EP1693199B1 - Method and apparatus for correcting an impression - Google Patents

Abstract

The method involves printing of product during a processing phase from several processing device. The method involves locating of sites of at least two print marks arranged on the product, analyzing the sites and automatic correcting the printing by means of sites of print marks. The correction involves correction of print length. An independent claim is also included for the device for print correction.

Description

The invention relates to a method for performing a pressure correction according to patent claims 1 and a device for pressure correction according to patent claim 13.

In printing today flexible printing tools are widely used. These are clamped on printing cylinders, which can lead to an expansion of the printing tools by the clamping of the printing tools on the printing cylinder. This results in a variable tool length, which results disadvantageously in a variable printing length. This is the case, for example, in the case of flexographic printing plates, which are designed to be flexible and stretchable in a rubber-like manner, so that unknown printing lengths result from the stretching of the flexographic printing plates onto the printing cylinders.

Furthermore, irrespective of a cliché height, the clamping length is the same for all clichés, so that, due to the different cliché heights, different rolling lengths for the individual clichés can result. You have the same state when used machining tools are not manufactured sufficiently accurate or manufacturing fluctuations are subject. An investigation of this effect is described, for example, in the article "Printing length compensation in corrugated cardboard direct printing" by the journal Flexoprint of April 2001.

Furthermore, it can occur with isolated substrates by a moisture entry or a drying process after a processing step to a change in the size of the printing material between individual machining operations.

As a result of the described variable printing lengths or sizes of the printing substrates, in the course of a printing process it is also disadvantageous to obtain variable printing lengths for the individual processing tools. One result of these are perfectly fitting printing processes for the individual processing tools and thus unclear appearance of the overall prints.

It is already known that the described variable tool lengths are corrected manually. For this purpose, the effective printing lengths of the individual processing tools on the printed sheets are measured individually. From these print lengths for the individual processing tools correction values are determined, which are manually entered into a printing device. This results disadvantageously in a complicated and cumbersome handling that prolongs the machining process in an undesirable manner by its time complexity. For a plurality of printing cylinders whose printing lengths are manually corrected, a disadvantageously high additional processing effort can arise in this way.

In the prior art, it is also already known, by means of a so-called register control function to use so-called register marks of various printing tools to positionally align various partial prints. From the DE 102 41 609 . DE 42 18 761 A1 . US 5,327,826 or DE 42 18 760 A1 For example, a method and apparatus for determining and correcting a register error are known, for example.

It is the object of the present invention to provide a method and apparatus for improved pressure correction.

The invention is solved with a method according to claim 1 and with a device according to claim 13. Preferred Further developments of the invention are specified in the dependent claims.

• Erfassen von Lagen von mindestens zwei auf dem Erzeugnis angeordneten Druckmarken;
• Auswerten der Lagen; und
• Automatisiertes Korrigieren des Druckes anhand der Lagen der Druckmarken, wobei das Korrigieren ein Korrigieren einer Drucklänge umfasst.

The inventive method is provided for performing a pressure correction, wherein a product is printed during a processing operation of multiple processing facilities. The method comprises the following method steps:

• Detecting plies of at least two print marks disposed on the product;
• Evaluation of the layers; and
• Automated correction of the print based on the plies of the print marks, wherein the correcting comprises correcting a print length.

Advantageously, thereby an automated performing a pressure correction is supported, wherein the correction comprises a correction of a print length. Thus, the pressure correction principles known in the art can be improvedly applied. Advantageously, for example, set-up times for printing tools can be minimized. An efficiency of a printing operation may thus be favorably increased.

A preferred embodiment of the method according to the invention provides that, in addition to the correction of the printing length, a correction of a printing position is also carried out. As a result, print marks on the printed product can be regulated in terms of location, which supports improved alignment of individual prints and thus further improves the quality of a printing process.

A further preferred embodiment of the method according to the invention provides that at least one first print mark is arranged in a front in the transport direction of the printed product area and at least one second print mark in a rear direction in the transport direction of the printed product.

This advantageously utilizes a maximum range of the printed product for measuring the effective printing length and for the subsequent correction of the unequal tool lengths of different processing devices.

A further preferred embodiment of the method according to the invention provides that only a first of a plurality of processing devices applies the two print marks during the processing operation. It can thereby be achieved that, in the machining process, machining devices adjust their pressures in terms of their position to the pressure of the first machining device. It is achieved in this way so a position correction of the pressure, with the help of long-term drifts can be permanently eliminated from the printing process. Stability of the printing process is thus advantageously increased.

• Figur 1 eine prinzipielle Darstellung einer erfindungsgemäßen Druckkorrektur;
• Figur 2 zwei vereinzelte Druckerzeugnisse mit jeweils einer Druckmarke;
• Figur 3 einen Druckbereich eines Druckerzeugnisses in dem eine erste und eine zweite Bearbeitungseinrichtung jeweils zwei Druckmarken aufgebracht haben, wobei das Aufbringen ohne das erfindungsgemäße Verfahren durchgeführt worden ist;
• Figur 4 ein Druckerzeugnis an dem die erfindungsgemäße Druckkorrektur durchgeführt worden ist;
• Figur 5 einen Druckbereich eines Druckerzeugnisses in dem lediglich die erste Bearbeitungseinrichtung zwei Druckmarken aufgebracht hat;
• Figur 6 eine prinzipielle Darstellung einer Verschiebung von Druckmarken infolge einer Drucklängenkorrektur; und
• Figur 7 eine schematische Darstellung einer Vorrichtung zur Durchführung des erfindungsgemäßen Verfahrens.

The invention will be described in detail below with reference to figures. Showing:

• FIG. 1 a schematic representation of a pressure correction according to the invention;
• FIG. 2 two isolated printed products, each with one print mark;
• FIG. 3 a printing area of a printed product in which a first and a second processing device have each applied two printing marks, wherein the application has been carried out without the method according to the invention;
• FIG. 4 a printed product on which the printing correction according to the invention has been carried out;
• FIG. 5 a printing area of a printed product in which only the first processing device has applied two print marks;
• FIG. 6 a schematic representation of a shift of print marks due to a print length correction; and
• FIG. 7 a schematic representation of an apparatus for performing the method according to the invention.

FIG. 1 shows a diagram of a basic representation of a pressure correction according to the invention. In the diagram, a machine angle (for example, a working angle of a counter-pressure cylinder) of a printing device is plotted on the x-axis. An angle of a printing cylinder of the printing device is plotted on the y-axis. A region 9 on the x-axis defines a printing area and an area 10 on the x-axis defines a non-printing zone of the printing device, ie a region of the printing device in which no printing of the printed product is performed. A substantially linear course 1a represents an uncorrected course of the machine angle over the angle of the printing cylinder. In this area, the two angles are synchronous with each other, thereby achieving identical speeds of a printed product and a printing cylinder with a clamped printing plate. This can be seen in the diagram from the fact that the impression cylinder has performed a full revolution (360 °) at the same time as the impression cylinder.

A curve 1b represents a printing length-corrected course of the machine angle over the angle of the printing cylinder. The course 1b is made steeper than the course 1a, the printing cylinder thus already reaches a complete revolution earlier than the impression cylinder. In the FIG. 1 It is shown that the impression cylinder has performed approximately one complete revolution (from 0 ° to 360 °) at a time when the impression cylinder has only rotated from 0 ° to 300 °. This means that the impression cylinder rotates at a higher angular velocity than the axis of the printing device that drives the impression cylinder due to the flexo flexographic printing plate. As a result of these different angular velocities, a relative movement is formed between the printing cylinder with the unfolded flexographic printing plate and the printed product. Although this results in increased wear of the plate by friction, on the other hand, however, the printing area (area 9) of the printed product is advantageously completely filled by the printing length of the flexographic printing plate.

In the area 10 of the FIG. 1 is a course of a correction movement of the printing cylinder shown on the basis of a course 1c. In this area, the printing cylinder with the printing plate is positionally corrected so that it again assumes a defined common position together with the impression cylinder at the beginning of a next printing area at 360 ° or 0 °. In the FIG. 1 is shown that the pressure cylinder in the pressure-free zone performs a braking movement (negative slope of the S-curve). This has the consequence that the speed profile of the correction movement of the printing cylinder in the short term goes into the negative range, pressure cylinder and impression cylinder thus briefly have opposite angular velocities. Usually, however, the speed profile remains completely in the positive range, which means that the angular velocity of the printing cylinder has the same sign as the angular velocity of the impression cylinder.

The in the FIG. 1 in principle illustrated correction of an error of a printing length is known in the art as an APM function (anti-Printenlargement-Mode) and can by the inventive method advantageously be carried out automatically.

This means that a correction of the printing process due to different printing lengths, which conventionally represents a relatively complicated and cumbersome procedure and essentially requires a laborious and time-consuming manual work of a printing press, is performed comfortably and time-optimized with the aid of the method according to the invention. The individual print length-corrected courses 1b for the individual printing cylinders with the printing plates are stored as correction parameters in the printing device and are automatically converted in the print-free zone (area 10) into correction movements for the individual printing cylinders of the processing devices.

FIG. 2 shows two individual printed products 5, on each of which a single print mark 11 is arranged at a defined distance 12 to a sheet edge of the printed product 5. Conventional register controllers use these individual print marks as reference marks to align subsequent print stations to the reference marks.

FIG. 3 shows a printing area 13 of a printed product 5. In the printing area 13, a first print mark A from a first processing device and a second print mark B from the first processing device have been applied. Furthermore, in the printing area 13, a first print mark C has been applied by a second processing device and a second print mark D has been applied by the second processing device. Together with the print marks A, B, C, D, printed images of the processing stations can also have been applied. For clarity, these prints are in the FIG. 3 not shown. It can be seen that the first print marks A, C of the two processing devices have different distances in relation to a front edge of the printed product 5 in the material flow direction 14 exhibit. Furthermore, the FIG. 3 It can be seen that the second print marks B, D have different distances in relation to a rear edge of the printed product 5 in the material flow direction 14. The two printing marks A, B of the first processing device have smaller distances to the edges of the printed product 5, as the two print marks C, D of the second processing device. It follows that the printing length of the first processing device is greater than the printing length of the second processing device. It can further be seen that, in the material flow direction 14, the two first marks A, C of the first and the second processing device are arranged in the region of a front edge of the printing area 13 and the two second marks B, D of the two processing devices are arranged in a rear region of the printing area 13. FIG. 3 shows a state of the printed product 5 before performing the pressure correction according to the invention.

FIG. 4 shows the printed product 5 after a correction of the printing length according to the invention has been carried out. It can be seen that the first print marks A, C of the first and second processing devices have substantially identical spacings in relation to the second print marks B, D of the two processing devices. This means that the printing lengths of the two processing devices are corrected according to the invention or that the printing length of the second processing device has been adapted to the printing length of the first processing device.

Advantageously, different pressure lengths of the two processing devices are thus substantially compensated. The method according to the invention automatically advantageously performs the pressure correction in such a way that a relative movement between the impression cylinder and the impression cylinder due to different tool lengths is carried out in the print area (area 9). This allows the different Print lengths of the individual pressure cylinders are compensated.

In FIG. 4 Furthermore, it can be seen that by means of a preferred embodiment of the invention, a correction of the printing position can be carried out. This means that the two first print marks A, C are arranged substantially identically in relation to the front edge of the printed product 5. More specifically, it can be seen that the two first print marks A, C of the two processing devices are aligned so that they have substantially identical distances to the leading edge of the printing area 13 of the printed product 5. This corresponds to a position control for the two first print marks A, C by means of a printing device in the pressure-free zone (area 10).

In comparison with conventional pressure corrections, the method according to the invention is therefore characterized in that the correction is carried out automatically. This means that the previously described manual determinations of the effective printing lengths and the subsequent manual setup of the printing device can be omitted advantageously. As a result, the pressure correction according to the invention can work much more efficiently than the conventional methods. The positions of the corrected print marks C, D off FIG. 4 are merely exemplary to be seen, so that any predetermined positions of the first and second print marks C, D of the second processing device are conceivable. In essence, a fixed, predeterminable position of the print marks of the first and the second processing device relative to one another is the result of the method according to the invention. From the FIG. 4 a control strategy is recognizable, which is configured such that applied by the first processing means print marks A, B are used to control printing steps of subsequent processing facilities.

Based on FIG. 5 a further control strategy, which can be implemented by means of a development of the method according to the invention, explained. FIG. 5 shows within the printing area 13 of a printed product 5 two print marks A, B which have been applied by the first processing device. However, it is also conceivable that the two print marks A, B have already been printed before a processing operation in the first processing device. In this case, the printed product 5 is a pre-printed with two reference print marks printing material. The further control strategy is characterized in that the stations following the first processing device detect the position of the two print marks A, B of the first processing device and set their printing steps in relation to the print marks A, B. Advantageously, it can thus be achieved that the processing devices following the first processing device are always aligned at a fixed angle to the first processing device. Thus, this embodiment of the invention is an actuating mechanism that uses reference printing marks A, B to align the subsequent processing devices thereto.

In the case of changing ratios of the print marks of the first processing device A, B or of the print marks printed in advance, the printing steps of the downstream processing devices change as well. As a result, for example, a long-term drift of a relation between the processing devices can be eliminated in an advantageous manner. A printing process with multiple processing devices can thus be made stable in a sustainable manner. Furthermore, this results in the advantage that only print marks for a single printing ink have to be recorded in terms of location, which makes additional printing marks and recording devices, including their implicit inaccuracies unnecessary. As a practical application example of the other control variant is, for example a die-cutting punch is conceivable punching pre-printed sheets with two registration marks.

So far, a control of printing lengths of several processing facilities has been described. However, it is also possible with the aid of the method according to the invention for an absolute measurement of the positions of the print marks or the spacing of the print marks. As a result, absolute accuracies for printing processes can be achieved. The measurement can be carried out, for example, by means of a calibrated camera which detects absolute positions of the print marks and in this way determines an absolute distance between the first and second print marks. With this embodiment of the method according to the invention, it is conceivable, for example, that an absolute printing length of the first processing device is detected, to which the following processing devices synchronize with regard to the printing length.

An embodiment of the method according to the invention thus allows, as described above, an overall correction of a pressure in two sub-steps. In a first sub-step while the position of the second print marks B, D is controlled to each other (printing length correction), in a second sub-step, the position of the first print marks A, C to each other regulated (printing position correction). The described sub-steps can also be performed in reverse order to each other.

Using a suitable algorithm, it is also conceivable that the described two sub-steps are combined into a single sub-step. This makes it possible to carry out the described overall correction in a single step in which both the printing length correction and the printing position correction are executed in a single step from printed product to printed product. In terms of thought, this can be thought of as two interconnected sub-steps, whereby the results of the first sub-step are no longer due to the second sub-step to be influenced. In this case, the position of the first print marks A, B to each other is no longer changed by the printing length correction of the second substep.

Based on FIG. 6 illustrates the just described operation of a correction in a single step. In the event that the first print mark A of the first processing device is not applied at 0 °, but, as in FIG. 6 represented at 120 °, generates a different slope of the pressure length-corrected curve 1b of the angle of the impression cylinder over the angle of the printing cylinder a change in position of the first print mark A. In Figure 6, this position shift is shown as a result of a change in pressure length by the position shift 1d. From the FIG. 6 It can be seen that the position shift 1d is greater according to a set of radiation-type principles, the farther away the first print mark A is applied from the position 0 °. An algorithm for performing a total correction in a single sub-step must take these circumstances into account. 1e denotes the position of the first print mark on the printing cylinder, 1f denotes the position of the second print mark on the printing cylinder. Incidentally, for explanation of the reference numerals to the description FIG. 1 directed.

Based on FIG. 6 It can be seen that it is more appropriate to first perform the printing length correction and only then the printing position correction. This results from the fact that after a print length correction has been carried out, the print length has already been corrected and is fixed and only has to be shifted in position by means of the subsequent print position correction.

FIG. 7 shows a device 1 for pressure correction with which the inventive method can be performed. The device 1 comprises a plurality of processing devices 4a, 4b, 4c in which a printed product 5 of a respective printing cylinder 6 is printed. With the help of transport devices 3, the printed product 5 is transported from one processing device 4a, 4b, 4c to the next processing device 4a, 4b, 4c. A device 2 is used for detecting and evaluating the positions of the print marks on the printed products 5. The device 2 may comprise, for example, a light barrier, a camera and a computing unit, which are used to supply detected correction data to the processing devices 4a, 4b, 4c. Due to the correction data, it is possible for the processing device 4a, 4b, 4c to apply the print marks on the printed products 5 in a positionally variable manner. Controller outputs 7 of the processing devices 4a, 4b, 4c detect a result of the pressure correction according to the invention, ie they determine whether the result of the pressure correction are print length reductions or print length extensions.

As actuators of the method according to the invention, both the processing devices 4a, 4b, 4c and the transport device 3 can be used. In the first case, the transport of the printed product 5 by means of the transport device 3 takes place at a substantially constant speed, the printing cylinders 6 of the processing devices 4a, 4b, 4c performing a relative movement to the printed product 5. In the second case, the transport of the Drukkerzeugnisses 5 by means of the transport device 3 is carried out at a non-constant speed. This has the consequence that the transport process of the printed product 5 is corrected, which can be carried out for example by a correction of a speed control for the transport device 3.

Advantageously, therefore, one has two different options for a selection of the correction elements, wherein in particular for individual products the product transport as an actuator in contrast to the correction of the processing device 4a, 4b, 4c is used. This also corresponds to a choice in conventional register corrections.

In the following, the course of the method according to the invention in the device 1 for pressure correction will be described in principle. The printed product 5 is fed by means of the transport device 3 to the first processing device 4a. In the first processing device 4a, the first print mark A of the first processing device 4a and the second print mark B of the first processing device 4a are applied. Subsequently, the printed product 5 is supplied by means of the transport device 3 to the second processing device 4b. There, the first print mark C of the second processing device 4b and the second print mark D of the second processing device 4b is applied to the printed product 5. Thereafter, the printed product 5 is supplied with the applied print marks A, B, C, D by means of the transport device 3 to the third processing device 4c. The means 2 for detecting positions of print marks of the third processing means 4c detects the positions of the print marks A, B, C, D on the printed product 5 and evaluates the positions of the print marks A, B, C, D. If the device 2 determines that the distance of the print marks A to B deviates from the distance of the print marks C to D, this means that the effective print lengths of the first processing device 4a and the second processing device 4b are different.

As a corrective measure, the second processing device 4b is then activated via a controller output 7 of the third processing device 4c. Thereby, in the next print product 5 fed to the second processing means 4b, the impression cylinder 6 is moved by the transport means 3 or the processing means 4b in relation to the print product 5 such that the second processing means 4b is substantially identical to the first processing means 4a Print length generated on the printed product 5. A parameter value for the correction movement of the second processing device 4b can be stored in the second processing device 4b, so that for all other printed products 5 during their processing by the second processing device 4b the pressure correction according to the invention is carried out automatically.

As a further development of the method according to the invention, the second processing device 4b can be controlled via the controller output 7 of the third processing device 4c such that the positions of the first print mark C are also adapted to the position of the first print mark A of the first processing device 4a. As a result, a pressure position correction is advantageously carried out in addition to the printing length correction.

It goes without saying that the described correction method is not limited to a correction of the print marks C, D of only the second processing device 4b, but may extend to a plurality of different processing devices 4a, 4b, 4c. For the sake of simplicity, however, only the correction of print marks C, D of the second processing device 4b has been described above.

As a further improvement measure for carrying out the method according to the invention, an optimization of the expansion of the flexographic printing plates is conceivable to one another. As a result, different tool lengths can be roughly compensated even in advance of the method according to the invention, so that only a fine correction of the printing lengths has to be carried out by means of the method according to the invention. This can be achieved for example by measuring a tensile force during clamping of the clichés on the printing cylinders 6.

Furthermore, an optimization of a control algorithm in a cross-plant control / position is conceivable. If a plurality of processing devices 4a, 4b, 4c are controlled relative to each other, it may happen that some of the adjustments achieved thereby represent reduced print lengths and some print length extensions. However, it is known that print length shortenings, in contrast to print length extensions, cause serious deterioration of the printed image can have. Therefore, it is advantageous to design the method according to the invention in such a way that, in principle, no or only small, ie in terms of size very limited, print length reductions result. This can be achieved by firstly carrying out a printing of a reference ink without pressure extension or pressure reduction. Thereafter, the controller outputs 7 of the processing devices 4a, 4b, 4c are checked for possible reductions in print length. If one or more printing units are present due to the printing correction according to the invention with resulting printing length reduction, the reference pressure is changed such that no printing unit due to the control / position performs a print length reduction or only a maximum predetermined print length reduction. This can be achieved, for example, by correcting the printing unit of the reference color by a suitable amount (printing length extension of the reference print).

Example: Pressure length changes of the processing equipment (1st change is the reference pressure).

Before: 0 mm, +1 mm, -2 mm, -3 mm, +1 mm.

After: + 3mm, +4mm, +1mm, 0mm, +4mm (no more pressure length shortening).

The numbers indicate changes in the printing lengths of the individual processing devices 4a, 4b, 4c in millimeters, the first of the five numerical values representing a printing length change for the reference pressure. A positive sign means a print length extension and a negative sign a print length shortening of a following processing device 4a, 4b, 4c. Therefore, before applying the improved algorithm, a maximum print length change includes a 3mm print length reduction (previously: from 0mm to -3mm). After applying the improved algorithm, the Change in print length no reduction in print length. (After: from + 3mm to +4mm).

A modification of the algorithm can result in the reference pressure being changed in such a way that at least an absolute reduction in the maximum reduction of the printing length in the machine results.

Example: Printing length changes of the printing units (1st change is reference pressure)

Before: 0 mm, +1 mm, +2 mm, -3mm, + 1mm.

After: +1 mm, +2 mm, +3 mm, -2 mm, +2 mm (maximum reduction in printing length -2 mm).

In the comparison of the two series of numbers for the correction values, it can be seen that after the application of the algorithm, although a shortening of the printing length still occurs, this is shortened in comparison with the application without an algorithm. The reduction of the printing length reduction is 1mm (from - 3mm before to -2mm after).

Advantageously, in the described optimization of the algorithm, the reference pressure is printed such that reductions in printing no longer occur for subsequent prints of subsequent processing devices 4a, 4b, 4c. An improvement of the printed image is thereby supported in an advantageous manner.

The method according to the invention can advantageously be carried out with different types of processing devices 4a, 4b, 4c. For example, as a processing device 4a, 4b, 4c, a slotter, a punch or a cross cutter can be used. In this context, the term slot machines means 4a, 4b, 4c, the longitudinal slots in insert the printed product 5. Punching means processing means 4a, 4b, 4c which perform all other slitting and cutting operations on the printed products 5, such as transverse slits, corrugations or breakouts. Cross-cutters are to be understood as processing devices 4a, 4b, 4c which intersect in the transverse direction. Although the present invention has thus been described in the foregoing description in the context of printing units as a processing device 4a, 4b, 4c, it goes without saying that the invention can be carried out as a method for a processing correction with slotter, punching and cross-cutters. This can efficiently increase the overall accuracy and overall reproducibility of a total printing process in an efficient manner.

LIST OF REFERENCE NUMBERS

1

Device for pressure correction

1a

uncorrected pressure curve

1b

pressure-length-corrected pressure curve

1c

Speed course of a correction movement

1d

Position shift due to pressure length change

1e

Position of the first print mark on the printing cylinder

1f

Position of the second print mark on the printing cylinder

2

Device for detecting and evaluating layers of print marks

3

transport means

4a

first processing device

4b

second processing device

4c

third processing device

5

Printed Media

6

pressure cylinder

7

controller output

8th

Impression cylinder

9

pressure range

10

pressure-free area

11

Print mark of processing device

12

Distance print mark to sheet edge

13

pressure range

14

material flow

A

first print mark of the first processing device

B

second print mark of the first processing device

C

first print mark of the second processing device

D

second print mark of the second processing device

Claims (15)

1. Method for carrying out a printing correction, a product (5) being printed by a plurality of processing devices (4a, 4b, 4c) during a processing operation, having the following method steps:

   - detection of positions of at least two printing marks which are arranged on the product (5);

   - evaluation of the positions;

   characterized by automated correction of the print using the positions of the printing marks, the correction comprising correction of a printing length.
2. Method according to Claim 1, the automated correction of the print additionally comprising correction of a printing position.
3. Method according to Claim 1 or 2, at least one first printing mark being arranged in a front region in the transport direction (14) of the product (5) and at least one second printing mark being arranged in a rear region in the transport direction (14) of the product (5).
4. Method according to one of Claims 1 to 3, two printing marks being applied to the product (5) by two processing devices (4a, 4b, 4c), the first printing mark being applied by a first processing device (4a) and the second printing mark being applied by a second processing device (4b).
5. Method according to Claim 4, further processing devices (4b, 4c) being regulated during the processing operation using the printing mark which was applied by the first processing device (4a), in such a way that the printing marks are applied to the product (5) in a position which is fixed with respect to one another.
6. Method according to Claim 4 or 5, the positions of the first printing marks being regulated with respect to one another and the positions of the second printing marks being regulated with respect to one another.
7. Method according to Claim 1, only the first processing device (4a) applying the two printing marks during the processing operation.
8. Method according to Claim 7, the processing devices (4b, 4c) which follow in the processing operation of the first processing device (4a) being set using the applied printing marks.
9. Method according to one of Claims 1 to 8, absolute printing lengths being determined for the individual processing devices (4a, 4b, 4c) using the printing marks.
10. Method according to one of the preceding claims, it being possible for the spatial positions of the printing marks to be varied on the product (5).
11. Method according to one of the preceding claims, additionally having the following method steps:

    - application of a reference print to the product (5) by the first processing device (4a);

    - checking of regulator outputs (7) of the processing devices (4b, 4c) for possible shortening of printing lengths; and

    - changing of the reference print if a shortened printing length is present, so that only increases in printing length result as printing-length corrections for the following processing devices (4b, 4c).
12. Method according to Claim 11, the changing of the reference print being configured in such a way that shortening of the printing length which results from the printing-length corrections can have its magnitude limited.
13. Apparatus (1) for printing correction, the apparatus (1) comprising a device (2) for detecting positions of at least two printing marks on a product (5), at least one first printing mark being arranged in a front region in the transport direction (14) of the product (5) and at least one second printing mark being arranged in a rear region in the transport direction (14) of the product (5), characterized in that automated correction of the print can be carried out by means of a correction device (3, 4a, 4b, 4c), the automated correction comprising correction of a printing length.
14. Apparatus according to Claim 13, it being possible for automated correction of the print to be carried out by means of the correction device (3, 4a, 4b, 4c), the automated correction additionally comprising correction of a printing length.
15. Apparatus according to Claim 13 or 14, a transport device (3) and/or a processing device (4a, 4b, 4c) being provided as correction device (3, 4a, 4b, 4c) of the apparatus (1).

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