Patent Grant
7337035
The present invention relates to a method for carrying out a printing correction.
In the printing field, there is a widespread use of flexible production masters these days. These are tautly mounted on the plate cylinder, an extension of the production master being able to occur because of the mounting of the production masters on the plate cylinders. From this, there follows a variable production master length which disadvantageously results in a variable print length. This is the case, for example, for flexographic printing plates, which are designed to be flexible and stretchable in a rubber-like manner, so that unknown printing lengths result because of the mounting of the flexographic printing plate on the plate cylinder.
Furthermore, independently of the height of a printing plate, the mounting length is the same for all printing plates, so that different roll-over lengths are able to come about for the individual printing plates because of the different printing plate heights. The same condition obtains if the processing masters are prepared in an insufficiently accurate manner, or are subjected to fluctuations in the preparation. An examination of this effect is described, for instance, in the article, “Printing Length Adjustment in Corrugated Paper Direct Printing”, in the journal Flexoprint of April 2001.
Furthermore, in the case of the occasional printing carrier, it may happen that there is a change in the size of the printing carrier between individual processing procedures, on account of a moisture input or a drying procedure.
Because of the previously discussed variable printing lengths or sizes of the printing carriers, during the course of a printing procedure it may also happen, disadvantageously, that variable printing lengths result for the individual working masters. One result of this are register-inaccurate printing processes for the individual processing masters, and consequently blotted appearances of the overall prints.
It is known that the variable master lengths described are manually corrected. For this purpose, the actual printing lengths of the individual working masters are individually measured on the printed sheets. From these printing lengths for the individual working masters correction values are determined, and these are entered manually into a printing device. It is a disadvantage that this results in complicated and awkward handling, which delays the processing procedure in an undesired manner because it is time-consuming. For a plurality of plate cylinders, whose printing lengths are corrected manually, a disadvantageously high additional processing expenditure may be created.
In the related art it is moreover known that, using a so-called register control function, one may use so-called register marks of various production masters in order to align various part printings with respect to position. For example, from DE 102 41 609 a method and a device are known for determining and correcting an imperfect register.
It is the object of the present invention to make available a method and a device for an improved printing correction.
The method according to the present invention is provided for carrying out a printing correction, a product being printed on by a plurality of processing devices during a processing procedure. The method includes the following method steps:
Advantageously, this supports the automated carrying out of a printing correction, the correction including the correction of a printing length. Consequently, the printing correction principles known in the related art may be used in an improved manner. Advantageously, for instance, one is able to minimize set-up times for production masters. Thus the efficiency of a printing procedure may be favorably increased.
One preferred specific embodiment of the method according to the present invention provides that, in addition to the correction of the printing length, a correction of the printing position is carried out too. Thereby printing marks on the printing product can be controlled with respect to position, which supports an improved alignment of individual prints and consequently improves a quality of a printing procedure even more.
An additional preferred specific embodiment of the method according to the present invention provides that at least one first printing mark is situated in an area in front of the printing product in the direction of transportation, and at least one second printing mark is situated in an area in the rear of the printing product in the direction of transportation.
This advantageously utilizes a maximal area of the printing product for measuring the actual printing length for the subsequent correction of the unequal length of the masters of different processing devices.
An additional preferred specific embodiment of the method according to the present invention provides that, during the processing procedure, only a first of several processing devices applies both the printing marks. Thereby it may be achieved that, in the processing procedure, processing devices adjust their printing, with respect to position, to the printing of the first processing device. In this manner, therefore, a position correction of the printing is achieved with the aid of which long-term drifts may be permanently eliminated from the printing process. The stability of the printing procedure is increased advantageously thereby.
In the light of a diagram,
A curve 1b is a curve representing the machine angle corrected for printing length plotted against the angle of the plate cylinder. Curve 1b is steeper than curve 1a, and thus, the plate cylinder achieves a full rotation earlier than the impression cylinder.
In area 2 of
The correction of the imperfect register of a printing length, shown in principle in
Consequently, in an advantageous manner, different printing lengths of the two processing devices are essentially equalized. The method according to the present invention carries out the printing correction in an automated manner, advantageously in that, in the printing area (area 1), a relative motion between the plate cylinder and the impression cylinder is executed as a result of different production master lengths. The different printing lengths of the individual plate cylinders are able to be equalized thereby.
It may further be seen in
In comparison to customary printing corrections, the method according to the present invention is thus distinguished by the fact that the correction is carried out in an automated fashion. This means that the manual determinations, described above, of the actual printing lengths and the subsequent manual adjustment may advantageously be omitted. The printing correction according to the present invention may thereby work more efficiently, to some extent, than the usual methods. The positions of the corrected printing marks C, D in
In the light of
In the case of changing relationships of the printing marks of the first processing device A, B or the printing marks that were printed on ahead of time, the printing steps of the subsequent processing devices change along with them. Because of that, for example, in an advantageous manner a long-term drift of a relationship between the processing devices is able to be eliminated. A printing process having a plurality of processing devices may consequently be designed in a stable manner, in lasting fashion. In addition, the advantage therefore comes about that printing marks have only to be recorded as to position for a single printing color, which makes it possible to do without additional printing marks and recording devices, including their implicit inaccuracies. As a practical application example of the additional control variant, for instance, a rotary die-cutting machine is conceivable which die-cuts preprinted sheets having two register marks.
Up to this point, a control was described of printing lengths of a plurality of processing devices. However, with the aid of the method according to the present invention, one may also carry out an absolute measurement of the positions of the printing marks or the distance apart of the printing marks. Thereby absolute accuracy may be achieved for printing procedures. The measurement may be carried out, for example, using a calibrated camera which records absolute positions of the printing marks and in this way ascertains an absolute distance of the first from the second printing mark. Using this specific embodiment of the method according to the present invention, it is conceivable, for example, that an absolute printing length of the first processing device is recorded, to which the subsequent processing devices synchronize with respect to the printing length.
One specific embodiment of the method according to the present invention, as described above, permits an overall correction of a print in two partial steps. In a first partial step, in this context, the position of second printing marks B, D with respect to each other is controlled (printing length correction), and in a second partial step the position of first printing marks A, C with respect to each other is controlled (printing position correction). The partial steps described may also be carried out in the opposite sequence with respect to each other.
While using a suitable algorithm, it is also conceivable that the two partial steps described be unified into one single partial step. This makes it possible to carry out the overall connections described in a single step, in which, from printing product to printing product, both the printing length correction and the printing position correction are carried out in one single step. In one's mind one can imagine this as two partial steps that are connected to each other, the results of the first partial step being not influenced any more by the respective second step. In this context, the position of first printing marks A, B with respect to each other is no longer changed by the printing length correction of the second partial step.
The functioning of a correction just described is shown in a single step in the light of
This position shift as a result of a printing length change is shown in
It may be seen in
Both processing devices 4a, 4b, 4c and transportation device 3 may be used as actuators of the method according to the present invention. In the first case, the transportation of printing product 5 takes place with the aid of transportation device 3 using a largely constant speed, plate cylinders 6 of processing devices 4a, 4b, 4c executing a relative motion to printing product 5. In the second case, the transportation of printing product 5 takes place with the aid of transportation device 3 using a speed that is not constant. The result is that the transportation procedure of printing product 5 is corrected, which may be done, for instance, by the correction of a speed control for transportation device 3.
In an advantageous manner, there are two different possibilities for the selection of the correction elements, particularly in the case of single products, the product transportation being used as actuator as opposed to correction of processing device 4a, 4b, 4c. This also corresponds to a selection possibility in usual register corrections.
In the following, the sequence of the method according to the present invention in apparatus 1 for printing correction is described in principle. Printing product 5 is conveyed to first processing device 4a using transportation device 3. In first processing device 4a first printing mark A of first processing device 4a and second printing mark B of first processing device 4a are applied. In a further sequence, printing product 5 is conveyed to second processing device 4b, using transportation device 3. At that point, first printing mark C of second processing device 4b and second printing mark D of second processing device 4b are applied to printing product 5. Thereafter, printing product 5, along with applied printing marks A, B, C, D is conveyed to third processing device 4c, using transportation device 3. Device 2 for recording the positions of printing marks of third processing device 4c detects the positions of printing marks A, B, C, D on printing product 5, and evaluates the positions of printing marks A, B, C, D. If device 2 establishes that the distance of printing mark A to printing mark B deviates from the distance of printing mark C to printing mark D, this means that the actual printing lengths of first processing device 4a and second processing device 4b are different.
Thereupon, as a correcting measure, second processing device 4b is activated via a control output 7 of third processing device 4c. Because of this, for next printing product 5 that is conveyed to second processing device 4b, plate cylinder 6 is moved relative to printing product 5, using transportation device 3 or processing device 4b, in such a way that second processing device 4b produces an essentially identical printing length on printing product 5, in comparison to first processing device 4a. A parameter value for the correcting motion of second processing device 4b may be stored in second processing device 4b, so that, for all further printing products 5 during their processing, the printing correction according to the present invention is automatically carried out by second processing device 4b.
As a further development of the method according to the present invention, second processing device 4b can be activated, via control output 7 of third processing device 4c, in such a way that the position of first printing mark C is also adjusted to the position of first printing mark A of first processing device 4a. This has the favorable result that a printing position correction takes place in addition to a printing length correction.
It stands to reason that the correction method described is not limited to a correction of printing marks C, D only of second processing device 4b, but can be extended to a plurality of different processing devices 4a, 4b, 4c. However, to make it simpler, only the correction of printing marks C, D of second processing device 4b was described above.
As a further improving measure for carrying out the method according to the present invention, it is conceivable to perform an optimization of the extension of the flexographic printing plates with respect to one another. Thereby different production master lengths can be roughly adjusted even in the preliminary stages of the method according to the present invention, so that, when using the method according to the present invention, only a fine correction of the printing lengths still has to be performed. This may be achieved, for example, by taking a measurement of the pulling force when the printing plate is mounted on plate cylinder 6.
Furthermore, an optimization of an actuating algorithm in the case of a control/setting that affects the printing is conceivable. If a plurality of processing devices 4a, 4b, 4c are controlled with respect to one another, it may happen that some of the adjustments attained thereby represent printing length reductions and some represent printing length extensions. It is known, however, that printing length reductions are able to cause serious deteriorations in the printing image, as compared to printing length extensions. Therefore it is of advantage to design the method according to the present invention in such a way that, in principle, none or only small printing length reductions come about, that is, printing length reductions very limited in their size. This may be achieved in that, first of all, a print of a reference color is made without printing length extension or printing length reduction being made. After that, control outputs 7 processing devices 4a, 4b, 4c are checked for possible printing length reductions. If one or more printing unit are present having the resulting printing length reduction based on the printing control according to the present invention, the reference print is changed in such a way that no printing unit carries out a printing length reduction or only a maximum specifiable printing length reduction based on the control/setting. This may be attained, for example, in that the printing unit of the reference color is corrected by a suitable amount (printing length extension of the reference print).
Example:
Printing length changes of the processing devices (first change is the reference print).
Before: 0 mm, +1 mm, −2 mm, −3 mm, +1 mm.
After: +3 mm, +4 mm, +1 mm, 0 mm, +4 mm (there is no longer any printing length reduction).
The numbers give printing length changes of the individual processing devices 4a, 4b, 4c in millimeters, the first of the five numerical values represents a printing length change for the reference print. A positive sign means a printing length extension and a negative sign means a printing length reduction of a subsequent processing device 4a, 4b, 4c. Thus, before that application of the improved algorithm, a maximum printing length change includes a printing length reduction by 3 mm (Before: from 0 to −3 mm). After the application of the improved algorithm, the printing length change no longer includes any printing length reduction. (After: from +3 mm to +4 mm).
A modification of the algorithm may have the result that the reference print is changed in such a way that at least a reduction in absolute amount of the maximum print length reduction comes about in the machine.
Example:
Print length changes of the printing units (first change is reference print)
Before: 0 mm, +1 mm, +2 mm, −3 mm, +1 mm.
After: +1 mm, +2 mm, +3 mm, −2 mm, +2 mm (printing length reduction in absolute amount is a maximum of −2 mm).
From a comparison of the two rows of numbers for the correction values it may be seen that, after the application of the algorithm, a pressure length reduction still occurs, to be sure, but it is reduced in comparison with the case of the application without the algorithm. The reduction in the printing length reduction amounts to 1 mm (from −3 mm before to −2 mm after).
In the optimization of the algorithm described, advantageously the reference print is printed in such a way that print reductions in subsequent prints of subsequent processing device 4a, 4b, 4c no longer occur. An improvement in the printing image is thereby supported in an advantageous manner.
The method according to the present invention may be advantageously carried out, using various types of processing devices 4a, 4b, 4c. For example, a slotter, a punch or a cross cutter may be used as processing device 4a, 4b, 4c. In this context, a slotter is understood to mean a processing device 4a, 4b, 4c which insert longitudinal slits into printing product 5. A punch is understood to be a processing device 4a, 4b, 4c that executes all the remaining slits and cutting procedures in printing product 5, such as cross cuts, corrugated cuts or waste stripping. Cross cutters are understood to mean processing device 4a, 4b, 4c that cut in the transverse direction. Thus, although the present invention was explained in the above description in connection with printing units as processing device 4a, 4b, 4c, it goes without saying that the present invention may also be carried out as a method for a processing correction using a slotter, punches and cross cutters. This may favorably increase overall accuracy and overall reproducibility of an overall printing procedure in an efficient manner.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2005 007 435 | Feb 2005 | DE | national |
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| Number | Date | Country | |
|---|---|---|---|
| 20060271230 A1 | Nov 2006 | US |
