Ink printing method for continuously printing a top side and a side face of a three-dimensional object, an associated computer program and computer-readable storage medium

Abstract

The present invention relates to an ink-jet printing method for continuously printing ink onto at least one portion of a top side (110) and at least one portion of a side face (120) of a three-dimensional (3D) object (100). According to the invention, before the object (100) is printed on, the printing data for the printing nozzles A1 of a first printing nozzle row A are corrected with a first correction factor KA and / or the printing data for the printing nozzles B1 of a second printing nozzle row B are corrected with a second correction factor KB, wherein the first correction factor KA and / or the second correction factor KB are / is determined based on a previously generated comparison printed image, which was generated previously without correction, and wherein the first correction factor KA and / or the second correction factor KB are / is dependent on the distance d of the printed line DA, which was generated by the printing nozzles A1 of the first printing nozzle row A, to the printed line DB, which was generated by the printing nozzles B1 of the second printing nozzle row B, in the previously generated comparison printed image.

Description

[0001] Inkjet printing process for continuously printing a top and a side surface of a three-dimensional object, an associated computer program and a computer-readable storage medium

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to an inkjet printing method for continuously printing at least a portion of a top surface and at least a portion of a side surface of a three-dimensional (3D) object with ink. The present invention also relates to an associated computer program and a computer-readable medium on which the computer program is stored.

[0004] BACKGROUND OF THE INVENTION

[0005] There are a variety of different printing processes, such as offset lithography, flexography, screen printing, gravure printing, and digital printing. Digital printing, such as inkjet printing and xerography, prints a digital image directly onto various media.

[0006] Inkjet printing processes are often used for printing on paper, with a focus on two-dimensional surfaces. However, inkjet printing processes can also be used for other purposes. For example, they can be used to apply a functional layer or pattern to three-dimensional objects, such as applying conductive ink to a system-in-package (SIP) to protect it from electromagnetic interference.

[0007] SIP modules are playing an increasingly important role in the miniaturization of portable electronic devices. Due to the high density of electrical functions built into a SIP module, electromagnetic or electrical interference (EMI) can lead to complete module failure. For this reason, SIP modules must be shielded to prevent EMI radiation from being emitted and received by the SIP module. Traditionally, SIP modules use a metal housing for EMI shielding. However, a metal housing counteracts the goal of miniaturization. Instead of a metal housing, a functional layer can be applied, for example, using a physical vapor deposition (PVD) process. Alternatively, a silver-containing ink can be printed onto the surface of a SIP module using an inkjet printer. After the ink has been printed onto the surface of the SIP module, the ink is, for example,Cured with UV light to form a continuous functional layer on the surface of the SIP module. Other curing methods are also conceivable, such as IR radiation or plasma. Before the printing process, the surface of the SIP module can be pretreated for cleaning purposes. Plasma can also be used here.

[0008] Additive inkjet printing processes for printing a functional print pattern (or other layer) onto a three-dimensional object, such as an electronic device, differ significantly from inkjet printing processes used for graphical purposes. While in graphical printing processes the areal density (g / cm2) and, if applicable, the color tone of the ink applied to a specific substrate, such as paper, is the most important factor, when printing a functional print pattern onto an electronic device, such as a SIP module, the layer thickness, among other things, is of great importance. The final layer thickness, the material density (g / cm3), and the structural uniformity and homogeneity in the thickness directions as well as across the surface of the functional print pattern have a decisive influence on its function, whereby efficiency and economic aspects must also be taken into account.

[0009] However, it has been found that when using inkjet printing to print a layer onto a three-dimensional object, the layer edges on the side surfaces of the three-dimensional object, such as a cuboid electronic component, are usually blurred, i.e. they do not have a clearly defined edge. This blurriness is commonly referred to as waviness. This waviness usually manifests itself in a wavy print edge, which in turn means that the ink layer cannot be printed in the immediate vicinity of conductive components. To prevent electrical short circuits, a safety distance must be maintained. In addition, printing on surfaces that are not plane-parallel to the print head of an inkjet printer can result in inaccurate and wavy print edges.

[0010] US 2019 / 0270306 A1 describes an inkjet printing process in which a height profile of the object to be printed is created, which determines the distance between the object to be printed and each print nozzle of the print head. The firing times from the individual print nozzles are then controlled so that they depend on the relative speed between the object to be printed and each nozzle. In US 11,234,334 B2, any printing inaccuracies are corrected by determining a so-called ideal trajectory, which allows a precise drop impact position on the object to be printed to be achieved using transducer control.

[0011] How the wavy print edges mentioned above come about, or what they result from, will now be explained.

[0012] Typically, the print head of an inkjet printer is mounted relative to the object to be printed (printed object) in such a way that its print nozzle plane, i.e., the plane in which all of the print head's print nozzles are located, is parallel to the printed object. The print head is then moved in a straight line over the printed object so that each print nozzle is the same distance from the top of the printed object.

[0013] This situation is illustrated in Fig. 1, in which the print head 10 with its only schematically indicated print nozzle plane 14 is arranged parallel to a flat, two-dimensional print object 20. The reference symbols A and B indicate print nozzle rows of the print head 10. Each print nozzle row A, B comprises a plurality of print nozzles which are arranged linearly along each print nozzle row A, B and extend into the plane of the page in Fig. 1. The distance of the print nozzle row A to the two-dimensional print object 20 corresponds to SA, and the distance of the print nozzle row B to the two-dimensional print object 20 corresponds to SB. During the entire movement of the print head 10 across the two-dimensional print object 20, i.e. during the entire printing process, the distance SA is equal to the distance SB.Different impact points of the ink droplets on the two-dimensional print object 20 depend exclusively on the mechanically predetermined distance between the print nozzle row A and the print nozzle row B in the print nozzle plane 14 of the print head 10. The distance between the print nozzle rows A, B is a constant value, so that a sharp print edge, e.g., at the extreme left edge in Fig. 1, can be achieved on the two-dimensional print object 20 by firing the ink droplets from the print nozzle row A and the print nozzle row B at different times.

[0014] With reference to Fig. 2, it can be seen how the distance of the individual print nozzle rows A and B from the two-dimensional print object 20 changes when the print head 10 is tilted relative to the two-dimensional print object 20. In the example shown in Fig. 2, the distance SA of the print nozzle row A from the print object 20 is smaller than the distance SB of the print nozzle row B from the print object 20. If the print head 10 remains parallel to the print object 20 over its entire length of movement, from which it follows that the distances SA and SB also remain constant over the entire travel path of the print head 10, the height difference between the two print nozzle rows A and B from the print object 20 can be compensated for by adjusting the firing times of the ink droplets, and a clearly defined print edge can be achieved.Alternatively, a height profile of the print object 20 could be determined before the actual printing process according to US 2019 / 0270306 A1 or an ideal movement path according to US 11,234,334 B2.

[0015] Fig. 3 shows a situation in which the print head 10 is arranged at an angle to the print object 100, but the print object 100 is a three-dimensional print object 100 in contrast to the two-dimensional print object 20 in Fig. 2. The print head 10 is aligned with the top side 110 of the print object 100 by compensating for any height differences between the print nozzle rows A and B by varying the firing times of the ink droplets. The top side 110 of the print object 100, which is positioned on a planar plane 50, serves as the adjustment or reference plane 1000 for this purpose. Using this reference plane 1000, the inclined print head 10 behaves like a parallel print head 10 in Fig. 1, provided that the inclined print head 10 of Fig. 3 moves along a movement path that is parallel to the reference plane 1000.

[0016] However, when printing on the side wall 120 of the print object 100, the distances SA and SB of the print nozzle rows A and B from the side wall 120 are reversed, as can be seen in Fig. 4. In this case, the side wall 120 is at a 90° angle to the top side 110 of the print object 100, causing the print head 10 to "see" the side wall 120 rotated by 90°. This explains why the distance SA' of the print nozzle row A from the side surface 120 is greater than the distance SB' of the print nozzle row B from the side surface 120, while the distance SA of the print nozzle row A from the top side 110 is smaller than the distance SB of the print nozzle row B from the top side 110.

[0017] If the side wall 120 and the top side 110 are now printed in a continuous ("online") printing process, a clearly defined print edge no longer results on the side wall 120 if the print head 10, or more precisely the firing times of the nozzles of the two print nozzle rows A and B, are adjusted to the reference plane 1000, which in this case comprises the top side 110 of the print object 100. In contrast to the side wall 120, a straight, sharp, and clearly defined print edge without significant geometric deviations in the lateral direction (waviness) is obtained on the top side 120, as can be clearly seen in Fig. 5.In other words, a print line DA printed by print nozzle row A on top side 110 of print object 100 lies on the same line as print line DB generated by print nozzle row B on top side 110 of print object 100, while print lines DA and DB on side wall 120 have an offset (waviness) and thus a distance from each other. In order to obtain a clearly defined, straight print edge on side wall 120 as well, a multi-stage process would be necessary according to the prior art. For example, both a height profile of side wall 120 and a height profile of top side 110 could be generated according to US 2019 / 0270306 A1, or alternatively, an ideal trajectory path could be determined according to US 11,234,334 B2.Alternatively, the print head 10 could be aligned to the side wall 120 as a reference plane in a first step, and in a second step, the print head 10 could be aligned to the top side 110 as a reference plane 1000. The print head 10 could be arranged both parallel and inclined to the respective reference plane 1000. However, printing on the side wall 120 and the top side 110 could then only be performed in a multi-stage, non-continuous printing process.

[0018] It is therefore an object of the present invention to provide an inkjet printing method that mitigates or even overcomes the disadvantages existing in the prior art. In particular, it is an aim of the present invention to provide an inkjet printing method that improves the sharpness of the printed edges on both the top and side surfaces of a three-dimensional printed object in a continuous printing process.

[0019] These objects are achieved by the subject matter of the independent patent claims. Optional or preferred features of the present invention are the subject matter of the dependent claims.

[0020] SUMMARY OF THE INVENTION

[0021] According to a first aspect of the present invention, an inkjet printing method is provided for continuously printing at least a portion of a top surface and at least a portion of a side surface of a three-dimensional (3D) object with ink. This method comprises providing a three-dimensional object on a planar plane, providing a printhead having a plurality of print nozzles for ejecting ink in the form of drops, wherein the plurality of print nozzles extend in a two-dimensional print nozzle plane, and wherein a first part of the plurality of print nozzles are arranged in a first print nozzle row and a second part of the plurality of print nozzles are arranged in a second print nozzle row, and wherein the first print nozzle row is spaced from the second print nozzle row in the print nozzle plane, and wherein the print nozzle plane is arranged at an angle α to the planar plane.The method further comprises generating print data for each print nozzle of the plurality of print nozzles for both the top surface portion and the side surface portion of the object to be printed, and causing relative movement between the object and the print head and printing the top surface portion and the side surface portion of the object with ink in a line-like manner.The method according to the invention is characterized in that, before printing the section of the top side and the section of the side surface of the object, the print data for the print nozzles of the first print nozzle row are corrected with a first correction factor and / or the print data for the print nozzles of the second print nozzle row are corrected with a second correction factor, and in that the first correction factor and / or the second correction factor is determined on the basis of a previously generated comparison print image that was previously generated without correction, and in that the first correction factor and / or the second correction factor is dependent on the distance between the print line generated by the print nozzles of the first print nozzle row and the print line generated by the print nozzles of the second print nozzle row in the previously generated comparison print image.

[0022] The present invention is generally suitable for applying any type of coating to a three-dimensional object to be printed (hereinafter referred to as the printed object). Electrically conductive materials are preferably considered as materials for the coating. An example of such an electrically conductive material is preferably a conductive ink, i.e., a type of ink that produces electrically conductive properties during printing and preferably during curing. Examples of such ink types are a silver, gold, titanium, bismuth, nickel, chromium, or copper ink, or an ink containing silver, gold, titanium, bismuth, nickel, chromium, or copper, preferably an ink containing organometallic decomposition compounds (MOD), also known as MOD ink. The conductive ink can also contain conductive particles, e.g., silver, gold, titanium, bismuth, nickel, chromium, or copper particles.

[0023] Such an electrically conductive layer can serve to shield the printed object, preferably from electromagnetic interference (EMI). Such shielding is particularly advantageous when the 3D printed object is an electronic component, for example a 3D electronic assembly, in order to shield against electromagnetic interference (EMI) caused by electromagnetic induction or electromagnetic radiation emanating from an electronic device within the 3D electronic assembly or from an external source. However, the electrically conductive layer can preferably also be designed as a conductor track of an electronic circuit or be shaped such that it assumes a function, e.g., of an antenna in an antenna-in-package (AIP).

[0024] The thickness of the electrically conductive layer is preferably in a range from 0.0001 pm to 100 pm, more preferably in a range from 0.001 pm to 50 pm, even more preferably in a range from 0.1 pm to 5 pm, and even more preferably in a range from 1 pm to 4 pm. For example, if a conductive ink is used as the material for the electrically conductive layer, and so that the electrically conductive layer can act, for example, as an EMI shield, the printing must be carried out in such a way that the conductive ink forms a continuous layer on at least parts of the exposed surfaces of the electronic component, which layer has no gaps larger than a quarter wavelength of the frequency of the external or internal electromagnetic radiation to be blocked.

[0025] After each print run or a certain number of print runs, the electrically conductive layer can be cured. If an ink that requires cross-linking is used, the cross-linked ink can be subjected to a further chemical reduction step, during which metal is deposited in the form of nanoparticles. Any solvents evaporate, and the printed ink is sintered. Curing refers to all of these chemical processes that occur with certain printing inks.

[0026] Once the printed electrically conductive layer has cured, a functional layer is created, preferably with EMI shielding. Curing can be achieved using UV light, for example. Other curing methods are also conceivable, such as oven curing, IR radiation, or plasma. Before the printing process, the surface of the 3D electronic assembly can be subjected to a pretreatment for cleaning purposes, e.g., using plasma.

[0027] The electrically conductive layer may also contain a non-conductive layer, e.g., a protective layer, which protects the conductive layer beneath the protective layer from damage and / or other adverse environmental influences, such as excessive heat and corrosion-promoting substances, e.g., oxygen.

[0028] With the method according to the invention, the electrically conductive layer can be printed only on specific sections or on the entire exposed surface(s) of the electronic component, and the layer thickness can be selectively adjusted to vary across the printed sections of the exposed surface(s) of the electronic component or to be highly uniform and homogeneous. The final layer thickness can be achieved in one or more consecutive prints, naturally depending on the absolute thickness value. In this way, highly effective electrically conductive layers with properties that can be specifically adapted to the needs and requirements of users can be achieved.

[0029] The method of the present invention preferably uses SIPs. In general, however, any electronic component or 3D electronic assembly that must be at least partially covered by an electrically conductive layer, such as an AIP, can be used for the method of the present invention. The shape of the 3D electronic assembly can, in principle, be any desired. Preferably, the shape should have a flat top and flat side surfaces.

[0030] Cuboid or cube-shaped print objects, in which the sides are arranged at a 90° angle to the top, are generally preferred as print objects. However, it is also conceivable that geometrically different print objects could be printed using the inkjet printing process according to the invention, such as three-dimensional objects in the shape of a cylinder, a prism, a truncated cone, or even a truncated pyramid.

[0031] The present invention can in principle be used in any digital inkjet printing process with which conductive and non-conductive layers (layers, print patterns) can be applied with selectively adjustable thickness, high structural uniformity and homogeneity and high throughput.

[0032] Inkjet printers are generally known and can have different configurations specifically tailored to the user's needs. The method of the present invention is carried out using an inkjet printer with one or more print heads. Each print head has a plurality of print nozzles arranged in a print nozzle plane and in a plurality of rows. The invention is not limited to a print head with two print nozzle rows, but can also have multiple print nozzle rows. Each print nozzle row preferably comprises a plurality of print nozzles. The print width of a print head used in the method of the present invention can be selected depending on the size of the printed object, such as a 3D electronic assembly, for example 30.5 cm (12 inches) and larger.

[0033] In the inkjet printing method according to the invention, a comparison print image that was previously generated without the inventive correction is used to correct the print data for the print nozzles. It is important that the comparison print image has the same offset (distance) between two adjacent print lines generated by print nozzles of different print nozzle rows as if the side surface and the top surface, or even just sections thereof, of the print object were printed in a continuous printing process without the inventive correction of the print data. This offset of adjacent print lines in the comparison print image, which occurs without the inventive correction of the print data, will usually be visible on the side surface of the print object.It is also conceivable to align the print head in such a way that the side surface of the print object serves as the reference plane for the comparison print and consequently the offset of the print lines is shown on the top side of the print object.

[0034] According to a preferred embodiment, the comparison print image can be generated by simulation using a geometrically identical object or by printing at least a portion of the top surface or at least a portion of the side surface of an identical object. With the aid of a computer simulation, comparison print images can be obtained or simulated that take into account any differences in height and thus different flight times of the ink droplets. However, in order to account for the influence of gravity on the ink droplets as well as any mutual fluid dynamic effects between the ink droplets, such as surface tensions of the ink droplets, it is advantageous if a comparison print image is obtained experimentally beforehand by printing the side surface and the top surface, or at least portions thereof, in a continuous printing process without correction.Using this real comparison print image, any offset between two adjacent print lines can then be determined experimentally, for example by measuring.

[0035] According to a preferred embodiment, the first correction factor and / or the second correction factor depend on the distance d between the two print lines on the side surface of the object in the previously generated comparison print image. Thus, in the comparison print image, the top side of the print object is used as the reference plane for the print head, so that the offset of adjacent print lines on the side surface becomes apparent.

[0036] According to a preferred embodiment, the first correction factor varies within the first row of print nozzles and / or the second correction factor varies within the second row of print nozzles. By allowing the correction factors for the print nozzles to vary within a print nozzle row, even geometrically more complex three-dimensional print objects with a sharply defined print edge on the side surface (or top surface) can be printed, since any height differences or flight time differences can be compensated for even within a print line.

[0037] According to a preferred embodiment, the first correction factor and / or the second correction factor is determined based on a value k, wherein the value k results from the equation: k = tan ax d.

[0038] The value a is the angle of inclination of the print head relative to the planar plane on which the print object is arranged, and the value d corresponds to the line spacing of the print lines on the side surface or the top surface of an identical print object in the comparison print image. According to another preferred embodiment, the inkjet printing method further comprises the steps of generating three-dimensional geometric surface data of the top surface and the side surface of the three-dimensional object and generating two-dimensional geometric surface data of the top surface and the side surface of the three-dimensional object based on the three-dimensional geometric surface data of the top surface and the side surface of the three-dimensional object. In this embodiment, 3D geometric surface data of the 3D geometry of the print object is first determined or defined.This 3D geometric surface data can be converted into 3D vector graphic data (polygon data), which forms the basis for a digital 3D object file. The conversion of the 3D geometric surface data into 2D geometric surface data is preferably achieved by unwrapping. For this purpose, the exposed surfaces can be defined by a surface mesh. The surface mesh is placed so that it extends through certain points on the surfaces of the printed object. These points preferably define the 3D shape of the printed object to some extent. In the case of a cuboid, these shaping points would be, for example, the edges of the cuboid or the eight vertices of the cuboid.

[0039] According to a preferred embodiment, the two-dimensional geometric surface data of the side surface of the three-dimensional printed object are generated by projecting the side surface of the three-dimensional printed object into a reference plane, wherein the reference plane comprises the plane of the top side of the three-dimensional printed object. According to this embodiment, the side surface is projected into the plane of the top side of the printed object. Thus, there is the same reference plane for both the two-dimensional geometric surface data of the top side and the two-dimensional geometric surface data of the side surface of the printed object. In this way, even more complex three-dimensional shapes with side surfaces that are not at a 90° angle to the top side, as is the case with a cuboid, can be taken into account, since the projection of the side surface into the reference plane comprising the top side is independent of the geometry of the side surface.

[0040] Since the print head's nozzle plane is not parallel to the planar plane on which the print object is arranged, the (unfolded) 2D data of the geometric surface inherently contains distortions due to the fact that the planar plane is not parallel to the print nozzle plane. Since the distances of a 3D cuboid in a perspective view on a 2D plane appear shorter the further they are separated in the real world, the (unfolded) 2D geometric surface data does not necessarily reflect the real distances. Such distortions can then preferably be corrected by projecting the 2D geometric surface data onto the print nozzle plane (plane projection), thereby obtaining 2D print nozzle plane data of the print object. For this purpose, the print nozzle plane can be generated virtually, e.g.with the aid of software, and the correction is performed mathematically using matrix algebra, including rescaling by compression (by a specific factor) and subsequent shearing of the 2D geometric surface data. In this regard, reference is made to European patent application number EP 20 180 763, filed on June 18, 2020, which is incorporated herein by reference in its entirety.

[0041] According to a preferred embodiment, the three-dimensional geometric surface data of the top and side surfaces of the three-dimensional printed object are generated using 3D CAD data or 3D data obtained by an optical scanner. Both the use of 3D CAD data and 3D data obtained by optically scanning the printed object can easily obtain the three-dimensional geometric surface data of the printed object preferably used for generating the digital print file. For example, a large number of 3D CAD data are available in corresponding libraries. However, the printed object can also be optically scanned before each printing process in order to obtain data about its exact three-dimensional shape.

[0042] According to one embodiment of the invention, the firing times of the ink droplets ejected from the plurality of print nozzles vary among each other. In this way, any differences in the height of the print nozzles relative to the sections to be printed on the top and side surfaces of the printed object, and the resulting differences in flight time, can be compensated for.

[0043] According to one embodiment, the angle a between the printing nozzle plane and the planar plane is in a range of 20 to 70°, preferably in a range of 20 to 50°, and more preferably the angle a is equal to 22.5°.

[0044] According to a preferred embodiment, the relative movement between the print object and the print head is a linear, rectilinear movement. The linear, rectilinear movement parallel to the planar plane allows for optimized alignment of the print head or print nozzles to the top surface of the print object, requiring only compensation for the flight time differences (height differences) relative to the side surface of the print object to produce a sharply defined print edge.

[0045] According to a preferred embodiment, during the relative movement between the print object and the print head, the print object is moved relative to the print head. According to this embodiment, only the print object is moved, while the print head remains stationary. This significantly simplifies the structure of the inkjet printer in which the inkjet printing method described here is used.

[0046] According to a preferred embodiment, during the movement of the print object relative to the print head, a side edge connecting two adjacent side surfaces of the print object leads the way. The leading side edge is comparable to the prow of a ship connecting the hull surfaces of the ship. Similarly, the print head sees two adjacent side surfaces simultaneously and does not need to be rotated by a specific angle after printing one side surface and the top surface, allowing another side surface of the print object to be printed subsequently. This allows two side surfaces and the top surface of the print object to be printed in a continuous printing process.

[0047] A second aspect of the present invention relates to a computer program comprising instructions that cause a controller of an inkjet printer to perform the following steps to continuously print at least a portion of a top surface and at least a portion of a side surface of a three-dimensional object with ink.These steps are the generation of print data for each print nozzle of a plurality of print nozzles of a print head of the inkjet printer both for the section of the top surface to be printed and for the section of the side surface to be printed of the object, wherein the plurality of print nozzles extend in a two-dimensional print head plane, and wherein a first part of the plurality of print nozzles are arranged in a first print nozzle row and a second part of the plurality of print nozzles are arranged in a second print nozzle row, and wherein the first print nozzle row is spaced from the second print nozzle row in the print nozzle plane.Furthermore, the step of correcting the print data for the print nozzles of the first print nozzle row with a first correction factor and / or correcting the print data for the print nozzles of the second print nozzle row with a second correction factor is initiated in such a way that the first correction factor and / or the second correction factor is determined on the basis of a previously generated comparison print image that was previously generated without correction, and that the first correction factor and / or the second correction factor is dependent on the distance d of the print line generated by the print nozzles of the first print nozzle row to the print line generated by the print nozzles of the second print nozzle row in the previously generated comparison print image.

[0048] A third aspect of the present invention relates to a computer-readable storage medium having the above-described computer program stored thereon.

[0049] It should be noted that the above embodiments can be combined with one another in any order and regardless of the aspect in question. These and other aspects of the present invention will be explained using the preferred embodiments of the invention described below with reference to the drawings.

[0050] BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Fig. 1 is a schematic representation of a print head arranged parallel to a two-dimensional print object according to the prior art;

[0052] Fig. 2 is a schematic representation of a prior art print head tilted at an angle to a two-dimensional print object;

[0053] Fig. 3 is a schematic representation of a print head tilted at an angle to a three-dimensional print object and printing on its top surface, according to the prior art;

[0054] Fig. 4 is a schematic representation of a print head tilted at an angle to a three-dimensional print object and printing on its side surface, according to the prior art;

[0055] Fig. 5 shows the difference of the printed image on the one hand on the surface (left) and on the other hand on the side surface (right) of the printed object according to the prior art;

[0056] Fig. 6 is a schematic diagram showing the movement of a print head with two rows of print nozzles over a three-dimensional print object;

[0057] Fig. 7 shows the projection of the side surface into the plane of the top surface of a three-dimensional printed object;

[0058] Fig. 8 shows the offset of the print lines produced by two rows of print nozzles on the side surface of a three-dimensional print object according to the prior art;

[0059] Fig. 9 shows an erroneously performed correction of the print data for the print nozzles of the print nozzle row B according to a preferred embodiment of the invention;

[0060] Fig. 10 shows a correctly executed correction of the print data for the print nozzles of print nozzle row B according to a preferred embodiment of the invention; Fig. 11 shows a merely suboptimal correction of the print data for the print nozzles of print nozzle row B;

[0061] Fig. 12 shows a further suboptimal correction of the print data for the print nozzles of print nozzle row B;

[0062] Fig. 13 shows the print lines produced by the print nozzles of the print nozzle row A and B on the one hand on the top side (left) and on the other hand on the side wall of a three-dimensional print object with correction according to a preferred embodiment of the invention; and

[0063] Fig. 14 shows a comparison of the print image produced on the side surface without correction (left according to the prior art) and with correction (right according to a preferred embodiment of the invention).

[0064] DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0065] The present invention is based on the finding that when printing on the side surface, which is at an angle, preferably 90°, to the top side, and subsequently on the top side of a three-dimensional print object, an offset of the print image on the top side or the side wall occurs at the outermost printing edge, depending on whether the print head is aligned with the top side or the side wall. A print head aligned with the top side of the three-dimensional print object is understood to mean that the firing times of the ink droplets from the print nozzles arranged in rows, all of which are arranged in a two-dimensional print nozzle plane, can be varied such that any offset on the top side of the print object can be compensated for. An offset would also occur on the top side due to the physical spacing of the print nozzle rows in the print nozzle plane.

[0066] Since the height differences are reversed when the print head is aligned to the top side of the print object (see comparison of Fig. 3 and Fig. 4), the invention performs a correction of the print data (so-called "rowshift") for the print nozzles of each print nozzle row. The correction factor used can be constant for each nozzle in a print nozzle row, but can also vary within a print nozzle row.

[0067] Fig. 6 shows schematically the movement of a print head 10 over a three-dimensional object (print object) 100, specifically at different times t1, t2, t3. The print head 10 comprises a plurality of print nozzles 12 arranged in rows in a two-dimensional print nozzle plane 14. In the print head 10 shown in Fig. 6, the print nozzle row A comprises a total of eight print nozzles 12, which are designated as a group with the reference symbol A1. The print nozzle row B in the example shown in Fig. 6 also comprises eight print nozzles 12, which are designated as a group with the reference symbol B1. The number of print nozzles 12 per row A, B can vary within the meaning of the invention. Likewise, the print head 10 can have more than just two print nozzle rows A, B.

[0068] The print nozzle rows A, B are spaced apart from one another in the print nozzle plane 14. The reason for this is that the ink droplets ejected from the print nozzles 12 must not influence each other fluid-dynamically during ejection, as otherwise their trajectory would change unpredictably. For this reason, the print nozzles A1 of the print nozzle row A are arranged offset from the print nozzles B1 of the print nozzle row B. In other words, the print nozzle of the print nozzle row B designated by the number "1" in Fig. 6 is arranged centrally between the print nozzles 1 and 2 of the print nozzle row A in the longitudinal direction of the print nozzle rows A, B. The same applies to the remaining print nozzles A1 of the print nozzle row A.

[0069] As can be seen in Fig. 6, not all print nozzles 12 "see" only the top side 110 or only the side surface 120 of the print object 100 at a given time t1, t2 or t3. Depending on their position within each print nozzle row A, B and their position during the printing process (during the printing process, the print object 100 preferably moves relative to the print head 10), individual print nozzles 12 can already print the top side 110, while other print nozzles 12 of a different print nozzle row A, B or even print nozzles 12 within the same print nozzle row A, B are still printing the side wall 120, for example at time t2.

[0070] The table below shows very clearly at which time t1, t2 and t3 which of the print nozzles 12 of the print nozzle row A and the print nozzle row B, marked with Arabic numerals, “see” the side wall 120 and the top side 110 of the print object 100.

[0071] There is thus a temporal asynchrony in that, at a given time, print nozzles 12 of a print nozzle row A or B "see" the top side 110, while other print nozzles 12 of the same print nozzle row A or B already "see" the side wall 120. To compensate for this temporal asynchrony, the print data for each print nozzle 12 is dynamically corrected. For each print line DA, DB (Fig. 8), it is determined which print nozzle row A, B the respective print line DA, DB is assigned to.

[0072] Print line DA, DB refers to the line in the print image on the side wall 120 (or on the top side 110) of the print object 100 that was printed by the corresponding print nozzle row A or B. In other words, print nozzle row A prints print line DA, and print nozzle row B prints print line DB.

[0073] The output of an ink droplet from the respective print nozzle row A, B is then manipulated such that the firing time of the ink droplet is changed based on the determined correction factor KA, KB. Here, the correction factor KA is used to correct the print data for the print nozzles A1 of the print nozzle row A, and the correction factor KB is used to correct the print data for the print nozzles B1 of the print nozzle row B. As a result of the correction of the print data for the print nozzles A1, B1 of the print nozzle rows A, B, described in detail below, a sharp, clearly defined straight line (print edge) with reduced waviness is obtained not only on the top side 110, but also on the side wall 120 of the print object 100.

[0074] It is understood that the impact of the ink droplets on the side wall 120 can vary from print nozzle to print nozzle within a print nozzle row A, B. By digitally manipulating the print data, selectively with the aid of a constant or variable correction factor, the dynamic printing of the top side 110 and at least one side wall 120 with reduced waviness is enabled in a continuous printing process. This is also enabled regardless of the angle of inclination a of the print head 10 to the planar plane 50 on which the print object 100 is arranged. The prerequisite for this is that the top side 110 of the print object 100 is parallel to the planar plane 50. The angle of inclination a of the print head relative to the planar plane 50 only changes the flight times or the distances SA and SB.

[0075] As shown in Fig. 7, preferably the sidewall 120 is projected (unfolded) into the plane 1000 of the top surface 110, resulting in a virtual (projected) sidewall 120V.

[0076] Figures 8-12 show an example of how the correction factor KA, KB according to the invention can preferably be determined experimentally.

[0077] Fig. 8 shows the print lines DA, DB generated by the print nozzles A1, B1 of the print nozzle rows A, B on the side surface 120 of the print object 100. It can be seen that the print line DA is spaced from the print line DB on the side wall 120 by a distance d. This print image with the offset d is referred to as a comparison print image because it is generated without correcting the print data for the print nozzles A1, B1 of the print nozzle rows A, B. In an example in which the inclination angle was 22.5° and the print resolution was 2400 dpi and the side wall 120 was arranged at an angle of 90° to the top side 110 of the three-dimensional print object 100 and the print head 10 was aligned with the top side 110 of the print object 100, the distance d (offset) was approximately 120 pm. This was measured experimentally. Due to possible measurement inaccuracies (e.g.Due to the resolution of the optical microscope used) as well as the physical and chemical ratios of ink to the surface of the object, the measured value of 120 pm is subject to an uncertainty of approximately 50 pm. It is also conceivable to determine this offset using a simulation. However, not all fluid dynamic effects, such as the surface tension of the ink droplets, the mutual influence of the ink droplets on each other and the resulting altered trajectory to the sidewall, as well as the effect of gravity on the ink droplets, can be accounted for in a simulation.

[0078] To achieve a "rowshift" or a correction of this offset d, the virtual offset k is used, which results from the projection of the measured offset d into the plane 1000 of the top side 110 of the printed object 100. This is done using the equation: k = tan ax d.

[0079] In the example given here (a = 22.5°, d = 120 pm), the projected virtual offset (distance) k is equal to 50 pm. In other words, a projected virtual offset of 50 pm results in an offset of 120 pm on the side surface 120. In this example, the encoder associated with the print head 10 can only shift one of the two virtual print lines DA or DB in steps of 10.5 pm by correcting the print data for the nozzles A1, B1 of the print nozzle rows A, B. Under virtual print line DA V , DB V means the projection of the (real) print line DA, DB into the reference plane 1000.

[0080] Fig. 9 shows the result when the print line DA Vof the print nozzles A1 of the print nozzle row A is shifted upwards (plus) by five times the encoder pitch of 10.5 pm, i.e., by 52.5 pm. In this case, the real offset on the side surface 120 becomes even larger and amounts to approximately 250 pm. From this, it can be concluded that the print line DA is not V the print nozzles A1 of the print nozzle row A by 52.5 pm, starting from the print image shown in Fig. 8, must be shifted upwards, but rather the print line DB V of the print nozzles B1 of the print nozzle row B must be shifted upward (corrected) by 52.5 pm. This result is shown in Fig. 10.

[0081] In Fig. 10, the print lines DA and DB are aligned, and the print line offset by distance d seen in Fig. 8 has thus been significantly compensated or balanced, significantly reducing the so-called waviness. In Fig. 10, the offset (distance d) is ideally almost 0 pm. However, due to measurement inaccuracies, it can be assumed that the actual offset is approximately 50 pm.

[0082] Fig. 11 shows the result of a cross-check. Here, the print line DB V The print nozzles B1 of print nozzle row B are shifted upwards (plus) by four times the encoder pitch of 10.5 pm, i.e., by 42 pm. This leaves a distance of approximately 18 pm between print lines DA and DB. The waviness is thus worse than in Fig. 10.

[0083] A further check is shown in Fig. 12. Here the print line DB VThe print nozzles B1 of print nozzle row B are shifted upwards (plus) by six times the encoder pitch of 10.5 pm, i.e., by 63 pm. This leaves a distance of approximately 34 pm between print lines DA and DB. This cross-check also shows a poorer waviness result than the result in Fig. 10.

[0084] From this series of tests, it can be concluded that for the example presented here (tilt angle of 22.5° and encoder steps of 10.5 pm), the best correction factor is 52.5 pm. At a resolution of 2400 dpi, this corresponds to 5 pixels.

[0085] As can be seen in Fig. 13, the “row shift” or correction of the print data produces a sharply defined print edge without offset between the print lines DA, DB on both the top side 110 and the side wall 120.

[0086] With reference to Fig. 14, the result of the print data correction according to the invention is shown again for the sake of completeness, according to which without correction the print image on the side walls 120 is uneven and this leads to a pronounced offset of the individual print lines (waviness), whereas with the correction of the print data a clearly defined, sharply delimited print line can be generated on the side walls 120, or on the top side 110, depending on whether the print head 10 was initially aligned with the top side 110 or the side wall 120.

[0087] This reduced waviness of the print edge allows a more homogeneous layer thickness to be achieved across the entire print layer.

[0088] Waviness can be measured using a suitable imaging technique, e.g., a microscope or an automated optical inspection (AOI) system. For example, an average waviness can be determined by measuring the distance between the peaks and valleys of the wavy printed edge of the print layer relative to a reference position, preferably the printer setting where the printed edge should ideally lie, and by averaging the measurements from a series of printed objects, e.g., a series of 400 printed objects, thereby determining an average value for the waviness of the printed edge. Alternatively, an average value can be determined for each printed surface (each side surface separately).

[0089] It should be noted that the following data processing procedure is performed before the print data is corrected. This data processing procedure is described in detail in European patent application EP 20 180 763, filed on June 18, 2020, which is incorporated herein in its entirety by reference.

[0090] First, geometric 3D surface data of the 3D geometry of the printed object is determined or defined. This 3D surface data can be provided from an external database in the form of 3D CAD data, or it can be acquired using a laser scanner that scans the topography of the exposed surfaces of the 3D printed object on the planar plane. This geometric 3D surface data can be converted into 3D vector graphic data (polygon data), which forms the basis for a digital 3D object file.

[0091] In the next step, the 3D geometric surface data is converted into 2D geometric surface data, e.g., by unwrapping. The following, admittedly simplified example serves to illustrate this unwrapping step.

[0092] Assuming the 3D object is shaped like a cuboid, and the cuboid lies with its lower rectangle on a planar plane, the cuboid is cut along certain edges to unfold the 3D cuboid, and the unfolded cuboid is placed on the planar plane. The unfolded 2D cuboid then has the shape of a symmetrical cross with five rectangles: a central rectangle representing the upper rectangle of the 3D cuboid, and four rectangles adjacent to the four side edges of the central rectangle. The lower rectangle of the 3D cuboid is irrelevant due to the nature of the unfolding process and the fact that no layer will be printed on it.

[0093] To generate 2D geometric surface data of the exposed 3D surfaces of the printed object, the exposed surfaces can be defined by a surface mesh. The surface mesh is placed so that it extends through certain points on the surfaces of the printed object. These points preferably define the 3D shape of the printed object to some extent. In the case of the cuboid mentioned above, these shape-defining points would be, for example, the edges of the cuboid or the eight vertices of the cuboid. Due to the inclination of the print head relative to the printed object, the print nozzle plane is not parallel to the planar plane on which the printed object is placed. Therefore, the unfolded 2D geometric surface data may inherently contain distortions.Since the distances of a 3D cuboid in a perspective view on a 2D plane appear shorter the farther they are in the real world, the (unfolded) 2D geometric surface data does not necessarily reflect the real distances. Such distortions can then preferably be corrected by projecting the 2D geometric surface data into the print nozzle plane (plane projection), thereby obtaining 2D print nozzle plane data of the printed object. For this purpose, the print nozzle plane can be generated virtually, e.g., using software, and the projection into the print nozzle plane is performed mathematically using matrix algebra, including rescaling by compression (with a specific correction factor) and subsequent shearing of the 2D geometric surface data.

[0094] In a further exemplary embodiment, a computer program or computer program product is provided which is configured to cause a control unit of an inkjet printer to carry out the method steps described above such that at least a portion of a top surface and at least a portion of a side surface of a three-dimensional (3D) print object is continuously printed with ink.

[0095] The computer program product could therefore be stored on a data processing unit, which could also be part of one embodiment. This data processing unit can be configured to perform the steps of the method described above or to cause them to be performed. The computer program can be loaded into a working memory of a data processor. The data processor can thus be equipped to perform the method according to one of the preceding embodiments.

Claims

PATENT CLAIMS 1. An inkjet printing method for continuously printing at least a portion of a top surface (110) and at least a portion of a side surface (120) of a three-dimensional (3D) object (100) with ink, comprising the steps: Providing a three-dimensional object (100) on a planar plane (50); Providing a print head (10) with a plurality of print nozzles (12) for dispensing ink in the form of drops, wherein the plurality of print nozzles (12) extend in a two-dimensional print nozzle plane (14), and wherein a first part (A1) of the plurality of print nozzles (12) are arranged in a first print nozzle row (A) and a second part (B1) of the plurality of print nozzles (12) are arranged in a second print nozzle row (B), and wherein the first print nozzle row (A) is spaced from the second print nozzle row (B) in the print nozzle plane (14), and wherein the print nozzle plane (14) is arranged at an angle α to the planar plane (50); Generating print data for each print nozzle of the plurality of print nozzles (12) for both the portion of the top surface (110) to be printed and the portion of the side surface (120) to be printed of the object (100); Causing a relative movement between the object (100) and the print head (10); printing the portion of the top surface (110) and the portion of the side surface (120) of the object (100) with ink in a line-like manner;characterized in that, before printing the section of the top side (110) and the section of the side surface (120) of the object (100), the print data for the print nozzles (A1) of the first print nozzle row (A) are corrected with a first correction factor (KA) and / or the print data for the print nozzles (B1) of the second print nozzle row (B) are corrected with a second correction factor (KB), and in that the first correction factor (KA) and / or the second correction factor (KB) are determined based on a previously generated comparison print image that was previously generated without correction, and in that the first correction factor (KA) and / or the second correction factor (KB) are dependent on the distance d of the print line (DA) generated by the print nozzles (A1) of the first print nozzle row (A) to the print line (DB) generated by the print nozzles (B1) of the second print nozzle row (B) in the previously generated comparison print image.

2. Inkjet printing method according to claim 1, characterized in that the previously generated comparison print image was generated by simulation using a geometrically identical object (100') or by printing at least a portion of the top side (110) or at least a portion of the side surface (120) of an identical object (100).

3. Inkjet printing method according to claim 1 or 2, characterized in that the first correction factor (KA) and / or the second correction factor (KB) is dependent on the distance d of the print line (DA) to the print line (DB) on the side surface of the object (110) in the previously generated comparison print image.

4. Inkjet printing method according to one of the preceding claims, characterized in that the first correction factor (KA) varies within the first row of printing nozzles (A) and / or the second correction factor (KB) varies within the second row of printing nozzles (B).

5. Inkjet printing method according to one of the preceding claims, characterized in that the first correction factor (KA) and / or the second correction factor (KB) is determined based on a value k, the value k resulting from the equation: k = tan ax d.

6. Inkjet printing method according to one of the preceding claims, further comprising the steps: Generating three-dimensional geometric surface data of the top surface (110) and the side surface (120) of the three-dimensional object (100), and Generating two-dimensional geometric surface data of the top surface (110) and the side surface (120) of the three-dimensional object (100) based on the three-dimensional geometric surface data of the top surface (110) and the side surface (120) of the three-dimensional object (100).

7. Inkjet printing method according to claim 6, characterized in that the two-dimensional geometric surface data of the side surface of the three-dimensional object (100) are generated by projecting the side surface of the three-dimensional object (100) into a reference plane (1000), and that the reference plane (1000) comprises the plane of the top side (120) of the three-dimensional object (100).

8. Inkjet printing method according to one of claims 6 or 7, characterized in that the three-dimensional geometric surface data of the top surface (110) and the side surface (120) of the three-dimensional object (100) are generated using 3D CAD data or 3D data obtained by an optical scanner.

9. Inkjet printing method according to one of the preceding claims, characterized in that the firing times of the ink drops emitted from the plurality of printing nozzles (12) vary among each other.

10. Inkjet printing method according to one of the preceding claims, characterized in that the angle a between the printing nozzle plane (14) and the planar plane (50) is in a range of 20° to 70°, preferably in a range of 20° to 50°, and more preferably 22.5°. 11 . Inkjet printing method according to one of the preceding claims, characterized in that the relative movement between the three-dimensional object (100) and the print head (10) is a linear rectilinear movement.

12. Inkjet printing method according to one of the preceding claims, characterized in that during the relative movement between the three-dimensional object (100) and the print head (10), the three-dimensional object (100) is moved relative to the print head (10).

13. Inkjet printing method according to claim 12, characterized in that during the movement of the three-dimensional object (100) relative to the print head (10), a side edge connecting two adjacent side surfaces (120) of the three-dimensional object (100) leads.

14. A computer program comprising instructions that cause a control device of an inkjet printer to perform the following steps to at least to continuously print a portion of a top surface (110) and at least a portion of a side surface (120) of a three-dimensional (3D) object (100) with ink: Generating print data for each print nozzle of a plurality of print nozzles (12) of a print head (10) of the inkjet printer, both for the section of the top side (110) to be printed and for the section of the side surface (120) to be printed of the object (100), wherein the plurality of print nozzles (12) extend in a two-dimensional print head plane (14), and wherein a first part (A1) of the plurality of print nozzles (12) is arranged in a first print nozzle row (A) and a second part (B1) of the plurality of print nozzles (12) is arranged in a second print nozzle row (B), and wherein the first print nozzle row (A) is spaced from the second print nozzle row (B) in the print nozzle plane (14); and Correcting the print data for the print nozzles (A1) of the first print nozzle row (A) with a first correction factor (KA) and / or correcting the print data for the print nozzles (B1) of the second print nozzle row (B) with a second correction factor (KB), such that the first correction factor (KA) and / or the second correction factor (KB) is determined on the basis of a previously generated comparison print image that was previously generated without correction, and such that the first correction factor (KA) and / or the second correction factor (KB) is dependent on the distance d of the print line (DA) generated by the print nozzles (A1) of the first print nozzle row (A) to the print line (DB) generated by the print nozzles (B1) of the second print nozzle row (B) in the previously generated comparison print image.

15. A computer-readable storage medium having the computer program according to claim 14 stored thereon.

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