Methods for controlling the quality of printed products

Abstract

Method for controlling the quality of printed products (01) produced successively in a specific production run using several printing presses, wherein for each of these printed products (01) at least three printed images (03; 04; 06) are arranged at a distance (A; B; C; D) from each other on a respective surface of a substrate to be printed, wherein these at least three printed images (03; 04; 06) are printed using different printing processes, wherein, for controlling the quality of the respective printed product (01), two printed images (03; 04; 06) printed using different printing processes are selected by an inspection system to form a pair of printed images, wherein the pair of printed images is assigned a distance (A; B; C; D) between its printed images (03; 04;06) is assigned a specified distance dimension, wherein this distance dimension is provided with a tolerance defined depending on the printing processes used in the relevant print image pair before the commencement of the specific production, wherein the quality of the produced print products (01) is checked by means of a processing unit of the inspection system determining, during the specific production, at least for a subset taken from the quantity of all print products (01) produced successively in the specific production, a current value for the respective distance (A; B; C; D) between the print images (01) selected for this print image pair, wherein the processing unit compares the respective currently determined value of the relevant distances (A; B; C; D) with the value for this distance (A; B; C;D) The specified distance dimension is compared taking into account the associated tolerance, and taking into account the associated tolerance, a deviation of the respective currently determined value of the relevant distances (A; B; C; D) from its specified distance dimension is determined.

Description

[0001] The invention relates to a method for controlling the quality of printed products according to claim 1.

[0002] DE 10 2004 019 978 B3 discloses a method for assessing the quality of a printed item produced by a printing press, wherein, within the selected quantity of copies, a defect of a certain type or characteristic detected on one copy is assessed in relation to at least one defect detected on the same or another copy, taking into account a relation between at least one of the detected defect types and one of the characteristics of the detected defect.

[0003] EP 3 539 777 A1 discloses a method for increasing print quality by means of a print position correction of printing units in a printing machine by determining actual and target position values ​​and a difference value characterizing the deviation.

[0004] From DE 10 2004 038 542 A1 it is known that the printed image of a security element can be executed, for example, in screen printing, offset printing, indirect letterpress printing, letterpress printing, digital printing, ink-bearing or blind embossing intaglio printing, whereby combinations of printing processes can also be used.

[0005] It is also known from DE 10 2016 213 111 A1 that several different printing processes are used in the production of banknotes or other securities. For example, steel engraving and / or offset printing and / or screen printing and / or a printing formless printing process, i.e., a digital printing process, e.g., an inkjet printing process and / or a laser printing process, can be used in the production of banknotes.

[0006] The present invention lies primarily in the technical field of the industrial production of printed products, each designed as a security document, in particular as a banknote. The production of such printed products typically involves several different printing processes, which are either carried out in a single, integrated production plant or sequentially in successive production steps using spatially separated, independent printing presses. These printed products usually feature several different printed images, of which, for example, a first image is printed using a steel engraving process, a second image using an offset printing process, and a third image using a screen printing process. Each of these printed images is typically...A complex structure, composed of a multitude of printing elements, formed on a surface of the printed product to be printed. The printed products to be manufactured according to this invention are generally formed on a substrate fed by the production plant or the printing presses involved. In the present invention, the substrate preferably used is a sheet of printed material, wherein this substrate is in particular a material suitable for the production of banknotes and consists, for example, of paper, especially a special paper for security documents, or of a polymer material.

[0007] Such printed products typically have several different security features, such as a foil application, a window thread, a security thread embedded within the substrate, and / or a watermark. These security features are either incorporated into or applied to the substrate either at the paper mill producing the substrate or at the printing plant, using machines other than the printing presses that print the images.

[0008] The geometric arrangement of the printed images printed in several different printing processes on the surface of a printed product, each at a distance from the other, in their respective relationship to each other, and / or the geometric arrangement of one of these printed images to at least one security feature placed in or on the surface of this printed product, and / or the geometric arrangement of one of these printed images to an edge bounding the surface of this printed product, is hereinafter referred to as the print register.

[0009] Before commencing a specific production run, the respective print register for the print images involved in the production of the printed product in question is defined by specifying a spacing dimension with an associated tolerance for each intended geometric arrangement of these print images on the surface to be printed. At least after the production run has been completed, but preferably also during the production run, compliance with the previously defined print register must be checked in order to make a statement regarding the quality of the printed product.

[0010] Quality control of the printed product in question is therefore necessary because many different factors affecting production can negatively influence the desired quality and, in combination, can lead to the production of waste paper, even though the printing quality of the individual images involved in the printed product may be flawless. The present invention therefore does not concern an assessment of, for example,not a color register or registration of a single specific printed image, wherein the assessment of the color register or registration in a single specific printed image would concern the relationship of its printing elements to one another, but rather a method for controlling the quality of printed products successively produced in a specific production, wherein in each of these printed products at least three printed images, each printed in different printing processes, are arranged at a distance from one another on their respective printing surface, wherein the print register of these printed images, which is determined by the geometric arrangement of these printed images defined by the respective specified distance, is preferably checked inline, i.e. in an ongoing printing process.If this check leads to a result indicating that the desired quality of the printed product to be produced is not guaranteed in the current printing process, countermeasures can preferably be taken automatically, e.g. by a control unit or a computing unit, by changing at least one setting of the printing machine in question.

[0011] The quality of printed products can be impaired, for example, by one of the printing processes used. For instance, steel engraving, which can be either a gravure or intaglio printing process, deforms the printed sheet in a very noticeable way. This can have a particularly negative impact on the print register and thus on the quality of the printed products if the sheet in question has been pre-printed using at least one other printing process, such as offset printing and / or screen printing. This deformation caused by steel engraving is only partially predictable. It depends on various parameters, such as the material of the printed sheet, the pressure applied in the steel engraving press, or the printed image itself.Attempts are made to counteract this negative effect by partially pre-distorting the images to be printed in offset printing during a prepress stage prior to production, in order to account for the expected distortion caused by the steel engraving process. However, the results achieved are not always entirely satisfactory. This is because the printing plates used in steel engraving are subject to wear and tear, such as elongation, which can lead to a shift of the printed image, for example, towards an edge or margin of the sheet, and / or to a shift of different printed images relative to each other. Furthermore, several steel engraving plates are usually printed in the same production run on a steel engraving press, for example,Three steel engraving plates are used alternately, which, depending on their mounting in the steel engraving machine in question, can produce at least slightly different print registers.

[0012] To produce the printed products of this type, the various printing processes involved in the production are used sequentially, as mentioned, either in a production plant comprising several printing presses or in spatially separated, independent printing presses. The resulting print register is therefore also crucially dependent on the respective sheet feeder and / or sheet feeder on the printing press executing the respective printing process.

[0013] Furthermore, the print register is also influenced by factors resulting from paper manufacturing, such as deviations from the intended cutting position of a sheet edge or side edge. Printed sheets are typically cut from a web of material, preferably paper, with several sheets arranged side by side across this web, perpendicular to its longitudinal direction. The print register that results later during the printing process can also be influenced by the initial position of the printed sheet within the web, because a sheet cut from the center of the web behaves differently in the subsequent printing process than a sheet previously positioned at one of the web edges. Moreover, the moisture content of the substrate also affects the print register, particularly in the case of paper sheets.

[0014] Due to the aforementioned influences, it is necessary that when setting up the production plant or printing presses, and especially during ongoing production, i.e., during production of the generic printed products, the print register is checked and appropriately set up and / or corrected by assessing a printed image at a sheet edge and / or from printed image to printed image and / or from a printed image to a security feature.

[0015] While it is true that banknote designs are generally conceived in such a way that a certain degree of variation in the production process is not a problem, tolerances are permitted between the individual printing processes involved in the production of these printed products that far exceed the tolerances that, for example, the four printing colors of the CMYK offset printing process exhibit relative to each other. In offset printing, only a few hundredths of a millimeter are typically acceptable for the color register and / or registration, whereas several tenths of a millimeter are not a problem between the individual printing processes involved in the production of these printed products.

[0016] The invention is based on the objective of creating a method for controlling the quality of printed products that are produced successively in a specific production run using several printing machines.

[0017] The problem is solved according to the invention by the features of claim 1. The dependent claims relate to advantageous embodiments and / or further developments of the solution found.

[0018] The advantages achievable with the invention consist in particular in that the informative value of a determined pressure register is improved in order to recognize a trend in the pressure register, especially during the printing process, in the production of the generic printed products, and to be able to understand and counteract longer-term drift effects in the pressure register.

[0019] An embodiment of the invention is shown in the drawings and is described in more detail below.

[0020] They show: Fig. 1 a banknote with several printed images spaced apart from each other; Fig. 2 a representation of results obtained according to the invention on a monitor of a display device.

[0021] Fig. Figure 1 shows, by way of example and only schematically, a printed product 01 in the form of a security document 01, in particular a banknote 01, with printed images 03, 04, and 06 arranged at intervals from one another, wherein these printed images 03, 04, and 06 have each been printed successively using different printing processes. In this example, it is assumed that on a preferably rectangular, and in particular flat, surface 02 of the substrate used for the production of the printed product 01, preferably a sheet, the printed image with reference numeral 03 has been printed using an offset printing process, the several, e.g., three, printed images each with reference numeral 04 have each been printed using a steel engraving process, and the printed image with reference numeral 06 has been printed using a screen printing process. In the design of this printed product 01, the following were incorporated: Fig. 1 Dashed reference lines are defined, indicating the distances A, B, C, D between the printed images 03, 04, 06 to be printed or printed using different printing processes, as determined before production commences. Each of these distances A, B, C, D is assigned a distance dimension and a corresponding permissible tolerance. These distance dimensions, which define a target value for each of the distances A, B, C, D, and their respective permissible tolerances are stored in a preferably digital computing unit, wherein this computing unit is, for example, part of an optoelectronic inspection system, i.e., one comprising a camera. The quality control of printed products 01 is carried out, for example, by…by evaluating the photographic images 03; 04; 06 printed on the substrate, wherein these camera images are created by a camera of the inspection system preferably designed as a semiconductor camera.

[0022] A method for controlling the quality of printed products 01 is proposed, which are produced sequentially in a specific production run using several printing presses. For each of these printed products 01, at least three printed images 03, 04, 06, each printed using different printing processes, are arranged on a respective printing surface 02 of a substrate at a distance A, B, C, D defined for that printed product 01. The inspection system selects two printed images 03, 04, 06, each printed using a different printing process, to form a pair of printed images. The inspection system then assigns each pair of printed images a defined spacing dimension, e.g., for the respective distance A, B, C, D between the selected printed images.The respective distance dimension is assigned a tolerance in the inspection system before the start of the specific production run. This tolerance is determined based on the printing process used in the respective print image pair. The permissible tolerances can range, for example, from 0.3 mm to 3 mm.

[0023] The quality of the produced printed products 01 is now controlled by determining, preferably inline during ongoing production, a value for the respective distance A, B, C, D between the selected printed images 03, 04, 06 for each of the same printed image pairs in at least a subset of all printed products 01 produced consecutively in the production run, using a processing unit of the inspection system. The processing unit then compares the currently determined value of the relevant distance A, B, C, D with the defined distance dimension for this distance A, B, C, D, taking into account the associated tolerance, and determines any deviation of the currently determined value of the relevant distance A, B, C, D from its defined distance dimension, also taking into account the associated tolerance.In the event that the processing unit detects an intolerable deviation of the currently determined value of the relevant distance A; B; C; D from its defined distance dimension, the relevant printed product 01 is, for example, removed from the ongoing production process and / or a setting of the relevant printing press that affects the ongoing production process is preferably changed automatically, for example, by the processing unit, or at least such a change is initiated, so that subsequently printed products 01 produced by this printing press again meet the desired quality.

[0024] It may be provided that the inspection system generates several pairs of printed images for each printed product 01 to be checked for quality, wherein the respective distance dimension of at least two of these printed image pairs is assigned a tolerance by the inspection system before the start of the specific production, wherein the tolerances of printed image pairs that differ in at least one printing process are set differently, and wherein the processing unit of the inspection system determines a deviation of the respective currently determined value of the relevant distances A; B; C; D from the respective set distance dimension for each of the generated printed image pairs.

[0025] As mentioned, the printing processes used to print the images 03, 04, 06 involved in the production of each printed product 01 are steel engraving, offset printing, and screen printing. A steel engraving press is used for steel engraving, an offset printing press for offset printing, and a screen printing press for screen printing. The printed products 01 can be produced in a single pass in a production plant comprising several printing presses, or in successive production steps using spatially separated, independent printing presses.

[0026] In a preferred embodiment of the invention, the processing unit of the inspection system determines the current value for the respective distance A, B, C, D between the respective printed images 03, 04, 06 of the relevant subset consisting of several, e.g., 50 to 200 printed products 01 from the quantity of all printed products 01 produced successively in the specific production run, for at least one identical pair of printed images belonging to several of these printed products 01, wherein the processing unit calculates an average value from these currently determined values ​​for the distances A, B, C, D, and, taking into account the associated tolerance, determines a deviation of the calculated average value from its distance dimension defined for this distance A, B, C, D.

[0027] In a particularly advantageous embodiment of the invention, the processing unit of the inspection system determines, for each subset of several subsets, from the quantity of all printed products 01 produced successively in the specified production run, a current value for the respective distance A; B; C; D between the respective printed images 03; 04; 06 for at least one identical pair of printed images contained in the respective subsets. From these currently determined values ​​for the distances A; B; C; D, the processing unit calculates a first mean value for each subset. From these first mean values, the processing unit calculates a second mean value. Taking into account the associated tolerance, the processing unit determines a deviation of the calculated second mean value from its defined distance dimension for this distance A; B; C; D.

[0028] In both of the aforementioned embodiments of the invention, the processing unit advantageously checks the plausibility of a currently determined value of the respective distance A, B, C, D before calculating the respective average and excludes it from the average calculation if it is not plausible. Alternatively or additionally, the processing unit can also eliminate currently determined extreme values, i.e., at least one currently determined minimum value and / or at least one currently determined maximum value, in the respective subset for the respective distance A, B, C, D between the respective print images 03, 04, 06 before calculating the respective average. Furthermore, the processing unit can also calculate a standard deviation from the respective average value.

[0029] Printed products 01, designed as security documents 01 or banknotes 01, are often produced in a single sheet, so that the printed products 01 are arranged in several rows and columns on the sheet. The averaging methods described above are preferably applied to those printed products 01 that are located at the corners of the sheet, since these positions are where the greatest deviations of the currently determined value of the relevant distance A, B, C, D from the specified distance, taking into account the associated tolerance, are to be expected. This is because the aforementioned disturbances are most noticeable at these points.From the deviations of printed products 01, which are each located at the corner positions of a printed sheet, the computing unit can also calculate an elongation of the at least one printing form used in one of the printing processes, in particular an elongation of the at least one steel engraving plate carrying out the steel engraving process.

[0030] In a further important embodiment of the invention, several, e.g., three, steel engraving plates are used alternately in the steel engraving printing machine for the execution of the steel engraving printing process in the same production run, wherein, for at least two of the steel engraving plates involved in the execution of the steel engraving printing process or for all steel engraving plates involved in the execution of the steel engraving printing process, the deviation of the respective currently determined value of the relevant distances A; B; C; D from its defined distance dimension, or the deviation of the determined mean value from its defined distance dimension for this distance A; B; C; D, or the deviation of the determined second mean value from its defined distance dimension for this distance A; B; C; D, is selectively determined by the calculating unit.The calculation unit therefore determines the respective deviation and / or the respective first and / or second mean value separately for each relevant steel engraving plate.

[0031] The determined deviation of the respective currently determined value of the relevant distances A; B; C; D from its defined distance dimension and / or the determined deviation of the determined mean value from its defined distance dimension for this distance A; B; C; D and / or the determined deviation of the determined second mean value from its defined distance dimension for this distance A; B; C; D are, for example, controlled by the computing unit of the inspection system, preferably displayed on a monitor 07 of a display device.

[0032] Fig. Figure 2 shows an example of a display of results obtained according to the invention on the monitor of the display device. On the monitor 07, a Cartesian coordinate system, for example, is displayed, in which, with reference to the origin of this coordinate system, the respective deviations of the currently determined values ​​of at least one of the relevant distances A, B, C, D from the corresponding defined distance measure, as determined by the processing unit, and / or the determined deviations of the determined mean value from its defined distance measure for this distance A, B, C, D, and / or the determined deviation of the determined second mean value from its defined distance measure for this distance A, B, C, D are displayed.

[0033] Specifically, it shows Fig. 2. By way of example, the respective deviations determined by the processing unit of the currently determined values ​​of three distances A, B, and C between a printed image 03 printed using an offset printing process and a printed image 04 printed using a steel engraving process from the respective defined distance dimension. These three distances A, B, and C result, for example, from the use of three steel engraving plates P1, P2, and P3 alternately used in the same production run, e.g., on the circumference of the same printing cylinder. As mentioned previously, generic printed products 01 are often produced in a single unit on a printing sheet. The representation of the Fig. 2 relates, for example, to a printed product 01, which is positioned in a corner position on the relevant printing sheet. In the illustration of the Fig.Values ​​generated by the first steel engraving plate P1 are represented, for example, by a square; values ​​generated by the second steel engraving plate P2 by a diamond; and values ​​generated by the third steel engraving plate P3 by a triangle. In the immediate vicinity of the origin of the coordinate system, the permissible tolerance for the respective distance dimension is shown. This representation indicates a tolerance range which, in this example, extends from the coordinate value -0.5 to the coordinate value +0.5 on both the abscissa and the ordinate of the displayed coordinate system, thus indicating a permissible tolerance of ±0.5 mm for the respective distance dimension. Values ​​and / or deviations determined by the processing unit that are to be displayed outside this tolerance range are, for example,Values ​​are displayed in a different color than those within the permissible tolerance range. This representation makes it easy to identify trends in the print register during the production of the generic printed products 01. Furthermore, additional parameters can be calculated from the determined and / or displayed values ​​and / or deviations from the calculation unit, possibly using further information such as the position of a specific printed product 01 within the print run. These parameters include, for example, changes in the length of the printing forms, particularly the steel engraving plates P1, P2, and P3. Reference symbol list 01 Printed product; security document; banknote 02 Area to be printed on a substrate 03 Printed image in an offset printing process 04 Printed image in a steel engraving process 05 - 06 Printed image in a screen printing process 07 Monitor A distance B distance C distance D distance P1 steel engraving plate P2 steel engraving plate P3 steel engraving plate

Claims

[1] A method for controlling the quality of printed products (01) produced successively in a specific production run using several printing presses, wherein for each of these printed products (01) at least three printed images (03; 04; 06) are arranged at a distance (A; B; C; D) from each other on a respective area of ​​a substrate to be printed for each of these printed products (01), wherein these at least three printed images (03; 04; 06) are printed using different printing processes, wherein, for controlling the quality of the respective printed product (01), two printed images (03; 04; 06) printed using different printing processes are selected by an inspection system to form a pair of printed images, wherein the pair of printed images is assigned a distance (A; B; C; D) between its printed images (03; 04;06) is assigned a specified distance dimension, wherein this distance dimension is provided with a tolerance defined depending on the printing processes used in the relevant print image pair before the commencement of the specific production, wherein the quality of the produced print products (01) is checked by means of a processing unit of the inspection system determining, during the specific production, at least for a subset taken from the quantity of all print products (01) produced successively in the specific production, a current value for the respective distance (A; B; C; D) between the print images (01) selected for this print image pair, wherein the processing unit compares the respective currently determined value of the relevant distances (A; B; C; D) with the value for this distance (A; B; C;D) The specified distance dimension is compared taking into account the associated tolerance, and taking into account the associated tolerance, a deviation of the respective currently determined value of the relevant distances (A; B; C; D) from its specified distance dimension is determined. [2] Method according to claim 1, characterized by , that a steel engraving process, an offset printing process and a screen printing process are used as printing processes for printing the printed images (03; 04; 06) involved in the production of each printed product (01), wherein a steel engraving printing machine is used for carrying out the steel engraving process, an offset printing machine is used for carrying out the offset printing process and a screen printing machine is used for carrying out the screen printing process. [3] Method according to claim 1 or 2, characterized by, that the printed products (01) are produced in a production plant comprising several printing presses in a single pass through this production plant or by means of spatially separated, each independent printing press in successive production steps. [4] Method according to claim 1 or 2 or 3, characterized by , that this process is used to produce printed products (01) that can be designed as a security document (01) or as a banknote (01). [5] Method according to claim 1 or 2 or 3 or 4, characterized by, that the inspection system generates several pairs of printed images for each printed product (01) to be checked for quality, wherein the respective distance dimension of at least two of these printed image pairs is assigned a tolerance before the start of the specific production, wherein the tolerances of printed image pairs that differ in at least one printing process are set differently, and wherein the processing unit of the inspection system determines a deviation of the respective currently determined value of the relevant distances (A; B; C; D) from the respective specified distance dimension for each of the generated printed image pairs. [6] Method according to claim 1 or 2 or 3 or 4 or 5, characterized by, that the processing unit of the inspection system determines, for each of the at least one identical print image pairs belonging to several of the print images (03; 04; 06) in the relevant subset of all print products (01) produced consecutively in the specified production, a current value for the respective distance (A; B; C; D) between the respective print images (03; 04; 06) is determined by the processing unit, whereby an average value is determined from these currently determined values ​​for the respective distances (A; B; C; D), and, taking into account the associated tolerance, a deviation of the determined average value from its distance dimension specified for this distance (A; B; C; D) is determined by the processing unit. [7] Method according to claim 1 or 2 or 3 or 4 or 5, characterized by, that the processing unit of the inspection system, for several subsets, determines from the quantity of all printed products (01) produced successively in the specified production run, for each subset, a current value for the respective distance (A; B; C; D) between the respective printed images (03; 04; 06) for at least one identical pair of printed images contained in the respective subsets (01), wherein the processing unit determines a first mean value for each subset from these currently determined values ​​for the distances (A; B; C; D), wherein the processing unit determines a second mean value from these first mean values, and wherein the processing unit determines, taking into account the associated tolerance, a deviation of the determined second mean value from its distance dimension specified for this distance (A; B; C; D). [8] Method according to claim 6 or 7, characterized by, that the computing unit checks the plausibility of a currently determined value of the relevant distance (A; B; C; D) before the respective averaging and excludes it from the averaging if it is not plausible, and / or that the computing unit eliminates currently determined extreme values ​​in the respective subset for the respective distance (A; B; C; D) between the respective print images (03; 04; 06) before the averaging. [9] Method according to claim 2 or 3 or 4 or 5 or 6 or 7 or 8, characterized by, that for the execution of the steel engraving process in the steel engraving printing machine in the same production, several steel engraving plates are used alternately, wherein for at least two of the steel engraving plates involved in the execution of the steel engraving process or for all steel engraving plates involved in the execution of the steel engraving process, the deviation of the respective currently determined value of the relevant distances (A; B; C; D) from its specified distance dimension or the deviation of the determined mean value from its specified distance dimension for this distance (A; B; C; D) or the deviation of the determined second mean value from its specified distance dimension for this distance (A; B; C; D) is selectively determined by the calculating unit. [10] Method according to claim 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 or 9, characterized by, that the determined deviation of the respective currently determined value of the relevant distances (A; B; C; D) from its specified distance measure or the determined deviation of the determined mean value from its specified distance measure for this distance (A; B; C; D) or the determined deviation of the determined second mean value from its specified distance measure for this distance (A; B; C; D) is displayed on a display device. [11] Method according to claim 10, characterized by, that a coordinate system is displayed on a display device in which, with reference to the origin of this coordinate system, the respective deviations of the respective currently determined values ​​from at least one of the relevant distances (A; B; C; D) from the associated fixed distance measure and / or the determined deviations of the determined mean value from its fixed distance measure for this distance (A; B; C; D) and / or the determined deviation of the determined second mean value from its fixed distance measure for this distance (A; B; C; D) are displayed. [12] Method according to claim 11, characterized by, that the permissible tolerances are displayed around the origin of the coordinate system and indicate a tolerance range, whereby values ​​to be displayed outside this tolerance range are shown in a different color than values ​​to be displayed within the permissible tolerance range.

Images