DE4229267A1 - Method for controlling the printing process on an autotypically operating printing machine, in particular sheet-fed offset printing machine - Google Patents

Abstract

A method for printing process control on a printing press operating by the halftone method, in particular a sheet offset printing machine, in which, for example, measurement zones of the halftone and of the full tone are also printed and these are scanned photoelectrically, after which a conversion of these measurement values into an actual characteristic takes place, is to be improved to the effect that the characteristic achieved in printing can be matched to a given reference characteristic as far as possible over the entire course of the tonal value extent. The measurement values obtained are converted into an actual characteristic, a multiplicity of potentially achievable actual characteristics is calculated therefrom using process-related connections, and, from this group of achievable actual characteristics, the particular one is selected which corresponds to the greatest extent to the given reference characteristic based on a given quality criterion.

Description

The invention relates to a method for controlling the Druckpro zesses on an autotypical working printing machine, in particular Sheetfed offset printing machine, according to the preamble of claim 1.

The production of printed matter on autotypical working Printing presses, especially sheetfed offset presses, is because of that A large number of interdependent influencing variables complex process. When it comes to sheetfed offset printing, quality is affected of the printed product, i.e. on the color appearance of the print sheet, in particular the sizes of ink guide, dampening solution guide, Art of the substrate, type of ink and blanket, temperature, etc. crucial from. Because with autotypical print products not only that Amount of color but above all the geometric separation of colored and non-colored areas for the color appearance rash giving, has been used to control the printing process for a long time a characteristic curve is determined which, for example, shows the relationship between the Area coverage in the film and the optically effective area coverage of Reproduces screen tones in print. Such a characteristic can the tonal value increase of many screen tones in the print determined and on it out of the printing process are influenced so that certain maximum dot gain is not exceeded (e.g. FOGRA). It At this point there are also other ways of representing (Pressure) characteristics called, for example, the course of the tone value take over the area coverage in the film or the subject density in the print compared to the area coverage in the film.  

Automated control loops are particularly useful in sheet-fed offset printing presses for color management, for example from the DE 27 28 738 A1 and EP 0 228 347 B1 are known. Here are photo electrically the remissions of the measurements printed on the printed sheet fields determined and these actual remissions obtained in this way (Color densities, color locations) in connection with specified target draws Conversion of control data for color control. But this is also the use of video technology and image processing been proposed. For example, the measurement fields that are also printed Measuring fields of the full tone but also measuring fields of a certain screen value in question, the latter providing information about that in print Enable dot gain. It is also known to have remissions from im Locating the print image and from it corresponding Generate control commands for the color guide.

A disadvantage of a regulation that only reflects actual remissions used, which were obtained on a full-area measuring field, that only get information about the amount of paint applied can be. Are the actual remissions on measuring fields with a or more halftone tone values won (halftone tone regulation), then wins information about the dot gain is processed, but in practice the screen density only in conjunction with vorege target grid densities for control data for color control. According to the number of halftone measuring fields (with different Coverage), the characteristic curve is therefore only regulated in one or more points. Often it is not possible either Tone value increase, for example, in a 40% screen tone measuring field to correct only changing the color scheme, so that a tone value increase, for example, in an 80% screen tone measuring field is also close to the intended target value.

There is also a regulation for the color control of an auto typical working printing machine has been proposed, in which the dot gain for the individual printing inks are determined and the color scheme is then not primarily changed with the aim of the dot gain for the individual colors  to set predetermined target values, but the aim is to Dot gain for the individual colors in a selected reference to keep hung to each other. This probably results in an equalization in the color appearance of the printed products over the edition considered, but under certain circumstances a considerable deviation from the intended target characteristic is accepted and therefore a not inconsiderable loss in the dynamics of color Lichen appearance of the printed product.

An example of a print control strip with measuring fields of the full and Rastertons is the 6-color CCI print control strip from MAN Roland Druckmaschinen AG. This print control strip has halftone measurement fields of different area coverage (40% and 80%) as well as additional Full tone measuring fields.

The object of the present invention is therefore to implement a method according to to develop the preamble of claim 1 such that the im Pressure achieved actual characteristic curve in the best possible way to a predetermined target Characteristic curve can be brought up.

This task is solved by the characteristic features of the first claim. Further developments of the invention result from the subclaims.

In the method according to the invention, both a densitometric, a spectrophotometric, colorimetric (three-range or spectral measurement method) but also a video recording of the reflectance values of the measuring fields. In the explanation explained below The method according to the invention is used as an example a densitometric remission detection of the measuring fields is described. However, this is not intended to limit the utility of the invention represent. Likewise, no limitation in usability is intended consist in that the embodiment of the method on a Sheet offset machine describes. In principle, it would also be possible instead of extra printed measuring fields (print control strips) Determine remission values of screen tones directly in the image, the  Information about the halftone values of the image areas to be measured e.g. B. from prepress.

The method according to the invention for controlling the Coloring of printed products, which on a sheetfed offset printing machine can be manufactured. In the case of the printed sheets, an additional printing control strips that extend across the format width are also printed, which for each color metering zone (width of a color metering element mentes) a measuring field of the full tone and a halftone measuring field with each 40% and 80% area coverage in the film. The print control strip is measured by an automatic, traversing densitometer and the color density values thus obtained are compared in a Densitometer downstream computing device in the still to be converted to writing sizes.

After the sheetfed offset press for the print to be processed order was put into operation, for example with a setting development according to presetting data for ink and dampening solution management, can after a certain number of printed sheets, a first sample sheet removed and measured densitometrically. In each Color metering zones are therefore three, taking into account the color density value of the substrate even four measured values. From these An algorithm is used to evaluate values middle relationships between pressure-relevant quantities as well as mathematically contains writable parameterized characteristic models that are in print current actual characteristic curve reached is determined.

To determine the current actual characteristic curve but also when calculating The measurement points become the measurement of achievable characteristics (see below) used as support points to create a curve in the ent to describe the characteristic curve. It will be at this Type of interpolation in particular still used, which is typical Curves occur or through which numerical / analytical Approaches such as characteristic curves, for example in the tone value diagram acquisition / coverage film can be shown.  

From an actual characteristic curve obtained in this way and other known ones parameters involved in printing (temperature, substrate type, rubber wipe type, dampening solution management, etc.) is now applied technical laws and empirically derived relations achievable actual characteristic curves are calculated.

From the variety of available actual characteristic curves, the one is determined which best match one (or more) predetermined target characteristic results. This optimal selection is made based on a quality criterion that determines the pressure-relevant distance between the target characteristic and each individual characteristic from the generated Field of possible actual characteristic curves determined and evaluated. The parameters of the optimal characteristic curve found in this way is fed to a controller which causes a change in the machine parameters in question. After checking the effect of this control step by evaluating Another adaption is the described adaptation process repeated if necessary.

In a simple case, a family of curves can be generated be that, in the printable density range around the from the measurements on current drawn curve certain actual characteristic curve, the color density pa parameters of the full tone measuring field in steps of 0.05 density units varies and with the above algorithm the multitude of Actual characteristics is calculated. As a distance measure z. B. the (ge weighted) sum of the squares of deviation or the maximum absolute Deviation between target and actual characteristic curve can be used. Next the characteristic curve with the smallest distance determined in this way are still the two neighboring characteristic curves are added and squared interpolates the minimum. This finally gives the parameters for the controller.

The ver. Flowing into the algorithm for generating characteristic curves driving-related relationships between pressure-relevant Quantities as well as the parameters for the mathematical characteristic model can by analyzing the data generated during the printing process be updated adaptively.  

The selection of the optimal characteristic curve is based on constraints (predetermined ranges for dot gain and / or solid density, different weighting of lights, medium and shadow tones etc.) further restricted if necessary.

From an OK sheet or from standardization instructions Target tone value increases or a target characteristic curve are specified, according to which is to regulate the present process. Under certain circumstances Printer only very general specifications (e.g. "print with maximum Pressure contrast "). Then there is a whole host of target identifiers lines, all within a certain printing range Fluctuation range are optimal and the printer can choose from.

The selection of an achievable characteristic from a variety of calculated characteristic curves can be done in different ways, whereby Two procedures are briefly shown here as examples:

• 1. The selection of an achievable (theoretically calculated) actual Characteristic, which is as close as possible to the specified target characteristic is done only in a field of calculated and achievable actual characteristic curves, which can be achieved by varying a tens of parameters, for example the spot color density were. However, it can also be done as follows:
• 2. From the field of the calculated and attainable actual characteristic curves, which due to the variation of the parameter of the dampening solution guidance (speed of damping duct) was generated achievable actual characteristic curve, which is not that given quality criterion met, but in its course between the color density of paper white and the solid color density results in the greatest possible conformity of form and then this achievable actual characteristic curve by varying one other parameters, for example the solid color density for so long modified until the closest possible match the quality criterion with the specified target characteristic is present.

According to the procedure described under point 1 directly change the color guide in the individual ink metering zones certain amount can be increased or decreased, the color density difference between the actual characteristic curve (measurement) achieved in the print and as close as possible to the specified target characteristic theoretically calculated and achievable actual characteristic curve for change the positions of the ink metering elements is used.

In the procedure described under point 2, both a change change in the zonal color scheme as well as a change in moisture middle management are carried out around those units that are when the actual characteristic curve is arithmetically brought up to the previous one level target curve.

Of course, the method according to the invention can do this be modified that certain color density values or values of Tone value increase according to the print template a weight, for example wise between 0 and 1, and according to this weight the Deviations of the calculated and attainable actual characteristic from the predetermined target characteristic when using the quality criterion be taken into account.

The method according to the invention can directly control the pressure process, for example by using one of the auto matical color density measuring system downstream computer directly corresponding interfaces the change in the color scheme (Control of the ink metering elements), the dampening solution guide (rotation number of dampers) and the other machine parameters.

However, the method according to the invention can also be used in a known one Color density measuring system are used in such a way that the calculated Changes in color, dampening solution, etc. as so-called rule recommendations are displayed and thus it to the printer is left, subject to any modification according to his experience to bring accordingly to the setting.  

However, the method according to the invention can also be carried out in a known color control system in the form of an additional layered Control loop can be applied. For example, the Color control system primarily a control according to the specified full tone color density occur and only when the full tone achieved in the print color densities within a certain tolerance range to the pre given target solid color densities, this is done beforehand described procedure.

Furthermore, the explanation of an embodiment of the inventive method in conjunction with the drawings.

It shows:

Fig. 1 shows the basic components of the inventive method,

Fig. 2-4 different representations of characteristics.

A printed sheet 1 is measured by a measuring device 2 (color density measuring system) ( Fig. 1). On the basis of the measured values of the measuring device 2 , a large number of achievable actual characteristic curves is calculated in a characteristic curve generator 3 from the present actual characteristic curve using empirical and theoretical relationships. The characteristic curve generator 3 is connected to a memory 4 in an active connection, from which the corresponding parameters or relationships can be found as the results of process engineering tests. A setpoint characteristic curve to be achieved in printing is predefined (for example in the form of individual tone value increases) via a setpoint specification 5 , for example in the form of a manual data input device. In a comparator 6 , a characteristic curve is now selected from the family of calculated and attainable actual characteristic curves in accordance with a predetermined quality criterion. The comparator 6 is followed by a controller 7 which , on the basis of the actual characteristic curve which can be achieved, determines the necessary control commands, in particular their size, and forwards them to the controller 8 of the printing press 9 . The corre sponding actuators on the printing press 9 are then controlled by the controller 8 according to the intended settings. According to one embodiment of the invention, the measuring device 2 can also be connected directly to the controller 7 , so that a direct control of the printing machine is optionally also possible due to, for example, full tone color densities or the like. A display 10 is capable of graphically and / or numerically representing both the selection made in comparator 6 with respect to the actual characteristic which can be achieved and the control recommendations of controller 7 . Accordingly, the display 10 is connected downstream of the comparator 6 and / or the controller 7 .

In Figs. 2 through 4, the various types of characteristics are Darge sets, wherein according to Fig. 2, the measurement fields (scanning, full tone) detected color density D is plotted against the abscissa, plotted on the coverage in the film FDF.

Fig. 3 shows the typical type of the representation of a (pressure) characteristic, namely the area coverage in the print FDD over the area coverage in the film FDF.

In FIG. 4, in a representation derived from FIG. 3, the dot gain TZ achieved in print compared to the area coverage in the film FDF is plotted.

In Figs. 2 to 4, the coverage areas percent values 0%, 40%, 80% and 100% are registered in the abscissae respectively. The ordinates in the corresponding characteristic diagrams have either the dimensionally high unit of color density D or a division into percentages.

In each of the diagrams of FIGS. 2 to 4, the characteristic curves marked with (x), (y), (z) are shown, for example the characteristic curve (y) of the measured characteristic curve and the characteristic curves (y) and (z) in each case one corresponds to the theoretical characteristic curve that can be achieved, with a higher color density in case (x) and a lower density in case (z).

Reference list

1 sheet
2 measuring device
3 characteristic curve generator
4 memory
5 Setpoint specification
6 comparators
7 controllers
8 control
9 printing press
10 display
D color density
FDD coverage in print
FDF coverage in the film
TZ dot gain
(x), (y), (z) Characteristic curves with different colors

Claims (6)

1.Procedure for controlling the printing process on an autotypically operating printing machine, in particular sheetfed offset printing machine, in which measuring fields of the halftone tone and in particular the full tone are also printed for each color or are photoelectrically scanned and the reflectance values obtained in this way are converted into a characteristic curve, whereupon the Printing process is influenced in order to adjust the actual characteristic curve achieved in printing to a predetermined target characteristic curve, characterized in that a variety of theoretically achievable actual characteristic curves can be calculated from the actual characteristic curve achieved in printing by varying at least one parameter. that from the family of theoretically achievable actual characteristic curves, the one is selected which, according to a quality criterion, has the greatest possible agreement with the predetermined target characteristic curve and that the printing process is influenced by changing the parameters rd, which generate a theoretically achievable actual characteristic curve which results in the greatest possible agreement with the target characteristic curve according to the quality criterion. 2. The method according to claim 1, characterized, that the measuring fields are densitometric or spectrophotometric measured and these remissions converted into color densities and that from the actual characteristic curve reached in the print under Varying the parameter of spot color density a variety theoretically achievable actual characteristics can be determined.   3. The method according to claim 1 or 2, characterized, that from the actual characteristic curve achieved in the print, varying the Parameters of the dampening solution guidance (speed dampening roller) one Numerous theoretically achievable actual characteristic curves are determined become. 4. The method according to claim 1, 2 or 3, characterized, that the parameter or parameters of the theoretically achievable actual Characteristic curve, which is the largest possible according to a quality criterion Results in agreement with the specified target characteristic, directly for conversion into control commands for the printing press be used. 5. The method according to claim 1, 2 or 3, characterized, that from the parameter or parameters of the theoretically achievable Actual characteristic curve, which according to a predetermined quality criterion greatest possible agreement with the specified target characteristic results in sizes for display in the form of a quality diagnosis be formed. 6. The method according to any one of the preceding claims, characterized, that a comparison determines how large the maxi Male approximation of a selected according to quality criterion is a characteristic curve to a predetermined target characteristic, and that if a specified tolerance range is exceeded by the Value of the achievable approach a corresponding display he follows.