The present invention relates in a first aspect to a mounting device for a computer- assisted mounting of a flexible printing plate on a cylindrical carrier, and in a second aspect to a method of a computer-assisted mounting a flexible printing plate on a cylindrical carrier wherein a mounting device according to the first aspect of the invention is used.

In the relevant technical field, mounting devices for a computer-assisted mounting of a flexible printing plate on a cylindrical carrier are well-known, and comprise a support structure that is provided with: i) a table having a top surface on which a flexible printing plate can be placed in a fixated position, which table has a width Y and a length X defining a horizontal plane, in which horizontal plane the table is displaceable with respect to the support structure; ii) a carrier actuator which is configured to support a cylindrical carrier such that the longitudinal axis of the cylindrical carrier is held in a parallel orientation to horizontal plane, wherein the carrier actuator is arranged beneath the top surface of the table and is displaceable with respect to the support structure in a vertical direction Z, and wherein furthermore the carrier actuator is configured to rotate the cylindrical carrier over its longitudinal axis; iii) at least two cameras, movably mounted on a camera rail arranged above the table, which cameras are directed to the top surface of the table and configured to detect a flexible printing plate when placed in a fixated position on the top surface, wherein the cameras are capable to output detection data relating to the detection of the flexible printing plate; wherein the cameras, the table and the carrier actuator are provided with respective driving means for individually displacing the cameras, the table and the carrier actuator and for rotating the carrier actuator; iv) a computer which controls the respective driving means of the camera, the table and the carrier actuator, and which processes detection data output by the at least one camera, wherein the computer is programmed to: - process the detection data such that an actual position is established of a flexible printing plate which is in a fixated position on the table,

- to compare the established actual position with a predetermined target position of the flexible printing plate which is stored in the computer, and

- to control the driving means of the table in order to set the flexible printing plate in the predetermined target position.

The present applicant actually has developed and produced multiple types of such a mounting device, which are commonly referred to as an ‘automatic mounting machine’. Two types which have become particularly popular in the market, are sold and marketed under the brand names ‘SAMM 2.0’ and ‘FAMM 3.0’.

Several more specific features of these mounting devices that are produced and marketed by the applicant, are described in patents owned by the applicant, for instance in European patent EP1727677.

It is noted that within the context of the invention as described herein below, the term ‘table’ should be understood to perform the general functionality of a ‘manipulator’ of the printing plate, as the table is designed to move the fixated printing plate within the horizontal plane towards a correct position. The table as such is thus capable of manipulating the actual position of the printing plate. The term table in the context of the invention is therefore not restricted to merely the commonly used meaning of a table in every day life.

For instance, the table according to the invention could be configured as a conveyor belt having a belt that is movably arranged in the horizontal plane, and which is suitable to place a printing plate on in a fixated position.

When such a mounting device is used in practice, the following steps are performed in order to mount a flexible printing plate correctly on a cylindrical carrier:

- a flexible printing plate is manually placed by a user on the top surface of the table of the device, in such a way that specific parts of the plate are placed in the field of view of the cameras, which cameras have been set in a pre-determined position by the computer on the basis of specific settings for the type of printing plate that is used;

- the plate is fixated in its position on the top surface by creating a reduced pressure on the bottom side of the plate; - the cameras detect the specific parts of the plate in order to establish the actual position;

- the computer compares the actual position of the plate with the predetermined target position;

- the computer controls the driving means of the table so as to bring the plate in the predetermined target position;

- when the plate has reached its target position, the carrier actuator which supports a cylindrical carrier is displaced towards the printing plate such that the carrier contacts a free part of the plate which is not supported on the table, and subsequently the whole printing plate is transferred onto the outer surface of the cylindrical carrier during rotation thereof .

It is noted that the specific parts of the printing plate to be detected by the two cameras, are typically two specific parts that are distanced from each other, wherein each specific part is provided with a reference sign or reference marking, also known as a ‘mounting mark’.

During the mounting of the printing plate by the mounting device, a precise detection of the actual position of the plate is critical in order to bring the plate in its predetermined target position as accurately as possible. The accuracy of bringing the plate in its target position subsequently determines the accuracy of the positioning of the plate onto the cylindrical carrier.

According to the high standards that are presently required in flexographic printing, it is currently considered ideal when an accuracy of (pre)positioning of the plate on the cylindrical carrier is achieved by a margin of 5 micron or even less.

In view of the above requirements, it was found that achieving such a high accuracy of positioning of the plate can be a challenge, because a precise detection of the actual position of the printing plate on the table may be hampered by several practical aspects relating to the detection process.

It is common in the field, that the detection of the printing plate is based on the detection of reference markings which are provided on specific parts of the printing plate. The surface structure of the printing plates may however have irregularities which blur to some extent the image of the markings that are to be detected by the cameras. A first concern in this respect, is that printing plates are regularly made from a flexible material which has a microscopic relief on the outer surface to enhance ink transfer. This ‘microcell’ structure consequently disperses light due to the inherent non-reflective nature of its surface and may consequently alter or blur the detectable image of the markings.

Another practical concern is that printing plates are frequently used and therefore suffer from wear and tear, which distorts the evenness of the outer surface of the plate. Such a distorted evenness of the printing plate will further compromise a precise detectability of the of the reference markings on the plate surface.

The general objective of the present invention is to solve the above indicated drawbacks from the prior art, and to achieve a highly precise and reliable detectability of the reference markings on a printing plate by the two cameras, even when the surface structure of the printing plate has irregularities which may compromise the detectability of the reference markings of the printing plate during the mounting process.

The invention achieves the above objective, by the provision of a mounting device of the above indicated type, that additionally comprises: v) a lighting device which is arranged in the horizontal plane of the table and is configured to be switched on by the computer in order to emit a beam of light in an upward direction parallel to the vertical direction Z, which emitted beam of light extends above the horizontal plane defined by the table, such that the emitted beam of light illuminates a flexible printing plate when it is placed on the top surface of the table, wherein the lighting device is dimensioned as an elongated lighting source which extends over the width of the table, and is composed of an array of light emitting sources, preferably an array of light emitting diodes.

The lighting device as such provides a backlight for the detection by the cameras of the actual position of the flexible printing plate. Herein, the beam of light that is emitted upwardly, effectively raises the contrasting properties within the image of the printing plate that is detected by the cameras, and a sharper definition of the detectable image is achieved. This sharper definition is particularly advantageous when the surface structure of the printing plate has irregularities which blur the detectable image. Because of the sharper definition, the detectability of the reference markings of the printing plate is enhanced, and hence the accuracy by which the plate is set in its predetermined target position is improved. This improvement was found to result in an accuracy of positioning the printing plate on a cylindrical carrier, by a margin of 5 micron or less.

In addition, the lighting device is configured as an elongated lighting source which extends over the width of the table, so that the beneficial backlight effect is obtainable over the whole width of any flexible printing plate that is to be mounted. It is common practice, that merely specific areas of the printing plate are to be detected by the cameras to determine the precise position of the printing plate. As the width positions of these specific areas may vary largely for different printing plates, it is a prerequisite that an illumination by the backlight over the whole width of the table is achievable.

It is particularly preferred in mounting device according to the invention, that the computer is configured to selectively switch on at least two individual width sections from the array of light emitting sources, wherein the individual width sections to be switched on are separated from each other by an intermediate width section of the array which is not switched on, wherein the individual width sections to be switched on are pre-determined by the computer on the basis of the specific flexible printing plate that is to be mounted, and in particular on the basis of dedicated areas of the flexible printing plate that are to be illuminated by the emitted beam of light.

The elongated lighting source which extends over the width of the table already has the general advantage of allowing for an illumination of different printing plates of different sizes as explained above, however, it was found that the backlighting effect of such an array of light sources could be enhanced further, by selectively switching on individual width sections in accordance with the flexible printing plate that is to be mounted.

It has been observed that the beneficial backlight effect of the elongated lighting source could become impaired when the array of light emitting sources is switched on over a broad width, such as when it is switched on over its full width. The reason behind this, is that each individual light emitting source emits a beam of light in an upward direction parallel to the vertical direction Z, which beam has an intrinsic conical shape that diverges upwardly. Consequently, the outer part of each conical beam includes light that is emitted under a substantial angle from the vertical direction Z.

In view of illuminating the flexible printing plate, actually only the zones of the plate that are detected by the cameras have to be illuminated, and it was found beneficial that in this context only the light sources of the array that are vertically present under the zone to be detected are switched on. The selected width section of the array thus emits light towards the camera that detects the illuminated zones of the plate, wherein the light extends in a direction that aligns with vertical direction Z, or is approximate to this direction by about 5 degrees. As such, it is avoided that the part of the plate to be illuminated is additionally illuminated by adjacent light sources just outside of the width section, which would emit light towards the camera under an askew angle that is not vertical or approximate thereto.

In terms of achieving a precise detection of the actual position of the printing plate, it was found that illumination by light that is directed towards the camera under such an askew angle, gave less precise results in comparison to having a more uniform beam of light approximate to a vertical direction, which can be created by selectively switching on the light sources in individual width sections correspondent to the parts of the printing plate to be detected by the camera.

In practice, the array may be composed by a row of adjacent light sources, wherein each individual light source has a diameter of 5 mm to 10 mm. Dependent on the specific part of the plate to be illuminated, the width section of lights sources that is switched on may extend over 1 .0 cm to 5.0 cm of the array, and the width section thus could for example include 1 to 10 adjacent light sources. It is herein generally beneficial that the width section is relatively small in size but not smaller than the part of the plate to be illuminated.

It is furthermore preferable in the mounting device, that the computer is configured to control the movement of the cameras such that the cameras are set in preselected operational positions by the computer on the basis of the specific flexible printing plate that is to be mounted. This automated positioning of the cameras further contributes to a reliable and swift operation of the mounting device.

It is particularly preferred in the mounting device, that the cameras for detection of a flexible printing plate are capable of detecting reference markings which are applied on dedicated areas of the flexible printing plate.

Such a mounting device is highly suitable for its intended use, because reference markings on the printing plates are commonly used in the field.

It is especially preferred in the mounting device according to the above preferred embodiments, that each individual width section to be switched on is vertically opposed to the operational position of each individual camera, when viewed along the vertical direction Z of the beam of light emitted from each individual width section.

It is preferable in the mounting device according to the invention, that the computer is programmed to perform the consecutive steps of: processing the detection data to establish the actual position of a flexible printing plate that is fixated on the table, comparing the actual position with the predetermined target position, and subsequent displacement of the table on which the flexible printing plate is fixated, such that the flexible printing plate is brought towards the predetermined target position, wherein the above three consecutive steps are repeated until the established actual position coincides with the predetermined target position of the flexible printing plate.

The automated repetition of these steps is instrumental in achieving the highest level of accuracy of positioning the printing plate in its target position.

Advantageously, the mounting device according to the invention further comprises a display which shows both an actual position of an area of the flexible printing plate as detected by the camera, and a corresponding predetermined target position for that same area. Consequently, the positioning of the flexible printing plate towards its target position can be monitored and checked visually by the user, during operation of the device.

In the mounting device according to the invention, it is preferred that the lighting device functions as a backlight for the flexible printing plate, in particular as a backlight for areas of the flexible printing plate that are provided with reference markings.

As explained above, the functionality of a backlight for the printing plate raises the contrasting properties within the image of the printing plate and hence the sharpness of the definition of the image that is detected by the cameras, which consequently results in an enhanced accuracy of the mounting of the printing plate by the device.

According to another preferred embodiment of the invention, the lighting device is integrated in the table, or a separate structure which is configured to be actuated into a position adjacent to the table and coplanar with the horizontal plane of the table.

It is practically expedient, when the table of the mounting device according to the invention, is provided with orifices extending into the top surface, which orifices are configured to apply a reduced air pressure at the top surface for fixating a flexible printing plate that is placed on the top surface.

The orifices being suitable to apply a reduced air pressure, is an expedient feature for temporarily fixating a printing plate of the table during specific steps of the mounting process. During the different steps of the mounting process, the reduced air pressure can respectively be switched on or off either by the user, or by a program that runs on the computer.

It is preferable that in the mounting device according to the invention, the computer is programmed to perform an additional step, after the flexible printing plate is set in the predetermined target position, which additional step comprises the vertical displacement of the carrier actuator which is provided with a cylindrical carrier, to such a height that the outer surface of the cylindrical carrier contacts a first section of the flexible printing plate which is not supported by the top surface of the table, resulting in the adherence of the first section of the flexible printing plate onto the cylindrical carrier, and a subsequent step of rotation of the cylindrical carrier to transfer the whole flexible printing plate onto the cylindrical carrier while the flexible printing plate is no longer held in a fixated position on the top surface of the table.

Such a mounting device effectively accomplishes the mounting of the printing plate onto the cylindrical carrier in an automated way such that a high accuracy of the mounting is assured.

It is noted that initial adherence of the first section of the printing plate to the cylindrical carrier is typically established by virtue of the cylindrical carrier having an adhesive outer surface.

In an attractive embodiment of the mounting device according to the invention, the table comprises at least two abutting table parts which are divided from each other by a seam extending over the width of the table, each table part being independently from the other table part movable in the horizontal plane of the table, which includes that the table parts can be distanced from each other in the length direction X, such that a gap is created between the table parts.

The gap that is hereby created between the two table parts results in the flexible printing plate having one section which is effectively no longer supported by the table. It In a subsequent step of the mounting process, this section of the flexible printing plate functions as the first section which contacts the cylindrical carrier and which is adhered onto the carrier.

It is noted that during the creation of the gap, one table part is kept in its position and onto this table part the printing plate is kept in its fixated position which corresponds to the predetermined target position. The other table part moves away from the one table part, while the printing plate is no longer fixated onto this other table part.

When the table of the mounting device according to the invention comprises at least two abutting table parts, it is preferred that the lighting device is integrated in one table part, or in both table parts.

A second aspect of the invention relates to a method of a computer-assisted mounting a flexible printing plate on a cylindrical carrier, wherein a mounting device according to the first aspect of the invention is used, which method comprises the steps of: a) placing a flexible printing plate on the top surface of the table in a fixated position; b) setting the cameras in pre-selected operational positions for detection of the flexible printing plate, in accordance with the flexible printing plate to be mounted; c) illuminating the flexible printing plate by switching on pre-determined width sections of the lighting device, in accordance with the flexible printing plate to be mounted; d) allowing the computer to perform the consecutive steps of: processing the detection data to establish the actual position of a flexible printing plate that is fixated on the table, comparing the actual position with the predetermined target position, and subsequent displacement of the table on which the flexible printing plate is fixated, such that the flexible printing plate is brought towards the predetermined target position, which three consecutive steps are repeated until the established actual position coincides with the predetermined target position of the flexible printing plate.

It is furthermore preferred in the above method according to the second aspect of the invention, that each individual width section that is switched on is vertically opposed to the operational position of each individual camera, when viewed along the vertical direction Z of the beam of light emitted from each individual width section. Examples

The invention will be further explained by specific preferred embodiments which are shown in the appended figures, wherein:

- Fig. 1 shows a frontal view of a preferred embodiment of a mounting device according to the invention;

- Fig. 2 shows a cross-sectional view of a part of the embodiment of fig. 1 during an initial step of mounting of a printing plate;

- Fig. 3 shows a cross-sectional view analogous to fig. 2, during a subsequent step of mounting of a printing plate;

- Fig. 2B and 3B show analogously to fig. 2 and 3, another preferred embodiment of the mounting device;

- Fig. 4 shows a perspective view of parts of the mounting device shown in fig. 2B and 3B.

Figure 1 shows a frontal view of a mounting device 1 having a support structure 3 that is provided with: a carrier actuator 5 which is dimensioned as an axle 5 onto which a cylindrical carrier 7 is arranged in a co-axial manner, and wherein the longitudinal axis of the cylindrical carrier 7 is arranged in a parallel orientation to the horizontal plane. The carrier actuator 5 is provided with a motor (not visible) to displace the carrier actuator 5 in vertical direction, and a motor 9 to rotate the carrier actuator over its longitudinal axis. a table 10 having a top surface on which a flexible printing plate can be placed in a fixated position, which table 10 has a width Y (in accordance with the width direction in the figure) and a length X (perpendicular to the plane of the figure) defining a horizontal plane, wherein the table is provided with motors (not visible) for displacing the table 10 in the horizontal plane; a counter-roller 12 for applying additional pressure during mounting of the printing plate onto the cylindrical carrier 7; two cameras 11 , movably mounted on a camera rail 19 arranged above the table 10, which cameras 11 are directed to the top surface of the table 10, and which cameras are capable to output detection data relating to the detection of the flexible printing plate; a keyboard 16 and a touch-screen device 14 to control a computer (not visible) which controls the motors of the cameras 11 , the table and the carrier actuator, and which processes detection data that are output by the cameras 11 ; a large screen display 18 for monitoring the progress of the positioning of a printing plate during execution of the mounting process.

Figure 2 shows a cross-sectional view of a part of the embodiment of fig. 1 , wherein corresponding features are indicated by the same reference numerals. The cross- sectional view is made along the length direction of the table. Fig. 2 shows table 10 onto which a flexible printing plate 20 is fixated during an initial step of mounting of the printing plate 20, wherein the printing plate 20 is brought towards its predetermined target position by a movement of table 10 that is coordinated with the actual position of the plate 20 as detected by camera 11 . Camera 11 is mounted onto the rail 19 above the table 10, such that the field of view (indicated by the dashed lines) of the camera 11 is directed to a discrete area of plate 20 which encompasses a reference marking 22 (for instance the image of a cross).

The table 10 is composed of two abutting table parts 24 and 26, which both are provided with orifices 28 on their respective upper sides, which orifices 28 are connected to a central conduit 30 in which a reduced pressure can be created and which is connected to a pump (not shown). As such, the printing plate 20 can be fixated in its position on the upper sides of the table parts 24 and 26 as long as a reduced pressure is maintained in orifices 28. Below the table 10 the cylindrical carrier 7 is arranged which is mounted onto carrier actuator 7.

The table part 26 is furthermore provided with a lighting device 34 which is provided with a transparent casing 32 which are integrated in the upper side of table part 26, such that a beam of light from the lighting device 34 is emitted in an upward direction from the top surface of the table 10. Accordingly the beam of light from the lighting device 34 will shine through the flexible printing plate 20 and hence will function as a backlight for reference marking 22 when viewed from the perspective of camera 11 . The sharpness of definition of the detectable image of marking 22 is hereby enhanced, which results in the camera 11 being able to detect the position of the marking 22 with a higher accuracy, and hence the actual position of the printing plate 20. In the situation of fig. 2, the following consecutive steps are performed by the computer of the mounting device 1 : processing detection data that are output by the camera 11 to establish the actual position of the flexible printing plate 20 that is fixated on the table 10, comparing the actual position with a predetermined target position that is stored in the computer, and subsequent displacement of the table 10 on which the flexible printing plate 20 is fixated, such that the flexible printing plate 20 is brought towards the predetermined target position, which three consecutive steps are repeated until the established actual position coincides with the predetermined target position of the flexible printing plate 20. Accordingly, the mounting device is capable to set the flexible printing plate in its predetermined target position with an accuracy by a margin of 5 micron or less.

Figure 3 shows, analogously to fig. 2, a cross-sectional view of a part of the embodiment of fig. 1 , wherein corresponding features are indicated by the same reference numerals. The embodiment of fig. 3 comprises the same features as shown in fig. 2, but not all are visible in fig. 3 for the sake of simplicity. Fig. 3 shows a subsequent step of mounting of a printing plate that follows after the situation shown in fig. 2, wherein a first section of the printing plate 20 is contacted with the cylindrical carrier 7.

In the situation shown in fig. 3, the table part 26 has been displaced away from table part 24 during which displacement the printing plate 20 was no longer fixated onto this table part 26, while the printing plate 20 still remained fixated onto the table part 24 and is kept in its predetermined target position. The displacement of table part 24 results in a gap being created between table parts 24 and 26, such that an area of printing plate 20 is not longer supported by the table parts. This nonsupported area is subsequently approached from below by the cylindrical carrier 7, and approached from above by counter-roller 12, in order to press the nonsupported section of the plate 20 onto the carrier 7. Once the first area of the printing plate is adhered onto the carrier 7, adjacent areas of the printing plate are adhered onto the carrier by rotation of carrier 7. The accuracy by which the first section of the plate 20 is adhered onto the carrier 7 determines the accuracy of mounting the whole plate 20 onto the carrier 7. Figure 2B shows analogous to the cross-sectional view of fig. 2, an alternative embodiment of the invention wherein corresponding features are indicated by the same reference numerals. The embodiment of fig. 2B is an alternative, in that the lighting device 34 is provided within a separate lighting structure 40, i.e. separate from both table parts 24 and 26.

The separate lighting structure 40 is U-shaped profile having a bottom wall 42 and two side walls 44, wherein an array 34 of light emitting sources is disposed. A transparent casing 32 covers the top side of the structure 40. It is noted that this separate structure 40 may be fixedly connected to one of the table parts 24 or 26. When the lighting structure 40 is not connected to the table parts, it is provided with a separate actuator for moving the structure 40 in the horizontal plane of the table parts.

Figure 3B shows analogous to the cross-sectional view of fig. 3, the alternative embodiment of fig. 2B wherein corresponding features are indicated by the same reference numerals.

Figure 4 shows a perspective view of the separate lighting structure 40 and the cameras 11 according to the configuration of the mounting device shown in fig. 2B and 3B. The lighting structure 40 is a U-shaped profile having a bottom wall 42 and two side walls 44, wherein an array 34 of adjacent, light emitting sources 46 is disposed. The transparent casing 32 that covers the top side of the structure 40 is not shown in fig. 4. The structure 40 has an elongated shape which extends in the width direction Y of the mounting device.

Fig. 4 shows two selected width sections W1 and W2 of the array 34 of light sources 46, which are to be selectively switched on for a particular printing plate according to the invention. Vertically above the two individual width sections W1 ,W2 are two respective cameras 11 which are positioned in pre-selected operational positions by the computer on the basis of the specific flexible printing plate that is to be mounted. As such, the width sections W1 ,W2 are vertically opposed to the respective cameras 11 . In the situation shown in fig. 4, most of the light emitted from the respective width section will progress towards the correspondent camera 11 in a vertical direction Z or a near vertical direction. When in such a situation a flexible printing plate 20 is present between the lighting structure 40 and cameras 11 (i.e. in the configuration as shown in fig. 2B), the reference marking 22 of the of the plate 20 will be illuminated by beams of light that progress in a in a vertical direction Z or a near vertical direction. Accordingly, a very precise detection of the marking 22 is achieved, and effectively a more accurate positioning of the printing plate is made possible.