Method and machine for producing optical components by additive manufacturing

Abstract

A method and apparatus for producing an optical element (100) from a curable material by using an additive manufacturing technique. The method comprises a plurality of curing steps for curing the curable material by applying a curing surface energy to the curable material inside contours (C1), the geometry of these contours being determined according to the geometry of the optical element, the curing surface energy being higher in a first area (A1) extending significantly along the slice contour than in a second area (A2) located within the first area, the curing surface energy applied to the second area being strictly below a first predetermined energy threshold.

Description

Technical Field

[0001] The present invention relates to the manufacture of optical components, such as ophthalmic lenses.

[0002] More precisely, the invention relates to a method for manufacturing an optical element from a curable material using additive manufacturing techniques.

[0003] The present invention also describes a manufacturing system for manufacturing optical elements from curable materials using additive manufacturing techniques. Background Art

[0004] Additive manufacturing techniques are suitable for manufacturing many devices, especially for manufacturing prototype devices within the framework of new technology development, since the device finally obtained is directly formed to have the desired shape. However, at the current stage of development, additive manufacturing techniques are rarely suitable for use as industrial tools for large-scale production of ophthalmic devices.

[0005] Additive manufacturing techniques are usually based on a layer-by-layer or drop-by-drop building approach, whereby the desired device is formed by overlapping layers, pseudo-layers, or droplets.

[0006] With regard to the manufacture of ophthalmic lenses, in particular for spectacles, additive manufacturing techniques are used to produce ophthalmic lens models. However, these models are rarely suitable for use in frames to be worn by wearers. In fact, within the manufactured optical devices, the accumulation of interfaces between layers (or droplets and / or pixel traces present in the illumination tool) often forms slight optical defects, in particular diffraction defects.

[0007] These defects appear at the interface between the layers, because the materials on either side of this interface harden at different times, creating local differences in the optical properties of the materials, which causes diffraction between the layers (it has been noted that the formation of optical devices with a stack of multiple layers causes a pattern to repeat, and this repetitive alternation of optical properties causes the formation of diffraction defects). Moreover, the hardening of the material in a single layer does not occur uniformly, but point by point, which also causes diffraction between these points.

[0008] These defects are critical when the ophthalmic lens is ultimately used. Summary of the invention

[0009] In order to reduce these defects, the solution devised by the inventors for forming the optical element is to cure the material in multiple steps so that when overlapping material layers are formed on each other, each material layer is not fully cured in order to allow it to reorganize itself during hardening in such a way that the layers mix with each other.

[0010] This solution has major disadvantages. This solution actually means that before hardening, the layers have not yet completely solidified before the deposition of the overlapping layers, and they may even be in an intermediate state, which is neither solid nor liquid, but between these two phases (this phase is called "gel state" as explained later). Therefore, the layers in this intermediate state may be easily damaged by mechanical stresses due to insufficient mechanical strength. This damage may be particularly prone to occur when the layers move relative to the surrounding material or structural elements present in the vicinity of the layers, for example when additional layers are introduced or when the material moves. In other words, there is a risk of affecting the geometry of the contour of this layer and the geometry of the contour of the manufactured device during the manufacture of the layers located on one layer.

[0011] It is therefore an object of the present invention to provide an optical element which is free of defects between the layers and exhibits the exact desired geometry.

[0012] The above-mentioned object is achieved according to the present invention by providing a method, which includes multiple curing steps for curing the curable material by applying curing surface energy to the curable material inside the contour, the geometry of these contours being determined according to the geometry of the optical element, the curing surface energy being higher in a first area extending along the contour than in a second area located in the first area, and the curing surface energy applied to the second area being strictly below a first predetermined energy threshold.

[0013] In other words, a difference is created between the skin and the core of the optical element: according to the invention, the optical element is manufactured by curing the skin of this element faster than the core of this element. The skin thus acts as a dam of the core material and anchors it with the skin part of the previously formed or irradiated layer (such as the base material layer) in order to ensure the stability and conformality of the material layer. This principle is fully applicable to stereolithography, but it can also be applied to polymer jetting, the droplets are always arranged or deposited in a pseudo-layer.

[0014] This feature ensures that the optical element assumes the exact desired geometry even if the element is subjected to mechanical stresses during its manufacture.

[0015] The faster solidification of the material along the surface of the component may cause some of the above-mentioned optical defects, but because the width of this surface is thin relative to the size of the final product, the magnitude of the defects produced is extremely small and will not cause significant optical problems in the final product.

[0016] Other combinable features of the present invention are:

[0017] - the method comprises a further final step of enabling complete curing of both the curable material in the first region and the curable material in the second region;

[0018] - immediately before said final step, a major part of the second area receives a total cured surface energy higher than or equal to said first predetermined energy threshold;

[0019] - a curing surface energy applied to said first area is higher than or equal to a second predetermined energy threshold, said second predetermined energy threshold being equal to or greater than said first predetermined energy threshold;

[0020] - repeating said steps layer by layer for each profile to manufacture said optical element;

[0021] - said first predetermined energy threshold is strictly below a critical Jacobs energy defined for said curable material;

[0022] - the second predetermined energy threshold is equal to or greater than the critical Jacobs energy (Ec);

[0023] - said second predetermined energy threshold is equal to or greater than the Jacobs energy determined for the first region of a given layer by using the Jacobs equation defined as {EJ=EC*exp(th / DP)}, wherein

[0024] Ej is the Jacobs energy from which the second predetermined energy threshold is derived,

[0025] th is the thickness of the layer,

[0026] Dp is the light depth penetration value of the curing energy within the curable material, and

[0027] Ec is the critical Jacobs energy;

[0028] - determining said second predetermined energy threshold for a first region of a given layer by using the Jacobs equation;

[0029] -Critical Jacobs energy E C is determined using an empirical method based on the Jacobs equation (Paul F. Jacobs, "Fundamentals of stereolithography in International Solid Freeform Fabrication Symposium," 1992):

[0030] - said curable material is capable of being polymerized, said second predetermined energy threshold being determined such that after said step the degree of polymerization in the first region is greater than 95%;

[0031] - applying the curing surface energy directly to a third area located outside the first area with a certain intensity, the certain intensity is different from the intensity of the curing surface energy applied to the first area, and the certain intensity is preferably less than the intensity of the curing surface energy applied to the first area;

[0032] - applying curing surface energy directly to a fourth area located inside the first area with a certain intensity, the certain intensity being less than the intensity of the curing surface energy applied to the first area and different from the intensity of the curing surface energy applied to the second area;

[0033] - directly applying the curing surface energy to a fifth area located inside the first area with a certain intensity, wherein the certain intensity is higher than or equal to the intensity of the curing surface energy applied to the first area;

[0034] - It should be noted that the intensity comparison is defined relative to the intensity of the solidification surface energy received directly when irradiating the layer considered (in other words, the layer is located on top of the superposition of layers so that the energy is received without passing through other layers);

[0035] - repeating said steps layer by layer to manufacture said optical element;

[0036] - for at least one layer, applying curing energy in a sub-step such that the curing energy is applied to a portion of the surface of the curable material with a non-zero intensity that varies from area to area;

[0037] - for at least one layer, curing energy is applied to the surface of the curable material in several sub-steps, during one of said sub-steps, the intensity of the curing surface energy applied to a first area is non-zero, while the intensity of the curing surface energy applied to a second area is zero, and during another of said sub-steps, the intensity of the curing surface energy applied to the first area is non-zero and equal to the intensity of the curing surface energy applied to the second area; in that case, the several sub-steps of applying curing energy are done without substantially adding material on top of said at least one layer between each sub-step;

[0038] - during each sub-step, the solidification surface energy is shaped in a discrete manner so that each area consists of several irradiated discrete cells, the solidification surface energy being zero or being applied distinctly without intensity variations between discrete cells; in this case, the presence of shadow areas within discrete cells is not counted as intensity variations between discrete cells;

[0039] - the curing surface energy is applied by a curing unit adapted to generate a pixelated pattern on the surface of the curable material, the pixelated pattern generating voxels in the curable material, and wherein the first area is formed by a first set of voxels extending along a closed path, the width of the closed path depending on the geometry of the optical element and / or on the shape of each voxel and / or on a light depth penetration value;

[0040] - the curing surface energy is applied by a curing unit adapted to generate a pixelated pattern on the surface of the curable material, the pixelated pattern generating voxels in the curable material, and wherein the first area is formed by a first group of voxels extending along a closed path, the closed path having a width greater than 3 voxels and preferably less than 10 voxels, more preferably less than 5 voxels;

[0041] - determining a first set of voxels according to the determined geometry of the profile and according to any of the following parameters: the type of post-processing method, whether it is of subtractive or additive type, the geometry of the voxels, and a reference to a machine used to manufacture the optical volume element;

[0042] - defining the positions of the first group of voxels relative to the surface of the curable material according to the geometry of the contour and according to the geometry of the voxels;

[0043] - the positions of the first set of voxels are defined as minimizing the root mean square of a function of the surface error between the projection of the contour of the first set of voxels and the projection of said contour in the same plane, said function being defined taking into account the type of post-processing method;

[0044] - repeating said steps layer by layer to manufacture said optical element, the thickness of each voxel being equal to the thickness of the layer considered and wherein the positions of the first set of voxels are defined as minimizing the root mean square of the volume error between said contour and the outer contour of the first set of voxels;

[0045] - the optical element is designed to be post-machined by a finishing method of the subtractive type, the outer contour of the first region being located outside and / or above said contour;

[0046] - the optical element is designed to be post-machined by a finishing method of the additive type, the outer contour of the first area being located inside and / or on said contour;

[0047] - the optical element is an ophthalmic lens;

[0048] a first predetermined energy threshold being lower than or equal to a solid predetermined energy threshold corresponding to an energy sufficient to render the first portion of the optical element solid throughout the thickness of said first portion of the optical element;

[0049] - a second predetermined energy threshold equal to the induced surface energy;

[0050] - The method comprises:

[0051] a) a first step of forming a first part of the optical element by irradiating the surface of the curable material with a first curing surface energy, the first curing surface energy being strictly below a first predetermined energy threshold and above a second predetermined threshold, and

[0052] b) a second step of forming at least a second portion of the optical element by irradiating the first portion with at least a second curing surface energy, the second portion being different from the first portion of the optical element, the second curing surface energy being higher than a second predetermined energy threshold, the second curing surface energy irradiating both the second portion of the optical element and at least a portion of the first portion of the optical element, the sum of the first curing surface energy and the portion of at least the second curing surface energy received by the first portion of the optical element being sufficient to make the first portion of the optical element solid, the sum of the first curing surface energy and the portion of at least the second curing surface energy received by the first portion of the optical element being preferably higher than or equal to the first solid predetermined energy threshold.

[0053] The present invention also relates to a manufacturing system for manufacturing an optical element from a curable material using an additive manufacturing technique, comprising:

[0054] - a container suitable for containing a curable material,

[0055] - a support suitable for supporting the optical element to be formed,

[0056] a shaping unit adapted to solidify said curable material at least inside a contour, the geometry of which is determined according to the geometry of said optical element, and

[0057] - A computer element programmed to control the shaping unit so as to apply to the curable material a curing surface energy which is higher in a first zone extending along the contour than in a second zone located within the first zone, the curing surface energy applied to the second zone being strictly below a first predetermined energy threshold. DETAILED DESCRIPTION

[0058] 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 practiced.

[0059] In the attached picture:

[0060] - Figure 1 A curve showing the conversion rate of a curable material as a function of the curing surface energy applied to a surface of such material;

[0061] - Figure 2 An exemplary manufacturing system suitable for manufacturing optical elements according to the present invention is shown;

[0062] - Figure 3A shows a side view of a portion of an optical element to be manufactured according to the present invention;

[0063] - Figure 3B It indicated Figure 3A A top view of a portion of the optical element represented in;

[0064] - Figure 4 a plan view showing a slice profile of the optical element and pixels produced by the manufacturing system on the curable material;

[0065] - FIG. 5A to FIG. 5C represents the three steps of manufacturing optical components when the post-processing method is of the subtractive type;

[0066] - FIG. 6A to FIG. 6C represents the three steps of manufacturing optical components when the post-processing method is of additive type;

[0067] - 7A to 7D Four solutions for positioning the slice profile of the optical element relative to the pixels produced by the manufacturing system on the curable material are represented;

[0068] - Figure 8 The bottom portion of the optical element is similar to Figure 4 's view;

[0069] - Fig. 9 is the upper part of the optical element similar to Figure 4 's view;

[0070] - Fig.10 is similar to Figure 4 , showing different areas of the optical element.

[0071] The present invention generally relates to a method suitable for manufacturing an optical component using additive manufacturing techniques.

[0072] The present invention is more particularly applicable to the manufacture of various optical devices and components, such as ophthalmic components and devices. Non-limiting examples of ophthalmic components include corrective and non-corrective lenses, including single vision or multifocal lenses, which may be segmented or non-segmented (such as multifocal lenses or progressive lenses) and other elements used to correct, protect, or enhance vision, and protective lenses or visors, such as those found in spectacles, glasses, goggles, and helmets. The optical article of the present invention is preferably a lens, more preferably an ophthalmic lens, such as an ophthalmic lens suitable for mounting in a spectacle frame.

[0073] The expression "additive manufacturing technology" means a manufacturing technology as defined in the international standard ASTM 2792-12, which refers to a method of joining materials to manufacture an object according to 3D model data, usually layer by layer, in contrast to subtractive manufacturing methods such as conventional machining. Thus, a solid object is manufactured by juxtaposing volume elements, mainly layers or voxels, or droplets or droplets, or in some cases even blocks of matter. In the context of the present invention, the optical element will be described as being manufactured layer by layer, but the invention is not limited to such an embodiment.

[0074] Additive manufacturing techniques, which in practice can be stereolithography (SLA), digital light processing stereolithography (DLP-SLA), LED or L-COS stereolithography, or polymer jetting, include a number of methods that form an object by juxtaposing multiple volume elements according to a predetermined arrangement that can be defined in a CAD (computer-aided design) file.

[0075] Both stereolithography (SLA) and digital light processing stereolithography (DLP-SLA) work by focusing UV light onto vats of photopolymer liquid resin to form solid layers that are stacked up to form a solid object. With stereolithography (SLA), the liquid resin receives selective exposure by scanning a laser beam across the print area. Digital light processing stereolithography (DLP-SLA) uses a digital projector screen to project the image of each layer onto the entire surface of the resin. Since the projector is a digital screen, the image of each layer is made up of square pixels, resulting in layers formed by small rectangular bricks called voxels (the volume is defined by the square pixels and the thickness of the layer).

[0076] Alternatively, the pixels can have other shapes, such as hexagonal, diamond or elongated, depending on the use of micromirrors or digital screens or other devices to modulate and produce the image of each layer, and on the characteristics of such devices, such as the shape of the micromirrors, the use of LCD technology or LED technology in the digital screen, etc.

[0077] Polymer jetting technology uses an inkjet print head to eject droplets of liquid photopolymer resin onto a build platform. The liquid resin is immediately cured by UV light and solidifies (and forms a solid object) droplet by droplet to build a layer, or final optical element.

[0078] In the described embodiments, digital light machining stereolithography will be preferred, but the invention is not limited to such embodiments.

[0079] In practice, here, the additive manufacturing technology used is based on the projection of a UV light pattern on a curable material. The light pattern is, for example, an infrared pattern or a UV pattern. The curable material is, for example, a photopolymer resin and the optical element is manufactured by a photopolymerization method. For example, the photopolymer resin contains (meth)acrylate monomers.

[0080] In practice, the photopolymerization method can be achieved by the conversion rate C of the curable material. v (or polymerization rate). Conversion rate C v Related to the physical state of the substance of the curable material. Before being irradiated with curable energy, mainly light, the curable material is liquid. Conversion rate C v It is considered to be close to 0, because the curable material cannot withstand slight polymerization due to aging. When the curable surface energy is irradiated on the curable material, the curable material polymerizes and gradually changes from liquid to solid. The curable material will go through many states, especially the intermediate state, called the "gel state", and its corresponding conversion rate C v Depends on the curable material. The intermediate state corresponds to a state of matter that is neither liquid nor solid but somewhere in between, especially not strong enough according to the Jacobs methodology, but the monomers have begun to polymerize with each other and have begun to form a polymer network. The conversion rate C of the intermediate state of some acrylate monomers v The conversion may be, for example, between 20% and 80%, or some other intermediate state of the monomers may be higher than 10% and / or lower than 67%. For a conversion C of typically higher than 80% v , the curable material is considered to be in the solid state. For some acrylate monomers, for conversions above 67% C v , the curable material is considered to be in a solid state. Depending on the material, the curable material is considered to be in a solid state for a conversion rate above a critical conversion rate, which can be empirically determined to be between about 60% and about 80%.

[0081] The conversion rate that characterizes the intermediate state and the solid state depends on the curing surface energy E (or light dose) from the light source, the absorption characteristics of the curable material, and the efficiency of the initiator to polymerize the curable material. Figure 1 In the case of acrylate monomers, the conversion rate C varies according to the curing surface energy E of the irradiation curable material. v (in %).

[0082] As can be seen in the figure, in some cases, especially for free radical chain growth polymerization, as long as the curing surface energy is lower than the induced surface energy E I , the conversion rate remains close to 0. During this period (called the "induction period"), the curable material remains liquid and does not polymerize.

[0083] In the case of free radical chain growth polymerization, the reaction between the primary free radicals formed by the activation of the initiator and the monomers is quenched by the inhibitor (here dioxygen), which preferentially reacts with the free radicals, thereby preventing reaction with the monomers. During the induction period, the curing surface energy E received by the curable material is therefore used to consume the inhibitor, here dioxygen. When the curing surface energy E received by the curable material reaches the induction surface energy E I The polymerization process occurs.

[0084] When the curing surface energy received by the curable material reaches the induced surface energy E I The polymerization process begins.

[0085] It should be noted that some polymerization processes do not have an induction period, such as some cationic chain growth polymerizations. In such cases, the present invention is still applicable and the induced surface energy can be ignored.

[0086] As long as the total cured surface energy received remains below the intermediate surface energy E G , the curable material remains liquid but polymerization is taking place and the conversion rate C v increases (especially with the onset of polymer network formation). Figure 1 In the example shown in FIG. 1 , since the curable material is still in a liquid state, the conversion rate C of the acrylate monomer is v Keep it below 20%.

[0087] When the curing surface energy received by the curable material reaches the intermediate surface energy E G When the curable material is in an intermediate state, it can be considered that the curable material is in an intermediate state. In other words, this means that the curable material is between the hard state and the liquid state. According to the General Catalogue of Chemical Terminology (also known as the "IUPAC Gold Book" or more simply the "Gold Book" by chemists), the intermediate surface energy E G Defined as the energy of initial network formation during the polymerization process that forms a polymer network.

[0088] As long as the total cured surface energy received remains below the critical Jacobs energy E C , the curable material will remain in the intermediate state, but the polymerization process is still going on, and the conversion rate C v Increases (increases with monomer conversion). Critical Jacobs energy E C is defined as the surface energy provided to a given thickness of a curable material in order to form a measurable solid portion of the material. In other words, for a given curable material, the critical Jacobs energy E CCorresponds to the minimum surface energy that provides for polymerization of the desired thickness at an empirically determined minimum conversion, which is sufficient to make the element strong enough for measurement. Here, in the case of acrylate monomers, the corresponding conversion C v In the range of 60% to 80%. Within this conversion range, it should be noted that total monomer conversion need not be achieved to obtain solid polymeric material.

[0089] Critical Jacobs energy E C is to use an empirical method based on the Jacobs equation (Paul F. Jacobs, "Fundamentals of stereolithography in International Solid Freeform Fabrication Symposium", 1992): Where E is the curing surface energy, E C is the critical Jacobs energy, D P is the light penetration depth of the curing surface energy within the curable material, and th is the polymer thickness considered along the path of the light carrying the energy. P Corresponds to the distance that the UV light travels along the path before being completely absorbed. The critical Jacobs energy depends on the curable material.

[0090] The curing surface energy E is per surface unit (e.g. per m 2 )’s average energy.

[0091] The Jacobs experiment is set up to determine the critical Jacobs energy. The Jacobs experiment involves irradiating a curable material (here a resin) with a set of known curing surface energies and measuring the corresponding polymerized thickness of the measurable solid material. The Jacobs experiment is suitable for using these measurements of polymerized thickness (known curing surface energies received by the curable material) to determine the critical Jacobs energy E C and light depth penetration value D P .

[0092] Figure 2 A manufacturing system 1 suitable for manufacturing an optical element by a DLP-SLA method is shown. The manufacturing system comprises a shaping unit 3, a container 10, a support 15 and a displacement device 20 (here an actuator).

[0093] The shaping unit 3 comprises an energy source 2, an optical system 4, and a computer element 6. The shaping unit 3 is adapted to implement the method of manufacturing an optical element 100 as described below when executing instructions.

[0094] In practice, the computer element 6 includes a microprocessor and a memory (not shown). The microprocessor is suitable for executing instructions for manufacturing the optical element 100, and the memory stores these instructions. As an example, the computer element 6 is programmed to generate instructions about the size of the curing surface energy E of each successive step of providing the curing surface energy, and instructions about the image pattern or light pattern to be projected onto the surface 55 of the curable material 50. These instructions are transmitted to the energy source 2 and / or the optical system 4, for example.

[0095] The energy source 2 is adapted to irradiate a surface 55 of the curable material 50 with a curing surface energy E. The energy source 2 provides a light beam, such as an ultraviolet light beam, which is directed to the curable material 50 by the optical system 4 .

[0096] The optical system 4 is adapted to project light from the energy source 2 onto the surface 55 of the curable material 50 to form the image pattern. The imager 4 comprises a plurality of micro-mirrors 8 arranged in a grid format.

[0097] It should be noted that there are other alternative combinations of energy sources and imagers. For example, the formation of the image pattern can be completely produced by the energy source using micromirrors or digital screens, such as using LCD or LED pixels, and the imager only provides positioning and focusing effects; alternatively, the energy source can provide energy in a continuous or regular burst manner, and the imager produces the image pattern on top of the positioning and focusing effects.

[0098] In practice, the micromirrors 8 are separated from each other by gaps (in practice, it is impossible for two adjacent micromirrors to be completely joined); digital screens using LCD or LED pixels also have such gaps.

[0099] The micromirror 8 is, for example, a clearly square shape, with a size of, for example, 8×8 μm. 2 For a spacing between micromirrors of about 10.8 μm, the gaps are comprised between 1 μm and 10 μm, for example, about 2.8 μm. Once projected onto the surface 55 of the curable material 50, the micromirrors can form a projection pixel with a given spacing, including the direct projection of the micromirrors and the gaps, for example, the spacing can be about 40×40 μm, where about 30×30 μm corresponds to the projection of the micromirrors, which are separated by gaps of about 10 μm.

[0100] When the micromirror 8 is irradiated by the light beam, the micromirror reflects the light toward the surface 55 of the curable material 50 with a certain light intensity, or does not reflect the light toward the surface 55, depending on the individual control of each micromirror. Therefore, the micromirror 8 is suitable for drawing a pattern on the surface 55 of the curable material 50, which is pixelated (each pixel corresponds to a micromirror). Because the micromirrors 8 are separated from each other by gaps, the projection pattern on the surface of the curable material 50 therefore includes some shadow areas. Therefore, the pixels on this projection pattern are separated from each other by the inter-pixel spaces. The material located below these inter-pixel spaces is less polymerized than another part of the material. In some cases, the other part may even be insufficiently polymerized or not polymerized.

[0101] The repetition of this regular variation of the polymerization rate within the same layer and the succession of layers leads to the formation of observable diffraction defects due to the presence of insufficiently polymerized shadow areas. Such defects are incompatible with the expected optical quality of eyeglass lenses.

[0102] In fact, the inventors have noticed that even in the case where the curable surface energy is very high and the shadow area receives sufficient surface energy (but less than other areas) to become solid in the Jacobs sense during a single projection irradiation of the image pattern, or receives such energy in a post-curing step, the polymerization rate and / or rhythm of the shadow area will be different from that of the area corresponding to the projection of the micromirror, thereby resulting in the formation of observable diffraction defects.

[0103] In this specification, we consider the projected pattern to be composed of square pixels, resulting in a layer formed by small rectangular bricks called voxels (the volume is defined by the square pixels and the layer thickness).

[0104] like Figure 2 As can be seen in the figure, the optical system 4 here comprises a projection system 7 adapted to direct a UV beam from a plurality of micromirrors 8 to a surface 55 of a curable material 50. Further, the size of the micromirrors or LCD or LED pixels or projection pixels may differ from the current example without departing from the invention.

[0105] The curable material 50 is stored in a liquid state in the container 10. Once polymerized, the curable material 50 forms an optical element 100 supported by the support 15. In practice, the support 15 is partially immersed in a vat of curable material 50, so that a portion of the liquid curable material 50 is located on top of the support 15. The light beam provided by the energy source 2 is thus projected on this portion of the curable material 50. When this portion polymerizes, the portion of the optical element formed is thus on the support 15.

[0106] It should be noted that the support member may include a support beam formed from a cured curable material.

[0107] The manufacturing system 1 also comprises a displacement device 20. The displacement device 20 is suitable for displacing the support 15 on which the optical element 100 is formed relative to the vat of curable material. This displacement device 20 allows the support 15 to be displaced vertically relative to the vat of curable material along an axis that is substantially orthogonal to the surface 55 of the curable material 20. This vertical displacement of the support 15 allows controlling the thickness of the polymerized liquid curable material 50. Thus, the displacement device 20 allows controlling the thickness of the polymerized layer.

[0108] In the present example, the displacement device 20 also allows a horizontal movement along an axis substantially parallel to the surface 55 of the curable material 50 .

[0109] like Figure 2 , the manufacturing system 1 here comprises a recoater device 12. This recoater device 12 is suitable, for example, for spreading some curable material on top of a previous layer of curable material. An alternative method does not use a recoater and a film may be positioned on the surface of the curable material to achieve flatness of the material and control the thickness of the curable material added on top of the previous layer of curable material.

[0110] As explained below, the manufacturing system 1 is programmed to produce the optical element 100 from the curable material 50 by using an additive manufacturing method.

[0111] This optical element 100 advantageously comprises an ophthalmic lens. The optical element may comprise only this ophthalmic lens. In a variant, the optical element may comprise an ophthalmic lens and a stabilizer that immobilizes the lens on the support 15.

[0112] The method comprises a first step of acquiring the 3D geometry of the optical element 100 .

[0113] Then, this 3D geometry is divided into a plurality of volume units. Since the considered manufacturing system 1 is a DLP-SLA device, this 3D geometry is sliced ​​into several layers with the same thickness.

[0114] like Figure 3A and Figure 3B Here, the layers are arranged along a plane generally orthogonal to the optical axis L of the ophthalmic lens. L The axis L S Overlay (this optical axis L L For example, in the case of a monofocal lens, this is the axis about which light does not deviate when passing through the lens.) This example also shows by inference the superposition axis L S Relative to the optical axis L L Tilt more than 45 degrees.

[0115] It should be noted that when the superposition axis L S Relative to the optical axis LL The present invention is also applicable when the inclination is less than 45 degrees.

[0116] The intersection between the midplane of each layer and the outer 3D shape of the optical element 100 defines a contour hereinafter referred to as a "slicing contour C1". This slicing contour C1 thus extends in a 2-dimensional plane. It should be noted that the slicing contour C1 corresponds to the contour of a solid part of the device to be manufactured (e.g., the optical element 100).

[0117] It is noted that in most embodiments, the slices mentioned with respect to the slice profile correspond to the sliced ​​layers used for the manufacturing step.

[0118] Then, the method comprises a plurality of curing steps for curing (ie, hardening) the curable material 50 inside each slice contour C1 layer by layer by applying a curing surface energy E to the surface 55 of the curable material 50 .

[0119] To this end, each layer is irradiated one by one, the support being immersed between two irradiations to a depth equal to the layer thickness of the next layer, and the recoater device 12 spreading some curable material 50 on top of the last layer formed.

[0120] According to the invention, for at least one layer (and in practice for most layers), the intensity of the curing surface energy E applied to the surface 55 of the curable material 50 is greater in a first region A1 extending along the slice contour C1 than in a second region A2 located within the first region A1 so as to be visibly surrounded by the first region. It should be noted that in the case where the solid shell of the final device includes an internal cavity or an apparent cavity of a slice-forming layer in the shape of a device, the slice contour may include one or more external contours and one or more internal contours. Therefore, the first region may extend visibly along the external contour and along a possible internal contour. Further, the second region will appear to be surrounded by the first region, located between the external contour and the corresponding internal contour.

[0121] This energy redistribution is preferentially used to cure the majority of the layers of the optical element 100. In practice, this energy redistribution can be used to cure the entire optical element 100, excluding the bottom and top of the element (see Figure 3A ), wherein the surface layer portion (for one or more layers) may be required over the entire portion of the layer within the slice contour C1.

[0122] The curing surface energy E applied to the second area A2 is strictly below the first predetermined energy threshold T1 (here Jacobs energy E J or preferably the critical Jacobs energy Ec).

[0123] In other words, the second area A2 of each of these layers is only partially cured and not hardened and then covered by a new layer of curable material 50. More precisely, before being covered by the new layer, the previous layer is cured so that it has a surface layer 21 (first area A1) in a solid state and a core 22 (second area A2) in an intermediate state or liquid state (preferably in an intermediate state). The intermediate state in this specification refers to a state in which polymerization has begun, the first part of the polymer network is formed, but the material is not strong enough to be measured according to the Jacobs methodology.

[0124] Alternatively, before being covered by a new layer, the previous layer is solidified so that it has a core 22 (second region A2) in an intermediate or liquid state (preferably in an intermediate state) and one of the cores 22 also in an intermediate state and having a higher conversion rate than the core 22 (e.g. close to the core 22 that has received the Jacobs energy E J Or at least the conversion rate corresponding to the critical Jacobs energy Ec) of the surface layer 21 (first area A1).

[0125] According to the present invention, when more curable material 50 is added to the last formed layer while the core 22 is still in an intermediate state and susceptible to external stress, here using a recoater device 12, the skin layer 21 is polymerized enough to maintain its shape so that the skin layer 21 can maintain the shape of the core 22.

[0126] As will be explained in more detail below, some layers of the optical element 100 may include more than two different areas A1 , A2 polymerized differently to ensure different functionalities.

[0127] Before explaining how the skin layer 21 and these other areas solidify, we can give the example of the core 22 polymerization to understand why when a new layer of curable material is delivered to a layer, the core of this layer is still in the intermediate state layer.

[0128] To do this, we can consider layers that are located at a certain distance from the bottom and top of the optic.

[0129] The intensity I2 of the solidification surface energy E of the core 22 for polymerizing the layer under consideration is strictly below the critical Jacobs energy E C But it is higher than another predetermined energy threshold T2 (here the induced surface energy E I ).

[0130] The set of pixels projected onto the surface 55 of the curable material 50 to form this core 22 are separated from each other by inter-pixel spaces. Thus, the core 22 comprises alternations of intermediate state regions (which are directly irradiated and in which polymerization is occurring) and underpolymerized regions (which are still in the liquid state or are less polymerized than in the directly irradiated regions).

[0131] According to the invention, all these zones will further polymerize later, during another irradiation of the layer in question or preferably during irradiation of one or several other layers placed on the layer in question. These irradiations are preferentially performed in such a way that the polymerization of all these zones does not differ significantly.

[0132] In the described embodiment we will consider a single shot of radiation applied directly to each layer, but the invention is also applicable even if multiple shots are applied directly to each layer (or at least some of the layers).

[0133] Each curing surface energy E applied to the surface of the curable material 50 can be calculated based on the depth penetration value D of the curable surface energy within the curable material. P is determined, thus taking into account the light absorption of the curable material. In other words, each surface energy needs to be sufficient to penetrate several layers in order to polymerize the material of the layer located below the last layer formed.

[0134] To compensate for the shadowed areas, before irradiating the new layer of liquid curable material 50 with a new pixelated pattern, the manufacturing system 1 is adjusted in such a way that the pixels of this pattern cover the shadowed areas of the last formed layer. In practice, for this purpose, the support 15 is displaced along an axis substantially parallel to the surface of the curable material. According to an alternative solution that is easier to operate, the optical system 4 is controlled so as to displace the projection of the pattern onto the vat of material, for example by a value smaller than the pixel size.

[0135] In this example, due to the transmission of the curing surface energy E through the different layers, the considered layer is then fully polymerized because the sum of the curing surface energy it receives directly and indirectly (through other layers) is higher than or equal to the critical Jacobs energy Ec.

[0136] It should be noted that the present invention can also be applied to some parts of the second region (or the fourth region, if any) that are still in an intermediate state or have hardly received enough energy to reach the Jacobs energy. In these cases, after the additive manufacturing method, the hard surface layer and / or other solid parts of the device (such as the fifth region, or parts of the second region) make it possible to maintain the geometry and possibly manipulate the device. Thereafter, the device undergoes a final curing step to complete the hardening of all parts of the device. As explained below, the final curing step can be, for example, a UV oven curing step and / or a thermal curing step if the material is suitable for such a curing method.

[0137] The advantage of building the core region(s) according to this method is that the curable material in the core 22 of the optical element 100 has enough time to reorganize itself in such a way that its layers mix with each other due to the light dose distribution control, which reduces defects. Therefore, this characterization improves the optical quality of the lens.

[0138] In more detail, within the portion corresponding to the core region(s), the curable material of the stacked layers can reorganize itself in such a way that the materials of the layers penetrate each other (which reduces defects) due to the interlayer collapse process that occurs when in the intermediate state of the material. For this purpose, a high degree of control of the light dose distribution is required. In particular, the smaller the change in the state of the material between adjacent voxels, the better the defect reduction.

[0139] The use of this embodiment of the invention for the core region thus improves the optical quality with respect to optical defects associated with the stacking of the used material layers. In fact, it has been noted that the formation of an optical device with a stack of multiple layers leads to a pattern repetition formed by a variation of the optical properties between the core of the layer and the interface between two layers. This repeated alternation of optical properties leads to the formation of diffraction defects, hereinafter stacking defects. These stacking defects are even further pronounced if the optical device is constructed with the layers arranged significantly parallel to the optical axis.

[0140] Accordingly, using the present invention within the portion corresponding to the core region(s), the transition from one layer to another is more uniform and those stacking defects are minimized or even avoided.

[0141] In contrast, in this example, the surface layer 21 of each layer receives (once or several times) a curing surface energy E having an intensity I1 higher than or equal to the Jacobs energy E before placing a new layer on each layer. J The corresponding strength.

[0142] More specifically, the intensity I1 of the curing surface energy E applied to the surface layer 21 (first area A1) is higher than or equal to a second predetermined energy threshold T2, which is equal to or greater than the Jacobs energy E J .

[0143] This second predetermined energy threshold T2 is, for example, a recommended energy derived from the Jacobs equation introduced previously. In this example, the recommended energy is equal to the Jacobs energy E directly derived from the Jacobs equation. J Additional energy is added to ensure a high conversion rate of the curable material, for example, when the Jacobs equation is applied, the energy is sufficient to harden into a solid state, and the thickness of the virtual layer increases by about 50% to about 200%. This recommended energy can, for example, be the energy value recommended for directly printing a layer of the material by conventional practices in 3D printing in other fields outside of ophthalmology.

[0144] For example, determine the recommended energy E J The conversion in the surface layer 20 is such that it is greater than 95% before a new layer of curable material is placed over the layer in question.

[0145] In an alternative embodiment, the second threshold is the Jacobs energy E J .

[0146] An advantage of building the skin regions according to this method is that the core region(s) can be built according to the previously exposed method while enabling adherence to the shape of the device being manufactured. The skin layers anchor the partially solidified portions of the core regions to the previously formed layers. Thus, despite external stresses when the formed layers are displaced and / or more layers of material are applied, the slice contour is adhered to.

[0147] We can now explain how the geometry of the surface layer 21 is determined.

[0148] For this purpose, we will consider the optical element to be a simple block without any internal cavity. However, the invention is also applicable to optical elements with other shapes (e.g. to optical elements with a hole for attaching a frame to a lens - in this example, the outer shape of the hole can be considered to belong to the slice contour C1, even though for at least one layer the outer shape of the hole may actually be disconnected from the rest of the slice contour).

[0149] As explained above, a 2D slice contour C1 is determined for each layer.

[0150] like Figure 4 As shown in , because the projection pattern on the curable material 50 is pixelated, it cannot completely follow the slice contour C1.

[0151] Therefore, a rule that depends on the slice contour C1 and the shape of the pixel must be determined in order to produce a suitable curing surface energy E for each pixel.

[0152] To understand this rule, we can define the “pixelated contour C2 ” as the outer contour of the pixels of the surface layer 21 .

[0153] In a first simplified embodiment, we can consider that the pixels located outside this pixelated outline C2 must be switched off and the pixels of the surface layer 21 must be switched on.

[0154] like Figure 4 As shown in , a first rule may be to turn on a pixel when a major portion of the pixel is inside the slice contour C1 , and to turn off the pixel when a minor portion of the pixel is inside the slice contour C1 or when it is outside the slice contour C1 .

[0155] Here, both the slice contour C1 and the pixelated contour C2 are in two dimensions (in a plane orthogonal to the axis L). S In a variant, we can consider the three-dimensional slice contour (hereinafter referred to as C1 3D ) and applies another rule according to which the pixels turned on are those whose main part of the volume lies on the slice contour C13D The voxels inside are associated with pixels.

[0156] like Figure 4 As shown in , these two simple rules will create cavities and excess material on the surface of optical element 100.

[0157] This is why another rule is preferred. This other rule consists in determining a first set of voxels to be aggregated faster (ie the voxels of the surface layer 21 of the layer under consideration) according to:

[0158] - the geometry of the slice contour C1, and

[0159] - the type of post-processing method, whether it is subtractive or additive, and the type of post-processing machine used, and / or

[0160] - the geometry of the voxels, and / or

[0161] - The type of additive manufacturing machine used to manufacture the optical volume element 100 .

[0162] The type of AM machine and its characteristics may impose the geometry of the voxels and inter-pixel spaces and may limit the thickness of the layers and the irradiation strategy.

[0163] In a first embodiment, we can consider the case where the optical element 100 is designed to be post-machined due to a subtractive type finishing method.

[0164] In this case, since the optical element 100 is to be machined (surface treated, polished . . . ), it is preferred to generate excess material on the surface of the optical element 100 .

[0165] For this reason, Figure 5A As shown in , the pixelated contour C2 is determined in such a way that it is located outside (or above) the slice contour C1 (closest to it). In other words, the rule is to turn on a pixel whenever the slice contour C1 passes through it, or whenever the pixel is within the slice contour C1.

[0166] However, it should be noted that as long as further rules are followed, such as contour C2 involving predetermined over-thick material that may be larger than one pixel or voxel size, this rule is still consistent with turning on pixels outside of slice contour C1.

[0167] When all curing steps are completed (see Figure 5B ), the slice contour C1 is located inside the polymer voxel. Therefore, according to this method, when the optical element 100 is machined to achieve the final 3D shape of the device, no material deficiency will occur in the surface of this element (see Figure 5C ).

[0168] In this first embodiment, a two-dimensional slice profile C1 has been considered. In a variant, a three-dimensional profile C1 may be considered. 3D .

[0169] The problem with considering only the 2D slice contour C1 is that when no 2D slice contour passes through a pixel but the associated contour C1 3D When passing through the corresponding voxel, cavities may appear during the subtractive manufacturing step.

[0170] To prevent this, another solution consists in considering that the 2D slice contour C1 is not on the midplane of each voxel, but on the top and bottom faces of the voxel in order to check whether the slice contour C1 is positioned in the same way on these two faces.

[0171] Another solution is to distinguish between "upper surface conditions" and "lower surface conditions".

[0172] The “upper surface situation” corresponds to Fig. 9 In this case, the voxel to be polymerized is located below the slice contour C1 relative to the direction of the stacked material layers. In this case, the reference surface of the voxel can be the bottom surface (in other words, the slice contour C1 to be considered in order to determine whether the voxel must be polymerized is the slice contour extending on the bottom surface of the voxel). The bottom surface refers to the surface of the layer (or voxel) that is farther away from the energy source 2.

[0173] The “lower surface condition” corresponds to Figure 8 In the case of a voxel to be polymerized, the voxel is located above the slice contour relative to the direction of the stacked material layers. In this case, the reference surface of the voxel can be the top surface (in other words, the slice contour C1 to be considered is the slice contour extending on the top surface of the voxel). The top surface refers to the surface of the layer (or voxel) that is closer to the energy source 2.

[0174] In a second embodiment, we can consider the case where the optical element 100 is designed to be post-processed due to an additive type finishing method. This additive type finishing method may include a step of depositing a coating by any of inkjet printing, dip coating, spin coating, spray coating, press coating using a formed film, etc.

[0175] In this case, because the optical element 100 is to be coated, it is preferred to have cavities rather than excess material on the surface of the optical element 100 in order to comply with the geometry of the device to be manufactured.

[0176] For this reason, Fig. 6A As shown in , the pixelated contour C2 is positioned in such a way that it is located inside (or above) the slicing contour C1 (closest to it). In other words, the rule may then be to turn off a pixel when the slicing contour C1 passes through it.

[0177] When all curing steps are completed (see Figure 6B ), the slice contour C1 is located inside the polymer voxel. Therefore, according to this method, the optical element 100 does not need to be machined before coating (see Figure 6C ).

[0178] In this second embodiment, a two-dimensional slice profile C1 has been considered. In a variant, a three-dimensional profile C1 may be considered. 3D In another variation, "upper surface case" and "lower surface case" may also be used.

[0179] In this case, the “upper surface situation” corresponds to Fig. 9 In this case, the voxel to be polymerized is located below the slice contour relative to the direction of the stacked material layers. In this case, the reference face of the voxel can be the top face (in other words, the slice contour C1 to be considered in order to determine whether a voxel must be polymerized is the slice contour extending on the top face of the voxel). The top face refers to the face of the layer (or voxel) that is closer to the energy source 2.

[0180] The “lower surface condition” corresponds to Figure 8 , where the voxel to be polymerized is located above the slice contour relative to the direction of the stacked material layers. In this case, the reference face of the voxel is the bottom face (in other words, the slice contour C1 to be considered is the slice contour extending on the bottom face of the voxel). The bottom face refers to the face of the layer (or voxel) that is farther from the energy source 2.

[0181] The above rule enables the outer border of the surface layer 21 to be located. The rest of the surface layer 21 is defined according to another rule consisting in taking into account a predetermined width of the surface layer 21. Preferably, this width (in the X direction or in a direction orthogonal to the slice contour C1) is equal to or less than 10 voxels. Preferably, this width is equal to or less than 5 voxels. Preferably, this width is equal to or greater than 3 voxels.

[0182] More generally, the width of the skin needs to be sufficient to anchor the skin region of the layer to the skin region of a previously formed layer and to provide sufficient mechanical resistance to maintain the shape of the formed layer.

[0183] In other words, this width is selected to be thick enough to support mechanical stresses applied during the manufacturing process, such as by using a recoater, and thin enough to produce only negligible visual defects in the optical element 100 .

[0184] It is noted that in the case of subtractive post-processing, the slice profile C1 may have a shape that causes an additional thickness or a positive offset relative to the device to be manufactured. It is further noted that in the case of additive post-processing, the slice profile C1 may have a shape that locally causes a negative offset relative to the device to be manufactured.

[0185] The positive or negative offsets, their corresponding relative thickness and / or redistribution and / or uniformity along the device depend on the type of post-processing and / or machine to be applied. Therefore, the slice profile C1 includes any offsets related to post-processing.

[0186] As explained above, the position of the pattern projected onto the surface 55 of the curable material 50 can be adjusted to compensate for the low surface energy received by the shadow areas in the previous layer by displacing the support 15 along an axis substantially parallel to the surface of the curable material, or, using an operationally simpler alternative, by adjusting the optical system 4. This position of the pattern can also be adjusted for each layer to reduce errors caused by contour pixelation.

[0187] like 7A to 7D As shown in , the position of the pixel relative to the slice profile C1 can actually be modified. This position has a great influence on the extent of the volume of cavities or excess material created at the surface of the optical element (the goal is to reduce this volume as much as possible).

[0188] This goal can be achieved by trying several positions of the slice contour C1 relative to the pixel and by calculating, for each position, the volume error between the pixelated contour C2 and the slice contour C1. Alternatively, it can also be achieved using an error minimization algorithm that calculates the volume error between the pixelated contour C2 and the slice contour C1 from a given position of the pixel and a given pixelated contour C2 relative to the slice contour C1. i＝0 Start and iteratively or continuously modify the pixelated contour C2 i and / or the positions of the pixels in order to minimize the volume error while respecting the above mentioned rules related to post-processing. Thus, a random algorithm or a linear optimization algorithm may be used.

[0189] In the embodiment represented, several positions are at a distance of a maximum of 1 pixel from each other (along the X and Y axes orthogonal to the axis Ls).

[0190] In practice, the number of positions tried depends on the capabilities of the manufacturing system 1. For example, if the shifting device 20 allows movement increments of 1 μm along the X-axis and the Y-axis and if the pitch of each pixel is 20 μm, the number of possibilities is 20. 2 possibilities.

[0191] For each possibility, the position of the pixelated contour C2 is calculated according to one of the above rules.

[0192] Therefore, in order to calculate the error between the pixelated contour C2 and the slice contour C1 for each possibility, various functions may be used.

[0193] Here, the function used is that of minimizing the root mean square surface error between the pixelated contour C2 and the slice contour C1.

[0194] As described above, the pixelated contour C2 and the slice contour C1 are two-dimensional contours located in the same plane.

[0195] In a variant, the same type of calculation can be performed by considering the corresponding three-dimensional contour. In this variant, the function used consists of minimizing the external contour C2 of the voxel 3D With 3D Slice Contour C1 3D The root mean square volume error between .

[0196] The chosen position of the pixelated contour C2 relative to the slice contour Cl is the position that minimizes this function.

[0197] As explained above, the optical element 100 includes at least the skin layer 21 and the core 22 located inside the skin layer 21 .

[0198] The optical element may also include more than two different regions.

[0199] like Fig.10 As shown in , the optical element 100 may include a third area A3 located outside the first area A1 (the surface layer 20 ) and adjacent to the first area A1 .

[0200] Before giving details about the third area A3, we can Fig.10 It is noted above that the first area A1 is divided into two zones A1.1 and A1.2, the zone A1.1 being intended for polymerisation only if the post-processing is of the subtractive type.

[0201] In this exemplary embodiment, the width of the third area A3 is thinner than or equal to the width of the surface layer (eg, the width of 1 or 2 pixels).

[0202] The intensity I3 of the curing surface energy E applied to the third area A3 is different from the intensity I1 of the curing surface energy E applied to the first area A1, and the intensity I3 is preferably smaller than the intensity I1.

[0203] The strength I3 preferably keeps the curable material 50 in this third region A3 in an intermediate state after additive manufacturing of the device. Thus, this region can act as a primer or adhesive for a coating (e.g., a coating necessary for the step effect of the filtering optical element 100).

[0204] Due to their low mechanical strength, voxels in the intermediate state can also be used to smooth the surface by reducing the impact of using discrete contours and making the shape of the lens smoother and closer to the intended design, and then submitting the lens to the final curing step (this final step will be described later).

[0205] Taking into account the voxels in an intermediate state on the outer part makes it possible to relax the illumination conditions of the voxels close to the surface, which even becomes an opportunity, since the problems encountered with the penetration depth of the light and the polymerization of the accidental areas caused by it are solved. In fact, it is not necessary to strictly manage the illumination so that the voxels immediately outside the device to be manufactured remain unpolymerized, but it is possible to use an illumination scheme that causes the voxels outside the device to be manufactured to partially polymerize. Therefore, it is easier to generate a manufacturing file suitable for manufacturing an optical element of the desired shape while respecting the constraints mentioned above.

[0206] like Fig.10 As shown in , the optical element may include a fourth area A4 located between the first area A1 (the surface layer 20 ) and the second area A2 (the core 22 ).

[0207] The intensity I4 of the curing surface energy E applied to this fourth area A4 is different from the intensities I1, I2 of the curing surface energy E applied to the first area A1 and the second area A2, and the intensity I4 is smaller than the intensity I2.

[0208] The intensity I4 is preferably such that the curable material 50 in this fourth region A4 remains in a liquid or intermediate state (so as to have a lower mechanical strength than the core 22) during the irradiation of each layer of such voxels. It should be noted that such a fourth region ends up in a solid state, but the conversion rate is less than that in the first and second regions, taking into account the irradiation of the above layers. For example, the fourth region can remain in a liquid or intermediate state longer than the second region.

[0209] The fourth region is here indicated between the first and second regions, but it may alternatively be enclosed within the second region.Such a fourth region reflects that different balances between optical uniformity and conversion speed may be used in different parts of the optical device depending on the situation.

[0210] The optical element 100 may further include a fifth area A5 (not shown) located inside the first area A1. The intensity I5 of the curing surface energy E applied to this area may be higher than or equal to the intensity I1. For example, such an area enables the generation of a pattern (centered pattern, drawing, etc.) in the optical element.

[0211] As explained above, the curing step is repeated layer by layer to manufacture the entire optical element 100 .

[0212] In each step, the intensity of curing surface energy received by the curable material 50 may vary from pixel to pixel.

[0213] To this end, a first embodiment consists in applying a curing surface energy E at one time, having a non-zero intensity from an area within a contour C2 to another area of ​​said contour C2 (this embodiment is called "grayscale method") so as to reflect that the overall intensity of the curing surface energy received by the curable material 50 may vary from pixel to pixel within the irradiation of a given layer.

[0214] A second embodiment consists in applying the curing surface energy E on each layer in several sub-steps (this embodiment is called "multiple flash method").

[0215] During one of the sub-steps, the intensity of the curing surface energy E applied to the surface layer 21 is non-zero, while the intensity of the curing surface energy E applied to the core 22 is zero, and during another of the sub-steps, the intensity of the curing surface energy E applied to the surface layer 21 is non-zero and equal to the intensity of the curing surface energy E applied to the core 22.

[0216] In other words, at least two different patterns, each consisting of pixels that are either ON or OFF (no grayscale), are projected successively onto the same surface 55 of the curable material 50. One of these patterns represents only the skin 21, while the other pattern represents the core 22 or both the core and the skin.

[0217] In a third embodiment, the first embodiment and the second embodiment may be mixed: the curing energy of a layer is applied in several sub-steps, and in at least one sub-step, at least one zone within the contour C2 receives non-zero energy different from the non-zero energy received by another zone of the contour C2, and during the sub-step, a third zone within the contour C2 may not receive energy.

[0218] When all the curing steps are achieved, the optical element can be handled and transported for processing by another machine due to the rigidity of the skin 21. Here, this other machine is able to operate a further final step of final post-curing of all the curable material 50 of the optical element 100, due to UV light curing or thermal curing. Alternatively, the optical element can be post-processed as described above before and / or after the final post-curing, and / or cleaned before post-curing.

[0219] It should be noted that the invention is also applicable when the optical device is obtained without final post-curing and / or without post-processing.

[0220] At this stage of the description, we can present more detailed embodiments of the invention.

[0221] We consider an illustrative (not necessarily optimized) example in which the curable material is based on a methacrylate monomer with an experimentally determined critical Jacobs energy E C With a value of 7 mJ and a light depth penetration value Dp of 200 μm and an attenuation factor of 1 / Dp, the liquid state corresponds to a conversion rate below 30%, while the solid state occurs above 70%. In this example, a layer thickness of 10 μm and a surface width of 3 voxels are further selected.

[0222] Using grayscale or multi-flash mode, we apply directly on each layer a total dose of 2 mJ in the core 22 and "α" mJ in the surface layer 21 of the optical element 100. This corresponds to reaching the Jacobs energy in a given layer of the core region after irradiating the voxels of the given layer through more than 3 layers.

[0223] Between the two layers, the pattern shifts as follows:

[0224] The first time it is shifted by 0.5 pixels in the X direction,

[0225] The second time, it shifts 0.5 pixels in the Y direction,

[0226] The third time is shifted -0.5 pixels in the X direction,

[0227] A fourth shift in the Y direction of -0.5 pixels (then the shifting process restarts from the beginning).

[0228] The risk of the upper part of the optical element 100 is to apply too much energy in the regions of the core region immediately below the skin, since part of the UV light passes through the skin 21 to the core 22. In order to reduce this effect as much as possible, the chosen value of α is 7.56 mJ for this example for pixels located on the outer surface of the optical element 100. This value corresponds to the Jacobs energy Ej of a 10 μm layer of the material and is in fact the minimum value to ensure that the skin is in a solid state.

[0229] The risk for the lower part of the optical element 100 is that some energy is applied in the area located below the surface layer (outside the contour of the optical element), thereby generating shape errors. Nevertheless, since we want the surface layer 20 to be completely solidified, here again for the pixels located on the outer surface of the optical element, the selected value of α is 7.56 mJ (and in our example, the width of the obtained excess material is equivalent to 12 or 13 voxels). Alternatively, for the lower part, the pixelated contour C2 can be modified to take into account the obtained excess material after building all or most of the layers, so that the obtained excess material is not included in the slice contour C1 or the three-dimensional contour C1. 3D Additionally and or alternatively, the thickness of the surface layer may be reduced in the lower portion of the optical element 100 in terms of the number of layers.

[0230] This description relates to the DLP-SLA method, but it should be noted that the invention is also applicable to other methods when the material is cured layer by layer, or pseudo layer by layer, or drop by drop.

Claims

1. A method for producing an optical element (100) from a curable material (50), the optical element (100) having a desired outer shape by using an additive manufacturing technique, the additive manufacturing technique being operated layer by layer, the intersection between the midplane of each layer and the outer shape of the optical element (100) defining a slicing profile (C1), The method comprises a plurality of curing steps for curing the curable material (50) by applying a curing surface energy (E) to the curable material (50) inside the slicing contour (C1), the curing surface energy being higher in a first area (A1) extending along the slicing contour (C1) than in a second area (A2) located inside the first area (A1), the curing surface energy (E) applied to the second area (A2) being strictly below a first predetermined energy threshold (T1), in, The curing surface energy (E) applied to the first area (A1) is higher than or equal to a second predetermined energy threshold (T2), the second predetermined energy threshold (T2) is equal to or greater than the first predetermined energy threshold (T1), and in: - said first predetermined energy threshold (T1) is strictly below a critical Jacobs energy (Ec) defined for said curable material (50), - said second predetermined energy threshold (T2) is equal to or greater than said critical Jacobs energy (Ec).

2. The method according to claim 1, wherein: The second predetermined energy threshold (T2) is equal to or greater than the energy threshold defined by using E J =E C *exp(th / D P ) is the Jacobs energy (E J ),in E J is the Jacobs energy, th is the thickness of the layer, Dp is the light depth penetration value of the curing energy within the curable material, and Ec is the critical Jacobs energy.

3. The method according to claim 1, wherein: The steps are repeated layer by layer for each slice profile (C1) to manufacture the optical element (100).

4. The method according to claim 1, comprising a further final step of enabling both the curable material (50) in the first area (A1) and the curable material (50) in the second area (A2) to be fully cured, wherein: The total cured surface energy (E total ) is higher than or equal to the first predetermined energy threshold (T1).

5. The method according to claim 1, wherein: The curing surface energy (E) is directly applied to a third area (A3) located outside the first area (A1) with an intensity (I3), which is different from the intensity (I1) of the curing surface energy (E) applied to the first area (A1).

6. The method according to claim 5, wherein: The intensity (I3) is smaller than the intensity (I1) of the curing surface energy (E) applied to the first area (A1).

7. The method according to claim 1, wherein: The curing surface energy (E) is directly applied to the fourth area (A4) and / or the fifth area (A5) located inside the first area (A1) with intensities (I4) and (I5), respectively, which are less than, equal to or higher than the intensity (I1) of the curing surface energy applied to the first area (A1) and different from the intensity (I2) of the curing surface energy (E) applied to the second area (A2).

8. The method according to claim 1, wherein: - repeating said steps layer by layer to manufacture said optical element (100), - for at least one layer, applying the curing surface energy (E) in a sub-step such that the curing surface energy (E) is applied to a portion of the surface of the curable material (50) with a non-zero intensity that varies from area to area.

9. The method according to claim 1, wherein: - repeating said steps layer by layer to manufacture said optical element (100), - for at least one layer, applying said curing surface energy (E) in several sub-steps on the surface of said curable material (50), - during one of said sub-steps, the intensity of the curing surface energy (E) applied to said first area (A1) is non-zero, whereas the intensity of the curing surface energy (E) applied to said second area (A2) is zero, and - during another of said sub-steps, the intensity of the curing surface energy (E) applied to said first area (A1 ) is non-zero and equal to the intensity of the curing surface energy (E) applied to said second area (A2).

10. The method according to claim 1, wherein: The curing surface energy (E) is applied by a forming unit (3) suitable for producing a pixelated pattern on the surface of the curable material (50), the pixelated pattern producing voxels in the curable material (50), and wherein the first area (A1) is formed by a first group of voxels extending along a closed path, the width of the closed path being greater than 3 voxels and less than 10 voxels.

11. The method according to claim 10, wherein: The width of the closed path is greater than 3 voxels and less than 5 voxels.

12. The method according to claim 10, wherein: The first set of voxels is determined according to a determined geometry of the slice contour (C1) and according to any one of the following parameters: - the type of post-processing method, which is of subtractive or additive type, - the geometry of the voxels, and - Reference to a machine used to manufacture said optical element (100).

13. The method according to claim 10, wherein: The positions of the first group of voxels relative to the surface of the curable material (50) are defined according to the geometry of the slice contour (C1) and according to the geometry of the voxels.

14. The method according to claim 13, wherein: The steps are repeated layer by layer to manufacture the optical element (100), the thickness of each voxel being equal to the thickness of the layer under consideration, and wherein the positions of the first set of voxels are defined to minimize the slice contour (C1) and the outer contour (C2) of the first set of voxels. 3D ) is the root mean square of the volume error between .

15. The method according to claim 1, wherein: When the optical element (100) is designed to be post-processed by a subtractive type finishing method, the outer contour (C2) of the first area (A1) is located outside and / or above the slicing contour (C1), and when the optical element (100) is designed to be post-processed by an additive type finishing method, the outer contour (C2) of the first area (A1) is located inside and / or above the slicing contour (C1).

16. The method according to claim 1, wherein: The optical element (100) is an ophthalmic lens.

17. A manufacturing system (1) for manufacturing an optical element (100) from a curable material (50) using an additive manufacturing technique, the optical element (100) having a desired outer shape, the additive manufacturing technique being operated layer by layer, the intersection between a midplane of each layer and the outer shape of the optical element (100) defining a slice profile (C1), the manufacturing system (1) comprising: - a container (10) suitable for containing a curable material (50), - a support (15) suitable for supporting the optical element (100) to be formed, and a shaping unit (3) adapted to solidify the curable material (50) at least inside a slice contour (C1), the geometry of the slice contour being determined according to the geometry of the optical element (100), and - a computer element (6) programmed to control the shaping unit (3) so as to apply a curing surface energy (E) to the curable material (50), the curing surface energy being higher in a first area (A1) extending along the slice contour (C1) than in a second area (A2) situated within the first area (A1), the curing surface energy applied to the second area (A2) being strictly below a first predetermined energy threshold (T1), The curing surface energy (E) applied to the first area (A1) is higher than or equal to a second predetermined energy threshold (T2), the second predetermined energy threshold (T2) is equal to or greater than the first predetermined energy threshold (T1), and wherein, - said first predetermined energy threshold (T1) is strictly below a critical Jacobs energy (Ec) defined for said curable material (50), - said second predetermined energy threshold (T2) is equal to or greater than said critical Jacobs energy (Ec).

18. The manufacturing system (1) according to claim 17, wherein: The second predetermined energy threshold (T2) is equal to or greater than the energy threshold defined by using E J =E C *exp(th / D P The Jacobs energy (E) determined by the Jacobs equation for the first region (A1) of a given layer J ),in E J is the Jacobs energy, th is the thickness of the layer, Dp is the light depth penetration value of the curing energy within the curable material, and Ec is the critical Jacobs energy defined for the curable material (50).

19. The manufacturing system (1) according to claim 18, wherein: The second predetermined energy threshold (T2) is determined for the first region (A1) of a given layer by using the Jacobs equation.

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