Technical field

The present invention relates to an assembly for detecting geometric parameters of supports for printing plates, particularly for printing plate cylinders, sleeves and printing plate blankets that are adapted to accommodate on their surface, with the interposition of suitable layers of double adhesive, respective printing plates.

Background art

Recently provided apparatuses intended for mounting printing plates have made it possible to perform mounting in register by using virtual computer software (EPA 051 10941.1 in the name of this same Applicant) which, by using the file that identifies all the geometric parameters of the individual printing plate to be mounted, makes it possible to eliminate the print test (normally performed by using ink) and allows the operator to make precise comparisons of the position of individual corresponding parts between the real image, detected by means of image acquisition devices, and the virtual one that corresponds to the content of the file.

By adopting apparatuses designed for mounting printing plates that use the printing plate mounting system of the computerized virtual type (the comparison is performed between the image detected with the acquisition devices and the "ideal" image that corresponds to the content of the file), the actual print test has been eliminated, and in order to be able to control the geometric printing errors of printing plates an apparatus has been applied which comprises a sensor (WO2010/060884) which makes it possible to control the geometric errors of the printing plates mounted on the printing plate cylinders/sleeves in a preset number of points.

This detection and comparison method performed for monitoring the geometric parameters is considered valid but limited, since it can analyze up to a maximum of 40 points for each printing plate supporting cylinder/sleeve and has been considered too slow because a removable mask is required in order to be able to detect the surface of the printing plate.

It should be noted that in any case the greatest errors of a printing assembly with respect to its ideal configuration are to be sought in the double adhesive and in the printing plate supporting sleeves (or blankets): the thickness of a printing plate, instead, is in fact generally very regular and precise.

Double adhesive is instead constituted generally by a polymeric foam (generally made of polyethylene and polymers with similar chemical, physical and mechanical properties) provided with thin layers of adhesive material on both flat surfaces. The unevenness of the material, also caused by. the tendency to expand and contract of the air bubbles trapped therein as a function of temperature, often causes most of the dimensional, geometric and alignment errors of the entire printing assembly.

Disclosure of the invention

The aim of the present invention is to solve the problems described above, by proposing an assembly for detecting geometric parameters of supports for printing plates which is adapted to detect the dimensional parameters of a support on which the double adhesive is mounted.

Within this aim, an object of the invention is to propose an assembly for detecting geometric parameters of supports for printing plates that is adapted for the virtual superimposition, on the detected image of the support provided with double adhesive, of the file that represents the printing plate from a geometric and dimensional standpoint.

Another object of the invention is to propose an assembly for detecting geometric parameters of supports for printing plates on bands of predefined width of the lateral surface of the support being considered.

A further object of the present invention is to provide an assembly for detecting geometric parameters of supports for printing plates that has modest costs, is relatively simple to provide in practice and is safe in application.

This aim and these objects are achieved by an assembly for detecting geometric parameters of supports for printing plates, said supports being constituted by a substantially cylindrical body surmounted by at least one additional layer generally constituted by double adhesive tape, characterized in that it comprises at least one sensor, which is aligned with at least one portion of the outer surface of the support to be analyzed to detect the shape of the outer surface of the double adhesive tape that surmounts the cylindrical body.

Brief description of the drawings

Further characteristics and advantages of the invention will become better apparent from the description of a preferred but not exclusive embodiment of the assembly for detecting geometric parameters of supports for printing plates according to the invention, illustrated by way of non- limiting example in the accompanying drawings, wherein:

Figure 1 is a schematic front view of a possible embodiment of an assembly for detecting geometric parameters of supports for printing plates according to the invention arranged on a printing plate mounting unit;

Figure 2 is a schematic front view of a further simplified embodiment of an assembly for detecting geometric parameters of supports for printing plates according to the invention, arranged on a different printing plate mounting unit;

Figure 3 is a side view of a support for printing plates, on which a layer of double adhesive surmounted by respective printing plates is arranged;

Figure 4 is a front view of a support for printing plates on which a layer of double adhesive surmounted by two respective printing plates is arranged.

Ways of carrying out the invention

With reference to the figures, the reference numeral 1 generally designates an assembly for detecting geometric parameters of supports 2 for printing plates A.

With conventional apparatuses for mounting printing plates that adopt the printing plate mounting of the type known as "virtual computerized", the actual print test to check the geometric printing errors of the printing plates has been eliminated. In this case, an apparatus has been provided which comprises a sensor (WO2010/060884) that enables to check the geometric errors of the printing plates mounted on the printing plate sleeves/cylinders in a predefined number of points (a maximum of 8 points on the circumference for a maximum of 5 bands on the axial length of the printing support).

In order to allow and obtain highly precise measurements, it is necessary to position on the surface of the printing plate to be analyzed, at the beam of the sensor, a portion of removable adhesive tape with an opaque smooth surface (mask).

Masking has become indispensable in order to overcome the difference of the surfaces to be analyzed, for example:

- printing plates in various glossy, opaque, transparent colors.

- printing plates with and without engraving.

The apparatus for controlling geometric parameters makes it possible to check the total errors with respect to the nominal values combined from the cylinder/sleeve and from the double adhesive related to concentricity, roundness, circularity in the region of interest (i.e., the printing region).

As is known, photopolymeric plates for flexographic printing (the plates that constitute the raw material of which the printing plates will be made), prior to etching, have a manufacturing tolerance on their thickness with a very good class of precision, which on average is contained within ±0.01 mm with respect to the value of the nominal thickness. A measurement of the plates before etching makes it possible in any case to have assurance of the value of their dimensions. It is also known that geometric errors are caused

- by sleeves which, being made of a material such as plastic (therefore material of polymeric origin), over time undergo deformations of even ±0.05 mm,

- by double adhesive tapes, which have a precision tolerance that on average is contained within ±0.05 mm with respect to the value of the nominal thickness.

The printing supports 2, in the specific case, are constituted by a substantially cylindrical body 3 which is surmounted by at least one additional layer, which is generally constituted by double adhesive tape 4.

Specifically, an intermediate layer can also be provided which is constituted by a blanket/sleeve 5 designed to adapt the diameter of the cylindrical body 3 to the dimensions of the printing plate A.

The assembly 1 comprises at least one sensor 6, which is aligned with at least one portion of the outer surface of the support 2 to be analyzed in order to detect the shape of the outer surface of the double adhesive tape 4 arranged on the surface of the cylinder 3 (or on the surface of the blanket/sleeve 5).

The sensor 6, according to a particular constructive solution of unquestionable interest in practice and in application, is an apparatus for acquiring geometric errors on the double adhesive 4, considering the virtual existence of the regions in relief of the printing plate A (this assessment is calculated simply on the basis of the geometric information contained in the data banks that contain the files related to the printing plate A).

The apparatus is preferably of the type that comprises a laser emitter and a potential visual emulation detector (for example of the type known commercially as E ³ -CMOS).

According to an alternative constructive solution that is particularly efficient and certain in application, the sensor 6 comprises a laser emitter and a suitable detector of reflected signals, in order to acquire the distance between the emission plate of the laser emitter itself and the surface that faces it (the outer surface of the double adhesive tape 4 that faces the plate of the emitter).

The assembly 1 , according to a particularly functional application, comprises a control and management unit 7, which is provided with at least one respective memory element for storing the geometric and dimensional parameters of the printing plate A (in particular the dimensions actually detected during its production or the theoretical ideal dimensions related to its design specifications), the printing plate A being subsequently mounted on the double adhesive tape 4.

In this case, the assembly 1 further comprises a board for acquiring the information detected by the sensor 6.

The unit 7 is thus preset for the virtual superimposition of the geometric and dimensional parameters of the printing plate A on the dimensional and geometric information related to the double adhesive tape 4, detected by the sensor 6.

This virtual superimposition consists in adding, point by point, to the thickness of the printing support 2 detected by the sensor 6, the thickness of the corresponding point of the printing plate A, determining the actual thickness that the entire print roller will have once the printing plate A has been mounted on the support. The virtual superimposition enables to verify, even before mounting the printing plate A on the double adhesive tape 4, the presence of errors in positioning, alignment, concentricity and roundness of the entire roller, making it possible to eliminate or reduce the errors when in actual fact they have not yet occurred in practice.

It should be noted conveniently that the control and management unit 7 can comprise positively at least one adjustable filter, which is controlled by the card for the acquisition of the signals received from the sensor 6, in order to adjust the resolution of the sensor 6.

The adjustment becomes necessary in order to exclude the surface irregularities of the double adhesive tape 4 caused by the nature of the material of which it is constituted (polymeric foam, as mentioned earlier constituted preferably by polyethylene).

In many cases the double adhesive tape 4 also has microgrooves which are designed to convey outward any air bubbles, in order to prevent the inclusion of the bubbles between the tape 4 and the surfaces to which it is fixed from causing irregularities of the surface on which the printing plate A will be fixed. It is fundamental for the sensor 6 to be calibrated so as to not read these grooves, since they would alter the detections.

The assembly 1 conveniently can comprise at least one display 8 to be used by the operator and controlled by the control and management unit 7. Such display 8 is designed to represent an image that corresponds to the virtual superimposition of the geometric and dimensional parameters of the printing plate A contained in the storage element on the dimensional and geometric information related to the double adhesive tape 4 detected by the sensor 6.

As an alternative or in addition to the display 8, the assembly 1 can comprise an interface apparatus of the type of a printer, a screen, a display and the like, to be used by the operator and controlled by the control and management unit 7 in order to indicate the geometric and dimensional data related to the virtual superimposition of the geometric and dimensional parameters of the printing plate A contained in the storage element on the dimensional and geometric information related to the double adhesive tape 4 detected by the sensor 6.

It should be specified conveniently that the interface apparatus is designed to indicate the geometric and dimensional data of the virtual superimposition preferably only at the printing regions of the printing plate A, identified by the data that are present in the storage element with reference to the printing plate A.

This type of localized detection enables to minimize verification times. If the printing regions of the printing plate A are correctly positioned and therefore capable of printing in an optimum manner, what occurs in the other regions is in fact marginal in practice and is unimportant in terms of the assessment of any errors that might compromise the print.

Specifically, therefore, the sensor 6 must be of the type suitable to detect dimensional and geometric information related to the double adhesive tape 4 and to the support 2 (understood as the cylindrical body 3 that is optionally surmounted by a blanket/sleeve 5) on which it is mounted, the information being of the type of concentricity, roundness, deviation with respect to the theoretical ratio at preset angular positions.

It should be noted conveniently that the sensor 6 is suitable to detect continuously a predefined band of the support 2 surmounted by the double adhesive tape 4 that is aligned therewith and can rotate with respect to its own longitudinal axis in front of the sensor 6.

The breadth of the band depends on the breadth of the typical beam of the sensor 6 and on the distance between the sensor 6 and the double adhesive tape 4. The possibility to have means for adjusting the width in order to investigate very large or substantially point-like areas is provided.

The machine that is equipped with the assembly 1 according to the invention is generally the same one used for mounting and registering the printing plates A and allows:

- the insertion in the digital storage element of the measurements in 1 : 1 scale related to the theoretical image that corresponds to the printing plate A;

- the comparison by superimposition in 1 : 1 scale of the theoretical digital image of the printing plate A with the corresponding detected image on the printing plate A by means of a video camera B and a display 8;

- the comparison by superimposition in 1 : 1 scale of the theoretical digital image of the printing plate A with the corresponding detected image by means of the sensor 6, swapping the detection axis of the video camera with the detection axis of the sensor 6;

- the checking of the superimposition between the stored digital image and the virtual image detected by the sensor 6 with a continuous detection, thus comparing the entire scanned surface point by point, instant by instant, during the movement of the sensor 6 and during the rotation of the support 2;

- the positioning of the digital image of the printing plate A on the display 8 in relation to the mutual position of the video camera B (which can move parallel to the direction of the axis of the support 2) and of the printing support 2 (which can rotate about its own axis);

- the storage in a file of the entire positioning pattern of the graphical images of the printing plate A to be mounted, which corresponds to the printing circumference and printing width of the support 2.

The stored digital image is paired with the corresponding position detections of the sensor 6 (or of the video cameras B) along the respective sliding direction and of the support 2 (which can rotate about its own axis).

At each position of the sensor 6 and of the support 2, it is possible to see on the display 8 a portion of the printing plate A that is positioned virtually on the surface of the double adhesive tape 4.

The sensor 6 for detecting and checking the geometric parameters is mounted on a sliding carriage 9 which supports a video camera B and is arranged with a scanning direction that is perpendicular to the rotation axis of the support 2.

The detection axis of the two video cameras B is reset on the same reference point that exists on the file that contains all the dimensional and geometric parameters of the printing plate A and also the sensor 6 for checking the parameters must be reset to the same reference point during the operations for checking the geometric parameters.

Since the sensor 6 cannot measure precisely on the surfaces of the printing plates A provided with surface engraving, adopting the assembly 1 according to the invention enables to check the geometric parameters, measuring the surface of the double adhesive tape 4 only in the printing regions that correspond to the virtual image of the preprocessed graphical reproduction that can be arranged on the positioning scheme and that corresponds to the image on the printing plate A.

Conveniently the measurement of the thickness of the printing plate A can also be calculated virtually and corresponds to the measurement of the theoretical thickness or to the measurement of the previously detected thickness (for example during the production of the printing plate A).

After checking and storing the geometric parameters of the printing assemblies (printing support 2 on which the respective printing plate A has been superimposed virtually), it is possible (if allowed by the result) to mount the printing plates A on the double adhesive tape 4 of the support 2, always referring to the positioning pattern that is present in the digital storage element.

The reasons for which geometric checking is provided only in the printing regions of the printing plate A are as follows:

- to know the extent of the geometric errors only in the printing regions, since the other regions in fact are not interesting from an application standpoint;

- minimizing checking time.

The measurement of the surface of the double adhesive tape 4 to check the geometric parameters is performed advantageously by means of a detection sensor 6, which is arranged and can slide parallel to the axis of the support 2 and enables to acquire a large number of points on the width of approximately 50 mm and to detect a large number of points on the circumference that corresponds to the rotation through one turn of the support 2. During detection and checking of the geometric parameters, it is possible to verify whether the actual print radius or the practical deviation of the print radius is greater or equal or smaller on the virtual printing surface of the printing plate A that corresponds to the theoretical radius.

In any case, regardless of the result of the detection, one must consider that the important points to be stored are the ones that are have the highest and smallest value of the practical radius or of the deviation, for the following reasons:

- to know the ratio between the radius and the greatest and smallest displacement makes it possible to assess the suitable printing pressure that will have to be applied and therefore the suitability of the printing roller (support 2 surmounted by the double adhesive tape 4 and by the printing plate A) for printing.

- to know the ratio that exists between the radius or the smallest practical deviation with respect to the theoretical printing radius, which makes it possible to assess the printing pressure that must be applied with respect to the theoretical radius and therefore the suitability of the printing roller (support 2 surmounted by the double adhesive tape 4 and by the printing plate A) for printing the lowest points.

The sensor 6 is adjusted before beginning the geometric checks at a fixed and known distance from the pivoting and mounting axis of the support 2.

The assembly 1 for "geometric parameter checking" is normally applied to a printing plate mounting device that is adapted for mounting the printing plates A in register, but can also be included on a completely dedicated structure, constituting in practice an autonomous machine.

The sensor 6 is connected preferably by means of a flexible cable to the control and management unit 7, which by means of specific software can communicate with the computer that manages the printing plate mounting device (the control and management unit 7 might also constitute the computer of the printing plate mounting device in particular constructive solutions).

Operation of the assembly 1 is as follows. It is necessary first of all to acquire and store the geometric and dimensional parameters of the printing plate A. These data can be supplied by the manufacturer or obtained by means of specific measurement instruments.

It is then necessary to detect, by means of the sensor 6 that is aligned with the printing support 2 (constituted by a cylindrical body 3 surmounted by at least one additional layer constituted generally by double adhesive tape 4) and faces it, the distance between the sensitive surface of the sensor 6 and the outer surface of the double adhesive tape 4 in suitable predefined areas.

If the distance between the sensitive surface of the sensor 6 and the axis of the support 2 is known, it is possible to obtain the thickness of the printing support 2 that comprises the double adhesive tape 4 by means of the difference between the two indicated values. This operation must be performed at a plurality of points which are predefined by cylindrical coordinates constituted by a longitudinal position along the axis with respect to a linear reference and an extent of rotation with respect to an angular reference.

At each predefined point it is therefore necessary to add to the thickness of the printing support 2 (which comprises the double adhesive tape 4) the thickness of the printing plate A in the corresponding point, the thickness of the printing plate A being obtained from the acquired and stored data.

Advantageously, the assembly 1 according to the invention is suitable for detecting the dimensional parameters of a support 2 on which the double adhesive tape 4 is mounted.

Conveniently, the assembly 1 according to the invention is suitable for the virtual superimposition, on the acquired image of the support 2 provided with double adhesive tape 4, of the file that represents the printing plate A from a geometric and dimensional standpoint.

Positively, the assembly 1 according to the invention can perform detections on bands of predefined extent of the lateral surface of the support 2 being considered.

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

In the examples of embodiment shown, individual characteristics, given in relation to specific examples, may actually be interchanged with other different characteristics that exist in other examples of embodiment.

Moreover, it should be 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

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.