JP2873266B2 - How to control the printing process - 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

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a method for controlling a printing process in a halftone printing press, which prints and / or actually prints various predetermined proportions of the surface to be printed. A plurality of special measurement areas of the screen tone (screen tone) existing in the image are photoelectrically scanned for each ink in association with the measurement areas of the full gradation (full tone), and from the detected reflection value, An actual value characteristic curve representing a tone value increase is determined and the printing process is controlled by changing at least one parameter for modifying the actual value characteristic curve obtained during printing to a predetermined target characteristic curve. And a method for controlling a printing process.

[0002]

2. Description of the Related Art The production of prints on halftone printing presses, for example sheet-fed offset printing presses, is a complicated operating process due to the large interdependent influence. In sheet-fed offset printing, the quality of the printed matter, i.e. the appearance of the printed sheet in color,
Various factors such as dampening agent supply, type of printing material, type of ink and rubber blanket, and temperature have a decisive effect on the results. In halftone prints, not only the amount of ink but also the geometric dispersion between colored and non-colored areas in particular has a decisive effect on the visual appearance of the ink. The characteristic curve is determined for the above control. This characteristic curve reproduces, for example, the relationship between the surface coverage in the film and the optically active surface coverage of the screen gradation part in the printed matter. According to this kind of characteristic curve, it is possible to detect an increase in the tone value (dot gain) in a plurality of screen tone portions of the printed matter. The printing process is thereby controlled as follows. That is, control is performed so as not to exceed a predetermined maximum gradation value increase (maximum dot gain) (FOGRA-German Academic Association for Printing and Reproduction Technology). Here, means for expressing further (printing) characteristic curves can be cited. For example, there is a trend fluctuation of the gradation value increase of the surface coverage of the film, or the ink density in the printed matter with respect to the surface coverage of the film.

In sheet-fed offset printing presses, automatic control circuits, in particular automatic control circuits for the ink supply, are known, for example, from DE-A-2 287 838 and EP 0 228 347. Here, the reflectance of a control patch (measurement area) printed together on a printing sheet is photoelectrically detected, and the actual reflectance (ink density, ink distribution) obtained by this detection is determined by a predetermined target reflectance. And converted into control data for ink supply. However, for this, the introduction of video technology together with image processing has already been proposed. For example, a measurement area of all gradations or a measurement area of a predetermined screen gradation can be considered as the measurement area printed together. In this case, the screen gradation value is useful for understanding the increase in gradation value obtained during printing. It is also known to detect the reflectance from a certain point in the printed image and to generate a corresponding adjustment command for the ink supply therefrom.

A disadvantage of the control in which only the actual reflectivity (which is obtained in a perfectly planar measuring area) is used is that only information about the amount of ink applied can be obtained. If the actual reflectivity in the measurement area is obtained by one or more screen gradation values, information on the increase of the gradation values is also obtained. It is necessary to process the control data for ink supply simply by linking to the adjusted density. Therefore, the control of the characteristic curve is performed only at one or a plurality of places depending on the number of screen gradation measurement areas (having different surface coverages). Only by changing the ink supply, for example, the increase in the gradation value in the screen gradation measurement area of 40% is corrected, and the increase in the gradation value in the screen gradation measurement area of 80%, for example, is brought close to the vicinity of the predetermined target value. That is often impossible.

[0005] The following control of ink supply in a halftone printing machine has already been proposed. That is, instead of detecting the gradation value increase for each print ink and further changing the gradation value increase for each ink simply to approach each predetermined target value with respect to the ink supply, Controls have also been proposed for changing the tone value increment for each ink to maintain it in a selected relationship. Even if such a control achieves uniformity in the appearance of the colors of the printed matter over the course of the printing process, the risk of a large deviation from a predetermined target value in some cases is assumed. This results in invisible partial losses in the appearance movement of the colors of the printed matter.

An example of a print control patch having a measurement area for all gradations and screen gradations is, for example, a 6-color-CCI-printing control patch of Man Roland Printing Machine Co., Ltd. The print control patch has screen tone measurement areas of different surface coverage (40% and 80%) and an additional full tone measurement area.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to improve a control method of a printing process in a halftone printing press as follows. That is, an improvement is made so that the actual value characteristic curve obtained during printing can be best approximated to a predetermined target characteristic curve.

[0008]

SUMMARY OF THE INVENTION According to the present invention, the above objects are attained by modifying at least one parameter based on a model representing the effect of various printing parameters on the increase in tone value. The characteristic curve that best matches the predetermined target value characteristic curve is selected from the theoretically obtained actual value characteristic curve group, and the characteristic curve that best matches the predetermined target value characteristic curve is calculated. The problem is solved by controlling the printing process via the values of the parameters belonging to the obtained, theoretically modified actual value characteristic curve.

[0009] Advantageous embodiments of the invention are described in the dependent claims.

In the method according to the present invention, the reflectance of the measurement area is detected by a density measurement method, a spectrophotometry method, a color method (three-range measurement method or spectrometry method), a video technology method, or the like. In another embodiment described below, the method according to the invention is described based on the detection of the measurement area reflectivity by means of a density measuring method. However, this does not limit the scope of the present invention. Similarly, the description of an embodiment of the present invention as a method in a sheet-fed offset printing press does not indicate a limitation in the scope of application. It is also possible to detect directly the reflectivity of the screen gradation in the image, instead of the specially printed measurement area (print control patch). In this case, information on the screen tone value of the image location to be measured is received, for example, from a processing area for forming a printing plate from a printed copy.

A method according to the invention for controlling the coloring of the prints produced in a sheet-fed offset printing press is described below. The printing sheets are additionally printed with printing control patches which extend over the width of the plate. This print control patch has one full tone measurement area per ink metering zone (the width of the ink metering component) and each screen tone measurement area with 40% and 80% surface coverage in the film. Have. Print control patches are measured by an automatic, cross-type densitometer. The ink density value obtained based on this is converted into a characteristic amount, for example, a gradation value increase value (dot gain) by a computing device connected downstream to the densitometer.

After the sheet-fed offset printing press has been operated in accordance with a print command to operate with settings in accordance with, for example, pre-set data for ink supply guidance and dampening means guidance, a predetermined number of sheets are printed. After that, the first sample sheet is removed and the ink density value of this sheet is measured. In each ink metering zone, there are a total of three measurements in the colored image area, or a total of four if the density value of the substrate is taken into account. From these values, the current method reached during printing via an algorithm that includes methodically determined relationships between the amount of change related to printing and a parametric characteristic curve model that can be expressed mathematically. An actual value characteristic curve is determined.

For the detection of the actual actual value characteristic curve and for the calculation of the possible characteristic curve, the measuring points are used for: That is, it is used as a support point for curve trend input in the plot of the corresponding characteristic curve. In such an interpolation format, further information such as what type of characteristic curve course can occur, or what kind of mathematical or analytical formula is used to convert such a characteristic curve to, for example, the film surface coverage Information such as whether or not it can be plotted on a graph of gradation value increase is used.

From the actual value characteristic curve obtained in this way and other known parameters involved in printing (temperature, type of printing material, type of rubber blanket, guidance of dampening means, etc.), the method law and A number of achievable actual value characteristic curves are obtained with the aid of empirically obtained relationships.

From the actual value characteristic curves that can be achieved in a wide variety of ways, the actual value characteristic curve that best matches one (or more) predetermined target value characteristic curve is detected. This optimal selection is made based on quality criteria. This quality criterion determines and evaluates the printing-friendly distance between the target value characteristic curve and each individual characteristic curve from the area in which the possible actual value characteristic curves are formed. The parameters of the optimal characteristic curve thus detected are supplied to the controller. This controller causes a change in the machine parameters in question. After the effect of this control step has been checked by evaluation of the separately extracted sheets, the adaptation process is optionally repeated.

In a simple case, the characteristic curve group is formed as follows. That is, in the printable density range related to the actual value characteristic curve detected by the measurement on the sheet extracted at the present time, the ink density parameter of the entire gradation measurement area is set in steps of 0.05 density units. And by calculating a number of actual value characteristic curves according to the algorithm. As an indication of the interval, for example, the sum of the squares of the (weighted) deviations or the maximum absolute deviation between the desired value characteristic curve and the actual value characteristic curve is used. In addition to the characteristic curve having the minimum distance determined by comparing the actual value characteristic curve with the target characteristic curve, two further adjacent characteristic curves are added and interpolated by the least squares method. This ultimately forms the parameters for the controller.

The relationship between the methodically determined printing variables introduced into the algorithm for the characteristic curve formation and the parameters for the arithmetic characteristic curve model is based on the analysis of the data generated during the course of the printing process. Is updated as appropriate.

The selection of the optimum characteristic curve depends on the sub-conditions (increased gradation value and / or predetermined range for all gradation densities, different weighting of light tone, middle tone, shadow tone, etc.) as required. Limited further.

The target gradation value increase or the target characteristic curve is set from a sheet that satisfies the criterion or is set by a normalized command. The current printing process is controlled in accordance with this target gradation value increase or target characteristic curve. In some cases, only very basic instructions (e.g. "printing at maximum printing contrast") are given to the printing press. Thereafter, all the grooves of the target value characteristic curve are formed. All of the target value characteristic curves are optimal within a predetermined range of fluctuation that can occur in the printing technology, and are useful for a printer to select.

The selection of the achievable characteristic curve from the calculated large number of characteristic curves can be performed in different ways. Here, two methods are briefly described as examples.

1 Achievable (which can be theoretically calculated) which is as close as possible to a predetermined target value characteristic curve
The actual-value characteristic curve is only obtained in the region of the actual-value characteristic curve which is calculated and achievable by changing individual parameters, for example, the full-tone color density. However, it can also be performed as follows.

2. From the region of the calculated and achievable actual value characteristic curves resulting from the change of the parameter of the dampening agent supply (number of revolutions of the dampening device), the following achievable actual value characteristic curves are obtained: Ask. That is, an actual value characteristic curve that does not satisfy the predetermined quality criterion but has the most consistent form in the trend fluctuation between the ink density of the blank portion and the ink density of all gradations is obtained. This achievable actual value characteristic curve is then modified by changing another parameter (for example, full gradation ink density) until it best matches the predetermined target value characteristic curve according to the quality criteria.

According to the first method, for example, the ink supply in each of the ink metering zones can be increased or decreased by a predetermined amount. In this case, between the actual value characteristic curve obtained during printing (measured) and the achievable actual value characteristic value which is as close as possible to a predetermined target value characteristic value and which is theoretically calculated. The difference in ink density is used to change the adjustment of the ink metering component.

According to the above two methods, both the change in the ink supply and the change in the dampening agent supply for each area are performed in a unit that causes an arithmetic approximation between the actual value characteristic curve and the predetermined target value characteristic curve. be able to.

Of course, the method according to the invention can also be modified as follows. That is, the predetermined ink density value or gradation value increase value receives, for example, a weighting value between 0 and 1 according to the master copy, and according to the weighting value, calculates the achievable actual value characteristic curve. ,
Modifications can be made so that deviations from the predetermined target value characteristic curve are taken into account using the quality criteria.

The method according to the invention can be used directly for controlling the printing process as follows. That is, for example, a computer connected downstream to the automatic ink density measuring device changes the ink supply (control of the ink metering component) and the dampening means guidance (the number of revolutions of the dampening device) via a corresponding interface. , As well as other machine parameter changes directly.

However, the method according to the present invention can also be used in a known ink density measuring device as follows. That is, the calculated changes in ink supply, dampening means guidance, etc. are displayed as so-called control advice, so that the printer can use the settings accordingly, with appropriate modifications based on their own experience. it can.

The method according to the invention can also be used in known ink control systems in the form of additionally superimposed control circuits. For example, thereby, control according to a predetermined full gradation ink density can be preferentially performed via the ink control system. The above-described means is performed only after all the gradation densities obtained during printing are close to a predetermined target value full gradation ink density within a predetermined allowable deviation frame.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings.

The known sheet is measured by the measuring device 2 (color density measuring device). On the basis of the measured values of the measuring device 2, a large number of achievable actual value characteristic curves are calculated in the characteristic curve generator 3 from the actual value characteristic curves using empirical and theoretical relationships. For this purpose, the characteristic curve generator 3 is operatively connected to the memory 4. Corresponding parameters or relationships can be retrieved from this memory 4 as a result of method engineering trials. Via the target value presetting unit 5 (configured, for example, as a manual data input device), the target value characteristic curve to be obtained during printing is preset (for example, in the form of individual gradation values). The comparator 6 selects one of the calculated achievable actual value characteristic curves according to a predetermined quality standard.
A selection of two characteristic curves is made. A controller 7 is connected downstream of the comparator 6. The controller 7 determines a necessary adjustment command, for example, the characteristic amount, based on the detected achievable actual value characteristic curve, and outputs it to the control unit 8 of the printing press 9. Furthermore, the corresponding adjusting elements of the printing press 9 are activated by the control unit 8 in accordance with preset settings. According to an embodiment of the invention, the measuring device 2 can also be connected directly to the controller 7. This allows direct control of the printing press, for example, on the basis of, for example, full-tone ink densities or the like. The display device 10 can graphically and / or numerically represent the choices made in the comparator 6 with respect to the achievable actual value characteristic curve, as well as the control commands of the controller 7. Correspondingly, the display 10 is connected downstream of the comparator 6 and / or of the controller 7.

FIGS. 2 to 4 show different characteristic curve types. In this case, in FIG. 2, the ink density D (which is plotted on the vertical axis) detected in the measurement area (screen area, all gradation areas) and the surface coverage FDF on the film (this is plotted on the horizontal axis) Is plotted).

FIG. 3 shows a typical type of (printing) characteristic curve. In detail, the relationship between the surface coverage FDF on the film and the surface coverage FDD on the printed matter is shown. FIG. 4 shows the gradation value increase (dot gain) TZ achieved in printing and the surface coverage on the film. The relationship with the FDF is shown.

In FIG. 2 to FIG. 4, each surface coverage is plotted as a percentage (0%, 40%, 80%, 100%) on the horizontal axis. The ordinates in the characteristic curve diagrams of FIGS. 2 to 4 indicate the unit division of the ink density D, which is not particularly defined, the surface coverage FDD in the printed matter, and the gradation value increase (dot gain) TZ achieved in the printing, respectively. Has a percentage value category of

In each of the diagrams of FIGS. 2 to 4, characteristic curves are indicated by reference signs x, y, and z. In this case, for example, the characteristic curve y corresponds to the measured characteristic curve and the characteristic curve x
And z respectively correspond to the theoretically calculated characteristic curves as achievable. Alternatively, it may be assumed that x is a relatively high ink density and z is a relatively low ink density.

[0035]

According to the present invention, the actual value characteristic curve reached during printing can be best approximated to the predetermined target characteristic curve.

[Brief description of the drawings]

FIG. 1 shows the basic components for implementing the method of the invention.

FIG. 2 shows various characteristic curves.

FIG. 3 shows various characteristic curves.

FIG. 4 shows various characteristic curves.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sheet 2 Measurement device 3 Characteristic curve generator 4 Memory 5 Target value presetting unit 6 Comparator 7 Controller 8 Control unit 9 Printing machine 10 Display device D Ink concentration FDD Surface coverage in printed matter FDF Surface coverage in FTZ film TZ floor Tone value increase (dot gain) x, y, z Characteristic curves for various ink supplies

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Johannes Slotta Germany Gernhausen Zingerstraße 12 (72) Inventor Arnim Weichmann Germany Federal Republic Kissing Munchner Strasse 22nd (56) References JP-A-4- 226360 (JP, A) JP-A-4-223168 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B41F 31/02 B41F 33/00 B41M 1/14

Claims (6)

(57) [Claims] 1. A method for controlling a printing process in a printing machine for halftone printing, comprising the steps of:
Ratio both reside in the printed and / or actually printed image, multiple screen tone (screentone)
A special measuring area of number, measurement territory of all gradation (full tone)
Scans photoelectrically for each ink in association with the area, and from the detected reflection values, the actual value characteristic curve representing the increase in the gradation value
A line is determined and the printing process is compared to the actual value characteristic curve obtained during printing.
At least one correction for a predetermined target characteristic curve ;
In a control method of a printing process, which is controlled by changing a parameter, a model representing an influence of various printing parameters on a gradation value increase.
By calculating at least one parameter based on the at least one parameter, a large number of actual value characteristic curves obtained theoretically are calculated. Select the characteristic curve that is correct and theoretically correct it so that it can best match the desired target value characteristic curve
Controlling the printing process via the values of the parameters belonging to the actual value characteristic curve. 2. The method according to claim 1, wherein the measurement area is measured by a density measurement method or a spectrophotometry method, the reflectance obtained by the measurement is converted into an ink density, and a total gradation is obtained from an actual value characteristic curve obtained during printing. Adjusting the ink supply mechanism to adjust the ink density or the ink density
2. The method as claimed in claim 1, further comprising the step of determining a number of actual value characteristic curves which can be theoretically obtained with changes in the parameters of the adjustment . 3. From the actual value characteristic curve obtained during printing,
3. The printing process as claimed in claim 1, wherein a number of actual value characteristic curves which can be obtained theoretically with a change in the parameters of the dampening agent supply rate (damping material supply amount or the number of rotations of the dampening roller) are determined. Control method. 4. A best match a predetermined target value characteristic curve along the quality standards measure one or more parameters of a plurality of <br/> actual characteristic curve which can be obtained theoretically, the printing machine
The method according to any one of claims 1 to 3, wherein the method is directly used for appropriately converting the control command into a control command for the adjustment member . 5. A plurality of theoretically obtainable plural values which best match a predetermined target value characteristic curve according to a predetermined quality standard.
Indeed one or a plurality of parameters, indication of the value characteristic curve of
4. The method according to claim 1, further comprising forming a characteristic quantity for displaying the quality obtained by printing in a quality diagnosis format. 6. A was characteristic curve obtained therefore by selection quality criteria measure whether a maximum degree to which the approximation of the predetermined target value characteristic curve detected by appropriate comparison, predetermined tolerance frame The method according to any one of claims 1 to 5, wherein when the value of the approximation is exceeded , a display indicating this is performed by the obtained similarity value.