Method for operating an inkjet printing machine

Abstract

Method for operating an inkjet printing machine (01), wherein in a conversion process, rasterized print control data (41) for the at least one print head (03) are generated from template image data (38) of a template image (39), and wherein the template image data (38) contain a description of an overall image area, and wherein the rasterized print control data (41) comprise information corresponding to a rasterized overall raster area of ​​rows and columns, and wherein this rasterized overall raster area consists of individual raster cells (23; 24; 26), each comprising a plurality of rows (28) and a plurality of columns (27) of raster points (19; 29), and wherein each raster point (19; 29) is designed either as an empty point (19) or as a fill point (29), and wherein fill points (29) are linked to the instruction to eject ink, and wherein empty points (19) are linked to the instruction not to eject ink, characterized in that areas of the Total image area, whichhave a target area coverage between 14% and 50%, are converted into symbol raster cells (23) in the conversion process, all of whose fill points (29) together represent a plurality of spaced-apart rasterized ampersands (22), and that a rasterized ampersand (22) is a representation of an ampersand (21) in the form of filled rectangles (29) arranged in a matrix of rows (28) and columns (27), and that the filled rectangles (29) correspond to the fill points (29) in relation to raster cells (23; 24; 26), and that an ampersand (21) is a symbol (21) made up of four connected individual elements (E1; E2; E3; E4), and that a first individual element (E1) is a first circular arc (E1) with a first central angle of 270° and a first radius (r1) and that the first circular arc (E1) has a first end (X11) and a second end (X12) and that a second individual element (E2) is a second circular arc (E2) with asecond central angle of 270° and a second radius (r2) and that the second circular arc (E2) has a first end (X21) and a second end (X22) and that a third individual element (E3) is a first straight line (E3) with a first length (a1) and that the first straight line (E3) has a first end (L11) and a second end (L12) and that a fourth individual element (E4) is a second straight line (E4) with a second length (a2) and that the second straight line (E4) has a first end (L21) and a second end (L22) and that the second radius is greater than the first radius by a factor (F) and that the factor (F) is at least 1.2 and at most 1.3 and that the first length (a13) corresponds to the second radius (r2) with a deviation of at most 10% and that the second length (a2) with a deviation of not more than 10% of the first radius (r1) and that the second end (X12) of the first circular arc (E1) is aligned with the first end (X21)of the second circular arc (E2) and lies on a straight line connection (V) from the center point (M1) of the first circular arc (E1) to the center point (M2) of the second circular arc (E2), and that the second end (X22) of the second circular arc (E4) is closer to the first end (X11) of the first circular arc (E1) than to the first center point (M1) of the first circular arc (E1), and that the first end (L11) of the first straight line (E3) coincides with the second end (X22) of the second circular line (E2), and that the first straight line (E3) runs parallel to the straight line connection (V) from the center point (M1) of the first circular arc (E1) to the center point (M2) of the second circular arc (E2), and that the second end (L12) of the first straight line (E3) is closer to the center point (M1) of the first circular arc (E1) than to the center point (M2) of the second circular arc (E2) and that the first end (L21) of the second straight line (E4) coincides with the second end (X12) of the first straight line (E3) andthat the second straight line (E4) runs orthogonally to the first straight line (E3) and that the first end (L21) of the second straight line (E4) is arranged closer to the straight connection (V) from the center point (M1) of the first circular arc (E1) to the center point (M2) of the second circular arc (E2) than the second end (L21) of the second straight line (E4) and that areas of the total image area which have a target area coverage of less than 14% are converted into raster cells (24) in the conversion process, which differ from the symbol raster cell (23) exclusively by the missing fill points (29) compared to the rasterized ampersand (22) and that areas of the total image area which have a target area coverage of more than 24% are converted into raster cells (26) in the conversion process, which differ from the symbol raster cell (23) exclusively in that compared to the rasterized ampersand (22) additional fill points (29)are arranged.

Description

[0001] The invention relates to a method for operating an inkjet printing machine.

[0002] DE 199 29 904 A1 discloses a method by which printing elements in the offset printing process have been improved.

[0003] WO 2019 / 081493 A1 discloses a method for operating an inkjet printing machine, wherein rasterized print control data for a print head are generated from template image data in a conversion process, and wherein the template image data contain a description of an overall image area and the rasterized print control data have information which corresponds to a rasterized overall raster area consisting of rows and columns, and wherein this rasterized overall raster area consists of individual raster cells, each of which has a plurality of rows and columns of raster points, and each raster point is designed either as an empty point or as a fill point.

[0004] US 2003 / 0038974 A1 discloses a method for creating security documents that offers the possibility of creating raster cells for halftone images that have selectable symbols as a basis.

[0005] In inkjet printing, individual ink drops are ejected from nozzles, which then create dots on a substrate. Together, they create a printed image. To represent different tonal values, different numbers of drops per area and / or different sizes of drops can be used. There are different approaches to selecting the number and size of drops. For example, randomly distributed dots can be used. However, this can lead to artifacts, such as drops clumping together and thus uneven grayscale. Failing or slanted nozzles also produce image defects, particularly in the form of visible streaks.

[0006] The invention is based on the object of creating a method for operating an inkjet printing machine.

[0007] The object is achieved according to the invention by the features of claim 1.

[0008] The advantages achievable with the invention include, in particular, the ability to reduce or prevent banding caused by failing or slanted nozzles. This is achieved by positioning appropriate fill dots in the respective screen cell. Banding is thus minimized. This is achieved, in particular, by ensuring that the fill dots positioned for corresponding tonal values ​​do not form straight, continuous lines. The occurrence of the moiré effect can be prevented by skewed arrangement of the corresponding fill dots for different primary colors.

[0009] Embodiments of the invention are illustrated in the drawings and are described in more detail below.

[0010] They show: Fig. 1 A schematic representation of a web-fed printing press using an ink-jet printing process; Fig. 2 is a schematic representation of a sheet-fed printing press operating using an ink-jet printing process; Fig. 3 a schematic representation of a sequence of a method for operating an inkjet printing machine; Fig. 4a a schematic representation of an ampersand in an embodiment with a first line thickness; Fig. 4b a schematic representation of an ampersand in a design with a second line thickness; Fig. 5a a schematic representation of a screened ampersand in an embodiment for a first tonal value; Fig. 5b a schematic representation of a screened ampersand in an embodiment for a second tonal value; Fig. 6a is a schematic representation of a raster cell in an embodiment for a first tonal value, which has fewer fill points compared to a symbol raster cell; Fig. 6b a schematic representation of a symbol raster cell in an embodiment for a second tonal value; Fig. 6c is a schematic representation of a symbol raster cell in an embodiment for a third tone value; Fig. 6d is a schematic representation of a symbol raster cell in an embodiment for a fourth tone value; Fig. 6e is a schematic representation of a screen cell in an embodiment for a fifth tonal value, which has additional fill points compared to a symbol screen cell; Fig. 7 a schematic representation of an area filled with several diagonally arranged ampersands.

[0011] A printing press 01 designed as an inkjet printing press 01 preferably has at least one inkjet printing device 04 designed, for example, as an inkjet printing unit 04. The printing press 01 and / or the at least one inkjet printing device 04 preferably has at least one inkjet print head 03 or print head 03. The printing press 01 is preferably used to print on substrate 02 or printing material 02. The substrate 02 is designed, for example, as a substrate web 02 or as at least one and preferably a plurality of sheets 02. The printing press 01 is designed, for example, as a web-fed printing press 01 or as a sheet-fed printing press 01. The substrate 02 is preferably transported along a transport path and / or in a transport direction T through the printing press 01 and / or through the at least one inkjet printing device 04.

[0012] The printing press preferably has at least one material source 08; 09, which, depending on the design of the printing press 01, is designed, for example, as a sheet feeder 08 or, for example, as a roll unwinder 09 and / or roll changer 09. The printing press 01 preferably has at least one drying device 11. The printing press 01 has, for example, at least one substrate delivery device 12; 13, which, depending on the design of the printing press 01, is designed, for example, as a sheet delivery 12 or, for example, as a winding device 13.

[0013] The at least one inkjet printing device 04 has, for example, at least one print head arrangement that extends across an entire working width of the inkjet printing device 04 and / or the printing press 01. This print head arrangement has at least one print head 03 and preferably a plurality of print heads 03. In the case of only one print head 03 per print head arrangement, this one print head 03 preferably extends across the entire working width of the inkjet printing device 04 and / or the printing press 01. However, the case is preferred in which a plurality of print heads 03 together form the respective print head arrangement and, with their respective working areas, together cover the entire working width of the inkjet printing device 04 and / or the printing press 01.The working width of the inkjet printing device 04 and / or the printing machine 01 is preferably defined as the maximum width that a substrate 02 may have in order to still be able to be processed by means of the inkjet printing device 04 and / or the printing machine 01 and / or corresponds to the maximum width of the respective substrate 02 that can be processed by means of the inkjet printing device 04 and / or the printing machine 01.

[0014] The printing press 01 and / or the at least one inkjet printing device 04 preferably has at least one sensor device 07, which more preferably has at least one sensor module. The at least one sensor device 07 serves in particular to detect and / or evaluate at least one printed print image 42. The at least one sensor device 07 is preferably arranged aligned with the transport path provided for transporting the substrate 02 and / or with the substrate 03. The at least one sensor device 07 preferably extends over the entire working width of the printing press 01 and / or the at least one inkjet printing device 04. The at least one sensor device 07 is preferably an optical sensor device 07. The at least one sensor device 07 is designed, for example, as a line scan camera 07.

[0015] Preferably, in a conversion process, print control data 41 for the at least one print head 03 is generated from template image data 38 of a template image 39. The print control data 41 is preferably generated by means of a computer device 18, which is more preferably part of the printing press 01. The conversion process includes, for example, conventional processes such as halftoning, screening, etc., which are necessary to generate print control data 41. Preferably, in a printing process using the print control data 41, a printed print image 42 is generated on a substrate 02 by means of the at least one print head 03.

[0016] From digital template image data 38 of a template image 39, a target area coverage value can preferably be derived and / or at least indirectly stored for each location on the template image 39. However, depending on how the at least one print head 03, the substrate 02 and the ink used interact, different quantities of ink applied and / or different color impressions result on the substrate 02 with the same print control data 41. A color density and / or a tonal value or a determination of a color density and / or a tonal value is therefore particularly dependent on the respective substrate and its interaction with a respective printing ink or ink. A respective color density or a respective tonal value is usually related to a primary color, for example cyan, magenta, yellow or black. A respective determination of a color density and / or a tonal value is preferably carried out as follows.Preferably, a remitted light intensity is determined for an unprinted area of ​​the respective substrate as the lower reference. Preferably, a remitted intensity is determined for a maximum printed area (solid area) in the corresponding system as the upper reference. The system is understood in particular to mean the respective combination of substrate and primary color. In addition, a remitted light intensity, referred to here as the measured intensity, can be measured for each point on the substrate printed with the corresponding primary color. Using this lower reference and the upper reference, a respective remitted light intensity measured at a specific point is preferably converted into an actual tonal value and / or an actual color density value. Each actual color density value can be unambiguously converted into an actual tonal value and vice versa.This tonal value is only indirectly linked to an actual, particularly geometric, area coverage, for example due to increases in tonal value caused by dot enlargements and / or light trapping.

[0017] A method for operating an inkjet printing machine 01 is preferred, wherein, in a conversion process, rasterized print control data 41 for the at least one print head 03 are generated from template image data 38 of a template image 39. The template image data 38 preferably contain a particularly vector-based description of an overall image area. The rasterized print control data 41 preferably comprise information corresponding to a rasterized overall raster area consisting of rows and columns. This rasterized overall raster area preferably consists of individual raster cells 23; 24; 26. These raster cells 23; 24; 26 are, for example, rectangular. Alternatively or additionally, raster cells 23; 24; 26 are used which have other regular or irregular shapes. These raster cells 23; 24; 26 preferably result in their entirety in the rasterized overall raster area.The respective grid cells 23; 24; 26 preferably each have a plurality of rows 28 and a plurality of columns 27 of grid points 19; 29. ​​For example, each grid cell 23; 24; 26 has at least twelve rows 28, preferably at least fifteen rows 28, and more preferably at least seventeen rows 39. For example, each grid cell 23; 24; 26 has at most one hundred rows 28, more preferably at most fifty rows 28, and even more preferably at most twenty rows 28. For example, each grid cell 23; 24; 26 has at least eight columns 27, preferably at least ten columns 27, and more preferably at least twelve columns 27. For example, each grid cell 23; 24; 26 has at most fifty columns 27, preferably at most twenty columns 27, and more preferably at most fifteen columns 27.

[0018] Preferably, each raster point 19; 29 is configured either as an empty point 19 or as a fill point 29. The respective fill points 29 are linked to the instruction to eject ink. Additionally, information can be stored regarding the quantity or droplet size to be ejected with respect to the respective point. The respective empty points 19 are preferably linked to the instruction not to eject any ink.

[0019] Preferably, areas of the overall image area that have a target area coverage between 14% and 50% are converted into symbol raster cells 23 in the conversion process, more preferably those areas of the overall image area that have a target area coverage between 16% and 30%, and even more preferably those areas of the overall image area that have a target area coverage between 18% and 20%. A symbol raster cell 23 is understood to be a raster cell 23 whose all fill points 29 together represent at least one rasterized ampersand 22. Thus, preferably, areas of the overall image area that have a target area coverage as described above are converted into symbol raster cells 23 in the conversion process, whose all fill points 29 together represent a plurality of spaced-apart rasterized ampersand 22.This plurality of spaced-apart rasterized ampersands 22 are preferably constructed identically.

[0020] A rasterized ampersand 22 is a representation of an ampersand 21 in the form of filled rectangles 29 arranged in a matrix of rows 28 and columns 27. The filled rectangles 29 correspond to the fill points 29 in raster cells 23; 24; 26.

[0021] An ampersand 21 is preferably a symbol 21 that is constructed from preferably four connected individual elements E1; E2; E3; E4. A first individual element E1 is a first circular arc E1 with a first central angle of 270° and a first radius r1. The first circular arc E1 has a first center point M1. The first circular arc E1 has a first end X11 and a second end X12. A second individual element E2 is a second circular arc E2 with a second central angle of 270° and a second radius r2. The second circular arc E2 has a second center point M2. The second circular arc E2 has a first end X21 and a second end X22. A third individual element E3 is a first straight line E3 with a first length a1. The first straight line E3 has a first end L11 and a second end L12. A fourth single element E4 is a second straight line E4 with a second length a2.The second straight line E4 has a first end L21 and a second end L22. The second radius is larger than the first radius by a factor. This factor is preferably at least 1.2 and at most 1.3. The first length a1 corresponds to the second radius r2 with a deviation of at most 10%. The second length a2 corresponds to the first radius r1 with a deviation of at most 10%. The second end X12 of the first circular arc E1 coincides with the first end X21 of the second circular arc E2 and lies on a straight line connection V from the center point M1 of the first circular arc E1 to the center point M2 of the second circular arc E2. The second end X22 of the second circular arc E4 is closer to the first end X11 of the first circular arc E1 than to the first center point M1 of the first circular arc E1. The first end L11 of the first straight line E3 coincides with the second end X22 of the second circular line E2.The first straight line E3 runs parallel to the straight line connection V from the center M1 of the first circular arc E1 to the center M2 of the second circular arc E2. The second end L12 of the first straight line E3 is closer to the center M1 of the first circular arc E1 than to the center M2 of the second circular arc E2. The first end L21 of the second straight line E4 coincides with the second end X12 of the first straight line E3. The second straight line E4 runs orthogonal to the first straight line E3. The first end L21 of the second straight line E4 is closer to the straight line connection V from the center M1 of the first circular arc E1 to the center M2 of the second circular arc E2 than the second end L21 of the second straight line E4.

[0022] In an alternative or additional development, the method is preferably characterized in that areas of the total image area which have a target area coverage of less than 18%, more preferably less than 16% and even more preferably less than 14%, are converted in the conversion process into raster cells 24 which differ from the symbol raster cell 23 only in that fill points 29 are missing compared to the rasterized ampersand 22.

[0023] In an alternative or additional development, the method is preferably characterized in that areas of the total image area which have a target area coverage of more than 20%, more preferably more than 39% and even more preferably more than 50%, are converted in the conversion process into raster cells 26 which differ from the symbol raster cell 23 only in that, compared to the rasterized ampersand 22, additional fill points 29 are arranged.

[0024] Preferably, respective print control data 41 are generated for four primary colors. Preferably, symbol raster cells 23 as described above are used for one of the primary colors. Preferably, modified raster cells 23; 24; 26 and in particular modified symbol raster cells 23 are used for at least one other, and more preferably for the three other primary colors. The modified raster cells 23; 24; 26 and in particular the modified symbol raster cells 23 differ from the unchanged raster cells 23; 24; 26 or symbol raster cells 23 preferably by a modification which consists in shifting selected rows 28 in the row longitudinal direction. For example, for a primary color, every second row 28 of the raster cells 23; 24; 26 is shifted sideways by an additional raster point 19; 29, resulting in an oblique rasterized ampersand 22.

[0025] For example, the total image area has at least one empty area that has a target area coverage of zero. For example, the total image area has at least one template area called a light area that has a target area coverage that is greater than zero and less than 14%. For example, the total image area has at least one template area called a symbol area that has a lower target area coverage that is greater than 14% and less than 24%. For example, the total image area has at least one first template area called an intermediate area that has a lower target area coverage that is greater than 24% and less than 60%. For example, the total image area has at least one second template area called a symbol area that has a lower target area coverage that is greater than 60% and less than 70%.For example, the total image area has at least one original area called a dark area, which has a target area coverage greater than 70% and less than 100%. For example, the total image area has at least one original area called a solid area, which has a target area coverage of 100%.

[0026] In an alternative or additional development, the method is preferably characterized in that each raster cell 23; 24; 26 resulting from a part of an empty area is free of fill points 29. In an alternative or additional development, the method is preferably characterized in that each raster cell 23; 24; 26 resulting from a part of a light area at least partially has fill points 29 without directly adjacent fill points 29. In an alternative or additional development, the method is preferably characterized in that each raster cell 23; 24; 26 resulting from a symbol area is designed as a symbol raster cell 23 described above. In an alternative or additional development, the method is preferably characterized in that each raster cell 23; 24; 26 resulting from an intermediate area has a rasterized ampersand 22 and additional fill points 29 not connected thereto.In an alternative or additional development, the method is preferably characterized in that each raster cell 23; 24; 26, which emerges from a second symbol area and is designed as the symbol raster cell 23 described above, has a rasterized ampersand 22 and a black border line made up of fill points 29, separated therefrom by a line of blank points 19 that is one raster point 19; 29 wide. In an alternative or additional development, the method is preferably characterized in that each raster cell 23; 24; 26, which emerges from a second symbol area and is designed as the symbol raster cell 23 described above, has a rasterized ampersand 22 and a black border line made up of fill points 29, separated therefrom by a line of blank points 19 that is one raster point 19; 29 wide, and further fill points 29.In an alternative or additional development, the method is preferably characterized in that each raster cell 23; 24; 26 resulting from a solid tone area has exclusively fill points 29 as raster points 29. List of reference symbols 01 Printing machine, inkjet printing machine, web-fed printing machine, sheet-fed printing machine 02 substrate, substrate web, sheet 03 Print head, inkjet print head 04 Printing device, printing unit, inkjet printing device, inkjet printing unit 05 - 06 - 07 Sensor device 08 Material source, sheet feeder 09 Material source, roll unwinder, roll changer 10 - 11 Drying device 12 Substrate delivery device, sheet delivery 13 Substrate dispensing device, winding device 14 - 15 - 16 Computer setup 17 Computer setup 18 Computer setup 19 grid points, space points 20 - 21 ampersands 22 ampersands, rasterized 23 Symbol grid cell 24 grid cells 25 - 26 grid cells 27 column 28 lines 29 Grid point, fill point 30 - 31 - 32 - 33 - 34 - 35 - 36 - 37 - 38 template image data 39 template image 40 - 41 Pressure control data 42 Print image a1 length, first (E3) a2 length, second (E4) r1 radius, first (E1) r2 radius, second (E2) E1 circular arc, first; single element, first E2 circular arc, second; single element, second E3 line, first; single element, third E4 line, second; single element, fourth L11 end, first (E3) L12 end, second (E3) L21 end, first (E4) L22 end, second (E4) M1 center point, first (E1) M2 center, second (E2) V connection X11 End, first (E1) X12 end, second (E1) X21 End, first (E2) X22 End, second (E2)

Claims

[1] Method for operating an inkjet printing machine (01), wherein, in a conversion process, rasterized print control data (41) for the at least one print head (03) are generated from template image data (38) of a template image (39), and wherein the template image data (38) contain a description of an overall image area, and wherein the rasterized print control data (41) comprise information corresponding to a rasterized overall raster area of ​​rows and columns, and wherein this rasterized overall raster area consists of individual raster cells (23; 24; 26), each comprising a plurality of rows (28) and a plurality of columns (27) of raster points (19; 29), and wherein each raster point (19; 29) is designed either as an empty point (19) or as a fill point (29), and wherein fill points (29) are linked to the instruction to eject ink, and wherein empty points (19) are linked to the instruction not to eject ink, characterized by, in which areas of the total image area which have a target area coverage of between 14% and 50% are converted into symbol raster cells (23) in the conversion process, all of whose fill points (29) together represent a plurality of spaced-apart rasterized ampersands (22), and in that a rasterized ampersand (22) is a representation of an ampersand (21) in the form of filled rectangles (29) which are arranged in a matrix of rows (28) and columns (27), and in that the filled rectangles (29) correspond to the fill points (29) in relation to raster cells (23; 24; 26), and in that an ampersand (21) is a symbol (21) which is constructed from four connected individual elements (E1; E2; E3; E4), and in that a first individual element (E1) is a first circular arc (E1) with a first central angle of 270° and a first radius (r1) and that the first circular arc (E1) has a first end (X11) and a second end (X12) and that a second individual element(E2) is a second circular arc (E2) with a second central angle of 270° and a second radius (r2), and that the second circular arc (E2) has a first end (X21) and a second end (X22), and that a third individual element (E3) is a first straight line (E3) with a first length (a1), and that the first straight line (E3) has a first end (L11) and a second end (L12), and that a fourth individual element (E4) is a second straight line (E4) with a second length (a2), and that the second straight line (E4) has a first end (L21) and a second end (L22), and that the second radius is greater than the first radius by a factor (F), and that the factor (F) is at least 1.2 and at most 1.3, and that the first length (a13) corresponds to the second radius with a deviation of at most 10%. (r2) and that the second length (a2) corresponds to the first radius (r1) with a deviation of not more than 10% and that the second end (X12) of the firstcircular arc (E1) coincides with the first end (X21) of the second circular arc (E2) and lies on a straight line connection (V) from the center point (M1) of the first circular arc (E1) to the center point (M2) of the second circular arc (E2), and that the second end (X22) of the second circular arc (E4) is closer to the first end (X11) of the first circular arc (E1) than to the first center point (M1) of the first circular arc (E1), and that the first end (L11) of the first straight line (E3) coincides with the second end (X22) of the second circular line (E2), and that the first straight line (E3) runs parallel to the straight line connection (V) from the center point (M1) of the first circular arc (E1) to the center point (M2) of the second circular arc (E2), and that the second end (L12) of the first straight line (E3) corresponds to the center point (M1) of the first circular arc (E1) is closer than the center point (M2) of the second circular arc (E2) and that the first end (L21) of the second straight line (E4) coincides with the second end (X12) of thefirst straight line (E3) and that the second straight line (E4) runs orthogonally to the first straight line (E3) and that the first end (L21) of the second straight line (E4) is arranged closer to the straight connection (V) from the center point (M1) of the first circular arc (E1) to the center point (M2) of the second circular arc (E2) than the second end (L21) of the second straight line (E4) and that areas of the total image area which have a target area coverage of less than 14% are converted into raster cells (24) in the conversion process, which differ from the symbol raster cell (23) exclusively by the missing fill points (29) compared to the rasterized ampersand (22) and that areas of the total image area which have a target area coverage of more than 24% are converted into raster cells (26) in the conversion process, which differ from the Symbol grid cell (23) only differ in that, compared to the griddedampersand (22) additional fill points (29) are arranged. [2] Method according to claim 1, characterized by that this plurality of spaced-apart rasterized ampersands (22) are constructed identically. [3] Method according to claim 1 or 2, characterized by that each grid cell (23; 24; 26) has at least twelve rows (28) and / or that each grid cell (23; 24; 26) has at most one hundred rows (28) and / or that each grid cell (23; 24; 26) has at least eight columns (27) and / or that each grid cell (23; 24; 26) has at most fifty columns (27).

Images