WO2010060884A1

WO2010060884A1 - Apparatus for checking geometric parameters of printing assemblies consisting of flexographic printing plates mounted on respective cylinders, of flexographic printing plates mounted on respective printing plate sleeves and of inking cylinders/sleeves

Info

Publication number: WO2010060884A1
Application number: PCT/EP2009/065657
Authority: WO
Inventors: Alberto Zanoli; Stefano Sambri
Original assignee: Bieffebi - Societa' Per Azioni
Priority date: 2008-11-25
Filing date: 2009-11-23
Publication date: 2010-06-03
Also published as: ITBO20080709A1

Abstract

An apparatus (1) for checking geometric parameters of printing assemblies (2) consisting of flexographic printing plates (3) mounted on respective cylinders (4), of flexographic printing plates (3) mounted on respective printing plate sleeves (5) and of inking cylinders/sleeves; the apparatus (1) comprises at least one sensor (7), which faces at least one portion (8) of the outer surface of the printing assembly (2) to be analyzed. The sensor (7) is designed to detect the distance between the sensor (7) itself and the surface to be analyzed, and is arranged at a fixed and known distance from the pivoting and mounting axis (9) of the printing assembly (2).

Description

APPARATUS FOR CHECKING GEOMETRIC PARAMETERS OF PRINTING ASSEMBLIES CONSISTING OF FLEXOGRAPHIC PRINTING PLATES MOUNTED ON RESPECTIVE CYLINDERS, OF FLEXOGRAPHIC PRINTING PLATES MOUNTED ON RESPECTIVE PRINTING PLATE SLEEVES AND OF INKING CYLINDERS/SLEEVES Technical Field

The present invention relates to an apparatus for checking geometric parameters of printing assemblies consisting of flexographic printing plates mounted on respective cylinders, of flexographic printing plates mounted on respective printing plate sleeves and of inking cylinders/sleeves. Background Art

In flexographic printing, suitable printing plates are normally used which must be mounted on respective cylinders or sleeves (in practice, tubular bodies on the outer surface of which the printing plate can be fixed): in order to simplify the terminology used in the present document, the definition "printing assembly" shall be used hereinafter to identify the assembly consisting of a cylinder or sleeve on which a flexographic printing plate or the element consisting of an inking cylinder or sleeve is fixed (by means of any fixing element). The techniques for mounting printing plates on the respective supports (cylinders or sleeves) can rely on position-verifying devices of the semiautomatic type (as disclosed in EP 0 728 580 in the name of this same Applicant) or of a completely automatic/virtual type (as disclosed in EP 1 666 251 in the name of this same Applicant). Whereas the first type of device necessarily requires the execution of test prints to fme-tune the printing plate on the printing plate holder, with the second type it is possible to mount the printing plates in register, using virtual computer software which, by using the work file, makes it possible to do without the test print with inks and allows the operator to perform precise comparisons of the position and of the entire image between the preprocessed graphical reproduction of the image to be printed, which is made available on a digital storage medium, and the image of the printing plate mounted on the cylinder or printing plate sleeve.

With recently-built printing plate holders, therefore, the need for an actual test print has been eliminated, which is useful to verify the correct mounting of the position and the image in register, and a considerable reduction in the time needed to program the positions of the printing plates and perform the virtual print test has been achieved.

However, even with this type of device, it has not been possible to detect and store the geometric errors of the printing plates (or rather of the printing plate, of the printing plate holder and of the assembly consisting of the printing plate and the printing plate holder): knowledge of these errors would ensure reduction of the starting times of a printing process, since it would be possible to assess beforehand the suitability and print quality of each printing assembly during printing plate mounting.

Verification of the shape, geometry shape and mounting thickness errors of the printing assembly is therefore performed necessarily by means of test prints: the simplification introduced by automation of the verification of the match of the printing plate and of its correct mounting with respect to a virtual image therefore limits the checking activity to a first step, at the end of which it is nonetheless necessary to perform a test print in order to complete the checking of the printing assembly. Disclosure of the Invention

The aim of the present invention is to solve the problems described above, by providing an apparatus for checking geometric parameters of printing assemblies consisting of flexographic printing plates mounted on respective cylinders, of flexographic printing plates mounted on respective printing plate sleeves and of inking cylinders/sleeves, which is suitable for checking the geometric and dimensional parameters of the printing assembly in order to identify it completely and uniquely so as to verify its complete compliance with the requirements of use.

Within this aim, an object of the invention is to propose an apparatus for checking geometric parameters of printing assemblies consisting of flexographic printing plates mounted on respective cylinders, of flexographic printing plates mounted on respective printing plate sleeves and of inking cylinders/sleeves which is adapted to check the dimensional and geometric variation with respect to the ideal dimensions and shape, which are optionally preset and/or stored, in order to check that this variation is lower than a predefined limit value for this type of print assembly.

A further object of the present invention is to provide an apparatus for checking geometric parameters of printing assemblies consisting of flexographic printing plates mounted on respective cylinders, of flexographic printing plates mounted on respective printing plate sleeves and of inking cylinders/sleeves which has low costs and is relatively simple to provide in practice and safe in application.

This aim and these and other objects which will become better apparent hereinafter are achieved by an apparatus for checking geometric parameters of printing assemblies consisting of flexographic printing plates mounted on respective cylinders, of flexographic printing plates mounted on respective printing plate sleeves and of inking cylinders/sleeves, characterized in that it comprises at least one sensor, which faces at least one portion of the outer surface of the printing assembly to be analyzed and is designed to detect the distance between said sensor and the surface to be analyzed, said sensor being arranged at a fixed and known distance from the pivoting and mounting axis of the printing assembly. Brief description of the drawings

Further characteristics and advantages of the invention will become better apparent from the following detailed description of a preferred but not exclusive embodiment of the apparatus for checking geometric parameters of printing assemblies consisting of flexographic printing plates mounted on respective cylinders, of flexographic printing plates mounted on respective printing plate sleeves and of inking cylinders/sleeves according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a front view of an apparatus for checking geometric parameters of printing assemblies consisting of flexographic printing plates mounted on respective cylinders, of flexographic printing plates mounted on respective printing plate sleeves and of inking cylinders/sleeves according to the invention;

Figure 2 is a front view of the apparatus for checking geometric parameters of printing assemblies consisting of flexographic printing plates mounted on respective cylinders, of flexographic printing plates mounted on respective printing plate sleeves and of inking cylinders/sleeves according to the invention, mounted on a printing plate holder;

Figure 3 is a side view of the printing assembly consisting of a flexographic printing plate mounted on a respective cylinder;

Figure 4 is a front view of the printing assembly consisting of a flexographic printing plate mounted on a respective cylinder; Figure 5 is a schematic view of the functional block diagram of the apparatus for checking geometric parameters of printing assemblies consisting of flexographic printing plates mounted on respective cylinders, of flexographic printing plates mounted on respective printing plate sleeves and of inking cylinders/sleeves according to the invention, mounted on a printing plate holder.

Ways of carrying out the Invention

With reference to the figures, the reference numeral 1 generally designates an apparatus for checking geometric parameters of printing assemblies 2 consisting of flexographic printing plates 3 mounted on respective cylinders 4, of flexographic printing plates 3 mounted on respective printing plate sleeves 5 and of inking cylinders/sleeves.

The apparatus 1 comprises at least, one sensor 7, which faces at least one portion 8 of the outer surface of the printing assembly 2 to be analyzed.

The sensor 7 is designed to detect the distance between the sensor 7 itself (in particular the limit of the detection is the end surface of the sensitive area of the sensor 7) and the surface to be analyzed.

The sensor 7 is arranged at a fixed and known distance from the pivoting and mounting axis of the printing assembly 2.

The sensor 7 is coupled to a slider 10, which can slide along a rail 1 1 parallel to the pivoting and mounting axis 9 of the printing assembly 2.

The sliding of the slider 10 causes the alignment of the sensor 7 with different and contiguous positions (portions 8) of the printing assembly 2 for detecting the parameters in each position: in this manner it is possible to detect the parameters of interest at all the points of a generatrix of the printing assembly 2 being considered; the slider 10 moves along the direction that is parallel to the axis and identifies each position in which it is located with the distance X with respect to its initial reference (the respective distance X will be associated with each detection).

According to a particular embodiment of unquestionable interest in practice and in application, the slider 10 can move according to successive incremental steps of preset width (ΔX), for alignment with corresponding positions of the assembly 2 at a preset mutual distance. In this manner it is possible to discretize the surface being considered in order to define its geometric-dimensional characteristics in preset positions: the advantage is the availability of parameterized data, which will facilitate comparison with the data acquired by other assemblies 2 or with standard values stored in a suitable computer 12.

According to an alternative embodiment, the slider 10 can move continuously for continuous detection, by the sensor 7, of the geometric/dimensional parameters of the printing assembly 2 in all the positions that are successively aligned with the sensor 7.

This type of analysis provides a continuous and complete definition of the dimensional parameters and therefore can be particularly useful in cases in which the adjustment must be particularly precise in order to obtain high-quality printing results.

In order to achieve optimum dimensional verification, each printing assembly 2 can rotate about its own axis 9 continuously, causing an angular displacement α with respect to an initial reference; the sensor 7 designed to detect the geometric/dimensional parameters in this case operates continuously and in each instant during the rotation of the assembly 2 (the corresponding angle α will be associated with each detection).

In this case, an angular detection (as a function of an angle α) is performed continuously and makes it possible to investigate from a geometric standpoint each "ring" of the assembly 2 in order to discover the pattern of its actual radius and therefore be able to compare it with the ideal radius (which also is variable with variation of the angle as a consequence of the shape of the flexographic printing plate 3 that is needed to imprint the image to be printed).

As an alternative, for obtaining a detection of the angular incremental type, the printing assembly 2 can rotate about its own axis 9 according to successive angular increments of predefined extent (Δα); the sensor 7 is therefore designed to detect geometric/dimensional parameters at each stop between successive incremental angular movements.

For the rotation of the assembly 2 a suitable movement apparatus 13 is provided, which is controlled so as to cause precise rotations and provide incremental steps (Δα) even of extremely small extent (which can also be optionally obtained with high precision and resolution).

It is clear that by combining the movements of the slider 10, on which the sensor 7 is fixed, with respect to the rail 1 1 along the direction that is parallel to the axis 9 (corresponding to movements X), with the rotations of the assembly 2 about its own axis 9 (which correspond to angular rotations of extent α) it is possible to investigate and detect every point of the surface of the printing assembly 2.

The apparatus 1, in a complete version thereof which is suitable for immediate industrial application, comprises a memory unit for storing the detected geometric/dimensional parameters: in particular, according to the embodiment shown in the accompanying figures, the memory unit is comprised within the computer 12 cited earlier.

The possibility is not excluded to include directly on the cylinder 4 or on the sleeve 5 memory units which can be connected to the computer 12 of the apparatus 1 during the detection step: in this case, the detected data will be stored in the unit installed on the cylinder 4 or on the sleeve 5.

For facilitating data transfer operations, the apparatus 1 comprises a connection and communication component, such as a port and a corresponding cable; these components are associated with the computer 12 for storing and optionally analyzing the detected data.

The method for detecting geometric parameters of printing assemblies 2 consisting of flexographic printing plates 3 mounted on respective cylinders 4, of flexographic printing plates 3 mounted on respective printing plate sleeves 5 and of inking cylinders/sleeves consists of a first step a) for detecting the value of the actual radius of the printing assembly 2 at a preset distance X, along the axial direction 9, from the end of the assembly 2 and at a predefined angular position α of the assembly 2 with respect to an angular reference position. A second step b) compares the detected value of the actual radius with the value of the ideal theoretical radius, determining the extent of the deviation and the coordinates related thereto, i.e., in total, the coordinates of the detection point, i.e., the axial distance X and the angular position α, the detected actual radius and the deviation with respect to the theoretical radius, for a plurality of points of the printing assembly 2. The apparatus 1 makes it possible to check the geometric errors of the printing plates 3 mounted on cylinders 4 or printing plate sleeves 5.

It might also make it possible to store the data detected and optionally transmit them to the operator: in this manner, the operator might use them during the step for assessing the result of mounting of the printing plate, for a final check of the printing assembly 2.

The apparatus 1 makes it possible to detect, store and transmit the total errors and deviations with respect to the ideal geometric conditions, with regard to nominal values, caused by: a) machining tolerance of the printing plate cylinder 4 or sleeve 5 with respect to circularity, concentricity and diameter values. b) tolerance in the thickness of the double adhesive (which attaches the printing plate 3 to the respective printing plate holder): said thickness can be different from reel to reel. c) tolerance related to the thickness of the printing plate 3. In relation to the geometric printing errors of the printing plates 3 mounted on the printing plate cylinders 4/sleeves 5, it is necessary to register also the inking cylinders/sleeves (in particular, they draw the ink from a tank and distribute it on the outer surface of the printing plate 3).

The adoption of the apparatus 1 according to the invention allows a comparison of the theoretical printing radius with reference to the rotation axis 9 with the practical surface radius of the printing plate 3 on all the points deemed necessary of the circumference and of the width of the printing regions of the printing plates 3.

During detection it is possible to verify whether the practical radius of the printing plate 3 is larger, equal, or smaller, in various points of the circumference and length, with respect to the theoretical radius.

Whatever the result of the check, it must be borne in mind that the important points to be stored are the ones whose practical radius value is smaller than that of the theoretical radius, which points allow the operator to assess the mounting result and verify the suitability of the printing assembly for application to a specific printing process.

In order to be able to manage the data of the "preprint geometric detection" it is necessary to be able to recognize with a code all the technical information relating to the use and printing characteristics of each printing assembly 2.

The apparatus 1 is normally applied to a printing plate mounting unit 20 (as shown in Figure 2) which is suitable for mounting the printing plates 3 in register, but, as specified earlier and as shown in Figure 1 , it can be incorporated in a completely dedicated structure, constituting in practice an autonomous machine.

According to a particular embodiment, the detection sensor 7 can be connected to its controller 21 by means of a flexible cable, which cable can communicate with the computer 12 of the printing plate mounting unit 20 by means of specific software and the ports 22 (USB and RS-232C). The apparatus 1 for geometric detection also makes it possible to provide digital information for each printing plate sleeve 5 by means of the computer of the printing plate mounting unit 20: as already mentioned, this information can also be stored directly on memory units comprised within the printing assembly 2 being considered. The possibility is not excluded of reading the information contained within the memory unit installed in the printing assembly by means of wireless connections (electromagnetic couplings, such as frequency modulations, infrared and the like).

The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims; all the details may further be replaced with other technically equivalent elements.

In particular, in order to allow high-precision measurements, it may be convenient to associate with the surface to be analyzed, at the range of action of the sensor 7, a portion of adhesive tape of small size (for example 2.5 square centimeters). This tape should conveniently have a smooth and matt surface and must be easily removable so as to constitute an actual mask.

The presence of the mask is very important in order to overcome more easily the problems that arise from the different characteristics of the surfaces to be investigated:

- the printing plates 3, for example, can have extremely various surface characteristics (glossy, matt, transparent with engraving and without); - the printing plate sleeves 5 can be made of various materials;

- the sleeve supporting spindles 4 can have a chrome-plated surface, which generates strong luminous reflections, making the reading by the sensor 7 more difficult;

- the inking elements, by having an engraved surface, in order to accommodate the ink to be distributed, create reflections that make reading more complicated.

The removable mask provided by means of the tape is simply fixed to the surface and removal in any case leaves no trace of adhesive.

It is convenient to resort to the mask also for the calibration of the sensor 7, which will allow to have higher precision in the measurements performed subsequently.

In the exemplary embodiments shown, individual characteristics, given in relation to specific examples, may actually be interchanged with other different characteristics that exist in other exemplary embodiments. Moreover, it is noted that anything found to be already known during the patenting process is understood not to be claimed and to be the subject of a disclaimer.

In practice, the materials used, as well as the dimensions, may be any according to requirements and to the state of the art. The disclosures in Italian Patent Application No. BO2008A000709 from which this application claims priority are incorporated herein by reference.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

1. An apparatus for checking geometric parameters of printing assemblies (2) consisting of flexographic printing plates (3) mounted on respective cylinders (4), of flexographic printing plates (3) mounted on respective printing plate sleeves (5) and of inking cylinders/sleeves, characterized in that it comprises at least one sensor (7), which faces at least one portion (8) of the outer surface of the printing assembly (2) to be analyzed and is designed to detect the distance between said sensor (7) and the surface to be analyzed, said sensor (7) being arranged at a fixed and known distance (9) from the pivoting and mounting axis of the printing assembly (2).

2. The apparatus according to claim 1 , characterized in that said sensor (7) is coupled to a slider (10), which can slide along a rail (1 1) parallel to the pivoting and mounting axis (9) of the printing assembly (2), the sliding of said slider (10) causing the alignment of said sensor (7) with different and contiguous positions of said printing assembly (2) for detecting the parameters at each position.

3. The apparatus according to claim 2, characterized in that said slider ( 10) can move in successive incremental steps of preset extent for alignment with corresponding positions of the assembly at a preset mutual distance.

4. The apparatus according to claim 2, characterized in that said slider (10) can move continuously for continuous detection, on the part of said sensor (7), of the geometric/dimensional parameters of the printing assembly (2) in all the positions that are successively aligned with said sensor (7).

5. The apparatus according to claim 1, characterized in that said printing assembly (2) can rotate about its own axis (9) continuously, said sensor (7) being designed to detect the geometric/dimensional parameters continuously and at each instant during the rotation of said assembly (2).

6. The apparatus according to claim 1, characterized in that said printing assembly (2) can rotate about its own axis (9) according to successive angular increments of predefined extent, said sensor (7) being designed to detect the geometric/dimensional parameters at each stop between successive incremental angular displacements.

7. The apparatus according to one or more of the preceding claims, characterized in that it comprises a component, such as a port and a corresponding cable, for connection and communication with a computer (12) for the optional analysis of the data for the check.

8. A method for detecting geometric parameters of printing assemblies (2) consisting of flexographic printing plates (3) mounted on respective cylinders (4), of flexographic printing plates (3) mounted on respective printing plate sleeves (5) and of inking cylinders/sleeves, which comprises the steps of: a) detecting the value of the actual radius of the printing assembly (2) at a preset distance, along the axial direction, from the end of the assembly (2) and at a predefined angular position of said assembly (2) with respect to an angular reference position; b) comparing the detected value of the actual radius with the value of the ideal theoretical radius, determining the extent of the deviation and of its coordinates, i.e., axial distance and angular position, actual radius and deviation, for a plurality of points of the printing assembly (2).