Patent Publication Number: US-7708271-B2

Title: Non-contacting static brush for a sheet stacker

Description:
TECHNICAL FIELD 
   The present disclosure relates to a stacker for accumulating sheets, such as in a printing apparatus or a copier. 
   BACKGROUND 
   In a digital printer or copier, or in any situation in which sheets are transported through an apparatus and accumulated in a stack, the effects of static electricity must be taken into account. The charging events associated with xerography, or even just the sliding contact of sheets against structures within a machine, cause individual sheets to have static charges. When such charged sheets are accumulated in a stack, such as for stapling, the mutual repulsion of like-charged sheets causes the edges of upper sheets on the stack to rise a significant distance from each other, so that the top sheet at any time is not remotely flat. The raised edges, of course, interfere with subsequent activities such as stapling or collating. 
   A generally-known approach to this problem is to discharge each sheet as the sheet approaches the stack. The discharging is typically done by having the sheet contact a substantially grounded brush or other member as it moves toward the stack, thereby discharging the sheet. U.S. Pat. Nos. 2,883,190 and 5,123,893 show typical ways of applying a discharging brush to a moving sheet. 
   The use of a “static brush” contacting individual sheets directed toward a stack has some disadvantages, such as possible image area contamination, and does not necessarily fully address discharge of the accumulated additive charge of a thick stack of sheets having small retained charges, especially in dry ambient conditions. 
   SUMMARY 
   According to one aspect, there is provided an apparatus for accumulating sheets in a stack, comprising a tray for retaining sheets. A conductive member is disposed less than 10 mm from a location of an edge of the sheets, and does not contact any sheets on the tray. 
   According to another aspect, there is provided an apparatus for accumulating sheets in a stack, comprising a tray for retaining sheets, and a conductive member having brush filaments disposed less than 10 mm from a location of an edge of the sheets, disposed not to contact any sheets on the tray. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an overall view of a high-speed digital printer copier, as generally known in the art. 
       FIG. 2  is a perspective view showing the configuration of parts in a stacker module. 
       FIGS. 3-6  are simple elevational views of a portion of a stacker, showing various embodiments. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is an overall view of a high-speed digital printer copier, as generally known in the art. The machine includes one sheet input module  98 , that feeds blank sheets into a printing module  99 , which includes, as generally shown, a xerographic engine. Printed sheets output from printing module  99  are directed to a stacker module  100 . In this embodiment, stacker module  100  includes a tray  102 , mounted on an elevator mechanism (not shown), of general familiarity in the art, which operates to lower the tray  102  as sheets are accumulated thereon, so that the top sheet in the stack S is always at the same general elevation regardless of the size of the stack S. 
     FIG. 2  is a perspective view showing the configuration of parts in a stacker module. Sheets are added to the stack S by a pair of disk stackers  104 , of general familiarity in the art: sheets fed from the printing module  99  are first accumulated in a set in one of the slots along the circumference of each disk stacker  104 ; and when the sheets forming the set are completed, the disks rotate together to cause the whole set to be deposited on the stack S, which in turn is supported by tray  102 . Typically, as each set is deposited on the stack S, the elevator mechanism lowers the tray  102  a small amount to maintain the top sheet in stack S at a constant level. 
   In order to discharge static electricity from sheets in stack S, there is provided a conductive member  110  disposed in a predetermined location relative to an edge of the sheets in stack S. The conductive member  110  must have some conductive properties, and is effectively grounded, at least to the frame of the machine itself. In one embodiment, conductive member  110  includes tufts  112  of conductive filaments forming a brush directed toward the stack S: the conductive member  110  can comprise the same type of commercially-available “static brush” used in systems that contact sheets moving therepast. In the present embodiment, however, the conductive member  110  does not have to contact any sheet in stack S at any time to satisfactorily discharge sheets in the stack. A surface (such as a brush) of the conductive member  110  is disposed a distance D from any edge of the stack S, the distance being less than 10 mm. 
   Further as shown in the embodiment, a width (along dimension W) of the conductive member is less than 25 mm, and in the case where a piece of commercially-available static brush is used, is approximately 2 mm. The height of the conductive brush  110  is typically at least 25 mm, but should just be long enough to discharge a sufficient proportion of the stack S within typical heights of stack S. The conductive member can have a height greater than 25 mm. Also, the conductive member can have a width less than 10 mm. Although conductive member  110  is shown near the center of one edge of stack S, the conductive member  110  can be located near any corner of stack S. 
     FIGS. 3-6  are simple elevational views of a portion of a stacker, showing various embodiments. In each Figure, like numbers indicate equivalent elements.  FIGS. 3-6  (and  FIG. 2 ) show conductive members  110  spaced from disk stackers  104 . In  FIG. 3 , the conductive member  110  descends from an upper portion of the stacker module, suitably positioned to discharge sheets toward the top of tray  102 , regardless of the position of tray  102  at any time. 
   Also shown in  FIG. 3  is an adjusting mechanism  116  for adjusting a position of the conductive member  110  relative to an expected location of an edge of the sheets. That is, if it is known that the sheets to be accumulated on tray  102  are of a particular size, the position of conductive member  110  can be adjusted to bring the conductive member within a useful range of the accumulating stack S. The adjustment mechanism  116  can be manually operated, or can be moved via a device such as an electromagnet. The adjustment mechanism  116  can be associated with a larger control system; for example, in a digital printer/copier context, if it is known that blank sheets of a certain size are being fed from feeder module  98  or other upstream module, a control system can send a signal to cause adjustment mechanism  116  to position conductive member  110  suitably when the printed sheets are received in stacker module  100 . The adjustment mechanism  116  can also be used in conjunction with a conductive member  110  that extends upwardly from tray  102 , as in the  FIG. 2  embodiment. 
     FIG. 4  shows an embodiment wherein the conductive member  110  is oriented diagonally or obliquely. Such an arrangement may be useful for discharging sheets, regardless of size, as each sheet enters the stacker module. The conductive member  110  may be specially shaped to have obliquely-oriented portions, including portions curved in one or more dimensions. 
     FIGS. 5 and 6  demonstrate various embodiments wherein the conductive member  110  or  110 ′ largely comprises a flexible cord. A flexible cord can be disposed in any manner providing an effective discharge of the sheets approaching or in stack S. In  FIG. 5  the conductive member  110  or  110 ′ is attached to two fixed positions relative to the stacker module. In  FIG. 6  the flexible cord  110  is attached to two fixed positions “inboard” and “outboard” relative to the stacker module, and flexible cord  110 ′ simply hangs from one location within the cavity formed by the stacker module. 
   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.