Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41F—PRINTING MACHINES OR PRESSES
  • B41F33/00—Indicating, counting, warning, control or safety devices
  • B41F33/0036—Devices for scanning or checking the printed matter for quality control
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41P—INDEXING SCHEME RELATING TO PRINTING, LINING MACHINES, TYPEWRITERS, AND TO STAMPS
  • B41P2233/00—Arrangements for the operation of printing presses
  • B41P2233/50—Marks on printed material
  • B41P2233/51—Marks on printed material for colour quality control

Definitions

• the invention relates to a method for determining color and / or density values for monitoring and / or regulating the printing process in a printing device according to the preamble of independent claim 1.
• the invention also relates to a printing device designed for the method according to the preamble of the independent claim 27th
• the measured values are recorded directly during the printing process with a measuring arrangement which is located inside the printing device - e.g. a sheetfed offset printing machine or generally a printer.
• a measuring arrangement which is located inside the printing device - e.g. a sheetfed offset printing machine or generally a printer.
• This type of measurement value acquisition or measurement is referred to below as “inline”.
• “external” refers to measurement value acquisition outside the printing device in a stable state of the printed product.
• the ink application is not yet stable.
• the interfering effects during ink application are caused by various parameters of the printing process.
• the appearance of the printed product can be improved by subsequent processing steps, e.g. B. painting of the surface to be changed. Both effects lead to differences between the measured values measured inline and the corresponding measured values determined externally in a stable state of the printed product. Measured values determined inline and externally are therefore not directly comparable.
• the most general object of the invention is the correction of these measurement differences. This object is achieved by the measures listed in the characterizing part of independent claim 1. Further developments and particularly advantageous embodiments of the invention are the subject of the claims dependent on claim 1.
• Another general object of the invention is to provide a printing device in which the method according to the invention can be used. This object is achieved by the design of the printing device stated in the characterizing part of independent claim 27. Further training and Particularly advantageous embodiments of the printing device according to the invention are the subject of the claims dependent on claim 27.
• the above-mentioned correction of the measurement differences is achieved by means of arithmetical corrective measures and preferably in connection with a special design of the measuring arrangement (measuring technology).
• the invention is described below using the example of sheet-fed offset printing. However, the approaches according to the invention are generally applicable and can also be used for other printing processes and devices.
• CIE-compliant color values (XYZ or L * a * b *) are used to separate the color information of the subject from the entrance stage (template, camera , Scanner, monitor) via digital proofing, transferring the prepress to the press
• process standards were defined for efficient conversion of the absolute CIE color values into machine control parameters (eg color separation into the basic colors C, M, Y and K) for offset printing technology is defined in the standard DIN / ISO 12647-2
• the application of a process standard enables a flexible e Processing a print job with various printing machines. However, it requires characterization, adjustment and stable operation of the printing press in accordance with the requirements of the process standard.
• the measurement technology used must be able to output color and density values that conform to the standards for these tasks. This can e.g. can be achieved by a combination of a three-range color measuring device and a densitometer. Ideally, however, a spectrophotometer is used as measurement technology, since it supports both measurement modes and allows flexibility for the selection of the density filter.
• the current status in color measurement technology in the printing area is represented by two types of measurement systems: - portable hand-held measuring devices, such as the spectrophotometer SpectroEye and the densitometer Dl 9 from Gretag-Macbeth AG, and
• These measuring devices and systems are used externally, i.e. outside of the printing press.
• the printer can check individual measuring fields in the print control strip or in the image.
• the printer can manually load a single sheet.
• the complete print control strip (AxisControl) or the entire sheet (ImageControl) is then measured automatically.
• These measuring systems use standardized measuring geometries.
• a finished, finished product in a stable condition serves as a template. The measurement values obtained in this way correspond to CIE-compliant color measurement values and can be used directly for regulating and monitoring or controlling the printing process, for color communication or for display.
• inline measurement technology is significantly more complex than conventional external color measurement technology.
• the inline measurement must be carried out shortly after the paint application.
• the paint layer is not yet stable. It is influenced by various printing process parameters and color properties, which decay with different time constants. Depending on the situation, this can result in large differences between the inline measurement values and corresponding external measurement values on stable, dry samples.
• the process dependency complicates the interpretation of the measurement data. It is not clearly evident whether a measured variation was caused by a change in the paint application or by a change in the process parameters. A similar problem arises if the printed product is still processed after the inline measurement.
• a typical example is the application of a layer of paint in a subsequent coating unit.
• the present invention is concerned in particular with inline measurement in sheet-fed offset printing presses, but is also suitable for other printing processes and devices.
• the invention essentially includes a special design of the measurement technology and measurement geometry as well as correction methods for the inline measurement values, which enable conversion into standardized color and density measurement values for corresponding stable external samples (printed products).
• Inline measuring systems are available for web offset printing presses, e.g. B. the ColorControlSystem (CCS) system from QuadTech. However, these systems are installed at the end of the web offset printing press after the drying systems. At the time of measurement, the print material is already dry and in a stable condition. A process-dependent correction of the measured values is not necessary here.
• CCS ColorControlSystem
• 1 is a schematic representation of an embodiment of the printing device according to the invention
• 2 shows a basic diagram of a spectrally operating measuring arrangement suitable for use in the printing device according to FIG. 1,
• FIG. 4 shows a diagram to explain the measurement geometry of FIG. 3,
• FIG. 5 shows a general block diagram of the method according to the invention
• FIG. 6 shows a block diagram of a special exemplary embodiment of the method according to the invention
• a sheet-fed offset printing machine is designated as a whole by 1.
• the printing press has four (or possibly more) printing units 11-14 and prints sheets which are provided on a so-called feeder 15.
• the sheets are first printed in the first printing unit 11 with a first color, then passed on to the second printing unit 12, until finally they leave the last printing unit 14 with all the colors printed on them.
• a measuring arrangement 20 is provided on the last printing unit 14, which measures the sheets (at their designated measuring points) immediately after printing.
• the printed sheets are then processed further, e.g. a dryer unit and a coating unit 16 and finally output in a so-called boom 17. Except for the measurement during the printing process or immediately thereafter, the printing press is state of the art so that the person skilled in the art does not need any further explanation.
• the inline measuring arrangement 20 comprises, in a manner known per se, one or more measuring heads measuring simultaneously.
• the measuring heads can also be in different
• the measuring heads are preferably arranged in a row at right angles to the printing direction.
• the measuring unit 20 further includes an automated linear movement device perpendicular to the printing direction, so that each
• FIG. 1 also shows a correction computer 40, which receives the measured values recorded by the measuring arrangement and, after the correction, feeds them to a control computer 50, which ultimately controls the printing units 11-14 of the printing press 1 in a manner known per se.
• the correction computer 40 and its functions are discussed further below.
• Fogra research report No. 52.023 contains images showing the state of the ink layer immediately after the ink splitting at the printing nip. These pictures show the formation of threads, the so-called microstripes, between the rubber blanket and the printed sheet. These threads have a diameter of 30 to 60 micrometers and tear off after a certain distance from the printing nip. The result is a layer of paint with a macroscopic surface modulation in relation to the layer thickness, which has not yet subsided at the time of the inline measurement.
• the surface modulation is caused directly by the thread formation of the ink splitting.
• a reduced effect occurs which is caused by the interaction of the fresh color on the printing sheet with the rubber blanket of the last printing unit.
• An emulsion of paint residues and dampening solution is transferred to the ink layer.
• the surface modulations of the color layer influence the measured values. They depend on a variety of printing process parameters, such as printing speed, printing unit, substrate and ink type. In addition, differences between inline and externally determined measured values are also caused by the drying behavior of the paint on the substrate, which has a significantly longer time constant.
• the differences between inline and externally determined measured values must be corrected for the practical use of the measured values.
• the method according to the invention uses a metrological component (special design of the measuring arrangement 20) and computational components for this correction, the latter being carried out in the correction computer 40.
• the aim for the metrological component is to reduce the influence of the process-dependent interference effects as much as possible and to provide measured values that are as clear as possible.
• additional boundary conditions often have to be taken into account for the design of the measuring technology, such as installation space limitations in the printing press or varying measuring distance, which boundary conditions can be taken into account according to a further aspect of the invention by deviations from the standardized 0 45 ° measuring geometry.
• the remaining measured value deviations from externally determined, standardized measurement values are then compensated for by means of numerical correction measures or models in the correction computer 40.
• the arrows in FIG. 1 represent the data flow of the measured values.
• the measured values can be 20 density values, color values or reflectance spectra.
• the data flow between the components is actually bidirectional.
• the measurement data recorded by the measurement arrangement 20 are transmitted in digital form to the correction computer 40. This corrects the measurement data and forwards them to the control computer 50 of the printing press 1.
• the corrected measurement data can be displayed from the control computer 50 for the printer, stored, or used for the color control of the printing press.
• the (corrected) measurement data for the color control are compared with target values 51 in a manner known per se and the settings of the printing units 11-14 are determined therefrom and electronically transmitted to them.
• the correction computer 40 For the conversion of the measured values, the correction computer 40 requires process-specific correction parameters, which are made available in a correction database 41. For the selection of the correction parameters from the database 41, the correction computer 40 requires information 42 about the current printing process. This necessary information 42, for example substrate type, color type and printing unit assignment, is selected or entered by the printer on the control panel (not shown) of the printing press 1 and in practice is transmitted to the correction computer 40 via the control computer 50.
• This necessary information 42 for example substrate type, color type and printing unit assignment, is selected or entered by the printer on the control panel (not shown) of the printing press 1 and in practice is transmitted to the correction computer 40 via the control computer 50.
• the measuring unit 20 consists of a bar in which there are several measuring heads 21 mounted in a row transversely to the paper running direction, the bar being installed at the end of the last printing unit of an offset printing machine.
• the measuring heads themselves are mounted on a motor-driven carriage, which can be moved electronically controlled across the paper running direction within the bar. In this way it is possible to record any measurement location on the paper.
• the measuring arrangement 20 also has, apart from the measuring heads 21, also separate measuring heads for determining the paper and register position.
• the measuring arrangement is connected to a rotary encoder of the printing unit, so that the measuring sequence can be synchronized with the rotary movement of the printing cylinder.
• a typical measuring head 21 is shown schematically in FIG.
• the measurement geometry corresponds to the color measurement standard 0/45 ° according to DIN 5033.
• the illumination from a light source 22 takes place at 0 ° and is imaged into the measurement plane 24 by means of an optical system 23.
• a central flash light source is preferably used as the light source, the light of which is directed to the individual measuring heads with a fiber-optic multiple distributor.
• the measuring light reflected from the measuring point on the printed sheet is recorded at 45 °.
• An optical system 25 images the measurement spot in the measurement plane on an analyzer 26.
• the analyzer 26 is shown as a photodiode array grating spectrometer with a fiber coupling 27.
• the measuring head 21 in this design corresponds to a spectrophotometer.
• the measured values are a reflectance spectrum which corresponds to the spectral reflectance of the sample of typically 400 to 700 nm with a spectral resolution of 10 or 20 nm. Density and three-range color measuring heads use only a subrange of this spectrum.
• the metrological aspects and the correction models for these spectral sub-areas are, however identical to the general case and can be derived directly from the spectral case.
• the inline measurement technology must be able to supply compatible measured values to an external reference.
• the external reference is defined by measured values on stable samples with a standard-compliant spectrophotometer with 0745 ° measuring geometry.
• a stable test means that the effects of color splitting have subsided and that the. Sample is processed.
• the paint layer must be in a defined external state.
• polarization filters 28 and 29 are used for this purpose in the illumination and receiver channel of the measuring head 21.
• the polarization filters consist of linear polarizers and are installed with mutually perpendicular polarization axes in the lighting and receiver channel.
• the use of polarization filters is known per se for density measurement in handheld measuring devices. A description of this technique is contained in the publication "Color and Quality” by Heidelberger Druckmaschinen AG.
• a UV filter 30 is installed in the lighting channel, which suppresses the ultraviolet (UV) portion of the lighting spectrum below 400 nm.
• This UV blocking filter 30 can be implemented, for example, with a GG420 filter glass from Schott.
• the UV blocking filter prevents the fluorescence of the brightener additives in the paper from being excited. This results in better reproducibility of the measurement data from sheet to sheet and especially from job to job for the inline measurement, since the brightener components in the paper can fluctuate.
• the agreement with the external reference values is improved with the UV blocking filter 30, since the external measuring device can use a different illumination source.
• boundary conditions in the printing press can influence the design of the measuring arrangement 20, for example limited installation space in the printing press or unclean paper support in the measuring plane. According to a further important aspect of the invention, these boundary conditions can be taken into account by a measurement geometry that deviates from the standardized 0745 ° measurement geometry.
• FIG. 2 shows that the distance 31 from the lower edge of the measuring head 21 to the measuring plane 24 has a significant influence on the size of the measuring arrangement 20. In the standard geometry, it determines the distance between the lighting and receiver channels at the lower edge of the measuring arrangement. In addition, it can be seen that the receiver and illumination channels shift laterally against each other in the measurement plane (arrow 32) when the measurement distance 31 changes. The mutual shift limits the working range of the measuring optics.
• FIG. 3b An improvement for the installation space and the work area is achieved if the lighting and receiver channels are arranged on the same side from the vertical on the measuring plane.
• This configuration according to the invention is shown in FIG. 3b.
• Fig. 3a shows the standard geometry 0745 °. If the measuring distance changes, the lateral offset between the lighting and the receiver is reduced. The measuring angles no longer correspond to the standard geometry in FIG. 3b. Since every deviation from the standard geometry inevitably also entails measurement value deviations, the new measuring angles must be selected so that the smallest possible deviations for measurement with standard geometry result. Since measurements are carried out using polarization filters, this requirement corresponds to the condition that the path lengths of the light rays in the color layer are identical for the different measurement geometries.
• the corresponding illumination angle and receiver angle in air can be calculated from the angles in the color layer using the known refraction law (H. Haferkorn, Optik, p. 40).
• FIG. 4 The combinations of lighting and receiver angles in air which satisfy equation [1] are shown in FIG. 4 in the form of a diagram.
• the coordinate axes denote the illumination angle and the receiver angle in air, the points on curve 33 each correspond to an angle pair for the measurement geometry.
• Illumination angles greater than 10 ° with the corresponding receiver angles less than 45 ° are particularly expedient and advantageous for inline measurement.
• the measurement geometry according to the invention explained above is also interesting for a measurement technique without a polarization filter.
• the crossed polarization filters cause a large signal loss and cannot be used if, for example, a weak light source has to be used. In this case, too, it is necessary to reduce the reflection component from the modulated surface. According to a further aspect of the invention, this is achieved by tilting the lighting channel in the direction of the receiver channel. It can be seen in FIG. 3b that this increases the angular separation between the directed reflection on the surface and the receiver angle. In this case, the measuring angles should also satisfy equation [1].
• Advantageous measuring geometries are illumination angles in the range of 10 ° to 15 ° and receiver angles in the range of 40 ° to 45 °.
• the aim of all corrective measures i.e. both the metrological and the arithmetic, is to make the inline measured values compatible with corresponding external reference values.
• Reference values are understood to mean those measured values which are obtained with a color measuring device conforming to standards on finished printed sheets outside the printing press.
• three different states are distinguished, which are defined in more detail below.
• State 1 corresponds to the inline measurement in the printing press with measuring arrangement 20. At the time of measurement, the ink layer on the substrate is still wet. In addition, the surface of the ink layer is severely disturbed by the effects of ink splitting on the last printing unit.
• State 2 corresponds to the situation when a sheet is removed from delivery 17 directly after the printing process and a color measurement is carried out on it.
• the paint layer is still wet.
• the effects of color splitting have already subsided.
• the surface of the color layer can be assumed to be smoothly reflective with maximum gloss, there is only a minimal surface effect.
• Condition 3 corresponds to the situation when the color measurement is carried out on a printing sheet with completely dried ink.
• the drying process typically takes several hours. In this state, the color film assumed the microscopic surface roughness of the substrate.
• the color layer remains on the substrate during the drying process, the thickness of the color layer on the substrate is retained.
• part or even all of the color pigments penetrate into the substrate during the drying process. This effect changes the density and color measurements and must be corrected.
• correction models according to the invention described below enable the measurement values to be converted between these three states.
• the conversion is possible in both directions.
• a sequential sequence is advantageously selected in accordance with the invention, that is to say the inline measured values supplied by the measuring arrangement 20 corresponding to state 1 are first transformed into state 2 (external measurement wet) and then these measured values corresponding to state 2 are transformed into Measured values corresponding to state 3 (dry external measurement) are transformed.
• This sequential correction process is shown schematically in FIG. 5.
• the correction of the measured values from state 1 (Block 401) after state 2 (block 402) mainly includes the correction of the effects of color splitting (block 404).
• the correction from state 2 (block 402) to state 3 (block 403) corresponds to the correction of the drying behavior of the ink layer on the special type of substrate (block 405).
• state 2 there is exactly one external reference state (state 2, block 402) into which all inline measurement values (block 401) are transformed. Starting from this state 2, the measurement data are then processed for all applications. The typical applications are display of the measured values (block 406), storage of the measured values as setpoints for the print job (block 407), communication of the setpoints to another printing press (block 406) and use as the current actual value for the color control (block 407).
• the external measuring device For the determination of reference values in states 2 and 3, it makes sense that an external measuring device is used together with the inline measuring arrangement 20.
• the corrected measured values in states 2 and 3 must correspond to the reference values, which correspond to the measurement with a standard-compliant spectrophotometer, color measuring or density measuring device.
• the external reference values are carried out with a measuring device which is equipped with the same measuring filters as in the inline measuring arrangement 20. This means that in the preferred implementation of the method, the external reference values are determined using a measuring device which is equipped with polarization filters and a UV blocking filter.
• the inline measuring arrangement 20 and the external measuring device do not use the same bandwidth, for example spectrophotometers with 10 nm or 20 nm spectral resolution.
• the bandpass correction can be carried out as described in the ISO 13655 standard (ISO 13655 standard, Graphic Technology - Spectral measurement and colorimetric computation for graphic arts images, Annex A, 1996).
• an external measuring device is used together with the inline measuring arrangement 20, which has interchangeable measuring filters in the lighting and receiver channels.
• the measuring device should support the measuring modes without filter, with UV blocking filter and with polarization filters.
• An embodiment of such a measuring device is the SpectroEye spectrophotometer from Gretag-Macbeth AG. This functionality enables the transfer or transmission of measured values from or to other measuring systems that use other measuring filters.
• the external measuring device can measure a printed reference sheet in all measuring modes. The measured values with the corresponding measuring filter can then be passed on to the inline measuring arrangement 20 or to another external system. In particular, this enables the transfer of setpoints for the color control, which were measured with other measuring filters.
• the transformed measured values can be adjusted with a correction model that changes the layer thickness. This transformation can be carried out with the model for the layer thickness modulation, which is described below.
• the starting point for the correction or compensation of the inline measurement errors is the color layer at the time of the inline measurement with a modulated surface.
• the result of the correction must be a compatible measured value for external state 2, which corresponds to a homogeneous layer of paint.
• the necessary correction parameters and lines of freedom as well as their influence are derived from a color model that simulates the metrological behavior of the color layer.
• the color model is based on Hoffmann's theory, which enables a precise physical description of the reflection factor of a single, homogeneous, non-scattering color layer on a diffusely reflective substrate.
• Hoffmann's theory is designed for a diffuse measurement geometry. The adjustment for the reflection factor in the 0/45 ° measurement geometry is described in equation [2]:
• Ro and R 21 are calculated using the Fresnel formulas (H. Haferkorn, Optik, p.50):
• c 0 is a correction function that depends on the relevant printing process parameters.
• the surface effect is preferably eliminated by means of measurement technology, ie by using polarization filters in the measurement arrangement 20.
• the amplitude of the surface effect is influenced by the relevant printing process parameters.
• the correction function Co or the dependence on the printing process parameters is determined experimentally. The general procedure for this is explained below.
• the second component in equation [2] includes the absorption by the printing ink and the multiple reflections at the interfaces of the ink layer.
• the multiple reflections are referred to in the specialist literature as light trapping.
• the modulated surface of the color layer after the color splitting influences the absorption behavior and light trapping.
• the behavior and influence of both effects can be derived as follows.
• the modulation of the surface leads to the thickness of the color layer being smaller at certain points than the corresponding layer thickness without modulation. This effect reduces the average absorption capacity of the color layer.
• the effect can therefore be described in equation [2] by adapting the product of the absorption coefficient ⁇ and the layer thickness d.
• One possibility for implementation is multiplication by a process-dependent correction factor ci, which assumes values less than or equal to 1 as a function of the layer thickness modulation.
• the values after the correction of the layer thickness modulation are described by equation [4]
• ⁇ d c ⁇ d C]. [4] where ⁇ d c is to be substituted for ⁇ d in equation [2].
• C] is a correction function dependent on the relevant printing process parameters and, as will be explained further below, can be determined experimentally with characterization measurements.
• the modulated surface also influences the light trapping of the color layer, since the modulation influences the angle of incidence of the light rays and thus the critical angle for the total reflection on the surface.
• An elegant implementation of this dependency in equation [2] is achieved according to the invention by varying the refractive index of the color layer n 2 in the calculation.
• the surface modulation reduces the mean critical angle for total reflection, which means that more light remains trapped in the color layer. This behavior corresponds to an increase in the refractive index n 2 .
• One possibility for the correction of the light trap is described in equation [5]:
• n 2c is the refractive index after the correction and c 2 is a multiplicative correction function which, like the correction functions c 0 and C ! is process dependent and has to be characterized experimentally.
• the correction of the inline measurement errors can therefore be implemented with three different error types, namely surface effect, layer thickness modulation and light trapping according to equations [2] to [5].
• Kubelka-Munk's theory applies to a diffuse measurement geometry and scattering layers of color. Nevertheless, it can be used for the phenomenological explanation of the effects of the inline measurement errors in the 45/0 ° measurement geometry and their correction.
• the reflection factor of an absorbent color layer on a diffusely scattering substrate can be described with the following equation.
• the first additive component c 0 Ro again corresponds to the surface effect and is identical to equation [2].
• Equation [6] can be easily inverted, ie the absorption spectrum (extinction E) can be determined directly from the reflectance measurement. This relationship is shown in equation [7].
• the correction of the light trap is implemented in the Kubelka-Munk model as a scaling of the diffuse internal reflection coefficient R.
• R 2c R 2 c 2 , [9]
• Co, Ci and c 2 are in turn process parameter-dependent correction functions.
• the application of the algorithm for the correction of inline measurement errors with a color model is shown schematically in FIG. 6.
• the sequence shown corresponds to the correction of a spectral measurement value of the reflectance spectrum.
• the correction of the entire reflectance spectrum is achieved by performing the correction cycle for each reference point in the spectrum.
• the diffuse reflectance p p of the substrate is determined from the measured absolute reflectance value of the substrate (paper white measurement, block 411) (block 413).
• the absorbance spectrum is converted from the measured inline reflectance spectrum in state 1 (block 421) using the inverse KMS model according to equation [7] (block 422) E (block 423) calculated from state 1.
• the correction function c 0 that is valid for the specific print job and for the specific printing process parameters is read from the correction database 41 and applied.
• the next step is to transform the absorbance value according to state 2 (block 425) into the reflectance value from state 2 (block 427).
• the direct KMS model in equation [6] is used for this.
• the light trap correction is performed.
• the internal reflection factor R 2 is multiplied by the corresponding correction function c 2 , which is also read in from the correction database 41.
• the surface effect is set to zero in this transformation.
• the inline measurement values can also be corrected without a color model.
• the correction is advantageously carried out directly on the measured reflectance value R or the corresponding density value D.
• the density value D is calculated from the reflectance value R using the known formula:
• the measured value deviation is considered to be composed of the three error types surface effect, layer thickness modulation and light trap and corrected accordingly.
• the surface effect is added identically to equation (3) as an additive component to the reflection factor R.
• Equation [2] simulated behavior of the correction of the layer thickness modulation acc. Equation [4] and the correction of the light trap acc. Equation [5] is shown in Figures 7a and 7b.
• the diagram of the FIG. 7a shows the behavior of the relative density error Dc / D as a function of the density value D for the two correction types.
• the diagram in FIG. 7b shows the behavior of the relative remission error Rc / R as a function of the reflectance value R for the two correction types.
• FIGS. 7a and 7b also show that the layer thickness modulation error and the light trapping error have different signs and can compensate each other. This behavior can cause numerical instabilities in the correction.
• a threshold value D s is introduced for the correction with and without a color model. For high densities, the layer thickness modulation error is predominant. For low densities, the error caused by light trapping is dominant. The distinction between high and low densities is based on the threshold value, which is preferably selected in the range of approximately 1.0.
• the drying behavior on coated and uncoated papers is also characterized according to the invention with the three types of defects surface effect, layer thickness modulation and light trapping and corrected accordingly.
• the required correction functions co, ci, c 2 are (after their determination) also stored in the correction database 41 and correspond to a second data record in addition to the correction functions for the correction of the inline errors.
• the method according to the invention is again clearly summarized on the basis of a preferred exemplary embodiment.
• the correction computer 40 is connected to the measurement arrangement 20 and receives from it the data of the recorded spectra for each scanned measurement field.
• the control computer 50 transmits to the correction computer 40 the environmental parameters suitable for each measured field, ie machine, process and measuring field parameters. These parameters are in detail: printing speed, number of the printing unit in which the measuring arrangement 20 is located, paper class (for example glossy paper, matt paper, natural paper), color type class (for example process color cyan), measuring field type (for example full tone, screen 70%, gray) and the number of the printing unit in which the measuring field was printed.
• the correction is made on a case-by-case basis, with a single case defining a specific combination of environmental parameters.
• correction database 41 located in the correction computer 40, suitable correction parameters are assigned to each case occurring in practice, which define the already mentioned sets of (parameterized) correction functions c 0 , c ⁇ and c 2 .
• the correction database 41 is implemented as a table in which a correction case is dealt with in each line.
• a single line includes a set of condition parameters (corresponding to the environmental parameters) and a set of correction parameters.
• the correction computer 40 compares the relevant environmental parameters with the condition parameters in the correction database 41 for each measurement.
• the table is processed line by line until a first match is found. In this way, the right case and thus the right correction parameters are found.
• the table is run from top (table start) to bottom (table end).
• the cases are arranged in the table according to the degree of specificity, the table starting with very specific cases and ending with very generic cases. So it is always tried first to make a specific correction. If no cases are defined for this, the correction becomes gradually more generic.
• the correction computer 40 it is decided for each measurement for each individual value of the uncorrected reflectance spectrum whether it is in the absorption, transmission or transition range of the color.
• the remission values of the individual wavelengths are compared with defined threshold values D s (see above).
• Spectral values in the transmission range (D ⁇ D s ) are multiplied by the correction function c 2 (cf. equation [12]), which is defined by the correction parameters in the respective table line.
• Spectral values in the transition range (D ⁇ D s ) are not corrected.
• Spectral values in the absorption range (D> D s ) are logarithmized, multiplied by a density-dependent correction function C ⁇ (see equation [11]) and then delogarithmized again, with the correction function C ⁇ typically being a second-degree polynomial of density and its coefficients are also part of the correction parameters. Since measurements are carried out with polarization filters, there is no surface effect and therefore c 0 can be set to zero. The corrected spectrum is then forwarded to the control computer (50).
• correction database 41 must first be created before the actual inline correction.
• prints with defined fields are produced for all cases of interest (see definition above) and measured both with the inline measuring arrangement 20 and with an external measuring device. Since the correction parameters strongly depend on the layer thickness, prints are made for each case of interest with at least 3 different layer thicknesses and measured. A set of correction parameters is then calculated from the totality of these measurement data for each individual case, this, of course, preferably being computer-aided.
• the spectra of the inline measurements and the externally recorded measurements are offset against one another.
• a defined threshold value is used for each part of the spectrum to determine whether it is in the absorption, transmission or transition range of the color.
• the correction parameters required for these areas are determined, which define the correction functions C ⁇ and c 2 (c 0 is not necessary for the measurement with polarization filters).
• the correction function c 2 is obtained by dividing the spectral values of the transmission ranges of the inline and externally recorded measurements and then averaging them.
• the density-dependent correction function C] selected as the 2nd degree polynomial for the absorption range the density values of the measurements recorded inline and externally are divided by each other. With the density-dependent quotients obtained in this way, the least squares determines the coefficients of the correction polynomial and thus the correction function C ⁇ .
• the correction functions Ci and c 2 or their parameters are then stored in the correction database 41 structured according to cases.
• the method according to the invention also allows the corrected values to be made available only after averaging or another method for compensating fluctuations in the measured values.
• This fluctuation can be due to measurement technology, but in particular also comes from the printing process itself.
• offset printing in particular, it has long been known (for example “offset printing technology”, Helmut Teschner) that the printing process is subject to both systematic and random fluctuations, these fluctuations also being of a very short-term nature, ie in particular from sheet to sheet.
• offset printing technology Helmut Teschner
• the measured values also reflect the short-term fluctuations in the printing process. It is now an advantage of the method according to the invention that the measured values are offset by several Messzeitpun kte, especially the measured values of several consecutive sheets of paper measured in the machine, is possible without great expenditure of time and thus the measured values, which are subject to short-term fluctuations, can be corrected and process parameters can consequently be better estimated. This allows process control in particular to work more precisely.
• the corrected measured values are not only provided directly after a correction of the inline error as described above, but can also be subjected to further computational processing steps.
• One such processing step is, for example, the conversion between different measurement conditions.
• a particularly relevant case in practice is the conversion of measurements with different filters. If, for example, the corrected measured values are initially available as values measured with polarization filters, it may be necessary to compare these values with values measured without polarization filters in order to coordinate them with specifications from the preliminary stage. A computational component for converting polarization filters with Then measured values in values measured without a polarization filter then accomplishes this task.

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• Engineering & Computer Science (AREA)
• Quality & Reliability (AREA)
• Spectrometry And Color Measurement (AREA)
• Inking, Control Or Cleaning Of Printing Machines (AREA)
• Investigating Or Analysing Materials By Optical Means (AREA)
• Color, Gradation (AREA)
• Accessory Devices And Overall Control Thereof (AREA)

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• 2004
  • 2004-05-03 DE DE102004021599A patent/DE102004021599A1/de not_active Withdrawn
• 2005
  • 2005-04-29 WO PCT/EP2005/004608 patent/WO2005108083A1/fr active IP Right Grant
  • 2005-04-29 JP JP2007511973A patent/JP4879885B2/ja active Active
  • 2005-04-29 AT AT05736412T patent/ATE402014T1/de not_active IP Right Cessation
  • 2005-04-29 EP EP05736412A patent/EP1744884B1/fr active Active
  • 2005-04-29 CN CNB2005800142143A patent/CN100567001C/zh active Active
  • 2005-04-29 DE DE502005004811T patent/DE502005004811D1/de active Active
• 2006
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