EP1593505B1 - Method for controling the image position on a printing plate - Google Patents

Abstract

The method involves lying a printing plate (1) having fitting stampings on alignment pins. A trigger signal is released by one of the pins on recognition of an exact position of the plate, for a camera system. Information of reference positions (3, 4) is read by the camera system. The positions are correlated to a print image (2) in form of mark or coding found in or by the side of the image. The positions are determined by a computer system, at the stampings.

Description

The invention relates to a method for rapid position control of a printed image on a printing plate or artwork, as for example from the DE 4221482 C2 is known.

DE 4239089 A1 shows another exemplary method wherein a printing form is punched to a dowel pin.

For the production of color prints, a printing set of printing forms or printing plates for the various printing inks is usually produced from a colored original. Before you can start the actual printing process, when setting up the printing presses, the individual printing forms must be adjusted to each other on the printing cylinders so that the prints produced in the different colors match each other exactly, otherwise blurred images and / or incorrect colors would result.

The production of the printing plates or printing originals, which are usually printing plates, requires a high degree of precision. Initially, the printed image is usually applied to the printing plate by means of a laser or photochemically, this being positioned on side stops or optically in order to achieve a correct positioning of the printed image. Then two punch punches are usually attached to one side edge, by means of which the pressure plate is then later applied for positioning on corresponding dowel pins on the printing cylinder. Unfortunately, however, the Rims of a printing plate usually not processed so precisely that the desired accuracy of the assignment between printed image and pass punches is achieved. When mounting on the printing cylinder, therefore, the pressure plate and / or the dowel pins of the printing cylinder must be adjusted until the exact assignment to the printing plates on the other printing cylinders is reached. This is a very complex process, whereby the printing press must be started again and again to be able to check the result obtained. The paper consumption required for this also has a negative effect. In particular, when exceeding tolerances that can no longer compensate a readjustment, much time and material is wasted until it is recognized that such a printing plate can not be used because of exceeding the tolerance limits.

In the method according to the initially cited prior art, an attempt is made to solve this problem by integrating registration marks in the printed image which are so small that they do not disturb the print image. The printing plate provided with the printed image is placed on a measuring table, with movable cameras both the punch punches and the register marks scan. From the recorded images then the correctness or the tolerances of the assignment between pass punches and register marks is calculated, the calculated tolerances are used to compensate for the assignment errors in applying the printing plate on the printing cylinder of the printing press.

The disadvantage of the known arrangement is that the entire printing plate must be scanned by means of the movable cameras. This is very time consuming and requires expensive measuring or camera systems.

The object of the present invention is to improve the known method so that a faster position control is possible with a simpler camera system.

This object is achieved by a method having the features of claim 1.

The advantages of the method according to the invention are, in particular, that the scanning of the at least one punch fit by the camera system is eliminated. A reference position is produced by applying the printing original or printing plate to a corresponding number of dowel pins of the measuring arrangement with the aid of their punched or punched holes. The reference positions located inside or outside the printed image in the form of a mark or coding are known in their relative position to the punch punches, so that simple and immovable cameras or other image recording devices only have to be directed to these known positions. The scanning of the entire image is eliminated. If the fiducial marks lie outside the known position checked by the camera, at which the fiducial marks should actually be located, the tolerances are in any case unduly large, and the pressure plate can be rejected immediately.

The measures listed in the dependent claims advantageous refinements and improvements of claim 1 method are possible.

The data calculated by the computer system are machine-related and represent adjustment variables and / or deviations in the respectively correct unit of measurement. These are deviations of the correct position of the printed image relative to the punch punches or corresponding adjustment variables by which the printing plate is automatically corrected when placed on the printing cylinder of the printing press, provided that the tolerances and deviations do not exceed a predetermined size. In this case, the printing plate can not be used.

The data calculated by the computer system include the extent to which the print template matches one another with other print templates of a print set. This measure contains the correction quantity to change the position of the print templates so that all the print templates of a print set fit over each other.

After checking all the print templates of a printing set, all the printing units of a printing machine, for example an offset machine, are set to the same values, so that all the images fit exactly one above the other. This correction can be done automatically using the calculated values.

The deviations or tolerances of the artwork are expediently displayed in a numerical table and / or graphical representation.

A pressure plate applied to dowel pins is shown in the single figure and serves to explain the method described below as an embodiment of the invention.

In the figure, a provided with a printed image 2 printing plate 1 is shown. The pressure plate has at a longitudinal edge two punch punches 5, 6, which serve to receive dowel pins 7, 8.

To produce such a printing plate 1 serving as a printing master or printing plate, such a plate is usually still positioned without punching with the outer edges on stops or visually on a corresponding workstation, in which case the printed image 2 is applied by laser processing or by chemical processing. Simultaneously with the print image 2, the two reference positions 3, 4 are applied, which are in fixed spatial association with the print image 2. These reference positions 3, 4 are located outside the printed image 2, but they can also be arranged within the printed image 2, if they are sufficiently small and thus do not disturb the printed image. Such reference positions 3, 4 often have a square area of 0.9 x 0.9 mm. On this surface, a data code with various information can be applied, which ensure an assignment of the printing plates of a printing plate set. This data code may also contain information about dimensions, orientation, format and / or color of the printing plate. However, in the simplest case, the reference positions can also be only position marks.

After the application of the printed image 2 and the reference positions 3, 4, the punch punches 5, 6 are then made, with their positions again oriented with respect to the outer edges of the plate, which does not always have the required accuracy. As a result, it may happen that the correct assignment of punch punches 5, 6 to the printed image 2 or to the reference positions 3, 4 is not present. The method according to the invention serves to show or calculate tolerances with respect to the exact assignment positions, the deviations then being used to correct the position of the printing plates on the printing cylinders of a printing press in order to achieve that all printing plates of a printing set produce exactly superimposed images during the printing process.

In the method according to the invention, first of all a pressure plate 1 produced and to be tested in the manner described is supplied to the measuring system in such a way that the dowel pins 7, 8 of the measuring system engage in the punched passages 5, 6 according to the figure. Trained as sensors dowel pins 7, 8 recognize the exact position of the correct position of the printing plate and deliver a precise position characterizing trigger signal for a not-shown camera system. The camera system consisting of two cameras, for example, at two reference positions 3, 4, is firmly positioned so that the reference positions 3, 4, or their coded information, which are always arranged at the same positions, can be detected. They are read by the camera system, interpreted and forwarded as a data record to a computer system. Deviations from the correct position result in the computer system the extent to which the respective printing plate 1 fits one above the other with the other printing plates of the printing set. The calculated data are machine-related to the respective printing press and also include adjustment variables in the respectively correct unit of measure for the printing press, so that these can automatically make any required position corrections of the printing plates on the basis of these adjustment variables. This is done for example by moving or manually moving appropriate dowel pins on the printing cylinders of the printing press.

The entire setting process can be performed automatically, with the data being automatically managed and available at any time for follow-up orders or corrections. An operation can be omitted.

By the computer system, the acquired and calculated information can also be displayed in a numerical table or graphic representation, the deviations or tolerances are shown, divided according to perimeter, page and diagonal registers.

If tolerances are detected during the measurement which exceed a predetermined level, then the respective printing plate is immediately rejected, since a corresponding correction in the printing press would then no longer be possible.

When tolerances are detected within the allowable tolerance range, the computer system calculates from the information the data required to match all the printing plates of a printing system in the printing press. By correcting in the DTP or CtP imagesetter, all print templates can then be matched to one another so that corrections in the printing press are no longer necessary in the future.

It should also be noted that the production of the printing plates can also be carried out in a different order, wherein, for example, first the punch punches 5, 6 are produced and only later the printed image 2 is applied synchronously with the reference positions 3, 4.

In the single figure, two reference positions 3, 4 are shown. In the simplest case, only a single reference position may be sufficient, with a larger number of reference positions would be possible.

It can also be used printing plates or printing plates, which have an angled edge or other additional positioning element. In this case, enough ready a single, for example, attached to this angled edge punched in conjunction with a dowel pin for defined positioning.

Claims (7)

1. Method for a rapid alignment check of a printed image on a printing forme, comprising the following steps:

   a) placing of the printing forme (1) provided with at least one register notch (5, 6) on at least one register pin (7, 8) designed as sensor for the one or more register notch (5, 6);

   b) activation of a trigger signal for a camera system by the register pin or pins (7, 8) on detection of the exact position of the printing forme (1);

   c) reading by the camera system of data relating to at least one reference position (3, 4) associated with the printed image (2) in the form of a mark or coding in or adjacent to the printed image (2);

   d) passing on the read data to a computer system as a data record;

   e) determining by the computer system of the position of the reference position or positions (3, 4) containing the data relative to the register notch or notches (5, 6).
2. Method according to claim 1, characterised in that the data calculated by the computer system are machine-related and represent adjustment values and/or deviations in the relevant correct unit of measurement.
3. Method according to claim 1 or 2, characterised in that the data calculated by the computer system contain the measurement for adjustment of the printed image (1) superimposed on other printed images of a set of printing matter.
4. Method according to any of the preceding claims, characterised in that after checking of the printed image (1) and other printed images of a set of printing matter, all printing units of a printing machine, in particular an offset machine, are set to the same values.
5. Method according to any of the preceding claims, characterised in that deviations or tolerances of the printed image (1) are shown in a numerical table and/or in graphical form.
6. Method according to any of the preceding claims, characterised in that two register notches (5, 6) are used for two register pins (7, 8).
7. Method according to any of the preceding claims, characterised in that the coding also contains information regarding dimensions, orientation, format and/or colour of the printed image (1).

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