Method for determining position-dependent structural depth of flexographic stamp or screen surface

Abstract

The invention relates to a method for determining a position-dependent structure depth of a flexographic stamp or a reticulated surface, comprising the following steps: providing and using at least one light source which irradiates at least one section of a structured surface of the flexographic stamp or the reticulated surface with light; at least one camera is provided and used that produces an image of the structure at least in the section. The camera is provided as a one-dimensional camera or a two-dimensional camera. Light impinges on the structure in the section in a direction substantially parallel to the surface of the flexographic stamp or the reticulated surface. The structure produces a position-dependent shadow on the path of the light. The light source and the camera are arranged opposite each other such that the camera detects a position-dependent shadow. A computer is provided and used that calculates a structure depth related to the position from the detected shadows. The invention can advantageously determine the structural depth of the flexographic stamp and provide the result of improved printing quality. The invention is preferably used in the manufacture of printed products in flexographic printing machines.

Description

Technical Field

[0001] The present invention relates to a method for determining the position-dependent structural depth of a flexographic printing form or an anilox surface.

[0002] The present invention belongs to the technical field of plate-making industry (or graphic industry), especially the technical field of flexographic printing, that is, the operation of a flexographic printing press, namely a rotary printing press that uses a flexographic printing form for printing; and the operation of its peripheral equipment, especially a so-called installer, in which a plurality of flexographic printing forms are arranged on a drum or a drum sleeve according to the needs of a printing job. The present invention particularly relates to the sub-field of accurately measuring an "installed" flexographic printing form (for example, directly in an installer) or an anilox surface. Background Art

[0003] Various measurement methods have been disclosed and used in the plate-making industry.

[0004] EP3465169B1 discloses a method for determining the position of an embossed structure on a surface. Here, the method uses an image detection system that irradiates a line on the surface from different angles, detects the reflected light with a camera, and evaluates it with a computer.

[0005] MX2010000925A discloses an instrument for automatically and non-contact measuring the undulation and line depth of a flexographic printing form under industrial conditions. An interference sensor system is used here.

[0006] GB2170314A discloses a method for non-contact measuring the depth or undulation of a surface (such as a flexographic printing form). Here, the focus of a focusing unit used together with a sensor unit is changed.

[0007] EP3822080B1 discloses a method for inspecting and evaluating whether the undulation height of a flexographic punch is irregular. Here, a three-dimensional camera is used, which records images according to the triangulation method, the time-of-flight measurement method, or the interferometric measurement method.

[0008] WO2008049500A2 discloses a scanning roller for measuring a printing form.

[0009] DE102020111341A1 discloses a device for measuring the protrusions on the surface of a rotating body. The measurement process described here uses a reference object, such as a tensioned wire, that is, the protrusions are measured relative to the reference object.

[0010] Flexographic printing plates used in flexographic printing are usually either etched (i.e., usually locally treated with a solvent to locally corrode or dissolve the material of the flexographic printing plate) or directly imaged by laser machining, i.e., engraved. The resulting etching depth or engraving depth is crucial for the printing process and the achievable printing quality. Therefore, manufacturers of flexographic printing products desire to obtain information about the actual etching depth or engraving depth of the flexographic printing plate and be able to use this information to improve the printing quality. In addition, it is also desirable to obtain printing-related information about the surface of an anilox surface, such as an anilox roll or anilox sleeve. Summary of the Invention

[0011] Therefore, the object of the present invention is to improve the prior art, in particular to be able to determine the structural depth of a flexographic printing plate or an anilox surface and provide results for improving the printing quality. In addition, continuous quality inspection of the manufacturing process of the flexographic printing plate can also be carried out.

[0012] According to the present invention, the object can be solved by a method according to a preferred embodiment of the present invention.

[0013] Advantageous and thus preferred developments of the present invention can be derived from the alternative embodiments, the description and the drawings.

[0014] The present invention provides a method for determining the position-related structural depth of a flexographic printing plate or an anilox surface, comprising the steps of: providing and using at least one light source that irradiates at least one section of the structured surface of the flexographic printing plate or anilox surface with light; and providing and using at least one camera that generates an image of the structure in at least said section, characterized in that the camera is provided as a one-dimensional camera or as a two-dimensional camera; the light irradiates the structure in the section in a direction substantially parallel to the surface of the flexographic printing plate or anilox surface; the structure produces a position-related shadow in the path of the light; the light source and the camera are arranged relative to each other such that the camera detects the position-related shadow; and providing and using a computer that calculates the position-related structural depth from the detected shadow.

[0015] The present invention can advantageously determine the structural depth of a flexographic printing plate or anilox surface, preferably over the entire available length and width of the flexographic printing plate or anilox surface, and provide results for improving the printing quality. The present invention is preferably used in the manufacture of printing products in a flexographic printing press.

[0016] Measurements carried out according to the invention preferably do not require a reference object different from the impression or the reticulated surface. Instead, the (radial) structural depth is preferably determined relative to the bottom of the structure and can be determined, for example, from the width of the (radial) shadow caused by the structure or its protrusions. The (radial) position of the bottom of the structure can also be determined, preferably beforehand and in an area of the impression where there are no protrusions. "Radial" here means: extending in the radial direction or being at a specific radial position relative to the center point of the flexographic printing form (on a sleeve with a circular cross-section).

[0017] By knowing the structural depth of the flexographic printing form, especially its etching depth or engraving depth, the operator can draw conclusions about the etching process (dissolution by solvents, subsequent rinsing, and possibly brushing / using a certain type of brush). For example, the degree of anchoring of each protrusion (printing dot) to the bottom of the printing form (the so-called base thickness) can be summarized. If the critical areas of the measured flexographic printing form are below or above a predetermined threshold of the etching depth, the etching process of other printing forms can be corrected. The aging condition and / or the intensity of the exposure unit used can also be understood. The etching depth is preferably substantially constant over the width and length of the printing form. For example, a typical etching depth is in the range of 500 micrometers. For example, information about how long the printing form can be used without a significant reduction in printing quality can also be obtained. The information obtained during the measurement process can also be used for proper setting of 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. By this measure, the printing quality can be greatly improved. The same method also applies to printing forms that are not etched but imaged by laser treatment, such as laser engraving. In this case, the exposure intensity or exposure duration can be adjusted.

[0018] In addition, another advantage provided by the present invention is that the measurement of the printing form and the information about the structural depth obtained here can be used for further automation of the printing process. Therefore, it is possible to save operators or replace non-existent operators when necessary.

[0019] The present invention also provides the advantage that the method can be carried out without contact, so that a sensing roller or other scanning elements (such as the so-called paddles) used for measurement can be dispensed with, which are interfering and cannot be used for fine structures.

[0020] Therefore, according to the method of the present invention, the production cost can be reduced, the printing quality can be improved, and the production risk can be minimized in an advantageous manner through the automation of the printing process.

[0021] In a preferred embodiment of the invention described and shown in the present application, light for measurement is generated by an independent light source. Therefore, the light source is preferably a light source that exists only for this purpose. However, the term "light source" also includes a light source that already exists for at least one other purpose in the environment of measuring a flexographic printing plate or an anilox surface or is provided within the framework of the present invention. The term "light source" can also include a light source that is normally present in the environment of measuring a flexographic printing plate or an anilox surface, for example, illumination (sufficiently strong for the sensitivity of the camera) of a machine or the machine environment.

[0022] The preferred expansion options (abbreviation: expansion options) of the present invention will be introduced below. These implementation options can also be combined with each other if it is not technically impossible.

[0023] A feature of an expansion option can be that the position-related structural depth is the undulation depth of a flexographic printing plate or an anilox surface. A feature of an expansion option can be that the undulation depth is the etched undulation depth. A feature of an expansion option can be that the undulation depth is the laser-processed undulation depth. The undulation depth can be defined by an envelope curve, especially its distance from the bottom of the depression of the printing plate or anilox surface.

[0024] A feature of an expansion option can be that the undulation depth can be represented as a topographic map of a flexographic printing plate or an anilox surface. A feature of an expansion option can be that the undulation depth can be statistically evaluated and the evaluation result can be displayed.

[0025] A feature of an expansion option can be that the at least one camera is a row of multiple cameras.

[0026] A feature of an expansion option can be that the computer additionally calculates (i.e., determines) the thickness of a flexographic printing plate or an anilox surface based on the measurement values. The thickness is preferably determined at the edge of the flexographic printing plate or anilox surface. A feature of an expansion option can be that the computer additionally calculates the vacancies or free positions (Freistellen) of a flexographic printing plate or an anilox surface. These vacancies can be defined as areas of the printing plate without printing protrusions.

[0027] A feature of an expansion option can be that a flexographic printing plate or anilox surface can be rotated and the rotation is detected by an encoder. In this way, the position-related structural depth can have angular information (in the circumferential direction of the flexographic printing plate and / or the sleeve or anilox surface). This angular information can then be used in a flexographic printing press.

[0028] The features and combinations of features (in any combination) disclosed in the above technical field, summary of the invention, and expansion option paragraphs and the following embodiment paragraphs represent more advantageous expansion options of the present invention. Specific embodiments

[0029] ·Mount the flexographic stamper on the sleeve in the installer for subsequent measurement. Preferably, one or more flexographic stampers are mounted on the sleeve (adjacent to each other axially and / or circumferentially). Also preferably, a plurality of such sleeves are processed or measured in sequence. Alternatively, an etched or engraved sleeve can also be measured. Here, the installer can be provided separately from the flexographic printing press and, if necessary, can also be located away from the flexographic printing press. The installer is preferably also designed as a measuring device. Alternatively, the installer and the measuring device can also be provided separately and the sleeve can be transferred from the installer to the measuring device.

[0030] ·Optionally: Identify the sleeve using a unique ID assigned to the sleeve (preferably by coding, such as a barcode, QR code, RFID chip, or NFC chip).

[0031] ·According to the method of the present invention, non-contact measurement is performed on the diameters or radii (diameter or radius of the circumscribing circle, see figure) distributed at a limited number of points and preferably over the entire width and entire circumference of the sleeve, and the undulation depth is calculated. Here, a one-dimensional camera or a two-dimensional camera is preferably used. Alternatively, a 3D camera or laser triangulation can also be used.

[0032] ·Preferably: Technically classify the undulation depth according to a predetermined step height and technically investigate whether there are areas below or above the predetermined step height (one threshold or multiple thresholds); if necessary, display the results. The results or the values determined here can also be additionally stored digitally and can be retrieved by the flexographic printing press or the flexographic printing process. Critical areas can be informed to the operator, for example, by warning notifications, etc., and if necessary, the position of the critical areas can also be displayed. The operator can decide whether such a stamper can be printed; if necessary, a new stamper can be made, especially etched. For example, a critical situation means that the etched area of the stamper is too deep or the etched area is not deep enough. Both situations will result in a decline in printing quality. The decision on the usability of the stamper can also be made automatically, where corresponding knowledge about the optimal etching depth is provided for the technical execution of the decision through data collection, etc.

[0033] ·Optionally: Display the results, that is, preferably display the functional relationship between the undulation depth and the measurement position (x - y coordinates, x = width, y = circumference) on a monitor.

[0034] ·Optional: Calculate the free surface, that is, an area with a predetermined minimum size and / or shape without printing protrusions; if necessary, display it.

[0035] ·All measurement results can be directly transmitted to the flexographic printing press. Alternatively, the measurement results can be temporarily stored for retrieval by the flexographic printing press or forwarded to the flexographic printing press, for example, stored in a local digital memory or in the cloud.

[0036] · Remove this / these sleeves from the installer (or a separate measuring device) and push the corresponding sleeve(s) onto the corresponding flexographic printing cylinder of the corresponding flexographic printing unit in the flexographic printing press.

[0037] · For each sleeve: Read out the unique ID assigned to the sleeve and retrieve the stored measurement results (if not yet transmitted), in particular the undulation depth of the spatial resolution.

[0038] · Optionally, for each sleeve: Perform printing unit settings, such as the pressure between the flexographic printing cylinder and the impression cylinder and / or the pressure between the anilox roll and the flexographic printing cylinder or between, for example, the register device. Here, the anilox roll involved can optionally also be identified in advance by the unique ID.

[0039] · All information important to the operator and in particular the measured values can preferably be visually displayed on the monitor. Optionally, the critical areas can be directly displayed on the flexographic stamper, for example by irradiating the critical areas with a laser, thereby optically marking them. Description of the Drawings

[0040] Figure 1 A cross-sectional schematic view of the measuring device when implementing the preferred embodiments and expansion solutions of the present invention is shown. Detailed Description of the Invention

[0041] From Figure 1 The flow of the method of the present invention can be derived. The figure shows a running measuring device 1, for example a so-called installer, which has a rotatable cylinder 2. The cylinder 2 can rotate around a rotation axis 3. This rotation is driven by a motor 4. The motor 4 can be equipped with an encoder 5, in particular a rotary encoder 5; alternatively, there can also be a separate encoder. A sleeve 6 is received on the cylinder 2.

[0042] A flexographic stamper 10 is received or mounted, preferably adhered, on the sleeve 6. It has a surface 11, and the surface has a (printing) structure 11a composed of protrusions. A section 12 of the surface 11 is optically detected or measured. There is at least one printing protrusion 13 (for example, a flexographic printing surface or a flexographic printing dot) in the section 12. There is also an area including a non-printing depression 14 or a vacancy 14 in the section 12. The printing protrusions 13 define an envelope circle 15. The depression 14 has a bottom 16. The distance between the bottom 16 and the envelope circle 15 defines the depth 17 of the structure or the structure depth. The depth of the structure 11a can be determined, for example, by manufacturing processes such as etching / dissolving or laser processing.

[0043] Figure 1At least one light source 20 is also shown, which emits light 21 having 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 can reflect the light 21 and then the light is received by a camera 31 located at another position. As shown in the figure, the camera 31 can be arranged next to the light source 20. Alternatively, the light source 20 and the camera 31 can also form a common assembly, for example, the light source 20 can be mounted in the housing of the camera 31. It can be seen that the printed protrusion 13 produces a shadow 24 in the light 21, and 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 regard, an image 32 can be recorded by the camera 30 or 31, and from this image, the shadow 24 or its width 25 can be determined by computational techniques and accordingly the depth 17 of the structure 11a can be determined. In the simplest case, the depth 17 exactly corresponds to the width 25 of the shadow 24. The computer 40 can perform the necessary calculations via a connection 41. The light source 20 and the camera 30 or 31 and, if necessary, the reflector or mirror 23 can move individually, or preferably also move together by means of a motor. In this way, it is possible to respond to sleeves 6 and / or flexographic printing dies 10 with different outer diameters. Here, the movement is preferably perpendicular to the tangent plane of the surface to be measured. Alternatively, the light source 20 and the camera 30 or 31 and, if necessary, the mirror 23 can also be arranged as a group and rotated 90° or 180° and perform corresponding measurements.

[0044] Alternatively, the anilox sleeve 6 including the anilox surface 10 can be received on the drum 2 and measured accordingly.

[0045] The camera 30 or 31 preferably records an area 21 that is wide enough so that not only the structural depth 17 of the structure 11a (of the flexographic printing die 10 or the anilox surface 10) can be recorded in the above-described manner, but also, alternatively or additionally, the thickness of the flexographic printing die 10 or the anilox surface 10 can be recorded by its shadow 25a. Here, the thickness is preferably measured at the (lateral) edge of the flexographic printing die 10 or the anilox surface 10. After knowing the determined thickness of the flexographic printing die 10, it is possible, for example, to check whether it is a flexographic printing die 10 that has been used before (once or multiple times), because the thickness decreases with use.

[0046] List of reference numerals

[0047] 1 Measuring device, in particular installer

[0048] 2 Drum

[0049] 3 Axis of rotation

[0050] 4 Electric motors

[0051] 5 Encoders, especially rotary encoders

[0052] 6 Sleeves or anilox sleeves for flexographic printing formes

[0053] 10 Flexographic printing forme or anilox surface

[0054] 11 Surface of (flexographic printing forme or anilox surface)

[0055] 11a Structure

[0056] 12 Section of (the surface)

[0057] 13 Printing protrusions of the flexographic printing forme or protrusions of the anilox surface

[0058] 14 Non-printing recesses or voids, especially etched recesses

[0059] 15 Envelope circle

[0060] 16 Bottom of the recess

[0061] 17 Depth of the structure (structure depth)

[0062] 20 One or more light sources

[0063] 21 Recording area of the light or camera

[0064] 22 Width of the light field

[0065] 23 Reflector, especially a mirror

[0066] 24 Shadow

[0067] 25 Width of the shadow caused by the printing protrusions

[0068] 25a Width of the shadow caused by the flexographic printing forme or anilox surface

[0069] 30 One or more cameras

[0070] 31 One or more cameras at another position

[0071] 32 Image

[0072] 40 Computer

[0073] 41 Connection

[0074] 50 Radial direction

[0075] 52 Direction (substantially parallel to the surface of the flexographic printing forme).

Claims

1. A method for determining a position-dependent structure depth of a flexographic stamp or an anilox surface, comprising the following steps: providing and using at least one light source (20) which illuminates at least one section (12) of the structured surface (11) of the flexographic stamp (10) or the textured surface with light (21), and providing and using at least one camera (30, 31) which produces an image (32) of at least the structure (11a) in the section (12), It is characterized in that The camera (30, 31) is provided as a one-dimensional camera (30, 31) or as a two-dimensional camera (30, 31), The light (21) is irradiated onto the structure (11a) in the section (12) in a direction (52) substantially parallel to the surface (11) of the flexographic stamp (10) or the textured surface, The structure (11a) generates a position-dependent shadow (24) in the path of the light (21), The light source (20) and the camera (30, 31) are arranged relative to each other in such a way that the camera (30, 31) detects the position-dependent shadow (24), and A computer (40) is provided and used, which calculates the position-dependent structure depth (17) from the detected shadow (24).

2. The method according to claim 1, characterized in that The position-dependent structure depth (17) is the relief depth (17) of the flexographic stamp (10) or the textured surface.

3. The method according to claim 2, characterized in that The relief depth (17) is the relief depth (17) of the etching.

4. The method according to claim 2, characterized in that: The relief depth (17) is the relief depth (17) of laser processing.

5. The method according to any one of claims 2 to 4, characterized in that The relief depth (17) is displayed as a topographical image (32) of the flexographic stamp (10) or the textured surface.

6. The method according to any one of claims 2 to 5, characterized in that The fluctuation depth (17) is statistically evaluated and the evaluation result is displayed.

7. The method according to any one of the preceding claims, characterized in that The at least one camera (30, 31) is a row of a plurality of cameras (30, 31).

8. The method according to any one of the preceding claims, characterized in that The computer (40) additionally determines the thickness of the flexographic stamp (10) or the anilox surface.

9. The method according to any one of the preceding claims, characterized in that The computer (40) additionally calculates the voids (14) of the flexographic stamp (10) or the anilox surface.

10. The method according to any of the preceding claims, characterized in that The flexographic stamp (10) or the anilox surface rotates and the rotation is detected by an encoder (5).

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