CN112238683B

CN112238683B - Register measurement with white separation color

Info

Publication number: CN112238683B
Application number: CN202010691383.7A
Authority: CN
Inventors: S·埃尔哈特; J·鲁迪; J·克里格
Original assignee: Heidelberger Druckmaschinen AG
Current assignee: Heidelberger Druckmaschinen AG
Priority date: 2019-07-17
Filing date: 2020-07-17
Publication date: 2023-09-22
Anticipated expiration: 2040-07-17
Also published as: CN112238683A; DE102020117284A1

Abstract

The invention relates to a method for performing register correction by means of a computer (11) during printing in an inkjet printer (7), wherein register marks (15) are printed on individual sections of a printing substrate (12) in addition to printing a useful part (17, 17 a) on the printing substrate (12), these register marks (15) being digitally detected by a measuring device and evaluated by the computer (11) in terms of register errors that will occur and corrected accordingly, characterized in that the sections of the printing substrate (12) with the register marks (15) are set against at least one color separation (13 a,14 a) of the useful part (17, 17 a) prior to printing the register marks (15).

Description

Register measurement with white separation color

Technical Field

The invention relates to a method for correcting a printing plate during printing in an inkjet printer by means of a synthetic white background.

The present invention belongs to the field of ink jet printing technology.

Background

When printing using an inkjet printer, as is the case with most other multicolor printing processes, so-called register correction (Passerkorrektur) is also required. This involves accurate overprinting of multiple color separations (farbauszuge) because geometrical deviations of individual color separations can result in an unclear printed image with special printing artifacts (Druckartefakten). In order to monitor and subsequently correct an exact overprint (i.e. register), so-called register marks (Passermarken) are then printed for all color separations and it is measured whether all color separations are printed exactly where they were located at the nominal positions derived from the printed image, to be precise with respect to the freely selectable standard color aspects. The structure of the register marks used can be very flexible. One possible configuration is then as follows. A page-wide mark consisting of a plurality of individual elements, wherein each element exhibits a printed color. For example: black discs as reference, cyan discs as measured colors, arranged in groups of three for each print head, respectively. The marks may also be scaled down or up as desired. This triplet arrangement can be referenced to black as a horizontal mark (i.e., transverse to the printing direction) or as a vertical print mark (along the printing direction), respectively.

In the case of web-fed inkjet printers, that is to say in web printing, there is also a known method of way, namely: the conventional printing process is interrupted for register measurements with On-Demand test pages (On-Demand-Testbogen). Register marks are then printed on the on-demand test sheet and evaluated accordingly. With the knowledge thus obtained, the register is adapted accordingly for the original printing process. Since transparent printing substrates are often used in web inkjet printing (in particular for producing labels), they are used as a background in the region of individual labels or in the parts of these labels in a special color (white in most cases). In this case, the test-on-demand sheet for register measurement is likewise in the form of a white background in the case of such a printed image, wherein the label to be printed and the test-on-demand sheet differ in their background with respect to the amount of color applied and thus also with respect to the energy input into the substrate via the respective dryer. This then results in: the register measurement by means of the on-demand test page shows the result of a deviation from the measured register which does not correspond to the actual state during printing of the original label. Thus, accurate register correction cannot be performed during printing on an inkjet printer under the above conditions.

Disclosure of Invention

The object of the present invention is therefore to provide a method for performing register correction in an inkjet printer, which method enables reliable register correction even with transparent printing substrates.

This object is achieved by a method for performing register correction by a computer during printing in an inkjet printer, in which, in addition to printing a useful part (Nutzen) on a print substrate, register marks are printed on individual sections of the print substrate, which register marks are digitally detected by a measuring device and evaluated by the computer with respect to the register errors that occur, and the register errors are corrected accordingly, characterized in that section of the print substrate having register marks is brought to bear at least one color separation color/color separation (false separation) of the useful part prior to printing the register marks. That is, to ensure that the background of the register marks is consistent with the background of the otherwise printed useful portion to such an extent that systematic deviations between the register measurements on the on-demand test sheet and the otherwise printed process described above no longer occur, then at least one color of the otherwise useful portion is separated from the color of the register marks as background. This ensures that the customer's intention and the on-demand test page no longer differ in the amount of color applied, and that the register correction produced by printing and evaluating these register marks will also function correctly.

In this case, the color separation color of the useful part represents both the individual color separations of the printed image to be produced in the useful part and the corresponding color background settings of the printing substrate on which the useful part is printed.

Advantageous and therefore preferred developments of the method result from the preferred embodiments and from the description with the drawing.

In this case, a preferred development of the method according to the invention provides that the color separation of the segments of the register-marked printing substrate, against which the segments are against, is white. This is the color separation color used in most cases. White separation is the standard case, although other backgrounds are possible in addition to white separation as background.

In this case, a further preferred development of the method according to the invention provides that the color separation color used for printing register marks corresponds to the color separation color of the background on which the useful part is located. That is, if a customer useful part having a white background is printed, it is recommended that the white separation color is also used for the printing substrate of the register mark. Thereby ensuring that: the two substrates used for register measurement have similar properties and do not exhibit undesirable deviations in register measurement.

In this case, a further preferred development of the method according to the invention provides that the color separation colors used for printing the register marks correspond to the white resulting separation colors created by the sum of all the color separation colors of the useful part. If the useful part is not provided with a defined color separation (in most cases white separation) as background, but rather the useful part is applied directly to the transparent substrate, a color separation must be found for the background of the substrate as the register marks, since otherwise the applied color quantities for the two substrates differ again, and a sensible register correction cannot be achieved. Thus, in this case, all of the color separation colors of the useful part itself are collectively converted into white resultant separation colors and used for the backgrounds of these register marks in this color separation color.

In this case, a further preferred development of the method according to the invention is that the creation of the white result separation color is carried out in a computer by implementing an "or" link (ODER-verknupfung) of all color separation colors of the useful part. These register marked substrate materials can then accordingly be backed with the white resulting separation color thus created.

In this case, a further preferred development of the method according to the invention provides that the register marks are distributed by the computer over a section of the printing substrate in such a way that they are printed by different printing heads and are distributed as far apart as possible over the entire width of the section. This is necessary in order to obtain a more reliable estimate for the actual register errors and also to determine the error bit of the individual print heads. In this case, the individual register measurement marks (or measurement elements) are also ideally distributed repeatedly over the section of the printing substrate.

In this case, a further preferred development of the method according to the invention provides that the computer creates such a list for distributing the register marks over the sections of the printing substrate having the register marks: the list has the positions and nominal parameters of these register marks. In this case, the process can also be carried out by an external computer before the original printing process.

In this case, a further preferred development of the method according to the invention provides that the computer forwards the created list to a control device of the inkjet printer, which prints the register marks in a dynamic manner at given locations on the sections of the printing substrate having the register marks, and transmits these locations and setpoint parameters to the measuring device. If the computer that creates such a list with location and nominal parameters is identical to the control computer of the inkjet printer, it is naturally not necessary to communicate the created list. In this case, the control computer of the inkjet printer immediately uses the created list as given.

In this case, a further preferred development of the method according to the invention provides that the list is transmitted by the computer to a preprinting stage (vorstatus) of the printing process, in which printing stage the register marks are embedded in the printing job as a function of the position and setpoint parameters, while the position and setpoint parameters are transmitted to the measuring device. In this case, the list with the positions and setpoint parameters of the measuring marks is fixedly built into the print job, rather than being forwarded in a dynamic manner during printing. However, the position and the setpoint variable should also be transmitted to the corresponding measuring device, so that the latter can perform the register measurement accordingly.

Drawings

The invention and its structurally and/or functionally advantageous refinements are further described below on the basis of at least one preferred embodiment with reference to the accompanying drawings. In the drawings, elements corresponding to each other are denoted by the same reference numerals, respectively.

The drawings show:

fig. 1: examples of roll-to-roll inkjet printers used;

fig. 2: a schematic view of the white separation color of the receiving customer utility;

fig. 3: synthesizing a schematic view of the white separation color of the customer useful part;

fig. 4: examples of distributions of register marks (or register elements);

fig. 5: a schematic view of the progress of the method according to the invention.

Detailed Description

The field of application of the preferred embodiment variant is a roll-type inkjet printer 1. Fig. 1 shows an example of the basic structure of a machine 1 of this type, which machine 1 comprises an unwinder 2 up to a wind-up 10, which unwinder 2 serves to supply a web-shaped substrate to a print preparation stage 3, which print preparation stage 3 comprises, for example, a flexographic printing mechanism 4 for white/full-face and a flexographic printing mechanism 5 for priming, as well as to an otherwise intrinsic printing mechanism 6, in which printing mechanism 6 the substrate is printed by a print head 7. Furthermore, the reel-type inkjet printer 1 often also has a further processing stage 9, which further processing stage 9 comprises a flexo mechanism 8 for the varnish. The reel-up inkjet printer 1 is monitored by a control computer 11.

In the case of register measurements on such inkjet printers 1 for web printing, it is necessary here for the register measurement patterns 15 to be printed as far as possible under the same conditions as in the customer intentions 17,17a, in particular with regard to color coverage.

Fig. 5 shows the course of the method according to the invention required for this purpose in a preferred embodiment variant with a possible way (or alternative) to this. The method is performed by means of a computer, which may be the control computer 11 of the roll-type inkjet printer 1. But the computer may be an additional computer; examples of such a computer are: which evaluates the register measurements and transmits the necessary register corrections to the control computer 11 of the roll inkjet printer 1.

1. If the print job is in the background of white, then the white separation color 13 can be extracted for these measurement zones. Thus, these measurement sections also have a color coverage (intensity) similar to the customer's intent 17. The register marks 15 are then distributed automatically by the computer 11 on the extracted white background surface 13a, i.e. in such a way that the register marks 15 are located completely in the white surface 13a. If the position is insufficient, the white surface 13a may be slightly widened, provided that: whereby the amount and distribution of the applied color is not excessively changed. The degree of rasterization of the white face 13a may also be lighter than the original background of these measurement marks 15, if possible. Fig. 2 shows a print substrate 12 having an example for the method. In the uppermost part of fig. 2 a customer useful part 17 is shown, which customer useful part 17 comprises the individual elements of the useful part 14 together with a white background, i.e. the white separation color 13. The white separation color 13 is extracted as shown in the middle part of fig. 2 and then used for the background of the measurement section of the register measurement (i.e., the extracted white separation color 13 a). Thus, the lower part of fig. 2 shows the result of register marks 15 (or register elements 16) distributed on the correct white background 13a. The use of reduced register marks 15 is preferred here in order to make the most desirable use of these white surfaces 13a possible. In the case of distribution, it must be noted that register marks 15 are printed by different printing heads 7 and distributed as far as possible over the width of the printing section. It is desirable to repeat multiple times so that the results of these register marking elements 16 can be averaged to obtain a more reliable estimate of the actual register errors. Thereby, for example, also erroneous bit states of the individual printheads 7 which are not usually noticeable are compensated.

2. In contrast, if there is no or only little white background 13 in the print job, an alternative method approach must be used. Accordingly, it is preferable that all the color separation colors of the customer-useful part 17a where no background is provided are collected, so that the surface covered with at least one arbitrary color is also covered with the resulting separation color. The result of this process is then used to measure the white background of the section and distribute the register marks 15 thereon (in a manner similar to the first method described above). In this case, it is preferable to generate such a combined white separation color 14a in that all color separations of the individual elements 14 of the customer-useful part 17a are combined into such a combined white separation color 14a by means of the computer by means of digital or logical links of pixels. This simulates almost the same overall color application and should thus affect the web as would an original print job. Fig. 3 again shows the method in three parts for the example described above. The upper diagram of fig. 3 is the customer-useful part 17a without a white background, the middle diagram is the synthesized white separation color 14a produced by the computer 11 based on the color separation color of the individual elements 14 of the customer-useful part 17a, and the lower diagram is the measurement section created thereby (or against white) with the correspondingly distributed register marks 15.

The method for distributing these register marks 15 in a computer-supported manner is described somewhat more precisely below. These register marks 15 are preferably distributed as follows:

1. white separation colors 13a,14a are generated according to the above example, and are shown as an image "BACK/Bier" with (1=white, 0=blank). The image includes the entire printed area.

2. Iterating through all print colors or groups of print colors:

2.1. producing a separated image of the small register mark 15 for this/these colors, comprising two adjacent points of the reference color 18 and at least one point of each measured color, comprising a white background 13a,14a;

2.2. starting from the upper left image edge, the position for register mark 15 is found such that all or most (e.g. 90%) of the required pixels have a value of 1 in the image "BACK/Bier". For example, a mask (mask) can be moved over the image "BACK/beer" in succession for searching.

2.3. If a location is found, the location is stored for printing and all pixels covered by register mark 15 in "BACK/Bier" are set to 0.

2.4. Steps 2.2 and 2.3 are repeated starting from the top right, bottom left and bottom right image edges, optionally from more starting points, possibly from the middle left, middle right, top left half, etc.

3. The result of this method is a list with the positions and parameters of the register marks 15, which register marks 15 then preferably continue to be processed in one of the following ways:

3.1. the list is forwarded to the control computer 11 of the roll-type inkjet printer 1, which control computer 11 dynamically spreads the register marks 15 at given positions and communicates the orientations/parameters to register measuring means, such as a camera system with an image processing computer.

3.2. The list is processed in the computer of the RIP (or pre-press stage) and these register marks 15 are synthesized into the print job. It is then only necessary here to transfer these positions to the control computer 11 of the roll inkjet printer 1, so that the control computer 11 does not dynamically input anything, but must in turn transfer these marking positions/parameters to the measuring device.

The results of this distribution are shown in the lower part of fig. 2 and 3, respectively. Fig. 4 shows an example of such register marks 15 themselves having their elements.

The register mark 15 is implemented horizontally. It can be seen here well that: reference color black 18, there are two proxels between which there is a single measurement color measurement point (or element) 16. The register marks 15 can be arranged arbitrarily depending on the position on the print substrate 12. A vertical arrangement is also possible.

List of reference numerals

1. Ink jet printer

2. Unreeling device

3. Printing preparation stage

4. Flexo printing mechanism for white/full face

5. Flexo printing mechanism for bottom coating

6. Ink jet printing mechanism

7. Ink jet print head

8. Flexo printing mechanism for gloss oil

9. Continuing the treatment phase

10. Rolling device

11. Control computer

12. Printing substrate

13. White separation color as background

13a as background white separation color

14. Individual elements of customer usefulness

14a synthesized white separation color

15. Register mark

16. Register mark element

17. Customer-useful part with white background

17a customer-useful part without setting background

18. Reference colour "black"

Claims

1. A method for performing register correction during printing in an inkjet printer (7) by means of a computer (11),

wherein, in addition to printing the useful part (17, 17 a) onto the printing substrate (12), register marks (15) are printed onto individual sections of the printing substrate (12), which register marks are digitally detected by a measuring device and evaluated by a computer (11) with respect to the register errors that occur and corrected accordingly,

it is characterized in that the method comprises the steps of,

the section of the printing substrate (12) having the register mark (15) is set against at least one color separation (13 a,14 a) of the useful portion (17, 17 a) prior to printing the register mark (15).

2. The method according to claim 1,

it is characterized in that the method comprises the steps of,

the following color separation colors (13 a,14 a) relate to white separation colors: the section of the printing substrate (12) of the register mark (15) is backed by the color separation.

3. The method according to claim 1 or 2,

it is characterized in that the method comprises the steps of,

the color separation colors used for printing the register marks (15) correspond to the following color separation colors: the useful part takes the color separation color as a background.

4. The method according to claim 1 or 2,

it is characterized in that the method comprises the steps of,

the color separation color used for printing the register mark (15) corresponds to the following white result separation color: the white resulting separation color is created from a summary of all color separation colors of the useful part.

5. The method according to claim 4, wherein the method comprises,

it is characterized in that the method comprises the steps of,

the creation of the white result separation color (14 a) is done in the computer (11) by "or logic" linking all color separation colors of the useful part.

6. The method according to claim 1 or 2,

it is characterized in that the method comprises the steps of,

the computer (11) distributes the register marks (15) over the section of the printing substrate (12) in such a way that the register marks (15) are printed by different printing heads and are distributed as far apart as possible over the entire width of the section.

7. The method according to claim 6, wherein the method comprises,

it is characterized in that the method comprises the steps of,

the computer (11) creates a list of positions and setpoint parameters of the register marks (15) for distributing the register marks (15) on the section of the printing substrate (12) having the register marks (15).

8. The method according to claim 7,

it is characterized in that the method comprises the steps of,

the computer (11) transfers the created list to a control device of the inkjet printer (7), which dynamically prints the register mark (15) at a given position on the section of the printing substrate (12) having the register mark (15), and transmits the position and the setpoint parameter to a measuring device.

9. The method according to claim 7,

it is characterized in that the method comprises the steps of,

the list is transferred by the computer (11) into a pre-press stage of the printing process, in which the register marks (15) are embedded in the print job as a function of the position and the setpoint parameters, while the position and the setpoint parameters are also transferred to a measuring device.