Method for producing an optical element, optical element and device for producing an optical element

Abstract

The invention relates to a method for producing a coated lens (10), wherein the method comprises at least the following steps: vi. providing a substrate (18), vii. providing a three-dimensional model of the lens, viii. digitally cutting up the three-dimensional model from step ii. into individual layers, which are each divided into a grid (41) with surface elements, ix. providing at least one printing ink, preferably 3D printing ink, x. building up the lens on the substrate (18) from the sum of the individual layers from step iii. by means of a printing process in which the printing ink is applied to defined surface elements of the grid of an individual layer in the form of drops produced by a print-head nozzle arrangement (26) having a plurality of print-head nozzles. According to the invention, the print-head nozzles of the print-head nozzle arrangement (26) are actuated taking into account an assumed printing-ink drop volume p.

Description

[0001] Method for manufacturing an optical element, optical element and device for manufacturing an optical element Description

[0002] The invention relates to a method for manufacturing an optical element, in particular a lens, an intraocular lens, a contact lens, or a spectacle lens, wherein the method comprises the following steps: providing a substrate, providing a three-dimensional model of the optical element, digitally slicing the three-dimensional model into individual layers, each divided into a grid with surface elements, providing at least one printing ink, preferably 3D printing ink, and building up the optical element from the sum of the individual layers by means of a printing process on the substrate, in which the printing ink is applied in the form of droplets to defined surface elements of the grid of a single layer, generating a printhead-nozzle arrangement with multiple printhead nozzles. The invention also relates to an optical element manufactured in this way and to a device for manufacturing an optical element.

[0003] A method of the type mentioned above, such an optical element in the form of a lens and a device for manufacturing such an optical element are known from EP 3311 994 A1.

[0004] In the present invention, an optical element is understood to be a glass or plastic body that can be penetrated by light rays and deflect them. An optical element within the meaning of the invention can, for example, be a transparent body with two optically effective, i.e., light-refracting, surfaces that are opposite each other. In particular, an optical element within the meaning of the invention can be a so-called gradient lens. An optical element within the meaning of the invention can also be a spectacle lens designed for insertion into a spectacle frame. A spectacle lens can, for example, be a plano lens according to section 3.6.3 of DIN EN ISO 13666:2019-12, or a corrective lens (section 3.5.1), a protective lens (section 3.5.4), an absorption lens (section 3.5.5), a tinted lens (section 3.5.6), a clear lens (section 3.5.7), or a uniformly tinted lens (section 3.5.8) according to section 3.5 of DIN EN ISO 13666:2019-12.8), a gradient-tinted lens (section 3.5.9), a photochromic lens (section 3.5.11) or a polarizing lens (section 3.5.12).

[0005] The object of the invention is to provide a method and a device for manufacturing an optical element by means of a printing process that ensures good optical properties of the optical element, and to create an optical element that has good optical properties.

[0006] This problem is solved by the method for manufacturing an optical element specified in claim 1 and the optical element defined in claim 15, as well as a device with the features of claim 16. Advantageous embodiments and further developments of the invention are specified in the dependent claims.

[0007] A method according to the invention for manufacturing an optical element comprises the following steps:

[0008] i. Providing a substrate,

[0009] ii. Providing a three-dimensional model of the optical element, iii. Digitally slicing the three-dimensional model from step ii. into individual layers, each of which is divided into a grid of surface elements,

[0010] iv. Providing at least one printing ink, preferably 3D printing ink, v. Building up the optical element from the sum of the individual layers from step iii. by means of a printing process on the substrate in which the printing ink is applied in the form of drops onto defined surface elements of the grid of a single layer, which generates a printhead nozzle arrangement with several printhead nozzles, wherein the printhead nozzles of the printhead nozzle arrangement are controlled taking into account an assumed printing ink drop volume v.

[0011] The optionally pre-coated substrate defines the surface topography of the lens surface adjacent to the substrate. The lens surface opposite this surface is then selectively built up using a printing process, particularly 3D printing.

[0012] Information about the individual layers to be printed is provided to a printer, particularly a 3D printer, which includes a printhead with a printhead nozzle assembly comprising multiple nozzles to build a lens as a stack of individual printed layers that are at least partially overlapping. A layer is printed by applying volume elements of printing ink, preferably 3D printing ink, to a surface using the nozzles of a printhead nozzle assembly within the printhead. The smallest possible volume element corresponds to the volume of a droplet of printing ink, preferably 3D printing ink.

[0013] Several layers of adjacent volume elements can be positioned on top of each other, i.e., printed one on top of the other. The surface area and the number of layers to be printed depend on the desired dimensions of the lens to be printed. The curing of the individual layers can be carried out layer by layer, preferably using UV light, until the radiation-curable component has completely cured. Alternatively, incomplete curing can be performed after printing each layer, and final curing can be carried out after printing all layers, in each case preferably using UV light. A printer for printing a lens produced according to the method of the invention is, for example, a [printer type].A 3D printer with at least one printhead that generates volume elements via a piezoelectric element using the drop-on-demand method known from inkjet printing, and which always places a volume element precisely where it is needed. The at least one printhead of the printer can be moved over a substrate for the production of a lens according to the method of the invention, and / or the substrate can be repositioned under the at least one printhead.

[0014] The production of a lens according to the invention can be carried out using a 3D printing process that employs multi-jet modeling or PolyJet technology. For example, the Xaar 1001 printhead (Xaar), one of the Spectra S-Class, Spectra SE3, Spectra SX3, or Spectra Q-Class printheads (Spectra), the KM512 printhead (Konica Minolta), and / or the 256Jet S4 printhead (Trident) can be used as a printhead in a printer suitable for producing a lens according to the invention. The resolution of a printhead in a printer suitable for producing a lens according to the invention is preferably at least 300 x 300 dpi, more preferably at least 600 x 600 dpi, and particularly preferably at least 1200 x 1200 dpi.

[0015] These printheads are based on piezoelectric technology, in which electrical impulses deform a piezoelectric element, and the energy transferred to a fluid causes a droplet of printing ink to be ejected. The type of pulse applied to the piezoelectric element determines the shape, volume, and speed of the ejected droplet, allowing these three parameters to be controlled within certain limits.

[0016] The individual piezoelectric elements of a printhead cannot be controlled completely independently. On the one hand, it is very difficult to isolate the electrical control of, for example, over 1000 nozzles in a printhead from each other, and on the other hand, it is currently impossible to achieve complete fluid-dynamic separation of the cavities in the printhead.

[0017] The piezoelectric elements, through their movement, generate a pressure wave that is distributed across the fluid in the printhead's common reservoir. It is detrimental if the pressure frequency and the resulting sound waves in the fluid cause resonance within the printhead, as this prevents stable droplet formation. Besides such resonance phenomena, which must be avoided at all costs, more subtle effects also arise depending on the distance between nozzles firing simultaneously.

[0018] The droplet volume of individual ink droplets in a piezo printhead depends, among other things, on whether simultaneously firing nozzles on the nozzle plate of a printhead nozzle array are adjacent or not. If adjacent nozzles are firing, the droplet volume decreases in both nozzles; this is also known as crosstalk. Crosstalk must be included in the calculation of the layer thickness of a layer printed by the printhead if the influence of crosstalk between nozzles in a printhead nozzle array on the size of ink droplets is to be taken into account.

[0019] In this context, "adjacent" means that the affected nozzles must be located closest to each other on a nozzle row. In the case of a KM 1024i printhead with four rows of 256 nozzles each, this results in four rows in which this effect occurs independently.

[0020] The effect does not immediately drop to zero when a nozzle is left unoccupied between simultaneously firing nozzles, resulting in further correlations between volume reduction and nozzle spacing within a row. The effects become smaller with increasing distance. It should be noted that in a nozzle head with nozzles that have a nozzle chamber, printing ink droplets can be generated not only by deforming the nozzle chamber of a nozzle using a piezoelectric element, but also by transferring a heat pulse to the fluid in a nozzle chamber for the generation of printing ink droplets, causing the fluid to expand abruptly.

[0021] Printheads with nozzles that have a nozzle chamber into which a heat pulse can be introduced are called T1J systems. These printheads contain an electric resistance heater. The resistance heater is used to generate droplets by applying electrical pulses to it. The heat generated is transferred to the ink droplet fluid, which expands rapidly and is then forced through the nozzle opening due to the geometry of the nozzle chamber. Ink fluid containing solvents that evaporate when heated is particularly suitable for generating ink droplets using T1J systems.

[0022] In thermal inkjet printheads, as in printheads based on piezoelectric technology, fluid reservoirs are integrated that communicate with each other and are consequently coupled. This means that dispensing one droplet affects the droplet size of droplets dispensed simultaneously by a nozzle adjacent to the first or by a different nozzle altogether. The phenomenon of crosstalk is therefore also found in thermal inkjet printheads.

[0023] In thermal inkjet printheads and printheads based on piezo technology, where the ink droplets are generated by controlling nozzles at a constant frequency, the problem of crosstalk becomes less significant because it is a constant deviation that occurs reproducibly and can therefore be easily measured and taken into account as a constant in the calculation of a volume to be printed in the form of a layer or when printing a volume.

[0024] The inventors have discovered that it is irrelevant whether the nozzles for generating printing ink drops are controlled deterministically or stochastically in a so-called dithering process.

[0025] The stochastic control of printhead nozzles in a dithering process generates a binary image from a grayscale image that describes a spatially resolved layer thickness. The amount of material printed for the binary image corresponds to the desired amount of material, i.e., the specified, desired layer thickness at a particular location. Here, the process starts with the analogous print image for each nozzle—that is, the pixel of the grayscale image printed by the nozzle—and takes into account the error that arises when printing at a specific location with that nozzle. This error is then redistributed to surrounding nozzles by increasing or decreasing the probability that these nozzles will print.

[0026] To ensure that the droplet volume remains constant and is essentially independent of the printhead's operating state, a printhead can, in principle, be operated in such a way that a desired layer thickness or a desired number of ink droplets is printed without using adjacent nozzles. However, this results in a significant reduction in the printhead's theoretical resolution; in the case of the Konica Minolta KM 1024 printhead, for example, at least 50%.

[0027] When the printhead nozzles of a printhead are stochastically controlled (i.e., dithered) during layer generation, it is accepted that statistically distributed nozzles arranged next to each other will simultaneously produce ink droplets (i.e., shoot simultaneously), so that the volume of ink droplets produced also follows a statistical distribution. When adjacent nozzles produce ink droplets simultaneously, the resulting ink droplets are smaller than in the case of nozzles that are not directly adjacent.

[0028] This phenomenon can lead to deviations between the volume printed into a layer using a print head and the target volume of a model.

[0029] Preferably, at least one UV light source is attached to at least one side of the printhead; more preferably, at least one UV light source is attached to at least two sides of the printhead. Alternatively, several printheads can be installed, for example, in parallel with the printhead nozzle rows in a 3D printer and selectively controlled. The UV light source can then consist of several UV light sources also connected in parallel or of a few large UV light sources.

[0030] For the layer-by-layer construction of the lens, a printing ink suitable for 3D printing is preferably used. "Layer-by-layer construction" comprises the successive deposition of the printing ink, preferably 3D printing ink. This successive deposition can occur either side-by-side in a plane or stacked vertically. For example, if a first deposition of the printing ink, preferably 3D printing ink, is made in a plane on the pre-coated substrate, a further layer can be printed over the entire area of ​​the first deposition or a portion thereof. Preferably, the successive deposition of the printing ink, preferably 3D printing ink, first occurs side-by-side in a plane, before a further successive deposition of the printing ink, preferably 3D printing ink, is made in the layer above.A pre-coated substrate can be used as the printing substrate, which, starting from the substrate, is optionally coated with a) a removable adhesive layer and b) with the coating desired on the spectacle lens. The optional adhesive layer is a layer applied directly to the substrate, the adhesion of which can be altered by external influences, such as temperature changes or radiation. This allows the spectacle lens, produced by a printing process, preferably 3D printing, to be detached from the optional removable adhesive layer along with the coating present on it. In this way, a spectacle lens can be produced in the simplest way, with the desired coating already applied to its surface.It goes without saying that the substrate must be printed with a layer sequence that corresponds to the reverse order of the coating process desired on the spectacle lens. Any residues of the optional removable adhesive layer remaining on the resulting coated spectacle lens can be removed using a cleaning process.

[0031] The pre-coated substrate can be convex, concave, or planar. The surface topography of the pre-coated substrate can be selected from the group consisting of spherical, aspherical, toric, atoric, progressive, and planar.

[0032] The substrate can be made of, for example, polytetrafluoroethylene, glass, or metal. In one embodiment, the substrate can have a separating layer comprising alkyltrihalosilanes, preferably C12 to C22 alkyltrichlorosilanes, and most preferably octadecyltrichlorosilane.

[0033] The pre-coated substrate can be coated with at least one layer selected from the group consisting of at least one hard lacquer layer, at least one anti-reflective layer, at least one electrically conductive or semiconducting layer, at least one anti-fog layer, and / or at least one clean-coat layer. Preferably, the pre-coated substrate is coated with at least one anti-reflective layer, at least one hard lacquer layer, and at least one clean-coat layer.

[0034] One idea of ​​the invention is that the printhead nozzles of the printhead nozzle arrangement are controlled according to a control rule that assigns a printhead nozzle to the area element of the raster of a layer and that causes the generation of a droplet of printing ink by means of the assigned printhead nozzle depending on a criterion that takes into account a predetermined thickness t(n,m) of the layer in the area element of the raster and a thickness error e(n,m) which is determined from a comparison of the thickness t(n,m) of the layer predetermined for an area element of the raster of a single layer and an assumed thickness increment DZ for which the following applies:

[0035] DZ = 0 if no drop is produced, and

[0036] DZ = constant when a drop is produced.

[0037] In this way, it is possible to minimize the deviation of the actual thickness of a layer produced by applying individual drops of printing ink from a predetermined thickness.

[0038] It is particularly advantageous if the thickness error e(n,m) of the given thickness t(n,m) of the layer in the area element of the raster is added to a given thickness t(n,m) of at least one further area element of the raster using a correction factor to obtain a corrected thickness t(n,m) for this area element. In this way, the fact that a single drop of printing ink, when it comes into contact with the substrate or a layer on the substrate, spreads out depending on the viscosity of the printing ink, its surface tension, and the interfacial tension occurring at the interfaces between the drop and the substrate or between the drop and the layer on the substrate, and covers an area that comprises several area elements of the raster of a layer, each of which is assigned a printhead nozzle, can be taken into account.This measure makes it possible to reduce an undesirable deviation of the thickness of a layer applied to a substrate or the thickness of a layer applied to a substrate from a target value.

[0039] A preferred embodiment of the invention provides that the grid has rows and columns in which the surface elements are arranged, wherein the printhead nozzles of the printhead nozzle arrangement are displaced relative to the substrate in a direction parallel to the columns. The thickness error e(n,m) of the layer in a surface element of the grid is added to the predetermined thickness t(n,m) of the layer in the surface element of the grid to obtain a predetermined thickness t(n,m) of a first further surface element of the grid, applying a first correction factor. This first further surface element is adjacent to this surface element in a row of the grid, provided that the surface element is not a surface element in a last row, a first column, or a last column of the grid, in order to obtain a corrected thickness t(n,m) for this surface element.m) The thickness of the layer in the grid element of a given thickness t(n,m) is added to a second, further grid element, applying a second correction factor to the given thickness of the layer, which is adjacent to this grid element in a column of the grid, if the grid element is not a grid element in a last row or in a first column or in a last column of the grid, in order to obtain a corrected thickness for this grid element as a given thickness t(n,m), and the given thickness t(n,m) of the layer in the grid element of a given thickness t(n,m) is added to a third further grid element, applying a third correction factor to the given thickness of the layer, which is adjacent to the second further grid element in a row of the grid.If the area element is not an area element in a last row or in a first column or in a last column of the grid, in order to obtain a corrected thickness for this area element as a given thickness t(n,m), and the given thickness t(n,m) of the layer in the area element of the grid is added to a fourth further area element of the grid, applying a fourth correction factor to the given thickness of the layer, which is adjacent to a second further area element in a row of the grid, if the area element is not an area element in a last row or in a first column or in a last column of the grid, in order to obtain a corrected thickness for this area element as a given thickness t(n,m).

[0040] In this way, an undesirable deviation of the thickness of a layer applied to a substrate or of a layer applied to a substrate from a target value can be optimized.

[0041] The criterion, which takes into account a given thickness t(n,m) of the layer in the area element of the grid and a thickness error e(n,m) determined from a comparison of the thickness t(n,m) of the layer given for an area element of the grid of a single layer and an assumed thickness increment DZ, can be, for example:

[0042] tkorr[n,m] > k tmax[n,m],

[0043] meancorr[n+1, m] = t[n+1, m] + e[n,m]

[0044] tcorr[n-1 , m+1] = t[n-1 , m+1] + c2e[n,m]

[0045] tcorr[n, m+1] = t[n, m+1] + c3e[n,m]

[0046] tcorr[n+1, m+1] = t[n+1, m+1] + c4e[n,m]

[0047] where

[0048] e[n,m] := t[n,m] - p

[0049] where p is the change in the layer thickness of the layer to be printed on an area element in the nth column and the mth row of the grid caused by the application of a single drop of printing ink with the assumed printing ink drop volume v to this area element,

[0050] where tmax(n,m) is a maximum layer thickness that can be printed onto the substrate using the printhead nozzles of the printhead nozzle assembly,

[0051] where t(n,m) is a layer thickness specified for the surface element in the nth column and the mth row of the layer grid,

[0052] where tkorr(n,m) is a layer thickness corrected for the surface element in the nth column and the mth row of the layer's grid and

[0053] where:

[0054]

[0055] preferably e.g. = 7 and c2= 5 / ^ and c3=

[0056]

[0057] and c4=

[0058]

[0059] ,

[0060] and 0 < k < 1 , preferably This makes it possible to ensure that an undesirable deviation of the thickness of a layer applied to a substrate or of a layer applied to a layer on a substrate from a target value is particularly low.

[0061] The invention can also provide that the thickness error e(n,m) of the predetermined thickness t(n,m) of the layer in the area element of the grid is added to a further area element of the grid with a predetermined thickness t(n,m) by applying a first correction factor to the predetermined thickness of the layer, which is arranged in the same row of the grid as the area element and which, during a printing process, can receive printing ink in the form of a droplet from a printhead nozzle of the nozzle order which is arranged adjacent to a printhead nozzle in a nozzle row of the nozzle arrangement, which can provide printing ink in the form of a droplet for the area element.

[0062] The criterion, which takes into account a given thickness t(n,m) of the layer in the area element of the grid and a thickness error e(n,m) which is determined from a comparison of the thickness t(n,m) of the layer given for an area element of the grid of a single layer and an assumed thickness increment DZ, can then be, for example:

[0063] tkorr(n,m) > k tmax(n,m),

[0064] with

[0065] tcorr[n, m+1] := t[n, m+1] + 0.4e[n,m],

[0066] tcorr[n, m+z] := t[n, m+z] + 0.3e[n,m],

[0067] tcorr[n+1, m-1] := t[n+1, m-1] + 0.3e[n,m],

[0068] tcorr[n+1, m] := t[n+1, m] - 0.1e[n,m],

[0069] tkorr[n+1 , m+1] := t[n+1 , m+1] + 0,1e[n,m],where

[0070] ze N > 1

[0071] and

[0072] e(n,m) := t(n,m) - p

[0073] where z is the number of nozzle rows of a printhead and where p is the change in the layer thickness of the layer to be printed on a surface element in the nth column and mth row of the grid caused by the application of a single drop of printing ink to that surface element,

[0074] where tmax[n,m] is a maximum layer thickness that can be printed onto the substrate using the printhead nozzles of the printhead nozzle assembly,

[0075] where t[n,m] is a layer thickness specified for the surface element in the nth column and the mth row of the layer's grid,

[0076] where tkorr[n,m] is a layer thickness corrected for the surface element in the nth column and the mth row of the layer's grid,

[0077] and where: 0 < k < 1 , preferably k =

[0078]

[0079] It should be noted that the printhead nozzle arrangement in a nozzle row can contain a plurality of adjacent printhead nozzles that can be controlled simultaneously, each producing a droplet of ink when activated, with the average droplet volume for the printhead nozzles incorporating a probability with which adjacent printhead nozzles simultaneously produce a droplet of ink, so that a single layer in a defined area element of its grid has a predetermined thickness.

[0080] The assumed ink droplet volume can be an averaged volume for ink droplets of the printhead nozzle assembly that individual printhead nozzles of the printhead nozzle assembly produce.

[0081] The average ink droplet volume can be determined, for example, gravimetrically for the printhead nozzles of the printhead nozzle arrangement.

[0082] Alternatively, the average ink droplet volume for the printhead nozzles of the printhead nozzle assembly can be determined from at least one operating state variable that characterizes an operating state of the printhead nozzle assembly. In particular, the operating state variable can be at least one variable from the group consisting of print frequency, average number of ink droplets per area on the substrate, printhead temperature, the profile of a control voltage for printhead nozzles, and ink viscosity.

[0083] An optical element according to the invention is manufactured using a method specified above.

[0084] An apparatus according to the invention for manufacturing an optical element comprises a printhead with printhead nozzles that serve to supply printing ink droplets (23). A table is provided, designed to receive a substrate, which can be displaced relative to the printhead in a plane in two mutually perpendicular directions x, y. The apparatus includes a computer with a program memory into which a computer program for controlling the printhead nozzles is loaded. The computer program serves to control the printhead nozzles taking into account an assumed printing ink droplet volume v. The invention is explained in more detail below with reference to the exemplary embodiments shown schematically in the drawing.

[0085] They show:

[0086] Fig. 1 shows a device for manufacturing a spectacle lens, which includes a print head;

[0087] Fig. 2 shows a top view of the printhead with a printhead nozzle arrangement and with a device for providing UV light;

[0088] Fig. 3 shows a three-dimensional model of a spectacle lens divided into individual layers;

[0089] Fig. 4 shows a grid for a layer of the model of a spectacle lens with surface elements;

[0090] Fig. 5 shows a distribution of a given thickness of a layer on the substrate as a grayscale image;

[0091] Fig. 6 shows a control instruction that converts the grayscale image describing a local layer thickness into a black and white image that indicates which printhead nozzles provide a drop of ink when printing ink is applied by means of the nozzle head;

[0092] Fig. 7 the application of a control rule that specifies which printhead nozzles provide a droplet of ink when printing ink is applied by means of the nozzle head; Fig. 8 the determination of a control rule that specifies which printhead nozzles provide a droplet of ink when printing ink is applied by means of the nozzle head, at a predetermined layer thickness on a substrate;

[0093] Fig. 9 shows an algorithm of the tax regulation;

[0094] Fig. 10 shows a graph of the mean droplet volume of printing ink droplets as a function of a first printhead operating state;

[0095] Fig. 11a and

[0096] Fig. 11b Control rules for actuating the printhead nozzles in the printhead nozzle assembly of the printhead; and

[0097] Fig. 12 shows a graph of the mean droplet volume of printing ink droplets as a function of a second printhead operating state.

[0098] Fig. 1 shows a device 10 for manufacturing an optical element, in particular a lens, e.g., a spectacle lens. The device 10 includes a printhead 12 and has an xy-shifting unit 14 with a table 16, which serves to hold a substrate 18. On the table 14, the substrate 18 can be moved relative to the printhead 12 in a plane 20 in two mutually perpendicular directions x, y. The device 10 makes it possible to apply 3D printing ink 19 from a reservoir 22 to the substrate 18 layer by layer in the form of ink droplets 23 by means of the printhead 12 in order to manufacture a spectacle lens 24. It should be noted that in an alternative device to the one described above, the printhead 12 may be mounted on a shifting unit to move it relative to the substrate 118 arranged on a table 16.Furthermore, it should be noted that it may also be provided that both the printhead 12 and the table 16, which serves to hold a substrate 18, can each be adjusted by means of an xy-shift unit in order to move the printhead 12 relative to the substrate 18.

[0099] Fig. 2 is a top view of the printhead 12 with a printhead nozzle assembly 26 and a UV light supply device 27, which includes LEDs for curing 3D printing ink applied to the substrate 18 with UV light. The printhead nozzle assembly 26 has printhead nozzles 30.1.1, 30.1.2, 30.1.3 and 30.1.4, arranged in four parallel, straight rows 30.1, 30.1.2, 30.1.3 and 30.1.4, ...

[0100] 30.2.1, 30.2.2, 30.2.3, ... 30.3.1, 30.3.2, 30.3.3, ... each containing a piezo actuator. It should be noted that the printhead 12 can also be configured as a thermal inkjet printhead.

[0101] Each of the rows 30.1, 30.2, 30.3, and 30.4 contains 256 printhead nozzles. The distance AD ​​between two adjacent printhead nozzles 30.1, 30.2, 30.3, and 30.4 in a row is 282 pm. The distance AR30.1-30.2 of row 30.1 from row 30.2 is approximately 300 pm. The same applies to the distance AR30.3-30.4 of row 30.3 from row 30.4.

[0102] The printhead nozzles 30.1.1, 30.1.2, ... of the series 30.1 are arranged offset from the printhead nozzles 30.2.1, 30.2.2, 30.2.3, ... of the series 30.2 such that each printhead nozzle 30.1.1, 30.1.2, 30.1.3, ... of the series 30.1 spans an isosceles triangle 36 with two adjacent printhead nozzles 30.2.1, 30.2.2, 30.2.3 of the series 30.2.

[0103] The printhead nozzles 30.3.1, 30.3.2, 30.3.3 of series 30.3 are also arranged offset from the printhead nozzles 30.4.1, 30.4.2, ... of series 30.4 such that each printhead nozzle 30.3.1 of series 30.3 forms an isosceles triangle 36 with two adjacent printhead nozzles 30.4.1, 30.4.2 of series 30.4. The nozzles 30.1.1, 30.2.1, 30.3.1, 30.4.1 in successive rows 30.1, 30.2, 30.3 and 30.4 are arranged offset from each other. They each lie on parallel lines perpendicular to the direction of the rows, where the distance AG between two adjacent lines is given by: AG = 3 x 23.5 pm = 70.5 pm.

[0104] The device 10 shown in Fig. 1 has a computer unit 32 with a printhead controller 37, which serves to control the piezo actuators of the printhead nozzles 30.1.1, 30.1.2, 30.1.3 and 30.1.4 as well as 30.2.1, 30.2.2, 30.2.3, ... 30.3.1, ... 30.4.1, ... of the printhead nozzle arrangement 26. By actuating the piezo actuator of a printhead nozzle 30.1.1, ... a droplet of 3D printing ink can be generated and flung onto a defined position in an area on the substrate 18, which is determined by the position of the printhead nozzle 30.1.1, ... in the printhead 12 and the setting of the xy-shift unit 14 as well as the arrangement of the substrate 18 on the table 16 of the shift unit 18.

[0105] Fig. 3 shows a three-dimensional model 38 of a lens in the form of a spectacle lens, which is divided into individual layers 40.1, 40.2, 40.3, 40.4 ... .

[0106] Each of the layers 40.1, 40.2, 40.3, 40.4 ... is in turn divided into a grid with square surface elements.

[0107] Figure 4 shows the grid 41 of layer 40.3 with the surface elements 42.1.1, 42.1.2, 42.1.3, ... 42.2.1, 42.2.2, 42.2.3, ... 42.3.1, 42.3.2, 42.3.3, ..., into which a surface 43 of layer 40.3 is divided. The grid has N columns and M rows in which the surface elements are arranged, where N and M can be, for example, N = 10000 and M = 15000. The surface elements 42.1.1, 42.1.2, 42.1.3, 42.1.4, ... are arranged next to each other in a row 42.1.0 of the grid 41. The same applies to the surface elements 42.2.1, 42.2.2, 42.2.3, 42.2.4 and 42.3.1, 42.3.2, 42.3.3, 42.3.4, which are also located next to each other in a row 42.2.0 and 42.3.0 of the grid 41. The surface elements 42.1.1, 42.2.1, 42.3.1, 42.4.1 ... on the one hand, and the surface elements 42.1.2, 42.2.2, 42.3.2, 42.4.2, ... as well as 42.1.3, 42.2.3, 42.3.3, 42.4.3, ... and 42.1.4, 42.2.4, 42.3.4, 42.4.4, ... on the other hand, are arranged side by side in different columns 42.0.1, 42.0.2, 42.0.3 and 42.0.4 arranged.

[0108] By moving the printhead nozzle arrangement 26 of the printhead 12 relative to a substrate 18 parallel to the slits 42.0.1, 42.0.2, 42.0.3, ... of the grid 41 at a uniform speed, it is possible to control the printhead nozzles 30.1.1, 30.1.2, ... for each of the surface elements 42.1.1, 42.2.1, of the grid 41 so that exactly one drop 23 of printing ink 19 or no drop 23 of printing ink is placed in it.

[0109] Every fourth surface element 42.1.1 , 42.1.4, ... in a row of the grid 41 receives printing ink from two printhead nozzles 30.1.1, 30.1.2, ... 30.2.1, 30.2.2 ..., 30.3.1, 30.3.2, ... . arranged adjacent to each other in a nozzle row 30.1, 30.2 ... of the nozzle arrangement 26 of the printhead. Surface elements of the grid 41, which are arranged in the four different adjacent rows 42.1.0, 42.1.1, 42.1.2, ..., receive printing ink from printhead nozzles 12, which are located in different nozzle rows 30.1, 30.2, 30.3, 30.4 of the printhead 12, when the printhead 12 is operated.

[0110] Fig. 5 shows, as a grayscale image 44, a distribution of a given thickness of a layer 40 on the substrate 18. The local grayscale level in the grayscale image is a measure of the local thickness of the layer.

[0111] The local thickness of the layer is determined by digitally slicing a three-dimensional model 38 of a spectacle lens and divided into a grid with surface elements 42.nm with n = 1, 2, 3 ... and m = 1, 2, 3, ... which has rows 42.n with n = 1, 2, 3, ... and columns 42.m with m = 1', 2', 3', ...

[0112] In order to produce layer 40 with the specified, generally locally varying thickness, the printhead nozzles 30.1.1, ... of the printhead nozzle arrangement 26 are controlled in a clocked manner, taking into account an assumed printing ink droplet volume v, whereby the substrate 18 is displaced relative to the printhead 12.

[0113] The assumed ink droplet volume v can, for example, be an averaged ink droplet volume m, which is determined for the printhead nozzles 30.nm, m=1, 2, 3, ...; m=1, 2, 3, ... of the printhead nozzle assembly 26 as an operating state variable characterizing an operating state of the printhead nozzle assembly 26. Such an operating state variable, which may be multidimensional, can, for example, be a pressure frequency at which the printhead nozzle assembly 26 is operated in the printhead 12 and / or a relative number n / N of printhead nozzles 30.nm that simultaneously provide an ink droplet when the printhead 12 is operated, and / or a temperature T of the printhead and / or a control voltage for printhead nozzles 30.nm, m=1, 2, 3, ...; m=1, 2, 3, ... of the printhead nozzle arrangement 26 and / or a printing ink viscosity. Determining an average printing ink droplet volume m can be done, for example,in a gravimetric measurement in which a precisely defined number of printing ink drops 23 are applied to a substrate 16 by means of the printhead 12 based on a control rule and the substrate is then weighed.

[0114] Fig. 6 shows a control instruction 47 that converts the grayscale image 44 describing a local layer thickness into a black and white image that indicates which printhead nozzles 30.1.1, 30.1.2, ... provide a droplet of ink 44 in a surface element 42 nm with n = 1, 2, 3 ... and m = 1, 2, 3, ... when printing ink is applied by means of the nozzle head 12. Fig. 7 illustrates the application of droplets of ink 44 to the substrate 18 by means of the printhead nozzle arrangement 26 of the printhead 12 according to a control instruction. The printhead 12 with the printhead nozzle arrangement 30 is moved uniformly in the direction of arrow 45 over the substrate 18, whereby the printhead nozzles 30.1.1 , ... of the printhead nozzle arrangement 26 are controlled according to a control rule in order to apply drops 23 with 3D printing ink to the substrate 18.

[0115] Each printhead nozzle 30.1.1 ... makes it possible to arrange a printing ink droplet 23 for the application of a layer 40.1, 40.2, 40.3 ... shown in Fig. 3 on a substrate 18, as shown in Fig. 1, in a defined area element 42.nm, n = 1, 2, 3, ... and m = 1, 2, 3, ... of the layer.

[0116] The grid 41, in which the surface elements 42.nm, n = 1, 2, 3, ... and m = 1, 2, 3, ... are arranged, has rows 42.1.0, 42.2.0, 42.3.0, ... 42.N.0 and columns 42.0.1, 42.0.2, 42.0.3, ..., 42.0.M. The printhead nozzles 30.nm, n=1, 2, 3, ...; m=1, 2, 3, ... of the printhead nozzle arrangement 26 are displaced relative to the substrate 18 in a direction 45 parallel to the columns 42.0.1, 42.0.2, 42.0.3, ..., 42.0.M of the grid 41.

[0117] In an area on the substrate 18, an applied droplet of printing ink 23 spreads out and, according to the rheological properties of the 3D printing ink, spreads over several surface elements 42.nm of the grid 41 in an area 46.

[0118] Consequently, a droplet of printing ink 23 wets not only the surface element 42 nm into which it is applied, but also surface elements 42n-1.m-1, 42n.m-1, 42n+1.m-1, 42n-1.m, 42n+1.m, 42n-1.m+1, 42n.m+1, 42n.m+1 that surround the surface element 42 nm. The size of an area 46 wetted on the substrate 18 by a droplet of printing ink 23 is determined by the size of the droplet 23 with 3D printing ink, the surface tension of the printing ink, and the wetting properties of the substrate 18 or the layer on the substrate that is applied to the substrate 18.

[0119] The size and thus the volume of the ink droplets 23 produced in the printhead 12 by means of the printhead nozzles 30.1 , 30.2, 30.3 , 30.4 is subject to printhead nozzle-specific variations. The cause of these fluctuations, which can amount to up to 10% of the drop volume in relative terms and may even exceed this, is, on the one hand, manufacturing-related differences between individual printhead nozzles 30.1.1, 30.1.2, 30.1.3, 30.1.4, ... of the printhead 12. On the other hand, the droplet size of printing ink droplets 44 from a printhead nozzle 30.1.1, 30.1.2, 30.1.3, 30.1.4 depends on whether a printhead nozzle arranged adjacent to the printhead nozzle 30.1.1, 30.1.2, 30.2.1, 30.2.2, 30.3.1, 30.3.2, etc., in a row 30.1, 30.2, 30.3, 30.4, is simultaneously The ink droplets 44 are generated, so that the size of the ink droplets 44 also depends on the operating state of the printhead 12 or on the way in which the printhead 12 is operated.

[0120] The inventors have discovered that the manufacturing-related and operationally specific fluctuations in the droplet size of printing ink droplets 23, which are generated by the printhead nozzles 30.1.1, 30.1.2, 30.1.3, ... of the printhead nozzle arrangement 26 of the printhead 12, must not be neglected in the production of lenses by means of 3D printing, so that the lenses meet the quality requirements placed on them.

[0121] Fig. 8 shows different stages 45a, 45b, 45c, 45d, 45e, and 45f for determining a control rule 47 for controlling the printhead nozzles 30 nm, n = 1, 2, 3...; m = 1, 2, 3, ... in the printhead nozzle arrangement 26 of the printhead 12 to a predetermined, location-dependent layer thickness on a substrate. The predetermined, location-dependent layer thickness is shown in Fig. 8, as in Fig. 5, as a grayscale image.

[0122] Tax regulation 47 specifies on which surface element 42.nm with n = 1, 2, 3 ... and m = 1, 2, 3, ... of the surface of a layer a droplet of printing ink 23 is applied, and on which surface element 42.nm of the surface of a layer no droplet of printing ink 23 is applied. If a surface element 42.nm is black, a droplet of printing ink 23 is applied to it. If, on the other hand, it is not black, no droplet of printing ink 23 is applied to it.

[0123] Fig. 9 illustrates an algorithm 48 for determining the control rule 47 for controlling the printhead nozzles 30.1.1, 30.1.2, 30.1.3, ... of the printhead nozzle arrangement 26, which enables the production of a printing ink layer on the substrate 18 with a location-dependent layer thickness for an assumed droplet volume v of the printing ink droplets 23 generated by the printhead nozzles 30.1.1, 30.1.2, 30.1.3, 30.1.4, ... .

[0124] Algorithm 48 takes advantage of the fact that a drop of printing ink applied to the substrate spreads out as described above and extends, as indicated in Fig. 7, over an area 46 that covers several surface elements 42.nm, 42.n.m+1, 42.nm-1, 42.n-1.m-1, 42.n-1.m, 42.n-1.m+1, 42.n+1.m-1, 42.n+1.m, 42n+1.m+1 of the area 46 of the surface in a layer 40.1, 40.2, 40.3, 40.4 ... .

[0125] By having all printhead nozzles 30.1.1, 30.1.2, 30.1.3, ... of printhead nozzle order 26 of printhead 12 generate timed ink droplets 23 at the same time, while the substrate 18 is uniformly displaced under the printhead 12, an ink layer of constant thickness can be applied to the substrate 18. The control rule 47 contains a routine 52 for specifying a spatially referenced, spatially resolved local thickness t(x, y) = t[n,m] of a layer to be printed at the location (x,y) = [n,m] of a surface element 42.nm, relative to the printhead 12.

[0126] For a given local thickness t(x,y) of a layer to be printed at the location x,y of a surface element 42.nm, the control rule 46 calculates in the following steps along a serpentine counting path 50 through the grid 41 of the surface of the corresponding layer, as shown in Fig. 7 and Fig. 8, whether a printing ink droplet 23 is applied to this surface element 42.nm or not:

[0127] In a comparison stage 54, a comparison is made between the specified local thickness t of a layer to be printed at the location n,m of a first surface element with a maximum layer thickness tmax, which can be applied to a surface with surface elements 42.1 ... by means of the printhead nozzle arrangement 26, by generating ink droplets 23 at a predetermined rate with all printhead nozzles 30.1.1, 30.2.1, 30.3.1, 30.4.1 of the printhead nozzle arrangement 26 of the printhead 12.

[0128] If the criterion

[0129] t > tmax

[0130] If the condition is met, the printhead nozzle arrangement 26 provides a droplet of printing ink 23 at the location x,y of a first surface element 42.1 ... to a signal generated in a functional stage 56 for the printing layer. If, on the other hand, the criterion is met

[0131] If t > tmax is not fulfilled, function stage 56 causes the printhead nozzle arrangement 26 to not produce a printing ink droplet 23 at location n,m of the first surface element 42.1.

[0132] In error calculation stage 58, a thickness error e of the layer thickness t of the layer to be printed at the location x,y of the first surface element 42.nm is determined according to the following rule:

[0133] e(x,y) = t(x,y) - p,

[0134] where p is the assumed change in the layer thickness of the layer to be printed on the surface element 42.1 caused by the application of a single drop of printing ink 23 with the assumed printing ink drop volume v to the surface element 42.1.

[0135] In a correction step 60, the local thickness t(x,y) of the layer to be printed is calculated at the location x,y of the surface elements 42.n.m+1 and 42.n.m+4 located near the first surface element 42.nm in a row 42.n of the grid 41, in which the surface elements 42.n.m+1 and 42.n.m+4 are located, as well as the surface elements 42.n+1.m-1, 42.n+1.m and 42.n+1.m+1, which, as shown in Fig.

[0136] Figures 6 and 7 show that, in a row 42.m adjacent to row 42.m, the surface elements are arranged according to the following rule if they are not arranged in a last row or in a first column or in a last column of the grid 41:

[0137] tkorr[n, m+1] := t[n, m+1] + 0.4e[n,m], tkorr[n, m+z] := t[n, m+z] + 0.3e[n,m], tkorr[n+1, m-1] := t[n+1, m-1] + 0.3e[n,m],

[0138] tkorr[n+1, m] := t[n+1, m] - 0,1e[n,m], tkorr[n+1, m+1] := t[n+1, m+1] + 0,1e[n,m], where z = 4 is the number of rows 30.1, 30.2, 30.3, 30.4 with printhead nozzles 30.nm in the printhead nozzle arrangement 26 and [n,m] is the location of the surface element 42.nm in the surface of the layer to be printed.

[0139] For surface elements 42.nm in a last row M or in a first column 1 or in a last column N of the grid 41, the following applies: tkorr[n, m] := t[n, m].

[0140] This distributes the thickness error e determined for the surface element 42.nm to surface elements that are located near the surface element 42.nm.

[0141] In a comparison step 62, a comparison is then made of the corrected thickness tkorr of a layer to be printed at the location [n+i, m+j], i, j = 0, 1, 2, 3, ... of a surface element n+i, m+j using the criterion

[0142] tkorr > >2 tmax.

[0143] The area element 42n+i.m+j following an area element 42n.m on the counting path 50 is arranged in the same row of the grid 41 if the area element 42n.m is not located at one end of a row of the grid 41, in which case the following applies to the position (x,y) of the area element adjacent to the area element 42n.m:

[0144] (x,y) := [n,m+1]

[0145] If the area element 42n.m is located at the end of a row of the grid 41, the following applies to the position (x,y) of the area element following on the counting path 50.

[0146] (x,y) := [n+1,m]. If the criterion of comparison stage 62 is met, the printhead nozzle arrangement 26 provides a printing ink droplet 23 at the location of the corresponding surface element 42. n. m+1 ... of a layer to be printed, based on a signal generated in the signal output routine 56. If the above relation tkorr > tmax is not met, the printhead nozzle arrangement 26 does not generate a printing ink droplet 23 at the location [n,m] of the first surface element 42.1.

[0147] Then, according to the rule of error calculation stage 58, a thickness error of the layer thickness t of the layer to be printed is determined at the location x,y of the surface element and then, according to the rule of correction stage 60, the thickness error determined for the surface element 42.nm is distributed to further surface elements.

[0148] Then, on the counting path 50, the specified local thickness is compared with the corrected thickness tkorr of a layer to be printed at the location of the further surface element according to the criterion of the comparison stage 62, in order to then control the printhead nozzle arrangement 26 at the location of the corresponding surface element 23 on the basis of a signal generated in the functional stage 56.

[0149] It should be noted that an alternative embodiment of the algorithm 48 described above for determining the control rule 47 for controlling the printhead nozzles 30.1.1, 30.1.2, 30.1.3, ... of the printhead nozzle arrangement 26 may provide, in a correction stage modified to the correction stage 60 shown in Fig. 8, to determine a corrected local thickness tkorr according to the following rule if the surface elements are not arranged in a last row or in a first column or in a last column of the grid 41:

[0150] tkorr

[0151]

[0152] tkorr

[0153]

[0154] tkorr[

[0155]

[0156] tkorr[n+1, m+1] = t[n+1, m+1] +1 / i6 e [ n > m ]

[0157] For surface elements 42.nm in a last row M or in a first column 1 or in a last column N of the grid 41, the following also applies: tkorr[n, m] := t[n, m].

[0158] Furthermore, it should be noted that an alternative embodiment of the algorithm 48 described above for determining the control rule 47 for controlling the printhead nozzles 30.1.1, 30.1.2, 30.1.3, ... of the printhead nozzle arrangement 26 may provide, as a counting path along which the control rule 46 calculates for the surface elements of a grid 41 whether a drop of printing ink 23 is applied to this surface element 42.nm or not, a counting path in which the surface element 42n+i.m+j following a surface element 42n.m on the counting path is arranged adjacent to the surface element in the same column of the grid 41 if the surface element 42n.m is not located at an end of a column of the grid 41, wherein the following applies to the location (x,y) of the surface element adjacent to the surface element 42n.m:

[0159] (x,y) := [n+1,m]

[0160] and the following surface element applies to the location of the surface element 42n.m:

[0161] (x,y) := [n,m+1]

[0162] when the surface element 42n.m is located at the end of a column of the grid 41.

[0163] Figure 10 shows a graph 64 in which the mean droplet volume m of printing ink droplets 23 from printhead nozzle 30.1.4 in nozzle row 30.1 of the nozzle head 12 described with reference to Figure 2 is plotted as a first printhead operating state as a function of the number n of adjacent inactive printhead nozzles. Graph 64 shows that the mean droplet volume m of printing ink droplets 23 increases as more printhead nozzles adjacent to printhead nozzle 30.1.4 in nozzle row 30.1 are inactive. The mean ink droplet volume m of the ink droplets 23 produced by the printhead nozzle 30.1.4 depends on whether printhead nozzles adjacent to a printhead nozzle 30.1.4 in the nozzle row 30.1 simultaneously supply ink or not. The same applies to all printhead nozzles 30.nm of the nozzle head 12 arranged in a nozzle row 3.n with n = 1, 2, 3 or n = 1.

[0164] Figure 11a shows a control rule 47 for controlling the printhead nozzles 30.nm, n = 1, 2, 3...; m = 1, 2, 3, ... in the printhead nozzle arrangement 26 of the printhead 12, which causes an operating state of the printhead 12 in which printhead nozzles 30.1.m, 30.1.m+4, 30.1.m+8 as well as 30.2.m, 30.2.m+4, 30.2.m+8, 30.3.m, 30.3.m+4, 30.3.m+8 and 30.4.m, 30.4.m+4 and 30.4.m+8 are active for the simultaneous provision of a drop of printing ink. The tax regulation 47 has the following effect on the printhead nozzles 30.1.m-3, 30.1.m-2, 30.1.m+1, 30.1.m+2, 30.1.m+5, 30.1.m+6, 30.1.m+7, 30.1.m-9, 30.1.m+10, 30.1.m+11 as well as 30.2.m-3, 30.2.m-2, 30.2.m+1, 30.2.m+2, 30.2.m+5, 30.2.m+6, 30.2.m+7, 30.2.m-9, 30.1.m+10, 30.2.m+11; 30.3.m-3, 30.3. m-2, 30.3. m+1, 30.3. m+2, 30.3. m+5, 30.3. m+6, 30.3.m+7, 30.3. m-9, 30.3.m+10, 30.3. m+11 and 30.4. m-3, 30.4. m-2, 30.4. m+1, 30.4. m+2, 30.4. m+5, 30.4.m+6, 30.1. m+7, 30.4. m-9, 30.4.m+10, 30.4.m+11, that these are inactive.According to this control rule, an operating state of the printhead 12 is set in which only every fourth printhead nozzle in a nozzle row of the printhead is active for the simultaneous generation of ink droplets, while the remaining printhead nozzles of the printhead 12 are inactive. This operating state results in the ink droplets 23 generated by the printhead nozzles of the printhead 12 having a mean droplet volume m corresponding to graph point 66. In contrast, Fig. 11b shows a control rule 47 for controlling the printhead nozzles 30.nm, n = 1, 2, 3... ; m = 1, 2, 3, ... in the printhead nozzle arrangement 26 of the printhead 12, which causes an operating state of the printhead 12 in which printhead nozzles 30.1. m, 30.1. m+1, 30.1. m+2, 30.1.m+3 and printhead nozzles 30.2. m, 30.2. m+1, 30.2. m+2, 30.2. m+3, 30.3. m, 30.3.m+1, 30.3.m+2, 30.3.m+3 and 30.4. m, 30.4.m+1, 30.4.m+2, 30.4.m+3 are activated for the simultaneous provision of a drop of print ink. Control rule 47 causes the printhead nozzles 30.1.m-3, 30.1.m-2, 30.1.m+4, 30.1.m+5, 30.1.m+6, 30.1.m+7, 30.2.m-3, 30.2.m-2, 30.2.m+4, 30.2.m+5, 30.2.m+6, 30.2.m+7, 30.3.m-3, 30.3.m-2, 30.3.m+4, 30.3.m+5, 30.3.m+6, 30.3.m+7, 30.4.m-3, 30.4.m-2, 30.4. m+4, 30.4. m+5, 30.4. m+6, 30.4. m+7, that these are inactive. According to this control rule, an operating state of the printhead 12 is set in which four consecutive printhead nozzles in a nozzle row of the printhead are active for the simultaneous generation of ink droplets, while the remaining printhead nozzles of the printhead 12 are inactive. This operating state results in the ink droplets 23 generated by the printhead nozzles of the printhead 12 having a mean droplet volume m corresponding to graph point 68.

[0165] Fig. 12 is a graph 70 in which the relative number of printhead nozzles n / N is plotted when a layer of constant thickness is produced on a substrate by means of the printhead 12 by providing printing ink droplets 23.

[0166] The mean droplet volume m of printing ink droplets 23 from printhead nozzles 30.nm of the printhead nozzle arrangement 26 of the printhead 12 depends, firstly, on the relative number n / N of printhead nozzles 30.nm simultaneously producing printing ink droplets 23. Secondly, the mean droplet volume m of printing ink droplets 23 from the printhead nozzle arrangement 26 of the printhead 12 depends on whether the printhead nozzles 30.nm in the printhead nozzle arrangement 26 are operated in such a way that, with the same number of printing ink droplets 23 provided by the printhead 12 per unit of time, the distance between printhead nozzles 30.nm in a nozzle row 30.1, 30.2, 30.3, 30.4, which simultaneously provide a printing ink droplet, is as large as possible.

[0167] The graph points 72 show measurement points for the mean droplet volume m of printing ink droplets 23 when a layer is produced on a substrate by means of the printhead nozzle arrangement 26 of the printhead 12 by supplying printing ink droplets 23, without taking into account, when controlling the printhead nozzles 30 nm, whether and to what extent printhead nozzles 30.1, 30.2, 30.3, 30.4 simultaneously produce printing ink droplets 23. The inventors have recognized that the position in the graph 68, which depends on the relative number n / N of printing ink droplets 23 simultaneously producing printing ink droplets 23, can be described by a regression line 74. One idea of ​​the invention is therefore that for a given relative number n / N of printhead nozzles 30.nm, a mean drop volume m of printing ink droplets 23 from printhead nozzles 30.nm of the printhead nozzle arrangement 26 of the printhead 12 can be calculated by linear extrapolation of the graph points 70.

[0168] Furthermore, in Fig. 12, graph points 76 represent measurement points for the mean droplet volume m of printing ink droplets 23 when a layer is produced on a substrate by means of the printhead nozzle arrangement 26 of the printhead 12 by providing printing ink droplets 23, in that the printhead nozzles 30.nm of the printhead 12 are controlled for this purpose by means of a control rule which is determined in the algorithm 48 described above with reference to Fig. 10.

[0169] One insight of the invention, as shown in Fig. 12, is that for a given relative number n / N of printhead nozzles 30 nm of the printhead that simultaneously produce a printing ink droplet 23, the algorithm 48 described with reference to Fig. 10 maximizes a mean volume of the printing ink droplets 23. Furthermore, it is a finding of the invention that, as can be seen in Fig. 12, the mean droplet volume m of printing ink droplets 23 provided by the printhead nozzles 30 nm can be described with very good accuracy by a regression line 78. One idea of ​​the invention is therefore to use this knowledge to calculate with high accuracy a mean droplet volume m of printing ink droplets 23 for a given relative number n / N of printhead nozzles 30.nm of the printhead 12, when the printhead nozzles 30.n.m of the printhead 12 for building up a layer by applying printing ink in the form of drops by means of a control rule 47, which is determined in an algorithm described with reference to Fig. 10 to a predetermined location-dependent layer thickness.

[0170] The computer unit 32 of the device 10 for manufacturing an optical element contains a computer program that includes a program routine for determining a control instruction 47, which, by means of the algorithm described above with reference to Fig. 9, converts a grayscale image 44 describing a local layer thickness into a black and white image that indicates which printhead nozzles 30.1.1, 30.1.2, ... provide a droplet of print ink 44 in an area element 42 nm with n = 1, 2, 3 ... and m = 1, 2, 3, ... when printing ink is applied by means of the nozzle head 12. This control instruction is fed to the controller 37 of the computer unit 32, so that the piezo actuators of the printhead nozzles 30.1.1, 30.1.2, 30.1.3 and 30.1.4 as well as 30.2.1, 30.2.2, 30.2.3, ... 30.3.1, ... 30.4.1, ...the printhead nozzle arrangement 26 and the xy displacement unit 14 are controlled in such a way that printing ink drops 23 are applied to the substrate 18 arranged on the table 16 in the device 10 for the production of an optical element in accordance with the control instruction.

[0171] It should be noted that in a modified embodiment of the device 10, it may be provided that the program routine for determining the control rule 47, which is determined by means of the above with reference to the Fig.

[0172] The algorithm described in section 9 transforms a grayscale image 44 describing a local layer thickness into a black and white image that indicates which printhead nozzles 30.1.1, 30.1.2, ... provide a print ink droplet 44 in a surface element 42.nm with n = 1, 2, 3 ... and m = 1, 2, 3, ... when applying print ink by means of the nozzle head 12, wherein an assumed print ink droplet volume v is determined as an operating state variable characterizing an operating state of the printhead 12, which corresponds to a mean relative number n / N of simultaneously active printhead nozzles 30.nm in a section of the printhead nozzle arrangement 26, determined for a given mean local thickness t(x,y) in a region of a layer to be applied, which are used to generate print ink droplets 23.

[0173] In summary, the following preferred features of the invention are particularly noteworthy:

[0174] The invention relates to a method for producing a coated lens (10), wherein the method comprises at least the following steps:

[0175] i. Providing a substrate 18,

[0176] ii. Providing a three-dimensional model 38 of the lens,

[0177] iii. Digital cutting of the three-dimensional model 38 from step ii.

[0178] in individual layers 40.1 , 40.2, 40.3, ... , each of which is divided into a grid (41 ) with surface elements 42.nm, m= 1, 2, 3, ...; m=1, 2, 3, ... ,

[0179] iv. Providing at least one printing ink, preferably 3D printing ink, v. Building the lens from the sum of the individual layers 40.1, 40.2, 40.3, ... from step iii. by means of a printing process on the substrate 18, in which the printing ink is applied in the form of droplets to defined surface elements 42.nm, n= 1, 2, 3, ...; m=1, 2, 3, ... of the grid 41 of a single layer, which generates a printhead nozzle arrangement 26 with several printhead nozzles 30.nm, n=1 , 2, 3, ; m=1 , 2, 3, ... .

[0180] According to the invention, the printhead nozzles 30.nm, n=1, 2, 3, ...; m=1, 2, 3, ... of the printhead nozzle arrangement 26 are controlled taking into account an assumed ink droplet volume v. Reference numeral list:

[0181] 10 Device for manufacturing an optical element 12 Print head

[0182] 14 xy-shift unit

[0183] 16 Table

[0184] 18 Substrat

[0185] Level 20

[0186] 22 storage containers

[0187] 23 drops of printing ink

[0188] 24 spectacle lens

[0189] 26 Printhead nozzle arrangement

[0190] 30.nm printhead nozzle

[0191] 30th row

[0192] 32 computer units

[0193] 36 Triangle

[0194] 37 Even

[0195] 38 model

[0196] 40, 40th shift

[0197] 41 grids

[0198] 42.nm with n,m = 1, 2, 3

[0199] Surface element

[0200] 42.1.0, 42.2.0, 42.3.0, ...

[0201] Line

[0202] 42.0.1, 42.0.2, 42.0.3, ...

[0203] Split

[0204] 43 area

[0205] 44 grayscale image

[0206] 45 Arrow

[0207] 45a, 45b, 45c,45d, 45e, 45e stage

[0208] 46 area

[0209] 47 Tax Regulation

[0210] 48 Algorithm

[0211] 50 Counting path

[0212] 52 Routine

[0213] 54 Comparison level for thickness

[0214] 56 Functional level

[0215] 58 Error calculation level

[0216] 60 correction level

[0217] 62 Comparison stage for corrected thickness 64, 70 Graph

[0218] 66, 68, 72, 76 Graph point

[0219] 74, 78 Regression line

[0220] m mean printing ink drop volume p assumed change in layer thickness v assumed printing ink drop volume

Claims

- 39 - Patent claims 1. A method for manufacturing an optical element, comprising the following steps:

1. Providing a substrate (18), ii. Providing a three-dimensional model (38) of the optical element, iii. Digital slicing of the three-dimensional model (38) from step ii. into individual layers (40.1, 40.2, 40.3, ...), each of which is divided into a grid (41) with surface elements (42.nm, n= 1, 2, 3, ...; m=1, 2, 3, ...), iv. Provision of at least one printing ink, preferably 3D printing ink, v. Construction of the optical element from the sum of the individual layers (40.1, 40.2, 40.3, ...) from step iii. by means of a printing process on the substrate (18), in which the printing ink is applied in the form of droplets to defined surface elements (42.nm, n= 1 , 2, 3, ... ; m=1 , 2, 3, ...) of the grid (41) of a single layer, which generates a printhead nozzle arrangement (26) with several printhead nozzles (30.nm, m=1, 2, 3, ...; m=1, 2, 3, ...), characterized by the fact that the printhead nozzles (30.nm, n=1, 2, 3, ...; m=1, 2, 3, ...) of the printhead nozzle arrangement (26) are controlled taking into account an assumed printing ink droplet volume v.

2. Method according to claim 1, characterized in that the printhead nozzles (30.nm, n=1, 2, 3, ...; m=1, 2, 3, ...) of the-40 - The printhead nozzle arrangement (26) is controlled by a control rule (47) which assigns a printhead nozzle (30.nm, n=1, 2, 3, ...) to the surface element (42.nm, n= 1, 2, 3, ...) of the raster (41) of a layer (40.1, 40.2, 40.3, ...) and which causes the generation of a droplet (23) of printing ink by means of the assigned printhead nozzle (30.nm, n=1, 2, 3, ...; m=1, 2, 3, ...) depending on a criterion that a predetermined thickness t(n,m) of the layer (40.1 , 40.2, 40.3, ...) in the surface element (42.nm, n= 1 , 2, 3, ...) ... ; m=1, 2, 3, ...) of the grid and a thickness error e(n,m) is taken into account, which is determined from a comparison of the thickness t(n,m) of the layer (40.1, 40.2, 40.3, ...) specified for a surface element (42.nm, n= 1 , 2, 3, ... ; m=1, 2, 3, ...) of the grid (41) of a single layer (40.1, 40.2, 40.3, ...) and an assumed thickness increment DZ, for which the following applies: DZ = 0 if no drop is produced, and DZ = constant when a drop is produced.

3. Method according to claim 2, characterized in that the thickness error e(n,m) of the predetermined thickness t(n,m) of the layer (40.1, 40.2, 40.3, ...) in the surface element (42.nm, n= 1, 2, 3, ...; m=1, 2, 3, ...) of the grid (41) is added to a predetermined thickness t(n,m) of at least one further surface element (42.nm, n= 1, 2, 3, ...; m=1, 2, 3, ...) of the grid (41) by applying a correction factor to the predetermined thickness of the layer in order to obtain a corrected thickness for this surface element (42.nm, n= 1, 2, 3, ...; m=1, 2, 3, ...) as a predetermined thickness t(n,m).

4. Method according to claim 3, characterized in that the thickness error e(n,m) of the predetermined thickness t(n,m) of the layer (40.1, 40.2, 40.3, ...) in the surface element (42.nm, n= 1, 2, 3, ...; m=1, 2, 3, ...) of the grid (41) to a predetermined thickness t(n,m) is reduced to at least two, preferably at least three, particularly preferably at least four, most preferably five, six, 41 - seven or distributed over eight further surface elements (42.nm, n= 1, 2, 3, m=1, 2, 3, ...) of the grid (41).

5. Method according to claim 3 or 4, characterized in that the grid (41) has rows (42.1.0, 42.2.0, 42.3.0, ... 42.N.0) and columns (42.0.1, 42.0.2, 42.0.3, ..., 42.0.M) in which the surface elements (42.nm, n= 1, 2, 3, ... N; m=1, 2, 3, ... M) are arranged, wherein the printhead nozzles (30.nm, n=1, 2, 3, ...; m=1, 2, 3, ...) of the printhead nozzle arrangement (26) are displaced relative to the substrate (18) in a direction (45) parallel to the columns (42.0.1, 42.0.2, 42.0.3, ..., 42.0.M) and wherein the specified thickness t(n,m) of the layer (40.1, 40.2, 40.3, ...) in a surface element (42.nm, n= 1, 2, 3, ...; m=1 , 2, 3, ... ) of the grid (41 ) the thickness error e(n,m) - the specified thickness t(n,m) of the layer (40.1, 40.2, 40.3, ...) in the surface element 42.nm, n= 1 , 2, 3, ... , N-1 ; m= 2, 3, 4, ... , M-1) of the grid (41) to a given thickness t(n,m) to a first further surface element (42.n.m+1, n= 1, 2, 3, ..., N-1; m=1, 2, 3, ..., M-1) of the grid (41) applying a first correction factor to the given thickness of the layer (40.1, 40.2, 40.3, ...) which is adjacent to the surface element (42.nm, n= 1, 2, 3, ..., M-1; m= 2, 3, 4, ..., M-1) in a row (42.1.0, 42.2.0, 42.3.0, ...) of the grid (41 ) if the surface element (42.n.m+1, n= 1, 2, 3, ..., N-1; m= 2, 3, 4, ... M-1) is not a surface element (42.nm, n= 1, 2, 3, ..., N-1; m= 2, 3, 4, ..., M-1) in a last row (42.N.0) or in a first column (42.0.1) or in a last column (42.0.M) of the grid (41) in order to use the first further surface element (42.nm, n= 1 , 2, 3,. ... ; m= 2, 3, 4, ..., M-1) as a given thickness t(n,m) to obtain a corrected thickness, and. - the specified thickness t(n,m) of the layer (40.1, 40.2, 40.3, ...) in the surface element (42.nm, n= 1 , 2, 3, ... , N-1 ; m=2, 3, 4, ... , M-1) of the grid (41) is added to a second surface element (42.n-1.m+1, n= 1, 2, 3, ...N-1; m= 2, 3, 4, ...M-1) of the grid (41) with a specified thickness t(n,m) by applying a second correction factor to the specified thickness of the layer (40.1, 40.2, 40.3, ...) which is added to the surface element 42. nm, n= 1, 2, 3, ..., N-1; m= 2, 3, 4, ..., M-1) in a column (42.0.1, 42.0.2, 42.0.3, ...) of the grid (41 ) is adjacent if the area element (42.n.m+1, n= 1, 2, 3, ...; m=1, 2, 3, ...) is not an area element (42. nm, n= 1, 2, 3, ...; m=1, 2, 3, ...) in a last row (42.N.0) or in a first column (42.0.1) or in a last column (42.0.M) of the grid (41) in order to provide for the second further area element 42. nm, n= 1, 2, 3, ..., N-1; m=2, 3, 4, ...M-1) as a given thickness t(n,m) to obtain a corrected thickness, and - the given thickness t(n,m) of layer 40.1, 40.2, 40.3, ...) in the surface element (42. nm, n= 1, 2, 3, ...; m=1, 2, 3, ...) of the grid to a given thickness t(n,m) a third further surface element (42.n.m+1), n= 1, 2, 3, ..., N-1; m=2, 3, 4, ..., M-1) of the grid (41 ) applying a third correction factor to the specified thickness of the layer (40.1, 40.2, 40.3, ...) that is adjacent to the second further surface element in a row (42.1.0, 42.2.0, 42.3.0, ...) of the grid (41), if the surface element (42.n.m+1, n= 1, 2, 3, ...; m=1, 2, 3, ...) is not a surface element (42. nm, n= 1, 2, 3, ...; m=1, 2, 3, ...) in a last row (42.N.0) or in a first column (42.0.1) or in a last column (42.0.M) of the grid (41), in order to provide a specified thickness for the third further surface element to obtain a corrected thickness t(n,m), and. - the specified thickness t(n,m) of the layer in the surface element (42. nm, n= 1, 2, 3, ...; m=1, 2, 3, ...) of the grid (41) to a specified thickness t(n,m) of a fourth further surface element (42.n+1.m+1 , n= 1 , 2, 3, ... , N-1 ; m=2, 3, 4, ... , M-1 ) of the grid (41 ) is added to the specified thickness of the layer (40.1 , 40.2, 40.3, ... ) by applying a fourth correction factor, which is adjacent to the third further surface element (42. n. m+1, n= 1, 2, 3, m=1, 2, 3, ...) in a row of the grid (41), if the surface element (42. n. m+1, n= 1, 2, 3, m=1, 2, 3, ...) is not a surface element (42.nm, n= 1, 2, 3, m=1, 2, 3, ...) in a last row (42.N.0) or in a first column (42.0.1) or in a last column (42.0.M) of the grid (41) in order to obtain a corrected thickness for the fourth further surface element (42.nm, n= 1, 2, 3, ..., N-1; m=2, 3, 4, ..., M-1) as a given thickness t(n,m).

6. The method according to claim 5, characterized in that the criterion is: tkorr[n,m] > k tmax[n,m], with tcorr[n+1, m] = t[n+1, m] + e[n,m] tcorr[n-1, m+1] = t[n-1 , m+1] + c2e[n,m] tcorr[n, m+1] = t[n, m+1] + c3e[n,m] tcorr[n+1, m+1] = t[n+1, m+1] + c4e[n,m] where e[n,m] := t[n,m] - p where p is the change in the layer thickness of the layer to be printed at an area element in the nth column and the mth row of the grid caused by the application of a single drop of printing ink with the assumed printing ink drop volume v to that area element,- 44 - where tmax(n,m) is a maximum layer thickness that can be printed onto the substrate using the printhead nozzles of the printhead nozzle assembly, where t(n,m) is a layer thickness specified for the surface element in the nth column and the mth row of the layer grid, where tkorr(n,m) is a layer thickness corrected for the surface element in the nth column and the mth row of the layer's grid and where: SW = 1, preferably e.g. = 7 and c2= 5 / ^ and c3= and c4= i6' and 0 < k < 1 , preferably k = .

7. Method according to claim 5, characterized in that the thickness error e(n,m) of the predetermined thickness t(n,m) of the layer (40.1, 40.2, 40.3, ...) in the area element (42.nm, n= 1, 2, 3, ...; m=1, 2, 3, ...) of the grid (41) is added to a further area element (42.nm, n= 1, 2, 3, ... ; m=1, 2, 3, ...) of the grid (41) with a predetermined thickness t(n,m) by applying a first correction factor to the predetermined thickness of the layer (40.1, 40.2, 40.3, ...) which is arranged in the same row of the grid (41) as the area element and which, during a printing process, prints ink in the form of a droplet (23) from a printhead nozzle. (30.nm, m=1, 2, 3, ...; m=1, 2, 3, ...) of the printhead nozzle order (26) can be obtained, which is arranged adjacent to a printhead nozzle (30.nm, n=1, 2, 3, ...; m=1, 2, 3, ...) in a nozzle row of the printhead nozzle arrangement (26), the printing ink in form-45 - can provide a drop (23) for the surface element (42.nm, n= 1 , 2, 3, ; m=1 , 2, 3, ...).

8. Method according to claim 7, characterized in that the criterion is: tkorr(n,m) > tmax(n,m), with tkorr[n, m+1] := t[n, m+1] + 0.4e[n,m], tkorr[n, m+z] := t[n, m+z] + 0.3e[n,m], tkorr[n+1, m-1] := t[n+1, m-1] + 0.3e[n,m], tcorr[n+1, m] := t[n+1, m] - 0.1e[n,m], tcorr[n+1, m+1] := t[n+1, m+1] + 0.1e[n,m], where ze N > 1 and e[n,m] = t[n,m] - p, where p is the change in the layer thickness of the layer to be printed on a surface element (42.nm, n= 1, 2, 3, ...; m=1, 2, 3, ...) in the nth column and the mth row of the grid caused by the application of a single printing ink droplet (23) with the assumed printing ink droplet volume v to this surface element, where tmax[n,m] is a maximum layer thickness that can be printed onto the substrate (18) using the printhead nozzles (30.nm, n=1, 2, 3, ...; m=1, 2, 3, ...) of the printhead nozzle arrangement (26),- 46 - where t[n,m] is a layer thickness specified for the surface element in the nth column and the mth row of the grid (18) of layer (40.1 , 40.2, 40.3, ... ). where tkorr[n,m] is a layer thickness corrected for the surface element in the nth column and the mth row of the grid (41) of the layer (40.1, 40.2, 40.3, ...), and where: 0 < k < 1 , preferably k = , where the printing direction is given by arrow 45 orthogonal to lines 42.nm and the running direction of the control regulation.

9. Method according to one of claims 1 to 8, characterized in that the printhead nozzle arrangement (26) in a nozzle row comprises a plurality of printhead nozzles (30.nm, n=1, 2, 3, ...; m=1, 2, 3, ...) arranged adjacent to one another and simultaneously controllable, each of which produces a printing ink droplet (28) when activated, wherein the assumed droplet volume v is supplied by means of the printhead nozzles 30.nm, n=1, 2, 3, ...; m=1, 2, 3, ...) generated printing ink droplets (28) enter into a probability with which adjacent printhead nozzles (30.nm, n=1, 2, 3, ...; m=1, 2, 3, ...) simultaneously generate a droplet (23) of printing ink, so that a single layer in a defined area element of its grid (41) has a predetermined thickness.

10. Method according to any one of claims 1 to 9, characterized in that the assumed printing ink droplet volume v is an average volume for printing ink droplets (28) of the printhead nozzle arrangement (26) produced by individual printhead nozzles (30 nm, n=1, 2, 3, ...; m=1, 2, 3, ...) of the printhead nozzle arrangement (26). - 47 - 11. Method according to claim 10, characterized in that the average printing ink droplet volume is determined gravimetrically for the printhead nozzles (30.nm, n=1, 2, 3, m=1, 2, 3, ...) of the printhead nozzle arrangement (26).

12. Method according to claim 10, characterized in that the average printing ink droplet volume for the printhead nozzles (30.nm, n=1, 2, 3, ...; m=1, 2, 3, ...) of the printhead nozzle arrangement (26) is determined from at least one operating state variable that characterizes an operating state of the printhead nozzle arrangement.

13. Method according to claim 12, characterized in that the operating state variable is at least one variable from the group consisting of pressure frequency, mean number of printing ink drops per area on the substrate (18), temperature of the printhead (12), profile of a control voltage for printhead nozzles, and printing ink viscosity.

14. Method according to one of claims 1 to 13, characterized in that the optical element is an optical element from the group consisting of lens, intraocular lens, contact lens, and spectacle lens.

15. Optical element, in particular an optical element from the group consisting of lens, intraocular lens, contact lens, spectacle lens, manufactured by a method according to any one of claims 1 to 13.

16. Device for manufacturing an optical element with a printhead (12) with printhead nozzles (30 nm) for supplying printing ink droplets (23), with a table (16) designed to receive a substrate (18) and which can be displaced relative to the printhead (12) in a plane (20) in two mutually perpendicular directions x, y, and with a computer (32) which has a computer program for controlling the printhead nozzles (30 nm),-48- characterized by the fact that The computer program is used to control the printhead nozzles (30.nm) taking into account an assumed printing ink droplet volume v.

Images