阅读说明：本技术 用于喷墨印刷过程的元信息编码 (Meta-information encoding for inkjet printing processes ) 是由 A·舍曼 H·克勒 于 2019-09-11 设计创作，主要内容包括：本发明涉及一种用于借助计算机(3,6)进行喷墨印刷机(4)中的印刷品质分析的方法,其中,在印刷进程期间印刷、借助图像检测系统(2)测量并通过所述计算机(3,6)分析测试图案样式(11)并将所述分析的结果用于控制所述喷墨印刷机(4),其中,所述测试图案样式(11)的印刷和分析需要同步的进程,所述方法的特征在于,借助局部灰度值调整向所述测试图案样式(11)中集成入编码(9,13),所述编码(9,13)由所述图像检测系统(2)检测并由所述计算机(3.6)相应地分析以用于进行印刷品质分析。(The invention relates to a method for analyzing the printing quality in an inkjet printer (4) by means of a computer (3,6), wherein a test pattern (11) is printed during a printing process, measured by means of an image detection system (2), and analyzed by the computer (3,6), and the result of the analysis is used to control the inkjet printer (4), wherein the printing and the analysis of the test pattern (11) require a synchronous process, characterized in that a code (9,13) is integrated into the test pattern (11) by means of a local gray value adjustment, wherein the code (9,13) is detected by the image detection system (2) and correspondingly analyzed by the computer (3.6) for the analysis of the printing quality.)

1. A method for performing print quality analysis in an inkjet printer (4) by means of a computer (3,6),

wherein a test pattern (11) is printed during a printing process, measured by means of an image detection system (2), and evaluated by a computer (3,6), and the result of the evaluation is used to control the inkjet printer (4),

wherein the printing of the test pattern (11) and the analysis process need to be performed synchronously,

it is characterized in that the preparation method is characterized in that,

by means of local gray value adaptation, a code (9,13) is integrated into the test pattern (11), which code is detected by the image detection system (2) and correspondingly evaluated by a computer (3,6) for performing a print quality analysis.

2. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

it is characterized in that the preparation method is characterized in that,

as the code (9,13), the morse code (9,13) is used.

3. The method according to any one of the preceding claims,

it is characterized in that the preparation method is characterized in that,

the computer (3,6) assigns a layout ID to each test pattern (11), codes the layout ID accordingly, embeds the layout ID in the test pattern (11) as a code (9) by means of local gray-value adaptation, and, when evaluating the measured test pattern (11), first identifies the test pattern (11) by means of the detected coded layout ID (9) and thus synchronizes the printing of the test pattern (11) with the evaluation.

4. The method of claim 3, wherein the first and second light sources are selected from the group consisting of,

it is characterized in that the preparation method is characterized in that,

the coded layout ID (9) is always applied by the computer (3,6) to the same location in the test pattern (11), independently of the configuration of the test pattern (11).

5. The method of claim 4, wherein the first and second light sources are selected from the group consisting of,

it is characterized in that the preparation method is characterized in that,

different test pattern patterns (11) are printed, which are checked for different possible printing errors by means of an evaluation process carried out in a computer-supported manner.

6. The method of claim 5, wherein the first and second light sources are selected from the group consisting of,

it is characterized in that the preparation method is characterized in that,

as different test pattern patterns (11), different color separations of the test pattern patterns (11) are iteratively printed, wherein the encoded layout ID (9) also contains information about the respective color separation.

7. The method according to any one of the preceding claims,

it is characterized in that the preparation method is characterized in that,

the local gray value adaptation for generating the coded layout ID (9) is achieved by using minimum and maximum gray levels of one individual print nozzle or minimum and maximum gray levels of a plurality of adjacent print nozzles, respectively.

8. The method according to any one of the preceding claims,

it is characterized in that the preparation method is characterized in that,

in the case of a single printing nozzle, the information element of the code (9) is realized by generating one pixel with minimum and maximum grey levels or by generating a plurality of pixels with minimum and maximum grey levels.

9. The method according to any one of the preceding claims,

it is characterized in that the preparation method is characterized in that,

in addition or as an alternative to the generation of the layout ID, individual printing nozzles of the inkjet printer (4) integrate their own printing nozzle numbers as a code (13) into the test pattern (11) for identification, and when evaluating the measured test pattern (11), the computer (3,6) assigns the found printing errors (16) to the printing nozzle concerned by means of the code (13).

10. The method according to any one of the preceding claims,

it is characterized in that the preparation method is characterized in that,

the image detection system (2) is arranged in an inline manner in the inkjet printer (4) and has an image detection computer (6) which evaluates the detected test pattern patterns (11).

Technical Field

The invention relates to a method for analyzing the print quality of an inkjet printer by using encoded meta information (Metalnformation).

The invention belongs to the technical field of ink jet printing.

Background

In industrial inkjet printing, the state of the individual printing nozzles of the print head used in an inkjet printer is a decisive criterion for the print quality ultimately obtained by the inkjet printer used. Here, the state of these individual printing nozzles generally changes over time. Thus, for example, if the printing nozzles are not used for a while, the ink residue in the printing nozzles may dry out. These dried-out residues may then lead to a reduction in the ink discharge or, for example, to skewed ejection of the printing nozzles concerned. Even when printing at different loads, the print nozzle behavior is often not linear, which makes it difficult to predict its print behavior. These changes in the state of the printing nozzles and their corresponding influence on the printed image to be produced must therefore be checked regularly when operating the inkjet printer.

For this purpose, it is known to use different types of test pattern patterns (testmuterns) which are applied to the substrate at regular intervals (in addition to the print image to be produced) and which are correspondingly processed continuously in an evaluation with regard to the current state of the individual printing nozzles which are involved in printing the test pattern. The test pattern patterns are designed in such a way that all printing nozzles involved in the printing process are involved in the printing of the test pattern patterns. But there are different types of test pattern patterns. It is widely known to have, for example, a full tone surfaceBecause reduced printing, print skew, or even completely malfunctioning printing nozzles can be identified particularly quickly in such full-tone planes. In other words, such a malfunctioning printing nozzle that has a negative influence on the resulting printed image can thus be determined very well. However, these test pattern patterns with full tone facets have the disadvantage that: it is often not possible to identify individual printing nozzles that are malfunctioning, but in most cases only the area in which the probable percentage of individual printing nozzles that are malfunctioning is located. Therefore, it is usual to additionally print a second type of test pattern in which each participating printing nozzle prints an individual object (e.g. a scribe line) and in which the individual objects are arranged in such a way that each individual printing nozzle can be unambiguously identified from the scribe lines printed by the printing nozzles. In addition to this, by printing each stampThe analysis of the object printed by the printing nozzles also yields information about the current state of the printing nozzles with respect to inclination and printing intensity (also referred to as phase and amplitude). This test pattern is not simply printed and the current status of all printing nozzles is thus evaluated separately because: although the status of each individual printing nozzle can be evaluated, the effect of this status on the printed image to be produced cannot be known. After all, not all printing nozzles have the same effect on the corresponding printed image in the case of the same error image. Thus, combining the two types of test pattern patterns of printing and analysis processing enables a relatively reliable assessment of the status of the printing nozzles used by the inkjet printer concerned.

However, this approach has the disadvantage that it has to withstand the costs of regularly printing and analyzing two different types of printed image patterns together in addition to the printed image to be produced. It would therefore be advantageous to reduce this waste (or scrap) caused by printing two different test pattern patterns. There are various methods for this purpose in the prior art. The closest approach is of course: the status of the printing nozzles used is evaluated based on the print image that is originally to be printed. However, these approaches have not proven to be very effective because: in particular for very flexible inkjet printing with constantly changing material to be printed (Sujet), monitoring the print image produced does not allow reliable monitoring of all the print nozzles of the inkjet printer which are of importance. If too many printing nozzles are used, there is no way at all to participate in the printing with sufficient regularity for continuous monitoring.

The printed test pattern patterns are typically analyzed using an integrated image detection system. Many higher value printing presses have image detection systems in-line. That is, the image sensing system is installed in or after the last printing mechanism in the inkjet printer. The image detection system usually has one or more cameras which monitor the entire print image produced and transmit the image data thus produced to an image processing computer, which then compares the detected image data with the digitally present target image data. With such a system, high-value print quality analysis is performed on the generated print image. Of course, such a system may also be used to analyze the printed test pattern. If no such system is present, the test pattern must be checked at regular intervals either manually by the printer with the aid of a magnifying glass or supplied to an external image processing system.

In the case of an integrated image detection system, during a printing run, meta-information (for example, layout information about the type and position of the nozzle pattern or the image area) is exchanged between the printing control system and the monitoring system, which information is analyzed by the camera. Here, a series of layouts (Layout) is exchanged, which then have to be followed by a printing sequence. The description of the printing sequence is typically described using control commands, the original printing being ensured by electronic real-time signals between the printing system and the monitoring system. If such electronic signals are disturbed here (for example in the form of signal losses or in the form of excessive signal generation due to noise), then the synchronization between the printing layout and the actual printing can no longer be ensured.

Furthermore, loss of synchronicity may also result if the printing of a certain layout is intentionally repeated by the control electronics in a real-time manner, where such real-time behavior cannot be traced by pre-filling in the command interface. For example, if a print is marked as bad and "instantly" requires that the print be repeated, then special repeat layouts need to be made to do so. The reaction time involved in the repetitive layout in a synchronous manner by means of the command interface becomes significantly longer.

A further problem of quality monitoring of existing printing nozzles by means of printing and evaluation of test pattern patterns is that the evaluation of the corresponding test pattern and the printing thereof are to be synchronized precisely. Therefore, in order to correctly analyze the printed test pattern patterns, it is necessary to univocally know which test pattern has just been printed because: if the detected test pattern is compared to a wrong digital test pattern given to the computer, a wrong result will of course be obtained.

Disclosure of Invention

The object of the present invention is therefore to provide a method for detecting defective printing nozzles in an inkjet printer, which is more efficient and reliable than the methods known from the prior art.

This object is achieved by a method for analyzing the print quality in an inkjet printer by means of a computer, wherein test pattern patterns are printed during a printing process, measured by means of an image detection system and evaluated by the computer, and the results of the analysis are used to control the inkjet printer, wherein the printing and evaluation of the test pattern patterns requires a synchronous process, characterized in that codes are integrated into the test pattern patterns by means of local gray value adaptation (lokaler grace tastanspansing), which codes are detected by the image detection system and evaluated correspondingly by the computer for the analysis of the print quality. The core of the invention is: it is realized that the individual printing nozzles can be actuated in such a way that the local gray values of the pixels to be generated by the printing nozzles are changed. Certain information can then be transmitted by means of this change. Of course, such local grey value changes cannot be made in the print image to be produced, since this would change the desired print image. In contrast, changing the corresponding test pattern is far less critical, as long as the test pattern still fulfills its purpose (i.e. print quality monitoring). Such local grey value changes of course do not occur randomly but rather according to a specific code. This code can then be evaluated together by the image detection system used for quality monitoring. The information thus encoded can then be used for different purposes of print quality analysis.

Advantageous and therefore preferred developments of the invention emerge from the dependent claims and the description with the figures.

In this case, a preferred development of the method according to the invention is to use morse code (morcode) as the code. Many types of codes (e.g. two-dimensional codes, etc.) can of course be generated by means of local grey value changes. However, since each individual printing nozzle produces a vertical object (e.g. a scribe line) in the printing direction, such local grey value changes of the printing behaviour of course mean above all straight line printing, weakened printing or no printing of the printing nozzle. For this printing behaviour, morse coding is obviously the best choice.

In this case, a further preferred development of the method according to the invention provides that the computer assigns a Layout ID (Layout-ID) to each test pattern, encodes the Layout ID accordingly, embeds the Layout ID in the test pattern by means of local gray-scale value adaptation, and, when evaluating the test pattern measured, first identifies the test pattern by means of the Layout ID detected and thus synchronizes the printing and evaluation of this test pattern. This corresponds to the first application scenario: for those codes that are integrated into the test pattern by means of local grey value adaptation. The printed test pattern patterns and the very analysis of those test pattern patterns can be synchronized simply and efficiently by means of the layout ID. One or more printing nozzles print a certain Morse code in a certain area of the test pattern, the certain Morse code containing information of the layout ID. The image detection system responsible for the evaluation knows at which defined point of the test pattern the ID is located and isolates the relevant morse code, decodes the layout ID and checks whether the ID of the detected test pattern corresponds to the ID of the intrinsic test pattern present in digital form, and compares the detected test pattern with the intrinsic test pattern present in digital form. If this is not the case, a report of a synchronization error is output.

In this case, a further preferred development of the method according to the invention provides that the layout ID is always placed by the computer at the same location in the test pattern, irrespective of the test pattern configuration. As already explained, the layout ID must be always placed at the same position of the test pattern regardless of the configuration of the test pattern. Otherwise, the image detection system used for the analysis process may not be able to find the Morse code of the layout ID. This is of course extremely difficult, since it is known for the detection system to distinguish known local grey value adaptations corresponding to the morse code from the occasional grey value jumps at other parts of the test pattern. To do this, the image detection system must know which same location the encoded layout ID is placed on, which also includes the exact size of the region.

In this case, a further preferred development of the method according to the invention provides for different test pattern patterns to be printed, which are checked for different possible printing errors by means of an evaluation process implemented in a computer-supported manner. In this case, it is also significantly simpler to assign and synchronize a plurality of different test pattern patterns, which are used for evaluating possibly different printing errors, with the aid of the layout ID.

In this case, a further preferred refinement of the method according to the invention is to print different color separations of the test pattern iteratively as different test pattern patterns, wherein the layout ID also contains information about the individual color separations, one application for different test pattern patterns consists in the different color separations of the test pattern concerned, since in inkjet printers the different color separations must of course always be printed by different print heads, here, in order to apply the different inks of the individual color separations, the test pattern patterns belonging to themselves must be printed and analyzed for each color separation.

In this case, a further preferred development of the method according to the invention is that such a local gray value adaptation for generating the coded layout ID is carried out by using the minimum and maximum gray levels of an individual printing nozzle or the minimum and maximum gray levels of a plurality of adjacent printing nozzles, respectively. This enables the coding (particularly, morse coding) to be relatively reliably realized. Because the Morse code is ultimately composed of only pixels that are printed or not, the use of minimum and maximum gray levels, respectively, enables the desired contrast to be achieved for forming the Morse code (and other codes that may be used). Here, the moss code is realized by printing of a single printing nozzle or by printing a plurality of printing nozzles together, depending on various parameters, such as: resolution of the image detection system, space requirements on the print substrate for the layout ID.

In this case, a further preferred development of the method according to the invention provides that, in the case of a single printing nozzle, the coded information element is realized by generating a pixel with minimum and maximum gray levels or by generating a plurality of pixels with minimum and maximum gray levels. If only one single printing nozzle should be used to generate the involved morse code, this printing nozzle can of course both generate the code with only a single pixel having a contrast between the smallest and the largest available grey levels, and use a plurality of pixels having the smallest or the largest grey level for this purpose. Which way is preferably used here also depends on the criteria of the respective application scenario. First is the question of the coding type chosen: whether the encoded information unit (e.g. byte or morse encoded) or long or short can be implemented by a single pixel.

In addition or as an alternative to the generation of the layout ID, a further preferred development of the method according to the invention provides that the individual printing nozzles of the inkjet printer integrate their own printing nozzle numbers as a coding into the test pattern for the purpose of authentication, and that, when evaluating the test pattern measured, the computer assigns the printing errors found to the printing nozzle concerned by means of this coding. This is a second application scenario of the method according to the invention. In this case, instead of generating a layout ID of a specific test pattern, which is then used for synchronizing the printing and evaluation of the test pattern, the exact assignment of the relevant printing nozzles is achieved by printing their own printing nozzle numbers. This is of course premised on: the image detection system used for the analysis process is also able to identify the code of the individual printing nozzle that is printed, including the printing nozzle number. This is of great advantage if this is possible, because: in test pattern patterns with full tone or other gray level surfaces, it is not necessary to print a second test pattern to identify the individual print nozzles in order to analyze the effect of processing the state of one print nozzle on the resulting printed image. It is possible to simply print the individual printing nozzles with their own printing nozzle numbers in defined regions of the test pattern with full-tone or gray-scale values by means of coded local gray-scale value adaptation. Then, the image detection system as an analysis processing unit can decode such a number and thus immediately learn: which formation (artfakt) in the successive test pattern is caused by the printing nozzle with the printing nozzle number concerned. Since only a single printing nozzle can be used for coding in each case here, since this is the printing nozzle number concerned which is to be coded, only such coding is of course suitable for the above-described application case: the encoding can also be realized by means of such a one-dimensional encoding.

In this case, a further preferred development of the method according to the invention provides that the image detection system is arranged in an inline manner in the inkjet printer and has an image detection computer which evaluates the test pattern patterns measured. The method according to the invention is preferably carried out here using an inline image detection system provided in an inkjet printer. This has the advantages that: the printed test pattern patterns can be analyzed and processed instantly, almost online, and the method according to the present invention with respect to printing and analyzing the process layout ID and the printing nozzle numbers can be performed instantly, almost online, online. It is furthermore noted that inline image detection systems of the kind which are primarily used for print quality monitoring already exist, so that no additional hardware has to be used for carrying out the method according to the invention.

Drawings

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

The figures show:

FIG. 1: examples of inline image detection systems used;

FIG. 2: an example of adopting a layout ID;

FIG. 3: performing an example of printing nozzle numbering realized by means of morse coding;

FIG. 4: schematic procedures for synchronization with the aid of layout IDs;

FIG. 5: the schematic progression of the printing nozzles is identified by means of the printing nozzle numbers.

Detailed Description

Fig. 1 shows an example of an image detection system 2 employing a method according to the invention. The image detection system 2 comprises at least one image sensor 5 (typically a camera 5 integrated into the sheet printing press 4). The at least one camera 5 captures the printed image produced by the printing press 4 and transmits the data to the computers 3,6 for evaluation. The computers 3,6 may be separate computers 6 (for example, one or more specialized image processing computers 6) or may correspond to the control computer 3 of the printing press 4. At least the control computer 3 of the printing press 4 has a display 7, on which display 7 the results of the image monitoring are shown.

If meta-information 14 is to be displayed in addition to the regular printed image 8 in printing, there are several possible methods, such as: text or bar code. According to the method of the invention, it is proposed to encode the information by means of the Morse code 9,13 in the case of grey levels of the print head, which is very easy to implement and which can also be implemented by means of a system directly embedded in the print head control electronics, without the need to use complex, typically computer-based, rendering techniques.

Less expensive electronics located near the print head can produce autonomously generated scribes at the possible grey levels of the print head. In this way, the electronic device is able to supplement the printed image 8 with the Morse code 9,13 in addition to the original printed image 8 that it should receive and that it should print.

In addition, by presenting the moss code element "long/short/none", it is also possible to present information to an individual printing nozzle, in particular the printing nozzle, for example, records its own number in the printed image 8.

Furthermore, a microscopically small code, i.e. less than 100 μm, can be produced by using individual pixels with corresponding grey levels.

Here, two special application scenarios should be distinguished as a constituent of the method according to the invention:

I) encoding the printing layout ID as meta information 14 into the moss code 9 when printing the test pattern styles 10, 11;

II) the print nozzle number is coded to the moss code 13 in the print nozzle test pattern 11 realized by just this print nozzle.

With respect to I):

the procedure of the first application scenario is schematically illustrated in fig. 4. According to the method of the invention, a layout ID 14 is issued by the control computer 3 of the printing press 4 via a command interface, wherein, in real-time printing, the layout ID9 is printed together as an element by means of a Morse code. The image detection system 2 is now triggered by communication 15 to its image processing computer 6 by means of a real-time signal, so that the next print passes the image detection system 2. Here, the next layout in the order based on the received layouts is now not taken, but the morse code 9 (or the coded layout ID 9) is read out first to use the layout with the found ID9 for the scanning of the printed image 8. In this case, a layout can now be deleted or repeated by the control computer 3, since the printed code 9 is thereby also included again on the printed image 8.

This coding can always be printed, independently of the specific layout, in the same position defined before the start of printing, thus making it possible to always resolve the layout ID 14 so as to be the element that differs from one specific print to another by the image detection system 2 on the basis of the layout found.

One example here is: the printing nozzles on each sheet are monitored. On each individual sheet, a pattern 10 is printed which is iteratively repeated by color. Thus, in the seven-color inkjet printer, the pattern 10 for one color is printed on all/page. An example of this process is shown in figure 2. Here, the register mark 10 is printed as the pattern style 10, and the layout ID9 is printed after the register mark 10 as a main component of the meta information 14 in a morse code manner. If synchronization between printing of the register marks 10 and the image detection system 2 that checks these register marks 10 is a problem, the pattern can be analyzed under wrong color assumptions. The same principle is used when printing a test pattern of print nozzles.

Then, a color is also given in the command on the test pattern 10. If the trigger signal is lost or a page is repeated, the correct color can be determined by the layout code.

In addition, alternative embodiment variants of variant I) provide for: in order to code the layout ID 14 with a moss code which is generated by means of the largest and smallest ink drops (or the smallest and largest grey levels) by one individual printing nozzle, it is then also possible to generate a plurality of moss codes by a plurality of combined printing nozzles. Alternatively, it is also possible to use printing nozzles: instead of using a single pixel, the print nozzle uses multiple pixels to encode the "long/short" signal. It is also always provided here that the coded layout ID9 can be generated by electronics located in the vicinity of the print head, while the printed elements can also be resolved by the image detection system 2 with a smaller resolution.

To synchronize the printing with the image detection system 2, the principle of this layout coding may also be modified to another coding instead of the Morse coding.

With respect to II):

the progress of this preferred application scenario is schematically illustrated in fig. 5. In the case of detection of a defective printing nozzle 16 of the printing head, a marking pattern is generated in which the state of each printing nozzle with respect to position (deviation from the nominal position) and type of marking (for example continuity) is determined. The difficulty here is that the actual printing nozzle is assigned to the marking line. If not only a long scribe line is drawn for each print nozzle at this time, but also a thick/thin (or short) scribe line is drawn for each gray level, the ID of the print nozzle can also be directly read out. Fig. 3 shows an example of a print nozzle test pattern 11, in which print nozzle test pattern 11 individual numbers of print nozzle numbers are coded into individual moss code elements 13a,13b,13c,13d,13e in a print row 12 of individual print nozzles.

In this way, the typical problems are avoided:

1. such a printing nozzle number has been calculated by performing a nozzle assignment for each reference nozzle and counting the global camera pixels in the pattern. If this assignment is lost due to the mechanical movement of the printing head towards the monitoring system after measuring this assignment and before printing the pattern, the wrong printing nozzle number is calculated.

2. It is also possible that this assignment is universally correct, but due to the severe deviations in the positions of the printing nozzles in the scribing pattern, the printing nozzles jump their nominal positions, thereby also leading to incorrect numbering of the printing nozzles. In the method according to the invention these problems do not arise, since the nozzle number can be read directly from the scribe line of the printing nozzle.

In addition to the automatic evaluation by the image detection system 2, in an alternative embodiment variant it is also possible for the human user 1 to read out the moss code 13 by means of a magnifying glass, in order to thus also read out the number of the printing nozzles with absolute certainty.

List of reference numerals

1 user

2 image detection system

3 control computer

4 printing machine

5 image sensor

6 image processing computer

7 display

8 printing images

9 Morse coded meta-information

10 register mark

11 print nozzle test pattern

12 printing rows of individual printing nozzles

13,13a,13b,13c,13d,13e Morse coded print nozzle numbering

14-element information

15 control communication between computer and image processing computer

16 found defective printing nozzle