Method for surfacing a lens blank with a cutting tool

Abstract

The invention discloses a method for processing the surface of a lens blank by using a cutting tool. A computer-implemented method for determining compensated surface description data intended to be loaded into a surface processing machine to obtain a surface of an optical element by cutting a blank with a cutting tool of the surface processing machine, the method comprising:-providing surface description data, -providing contact data from the surface description data,-generating a compensation map by using a transfer function,-determining compensated surface description data from the surface description data and the generated compensation map.

Description

Technical Field

[0001] The invention belongs to the field of ophthalmology and relates to a computer-implemented method for determining compensated surface description data representing the surface of an optical element obtained by cutting a blank with a cutting tool of a surface machining machine. The invention also relates to a computer program product comprising a series of instructions which, when loaded on a computer, cause said computer to perform the steps of the method according to the present description; and a system comprising the computer program product. Background Art

[0002] Typically, spectacle lenses are specifically manufactured according to the needs of each wearer, which spectacle lenses may take the form of specifications defined in a prescription drawn up by an ophthalmologist or optometrist.

[0003] To manufacture a lens, a lens blank undergoes various steps (particularly a surfacing step, also called a cutting step) to form the desired lens, during which the shape of the lens blank is processed to produce what may be called a surface-processed lens, so that the surface-processed lens exhibits the desired optical properties. The shape of the surface of the lens or lens blank may be obtained by direct cutting of the surface, or may be obtained by molding through a mold previously cut according to the desired optical properties.

[0004] In practice, the operation may be performed, for example, on a blank or semi-finished lens blank whose front surface has been previously machined, the surface machining operation essentially affecting one of the surfaces of the lens blank, typically the back surface, according to the prescription.

[0005] In addition to the desired desired optical properties, the surface quality obtained must be such that no irregularities occur which would be transmitted to the resulting product and cause deviations from the desired desired optical properties. In fact, the resulting product may be very sensitive to these surface irregularities. Therefore, a method is needed that enables these surface irregularities to be reduced.

[0006] Irregularities may have various origins. In particular, the surfacing operation is a turning operation performed with a cutting tool, such as a diamond tool. During the cutting step, the edge of the cutting tool comes into contact with the blank lens. The point of contact between the lens blank and the cutting tool moves along the edge of the cutting tool. This results in a non-uniform wear state along the edge of the cutting tool, depending on the lens being surfaced. Consequently, the non-uniform wear state along the edge of the surfacing tool results in irregularities along the edge of the surfacing tool, which are replicated on the lens surface. Consequently, this may result in local or global surface irregularities, such as wrong optical power, ring and center irregularities.

[0007] In order to obtain a suitable product without irregularities, precision down to the micron level is required.

[0008] In order to obtain such precision, application FR2984197 describes a method related to the correction of surface irregularities introduced in a reproducible manner, comprising a step of determining the surface irregularities of a surface-machined lens and a transformation step of compensating the surface irregularities of the surface-machined lens using an irregularity model. However, this method solves the surface irregularities of the surface-machined lens but does not solve the source of the surface irregularities (such as irregularities of the surfacing tool).

[0009] What is needed is a method and system for directly addressing irregularities introduced by surfacing tools in order to improve the accuracy of the final lens and reduce rejected lenses. Summary of the invention

[0010] According to the present disclosure, this object is achieved by a computer-implemented method for determining compensated surface description data intended to be loaded into a surface machining machine to obtain the surface of an optical element by cutting a blank with a cutting tool of the surface machining machine, the method comprising:

[0011] - provide surface description data,

[0012] The surface description data represents a surface of the optical element;

[0013] - provide contact data based on surface description data,

[0014] The contact data represent contact points which are used with a cutting tool to obtain the surface represented by the surface description data,

[0015] The contact point is the point of contact between the cutting tool and the surface of the blank to obtain the surface of the optical element, and

[0016] The contact point is defined in the cutting tool coordinate system;

[0017] - Generate compensation maps by using transfer functions,

[0018] An input to the transfer function is at least contact data, and an output of the transfer function is a compensation map;

[0019] - Determining compensated surface description data based on the surface description data and the generated compensation map.

[0020] In the present disclosure, an "optical element" means a lens, a semi-finished lens, or a mold used to manufacture a lens or a semi-finished lens.

[0021] In the present disclosure, "blank" means a semi-finished lens or a blank for making a lens, or a blank for making a mold for making a lens or a semi-finished product.

[0022] In the present disclosure, contact data are contact points used together with a cutting tool to obtain the surface represented by the surface description data. The contact points are the points of contact between the cutting tool and the surface of the blank to obtain the surface of the optical element. The contact points are defined in the cutting tool coordinate system.

[0023] The cutting tool coordinate system can be a Cartesian coordinate system or a polar coordinate system. The origin of the cutting tool coordinate system is fixed relative to the cutting point, in other words, fixed in the cutting tool coordinate system. When the cutting tool moves relative to the surface processing machine, the origin of the cutting tool coordinate system moves with the cutting tool and remains fixed in the cutting tool coordinate system. The origin can be defined in the cutting tool as the center of the cutting tool or it can be defined outside the cutting tool.

[0024] Contact data can be defined as contact angle data in a polar coordinate system.

[0025] In order to perform surface machining on the blank using the cutting tool, the blank can be rotated and the cutting tool can also be rotated. When rotating the blank, the surface machining machine can have a rotation axis around which the blank to be cut rotates. When rotating the cutting tool, the surface machining machine can have a rotation axis around which the cutting tool rotates. According to embodiments, the blank and / or the cutting tool can move according to at least one or two or three (x, y, z) or four degrees of freedom.

[0026] According to the present disclosure, the optical power defects on the ophthalmic device to be manufactured can be limited by taking into account the cutting tool and the errors generated by the cutting tool, and in particular by recalculating the position of the tool during the cutting step in manufacturing a given ophthalmic device based on the contact points defined in the cutting tool coordinate system.

[0027] Furthermore, by recalculating the position of the cutting tool based on the contact points defined in the cutting tool coordinate system, the method can be general and applicable to any kind of surface machining machine, in particular when machining successively different surface description data, without the need to re-evaluate the transfer function for each different surface description.

[0028] According to the present disclosure, the compensation map can be a moire compensation map. The moire compensation map means a compensation map related to the moire of the tool, such as wear of the tool, defects of the tool, such as surface defects (in other words, the actual surface of the tool that comes into contact with the optical element during surface machining), material properties, or all kinds of moire sources. The origin of such moire can be obtained according to the embodiments described below.

[0029] The inventors have shown that the accuracy of surface machining is improved by taking into account the waviness of the tool and that, by working with a reference tool, the method can be general and applicable to any kind of surface machining machine.

[0030] In the present disclosure, the transfer function may include at least deviation information. Deviation information means direct or indirect information of the deviation between the nominal information of the tool and the actual information or predicted information. The deviation may be related to the ripple of the tool. As described in the following embodiments, at least the deviation information can be obtained.

[0031] The step of generating a compensation map may further include:

[0032] - provide material description data,

[0033] the material description data represent the material of the cutting tool and / or the material of the blank and / or the interaction between the material of the blank and the material of the cutting tool during cutting of the blank to obtain the optical element,

[0034] - determining a transfer function based at least on the provided material description data.

[0035] In the present disclosure, "material interaction between the material of the blank and the material of the cutting tool" means the behavior of the material of the blank when the material of the blank interacts with the material of the cutting tool under given wear conditions.

[0036] Material description data can be of the cutting tool and / or the blank: ductility, hardness, elasticity, brittleness, forgeability, elasticity, rigidity, viscosity.

[0037] The inventors have pointed out that the material interaction between the material of the cutting tool and / or the material of the blank and the material of the cutting tool changes the tool wear effect and therefore, errors may be introduced during the manufacturing step if this parameter is not taken into account. This embodiment presents the advantage of limiting irregularities related to the material description of the cutting tool.

[0038] The step of generating a compensation map may further include:

[0039] - providing reference component description data representing a surface of a component previously cut by a cutting tool;

[0040] - determining a transfer function based at least on the provided reference element description data.

[0041] The reference element thus allows a precise adjustment of the transfer function.

[0042] Reference component description data may provide material description data.

[0043] The step of generating a compensation map may further include:

[0044] - providing a prediction model which predicts the wear of the cutting tool under given conditions,

[0045] - Determining a transfer function based at least on the predicted cutting tool wear.

[0046] Therefore, the predictive model allows the transfer function to be adjusted based on previous cutting experience.

[0047] The predictive model can be trained machine learning or simulation so that the transfer function can be adjusted for unknown conditions.

[0048] The step of generating a compensation map may further include:

[0049] - Provide cutting speed and / or cutting depth at each contact point;

[0050] - A transfer function is determined based at least on the provided cutting speed.

[0051] In the present disclosure, the cutting speed is the relative speed between the cutting tool and the blank at the contact point during cutting of the blank to obtain the optical element. The cutting speed can also be defined as the speed at which material is removed from the blank by the cutting tool.

[0052] In this disclosure, the depth of cut is the amount of material removed by the cutting tool per cut. It can vary and depends on the tool type and blank material.

[0053] By taking into account cutting speed and cutting depth, the errors associated with the cutting of the tool are reduced and the cutting step is more precise on all surfaces.

[0054] The step of generating a compensation map by using a transfer function may further include:

[0055] - provide a compensation model to compensate for the defects caused by the manufacturing method,

[0056] - Generate compensation maps by using the transfer function and the provided compensation model.

[0057] According to this embodiment, moreover, the errors related to the cutting of the tool make it possible to take into account any kind of defects arising from the manufacturing method, thus limiting the optical defects of the final product.

[0058] The computer-implemented method may further include:

[0059] - Provide optical power description data;

[0060] - providing opposite surface description data, which represent the opposite surface of the surface to be obtained;

[0061] The step of providing surface description data includes:

[0062] - Determining the surface description data from the counter surface description data and the optical power description data.

[0063] The power description data is a redistribution of the power of the optical element. The power description data may be the power of the optical element to be obtained. The power may be obtained from the wearer's prescription or from the desired design of the optical element to be obtained.

[0064] Providing opposite surface description data enables measurement of the opposite surface.

[0065] Embodiments allow taking into account the cutting of the opposite surface to determine the surface description data of the surface to be obtained.

[0066] The data providing the reverse surface description may be obtained by measurement or by simulation.

[0067] The opposite description may include errors of the opposite surface.

[0068] The step of providing contact data may further comprise:

[0069] - Providing cutting tool description data for providing contact data, the cutting tool description data representing at least a portion of an edge of the cutting tool, said edge of the cutting tool being intended to come into contact with the blank during surfacing.

[0070] According to a second aspect, the present disclosure also provides a surface processing machine for surface processing a blank to obtain a surface of an optical element by cutting the blank using a cutting tool of the surface processing machine, the system comprising

[0071] A cutting tool for cutting a blank to obtain a surface of an optical element, a computer, and

[0072] A computer program product comprising a series of instructions,

[0073] Wherein, when the instructions are loaded into the computer, they are capable of implementing the steps of a method for determining compensated surface description data intended to be loaded into the surface processing machine, the method comprising:

[0074] - providing surface description data which represent the surface of the optical element and are independent of the cutting tool;

[0075] - provide contact data based on surface description data,

[0076] The contact data represent contact points which are used with a cutting tool to obtain the surface represented by the surface description data,

[0077] The contact point is the point of contact between the cutting tool and the surface of the blank to obtain the surface of the optical element, and

[0078] The contact point is defined in the cutting tool coordinate system;

[0079] - generating the compensation map by using a transfer function, the input of the transfer function being at least the contact data and the output of the transfer function being the compensation map;

[0080] - Determining compensated surface description data based on the surface description data and the generated compensation map.

[0081] The method of loading into a surface processing machine may further include

[0082] - providing material description data, which material description data represent the material of the cutting tool and / or the material of the blank and / or the interaction between the material of the blank and the material of the cutting tool during cutting of the blank to obtain the optical element;

[0083] - determining a transfer function based at least on the provided material description data.

[0084] The surface processing machine may further comprise a reference sensor for detecting at least one reference element and for generating reference element description data,

[0085] The reference element is obtained from a blank that has been surface machined using the system's cutting tools.

[0086] A transfer function is determined based at least on the provided reference component description data.

[0087] The system may further include a cutting tool sensor for detecting the cutting tool to provide the surfacing tool description data.

[0088] According to a third aspect, the present disclosure further provides a computer program product comprising a series of instructions which, when loaded onto a computer, cause the computer to perform the steps of the method according to the present specification; and a system comprising the computer program product. BRIEF DESCRIPTION OF THE DRAWINGS

[0089] For a more complete understanding of the description provided herein and the advantages thereof, reference is now made to the following brief description taken in conjunction with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.

[0090] Figure 1 A manufacturing system (such as a digital surfacing machine) according to the present disclosure is partially and schematically depicted, the manufacturing system being configured to perform the steps of a method for manufacturing a component as an optical element.

[0091] Figure 2APartially and schematically depicted Figure 1 The cutting tool of the surface processing machine shown faces the optical element to be manufactured, which is fixed to the lens holding system;

[0092] Figure 2B Partially and schematically depicted Figure 2A Two contact angles of the cutting tool at two different contact points;

[0093] Figure 3 is a block diagram showing the operational steps of a method for determining compensated surface description data according to the present disclosure, the compensated surface description data being intended to be loaded into a Figure 1 In the surface processing machine shown, the surface of the optical element is obtained by cutting a blank using a cutting tool of the surface processing machine.

[0094] Figure 4A and Figure 4B Horizontal and vertical cross sections from two compensation diagrams according to the present disclosure are shown.

[0095] Figure 5A and Figure 5B Represents a measurement of a surface of a reference element according to the present disclosure.

[0096] Figure 6 Surfaces that can be used to reference component surfaces according to the present disclosure are shown.

[0097] Figure 7 The Z difference at different tool angles according to the present disclosure is shown. DETAILED DESCRIPTION

[0098] In the following description, the drawings are not necessarily drawn to scale and certain features may be shown in generalized or schematic form for the purposes of clarity and simplicity or for information purposes. In addition, although making and using various embodiments are discussed in detail below, it should be understood that many inventive concepts are provided as described herein that can be implemented in a wide variety of contexts.

[0099] The embodiments discussed herein are merely representative and do not limit the scope of the present invention. It is also obvious to those skilled in the art that all technical features defined relative to the method can be transposed to the device individually or in combination, and conversely, all technical features relative to the device can be transposed to the method individually or in combination.

[0100] To avoid detail not necessary to practice the invention, the description may omit certain information known to those skilled in the art.

[0101] The present disclosure relates to a method for manufacturing an ophthalmic element, which method comprises a machining step, in particular a cutting step, also referred to as a surface machining step.

[0102] Figure 1 A system for manufacturing an optical element 10 is shown, the system comprising a digitally controlled “free form” surface processing machine 1 , the digital control denoting a set of devices and software whose function is to give movement instructions to all the elements of the surface processing machine 1 .

[0103] The surface machining machine 1 is configured for machining by turning and / or surface machining (and optionally polishing) at least one surface on at least one face 12 of an optical article 10 .

[0104] The surface processing machine 1 comprises a movable machining arm 7 and a data processing system or a control unit (not shown) configured for controlling the movable arm 7. The system further comprises system components generally formed by at least one control unit 2, which is configured to communicate with the data processing system (or control unit) of the surface processing machine 1.

[0105] The control unit 2 comprises a microprocessor 3 having a memory 4 , in particular a non-volatile memory, allowing it to load and store software (in other words a computer program) which, when executed in the microprocessor 3 , allows the manufacturing method according to the invention to be implemented.

[0106] This non-volatile memory 4 is, for example, of the ROM (“Read Only Memory”) type.

[0107] The control unit 2 further comprises a memory 5 , in particular a volatile memory, allowing data to be stored during the execution of the software and the implementation of the method.

[0108] This volatile memory 5 is, for example, of RAM or EEPROM type (“Random Access Memory” and “Electrically Erasable Programmable Read Only Memory”, respectively).

[0109] The control unit may be integrated only at least partially into the machine. In other words, the control unit may be partially or completely arranged outside the machine.

[0110] The control unit 2 may at least partially form part of the surface processing machine 1 and may comprise one or more control modules located internally and / or externally to the machine.

[0111] The optical article 10 may be an ophthalmic lens and / or an inspection piece. In the case of an ophthalmic lens, the machine 1 may also be configured for polishing the face 12 and / or for edging the peripheral edge 13 (see FIG. 2 ) in order to form an ophthalmic lens.

[0112] The movable machining arm 7 is configured to carry a lens machining tool 24 ( Figure 2A ) device 20, and the control unit 2 is configured to control each step of the machining method by surface machining the surface of the ophthalmic lens using the lens machining tool 24 in the surface machining machine 1. Figure 2A A lens holding system 8 of a surface processing machine 1 is shown, which is configured to block an optical product, here formed by a blank 10 for forming an ophthalmic lens, in a predetermined position. The movable machining arm can be, for example, a slow tool servo or a fast tool servo. The arm 7 can be a slow tool servo or a fast tool servo.

[0113] The blank 10 includes an upper surface 12 , a lower surface 11 opposite to the upper surface 12 , and a peripheral edge 13 connecting the lower surface 11 and the upper surface 12 .

[0114] The upper surface 12 is configured to form a first face (also referred to as a rear face), and the lower surface 11 is configured to form a second face (also referred to as a front face). The second face is opposite to the first face.

[0115] The peripheral edge 13 is configured to form a peripheral contour having a first edge 15 connecting the peripheral edge 13 to the first face 12 and a second edge 14 connecting the peripheral edge 13 to the second face 11 .

[0116] Here, the second face 11 and the first face 12 of the blank 10 are both flat. The blank may have any ophthalmic geometry, such as a curved face or a face with discontinuities or microstructures.

[0117] The lens holding system 8 comprises, for example, an adhesive film (not shown) having an adhesive surface configured to be fixed on the lower surface 11 of the blank 10. With regard to the lens holding system, any blocking technology can be used. A first example is an alloy technology using an adhesive film (not shown) having an adhesive surface configured to be fixed on the lower surface 11 of the blank 10. A second example is a gluing technology using some kind of glue (not shown) that is adhered to the lower surface 11 of the blank 10.

[0118] The lens holding system can be configured to receive the blank 10 for first rough machining (e.g. milling) and then machining by surfacing the first face 12 using the device 20 to form a semi-finished lens. Next, the lens holding system 8 can be configured to receive the semi-finished lens for machining by surfacing the second face 11 (e.g., the front face) using the same device 20 to form an ophthalmic lens. A preliminary step can be to first rough machine (e.g. mill) the first or second face.

[0119] The lens holding system 8 is configured to be mounted on a spindle of the machine 1 which rotates during the step of manufacturing the blank 10 , for rotating the blank 10 itself during machining.

[0120] The machine 1 includes three directions, namely a first direction 16 (ie, X direction), a second direction 18 perpendicular to the first direction 16 (ie, Y direction), and a third direction 17 perpendicular to both the first direction 16 and the second direction 18 (ie, Z direction).

[0121] The position of the lens machining tool 24 is defined in the surface machining machine in three directions 16 to 18. Here, the Z direction 17 corresponds to the turning axis of the blank 10 (also called turning center or rotation axis).

[0122] The device 20 may include: a pin 21 configured to be fastened to the movable machining arm 7, a base 22 from which the pin 21 protrudes, a tool support 23 formed by a protrusion of the base 22 on the opposite side of the pin 21, and a lens machining tool 24 fixed to the tool support 23.

[0123] The lens machining tool 24 may be of the half-radius type or the full-radius type and generally has a predetermined aperture (in degrees).

[0124] A full radius type lens machining tool can be mounted on the apparatus 20 so that the tool 24 is tilted relative to the tool support 23 to form a tool with an asymmetrical arrangement of apertures. The asymmetrical arrangement of the apertures can be defined by a plane including the turning axis 17 (or Z direction), the Y direction 18 and the center of the tool.

[0125] Figure 2B Partially and schematically depicted Figure 2A The cutting tool has two contact angles α', α" at two different contact points 25' and 25". Figure 2BIt helps to define the contact points and the contact angles. The upper figure relates to a surface 12' with a low curvature. The lower figure relates to a surface 12" with a high curvature. In this figure, a turning axis 17 in the Z direction, also called the rotation axis, is also shown. An axis 18 parallel to the rotation axis in the Z direction is shown to help understanding. The cutting tool 24 is schematically represented by a circle. The contact points 25' and 25" are the contact points between the cutting tool and the surface. The tool angles α', α" are defined as the angles between the rotation axes 17, 18 and the axis passing through the reference point 26 of the cutting tool 24 and the contact points 25', 25". Since the axes 17 and 18 are parallel, the angles between the axes 18 or between the axes 17 are the same. The reference point can be the center of the cutting tool or any other point of the cutting tool, as long as this point remains the same for each contact point in the reference system of the cutting tool. As shown in the figure, the contact angle depends on the position of the contact point. Therefore, the contact angle can depend on the curvature of the surface and / or the position of the cutting tool on the surface.

[0126] Thus, as explained, in the Rx Lab, the actual final step of surface generation is a turning operation with a cutting tool. Initially, the cutting tool can be considered approximately circular (e.g., with a radius of 30 μm to 12 mm, preferably 2 to 5 mm) based on the specifications provided by the cutting tool manufacturer. During turning (also called surface machining or cutting), the contact point between the blank and the cutting tool moves along this circular portion. This results in a non-uniform wear state along the tool radius, depending on the surface to be obtained.

[0127] Roundness defects of the tool are replicated on the cut surface and can result in local or global surface defects such as wrong power, rings and center defects on the lens or semi-finished lens. Similar defects can also be generated on the semi-finished molded surface. This can result in wrong power on the lens.

[0128] The inventors point out that to solve this problem, a solution may be to take the cutting tool into account when calculating the surface description data intended to be loaded into the circular portion of the surface machining machine. Thus, the tool position is recalculated to compensate for the influence of the cutting tool. The recalculated tool position may be an X position or a Y position, preferably a Z tool position or a combination of X / Y / Z positions or any other kind of degree of freedom position.

[0129] Figure 3 is a block diagram showing the operational steps of a method for determining compensated surface description data according to the present disclosure, the compensated surface description data being intended to be loaded into a Figure 1 In the surface processing machine shown, the surface of the optical element is obtained by cutting a blank using a cutting tool of the surface processing machine. Figure 3 The overall solution is shown with examples in blocks and blocks. The solution is based on the calculation of compensation maps for the cutting tool position.

[0130] The compensated surface description data represent the surface of the optical element to be obtained by cutting the blank using a cutting tool of a surface machining machine.

[0131] The compensated surface description data are shown in block 36. The compensated surface description data depend on the cutting tool. As mentioned before, in particular, the compensated surface description depends on the contact points of the cutting tool. The compensated surface description data are intended to be loaded into a surface processing machine.

[0132] Figure 3 The main steps of the method are shown, and the method comprises the following steps:

[0133] - providing surface description data 30,

[0134] The surface description data represents a surface of the optical element;

[0135] - providing contact data 32 based on the surface description data,

[0136] The contact data represent contact points which are used together with the cutting tool 24 to obtain the surface represented by the surface description data,

[0137] The contact points 25', 25" are the contact points between the cutting tool 24 and the surface 12, 12', 12" of the blank 10 to obtain the surface of the optical element, and

[0138] The contact point is defined in the cutting tool coordinate system;

[0139] - generating a compensation map 34 by using a transfer function,

[0140] An input to the transfer function is at least contact data, and an output of the transfer function is a compensation map;

[0141] - Determining compensated surface description data 36 from the surface description data and the generated compensation map.

[0142] The diamond turning operation (also called cutting operation or surface machining operation) is critical to guarantee the final optical properties of the lens. The tool wear mechanism is controlled by the distance reached by each section of the cutting radius, the cutting parameters and the mix of materials. During operation, the tool wear at each point of the cutting edge can be measured by optical or mechanical probing of the lens, or predicted by calculation.

[0143] Therefore, the first step 30 is to provide surface description data. The surface may be a spherical, aspherical or free-form surface. The surface description data represents the surface of the optical element. The surface description data is independent of the cutting tool. The optical element may be a lens, a semi-finished lens or a mold intended for molding the surface of a lens or a semi-finished lens. Figure 3As shown, the surface description data may be a 3D diagram such as element 34 - XY in a plane and Z depending on the grayscale, or cylindrical coordinates such as on elements 30, 32, 36. XY may be expressed in an angular reference system. Such representations are well known to those skilled in the art. The reference system for the surface description may be the reference system of the cutting machine, or a 3D coordinate system such as on the element 34. Figure 2A Reference frame of the blank shown.

[0144] A second step 32 is to provide contact data based on the surface description data.

[0145] In the present disclosure, contact data are contact points used together with a cutting tool to obtain the surface represented by the surface description data. The contact points are the points of contact between the cutting tool and the surface of the blank to obtain the surface of the optical element. The contact points are defined in the cutting tool coordinate system.

[0146] The cutting tool coordinate system can be a Cartesian coordinate system or a polar coordinate system. The origin of the cutting tool coordinate system is fixed relative to the cutting point, in other words, fixed in the cutting tool coordinate system. When the cutting tool moves relative to the surface processing machine, the origin of the cutting tool coordinate system moves with the cutting tool and remains fixed in the cutting tool coordinate system. The origin can be defined in the cutting tool as the center of the cutting tool or it can be defined outside the cutting tool.

[0147] In order to perform surface machining on the blank using the cutting tool, the blank can be rotated and the cutting tool can also be rotated. When rotating the blank, the surface machining machine can have a rotation axis around which the blank to be cut rotates. When rotating the cutting tool, the surface machining machine can have a rotation axis around which the cutting tool rotates. According to embodiments, the blank and / or the cutting tool can move according to at least one or two or three (x, y, z) or four degrees of freedom.

[0148] The contact data may represent contact points in function of tool angles used with a cutting tool to obtain the surface represented by the surface description data. Figure 2B As explained, the contact point is the contact point between the cutting tool and the surface, and the tool angle is the angle between the rotation axis and the axis passing through the contact point and the reference point of the cutting tool. The tool angle diagram can be represented in the reference system of the cutting tool. As shown in the block, the diagram of the cutting tool can be represented according to the XY in the plane expressed in degrees and the Z grayscale expressed in degrees. In other words, this step is based on the tool calculation of the surface description data. As shown in Figure 2, the contact point and the contact angle are calculated for each point of the surface description data to obtain the contact angle data. In order to calculate it, the tool can be regarded as circular or partially circular or elliptical or non-circular; the tool can also be regarded as spherical or non-spherical, preferably spherical.

[0149] The third step 34 is to generate a compensation map by using a transfer function. The input of the transfer function is the contact data and the output of the transfer function is the compensation map. The transfer function can be based on different parameters: material parameters or cutting conditions.

[0150] The compensation map may be shown in 3 dimensions as in element 341, or in 2 dimensions as in element 342, where the light grey curve represents the Y direction and the dark grey curve represents the X direction. The Z direction is represented by the vertical axis for both.

[0151] According to the present disclosure, the compensation map can be a moire compensation map. The moire compensation map means a compensation map related to the moire of the tool, such as wear of the tool, defects of the tool, such as surface defects (in other words, the actual surface of the tool that comes into contact with the optical element during surface machining), material properties, or all kinds of moire sources. The origin of such moire can be obtained according to the embodiments described below.

[0152] The inventors have shown that the accuracy of surface machining is improved by taking into account the waviness of the tool and that, by working with a reference tool, the method can be general and applicable to any kind of surface machining machine.

[0153] In the present disclosure, the transfer function may include at least deviation information. Deviation information means indirect information or indirect information of the deviation between the nominal information of the tool and the actual information or predicted information. The deviation may be related to the ripple of the tool. As described in the following embodiments, at least the deviation information can be obtained.

[0154] According to one embodiment, the transfer function is determined based at least on material description data.The material description data may be the material of the cutting tool and / or the interaction between the material of the blank and the material of the cutting tool during cutting of the blank to obtain the optical element.

[0155] Material description data can be of the cutting tool and / or the blank: ductility, hardness, elasticity, brittleness, forgeability, elasticity, rigidity, viscosity.

[0156] Ductility is the ability to stretch without breaking and retain its new shape. Hardness is the ability to resist penetration and scratching. Elasticity is the ability to deform and then return to its original shape. Brittleness is the ability to break easily. Forgeability is the ability to flatten or bend without breaking and retain its new shape. Elasticity is the ability to withstand impact. Rigidity is the ability to resist deformation.

[0157] The material description may depend on the conditions of the cutting step, such as temperature, pressure, application speed, deformation speed, kinematics, depth of cut (depth of cut), or contact point of the cutting tool.

[0158] Figure 4A and Figure 4BCompensation plots for two different blank materials (CR39 and polycarbonate, respectively, cut with the same cutting tool) are shown. The white-grey color is the Y direction, the dark grey is the X direction, and the vertical axis is the Z direction.

[0159] As shown in this figure, the compensation map clearly depends on the descriptive material data. Figure 4A The shape of the curve is different from that in Figure 4b.

[0160] The cutting tool material may be single crystal diamond (natural or synthetic), CVD (chemical vapor deposition), polycrystalline diamond (PCD) or carbide or cubic boron nitride (c-BN) or other materials.

[0161] The blank material may be a polymer in the case of a lens, or a metal such as steel or steel alloys, aluminum, NiP, nickel alloys, glass, brass or other metals in the case of a mold.

[0162] According to another embodiment, the transfer function is determined based on at least reference element description data, alone or in combination. The reference element description data are surfaces of elements previously cut by a cutting tool. The reference element description data allow, for example, an adjustment of the transfer function during tool life or during changes to the surface description data for manufacturing. There are several methods for obtaining reference element data: a first method, a characterization model, such as optical measurements, surface measurements or tool edge measurements; a second method, a predictive model.

[0163] The reference element can be a reference lens or a reference surface.

[0164] For example, when the reference element is a reference lens, the reference element can be optically measured using an optical device (such as a deflectometry commercial device, a dual lens mapper (DLM), a Promapper or an auto mapper, or any kind of device with optical power mapping) to reconstruct the surface as the reference element description data. Then, by calculation, the difference between the reference element description data and the surface description data used to manufacture the reference element is calculated according to the Z direction and translated on the Z difference surface. Finally, each Z difference is associated with a tool contact point.

[0165] The reference element can be measured in whole or in part.

[0166] The reference lens can be a specific lens or a production Rx lens, which can be spherical or aspherical.

[0167] As another example, when the reference element is a reference surface, the reference element is measured using an optical device (such as a laser profiler or interferometer), or a detection tool inside a cutting machine or outside a surface processing machine, or an integrated topography measurement. Then, by calculation, the difference between the reference element description data and the surface description data used to manufacture the reference element is calculated according to the Z direction and translated on the Z difference surface. Finally, each Z difference is associated with a tool contact point (which can be a tool contact angle). In other words, the calculated Z difference is associated with the tool contact angle to evaluate the wear effect of each tool contact point (which can be a tool contact angle) on the surface, thereby feeding the transfer function of the compensation model.

[0168] Respectively Figure 5A and Figure 5B As shown, the measurement can be performed over the entire surface, or only on one or several diameter (or radius) curves.

[0169] The quality of the measurement can be considered, since all the artifacts will have been compensated during the manufacture of the lens. These artifacts may reduce the optical power instead of increasing it. Therefore, the measurement can be validated based on the following criteria: standard deviation, difference between two consecutive measurements, data mining, ...

[0170] For deviations of the measuring device, compensation of this deviation can be corrected at the Z difference. For example, the wear of the probe tool can be evaluated according to a standard and removed from the measurement.

[0171] In case the material of the blank and the material of the cutting tool are the same as the material used to obtain the optical element, the reference element description data may provide the material description data.

[0172] Tool wear effects can be applied to a reference surface of the same or similar material in order to use the tool wear effect on another material.

[0173] Material features can be separated from tool wear features because the behavior of the material changes the tool wear effect.

[0174] According to an embodiment, the step of generating a compensation map may further include:

[0175] - Provides the cutting speed at each contact point, and

[0176] - A transfer function is determined based at least on the provided cutting speed.

[0177] The cutting speed is the relative speed between the cutting tool and the blank at the contact point during cutting of the blank to obtain the optical element.

[0178] The way to provide the cutting speed may be thanks to the surface of the reference element which can help to separate for example the tool contact point and the low cutting speed in the center of the surface. There are different kinds of surfaces that allow to extract this information like spherical surfaces or W surfaces.

[0179] Spherical surfaces are surfaces of revolution that are easy to calculate, manufacture, measure and extract wear effects. However, spherical surfaces can be positive ranges of tool angles and low cutting speeds (turning processes) can be superimposed to a 0° tool angle in the center, which is usually the most sensitive wear point.

[0180] In order to decorrelate the superposition of low cutting speed and 0° tool angle, and / or to obtain negative and positive tool angles in the same surface, a complex surface called W-surface can be used, which consists of several functions (e.g., a combination of polynomials or sinusoidal functions) intended to have a concavity variation. This configurable surface is a surface of revolution, where the diameter curve is defined by:

[0181] -Centrosymmetric,

[0182] - the maximum tool angle is at the edge of the surface,

[0183] - and the minimum angle is between the center and the edge of the surface.

[0184] Figure 6 A W surface as described above is shown, which can be used as the surface of a reference element.

[0185] Furthermore, there may be an interaction between cutting and lens stiffness. Therefore, reference elements may be performed on a reference lens that is close to a standard production lens to get a representative response. For example, the thickness of the lens should be similar to the production lens (e.g. + / - 10 mm).

[0186] The range of tool angles characterized can depend on the surface of the reference component. The flatter the surface, the smaller the range. Therefore, to compensate for surfaces that are more curved or larger than the reference surface, the model may lack data from unused tool angles. Therefore, the compensation map or transfer function can be extrapolated.

[0187] The reference element can be used at different moments in the life of the cutting tool, or for each optical element manufactured according to the required optical properties.

[0188] The reference element can be a specific lens, a specific blank, a semi-finished lens or a specific mold. The reference element can be spherical or aspherical.

[0189] The reference element may be a semi-finished lens or a finished lens intended for use in manufacturing an optical element.

[0190] The reference element can be reused to manufacture an optical element or another reference element.

[0191] Depending on the wear of the tool, the reference element can have a specific geometry.

[0192] New reference elements cut or re-cut by the cutting tool can be used regularly (weekly or monthly or every given number of surface-machined optical elements or according to the wear of the cutting tool).

[0193] The frequency of providing the reference element can be triggered by a trigger based on the deviation of the optical element control measurement by using optical mapping (such as DLM, automatic mapper or other), or by using surface mapping (such as mechanical or optical sensor), or by using a flexometer, or by using a front photometer, or by using the control of a tool (microscope or profilometer). If a significant deviation of this trigger value is found, the reference surface is redeployed to readjust the compensation.

[0194] According to an embodiment, the step of providing contact data may further include:

[0195] - Provide cutting tool description data to provide contact data,

[0196] The cutting tool description data represent at least a portion of an edge of the cutting tool, which edge of the cutting tool is intended to come into contact with the blank during surfacing.

[0197] In fact, tool wear effects can be compensated by characterizing the waviness of the tool edge. In fact, the rounded edge section of the tool can be measured at different tool angles. The measurements can be performed by optical means (e.g. microscope, laser) or tactile means (e.g. probe tool); AFM on multiple cross sections at different wear states. Then, as Figure 7 As shown, the difference between the corrugation and the nominal (or theoretical) shape is defined as the Z difference at different tool angles. As mentioned earlier, the Z difference can be the difference between the surface description data and the surface of the reference element. For example, at the end of its life, the range of local wear on the cutting edge can be close to 5μm. This wear level may cause local surface errors. When the radius wears, the cutting edge may not be in the exact position expected by the calculator. In addition, the wear of the cutting edge radius along the tool radius may not be uniform. This difference curve in tool roundness varies with the material, resulting in a transfer function of the difference on the raw surface as the tool angle varies.

[0198] As previously mentioned, according to another embodiment, generating the compensation may include, alone or in combination:

[0199] - provide predictive models, and

[0200] - Determining a transfer function based at least on the predicted cutting tool wear.

[0201] The prediction model predicts the wear of the cutting tool under given conditions.

[0202] In fact, ophthalmic companies produce hundreds of millions of lenses with prescription corrections. Therefore, based on advances in measuring equipment and data mining (artificial intelligence), tool wear and the effect of wear on the optical function of the lens can be predicted and compensation maps can be calculated.

[0203] Statistical models obtained from previous products can also be used.

[0204] The compensation map is the Z difference required to correct the initial surface as described previously.

[0205] The predictive model can be adjusted during the tool life through sampling / intermediate measurements (a hybrid model between predictive and characterization models).

[0206] The predictive model can be a trained machine learning. The inputs to the trained machine learning can be: tool geometry, distance traveled by the tool at each contact point, material, cutting speed, type of optics, thickness, type of surface, type of blockage, kinematics of the cutting machine. The output can be the state of the cutting tool edge or compensation surface.

[0207] According to another embodiment, the step of generating a compensation map by using a transfer function may further include, alone or in combination:

[0208] - Provides compensation models to compensate for defects caused by the manufacturing method rather than the cutting tool

[0209] - Generate compensation maps by using the transfer function and the provided compensation model.

[0210] The method of this embodiment and more particularly the compensation model are described in application FR2984197.

[0211] The next step of the method of the present disclosure is to determine compensated surface description data 36 based on the surface description data and the generated compensation map.

[0212] In fact, the ultimate purpose of this step is to adjust the tool position and tool path taking into account the measured or predicted local edge wear effects, especially the wear effects in the Z direction. By doing so, optical power rejects due to the shape or material of the cutting tool can be eliminated.

[0213] To obtain compensated surface description data, the surface description data of the optical element is added with the calculated compensation map (obtained from the predictive model, or characterization of the tool or surface). This new surface is sent to the machine to modify the tool axis trajectory.

[0214] The compensated surface description data are obtained from a transfer function based on the tool contact point, and optionally cutting conditions (such as cutting speed, acceleration, vibration, . . . ) and / or material properties (such as Young's modulus, . . . ).

[0215] The compensation surface description data may be shorter than the description surface data, so it can be extrapolated and / or smoothed (optimized) to avoid edge effects or noisy surfaces.

[0216] Finally, if Figure 3 As shown, the compensation map is added to the surface description data using element 35.

[0217] While representative processes and apparatus have been described in detail herein, those skilled in the art will recognize that various substitutions and modifications may be made without departing from the scope described and defined by the appended claims.

Claims

1. A computer-implemented method for determining compensated surface description data intended to be loaded into a surface machining machine (1) in order to obtain the surface of an optical element by cutting a blank (10) using a cutting tool (24) of the surface machining machine (1), the method comprising: - providing surface description data (30), The surface description data represents the surface of the optical element; - providing contact data (32) based on said surface description data, the contact data represent the contact points which are used together with the cutting tool (24) to obtain the surface represented by the surface description data, The contact points (25', 25") are the contact points between the cutting tool (24) and the surface (12, 12', 12") of the blank (10) to obtain the surface of the optical element, and The contact point is defined in a cutting tool coordinate system; - generating a compensation map (341, 342) (34) by using a transfer function, An input to the transfer function is at least the contact data and an output of the transfer function is the compensation map; - determining compensated surface description data (36) based on the surface description data and the generated compensation map.

2. The computer-implemented method of claim 1 , wherein: The step of generating a compensation map further comprises: - provide material description data, the material description data represent the material of the cutting tool and / or the material of the blank and / or the interaction between the material of the blank and the material of the cutting tool during cutting of the blank to obtain the optical element, - determining said transfer function at least based on the provided material description data.

3. The computer-implemented method of claim 1 or 2, wherein: The step of generating a compensation map further comprises: - provide reference component description data, The reference component data represents a surface of a component previously cut by the cutting tool, - determining said transfer function based at least on provided reference element description data.

4. The computer-implemented method according to claims 2 and 3, wherein: The reference component description data provides the material description data.

5. A computer-implemented method according to any one of the preceding claims, wherein: The step of generating a compensation map further comprises: - Provide prediction models, The prediction model predicts the wear of the cutting tool under given conditions, - The transfer function is determined at least based on the predicted cutting tool wear.

6. The computer-implemented method of claim 5, wherein: The predictive model is a trained machine learning.

7. A computer-implemented method according to any one of the preceding claims, wherein: The step of generating a compensation map further comprises: - Provide cutting speed and / or cutting depth at each contact point; - The transfer function is determined at least based on a provided cutting speed.

8. A computer-implemented method according to any one of the preceding claims, wherein: The optical element is an ophthalmic lens, an ophthalmic semi-finished lens, or a mold intended for the manufacture of an ophthalmic lens.

9. The computer-implemented method of any preceding claim, further comprising: - Provide optical power description data, The optical power description data represents the distribution of the optical power of the optical element; - provide reverse surface description data, The opposite surface description data represent the opposite surface of the surface of the optical element to be obtained; Wherein, the step of providing surface description data comprises: - determining said surface description data from said opposite surface description data and said optical power description data.

10. A computer-implemented method according to any one of the preceding claims, wherein: The step of providing contact data further comprises: - providing cutting tool description data to provide said contact data, The cutting tool description data represent at least a portion of an edge of the cutting tool, the edge of the cutting tool being intended to come into contact with a surface of the blank in order to obtain the surface of the optical element.

11. A surface machining machine for surface machining a blank to obtain the surface of an optical element by cutting the blank with a cutting tool of the surface machining machine, the system comprising a cutting tool for cutting the blank to obtain the surface of the optical element, Computers, and A computer program product comprising a series of instructions, in, Said instructions, when loaded into said computer, are capable of implementing the steps of a method for determining compensated surface description data intended to be loaded into said surface machining machine, The method comprises the following steps: - provide surface description data, The surface description data represents the surface of the optical element; - providing contact data based on said surface description data, the contact data representing the contact points used with the cutting tool to obtain the surface represented by the surface description data, The contact point is the point of contact between the cutting tool and the surface of the blank to obtain the surface of the optical element, and The contact point is defined in a cutting tool coordinate system; - Generate compensation maps by using transfer functions, An input to the transfer function is at least the contact data and an output of the transfer function is the compensation map; - determining compensated surface description data from said surface description data and the generated compensation map.

12. The surface processing machine according to claim 11, wherein: The method further comprises - provide material description data, the material description data represent the material of the cutting tool and / or the material of the blank and / or the interaction between the material of the blank and the material of the cutting tool during cutting of the blank to obtain the optical element, - determining said transfer function at least based on the provided material description data.

13. The surface processing machine according to claim 11 or 12, further comprising a reference sensor for detecting at least one reference element and for generating reference element description data, The reference element is obtained from a blank surface-machined by means of a cutting tool of the system, The transfer function is determined based at least on provided reference component description data.

14. The system according to any one of claims 11 to 13, further comprising A cutting tool sensor is used to detect the cutting tool to provide surface processing tool description data.

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