Abstract:
A plate handling system provides for movement from storage of a variety of image-ready printing plates, organized in plate stacks with interleaf protective slipsheets. Each stack contains plates of a particular size, corresponding to the capabilities of an associated imaging system. Each plate stack is supported by a pallet, which facilitates easy loading and unloading into the plate handling system. A plate picker aligns with the desired plate and transports the appropriately sized plate to an imaging system. The corresponding slipsheet is transported to a storage area where it is stored with a flat orientation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     FIELD OF THE INVENTION 
     This invention pertains to apparatus, systems and methods for handling plates in the context of a plate imaging system. In particular, the invention relates to the convenient storage of image-ready plates of a variety of sizes, delivery of a particular-sized plate from storage to an imaging system while disposing of an interleaf protective slipsheet. 
     BACKGROUND OF THE INVENTION 
     Imaging systems, such as computer to plate (CTP) systems, are well known in the art. Imaging systems record an image on a film or plate. Plates are typically made of an aluminum substrate with a photosensitive emulsion applied to one surface. Plates of a variety of substrate and emulsion compositions are possible, including emulsions with a variety of imaging characteristics (e.g. exposure energy density, image working sense, and run length). Additionally, plate formats range to accommodate a variety of page (e.g. letter size) layouts. For example, plates sized to accommodate a single page up to a plate sized to accommodate thirty-two, sixty-four or more pages are known in the art. Thus, an imaging system can be called upon to process a wide variety plate types. 
     Manufacturers typically deliver plates in a stack of equivalently sized plates, separated by protective interleaf slipsheets. A plate stack can be delivered on a pallet or other structure that provides support and simplifies conveyance. Alternatively, a plate stack can be delivered in a carton or other protective enclosure. Larger sized plates are difficult to transport and store because of their size, weight and susceptibility to damage. 
     For many reasons, such as maximizing throughput, and maximizing unattended operating time, many imaging systems provide integrated storage facilities for a quantity of plates that are likely to be used and automated mechanisms for selecting and transporting a plate to be imaged. Prior art imaging systems have incorporated integrated storage of plate stacks. However, it is a challenge to provide for a sufficient quantity of an appropriate variety of plate sizes while minimizing floor space usage. 
     Loading of a quantity of plates into an imaging system&#39;s integrated storage facility, especially large format plates, can be difficult because of their size and weight. Individual plates can weigh between at least 700 g for an 8-up format and at least 2 kilograms for large formats. Storage of 50 plates or more of a given size is desirable to allow the imaging system to operate without user attendance. 
     Imaging system cassettes, trays, bays or other mechanisms have traditionally been used to constrain the orientation of loaded plates so that plate picking and transport can be reliably accomplished. Storage areas typically contain one or more plate edge stops, guides or other mechanical devices to constrain the loaded plate orientation. For example, a plate bay, housing a carton of plates stacked horizontally and resting on one edge, comprises a stop (bay floor) for supporting one end of the carton which constrains the horizontal plate stack in one dimension. As another example, a plate cassette will typically have at least two stops for adjacent plate edges to constrain the plate stack orientation in two dimensions. Manual loading of a significant quantity of plates into an imaging system storage facility that restricts placement may thus be a time consuming process. 
     Obtaining and disposing of protective interleaf slipsheets in response to a plate imaging operation presents additional challenges. Slipsheets tend to be attracted to either the plate picked for imaging or to the plate remaining on the top of a plate stack. Slipsheets are typically made of a flimsy and slippery material and so are easily damaged or can become misaligned with an adjacent plate. These characteristics make locating, obtaining and transporting a slipsheet challenging. Additionally, if a slipsheet becomes creased or folded, it can damage the emulsion on the plate it is protecting if it is subsequently dragged across the emulsion surface. 
     Disposal presents an additional challenge with prior art systems ejecting them from the imaging system or crumpling them and storing them in an internal storage bin. The former method results in additional floor space requirements and can present aesthetic or safety problems. The latter method provides for an efficient use of floor space but suffers from problems of limited capacity, complicated and error-prone mechanics (e.g. slipsheet jams). An additional object of the present invention is to dispose of slipsheets internal to the plate handling system by stacking them vertically. This minimizes storage space, simplifies unloading and transport for final disposal, and presents an opportunity for reuse of the slipsheets. 
     SUMMARY OF THE INVENTION 
     The present invention provides a plate handling system to be used in conjunction with an imaging system. The plate handling system enables a significant period of unattended imaging system operation while requiring limited floor space by arranging plate storage areas in a vertical fashion with elevating pick and transport mechanisms. Plates, organized in stacks, can be easily loaded into the plate handling system by one person. Interleaf slipsheets are obtained and are stacked with a flat profile in an internal storage area to minimize storage requirements, increase reliability, protect plate surfaces and enable slipsheet reuse. The invention can be adapted to imaging systems of a variety of types and sizes but is particularly well suited to imaging systems that image plates of a very large size. 
     In a preferred embodiment of the invention, a plate handling apparatus, coupled with a plate imaging apparatus includes a plate handling system for supplying plates to an imaging system with plate storage facility that has at least one storage area having a plate, that may be part of a plate stack, with an actual storage placement in an actual position and rotation, a controller for controlling a plate handling operation, a plate picker for picking the plate wherein the controller is operative to automatically determine the actual position and rotation of the plate and align the plate picker with the actual position and rotation of the plate prior to picking, and a plate transporter for transporting the plate to the imaging system for exposure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In drawings which illustrate non-limiting embodiments of the invention: 
       1.  FIG. 1  is a side view of a plate handling system and imaging system according to one embodiment of the invention. 
       2.  FIG. 2  is a side view of a plate storage unit according to one embodiment of the invention. 
       3.  FIG. 3  is a perspective view of a plate handling system depicting main operational elements according to one embodiment of the invention. 
       4.  FIGS. 4A-4E  are perspective and side views illustrating plate picking according to one embodiment of the invention. 
       5.  FIG. 5A  is a perspective view of a plate picker transferring a picked plate to a plate transport unit according to one embodiment of the invention. 
       6.  FIG. 5B  is a perspective view of a plate transport unit transferring a picked plate to an imaging system according to one embodiment of the invention. 
       7.  FIG. 6  is a side view of a plate handling system illustrating slipsheet disposal according to one embodiment of the invention. 
       8.  FIG. 7  is a side view of a plate handling system illustrating slipsheet disposal according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention can be practiced without these particulars. In other instances, well known elements have not been shown or described in detail to avoid unnecessarily obscuring the invention. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than restrictive sense. 
       FIG. 1  depicts a plate handling system (PHS)  110  connected with an imaging system (IS)  102 . PHS  110  is configured to:
         store a quantity of plates of various sizes, organized in stacks of varying quantities wherein each stack is comprised of plates of the same size;   pick a plate of a particular size required by IS  102 ;   transport a picked plate along a plate path  120  to a plate inlet  104  on IS  102 ; and   dispose of a protective interleaf slipsheet by transporting it from the top of a plate stack along a slipsheet path  130  to a storage area.       

     PHS  110  comprises a plate storage unit (PSU)  112  and a plate transport unit (PTU)  114 . PHS  110  can obtain power, compressed air and other operating requirements directly from an external source or from IS  102 . PHS  110  can include one or more controllers operative to determine the state of various components and contents of PHS  110 , to control the operation of various actuating components of PHS  110 , to communicate with IS  102  controller, and to provide a user with one or more status indicators and operational controls. Alternatively, an IS  102  controller or another system connected to both PHS  110  and IS  102  may perform one or more PHS  110  control functions remotely. 
     PTU  114  is located horizontally adjacent to one side of IS  102  and is of a height enabling it to both access all plates within PSU  112  and transport a plate along a plate path  120  (one possible path shown) to a plate inlet  104  (e.g. a load table). PTU  114  can fasten to IS  102  with removable fasteners to facilitate modular installation and to ensure their alignment during operation. Removable power, air, communication and other connections can be made between the two units. PTU  114  is enclosed in a protective cover with permanent openings for plate transport and removable covers for maintenance access. 
     In a preferred embodiment of the invention, PTU  114  comprises a horizontally mounted plate transporter, which transports a picked plate from PSU  112 , first horizontally to a supporting platform within the plate transporter and then vertically to a plate inlet  104  at which point IS  102  completes the horizontal transport into the IS  102 . The plate transporter is preferably mounted on an elevating structure to enable it to pick up and transfer a plate from any number of vertical positions in PSU  112  and IS  102 , respectively. 
     During transport, the plate has a horizontal orientation on the supporting platform with the plate edge, proximal to plate inlet  104 , oriented approximately perpendicular to the direction of horizontal motion. The emulsion side of the plate is preferably oriented on top but can be reversed if necessary. 
     Alternative PTU  114  mechanisms and orientations are also possible. As an example, the plate transporter can be inclined. As another example, PTU  114  can include a plate rotation unit to change direction of movement or to establish an alternate horizontal orientation, independent of plate orientation in PSU  112 . As another example, PTU  114  can include a plate-flipping unit to change the emulsion side orientation. 
     In a preferred embodiment of the invention, PTU  114  also comprises a horizontally mounted slipsheet transporter, which transports a picked slipsheet along a slipsheet path  130  (one possible path shown). Transport occurs first horizontally from the PSU  112  onto a supporting structure within the slipsheet transporter and then down to a slipsheet storage area located near the bottom of the PTU  114  housing where it released for subsequent disposal. The slipsheet transporter is preferably located directly below the plate transporter and mounted on the same elevating structure. 
     The sheet storage facility is sized to hold approximately 1000 slipsheets in a vertically stacked arrangement. A removable cover allows access to the storage unit so that slipsheets may be discarded. 
     PSU  112  is located horizontally adjacent to one side of PTU  114  and fastened to PTU  114  with removable fasteners to facilitate modular installation and alignment during operation. Removable power, air, communication and other connections can be made between the two units. PSU  112  is enclosed in a protective cover. 
     PSU  112  includes a predetermined number of adjustable-height, storage shelves. Each shelf demarcates the bottom of a plate storage area, suited for storing a plurality of horizontally oriented plates and protective interleaf slipsheets stacked on a pallet or other suitable supporting conveyance structure. In a preferred embodiment, each shelf is approximately rectangular, consistent with the enclosure, and all corresponding plate storage areas are accessible through a permanent opening one the side proximal to PTU  114 . All plate storage areas are accessible through at least one removable cover on one of the other sides to allow horizontal access for loading and unloading a pallet. All plate storage areas are accessible through a second permanent opening on one of the other sides, but in a preferred embodiment, on the side distal to PTU  114 , to allow access by a plate picker. The remaining side is either permanently covered or has a removable cover for maintenance access. 
     In a preferred embodiment, PSU  112  also comprises a plate picker capable of lifting two adjacent corners of the top plate of a stack of plates. The plate picker also includes a capability to pick and hold the slipsheet located directly below the picked plate. The plate picker is dynamically mounted to an elevating structure capable of precisely positioning the plate picker at the top of any plate stack. The plate picker mounting facilities on the elevating structure are movable in a horizontal direction to enable the plate picker to reach into a shelf area to pick a plate or to withdraw from the shelf area to permit elevation. In some embodiments, the plate picker pulls the held slipsheet away from the plate stack for disposal externally or in an alternative slipsheet storage area. 
     It is understood that equivalent embodiments to those described above are within scope of the invention. As an example, the plate picker could be a modular unit that is fastened to PSU  112 . 
       FIG. 2  is a side view of PSU  112  according to one embodiment of the invention. It depicts a view of PSU  112 , without its protective covering, from the side where pallets are loaded and unloaded. For clarity, the plate picker and associated moving structures are not shown. Vertical members  202  and horizontal members  204  provide structural support for PSU  112 . Vertical members  202  contain a plurality of shelf mounting facilities  206  (e.g. threaded holes), each with a consistent vertical spacing such that a shelf  210  may be mounted in any number of vertical positions. A predetermined number of shelves  210 A- 210 D, mounted in exemplary positions, are depicted for a variety of exemplary plate pallets  230  and vertical plate (with interleaf slipsheet) stacks  240 . Configuration of shelves  210  is performed either during construction of PSU  112  or at a customer site. Exemplary plate storage areas  220 A- 220 D are depicted. In some embodiments (not shown), shelves  210  can be equipped with an extendable table to allow plates to be stacked by hand or to be lowered by a mechanism such as a crane. 
     Plate stacks  240  are loaded proximal to the transport side of PSU  112  (the side adjacent PTU  114 ). Plate stacks  240  can have a variety of sizes, constrained only by the limitations of IS  102  and PHS  110 . A plate stack  240  should nominally be loaded with its nearest side approximately parallel with the transport side of PSU  112 . Some rotational variance is permitted as will be described later. Plate stacks  240  should be loaded with a plate setback  260  from the transport side. PTU  114  establishes a maximum value for plate setback  260  to ensure accessibility. In one embodiment, the maximum plate setback  260  is configured to be less than eight inches. Plate storage areas  220 C and  220 D are depicted as having adequate room for alternative slipsheet storage areas  250 A and  250 B, based on the size of loaded plates. 
       FIG. 3  is a perspective view of PHS  110  depicting main operational elements according to one embodiment of the invention. For clarity, portions of the enclosing covers, supporting structures and other details are not depicted. 
       FIG. 3  depicts PSU  112  as including a picker elevator  302 , comprising three horizontal support members positioned outside the vertical support members  202  of PSU  112 . Picker elevator  302  is suspended by a set of attached suspension mountings (not shown), which are flexibly coupled to vertical movement members, such as guides or leadscrews (not shown), which are in turn fastened to support members of PSU  112 . Picker elevator  302  vertical motion can be accomplished by a variety of means. For example, one or more motors, each coupled with a leadscrew, pulley mechanism, or other linear motion system can be employed to move picker elevator  302  vertically. 
     Picker elevator  302  also includes a plate picker shelf  304 , which is fastened to the supporting members of picker elevator  302 . While picker elevator  302  is moving between plate storage shelves  210 , plate picker  310  is parked on plate picker shelf  304  so that plate picker  310  does not impinge a shelf support member  305 . Picker elevator  302  also includes plate picker mounts  306 , flexibly coupled to horizontal movement members, such as guides or leadscrews (not shown), which are in turn fastened to picker elevator  302  support members. Each plate picker mount  306  can move independently towards (and away from) PTU  114 . Plate picker mount  306  motion can be accomplished by a variety of means. For example, a motor coupled to a leadscrew, pulley system or other linear motion system can be employed to move each plate picker mount. The controller for picker elevator  302  can be configured to postpone vertical motion while plates are being loaded in a plate storage area. This enables an operator to load plates in one plate storage area  220  while PHS  120  is picking or transporting plates from a different plate storage area  220 . 
     Plate picker  310  is fastened to each plate picker mount  306  by means of a retractable fastener  308 . For example, a retractable fastener  308  can comprise a pair of solenoid driven pins. One retractable fastener  308  is positioned at each longitudinal end of plate picker  310 . Before releasing a retractable fastener  308 , plate picker  310  must be moved so that it is positioned over plate picker shelf  304 . Once, retracted plate picker  310  is parked on plate picker shelf  304  and can be moved vertically without impinging shelf support members  305 . During a picking operation, retractable fasteners  308  are extended to rigidly couple plate picker  310  with both plate picker mounts  306 . Since, plate picker mounts  306  can move independently, one or both of the plate picker mounts  306  or the retractable fasteners  308  are configured to provide some degree of rotational freedom. 
     Plate picker  310  comprises at least one picker element  312  capable of lifting a portion of the top plate from a plate stack  240 . Picker element  312  also obtains and holds a portion of the corresponding slipsheet protecting the plate immediately below the top plate. In a preferred embodiment, two picker elements  312  are configured so that picker elements lift adjacent corners of a plate on the side distal to PTU  114 . Each picker element  312  moves independently along the longitudinal axis of plate picker  310  to position at a respective plate corner. In an exemplary alternate embodiment, plate picking rotational freedom can also be obtained by configuring picker elements  312  with the ability to independently move in a direction perpendicular to the axis of plate picker  310  (e.g. plate path  120  direction). 
     Each picking element  312  is fastened to a separate picker element mount (not shown), which is flexibly coupled to a horizontal movement member that are aligned with longitudinal axis of plate picker  310 . A horizontal movement member, such as a guide or leadscrew (not shown), is in turn fastened to plate picker  310 . Each picker element mount can move independently. Mount motion can be accomplished by a variety of means. For example, a motor coupled to a leadscrew, pulley system or other linear motion system can be employed to move each picker element mount. 
       FIG. 3  depicts PTU  114  as including vertical support members  324 , horizontal support members  326 , protective cover  320  (partially shown), and a plate outlet  322  corresponding to plate inlet  104 . It also depicts an elevating transporter  330  and a slipsheet storage area  350  (e.g. removable pallet or tray). Transporter  330  depicts an integrated unit providing both picked plate and slipsheet transport capabilities within one elevating structure. Implementation of the elevating structure can be accomplished in a manner similar to that describe above for picker elevator  302 . 
     Transporter  330  is comprised of a horizontal support structure  332  for supporting and transporting a picked plate. Support structure  332  is configured with two or more slots  334  positioned longitudinally between PSU  112  and plate outlet  322 . Each slot  334  provides an opening through support structure  332  from the top to bottom surface. Each slot  334  extends to approximately each longitudinal end of support structure  332 . In one embodiment, a movable vacuum bar system (not shown) is mounted transversely to slots  334 . Plate suction cups  336  are mounted to the movable vacuum bar, and protrude through slots  334 . Plate suction cups  336  are vertically positioned in approximate alignment with the top surface of support structure  332 , so that a picked plate is both supported with a substantially flat profile and is firmly held on the non-emulsion side during transport. 
     The movable vacuum bar system can be moved by a linear motion system similar to those described above for plate picker mount  306 . Plate suction cups  336  can thus be moved together approximately the full length of slots  334 . Detailed plate transport operation is described below. The structure of slipsheet transport mechanisms and their operation is also described below. 
       FIGS. 4A-4E  are perspective and side views illustrating plate picking according to one embodiment of the invention.  FIG. 4A  is a perspective view of PSU  112  during an exemplary plate picking operation of a plate from the top shelf. Picker elevator  302  ascended to enable access to plate stack  240 D located on shelf  210 D. Plate picker  310  moved to a first pick position (as shown) for plate stack  240 D from its parked position on plate picker shelf  304 . In the first pick position, plate picker  310  is ready to pick the top plate. In this example, plate stack  240 D was loaded such that the plate stack is rotated with a small clockwise rotation relative to PSU  112 . Plate picker  310  moved at high speed to an estimated plate stack position, based on information configured about the plate stack and information from the last pick from this stack. Plate picker  310  then moved at low speed until it was in a first pick position. Umbilical arm  402 , or other flexible cabling mechanism, provides for compressed air, vacuum, electrical and other connections to couple plate picker  310  with fixed receptacles on plate picker shelf  304 . Flexible cabling (not shown) from plate picker shelf  304  to fixed terminations in PSU  112  complete the connections. 
     Plate stack  240  rotational variations from an intended orientation of at least ten millimeters for picking edge (edge proximal to plate picker  310 ) corner positions is desirable to simplify loading. For example, one corner of the picking edge can have a position that is ten millimeters different in the plate path direction than the other picking corner. Positional variations of at least 10 millimeters, laterally, from an intended position the top plate can be desirable to simplify loading. Many references can be used for determining plate position. One exemplary reference is the center point of the picking edge. Practically, moving or loading a pallet of plates, without some holding mechanism may cause plates to shift so that their edges are not aligned. Thus, even accurate positioning of pallet  230  may cause at least some plates in plate stack  240  to rotate or shift position. In one embodiment, positional variations of up to 50 millimeters and rotational variations of up to 30 millimeters from an intended placement can be accommodated. 
     An intended placement can be determined by a number of methods. One exemplary method is for PHS  110  to specify the intended placement and for the user to attempt to load plate stack  240  close to the intended placement. Another exemplary method is for the user to load plate stack  240  with an arbitrary position and provide PHS  110  with information about the plate stack to enable PHS  110  to estimate plate stack  240  position. For example, the user could provide PHS  110  with an approximate measured position of plate stack  240 , an approximate measured height of plate stack  240  or pallet  230 , as well as dimensions for and a quantity of plates in plate stack  240 . PHS  110  can then estimate plate stack  240  position and elevation and estimate how to position plate picker  310  on approach to the picking edge of the top plate. 
     As plate picker  310  approached plate stack  240 D at low speed, horizontal and vertical sensors, mounted, for example, on each picker element  312 , detected the top and proximal edges of plate stack  240 D respectively. Picker elevator  302  moved to position both picker elements  312  at the top of plate stack  240 D. Plate picker mounts  306  moved independently to position each picker element  312  at their initial proximal edge position. Then, each picker element  312  moved transversely to position themselves at their corresponding plate stack  240 D corners. Plate picker mounts  306  moved independently to maintain picker elements  312  in position at the proximal edge while moving to the corners. In the resulting first pick position; plate picker  310  longitudinal axis is approximately parallel to the proximal edge of plate stack  240 . During subsequent plate picking movements, this alignment is preserved. 
       FIG. 4B  is a side view of plate picker  310  in a second pick position corresponding to two top plate corners lifted and the interleaf slipsheet held.  FIG. 4C  is an expanded side view of plate picker  310  in a second pick position. Plate picker  310  comprises a plate picker bar  430  that extends between plate picker mounts  306  (not shown). One picker element  312  is depicted, which comprises, according to a preferred embodiment:
         a picker arm  432 , mounted to plate picker bar  430 ;   a horizontal sensor  444 , such as an electro-optic sensor, mounted near the bottom of plate picker bar  430  and aligned with the longitudinal axis of picker arm  432 ;   a slipsheet shoe  438  mounted above horizontal sensor  444  and aligned with the longitudinal axis of picker arm  432 ; and   an extendable plate pusher  440 .       

     Picker arm  432  includes a vertical sensor  442 , such as an electro-optic sensor, mounted at the leading edge the arm. It also includes a plate lifter  434 , which is attached to picker arm  432  by coupling  436 . In one embodiment, plate lifter  434  is a plate cup, which blows air onto the top surface of a plate to lift the plate, without making contact, according to the Bernoulli principle. Different plate lifting mechanisms can be substituted in other embodiments of the invention. For example, a suction cup can be used to lift the plate. 
     When picker element  312  was in a first pick position vertical sensor  442  was approximately aligned with proximal edge  450  and horizontal sensor  444  was approximately aligned with top edge  460  of plate stack  240 . Plate picker  310  moved in the direction of plate path  120  while picker element  312  simultaneously activated plate lifter  434 . As each picker element  312  advanced, picked plate  410  was lifted creating a gap between plate  410  and plate stack  240  of sufficient height to allow slipsheet shoe  438  to extend into the gap a predetermined distance. This new picker element  312  position (as shown) corresponds to a second pick position. 
     Slipsheet  420 A and  420 B correspond to one slipsheet  420 , located directly below picked plate  410 , in one of two exemplary positions. Slipsheet  420 A corresponds to slipsheet  420  being attracted, by static or other weak forces, to picked plate  410 . Slipsheet  420 B corresponds to slipsheet  420  being attracted, by static or other weak forces, to plate stack  240 . In either case, slipsheet shoe  438  (shown in a perspective view in  FIG. 4D ) attracts and holds slipsheet  420 . In a preferred embodiment, holes  470 , located on both top and bottom surfaces of slipsheet shoe  438 , attract slipsheet  420  using a vacuum. Once attracted, slipsheet  420  is pierced by pins  480 , located on both top and bottom surfaces of slipsheet shoe  438 , which limit lateral slipsheet movement. Different mechanisms for attracting and holding a slipsheet can be substituted in other embodiments of the invention. For example, once attracted a mechanical clamp or high friction shoe surface can aid in holding slipsheet  420 . 
     Once both picker elements  312  are in the second pick position, they are actuated to achieve a third pick position. The third pick position (depicted in  FIG. 4E ) corresponds to picked plate  410  moved in the plate path  120  direction while slipsheet  420  is held fast. This is accomplished by first extending plate pusher  440 , using a linear motion system, with limited force until the proximal edge  450  of picked plate  410  is contacted. The axis of plate pusher  440  is preferably offset towards the center of picked plate  410  and parallel with the longitudinal axis of picker arm  432 . When each plate pusher  440  has made contact, plate lifters  434  release picked plate while plate pushers  440  move in a coordinated fashion to a fully extended position using higher force so that the distal end of picked plate  410  extends into PTU  114 . Different mechanisms for moving picked plate into PTU  114  can be substituted in other embodiments of the invention. For example, extendable arms that hook over the top of the lifted plate corners can pull picked plate. 
       FIG. 5A  is a perspective view of plate picker  310  transferring a picked plate (depicted with partial transparency for clarity) to transporter  330  according to one embodiment of the invention. For clarity, some aspects of PSU  112  and PTU  114  are not illustrated. The third pick position, described above, is depicted. Before progressing to the third pick position, transporter  330  must be moved into position to receive picked plate  410 . First, transporter  330  ascended to a height where the top surface of support structure  332  is approximately aligned with the top surface of plate stack  240 D. This positioning can be based on information used to position plate picker  310  or can be performed independently by information obtained from a plate sensor mounted on transporter  330 . 
     Next, plate suction cups  336  moved to a pick up position located at the end, proximal to PSU  112 , of slots  334 . Picked plate  410 , when moved into PTU  114  (as shown), is positioned directly above plate suction cups  336 . Next, suction is applied so that picked plate  410  is firmly grasped on its bottom surface. Next, plate suction cups move in the direction of plate path  120 , pulling picked plate  410  out of PSU  112  until it is completely supported by support structure  332 . Different horizontal transporting mechanisms can be substituted in other embodiments of the invention. For example, a picked plate can be moved partway onto a conveyor belt support structure, which then pulls the picked plate into PTU  114 . 
     Once picked plate  410  is completely supported by support structure  332 , various optional mechanisms can be used to alter the positioning and path of the plate. For example, support structure  332  can be mounted on a turntable, which allows the plate path  120  to be altered, for example perpendicularly. This can facilitate an advantageous footprint for IS  102  and PHS  110 . As another example, support structure  332  can include a turntable mounted in the top surface of the structure to allow picked plate  410  to be rotated by ninety degrees to facilitate a preferred load orientation in IS  102 . As another example, support structure  332  can include a plate alignment mechanism to correct any small rotational misalignment caused by loading or picking plates. 
     Additionally, once picked plate  410  is completely supported, plate picker  310  can be retracted to either begin picking another plate from plate stack  240 D or it can be parked on plate picker shelf  304  and elevated to the next plate stack  240 . Before moving, however, slipsheet shoe  438  must release slipsheet  420 . This can be accomplished, for example, by briefly changing airflow direction in holes  470  so that slipsheet  420  is blown off pins  480 . Alternatively, pins  480  can be fastened to slipsheet shoe  438  by pivoting fasteners, which pivot on an axis that is horizontally transverse to plate path  120 . Pivoting can be controlled by, for example, a solenoid. When slipsheet shoe  438  is retracted, pins  480  are pivoted in the direction of plate path  120  so that the slipsheet slides off the pins. 
       FIG. 5B  is a perspective view of PTU  114  transferring a plate a picked plate to IS  102  according to one embodiment of the invention. The figure depicts transporter  330  at the plate pick up elevation with picked plate  410  in the completely supported position, having traversed plate path  120 A. Next, transporter  330  moves picked plate  410  along plate path  120 B to plate inlet  104  (not shown) height. Finally, picked plate is moved into plate inlet  102  where IS  104  pulls it along the remainder of plate path  120 C. The initial movement along plate path  120 C can be accomplished, for example, by turning off the vacuum on plate suction cups  336 , moving them partway towards PSU  112 , reapplying vacuum and moving plate suction cups  336  back towards IS  102 . Different movement mechanisms can be substituted in other embodiments of the invention. The final movement along plate path  120 C is accomplished by IS  102 . 
       FIG. 6  is a side view of PHS  110  illustrating slipsheet disposal according to one embodiment of the invention. Transporter  330  is depicted in two positions. In the first position, transporter  330 A is ready to pick up slipsheet  420  from plate stack  240 D. Transporter  330  includes a slipsheet transporter  602 , which reaches into PSU  112  to obtain slipsheet  420  (depicted as  420 A when positioned on the plate stack). In a preferred embodiment a vacuum bar accomplishes this. The vacuum bar  606  is located inside slipsheet transporter  602  and can move along a track  604  which is capable of extending partway into PSU  112 . Vacuum is supplied to vacuum bar  606  by a hose in a flexible cable track or by other similar methods. Vacuum bar  606  has openings on its bottom surface that attract and hold slipsheet  420 . 
     To obtain slipsheet  420 A, vacuum bar  606  and track  604  is extended by a motorized leadscrew or other linear motion system for example, so that vacuum bar  606  is positioned ( 606 A) directly above slipsheet  420 A. An electro-optic sensor, for example, can be used to determine the correct position above slipsheet  420 SA. In another embodiment, vacuum bar  606  can be coupled to the lower side of the plate vacuum bar system. In this case, transporter  330  may need to elevate to a new position to allow access to slipsheet  420 A. 
     Next, vacuum is applied to attract slipsheet  420 A. Then, vacuum bar  606  and track  604  is retracted and vacuum bar  606  is moved in the direction of slipsheet path  130 A. At the end of the movement, vacuum bar  606  is positioned as shown ( 606 B). Slipsheet  420  is positioned ( 420 B) inside slipsheet transporter  602  and is partially supported by a sectional platform  610  positioned in a support position ( 610 A). Sectional platform  610  can comprise a series of lightweight bars flexibly attached to each other at their extremities and supported by wheels or other low-friction supports that can travel along oval track  612 . Vacuum bar  606 B continues to hold slipsheet  420 B in position. 
     Next, transporter  330  descends along slipsheet path  130 B to a point just above slipsheet storage area  350 . This position is depicted as transporter  330 B. Next, platform  610  is moved, by a motorized pulley system for example, along oval track  612  to a release position ( 610 B). As platform  610  moves and removes support, slipsheet  410  falls with an approximately flat profile on top of previously deposited slipsheets in slipsheet storage area  350 . Finally, vacuum is removed and vacuum bar  606  releases the edge of slipsheet  410 , allowing it to fall and lie flat on top of the slipsheet stack. Deposited slipsheets can be subsequently removed from slipsheet storage area  350 . 
       FIG. 7  is a side view of a PHS  110  illustrating slipsheet disposal according to another embodiment of the invention. This embodiment is possible when alternative slipsheet storage area  250  occupies at least half the corresponding plate storage area  220 . Plate picker  310  and slipsheet  420  are illustrated in two positions. In the first position, plate picker  310 A is holding slipsheet  420 A, with a picked plate having just transferred to PTU  114 . Plate picker  310  then moves towards its parked position, pulling slipsheet  420  with it. When plate picker  310  reaches a position ( 310 B), near its parked position, it releases slipsheet  420 B. The edge of slipsheet  420 B falls to storage shelf  210 , coming to rest with an approximately flat profile.