Abstract:
An apparatus for mounting and demounting a materials sheet onto and from a cylindrical surface of a drum ( 10 ) has clamps ( 40 ) pivotably arranged upon the sheet materials drum. The clamps have a first region ( 80 ) and a second region ( 70 ) either side of a pivot axis. The second region ( 70 ) clamps the materials sheet to the cylindrical surface ( 20 ) of the drum. A backbone ( 120 ) extends along the length of the drum and is removably attached to the drum. Push rods ( 90 ) movably arranged on the backbone are capable of being operated to push against the first region of the clamps to pivot the clamps to move the second region of the clamps. Any existing clasped materials sheet is thereby unclasped from the cylindrical surface.

Description:
FIELD OF THE INVENTION 
   The invention relates to methods and apparatuses for loading sheet materials on drums such as those employed in plate-setting machines in the printing industry. 
   BACKGROUND OF THE INVENTION 
   In the printing industry, the inclusion of a computer-to-plate (CTP) system in a printing operation suggests a great extent of automation. A full CTP process can automate, through the use of computers and special equipment, the transfer of information from the original layout to the press plate. A computer-to-plate (CTP) system accepts input jobs/pages written in a page description language, for example, Postscript, and the jobs are sent through a raster image processor to a platemaker for exposure. The platemaker engine images the raster data on a plate, which is later mounted on a press, inked and made ready for printing. 
   Also included in the automation of a CTP system is the media handling. It is necessary to supply plates individually from a plate supply area to the platemaker engine and it is desirable to reduce the amount of operator handling involved. Unexposed plates are normally supplied in packages of 10 to 100 plates, with interleaf paper-sheets between the plates for protecting the emulsion side of the plates, which is extremely sensitive to scratches. The stack of plates is loaded into a supply area of a platemaker in a manner that keeps the stack of plates aligned with automation mechanisms for removing a plate from the stack, and for discarding the interleaf sheets from the stack. 
   While smaller plates can be loaded by hand, the advent of large printing plates has necessitated the automatic loading of plates onto the sheet materials drum or imaging drum of the CTP platesetter apparatus. While medium-sized platemaking machines with imaging drums of a few feet in length are common-place and printing plates are comparatively easy to load onto or unload from such machines, the same cannot be said for larger machines. The printing industry requires placement of plates with great accuracy when moving over distances of a meter or more. Under pressure from the printing industry for ever greater throughput, the latest generation of extra large format platemaking machines being developed at this time has imaging drums of more than 3 meters in length. At the same time there is no quarter to be sacrificed in quality and precision. It is therefore necessary to be able to load and unload extremely large and heavy materials sheets of the order of 3.15×1.60 meters in size automatically with great accuracy and precision. 
   One of the proven ways of securing a printing plate for imaging to an imaging drum is to employ spring loaded clamps to clamp the leading edge of the plate to the drum, to then wrap the plate around the drum and to then secure the trailing edge of the plate. In view of the larger and heavier plates being employed, one of the mechanisms developed to automatically open the clamps is to have a push rod, movably attached to a backbone that typically runs the length of the drum, that is moved down towards the clamp to push upon it in such a way as to compress the spring providing the clamping force, thereby opening the clamp and allowing the edge of the plate to be removed from the clamp. 
   While this was a relatively simple matter in the case of smaller machines, it becomes a rather more complex matter in systems with long imaging drums. In such large systems the sheer length of the backbone carrying the push rods, together with the greater pushing forces required to release large heavy plates from more substantial clamps, can cause the very backbone itself to flex in reaction. This complicates the loading and unloading of the printing plate involved. The same challenge translates to the presses used for printing with such large plates. Both kinds of machines have a drum, the platemaking machine and imaging drum and the press having a drum for mounting the plate imaged by a platemaking machine. 
   Thus, there remains a need for a simple, flexible and efficient method to load very large printing plates automatically with accuracy and precision onto a sheet materials drum for imaging, and to unload the imaged plates from the drum. 
   SUMMARY OF THE INVENTION 
   Briefly, according to one aspect of the present invention a method and apparatus provides for mounting and demounting a materials sheet onto and from a sheet materials drum such as those used in the printing industry. A drum has at least one clamp pivotably arranged upon it. The clamp has a first region and a second region, and the second region clamps the materials sheet to the cylindrical surface of the drum. The pivot axis of the clamp is between the first region and the second region of the clamp, allowing the second region to clamp the materials sheet to the cylindrical surface when the first region of the clamp rises and allowing the second region to release the materials sheet when the first region is depressed by a push rod. The push rod is mounted movably on a backbone that extends along the length of the sheet materials drum proximate the cylindrical surface. In order to prevent the backbone flexing and thereby impeding the mounting and demounting of the materials sheet, the backbone is removably attached to the sheet materials drum prior to the pushing by the push rod. The pushrod is then pushed against the second region of the clamp to thereby raise the first region. This makes it possible to either remove a materials sheet that was clasped by the second region of the clamp, or to position a materials sheet in that location. In the case of the latter, the second region of the clamp then clasps the materials sheet to the cylindrical surface when the push rod is operated to not push on the second region of the clamp. 
   In one embodiment of the present invention the removably attaching is accomplished by attaching the backbone to the sheet materials drum using a latching arrangement. The latching arrangement comprises a latch that is pivotably arranged on the backbone and which engages with a slot in the sheet materials drum. More specifically, a protrusion on the latch engages with a ledge of the slot. A plurality of clamps, push rods and latches may be arranged along the length of the backbone and sheet materials drum to thereby reduce flexing of the backbone and improve the handling of materials sheets. Before removably attaching the backbone to the sheet materials drum, the backbone can be positioned proximate the cylindrical surface of sheet materials drum. After detaching the backbone from the sheet materials drum, the backbone can be relocated away from the cylindrical surface of the sheet materials drum. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings which illustrate non-limiting embodiments of the invention: 
       FIG. 1  shows a sheet materials drum with an latch, slot, clamp and pushrod arrangement for clamping a materials sheet to the cylindrical surface of the sheet materials drum; 
       FIG. 2  shows a drum with an latch, slot, clamp and pushrod arrangement for clamping a materials sheet to the cylindrical surface of the drum, the arrangement being in the configuration where the materials sheet is released from the surface of the cylindrical surface of the drum; 
       FIG. 3  shows the arrangement and working of the latch, slot and clamp of  FIG. 1  and  FIG. 2  in more detail; 
       FIG. 4   a  shows the arrangement and working of the clamp and pushrod of  FIG. 1  and  FIG. 2  in more detail, with the clamp in the closed orientation; 
       FIG. 4   b  shows the arrangement and working of the clamp and pushrod of  FIG. 1  and  FIG. 2  in more detail, with the clamp in the open orientation; 
       FIG. 5  is a flow diagram for a method to mount a materials sheet on a sheet materials drum; 
       FIG. 6  is a flow diagram for a method to remove a materials sheet from a sheet materials drum; 
       FIG. 7  is a flow diagram for a method for clasping materials sheet to a cylindrical surface of a drum; and 
       FIG. 8  is a flow diagram for a method for releasing materials sheet from a cylindrical surface of a drum. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements have not been shown or described in detail to avoid unnecessarily obscuring the invention. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive, sense. 
     FIG. 1  shows the apparatus of the present invention as a drum  10  having cylindrical surface  20 . Drum  10  is arranged to be rotatable around cylindrical axis  30 . The term “drum” is used to describe a drum in that is generally used for mounting sheet materials such as printing plates, as in the case of offset presses, or for mounting un-imaged lithographic precursor plates as in the case of platesetter machines. 
   At least one clamp  40  is arranged on cylindrical surface  20  of drum  10  to pivot about pivot axis  60 , thereby to clamp the leading edge of materials sheet  50  by means of clamp proximal end  70 . Pivot axis  60  and distal end  80  of clamp  40  can optionally be recessed below cylindrical surface  20  of drum  10 . Proximal end  70  of clamp  40 , however, is arranged to allow materials sheet  50  to be clamped to cylindrical surface  20  by clamp proximal end  70  and therefore proximal end  70  at least partially protrudes outside of cylindrical surface  20 . In this arrangement clamp proximal end  70  rises with respect to drum  10  when clamp distal end  80  is depressed toward cylindrical axis  30 . Conversely, clamp proximal end  70  closes down towards cylindrical surface  20  when clamp distal end  80  rises away from drum  10 . Clamp distal end  80  is spring loaded (shown in more detail in  FIG. 3 ,  FIG. 4   a  and  FIG. 4   b ) to ensure that, in its relaxed state, at least one clamp  40  assumes a closed state in which proximal end  70  will clamping down onto materials sheet  50 , when materials sheet  50  is present. In  FIG. 1  at least one clamp  40  is shown in its closed state, clamping down onto materials sheet  50 . For the sake of clarity,  FIG. 1  is not drawn to scale. 
   Push rod  90  is movably arranged on backbone  120  and latch  130  is rotatably arranged on backbone  120 . Latch  130 , having latch protrusion  160 , can be rotated in direction  140  about latch rotation axis  150 . Push rod  90  can be moved in direction  100  to press upon distal end  80 . When push rod  90  pushes against clamp distal end  80 , materials sheet  50  is no longer clamped by clamp  40  and can be removed. 
     FIG. 2  shows push rod  90  pressing upon distal end  80  of clamp  40  and latch  130  is rotated in direction  140  to mechanically engage drum  10  and removably attach backbone  120  to drum  10 . For the sake of clarity,  FIG. 2  is not drawn to scale. 
     FIG. 3 , being a partial cutaway diagram of drum  10  in the vicinity of at least one clamp  40  and slot  170 , shows a more detailed view of how latch protrusion  160  of latch  130  engages mechanically with slot ledge  180  of slot  170  of drum  10 . For the sake of clarity, push rod  90  is not shown in  FIG. 3 . Latch is  130  shown in its disengaged position as  130 ′ in dotted outline. Springs  190  provide the force to keep at least one clamp  40  in the closed position when distal end  80  is not pushed down by push rod  90 . 
     FIG. 4   a  and  FIG. 4   b  show a more detailed view of the working of push rod  90  in opening and closing clamp  40 . In  FIG. 4   a  and  FIG. 4   b  latch  130  and slot  70  are omitted for the sake of clarity. For the sake of clarity,  FIG. 4   a  and  FIG. 4   b  are not drawn to scale. 
     FIG. 4   a  shows clamp  40  in its closed position, clamping materials sheet  50  to cylindrical surface  20  of drum  10  by means of proximal end  70 . Springs  190  provide the force on distal end  80  of clamp  40  to thereby close clamp  40  by pivoting it about pivot axis  60 . Push rod  90  is in its retracted position on backbone  120 , having been moved along direction  100 . 
     FIG. 4   b  shows clamp  40  in its open position, releasing materials sheet  50  from cylindrical surface  20  of drum  10  by proximal end  70  being in a raised orientation. Springs  190  are compressed by the action of push rod  90  on backbone  120  pushing on distal end  80  of clamp  40  along direction  100 . Clamp  40  is pivoted about pivot axis  60 . 
   The apparatus of the present invention may have a plurality of clamps  40  and may have a plurality of push rods  90  and a plurality of latches  130 , a plurality of sets of these devices being required to attach large materials sheets to extra large format drums, 3.15×1.6 meter plates having to be attached to drums of length greater than 3.15 meters in some cases. In a further embodiment of the present invention backbone  120  is capable of being relocated closer to or further away from cylindrical surface  20  of drum  10 . 
   In operation, as shown in the flow diagram of  FIG. 5 , the apparatus of the present invention provides a method for clasping a materials sheet  50  to a cylindrical surface  20  of a drum  10 , the drum  10  comprising at least one clamp  40 , the method comprising positioning ( 200 ) backbone  120  proximate cylindrical surface  20  of drum  10 , removably attaching ( 210 ) onto drum  10  a backbone  120  comprising at least one push rod  90  movably arranged on backbone  120 , pushing ( 220 ) on a first region of at least one clamp  40  with the push rod to open clamp  40 , the first region in the case of the embodiment described here being distal end  80 , positioning ( 230 ) the materials sheet under a second region of the clamp, the second region in the case of the embodiment described here being proximal end  70 , withdrawing ( 240 ) the push rod  90  to let the second end of the clamp  40  clasp materials sheet  50  to the cylindrical surface  20 , detaching ( 250 ) backbone  120  from sheet materials drum  10 , and relocating ( 260 ) backbone  120  away from cylindrical surface  20 . 
   In operation, as shown in the flow diagram of  FIG. 6 , the apparatus of the present invention furthermore provides a method for releasing a materials sheet  50  from a cylindrical surface  20  of a drum  10  to which it is clasped by at least one clamp  40 , the method comprising positioning ( 300 ) backbone  120  proximate cylindrical surface  20  of drum  10 , removably attaching ( 310 ) onto the drum  10  backbone  120  comprising at least one push rod  90  movably arranged on backbone  120 , pushing ( 320 ) on a first region of at least one clamp  40  with the push rod  90  to open clamp  40 , the first region in the case of the embodiment described here being distal end  80 , removing ( 330 ) materials sheet  50  from under clamp  40 , withdrawing ( 340 ) at least one pushrod  90  to cease pushing on the first region of at least one clamp  40  to thereby relax at least one clamp  40 ; detaching ( 350 ) backbone  120  from sheet materials drum  10 , and relocating ( 360 ) backbone  120  away from cylindrical surface  20 . 
   In a further embodiment of the present invention, backbone  120  is maintained in a fixed position proximate cylindrical surface  20 , but with suitable clearance for drum  10  and any clamps  40  to safely rotate past it. In this embodiment neither the method for clasping materials sheet  50  to cylindrical surface  20  of drum  10 , as shown in the flow diagram of  FIG. 7 , nor the method for releasing materials sheet  50  from cylindrical surface  20  of drum  10 , as shown in the flow diagram of  FIG. 8 , require backbone  120  to be re-positioned or relocated during execution of the respective methods. 
   In both the method of clasping and the method of releasing described herein backbone  120  may be removably attached onto drum  10  by a number of different alternative mechanisms, including but not limited to that of a latch  130  having a protrusion  160  that engages a ledge  180  of a slot  170  in drum  10 . 
   Furthermore, slot  170  is not limited to being parallel to cylindrical axis  30  and may have any other orientation that allows a part of latch  130  to engage with it or any part of it, including but not limited to slot  170  being aligned perpendicular to cylindrical axis  30 . Latch  130  can correspondingly be arranged on backbone  120  in any orientation that allows it to engage with slot  170  or any part of it. 
   The arrangement as described here prevents backbone  120  from flexing when a plurality of push rods push against a plurality of distal ends  80  of a plurality of clamps  40  arranged along the length of a long sheet materials drum  10 . The invention thereby ensures smooth functioning of automated sheet materials loading and unloading operations. 
   The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention. 
   PARTS LIST 
   
       
         10  drum 
         20  cylindrical surface 
         30  cylindrical axis 
         40  clamp 
         50  materials sheet 
         60  pivot axis 
         70  proximal end of clamp  40   
         80  distal end of clamp  40   
         90  push rod 
         100  direction of motion of push rod 
         120  backbone 
         130  latch 
         130 ′ disengaged latch position 
         140  direction of rotation of latch  130   
         150  latch rotation axis 
         160  latch protrusion 
         170  slot 
         180  slot ledge 
         190  springs 
         200  positioning backbone proximate cylindrical surface 
         210  removably attaching backbone onto sheet materials drum 
         220  pushing on first region of clamp with push rod to open clamp 
         230  positioning materials sheet under second region of clamp 
         240  withdrawing push rod to let second region of clamp clasp materials sheet to cylindrical surface 
         250  detaching backbone from sheet materials drum 
         260  relocating backbone away from cylindrical surface 
         300  positioning backbone proximate cylindrical surface 
         310  removably attaching backbone onto sheet materials drum 
         320  pushing on first region of clamp with push rod to open clamp 
         330  removing materials sheet from under clamp 
         340  withdrawing push rod to relax clamp 
         350  detaching backbone from sheet materials drum 
         360  relocating backbone away from cylindrical surface