EP1577085B1 - Visual control device for exposed printing plates - Google Patents

Abstract

Visual control device on illuminated printing plates (5) for printing machines is applied onto the printing plate during illumination in the form of at least one control marking (3) consisting of two parallel strips (32, 33). One strip (32) shows the non-calibrated tone value course and the other strip (33) shows the calibrated defined half-tone value. At least the region in which the non-calibrated tone value course and the calibrated defined half-tone value visually agree is shown on the control marking. Independent claims are also included for: (1) Alternative visual control devices; (2) Printing plate comprising a control device; and (3) Printing plate comprising at least two different control devices.

Description

The present invention relates to a visual inspection device on exposed printing plates for printing machines, which is applied on exposure of the printing plate in the form of at least one control mark on the printing plate.

The printing process is basically divided into prepress, printing press and postpress. The goal of any printing process is to produce print products that match as closely as possible a print template. The print template may once be present as a template print, but it may also be available digitally as an image file. A print template as an image file is processed digitally in the prepress stage by means of a raster image processor for printing, so that the data available thereafter are suitable for the exposure of a printing plate for offset printing presses. In addition to the actual print image also different markings and control areas are applied to the printing plate, which are located in the edge regions of the printing plate and z. B. Tonwertkeile on printing plates in non-printing areas as well as print control strips and register marks in printing areas include. Every printing process requires the printing staff to ensure that the finished print product matches the original. If deviations occur, the printing process must be corrected, ie the settings in the pre-press and / or on the press must be changed. If the print quality of the finished printed product is insufficient, this print product must be rejected as waste, which is undesirable because of the added cost. For this reason, operators in printing shops want to be able to recognize possible process deviations from the settings made as early as possible in the entire printing process. Such process deviations can arise during the processing of the data of the printing original in the prepress, which is why printing plates have control devices in the form of tonal wedges. Such a control device as in Fig. 1 is in itself known from the state of the art, here in a first elongated strip the reference tone values are shown in a fixed grid, for example 200 lines / inch at an angle of 45 ° with respect to the printing plate leading edge obliquely offset in a range of 1 to 100%, while in a parallel second strip the tonal values after process calibration are plotted in the RIP (Raster Image Processor) of the prepress. The reference tonal values are unaffected by the RIP and provide a reference. Based on their respective superimposed tonal values for specific percentages, a comparison for the printing personnel by visual inspection is possible and the deviations can be estimated roughly quantitatively within the scale provided with percentages.

Especially in the digital exposure of printing plates (CtP), ie Computer to Plate, in the pre-press, it is enormously important that the deviations are kept within narrow tolerance ranges. In the case of conventional control devices such as a control wedge in Fig. 1 is only a control of the differences between uninfluenced and influenced settings visually possible. Thus, a comparison of the template tone values and so-called linearized tone values, which are used in some exposure processes, is lacking. It is also not possible to visually, quantitatively detect the difference in deviation at the important 50% tone value between uncalibrated and calibrated state.

From the European Patent Application EP 0 847 858 A1 a control strip is known which optically converts unwanted influences when producing a printing plate in visible to the operator deviations. These influences are summarized in so-called "Image Spot Size Deviation Variables" (ISSDV). The ISSDVs influence the imaging process of a printing plate so that the dots actually formed on the printing plate deviate from the desired size. The actual size of a halftone dot applied to a medium to be imaged depends not only on the exposure and development, but also on the properties of the medium to be imaged. In order to visualize these effects, the control strip has control fields that are relatively insensitive to the ISSDV factors, whereas a background field reacts very sensitively to the ISSDV factors. If the consistency of the control fields does not appear at the number "0", the medium was not optimally imaged or exposed.

From the Patent US 5,748,331 a control device in the form of a control strip is known, which makes the correct setting of the parameters for exposure verifiable. These are process parameters such as the intensity of the exposure light beam or the development temperature during film development. The control strip has tonal values in a first stripe which are relatively insensitive to the exposure process, and the control stripe has a second stripe with tonal values, which are executed as fine grid points and are strongly influenced by the exposure process. By means of the control strip it is thus possible to visually check the exposure process.

From the European Patent Application EP 1 006 712 A1 An optical sensor is known which checks the plate exposure. For this purpose, the optical sensor detects certain parameters in the imaging process such as the intensity of the exposure beam, the modulation of the exposure beam and the grid dot size and shape. For this purpose, a first image and a second image with different imaging characteristics are acquired. One of the two images is less susceptible to changing imaging parameters than the other image. In this case, the first or second image in each case comprises a symbol and is surrounded by the other image in the form of a background. On the basis of the images thus arranged in the form of a control field, the exposure process can be evaluated and evaluated by means of the optical sensor, and the quality of the exposure can thus be checked.

It is an object of the present invention to provide a visual inspection device on exposed printing plates, which allows a better visual quantitative assessment of the differences in the result of the exposure process.

The present object is achieved by claim 1. Further advantageous embodiments are given in the dependent claims and the drawings. According to claim 1, when exposing a printing plate in the prepress next to the printed image and a control mark applied to the printing plate in particular in the non-printing area, which consists of two substantially parallel strips. In another solution not according to the claimed invention, a strip represents an uncalibrated tone scale enlarged by a particular halftone tone value, ie the tonal values of that strip are in the uninfluenced state while the second strip shows the determined halftone tone value as changed by the calibration in the RIP. The control mark in the first strip shows a section of the uncalibrated tonal curve in Fig. 1 finely graduated resolved, the section should be chosen so that an overlap area of the two strips is visible. Under the overlap is to understand the tone, in which the parallel stripes optically show the same tone, ie the continuous tone of the second stripe is equal to a tone level of the first stripe. The strips are preferably shown in a gray value representation, which means in the case of overlapping that the superposed tone values show the same gray value. If the overlap value is not exactly below the zero mark, there is a deviation in the exposure between the unaffected reference values and the values calibrated during the manufacture of the printing plate. If this deviation does not match the deviation set by the operator or wanted, the exposure process must be changed. The big advantage of the visual assessment on the printing plate lies above all in the fact that not only waste has to occur in the printing press, but that even on the printing plate unintentional deviations can be detected and the printing plate is optionally replaced with an improved, before the printing process in the printing press is started.

In a first embodiment of this other solution, it is provided that the uncalibrated tone value progression increases or decreases in steps in its tonal values. In order to enable an exact assessment by the printing staff, the Tonwertverlauf is executed stepped, since then in the comparison of the uncalibrated Tonwertverlaufs even the smallest deviations are clearly visible and thus the overlap value can be visually reliably detected in a relatively small area with small deviations. The steps are sufficiently fine but not too finely chosen, so that they are still visually perceptible, but also show small deviations, which are no longer tolerable.

It is further contemplated that the particular halftone tone value be the 50% tone value. The 50% raster tone value plays an important role in the visual assessment of print products, as this raster tone value has the greatest dynamics in the production process of printing plates and throughout the printing process occurs. For this reason, it is particularly important for the printing staff to be able to detect deviations in the range of the 50% tone value. Therefore, the control device enlarges the range by the 50% value so that the printing personnel can judge it accurately.

Furthermore, it is provided that a display scale with associated percentages is present on the control mark parallel to the two strips. The plotted percentages parallel to the stripes make it possible to assess the difference between the tonal values purely visually and quantitatively. Is the overlap point with the same tone values z. B. at minus 7%, it means that at a halftone tone value of 50%, a reduction has been made by the process calibration in the prepress to 43%. By means of this reading, the operating personnel can check the production process of the printing plate to see whether the settings have been correctly implemented. If the settings resulted in a reduction of the halftone tone value from 50% to 43%, then the manufacturing process for this halftone tone value has been optimally adjusted. However, if the reduction in this example should have been less than or more than 7%, e.g. only 6% of the staff can see on the printing plate that the manufacturing process still needs to be improved because the desired settings were not achieved. Since the differences tend to be in the negative range, it is advantageous if the display scale ranges from minus 15% to plus 3%. With such a scale, the overlap value is usually always visible. If, however, this tone equality of the overlap value can not be recognized, this in turn means that the tone change is greater than 3% or less than minus 15% and thus lies outside the display range of the control element.

In the invention according to the present claims, it is provided that reference tone values, which are uninfluenced by the printing process, increase or decrease stepwise in an oblong strip such that a specific raster tone value within the same strip is shown in multiple fine resolution and the particular raster tone value within the same strip is bounded by polygons. Also this kind of representation a control device always refers to a specific raster tone value such. B. the 50% value. In this control device, the operator searches the area of the control device in which the unimpeachable reference tone values of the background in the strip and the constant, finely resolved raster tone values of the polygons located therein coincide. Due to the polygonal configuration, even slight deviations in the tonal values can still be assessed visually. Here, an optimum manufacturing process is achieved when the tone value of the polygon and the tone value of the background of the elongate strip in the zero portion of the control mark match. In the event of a deviation by one field to the left or right, a deviation to be read in accordance with the reference grid and the determined halftone tone value results. If the tone equality sets in the zero section, it means that the exposure energy and the chemical development process in the printing plate production are correctly set.

In addition, it is envisaged that the polygons will essentially be enveloped by a diamond shape. The polygons can also have right-angled corners. These two embodiments of the polygons have proven in practice to be particularly suitable for detecting and distinguishing even small changes between the two tonal values. Due to the diamond shape and the right-angled corners, even the slightest deviations can still be detected visually and the point of intersection of the tone value uniformity on the control mark can thus be reliably detected.

It also proves to be advantageous that a tone scale with numerically specified tone changes is present parallel to the stripes. This tonal scale allows a quantitative assessment of the deviation of the two Tonwertverläufe each other. In practice, the numerically specified tone value changes range from minus 5 to plus 5. This is a sufficiently large area which contains the tone equality at the point of intersection.

In another solution not according to the present invention, a visual inspection device is provided on exposed printing plates for printing presses, in which at least a first elongated strip of the entire Tonwertverlauf is plotted as reference values, that in at least one second strip extending substantially parallel thereto the entire Tonwertverlauf is calibrated and that in at least a third substantially parallel elongated strip, a linearized Tonwertverlauf is applied. In addition to the already from the prior art according to Fig. 1 This comparison of the invention over the entire tonal range from 1 to 100% additionally shows a linearized tonal value curve for known comparisons of uninfluenced and uncalibrated reference values and the exposure with process calibration. Because some plates use linearization of the base exposure during exposure of the plate in prepress, such a check mark also allows for comparison of basic exposure, linearization, and process calibration, with process calibration also including linearization. Parallel to the three tonal gradients, here a tonal scale is plotted, which indicates the tonal values in percent and is spread at both ends. This is necessary because in the peripheral areas, ie at 1 and 100%, the resolution for detecting differences must be greater.

Particularly advantageous embodiments of the invention result from the fact that a pressure plate has several or all control marks according to the invention. In this case, the manufacturing process of printing plates is comprehensively controllable visually by the operator.

The present invention will be described and explained in more detail with reference to several figures.

Fig. 1:

eine Kontrolleinrichtung nach dem Stand der Technik,

Fig. 2:

eine Kontrolleinrichtung mit zusätzlich visualisiertem, linearisiertem Tonwertverlauf,

Fig. 3:

eine Kontrolleinrichtung gemäss der beanspruchten Erfindung zur Beurteilung der Belichtungsenergie und des Chemischen Entwicklungsprozesses bezogen auf einen bestimmten Rastertonwert und

Fig. 4:

eine Kontrolleinrichtung zur Beurteilung der Prozesskalibrierung eines bestimmten Rastertonwertes.

Show it:

Fig. 1:

a control device according to the prior art,

Fig. 2:

a control device with additionally visualized, linearized tone value curve,

3:

a control device according to the claimed invention for assessing the exposure energy and the chemical development process based on a specific raster tone value and

4:

a control device for assessing the process calibration of a particular raster tone value.

In Fig. 1 a conventional control mark 1 is shown, which can be seen after the exposure of a printing plate 5 in the prepress on the same. This control mark 1 is also called a Tonwertkeil and serves to control the process calibration in the prepress stage over the entire Tonwertverlauf of 1 to 100%. The tonal values are shown in gray scale, the upper strip 11 representing the reference tone values unaffected by precursor processes, while the lower strip parallel thereto shows calibrated tonal values 12. In the upper area, a tone scale 10 is also present, which indicates the tone values in percentages. The tone values are given in the range of 10% to 90% in 10% increments, while the values in the range of 1% to 10% and the values in the range of 90% to 100% are drawn apart to the lower there Nevertheless, make differences visually recognizable.

In Fig. 2 a modified control mark 4 is shown, which differs from the control mark 1 in FIG Fig. 1 is distinguished by an additional strip 41 with linearized tonal values. Here, too, the tone scale 10 ranges from 1 to 100%, which not only makes it possible to detect changes which are caused by the process calibration of the preliminary stage in comparison to the reference tone values 11, but also additional changes in the linearized range by comparing linearized tone values 41 and reference tone values 11 can be visually recognized. In the case of some printing plates, since such a linearization is carried out during the exposure, it is necessary in this case to be able to judge these linearized tone values 41 in comparison with the reference values 11, which is the control mark 1 in FIG Fig. 1 not possible.

With the fine-resolution control mark 2 in Fig. 3 It is also possible, quality and consistency in the printing plate production in the precursor even with tight tolerances to judge visually. For this purpose, reference tone values 22 of the original which are uninfluenced by the original are shown in an elongated strip as gray levels, wherein within these non-influenceable reference tone values 22 are geometrically delimited areas of a finely resolved specific raster tone value 23 which cover the unimpeachable reference tone values 22 at these locations. As the inductive reference tone values 22 increase from left to right, the finely resolved particular halftone tone value 23 remains constant. The finely resolved specific raster tone value 23 has a screening of 30 μm × 30 μm. In Fig. 3 For example, the control mark 2 is shown for a 50% raster tone value, with a deviation of plus / minus 5 being shown upwards and downwards, which, with a reference raster of 80 lines / centimeter per stage, is a deviation of about 0.7% from one 50% raster tone value means. By means of the control marking 3, the influence of the exposure energy and the chemical development, ie the total effect of the production process and the consequent deviation of the finely resolved specific halftone tone value 23 from non-influenceable reference tone values 22, can be assessed purely visually and quantitatively within a narrow tolerance range. In the region in which there is no longer any visual difference between a gray level of the unimpeachable reference tone values 22 and the finely resolved specific halftone tone value 23, there is equality of tonal values. Ideally, this field should be at the zero value of the tone scale 21, since in this case an optimal pre-stage manufacturing process is maintained. The black borders of the polygon surfaces in Fig. 3 are not present in practice, they are only for better visibility on the drawing attached. In practice, the contrasts of the gray levels of the control mark 2 on the printing plate 5 are sufficient to be able to distinguish the polygons of the finely resolved specific halftone tone value 23 from the background of the non-influenceable reference tone values 22. The finely resolved particular raster tone values 23 are in Fig. 3 represented as diamond-shaped polygons, these polygons have right-angled steps, which can be sharply defined by the therefore unimpeachable reference tone values 22. By means of this special geometric design of the finely resolved specific raster tone values 23, the visual assessment by the operating personnel is considerably facilitated and even small deviations in the narrow tolerance range are made visible.

In addition, the fine-resolution control mark 2 still has a measuring field 24 for the measurement by means of a densitometer. The measuring field 24 consists of a defined grid area of the 50% tone value and has a circular spot of a 100% full tone 25 inside. The solid surface 25 serves for the density compensation of a densitometer.

With the control mark to check the calibration 3 according to Fig. 4 The differences between uncalibrated tone values 32 and a specific halftone tone value 33 produced by the calibration can be recognized. In Fig. 4 For example, the range is plotted for a 50% blank tone value, with the uncalibrated tone values 32 increasing in an oblong strip from left to right and the determined halftone tone value 33 constantly plotted in a parallel strip. The Tonwertverlauf 32 runs stepped, for example, in 1% steps from left to right increasingly, so that even the smallest differences can be seen. Parallel to the strips 32, 33 runs a tone scale 31 with applied percentages in the range of minus 15 to plus 3%. Here, the intersection point is to be sought in which a gray level of the uncalibrated tone values 32 and the determined halftone tone value 33 are the same. If this point of intersection is at zero (none), there is no difference at the determined raster tone value 33, that is, the determined raster tone value 33 is uncalibrated. Is the point of intersection but z. For example, at minus 7, this means a reduction of 7% downwards, ie in the prepress stage, the specific tone value 33 was reduced from 50% to 43% in the process calibration. If the reduction of 7% was intended and set, the manufacturing process is okay. But if another reduction or even an increase was intended, the manufacturing process must be reviewed.

However, it should be noted that even if the intersection point 6 with the tone value equality is zero, this does not mean that no characteristic curve was used for all raster tone values. In fact, it is also possible to use a characteristic which has no change exactly at the 50% raster value. However, this can be checked by means of the control marks 1 or 4 which show all tonal values from 1 to 100% show. For the important 50% -Rastertonwert but by means of the 50% control mark 3 is a very precise visual control by the printing personnel possible. Before the printing plate 5 is used in a printing press, so incorrectly exposed printing plates 5 can be sorted out before printing and thus unnecessary waste can be avoided. For Fig. 4 It is also true that the black limits of the tonal values 32, 33 are not available for clarification in practice. They are only for better visibility on the drawing attached. In practice, too, the contrasts of the gray levels of the control mark 3 on the printing plate 5 are sufficient to be able to judge the determined halftone tone value 33 with respect to the uncalibrated tone values 32.

LIST OF REFERENCE NUMBERS

1

checkmark

10

tonal scale

11

reference values

12

calibrated tonal values

2

fine-resolution control mark

21

Process deviation scale

22

non-influenceable reference tone values

23

finely resolved specific raster tone value

24

measuring field

25

solid area

3

Control mark for calibration

31

Tone deviation scale in percentages

32

uncalibrated tone scale

33

calibrated certain raster tone value

4

modified control mark

41

linearized tonal values

5

printing plate

6

intersection

Claims (5)

1. A visual control device on an exposed printing plate (5) for a printing press, the visual control device being applied to the printing plate (5) in the form of at least one control marking (1, 2, 3, 4) during exposure of the printing plate (5), characterized in that reference tonal values (22) non-influenceable by the printing process stepwise increase or decrease, respectively, in an elongated strip; a defined halftone value (23) is depicted repeatedly in a high resolution within the same strip; and said defined halftone value (23) is delimited within the same strip (22), respectively, by polygons.
2. The visual control device according to claim 1, characterized in that the polygons are substantially enclosed by a diamond form.
3. The visual control device according to claim 1 or 2, characterized in that the polygons have right-angled corners.
4. The visual control device according to any one of the preceding claims, characterized in that it comprises a process discrepancy scale having numerically specified tonal value changes parallel to said strips (22, 23).
5. The visual control device according to claim 4, characterized in that the numerically specified process discrepancies extend from minus 5 to plus 5.

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