DE102007059842A1 - Method for controlling the coloring in an offset printing machine - Google Patents

Abstract

The invention relates to a method for controlling the color in at least one inking unit of an offset printing machine, namely for controlling the Farbzonestellelemente and preferably a ductor roller and roller or film roll of the respective inking adjustable zonal color scheme, for this print control elements of a printed substrate, the outside of the actual subject on the printed matter are printed, measured using a camera and thereby determined color density actual values are compared with predetermined color density setpoints to produce depending on the comparison between the actual values and the setpoints control signals for the ink zone positioning elements and optionally the ductor roller and the squeegee roller or film roll. According to the invention, color register marks are measured as print control elements for determining the color density actual values.

Description

The The invention relates to a method for controlling the coloring in an offset printing machine according to the preamble of claim 1 or 12 or 17.

At the Printing is a substrate successively through several printing units a printing press moves, wherein in each printing unit in the rule an ink is applied to the substrate. At the autotypical Compression will usually be the four scale colors black, Magenta, cyan and yellow and possibly special colors, being for Each of these inks has a separate printing unit and therefore inking unit is available. The inking unit of each printing unit has one Farbdosiereinrichtung, wherein the Farbdosiereinrichtung one of Number of color zones corresponding number of color zone setting elements includes. The ink zone control elements are also called color slides or colorimeter. Depending on the position of the ink zone setting elements Ink is applied to a ink fountain roller, which is also called a ductor roller is designated, applied. The function of the ink zone setting elements per color zone on the ductor roller applied color amount is from a squeegee roll or a film roll on a downstream Transfer inking roller of the inking unit. The printing ink is over several Ink fountain rollers in the direction of a forme cylinder or plate cylinder of the respective printing unit moves. On the form cylinder of a printing unit rolls at least one serving as inking roller inking roller of the respective inking unit. about the or each inking roller thus receives the ink at least one pressure plate positioned on the forme cylinder. With the form cylinder acts a so-called transfer cylinder or rubber cylinder together, which transfers the ink from the forme cylinder to the substrate.

The color design of a printed product to be printed set in a so-called pre-press. Here are the example for All inks to be printed and thus all involved in printing Inking units of the printing press for each color zone so-called area coverage values established. Dependent on these area coverage values the color zone setting elements are adjusted and thus the zonal Coloring determined.

Out It is already known in the prior art that during the To measure printing on the substrate adjusting color and dependent of which the zonal coloring of the inking units involved in the printing to regulate. These are usually outside of a subject on the Printed material printed measuring ranges, so-called pressure control elements, measured. For each color zone, there are typically more than so-called full-tone fields, Grids or gray balance fields executed print controls present, each having a size of z. B. 2 × 2 mm or 3 × 6 mm or 5 × 5 mm have. The Druckkotrollelemente can be part of continuous pressure control strip. Actual values of the zonal coloring determined here are sent to a Control device of the printing press transmitted, in which the Actual values are compared with setpoints, depending on the Comparison between the actual values and the setpoints and thus dependent on the deviation between the measured actual values and the given Setpoints Control signals for to create the color zone actuators. This is already one automatic control of zonal coloring possible.

Especially in newspaper printing, where there is no trimming of printed copies, be outside of the subject printed on the substrate pressure control elements as disturbing felt. Therefore, it is also already known measuring ranges within of a subject and dependent thereon the zonal coloring to regulate. The measurement of measuring ranges within the subject is but more error prone and thus more inaccurate than the measurement from outside the subject on the substrate printed pressure control elements.

Of these, Based on the present invention, the problem is based a novel method for controlling the color in an offset printing press to accomplish.

To In a first aspect, this problem is solved by a method according to claim 1 solved. hereafter are used as pressure control elements to determine the color density actual values Measure color register marks.

According to the first aspect of the present invention, color density actual values for controlling the zonal coloration are determined by measuring color registration marks, which are usually measured to determine actual values for a color register control, by means of a camera. According to the inventive method of the first aspect of the present invention is therefore dispensed with separate pressure control elements for determining color density actual values. Rather, the color density actual values are detected by measuring the color register marks. The color register marks are typically relatively small, dot-shaped or rectangular print control elements having a size between 0.5 mm and 2 mm. Further, such color register marks are typically not in each Ink zone of the substrate available, but distributed over the substrate at a relatively large distance. Therefore, the presence of such Farbregistermarken perceived as not disturbing even in the newspaper printing, in which no trimming of printed copies.

at Need can additionally fields rasterized to the color register marks of the same size as the Measure color register marks and used for control. Hereby can then additional information about the color reproduction behavior of the printing press can be obtained and thus improving the color fidelity of printing in halftone and mixed colors become.

To In a second aspect, this problem is solved by a method according to claim 12 solved. hereafter is used to compensate for stray light effects in a first step the field of view of the camera flat illuminated, with only such sections in a second step the field of view of the camera are illuminated, within which Measuring ranges for recording the color density actual values are.

To In a third aspect, this problem is solved by a method according to claim 17 solved. hereafter are used to compensate for stray light effects during surveying the measured ranges determined color density actual values using of image data of the measurement ranges and using data on the Camera optics corrected.

The Method according to the second aspect of the present invention and / or the method according to the third aspect of the present invention Invention preferably find in combination with the method the first aspect of the present invention use.

There Color register marks are relatively small pressure control elements it is when determining color density actual values by Measurement of color register marks of importance, stray light effects to compensate. This can be done according to the second aspect and / or after the third aspect of the present invention.

As well but it is also possible the method according to the second aspect of the present invention and / or according to the third aspect of the present invention then to use when determining color density actual values Cutouts or measuring ranges of the actual subjects of the printing material be measured. Also in this case, the determination of color density actual values done more precisely by the compensation of stray light effects.

preferred Further developments of the invention will become apparent from the dependent claims and the following description. An embodiment of the invention is without limitation to be closer to the drawing explained. Showing:

1 : a schematic representation of a flatly illuminated field of view of a camera with measuring ranges for determining color density actual values;

2 : the field of vision of 1 , wherein for metrological compensation of scattered light effects only those portions of the field of view are illuminated, within which the measuring ranges for detecting the color density actual values are; and

3 and 4 : Schematic representations of a field of view of a camera for determining color density actual values using a computational compensation of scattered light effects.

The The present invention relates to a method for controlling the Coloring in at least one inking unit of an offset printing press, namely for Control of by Farbzonenstellelemente the respective inking unit adjustable zonal coloring. For this purpose, measuring ranges of a printed Measured the substrate with the help of a camera and thereby determined Color density actual values compared to predetermined color density setpoints, dependent on from the comparison between the color density actual values and the color density set values Actuating signals for to produce the Farbzonenstellelemente the respective inking unit.

To A first aspect of the present invention is assumed as pressure ranges for determining color density actual values pressure control elements of the substrate outside the actual subjects printed on the substrate, measured become.

there It is according to the first aspect of the present invention according to the invention by color register marks. Accordingly, in the sense of the first aspect of the present invention Color density actual values captured by the fact that color register marks with Help of a camera can be detected metrologically. The color register marks are used thus not only the provision of actual values for color register control but according to the invention also the Providing actual values for controlling zonal coloration. Preferably, the color register marks continue to serve of actual values for the cut register regulation. To additional information for to get the scheme the color register marks are supplemented by rastered fields of the same size.

It is therefore within the meaning of the first aspect of the present here Invention, outside of the subject printed on the substrate color register marks such metrologically detect that the same actual values for color register control and for cutting register control and zonal color control deliver.

hereby may be the number of pressure controls outside of the actual subjects are printed on a substrate on an absolute minimum, so even in newspaper printing, in which no trimming of printed copies takes place, the Pressure control elements are perceived as not disturbing.

There Color register marks typically not in each color zone of one printed substrate are used in the regulation of Zonal coloring so proceeded that for such color zones, within of which lies a color registration mark which, when measuring the color registration mark determined color density actual value for the regulation of the coloring in the respective color zone is used.

For such Color zones, within which no color register mark lies, becomes the corresponding color density actual value using an interpolation between the color density actual values determined by measuring the register marks or by derivation from zonal presetting values of these color zones determined in combination with color density actual values. Possibly can in the process, empirically obtained correction values from previous printing processes considered become. However, such color register marks can also be in each color zone to be available.

As already mentioned, the measurement of color register marks is carried out for metrological purposes Recording of color density actual values with the help of a camera, whereby Preferably, the camera is a CCD camera or CMOS camera is. This can be a colored camera with white illumination of the substrate or a black and white camera be used with colored illumination of the substrate. The Field of view of the camera used captures at least one to be measured Color register mark complete.

at The color register marks are relatively small, punctiform or rectangular pressure control elements, typically a diameter or size between 0.5 mm and 2 mm. When determining color density actual values on such relatively small, dot-shaped pressure control elements There is the problem that the metrologically recorded color density actual values by Stray light effects distorted could be. Therefore, according to an advantageous development of the present here Invention in the measurement of the register marks for determining the Color density actual values carried out a compensation of scattered light effects.

A first possibility for compensation of scattered light effects in the metrological detection of color density actual values at relatively small color register marks will be described below with reference to FIG 1 and 2 described.

1 and 2 each show a field of vision 10 a camera schematized, being in the field of view 10 four punctiform color register marks 11 . 12 . 13 and 14 lie. In a first step (see 1 ) becomes the entire field of vision 10 the camera illuminated areally. Here, the position of the color register marks becomes 11 . 12 . 13 and 14 determined, in which case in a second step (see 2 ) depending on the position of the color register marks 11 . 12 . 13 and 14 only those sections of the field of vision 10 the camera are illuminated, within which the color register marks 11 . 12 . 13 and 14 lie. Accordingly, the first step primarily serves to determine the position of the color register marks, furthermore, measured values of the color register marks determined in the first step can be used as actual values for color register control and / or cut register control. In the second step, measured values of the color register marks are used as actual values for controlling the zonal coloration. The determination of the position of the color register marks in the first step can be carried out using known image processing techniques, e.g. By segmentation and feature extraction, or using cross-correlation techniques.

For flat illumination of the entire field of view of the camera in the first step and for partial illumination of the field of view of the camera in the second step, one and the same source of illumination can be used, which then has to be designed to be switchable over a wide area. In the beam path of such a surface switchable illumination source is at least one switchable element, which either transmits or blocks radiation depending on the switching state or refelcted or reflected at different angles. In the first step, in which the field of vision 10 the camera is illuminated areally, the or each switchable element of the camera is permeable or in employment, in contrast, in the second step, in which the field of view of the camera is illuminated only in those sections in which the Farbregistermarken are, is at least one of switchable elements impermeable or in exhibition. Alternatively, the full-surface illumination of the field of view of the camera in the first step and the selective illumination of the field of view in the second Step also be realized by using different sources of illumination.

The Compensation of scattered light effects when measuring the color register marks to determine the color density actual values can additionally or alternatively also via a mathematical correction, that of image data of the color register marks to be measured and from data about the optics of the camera dependent is. In the mathematical correction of metrologically acquired color density actual values for compensation of stray light effects is preferably an angle-independent correction and an angle-dependent one Correction performed, using them when measuring color register marks corrected color density actual values are corrected.

The correction of metrologically acquired color density actual values using an angle-independent correction factor and an angle-dependent correction factor is based on the finding that in a camera a measuring location 16 and a background 15 through an optic 17 imaged and scattered on the camera.

In the angle-independent case of scattering (see 3 ) is a light beam repeatedly to z. B. a tube 18 the camera scattered and achieved as a constant offset 19 the measuring location on a camera chip of the camera.

In the angle-dependent case (see 4 ) becomes a light beam at the optics 17 scattered and gives a drop in intensity with the scattering angle offset 20 which is largest at an edge of a color register mark to be measured. For round color register marks, an angle-dependent correction factor that depends on the size of the color register mark can be determined.

Of the angle-independent Correction factor and the angle-dependent correction factor then metrologically detected for correction to Farbregistermarken Color density actual values used.

wobei I die Intensität, I₀ die Intensität aus Weißmessung, R die Remission und D die Farbdichte ist.In order to determine the angle-independent correction factor and the angle-dependent correction factor for the mathematical correction of the color register marks metrologically determined color density actual values is proceeded in detail so that a preferably black full-tone field is positioned in the field of view of the camera and covered with a white element in half, on the one hand a Density distribution of the full black solid field and on the other hand, a density distribution of half-covered with the white element solid field is determined. The distribution of the color density can then be determined according to the following formula:

where I is the intensity, I ₀ the intensity of white measurement, R the remission and D the color density.

wobei D_korr der winkelunabhängig korrigierte Farbdichte-Istwert ist, β das Verhältnis der Remissionen (gleich dem Verhältnis der Intensitäten bei gleichem I₀) ist und weit weg von der Kante gebildet wird, wobei I_S die Streuintensität ist, wobei I_R die Referenzintensität des Volltons des unabgedeckten Feldes ist und AR der Anteil der weißen Fläche ist.A ratio of the reflections is then formed far away from the edge formed by covering the solid field with the white element, and an angle-independently corrected color density is calculated from this ratio of reflections by means of the reference intensity of the solid of the uncovered field and by means of the proportion of the white area can: I S = 2 (1-β) I R

wherein D _corr of the angle-independent corrected color density value is the ratio of the remissions β (equal to the ratio of the intensities at the same I _0), and is formed away from the edge, where I _S is the scattering intensity, where I _{R is} the reference intensity of the Solid color of the uncovered field is and AR is the proportion of white plane.

For the angle-dependent correction of the metrologically recorded color density actual values, the edge produced by covering the full-tone field with a white element is examined in more detail, with a curve fit being carried out by means of a least square fit for the color-independent actual values corrected for angle. From this, a normalized correction factor f (x) can be determined and the angle-dependent correction of the metrologically recorded color density actual values can be carried out according to the following formula: f (x) = D ∞ / D (x) D korr2 = D corr (1 + 2 · f (x) - 1) where D _{korr2 is} the angle-dependent corrected color density actual value, f (x) is the normalized correction factor and D _{∞ is} the density far away from the edge. In the corrected density, the radius of the pressure control element is to be used here for x.

The above-described correction of scattered light effects can also be used if sections of the actual subject of the printed printing material are measured as measured objects. In particular, in this case the spatially resolved lighting according to 1 and 2 Use, in which case the subject can be illuminated with white light and converted metrologically detected RGB values into LAB values using a Bradford matrix can be net. Alternatively, it is also possible to record several images sequentially when the subject is illuminated with different wavelengths, wherein the illumination with different wavelengths can be achieved by either assigning different filters to a white light illumination source or by using different colored light sources to illuminate the subject ,

The inventive method preferably find in-line for printing within the printing press of the substrate used. Alternatively, however, it is also possible that the procedures outside used offline to print the substrate become.

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field of vision

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Color register mark

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Color register mark

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Color register mark

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Color register mark

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background

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Measuring location

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optics

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tube

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offset

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offset

Claims (20)

Method for controlling the color scheme in at least one inking unit of an offset printing machine, namely for controlling the zonal coloration which can be set by ink zone setting elements and preferably a fountain roller or film roller of the respective inking unit, with pressure control elements of a printed substrate printed on the substrate outside the actual subject , measured with the aid of a camera and thereby determined color density actual values are compared with predetermined color density setpoints to produce depending on the comparison between the actual values and the setpoints control signals for the ink zone positioning elements and optionally the ductor roller and the vibrating roller or film roller, characterized in that as print control elements to determine the color density actual values Farbregistermarken be measured. Method according to claim 1, characterized in that that the color register marks for color register control and for regulation the zonal coloring can be measured. Method according to claim 2, characterized in that that the color register marks continue to cut register control be measured. Method according to one of claims 1 to 3, characterized that for such color zones within which a color registration mark lies, the color density actual values determined by measuring the color registration mark used to control the zonal coloration of the respective color zone becomes. Method according to claim 4, characterized in that that for such color zones within which there is no color registration mark, dependent on the color density actual values from an interpolation between when measuring the color registration mark determined color density actual values or by derivation from zone presets in combination with color density actual values. Method according to one of claims 1 to 5, characterized that for the compensation of stray light effects in a first step the field of view of the camera flat is illuminated, and that in a second step only such Sections of the field of view of the camera are illuminated within of which color register marks are located. Method according to Claim 6, characterized that in the first step determined measured values of the color register marks as actual values for color register control and / or cut register control be used. Method according to claim 6 or 7, characterized in the second step, measured values of the color register marks be used as actual values for controlling the zonal color scheme. Method according to one of claims 1 to 8, characterized that for the compensation of stray light effects during the measurement using the color register marks, determined color density actual values of image data of color register marks and using data about Optics of the camera are corrected. Method according to claim 9, characterized that in this case an angle independent Correction factor and an angle-dependent correction factor determined using these when measuring color register marks corrected color density actual values are corrected. Method according to one of claims 1 to 10, characterized that in addition Measure equal to the color register marks of the same size and measured values for the regulation and, if necessary, compensation of scattered light effects be used. Method for controlling the coloring in at least one inking unit of a Offsetdruckma namely, for controlling the zonal coloration which can be set by means of ink-zone actuating elements and preferably a fountain roller or film roller of the respective inking unit, measurements of a printed substrate being measured with the aid of a camera and color density actual values determined with predetermined color density desired values being compared from the comparison between the actual values and the desired values, to generate control signals for the ink zone actuating elements and, if appropriate, the ink fountain roller or film roller, characterized in that the field of view of the camera is illuminated in a planar manner in order to compensate for scattered light effects, and in a second step only those portions of the field of view of the camera are illuminated within which measuring ranges for detecting the color density actual values lie. Method according to claim 12, characterized in that that as measuring ranges pressure control elements of a printed substrate, the outside the actual subject printed on the substrate, measured become. Method according to claim 12, characterized in that that as measuring ranges measure sections of the actual subject become. Method according to one of claims 12 to 14, characterized that to the plane and for partial illumination of the field of view of the camera a single, flat switchable illumination source is used. Method according to one of claims 12 to 15, characterized that to the plane and for the partial illumination of the field of view of the camera different Lighting sources are used. Method of controlling the color in at least an inking unit of an offset printing machine, namely for the regulation of Farbzonenstellelemente and preferably a ductor roller and squeegee roller or film roll of the respective inking adjustable zonal coloration, in this case measuring ranges of a printed substrate with the aid of a camera and thereby determined color density actual values with predetermined color density setpoints be compared to dependent from the comparison between the actual values and the setpoints, control signals for the Farbzonenstellelemente and optionally the ductor roller and To produce a fountain roller or film roll, characterized in that to compensate for stray light effects when measuring the measuring ranges determined color density actual values using image data of Measurement ranges and corrected using data on the optics of the camera become. Method according to claim 17, characterized in that that as measuring ranges pressure control elements of a printed substrate, the outside the actual subject printed on the substrate, measured become. Method according to claim 17, characterized in that that as measuring ranges measure sections of the actual subject become. Method according to one of claims 17 to 19, characterized that in this case an angle independent Correction and an angle-dependent correction be determined using those in the survey Corrects the color density actual values determined for the color register marks become.