Nozzle Arrangement of Droplet Ejection Device

Abstract

a nozzle plate for a droplet ejection head, the nozzle plate including a first row of nozzles arranged to deposit droplets onto a deposition medium; the first row of nozzles extends in a row direction and includes two or more nozzle clusters, each nozzle cluster being arranged along the row direction by a cluster length c and extending along a cluster depth direction perpendicular to the row direction by a cluster depth d; each nozzle cluster comprising a plurality of nozzles, wherein one or more nozzles in each nozzle cluster define the cluster length c and two or more nozzles in each nozzle cluster define the cluster depth d; each nozzle cluster is spaced apart from an adjacent nozzle cluster along the row direction by a cluster spacing a, thereby creating an air flow path for forced air to pass through the row of nozzles in a controlled manner; a nozzle plate, wherein when the first row is projected laterally onto the row direction, a transition region between adjacent nozzle clusters consists of two or more nozzles of a first cluster and two or more nozzles of a second cluster, the second cluster adjacent to the first cluster, and the nozzles in the transition region are spaced equidistant from each other at a projected nozzle spacing.

Description

Technical Field

[0001] The present disclosure relates to a nozzle plate for a droplet ejection device, a method of droplet ejection using such a nozzle plate, and a droplet ejection device comprising such a nozzle plate for a droplet ejection device. The nozzle plate can be particularly advantageously used in applications where it is necessary to print high-resolution images at high speed on a rough or flexible surface.

Background Art

[0002] Droplet ejection devices are currently widely used, regardless of more conventional applications such as inkjet printing, or 3D printing, or other rapid prototyping technologies. In particular, droplet ejection devices or inkjet print heads have been developed that can deposit ink directly onto paper, cards, ceramic tiles, and other deposition media with high reliability and throughput. In other applications, the droplet ejection head can be used to form elements such as color filters in LCD or OLED displays used in the manufacture of flat screen televisions.

[0003] Droplet ejection devices and their components continue to evolve to meet the requirements of increasingly challenging applications, and in general, the resolution and throughput at high print quality are improving.

Summary of the Invention

[0004] Aspects of the invention are set out in the appended independent claims, and specific embodiments of the invention are described in the appended dependent claims.

[0005] The following disclosure, in one aspect, describes a nozzle plate for a droplet ejection head, the nozzle plate comprising a first row of nozzles arranged to deposit droplets onto a deposition medium, the first row of nozzles extending in a row direction and comprising one or more nozzle clusters, each nozzle cluster being arranged with a cluster length c along the row direction and extending with a cluster depth d along a cluster depth direction perpendicular to the row direction, each nozzle cluster comprising a plurality of nozzles, one or more of the nozzles within each nozzle cluster defining the cluster length c, and two or more of the nozzles within each nozzle cluster defining the cluster depth d, each nozzle cluster being spaced a cluster spacing a from an adjacent nozzle cluster along the row direction, such that an air flow path for forced air to pass through the row of nozzles in a controlled manner is created, and at least a majority of the nozzles in the first row being equally spaced from each other with a projected nozzle spacing when projected laterally in the row direction.

[0006] In one exemplary embodiment, the first row of nozzles comprises a first set of sub - rows consisting of a first and a second sub - row extending side - by - side in respective sub - row directions, the first and second sub - rows extending parallel to the row direction, the first and second sub - rows being spaced a first sub - row spacing b from each other in a lateral direction perpendicular to the row direction, each of the first and second sub - rows comprising one or more nozzle clusters, each nozzle cluster within a sub - row being spaced a cluster spacing a from an adjacent nozzle cluster, and each projected nozzle cluster of the first and second sub - rows being spaced a projected nozzle spacing from an adjacent projected nozzle cluster.

[0007] In another exemplary embodiment, each nozzle cluster is spaced a cluster spacing a greater than a nozzle spacing ns between adjacent nozzles of the nozzle cluster from an adjacent nozzle cluster along the row direction.

[0008] A method of depositing droplets (e.g., printing) using such a nozzle plate, a drive signal controller operable to perform such a method, a droplet ejection device (e.g., a print head) comprising such a nozzle plate, and a droplet discharge device (e.g., a printer) comprising such a nozzle plate are also provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Here, embodiments of the present invention are described by way of example only and with reference to the following drawings.

Figure 1A

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[0010] In the drawings, like elements are denoted by like reference numerals throughout.

DETAILED DESCRIPTION OF THE INVENTION

[0011] To highlight the functions of the embodiments described with respect to FIGS. 2 to 22 and their various examples, first refer to the known test apparatus of FIG. 1A.

[0012] FIG. 1A shows a droplet ejection device 1 including a droplet ejection device, such as a droplet ejection head 2, attached above a deposition medium 3 movable by a transport mechanism 5. The droplet ejection head 2 includes a nozzle plate 6 having nozzles 12 for ejecting droplets onto the deposition medium in response to signals transmitted by a controller 4. The droplet ejection head 2 is attached such that there is a gap G between the deposition medium 3 and the droplet ejection head 2.

[0013] Details of a typical pattern of the nozzles 12 are shown in the plan view of FIG. 1D. FIG. 1D shows a part of the plan view of the nozzle plate 6 provided in the inkjet print head 2. A part of the row 13 of the nozzles 12 is configured behind the nozzle plate 6 and is shown in relation to a fluid channel (broken line) including a pressure chamber 14 in fluid communication with restrictors 18a, 18b and ink ports 16a, 16b. In FIG. 1D, an exemplary print head having a flow path shown behind the nozzle plate has recirculation through each nozzle 12. One of the ink ports 16a supplies ink to the pressure chamber 14 via the restrictor 18a from one end, and any ink not ejected from the nozzle 12 is returned to the ink flow path via the restrictor 18b and the ink port 16b at the opposite end.

[0014] In FIG. 1D, the pressure chamber 14 has an elongated shape and is arranged in a corresponding relationship with the nozzles 12 arranged at the center of each pressure chamber 14 along the elongation direction of the chamber. Each nozzle 12 is spaced apart from the nozzles in adjacent chambers by a nozzle distance ns / 2 along the column direction 26 (y direction).

[0015] In FIG. 1D, the nozzles 12 are arranged in a typical configuration that reduces or prevents fluid and / or mechanical “cross-talk,” where cross-talk is the effect of the ejection of droplets from one nozzle on the meniscus of an adjacent nozzle. The pattern is a staggered nozzle configuration pattern, whereby each alternating nozzle 12 is offset from its neighbor by an offset distance sd along a direction (x-direction) orthogonal to the column direction 26. The column direction 26 is defined by the overall direction in which the staggered nozzles extend. The nozzles are spaced apart by a nozzle spacing ns from the nearest adjacent nozzle having the same staggered offset.

[0016] The staggered offset distance is related to a combination of mechanical, electrical, and fluidic considerations and is typically determined empirically. The offset distances in FIGS. 1D and subsequent figures are illustrative only with respect to the general concept of nozzle offset for reducing cross-talk. In other devices where the flow paths are designed differently, such an offset may not be necessary and the nozzles may instead be arranged in non-offset columns. The presence or absence of cross-talk is not essential with respect to the various embodiments and examples described.

[0017] In some situations where a conventional nozzle arrangement of FIG. 1D is used, when operating the test apparatus 1 using the nozzle plate 6 of the droplet ejection head 2, a "wood grain pattern" phenomenon may occur. As used herein, the "wood grain pattern" phenomenon is an undesirable printing artifact that is thought to be the result of an induced or forced air flow within the gap between the nozzle plate 6 of the droplet ejection head 2 and the deposition medium 3 being printed, due to the relative movement between the droplet ejection head 2 and the deposition medium 3. The forced air flow causes a large, uncontrollable deviation in the trajectory of the ejected droplets, changes their landing positions, and deposits mist and satellites at unpredictable positions on the deposition medium and on the portion of the droplet ejection head 2 surrounding the nozzles 12. One visual phenomenon may be a wavy "wood grain pattern" phenomenon, but other irregular patterns may be clearly visible in the printed image due to this phenomenon. Wood grain is particularly likely to occur in applications that require a larger gap distance G, for example, applications where the surface of the deposition medium 3 is rough, flexible or granular, such as fibers or cardboard.

[0018] A diagram of a typical wood grain pattern is shown in the test print sample of FIG. 1B. The test print sample was achieved by ejecting at full load (printing with all nozzles) using the head arrangement of FIG. 1A, with a nozzle pitch of 84.7 μm (300 nozzles / inch) and a gap G distance of 3 mm. The media speed for this sample was 80 m / min, and the drop speed measured at a distance of 1 mm from the nozzle plate was 6.1 m / s. The pattern expected in the absence of the wood grain pattern phenomenon would be a uniform coating pattern. The actual pattern is caused by the deviation of the main droplets (where "main droplets" refers to droplets of the desired target volume or droplets near it), forming an irregular, branched, and wavy pattern across the image along the media transport direction x, as well as dark "irregular streaks" similar to the wood grain pattern. Wood grain is not only due to the deviation of the main droplets. Various flows also result in mist or satellites, forming a visible change in density recognized as "wood grain".

[0019] For some applications, it is desirable to use a droplet ejection device 1 as shown in FIG. 1A, in which the droplet ejection head 2 is firmly attached and the deposition medium 3 to be printed passes thereunder. This is often referred to as single-pass printing. In the setup of this device, the moving deposition medium 3 generates a forced air flow within the gap G with a velocity profile characteristic of the single-pass printing situation.

[0020] Another arrangement is that of a scanning droplet ejection device in which the droplet ejection head 2 is moved back and forth in the y-direction orthogonal to the medium conveyance direction x. In this arrangement, the droplet ejection head 2 moves at high speed relative to the surrounding (static) air, causing air to flow around the droplet ejection head 2. As part of this air flow around the droplet ejection head 2, some air flow is pushed into the gap between the deposition medium 3 and the nozzle plate of the droplet ejection head 2 with a velocity profile characteristic of the scanning application. The state of the air flow in such an arrangement is different from that of the single-pass setup, but droplet misalignment and grainy patterns may still occur.

[0021] More generally, regardless of whether the droplet ejection head 2 is moved relative to the deposition medium 3 or the deposition medium 3 is moved relative to the droplet ejection head 2, there is a velocity difference between the droplet ejection head 2 and the deposition medium 3, thereby causing a forced air flow around the droplet ejection head 2 and / or in the gap G between the head droplet ejection 2 and the deposition medium 3. In particular, in high-gap distance applications that require a higher resolution nozzle density and / or a higher throughput (high relative velocity between the droplet ejection head and the deposition medium) and / or a higher printing frequency when the gap G is several millimeters, it is necessary to carefully manage the forced air flow to maintain high print quality.

[0022] The inventors have found that the grainy phenomenon can be reduced or eliminated by arranging modified nozzles on the nozzle plate 10 described with respect to FIGS. 2 to 22 here.

[0023] Summary FIG. 2 is a block diagram illustrating the principle following the described embodiment. The column 20 of nozzles is arranged such that all the nozzles are grouped into different clusters 24. The nozzles within a cluster may be arranged in an (x, y) array. The clusters are spaced apart from each other at a cluster spacing along the column direction 26. Thus, an air flow path is provided between the clusters 24 at the cluster spacing, and forced air indicated by a large arrow reaching in front of the column passes through the column of clusters indicated by small arrows in a controlled manner and then recombines again, reducing the wood grain phenomenon. Such a column 20 of nozzles still shows the nozzle spacing along the column, the same as the conventional column described, for example, in FIG. 1D. When reduced and looking at the projection direction along x, the nozzles within the transition region T between two adjacent clusters 24 are equally spaced apart. This can be achieved according to the embodiments described below and their various examples.

[0024] Generally, the present embodiment of the nozzle plate for the droplet ejection head uses a comprehensive principle in which the nozzle plate includes a first row of nozzles arranged to deposit droplets on a deposition medium, the first row of nozzles extends in a row direction, and includes two or more nozzle clusters. Each nozzle cluster is arranged with a cluster length c along the row direction and extends with a cluster depth d along a cluster depth direction perpendicular to the row direction. Each nozzle cluster includes a plurality of nozzles, one or more nozzles within each of the nozzle clusters define the cluster length c, and two or more nozzles within each nozzle cluster define the cluster depth d. Each nozzle cluster is spaced apart from an adjacent nozzle cluster by a cluster interval a along the row direction, and as a result, an air flow path is created for forced air to pass through the row of nozzles in a controlled manner, and at least most of the nozzles in the first row of nozzles are equally spaced from each other at a projected nozzle interval when projected laterally in the row direction. In other words, when the first row is projected laterally in the row direction, the transition region between adjacent nozzle clusters consists of two or more nozzles of the first cluster and two or more nozzles of the second cluster, the second cluster is adjacent to the first cluster, and the nozzles in the transition region are equally spaced from each other at the projected nozzle interval.

[0025] In the first embodiment, the first row of nozzles includes a first set of sub-rows consisting of a first sub-row and a second sub-row that extend side by side in the direction of each sub-row, and the first and second sub-rows extend parallel to the row direction. The first sub-row and the second sub-row are spaced apart by a first sub-row interval b in a lateral direction perpendicular to the row direction, and each of the first and second sub-rows includes one or more nozzle clusters. Each nozzle cluster within the sub-row is spaced apart from an adjacent nozzle cluster by a cluster interval a, and two or more nozzles of the first cluster and two or more nozzles of the adjacent second cluster provided in the transition region are provided in the first and second sub-rows respectively, and each projected nozzle cluster of the first and second sub-rows is spaced apart from an adjacent projected nozzle cluster by a projected nozzle interval.

[0026] In some variations, the cluster depth d may be the same as the staggered offset distance sd. In other words, the cluster depth may be the depth of one sub-column.

[0027] Optionally, the first set of sub-columns may further include a third sub-column, and one or more nozzle clusters of each of the first, second, and third sub-columns define a first sub-column spacing between the first and second sub-columns and a second sub-column spacing between the first and third sub-columns. The first and second sub-column spacings may be the same as each other, or they may be different from each other.

[0028] Optionally, the nozzle plate may have a second row of nozzles extending in a second row direction, the second row direction being parallel to the direction of the first row. The second row of nozzles comprises a second set of sub-rows consisting of a first and a second sub-row extending side by side in the direction of each sub-row, the first and second sub-rows of the second set of sub-rows extending parallel to the second row direction. The first and second sub-rows of the second set of sub-rows are laterally spaced apart by a third sub-row spacing b in a lateral direction perpendicular to the second row direction. Each of the first and second sub-rows of the second set of sub-rows comprises one or more nozzle clusters, each nozzle cluster comprising a plurality of nozzles extending along the respective sub-row direction with a cluster length c. Each nozzle cluster within a sub-row of the second set of sub-rows is spaced apart from an adjacent nozzle cluster by a cluster spacing a. At least most of the nozzles of the first and second sub-rows of the second set of sub-rows are equally spaced from each other by a second projected nozzle spacing when projected laterally in the second row direction, and each projected nozzle cluster of the first and second sub-rows of the second set of sub-rows is spaced apart from an adjacent projected nozzle cluster by the second projected nozzle spacing. In other words, the second transition region between adjacent nozzle clusters of the first and second sub-rows of the second set of sub-rows consists of two or more nozzles of the first sub-row and two or more nozzles of the second sub-row of the second set of sub-rows, and the nozzles within the second transition region are equally spaced from each other by the second projected nozzle spacing. The air flow path is created by the cluster spacing to create a flow path for the forced air to pass through the second row of nozzles in a controlled manner.

[0029] When projected laterally in the row direction, at least most of the nozzles of the first and second sets of sub-rows may be equally spaced from each other by a third projected nozzle spacing, the third projected nozzle spacing being smaller than the first projected nozzle spacing. In other words, when projected laterally in the row direction, in the overlapping region of the first and second transition regions, consecutive projected nozzles are equally spaced from each other by the third projected nozzle spacing, the third projected nozzle spacing being smaller than the first projected nozzle spacing.

[0030] Optionally, one or more nozzle clusters of the first sub-column of the first set of sub-columns may have a cluster length different from the cluster length of one or more nozzle clusters of the second sub-column of the first set of sub-columns.

[0031] Optionally, one of the sub-columns comprises first and second subsets of nozzle clusters, and the cluster length of the first subset of nozzle clusters is different from the cluster length of the second subset of nozzle clusters.

[0032] The first sub-column spacing b is greater than 150 μm, optionally greater than 300 μm, and further optionally greater than 500 μm.

[0033] In embodiments having sub-columns, it will be understood that the air flow path is created by the cluster spacing a in combination with the sub-column spacing b.

[0034] In a second embodiment, each nozzle cluster can be spaced apart from an adjacent nozzle cluster along the column direction by a cluster spacing a that is greater than the nozzle spacing ns between adjacent nozzles of the nozzle cluster.

[0035] Optionally, each projected nozzle cluster of the first column may be spaced apart from an adjacent projected nozzle cluster by a projected nozzle spacing.

[0036] Furthermore, or alternatively, in some variations, one or more of the plurality of nozzle clusters may comprise two or more sub-clusters of nozzles extending substantially along the column direction, the sub-clusters being arranged parallel to each other to form a matrix of nozzles, and each nozzle cluster is arranged to overlap with adjacent nozzle clusters along the column direction and in a direction perpendicular to the column direction.

[0037] Furthermore, or alternatively, in some variations, the nozzle clusters can be arranged in one or more of a parallelogram, trapezoid, or triangular shape.

[0038] In some hybrid variations, the nozzle clusters of the variations according to the first embodiment arranged adjacent to each other along the column direction may be offset from each other along the depth direction of the cluster. In other words, two sub-columns of clusters may be created, each sub-column extending parallel to the column direction, the sub-columns being laterally spaced apart from each other by a sub-column spacing b, the lateral direction being perpendicular to the column direction.

[0039] In some variations of any of the embodiments, one or more of the plurality of nozzle clusters may comprise two or more sub-clusters of nozzles extending substantially along the column direction, the sub-clusters being arranged parallel to each other to form a matrix of nozzles. The sub-clusters can be offset from each other by a staggered offset distance sd in a direction perpendicular to the column direction.

[0040] First Embodiment of the Nozzle Plate FIG. 3A shows a cross-sectional plan view of a nozzle plate 10 according to a first exemplary embodiment provided in the droplet discharge head 2. A portion of the column 20 of nozzles 12 is shown in relation to a fluid channel (broken line) comprising a pressure chamber 14 in communication with a restrictor 18 and an ink port 16 that can be configured behind the nozzle plate 10 to supply ink to the nozzles. The column 20 of nozzles 12 extends in a column direction 26.

[0041] In contrast to FIG. 1D, the nozzles 12 are arranged in a clustered configuration such that the alternating nozzle clusters 24 comprising a plurality of nozzles 12 are offset from each other along a direction orthogonal to the column direction (along the x direction). This nozzle arrangement creates first and second sub-columns 22_1 and 22_2, the first sub-column 22_1 being defined by the nozzle cluster 24_1 and the second sub-column 22_2 being defined by the nozzle cluster 24_2.

[0042] The first and second sub-columns 22_1 and 22_2 extend parallel to each other in their respective sub-column directions, and the sub-column directions extend parallel to the overall column direction 26 of column 20. Thus, the first sub-column and the second sub-column are separated by a sub-column spacing b, which, in FIGS. 3B and 7-11, is the shortest distance along the distance orthogonal to the column direction 26 between the inner nozzles of the two sub-columns, representing the spacing not occupied by the nozzles.

[0043] This is further illustrated in FIG. 3B, which shows in more detail the arrangement of the nozzles 12 of the nozzle plate 10 of FIG. 3A. Specifically, in the excerpt of the nozzle plate 10, each sub-column 22_1 and 22_2 of column 20 has two nozzle clusters, and it is shown that sub-column 22_1 has at least nozzle clusters 24_1a and 24_1b arranged adjacent to each other in their respective sub-column directions, and sub-column 22_2 has at least nozzle clusters 24_2a and 24_2b arranged adjacent to each other in their respective sub-column directions.

[0044] The nozzles 12 of each nozzle cluster 24_1a, 24_1b, 24_2a, and 24_2b extend over a cluster length c along their respective sub-column directions, and the cluster length c, in FIGS. 3A and 3B and FIGS. 7-11, is represented as the distance between the outermost nozzles of each cluster measured along their respective sub-column directions.

[0045] Cluster 24_1a is spaced from the adjacent cluster 24_1b by a cluster spacing a in their respective sub-column directions. In FIGS. 3A and 3B and FIGS. 7-11, the cluster spacing a is represented as the distance between the outermost nozzles of adjacent clusters in the same sub-column, measured along their respective sub-column directions, representing the spacing not occupied by the nozzles.

[0046] Cluster 24_2a is also spaced from the adjacent cluster 24_2b by a cluster pitch a in each respective sub-column direction. Nozzle clusters 24_1a and 24_1b define sub-column 22_1, and nozzle clusters 24_2a and 24_2b define sub-column 22_2. Sub-column 22_1 extends to sub-column 22_2 with a sub-column pitch b in parallel with sub-column 22_2.

[0047] Accordingly, in this embodiment, a nozzle plate 10 for the droplet ejection head 2 is provided, and the nozzle plate 10 includes at least a first row 20 of nozzles 12 arranged to deposit droplets onto a deposition medium. The first row of nozzles extends in a row direction 26 and includes a first set of first and second (or more) sub-columns 22 extending side by side in each respective sub-column direction, and the sub-column direction extends parallel to the row direction 26. The first and second sub-columns 22 are spaced apart by a first sub-column pitch b in a lateral direction perpendicular to the row direction 26, and each sub-column includes one or more nozzle clusters 24. Each nozzle cluster 24 includes a plurality of nozzles 12 extending with a cluster length c along each respective sub-column direction, and each nozzle cluster 24 within the sub-column 22 is spaced from adjacent nozzle clusters by a cluster pitch a. Preferably, the first sub-column pitch b is greater than 300 μm. When the nozzles 12 of the first set of sub-columns are projected laterally on the row direction 26, they are equally spaced by a nozzle pitch projected from adjacent projected nozzles, and each projected nozzle cluster of the first and second sub-columns 22 is spaced from an adjacent projected nozzle cluster by a nozzle pitch projected from the adjacent projected nozzle cluster. In some embodiments, the sub-column pitch may be less than 900 μm. Alternatively, the sub-column pitch may be greater than 400 μm or greater than 500 μm.

[0048] In the exemplary embodiment of FIG. 3A, the nozzles within the cluster are shown in a pattern of a staggered nozzle configuration as in FIG. 1D, whereby the alternately arranged nozzles 12 are offset by a distance sd from their adjacent nozzles in a direction orthogonal to the column direction (in the x direction). The nozzles 12 are spaced apart by a nozzle pitch ns from their nearest neighbor nozzles with the same staggered offset (along the y direction) as shown in FIG. 3B. However, this is not essential. In some droplet ejection heads, it may be possible to avoid crosstalk in different ways, for example, by providing fluid dampers in the fluid paths or by sufficient separation between the flow paths of adjacent pressure chambers 14, and the nozzles 12 should not be offset by the distance sd. The sub-column pitch b may be at least 300 μm or at least 400 μm. In some embodiments, the sub-column pitch b may be of a size similar to the cluster pitch a. For example, if each cluster comprises four nozzles and, for example, ns / 2 = 84.67 μm, the cluster pitch a may be 423.35 μm, the cluster length may be 254 μm, and the pitch b between sub-columns may be a = b = 423.35 μm.

[0049] In the exemplary embodiments of FIGS. 3A and 3B, the first and second sub-columns 22_1 and 22_2 defined by the nozzle clusters 24_1a, b and 24_2a, b respectively define a complete column 20 in the sense of the column 13 shown in FIG. 1D. This means that the column 20 of nozzles 12 is used to deposit droplets on the same "line pixels" on the deposition medium 3 according to the image data. Further, when looking along the x-direction in FIG. 3A, along the direction of laterally projecting one sub-column onto the other sub-column, the nozzles 12 within the transition region T having a plurality of nozzles (as shown, for example, three nozzles from each of the clusters 24_1b and 24_2a) from each nozzle cluster 24 are arranged equidistantly and without overlapping between the nozzles, achieving a constant nozzle pitch ns / 2 in the transition region, as in the case of the column 13 of FIG. 1D, with all the nozzles 12 being spaced apart by the nozzle pitch ns / 2. In the example shown in FIG. 3B, all the nozzle clusters 24 define a complete column 20 without overlapping between the nozzle clusters 24, as in the case of the column 13 of FIG. 1D, and all the nozzles 12 are spaced apart by the nozzle pitch ns / 2. This is distinguished from the transition between nozzle plates with individual columns of nozzles, where in this case the columns of nozzles of one nozzle plate usually partially overlap the columns of nozzles of the other nozzle plate, creating some redundancy in the overlapping region, and as a result, an optimal transition from one nozzle plate to the next may need to be selected. In such an arrangement, the projected nozzle pitch is not constant as a result of misalignment between the nozzle plates, and the nozzle plates may be individual silicon dies attached to a common frame.

[0050] The two sub-columns shown in FIG. 3B may be part of a first set of sub-columns that define a complete column, as will be described later.

[0051] The specific fluid arrangement behind the nozzle plate shown in FIG. 3A is not important and merely serves to illustrate how the nozzles 12 can be supplied with fluid. The nozzles 12 in the exemplary embodiment of FIG. 3A are shown to be arranged along the elongated direction of the pressure chamber 14 so as to define a cluster of nozzles arranged along the sub-column direction, although the pressure chamber does not contribute to the definition of the two sub-columns. The ink ports 16a, 16b are in fluid communication with the pressure chamber 14 via the restrictors 18a, 18b. This arrangement allows for recirculation, for example, through the fluid supply portions at both ends of the nozzles or the pressure chamber. For recirculation, one of the ink ports 16a supplies ink to the respective pressure chamber 14 via the corresponding restrictor 18a from one end of the pressure chamber, and all the ink that was not ejected from the nozzles 12 is returned to the corresponding ink port 16b via the restrictor 18b at the other end of the pressure chamber 14. The pressure chamber 14 is shown to have one nozzle each, but this is not essential. Each pressure chamber can have, for example, two nozzles arranged side by side.

[0052] Returning to FIG. 1A, this illustrates the effect of the forced gas flow caused by the movement of the deposition medium 3 with respect to the droplet landing position in the absence of mitigation of the wood grain phenomenon. The forced air flow, or quiescent flow, within the gap G created by the deposition medium 3 moving in the media transport direction x is indicated by a series of parallel arrows of different lengths, with the longer arrows indicating a faster air flow than the shorter arrows. As can be seen, the droplets ejected from the nozzle plate 6 are displaced over time from the position directly below the nozzle 12 at the time of ejection to the landing position on the deposition medium 3 after moving across the gap G.

[0053] Thereafter, the droplet displacement caused by the forced air flow, called the primary flow, is considered to be uniform across the entire droplet head 2. This part of the droplet displacement can be managed by knowing the speed of the medium and adjusting the timing of ejection accordingly.

[0054] On the other hand, the secondary air flow and its interaction with their primary flows can result in another unpredictable displacement of the droplets in the direction of media conveyance, x, or in the column direction. This part of the deviation cannot be controlled by conventional means, for example, by timing.

[0055] An example of the secondary air flow is considered to be caused by the ejection of droplets from the nozzle 12. For example, each droplet moving at 6 m / s pulls air downward together with the droplet, causing a downward cylindrical air flow. Such air columns can be combined along the column direction to form an "air curtain" of air flow around a group of adjacent nozzles 12. This is particularly true for high-resolution droplet ejection heads with narrow nozzle spacing and denser-packed columns.

[0056] The "air curtain" and the related flow become stronger as the droplets speed up and the frequency at which the droplets are ejected may become higher. The forced flow induced by the droplets colliding with the deposition medium 3 and the interaction between the air curtain and the forced flow result in the formation of circulating vortices. This is schematically shown in FIG. 1C. The intensity and degree of these vortices in the droplet ejection direction are considered to depend on the speed and volume (weight) of the droplets.

[0057] The inventor believes that the forced air flow breaks through the "air curtain" created by the droplet curtain and forms vortices with a circulating motion across the media conveyance direction when passing through the droplet curtain. This may occur particularly at weak points or gaps in the droplet curtain. The weak points of the droplet curtain, and thus the gaps in the barrier indicated by the "air curtain", may occur due to non-uniformity across the entire nozzle column, for example, some nozzles producing a smaller droplet volume and / or slower droplets compared to adjacent nozzles, some nozzles not ejecting droplets coaxially with the nozzle axis, or due to inactive nozzles based on image information.

[0058] Alone or in combination, various sources of eddies or vortices introduce flow components into a gap G that crosses the media direction x and is anti-parallel to the droplet ejection direction, and these components cause the recognized "wood grain" pattern shown in FIG. 1B. The generation of this pattern and the effect of arranging the nozzles in a cluster were further confirmed by simulation.

[0059] Considering first the conventional nozzle array 13 according to FIG. 1D, FIG. 1C is a contour map of the magnitude of the air velocity between the nozzle plate 6 and the deposition media 3. The aspect of the figure is downward in the direction perpendicular to the nozzle plate 6. The magnitude of the velocity is evaluated on the middle of a parallel plane between the nozzle plate 6 and the deposition media 3 and is the maximum magnitude of the air velocity at a particular location regardless of the direction of the flow. Thus, for a 3 mm gap, the plane is located 1.5 mm away from the deposition media 3 where the contours of the magnitude of the velocity are plotted. The simulation was set with a droplet size of 3 pl, and with a printing frequency of 20 kHz and a media velocity of 0.416 m / s, a resolution of 1200 dpi (dots per inch) was obtained in the printing direction (i.e., along the x direction in FIG. 1C).

[0060] The dark regions in Fig. 1C represent a low speed (close to zero), and the bright regions represent a speed magnitude of approximately 1.5 m / s. The nozzle rows 13 are arranged along the upper horizontal line of high speed and are further indicated by the row direction (arrow) 26 in Fig. 1C. The direction of the quiescent flow in Fig. 1C is along the movement direction of the deposition medium 3, i.e., along the x-direction. At the start of printing, a forced air flow is generated along the movement direction of the deposition medium (along the x-direction) and in a direction perpendicular to the row direction 26. Further, a droplet curtain that blocks the forced air is generated. This forced air flow generates a vortex 60 in front of the droplet curtain. This vortex 60 is continuously energized by the moving substrate, and the vortex breaks through the droplet curtain and generates a downstream air flow 62 behind the nozzles through the droplet curtain. Those downstream air flows 62 cause a displacement of the droplet landing position, which results in a visual wood grain-like phenomenon. Since the position where the vortex 60 breaks through the droplet curtain changes dynamically and unpredictably over time, the downstream air flow 62 continuously changes and produces a wood grain-like pattern that evolves along the image.

[0061] The inventors propose that by providing the nozzle cluster 24, instead of the droplet curtain of the conventional nozzle row 13 in Fig. 1D being uncontrollably broken through, the vortex 60 caused by the forced air flow can be controllably dissipated of energy through the droplet curtain, and the print quality can be maintained.

[0062] To illustrate this proposal, FIG. 4A shows the streamlines of the forced air passing through the row 20 of the nozzle cluster 24 of the nozzle 12 along a path provided by the nozzle spacing between adjacent clusters of the same sub-rows 22_1, 22_2, and the sub-row spacing between the sub-rows 22_1 and 22_2 defined by the nozzle cluster 24. The simulation of FIG. 1C was repeated using the nozzle arrangement of the nozzle plate 10 according to the arrangement of FIG. 3B of a cluster with six staggered nozzles arranged with ns / 2 = 84.67 μm, shift distance sd = 84.67 μm, cluster spacing a = 592.67 μm, and sub-row spacing 677.33 μm, respectively. FIG. 4B shows a snapshot of the resulting magnitude of the air flow velocity in the evolution of printing using the same process conditions and gap distances as used in the simulation of FIG. 1C for the conventional nozzle row 13. Here, the high-speed positions can only be observed at the positions of the clusters 24_1 and 24_2 of the sub-rows 22_1 and 22_2 (where all nozzles are printing). The inventors propose that these high magnitudes in front of the clusters are generated not by the moving deposition medium, but rather by the droplet curtain. The magnitude of the velocity in front of row 20 is significantly reduced compared to the plot of FIG. 1C. The inventors believe that this suggests that no vortex 60 is generated in front of the curtain because there is an easy opportunity to pass through the curtain between the gaps of the clusters. Importantly, the downstream air flow 62 not only has a much smaller magnitude compared to that of FIG. 1C, but is also uniformly distributed in a stable pattern, contrary to the dynamic pattern of FIG. 1C. Thus, FIG. 4B shows how the presence of the nozzle cluster 24 provides a path through the droplet curtain for the forced air flow to pass through in a controlled manner. The stable pattern of the controlled downstream air flow 62 can be adjusted by changing the droplet volume and / or velocity (by "trimming"), and since these shifts are constant over time, the droplet shifts along the column direction can be explained.

[0063] To evaluate various cluster designs, simulations of the droplet landing positions were performed using a customized MPPICFoam solver (OpenFOAM software). The simulations were carried out in a rectangular box of the following dimensions, 7.5 cm in the printing direction (x - direction), 9 cm in the width direction (y - direction), and the height of the domain was restricted by the gap distance G. The top wall of the domain was constrained as a fixed wall with zero - velocity condition. The bottom wall simulated a moving deposition medium with appropriate velocity conditions set. The nozzle was placed 3 cm downstream (in the direction of media conveyance) from the inlet into the gap G. The total length of the row of nozzles 20 was equal to 3 cm, and as a result, for the 9 - cm domain width, the flow could flow around the ends of the droplet curtain. A plug - flow velocity profile was set at the inlet and a zero - pressure boundary was set at the outlet. All simulations were time - adjusted to generate an image 12 cm long in the printing direction (along the x - direction).

[0064] In the simulations, three types of nozzle clusters 24, with 4, 6, and 8 nozzles per nozzle cluster, were evaluated. The nozzles 12 were offset by a shift distance sd = 84.67 μm according to the same interval definition shown in Fig. 3 and spaced with a nozzle - to - nozzle spacing ns / 2 = 84.67 μm. Gap distances G of 3 mm and 4 mm between the nozzle plate 10 and the deposition medium 3 were tested with a droplet volume of 3 pl and an initial droplet velocity up to 8 m / s, and the density of the droplets was 1100 kg / m 2 ³. To obtain a resolution of 1200 dpi, two printing frequencies, 20 kHz and 60 kHz, corresponding to media velocities of 1.248 m / s and 3.744 m / s, were evaluated.

[0065] Figures 5 and 6 are images of droplet displacement by simulation, showing the magnitude of the displacement in the y-direction of all nozzle prints, and are representative results from test runs described in Tables 1 and 2 shown as *(6×6 and 8×8 with the maximum sub-column spacing). The three nozzle cluster types, "4×4", "6×6", and "8×8", have both sub-columns 22 corresponding to the same nozzle cluster size, with 4 nozzles per nozzle cluster for the "4×4" cluster, 6 nozzles per nozzle cluster for the "6×6" cluster, and 8 nozzles per nozzle cluster for the "8×8" cluster. The following nozzle cluster spacings and lengths are applied. - 4×4 cluster: a = 423.34 μm and c = 254.00 μm, - 6×6 cluster: a = 592.67 μm and c = 423.34 μm, - 8×8 cluster: a = 762.00 μm and c = 592.67 μm. Each cluster type was tested at four different sub-column spacings b that are multiples of the nozzle distance ns, 2, 4, 6, 8 times, i.e., 169.33 μm, 338.67 μm, 508.00 μm, and 677.34 μm.

Table 1

Table 2

Table 3

Table 4

[0066] The table includes the image quality indicator DE for the visual perception of the dynamic elements (DE) of the wood grain phenomenon. The analysis is performed for the same gaps, cluster arrangements, and frequencies, and essentially compares the visual quality of the smallest sub-column spacing with the next larger sub-column spacing, and so on up to the largest sub-column spacing. "DE removed" means that when the dynamic elements of the wood grain phenomenon are not visible, "yes" is entered in the vertical column. The increase in the appearance of the dynamic element DE is indicated by "almost", "substantially reduced", and "no", where "no" indicates the strong presence of the DE.

[0067] For the selection of the simulation images indicated by (*) in Tables 1A, 1B and 2A, 2B (6×6 and 8×8 with the largest sub-column spacing), FIGS. 5A to 5D and 6A to 6D show the displacement of the droplets of each nozzle 12 along the printing direction (along the x direction). The displacement of each droplet is represented by a stepped scale and is calculated as the difference between the target nozzle coordinates and the actual (simulated) droplet landing coordinates, where black is the maximum displacement and white is no displacement. FIGS. 5 and 6 show only the absolute value of the displacement along the y direction for the purpose of evaluating the dynamic changes of the wood grain pattern. As shown in the scale below the figures, in the case of FIG. 5, the maximum displacement in the y direction was 2.5 μm in absolute value, and in the case of FIG. 6, it was 5 μm in absolute value.

[0068] For the 3 mm gap test and a subarray pitch b = 677.34 μm, FIGS. 5A - 5D show images of a 6×6 cluster at 20 kHz (FIG. 5A, test number 24) and an 8×8 cluster at 20 kHz (FIG. 5B, test number 40), as well as a 6×6 cluster at 60 kHz (FIG. 5C, test number 28) and an 8×8 cluster at 60 kHz (FIG. 5D, test number 44). As can be seen from FIG. 5A of the 6×6 cluster operating at 20 kHz, irregular displacements of the droplets may be seen along the y - direction over time, and in particular, a weak “wood - grain - like” pattern appears on the left side of the image at startup. The other three figures, FIGS. 5B - 5D, show more regular patterns. In all images, the patterns are caused by forced air flow. If the displacement along the y - direction is constant over time (after the startup time at the left side of the plot), this indicates that only the non - dynamic elements of the wood - grain - like pattern are present while the dynamic elements are prevented. The resulting pattern is a “band” pattern due to a certain amount of droplet displacement. Such “banding” can be reduced by appropriately adjusting the droplet size of the corresponding nozzles to deposit less droplet amount in the darker band - like regions and more droplet amount in the brighter band - like regions. The adjustment of the droplet amount is also called “trimming” of the droplets and achieves various droplet amounts, and thus dye densities, on the deposition media surface. Thus, for the simulations of FIGS. 5A - 5D, after the startup time, the DE of the wood - grain - like phenomenon is removed (shown as “yes” in the DE column of the table).

[0069] Comparing FIG. 5A with 5C and FIG. 5B with 5D, the patterns suggest that better control can be achieved by using an 8×8 cluster rather than a 6×6 cluster. Further, Table 1A suggests that for both 6×6 and 8×8 clusters, with a larger subarray pitch of 677.34 μm, the DE is removed earlier at 20 kHz. For the 6×6 case, b > a and b > c. Even for the second - largest subarray pitch b = 508 μm tested, the DE is either removed early (8×8) or significantly reduced (6×6).

[0070] At 60 kHz, the 6×6 clusters (Figure 5C) and 8×8 clusters (Figure 5D) each show a pattern of stronger but constant deviation over time after the startup period on the left side of the image. The simulation suggests that, depending on the application conditions, a good reduction of the wood grain phenomenon can be achieved by selecting a sufficiently high sub-column spacing. For example, in the case of 6×6 or 8×8 clusters, the sub-column spacing may be greater than 300 μm. At 20 kHz or 60 kHz, and with a 3 mm gap, the sub-column spacing may be greater than the cluster length in some cases b>c.

[0071] For a 4 mm gap, Figures 6A - 6D show the simulation results of the displacement of droplets over time for 6×6 and 8×8 clusters at a maximum sub-column spacing b = 677.34 μm. Figure 6A relates to test number 32 (6×6 cluster, 20 kHz), Figure 6B relates to test number 48 (8×8 cluster, 20 kHz), Figure 6C relates to test number 36 (6×6 cluster, 60 kHz), and Figure 6D relates to test number 52 (8×8 cluster, 60 kHz).

[0072] At 20 kHz, both 6×6 and 8×8 clusters exhibit a typical wavy grain pattern phenomenon (DE is not removed). Although not completely removed for any of the tested subarray spacings b, the DE of the grain pattern phenomenon is less visible in the 8×8 cluster with a subarray spacing b of 677.34 μm than in the 6×6 cluster with the same subarray spacing b. However, the DE is more prominent in the 6×6 arrangement than in the 8×8 arrangement. In the case of the 6×6 arrangement, the maximum subarray spacing of b = 677 μm has a significantly reduced DE compared to the minimum subarray spacing (b = 169 μm) of that arrangement, as shown in FIG. 7A tested under the same conditions. It should be noted that, therefore, in the case of FIG. 6B, most of the printed image can be adjusted by reducing the droplet amount. In the case of FIG. 6B, the subarray spacing is larger than the cluster length, i.e., b > c. Increasing the subarray spacing may further reduce the grain pattern phenomenon or, alternatively or additionally, increase the cluster length, for example, a 10×10 type cluster, for example, c = 762 μm and / or b > 677.34 μm or 762 μm or more. It will be understood that a cluster length significantly longer than that described herein will ultimately show a droplet curtain of a considerable length against the incoming forced air flow that cannot be controllably passed through and may cause the grain pattern phenomenon.

[0073] As described in Table 2B, the DE of the grain pattern phenomenon at a droplet frequency of 60 kHz and a gap of 4 mm appears to be not superior compared to a droplet frequency of 20 kHz. Tables 2A and 2B suggest that the smallest 4×4 type clusters reduce DE but are not more advantageous than 6×6 and 8×8 clusters, and 6×6 and 8×8 clusters reduce DE to a suitable extent at any subarray spacing b greater than b = 169 μm. Therefore, at higher droplet frequencies, the cluster length c and / or the cluster spacing a may have a greater impact on reducing the DE of the grain pattern phenomenon than the subarray spacing b.

[0074] The decrease in the dynamic element DE of the wood grain phenomenon with the increase in the sub-column interval b can be clearly seen in FIGS. 7A to 7D. In these figures, the simulated images show the dynamic progress of the droplet arrangement with a 4 mm gap G at 20 kHz for a 6×6 cluster arrangement according to the same dimensions and process as the 6×6 clusters tested in FIGS. 5A to 5D and 6A to 6D. The figures correspond to test numbers 33 to 36 (indicated by the symbol +) in Table 2A, and the initial sub-column interval of 169.33 μm increases to 338.67 μm (FIG. 7B), then to 508.00 μm (FIG. 7C), and finally to 677.34 μm (FIG. 7D). The minimum sub-column interval in FIG. 7A results in a strong DE that shows a "scaled skin" pattern that changes rapidly due to the dynamic phenomenon. In FIG. 7B, the displacement of the droplets begins to stabilize and the DE decreases. The sub-column interval of 508 μm (FIG. 7C) shows a significant decrease in DE compared to the sub-column interval of 169 μm, and b = 677.33 μm results in a further excellent decrease in DE (FIG. 7D). Although a certain degree of DE (shown as "significantly decreased" compared to other sub-column intervals) is possible even at b = 677.33 μm, FIGS. 7A to 7D clearly show that the DE gradually decreases as the sub-column interval b increases.

[0075] The simulations shown in FIGS. 5A to 5D, FIGS. 6A to 6D, and FIGS. 7A to 7D suggest that even improved reduction or prevention of DE depends on a specific combination of medium speed, droplet frequency, droplet volume (mass), and the specific gap G for a particular application. Therefore, a nozzle cluster arrangement suitable for a given application can be specified by varying the cluster length c, the cluster interval a, and the sub-column interval b.

[0076] To explain the visual effects by providing a flow path through the cluster when suitable cluster dimensions and intervals (cluster and sub-column) are selected, another simulation result of the dynamic progress of the droplet arrangement at low frequency / small gap (20 kHz, 3 mm) is shown in FIGS. 20 and 21, and for a 4x4 cluster at high frequency / small gap (60 kHz, 3 mm) in FIG. 22. In these figures, the effect of increasing the sub-column interval is further illustrated.

[0077] Figures 20A - 20C (test numbers 5, 7, and 8 in Table 1A indicated by the symbol □) show images simulated at 20 kHz with a 3 - mm gap for the 4×4 cluster arrangements of test numbers 5, 7, and 8 in Table 1A, i.e., arrangements with sub - column spacings b = 169.33 μm (A), b = 508 μm (B), and b = 677.34 μm (C). In this cluster arrangement, the dynamic element DE of the wood - grain phenomenon is not completely removed within the tested range, but as the sub - column spacing increases from 169.33 μm to 677.34 μm, the image clearly shows a significant reduction in DE. For the maximum sub - column spacing tested (677.34 μm), the DE component of the wood - grain phenomenon is almost completely removed, and mainly only the banding phenomenon is seen.

[0078] Similarly, Figures 21A - 21C (test numbers 37, 38, and 40 in Table 1A indicated by the symbol o) show images simulated at 20 kHz with a 3 - mm gap for the 8×8 cluster arrangements with sub - column spacings b = 169.33 μm (A), b = 338.67 μm (B), and b = 677.34 μm (C). DE is very dominant at the minimum sub - column spacing b = 169.33 μm (Figure 21A), but is almost removed by slightly increasing the sub - column spacing to b = 338.67 μm (Figure 21B). At the maximum sub - column spacing tested, b = 677.34 μm, DE appears to be completely removed (Figure 21C). Therefore, for some applications of printing low - resolution images, a sub - column spacing b of about 338 μm may be sufficient. For example, the sub - column spacing is at least 300 μm, but for more demanding applications, a sub - column spacing b of about 677 μm is required, for example, at least 600 μm.

[0079] Figures 22A to 22D show images simulated at 60 kHz with a 3 mm gap for test numbers 9, 10, and 41, 42 in Table 1B (indicated by the symbol Δ) for a 4×4 cluster arrangement (A) and an 8×8 cluster arrangement (C) with a minimum sub-column spacing b = 169.33 μm, and for a 4×4 arrangement (B) and an 8×8 arrangement (D) with the following spacing size b = 338.67 μm. It can be seen that the higher the frequency of droplet ejection, the less likely the droplets are to cause dynamic deviation (DE) due to the grainy phenomenon. In these cases, the minimum sub-column spacing b = 169.33 μm significantly reduced DE compared to the case without clusters (b = 0, not shown). At the next sub-column spacing b = 338.67 μm, the DE is completely removed. Therefore, for higher frequency applications and less stringent resolution requirements, a sub-column spacing of at least 150 μm in size may provide acceptable image quality. For more demanding applications, the sub-column spacing may have to be greater than 170 μm, preferably greater than 250 μm, and more preferably greater than 300 μm.

[0080] The above simulation results are similar to the 6×6 nozzle arrays of test numbers 23 and 24, but were tested by experiments using a nozzle plate array having an inter-subarray spacing in the middle of the array. When the nozzle spacing ns / 2 = 84.67 μm, the 6×6 experimental nozzle cluster array has a cluster length c = 423.3 μm, a cluster spacing a = 592.7 μm, and an inter-subarray spacing b = 592.7 μm, so in this case a = b. These nozzle plates were incorporated into a droplet ejection head and compared with a conventional droplet ejection head having the same ns / 2 but no nozzle clusters (i.e., using the arrangement of FIG. 2). FIGS. 8A - 8C show printed test samples printed with a 3 mm gap for (i) a conventional nozzle plate and (ii) an experimental nozzle plate having a 6×6 cluster. In both cases, by appropriately varying the media speed (0.416 m / sec at 20 kHz, 0.635 m / sec at 30 kHz, and 0.995 m / sec at 47 kHz), a resolution of 1200 dpi is achieved in the printing direction at 20 kHz (FIG. 8A), 30 kHz (FIG. 8B), and 47 kHz (FIG. 8C). At all frequencies tested, (i) the printed samples using the conventional nozzle plate show a typical wood grain pattern with clearly visible dynamic elements. The corresponding printed samples using a nozzle plate having a 6×6 cluster show only normal "banding" with the DE removed.

[0081] Therefore, the experimental tests show a method of using a 6×6 cluster arranged in two subarrays separated by an inter-subarray spacing b to remove the dynamic element DE of the visible wood grain phenomenon and leave only the "banding" of the static phenomenon, and it can be further reduced by adjusting (trimming) the droplet amount to also remove the banding phenomenon. This will be further explained below.

[0082] Returning to the exemplary embodiment of FIG. 3, the cluster spacing a, the cluster length c, and the inter-subarray spacing b are constant for all nozzle clusters 24 in the columns of the subarrays. In other words, in some embodiments, the inter-subarray spacing b may be substantially equal between two subarrays. Further, or alternatively, the cluster spacing a may be substantially equal for each subarray.

[0083] Optionally, the first sub-column interval b between the first sub-column and the second sub-column may be equal to the cluster interval a between the nozzle clusters of the first sub-column. Further, or alternatively, the sub-column interval b may be substantially equal to the cluster length c, for example, the first sub-column interval b between the first sub-column and the second sub-column may be equal to the cluster length c of the first sub-column.

[0084] Further, or alternatively, the cluster interval a may be substantially equal to the cluster length c within the same sub-column and / or the cluster length c of different sub-columns.

[0085] Alternatively, FIG. 9 shows an embodiment in which at least the first nozzle cluster 24_1a of the first sub-column 22_1 of the nozzle 12 has a first cluster length c 12 different from the second cluster length c 11 of the second nozzle cluster 24_1b of the first sub-column. In other words, the first sub-column comprises first and second subsets of nozzle clusters, and the cluster length of the first subset of nozzle clusters is different from the cluster length of the second subset of nozzle clusters. Further, or alternatively, at least the first nozzle cluster 24_1a of the first sub-column of the nozzles has a first cluster interval a 11 with respect to the adjacent second nozzle cluster 24_1b, and the interval a 11 is different from the second cluster interval a of the second nozzle cluster 24_1b with respect to the adjacent third nozzle cluster 24_1c of the first sub-column. 12 In some embodiments, the intervals between the nozzle clusters of separate sub-columns may be different. For example, by defining at least three sub-columns 22_1, 22_2, 22_3 of the nozzle column, the first sub-column 22_1 is spaced from the second sub-column 22_2 by a sub-column interval b 12 and the first sub-column is spaced from the third sub-column 22_3 by a sub-column interval b 13 ​They are spaced apart. In other words, one or more nozzle clusters of each of the first, second, and third sub-columns define a first sub-column spacing between the first and second sub-columns and a second sub-column spacing between the first and third sub-columns. The first sub-column spacing may be different from the second sub-column spacing. This may be advantageous for changing the air flow along the printing direction (x-direction) with respect to the front of the droplet curtain of the nozzle plate 10 of the droplet ejection head 2 (in the y-direction). For example, the forced air flow around the side of the droplet ejection head 2 may cause more deviation of the droplets ejected from the nozzles 12 closer to the side of the print head or closer to the end of the nozzle row than the droplets ejected from the nozzles 12 near the center of the droplet ejection head 2 or near the center of the nozzle row.

[0086] For example, the nozzle cluster 24 closer to the side of the droplet ejection head 2 can be arranged so that a wider flow path for the forced air to pass through the droplet curtain is obtained.

[0087] Referring now to FIG. 9, this shows an exemplary embodiment providing various cluster lengths c and various sub-column spacings b within the end regions of the rows of nozzles. The row 20 of nozzles 12 comprises nozzle clusters 24. The nozzles are spaced apart from each other at a constant nozzle spacing ns. The nozzle clusters define three sub-columns 22_1, 22_2, and 22_3. The sub-column 22_1 has nozzle clusters 24_1a, 24_1b, 24_1c,... The sub-column 22_2 has nozzle clusters 24_2a, 24_2b, 24_2c,... The sub-column 22_3 has nozzle clusters 24_3a and 24_3b. The nozzle cluster 24_3b is not shown as it is located at the other end of the row of nozzles. The three sub-columns define two sub-column spacings. The sub-columns 22_1 and 22_2 are spaced apart by a sub-column spacing b 12 and the sub-columns 22_1 and 22_3 are spaced apart by a sub-column spacing b 13They are spaced apart. The first nozzle cluster 24_1a of the secondary column 22_1 and the first nozzle cluster 24_3a of the secondary column 22_3 are examples of "8×8" clusters, and each nozzle cluster has 8 nozzles. In this embodiment, c 11 =a 11 =b 12 That is, the cluster interval a between the first nozzle cluster 24_1a and the second nozzle cluster 24_1b of the first secondary column 22_1 11 is defined by the cluster length c of the first nozzle cluster 24_3a of the third secondary column 22_3 31 (not shown), which is the same as the cluster length c of the first nozzle cluster 24_1a of the first secondary column 22_1 11 Furthermore, for example, the interval between nozzles arranged at the ends of adjacent nozzle clusters, such as between nozzle clusters 24_1a and 24_3a, is the same as the nozzle interval ns between nozzles within the same nozzle cluster 24 when viewed along the direction in which the set of secondary columns is projected in the column direction. This means that when viewed along the direction in which the set of secondary columns is projected in the column direction, the nozzles 12 of the first nozzle cluster 24_1a of the first secondary column 22_1 and the first nozzle cluster 24_3a of the third secondary column 22_3 form a continuous row of nozzles 12 with a constant nozzle interval ns. In this embodiment, a similar pair of nozzle clusters, 24_1n and 24_3b, are arranged at the opposite ends of the column 20 (not shown) and have the same configuration as the pair of nozzle clusters 24_1a and 24_3a.

[0088] The second and third nozzle clusters 24_1b, 24_1c of the first secondary column 22_1, and the first and second nozzle clusters 24_2a and 24_2b of the second secondary column 22_2 are examples of "6×6" clusters, and each nozzle cluster has 6 nozzles. In this embodiment, c 12 =a 12 =b 12 That is, the cluster interval a between the second nozzle cluster 24_1b and the third nozzle cluster 24_1c of the first secondary column 22_1 12is defined by the cluster length of the first cluster 24_2a of the second sub-column 22_2, which is the cluster length c of the second nozzle cluster 24_1b of the first sub-column 22_1 12 is the same as that.

[0089] Furthermore, when looking along the direction in which the set of sub-columns is projected horizontally upward in the column direction 26, the distance between the nozzles 12 arranged at the ends of adjacent nozzle clusters, for example, between the nozzle clusters 24_1b and 24_2a, is the same as the nozzle interval ns between the nozzles within the same nozzle cluster 24. This means that when looking along the direction in which the set of sub-columns is projected upward in the column direction, the nozzles 12 of the nozzle clusters of the first sub-column, the second sub-column, and the third sub-column form a continuous row of nozzles 12 with a constant projected nozzle interval.

[0090] In the arrangement of FIG. 9, there is a wider path near the end of the row because the forced air flow caused by the droplets ejected from the nozzles 12 passes through the air curtain. The path between the nozzle clusters 24_1a, 24_1b, and 24_3a has less resistance for the air to pass through than, for example, the path between the nozzle clusters 24_1b, 24_1c and 24_2a, 24_2b.

[0091] In another embodiment, a plurality of pairs of nozzle clusters may have a longer length and sub-column interval near the end of the row. The nozzle clusters near the end of the row can have a gradually widening path for the forced air flow to pass through, by nozzle clusters that gradually become longer and have more nozzles 12 closer to the end of the row than near the center of the row.

[0092] Separate from the embodiment of FIG. 9, the cluster length may be reduced and may have a shorter length and sub-column spacing near the ends of the columns. The nozzle clusters near the ends of the columns may have a path that gradually narrows in order to provide a faster and smaller flow path for the forced air flow passing through the air curtain generated by the droplets closer to the ends of the columns compared to the center of the columns. In this alternative embodiment, the sub-column spacing can be maintained constant such that all nozzle clusters are provided within two sub-columns.

[0093] To address the requirements of many applications in the field of printing, the resolution of the droplet ejection head may require more columns than provided in one column, as shown in the above embodiments and their various embodiments. This can be achieved by providing another column of nozzles 12 such that when viewing the set of sub-columns along the projection direction in the column direction, the nozzles 12 of the other column are arranged in an intermediate position with respect to the nozzles 12 of the first column. An example of the nozzle configuration of two columns of nozzles 12 to double the resolution of one column is shown in FIG. 10. Two columns 20A and 20B extend parallel to each other in the column direction (along the y direction). Each column includes nozzle clusters 24A and 24B, respectively. The nozzle clusters of column 20A each extend in their respective column directions 26A and define two parallel sub-columns 22A_1 and 22A_2 separated by a sub-column distance b A and the nozzle clusters of column 20B also each extend in their respective column directions 26B and define two parallel sub-columns 22B_1 and 22B_2 separated by a sub-column distance b B .

[0094] In the embodiment of FIG. 10, each column includes nozzles 12 that are separated from adjacent nozzles 12 of the same staggered offset group, also called a sub-cluster group, by a nozzle pitch ns. Further, when viewing along the direction in which two staggered offset groups (or sub-cluster groups) of a nozzle cluster are projected in the column direction (y direction), the projected nozzle pitch between adjacent nozzles of separate staggered offset groups is equal to ns / 2. Columns 20A and 20B are further arranged along the column direction, and when viewing the columns along the direction in which they are projected in the column direction, the projected nozzles of column 20B are separated from the projected nozzles of adjacent column 20A by a nozzle pitch ns / 4, i.e., one quarter of the nozzle pitch. This means that the nozzles of the second column are projected to an intermediate position between the projected nozzles of the first column. Thus, when used as one row for printing within the same line pixel, the effective nozzle pitch of the combination of two columns is ns / 2, and a resolution twice that of a single column 20A or 20B is obtained. This condition may not hold over the entire length of the first and second columns. For example, near the ends of the columns, the nozzle pitch may not be the same as the nozzle pitch near the center of the column, for example, to enable accurate alignment between columns of different nozzle plates. However, in the transition region between two or more nozzles of each adjacent projected nozzle cluster, the projected nozzle pitch is constant, i.e., the nozzles within the transition region can be expected to be equidistant. In FIG. 10, this is shown by transition region T1 between adjacent ends of nozzle clusters 24A_1 and 24A_2, as well as by transition region T2 between adjacent ends of nozzle clusters 24B_1 and 24B_2. In this example, transition regions T1 and T2 overlap when projected in the column direction, and the overlapping region is the same as the transition region.

[0095] Further, the nozzle clusters of column 20A each extend by a cluster length c A and are separated from adjacent nozzle clusters of the same sub-column 22A_1, 22A_2 by a cluster pitch a A apart. Similarly, the nozzle clusters of column 20B each extend by a cluster length cB extends and is spaced apart from adjacent nozzle clusters of the same sub-columns 22B_1, 22B_2 by a cluster interval a B In the embodiment of FIG. 10, the nozzle clusters are arranged such that the cluster length c, the cluster interval a, and the sub-column interval b are constant within each column, but this is not essential. Further, the nozzle clusters within column 20B are arranged in the same manner as the nozzle clusters within column 20A, and as a result, the interval between the sub-columns is the same, b A =b B and the cluster length and the cluster interval are the same, c A =c B , and a A =a B However, this is not essential, and in another embodiment, there may be three or more sub-columns per column, so the distance between the sub-columns varies along the direction of the column. Further, or alternatively, the cluster length c may vary within the same column, and / or the cluster interval a may vary within the same column. Further, it is not essential that two columns constitute a similar arrangement of nozzle clusters. By having a different number of nozzles 12 within another nozzle cluster, for example, the sub-column interval may not be the same, b A ≠b B and / or for example, the cluster length c and / or the cluster interval may not be the same, c A ≠c B and a A ≠a B There may be cases like this.

[0096] Accordingly, the nozzle plate 10 can comprise a second row of nozzles 12 comprising a second set of two or more sub - rows extending side - by - side in respective sub - row directions. At least two sub - rows (i.e., the first and second sub - rows) of the second set of sub - rows are laterally spaced apart in a third sub - row spacing perpendicular to the row direction. Each sub - row 22 of the second set of sub - rows is composed of one or more nozzle clusters 24, each of which comprises a plurality of nozzles 12. Further, each nozzle cluster 24 extends along the respective sub - row direction with a cluster length c and is spaced apart from adjacent clusters 24 by a cluster spacing a. Preferably, the third sub - row spacing is greater than 300 μm.

[0097] Depending on the application, the sub - row spacing between the first and second sub - rows of the set of sub - rows may be greater than 400 μm or greater than 500 μm. In some embodiments, the sub - row spacing may be less than 900 μm.

[0098] The second set of sub - rows may comprise three or more sub - rows. For example, one or more nozzle clusters of the first, second, and third sub - rows of the second set of sub - rows define a third sub - row spacing b3 between the first and second sub - rows of the second set of sub - rows and a fourth sub - row spacing b4 between the first and third sub - rows of the second set of sub - rows, and the third sub - row spacing is different from the fourth sub - row spacing.

[0099] An embodiment in which row 20A has an arrangement of nozzle clusters 24A different from that of a second row 20B having nozzle clusters 24B is shown in FIG. 11. The nozzle clusters 24A_1 and 24A_2 of row 20A are arranged to define two sub - rows 22A_1 and 22A2 spaced apart by a sub - row distance b A The nozzle clusters 24A_1a, b… and 24A_2a, b… are arranged according to a "6×6" pattern, and each nozzle cluster comprises six nozzles having a cluster length c A and a cluster spacing a A The nozzle clusters 24B_1a, b… and 24B_2a, b… of row 20B are separated by a sub - row distance bB They are arranged to define two spaced-apart sub-columns 22B_1 and 22B_2. The nozzle clusters 24B_1a, b and 24B_2a, b are arranged according to an "8×8" pattern, and each nozzle cluster 24B has a cluster length c B and a cluster spacing a B and includes eight nozzles. In this embodiment, the sub-column spacing between columns is not the same, b A ≠b B and the cluster length and cluster spacing are also not the same, c A ≠c B and a A ≠a B either.

[0100] The specific arrangement of the nozzle clusters can vary according to the requirements of the application, such as the gap G, the printing frequency, and / or the droplet velocity and mass. For example, the first sub-column or the first column of nozzles 12 that is subject to a forced air flow may require an arrangement that allows for a faster or specially adjusted air escape path than the second column of nozzles 12.

[0101] This can be achieved by spacing nozzle clusters 24 of short length c1 within a column by a short cluster spacing a1 from adjacent nozzle clusters within the first sub-column of the column of nozzles, and by a similar arrangement of spacing nozzle clusters of short length c2 by a cluster spacing a2 from adjacent nozzle clusters within the second sub-column of the column of nozzles, where c1 = a2 and a1 = c2. For example, the nozzle clusters may each include only 4, 6, or 8 nozzles. Further, a third sub-column with several nozzle clusters may provide a second sub-column spacing b2 to the first sub-column, for example near the end of the column, to reduce any side flow effects due to the forced air flow passing along the side of the print head. In this case, the first and second sub-columns have nozzle clusters near the center of the column, and the first and third sub-columns have nozzle clusters near the ends of the column.

[0102] An embodiment of such an arrangement is schematically shown in FIG. 12A. Column 20 has three sub-columns 22_1, 22_2, 22_3 that provide two sub-column spacings. The first sub-column spacing b1 is defined by nozzle clusters 24_1 and 24_2, and the second sub-column spacing b2 is defined by nozzle clusters 24_1 and 24_3. In this embodiment, the nozzle cluster of sub-column 22_2 is missing near the end of column 20. In the case of sub-column 22_3, the nozzle cluster is provided only near the end of the column. When looking at the three sub-columns along the direction of projection onto the column direction (along the x-direction) along the y-direction, the nozzles of all clusters form one continuous column, and each nozzle is spaced from the adjacent (projected) nozzle by a constant nozzle spacing ns. The cluster lengths of all three sub-columns are the same, c1 = c2 = c3, and as a result, the cluster spacings are also the same, a1 = a2 = a3. Due to the arrangement of the nozzle clusters, the two sub-column spacings are such that the first sub-column spacing b1 between the first sub-column and the second sub-column is smaller than the second sub-column spacing b2 between the first sub-column and the third sub-column, b2 > b1. However, it is not necessary to space the second and third sub-columns the same distance as the first and second sub-columns. FIG. 12A is merely an exemplary arrangement.

[0103] The object of the embodiment of FIG. 12A is that the sub-column spacing between nozzle clusters near and / or at the ends of the columns creates a greater distance between the nozzle clusters near and / or at the ends of the columns as compared to that near the center of the column. In this embodiment, between the nozzle clusters 24 of the separate sub-columns near the center of the column, in this embodiment, at least between the adjacent nozzle clusters of separate columns 24_1c and 24_2a, 24_2a and 24_1d, 24_1d and 24_2b, 24_2b and 24_1e, there is a greater sub-column distance between the nozzle clusters 24_1a, 24_3a, 24_1b and 24_3b, as well as this wider flow path for the forced air to pass through. On the other hand, the specific dimensions of at least the cluster length a1 and the cluster spacing c1 of the first sub-column create a break in the droplet curtain with a width and frequency sufficient to allow the forced air flow to pass through to the extent of visually shifting the droplets in the y-direction without creating cross-flow caused by the vortices. To adjust the design to a specific application, the sub-column spacing may be adjusted to vary the difference between b1 and b2 as needed, increasing the space available for the forced air to pass between the nozzle clusters. Additionally, or alternatively, the cluster length and / or spacing of each sub-column may be adjusted.

[0104] As an alternative to the embodiment of FIG. 12A, the first row of nozzle clusters of the first row can comprise nozzle clusters of short length c1 with a relatively long cluster spacing a1 with respect to adjacent nozzle clusters, where c1 < a1, and the second sub-column of the first row can comprise relatively long nozzle clusters of length c2 with a short cluster spacing a2 with respect to adjacent nozzle clusters, where c2 > a2. Since the nozzles 12 of the two sub-columns form a continuous row of equally spaced nozzles when viewed along the direction in which the sub-columns project onto the first row, this means that the nozzle cluster length c1 of the first sub-column is equal to the nozzle cluster spacing a2 of the second row, c1 = a2. Similarly, the nozzle cluster length c2 of the second sub-column is equal to the spacing a1 between the nozzle clusters of the first row, c2 = a1. An exemplary embodiment is schematically shown in FIG. 12B.

[0105] As can be seen from FIG. 12B, the row 20 of nozzles (not specifically shown) has two parallel sub-rows 22_1, 22_2 spaced apart by a first sub-row spacing b1 defined by the nozzle cluster 24_1 of the sub-row 22_1 and the nozzle cluster 24_2 of the sub-row 22_2. The nozzle cluster 24_1 of the first sub-row 22_1 has a length shorter than that of the nozzle cluster 24_2 of the second sub-row 22_2, i.e., c1 < c2. As a result, the cluster spacing of the first sub-row is larger than that of the second sub-row, i.e., a1 > a2. In other words, the cluster length of the first sub-row is equal to the cluster spacing of the second sub-row, and vice versa, i.e., c1 = a2 and c2 = a1. In this embodiment, although not strictly necessary, the nozzle clusters and the spacing of the first sub-row remain constant, as well as the nozzle clusters and the spacing of the second sub-row. For example, the length and the spacing may vary towards the ends of the row in another embodiment. When looking along the direction (along the x-direction) in which the two sub-rows are projected horizontally in the column direction (y-direction), the nozzles of all the nozzle clusters form one continuous row, and each nozzle is spaced apart from the adjacent (projected) nozzle by a constant nozzle spacing ns.

[0106] Due to the nozzle cluster arrangement of the embodiment of FIG. 12B, the first sub-row has less resistance to the forced air flow, and the second sub-row has greater resistance to the forced air flow. When the forced air flow passes through the first sub-row, some energy is consumed, so the second sub-row contacts the slightly weakened forced air flow. The sub-row spacing b1 can be selected to be at least as large as the minimum length of the clusters, for example, b1 = c1. More preferably, it is selected such that it does not exceed the maximum cluster spacing, i.e., 最小 c ≦ b1 ≦ a 最大 as can be.

[0107] In some nozzle plates 10, the arrangements according to the embodiments of FIGS. 12A and 12B may be present in the same column. Further, in some droplet discharge heads including a nozzle plate 10 having a plurality of columns of nozzles 12, the arrangements according to the embodiments of FIGS. 12A and 12B may be applied to different columns.

[0108] The nozzle clusters of the nozzle plate according to the above embodiment and its various embodiments can be further arranged as follows.

[0109] Furthermore, or alternatively, the first sub-column interval b1 may be substantially equal to the cluster interval a. Furthermore, or alternatively, the first sub-column interval b1 may be substantially equal to the cluster length c.

[0110] Furthermore, a first group including one or more nozzle clusters of the first sub-column of the nozzle column has a cluster length c of the second group of one or more nozzle clusters of the first sub-column 12 different from the cluster length c 11 can have.

[0111] Furthermore, or alternatively, a first group including one or more nozzle clusters of the first sub-column of the nozzle column has a cluster length c of the first group of one or more nozzle clusters of the second sub-column 21 different from the cluster length c 11 can have.

[0112] Furthermore, or alternatively, the nozzle cluster length c of one or more clusters of one or more sub-columns can be defined by including four or more nozzles 12.

[0113] Furthermore, or alternatively, the nozzle cluster length c of one or more clusters of one or more sub-columns can be defined by including six nozzles 12.

[0114] In the case of the nozzle plate 10 having two or more columns and the second column including a second set of sub-columns, the cluster length of the nozzle clusters of the first set of sub-columns may be the same as the cluster length of the nozzle clusters of the second set of sub-columns, and the cluster interval of the nozzle clusters of the first set of sub-columns is the same as the cluster interval of the nozzle clusters of the second set of sub-columns. On the other hand, in another embodiment, the cluster interval between the nozzle clusters of the first set of sub-columns is different from the cluster interval between the nozzle clusters of the second set of sub-columns.

[0115] Furthermore, each nozzle 12 of each column may be directly adjacent to another nozzle 12 of another column when projected upward in the column direction. In other words, all the nozzles 12 of all the columns contribute to the resolution of the droplet ejection head 2 and can be used to print within the same pixel line. Further, for example, in order to enable alignment between a plurality of nozzle plates 10, more than 50% (i.e., a majority) or at least 75% of the projected nozzles are equidistant from adjacent projected nozzles, allowing for different distances between the nozzles near each end of the column. This means that when viewing the first and second sets of sub-columns along the direction of projection upward in the column direction, the nozzles 12 of all the nozzle clusters 24 of the first and second sets of sub-columns form a continuous column of nozzles 12 with a changed constant projected nozzle interval. For example, the projected nozzle interval may be half of the projected nozzle interval between adjacent projected nozzles of the first set of sub-columns. Therefore, the resolution of the nozzle plate can be doubled by using two sets of sub-columns. The ends of the first and second sets of sub-columns may, in some cases, have different projected nozzle intervals in order to enable accurate alignment, for example, between the columns of nozzles of two partially overlapping nozzle plates. The number of nozzles in each column having different projected nozzle intervals may approach, for example, 25% or 50% of the total number of nozzles in the column.

[0116] In any of the above embodiments, the nozzles of each nozzle cluster may be arranged in parallel sub-clusters extending along the column direction, and the sub-clusters are spaced apart from each other by a sub-cluster spacing sd in a direction perpendicular to the column direction. For example, in FIG. 3A, each nozzle cluster 24 of six nozzles 12 each comprises two sub-clusters of three nozzles each, such that the nozzles within the same sub-cluster can be described as having the same staggered offset along the x direction.

[0117] Considerations Regarding Nozzle Misalignment Returning to FIG. 3A, the nozzle clusters in this embodiment are achieved by providing the nozzles 12 at specific positions with respect to the side surfaces of the corresponding pressure chambers 14, and the pressure chambers 14 are shown elongated in a direction orthogonal to the column direction (i.e., along the x direction). The side surfaces of the pressure chambers 14 with the nozzles 12 are planar with respect to the surface of the nozzle plate 10. The pressure chambers are arranged parallel to each other along the column direction (y direction). In this type of "side shooter" pressure chamber 14, it has been found that when the nozzles 12 are moved to an offset position from the central position towards one of the ends of the pressure chamber 14 with respect to the elongated side of the pressure chamber 14, the droplet ejection characteristics remain within an acceptable level. This misalignment is several hundred μm from the central position and can be up to about 400 μm in a specific pressure chamber design having a length of 1 mm along its elongated side. Thus, in some embodiments, it is possible to create the nozzle clusters 24 without providing clusters of the pressure chambers 14, for example, it may be possible to create the nozzle clusters 24 by shifting the nozzles 12 without the need to shift the pressure chambers 14. For example, a 6×6 cluster arrangement spanning two sub-columns may have six nozzles with a nozzle pitch ns / 2 of 84.67 μm, so that the cluster length is 5×84.67 μm = 423.35 μm. The distance between the nozzle clusters may be equal to the sub-column spacing, i.e., a = b = 7×84.67 μm = 592.69 μm. To create this sub-column spacing b, the nozzle clusters are centered on the center line C of the arrangement of the pressure chambers 14L It may be shifted 296.35 μm in the opposite direction from [a certain point]. When the length of the modeled pressure chamber is about 1 mm, this sub-column interval is nearly 50% of the total length of the pressure chamber.

[0118] Therefore, in the above-described embodiment and its various embodiments, the sub-column interval b of each sub-column can be greater than 300 μm and less than 900 μm. In some embodiments, the sub-column interval b of each sub-column may be greater than 500 μm or greater than 600 μm. In some cases, the sub-column interval may be up to 75% of the total length of the pressure chamber.

[0119] The entire range in which the sub-column interval can be created is limited by the length of the pressure chamber 14. The pressure chamber 14 is elongated and extends along the plane of the nozzle plate 10 (i.e., in the x direction), creating a nozzle cluster 24 by shifting the nozzle with respect to the center line C L while not shifting the pressure chamber 14, and enabling a simpler fluid supply path compared to a design with a staggered cluster of pressure chambers 14 where the nozzles 12 remain centered or nearly centered with respect to the long side of the pressure chamber 14.

[0120] FIG. 13 shows such another embodiment in which the pressure chambers 14 are clustered to maintain at least near the central nozzle position with respect to the length of the chamber. In FIG. 13, the nozzle cluster 24_1 of the first sub-column 22_1 of the nozzles 12 and the nozzle cluster 24_2 of the second sub-column 22_2 of the nozzles 12, as well as the column 20 of the nozzle plate 10, are formed centrally along the long face of the pressure chamber 14. How the pressure chambers 14 themselves are clustered by the nozzle clusters 24_1a, 24_2a, and 24_1b can be seen. Thus, the nozzle plate configuration may remain the same for different fluid arrangements that support the nozzle plate 10 within the printhead 2.

[0121] The nozzle clusters of the embodiments shown in FIGS. 3 to 13 are not limited to an even number of nozzles per nozzle cluster. Instead, any number of nozzles, for example, 5 or 7 nozzles per nozzle cluster, may be suitable. In a nozzle cluster of an odd number of nozzles arranged in a staggered (or "sub-cluster") configuration as shown, the flow path from one sub-row to the next can be made more uniform. As can be seen from FIG. 3B, for example, it is the flow path for forced air formed around the 6×6 cluster 24_1b and at the tip / around the clusters 24_2a, b, and the narrowest portions of the flow path are indicated by P1 and P2. Due to the staggered offset of an even number of nozzles per nozzle cluster, in this arrangement, the flow path is slightly asymmetric and can be important when the sub-row spacing is smaller. An odd number of nozzles per nozzle cluster will reduce this effect and make the flow path symmetric.

[0122] Second Embodiment of the Nozzle Plate Creating a controlled path through the droplet curtain is not limited to nozzle plates having the nozzle arrangements as described above. In some nozzle plates, according to a second embodiment, the nozzle cluster can comprise a plurality of nozzles arranged in an array that extends along the column direction and across several nozzles along the cluster depth direction, where the cluster depth direction is perpendicular to the column direction. Each nozzle cluster is arranged at a cluster spacing from its nearest neighbor along the column direction. The nozzle plate can comprise one or more columns of such nozzle clusters, and the nozzle clusters of each column can be further offset from each other in a direction perpendicular to the column direction. The arrangement of the nozzle clusters of this type of embodiment also defines a path between the nozzle clusters through which forced air can pass in a controlled mechanism manner, similar to the previous embodiment and its various embodiments. The nozzle clusters of the second embodiment can have a shape having a side surface extending along an angle with respect to the cluster depth direction. For example, the nozzle cluster can be trapezoidal, triangular, or parallelogram-shaped. Each nozzle cluster can be defined by a plurality of sub-columns each having one or more nozzles 12. When viewed along the direction in which the sub-columns are projected onto the column direction (in this case the cluster depth direction), the plurality of nozzles of all the nozzle clusters form a continuous column of nozzles, and each projected nozzle is equidistantly spaced from the nearest projected nozzle by a projected nozzle spacing. In other words, since the projected nozzles do not overlap, during use, each nozzle of the column of nozzle clusters deposits one or more droplets onto the corresponding pixels within the same pixel line.

[0123] Embodiments according to examples of nozzle arrangements suitable for reducing or preventing the wood grain phenomenon are shown in FIGS. 14A - 14B and FIG. 15.

[0124] Figures 14A - 14B illustrate a part of column 20 of nozzle 12. In Figure 14A, nozzle clusters 24 are arranged for every four nozzles along the column, and consecutive nozzle clusters 24a, 24b, and 24c are shown. The nozzle clusters are arranged along the column direction 26 and extend over a cluster depth d measured along a direction perpendicular to the column direction 26. The pressure chambers 14 that supply the nozzles 12 can be elongated along the x - direction along the cluster depth direction and extend parallel to each other, and a group of four nozzles that define the nozzle cluster 24 is supplied by four adjacent pressure chambers 14. The nozzle cluster 24 in this embodiment angles acutely in the column direction by spacing the nozzles within the nozzle cluster at a constant nozzle spacing indicated by ns along the column direction and a constant spacing sd between consecutive nozzles along the cluster depth direction. This arrangement results in a linear path of width w for air to pass through the nozzle cluster.

[0125] However, it is not essential that the nozzles within each nozzle cluster be spaced apart by a constant interval sd. Instead, sd may vary between consecutive nozzles. This would create a non - linear path for air to pass between the nozzle clusters.

[0126] Figure 14B shows a similar nozzle arrangement, but this time there are only two nozzles per nozzle cluster. Of the plurality of nozzle clusters provided in column 20, three nozzle clusters 24a, 24b, 24c are shown. The two nozzles within each nozzle cluster 24 define a cluster depth d by being spaced apart by a distance sd in a direction perpendicular to the column direction 26. Along the column direction 26, the nozzle clusters are spaced apart by a cluster spacing a. When projected onto the column direction 26, all the nozzles are spaced apart by a constant nozzle spacing ns. In other words, all the nozzles in column 20, when projected onto the column direction 26, form a continuous row of projected nozzles that are equidistant from each other with the projected nozzle spacing, and within which no nozzle overlaps any other nozzle in the same row. Thus, during use, each nozzle in the row of nozzle clusters deposits one or more droplets onto the corresponding pixel of the same pixel line. This arrangement also provides a linear path of width w for air to pass through the clusters of nozzles, and also results in a greater distance between the nozzles within each nozzle cluster along the cluster depth direction along x.

[0127] In both FIGS. 14A and 14B, the cluster spacing a provides a path of width w for forced air to flow between the nozzle clusters 24 in column 20. In these embodiments, the flow path is linear and angled at an acute angle towards the column direction 26. The angle formed between the side faces of the nozzle clusters along the depth direction and the column direction 26 is defined by the nozzle spacing ns and the cluster depth d of a linear arrangement of n nozzles where tan(angle) = d / (n - 1)×ns.

[0128] The nozzle arrangements shown in FIGS. 14A and 14B were provided on a nozzle plate and assembled into the same print head as those in experiments (i) and (ii) of FIG. 7. The print head was tested under the same conditions of using a 3 mm gap and achieving a resolution of 1200 dpi in the printing direction by appropriately changing the media speed for 20 kHz (FIG. 8A), 30 kHz (FIG. 8B), and 47 kHz (FIG. 8C) (0.416 m / s at 20 kHz, 0.635 m / s at 30 kHz, and 0.995 m / s at 47 kHz).

[0129] The nozzle arrangement according to FIG. 14A was provided on the nozzle plate 10 such that ns = 84.67 μm, a = 338.7 μm, sd = 254 μm, and thus d = 762 μm.

[0130] The nozzle arrangement according to FIG. 14B was provided on the nozzle plate 10 such that ns = 84.67 μm, a = 169.3 μm, sd = 677.3 μm, and thus d = 677.3 μm.

[0131] It can be seen that for any of the embodiments, a significant reduction in the wood grain phenomenon can be achieved, and depending on the application, an acceptable image quality, or an image quality that can be further improved by other means combined with the current embodiments, can be provided.

[0132] Therefore, it is clear that providing a flow path through the nozzle rows according to the implementation of this embodiment can reduce or prevent the occurrence of visible wood grain patterns by controlling the passage of air through the nozzle rows, thereby reducing or preventing at least the dynamic elements of the wood grain phenomenon.

[0133] In the variations shown in FIGS. 14A and 14B, the cluster length is the length of one nozzle, or c = ns. The cluster length can be assumed as the width of the droplet curtain that comes into contact with the forced air when the forced air first reaches the cluster.

[0134] Next, another embodiment with two or more nozzles per nozzle cluster along the cluster length c will be described with reference to FIG. 15. FIG. 15 shows a row of identical nozzle clusters 24. Each nozzle cluster has a plurality of nozzles, in this case arranged in a matrix of nine nozzles 12.

[0135] Each nozzle cluster 24 is in the shape of a parallelogram, with both the short side and the long side forming acute angles in the row direction 26. In some embodiments of this nozzle arrangement, the nozzle plate 10 itself is a parallelogram formed to follow the long side of the nozzle cluster, for example, to help adjacent nozzle plates be arranged side by side, but the nozzle plate may take different shapes.

[0136] The row 20 is shown along the y - direction, along the general direction of the row of nozzle clusters. The nozzle clusters are spaced apart by a cluster spacing a measured along the row direction so as to define parallel flow paths of width w for air to pass between the nozzle clusters. As in FIGS. 14A and 14B, the paths are straight and extend at an acute angle to the row direction 26.

[0137] Each nozzle cluster 24 comprises sub - clusters of nozzles arranged along the cluster depth direction and is defined to define a cluster depth d, whereby each sub - cluster can be spaced apart from the subsequent sub - row by a sub - cluster spacing sd. The nozzles within each sub - cluster are spaced apart from the nearest nozzles by a nozzle spacing sd along the row direction. Each sub - cluster extends at an acute angle to the row direction 26. The cluster depth direction extends perpendicular to the row direction 26 as before.

[0138] When all the nozzles in all the nozzle clusters are projected upward in the column direction 26, the nozzles 12 in the nozzle cluster 24 of column 20 form a continuous row of equally spaced nozzles 12 that are spaced apart at a constant interval smaller than ns. This is shown by the pixel line 8 where each pixel corresponds to one nozzle in the row, and the nozzles 12 of column 20 correspond one-to-one to the pixels of pixel line 8.

[0139] In this way, using the nozzles arranged in an n×m matrix within each nozzle cluster of column 20, one or more droplets can be deposited within the same pixel line on the deposition medium such that each nozzle deposits one or more droplets onto one pixel respectively. Using the nozzle cluster arrangement of the figure, a parallel flow path can be created through the nozzles arranged in an n×m matrix within each nozzle cluster of column 20 for passing forced air, and as a result, the wood grain phenomenon can be transformed into a non-dynamic element that can be further reduced by reducing the droplet amount.

[0140] In some embodiments, the short side of the nozzle cluster may not form an acute angle with the column direction. For example, each of the sub-rows of three nozzles can be aligned parallel to the column direction. The specific positions of the nozzles along the depth direction of the nozzle cluster determine the timing at which each nozzle needs to eject droplets so that all the droplets land on the pixel line 8 on the deposition medium. Further, each nozzle cluster is not limited to having nine nozzles each, and nozzle clusters with various numbers of nozzles arranged in an n×m matrix can be envisioned that achieve the same purpose of creating a flow path for forced air to pass through the row of nozzles.

[0141] The flow paths of any of the embodiments of FIGS. 14 and 15 may be further modified by offsetting clusters of nozzles that are arranged alternately along the depth direction of the cluster. For example, they may be offset until they create separate sub-columns 22_1 and 22_2 similar to the sub-columns of the previous figure, and this provides a sub-column spacing b in addition to doubling the inter-cluster spacing between the nozzle clusters of the same sub-column.

[0142] Next, a variant will be described that shares the concepts of the first and second embodiments and can be considered a hybrid having the same purpose of creating a flow path for forced air to pass through the rows of nozzles to prevent or reduce the dynamic elements of the graining phenomenon.

[0143] FIG. 16A shows a part of a conventional row 13 having a plurality of nozzles 12 arranged in an m×n matrix, where m is 3, and where n is the number of nozzles along the x direction and m is the number of nozzles along the y direction. In other words, row 13 is three nozzles deep. Each nozzle of the conventional row 13 is offset along the row direction with respect to all other nozzles, such that with each nozzle, one or more droplets can be deposited on the corresponding pixels of pixel line 8. This conventional row 13 can be rearranged to form a row 20 having two sub-columns 22_1, 22_2 each comprising nozzle clusters 24_1a, b and 24_2a, b. The position of each nozzle along the row direction is maintained with respect to the conventional row 13 such that the nozzles and the pixels of pixel line 8 maintain a 1:1 correspondence. This is shown by the dashed leader lines between the pixels and the first nozzle of each nozzle cluster.

[0144] To achieve the nozzle arrangement of column 20, column 13 is divided into equal sub-matrices each having a 5×3 nozzle array, and the alternating 5×3 matrices are translated along a direction perpendicular to the column direction to form nozzle clusters 24 that create flow paths through column 20 that allow forced air to pass through. In this embodiment, each nozzle cluster 24 has a parallelogram shape defined by five nozzles spaced nozzle interval ns along the column direction 26 and three nozzles spaced offset interval sd along the cluster depth direction, and has a length c. In addition to the linear paths between nozzle clusters in the same sub-column, the sub-column interval b between sub-columns defines a flow path for air to pass around the nozzle clusters 24_2 of the second sub-column 22_2. This nozzle arrangement may be provided on a nozzle plate having a parallelogram shape, but the shape of the nozzle plate is not essential for generating the nozzle arrangement of column 20.

[0145] Using an approach similar to that of FIG. 16A, FIG. 16B shows a conventional column 13 moved to column 26. The figure is the same except for the nozzle clusters 24_1a, b of sub-column 22_1 that are inverted in shape around their centerlines parallel to the column direction as compared to those of FIG. 16A. The cluster length cc and the cluster interval aa are maintained, but the flow paths between sub-columns and between the nozzle clusters of the first sub-column and the nozzle clusters of the second sub-column may have more similar flow characteristics because the intervals P1, P2 between the inner cluster corners between the two sub-columns are similar.

[0146] In another embodiment shown in FIG. 17A, the nozzles of the conventional column 13 are assigned a trapezoidal shape, and the alternating trapezoidal regions are offset in a direction perpendicular to the column direction to form nozzle clusters 24 disposed in two sub-columns 22_1 and 22_1 of column 20. The two sub-columns are spaced a sub-column distance b, which is the flow path width defined by the inner nozzles of the clusters of the separate sub-columns.

[0147] Each nozzle cluster comprises a sub-cluster of nozzles arranged along the cluster depth direction, whereby each sub-cluster is spaced apart from the subsequent sub-cluster by a sub-cluster spacing s. Each nozzle within each sub-cluster is spaced apart from the nearest nozzle along the column direction 26 by a nozzle spacing n. The nozzles of each sub-cluster are offset with respect to the adjacent nozzles in the adjacent parallel sub-clusters, such that when all the nozzles of all the nozzle clusters are projected onto the column direction 26, the nozzles across the entire column 20 form a continuous column of equally spaced nozzles 12.

[0148] In this way, using all the nozzles of column 20, each of one or more droplets can be deposited on the same pixel line on the deposition medium. When viewed along the printing direction (along the x direction), which is the same direction as the direction in which the depth of the cluster extends, the first sub-cluster of nozzles of the nozzle clusters 24_1a, b has a cluster length c1, and the first sub-cluster of the nozzle clusters 24_2a, b has a cluster length c2. In the case of the nozzle clusters 24_1a, b, the cluster length gradually increases along the cluster depth direction up to the cluster length c2, and in the case of the nozzle clusters 24_2a, b, the cluster length gradually decreases along the cluster depth direction down to the cluster length c1.

[0149] The trapezoidal nozzle cluster arrangement can be used with a parallelogram-shaped nozzle plate or a trapezoidal nozzle plate as shown in Figure 16B, creating a forced air flow path to turn the wood grain phenomenon into a passive element and further improve it by reducing the droplet volume. In Figure 17A, the flow paths created between nozzle clusters in the same sub-column are flow paths that merge or branch. In another embodiment, similar to the nozzle clusters in the first sub-column of Figure 16B, the nozzle clusters in the first (or second) sub-column can be inverted about the center line, and the flow paths branch or merge between all the nozzle clusters in column 20 to create equal flow path resistances. Further, this will change the length of any narrow passages of the flow paths between the inner corners of the nozzle clusters in separate sub-columns, particularly the flow paths along the column direction 26. The arrangement in Figure 17A can show a narrow flow path region NR between the nozzle clusters in the first sub-column and the nozzle clusters in the second sub-column as indicated by the arrow in Figure 17A. In other words, when projected onto the column direction 26, the overlap of the cluster lengths measured adjacent to the center line CL between the two sub-columns can have a length that provides a significant flow resistance to the forced air when passing through column 20.

[0150] The narrow flow path region NR between the nozzle clusters can be reduced or prevented by increasing the sub-column spacing b and / or by inverting one of the nozzle clusters in a sub-column such that the short length of one sub-column and the long length of the other sub-column face each other. The inversion of the nozzle cluster is shown in Figure 17B. In this case, the opposing forced air passes through the nozzle clusters in the first and second sub-columns through the branched flow paths between the nozzle clusters in the same sub-column. As a result, the length of the flow path between the nozzle clusters in separate sub-columns becomes shorter compared to the flow path NR in Figure 17A. Further, the initial lengths c1 and c2 of the nozzle clusters in the two sub-columns contacted by the forced air when contacting the column of nozzles 20 are the same, and the cluster spacings a1, a2 contacted by the forced air when passing through the flow paths between the nozzle clusters in any of the sub-columns are the same. In other words, when projected onto the column direction 26, the center line C between the two sub-columns LThe overlap of the cluster lengths measured adjacent to [it] decreases in the arrangement of FIG. 17B compared to the arrangement of FIG. 17A.

[0151] In all embodiments of FIGS. 15 and 16, the flow path characteristics can be changed by changing the cluster length and / or the spacing, as well as the sub-column spacing b, and can be adapted to specific applications and even reduce or prevent the dynamic elements of the wood grain phenomenon.

[0152] If necessary, the number of sub-columns is not limited to two sub-columns. Instead, the nozzle cluster can be arranged in two or more sub-columns, for example, 3 or 4 sub-columns, to further increase the width of the narrow flow path and / or shorten its length to reduce the flow resistance of the flow path through the nozzle cluster.

[0153] Therefore, according to the second embodiment and its implementation, a nozzle plate 10 for a droplet ejection head is provided, which includes at least a first row 20 of nozzles 12 arranged to deposit droplets on a deposition medium. The first row 20 of nozzles extends in the row direction 26 and includes one or more nozzle clusters 24. Each nozzle cluster 24 is arranged with a cluster length c along the row direction 26 and extends with a cluster depth d along the cluster depth direction perpendicular to the row direction. Each nozzle cluster 24 includes a plurality of nozzles 12, one or more of which within each nozzle cluster define the cluster length c, and two or more nozzles within each nozzle cluster define the cluster depth d. Each nozzle cluster 24 is spaced apart from adjacent nozzle clusters along the row direction 26 by a cluster spacing a that is greater than the nozzle spacing ns between adjacent nozzles within the same nozzle cluster. Further, the nozzles in the first row are equally spaced from adjacent projected nozzles by the projected nozzle spacing when projected onto the row direction 26.

[0154] Optionally, each projected nozzle cluster in the first column may be spaced apart from an adjacent projected nozzle cluster by a nozzle spacing projected therebetween. For example, this is the case for the nozzle clusters 24 in FIGS. 13 and 14. When projected in the column direction, the nozzle clusters in these figures do not fit together. On the other hand, the nozzle clusters in FIGS. 16 and 17 fit together when projected upward in the column direction.

[0155] In some embodiments, the cluster spacing a may be greater than the spacing between four adjacent nozzles.

[0156] Furthermore, or alternatively, a plurality of nozzle clusters in column 20 can comprise two or more sub-clusters of nozzles. The sub-clusters extend substantially along the column direction and are arranged parallel to each other to form a matrix of nozzles. An example of such sub-clusters is shown in FIGS. 15-17, where the nozzle clusters take the form of a matrix of nozzles. From FIG. 15, it can be seen that the sub-clusters are angled at an acute angle in the column direction and "extend substantially along the column direction" at an angle of less than 45° to the column direction 26.

[0157] In some embodiments, the nozzle clusters can be arranged in one or more of the shapes of a parallelogram, a trapezoid, or a triangle. The parallelogram or trapezoid cluster shapes are shown in FIGS. 15-17. The inclined sides of the nozzle clusters serve to overlap or fit into the nozzle clusters along the column direction.

[0158] Furthermore, as shown in FIGS. 16 and 17, nozzle clusters adjacent to each other along the column direction can be offset from each other along the depth direction of the clusters. For example, the nozzle clusters can be arranged in two sub-columns 22_1 and 22_2, and the flow path created between the two sub-columns has a width defined by the sub-column spacing b, where the sub-column spacing b is the center line C of the columns of the nozzle clusters of the separate sub-columns LIt is the distance along the depth direction between the innermost nozzles closest to it. This is shown, for example, in FIGS. 17A and 17B.

[0159] In the clusters shown in FIGS. 15 to 17B, the cluster 24 is arranged so as to overlap with adjacent clusters in both the column direction (along y) and the direction perpendicular to the column direction (along x).

[0160] In all of the above-described embodiments and their various examples, the air flow path is created by the cluster spacing a so as to create a flow path for the forced air to pass through the rows of nozzles in a controlled manner. "In a controlled manner" means reducing or preventing the dynamic elements of the wood grain phenomenon, and can be understood, for example, as meaning reducing the phenomenon only for banding which is not a dynamic phenomenon.

[0161] Thus, generally, the nozzle plate 10 is provided for the droplet discharge head 2 including at least a first row 20 of nozzles 12 arranged to deposit droplets on the deposition medium. The first row of nozzles extends in the column direction 26 and includes one or more nozzle clusters 24. Each nozzle cluster 24 is arranged with a cluster length c along the column direction 26, and each nozzle cluster is spaced apart from an adjacent nozzle cluster by a cluster spacing a along the column direction 26, creating a flow path for the forced air to pass through the rows of nozzles in a controlled manner. When viewing the nozzle cluster 24 along the direction of projection onto the column direction 26, the plurality of nozzles 12 in the row 20 form a continuous row of nozzles in which the projected nozzles are equally spaced from each other by the projected nozzle spacing. In other words, since none of the projected nozzles completely overlap with any other nozzles in the same row, in use, each nozzle in the row of nozzle clusters can be used to deposit one or more droplets onto corresponding pixels within the same pixel line on the deposition medium.

[0162] In some embodiments, the cluster spacing can vary along the column direction. For example, the nozzle cluster spacing between the first pair of adjacent nozzle clusters may be different from the cluster spacing between the second pair of adjacent nozzle clusters in the column.

[0163] Furthermore, or alternatively, the spacing between nozzle clusters can vary along the depth direction of the cluster, and the depth direction of the cluster is perpendicular to the direction of the nozzle column.

[0164] The nozzle clusters may be arranged in two or more sub-columns, the sub-columns extend along the column direction, are parallel to each other, create a flow path of width by the sub-column spacing b between adjacent sub-columns, and forced air passes from one sub-column to the next sub-column. The sub-column spacing between the first sub-column and the second sub-column may be the same as or different from the sub-column spacing between the second sub-column and the third sub-column.

[0165] The nozzle clusters may further, or instead of being arranged in sub-columns, comprise two or more sub-clusters, each sub-cluster within the nozzle cluster extends substantially along the column direction, the sub-clusters within each nozzle cluster are arranged parallel to each other, and are separated by a sub-cluster spacing sd.

[0166] The sub-clusters can be arranged to extend at an acute angle to the column direction, and "extending substantially along the column direction" can mean an acute angle of up to 45° with respect to the column direction.

[0167] The clusters of the second embodiment are shown to each comprise a matrix of up to 15 nozzles. The modeled results of the variant of the first embodiment suggest that it is the combination of the cluster length c and the air gap formed by the cluster spacing a / sub-column spacing b for the forced air to pass through the rows of nozzles in a controlled manner that determines the reduction of the wood grain phenomenon. Similar results can be expected for the second embodiment with respect to the first row of nozzles contacted by the forced air or by the first sub-cluster of the first sub-column, for example, for a cluster length of up to 10 nozzle widths and a cluster length c of 800 μm or less.

[0168] Method FIG. 18 is a schematic diagram of the timing event t of the drive pulse 32 applicable to an embodiment of one row 20 comprising two sub-rows having a nozzle cluster 24_1 in the first sub-row and a nozzle cluster 24_2 in the second sub-row. The nozzles 12 of each nozzle cluster 24 are offset in a direction perpendicular to the row direction within the staggered group 28. When a deposition medium including the pixel positions of the pixel line 8 passes under the nozzles of the row 20, all the nozzles of the row 20 can be individually controlled to deposit each of one or more droplets onto the corresponding pixels of the pixel line 8 on the deposition medium.

[0169] Alongside the nozzle cluster 24 and the drive pulse 32, the effect on the pixel line 8 on the deposition medium is illustrated at different timings t of the drive pulse 32.

[0170] A method of controlling an actuator corresponding to nozzle 12 to eject one or more droplets per line pixel from each nozzle 12 is based on a staggered group 28 of nozzles 12 within the same sub-column arranged at the same staggered offset distance in a direction orthogonal to the column direction (along the y direction). The staggered groups 28_1(i) and 28_1(ii) are provided within the nozzle cluster 24_1 of the first sub-column, and the staggered groups 28_2(i) and 28_2(ii) are provided within the nozzle cluster 24_2 of the second sub-column. The cluster group 28_1(i) of the nozzle cluster 24_1 needs to eject droplets first when the deposition medium passes below in the printing direction (along the x direction), followed by the cluster group 28_1(ii), the cluster group 28_2(i), and finally the cluster group 28_2(ii).

[0171] The actuator signal 30 applied to the actuator of the corresponding nozzle 12 includes a drive pulse 32 and is offset along the amplitude (V) axis for visual simplification. Each staggered group 28 is arranged to eject droplets in response to the application of the corresponding drive pulse 32 within the actuation signal 30. Each drive pulse is associated with each staggered group by a dotted line. For simplification, only one drive pulse for ejecting one droplet is shown, but in reality, several droplets can be ejected from the same nozzle and deposited on the same pixel.

[0172] For visual simplification, FIG. 18 illustrates a printing that uses all nozzles to eject droplets onto a pixel line. In reality, depending on the image data, only one or more nozzles can deposit droplets onto a pixel line.

[0173] When the position of the pixel line 8 to be printed passes under the droplet ejection head 2, the operation of the droplets from the four staggered groups 28 is actuated at a specified time. When the pixel line 8 passes under the first staggered offset group (sub-cluster group) 28_1(i) of column 20, the first staggered offset group 28_1(i) receives the drive pulse 32_1(i) first at time t0, and ejects droplets from each of the nozzles 12 of the staggered offset group 28_1(i) to the corresponding pixels on the pixel line 8.

[0174] When the pixel line 8 further moves and passes under the second staggered group 28_1(ii), the staggered group 28_1(ii) receives its drive pulse 32_1(ii) at time t1, and ejects droplets from each nozzle 12 of the staggered offset group 28_1(ii) to the corresponding pixels on the pixel line 8.

[0175] Next, when the position of the pixel line on the deposition medium moves under the third staggered group 28_2(i) of column 20, which is the first staggered offset group of the second sub-column, the drive pulse 32_2(i) is applied at time t2, and droplets are ejected from each nozzle 12 of the staggered offset group 28_2(i) to the corresponding pixels on the pixel line. Finally, when the pixel line passes under the fourth staggered offset group 28_2(ii) of column 20, which is the second staggered offset group of the second sub-column, the drive pulse 32_2(ii) is applied at time t3, and droplets are ejected from each nozzle 12 of the staggered offset group 28_2(ii) to the corresponding pixels on the pixel line. Thus, the pixel line 8 is completed.

[0176] FIG. 18 illustrates a completely printed pixel line, and each nozzle 12 ejects droplets to its corresponding pixel on the pixel line. Of course, this is not always the case, but in most images, at a specific time of the printing process, according to the image data, some or all of the nozzles 12 will not receive drive pulses. However, all the nozzles 12 always remain members of the same staggered group.

[0177] The same principle is applied to print on the same pixel line from two or more sub-columns of column 20, or from two or more columns 20 each having one or more sub-columns.

[0178] FIG. 18 is based on a nozzle arrangement according to a first embodiment in which nozzle clusters are generated within sub-columns of column 20, but the same principle of printing one pixel line with all the nozzles of column 20 uses an arrangement according to a second embodiment, where the nozzle clusters are not arranged in two sub-columns, but angled flow paths are generated between the nozzle clusters by shifting the nozzles in the depth direction of the cluster within the same nozzle cluster, and when viewed along the column direction, the nozzle clusters overlap. In the arrangements of FIGS. 14 and 15, the sub-clusters preferably operate at a specified time such that all the nozzles within those sub-clusters having the same position along the printing direction (along the x direction) operate at the same timing t. Thus, the sub-clusters are processed in a manner similar to the staggered offset group 28 of FIG. 18.

[0179] The hybrid arrangements of FIGS. 16 and 17 include sub-clusters as well as sub-columns. From the perspective of timing, successive sub-clusters arranged at increasing distances from the front of the column along the printing direction are operated with an increasing timing delay so as to eject droplets onto the same pixel line 8.

[0180] A method of using the nozzle plate 10 according to the above embodiments and steps in which one or more droplets are deposited on a pixel line from one or more nozzles of a nozzle cluster of a column, each nozzle of the column corresponding to one pixel of the pixel line, including the step of depositing.

[0181] In some embodiments where column 20 comprises a first sub-column and a second sub-column, each sub-column extends parallel to each other in the column direction, the first sub-column constitutes a first group of nozzle clusters, and the second sub-column constitutes a second group of nozzle clusters. The method may further include depositing droplets from the nozzles of the first group of nozzle clusters onto the pixel line at time t1, and depositing droplets from the nozzles of the second group of nozzle clusters onto the pixel line at time t2.

[0182] In the case of a two-column nozzle plate, the method may further include depositing droplets from the nozzles of the nozzle cluster of the first sub-column of the second column onto the pixel line at time t3, and depositing droplets from the nozzles of the nozzle cluster of the second sub-column of the second column onto the pixel line at time t4.

[0183] Alternatively, when one or more nozzle clusters include a plurality of sub-clusters, the sub-clusters generally extend parallel to each other along the column direction. Instead, the method may further include depositing droplets from the nozzles of the first sub-cluster onto the pixel line at time t1, and depositing droplets from the nozzles of the second sub-cluster onto the pixel line at time t2.

[0184] For example, the method executed by the control system may include receiving image data of the pixel line, receiving the media encoder signal, and determining drive data 33 based on the image data and the media encoder signal. The drive data defines the timing t for actuating one or more nozzles in one or more nozzle clusters to deposit droplets onto the corresponding pixels of the pixel line.

[0185] Furthermore, the step of determining the drive data 33 may further include determining the drive data of the second set of sub-columns of the second column. The drive data of the second set of sub-columns defines the timing t of the nozzles of each sub-column of the second set of sub-columns to deposit droplets onto the pixel line.

[0186] The method may further include a step of generating an actuation signal 30 based on drive data 33 for depositing droplets on a pixel line at one or more nozzles of one or more sub-columns, and a step of providing the actuation signal 30 to an actuator 11 corresponding to the nozzle in order to deposit droplets on a pixel line at the one or more nozzles. In some embodiments, this step can be performed from the droplet ejection head 2 by a droplet ejection head controller provided in the droplet ejection head 2.

[0187] Optionally, the method may include adjusting the droplet volume of each nozzle in response to the printed image data so as to reduce or prevent banding by forced air flow. This step can be used to reduce the non-dynamic elements of the banding of the wood grain phenomenon. This is achieved by generating test print data of darker and lighter bands and adjusting the droplet volume deposited on the bands in order to reduce or prevent the visual change in the dye density along the pixel line. For example, the test print data 40 can be generated from a test print by measuring the pixel density across the pixel line achieved at a particular process setting (e.g., gap distance, pixel frequency, media speed) for the range of measured print pixel densities, and determining the adjustment value 42 for achieving the target density required to prevent banding. This can be done, for example, by using a look-up table that converts the perceived dye density to the target dye density for each pixel and each nozzle by applying the adjustment value to each nozzle. This adjustment value may be, for example, an adjustment value of the nominal drive voltage of the actuation pulse for ejecting droplets from the nozzle. The peak-to-peak actuation pulse voltage can be reduced, for example, to reduce the droplet volume of the nozzles contributing to the darker bands of the printed image. Additionally, or alternatively, the voltage may be increased to increase the droplet volume of the nozzles contributing to the lighter bands of the printed image. The adjustment value 42 is empirically determined for the changed droplet volume per nozzle across column 20 by a series of experimental print tests, stored in a look-up table, and can be used to increase or decrease the droplet volume per nozzle during printing to reduce or prevent the visual banding phenomenon. For example, as a result of the adjustment value 42 identified and used to change the drive pulse 32, fewer droplet volumes can be ejected by the nozzles contributing to the dark bands, resulting in a lower pixel density, while larger droplet volumes can be ejected by the nozzles contributing to the lighter bands, resulting in a higher pixel density. The adjustment value may be provided as an adjustment signal to the droplet ejection head controller as part of the drive data 33.

[0188] Therefore, if the drive data 33 is further determined based on the adjustment value and includes an adjustment signal based on the adjustment value, the adjustment signal causes the droplet amount of one or more nozzles in a column to be changed in order to reduce the influence of banding.

[0189] Controller FIG. 19 is a block diagram of a control system 50 for implementing a method aimed at printing using the above nozzle arrangement and reducing or preventing at least the dynamic elements of the wood grain phenomenon by forced air passing through the droplet curtain.

[0190] The timing for actuating the actuators of the staggered offset group 24 can be controlled by a drive signal controller 4 shown as part of the droplet ejection device 1 of FIG. 1A. The drive signal controller 4 is part of the control system 50 of the droplet ejection device as shown in FIG. 19.

[0191] The control system 50 of FIG. 19 further includes a media encoder circuit 7. The media encoder circuit 7 receives an input related to the position of the media on the media transport port system 5 from the media transport port system 5. The media encoder circuit 7 provides a media encoder signal 34 to the drive signal controller 4, enabling the controller to determine the position of the pixel line 8 on the deposition media.

[0192] The drive signal controller 4 is configured to receive the media encoder signal 34 and is further configured to receive image data 36 from, for example, a PC provided in or associated with the droplet ejection device 1. The drive signal controller 4 determines a drive signal from the media encoder signal 34 and the image data 36 and is configured to provide the drive signal to the droplet ejection head controller 9 of the droplet ejection head 2.

[0193] The droplet ejection head 2 includes actuators 11, and each actuator 11 is configured to eject droplets to each of at least one nozzle 12 based on an actuation signal 30. The actuation signal 30 is provided to the actuator 11 by the droplet ejection head controller 9 based on drive data 33 received from the controller 4, and the droplets of each staggered group are deposited on the pixel line at the correct timing t. Therefore, the timings from t0 to t3 in FIG. 18 are based on the dynamic media position (and thus the media speed), and can be adjusted dynamically for consecutive line pixels, or for consecutive staggered offset (sub-cluster) groups, for example, for changes in the media speed such as during acceleration and deceleration at the start and end of image printing.

[0194] Therefore, the drive signal controller 4 is provided to execute the method described using the above embodiments and their various nozzle arrangements. The drive signal controller receives image data and a media encoder signal, and is configured to determine drive data 33 based on the image data and based on the media encoder signal. The drive signal controller further provides the drive data 33 to the droplet ejection head controller to eject each of one or more droplets to each pixel of the pixel line 8 corresponding to different nozzles in the column 20 among the nozzles 12 of one or more nozzle clusters 24 provided in the nozzle row 20.

[0195] In some embodiments, the drive signal controller further provides a timing signal as part of the drive data 33 to the droplet ejection head controller to cause droplets to be ejected onto the pixel line at time t1 to the nozzles 12 of the first group of nozzle clusters 24_1 of the nozzle cluster 24, and to cause droplets to be ejected onto the pixel line at time t2 to the nozzles 12 of the second group of nozzle clusters 24_2 of the nozzle cluster 24. The first group of nozzle clusters is provided within the first sub-column 22_1, and the second group of nozzle clusters is provided within the second sub-column 22_2 of the column 20.

[0196] Further, or alternatively, the drive signal controller is further configured to provide drive data 33 to the droplet ejection head controller to cause droplets to be ejected onto the pixel line at time t1 to the nozzles 12 of one or more sub-clusters provided within at least one of the nozzle clusters 24, and to cause droplets to be ejected onto the pixel line at time t2 to the nozzles 12 of one or more nozzle clusters 24_2 of the second sub-column 22_2.

[0197] Optionally, the drive signal controller may be configured to receive data based on a test print image.

[0198] This data can include adjustment values 42 for reducing the effect of banding due to non-dynamic elements of the grainy phenomenon caused by forced air passing around the nozzle cluster 24. Alternatively, the data may be in the form of a test print pixel density achieved at specific application process settings (e.g., gap distance, pixel frequency, media speed), and the drive signal controller can use the test print pixel density to determine the adjustment value 42 for each nozzle from a look-up table accessible by the drive signal controller. The look-up table can include, for example, pixel density data for a range of measured print pixel densities determined prior to printing, and adjustment values for achieving the required target density.

[0199] Accordingly, if necessary, the drive signal controller circuit can be further configured to receive the printed image data, determine an adjustment value for the amount of droplets to reduce or prevent banding by forced air flow based on the printed image data, and provide an adjustment signal to the print head controller based on the adjustment value to adjust the amount of droplets ejected from the nozzles.

[0200] In either case, the drive signal controller 4 is configured to provide an adjustment signal 44 based on the adjustment value 42 and provide the adjustment signal 44 as part of the drive data 33. The adjustment signal 44 causes droplets with an increased or decreased amount of droplets to be ejected in the actuation signal 30, achieving an adjusted density for the entire pixel line that reduces the banding phenomenon due to the non-dynamic elements of the wood grain appearance. For example, as a result of the adjustment signal 44 provided by the drive signal controller 4, nozzles contributing to a dark band can eject a smaller amount of droplets, while nozzles contributing to a brighter band can eject a larger amount of droplets.

[0201] In some embodiments, the drive signal controller 4 may be disposed outside the droplet ejection head, as shown in FIG. 19.

[0202] In another embodiment, the drive signal controller 4 may be disposed within the droplet ejection head 2 and may include a droplet ejection head controller 9.

[0203] In addition to any of the above embodiments, the drive signal controller 4 can be configured to generate drive data 33 that includes a timing signal based on the image data 36 and an image signal common to two or more actuators 11 and a media encoder signal 34 specific to each actuator, and to provide the drive data 33 to the droplet ejection head controller in the form of a synchronized stream of the common image signal and the individual timing signals.

[0204] Each timing signal can further include an adjustment signal 44 for each actuator to adjust (reduce) the amount of liquid droplets ejected from the corresponding nozzle so as to reduce the influence of banding.

[0205] In an embodiment where the drive controller is mounted on and disposed in the droplet ejection head 2, the drive signal controller and the droplet ejection head controller may be provided within the control system.

[0206] The droplet ejection head controller can be configured to generate an actuation signal 30 based on the timing signal and the image data and provide the actuation signal 30 to the actuator 11 corresponding to the nozzle, so that one or more droplets are deposited on the pixel line 8 for at least one of the nozzles in the nozzle cluster 24.

[0207] In some control systems, the drive signal controller 4 may include the droplet ejection head controller 9 and may be mounted on and disposed in the droplet ejection head 2.

[0208] General Introduction In some embodiments, it may be advantageous to arrange the nozzle cluster 24 so as to create a balanced flow of forced air through the nozzle cluster. To achieve this, the nozzle clusters 24 may be of the same length and the same spacing, and further, may be arranged between the sub-columns such that the length of the clusters 24 in one sub-column is equal to the cluster spacing in the other sub-column. This means that the forced air flow contacting the first column of nozzles 12 is divided into evenly spaced portions and the evenly spaced portions are recombined again. This is thought to avoid or reduce a large difference in pressure between separate regions along the length of the column.

[0209] In the above-described embodiment, when viewed along the direction in which the nozzles 12 in each column of nozzle clusters project in the column direction, the nozzles 12 of all the nozzle clusters 24 in the column form consecutive columns of nozzles 12 that are equally spaced apart from each other at a constant projected nozzle spacing. In other words, all the nozzles in column 20, when projected in the column direction, form consecutive columns of projected nozzles that are equally spaced apart from each other at the projected nozzle spacing, and among them, no nozzle overlaps with any other nozzle in the same column. Therefore, during use, each nozzle in the column of nozzle clusters deposits one or more droplets on the corresponding pixels of the same pixel line.

[0210] Furthermore, the spacing between the nozzles 12 disposed at the ends of adjacent nozzle clusters 24 may be the same as the projected nozzle spacing when viewed along the direction in which the column projects in the column direction. In another embodiment, when projected in the column direction, some of the nozzles of adjacent nozzle clusters can be fitted such that two or more of the projected nozzles in one nozzle cluster are adjacent to the projected nozzles of the adjacent nozzle cluster.

[0211] In some embodiments, the beginning and end of the column of nozzles 12 can have different nozzle spacings compared to the nozzle clusters closer to the center of the column. For example, the nozzle spacing in one or more nozzle clusters near the end of the column of nozzles may be larger compared to the nominal nozzle spacing ns at one end and smaller compared to the nominal nozzle spacing ns at the opposite end of the column.

[0212] Alternatively, the nozzle spacing in one or more nozzle clusters near the end of the column of nozzles 12 may gradually change from the nominal nozzle spacing ns at the center or closer to the column to a smaller or larger nozzle spacing towards the end of the column. Thereby, accurate alignment between the columns of nozzles 12 of separate nozzle plates 10 within the same print head 2 can be achieved.

[0213] Accordingly, some or all of the rows of nozzles 12 of the nozzle plate 10 described in accordance with various embodiments and implementations are such that for each sub-row, each nozzle 12, when projected in the column direction, is directly adjacent to another nozzle 12, and more than 50% (i.e., the majority) or 75% of the nozzles 12 are spaced apart from an adjacent nozzle 12 by a certain distance. Preferably, none of the projected nozzles completely overlap, so that in use, each printed pixel is addressed by a corresponding nozzle.

[0214] In other words, for at least two adjacent clusters, for the nozzles 12 of each sub-row, when the nozzles 12 are projected in the column direction, in the transition region from a plurality of nozzles 12 of at least the first cluster to a plurality of nozzles 12 of an adjacent cluster, each nozzle 12 is directly adjacent to another nozzle 12, and each nozzle 12 is spaced apart from an adjacent nozzle 12 by a certain distance. The transition region represents a region consisting of nozzles from the ends of adjacent (adjacent when projected in the column direction) sub-rows.

[0215] The above embodiments and their various implementations provide a nozzle cluster of nozzles arranged such that a flow path for forced air to pass through the rows of nozzles is obtained, reducing or preventing at least the dynamic elements of the moiré phenomenon. The degree of reduction depends on a specific combination of media speed, droplet frequency, droplet volume (mass), and gap G for a particular application, and may be further reduced by varying the cluster length c and cluster spacing a, and, where applicable, the sub-row spacing b. The non-dynamic element of the moiré phenomenon called banding can be further reduced by adjusting the droplet volume of the associated nozzles.

[0216] The pressure chamber 14 that supplies the nozzle 12 may be elongated in the x direction along the depth direction of the cluster and extend parallel to each other as shown in FIGS. 3A and 13. The pressure chambers may be further arranged side by side in the column direction along y, and the columns of nozzles may extend along most of the length of the actuator unit. In other words, the columns of pressure chambers may be formed within a single silicon piece or within a single piezoelectric material or the like. Thus, the cluster may be formed within a single actuator unit, as opposed to an arrangement that can be created by arranging a plurality of actuator units in a clustered arrangement. However, arranging a large number of small clusters (e.g., the length of 8 nozzles, or the length of 10 nozzles) would mean carefully attaching and aligning a large number of units, in addition to manufacturing complexity, time, cost, and compromising yield, so clustering the entire actuator unit may limit the cluster size. Instead, the cluster can be formed with a single actuator unit without alignment and other issues of manufacturing time and manufacturing yield.

[0217] The above example of a droplet ejection device including a nozzle cluster shows a recirculation path behind the nozzle 12 in some embodiments of the nozzle plate 10 in the inkjet droplet ejection head 2. The nozzle plate 10 can be similarly utilized in a droplet ejection head that does not have recirculation or supply from both ends of the pressure chamber 14. In some droplet ejection heads, the pressure chamber 14 may be elongated in a direction not perpendicular to the column direction or in a direction extending along the plane of the nozzle plate 10. In some droplet ejection heads, the pressure chamber 14 can extend in a direction perpendicular to the plane of the nozzle plate 10 according to the embodiments described herein. In other droplet ejection heads, the pressure chamber extends along the plane of the nozzle plate 10 but is not perpendicular to the column direction. For example, they may be angled less than 90° with respect to perpendicular to the column direction.

[0218] In another nozzle plate 10, the pixel lines can be printed such that two or more nozzles 12 in one or more columns of the nozzle plate 10 eject one or more droplets onto the same pixel of the pixel line. In some droplet ejection heads, the pressure chamber may be circular or square with a maximum dimension smaller than the pixel width. Such a droplet ejection head can also be used with the nozzle plate 10 described in the embodiments of this specification or a modification thereof, and provides a cluster of a suitable size to reduce the influence of forced air.

[0219] In some variations, the nozzle clusters 24 of the nozzles 12 that define the sub-columns may not be aligned along the column direction. Instead, they may be angled with respect to the column direction while being parallel to adjacent nozzle clusters 24 of the same sub-column. In this case, the sub-column direction is the average direction described by the sub-column of the nozzle clusters, and the column direction is the average direction of the sub-columns.

[0220] Finally, the nozzle plate 10 according to the above embodiments and their various implementations may be provided within the droplet ejection device 1. The droplet ejection device 1 may include a droplet ejection device, such as a droplet ejection head 2.

[0221] The droplet discharge device can be configured such that the first column of the nozzles 12 is arranged to be in fluid communication with the corresponding first column of the pressure chambers 14.

[0222] Furthermore, the pressure chambers 14 in the first column of the pressure chambers 14 may be elongated in a direction not parallel to the direction of the column and can extend side by side. The nozzles 12 are arranged on the elongated side walls of the respective pressure chambers 14. The side walls are formed by the nozzle plate. At least one group of the nozzles 12 is arranged offset from the center with respect to the pressure chambers 14 in the elongation direction such that the nozzle positions in the first column of the pressure chambers 14 define the nozzle clusters 24 and the air flow path for the forced gas to pass through the first column of the nozzles.

[0223] In this case, since the nozzles are offset from the center of the pressure chamber, the Helmholtz frequency of the chamber is maintained at substantially the same value for all chambers, and the drive voltage for achieving the target droplet velocity is maintained at substantially the same value for all nozzles.

[0224] The nozzles of one cluster in the first row can be arranged at a first distance in the elongation direction from the center of the pressure chamber, and the nozzles of adjacent clusters along the row direction can be arranged at a second distance in the elongation direction from the center of the pressure chamber. As a result, the first cluster is spaced apart from the adjacent clusters along the row direction by a cluster interval a to create an air flow path.

[0225] Furthermore, accordingly, the first distance and the second distance define the interval between the first and second sub-rows, and the first row of nozzles can comprise a first set of sub-rows consisting of first and second sub-rows extending side by side in their respective sub-row directions, and the first and second sub-rows extend parallel to the row direction. Accordingly, the first and second sub-rows are spaced apart by a first sub-row interval b in the lateral direction perpendicular to the row direction, and the first and second distances define the sub-row interval b.

[0226] Such an arrangement may be advantageous in a droplet ejection head that may not be easily manufactured in a way that enables clustering of the pressure chambers themselves, and the nozzles can be maintained at or near the center of the elongated pressure chamber. An example of such a droplet ejection head is a shared wall head, where the opposing walls are formed from a sheet of piezoelectric material in which parallel grooves are cut to form the pressure chambers. In such an apparatus, the pressure chambers are arranged parallel to each other such that they are 100% overlapping in the column direction, and clustering can only be achieved by providing nozzles according to the required cluster length and sub-column spacing. As described, it has been found that the nozzles can be offset from the center position midway along the length of the pressure chamber without significantly changing the performance. Thus, the required clusters can simply be formed at the nozzle drilling stage. Since devices of this type are not fabricated by MEMS manufacturing, the proposed embodiments can be easily applied to existing designs of ejection heads within a short time frame without significantly changing the process.

[0227] In another droplet ejection head, the fluid path within the head can be defined by only a few layers covered by a cap wafer that can provide a fluid path common to the pressure chambers, for example, by a nozzle plate, a pressure chamber layer, and an actuator layer. Such a head may be fabricated by a MEMS manufacturing method that allows for greater flexibility in the arrangement of the flow paths. However, in a compact device, the nozzles are provided directly within the pressure chamber rather than at the ends of the supply paths leading from the pressure chambers. Such pressure chambers can eject droplets by utilizing the reflection of pressure waves from each end of the elongated chamber and their subsequent interference to an enhanced pressure profile near the center of the chamber. Although it may be possible to create a clustering of pressure chambers by a MEMS method, some pressure chambers recirculate through the nozzles by supplying ink to one end and returning the ink to the other end. Chamber clustering can complicate the ink supply from a common manifold or can be very time-consuming to manufacture. Thus, in such a device, it may be beneficial to create the clustering only through the nozzle plate at the nozzle formation stage and offset the nozzles within at least some of the clusters from the center of each longitudinal chamber to define the clusters.

[0228] Furthermore, in some ejection heads, the first row of pressure chambers 14 of the pressure chamber 14 may be elongated in a direction not parallel to the row direction and can extend side by side, and the nozzles 12 are disposed centrally with respect to the elongation direction on the elongated side walls of the respective pressure chambers 14, and the pressure chambers 14 are arranged to define a nozzle cluster 24 and an air flow path for the forced gas to pass through the first row 20 of nozzles.

[0229] Furthermore, or alternatively, the first row of nozzles 12 may be supplied from a common manifold through the corresponding first row of pressure chambers 14.

[0230] The droplet ejection device 1 and / or the droplet ejection device can be configured to provide a pixel line frequency of 50 kHz or more.

[0231] Each nozzle 12 can be configured to eject droplets independently of all other nozzles 12.

[0232] The above and references in this specification to "air" around the print head 2 or in the gap G between the print head and the substrate (deposition medium) apply equally to all gases that form the environment around the print head and / or between the print head and the substrate (deposition medium). The environment may be an ambient air atmosphere or, for example, a chamber containing a desired gas (e.g., an inert gas such as helium or argon) or a mixture of gases during use, provided by housing the droplet ejection device 1 therein, which may be a imposed / controlled gas environment.

[0233] The nozzle arrangements of FIGS. 3 and 7 to 12 and FIGS. 13 to 14 provide a flow path for forced air entering the gap between the nozzle plate and the deposition medium to pass through the droplet curtain in a controlled manner. For example, the generation of vortices is prevented or reduced to such an extent that their influence on the droplet arrangement is invisible to the eye of the printed image. These arrangements may achieve a reduction or prevention of the occurrence of the grained appearance phenomenon when they match specific application requirements.

[0234] Therefore, in order to achieve this effect, it is not essential that the nozzle arrangement of the embodiments according to FIGS. 3 and 7 to 12 be provided, for example, by a fluid path configured such that the pressure chamber is elongated along a direction in the plane of the nozzle plate, as shown in FIG. 3A.

[0235] To achieve a reduction or prevention in the occurrence of the wood grain phenomenon, it is not essential for the fluid path to recirculate behind the nozzle 12. For example, in some embodiments of the nozzle arrangements shown in FIGS. 3 and 7 - 12, the fluid path may be arranged such that the fluid is supplied to the nozzle along a path parallel to the nozzle axis. This path may be the pressure chamber itself, or it may be a supply path connecting the pressure chamber (provided elsewhere) to the nozzle. In such an arrangement, the fluid may be recirculated as necessary by providing a return path next to the nozzle. In another example, the pressure chambers of FIGS. 3 and 7 - 12 may be arranged behind the nozzle plate such that the pressure chamber is closed immediately after the nozzle position, i.e., the return is omitted.

Claims

1. A nozzle plate (10) for a droplet ejection head, wherein the nozzle plate (10) comprises a first row (20) of nozzles (12) arranged to deposit droplets onto a deposition medium, the first row (20) of the nozzles (12) extends in a row direction (26) and comprises two or more nozzle clusters (24), each nozzle cluster (24) being arranged with a cluster length c along the row direction (26) and extending with a cluster depth d along a cluster depth direction perpendicular to the row direction (26), each nozzle cluster (24) comprises a plurality of nozzles (12), one or more of the nozzles (12) within each nozzle cluster (24) defining the cluster length c, and two or more of the nozzles (12) within each nozzle cluster (24) defining the cluster depth d, each nozzle cluster (24) is spaced from an adjacent nozzle cluster (24) along the row direction (26) by a cluster spacing a, thereby creating an air flow path for forced air to pass through the row of nozzles (12) in a controlled manner, and the cluster spacing a is greater than a nozzle spacing ns which is the spacing between adjacent ones of the nozzles (12) of the nozzle cluster (24), when the first row (20) of the nozzles (12) is projected laterally onto the row direction (26), a transition region between adjacent nozzle clusters (24) consists of two or more nozzles (12) of a first cluster and two or more nozzles (12) of a second cluster, the second cluster being adjacent to the first cluster, and the nozzles (12) within the transition region being equally spaced from each other at a first projected nozzle spacing, a nozzle plate (10), the first row (20) of the nozzles (12) comprises a first set of sub - rows consisting of a first and a second sub - row (22_1, 22_2) extending side - by - side in the direction of respective sub - rows, the first and second sub - rows (22_1, 22_2) extending parallel to the row direction (26), the first and second sub - rows (22_1, 22_2) are spaced apart by a first sub - row spacing b in the lateral direction perpendicular to the row direction (26), each of the first and second sub - rows (22_1, 22_2) comprises one or more nozzle clusters (24_1, 24_2), Each nozzle cluster (24) within the sub-column is spaced from an adjacent nozzle cluster (24) by the cluster interval a, and the cluster interval a is the distance measured along the respective sub-column direction between the outermost nozzles (12) in adjacent clusters within the same sub-column (22_1, 22_2). Two or more nozzles (12) of the first cluster and two or more nozzles (12) of the second cluster provided within the transition region are respectively provided within the first and second sub-columns (22_1, 22_2), the nozzle plate (10).

2. The nozzle plate (10) according to claim 1, wherein the cluster depth d is the same as the staggered offset distance sd.

3. The first set of the sub-columns further comprises a third sub-column (22_3). One or more nozzle clusters (24) of each of the first, second, and third sub-columns (22_1, 22_2, 22_3) define a first sub-column interval (b1) between the first sub-column (22_1) and the second sub-column (22_2), and a second sub-column interval (b2) between the first sub-column (22_1) and the third sub-column (22_3), the nozzle plate (10) according to claim 1 or claim 2.

4. Further comprising a second row (20B) of nozzles (12) extending in a second row direction (26B), the second row direction (26B) being parallel to the first row direction (26A). The second row (20B) of the nozzles (12) comprises a second set of sub-columns comprising first and second sub-columns (22B_1, 22B_2) extending side by side in the direction of each sub-column, and the first and second sub-columns (22B_1, 22B_2) of the second set of sub-columns extend parallel to the second row direction (26B). The first and second sub-columns (22B_1, 22B_2) of the second set of sub-columns are spaced apart by a third sub-column interval b in a lateral direction perpendicular to the second row direction (26B). Each of the first and second sub-columns (22B_1, 22B_2) of the second set of sub-columns includes one or more nozzle clusters (24B), and each nozzle cluster (24B) includes a plurality of nozzles (12) extending along the respective sub-column direction with a cluster length c. Each nozzle cluster (24B) within the sub-columns of the second set of sub-columns is spaced apart from an adjacent nozzle cluster (24) by a cluster spacing a. The second transition region between adjacent nozzle clusters (24) of the first and second sub-columns (22B_1, 22B_2) of the second set of sub-columns includes two or more nozzles of the first sub-column and two or more nozzles of the second sub-column (12) of the second set of sub-columns. The nozzles within the second transition region are equally spaced from each other at a second projected nozzle spacing. Each projected nozzle cluster (24) of the first and second sub-columns (22B_1, 22B_2) of the second set of sub-columns is spaced apart from an adjacent projected nozzle cluster (24) by the second projected nozzle spacing. The nozzle plate (10) according to any one of claims 1 to 3. **Claim 5** When projected laterally in the column direction (26), in the overlapping region of the first and second transition regions, the consecutive projected nozzles (12) of the first and second sets of sub-columns are equally spaced from each other at a third projected nozzle spacing, and the third projected nozzle spacing is smaller than the first projected nozzle spacing. The nozzle plate (10) according to claim 4. **Claim 6** One or more nozzle clusters (24) of the first sub-column of the first set of sub-columns have a cluster length different from the cluster length c of one or more nozzle clusters of the second sub-column of the first set of sub-columns. The nozzle plate (10) according to any one of claims 1 to 5. **Claim 7** One of the sub-columns includes first and second subsets of nozzle clusters (24), and the cluster length c of the first subset of the nozzle clusters (24) is different from the cluster length of the second subset of the nozzle clusters (24). The nozzle plate (10) according to any one of claims 1 to 6. **Claim 8** The nozzle plate (10) according to any one of claims 1 to 7, wherein the first sub-column interval b is greater than 150 μm and less than 900 μm.

9. The nozzle plate (10) according to any one of claims 1 to 8, wherein each cluster includes at most 4 to 10 nozzles (12).

10. The nozzle plate (10) according to any one of claims 1 to 9, wherein the cluster length c is 800 μm or less.

11. The nozzle plate (10) according to any one of claims 1 to 10, wherein each cluster includes at most 10 nozzles (12).

12. A droplet discharge device including the nozzle plate (10) according to any one of claims 1 to 11.

13. The first row (20) of the nozzles is arranged in fluid communication with the first row (20) of the corresponding pressure chambers. The pressure chambers (14) of the first row (20) of the pressure chambers extend in a direction not parallel to the direction of the row, extend side by side, and each at least partially overlaps with an adjacent pressure chamber (14). The nozzles are arranged on the elongated side walls of the respective pressure chambers, and the side walls are formed by the nozzle plate (10). At least one group of the nozzles (12) is arranged off-center with respect to the pressure chambers (14) in the extending direction. The nozzle positions of the first row (20) of the pressure chambers define the nozzle clusters (24) of the first row (20) and the air flow path for the forced gas to pass through the first row (20) of the nozzles (12). The droplet discharge device according to claim 12.

14. The nozzles (12) of one cluster of the first row (20) are arranged at a first distance from the center of the pressure chamber (14) in the extending direction. The nozzles (12) of the adjacent clusters along the row direction (26) are arranged at a second distance from the center of the pressure chamber (14) in the extending direction. The first cluster is spaced from the adjacent cluster by the cluster interval a along the row direction (26), thereby creating the air flow path. The droplet discharge device according to claim 13.

15. The first row (20) of the nozzle (12) is arranged in fluid communication with a corresponding first row (20) of the pressure chamber (14), and the pressure chamber (14) of the first row (20) of the pressure chamber (14) is elongated in a direction not parallel to the direction of the row and extends side by side. The nozzle (12) is arranged centrally with respect to the elongation direction on the elongated side wall of each pressure chamber (14). The pressure chamber is arranged to define a nozzle cluster (24) and an air flow path for the forced gas to pass through the first row (20) of the nozzle (12). The droplet ejection device according to claim 12.

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