BACKGROUND OF THE INVENTION 
   Plates are typically large substrates that have been coated with photosensitive or thermally-sensitive material layers. Depending on the type of plate, they can be sensitive or insensitive to ambient light. The plates are usually used in commercial printing operations. For large run applications, the substrates are fabricated from aluminum, although organic substrates, such as polyester or paper, are also available for smaller runs. Because of the composition, the plates can be somewhat heavy, especially in the context of a stack of relatively large plates. 
   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 a platesetter. The engine selectively exposes the surfaces of these plates. 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. 
   Typically, one of two different strategies is used to feed the plates to the imaging engine. In the simplest case, an operator manually places individual plates into a feeder that then conveys the plates through a feed port to the drum scanner. This approach, however, has some obvious drawbacks, since an operator must be dedicated to feeding the plates. Moreover, the printing system must be housed within a light-safe environment, if the plates being used have any sensitivity to ambient light. The alternative approach is to use a plate manager. 
   Plate managers typically house multiple plate cassettes. Each cassette holds tens of plates in a stack. For example, in one common implementation, each cassette holds about thirty to fifty plates. The plate manager selects plates from one of its cassettes and then feeds the plates, automatically, into the imaging engine. 
   In these designs, cassettes are loaded into the plate manager on separate tables. The tables are then raised and lowered inside the manager to bring the plates of a selected cassette into cooperation with a plate picker that grabs individual plates and feeds them to the imaging engine. 
   In some applications, the plates can be shipped and stored in these cassettes. In other cases, the plates are shipped to the end user in a crate and then transferred to the cassettes by an operator. 
   SUMMARY OF THE INVENTION 
   Some institutions that use these platesetters require or have a need for an automated solution for feeding plates to the imaging engine. It is not cost effective for these institutions to devote personnel to the task of feeding plates one at a time into the imaging engine. At the same time, however, these institutions may not have the space or the need for a full plate manager that can handle multiple cassettes, since these plate managers can be relatively large and expensive. 
   This need is addressed to some degree by proposed, automated plate de-crating solutions. These systems, however, can be somewhat dangerous, having many exposed moving parts and are susceptible to mis-feeding, either when the plate is initially engaged, or when it is being conveyed to the infeed port to the imaging engine. They further require a light-controlled environment. 
   The present invention concerns a plate cassette loader for a platesetter. The plate cassette loader comprises a cassette holder for receiving a cassette, containing a stack of plates. A cassette inverter then rotates this cassette to a feed position in which the plates can be fed into the imaging engine of the platesetter. In this way, the somewhat unwieldy process of loading plates into the imaging engine is handled by the cassette inverter, in combination with the fact that the stack of plates, contained in the cassette, can be loaded in one step, rather than requiring the feeding of individual plates by a dedicated operator. 
   In the present embodiment, the cassette holder comprises a frame into which the cassette is inserted by the operator. This frame comprises tracks for guiding the cassette upon insertion. Springs are used on either side of the cassette to urge the cassette into engagement with the tracks. These springs also help to constrain the cassette during its rotation by the cassette inverter. A latch is provided for retaining the cassette in the holder, especially during rotation to the feed position. 
   Plate picker is also preferably provided. It is installed on the cassette holder in the present invention to pick a plate from the stack of plates so that it can be fed to the imaging engine. 
   In the present configuration, the cassette is inserted into the cassette holder by the operator in a generally horizontal position. The cassette inverter then translates a mouth of the cassette to the infeed port, while raising a distal end of the cassette to pivot the cassette around a horizontal axis. In this way, it inverts the cassette from a generally horizontal orientation, for ease of loading by the operator, to a generally vertical orientation, compatible with the angle of the infeed port. 
   In order to rotate this cassette, the cassette inverter comprises an actuation system and an inverter track for guiding the movement of a distal end of the cassette. The present configuration mimics the operation of a four-bar linkage. A link arm connects between the cassette holder and a frame to control its movement. 
   In general, according to another aspect, the invention can also be characterized as a method for loading a plate cassette in a platesetter. This method comprises receiving a cassette containing a stack of plates, and then rotating the cassette to a feed position. Plates are then fed into an imaging engine of the platesetter. 
   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 side elevation showing the plate cassette loader in the load position and its relationship to the imaging engine of the platesetter, according to the present invention; 
       FIG. 2  is a side elevation showing the plate cassette loader in an intermediate phase of operation where it is rotating the cassette to a feed position, according to the present invention; 
       FIG. 3  is a side elevation showing the plate cassette loader at the feed position, according to the present invention; 
       FIG. 4  is a front perspective schematic view showing the internal construction of the inventive cassette inverter; 
       FIG. 5  is a perspective view showing the interaction between the inverter track, drive arm, and cassette frame during an intermediate stage of operation; 
       FIG. 6  is a perspective view of a section of the underside of the cassette frame showing a latch mechanism for holding the cassette in the cassette frame; 
       FIG. 7  is a side perspective view with partial cut-away showing a spring for constraining the movement of the cassette in the cassette frame; 
       FIG. 8  is a perspective view showing an air cylinder actuation system for the cassette inverter; and 
       FIG. 9  is a perspective view showing a pulley system of the actuation system that provides mechanical advantage to the air cylinder. 
   


   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a platesetter  10  with a plate cassette loader  100  comprising a cassette holder  110  and a cassette inverter  105 , which have been constructed according to the principles of the present invention. 
   In more detail, the platesetter  10  generally comprises an infeed port  16  that conveys plates to an imaging engine in the general region of  12 . The plates are typically loaded onto an imaging drum of the image engine and exposed, typically in a raster fashion by a scanning laser. Plates are thereafter ejected through an outfeed port  18  to a finished plate location  20 . Thereafter, the plates are typically transported for further processing including development. 
   The plate cassette loader  100  generally comprises a cassette holder  110  and a cassette inverter  105 . 
   The cassette holder  110  comprises a cassette frame  112 . A cassette  14  is inserted into this frame  112  by an operator by sliding the cassette in the rearward direction into the frame  112 . 
   The cassette holder  110  further comprises, in the illustrated embodiment, a plate picker system  114 . This plate picker engages a top plate of a stack of plates held in the cassette  14 , and then conveys that picked plate to the picker mouth  116 . 
   The cassette inverter  105  comprises two stationary inverter arms  118  and two link arms  124 . The inverter arms  118  generally extend vertically from the frame or body of the platesetter  10  in the fashion of a cantilever. Each inverter arm comprises an inverter track  120 , which is generally arcuate, curving upward from the body of the platesetter and slightly rearward. A roller  122 , which is journaled to the cassette frame  112 , rides in and is confined by the inverter track  120  in the inverter arm  118 . 
   One end of the link arm  124  is journaled to the inverter arm  118  near the base of the inverter arm  118 , where it connects to the body of the platesetter  10 . This allows the link arm  118  to pivot on the inverter arm  118 . In the illustrated load position of  FIG. 1 , the link arm extends from the base of the inverter arm  118 , generally forward. The proximal or other end of the link arm  124  is journaled to a pin  126  on the cassette frame  112 . 
     FIG. 2  shows the plate cassette loader  100  in an intermediate position, between a load position and a feed position. An actuation system  200  of the cassette inverter  105  is lifting the rear or distal end of the cassette  14  and frame  112 , while lifting and rotating the proximal end of the cassette  14  in the rearward direction. This action moves the picker mouth  116  in the direction of the infeed port  16 . The path of this translation and inversion of the cassette  14  is controlled by the movement of roller  122  in the inverter track  120 , which constrain the movement of the distal end of the frame  112 , while the path of the proximal end of the frame and cassette is controlled by the link arm  124 . 
     FIG. 3  shows the plate cassette loader  100  in the feed position. In the illustrated embodiment, the cassette  14  is oriented in a position that is 15 degrees from vertical. It corresponds to the typical feed position for plates into the imaging engine  12 . 
   An important aspect of the inverter&#39;s operation is the fact that the cassette  14  has never been moved through a vertical position. As a result, a stack of plates contained in the cassette will never be oriented such that they would not fall out of the cassette  14  or flop against a top of the cassette. This characteristic is important since, in the current implementation, the stack of plates is not constrained in the z-axis direction in the frame of reference of the cassette  14 . The z-axis is orthogonal to the plane of the cassette (the vertical direction in the orientation of  FIG. 1 ). 
   In this feed position, the picker mouth  116  is cooperating with the infeed port  16  of the imaging engine  12 . This allows individual plates to be picked-off of the stack of plates in the cassette  14  and fed through the picker mouth  116 , into the infeed port  16  and to the drum of the imaging engine  12 . 
     FIG. 4  shows some more details of the plate cassette loader  100  and specifically the cassette holder  110  and the two inverter arms  118  of the cassette inverter  105 , with the picker  114  removed. Specifically, the two arms  118  are located on either side of the cassette holder&#39;s frame  112 . The inverter arms  118  are connected to the platesetter body  22  by corresponding brackets  160 . The imaging engine  12  is located within the platesetter frame  22 . 
     FIG. 5  is a more detailed view of the interconnection between the inverter arm  118  shown in phantom, the link arm  124 , and the frame  112  of the cassette holder. Generally, the cassette frame  112  comprises a U-shaped member  132  that wraps under and over the cassette  14 . Specifically, a lower leg  162  extends under a bottom of a tray portion  130  of the cassette  14 . An upper leg  164  extends over a cover portion  166  of the cassette. A cross member  170  extends laterally across the cassette frame  112  to another U-shaped member on the other side of the frame. 
   The U-shaped member  132  defines an insertion channel  168  into which the operator inserts the cassette  14  between the upper and lower legs  164 ,  162  of the U-shaped member  132 . 
   A reinforcing frame member  134  is attached to the side of the U-shaped member  132 . It carries the journaled pin  126  that engages the link arm  124  to provide the pivot engagement and the roller  122  that rides in the inverter track of the inverter arm  118 . 
     FIG. 6  shows an underside of the cassette frame and cassette  14  with the U-shaped member  132  partially cut-away. This exposes a track  140 , which that is secured to the lower leg  162  of the U-shaped member  132 . This track  140  comprises outer and inner rails  170 ,  172  are riveted to the lower leg  162 . Wheels  22  of the cassette  14  ride in a V-shaped trough between these outer and inner rails  170 ,  172  so that the cassette  14  may be smoothly inserted into the channel between the U-shaped brackets  132  on either side of the frame. 
   Also shown is a latching mechanism  141 , which is bolted to lower leg  162 . The latching mechanism  141  is used to retain the cassette  14  in the channel of the cassette holder. Specifically, a pin  124 , on the cassette  14 , is provided that projects down from the bottom of the tray  130  of the cassette  14 . Upon full insertion, it engages the latching mechanism  141  that is secured onto the lower leg  162 . This latching mechanism  141  retains the pin  124 , and thus holds the cassette  14  in the cassette holder  110  during the process of inverting the cassette  14  to the feed position. 
     FIG. 7  shows a spring member  151  that is used to constrain the cassette  14  in the channel defined by the U-shaped bracket  132 . Specifically, two spring members are provided on each U-shaped member  132 . The spring members  151  are secured to an inter side of the upper legs  164  such that they project down into the insertion channel  168 . The spring members  151  each include a nib  150  that engages a top edge  32  of the cassette  14 . The leaf spring portion  152  then urges the cassette  14  downward so that the wheels  22  stay within the track  140 . The leaf spring portion is bolted to the upper leg  164  with intervening resilent blocks  154 ,  156 . This way, the cassette  14  is securely held in the cassette holder  105  during its movement between the load position and the feed position. 
     FIG. 8  shows the detail of the actuation system  200 . It comprises an air cylinder system  203 , which includes an outer cylinder  204  and an inner piston  206 . The cylinder&#39;s base is attached to a bracket  216  that is bolted to the inverter arm  118 . A piston pulley block  208  is attached to the head of the piston  206 . The piston pulley block  206  carries a pulley  210 . Tackle wire  214  is further terminated  212  on the piston pulley block  206 . 
     FIG. 9  shows a top pulley block  220  that is attached at the top of the inverter arm  118 . The wire tackle  214  extends from termination  212  over pulley  222  on the top block  220  to pulley  210  on the piston block  208 , to pulley  224  on the top block  220 . The tackle then runs over pulley  226 , with the other end attaching to roller  122 . In this way, the movement of the air cylinder system  202  is transferred to the cassette holder  110  and specifically controls the progress of the roller  122  in its track  120 . The system of pulleys provides a mechanical advantage of one third (⅓). In the specific example, the piston displacement is 8 inches thereby moving the slide joint 24 inches. 
   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.
A plate cassette loader for a platesetter comprises a cassette holder for receiving a cassette, containing a stack of plates. A cassette inverter then rotates this cassette to a feed position in which the plates can be fed into the imaging engine of the platesetter. In this way, the somewhat unwieldy process of loading plates into the imaging engine is handled by the cassette inverter, in combination with the fact that the stack of plates, contained in the cassette, can be loaded in one step, rather than requiring the feeding of individual plates by a dedicated operator.