EP0505323A1 - Method of adjusting the screendot sizes of a rotary offset printing machine - Google Patents

Abstract

The invention relates to a method for adjusting the sizes of the matrix dots of a rotary offset printing machine, in which method mean set values, based on technical production conditions, for the sizes of the matrix dots of the printing forme are preset, the printing characteristic lines of the rotary offset printing machine are detected and, in the case of deviations of the printing characteristic lines from set values, compensation measures are initiated; in order to improve the reproduction accuracy, the mean set values of the sizes of the matrix dots for adjusting the individual inking mechanisms of the rotary offset printing machine are varied for each inking mechanism during the production of the printing forme taking into account the deviation trends of the updated printing characteristic lines; as an alternative, or additionally, colour extracts of the original are displayed on the screen of a colour simulation computer; the sizes of the matrix dots of the colour extract representations on the screen are varied within predetermined tolerances and on the basis of read-back printing characteristic line data of previous productions; and the rotary offset printing machine is controlled in accordance with the tolerance sensitivity of the original. <IMAGE>

Description

The invention relates to a method for setting the halftone dot sizes for an offset rotary printing press, in which mean-target values for the halftone dot sizes of the printing form are predefined based on production engineering conditions, the printing characteristics of the offset rotary printing press are recorded, and in the event of deviations of the printing characteristics from nominal Compensation measures.

For many years, attempts have been made to improve and in particular to automate the setting and control of the essential operating parameters, in particular the color setting, of printing presses. Typical examples of the corresponding efforts are given in GB-OS 2 165 801, DE-OS 33 14 333, DE-OS 38 06 100, DE-OS 37 35 785, DE-OS 39 29 085, DD- PS 256 292, DD-PS 256 291, GB-OS 2 064 113, DE-PS 32 04 501, DE-OS 37 30 625 and EP-PS 61 596.

Essentially, measurement and control elements that are independent of the original are used. In order to enable the ink guidance per inking zone of the printing machine to be influenced as precisely as possible, these measuring and control elements are put together in a set for each inking zone and over the printing width to form so-called control strips which are arranged outside the printed image in the "white" edge of the printing sheet . These control strips are scanned either on-line, i.e. directly in the running printing press, or off-line on the printing material, i.e. print samples are checked outside the printing press so that appropriate adjustments can then be made.

However, the use of measurement and control elements independent of the original has the disadvantage that it cannot create a direct reference to the tolerance-sensitive image points of the original. As a result, more control elements are to be used per print page than would actually be necessary, and there are no setpoint-specific target values for these elements either. In addition, the handling of measuring and control elements requires considerable effort for the production of the printing form.

Various suggestions have now been made to remedy these deficiencies in order to determine the quality-determining factors, in particular screen dot size and solid density, without specific control strips directly from the printed image.

EP-OS 0 136 542 is concerned with a method for determining the solid color density and the dot gain on two three-color halftone elements by means of densitometric measurements, calculation formulas and calibration curves. This process is very complex and can only be implemented in practice with extremely great effort.

Furthermore, DE-OS 39 25 011 discloses a method for monitoring the print quality of multicolored printing originals of an offset printing press, in which color separation images of the image segment to be checked are generated in the spectral ranges red, green and blue with the aid of a camera with color-selective sensor fields, and these are generated are processed in an image processing system by means of image analytical methods in such a way that the color layer thickness of the color screen dots of the individual primary colors can be determined by means of a gray value measurement. This method is based on the desired mean color dot density in the measuring segment, but does not take into account the tolerances permitted on the basis of the perception of the human eye.

DE-OS 28 29 341 deals with data acquisition for color control systems, a hand-held densitometer being connected to a color control system. To simplify operation, user guidance is provided by a display device coupled to the densitometer. The hand densitometer can be used to measure on a print sheet in freely selectable image zones that are adapted to the subject; since the measuring points can be located in the image area, the above-mentioned color control strips are unnecessary. However, it is not described how these image zones and their associated target values are determined.

From DE-OS 2 728 738 it is known to draw printed sheets for samples with regard to the quality-determining process parameters, to carry out measurements and to carry out control interventions based on the results found in accordance with the usual techniques of control technology.

Furthermore, US Pat. No. 4,468,692 discloses a method for varying the colors of an image, in which density signals for the colors cyan, magenta, yellow and black, which are taken from an original, are added to the color display. Color signals for cyan, magenta and yellow are converted into color separation density signals for red, green and blue using table memories; then the converted color separation density signals are added individually.

Correction values for printing the colors, which are obtained from a second table memory as a function of the color signals, are then added to the added color separation density signals. A correction value for the black print on the other colors, which is read out from a third table memory, can be added to the signals thus obtained.

Furthermore, DE-OS 33 19 941 shows a method for displaying a color image simulating a multi-color print on a screen, in which data, which are determined for the production of a colored print, are called up from a storage device and added selectively for all print colors, specifically for the production a density signal which, after being processed, controls a color picture tube to display the color picture emulating the multicolor print.

US Pat. No. 4,414,636 shows a color control simulator in which a variation of the different color signals can be carried out with the aid of table memories.

From US Pat. No. 4,843,379 a monitor for the reproduction of color images is known, in which the saturation of the image colors is influenced by means of a predetermined algorithm, while the color tone and the color intensity remain unaffected.

Japanese Patent Application 1-131568, published in Patents Abstract of Japan P-922 August 22, 1989, Vol. 13 / No. 377 shows a print simulator in which signals for the yellow, magenta and black color are digitally processed and stored. The output signals of the memories are switched in such a way that the read signals are each displayed half in horizontal and vertical targets. For this reason, for example, two images from two memories can be displayed simultaneously and compared with one another on the screen of the color monitor.

Furthermore, attempts have already been made to analyze and determine the permissible tolerance depending on the print template. For this purpose, DE-OS 35 43 444 describes a method in which halftone dot sizes, possibly also solid densities, are repeatedly determined on measuring fields printed within the color zones and, if the tolerance ranges assigned to them fall out, corrective intervention in the printing process is carried out by actuating actuators. Each print job is classified into an image contrast class with the help of a catalog of typical test images and color charts. The tolerance to be observed can then be determined based on the classification in this class. The corresponding target values relate to the control elements for full and screen densities, which are standardized regardless of the image. However, this method has the following disadvantages: a test image must first be searched for and found for each print template; if it turns out on the basis of this test pattern that the tolerance range for the intended printing process is too narrow, it becomes difficult to estimate how the print template reacts when the tolerances due to the printing process are "stretched", ie when the limit values of the tolerance range are reached; also taken into account This process does not change the different colored structures of the color separations; and finally it becomes very time-consuming if the artwork has to be classified in terms of different image zone sensitivities.

A further development of this method is described in DE-OS 36 04 222, according to which measuring fields in the form of combination measuring fields are formed in selected color zones; For this purpose, single-color measuring fields of at least two different printing inks are printed one above the other in order to be able to reduce the number of measuring elements per color zone in the control strip. Corrected values for the solid densities and / or screen dot sizes are obtained from the measured values determined in these combination measuring fields. It is not possible to include the permissible tolerance range and to check the effects of fluctuations in the operating parameters in this tolerance range visually.

The invention has for its object to provide a method for adjusting the screen dot sizes for an offset rotary printing press, in which the disadvantages mentioned above do not occur. In particular, a method is to be proposed which enables true-to-life reproduction of even complicated print templates.

According to a first aspect, defined by the features of claim 1, this object is achieved in a method for setting the screen dot sizes for an offset rotary printing press in that the average target values of the screen dot sizes during the production of the printing form and / or during the presetting the offset rotary printing press be adjusted taking into account the deviations of the printing characteristics updated per inking unit.

This aspect of the solution is based on the following considerations: When presetting and controlling the ink / water balance of an offset rotary printing press, systematic deviations from the actual values of the quality-determining operating parameters, in particular the screen dot sizes, can occur. The screen dot size, which makes a decisive contribution to the mapping, has turned out to be a particularly important parameter.

For the appropriate setting of an offset rotary printing press, standards for the newspaper printing process, e.g. according to UGRA 73/11, according to which, for example, a printing form is produced. An essential parameter of this standard is also the dot size.

The printing form is produced in accordance with the usual methods, taking these standards into account, which then gives rise to deviations in the so-called "printing characteristics" for the current printing. These consist of the differences between the process pressure characteristic mean according to the standard and the current print characteristic per inking unit, i.e. statements about the actual printing and the systematic deviations from the standard values that occur, in particular with the tonal value increases.

As long as the current actual mean values for the printing characteristics per inking unit are not known in the work area of the "prepress", the color separations and the page break with the specified characteristic mean values of the newspaper printing process, for example according to UGRA 73/11.

If you query the current average actual values of the screen dot sizes for the individual inking units shortly before the production of the printing form, the deviations between the target values and the actual values of the screen dot size can still be taken into account when producing the printing form. With this procedure, differences in tone value shifting between the individual colors can be restricted before the offset rotary printing press starts up. Of course, it is assumed that the mean color values are within the process tolerance.

In this way, systematic, machine-related deviations between target and actual values for the screen dot size can be detected and compensated, whereby according to a preferred embodiment, the average target values of the screen dot sizes taking into account the expected actual changes during production and the print template-specific dependencies of Inks are adjusted to each other.

According to a second aspect of the invention, which has been reflected in claim 3, color separation images of the artwork are displayed on the screen of a color simulation computer; the halftone dot sizes of the color separation representation on the screen are varied within predetermined tolerances and on the basis of read-back printing characteristic curve data from previous productions; The offset rotary printing press is regulated according to the tolerance sensitivity of the print template.

In this way, random errors that can occur in offset printing due to the numerous sensitive dependencies and variables can be compensated; Because with offset printing, the perfect print image depends on the ink / water balance, which, regardless of the ink type, must always be formed anew for each printing form. Since numerous disruptive factors impair the constancy of this balance and cause random errors, regulation, be it manual or automatic, is always necessary in the case of high quality requirements.

From DE-OS 35 43 444 and DE-OS 36 04 222 it is known that fluctuations in tone values are primarily perceived as color balance deviations in the midtones. It follows that an optimal regulation should not only correct the individual colors independently of one another, but rather should take into account the relationships between the colors. In addition, since the sensations regarding the deviations from tonal value shifts are strongly dependent on the original image, the tolerance for the individual colors and their relationships with one another result in very different requirements depending on the original. In order to quickly implement these requirements in the sense of control processes, a color simulation computer is used according to the invention, on which color separation images of the print template are displayed.

On the screen of this color simulation computer, the image to be analyzed, for example a newspaper page, can be checked for its sensitivity to deviations by using the halftone dot sizes of the color separation representations can be varied within specified tolerances. This imaging is expediently carried out in a manner analogous to that on the offset rotary printing press, namely analogously to the ink zones and, in the alternative, with corresponding input keyboards.

In a first stage of expansion, this process can be carried out purely manually and in principle without coupling to the offset rotary printing press, in particular if the press already has optimal setting values for the start of production, for example due to the first aspect of the solution. At this stage of expansion, the color simulation computer would only serve as a "behavior trainer" for the printer to give it a feeling of how it should behave in the event of random deviations.

For this purpose, both the target template and the test image for the deviations should be shown on the screen, since a comparison between images on paper and on the screen cannot be made with sufficient accuracy and, moreover, lighting technology cannot be carried out properly.

Since the image analysis is carried out on the basis of a relative target / actual comparison, this is not necessarily a disadvantage, especially since the screen comparison allows numerous deviation combination options to be carried out quickly and efficiently.

If, on the other hand, you want to keep target specifications for the direct cross-comparison with the printed copy for the target / actual comparison during printing, this would have to be output on a suitable, high-resolution printer precise cross-comparison is possible under standard lighting conditions.

The correction measures developed in this expansion stage can advantageously be stored with control strategies that operate according to fuzzy logic, such as "fuzzy logic", and used for automatic control of the offset rotary printing press; this results in a significant relief for the printer during the ongoing work on the offset rotary printing press, even with the highest quality standards.

In order to increase the accuracy even further, the printer receives a timely warning during production data acquisition and evaluation via tolerance monitoring when the automatically supported control has reached the limits of its possibilities.

The conversion software of the main simulation computer is used to specify the target values for the screen dot sizes, possibly also for the full-tone density. The conversion software uses the subtractive process colors cyan-blue, magenta-red and yellow alternately in the additive process colors violet-blue, orange- can implement red and green; as a result, the print template can be represented very precisely in the sense of a visual target specification on a high-resolution screen; the image information required for this about the color separations of the three subtractive process colors and black can be obtained from the corresponding film or printing plates with the aid of a scanner or by direct transmission of the image information from a color separation computer.

Another problem can be pressure disorders, which undesirably change the area coverage of the raster image. The associated changes in the screen dot sizes can in principle have two different causes, namely irregularities in the ink flow behavior, which can be influenced to a certain extent via the ink guide actuators of the offset rotary printing press, and so-called "development errors", which affect the print image due to errors in the run-up between paper and affect the impression cylinder. This leads to deformations of the halftone dot and thus also to changes in the halftone dot size. In order to clearly differentiate between these two possible errors, the conventional control measuring strips have special analysis elements that record the so-called pushing and / or doubling of the grid points.

Since no control strips are used in the conventional sense in the solution described here, this analysis option is also eliminated. To record these disturbances, an electronic planimeter can be used, which records the grid points individually and defines them with the help of an image data processing system according to size and shape. By means of a target / actual comparison for the essential quality parameters, namely screen dot size and possibly solid color density and screen dot shape, the possible causes of the malfunction can be separated from one another and countermeasures can thus be initiated.

It has proven to be expedient to use a color simulation simulation tablet for the development of troubleshooting strategies and to provide it with a second row of input keys oriented in accordance with the color control zone. This enables the parallel change of screen dot sizes two process colors or the simulation of the conversion from the target state into a disturbing change and its correction. If these correction options are saved, the system has a ranked list of correction suggestions for typical image disturbances.

In order to determine the metrological target values, the mechanical screen dot sizes can be specified directly on the basis of the printing characteristics on the electronic planimeter, while for the screen dot shape a library with screen-process-dependent patterns may have to be used.

To determine the densitometric and / or spectrophotometric target values, but also as a "hard copy" for the visual target specification, a color printer, e.g. B. working according to the electrophotographic process. Another alternative is the arithmetic specification of these values. The basic setting of this color printer as well as that of the screen can be made parallel to the basic setting of the offset rotary printing press using suitable test forms.

When controlling the densitometric or spectrophotometric measuring devices and / or the electronic planimeter for recording the actual values, the image control zone priority series, which is formed when the target values are specified, is used.

The measures to reduce the discrepancies between target and actual values are based on the priorities for action that are specified when the target values are specified. The invention is explained in more detail below on the basis of exemplary embodiments with reference to the accompanying schematic drawing, the single figure of which gives an overall overview of the individual components of the overall system.

A color separation computer 1, which is generally provided in the reproduction department, separates the originals / originals into the color separations for the four process colors cyan, magenta, yellow and black, which are then to be transferred to the printing forms for the four process colors. The entire page to be printed is then designed with this information and the corresponding text in the page break. The color separation computer 1 is understood here as synonymous with the color separation and page break system.

The page to be printed with the four color separations is fed from the color separation computer 1 via a data line 11 to a color simulation computer 9, which receives further input signals from a color simulation tablet 21, via a data line 16 from a densitometer or spectrophotometer 14, via a data line 19 from an electronic planimeter 18, via a data line 17 from an on-line measuring densitometer or spectrophotometer or / and electronic planimeter 15, via a data line 22 from an AVOR (work preparation) computer 4, and via a data line 10 from a film or plate scanner 2 receives.

The color simulation computer 9 is connected to the printing form production 31 via a data line 30.

In addition, the output signals of the color simulation computer 9 via a data line 20 to a control station 6 of the rotary printing press 8 and via a data line 12 to a monitor 13, which is usually located in the vicinity of the control center 6.

The film or plate scanner 2 is connected via a data line 3 to the AVOR (work preparation) computer 4, which supplies the control center 6 with 5 additional input signals via a data line.

The control station 6, which serves as a rotation control, controls the actuators to be acted upon (not shown) in the individual printing units 8 of the offset rotary printing press via a data line 7.

All the key system elements for the overall system are thus described schematically, and it should also be mentioned that the individual bit-serial individual connections in the data line network can also be replaced by a more universal BUS architecture with any data traffic between the individual participants.

The mode of operation of this system is discussed in more detail below, with the image quality-determining parameters which are decisive for the process control in offset printing being briefly discussed for the time being. These are the ink layer thickness, which is described quantitatively with the so-called solid color density, on the one hand, and the screen dot size, on the other hand, which is quantified as a percentage of the ink layer coverage. In terms of screen dot size, a distinction is made between mechanical, i.e. effective, and optical screen dot size. The optical halftone dot size results from a full tone and halftone density measurement using the so-called Murray / Davis formula, according to which the optical dot size differs from the mechanical dot size by the value of the so-called "light trap", which quantifies an optical light scattering phenomenon. For the purpose described here, this difference is only important insofar as the two percentages must not be confused with one another.

For ink dosing in offset printing, the corresponding ink volume must now be determined from the ink layer thickness and the area coverage of all halftone dots and solid areas within a inking zone. In principle, the principle of so-called normal coloring is used. The contrast function is then maximized for a specific inking unit, a specific color formulation (color batch) and a specific paper. This contrast function is defined as the percentage difference in density of the full tone and screen tone related to the corresponding full tone with 3/4 film surface coverage. The maximum of contrast limits the color or solid density upwards for given materials and printing conditions to the extent that with an additional color layer thickness, the halftone dots, especially in three-quarter tone, tend to go up and thus reduce the proportion of paper white.

According to this principle, the solid density is basically defined for given materials, so that the printing process can theoretically only be controlled on the basis of the detection / monitoring of area coverage and dot size. In practice, however, the relationship between full-tone density and screen dot size is not constant, so that screen-dot size and full-tone density must be monitored in the printing process; however, the solid color density is of less relevance than the dot size.

A decisive attribute of these two quality-determining features are their respective tolerances. Thanks to decades of efforts to standardize offset printing by various national and international institutions, tolerance specifications for full-tone density and screen dot size have been specified for the various areas of application of offset printing. There are two problems with this: firstly, these tolerance specifications for the four process colors are made independently of the print template, and secondly, the opposites must be mastered by the narrowest possible tolerances and the associated economically justifiable effort.

The first problem is known that fluctuations in the screen dot sizes and the ink layer thicknesses are first perceived as disturbances in the color balance, that is, the overprinting of the printing colors in the midtones. In addition, the perceptions of the deviations in the screen dot sizes depend heavily on the original image: Images with strong chromatic colors and large color contrasts reduce the sensitivity of the viewer in this regard, whereas homogeneous gray areas with extremely low-contrast viewing situations significantly increase the sensitivity of the viewer, i.e. even small screen dot size changes still perceived. This results in the requirement to analyze and monitor the systemic tolerances depending on the print template.

Basically, two different inking unit types are now available for ink metering on the offset rotary printing press, namely ink zone-controlled gap inking units and inking zone-free short inking units. These ink types have specific advantages and disadvantages, which are not relevant for the present considerations and therefore do not need to be discussed further. It is essential, however, that the quality management system presented here can be used optimally for both inking types.

In the case of the gap inking unit, which is controlled in accordance with the ink zone, the ink metering in the sense of the normal inking is adjusted on the basis of the printing template using several ink screws in corresponding ink zones and in accordance with the ink requirement of the artwork over the printing width. In addition, with offset printing, the corresponding dampening must then be adjusted on the dampening unit assigned to the inking unit. For setting and regulating the inking on the gap inking unit, actuators must be actuated on both the inking unit and the dampening unit, depending on the print template.

In the case of the short inking unit without ink zones, the ink is metered in the sense of normal inking using a doctored anilox roller, regardless of the artwork. Color guide irregularities within the edition can practically not be influenced here, unless to a certain extent with the help of the variable dampening. The following explanation of the system's functionality points out the differences between zone-oriented and zone-less inking units.

With the help of the color separation computer 1, the originals / originals in the reproduction department are broken down into the color separations for the four process colors cyan, magenta, yellow and black. Depending on the order and the print template, different principles for the color structure can be used, such as "achromatic" or "reduction of undercolors". After that the entire page to be printed is designed with text and images during the so-called page break. Recently, this can be done completely computer-aided, so that the information relevant to printing technology of the pages to be printed is available in digital form and can be passed on via the data line 11. In this sense, the computer 1 is here schematically representative of the color separation computer and electronic typesetting system.

The pages with the four-color separations prepared for printing are then converted into the printing forms (at 31). In the case of an offset printing plate, this can be done for example with the aid of raster films or, according to a more recent development, by direct laser exposure of a light-sensitive plate layer with the raster image information stored in digital form. This raster image information is precisely defined in the reproduction department with regard to screen fineness (lines / cm), screen angulation, screen dot shape and screen dot size. When determining the screen dot size, the reproduction department must also pre-compensate for the dot gain typical for an offset printing process. To do this, it requires the corresponding tolerances from the press room (e.g. optical halftone dot enlargement in the midtone 30 +/- 3%)

As will be described below, the color simulation computer 9 receives the current actual values in the form of printing characteristics from the offset printing press. Systematic errors can be derived from these pressure characteristics, which can be taken into account in the color simulation computer 9 when checking the average target values of the screen dot sizes. The production of the printing form in the device 31 thus takes place with mean setpoints for the screen dot sizes that the Consider deviations of the updated printing characteristics per inking unit of the offset rotary printing press.

The color simulation computer 9 is equipped with conversion software which can convert the subtractive process colors cyan-blue, magenta-red and yellow alternately into the additive process colors violet-blue, orange-red and green; As a result, the print template is reproduced on the high-resolution screen of the color simulation computer 9 in the sense of a visual target specification.

The image information required for this conversion from the color separations of the three subtractive process colors and black can be entered into the color simulation computer 9 using the scanner 2 from the corresponding films or printing plates. Another possibility is the direct transmission of the corresponding image information from the color separation computer 1. The second solution has the advantage that a quality control of the plate copy by comparing the information on the data lines 10 from the scanner 2 and 11 from the color separation computer 1 is possible. In particular, this enables the exact functioning of the plate exposure to be checked.

In order to use an objective quality control in addition to the "subjective" quality control on the screen of the color simulation computer 9 and to be able to precisely monitor the tolerances caused by the printing press, at least one densitometer or spectrophotometer is provided, namely either as an off-line system 14 or as an on -Line system 15; the corresponding signals are fed to the color simulation computer 9 via the data line 16 or 17 as actual values for quality control.

The on-line devices 15 scanning the printed paper on the rotary printing press work much faster and fully automate the quality control loop, but have the disadvantage that they require at least one measuring head and one uniaxial positioning device for each web page to be monitored; in machines for multi-line production, the on-line devices 15 are therefore very complex.

The following explanations are therefore limited to the use of off-line devices 14, which in the simplest version consist of a measuring table and a manually operated measuring device (densitometer or spectrophotometer); a direct measurement point location display with the help of, for example, a light point is highly recommended.

A much more convenient solution for recording the actual value for quality control is to mount the measuring head, which works densimetrically or spectrophotometrically, on an automatically controlled cross slide. The measuring point coordinates required for each image are specified directly by the software of the color simulation computer 9.

In particular when increased demands are made, a further recording device for the actual values of the quality control should be used, namely an electronic planimeter 18; This device can scan the halftone dots of the individual process colors in the finished print and describe their size and shape using appropriate optics. The corresponding information is also fed to the color simulation computer 9 for the target / actual comparison. A particularly noteworthy option that arises with this device is monitoring and, if necessary the correction of the so-called color register or color register. This means the positional accuracy of the color separations printed on top of each other and on the print sheet.

An advantageous embodiment of the devices 14 and 18 also consists in a combination of the corresponding measuring heads on only one cross slide unit.

Based on a deviation sensitivity analysis of the quality-determining features, in particular the screen dot size, from the print template with the aid of the color simulation computer 9, its critical image areas are examined with appropriate color compositions. This then forms the basis for the control and regulation strategy during the printing process. If the quality management system does not yet have the measuring devices 14 and / or 18 in a simple expansion stage, the monitoring is carried out "subjectively" via the target specification on the monitor 13. On the other hand, due to the deviation analysis, targeted setpoints can be used for the measurement technology and automated support either in Print image or specified in a template-specific digital wedge. In special cases, a combined application of these techniques is of course also possible. The digital wedge consists of precisely defined control elements, in particular for the screen dot size and solid density, and can be stored in digital form in a computer system. In film or direct plate exposure, this digital wedge is then also transferred to the printing form. Its elements can be part of the image or can be applied outside the actual print image on the white edge of the image. In the procedure described here can this digital wedge with regard to the composition, design and arrangement of its control elements is optimally adapted to the print template on the one hand and to the ink metering technology on the other hand and transmitted from the color simulation computer 9 to the film or platesetter 31.

A particular problem with quality management is the collective production of double-cut machines. In this type of production, two different printing forms lie one behind the other on the same cylinder, so that the same ink guide actuators act in their corresponding zones on printing forms of originals with different requirements. This problem can be counteracted effectively by examining both templates on the monitor of the color simulation computer 9 for their tolerance sensitivity at the same time and determining optimal target values and control elements accordingly.

• 1. Nach dem Prinzip der erwähnten Normaleinfärbung werden die Druckkennlinien und die Farbwerkgrundeinstellungen ermittelt. Dabei werden die auftretenden Streuungen für die Reproduktionsabteilung ausgemittelt. Die Toleranzbandbreite der Druckkennlinie setzt sich zusammen aus systematisch und zufällig bedingten Abweichungen. Es wird nun grundsätzlich angestrebt, die systematischen Abweichungen durch Nachführen der Maschinengrund- und Voreinstellungen zu reduzieren und die zufälligen Abweichungen nach Möglichkeit im Druckprozeßauszuregeln.
• 2. Die am Farbauszugs-Rechner 1 ermittelten Farbauszüge werden dem Farbsimulations-Rechner 9 übermittelt. Dieser analysiert die Abweichungsempfindlichkeit der Druckvorlage durch gezielte Größenvariation der bildbeschreibenden Qualitätsmerkmale, insbesondere der Rasterpunktgröße. Aufgrund diser Untersuchung werden Kontrollelemente und entsprechende Sollwerte festgelegt. Danach werden die Rasterpunktgrößen und die Anzahl Rasterpunkte über die Drucklänge des Druckzylinderumfanges zu Flächendeckungssummen aufintegriert und diese Daten dann dem AVOR-Rechner 4 eingegeben, der unter anderem die sogenannten Maschinenbelegungsprogramme verwaltet; diese geben Auskunft über die Lage der Druckform in der Offset-Rotationsmaschine, wodurch die Zuordnung der entsprechenden Flächendeckungssumme zu einer spezifischen Einheit der Druckmaschine 9 und dem dazugehörigen Farb- und Feuchtwert möglich werden. Diese Informationen werden über die Datenleitung 5 zur Steuerung der Offset-Rotationsmaschine 8 gegeben, die schematisch nur als Leitstand 6 dargestellt ist. Die Maschinensteuerung rechnet mit Hilfe von Eichkurven die Flächendeckungssummen um. Diese Informatienen werden über die Datenleitung 7 auf die entsprechenden Stellglieder der Offset-Rotationsmaschine 8 gegeben. Nebst den Farbwerken werden hernach auch die Feuchtwerke voreingestellt. Zur Eichkurvenermittlung wird das bereits erwähnte Prinzip der Normaleinfärbung angewendet.
  Beim farbzonenlos arbeitenden Farbwerk wird für die Ermittlung der Kontrollelemente und Soll-Werte grundsätzlich gleich verfahren, hingegen entfällt der Voreinstellvorgang für die Farbschrauben. Hier können lediglich Stellgrößen für die Feuchtwerke übermittelt werden.
• 3. Im Auflagendruck werden nun die Qualitätsmerkmale gemäß den vorstehenden Bildkontrollzonen und/oder Kontrollelementen mit den entsprechenden Sollwerten überwacht. Bei unzulässigen Abweichungen werden entweder automatisch Korrekturen ausgeführt oder entsprechende Vorgaben dem Drucker übermittelt. Dieser veranlaßt sodann die vorgegebenen Korrekturen am Leitstand 6 durch Eingabe entsprechender Soll-Werte für die Stellglieder. Führt die quantifizierte Empfehlung nicht zum Ziel, wird der Drucker diese übersteuern oder aber andere Maßnahmen ergreifen.
• 4. Bei Produktionsende werden die vorgegebenen und effektiven Einstelldaten miteinander verglichen, abgespeichert und periodisch ausgewertet.
  Ergeben sich jetzt Abweichungen der Flächendeckungssummenvorgabe mit den entsprechenden effektiven Einstellwerten an der Rotation und treten bei Folgeproduktionen die gleichen manuellen Korrekturen im Sinne von systematischen Abweichungen am Anfang oder im Verlauf der Produktion auf, so kann die Steuerung dem Drucker eine Empfehlung zur Anpassung der Eichkurve geben oder dies im Sinne eines Selbstlernprogrammes selbst vornehmen, wobei mit zugehörigen Kontrollelementen der Kontrast und die entsprechend optimale Volltondichte überprüft werden muß. Mit dieser Vorgehensweise kann sichergestellt werden, daß die Bandbreite der systematischen Abweichungen sukzessive besser eingegrenzt werden kann.
  Bei den zonenlosen Kurzfarbwerken treten ebenfalls systembedingte Abweichungen auf, und zwar beispielsweie durch andere Farbchargen oder den Rakel- und Rasterwalzen-Verschleiß. Um diese Abweichungen möglichst in ihren Auswirkungen zu beherrschen, empfiehlt es sich, ebenfalls die druckvorlagenabhängige Toleranzanalyse am Farbsimulations-Rechner 9 mit der Festlegung entsprechender Kontrollelemente und Sollwerte durchzuführen. Werden nun die Überwachungsergebnisse nach der Produktion systematisch ausgewertet und verwaltet, zum Beispiel mit dem AVOR-Rechner 4, so können diese Daten sukzessive bei der Bildtoleranzanalyse mitberücksichtigt werden, indem sie über die Datenleitung 22 in den Farbsimulations-Rechner 9 übernommen werden. Werden hierbei jetzt störende Abweichungen festgestellt, die auf diesen Farbwerken kurz vor Produktionsbgeinn nicht mehr korrigiert werden können, so müssen gezielte Rasterpunktgrößenkorrekturen vom Farbimulations-Rechner 9 an den Plattenbelichter 31 weitergeleitet werden. Dies bedingt natürlich einen fortgeschrittenen Qualitätsleitsystemausbau, bei dem die Vorlagenanalyse im Zusammenhang mit den systematischen Farbwerkabweichungen vor der Plattenbelichtung ausgeführt werden kann.
  Zur Verbesserung des Regelungsverhaltens bei farbzonenorientiert arbeitenden Farbwerken zur Verringerung der Bandbreite der zufälligen Abweichungen können am Schluß der Produktion die Veränderungen der Flächendeckungssummenvorgabe und der Einstellwerte abgespeichert und analysiert werden, um daraus Regelungsvorgaben abzuleiten, wie zum Beispiel, daß Rasterpunktgrößenkorrekturen nach oben einfacher zu realisieren sind als nach unten oder/und, daß zweite, dritte und vierte Faben im übereinanderdruck aufgrund des Farbannahmeverhaltens schwieriger einzustellen sind. Diese Regeln können nun im Farbsimulations-Rechner 9 aufgrund der laufenden Produktionsauswertungen zur sukzessiv optimalisierten Automation gebildet und verwaltet werden. Bei den zonenlos arbeitenden Kurzfarbwerken können ebenfalls zufällige Abweichungen auftreten, und zwar beispielsweise bedingt durch das Raumklima und/oder das druckformbeeinflußte Farb/Wasser-Gleichgewicht. Zur Korrektur solcher Einflüsse ist man bei diesen Farbwerken nachteilig eingeschränkt. Immerhin bestehen aber Möglichkeiten, über die Farbtemperierung oder die gezielte Veränderung der Feuchtung gewisse Korrekturen in der Produktion vorzunehmen. Damit können auch bei zonenlosen Kurzfarbwerken mit dem hier beschriebenen Qualitätsleitsystem zweckmäßige Regelstrategien entwickelt werden.
• 5. Die in dem vorstehenden Abschnitt erörterten maschinenorientierten Verstellungsregeln können nun am Farbsimulations-Rechner 9 mit den druckvorlagenabhängigen Soll-Werten und ihren Abhängigkeiten untereinander zu produktionsspezifischen Regelungsstrategien kombiniert werden. Zur Entwicklungserleichterung dieser Regelungsstrategien ist beim Farbsimulations-Rechner 9 das Farbsimulations-Tablett 21 vorgesehen, das beispielsweise die zonenweise Veränderung der Punktgrößen im Farbsimulationsrechner 9 in genau gleicher Weise simuliert wie die Farbschraubenverstellung am Leitstand 6 der Offset-Rotationsmaschine 8. Zweckmäßigerweise wird dieses Simulationstablett mit einer zweiten Reihe von farbstellzonenorientiert arbeitenden Eingabetasten versehen. Dies ermöglicht die parallele Veränderung von Rasterpunktgrößen zweier Verfahrensfarben oder die Simulation des Überführens vom Soll-Zustand in eine störende Veränderung und deren Korrektur auf unterschiedlichen Wegen. Durch Abspeichern dieser Korrekturmöglichkeiten verfügt das System für typische Bildstörungen über eine Rangreihe von Korrekturstrategien.
• 6. Für besonders heikle und wiederkehrende Farbtöne wie Haut-, Möbel- oder gewisse Modefarben kann mit Hilfe des produktionsspezifischen Regelungssystems aus verschiedenen Farbzusammensetzungsvarianten die optimalste in Bezug auf die Wiedergabetreue und Abweichungsstabilität erarbeitet und beim wiederholten Bedarf abgerufen werden.

To further discuss the flow of information and the various possible uses of the quality control system shown here, the individual procedural steps are now summarized schematically below, with special attention to the data feedback for monitoring and self-adaptation of the system.

• 1. The printing characteristics and the inking unit basic settings are determined according to the principle of the normal inking mentioned. The scatter that occurs is averaged out for the reproduction department. The tolerance range of the pressure characteristic curve is made up of systematic and random deviations. The basic aim now is to reduce the systematic deviations by updating the machine basic and default settings and to compensate for the random deviations in the printing process if possible.
• 2. The color separations determined on the color separation computer 1 are transmitted to the color simulation computer 9. This analyzes the sensitivity to deviation of the print original by specifically varying the size of the quality features describing the image, in particular the dot size. Control elements and corresponding target values are determined on the basis of this examination. Then the screen dot sizes and the number of screen dots over the printing length of the printing cylinder circumference are integrated into area coverage amounts and this data is then input to the AVOR computer 4, which among other things manages the so-called machine occupancy programs; these provide information about the position of the printing form in the offset rotary machine, which makes it possible to assign the corresponding area coverage to a specific unit of the printing machine 9 and the associated color and moisture value. This information is provided via the data line 5 for controlling the offset rotary machine 8, which is shown schematically only as a control station 6. The machine control uses the calibration curves to convert the total area of coverage. This information is given via the data line 7 to the corresponding actuators of the offset rotary machine 8. In addition to the inking units, the dampening units are then preset. The principle of normal coloring mentioned above is used to determine the calibration curve.
  In the inking unit that works without ink zones, the procedure for determining the control elements and target values is basically the same, on the other hand, the presetting process for the is omitted Color screws. Only manipulated variables for the dampening units can be transmitted here.
• 3. In the print run, the quality features are now monitored in accordance with the above image control zones and / or control elements with the corresponding target values. In the event of impermissible deviations, corrections are either carried out automatically or corresponding specifications are sent to the printer. This then initiates the predefined corrections at the control center 6 by entering corresponding target values for the actuators. If the quantified recommendation does not lead to the goal, the printer will override it or take other measures.
• 4. At the end of production, the specified and effective setting data are compared with one another, stored and periodically evaluated.
  If there are deviations in the area coverage total specification with the corresponding effective setting values on the rotation and if subsequent productions have the same manual corrections in the sense of systematic deviations at the beginning or in the course of production, the controller can give the printer a recommendation to adjust the calibration curve or do this yourself in the sense of a self-learning program, the contrast and the corresponding optimal solid density must be checked with the associated control elements. This procedure ensures that the range of systematic deviations can gradually be better narrowed down.
  System-related deviations also occur in the zone-less short inking units, for example due to others Ink batches or wear on doctor blades and anilox rollers. In order to control the effects of these deviations as far as possible, it is advisable to also carry out the tolerance analysis dependent on the printing template on the color simulation computer 9 with the definition of corresponding control elements and target values. If the monitoring results are now systematically evaluated and managed after production, for example using the AVOR computer 4, this data can be taken into account successively in the image tolerance analysis by being transferred to the color simulation computer 9 via the data line 22. If disturbing deviations are now found here, which can no longer be corrected on these inking units shortly before production begins, then targeted dot size corrections must be forwarded from the color simulation computer 9 to the platesetter 31. Of course, this requires an advanced quality control system expansion, in which the template analysis can be carried out in connection with the systematic inking unit deviations before the plate exposure.
  In order to improve the control behavior in ink zone-oriented inking units to reduce the range of random deviations, at the end of production, the changes in the area coverage specification and the setting values can be saved and analyzed in order to derive control specifications, such as that screen dot size corrections can be implemented more easily than downwards and / or that the second, third and fourth colors are more difficult to set in the overprint due to the ink acceptance behavior. These rules can now be formed and managed in the color simulation computer 9 on the basis of the ongoing production evaluations for successively optimized automation. Random deviations can also occur in the zone-less short inking units, for example due to the room climate and / or the ink / water balance influenced by the printing form. In order to correct such influences, these inking units are disadvantageously restricted. At least there are possibilities to make certain corrections in the production via the color temperature control or the targeted change of the dampening. Appropriate control strategies can be developed with the quality control system described here, even for zoneless short inking units.
• 5. The machine-oriented adjustment rules discussed in the previous section can now be combined on the color simulation computer 9 with the target values dependent on the template and their interdependencies to form production-specific control strategies. To facilitate the development of these control strategies, the color simulation tablet 21 is provided in the color simulation computer 9, which, for example, simulates the zone-by-zone change of the dot sizes in the color simulation computer 9 in exactly the same way as the color screw adjustment on the control station 6 of the offset rotary machine 8. This simulation tablet is expediently equipped with a the second row of input keys that work in a color-specific zone. This enables the parallel change of halftone dot sizes of two process colors or the simulation of the conversion from the target state into a disturbing change and its correction in different ways. By storing these correction options, the system has a ranked series of correction strategies for typical image disturbances.
• 6. For particularly delicate and recurring colors such as skin, furniture or certain fashion colors can be with the help of Production-specific control system from various color composition variants the most optimal in terms of fidelity and deviation stability can be worked out and called up when required repeatedly.

Claims (11)

Process for setting the screen dot sizes for an offset rotary printing press, in which a) average target values for the halftone dot sizes of the printing form, which are based on technical production conditions, are specified, b) the printing characteristics of the offset rotary printing machine are detected, and c) compensation measures are initiated in the event of deviations in the pressure characteristic curves from target values,
characterized by the following characteristic: d) the mean setpoints of the screen dot sizes are adjusted during the manufacture of the printing form or when presetting the offset rotary printing press, taking into account the deviations of the printing characteristics updated per inking unit of the offset rotary printing press. A method according to claim 1, characterized in that the mean setpoints of the screen dot sizes are adapted to one another, taking into account the expected actual value changes during production and the print template-specific dependencies of the inking units. Process for setting the screen dot sizes for an offset rotary printing press, in which a) average target values for the halftone dot sizes of the printing form, which are based on technical production conditions, are specified, b) the printing characteristics of the offset rotary printing machine are detected, and c) compensation measures are initiated in the event of deviations in the pressure characteristic curves from target values, in particular according to one of claims 1 or 2,
characterized by the following features: d) color separation images of the print template are displayed on the screen of a color simulation computer (9); e) the halftone dot sizes of the color separation representations on the screen are varied within predetermined tolerances and on the basis of read back printing characteristic curve data from previous productions; and f) the offset rotary printing press is regulated in accordance with the tolerance sensitivity of the print template. Method according to one of Claims 1 to 3, characterized in that the automatic control of the offset rotary printing press is carried out using control strategies such as fuzzy logic which operate according to imprecise logic. Method according to one of claims 1 to 4, characterized in that the color separation images are generated by a color separation computer (1). Method according to one of Claims 1 to 4, characterized in that the color separation images are generated by reading in data from the printing original by means of a film or printing form scanner (2). Method according to one of Claims 3 to 6, characterized in that the print template is divided into control zones with different sensitivity to sensitivity by means of targeted variation of the screen dot sizes and possibly the color intensities and corresponding target values for the screen dot sizes are defined for these zones. Method according to one of claims 1 to 7, characterized in that the dot size and optionally the dot shape is determined by means of an electronic planimeter (18) on the printed copy. Method according to one of Claims 1 to 8, characterized in that, for contrast monitoring, the solid color density of the printed specimen is determined by means of a densitometer (14, 15) or a spectrophotometer. Method according to one of Claims 1 to 9, characterized in that the ink screw position and / or the dampening unit setting is regulated in order to regulate the screen dot sizes on the offset rotary printing press. Method according to one of claims 1 to 10, characterized in that before, during and after the completion of a print job, the predetermined setting values for the screen dot sizes and shape and their change for the inking unit calibration and for the control behavior of the offset rotary printing press with the effective setting values saved and periodically evaluated in the sense of a self-learning program.

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