Method for determining the location-dependent structural depth of a flexographic printing form or screen surface

Abstract

A method according to the invention for determining the location-dependent structure depth of a flexographic printing form or screen surface, comprising the steps of: providing and using at least one light source (20) which irradiates at least one section (12) of a structured surface (11) of the flexographic printing form (10) or screen surface with light (21), and providing and using at least one camera (30, 31) which generates an image (32) of the structure (11a) at least in the section (12), is characterized in that the camera (30, 31) is provided as a 1D camera (30, 31) or as a 2D camera (30, 31), that the light (21) in the section (12) strikes the structure (11a) in a direction (52) substantially parallel to the surface (11) of the flexographic printing form (10) or screen surface, that the structure (11a) has a location-dependent shading (24) in the path of the light (21) such that the light source (20) and the camera (30, 31) are arranged relative to each other in such a way thatthat the camera (30, 31) detects the location-dependent shadowing (24), and providing and using a computer (40) which calculates the location-dependent structure depth (11a) from the detected shadowing (24). The invention advantageously makes it possible to determine the structure depth of a flexographic printing plate and to provide the result for improving print quality. The invention is preferably used in the production of printed products in flexographic printing machines.

Description

invention

[0001] The invention relates to a method for determining the location-dependent structural depth of a flexographic printing plate or screen surface with the features of the preamble of claim 1. field of technology

[0002] The invention lies in the technical field of the graphic arts industry, and therein in particular in the area of ​​flexographic printing, i.e., the operation of a flexographic printing press, i.e., a rotary printing press for printing with flexographic printing plates; and the operation of its peripheral devices, in particular a so-called mounter, in which several flexographic printing plates are arranged on a cylinder or cylinder sleeve depending on the print job. In particular, the invention lies in the subfield of the precise measurement of "mounted" flexographic printing plates, e.g., directly in the mounter, or of screen areas. State of the art

[0003] In the graphic industry, various measuring methods are already known and in use.

[0004] EP3465169B1 discloses a method for determining the position of an (embossed) structure on a surface. This method uses an image acquisition system that illuminates a line on the surface from different angles, captures the reflected light using a camera, and evaluates it using a computer.

[0005] MX2010000925A discloses an instrument for the automatic and non-contact measurement of the relief and line depth of a flexographic printing plate under industrial conditions. This instrument utilizes an interferometric sensor system.

[0006] GB2170314A discloses a method for contactless measurement of the depth or relief of a surface, e.g., a flexographic printing plate. The focus of a focus unit used in conjunction with a sensor unit is changed.

[0007] EP3822080B1 discloses a method for examining and assessing flexographic printing plates for irregularities in the relief. This method uses a 3D camera that captures images based on triangulation methods, a time-of-flight measurement, or an interferometric method.

[0008] WO2008049500A2 discloses sensing rollers for measuring a printing form.

[0009] DE102020111341A1 discloses a device for measuring elevations on the surface of a rotating body according to the preamble of claim 1. The measuring process described therein uses a reference object, for example a taut wire, i.e. the measurement of the elevations is carried out relative to the reference object.

[0010] Flexographic printing plates used in flexographic printing are usually either etched, i.e. treated locally with a solvent that locally attacks or dissolves the material of the flexographic printing plate, or directly imaged, i.e. engraved, using a laser, depending on the print image to be created. The resulting etching or engraving depth is critical for the printing process and the achievable print quality. Manufacturers of flexographic printing products therefore want to obtain information about the actual etching or engraving depth of a flexographic printing plate and to be able to use this information to improve print quality. There is also a desire to obtain printing-relevant information about screen surfaces, e.g. surfaces of anilox rollers or anilox sleeves. Technical task

[0011] It is therefore an object of the present invention to provide an improvement over the prior art, which in particular makes it possible to determine the structural depth of a flexographic printing plate or screen area and to use the result to improve print quality. It also enables continuous quality control of the flexographic printing plate manufacturing process. Inventive solution to the problem

[0012] This object is achieved according to the invention by a method according to claim 1.

[0013] Advantageous and therefore preferred developments of the invention emerge from the subclaims as well as from the description and the drawings.

[0014] A method according to the invention for determining the location-dependent structure depth of a flexographic printing form or screen surface, comprising the steps of: providing and using at least one light source which irradiates at least a portion of a structured surface of the flexographic printing form or screen surface with light, and providing and using at least one camera which generates an image of the structure at least in the portion, is characterized in that the camera is provided as a 1D camera or as a 2D camera, that the light in the portion strikes the structure in a direction substantially parallel to the surface of the flexographic printing form or screen surface, that the structure generates a location-dependent shadowing in the path of the light, that the light source and the camera are arranged relative to one another in such a way that the camera detects the location-dependent shadowing, and

[0015] Provision and use of a computer that calculates the location-dependent structure depth from the recorded shading. Advantageous embodiments and effects of the invention

[0016] The invention advantageously enables the determination of the structural depth of a flexographic printing plate or screen area, preferably across the entire usable length and width of the flexographic printing plate or screen area, and the use of the result to improve print quality. The invention is preferably used in the production of printed products in flexographic printing machines.

[0017] The measurement according to the invention preferably does not require a reference object other than the printing form or screen surface. The (radial) structure depth, on the other hand, is preferably determined relative to a base of the structure and can be determined, for example, from the width of a (radial) shadow caused by the structure or its elevations. The (radial) position of the base of the structure can also be determined, preferably in advance and in an area of ​​the printing form without elevations. The term "radial" means: extending in the radial direction or lying at a specific radial position; with reference to a center point of the flexographic printing form (located on a sleeve with a circular cross-section).

[0018] By knowing the structural depth of a flexographic printing plate, in particular its etching depth or engraving depth, the operating personnel can draw conclusions about the etching process (dissolving with solvent, subsequent washing out and, if necessary, brushing / using a certain type of brush). For example, information can be gained about how firmly the individual elevations (printing dots) are anchored to the base of the printing plate (so-called base thickness). If a measured flexographic printing plate shows critical areas that are, for example, below or above a predetermined threshold for the etching depth, corrections can be made to the etching process for further printing plates. Information can also be gained about the aging state of the exposure unit used and / or its intensity. An etching depth that is essentially constant across the width and length of the printing plate is preferred. Typical etching depths are, for example, in the range of 500 µm.For example, insights can be gained into how long the printing form can be used without significant loss of print quality. The information from the measurement process can also be used to make suitable settings on the flexographic printing form. For example, the optimal contact pressure can be set for a flexographic printing form with a given and measured etching depth. Print quality can be significantly improved by this measure. The same applies to printing forms that have not been etched, but have been imaged, for example, by treatment with laser light, or have been laser engraved. In this case, the exposure intensity or exposure time, for example, can be adjusted.

[0019] The invention also offers the further advantage that the measurement of the printing form and the resulting information about the structure depth can be used for further automation of the printing process. This can potentially reduce the number of operating personnel or replace unavailable operating personnel.

[0020] The invention also offers the advantage that the method can be carried out without contact and that disturbing sensing rollers or other sensing elements, e.g. so-called paddles, which cannot be used for fine structures, can thus be dispensed with for measuring.

[0021] The method according to the invention therefore advantageously allows production costs to be reduced, print quality to be increased and production risks to be minimized by automating the printing process.

[0022] The invention is described and shown in this application in a preferred embodiment with its own light source for generating the light used for the measurement. The light source is therefore preferably a light source that is present solely for this purpose. However, the term "light source" is also intended to encompass a light source that is already present for at least one other purpose in the context of measuring the printing form or screen area or is provided within the scope of the invention. Likewise, the term "light source" can encompass a light source generally present in the context of measuring the printing form or screen area, such as illumination of the machine or the machine environment that is sufficiently strong for the camera sensitivity. Further developments of the invention

[0023] Preferred developments of the invention (hereinafter referred to as "developments") are described below. These can also be combined with one another where not technically impossible.

[0024] A further development can be characterized in that the location-dependent structural depth is a relief depth of the flexographic printing form or screen area. A further development can be characterized in that the relief depth is an etched relief depth. A further development can be characterized in that the relief depth is a lasered relief depth. The relief depth can be defined by an envelope curve, in particular its location-dependent distance from a bottom of the depressions of the printing form or screen area.

[0025] A further development can be characterized by the relief depth being represented as a topographic image of the flexographic printing plate or screen surface. A further development can be characterized by the relief depth being statistically evaluated and the results of the evaluation being presented.

[0026] A further development can be characterized by the fact that at least one camera is a series of several cameras.

[0027] A further development can be characterized by the computer additionally calculating, i.e., determining, the thickness of the flexographic printing form or screen area from the measured values. This thickness is preferably determined at the edge of the flexographic printing form or screen area. A further development can be characterized by the computer additionally calculating clearances of the flexographic printing form or screen area. Such clearances can be defined as areas of the printing form in which there are no printing elevations.

[0028] A further development can be characterized by rotating the flexographic printing plate or screen surface, and by detecting the rotation with an encoder. In this way, the location-dependent structure depth can be provided with angle information (in the circumferential direction of the flexographic printing plate and / or sleeve or screen surface). This angle information can later be used in the flexographic printing press.

[0029] The features and combinations of features disclosed in the above sections Technical Field, Invention and Further Developments as well as in the following section Exemplary Embodiments represent - in any combination with one another - further advantageous developments of the invention. Concrete example

[0030] Mounting a flexographic printing form on a sleeve in a mounter for subsequent measuring. Preferably, one flexographic printing form or several flexographic printing forms (axially and / or circumferentially next to each other) are mounted on a sleeve. Likewise preferably, several such sleeves are processed or measured one after the other. Alternatively, etched or engraved sleeves can be measured. The mounter can be provided separately from the flexographic printing machine and, if necessary, also arranged remotely from it. The mounter is preferably also designed as a measuring device. Alternatively, the mounter and measuring device can be provided separately and the sleeve can be moved from the mounter into the measuring device. Optional: Identification of the sleeve using a unique ID assigned to the sleeve, preferably via coding, for example a barcode, QR code, RFID chip or NFC chip. Contactless measurement of the diameter or radius (of the enveloping circle, cf.Figure) distributed at a finite number of locations and preferably over the entire width and the entire circumference of the sleeve and calculating the relief depth according to the method according to the invention. A 1D camera or 2D camera is preferably used here. Alternatively, a 3D camera or a laser triangulation method could also be used. Preferably: computational classification of the relief depth according to predetermined step heights and computational investigation as to whether areas exist which fall below or exceed a predetermined step height (one threshold or several thresholds); if necessary, presentation of the result. The result or the values ​​determined can also be digitally stored and thus be retrievable for the flexographic printing machine or the flexographic printing process. Critical areas can be made clear to the operating personnel, e.g.A warning message and, if necessary, a display of the location of the critical area are provided, and the operating personnel can decide whether such a printing form can be printed or not; if necessary, a new printing form is produced, in particular etched. Critical cases include printing forms with areas that are etched too deeply or areas that are etched too shallowly. Both cases can lead to a reduction in print quality. The decision regarding the usability of the printing form can also be automated, with corresponding knowledge about the optimal etching depth being provided for a computational implementation of the decision, e.g., as a data collection. Optional: Display of the result, i.e., the relief depth as a function of the measurement location (xy coordinates with x= width and y= circumference), preferably on a monitor. Optional: Calculation of free areas, i.e.of areas of a specified minimum size and / or shape without printed elevations; representation of these, if applicable. All measurement results can be transmitted directly to the flexographic printing press. Alternatively, the measurement results can be temporarily stored for retrieval by the flexographic printing press or for forwarding to the flexographic printing press, for example in a local, digital storage or in the cloud. Removal of the sleeve(s) from the mounter (or separate measuring device) and sliding of the respective sleeve onto an assigned flexographic printing cylinder of an assigned flexographic printing unit in the flexographic printing press. For each sleeve: reading out the unique ID assigned to the sleeve and (if not already transmitted) retrieving the temporarily stored measurement results, in particular the spatially resolved relief depth.Optionally, for each sleeve: Making printing unit settings, for example, the pressure between the flexographic printing cylinder and impression cylinder and / or between the anilox cylinder and the flexographic printing cylinder, or, for example, the register. Optionally, the anilox cylinder involved can also be identified in advance using a unique ID. All information important to the operating personnel, and in particular measured values, can be displayed visually, preferably on a monitor. Optionally, critical areas can be displayed directly on the flexographic printing form, for example using a laser that illuminates the critical areas and thus visually marks them. Embodiments of the invention and figures

[0031] The Figure 1 shows a schematic representation of a sectional view of a measuring device when carrying out a preferred embodiment of the invention and the further developments.

[0032] Figure 1The sequence of the method according to the invention can be seen. Shown is a measuring device 1 in operation, e.g., a so-called mounter, with a rotatable cylinder 2. The cylinder 2 can rotate about a rotation axis 3. The rotation is driven by a motor 4. The motor 4 can be equipped with an encoder 5, in particular a rotary encoder 5; alternatively, a separate encoder can be present. A sleeve 6 is mounted on the cylinder 2.

[0033] A flexographic printing form 10 is received or mounted, preferably glued, on the sleeve 6. This form has a surface 11 with a (printing) structure 11a made up of elevations. A section 12 of the surface 11 is optically detected or measured. In section 12 there is at least one printing elevation 13 (e.g. a flexographic printing area or a flexographic printing dot). Likewise, in section 12 there is an area with non-printing depressions 14 or clearances 14. The printing elevations 13 define an enveloping circle 15. The depressions 14 have a base 16. The distance between this base 16 and the enveloping circle 15 defines a depth of the structure 17 or the structure depth. The depth of the structure 11a can be determined, for example, by the manufacturer's process of etching / dissolving or laser processing.

[0034] Figure 1also shows at least one light source 20, which emits light 21 with a width 22. The light 21 is received by a camera 30, which is preferably arranged opposite the light source 20. Alternatively, a reflector, in particular a mirror 23, can be provided, which reflects the light 21, which is then received by a camera 31 at an alternative position. The camera 31 can be arranged next to the light source 20, as shown. Alternatively, the light source 20 and camera 31 can also form a common assembly; for example, the light source 20 can be installed in the housing of the camera 31. It can be seen that the printing elevation 13 creates a shadow 24 in the light 21, and that this shadow 24 is also detected by the camera. The shadow 24 has a width 25. The width 25 of the shadow can correspond to the depth 17 of the structure 11a.In this respect, an image 32 can be recorded by camera 30 or 31, from which the shadow 24 or its width 25 and, from this, the depth 17 of the structure 11a can be determined mathematically. In the simplest case, the depth 17 corresponds exactly to the width 25 of the shadow 24. A computer 40 is available via connections 41 for the necessary calculations. The light source 20 and the camera 30 or 31 and, if applicable, the reflector or mirror 23 can be moved individually or, preferably, together by a motor. In this way, it is possible to react to different outer diameters of the sleeve 6 and / or the flexographic printing form 10. The movement preferably takes place perpendicular to a tangential plane to the surface to be measured. The light source 20 and the camera 30 or 31 and, if applicable, the mirror 23 can be arranged as a group, alternatively rotated by 90° or 180°, and carry out the measurement accordingly.

[0035] Alternatively, a grid sleeve 6 with a grid surface 10 can be mounted on the cylinder 2 and measured accordingly.

[0036] The camera 30 or 31 preferably records an area 21 that is sufficiently wide so that, in the manner described, not only the structure depth 17 of the structure 11a (of the flexographic printing form 10 or the screen area 10) can be detected, but alternatively or additionally the thickness of the flexographic printing form 10 or the screen area 10 via its shading 25a. The thickness can preferably be measured at the (lateral) edge of the flexographic printing form 10 or the screen area 10. Knowing the determined thickness of the flexographic printing form 10, it can be checked, for example, whether it is a flexographic printing form 10 that has already been used previously (once or several times), since the thickness decreases with use. List of reference symbols

[0037] 1Measuring device, in particular mounter 2Cylinder 3Rotary axis 4Motor 5Encoder, in particular rotary encoder 6Sleeve for flexographic printing forms or screen sleeve 10Flexographic printing form or screen surface 11Surface (of the flexographic printing form or screen surface) 11aStructure 12Section (of the surface) 13Printing elevations of the flexographic printing form or elevations of the screen surface 14Non-printing depressions or free spaces, in particular etched depressions 15Enveloping circle 16Bottom of the depressions 17Depth of the structure (structure depth) 20Light source(s) 21Light or recording area of ​​the camera 22Width of the light field 23Reflector, in particular mirror 24Shading 25Width of the shadowing by the printing elevation 25aWidth of the shadowing by the flexographic printing form or screen surface 30Camera(s) 31Camera(s) on alternative position 32Image 40Calculator 41Connections 50radial direction 52Direction (essentially parallel to the surface of the flexographic printing plate)

Claims

1. A method for determining the location-dependent structure depth of a flexographic printing form or screen area, comprising the steps of: providing and using at least one light source (20) which irradiates at least one section (12) of a structured surface (11) of the flexographic printing form (10) or screen area with light (21), and providing and using at least one camera (30, 31) which generates an image (32) of the structure (11a) at least in the section (12), characterized by that the camera (30, 31) is provided as a 1D camera (30, 31) or as a 2D camera (30, 31), that the light (21) in the section (12) strikes the structure (11a) in a direction (52) substantially parallel to the surface (11) of the flexographic printing plate (10) or screen surface, that the structure (11a) creates a location-dependent shading (24) in the path of the light (21), that the light source (20) and the camera (30, 31) are arranged relative to each other in such a way that thatthe camera (30, 31) detects the location-dependent shading (24), and providing and using a computer (40) which calculates the location-dependent structure depth (17) from the detected shading (24).

2. Method according to claim 1, characterized by that the location-dependent structure depth (17) is a relief depth (17) of the flexographic printing form (10) or screen area.

3. Method according to claim 2, characterized by that the relief depth (17) is an etched relief depth (17).

4. Method according to claim 2, characterized by that the relief depth (17) is a lasered relief depth (17).

5. Method according to one of claims 2 to 4, characterized by that the relief depth (17) is represented as a topographic image (32) of the flexographic printing form (10) or raster area.

6. Method according to one of claims 2 to 5, characterized by thatthe relief depth (17) is statistically evaluated and the result of the evaluation is displayed.

7. Method according to one of the preceding claims, characterized by that the at least one camera (30, 31) is a series of several cameras (30, 31).

8. Method according to one of the preceding claims, characterized by that the computer (40) additionally determines a thickness of the flexographic printing plate (10) or screen area.

9. Method according to one of the preceding claims, characterized by that the computer (40) additionally calculates the cut-outs (14) of the flexographic printing form (10) or raster area.

10. Method according to one of the preceding claims, characterized by that the flexographic printing plate (10) or screen surface is rotated and that the rotation is detected by an encoder (5).

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