DE102018215388B3 - DUMC profile transition - Google Patents

Abstract

Method for compensating position-dependent density fluctuations of printing nozzles of an inkjet printing machine (7) by a computer (6), wherein the computer (6) controls the printing nozzles of the inkjet printing machine (7) according to a compensation profile (8), which provides information about the compensation the density fluctuations necessary ink ejection of the printing nozzles of the inkjet printing machine (7) and wherein the compensation profile (8) is regularly updated in the course of a printing process, which is characterized in that in the case of a print substrate change from a narrow to a wider print substrate (2) or a change of an inkjet printhead (5) the computer (6) an updated compensation profile (13) for the narrow print substrate (2) or the area of the changed inkjet printhead (5) in a non-updated compensation profile (14) for the remaining area integrated and the thus generated updated overall profile (15) for compensation de r applies position-dependent density variations.

Description

The present invention relates to a method for compensating position-dependent density fluctuations of printing nozzles in an inkjet printing machine during a printing substrate change.

The invention is in the technical field of inkjet printing.

When operating inkjet presses, the current state of the print nozzles of an inkjet printhead plays a crucial role in the resulting print quality. There are two influencing factors which influence the print quality accordingly. For example, the malfunction of a single printing nozzle to strip-shaped artifacts in the print image along the corresponding printing direction of this pressure nozzle concerned. The extent to which this artifact affects the resulting print quality depends on the type of ink nozzle malfunction. These inferior functions range from slight geometric deviations of the pressure point of the pressure nozzle over a reduced ink discharge to the complete failure of the pressure nozzle. In addition, pressure nozzles that deviate too much from the desired behavior, deactivated by the control of the inkjet printing press, so that a clean and systematic compensation of this defective pressure nozzle is possible. For the compensation of such defective or deactivated pressure nozzles different approaches are known. The most common is the compensation by the adjacent pressure nozzles, which usually produce an increased ink ejection in order to fill the resulting white line due to the failure or shutdown of the respective pressure nozzle.

A second major factor influencing the print quality of an inkjet printing press is the fact that the print nozzles differ slightly in terms of their ink ejection behavior. These deviations are on the one hand production-related, on the other hand, they depend on the different aging of the pressure nozzles, which can also be influenced by a different load on the pressure nozzles from. As a consequence, this leads to pressurized nozzles, e.g. should print the same hue value slightly different in terms of their ink ejection to achieve this same hue value. Or the other way around: If one controls these two pressure nozzles with regard to their ink ejection identically, then one nevertheless obtains slightly different resulting color tone values. This phenomenon is also referred to as a density variance because identically driven print nozzles produce a different resulting print density on the substrate.

To compensate for these density fluctuations so-called compensation profiles (DUMC) are used. These compensation profiles are in the end nothing different than drive profiles, which have a minimum positive or negative offset for each pressure nozzle, which ensures that each pressure nozzle delivers the same resulting hue value with the same drive. Prints a nozzle e.g. Due to their density fluctuations, too little ink, based on a standard setpoint, the compensation profile for this pressure nozzle would include a small negative offset, with which the density variation of this pressure nozzle is compensated. These compensation profiles are provided on the one hand by the manufacturer of the inkjet printheads and then contain the production-related density fluctuations accordingly. Furthermore, they can and will also be regularly updated by the manufacturer of the corresponding inkjet printing machine into which the inkjet print heads are installed and / or by the user of the inkjet printing press. This is usually done more or less regularly as part of test printing of a calibration process. With these updated compensation profiles, the age-related density fluctuations of the pressure nozzles are then compensated.

However, because the compensation profiles are created specifically for a printhead and an inkjet printing press normally employs many printheads, this causes a problem. Thus, when replacing one of the inkjet printheads, which is required regularly during operation of the inkjet printing machine, the compensation profile, which extends as a resulting compensation profile across all printheads used, must be updated. As a rule, a complete calibration process is necessary, in which a new compensation profile has to be created for all printing substrates used. This is associated with correspondingly great expense, which greatly affects the performance of the inkjet printing press. Especially with frequent printhead replacement, which already represents a significant economic burden anyway, the recalibration leads to additional, undesirable expenses.

A known from the prior art approach to compensate for such position-dependent density variations of pressure nozzles is disclosed in US Patent US 9,152,890 B2 disclosed. Here, how to calculate a compensation profile for density fluctuations of printing nozzles when the substrate width is changed in a roll type ink jet printing machine will be described. However, in this writing discloses the adaptation of a wider compensation profile to a narrower print substrate. No adaptation to a wider print substrate is possible; For this purpose, a recalculation of the compensation profile is required, which entails a corresponding expense.

The object of the present invention is therefore to disclose a method for compensating position-dependent density fluctuations in printing nozzles of an inkjet printing press, which is flexible with respect to the geometric dimensions of the printing substrate used.

This object is achieved by a method for compensating position-dependent density fluctuations of printing nozzles of an inkjet printing machine by a computer, wherein the computer controls the printing nozzles of the inkjet printing machine according to a compensation profile, which provides information about the necessary for the compensation of the density fluctuations ink ejection of the printing nozzles of the inkjet Printing machine contains and wherein the compensation profile is updated regularly in the course of a printing process and which is characterized in that in the case of a printing substrate change from a narrow to a wider print substrate or a change of inkjet print head, the computer an updated compensation profile for the narrow print substrate or area of the changed inkjet printhead is integrated into a non-updated compensation profile for the rest of the range and the updated overall profile so generated to compensate for the position-dependent Applies density variations. The method according to the invention thus revolves around the application that an updated compensation profile for occurring density fluctuations, which covers only a part of the width of the printing substrate to be printed, is to be integrated into the overall profile, which covers the entire width of the printing substrate to be printed. This can e.g. occur when it is intended to change from a narrower printing substrate to a wider one, in which case there is an updated compensation profile for the previously used narrower printing substrate, while for the areas of the now wider printing substrate there is only the original standard compensation profile or, in general, an older, not updated compensation profile. On the other hand, this application can also occur when a single printhead is replaced, which then also apply a new compensation profile for this area, which must also be integrated into the overall profile.

Advantageous and therefore preferred developments of the method will become apparent from the accompanying dependent claims and from the description with the accompanying drawings.

A preferred development of the method according to the invention is that the updated compensation profile represents a partial section which is integrated by means of the computer into two sections of the non-updated compensation profile, taking into account both the absolute value and the slope of all sections. Since an updated compensation profile therefore exists in the application for the subarea and this must therefore be integrated into the broader, older, or not updated compensation profile, there are certain rules for this to be adhered to in the course of the method according to the invention. If these are taken into account, the newly obtained overall profile, which then includes both the updated partial area and the non-updated total area, can be used for continuous compensation of the position-dependent density fluctuations of the ink jet printing nozzles.

A further preferred development of the method according to the invention is that the computer calculates for the integration of the subsection of the updated compensation profile into the two subsections of the non-updated compensation profile three offset values for the three subsections, which the boundary conditions of continuity at the two interfaces, the preservation of Increase in the three sections and the preservation of the average of the three sections considered. This approach has proved to be the most promising so far, since the most important criterion in the integration of the updated partial compensation profile in the rest, not updated compensation profile is to change both profiles as little as possible and still a trouble-free transition as possible at the edge regions of both profiles, ie there where they merge into one another. This applies above all to the continuity at the two seams. Other points to consider include preserving the slope of all three sections, ie the updated profile in the middle and the two sections of the non-updated profile on the outside. Despite the offset necessary to bring the updated compensation profile and the non-updated parts into a smooth transition, the average of the corresponding three subsections should nevertheless be taken into account. By using offset values for the subsections, one achieves a good compromise of these three conditions.

A further preferred development of the method according to the invention is that the calculation of the three offset values by means of the computer takes place via the solution of a linear system of equations. This represents the most obvious solution for calculating the three offset values for all three subsections, since three unknown values are to be calculated by means of three equations for the three subsections under given boundary conditions.

A further preferred development of the method according to the invention is that, as a third boundary condition, in addition to the preservation of the mean value of the three subsections, alternatively the unchanged preservation of the value of the right subsection or the preservation of the slope at one of the two interfaces is considered. This represents another possible boundary condition with which good results with regard to the resulting calculated offset values for the three subsections are achieved.

A further preferred development of the method according to the invention is that the method is used in an inkjet web press. Since the method deals with the compensation of position-dependent density fluctuations of printing nozzles in an inkjet printing press, it must obviously also be used in an inkjet printing press. The background of the problem, however, mainly relates to web presses, since the case of a print substrate change from a narrower to a wider print substrate during a continuous printing process, then a compensation profile for the wider print substrate must be applied and with the updated compensation profile for the previous printing on the narrower print substrate must be integrated into the wider compensation profile for the wider print substrate, which is a classic application for a web press. Theoretically, of course, an application on an inkjet sheet-fed press would be conceivable, where during the continuous printing process, the printing substrate changes from a narrower to a wider arc.

The invention as such as well as structurally and / or functionally advantageous developments of the invention will be described below with reference to the accompanying drawings with reference to at least one preferred embodiment. In the drawings, corresponding elements are provided with the same reference numerals.

• 1: ein Beispiel des Aufbaus einer Rollen-Inkjet-Druckmaschine
• 2: ein Beispiel für ein aktualisiertes, schmales Kompensationsprofil in Gegenüberstellung zu einem älteren, breiten Kompensationsprofil
• 3: das aktualisierte, schmale Kompensationsprofil integriert in das breitere Kompensationsprofil
• 4: den schematischen Ablauf des erfindungsgemäßen Verfahrens

The drawings show:

• 1 : an example of the construction of a roll inkjet printing machine
• 2 : an example of an updated, narrow compensation profile in comparison to an older, broad compensation profile
• 3 : the updated, narrow compensation profile integrated into the wider compensation profile
• 4 : the schematic sequence of the method according to the invention

The field of application of the preferred embodiment is an inkjet printing press 7 , An example of the basic structure of such a machine 7 consisting of investor 1 for the supply of the printing substrate 2 in the printing unit 4 where it's from the printheads 5 is printed to the boom 3 , is in 1 shown. This is a roll inkjet printing machine 7 which from a control computer 6 is controlled.

During the partial update of compensation profiles 8th , eg if a compensation profile 16 for a narrow print substrate 2 applied and updated as part of the application, now often creates the problem that at the seams 9 between existing compensation profile 14 and new subprofile 13 no steady course exists. Without further action, the resulting compensation profile would 15 have jumps at these points, which would represent in printing as a disturbing streaks.

To avoid this problem, the levels of subprofiles need 10 . 11 . 12 be adjusted so that at the seams 9 Continuity is present. 4 schematically shows the flow of the process necessary for this. In the general case, a new, narrow compensation profile 13 so in an existing compensation profile 14 be inserted that three sections 10 . 11 . 12 arise. An example of this problem shows 2 , In the middle is the new section 11 and to the right and left of it are the sections of the existing profile 10 . 12 , The new section 11 differs from both the absolute value and the slope of the corresponding area of the existing compensation profile 10 . 12 ,

1. 1. Stetigkeit an den zwei Nahtstellen 9
2. 2. Erhaltung der Steigung der drei Teilbereiche 10, 11, 12
3. 3. Erhaltung des Mittelwertes der drei Teilbereiche 10, 11, 12

For the purposes of the invention will now be for the three subsections 10 . 11 . 12 calculates three offset values that meet the following constraints:

1. 1. Steadiness at the two seams 9
2. 2. Preservation of the slope of the three subareas 10 . 11 . 12
3. 3. Conservation of the mean value of the three subareas 10 . 11 . 12

In the third boundary condition, other criteria can also be set, eg the value of the right part 12 must remain unchanged or the slope at a seam 9 should be preserved.

One way to fulfill this requirement is to solve a linear equation system of the form: Y01L Y01R Y12L Y12R Y01LS Y01RS Y12LS Y12RS DY0 dY1 dY2 A = 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 -1 1 0 0 0 0 0 0 0 0 0 0 0 -1 1 0 0 0 -1 0 0 0 1 0 0 0 -1 0 0 0 0 -1 0 0 0 1 0 0 -1 0 0 0 0 -1 0 0 0 1 0 0 -1 0 1 -1 0 0 -1 1 0 0 0 0 1 1 1 1 -1 -1 -1 -1 0 0 0 Y = A * X

With values for A according to the following table:
and Y = Y01L Y01R Y12L Y12R 0 0 0 0 0 0 0 such as X = Y01L Y01R Y12L Y12R Y01LS Y01RS Y12LS Y12RS DY0 dY1 dY2 then follows: $$\text{X}=\text{A}-1*\text{Y}$$

It says: Y01L Left value at 1st stitching point Segment 0-1 before compensation Y01R Right value at 1st stitching point Segment 0-1 before compensation Y12L Left value at 2nd stitching point Segment 1-2 before compensation Y12R Right value at 2nd stitching point, segment 1-2 before compensation Y01LS Left value at 1st stitching point Segment 0-1 after compensation Y01RS Right value at 1st stitching point Segment 0-1 after compensation Y12LS Left value at 2nd stitching point Segment 1-2 after compensation Y12RS Right value at 2nd stitching point Segment 1-2 after compensation DY0 Offset segment 0 dY1 Offset Segment 1 dY2 Offset Segment 2

In the mentioned case there are eleven variables. Line one to ten in matrix A define the current values and the conditions for continuity and conservation of slope in the first section 10 , Line twelve of A Defines the preservation of the mean before and after the adjustment. The solution of this linear system of equations leads to the desired values for absolute value and the slope with which the middle, new section 11 of the updated compensation profile 13 in the two older parts 10 . 12 optimally integrated. The calculation of the linear system of equations is computer-aided. This is preferred by the control computer 6 the relevant inkjet printing press 7 be performed.

3 shows the resulting compensation profile 15 with all three parts 10 . 11 . 12 , the middle section 11 integrated, which fulfills all three boundary conditions. By adjusting the compensation profile 14 Although the absolute values of the sections are changed, the compensation profiles 13 . 14 but stay within the cuts 10 . 11 . 12 unchanged and at the seams 9 There is no visually visible, erratic change. The compensation profile obtained in this way 15 can then be used for optimized control of the inkjet printing press 7 be used to compensate for occurring density variations.

LIST OF REFERENCE NUMBERS

1

investor

2

current print substrate

3

boom

4

Inkjet printing unit

5

Inkjet printhead

6

calculator

7

Inkjet press

8th

total, applied density compensation profile

9

Interface between two subareas

10

first part of the older compensation profile

11

middle section of the updated compensation profile

12

third part of the older compensation profile

13

updated, narrow density compensation profile

14

older, wide density compensation profile

15

resulting, wide density compensation profile with integrated middle section

16

original, narrow density compensation profile

Claims (6)

Method for compensating position-dependent density fluctuations of printing nozzles of an inkjet printing machine (7) by a computer (6), wherein the computer (6) controls the printing nozzles of the inkjet printing machine (7) according to a compensation profile (8), which provides information about the compensation the density fluctuations necessary ink ejection of the printing nozzles of the inkjet printing machine (7) and wherein the compensation profile (8) is regularly updated in the course of a printing process, characterized in that in the case of a Drucksubradatwechsels of a narrow to a wider print substrate (2) or a change an inkjet printhead (5) the computer (6) an updated Kompensationsprofil (13) for the narrow print substrate (2) or the area of the changed inkjet printhead (5) in a non-updated Kompensationsprofil (14) for the remaining area integrated and the updated overall profile (15) thus produced for compensating the positions dependent density fluctuations applies. Method according to Claim 1 , characterized in that the updated compensation profile (15) represents a subsection (11) which is integrated by means of the computer (6) into two subsections (10, 12) of the non-updated compensation profile (14), both the absolute value and the absolute value Slope of all sections (10, 11, 12) are taken into account. Method according to Claim 2 , characterized in that the computer (6) for integrating the subsection (11) of the updated compensation profile (13) into the two subsections (10, 12) of the non - updated compensation profile (14) has three offset values for the three subsections (10, 11 , 12), which takes into account the boundary conditions of the continuity at the two seams (9), the maintenance of the slope of the three sections (10, 11, 12) and the preservation of the average of the three sections (10, 11, 12). Method according to Claim 3 , characterized in that the calculation of the three offset values by means of the computer (6) via the solution of a linear system of equations happens. Method according to Claim 3 or Claim 4 , characterized in that as a third boundary condition in addition to the preservation of the mean value of the three subsections (10, 11, 12) alternatively the unchanged preservation of the value of the right subsection (12) or the receipt of the slope at one of the two interfaces (9) is considered , Method according to one of the preceding claims, characterized in that the method is used in an inkjet web printing machine (7).

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