Abstract:
In a finishing apparatus, as would be used with a printer or copier, sheets to be stapled are accumulated in a compiler tray. A set of pivotably-mounted fingers are pressed, by their own weight, against a top sheet as sheets enter the compiler tray. The mount on which the fingers are mounted can be moved to accommodate a growing stack and maintain a parallel contact between the fingers and the top of the stack. The even distribution of pressure from the fingers avoids curling or buckling of the sheets in the stack prior to stapling.

Description:
TECHNICAL FIELD 
   The present disclosure relates to automated finishing apparatus, such as a stapling or binding apparatus, as would be used, for example, in a mid- or high-volume printer or copier. 
   BACKGROUND 
   The use of automated stapling devices is well known in the context of mid- or high-volume office equipment such as copiers and printers (hereinafter generically called “printers”). Typically, a stapling apparatus downstream of the engine of a printer includes a “compiler tray,” which is a vertical or angled (i.e., non-horizontal) container for temporarily retaining sheets output from the printer. Associated with the compiler tray are any number of mechanisms for accepting or ejecting sheets in or from the container. As each multi-page document is output from the printer, the sheets thereof accumulate in the compiler tray. When the multi-page document (“set”) is completely printed, the sheets accumulated in the compiler tray are stapled, and the stapled set is then ejected from the compiler tray. 
   In a typical arrangement of a compiler tray, there is an effective hard surface at the bottom of the tray, against which edges of sheets in the set are placed, mainly by gravity. The bottom surface acts as an aligning surface so that, just before a staple is driven into the set of sheets, the bottom edge of the set is properly aligned, resulting in a neat stapled set. 
   As a practical matter, particularly with large stapled sets, it becomes difficult to maintain an aligned edge of a set prior to stapling. Buckling of sheets within the compiler tray while sheets are being accumulated can result in an unsatisfactory stapled set. 
   PRIOR ART 
   U.S. Pat. No. 5,478,062 discloses a compiler tray having associated therewith a “pressing bar,” which can hold a stack of sheets downward as the sheets accumulate. 
   U.S. Pat. No. 6,145,825 discloses a compiler tray having associated therewith a “pressing member,” which can hold a stack of sheets downward as the sheets accumulate. 
   Japanese patent document number JP2001-019268A discloses a booklet maker in which sheets are accumulated in an “aligning tray.” The aligning tray includes springably-mounted “presser members” which hold a bundle of sheets against a surface of the aligning tray. 
   SUMMARY 
   According to one aspect, there is provided a apparatus for collating sheets. A main surface contacts a bottom sheet of a stack of sheets, and a stop contacts an edge of the stack of sheets. At least one finger defines a main surface for substantially parallel contact with a top sheet of the stack of sheets. The finger is movably mounted on a mount, and the mount is movable relative to the stack to maintain substantially parallel contact of the finger with a top sheet of the stack of sheets, as the stack of sheets increases. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an elevational view of a compiler tray and associated mechanisms. 
       FIG. 2  shows a pivotably-mounted finger as used with the compiler tray of  FIG. 1 , in isolation. 
       FIG. 3  is a perspective view showing a set of pivotably-mounted fingers, along with ancillary mechanisms. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is an elevational view of a compiler tray and associated mechanisms. Sheets are emitted one at a time from a copier or printer, partially shown as  99 , and enter a finishing module generally indicated as  100 . Although the finishing module  100  shown here is simply a collating and stapling device, other types of finishing module may include, for example, a hole-punching mechanism, a booklet maker, a C- or Z-folder, etc. In the finishing module  100 , the sheets of a multi-page document emitted by the printer  99  are accumulated and stapled into a set, which is ejected into external catch tray  102 . Catch tray  102  may have associated therewith a stacking elevator (not shown), as is generally known in the art. 
   When stapling or collating multi-page documents from printer  99 , the sheets enter finishing module  100  and travel along a path  104  to be accumulated as a set in a compiler tray generally indicated as  10 . Compiler tray  10  defines a main surface  14 , for contact with a bottom side of a bottom sheet of a stack of sheets, such as shown as S. Disposed near a bottom of compiler tray  10  is a stapler, generally indicated as  12 . The stapler  12  is positioned to place a staple in a stack of sheets, in a location generally near the bottom of the compiler tray. Compiler tray  10  need have only sufficient surfaces to temporarily retain a stack of sheets long enough to be stapled as needed; among these surfaces are a main surface  14  and at least one stop  16 . The main surface  14  can be a substantially flat single surface, or can comprise ribs or other small structures which together act to support the stack S. Stop  16  contacts an edge of the stack of sheets S and maintains a straight edge of the stack, generally so that a straight-sided set of sheets is maintained prior to stapling. 
   In the illustrated embodiment, the main surface  14  of compiler tray  10  is sloped so that incoming sheets accumulate against stop  16  largely by gravity. However, in addition, sheets can be directed to and/or urged against stop  16  by urging means, such as including rollers, belts, or flappers as desired for maintaining, for instance, a suitable overall process speed. In the illustrated embodiment, a free-hanging, rigid compiler belt  30  urges sheets against stop  16  in a generally familiar manner. When such rollers, belts, flappers, etc., are used in compiler tray  10 , the main surface  14  need not be sloped, but could be horizontal. 
   In a practical application, sheets from printer  99  which accumulate in compiler tray  10  are prone to buckle or bend within the space of the compiler tray, and when such bent sheets are stapled by stapler  12 , the resulting stapled set is unsatisfactory in quality; the edges of the stapled stack, for example, may be crooked in one or more dimensions, or the staple does not sit neatly in the stack. 
   To address the buckling problem, there is provided at least one finger  20 , which is pivotably mounted on a mount  22  and disposed as shown toward the bottom of compiler tray  10 . With reference to  FIG. 2 , which shows a finger  20  and associated mount  22  in isolation, it can be seen that finger  20  is loosely (i.e., not springably) mounted on the mount  22 , and is allowed to move freely relative to the mount  22 , as shown by the position of finger  20 ′ in phantom. Returning to  FIG. 1 , it can be seen that finger  20  is placed on a top sheet of the stack of sheet S so that a main lower surface of the finger  20  maintains substantially parallel contact of the finger with a top sheet of the stack of sheets. As such, regardless of the size of stack S at any time, the weight of the finger  20  is distributed around a reasonably large area of the finger against the top sheet. In one embodiment, the downward pressure against the top of the stack S is provided substantially exclusively by the weight of one or more fingers  20 . 
   Further, in this embodiment, finger  20  and mount  22  work together so that the substantially parallel contact of the finger  20  is maintained even as more sheets enter compiler tray  10  and the stack of sheets increases in size.  FIG. 3  is a perspective view showing a set of pivotably-mounted fingers  20 , along with their respective mounts  22  and ancillary mechanisms. A set of fingers  20  are arranged along an edge of stack S near the stops  16  (the stapler  12  is also adjacent this edge, but is not shown in this Figure). In this embodiment, the main surface of each finger  20  extends beyond the edge formed by stops  16 . 
   Each finger  20  is pivotably mounted on an associated mount  22 , and the mounts  22  are in turn rigidly mounted on an axle  24 . Axle  24  is associated with a mechanism  26 , which may be of any suitable mechanical design, and may be driven by a motor or solenoid (not shown) for its intended motion. As sheets accumulate in stack S, axle  24  can rotate and/or translate (such as shown in direction I in  FIG. 1 ) to maintain the parallel relationship between each finger  20  and whatever sheet is on top of stack S at a given time. By providing a plurality of fingers  20  along one edge of stack S, buckling or curling of sheets in the stack is avoided along the entire length of the edge. 
   The avoidance of buckle in the stack of sheets on main surface  14  is dependent on how close the downward force of fingers  20  is from the driving force, from gravity and/or from urging means such as compiler belt  30 , of sheets being urged against stop  16 . The shorter the effective length that can buckle, the less prone the sheets are to buckle. At the same time, to control the effects of curl the fingers  20  should press down at the edge of the sheets, where the sheets touch the stop  16 . 
   As shown in  FIG. 3 , stops  16 , which can be disposed between pairs of fingers  20 , can also be associated with a mechanism (not shown) for ejecting collated or stapled stacks S from the compiler tray to an output tray, such as  102  in  FIG. 1 . 
   Although the illustrated embodiment shows a finishing module for stapling a stack near an edge thereof, such as for corner or edge stapling, the embodiment can be adapted for a compiler tray useful in compiling signatures for folded booklets which are stapled along the fold thereof, or for other binding systems such as saddle-stitching or glue-binding. 
   The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.