachment adhesively bonded to the lens centered on the frame center, so that the frame center is centered on the clamping axis A7.

[0096] Then, forming is performed in two operations, a roughing operation and a finishing operation.

[0097] For rough machining of the lens, a roughing cylindrical grinding wheel 210 is used to roughly reduce the radius of the lens 20 to the shape of the final profile 22. More precisely, the shafts 202, 203 and the shaker 201 are here controlled relative to each other so that for each angular position θ of the lens about the clamping axis A7 i Reduce the radius of the lens to a radius r equal to the final profile 20 i Length.

[0098] To finish the lens, a "bevel" or groove or any suitable form is formed on the edge face of the lens using a profiled grinding wheel and / or any other finishing tool, and the resulting edge is polished.

[0099] The invention relates more particularly to the roughing step.

[0100] During this step, the grinding wheel 210 follows a first path Pa1, radial relative to the axis A7, with respect to the lens 20, until its peripheral edge reaches the final profile 22. The grinding wheel then follows a second path Pa2 along the final profile 22 (see Figure 2 ).

[0101] The lens 20 is therefore machined in a single pass about the axis A7.

[0102] According to the present invention, a roughing step is performed in order to reduce the time required to machine the edge of the lens 20 .

[0103] To do this, during the roughing step:

[0104] - The value F measured by the strain gauge 234 meas ,and

[0105] - Continuously adjust the machining speed MSp so that the measured value F meas Maintain equal to target value F targ .

[0106] To this end, according to these values ​​F meas 、F targ The difference between them is used to control the rotation of shafts 202 and 203.

[0107] Before explaining more precisely how the method is carried out, the concept of "machining speed MSp" (also called "machining rate") may be defined.

[0108] The machining speed may be defined as the rotational speed of the shafts 202 , 203 .

[0109] Preferably, however, the machining speed is defined as the speed of the contact point between the lens 20 and the grinding wheel 210. This machining speed MSp therefore depends on the rotation speed of the shafts 202, 203 and on the radius of the contact point relative to the axis A7.

[0110] It should be noted here that the grinding machine 200 is designed so that the machining speed MSp can reach a known “maximum machining speed” or a known axis rotation speed.

[0111] It should be noted here that the grinding machine 200 is designed so that it can reach a known “maximum axis rotation speed” or so that the machining speed MSp can reach a known “maximum machining speed”.

[0112] The method for rough machining of a lens 20 is performed cyclically, so that the machining of the lens edge is performed point by point along the final contour 22 in each cycle.

[0113] In the following, the concept of "sampling interval Δt" will be defined as the time between two consecutive cycles.

[0114] Here, the idea of ​​the invention is to discretize the final profile 22 into several main points and to search in real time for the next point to be reached at the end of each instantaneous sampling interval Δt. In parallel, it is proposed to periodically adjust the target value F taking into account the power consumed by the grinding machine 200. targ (Not necessarily in every loop, but at least once a second).

[0115] First, it may be explained how to define the main points of the discretized final contour 22 .

[0116] The first principal point P0 may be chosen randomly.

[0117] Then, the main point P is determined according to the maximum machining speed and / or the maximum axis rotation speed. i The number N of (where i ranges from 0 to N-1).

[0118] For example, for simplicity, consider the maximum shaft rotation speed. In this example, when the sampling interval Δt is stable at 1 ms, the maximum shaft rotation speed is considered to be equal to 10 rpm.

[0119] In this example, the principal point P is calculated in the following way i The number N:

[0120] N = 60 / 10.1000 = 6000

[0121] In other words, the final contour 22 initially consists of 6000 principal points P i Characterize the coordinates of these main points (ri ,θ i ,z i ) is defined.

[0122] exist Figure 3 In the top figure, a part of the final contour 22 and three of the 6000 main points, named P0, P1 and P2, are shown.

[0123] It can be understood that if the machining speed MSp is equal to its maximum value, the time required to machine the lens from point P0 to point P1 (or from point P1 to point P2) is equal to 1 ms.

[0124] These main points i It is defined before the roughing step.

[0125] However, during the roughing step, if the force value F is measured meas If the value is too high, it is necessary to slow down the machining speed MSp to reduce this value. To achieve this goal, at the main point P i Add an intermediate point P between 0j (where j ranges from 1 to n). Due to these points, the grinding wheel 210 will not have to move from one main point P to another in each cycle. i Arriving at another major point P i+1 , but it will be able to reach only the intermediate point P 0j one of the.

[0126] In fact, these intermediate points P 0j are added in real time during the roughing step, and they are defined by only one of their coordinates: their orientation θ j Therefore, using the middle point P 0j Instead of a larger number N of main points P i This eliminates the need to determine a large number of triples (r i ,θ i ,z i ).

[0127] To add these intermediate points P 0j The method is named sampling. In fact, it consists in sampling at each cycle and only when necessary at the next two principal points P i Add a predefined number n of intermediate points P between 0j .

[0128] like Figure 3 As shown in the top figure of FIG, at the first sampling time t (at the beginning of the first cycle), these intermediate points P are added between the main points P0 and P1 0j The added intermediate point P 0j The predefined number n of is at least equal to 10, here equal to 100.

[0129] Then, at these intermediate points P 0j The next point P to be reached at the next sampling time t+1 (at the end of the first cycle) is selected between the second main point P1 and t+1 , so that the measured value F meas Maintain equal to target value F targ (See Figure 3 ).

[0130] like Figure 3 As shown in the last figure, in each cycle, the method is repeated, and new sampling is performed only when necessary.

[0131] As explained above, in order to select the next point in each cycle, it is proposed to determine two parameters in parallel.

[0132] The first parameter is the target value of the measured force F targ , and the second parameter is the machining speed Msp.

[0133] exist Figure 4 The left part of FIG. 1 shows the method for adjusting the target value F according to the inherent characteristics of the lens material (material type, amount of material to be processed, etc.) and the operating conditions of the machine (voltage, maintenance status, etc.). targ The method comprises several steps.

[0134] These steps are performed in cycles, but these cycles may be asynchronous with the above cycles. In other words, the sampling intervals of these asynchronous cycles may be different from the sampling interval Δt and may vary between cycles.

[0135] Figure 4 The first step S0 shown represents the beginning of the roughing step.

[0136] The second step S2 comprises determining an initial target value F targ Here, this initial target value depends only on the operating conditions of the grinding machine 200 and more specifically on its nominal power.

[0137] Then, machining of the lens begins and the following steps are performed.

[0138] At step S4, the determined target value F targ With the predetermined threshold F up Make a comparison.

[0139] The predetermined threshold F up Depends on the grinder 200 used. The predetermined threshold is, for example, equal to 2500 g. The predetermined threshold corresponds to a minimum value of force, below which no problem is considered to occur.

[0140] If the target value F targ Below the predetermined threshold F up , then execute step S12 (described below).

[0141] Otherwise, during step S6, the instantaneous electric power P consumed by the grinding machine 200 is obtained. el And compare it with the power threshold P max Make a comparison.

[0142] The power threshold P max Depends on the grinder used. It is for example equal to 900 W. It corresponds to a power equal to or close to the maximum power that the grinder may consume.

[0143] If the instantaneous electric power P el Below the power threshold P max , then implement step S12.

[0144] Otherwise, during step S8, the target value F targ Reduce by a predetermined amount. This amount is, for example, equal to 500 g.

[0145] Then, during step S10, a delay is triggered and then step S12 is implemented. The delay is, for example, 0.8 s.

[0146] Step S12 is to determine whether the rough machining step is completed.

[0147] If completed, the method ends (step S14). Otherwise, the method restarts at step S4.

[0148] Thanks to this method, the target value F is adjusted according to the grinding machine possibilities targ .

[0149] Concomitantly, a new machining speed Msp is determined at each cycle defined by the sampling interval Δt.

[0150] In other words, the process for determining the target value according to the target value F is carried out in parallel with the determination of the target value. targ and the measured value F meas Method to adjust the machining speed MSp.

[0151] The method is based on a proportional-derivative controller and comprises the following steps.

[0152] During a first step S20, the processing unit 251 determines the measurement value F meas With the target value F targ The first difference between (named as force error ΔF).

[0153] Then, during a second step S22, it roughly estimates the measured value F measTo this end, here it calculates the measured value F at the sampling instant t and at the previous sampling instant t-1 meas The difference between .

[0154] Thereafter, during a third step S24 , the processing unit 251 calculates the machining speed MSp according to the force error ΔF and the derivative δF.

[0155] Here, the calculation is based on the following equation:

[0156] MSp=Kp.ΔF+Kd.δF

[0157] In this equation, the constants Kp and Kd are determined by means of a test phase on the grinding machine 200 .

[0158] Finally, due to the machining speed MSp, the processing unit is able to determine the next point P to be reached at the end of the sampling interval Δt t+1 .

[0159] Then, if the next point does not belong to the main point P i , the processing unit determines its coordinates (r j ,θ j ,z j ). In fact, only the middle point P 0j The orientation of θ j is known. It can be based at least on the orientation θ j and at the next point P t+1 The coordinates of the two main points on both sides of i ,θ i ,z i ) and (r i+1 ,θ i+1 ,z i+1 ) The other coordinates are determined by interpolation.

[0160] Then, during the instantaneous sampling interval Δt, the shafts 202, 203 rotate so that the contact point between the lens 20 and the roughing wheel 210 reaches the next point P t+1 . And the method starts a new cycle again.

[0161] The invention is in no way limited to the described and shown embodiments.

[0162] In particular, the method may be applicable to the machining of other ophthalmic products, such as the machining of molds suitable for molding ophthalmic lenses.

Claims

1. A method for forming an ophthalmic product (20) using a machining apparatus (200), the machining apparatus being provided with a clamping device (202, 203) for clamping the ophthalmic product (20), a machining tool (210) for machining the ophthalmic product (20), and a force sensor (234) adapted to measure a force related to a force applied by the machining tool (210) to the ophthalmic product (20), the method comprising: - a step of clamping the ophthalmic product (20) in the clamping device (202, 203); as well as - a step of rough machining the ophthalmic product (20) by means of the machining tool (210) so as to bring the initial contour (21) of the ophthalmic product (20) to a final contour (22) of a different shape, Characterized in that during the roughing step: - The force value (F) is measured by the force sensor (234) meas ),and -Continuously adjust the machining speed so that the measured value (F meas ) is maintained equal to the target value (F targ ), the target value (F targ ) is based on the electric power (P) consumed by the machining equipment (200) el ) to determine.

2. The method for forming according to claim 1, wherein: During the roughing step, the machining tool (210) follows a first path (Pa1) that is radial relative to the clamping devices (202, 203) until the final contour (22) is reached, and a second path (Pa2) that follows the final contour (22).

3. The method for forming according to claim 1 or 2, wherein: The force sensor (234) is adapted to measure a force component which is radial relative to the clamping device (202, 203).

4. The method for forming according to any one of claims 1 to 3, wherein: During the roughing step, a comparison operation is performed to compare the electrical power (P el ) and power threshold (P max ) is compared, and when the electric power (P el ) is greater than the power threshold (P max ), the target value (F targ ) is reduced by a predetermined amount.

5. The method for forming according to claim 4, wherein: Only when the target value (F targ ) is greater than the predetermined threshold (F up ) when performing the comparison operation.

6. The method for forming according to any one of claims 1 to 5, wherein: The machining speed is determined by means of a proportional-derivative controller.

7. The method for forming according to claim 6, wherein: The machining speed is determined according to: - The measured value (F meas ) and the target value (F targ ), and - the measured value (F) measured at the current time (t) meas ) and the measured value (F meas ) between the first and second differences.

8. The method for forming according to any one of claims 1 to 7, wherein: The final profile (22) is characterized by a first point (P0, P1, P2): -Midpoint(P 01 , P 02 , P 03 ) is defined between the first points (P0, P1, P2), and - During the roughing step, at each sampling moment (t), the machining device (200) is programmed to: ¤According to the measured value (F meas ) and the target value (F targ ), between the first point (P0, P1, P2) and the middle point (P 01 , P 02 , P 03 ) to select the next point to be reached, and ¤ Controlling the machining tool (210) and the clamping device (202, 203) so that the machining tool (210) reaches the next point in a constant predetermined amount of time (Δt) from a sampling moment (t) to another sampling moment.

9. The method for forming according to claim 8, wherein: The number of the first points (P0, P1, P2) is determined according to the maximum machining speed and / or the maximum speed of the machining equipment (200).

10. The method for forming according to any one of claims 1 to 9, wherein: The ophthalmic product (20) is an ophthalmic lens or a mold for molding an ophthalmic lens.

11. The method for forming according to any one of claims 1 to 10 comprises a finishing step after the roughing step, wherein the finishing step is performed on a part of the ophthalmic product (20) machined by the machining tool (210) by means of a finishing tool (222, 223) different from the machining tool (210).

12. The method for forming according to any one of claims 1 to 11, wherein: During the rough machining step, the ophthalmic product (20) is machined in a single pass by the machining tool (210) around the clamping device (202, 203).

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