EP1759844B1 - Process for printing correcting - Google Patents

Description

State of the art

The invention relates to a method for printing correction with a register control device for a multi-color printing machine with individual printing units according to the preamble of the independent claims 1 and 7.

In multi-color printing in printing presses, for example in rotary printing presses, the application of the individual color separations, in particular for cyan, magenta, yellow and black, takes place in successive printing units. The printing material is provided as a roll material and passed endlessly through the printing unit. Decisive for the achieved print quality is that the print images of the individual colors are exactly on top of each other. The superposition of the printed images is referred to as a register. For mutual alignment of the individual printing units, register marks or generally printed marks, for example in the form of register marks, are printed in addition to the actual printed image of each printing group. Using these marks, an offset between the individual print images can be recorded online by means of an optical measuring system. As an alternative to the stamping of marks, these errors can be determined in the printed image on the basis of a print image acquisition with image evaluation.

In rotary printing systems, this measuring system is generally part of a control system known as register control. The register control intervenes via suitable actuators in the printing process and compensates detected by the optical measuring system register deviations. In particular, the actuators can change the web length of the printing material between successive printing units so that the printed images of successive printing units are superimposed.

The cause of deviations between the individual prints are, in addition to the relative position of the printing units, changes in the geometry of the printing material. These geometry changes are caused, for example, by the influence of moisture and by drying steps arranged between the printing units. This is made even more difficult if the printing material is at least partially stretchable.

During the printing process, the web tension is kept largely the same, which allows a good print quality without significant corrections. The control parameters of the register control are adapted to this operating state. For both positive and negative acceleration processes, however, the web tension changes with a negative influence on register accuracy. This can usually not be sufficiently compensated by the control system, resulting in this phase of operation to appropriate committee. Even after the acceleration phase, the control system requires a certain running time to get back to the appropriate manipulated variables. This can also cause rejects.

In the DE 40 37 728 C1 is a device for register control for multi-color web-fed rotary printing presses according to the web / web method described with a controller having a central unit for detecting and storing all control parameters and the control behavior, with a scanner for detecting web register marks and with actuators for controlling the longitudinal register. The device includes a monitoring unit which has an acceleration detection device, which deviates from a stable path velocity speed change of Detects printing press on the printing cylinders and having a shutdown device, which is in signal communication with the acceleration detection means, and which interrupts the control activity on the occurrence of a signal representing this change in speed until again a constant operating speed is reached.

DE 10 246 072 A1 describes a method for printing length correction wherein multiple registration marks per product and printing process are printed. WO 2004/096546 A1 describes a method of printing correction based on a comparison between the data obtained from the print image detection and comparison image data.

During machining operations with flexible tools, stretching of the tool in the material flow direction causes stretching. This is e.g. in the case of flexographic printing clichés, which are rubbery flexible and thus stretchable.

Furthermore, the modulus of elasticity depends on the cliché thickness, which varies depending on the pattern to be printed. At a constant clamping force, this results in a cliché-dependent and thereby printing pattern-dependent differential elongation of the plate in the printing direction on the printing cylinder. The same condition occurs when the machining tools are not sufficiently accurate to manufacture or subject to severe manufacturing variations within the format. This complicates the exact positioning of the print images to each other.

Up to now, a maximum of one print correction per format and print has been performed. On the basis of trial prints, the resulting correction value is determined by manual measurement and entered manually into the control system. However, it has been shown that these measures are not sufficiently accurate, especially with flexible printing plates.

It is therefore an object of the invention to provide a method for pressure correction ready, which compensates for manufacturing tolerances in these printing plates as well as errors when mounting these printing plates.

Advantages of the invention

The problem is solved according to claim 1 or 7, wherein at least one first print mark and one second print mark are printed per product and printing process and these are compared for register control with Referenzpuukten or wherein the register control based on a comparison between the of Print image obtained data and comparison image data is done. This method makes it possible to compensate for manufacturing tolerances, especially in the case of flexible printing plates, such as errors, such as can occur during the clamping of such printing plates. In addition, distortions that can occur due to different cliché heights can be corrected more effectively.

If further print marks are printed per product and printing process and these are evaluated for register control, complex distortions, in particular those which have a higher order, i. are not linear, better detected and evaluated.

In this case, the substrate can be divided into several areas to be evaluated. These may be, for example, several areas of the cliché in which the cliché prints, i. E. in contact with the printing material.

A variant of the method provides that the areas to be evaluated are arranged within a printing area and / or outside the printing area. This allows a particularly flexible adaptation to the print templates.

In a preferred variant of the method, the print marks are scanned automatically. Thus, an automatic register control can be realized, in which several areas per format can be corrected.

If the print marks are detected in an evaluation unit by means of mark readers and / or by means of one or more cameras and subsequent image evaluation, the entire print area can serve as a correction area instead of a fixed number of print marks, so that the unrolling of the print tool can be predistorted in accordance with the processing errors of the print tool Druckklischees or according to the Aufspannfehler of the cliché, that overall results in an optimal pressure.

A variant of the method provides that the respective printing unit, for which the respective print marks or the print image have been evaluated, is adapted in its positioning for correction. This allows for the next printing process optimal alignment of the printing unit.

Alternatively or additionally, it can be provided that, for correction purposes, the printing units downstream of the respective printing unit for which the print marks have been evaluated are adjusted in terms of their positioning in a material flow direction. This does not optimize the absolute pressure. It is advantageous, however, that the different printing stations are corrected to each other
can, which is of particular interest in multi-color printing, where, for example, the four primary colors cyan, magenta, yellow and black to each other must be adjusted very precisely.

An alternative variant provides that, for correction, the evaluation device for detecting the print marks is connected directly to a correcting drive designed as an actuator. As a result, a particularly fast correction is possible.

If the correction is carried out within specifiable correction areas on the printing substrate, this results in the advantage that, for example, the correction can be carried out selectively outside the printing area. A "smearing" of the pressure is thus avoided. Likewise, a shift of the correction ranges in pressure ranges possible in which a slight correction only slightly disturbs and thus has only a minimal effect on the print result.

A preferred application of the method provides that the method in the paper printing, in paperboard printing, corrugated cardboard printing, plastic or metal foil printing, in the wood printing, in the
Printing of fabrics or metals with the use of flexible and / or stretchable printing plates is used. In particular, in this application results in the previously described
Advantage, because often the input mentioned problems can occur here.

If flexographic printing plates are used as printing plates, which is the case in particular for direct printing of corrugated cardboard, the correction method can effectively also be used to carry out complex corrections of the distortions that can occur, in particular, through the use of the flexographic printing plates.

A further preferred application of the method provides that in the case of several printing units which can be regulated relative to each other, first in a first printing unit a first printing without
Correction takes place and all determined correction values are checked for possible reductions in printing length and modified together with the printing of the first printing unit in such a way that reductions in printing length are excluded. This is particularly advantageous in terms of printing on paper or corrugated board, where in certain cases can lead to critical print length shortening, which can then have particularly serious effects on the printed image. Although this method variant, no absolute printing accuracy is achieved. However, the print stations remain error-free to each other, without critical Drucklängenverkürzungen can occur.

drawings

• Figur 1 in schematischer Darstellung ein Bewegungsprofil ohne und mit Drucklängenkorrektur,
• Figur 2 schematisch einen Ausschnitt eines Bedruckstoffes mit zwei Druckmarken,
• Figur 3 schematisch einen Ausschnitt eines Bedruckstoffes mit mehreren Druckmarken.

The invention will be explained in more detail below with reference to the exemplary embodiments illustrated in the figures. Show it:

• FIG. 1 a schematic representation of a motion profile without and with print length correction,
• FIG. 2 schematically a section of a printing material with two print marks,
• FIG. 3 schematically a section of a substrate with multiple print marks.

Description of the embodiments

A prior art print correction assumes that errors of the print lengths are corrected in a print-free area in which a correction movement is performed.

FIG. 1 shows a schematic representation of a movement profile without and with pressure length correction. Without print length correction results in a motion profile without correction 60th This is through
a, over the entire range linear course marked. The speed of a printing material 10 is constant.

With a printing length correction, a motion profile with correction 70 typically results, which has a speed that is initially constant in a printing area 30, and slightly higher than the motion profile without correction 60. In a correction area 40, which adjoins the printing area 30, the printing substrate 10 is first decelerated and then accelerated again until the necessary previously determined printing length correction has been achieved. A corresponding velocity profile with correction 80 is also shown in this diagram.

Previous automatic solutions only work with one correction per product and thereby only correct one error per product. At most one or two print corrections are executed per format. On the basis of pressure samples, the resulting correction value is determined by manual measurement of print marks and entered manually into the control system. Print marks are generalized for measurable variations in pressure and may be e.g. be replaced by evaluation of a printed image. The advantage of print marks is their easy measurability.

In an inventive embodiment it is provided that additional printed marks are printed per product and printing process and these are compared for register control with reference points or reference areas. This can be done for example by comparison with a Leitachsposition. The printing material 10 is divided into several areas to be evaluated. These may be, for example, several areas of the cliché in which the cliché prints, i. E. is in contact with the printing material 10. In addition, there are, for example, areas in which the cliché is not in contact with the printing material 10. Suitably one corrects within these ranges, since thereby no "smearing" of the pressure occurs. This results in no impact on the transport process of the printing material 10th

If the tool is constantly in contact with the printing material 10, as is the case, for example, in offset printing, then one will rather select correction areas based on the image to be printed, in which the correction has a minimal effect on the process or on the printing result. In general, only very small corrections are possible in this case, since otherwise the correction process has negative effects on the transport of the printing material 10, such as web tension fluctuations.

FIG. 2 shows by way of example in schematic representation a printing material 10, which has a first correction area 41 and a second correction area 42. In the example shown, a first print mark 51 is in the direction of a material flow direction 20 before first correction area 41 is arranged. A second print mark 52 is arranged between the first correction area 41 and the second correction area 42 in the example shown.

In FIG. 3 is shown in schematic representation another example. In this case, in the material flow direction 20, the printing substrate 10 has a first correction area 41, which is adjoined by a second correction area 42, and subsequently by a third correction area 43 and subsequently by a fourth correction area 44. At the beginning of the first correction area 41 is located on the substrate 10, a first print mark 51. Repeated, a second print mark 52 is directly at the beginning of the second correction area 42, a third print mark 53 right at the beginning of the third correction area 43 and a fourth print mark 54 right at the beginning of the fourth correction area.

Using an image evaluation instead of the evaluation of print marks 51, 52, 53, 54, it is possible, instead of a fixed number of correction areas 41, 42, 43, 44 to use the entire printing area 30 as a correction area 40 and by the correction movement, the unrolling of the printing tool to distort so that there is an optimal pressure.

Another variant of the method provides for a correction of the subsequent printing stations. Instead of correcting the printing station whose print image has been evaluated, all subsequent printing stations can also be corrected according to their position. This option can be further enhanced by also correcting the print station that prints the print image to be evaluated, which, however, only affects the next print of the next product.

A particularly rapid correction can be made possible if the evaluation device, for example a brand reader or a camera system, is connected directly to the correcting drive, the actuator. This option, however, does not match the options of one Correction of the subsequent printing stations or in combination the correction of printing stations and subsequent printing stations possible.

• Angenommen ist zunächst ein Druck einer ersten Druckstation, die zunächst ohne Korrektur gedruckt wird.
• Alle daraus errechneten Korrekturwerte werden dann auf mögliche Drucklängenverkürzungen überprüft, die im Hinblick auf das Gesamtdruckergebnis als besonders kritisch gelten.
• Ergeben sich Drucklängenverkürzungen, so werden diese nicht durchgeführt. Stattdessen werden die Korrekturwerte dergestalt modifiziert, dass sich keine Verkürzungen ergeben.

Another option is an optimization of the setting algorithm by a cross-control system or position. If several printing units are controlled to each other, it may happen that some of the adjustments result in pressure reductions and at the same time also pressure extensions. In particular, however, pressure reductions can have serious effects on the printed image. Therefore, the following procedure is provided in this option:

• Initially, a print of a first print station is assumed, which is initially printed without correction.
• All calculated correction values are then checked for possible reductions in print length, which are considered to be particularly critical with regard to the overall pressure result.
• If print length reductions result, these are not performed. Instead, the correction values are modified in such a way that no shortenings result.

As a result, although no absolute printing accuracies can be achieved, the printing stations remain error-free with respect to each other and the critical printing length shortenings are avoided.

The described method and its variants make it possible, in particular, to compensate for distortions such as may occur, for example, when printing on paper or paperboard, corrugated cardboard, plastic or metal foils, wood, materials or metals with flexographic printing plates. On the one hand, the manufacturing tolerances of the printing plates, which may vary depending on the cliché height, and on the other hand possible Aufspannfehler be corrected as a result of a partially different elongation of this cliché.

Method for pressure correction

10

substrate

20

Material flow direction

30

pressure range

40

correction range

41

first correction area

42

second correction area

43

third correction area

44

fourth correction area

50

print mark

51

first print mark

52

second print mark

53

third print mark

54

fourth print mark

60

Movement profile without correction

70

Movement profile with correction

80

Speed profile with correction

Claims (17)

1. Method for printing length correction having a register regulating device for a multiple-colour printing press with individual printing units, in which method printing marks are applied on a printing material (10), which printing marks are detected by means of sensors, a printing length being corrected by the printing material (10) being moved relative to a printing unit, at least one first printing mark (51) and one second printing mark (52) being printed in the material flow direction (20) per product and printing operation by a printing unit and the said printing marks (51, 52) being detected, characterized in that the positions of the detected printing marks (51, 52) are compared with reference points for printing length correction.
2. Method according to Claim 1, characterized in that further printing marks (53, 54) per product and printing operation are printed and are evaluated for printing length correction.
3. Method according to either of Claims 1 and 2, characterized in that the printing marks (51, 52, 53, 54) are sensed automatically.
4. Method according to one of Claims 1 to 3, characterized in that the printing marks (51, 52, 53, 54) are detected by means of mark readers.
5. Method according to one of Claims 1 to 4, characterized in that, for correction, the respective printing unit, by which the at least one first and one second printing marks (51, 52, 53, 54) are printed, has its positioning adapted.
6. Method according to one of Claims 1 to 5, characterized in that, for correction, the printing units which are arranged in a material flow direction (20) downstream of the respective printing unit, by which the at least one first and one second printing marks (51, 52, 53, 54) are printed, have their positioning adapted.
7. Method for printing length correction having a register regulating device for a multiple-colour printing press with individual printing units, in which method at least partial printed-image detection takes place using an image evaluation means and an evaluation is performed in the register regulating device, a printing length being corrected by the printing material (10) being moved relative to a printing unit, characterized in that the printing length correction takes place on the basis of a comparison between the data which are obtained from the printed-image detection and comparison image data.
8. Method according to Claim 7, characterized in that the printing material (10) is divided into a plurality of regions to be evaluated.
9. Method according to Claim 8, characterized in that the regions to be evaluated are arranged within a printing region (30) and/or outside the printing region (30).
10. Method according to one of Claims 7 to 9, characterized in that the printed image is sensed automatically.
11. Method according to one of Claims 7 to 10, characterized in that the printed image is detected by means of one or more cameras and an image evaluation means which is connected downstream of it/them.
12. Method according to one of Claims 7 to 11, characterized in that, for correction, the respective printing unit, for which the printed image has been evaluated, has its positioning adapted.
13. Method according to one of Claims 7 to 12, characterized in that, for correction, the printing units which are arranged in a material flow direction (20) downstream of the respective printing unit, for which the printed image has been evaluated, have their positioning adapted.
14. Method according to one of Claims 1 to 13, characterized in that the printing length correction is carried out within predefinable correction regions (40) on the printing material (10).
15. Method according to one of Claims 1 to 14, characterized in that, in the case of a plurality of printing units which can be regulated with respect to one another, first of all a first print takes place without correction in a first printing unit and all determined correction values are checked for possible shortening of the printing length and are modified with the print of the first printing unit in such a way that shortening of the printing length is ruled out.
16. Use of the method for printing length correction according to at least one of Claims 1 to 15, characterized in that the method is used in paper printing, in cardboard printing, corrugated cardboard printing, plastic-film or metal-foil printing, in wood printing, in the printing of materials or metals with the use of flexible and/or elastic printing plates.
17. Use of the method for printing length correction according to Claim 16, characterized in that flexographic printing plates are used as printing plates.

Images