Abstract:
A conveyor system for transporting a printing plate in a platemaking system, includes: a carriage riding on a track and one or more low friction substantially horizontal planar support surfaces provided as a high wear laminate, positioned above the carriage and the track, for supporting the printing plate on the non-emulsion side without the use of rollers, belts, bearings or air cushioning. The carriage includes one or more engagement mechanisms for engaging a bottom, non-emulsion side of the printing plate, and the track includes an air cylinder. The engagement mechanisms can be, for example, suctions cups which engage the plate by a vacuum, suction cups which engage the plate by pressure and adhesion, other adhesive devices, or a mechanical gripper for gripping the plate. The track or linear actuating system is preferably an air cylinder. Alternatively the linear actuating system could include a belt and pulleys, a chain and gears, or a threaded lead screw.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Imagesetters and platesetters are used to expose media that are used in offset printing systems. Imagesetters are typically used to expose the film that is then used to make the printing plates (also referred to as “plates”) for the printing system. Platemaking systems include platesetters also known as platemakers for directly exposing the printing plates with a laser imaging head.  
         [0002]     For example, printing plates are typically pre-cut, various-sized and coated with photosensitive or thermally-sensitive material layers, referred to as the emulsion. For large run applications, the plates are often fabricated from aluminum, although organic substrates, such as polyester or paper, are also available for smaller runs.  
         [0003]     Computer-to-plate printing systems are used to render digitally stored print content onto these printing plates. In a platemaking system a computer system is typically used to drive an imaging engine of the platesetter. In a common implementation, the printing plate is fixed to the outside or inside of a drum or held on a flat bed and then scanned with a modulated laser source in a raster fashion.  
         [0004]     The imaging engine selectively exposes the emulsion that is coated on the printing plates with the desired image. After this exposure, the printing plate is typically further processed in machines called processors so that, during the printing process, inks will selectively adhere to the printing plate&#39;s surface to transfer the ink to the print medium. Often the post-exposure plate processors include a developer stage for developing the printing plates. Sometimes intervening ovens are used to bake or harden the emulsion before development.  
         [0005]     Platesetters are typically used in commercial, production environments. They are used in the manufacture of printing plates for newspapers, books, and magazines, for example. Once imaged and developed, the printing plates are mounted onto large offset printing presses for the printing run.  
         [0006]     Since platemakers are used in these commercial environments, metrics, such as initial cost and total cost of ownership, are critical in differentiating between products of various manufacturers. In order to keep the cost to manufacture the machines low, reductions in component costs are often an objective in machine redesigns. Relative to total cost of ownership, machine up-time, average cycle time, and amount of operator intervention required during operation, are very important to the potential buyers of these machines. To decrease the amount of operator intervention in the operation of the platemakers, system manufacturers often provide automation for such jobs as transferring or moving the printing plates to a staging area, to the imaging engine, and from the imaging engine to a developer, stacker or other processing stage.  
         [0007]     Often, the cost of the automation accessories are high due to the challenges associated with moving these sometimes very large printing plates without damage or contamination. Thus, it is often not clear from a purely economic standpoint, whether a given owner should purchase the various available automation accessories, because these accessories are expensive and difficult to weigh against the cost to employ operators over the course of the platesetter&#39;s lifetime to perform the functions that would otherwise be performed by the automation accessories.  
         [0008]     As noted above, one specific area of automation concerns the movement of the printing plates throughout the platemaking system, for example, moving a printing plate from the imaging engine to a stacker, developer, chemical bath, rinser, baking or fixing unit.  
         [0009]     In most platemaking systems, the printing plates when ejected from the imaging engine are simply placed on an unload table. An operator must then manually move the printing plates to another location such as a plate stack or plate processor. In contrast, an automated conveyor system receives a printing plate as it is ejected from the imaging engine and automatically moves the printing plate to another location or processor without operator intervention.  
         [0010]     Printing plate conveyor systems can be very expensive to manufacture and maintain, typically having many moving parts such as rollers, belts, chains, gears and mechanical linkages. Further, these conveyor systems preferably should include features to change the direction of plate movement. Specifically, since the processor in many environments is located next to the platesetter in order to preserve floor space, the printing plate is consequently ejected from the platesetter along one axis, and must be initially drawn along that same axis by the conveyor, thereafter changing the direction of the movement of the printing plate by 90° to move the printing plate to the processor.  
         [0011]     In one example, a printing plate conveyor system includes a conveyor with a series of belts and pulleys for receiving and transporting the printing plate as it is ejected from the imaging engine. Once the plate is completely ejected, a set of rollers extends upward between the pulley belts to pick the plate off of the belts and move the plate in an orthogonal direction to the direction from which the plate was initially ejected.  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention is directed towards a conveyor system for transporting a printing plate in a platemaking system, where the conveyor system includes: a carriage riding on a track and one or more low friction substantially horizontal planar support surfaces made of a high wear laminate, positioned above the carriage and the track, for supporting the printing plate on the non-emulsion side without the use of rollers, belts, bearings or air cushioning. The carriage includes one or more engagement mechanisms for engaging a bottom, non-emulsion side of the printing plate, said track comprising an air cylinder.  
         [0013]     The engagement mechanisms can be, for example, suctions cups which engage the plate by a vacuum, suction cups which engage the plate by pressure and adhesion, other adhesive devices, or a mechanical gripper for gripping the plate.  
         [0014]     The track or linear actuating system can be one or two-directional and can include, for example, an air cylinder, a belt and pulleys, a chain and gears, or a threaded lead screw.  
         [0015]     In another embodiment the present invention is directed towards a method for transporting a printing plate in a platemaking system. The method includes the steps of: using an engagement mechanism to attach a bottom, non-emulsion side of the printing plate to a movable carriage positioned beneath the printing plate; moving the carriage with an air cylinder to drag, without the use of rollers, belts, bearings or an air cushion, the printing plate along the bottom, non-emulsion side along a low friction substantially horizontal planar high wear laminate support surface; and controlling the engagement mechanism, carriage and air cylinder with a programmable controller.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention.  
         [0017]      FIG. 1  is a side cross-sectional view of a platesetter, including a single-axis conveyor system for moving printing plates according to a preferred embodiment of the present invention.  
         [0018]      FIG. 2  is a schematic perspective view of a platemaker system including the platesetter of  FIG. 1  which includes a two-axis plate moving conveyor system, according to another embodiment of the present invention.  
         [0019]      FIG. 3  is a schematic plan view of a portion of the conveyor system of  FIG. 1 .  
         [0020]      FIG. 4  is a perspective view of a portion of the conveyor system of  FIG. 1 .  
         [0021]      FIG. 5  is an enlarged perspective view of the carriage mechanism of the conveyor system of  FIG. 4 .  
         [0022]      FIG. 6  is a flow diagram showing the steps of moving the printing plates in a conveyor system according to an embodiment of the inventive method.  
         [0023]      FIG. 7  is a flow diagram showing the steps of moving the printing plates according to another embodiment of the inventive method.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]      FIG. 1  shows one embodiment of a platesetter or platemaking system having a conveyor system constructed according to the principles of the present invention for moving printing plates from the platesetter&#39;s imaging engine.  
         [0025]     Printing plates are initially stored or queued onto a load table  14  for insertion into the imaging engine  12  of the platesetter  10  via a load port  16 . In a preferred embodiment, the load table  14  includes a low friction surface that allows a printing plate  8  to be gravity fed through the load port  16  into the imaging engine  12 . For example, in one specific embodiment, the load table  14  includes an “air hockey” style surface that creates an air bearing between the surface of the load table  14  and the underside of the plate  8  so that the plate  8  has an almost frictionless engagement between the load table  14 , and thus slides easily through the load port  16  into the imaging engine  12 .  
         [0026]     Once in the imaging engine  12  of the platesetter  10 , the leading edge  3  of the printing plate  8  is engaged by a leading edge clamp  24 . This clamp  24  pins the leading edge  3  of the printing plate  8  to be held in a fixed position, relative to the external drum  22 . An ironing roller  20  is used to urge the printing plate  8  against the outer periphery of the external drum  22 , while the external drum  22  is advanced in the direction of arrow  7 , until the trailing edge  5  of the printing plate  8  can be engaged by the trailing edge clamp  18 , which holds the trailing edge  5  of the printing plate  8  against the outer surface of the external drum.  
         [0027]     Next, during the imaging or exposure phase, an exposure system  26  generates a modulated light beam  28  that is scanned in a helical fashion over the printing plate  8 . This allows for the selective exposure of the printing plate with the desired image.  
         [0028]     Once completely exposed, the printing plate  8  is ejected from the imaging engine  12 . In the illustrated embodiment, the trailing edge  5  of the printing plate  8  is first fed through ejection rollers  30  that feed the printing plate through an unload port  32 .  
         [0029]     According to the present invention, as the printing plate  8  is ejected through the unload port  32 , it is received onto an unload table  100  having one or more low friction substantially horizontal planar support surface  101 . The support surface  101  allows for low friction contact with the bottom non-emulsion side  9  of the printing plate  8 , which prevents damage to the emulsion side of the printing plate  8 . The low friction nature of the support surface  101  enables sliding of the printing plate  8  along the unload table  100 . The support surface  101  is preferably Wilsonart® High Wear Laminate or Formica®. The support surface  101  is a high wear laminate having high wear surface papers which are impregnated with melamine resin pressed over core sheets impregnated with phenolic resin. These sheets then are bonded at pressures greater than 1000 pounds per square inch at temperatures approaching 300° F. (149° C.). Support surfaces of the same composition are preferably used throughout the conveyor system for low friction sliding or dragging of the printing plates.  
         [0030]     According to the invention, a conveyor system  102  is used to drag or slide the printing plate  8  across the support surface  101  of the unload table  100 . The fact that the printing plate  8  is dragged by the conveyor system  102  generally allows for the conveyor system and table  102  to be relatively inexpensive since a conveyor roller or belt system is not required. Furthermore, system reliability is improved and less maintenance is required due to fewer moving parts and mechanisms which are prone to malfunction and wear.  
         [0031]     Specifically, in a preferred embodiment, the conveyor system  102  includes a track  110  and a carriage  150 . The carriage  150  moves over the track  110  in the direction of arrow  112  to drag the printing plates  8  as they are ejected from the imaging engine  12  of the platesetter  10 . In the preferred embodiment, an engagement mechanism is used to engage the printing plate  8 , preferably by engaging the bottom non-emulsion side of the printing plate  8 , so that the printing plate  8  moves with the carriage  150 . The table  100  is preferably positioned above the carriage  150  and the track  110 . Further, the table  100  is preferably provided with a home position detector  172  and an end travel position detector  170  for determining the home and end travel positions on the table of the printing plate, respectively. Other detectors can be placed incident to table  100 , for example, for detecting different sized printing plates, centering an ejected printing plate and otherwise determining plate positioning as desired.  
         [0032]      FIG. 2  is a perspective view showing a dual axis embodiment of a plate conveyor system according to the present invention. Specifically, the unload table  100  is, in the illustrated example, divided into four quadrants by a first channel  104 A that extends away from the platesetter  10  and a second channel  104 B that extends orthogonally to the first channel  104 A or in a lateral direction to the platesetter  10 . The first axis conveyor  102 A includes a first channel  104 A that accommodates the movement of a first axis carriage  150 A. As described previously, this first axis carriage  150 A has its own plate engagement mechanism  160 A. This carriage  150 A rides on its own track or air cylinder not shown in this view.  
         [0033]     The second axis conveyor  102 B comprises a track or air cylinder  110 B, a carriage  150 B and its own plate engagement mechanism  160 B. It rides in the orthogonal channel  104 B. The first axis conveyor system  102 A in combination with the second axis conveyor system  102 B allow printing plates being drawn from the unload port  32  of the platesetter  10  to be passed on for further processing.  
         [0034]     For example, in one embodiment, only the first axis conveyor  104 A is used. This allows the printing plate  8  to be moved from the unload port  32  to a next station such as a stacker  20 B. Alternatively, block  20 B can be a work area for an operator that manually moves the printing plates as they are ejected from the platesetter  10 .  
         [0035]     The second axis conveyor  104 B is provided to allow the printing plates  8  to be moved to either processor  20 A or  20 C that are located at an angle of 90 degrees, e.g. on a side or lateral to the platesetter  10 . These processors  20 A,  20 C can be, for example, chemical developers, rinsing units or bake systems for hardening the emulsion of the printing plates  8 .  
         [0036]      FIG. 3  shows an exemplary embodiment of a plate conveyor system  102 . Generally, the conveyor system includes one or more tracks  110 . In the preferred embodiment, each track is a rodless air cylinder  110  controlled by programmable controller  312 . The carriage  150  rides on the air cylinder  110  back and forth as illustrated by arrow  310 .  
         [0037]     In other embodiments, the track  110  can include a chain and gears, a belt and pulleys, or a piano screw. An important cost saving and reliability feature of the track  110  is that it acts as a linear actuating system in one or more directions. Also, the track  110  is physically narrow along the length of the first and second channels  104 A,  104 B so as to take up less space and require fewer working parts subject to maintenance and failure.  
         [0038]     The carriage  150  includes an engagement mechanism  160  which, in the preferred embodiment, includes a suction cup extension arm  171  that moves vertically under the operation of the controller  312 . By extending the suction cup extension arm  171  vertically, suction cups are brought into engagement with the bottom, non-emulsion side of the printing plate  8 . Specifically, in the illustrated embodiment, the engagement mechanism  160  comprises four separate suction cups  162 ,  164 ,  166 ,  168 . First and second suction cups  162 ,  164  are used to engage the printing plate  8  near its trailing edge  5 . Suction cups  166 ,  168  engage the printing plate  8  nearer its leading edge  3 . A vacuum generator  315  controlled by controller  312  is preferably located on the carriage  150  to provide for the generation of a vacuum for the operation of the suction cups  162 ,  164 ,  166 ,  168  so that the suction cups grip or engage the bottom, non-emulsion side of the printing plate  8  when vacuum is activated. The vacuum generator  315  is connected to the suction cups via hoses not shown in the figures.  
         [0039]     Other known engagement mechanisms can be used in other embodiments such as adhesive and mechanical grippers. In some embodiments, the bottom or an edge of the printing plate  8  is engaged by the suction cups by a mechanical gripping mechanism without the use of a vacuum to move the plate along the support surface  101  of the table  100 .  
         [0040]     An extension arm plate sensor  169  is provided on the extension arm  171  to determine the presence and location of a printing plate  8  on the table  100  as the extension arm is moved along the table by detecting a reflective backing on the printing plate  8 . Vacuum switch detector  516  detects that the plate has been engaged by the suction cups and is ready to be moved by the extension arm  171 .  
         [0041]     The air cylinder  110  is operated by a series of valves under the control of the controller  312 . The controller  312  is programmed to automatically control all aspects and mechanisms of the plate conveyor system  102 . A first valve  314  controls the provision of pressurized air to, or the venting of, a first end  316  of the air cylinder  110 . A second valve  318  controls the provision of pressurized air to, or venting of, the second end  320  of the air cylinder  110 . Specifically, an air compressor  325  provided as part of the platemaking system is used to provide the compressed air through the first and second valves  314 ,  318  for controlling the rodless air cylinder  110 .  
         [0042]     When the carriage  150  is moved to the left, for example, the controller  312  controls the second valve  318  to provide compressed air to the second end  320  of the air cylinder. This causes the air cylinder to move to the left, moving the carriage  150  to the left in the perspective of  FIG. 3 . Simultaneously, the first valve  314  is controlled to vent the air moving from the first end  316  of the air cylinder to the surrounding air.  
         [0043]     Further, the controller  312  is able to hold the carriage  150  at a specific location by closing both the first valve  314  and the second valve  318 . This prevents the air cylinder and the attached carriage  150  from any further movement.  
         [0044]     In order to provide for the precision movement of the carriage  150  using the air cylinder  110 , a series of absolute and relative carriage position sensors are used. Specifically, the home position sensor  172  is provided at the first end  316  of the air cylinder  110 . The end travel sensor  170  is provided at the second end  320  of the air cylinder. These sensors provide information to the controller  312  so that the controller is able to detect the home or end travel positions of the printing plate  8 .  
         [0045]     The movement of the carriage  150  between the position sensors  172 ,  170  is provided by a relative position sensor  348 . In one embodiment, the relative position sensor  348  is a tooth detector for measuring position along a tooth array  350 . Specifically, the position sensor  348  is attached to the carriage  150  and rides adjacent to the tooth array  350 . The sensor  348  functions to count the passing of the teeth along the tooth array  350 . The sensor  348  can, for example, be an optical detector that detects the reflective metal that interrupts the transmission of an optical signal between an optical sensor and the detector. In this way, the controller  312  is able to count the progression of the tooth array  350  relative to the sensor  348 , and thereby is able to detect movement of the carriage  150  between the home and end travel positions.  
         [0046]     The extension arm  171  is controlled by controller  312  and moved vertically in a direction depicted by arrows  311  by an extension arm air cylinder  410 . It moves the air cylinder vertically up or down to bring the suction cups  162 ,  164 ,  166 ,  168  of the engagement mechanism  160  into and out of engagement with the bottom non-emulsion side  9  of the printing plate  8 .  
         [0047]      FIGS. 4 and 5  show one specific implementation of the conveyor system  102 .  FIG. 5  shows a close up view of the carriage  150 . Specifically, the conveyor system  102  is provided with a tray-like frame  420 . The track or air cylinder  110  is secured to the frame  420 . The carriage  150  rides on the track  110  and supports the extension arm air cylinder  410 . In the illustrated example, the tooth array  350  is oriented on the frame  420  so that the optical detector  348  can detect the individual teeth of the array  350  as the carriage  150  moves along the air cylinder  110 .  FIG. 5  further shows control valve  512  that is used to control the operation of the extension arm air cylinder  410 , and control valve  510  that is used to control the vacuum generator  315 .  
         [0048]      FIG. 6  is a flow diagram illustrating the operation of a one dimensional conveyor system for moving printing plates in a platemaking system. Specifically, the air cylinder  110  first moves the carriage  150  to the home position opposite the first absolute carriage position sensor  340  in step  610 . It then waits for the printing plate  8  to be released from the leading edge clamp and feed rollers  30  in the platesetter  10  in step  612 . Then, in step  614 , the plate size is used to compute the number of teeth in the tooth array  350  that the carriage  150  must move to end up in a desired location on the support surface  101  of the table  100 . In step  616 , the printing plate is captured by the engagement mechanism  160  of the conveyor system  102 . Specifically, the extension arm air cylinder  410  is activated to raise the extension arm  171 . The vacuum generator  315  is simultaneously activated so that the appropriate one or more of the suction cups  162 ,  164 ,  166 ,  168  engage the bottom non-emulsion surface of the printing plate  8 .  
         [0049]     In one implementation, the generated vacuum is monitored by a vacuum level detector  516  to ensure that the suction cups  162 ,  164 ,  168 ,  166  have made a good contact with the bottom of the printing plate  8 . Specifically, if the vacuum generator  315  is not able to maintain a predetermined level of vacuum, then the controller  312  will receive a signal from the vacuum level detector  516  and the system will go into an error status indicating that the bottom non-emulsion side of the printing plate  8  was not properly engaged.  
         [0050]     Next, with the plate engaged, the carriage  150  is moved a predetermined distance corresponding to a computed number of teeth of the tooth array  350  toward the second absolute carriage position sensor  342  in step  618 . Once at the desired location, the plate is released by de-energizing the vacuum generator  315  and lowering the extension arm  171  by controlling the extension arm air cylinder  410  in step  620 .  
         [0051]     At this time, it is determined whether the edge of the printing plate was detected by edge sensor  170 . If the trailing edge  5  of the printing plate  8  is not yet at the plate edge sensor  170 , then the vacuum is de-activated and the plate is released by the suction cups while the carriage  150  is moved toward the first absolute carriage position sensor  340  in step  630 . Then the printing plate is re-engaged in step  616  and again, moved toward the second absolute carriage position sensor  342  in step  618 . Depending on the plate size, the printing plate can be moved a calculated distance. In other cases it is moved based upon detection of the trailing edge  5  by the first edge detector  170 . In one embodiment, the printing plate is passed to a stacker. Here, a portion of the plate is actually moved off of the table  100  to engage with the stacker, which then takes up the plate and removes it from the unload table  100 .  
         [0052]      FIG. 7  is a flow diagram illustrating the operation of a two-dimensional plate conveyor. Specifically, the air cylinders first move the carriages  150 A and  150 B to the home positions opposite their first absolute carriage position sensors  340  in step  710 . They then wait for the printing plate  8  to be released from the leading edge clamp and feed rollers  30  in the platesetter  10  in step  712 . In some systems, no feed rollers are needed to eject the plate from the platesetter. Then, in step  714 , the plate size is used to compute the number of teeth in the tooth array  350  that the carriage  150 A must move in order to center the printing plate  8  on the table  100  and over the track of the second conveyor  102 B. In step  716 , the printing plate is captured by the engagement mechanism  160 A of the conveyor system  102 A.  
         [0053]     Next, with the printing plate engaged, the carriage  150 A is moved to center the printing plate, moving in the direction of the second absolute carriage position sensor  342  in step  718 . Once at the desired location, the printing plate  8  is released by de-energizing the vacuum generator  315  and lowering the extension arm  171  by controlling the extension arm air cylinder  410  in step  720 .  
         [0054]     At this time, the tooth count needed for the second conveyor  102 B to move the printing plate  8  to the processor  20  is calculated in step  722 . The second conveyor  102 B then engages the printing plate  8  and slides it along the low friction high wear laminate support surface  101  to the processor in step  724 . If the printing plate is not at the processor, the second conveyor  102 B repeats the dragging operation by disengaging from the plate, moving back a predetermined distance, then re-engaging and dragging the plate.  
         [0055]     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.