Abstract:
A clamping device, a cylinder including a clamping device, and a method for clamping a plate onto the outer surface of the cylinder. The clamping device includes a base body extending in the axial direction and fixed to, or incorporated into the cylinder. The clamping device also includes a clamping element extending in the axial direction. The clamping device also includes a lifting bar located in the interior of the base body and coupled to the clamping element by at least one guiding shaft. The lifting bar being movable in a first radial direction to move the clamping element away from the outer surface of the cylinder to form a gap between the outer surface and the clamping element. The lifting bar also is movable in the radial direction opposite the first radial direction to close the gap formed between the outer surface of the cylinder and the clamping element. The clamping device also includes a mechanism to impart and maintain compressive force between the clamping element and the outer surface of the cylinder such that any gap formed is maintained closed unless forcibly opened. The apparatus is arranged such that when the gap is formed by moving the lifting bar in the first radial direction, the edge of a flexible plate can be placed in the gap, and such that when the gap is closed, the plate is maintained clamped onto the outer edge of the cylinder.

Description:
RELATED PATENT APPLICATIONS 
   The present invention is claims benefit of U.S. Provisional Patent Application Ser. No. 60/651,095, filed Feb. 7, 2005, and titled METHOD AND APPARATUS TO CLAMP AND RELEASE FLEXIBLE PLATES ONTO AN IMAGING CYLINDER. 

   BACKGROUND 
   The present invention is related to the field of printing, and in particular, to a method and an apparatus for clamping flexible plates of different thickness and format onto an imaging cylinder, e.g., for exposure in a computer-to-plate imaging device by light energy according to imaging data. 
   Flexographic plates are frequently exposed from computer data using computer-to-plate (CTP, C2P) imaging. Mounting such plates on a cylinder, e.g., the cylinder or drum of an external drum imaging device is recognized as a problem. For example, one method to mount a flexographic plate on a cylinder is to fix the plates with adhesive tape at the edges. More modern methods use a clamping bar, which clamps the top and bottom edge of a full-size flexographic plate onto the cylinder. First adhesive tape method is very time consuming and second method using a clamping bar only works with full format plates. Since flexographic plate material is relatively expensive a modern method to mount partial plates on a full format cylinder are becoming more and more important. 
   An example of an external drum imaging device for which such a method and apparatus is applicable is the Esko-Graphics Cyrel Digital Imager (CDI) made by Esko-Graphics A/S, Ballerup, Denmark, the assignee of the present invention. 
   There is a need in the art for an economical easy-to-use method and apparatus to mount plates of different thickness and format directly onto the imaging cylinder. 
   In this description and in the claims, by a full-format plate is meant a plate that covers the whole imaging area of the cylinder. By a partial-format plate is meant a plate that covers part of the overall imaging area, such that several partial-format plates (also called plate segments) may be combined to cover the whole imaging area. 
   One prior art method is for a machine operator to manually mount a full-format plate or partial-format plates onto a cylinder with adhesive tape. Such a method is used, for example, by external drum imaging machines such as the ThermoFlex™ product line made by CREO Inc. of Burnaby, BC, Canada. However, to mount full-format or partial-format plates with adhesive tape is highly time consuming, the operator first mounts a first edge of the plate on the cylinder, fixes it with adhesive tape, turns the cylinder around so that the plate covers the cylinder, and then tapes all the rest of the edges of the plate. 
   Another prior art solution is for the machine operator to mount full-format plates—those that fully cover the circumference of a cylinder—with the use of a clamp, which is activated manually. An example of a device for so mounting full-format plates is a device used with an imaging drum, called EasyClamp™, made by Esko-Graphics A/S, Ballerup, Denmark, the assignee of the present invention. If partial-format plates are used, the machine operator first mounts partial-format plates onto the cylinder with the use of adhesive tape. The mounting by use of adhesive tape, as stated above, is time consuming. 
   Yet another prior art solution is for the machine operator to mount full-format plates—the case of the circumference of the cylinder being fully covered by the plate—using a terminal strip, which is activated manually. For mounting a plate, the terminal strip has to be opened manually, the plate has to be fixed under the terminal strip, the terminal strip has to be closed manually, the cylinder then has to be turned around, the terminal strip has to be opened manually again, the second plate edge has to be positioned under the terminal strip and then the terminal strip has to be closed manually. In all cases with the use of a terminal strip, the activation is done by manually by turning a key. This method is suggested, for example, in the HelioFlex® range of products made by HELL Gravure Systems GmbH of Kiel, Germany. 
   Note that as is the case with the Esko-Graphics EasyClamp™, the terminal strip is only for full-format plates. The machine operator mounts partial-format plates with the use of adhesive tape. The mounting by use of adhesive tape, as stated above, is time consuming. 
   There thus is a need in the art for a method and apparatus that avoids the manual steps of opening and closing clamping devices or a terminal strip, and for an apparatus therefore. 
   There further is a need in the art for a imaging cylinder that includes a plurality of clamping devices, positioned in a respective plurality of different axial positions, in a respective plurality of different circumferential positions, and/or in a respective plurality of both different axial and different circumferential positions, in order to avoid having to use adhesive tape to fix a partial-format plate to a imaging cylinder. 
   Thus both partial and full-format plates can be directly clamped at the end edges by the clamping device. 
   There also is a need in the art to automatically clamp a flexible plate automatically on a imaging cylinder. 
   There have been previous attempts at automating plate clamping. For example, U.S. Pat. No. 106,561,094 titled “DEVICE FOR FIXING A FLEXIBLE PLATE ON A IMAGING CYLINDER” and U.S. Pat. No. 106,598,530 titled “METHOD FOR FASTENING A FLEXIBLE PLATE,” both assigned to Koenig &amp; Bauer AG, of Würzburg, Germany, describe some such other attempts. These are referred to herein as the Koenig &amp; Bauer methods and mechanisms, as the case might be. 
   The Koenig &amp; Bauer clamping mechanisms are relatively complicated and more expensive. Therefore there is still a need in the art for new clamping methods, e.g., that are simpler and less expensive than the Koenig &amp; Bauer methods and mechanisms. 
   The Koenig &amp; Bauer methods are applicable to flexible plates that have bent suspension legs. Typical flexographic plates need to be clamped at the end edges, and such do not typically have bent suspension edges. Therefore there still is a need in the art for clamping both full-format and partial-format flexible plates at the end edges, such plates not having bent suspension edges. 
   The patents describe the use of automatic loading in imaging cylinders; the present invention related to loading on imaging cylinder for CTP systems. 
   The Koenig &amp; Bauer methods and apparatuses limit the number of clamps on the peripheral cylinder surface to two. Therefore there still is a need in the art for a clamping method and clamping apparatuses such that the number of clamping devices on a cylinder is not limited to a relatively small number. 
   There further is a need in the art for integrating a mechanism into an imaging cylinder to clamp and release flexible plates. There further is a need in the art for a clamping mechanism and clamping method that can work for a relatively large number of plate formats and thicknesses. 
   SUMMARY 
   An aspect of the present invention is a method for fastening flexible plates onto an imaging cylinder, e.g. for digital flexo plates or rubber, e.g., elastomere plates, or conventional flexo plates. Another aspect of the present invention is an apparatus to fasten such flexible plates onto an imaging cylinder. 
   In one embodiment, an imaging cylinder includes a clamping device, and the method includes placing end edges of a flexible plate between a clamping element of the clamping device and the outer surface of the cylinder. Springs are used to impart a force on to the placed plate towards the outer surface of the cylinder. An inflatable hose and springs are used to open a space between the clamping element and the outer surface to provide for mounting and unmounting plates. 
   In one embodiment, opening the clamping device is activated by applying air pressure from a pump or external connection. In such a manner, the operator only has to press a button or a foot panel to open or close the clamping device. 
   Another aspect of the invention is that by using more clamping devices, placed axially and/or in the circumferential direction, the need for adhesive tape to fix partial format plates onto the cylinder might be avoided. Partial and full-format plates are thus directly clamped at the end edges by the clamping devices. 
   Described herein are a clamping device embodiment, a imaging cylinder that includes a clamping device, and a method for clamping a plate onto the outer surface of the cylinder. One embodiment of the clamping device includes a base body extending in the axial direction and fixed to, or incorporated into the cylinder. The clamping device also includes a clamping element extending in the axial direction. The clamping device also includes a lifting bar located in the interior of the base body and coupled to the clamping element by at least one guiding shaft. The lifting bar is movable in a first radial direction to move the clamping element away from the outer surface of the cylinder to form a gap between the outer surface and the clamping element. The lifting bar also is movable in the radial direction opposite the first radial direction to close the gap formed between the outer surface of the cylinder and the clamping element. The clamping device also includes a mechanism to impart and maintain force between the clamping element and the outer surface of the cylinder such that any gap formed is maintained closed unless forcibly opened. The apparatus is arranged such that when the gap is formed by moving the lifting bar in the first radial direction, the edge of a flexible plate can be placed in the gap, and such that when the gap is closed, the plate is maintained clamped onto the outer edge of the cylinder. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  shows a cross section of a cylinder that includes a clamping device embodiment of the present invention. The cylinder&#39;s clamping device is shown in the plate holding (“closed”) position, with one plate clamped on the circumference of the cylinder using an embodiment of a clamping device in accordance with an aspect of the present invention. 
       FIG. 1B  shows a representation of a of air pressure supply coupled to work with the clamping device embodiment shown in  FIG. 1A .  FIG. 1C  shows an alternate embodiment that includes a valve element used by an operator or by a control system to automatically switch air pressure on or off while the pump is in operation. 
       FIG. 2  shows a cross-sectional representation of an embodiment of the clamping device of  FIG. 1A  in an enlarged scale. The clamping device is shown in the closed position. 
       FIG. 3  shows a cross-sectional representation of an embodiment of the clamping device shown in the release (“open”) position. 
       FIG. 4  shows the section shown in  FIG. 3  and marked A—A, with the clamping device in the release position, and for an embodiment that includes several sections of a clamping device that provides for clamping a plurality of plate segments onto the surface of the cylinder. 
       FIG. 5  shows in cross section an embodiment of a imaging cylinder with three instances of the clamping device distributed in the circumferential direction. 
       FIG. 6  shows one example of a clamping device on a cylinder, wherein the cylinder includes an indentation to accommodate the clamping element  101  of the clamping device  100 . 
   

   DETAILED DESCRIPTION 
     FIG. 1A  shows a cross section of a cylinder  107  that includes a clamping device embodiment  100  of the present invention. The cylinder  107  is, for example, the cylinder of an external drum imaging device for imaging flexographic plates or flexographic plate segments. The cylinder&#39;s clamping device  100  is shown in the plate holding (“closed”) position, with one plate  108  clamped on the circumference of the cylinder  107 . 
     FIG. 2  shows a cross-sectional representation of the clamping device  100  of  FIG. 1  in an enlarged scale. The state of the clamping device shown is closed. 
   The clamping device  100  includes a clamping element  101  that has a width and that extends in the axial direction of the cylinder, i.e., in the direction perpendicular to the plane of the drawing. The clamping element  101  and its width are configured to receive a flexible plate in the gap formed between the clamping element and the outer surface of the cylinder, one such plate  108  is shown in  FIGS. 1 and 2  located on the circumferential surface of the cylinder  107 . The clamping device  100  includes a base body  105  that has a hollow interior  110 , which in one embodiment has an approximately rectangular cross-section, and in another, an elliptical or circular cross-section. The base body  105  extends in the axial direction, and in one embodiment is fixed to the inner wall of the cylinder  107 , and in another embodiment, is incorporated with the inner wall of the cylinder  107 . 
   A inflatable air hose  106  made of an inflatable material—a rubber compound in one embodiment—is mounted in the hollow interior  110  of the base body  105 . The air hose  106  has an inflated state and an uninflated state. A lifting bar  103  is mechanically coupled to the clamping element  101 , in one embodiment using at least one guiding shaft  102 . At least one spring  104  is positioned between the lifting bar  103  and the base body  105  to exert a force onto the lifting bar  103  to compress the inflatable air hose  106  when the hose  106  is not inflated. In one embodiment, there is one spring per guiding shaft. 
     FIG. 1B  shows a source of air pressure, e.g., a pump  112 , that is coupled to the interior of the inflatable air hose  106  and configured to provide air pressure to the interior of the inflatable air hose  106  to inflate the hose  106 . In one embodiment, the pump includes a motor  114  and is electrically activated by an electric switch  116  that can be operated, e.g., by the operator pushing a button or activating the pump by a foot panel. 
   In an alternate embodiment, shown in  FIG. 1C , a valve element  137 , such as an air pressure switching device, e.g., a magnetic valve is included, and used by an operator or by a control system to automatically switch air pressure on or off while the pump is in operation. In yet another alternate embodiment, an external source of compressed air is used, and a switching device, such as a magnetic valve, is used for switching the air pressure on or off. 
   While the embodiment described herein is for manual operation under control of an operator, those in the art will easily recognize that the method and apparatus is readily adaptable for automatic operation under control of a control system that automatically switches the air supply on or off, as required, at the correct moments. Such an embodiment is shown in simplified form in  FIG. 1C  where an automatic loader/unloader  131  is shown with an imaging cylinder  133  of an external drum imager. Other components of the imager are not shown, as would be clear to those in the art. The method and apparatus described herein is readily adaptable to work in conjunction with an automatic loading device such as loader/unloader  131 . At least one instance of the clamping device  100  is included on the imaging cylinder  133 . Each instance includes a corresponding inflatable hose. A pump  135  is included and is on during operation. The pump is coupled via at least one individual valve device  137  to a corresponding instance of a clamping device. In one embodiment, each valve element is a magnetic valve. While in one embodiment, an operator switches the supply on or off to the corresponding clamping device&#39;s inflatable air hose to selectively provide an air supply to any selected clamping device or devices, in the example shown in  FIG. 1C , a control system  139  is included to automatically switch the air supply according to the sequence of loading or unloading of the automatic loader/unloader. One example of a control system  139  is a programmable microcontroller programmed to control the sequence of operation of the automatic loader/unloader  130  and of the at least one switching device  137  and corresponding clamping device. 
   Referring again to  FIG. 1B , in an alternate embodiment, a control system of an automatic loader/unloader (not shown in  FIG. 1B ) is coupled to the switch controlling the pump, such that the air supply is switched on or off automatically according to the loading/unloading sequence. 
   Therefore, whenever the description herein describes the operator switching on or off the air supply, those in the art will recognize that in an automated system, the operator is readily replaced by a control system, e.g., a programmed microcontroller, to switch the air supply on or off, as required, e.g., by an automatic loading system coupled to or also controlled by the control system, such a controlling system controlling the pump switch in one version, and a pressure switching element such as a magnetic valve in another embodiment. 
   Continuing with the operator-assisted operation, and referring still to  FIG. 1B , to load (or unload) a plate, the operator causes the source  112  of air pressure to provide air pressure to the interior of the inflatable air hose  106  to inflate the hose  106 . So inflating the inflatable air hose  106  causes the cross section of the hose to expand. The air hose expanding imparts a force onto the lifting bar  103  that causes the at least one spring  104  to compress the guide shaft and this causes the clamping bar to move such that a gap is created between the clamping element  101  and the outer surface of the cylinder  107 . Such a gap provides for inserting or removing the edge of a flexible plate between the clamping element  101  and the outer surface of the cylinder  107 . This state of the clamping device  100  is called the open state, and also the release state herein. 
     FIG. 3  shows the clamping device  100  in an open state. When in the open state, a plate  108  can be placed in the gap on the outer, peripheral, i.e., outer surface of cylinder  107  with the end edges of the flexible plate  108  placed in the gap formed between the clamping element  101  and the outer surface of the cylinder  107 . 
   After a plate is placed in the gap, the air pressure is removed from air hose  106 , e.g., by using switch  116  to stop the pump  112  providing air pressure to the interior of the inflatable hose  106 . The bias of the at least one spring  104  is such that the spring(s)  104  cause the lifting bar to move away from the surface of the cylinder, and thus the guide shaft  102  to cause the clamping element to press against the outer, peripheral surface of cylinder  107 , and thus clamp the end of the plate  108  to the cylinder. This is called the closed state of the clamping device  100 , and is as shown in  FIGS. 1A and 2 . 
   Thus, the edges of the flexible plate  108  are clamped with the force of the at least one spring  104 . 
   The unclamping and removal of the flexible plate  108  takes place in reverse order to the clamping. That is, starting from the closed state shown in  FIG. 2 , the operator causes the source  112  of air pressure to provide air pressure to the interior of the inflatable air hose  106  to inflate the hose  106  in order to cause the cross section of the hose to expand. The air hose&#39;s expanding imparts a force onto the lifting bar  103  that causes the at least one spring  104  to compress, and also to move the guide shaft and hence the clamping bar such that a gap is created between the clamping bar  101  and the outer surface of the cylinder  107 . Such a gap provides for removing the edge of a flexible plate between the clamping element  101  and the outer surface of the cylinder  107 . 
   One embodiment includes a plurality of clamping elements such as  101  oriented along the axial direction such that the clamping of more than one flexible plates in the axial direction is possible.  FIG. 4  shows the section A—A shown in  FIG. 3 , with the clamping device  100  in the open position. In addition to the clamping element  101 , part of two adjacent clamping elements  401  and  411  are shown. Each clamping element is attached to its own set of guiding shafts, three shafts  102  shown for clamping element  101 , and one guiding shaft  402 ,  412  of the respective sets of shafts attached to the clamping elements  401  and  411  are shown. The other ends of the guiding shafts are attached to respective lifting bars. Lifting bar  103  is coupled to shafts  102  and clamping element  101 , while parts of lifting bars  403  and  413  are coupled via shafts  402  and  412 , respectively, to the clamping elements  401  and  402 , respectively. A first set of springs  104  is shown around shafts  102 , a second set  404  around shafts  402 , and a third set  414  around shafts  412 . 
   By so arranging each clamping element to have its own guiding shafts, lifting bars, and springs, the different clamping elements can clamp plates of different thicknesses. 
   Note that in the embodiment shown, only one inflatable hose  106  is used for the whole axial length, i.e., for all the clamping elements. In an alternate embodiment, independent hoses are used such that individual clamping elements may be individually controlled by switchably supplying air pressure to respective hoses. 
   Thus, an alternate embodiment includes a plurality of instances of the clamping device, such clamping devices distributed along the in axial direction of the cylinder, each clamping device adapted to clamp a plate independently of the clamping by the other clamping device(s). 
   In one embodiment, the cylinder has a circumference of approximately 129 cm and an axial length of 210 cm. Such a cylinder, can accommodate, for example, plates of 50 in by 80 in. In one embodiment, 20 clamping devices are distributed in the axial direction. 
   Another aspect of the invention is that a plurality of clamping devices are provided in the circumferential direction.  FIG. 5  shows a cylinder  507  with three instances of the clamping device: the clamping device  100 , and additional clamping devices  500  and  520  that respectively include clamping elements  501  and  511 . All three clamping devices are shown in the closed (clamping) position. No plate is shown on the cylinder  507 . Having a plurality of clamping devices in the circumferential direction provides for a plurality of plate segments that are shorter in the circumferential direction to be loaded. 
   One embodiment includes clamping elements distributed at two locations in the circumferential direction. In an alternate embodiment, three locations are used in the circumferential direction. The design decision as to how many locations depends on the number of “standard” plate formats available. 
   While apparatus embodiments are described above, another aspect of the invention is a method of loading a plate onto a imaging cylinder by using the apparatus as described herein. 
   Note that while in one embodiment, the inflatable air hose  106  is inflated with air, in alternate embodiments, another gas is used, and in yet another embodiment, a liquid is used. 
   Note that while the gap is shown being formed between the clamping element  101  and the outer surface of the cylinder  107 , the term outer surface in this context includes the case that the outer surface is somewhat indented in the area of the clamping element.  FIG. 6  shows one such example wherein a cylinder  607  includes an indentation  605  to accommodate the clamping element  101  of the clamping device  100 . 
   It should be appreciated that although the invention has been described in the context of flexography, the invention is not limited to such contexts and may be utilized in various other applications and systems for mounting one or more plates or plate segments onto a imaging cylinder. 
   Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments. 
   Similarly, it should be appreciated that in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of this invention. 
   Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination. 
   Furthermore, some of the embodiments are described herein as a method or combination of elements of a method that can be implemented by a processor of a computer system or by other means of carrying out the function. Thus, a processor with the necessary instructions for carrying out such a method or element of a method forms a means for carrying out the method or element of a method. Furthermore, an element described herein of an apparatus embodiment is an example of a means for carrying out the function performed by the element for the purpose of carrying out the invention. 
   All publications, patents, and patent applications cited herein are hereby incorporated by reference. 
   In the claims below and the description herein, any one of the terms comprising, comprised of or which comprises is a an open term that means including at least the elements/features that follow, but not excluding others. Thus, the term comprising, when used in the claims, should not be interpreted as being limitative to the means or elements or steps listed thereafter. For example, the scope of the expression a device comprising A and B should not be limited to devices consisting only of elements A and B. Any one of the terms including or which includes or that includes as used herein is also an open term that also means including at least the elements/features that follow the term, but not excluding others. Thus, including is synonymous with and means comprising. 
   Similarly, it is to be noticed that the term coupled, when used in the claims, should not be interpreted as being limitative to direct connections only. Thus, the scope of the expression a device A coupled to a device B should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. 
   Thus, while there has been described what are believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as fall within the scope of the invention. For example, any formulas given above are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention.