DE102020117284A1 - Register measurement with white separation - Google Patents

Abstract

Method for register correction in a printing process of an inkjet printing machine (7) by a computer (11), wherein in addition to printing of panels (17, 17a) on a printing substrate (12) registration marks (15) on a separate section of the printing substrate (12) printed, digitally recorded by a measuring device and evaluated by the computer (11) with regard to an occurring registration error and the registration error is corrected accordingly, which is characterized in that the section of the printing substrate (12) with the registration marks (15) before the printing of the registration marks (15) with at least one color separation (13a, 14a) the benefit (17, 17a) is deposited

Description

The invention is concerned with a method for register correction in a printing process of an inkjet printing machine with synthetic white background.

The invention lies in the technical field of inkjet printing.

When printing with inkjet printing machines, as with most other multi-color printing processes, a so-called register correction is necessary. This concerns the exact overprint of several color separations, since geometric deviations of individual color separations lead to an unclean print image with specific printing artifacts. In order to check and later correct the correct overprint, i.e. the register, so-called register marks are printed from all color separations, and it is measured whether all color separations print exactly at the positions at which their target positions resulting from the print image are present, based on a freely selectable standard color, for reference. The construction of the registration marks used is very flexible. One possible structure is as follows. A page-wide mark made up of several individual elements, each element representing a printing color. Example: black disks as reference, cyan disks as measurement color, each arranged as a group of 3 per printhead. The mark can also be reduced or enlarged if necessary. The arrangement of the group of 3 can be as a horizontal mark, i.e. transverse to the printing direction, or as a vertical printing mark, in the printing direction, each with black as a reference.

In the case of web-fed inkjet printing machines, that is to say in web printing, a known procedure is that the normal printing process for performing the registration measurement is interrupted by means of an on-demand test sheet. The registration marks are then printed on this on-demand test sheet and evaluated accordingly. The knowledge gained from this is used to adapt the register for the actual printing process. Since transparent printing substrates are often used in web inkjet printing, especially for the production of labels, this transparent printing substrate is deposited with a special color, mostly white, in the area of the individual labels or parts of them. In the case of such a print image, the on-demand test sheets for register measurement are also backed up in white, with the actual label to be printed and the on-demand test sheet being deposited with regard to the amount of color applied and thus also the amount of energy that is generated by the corresponding dryer is entered into the substrate. However, this means that the register measurement using the on-demand test sheets shows deviating results for the measured register, which does not correspond to the real state during the printing of the actual labels. Correct register correction in a printing process on an inkjet printing machine with the specified conditions is therefore not possible.

The object of the present invention is therefore to find a method for register correction in an inkjet printing machine which enables reliable register correction even in the case of transparent printing substrates.

This object is achieved by a method for register correction in a printing process of an inkjet printing machine by a computer, with registration marks being printed on a separate section of the printing substrate in addition to being useful on a printing substrate, digitally recorded by a measuring device and recorded by the computer with regard to a registration error that occurs are evaluated and the registration error is corrected accordingly, which is characterized in that the section of the print substrate with the registration marks is deposited with at least one color separation of the benefits before the registration marks are printed. In order to ensure that the deposit of the registration marks coincides with the deposit of the actual print so that there are no longer the systematic deviations described above between the registration measurement on the on-demand sheets and the actual print, at least one Color separation of the actual benefit, the registration marks deposited. This ensures that the customer motif and the on-demand test sheet no longer differ in terms of the amount of color applied and that the register correction generated by printing and evaluating the registration marks also works correctly.

In this case, color separation of the panels means both the individual color separations of the print image to be generated in the panel, as well as a correspondingly implemented color background of the printing substrate on which the panels are printed.

Advantageous and therefore preferred developments of the method emerge from the associated subclaims and from the description with the associated drawings.

A preferred development of the method according to the invention is that the color separation with which the section of the print substrate of the registration marks is deposited is a white separation. This is the color separation used in most cases. It is true other deposits than with a white separation are also possible; however, white separation is the standard case.

Another preferred development of the method according to the invention is that the color separation for printing the registration marks corresponds to a color separation with which the benefit is stored. If the customer benefit is printed with a white background, it is advisable to use this white color separation for the print substrate of the registration marks. This ensures that both substrates have similar properties for a register measurement and that there are no undesirable deviations in the register measurement.

Another preferred development of the method according to the invention is that the color separation for printing the registration marks corresponds to a white result separation, which is created from a combination of all color separations of the benefits. If the panels are not backed with a specific color separation, usually a white separation, but the panel is applied directly to the transparent print substrate, a color separation must still be found for the backing of the print substrate of the registration marks, otherwise the amount of paint applied will differ again for both print substrates , and therefore no realistic registration correction is possible. In this case, all of the color separations of the panel itself are then combined into a white result separation and used to store the registration marks with the color separation.

A further preferred development of the method according to the invention is that the creation of the white result separation is done in the computer by ORing all color separations of the benefits. With this white result separation created in this way, the print substrate of the registration marks can then be stored accordingly.

A further preferred development of the method according to the invention is that the computer distributes the registration marks on the section of the print substrate in such a way that the registration marks are printed by different print heads and distributed as widely as possible over the entire width of the section. This is necessary to get more robust estimates for the actual registration error and also to average out misalignments of individual print heads. In the ideal case, several repetitions of the individual register measurement marks or measurement elements are also distributed over the section of the printing substrate.

Another preferred development of the method according to the invention is that the computer creates a list with the positions and nominal parameters of the measurement marks for distributing the registration marks on the section of the print substrate with the registration marks. This process can also be carried out by an external computer before the actual printing process.

Another preferred development of the method according to the invention is that the computer transfers the list created to the control of the inkjet printing machine, which prints the registration marks dynamically at the given positions on the section of the print substrate with the registration marks and displays the positions and target parameters the measuring device transmits. If the computer that creates the list with the positions and setpoint parameters is identical to the control computer of the inkjet printing machine, it is of course not necessary to transmit the list created. In this case, the control computer of the inkjet printing press immediately uses the list as specified.

Another preferred development of the method according to the invention is that the list is transferred from the computer to the preliminary stage of the printing process, where the registration marks are inserted into the print job according to the positions and target parameters, while positions and target parameters are also transferred to the measuring device will. In this case, the list with positions and nominal parameters of the measurement marks is built into the print job and is not transferred dynamically during printing. Here too, however, positions and nominal parameters are to be transmitted to the corresponding measuring device so that it can carry out the register measurement accordingly.

The invention as such as well as structurally and / or functionally advantageous developments of the invention are described in more detail below with reference to the associated drawings using at least one preferred exemplary embodiment. In the drawings, elements that correspond to one another are provided with the same reference numerals.

• 1: ein Beispiel einer verwendeten Rollen-Inkjet-Druckmaschine
• 2: eine schematische Darstellung der Übernahme der Weiß-Separation des Kundenutzens
• 3: eine schematische Darstellung einer Synthese der Weiß-Separation des Kundenutzens
• 4: ein Beispiel einer Verteilung der Passermarken, bzw. -elemente
• 5: eine schematische Darstellung des Ablaufs des erfindungsgemäßen Verfahrens

The figures show:

• 1 : an example of a roll inkjet printing machine used
• 2 : a schematic representation of the assumption of the white separation of the customer benefit
• 3 : a schematic representation of a synthesis of the white separation of the customer benefit
• 4th : an example of a distribution of the registration marks or elements
• 5 : a schematic representation of the sequence of the method according to the invention

The area of application of the preferred embodiment variant is a roll inkjet printing machine 1 . An example of the basic structure of such a machine 1 , consisting of unwinder 2 for feeding the web-shaped printing substrate into the prepress stage 3 , consisting, for example, of a flexo plant for white / full area 4th , as well as a flexo plant for primers 5 , as well as in the actual printing unit 6th where it is from the printheads 7th is printed up to the rewinder 10 , is in 1 shown. It also has a roll inkjet printing machine 1 often also via a further processing stage 9 , consisting of a flexographic unit for coating 8th . The roll inkjet printing machine 1 is done by a control computer 11 controlled.

When measuring the register on such an inkjet printing machine 1 for the web printing it must now be achieved that the register measurement forms 15th under the same conditions as possible, especially with regard to the color coverage, as in the customer motif 17th , 17a to be printed.

1. 1. Ist der Druckjob mit weiß hinterlegt, kann die Weiß-Separation 13 für die Messabschnitte extrahiert werden. Somit haben auch die Messabschnitte eine ähnliche Farbbedeckung wie das Kundenmotiv 17. Auf die extrahierten, weiß hinterlegten Flächen 13a werden nun die Passermarken 15 durch den Rechner 11 automatisiert, d.h. so verteilt, dass sie vollständig in den weißen Flächen 13a zu liegen kommen. Ist nicht genügend Platz vorhanden, so kann die weiße Fläche 13a auch etwas erweitert werden, wenn dadurch die aufgetragene Farbmenge und -verteilung nicht zu sehr verändert wird. Eventuell kann auch die weiße Fläche 13a leichter gerastert sein, als die eigentliche Hinterlegung der Messmarken 15. 2 zeigt ein Drucksubstrat 12 mit einem Beispiel für diese Vorgehensweise. Im obersten Teil der 2 wird der Kundennutzen 17, bestehend aus einzelnen Elementen des Nutzens 14 samt weißer Hinterlegung, also der Weiß-Separation 13, gezeigt. Diese wird extrahiert, wie im mittleren Teil der 2 zu sehen ist und dann für die Hinterlegung, also die extrahierte Weiß-Separation 13a, der Messabschnitte für die Passermessung verwendet. Der untere Teil von 2 zeigt dann das Ergebnis mit den verteilten Passermarken 15, bzw. -elementen 16 auf korrekter Weiß-Hinterlegung 13a. Hier werden bevorzugt verkleinerte Passermarken 15 verwendet, um die weißen Flächen 13a möglichst ideal auszunutzen. Bei der Verteilung muss darauf geachtet werden, dass Passermarken 15 von verschiedenen Druckköpfen 7 und möglichst weit-verteilt über die Druckabschnittsbreite gedruckt werden. Ideal sind mehrere Wiederholungen, sodass die Ergebnisse der Passermarkenelemente 16 gemittelt werden können, um robustere Schätzwerte für den tatsächlichen Passerfehler zu ergeben. So werden z.B. Fehlstellungen einzelner Druckköpfe 7, die oft nicht erheblich sind ausgeglichen.
2. 2. Ist dagegen im Druckjob keine, oder nur sehr wenig weiße Hinterlegung 13 vorhanden, so muss eine alternative Vorgehensweise angewandt werden. So werden hier dann bevorzugt alle Farbseparationen des nicht hinterlegten Kundennutzens 17a zusammengefasst, sodass eine Fläche, die in mindestens einer beliebigen Farbe belegt ist, auch in der Ergebnisseparation belegt ist. Das Ergebnis dieses Vorgangs wird dann zur weißen Hinterlegung 14a der Messabschnitte verwendet und darauf, analog zur ersten Vorgehensweise, die Passermarken 15 verteilt. Diese synthetische Weiß-Separation 14a wird dabei bevorzugt erzeugt, indem alle Farbseparationen der einzelnen Elemente 14 des Kundennutzens 17a mittels einer digitalen ODER-Verknüpfung der Pixel durch den Rechner zur synthetischen Weiß-Separation 14a kombiniert werden. Dies simuliert ungefähr den gleichen Gesamtfarbauftrag und sollte somit die Bahn ähnlich beeinflussen, wie der eigentliche Druck-Job. 3 zeigt für das bereits vorgestellte Beispiel diese Vorgehensweise wieder in drei Teilen. Oben der Kundennutzen ohne Weiß-Hinterlegung 17a, in der Mitte die aus den Farbseparationen der einzelnen Elemente 14 des Kundennutzens 17a vom Rechner 11 erzeugte synthetische Weiß-Separation 14a und unten der daraus erstellte, bzw. weiß hinterlegte Messabschnitt mit den entsprechend verteilten Passermarken 15.

5 shows the sequence of the method according to the invention necessary for this in a preferred embodiment variant with the possible procedures or alternatives. The method is carried out by means of a computer, which is the control computer 11 the roll inkjet printing machine 1 can be. But it can also be an additional one; For example, the computer that evaluates the register measurement and any necessary register corrections to the control computer 11 the roll inkjet printing machine 1 transmitted.

1. 1. If the print job has a white background, the white separation 13th for the measurement sections are extracted. Thus, the measuring sections also have a similar color coverage as the customer motif 17th . On the extracted areas with a white background 13a are now the registration marks 15th through the calculator 11 automated, ie distributed so that they are completely in the white areas 13a come to rest. If there is not enough space, the white area can 13a can also be expanded a little if this does not change the amount and distribution of paint too much. Possibly also the white area 13a be rasterized more easily than the actual storage of the measurement marks 15th . 2 shows a print substrate 12 with an example of this approach. In the top part of the 2 becomes the customer benefit 17th , consisting of individual elements of benefit 14th including the white background, i.e. the white separation 13th shown. This is extracted as in the middle part of the 2 can be seen and then for the deposit, i.e. the extracted white separation 13a , which uses measurement sections for register measurement. The lower part of 2 then shows the result with the registration marks distributed 15th , or elements 16 on correct white background 13a . Reduced registration marks are preferred here 15th used the white areas 13a as ideally as possible. When distributing it must be ensured that registration marks 15th of different print heads 7th and are printed as widely distributed as possible over the width of the printing section. Several repetitions are ideal so that the results of the registration mark elements 16 can be averaged to give more robust estimates of actual misregistration. For example, individual print heads are misaligned 7th which are often not significantly balanced.
2. 2. If, on the other hand, there is no or very little white background in the print job 13th an alternative procedure must be used. So all color separations of the not stored customer benefit are preferred here 17a summarized so that an area that is occupied in at least one arbitrary color is also occupied in the result separation. The result of this process then becomes a white background 14a of the measuring sections and on them, analogous to the first procedure, the registration marks 15th distributed. This synthetic white separation 14a is preferably generated by all color separations of the individual elements 14th of customer benefit 17a by means of a digital OR link of the pixels by the computer for synthetic white separation 14a be combined. This simulates roughly the same total inking and should therefore affect the web in a similar way to the actual print job. 3 shows this procedure in three parts for the example already presented. Above the customer benefit without a white background 17a , in the middle those from the color separations of the individual elements 14th of customer benefit 17a from the computer 11 generated synthetic white separation 14a and below the measurement section created from it or with a white background with the correspondingly distributed registration marks 15th .

1. 1. Erzeugen der Weiß-Separation 13a, 14a nach obigem Beispiel und darstellen als Bild „BACK“ mit (1=weiß, 0=leer). Das Bild umfasst den gesamten Druckbereich.
2. 2. Iterieren über alle Druckfarben, oder Gruppen von Druckfarben:
   • 2.1. Erzeugen eines separierten Bildes einer kleinen Passermarke 15 für diese Farbe(n) mit zwei umliegenden Punkten der Referenzfarbe 18 und mindestens einem Punkt jeder Messfarbe, inklusive weißer Hinterlegung 13a, 14a
   • 2.2. Suchen einer Position für die Passermarke 15 ausgehend vom linken oberen Bildrand, sodass alle oder ein Großteil, z.B. 90%, der benötigten Pixel in dem Bild „BACK“ den Wert 1 aufweisen. Zu Suche kann die Maske z.B. sukzessive über das Bild „BACK“ geschoben werden.
   • 2.3. Wenn eine Position gefunden wurde, hinterlegen der Position für den Druck und setzen aller von der Passermarke 15 überdeckten Pixel in „BACK“ auf 0
   • 2.4. Wiederholen der Schritte 2 und 2.3 vom rechten oberen, linken unteren und rechten unteren Bildrand ausgehend - optional. kann hier von noch mehr Startpunkten aus gesucht werden, evtl. Mitte-links, Mitte-rechts, Oben-halblinks usw.
3. 3. Ergebnis dieses Verfahrens ist eine Liste mit den Positionen und Parametern der Passermarken 15, die dann weiterverarbeitet werden, bevorzugt auf einem der folgenden Wege:
   • 3.1. Die Liste wird an den Steuerungsrechner 11 der Rollen-Inkjet-Druckmaschine 1 übergeben, der diese Passermarken 15 dynamisch an den gegebenen Positionen einstreut und die Lage/Parameter an die Passer-Messeinrichtung, z.B. ein Kamerasystem mit Bildverarbeitungsrechner, überträgt
   • 3.2. Die Liste wird im Rechner des RIP, bzw. Vorstufe verarbeitet und die Passermarken 15 werden in den Druckjob synthetisiert. Hier müssen dann nur noch die Lagen an den Steuerungsrechner 11 der Rollen-Inkjet-Druckmaschine 1 übertragen werden, welcher dann nichts dynamisch einträgt, aber die Marken-Lage/Parameter wieder an die Messeinrichtung übertragen muss.

The following is the computer-aided method for distributing the registration marks 15th described in more detail. The registration marks 15th are preferably distributed according to the following procedure:

1. 1. Create the white separation 13a , 14a according to the example above and display "BACK" as a picture with (1 = white, 0 = empty). The image covers the entire print area.
2. 2. Iterating over all inks, or groups of inks:
   • 2.1. Creation of a separated image of a small registration mark 15th for this color (s) with two surrounding points of the reference color 18th and at least one point of each measurement color, including a white background 13a , 14a
   • 2.2. Find a position for the registration mark 15th starting from the upper left edge of the picture, so that all or a large part, eg 90%, of the required pixels in the picture “BACK” have the value 1 exhibit. To search, the mask can, for example, be pushed successively over the "BACK" screen.
   • 2.3. When a position has been found, store the position for printing and set all of the registration marks 15th covered pixels in "BACK" to 0
   • 2.4. Repeat the steps 2 and 2.3 starting from the upper right, lower left and lower right edge of the image - optional. Here you can search from even more starting points, possibly center-left, center-right, top-half-left, etc.
3. 3. The result of this process is a list with the positions and parameters of the registration marks 15th , which are then further processed, preferably in one of the following ways:
   • 3.1. The list is sent to the control computer 11 the roll inkjet printing machine 1 passed those registration marks 15th sprinkles dynamically at the given positions and transmits the position / parameters to the register measuring device, e.g. a camera system with image processing computer
   • 3.2. The list is processed in the computer of the RIP or prepress and the registration marks 15th are synthesized into the print job. Here only the layers have to be sent to the control computer 11 the roll inkjet printing machine 1 which then does not enter anything dynamically, but has to transmit the mark position / parameters back to the measuring device.

The result of this distribution is in each case in the lower parts of the 2 and 3 shown. An example of such a registration mark 15th with its elements in itself shows the 4th .

This registration mark 15th is carried out horizontally. The two surrounding points of the reference color black are good here 18th see, between which the measuring points or elements 16 , of the individual measurement colors. The registration mark 15th can be arranged however you like; depending on how space is on the print substrate 12 is. A vertical arrangement is also possible.

List of reference symbols

1

Inkj et printing machine

2

Unwinders

3

Prepress stage

4th

Flexo plant for white / full area

5

Flexo plant for primer

6th

Inkjet printing unit

7th

Inkjet printhead

8th

Flexo plant for paint

9

Further processing stage

10

Rewinder

11

Control computer

12

Print substrate

13

deposited white separation

13a

extracted deposited white separation

14th

individual elements of customer benefit

14a

synthesized white separation

15th

Registration marks

16

Registration mark elements

17th

customer benefit highlighted in white

17a

Customer benefits without deposit

18th

Reference color "black"

Claims (9)

Method for register correction in a printing process of an inkjet printing machine (7) by a computer (11), wherein in addition to printing of panels (17, 17a) on a printing substrate (12) registration marks (15) on a separate section of the printing substrate (12) printed, recorded digitally by a measuring device and evaluated by the computer (11) with regard to a registration error that occurs and the registration error is corrected accordingly, characterized in that the section of the printing substrate (12) with the registration marks (15) before the printing of the registration marks (15 ) the benefit (17, 17a) is deposited with at least one color separation (13a, 14a) Procedure according to Claim 1 , characterized in that the color separation (13a, 14a) corresponds to that of the section of the printing substrate (12) the registration marks (15) is deposited, is a white separation (13a, 14a). Method according to one of the preceding claims, characterized in that the color separation (13a) for printing the registration marks (15) corresponds to a color separation (13) with which the benefit (17) is stored. Method according to one of the Claims 1 or 2 , characterized in that the color separation (14a) for printing the registration marks (15) corresponds to a white result separation (14a) which is created from a summary of all color separations of the benefits (17a). Procedure according to Claim 4 , characterized in that the creation of the white result separation (14a) is done by ORing all color separations of the benefits (17a) in the computer (11). Method according to one of the preceding claims, characterized in that the computer (11) distributes the registration marks (15) on the section of the printing substrate (12) in such a way that the registration marks (15) from different print heads (7) and as widely distributed as possible the entire width of the section can be printed. Procedure according to Claim 6 , characterized in that the computer (11) for distributing the registration marks (15) on the section of the printing substrate (12) with the registration marks (15) creates a list with the positions and nominal parameters of the registration marks (15). Procedure according to Claim 7 , characterized in that the computer (11) transfers the list created to the control of the inkjet printing machine (7), which dynamically places the registration marks (15) at the given positions on the section of the printing substrate (12) with the registration marks (15) prints and transfers the positions and target parameters to the measuring device. Procedure according to Claim 7 , characterized in that the list is transferred from the computer (11) to the preliminary stage of the printing process, where the registration marks (15) are inserted into the print job according to the positions and target parameters, while positions and target parameters are also transferred to the measuring device will.

Images