Abstract:
An apparatus is provided for positioning a plurality of cassettes within an automated printing plate handler. In a plate handler, a plurality of cassettes each contain a supply of printing plates for delivery to an automatic plate-recording device. The apparatus includes a separate support table for supporting each of the plurality of cassettes within the plate handler and an elevator device for moving each of the support tables along a vertical axis of the automated plate handler. The automated plate handler is configured to automatically position a selected cassette in a first position to facilitate removal of the cassette from the handler. The plate handler further includes a platform, which substantially forms an extension of the support table supporting the selected cassette in the first position. The platform provides a second position, at which the selected cassette is to be one of, loaded or unloaded. The selected cassette may be filled with a new supply of plates on the platform or the selected cassette may be removed from the platform and replaced by another cassette.

Description:
[0001]     This application is a continuation application of commonly assigned U.S. patent application Ser. No. 10/807,085, filed Mar. 23, 2004; which is a divisional of U.S. Pat. No. 6,726,433, filed Jul. 13, 2000; which is a divisional of U.S. Pat. No. 6,113,346, filed Aug. 7, 1996; and U.S. Pat. No. 5,738,014, filed Jul. 31, 1996, all of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     Printing processes utilize a vast array of different technologies to transfer written content to various distribution media. Organizations using varying printing processes include modest-volume quick printers, book and financial publishers, newspaper companies, forms companies, all sizes of commercial printers (for advertising etc.), and, publication printers (for magazines and periodicals). These types of organizations have a common process whereby information is transferred from some original layout form to an intermediate aluminum or polyester plate material which is then hung on a standard printing press to enable multiple identical replication of that information on paper or some similar print media.  
         [0003]     This process has typically been performed by optically creating a polyester film which contains the information, optically transferring the information from the film to a plate material by use of a light transfer or contact to a light-sensitive chemical emulsion which is bonded to the plate, and then hanging the developed plate on a press in alignment (one for each color separation desired). The plates rotate along with the press cylinder and alternately come in contact with ink rollers and then an intermediate transfer blanket. The ink which is accepted by the transfer blanket then transfers the information to the paper during rotational contact.  
         [0004]     Recently the development of computer-to-plate, hereinafter C2P, systems and processes have provided alternative printing options. The C2P process eliminates the film as an intermediate transfer mechanism and allows the optical exposure of the plate directly. This reduces the number of steps required in the printing process of the information and potentially reduces the cost related to the generation of the intermediate film and its handling. C2P systems more readily allow a process which creates plates for shorter-run printing (below around 50,000 impressions).  
         [0005]     In basic terms, a C2P system accepts input jobs/pages written in a page description language, for example, POSTSCRIPT®. These jobs are controlled through execution by priority and scheduling workflow software. Jobs are then sent through a raster image processor to a platemaker for exposure. The data is being transformed throughout this process. The platemaker engine takes this data and prints it on a metal sheet of aluminum which is later notched, bent, hung on the press, inked and made ready to image paper. An imaging engine and process for imaging a plate is described in commonly owned U.S. Pat. No. 5,345,870, hereby incorporated by reference into the present application.  
         [0006]     The inclusion of a C2P system into a printing operation suggests a greater extent of automation which can be achieved. A full C2P process can automate, through the use of computers and special equipment, the transfer of information from the original layout to the press plate. As such, C2P is not only an improvement in the specialized equipment but also in the process which utilizes that equipment. Viewing C2P as a process includes a high level of workflow management to replace manual effort with computer-driven effort with a goal to increase productivity and efficiency. Workflow encompasses such concepts as queue management, color calibration, revision control, press consumables control, inventory tracking, job and cost tracking, etc.  
         [0007]     Also included in the automation of a C2P 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 25 to 100 with interleaf sheets between the plates for protecting the sensitive emulsion side of the plates, which is extremely sensitive to scratches. The stack of plates needs to be loaded into a supply area of a platemaker in a manner to keep the stack of plates aligned with automation mechanisms for removing a plate from the stack, and for discarding the interleaf sheet from the stack. These functions are optimally performed within a covered light-tight environment to prevent unintentional exposure of the light sensitive plate surface. The platemaker engine requires plates of varying sizes and formats on demand. It is beneficial to present a variety of plate sizes and formats to an automated mechanism for selecting the plate needed by the platemaker engine. It is important to be able to reload the plate supply area without interrupting the operation of the platemaker engine. These functions generally will maximize the output of the platemaker engine, by eliminating time which an operator would manually handle the plates and during which the platemaker engine might be interrupted.  
         [0008]     Accordingly it is an object of the present invention to provide an automated C2P system having a workflow software capable of controlling and sequencing the tasks performed by the C2P system from accepting a job input to the system as POSTSCRIPT® and output the job from the system as exposed images on printing plates.  
         [0009]     It is a further object of the invention to increase productivity and efficiency in a C2P system by providing automated queue management.  
         [0010]     It is a specific object of the invention to automate the operation of supplying plates on demand from a plate storage area within a C2P system to the platemaker engine.  
         [0011]     It is a further object of the invention to provide a plate handling mechanism to position a plurality of plate cassettes containing varying plate sizes within the plate storage area, making a desired plate cassette accessible to a plate picking mechanism.  
         [0012]     It is another object of the present invention to automatically remove and discard the interleaf sheets from between plates after a plate is individually removed from the stack of plates.  
         [0013]     It is another object of the invention to automatically pick a plate from the top of a stack of plates and deliver the plate to the platemaker engine in a manner which accommodates a variety of plate sizes and formats.  
       SUMMARY OF THE INVENTION  
       [0014]     A method for handling, loading and unloading a plurality of cassettes containing a supply of plates in an automated plate handler includes supporting each cassette on a support table within the plate handler. The support tables and the cassettes of plates supported on the tables are automatically positioned in order to place a cassette to be removed from the plate handler in a cassette loading position. The cassette to be removed is moved horizontally along the table onto a loading platform adjacent to the cassette loading position guiding the cassette to be removed off of the support table and onto the loading platform while removing the cassette from the plate handler.  
         [0015]     An apparatus for handling, loading and unloading a plurality of cassettes containing a supply of plates in an automated plate handler includes support tables supporting each of the cassettes within the plate handler. The support tables and the cassettes of plates on the support tables are automatically positioned in order to place a cassette to be removed from the plate handler in a cassette loading position. The cassette to be removed is moved horizontally by a first mechanism along the table and onto a loading platform adjacent to the cassette loading position. A guide member guides the cassette to be removed off of the support table and onto the loading platform while the cassette is removed from the plate handler. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The objects and features of the invention will be better understood and further objects and advantages of the invention will become apparent in the following detailed description of the invention, when taken with the accompanying drawing(s), in which:  
         [0017]      FIG. 1  is a schematic illustration of an electronic prepress system employing a platesetter shown from a side view with a plate handler and plate picker mechanism according to the present invention;  
         [0018]      FIG. 2  is a partial sectional front view of the plate handler viewed in  FIG. 1 ;  
         [0019]      FIG. 3  is an isometric view of an assembly portion of the plate handler shown in  FIG. 2 , particularly featuring an elevator mechanism and a table supporting mechanism according to the present invention;  
         [0020]      FIG. 4  is a detailed isometric view of the plate picker mechanism shown in  FIG. 1 ;  
         [0021]      FIG. 5  is a simplified top view of the picker mechanism of  FIG. 4  positioned over a handler cassette within the plate handler according to the present invention;  
         [0022]      FIG. 6  is a side view of a portion of the plate handler showing the plate picker in the process of picking a plate from a cassette, and also featuring a slip sheet removal mechanism according to the present invention;  
         [0023]      FIG. 7  is an isometric view of a plate cassette used in the plate handler according to the present invention; and  
         [0024]      FIG. 8  is a detailed side sectional view of a portion of a plate cassette as shown in  FIG. 7 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     The computer to plate imaging system shown in  FIG. 1  and generally referred to as reference number  10 , is a complete system for plate production, where digital data files representing a publication (or printed image) are input to the system  10 , and plates ready to go on a printing press are output from the system  10 . Most of the operation of the system is automated, requiring a minimum of operator intervention. The system is comprised of a front-end server  12 , a raster image processor (RIP)  14  and a platemaker or platesetter  16 . The front-end  12  sends jobs to the platesetter  16 . The platesetter  16  has three major components. An optional on-line plate handler  18 , the imaging engine  20  and an optional on-line plate processor/plate stacker  22 . The plate handler  18 , hereinafter handler, contains a supply of plate containers or cassettes  24 . The handler can hold as little as two cassettes or as many as three, four, or five depending on user requirements. Each cassette is a light tight container that houses a stack of plates  26 . The cassettes  24  can be vertically adjusted by the handler  18  to make plates  26  stored within a particular cassette available to a plate shuttle mechanism  28 , hereinafter referred to as the picker  28 . The picker  28  removes a single plate from the selected cassette and transports the plate between the handler  18  and the engine  20 , which will be described in detail hereinafter.  
         [0026]     The primary function of the handler  18  is to make plates  26  available on demand to the imaging engine  20 . A multitude of plates  26  are stacked in each cassette  24  and the cassettes  24  are side-loaded into the handler  18  by an operator. Between each plate in a stack there may be a protective interleaf sheet or slip sheet which is removed by the handler  18  and discarded by a slip sheet removal mechanism  25 . The handler  18  receives commands from the engine  20  by workflow software, which provides instructions to the handler  18  about what cassette  24  needs to be accessed to make a plate available to the picker  28  so the plate may be conveyed to the imaging engine  20 . The handler  18  in turn provides status information to the engine  20  through the workflow software to make full interaction with the system  10  possible.  
         [0027]     The front-end  12  sends data to the engine  20  through an interface connection. Typically this data represents a “job” which requires the imaging of plates. This data contains information about the job&#39;s requirements, such as the type of plate, its size and plate thickness, the number of plates that are part of the same job, etc. The engine  20  interfaces electrically with the handler  18  to exchange machine functional and operation data which is input into the workflow software. The handler  18 , through the engine  20 , sends data to the workflow software from data stored in each loaded cassette  26  representing plate size and quantities available in the cassettes  24 . The handler  18  includes a device  61  for reading an ID tag  187 , for example, a conventional bar-code reader on each cassette which has a description of the plate type inside. This ID tag  187  is in the form of a bar-code or other means. If a required plate size is unavailable, the engine  20  notifies an operator through a platemaker control terminal  30 , so the operator can load the needed cassette into the handler  18 . The engine  20  passes information to the handler  18  defining the next plate size or thickness required for imaging and which cassette  24  is to be placed in the queue, or in the correct position for access by the picker  28 . The cassettes  24  store different sizes and/or thicknesses of plates  26  so the handler  18  positions a specific cassette  24  so that the picker  28  can access the required plate inside the specific cassette. The handler  18  insures the slip sheet, if present, has been removed from the surface of the top plate with the slip sheet removal mechanism  25 . The picker  28  then moves over the positioned cassette, the plate is “picked,” and the picker  28  returns to the imaging engine (home) position to deliver the plate. The imaging engine  20  accepts the plate and while the picker is in the engine  20  in the home position, the handler  18  is free to position the cassettes  24  in preparation for the next plate to be imaged.  
         [0028]     Referring to  FIG. 2 , some basic elements of the handler  18  are shown. The handler  18  has a support frame  32  which surrounds several tables  34 ,  36 . The lowermost table  36  is attached to and supported by a brace  38  on the underside of the lowermost table  36 . The brace  38  is attached to an elevator mechanism, referred to generally as  40  and to be described hereinafter, which raises and lowers the brace  38  and the lowermost table  36  supported by the brace  38 . The upper three tables  34  positioned above the lowermost table  36  rest upon the lower table  36  on table spacers  42  which are secured to the outer ends of the undersides of the upper three tables  34 . In  FIG. 2 , the upper three tables  34  are shown being supported by a table support mechanism, referred to generally as  44  and to be described hereinafter, which separates the tables to allow clearance space for the picker to enter into above the cassette from which a plate is going to be picked. When the table support mechanism  44  is inactive, the table spacers  42  contact the table immediately below the table which the spacers are attached to, in a manner so as to support that table. The tables  34 ,  36  can be positioned by the elevator mechanism  40  as a group, with the three upper tables  34  resting on the lowermost table  36  on the brace  38  of the elevator mechanism  40 .  
         [0029]     Referring additionally to  FIG. 3 , the support frame  32  has four vertical support beams  46  provided with guide tracks  48  for guiding the tables while being raised or lowered. Each table has four rotatable guide wheels  50  (only two shown as viewed in  FIG. 2 ) which ride in the guide tracks  48  at the corners of each table. The table support mechanism  44  comprises four vertical shafts  52  with bearing mounts  54  at the upper ends of each shaft  52 . The shafts  52  are rotatable relative to the bearing mounts  54  which are attached to the topside of the support frame  32 . The support frame  32  has bores (not shown) which the shafts pass through to extend downward to the tables  34 ,  36 . At the lower ends of the shafts  52  are support bars  56  which protrude horizontally outward from the shaft  52  at a right angle therefrom, and lower bearing mounts  58  attached to the four vertical support beams  46 . In an inactive position, the support bars  56  face outward and away from the tables, as shown in  FIG. 3 . A linkage  60  connecting the shafts  52  transmits rotary motion from a drive motor  62  to rotary plates  64  fixed to the tops of each shaft  52  and to the shaft of the drive motor  62 . Upon a predetermined rotation by the drive motor  62 , the linkage  60  connecting the rotary plates causes the four shafts  52  to rotate 90 degrees, positioning the horizontal support bars  56  facing inward toward the tables, in the active position as in  FIG. 2 . The support bars  56  are in position to support the tables  34  above the cassette  24  to be accessed by the picker  28 .  
         [0030]     The elevator mechanism  40  comprises a chain drive system having four chain drives  66 , one mounted on each support beam  46 . Two rotatable sprockets  68 ,  70  are mounted on each support beam  46  in an upper and lower position to cooperate with the chains  66  and transmit rotary motion of the sprockets  68 ,  70  into linear motion of the chains  66 . The lower sprockets  70  are attached to two horizontal shafts  72  which transmit rotary motion from a main drive shaft  74  through several gear boxes  76  and couplings  78 . The main drive shaft  74  is powered by a drive motor  80  through a belt  82  and pulley  84  connection.  
         [0031]     The brace  38  is connected to the chains  66  on the inner sides of the support beams  46  so that upon rotation of the drive motor  80 , the chain drive system raises or lowers the brace  38 , the lowermost table  36 , and any upper tables  34  resting thereon which are not supported by the table support mechanism  44  at the time.  
         [0032]     Referring now to  FIG. 4 , the picker  28  is shown supported on parallel rails  90  which are fixed to the interior of the engine compartment  20  ( FIG. 1 ). Complementary rails  92  are mounted inside of the handler  18  as shown cross section in  FIG. 2  and isometrically in  FIG. 3 , allowing the picker to move smoothly between the engine  20  and handler  18 . The rails  92  inside the handler are secured to the support beams  46  of the handler frame  32 . The picker  28  has a carriage  94  which is supported on the rails ( 90  or  92  depending on whether the handler is in the engine or the picker respectively) by three guide wheels  96  which engage the rails  90  (or  92 ) on each side of the carriage  94 . Also two friction wheels  98  engage the rails  90  (or  92 ). The friction wheels  98  are driven by a motor  100  mounted on the carriage  94  through a connection to a drive shaft  102  and a belt and pulley mechanism  104  on each side of the carriage  94 . The motor  100  operates in two directions to effectively propel the picker carriage  94  in forward and reverse from the engine compartment  20  to the handler  18 . The carriage  94  supports three rows  106 ,  108 ,  110  of suction cups and an associated vacuum manifold  112  and vacuum tubing (not shown) between the manifold  112  and the three rows  106 ,  108 ,  110  of suction cups. Three manifold vacuum switches  113  connect to vacuum manifold  112  via vacuum hoses (not shown) to sequence vacuum to rows  106 ,  108  and  110  while a bi-directional motor  111  operates a movably disposed manifold plunger  115  to sequence vacuum to the suction cups  114  according to the size of the single plate being picked. The suction cups  114  are mounted on spring loaded fittings  116  to allow compression of the suction cups  114  against a plate during picking to ensure attachment of the plate to the picker  28 . The first row  106  of suction cups that extends the furthest into the handler  18  is pivotable with respect to the carriage  94 . An eccentric drive  118  and linkage  120  pivots the first row  106  of suction cups in a “peeling” motion. The eccentric  118  is driven by a motor  122  mounted on the carriage  94  to break or peel the edge of the plate being picked away from the stack. The middle row  108  of suction cups remains fixed with respect to the picker carriage  94 . The third row  110  of suction cups slides out from the middle row  108  of suction cups. Two rails  124 ,  126  are mounted for sliding through complementary bearings (not shown) in the carriage body  94  on the both sides of the picker  28 . On the right side of the picker viewed in  FIG. 4 , the rail  126  has a friction drive wheel (not shown) in driving contact with the rail  126 . The drive wheel is driven by a drive motor  128  through a belt and pulley mechanism (not shown), all of which are mounted to the carriage body  94  so as to transmit rotary motion of the drive wheel into linear motion of the rails  126 ,  124  relative to the carriage body  94 . The third row  110  of suction cups being movable relative to the other rows  106 ,  108  of suction cups expands the overall size of the picker  28  and the coverage area of the suction cups  114  to accommodate for various sized plates.  
         [0033]      FIG. 5  illustrates a simplified top view of the picker  28  positioned over a cassette  24  in the handler. The first row  106  of suction cups  114  is positioned near an inner edge  130  of the cassette  24  against which the plates are referenced regardless of the plate size. Four different plates having different sizes are depicted by dashed lines and are indicated as plates A, B, C, and D. Plate A is the smallest plate and the middle row  108  of suction cups of the picker  28  is positioned near the opposite edge  132  of plate A from the reference edge  130 . Vacuum is sequenced to four suction cups  114 , two within row  106  and two within row  108  according to the size of plate A. The middle row  108  has a fixed position relative to the first row  106  (excepting that the first row is pivotable) to pick up plate A without the use of the third row  110  of suction cups. The third row  110  is shown in an extended position by solid lines, at the far edge  134  of the largest plate D opposite from the reference edge  130 . The third row  110  of suction cups is also shown by dashed lines in a non-extended position. The third row  110  of suction cups is used to expand the size of the picker  28  to cover the areas for various size plates, such as B, C, and D, larger than the smallest plate A and smaller than or equal to the largest plate D, as indicated by arrow  136 . Vacuum is sequenced to the suction cups  114  within rows  106 ,  108  and  110  according to the size of plats B, C and D. Arrow  138  shows the relative movement of the picker  28  including all three rows  106 ,  108 ,  110  of suction cups  114  with respect to the handler cassette  24  and the engine.  
         [0034]     Referring now to  FIG. 6 , the slip sheet removal mechanism is generally indicated as  25 . The mechanism  25  is for the purpose of preventing a slip sheet  140  from sticking to the bottom of a plate  142  which is attached to the picker  28 , securing the slip sheet  140  on the top of the stack of plates in a cassette  24  to the slip sheet removal mechanism  25 , and subsequently completely removing the slip sheet  140  from the stack of plates in the cassette  24 . The mechanism  25  comprises a plurality of suction tubes  144  mounted on a first pivotable shaft  146 , an optional peeler air blast  148 , a plurality of fingers  150  mounted on a second pivoting shaft  152 , a plurality of nip wheels  154  mounted on a third pivoting shaft  156  (only one of each seen in drawing due to side view), and a rotatably driven roller  158  positioned below the nip wheels  154  which are in rolling contact during part of the slip sheet removal process, to be described hereinafter. A slip sheet detector device  902  is provided on one of the plurality of suction tubes  144 . The detector device  902  provides a signal which is calibrated to provide a slip sheet present or not present condition to the handler  18 . The suction tubes  144  are fixed to the pivoting shaft  146  to pivot upon being driven by motor  160  through a drive belt and pulley connection  162 . The fingers  150  are fixed to pivoting shaft  152  which is driven by a similar drive connection to a motor (not shown). The nip wheels  154  are each mounted to an extension arm  164  which is attached to a bracket  166  mounted on the pivoting shaft  156 . The extension arm  164  is spring loaded at the connection to the bracket to allow for the extension arm  164  to pivot or give slightly while pressure is applied between the nip wheel  154  and the roller  158 . The shaft  156  is rotated in forward and reverse by the drive motor  168  through a drive belt and pulley connection  170 . The roller  158  is driven by a motor  172  also through a belt and pulley connection  174 . It will be understood by those skilled in the art that equivalent means for rotating the pivoting shafts  146 ,  152 ,  156 , and rotating roller  158 , may be substituted therefor without departing from the spirit of the invention. The driven shafts and motors for driving the shafts are all mounted to a mounting bracket  176  which is connected to the support beams  46  of the handler  18 . Operation of the slip sheet removal mechanism  25  will be described hereinafter.  
         [0035]     Referring now to  FIG. 7  and  FIG. 8 , a cassette  24  for loading into the plate handler is shown. The cassette has a removable cover  180 , which is removed and replaced in a vertical direction relative to a rectangular bottom container  182  as indicated by arrows. The bottom container  182  comprises a base plate  184  surrounded by four aluminum side extrusions  186 . The extrusions  186  are attached at the four 90 degree corners by spring clips and adhesive (not shown). The base plate  184  is contained within a slot  188  in the edge of each extrusion  186  and is held in place with an adhesive on the top side  190  of the base plate  184  and a piece of continuous round flexible urethane belting  192  on the bottom side of the base plate  184 . The round belting  192  is retained in a thin groove  194  provided in the extrusion  186 .  
         [0036]     Three channels  196  (one shown) are fastened to the bottom side of the base plate  184 . The channels  196  act as reinforcing stiffeners for the bottom container  182 , and also are housings for three locator bars  198 . Each locator bar  198  is attached within a channel  196  by an adhesive. An adjustable stop  200  is provided on each locator bar  198  to slide along the locator bar and be fastened to a set position by a lock screw  202  which screws into holes  204  drilled into the locator bars  198 . The three adjustable stops  200  locate and secure a stack of plates  26  against several reference blocks  206  fastened to the side extrusions  186 . The adjustable stops  200  allow multiple sizes of plates  26  to be held against the reference blocks  206  within a single bottom container  182 . The base plate  184  is provided with embossed areas  208  for the reference blocks  206  to be set within, which prevents the plates referenced against the reference blocks  206  from sliding between the reference block  206  and the base plate  184  and maintaining alignment of the plates with respect to the reference block  206 .  
         [0037]     The cover  180  comprises a top plate  210  and four side extrusions  212  surrounding the top plate  210 . The extrusions  212  are fastened together at the four corners of the top plate  210  by spring clips and adhesive (not shown). The top plate is secured to a ledge portion  214  of the extrusions  212  by an adhesive. Two of the four side extrusions have a handle portion  216  formed in the extrusion  212  which cooperate with hooks on the undersides of the cassette tables in the handler to remove and replace the cassette cover (to be described hereinafter). The inside of the top plate  210  has a layer of foam  218  attached, to ensure that the plates on the top of a full stack of plates  26  do not slide over the tops of the reference blocks  206  during loading of a cassette  24  into the handler  18 . The cover  180  and the bottom container  182  are constructed from light proof materials, so that when the plates are enclosed within a covered cassette, there is no exposure of the light sensitive plate contained within the cassette. The attachment area between the bottom extrusions  186  and the cover extrusions  212  has magnetic strips  220  which ensure the cover  180  is attached securely to the bottom container  182  and that no light will enter the cassette  24  during handling.  
         [0038]     The side extrusions  186  are provided with a beveled portion  230  which aid in the loading of the cassette  24  into the plate handler  18 . The handler  18  has a loading platform  232  shown in  FIG. 2 , extending horizontally from the vertical beams  46  of the handler. The loading platform  232  has rows of grooved wheels  234  mounted for rotation within the loading platform  232 . The grooved wheels  234  cooperate with the beveled portion  230  of the side extrusions  186  of the cassette  24  during loading and serve to register the cassettes in a reference position within the handler. All tables  34  and  36  within the handler are also provided with the rows of grooved wheels to facilitate smooth and easy loading of the cassette from the loading platform onto the support tables in the handler, while maintaining the cassette in register. The beveled portions  230  cooperate with the V-grooved surface  236  of the grooved wheels  234  on opposite outer sides of the cassette  24  for proper alignment. The cassette is designed to align the plates inside the cassette against the reference blocks provided on the interior of the cassette, and also register the cassette into a reference position within the handler, as shown in  FIG. 5 , regardless of the plate size contained in the cassette. The parallel rails  92  in the handler are fixed relative to the wheels of the selected table in the access position. This ensures the registration of the plates within the cassette relative to the rails  92 , and the registration is transferred to the complementary rails  90  in the engine compartment, and thereby the plate is delivered in register into the engine from the handler.  
         [0039]     Additional locator stops  238  are provided on each table to assist in registering the cassette  24  in the loading direction so that the cassette  24  is pushed into the handler  18  along the grooved wheels  234  of the table  36 , but only to a predetermined location so that the cassette  24  is registered with respect to two dimensions and to the picker rails  92 . These additional locator stops  238  are spring loaded and are located between the grooved wheels  234  within each row of grooved wheels on a table  36 . The stops  238  contact an underside  240  of the side extrusions  186  while the cassette  24  is being loaded, and when the stop  238  comes into contact with a recess (not shown) formed in the underside of the extrusion, the spring force behind the stop  238  forces the stop into the recess and locks the cassette  24  into a predetermined position on the table. The wheels  234  register the cassette with respect to the two reference blocks  206  on one side of the cassette, while the locator stops  238  within the rows of the wheels  234  register the cassette  24  with respect to the third, alone reference block  206  on the neighboring side of the cassette. Then the plates are registered in a known location relative to the picker, as depicted in  FIG. 5 .  
         [0040]     The loading platform  232  can be incorporated into the design of the doors and covers for enclosing the handler in a light tight environment. The loading platform can function both as a door into the cassette loading area, and as the loading platform. This is accomplished by providing an attachment hinge on the handler frame for the loading platform  232  to pivot between the two functional positions. The loading platform  232  is pivoted up for a closed door position, and down and horizontally as shown in  FIG. 2  for an open, cassette loading position.  
         [0041]     Cassettes loaded into the handler house the plates. At any one time, a cassette holds only like plates (same type, gauge, size, etc.). Typically, there is a maximum of 50 plates of 0.012″ gauge, 75 plates of 0.008″ gauge, or 100 plates of 0.006″ gauge, in a single cassette. There are several distinct cassette sizes. A cassette of a specific size holds a range of plate sizes inside, however only one size plate is loaded into a cassette at any one time. Fillers or guides are used to take-up the space between plate and cassette boundaries. The reference position of the plates within the cassette is described above with reference to  FIG. 5 . Packaging of plates within a cassette is related to both handler operation and cassette transportability. There may be a mix of cassettes in the handler (two, three or four cassettes). All cassettes can be different from each other, in that each houses a distinct set of plate characteristics (type, size, gauge, etc.) There may be instances where some or all cassettes inside the handler have the same plate characteristics.  
         [0042]     Now, with reference to all the Figures, the method for using the plate handler  18  and picker  28  will be described. The primary function of the handler  18  is to position a required plate on demand in an access position for the picker  28 , which picks and delivers the required plate to the engine  20 . Once the handler  18  receives a request from the engine  20  for a specific plate, the following actions take place in the handler, in cooperation with the engine  20 . The picker  28  begins in the home position within the engine  20 . The slip sheet removal mechanism  25  is positioned with the suction tubes  144 , fingers  150 , and nip wheels  154  retracted (as shown in dotted lines for the suction tubes and nip wheels in  FIG. 6 ) to clear the path of the tables  34 ,  36  for repositioning by the elevator mechanism  40 . The elevator mechanism  40  moves the brace  38 , lower table  36 , and upper tables  34  supported thereon, if any, to a cover removal/replacement position. In the cover removal/replacement position, the selected table  36  is located directly below the table  34  supported by the support bars  56  of the table support mechanism  44 . Hooks on the bottom of the supported table  34  engage the cover  180  of the selected cassette  24  for either removal or replacement, so that the cover  180  is separated from or rejoined with the selected cassette  24 .  
         [0043]     In  FIG. 2 , the cover removal/replacement position for the lower table  36  is at a position where the open cassette  24  on the lower table  36  contacts the cover  180  supported by the table  34  immediately above the lower table  36  held by the support bars  56 . When the selected cassette  36  is in the cover removal/replacement position, the upper tables  34  are all then supported by the brace  38 . Then the support bars  56  and shafts  52  are turned 90 degrees by means of the linkage  60  and drive motor  64 . Once the support bars  56  are retracted from the path of motion of the tables  34 ,  36 , the elevator mechanism  40  moves to the cover removal/replacement position for the next selected table and cassette. The table support mechanism  44  moves the support bars  56  into the supporting position underneath the table directly above the selected cassette  24 . The elevator mechanism  40  then moves the selected table down thereby separating the cover  180  of the selected cassette  24  from the selected cassette  24  so that the picker can access the plates  26  contained within the cassette  24 .  
         [0044]     The picker  28  is then moved from the home position in the engine  20  into the handler  18  along the rails  90  and  92 . Depending on the size of the plate in the selected cassette  24  the picker  28  adjusts the third row  110  of suction cups relative to the middle row  108  of suction cups to accommodate for various plate sizes, if necessary ( FIG. 5 ). The elevator mechanism  40  moves the selected cassette  24  and plates therein upward to come into contact with the suction cups  114  on the picker  28  ( FIGS. 4 and 6 ). The suction cups  114  retract into the spring loaded fittings  116  to accommodate for variations in the stack height of the plates  26  in the cassettes  24 , as the elevator  40  moves the cassette  24  up to the picking position which is at a set vertical height relative to the picker rails  90 ,  92 . Therefore for a maximum stack height of a full stack of plates, the suction cups  114  compress against the spring loaded fittings  116  and retract a length into the fittings, and for a depleted stack of plates, the suction cups  114  compress against the spring loaded fittings and retract substantially the same length minus the height of the stack depletion. The spring loaded fittings  116  also ensure that the plate and the suction cups  114  make contact to secure the plate onto the picker  28 . After the plate is attached to the picker  28  by the vacuum suction, the first row  106  of suction cups on the picker  28  is pivoted upward, peeling back the edge of the plate  142  and creating a gap between the plate  142  and the slip sheet  140  underneath.  
         [0045]     The slip sheet removal mechanism  25  activates the peeler air flow  148 , and the fingers  150  are pivoted into position to hold down the edge of the slip sheet  140  while the elevator mechanism  40  lowers the cassette  24  to a slip sheet removal position. The peeler air blast  148  remains on while the cassette  24  moves downward to separate the slip sheet  140  from the bottom of the plate  142  being picked by the picker  28 , which may stick to the plate due to electrostatic charge. The fingers  150  are pivoted away from the slip sheet  140  and the suction tubes  144  are pivoted into position above the slip sheet edge. The suction cups on the ends of the suction tubes are compliant and flexible so that when the vacuum is applied and contact is made between a suction cup and the slip sheet, the slip sheet material is drawn into the suction cup and the separation of the slip sheet from the plate below it is initiated. The compliant suction cup deforms to break the slip sheet away from the lower plate as typically an attractive force exists between the slip sheet and the plate. This is also an important step in the process of removing the slip sheet because the slip sheet may be a porous material and the vacuum applied through the suction tubes can pass through the slip sheet material and be applied to the plate below, which is undesirable when attempting to remove the slip sheet. The selected cassette  24  is elevated to bring the slip sheet  140  into contact with the suction tubes  144  while the vacuum is on. The suction tubes  144  pivot upward slightly to break the adhesion of the slip sheet  140  to the plate below. The elevator  40  then moves the selected cassette  24  downward from the slip sheet removal mechanism  25  and the suction tubes  144  pivot back downward to the roller  158  with the slip sheet  140  attached. The vacuum for the suction tubes  144  is turned off and the slip sheet  140  is released to the rotating roller  158  to pull the slip sheet  140  away from the stack. The nip wheels  154  pivot from the position shown in solid lines to the position shown in dotted lines to cooperate with the roller  158  and remove the slip sheet  140 . A sensor  902  indicates that the removal of the slip sheet  140  is completed and the rotating roller  158  is then halted. Meanwhile the picker  28  lowers the first row  106  of suction cups from the peeling position, and the picker  28  travels back into the engine  20  to the home position. For the next plate to be selected by the picker  28 , the steps are partially repeated if the same cassette  24  is being picked from, or the steps are repeated from the beginning of the sequence for another cassette.  
         [0046]     In order to load cassettes into the handler, the following method steps occur in conjunction with the plate handler apparatus and the workflow software as described previously. The handler has sensors positioned appropriately (not shown) to monitor the level of the plates contained in each cassette. Additionally the handler has the capability of knowing the types of plates available so that when a plate needed by the engine is not available, or upon a sensor detecting an empty cassette, a signal is communicated to the engine and the operator is alerted through the operator control terminal  30 .  
         [0047]     The picker  28  is returned (if not already there) to begin in the home position within the engine  20 . The slip sheet removal mechanism  25  is positioned with the suction tubes  144 , fingers  150 , and nip wheels  154  retracted (as shown in dotted lines for the suction tubes and nip wheels in  FIG. 6 ) to clear the path of the tables  34 ,  36  for repositioning by the elevator mechanism  40 . The elevator mechanism  40  moves the brace  38 , lower table  36 , and upper tables  34  supported thereon, if any, to the cover removal/replacement position previously described. Then the support bars  56  and shafts  52  are turned 90 degrees by means of the linkage  60  and drive motor  64 . Once the support bars  56  are retracted from the path of motion of the tables  34 ,  36 , the elevator mechanism  40  moves to the cassette loading position for the selected table and cassette needing replacement. The cassette loading position is located where the selected table is adjacent to the loading platform  232  shown in  FIG. 2  extending out from the handler  18  to support the cassette  24  to slide horizontally between the selected table and the loading platform  232  during loading and unloading. Covers and doors (not shown) are provided to enclose the entire handler frame to maintain the cassette in a light tight environment. The doors are provided to access the interior of the handler and at this time the door locks are released to allow operator access. Then the empty cassette is removed by sliding the cassette out horizontally along the path formed by the grooved wheels in the selected table and the loading platform, and then the cassette is either reloaded or replaced with another cassette. The cassette presence is monitored by sensors. After detecting the cassette on the selected table, the handler waits for the doors to be closed and then the door locks are activated. The elevator moves up to the cover removal/replacement position for the selected cassette and normal operation is resumed.  
         [0048]     It will be understood that the preferred embodiment of the system described herein being a platesetter for imaging aluminum plates, can be used also with polyester plates, can be modified to perform as a proofing device rather than a platesetter, such as in commonly owned, U.S. Pat. No. 5,699,099, entitled “Electronic Prepress System With Multi-Function Thermal Imaging Apparatus,” hereby incorporated by reference. Additionally the apparatus described herein is applicable to production of thermally recorded printing plates as well as photosensitive lithographic printing plates recorded by light exposure, with various modification to the system&#39;s processing and imaging components, as appreciated by those familiar with the art.  
         [0049]     While this invention has been described in terms of various preferred embodiments, those skilled in the art will appreciate that various modifications, substitutions, omissions and changes may be made without departing from the spirit thereof. Accordingly, it is intended that the scope of the present invention be limited solely by the scope of the following claims, including equivalents thereof.