Abstract:
A substrate manager for a substrate exposure machine is used, in one example, as a platesetter. As such, it comprises a substrate storage system, containing one or more stacks of substrates, such as plates in one implementation. A substrate picker is provided for picking substrates from the stack of substrates. The substrates are then handed to a transfer system that conveys the substrates to an imaging engine. According to the invention, a substrate inverter system is also provided. This system inverts the substrates from being imaging or emulsion side down to emulsion side up in the present implementation. This allows plates, for example, which are stored emulsion side down in cassettes to be flipped to an emulsion side up orientation, and then transferred, using the substrate transfer system to the imaging engine. This flipping process has two advantages. First, the plates can be emulsion side up during the transfer. This prevents any damage to the sensitive plate emulsions. Moreover, the plates, now in an emulsion side up configuration are in the right orientation for being installed on the outside of a drum on an external drum imaging system, as is common in many platesetters. Also, the plates are picked from the non emulsion side. Thus the system is less sensitive to emulsion formulation changes. A slip sheet capture mechanism is also provided to pass slip sheets separating the plates to a storage location.

Description:
BACKGROUND OF THE INVENTION 
   Imagesetters and platesetters are used to expose substrates that are used in many conventional offset printing systems. Imagesetters are typically used to expose the film that is then used to make the plates for the printing system. Platesetters are used to directly expose the plates. 
   For example, plates are typically large substrates that have been coated with photosensitive or thermally-sensitive material layers, referred to the emulsion. For large run applications, the substrates are fabricated from aluminum, although organic substrates, such as polyester or paper, are also available for smaller runs. 
   Computer-to-plate printing systems are used to render digitally stored print content onto these printing plates. Typically, a computer system is used to drive an imaging engine of the platesetter. In a common implementation, the plate is fixed to the outside or inside of a drum and then scanned with a modulated laser source in a raster fashion. 
   The imaging engine selectively exposes the emulsion that is coated on the plates. After this exposure, the emulsion is developed so that, during the printing process, inks will selectively adhere to the plate&#39;s surface to transfer the ink to the print medium. 
   Typically, one of two different strategies is used to feed substrates to the imaging engine in the printing system. In the simplest case, an operator manually places individual substrates into a feeder that then conveys the substrates through a feed port to the drum scanner. This approach, however, has some obvious drawbacks, since an operator must be dedicated to feeding the substrates. Moreover, the printing system must be housed within a light-safe environment, if the substrates being used have any sensitivity to ambient light. The alternative approach is to use a substrate manager. 
   Managers typically house multiple substrate cassettes. Each cassette is capable of holding many substrates in a stack. The substrates are separated by slip sheets that are used to protect plate emulsions from damage. For example, in one common implementation, each cassette holds up to one hundred substrates. The manager selects substrates from one of its cassettes and then feeds the substrates, automatically, into the imaging engine, while removing the slip sheets. 
   In these designs, cassettes are loaded into the manager on a table. The table is then raised and lowered inside the manager to bring the substrates of a selected cassette into cooperation with a picker that grabs individual substrates and feeds them to the imaging engine. 
   SUMMARY OF THE INVENTION 
   In the past, these substrate managers have removed the slip sheets using suction cups. These systems enable the machine to pick up the slip sheets and move them to a storage location. 
   The problem with this approach is that it is not compatible with all types of slip sheets. Some are porous to air. This prevents the establishment of predictable vacuum levels that would ensure the proper handling of the slip sheets. 
   In general according to one aspect, the invention features a slip sheet capture mechanism for a substrate processing machine. It comprises a foot for holding a portion of the slip sheet and a nip roller for engaging and drawing the slip sheet in the direction of the foot and into a nip. Thus, the suction cup systems are avoided, enabling the system to work for a broad range of different types of slip sheets. 
   In the current embodiment, the foot comprises a foot frame and a friction pad on the foot frame for engaging the slip sheet. The nip roller draws the slip sheet into the nip by rotating in the direction of the foot a predetermined amount. This draws the slip sheet between the nip roller and a follower roller, which cooperates with the nip roller to hold the slip sheet. 
   Preferably, a slip sheet sensor is used to determine whether a slip sheet is under the slip sheet capture mechanism. 
   In general according to another aspect, the invention features a method for capturing a slip sheet. The method comprises holding a portion of the slip sheet and engaging and drawing the slip sheet in the direction of the foot and into a nip. 
   The step of engaging and drawing the slip sheet preferably comprises urging a nip roller into engagement with the slip sheet and then rotating the nip roller in the direction of the foot. 
   After drawing the slip sheet into the nip, the slip sheet is extracted from a stack of substrates in concert with the extraction of a substrate. The slip sheet is later expelled from the nip after extraction from the stack of substrates. 
   The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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. Of the drawings: 
       FIG. 1  is a schematic side plan view of a plate manager according to the present invention; 
       FIG. 2  is a perspective view of a plate inverter and slip sheet capture system, according to the present invention, in a home position; 
       FIG. 3  is a perspective view of the inventive plate inverter system in a plate feeding, or intermediate, position; 
       FIG. 4  is a side plan view of a slip sheet capture mechanism, according to the present invention; 
       FIG. 5  is a perspective view of a bottom of the slip sheet capture mechanism showing its actuation mechanism, according to the present invention; 
       FIG. 6  is a top perspective view of the slip sheet capture mechanism showing a pivot detector, according to the present invention; 
       FIGS. 7A ,  7 B, and  7 C are flow diagrams illustrating a method for plate capture and inversion and slip sheet capture according to the present invention; 
       FIGS. 8A ,  8 B,  8 C,  8 D,  8 E, and  8 F are side plan views of the plate inverter system and slip sheet capture mechanism during various phases of operation; and 
       FIG. 9  is a schematic perspective view of a plate inverter system according to another embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Plate Manager 
     FIG. 1  shows a substrate, and more specifically a plate, manager  20 , which has been constructed according to the principles of the present invention. 
   Generally, the plate manager  20  comprises a plate store  200 , a plate inverter system  300 , a plate transfer system  400 , and a plate inserter  600 , all of which are controlled by a system controller  50 . A plate imaging engine  500  is further provided to expose the substrates. 
   The plate store system  200  comprises, when loaded, multiple cassettes  210 . Each of these cassettes  210  holds a stack of plates  212 . The cassettes are moved vertically within the plate store system  200  by a cassette elevator or lifter  214 . 
   In one example, the cassettes themselves are stacked atop one another, or in stacks of cassettes, that are moved vertically by the cassette elevator  214  so that the stack of plates  212  of a specific cassette  210  is raised to the level of a plate picker system  216 . Once the cassette  212  is at the proper height, a cassette translator  218  moves it laterally. The cassette  212  is thereby positioned underneath the plate picker system  216 , which then picks a plate off of the stack of plates  212 . 
   The plate picker or peeler system  216  provides individual plates from the stack of plates  212  to the plate inverter system  300 . The plate inverter system  300 , in the preferred embodiment, comprises an arcuate transfer path  310  over which the plates are conveyed to effect the inversion. 
   Simultaneously with the picking of the plate  10  and its transfer across the transfer path  310 , a slip sheet handler  100  captures a slip sheet SS, that is typically located between the individual plates in the stack of plates  212  and subsequently transfers the slip sheet SS with the plate  10  over the transfer path  310 . Typically, the slip sheet handler  100  then passes the slip sheets off for storage. 
   In the present embodiment, the cassettes  210  are as described in U.S. application Ser. No. 10/117,749, filed on Apr. 5, 2002, entitled Plate Cassette for Platesetter, by DaSilva, et al., which is incorporated herein by this reference in its entirety. This cassette system has a second, slightly wider slip-sheet removal groove that extends laterally across the cassette&#39;s tray between a leak groove and a registration guide. This groove is a depressed portion or recess in the otherwise planar surface of the cassette&#39;s tray. It is used to facilitate the removal of slip sheets for small plates. 
   Further, in the present embodiment, the plates  212  are held in the cassettes  210  in a center justified configuration. And, the plates are transferred through the plate manager  20 , center justified. However, in other implementations, the plates can be edge justified in both the cassettes and during transfer through the machine. 
   The plate inverter system  300  transfers the plate  10  over the arcuate transfer path  310  from the plate picker or peeler system  216  of the plate storage system  200  to the plate transfer system  400 . This transfer system  400 , in the present implementation, comprises a conveyer  410  that receives the plate  10  and then moves the plate  10  laterally in the plate manager  20  toward the plate imaging engine  500 . 
   Between the plate imaging engine  500  and the transfer system  400  is a plate inserter system  600 . The angle of the plate is moved from generally a horizontal orientation as it is received from the transfer system  400  to a more vertical orientation for insertion into the plate imaging engine  500 . Specifically, the plate is angled at 75 degrees from horizontal for insertion into the engine. 
   The plate inserter system  600  comprises an inserter transfer path  610 . It moves the plate from its horizontal position as it is transferred across the conveyer  410  to a more vertical orientation. It transfers the plate  10  so that it is received by a first set of output pinch rollers  612 , and transferred to a second set of pinch rollers  614 . 
   The plate imaging engine  500  receives the plate  10  from the plate inserter system  600 . The plate is brought into engagement with a header clip  510  on the exterior of drum  512  of the imaging engine  500 . The drum  512  is then advanced so that the plate  10  is progressively installed on the outside perimeter of the drum  512  by ironing roller  540  until its lagging edge is engaged by a lagging edge clip  514 . 
   At this stage, the plate  10  is selectively exposed by a laser scanning system  516 . Typically, this is a high speed, high power laser scanning system that selectively exposes the emulsion on the plate  10  with the desired image, in a raster fashion. Afterward, the plate  10  is typically ejected from the plate imaging engine  500  for development and further processing. For example, in one configuration, the exposed plate is ejected to a conveyor system, not shown, and transported to a plate processor. 
   Plate Inverter System 
     FIG. 2  shows the present embodiment of the plate inverter system  300 . It generally comprises a left lagging arm  312 -L and a right lagging arm  312 -R. The right and left lagging arms  312 -R,  312 -L support lagging arm nip rollers  314  and  316 . These lagging arm nip rollers  314 ,  316  extend between the right and left lagging arms, parallel to each other, to thereby define a nip between the first lagging arm nip roller  314  and the second lagging arm roller  316 . 
   Also, a support plate  326  is typically required. It extends between the right lagging arm  312 -R and the left lagging arm  312 -L, being connected to the lagging arms via L brackets  328 . This increases the rigidity of the system of lagging arms  312 . 
   The right and left lagging arms  312 -R,  312 -L are in turn supported by a hollow axle  318 . Right and left flanges  324 -R,  324 -L are secured to the ends of the hollow lagging arm axle  318 . The right lagging arm  312 -R is bolted to the right axle flange  324 -R and the left lagging arm  312 -L is bolted to the left axle flange  324 -L such that the lagging arms  312  are secured to the lagging arm hollow axle  318 . 
   In the specific implementation, a lagging arm gear  320  is disposed near the center of the lagging arm&#39;s hollow axle  318 . It engages a drive gear  322  of a lagging arm drive motor  324 . As a result, by driving the lagging arm motor  324 , the lagging arm hollow axle  318  is rotated to thereby allow the lagging arms  312 -R,  312 -L to traverse the arcuate transfer path  310 . The drive motor  324  has an integral brake and an encoder  324   e . This allows the motor  324  to hold the position of the arms  312  and also move the arms  312  through predetermined arcs under control of the system controller  50 . 
   The lagging arms  312  additionally support a lagging arm nip actuation and roller drive mechanism  330 , which allows the controlled separation of the first lagging arm nip roller  314  from the second lagging arm nip roller  316  and the driving of the nip rollers to feed a plate in the nip. The mechanism further has a motor encoder for measuring the number of rotations of the rollers  314 ,  316 . This opens the nip between these two rollers enabling insertion of a plate or other substrate into the opened nip. Thereafter, the lagging arm nip actuation mechanism  330  closes the nip between the lagging arm nip rollers  314 ,  316  to thereby engage the plate. 
   The plate inverter system  300  also includes right and left leading arms  332 -R,  332 -L. The leading arms  332 -R,  332 -L similarly support first and second leading arm nip rollers  334 ,  336 . A leading arm nip actuation mechanism  338  is provided on each of the right leading arm  332 -R and the left leading arm  332 -L to control the opening and closing of the nip between the first leading arm nip roller  334  and the second leading arm nip roller  336 . In this way, the rollers on the leading arms  332  can thereby be opened and closed to release and engage a plate between nip rollers  334  and  336 . 
   The right and left leading arms  332 -R,  332 -L are supported on a solid leading arm axle  340 . This axle includes a leading arm gear  342 , which is engaged by a leading arm motor  344  via a leading arm drive gear  346 . In this way, when the leading arm motor  344  is driven, the right and left leading arms  332 -R,  332 -L are rotated so that the nip of the leading arm nip rollers  334 ,  336  moves through the arcuate transfer path  310  of the plate inverter system  300 . The leading arm motor  344  also has an integral brake and an encoder  344   e . A leading arm support member  350  is also provided. It extends between the right leading arm  332 -R and the left leading arm  332 -L. It is secured to the leading arms via L brackets  352 . It similarly increases the rigidity of the leading arm system. 
   A plate lagging edge detector  354  is provided on the lagging arm system. Specifically, it is attached to the lagging arm support member  326 . It projects down near a plane that extends between the nip of the first lagging arm nip roller  314  and the second lagging arm nip roller  316 . In the preferred implementation, it detects the level of reflected light. As a result, it can detect whether a reflective substrate, such as a plate, is being held in the nip of the lagging arm nip rollers  314 ,  316 . This arrangement for detecting the plate requires that the plate surface opposite the detector be reflective, which is a characteristic of the non-emulsion side of the plate. 
   Supported by the leading arms  332  is a slip sheet capture mechanism  110  of the slip sheet handler  100 . This is used to grab the slip sheet that is underneath a plate that is being held between the nip rollers of the lagging arms. 
     FIG. 3  shows the plate inverter system  300  in a feed or intermediate position. Specifically, the leading arm motor  344  has been driven to rotate the right leading arm  332 -R and the left leading arm  332 -L upward along the arcuate transfer path  310 . This view better shows the first leading arm nip roller  334  and the second leading arm nip roller  336 . 
   Also shown is a plate header detector  370 . It detects the presence of a plate that is held between the leading arm nip rollers  334 ,  336  by detecting the plate&#39;s reflective non-emulsion surface as in the case of the lagging edge detector  354 . 
   The lagging arms  312 -R,  312 -L further carry a first or upper air bar  360  and a second or lower air bar  362 , in one embodiment. These are connected to a compressor system  364 , which provides compressed air to the first air bar  360  and the second air bar  362  of the lagging arm system to facilitate the separation of slip sheets from the plates, under the control of the system controller  50 . 
   Slip Sheet Capture Mechanism 
     FIG. 4  shows the slip sheet capture mechanism  110 . Specifically, it comprises a first member  112  that is rigidly connected to the right and left leading arms  332 -L,  332 -R. A series of second members  114  are bolted to the first member  112  via bolts  116 . A distal end  118  of the second member  114  has a bore through which a shaft  120  extends. The shaft  120  similarly extends through a pivot frame member  122 . As a result, the pivot frame member  122  can rotate with respect to the second frame members  114 . A spring member  124  is bolted to the first member  112  and spring loaded to a pivot point  126  of the pivot frame member  122 . This resiliently biases the pivot frame member  122  relative to the first member  112  to rotate about shaft  120  in the direction of arrow  128 . 
   The slip sheet capture mechanism  110  engages a slip sheet via three components. Specifically, the slip sheet capture mechanism has a foot frame  130  that is bolted to the end of the pivot frame member  122 . The foot frame  130  supports a foot pad  132  for holding a slip sheet. The mechanism  110  further comprises a drive slip sheet roller  136  that is journaled to rotate on the pivot frame  122  via axle  138  and a slip sheet follower roller  134  that is similarly journaled to rotate relative to the pivot frame  122  that supports it. The drive nip roller  136  includes a gear  137  that engages an intermediate gear  139 , which is also journaled to rotate on the pivot frame  122 . The gear  139  is engaged by a rack  140  that is connected to the actuation shaft  144  of a double acting air cylinder  142 . As a result, actuation of the air cylinder  142  moves the shaft  144  in the direction of arrow  146  to move the rack  140  in both the right and left directions in the orientation of FIG.  4 . This rotates the intermediate gear  139 , and in turn, the nip drive slip sheet roller  136 . 
   Slip sheet detector probes  150  are further provided on the pivot frame  128 . They extend below the outer periphery of the follower roller  134  to verify the presence or not of a slip sheet. Generally conductivity is detected between the probes. A slip sheet will be non-conductive yielding a very high resistance between the probes  150 . A plate will be conductive resulting in a low resistance. 
     FIG. 5  better shows the arrangement of the double acting air cylinder  142  and its rack  140 . It rotates gear  139  to in turn drive the drive roller  136  via its drive roller gear  137 . It allows the selective rotation of the drive roller  136 . 
     FIG. 6  shows a system for detecting the degree to which the pivot frame  122  is pivoting with respect to the first member  112 . Specifically, a flag arm  152  is provided, which is bolted to the first member  112 . It comprises a flag portion  154  that passes in proximity to a sensor  156 . As a result, the pivoting of the pivot frame  122  can thereby be detected by this detector  156  and specifically when the pivot frame  122  has rotated a predetermined amount such that the flag portion  154  is within the slot of the U-shaped element of the sensor  156 . 
   Plate Inversion and Slip Sheet Capture Method 
     FIGS. 7A-7C  are flow diagrams that are used to describe the operation orchestrated by the system controller  50  of the preferred embodiment of the plate inverter  300 . These flow diagrams are described with reference to  FIGS. 8A-8F , which show the plate inverter system  300  at various stages of operation in the inversion of the plate according to the invention. 
   In more detail, with reference to step  710  of  FIG. 7A , in the first phase of the operation, the cassette elevator  214  raises the cassette  210 . The cassette is also horizontally moved via the cassette translator  218 . Simultaneously with the raising of the desired cassette  210 , the leading arms  332  and the lagging arms  312  are moved out of the home position to provide clearance for the cassette&#39;s movement. 
     FIGS. 8A and 8B  illustrate the operation of step  710 . Specifically, in  FIG. 8A , the leading arms  332  and the lagging arms  312  are in the home position. However, as illustrated in  FIG. 8B , for the cassette  210  to be raised by the elevator  214 , both the leading arms  332  and the lagging arms  312  move to provide clearance for the cassette  210 . This brings the top plate in the stack of plates  212  in the cassette  210  into engagement with the peeler mechanism  216 . The peeler mechanism  216  includes an array of suction cups  230  that are brought into engagement with the top plate in the plate stack  212 . 
   The height to which the cassette  210  is raised by elevator  214  is controlled by feedback from sensor probe  232  that functions as a plate stack height detector. It engages or contacts and thus detects the top plate to thereby control the height of the plate/cassette such that the suction cups  230  can engage the top plate. It should be noted that since the stack  212  in the cassette  210  can contain a variable number of plates, the elevator could not simply raise the cassette  210  to a fixed height, thus leading to the requirement of the stack height detector  232 . Also provided is a pair of conductive springs  231  that make contact with the non-emulsion side of the plate. The springs  231  are compliant so as to not damage the non-emulsion side of the plate. The electrical continuity between the springs  231  signifies whether a plate is present. This conductivity test determines whether it is in contact with a plate. Plates are typically metal and therefore conductive, whereas a slip sheet or the bottom of the cassette is non-conductive. 
   As the elevator raises the cassette, the plate sensor  231  detects the presence of a plate. When a plate is detected, in step  711 , vacuum is provided to the suction cup array  230  in step  714  to engage with the plate. The elevator  214  continues to raise the cassette until the plate stack height detector  232  detects the plate stack at the proper height in step  712  and to ensure plate contact with suction cups. 
   In step  716 , it is determined whether a plate is detected. If the conductive springs  231  do not detect a plate before the sensor probe  232  activates the plate stack height detector, this indicates that contact has been made with a non-conductive surface. This implies that cardboard at the bottom of the cassette or the cassette bottom has been detected, and the cassette is empty of plates, as determined in step  718 . Alternatively, it may also indicate that a slip sheet is present, which would lead to an error condition or the activation of the slip sheet removal system to remove the slip sheet. 
   In contrast, if a plate is detected, the plate is peeled up by the action of the suction cup array  230  pivoting around pivot point  282  in the clockwise direction of arrow  215  in step  720  (see FIG.  8 A). During this peeling of the top plate in step  720 , pressurized air is also provided to the first air bar  360  in step  722 . The air bar has a series of holes spaced along the length and is rotationally aligned to optimize the direction of air flow to separate the slip sheet from the emulsion side or the bottom of the peeled plate. This action is illustrated in FIG.  8 B. However, activation of the air bar can be avoided in situations in which slip sheet-plate separation occurs predictably without such facilitation. 
   Next, in step  724 , the cassette  210  is lowered by the elevator  214 . The peeler mechanism  216  rotates about pivot point  282  in the counterclockwise direction, see arrow  284 , in FIG.  8 C. The leading edge  10 -L of the plate  10  is thereby moved to a horizontal position in step  726 . The cassette is lowered another set or predetermined amount in step  728  to provide clearance to the leading and lagging arms. The leading arm  332  and the lagging arm  312  begin to be rotated back to their home position as shown in FIG.  8 C. The lagging arm nip actuation mechanism  330  is also actuated in step  730  so that the nip between the first and second lagging arm rollers  314 ,  316  is opened. The lagging arms  312  are then rotated fully to the home position to receive the plate  10 , which is being handed off from the peeler  216 , in step  732 . The lagging arm drive roller  314  is rotated to aid in the introduction of the plate leading edge into the nip of the rollers  312 ,  314 . 
   The configuration is shown in FIG.  8 C. The plate header  10 -L is being held up by the suction cup array  230  so that the header extends into the nip between nip rollers  314 ,  316 . 
   Also shown is a flexible electrostatic discharge member  281  that makes electrical contact with the non-emulsion side of the plate. The member  281  is connected to electrical ground. In the preferred embodiment, member  281  is a chain. This discharges any electrostatic charge on the plate  10 . 
   In step  734 , the lagging arm nip actuation mechanism  330  is activated to close the nip between the first and second nip rollers  314 ,  316  of the lagging arms  312  and the lagging drive roller  314  rotation is stopped. 
   At this stage, the leading edge  110 -L has been handed off to the lagging arm nip rollers  314 ,  316 . As a result, in step  736 , the vacuum to the suction cup array  230  is removed and the peeler mechanism  216  rotates out of engagement with the plate  10 . Next, in step  738 , the leading arm nip actuation mechanism  338  is activated to open the nip between the first and second leading arm nip rollers  334 ,  336 . The leading arms  332  are then rotated to the home position in step  740 . 
   Next in step  742 , the slip sheet is captured. 
     FIG. 8D  shows the process for capturing the slip sheet SS. With the plate held between the nip rollers of the lagging arms,  312  and the leading arms  332  in the home position, the elevator  214  is activated to raise the cassette so that the slip sheet SS comes into contact with the slip sheet mechanism  110 , and specifically, the foot pad  132 . 
   The raising of the cassette  210  by the elevator  214  causes the top slip sheet to engage the foot pad  132  of the foot  130 . Continued rising of the cassette by the elevator causes the pivot frame  122  to rotate in the direction of arrow  128 ′ around shaft  120 . This causes the stationary interrupt flag  154  of the rotating flag arm  152  to be detected by the elevation control sensor  156 , which is attached to the pivot frame  122  is best illustrated in FIG.  6 . When sensor  156  is activated, the elevator  214  is controlled to cease to raise the cassette  210  by the controller  50 . In this configuration, shown in  FIG. 8D , the pivot frame  122  is biasing the foot pad  132  against the top slip sheet SS, pinning it against the stack of plates beneath the slip sheet in the cassette. The drive roller  136  is also in contact with the slip sheet SS, but the follower roller  134  does not contact the slip sheet in the cassette. 
   Further, the pair of compliant conductive springs  150  are used to determine whether a slip sheet or plate is present under the slip sheet capture mechanism  110 . If they make contact with a conductive surface, electrical continuity between the springs is detected and a plate is determined to be present. A slip sheet will in contrast be an electrical insulator. Thus, the springs can sense if a plate is present when a slip sheet is expected. If at any time prior to activation of sensor  156 , the springs  150  detect continuity, the elevator stops raising the cassette and the process continues without a further effort to capture the slip sheet. 
   At this stage, if a slip sheet is detected, the slip sheet capture mechanism is activated. The double acting air cylinder  142  is activated by a solenoid to move the rack  140  to rotate gear  139 . Gear  139  is meshed with gear  137  which is attached to roller  136 . Thus, the limited motion of rack  140  in turn rotates roller  136  through a predetermined angle. 
     FIG. 8D  shows the path of the slip sheet SS during slip sheet capture. Follower roller  134 , forced by spring  121 , is in contact with roller  136 . This allows roller  136  and  134  to rotate together as best illustrated by FIG.  4 . With foot  132  and roller  136  in contact with the slip sheet SS, rotation of roller  136  forces slip sheet SS toward the foot  132  with the foot  132  holding the slip sheet in place. The slip sheet is thus forced upward into the nipped rollers  136 ,  134  as indicated by path A, in FIG.  8 D. 
   Returning to  FIG. 7B  in step  744 , the pressurized air is optionally provided to the second air bar  362  to minimize adhesion between the slip sheet and the emulsion side of the plate  10 . The plate  10  is then advanced by driving the lagging arm nip rollers  314 ,  316  until the plate header is detected between the first and second leading arm nip rollers  334 ,  336  by the plate header detector  370 . This detection occurs in step  746 . 
   Whether or not the slip sheet SS is captured, the leading arm nip actuation mechanism closes the nip between the leading arm nip rollers  334  and  336  in step  748 . So, with plate  10  being held by the plate inverter system  300  and the slip sheet SS being held by the slip sheet capture mechanism  110 , the cassette  210  is lowered further by the elevator  214 . The leading arms  332  are then rotated to draw the header  10 -A of the plate  10  toward the plate transfer system  400 , in step  750 . In concert, the lagging arm nip rollers  314  and  316  are driven to feed the plate. This is shown in  FIG. 8E , where the plate  10  makes an arc through the arcuate transfer path between the leading arms  332  and the lagging arms  312 . The slip sheet SS held by the slip sheet capture mechanism  110  covers a similar arc. Of note is the fact that the slip sheet SS and the plate  10  are drawn together off of the stack of plates  212  held in the cassette  210 . As a result, the emulsion is preserved and not damaged and the time between picking plate, slip sheet and transporting is reduced, increasing plate throughput. 
   At a predetermined point in the arc of the leading arms  332 , which is determined by encoder counts of motor encoder  344   e  (See FIG.  2 ), in step  756 , the transfer system  400  is configured to receive the plate header  10 A. In one example, nip rollers in the transfer system  400  are opened when the leading arms are at 170 degrees. 
   In step  762 , the lagging arm nip rollers  314 ,  316  continue to rotate, while the leading arms  332  rotate through the arcuate transfer path  310 . In one embodiment, the lagging arm nip rollers  314 ,  316  slightly over-feed the plate  10  to ensure that the plate forms an arc through the arcuate transfer path  310 . This prevents any sharp bending or binding of the plate, and prevents the plate from being tugged by the leading arms  332 . 
   In step  764 , the controller  50  determines whether the motor encoder count associated with the lagging arm nip actuation and roller drive mechanism  330  corresponds or is nearly equal to the length of the plate  10 . That is, the rollers  314 ,  316  have almost entirely fed the plate  10 . This state is illustrated in FIG.  8 E. The plate header  10 A is being brought into proximity to the transfer system  400  and the plate tail or trailing end  10 B is being held in the nip of lagging arm rollers  314 ,  316 . 
   At this point, the slip sheet SS is handed off to slip sheet storage, in preferred embodiment. This typically involves its ejection by the slip sheet capture mechanism  110 . 
   Then, in step  766 , the lagging arm rollers  314 ,  316  stop rotating to hold the tail  10 B of the plate  10  and the lagging arms  312  rotate through the transfer path  310 . In this mode, both the leading arms  332  and the lagging arms  312  are rotating, moving the plate through path  310 . 
   The rotation of arms  312 ,  332  continues until the leading arms  332  reach the away position at 180 degrees. When this state is determined in step  768 , the leads arms  332  stop rotating in step  770 . Further, the nip of lead arm rollers  334 ,  336  is opened. And, the transfer system  400  is configured to feed or draw the plate  10 . 
   The lagging arms  312  continue to rotate until they reach their away position of 150 degrees. This configuration is illustrated in FIG.  8 F. When this state is detected in step  772 , the lagging arms  312  stop rotating and the nip of the lagging arm rollers  314 ,  316  is opened in step  774  completing the hand off of the plate to the transfer system  400 . 
   In one embodiment, a different process is implemented depending on the plate size or length. 
   To summarize the typical operation, the leading arms carry the leading edge  10 A of the plate to the plate transfer system  400 . The nip rollers of the lagging arms feed the plate  10  until the lagging edge of the plate  10  is detected or determined to be present, at which time the nip rollers  314 ,  316  of the lagging arm  312  cease to drive and instead, the lagging arms  312  begin to follow the leading arms  332  through the arcuate transfer path  310 . 
   Thus, through this concerted operation of the leading and lagging arms  332 ,  312 , the plate  10  is inverted from an emulsion side down orientation to an emulsion side up orientation and provided to the plate transfer system  400 , so that the plate can be carried to the imaging engine. 
   It is preferable in this invention to allow the upper nip rollers  314 , in contact with the non-emulsion side of the plate to be under motor control for several reasons. First, it is preferred to have direct roller contact rotation on the non-emulsion side of the plate to prevent roller scuffing of the plate emulsion side and second to aid in the introduction of the leading edge of the plate from the peeler. 
     FIG. 9  shows another embodiment of the plate inverter  300 . Here two opposed races of rollers  910  and  912  are journaled to a two-sided arcuate frame  914  that defines the arcuate transfer path  310 . The rollers  910  and  912  freely rotate to enable a plate to move along this transfer path  310 . The outer race of rollers  910  in combination with the inner race of rollers  912  maintain the radius of the plate while a carrier  916  pulls the plate header through the path  310 . 
   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.