Abstract:
A sheet separating mechanism and a method of separating sheets that includes a retard surface carrier that causes a retard surface to apply an alternately higher and lower friction force against the edge of an underlying sheet. The alternation of the higher and lower friction force can be coupled to a vacuum sheet feeder. The retard surface can be translated to present a next portion of the retard surface to the edge of the next underlying sheet with the translation coupled to the vacuum sheet feeder.

Description:
TECHNICAL FIELD 
     This disclosure is related to the feeding of sheets in a printer or copier and more particularly to preventing multifeeds of sheets. 
     BACKGROUND 
     Multifeeds of sheets in a printer or copier can be typically caused by welding of sheet edges, porosity of sheets, adhesion and static charge between sheets. A vacuum sheet feeding system can reduce some but not all multifeeds of sheets. When multifeeds do occur, the multiple sheets can jam the printer or copier forcing an operator to fix the jam and possibly even damaging the printer or copier. 
     One way to provide a sheet separating force is to position a stationary rubber pad at the edge of the stack of feeding sheets. The stationary rubber pad provides a static friction force against the leading edge of the underlying sheet or sheets. As the top sheet is fed into the printer or copier, if the underlying sheets follow the top sheet, the stationary pad blocks the path of the underlying sheet or sheets. 
     SUMMARY OF THE DISCLOSURE 
     A sheet separating mechanism and a method of separating sheets is provided to prevent multi-feeds of sheets into printers or copiers. As a top sheet is fed from a stack of sheets by a sheet feeding system, the sheet separating mechanism applies an alternately higher and lower friction force from a portion of a retard surface against the edge of the underlying sheet. While the top sheet is fed, the higher friction force is applied. After the top sheet is fed, the lower friction force is applied. Alternating the higher and lower friction force can be coupled to the motion of the sheet feeding system. 
     The sheet separating mechanism can translate the retard surface to position a next portion of the retard surface for contacting the edge of the next sheet, with the translation of the retard friction surface coupled to the motion of the sheet feeding system. The translatable retard friction surface can be a relatively high friction surface on a roller and can be a relatively high friction surface of a belt. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevation view of a sheet feeding system including a sheet separating mechanism. 
         FIG. 2  is a side elevation view of the sheet separating mechanism of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of the sheet separating mechanism of  FIG. 2  taken along line  3 - 3  in  FIG. 2 . 
         FIG. 4  is side elevation depiction of the sheet feeding system of  FIG. 1  showing a sheet separating mechanism drive configuration. 
         FIG. 5  is a side elevation view of another sheet feeding system including a sheet separating mechanism. 
         FIG. 6  is a side elevation view of the sheet separating mechanism of  FIG. 5  showing the spring in an uncompressed position. 
         FIG. 7  is a side elevation view of the sheet separating mechanism of  FIG. 5  showing the spring compressed by the cam follower. 
         FIG. 8  is a cross-sectional view of the sheet separating mechanism of  FIG. 7 , taken along line  8 - 8  in  FIG. 7 , showing a drive configuration. 
         FIG. 9  is a perspective view of the sheet feeding system of  FIG. 6  showing the sheet separating mechanism being driven by the shuttle drive motor. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a side elevation view of sheet feeding system  20 . Sheet separating mechanism  22  is positioned below vacuum feed head shuttle  24  which can be arranged to feed a top sheet  26  from stack of sheets  28 . The sheet separating mechanism  22  can be positioned to apply a friction force against underlying sheet  30  while the shuttle  24  feeds the top sheet  26  to a printer or copier (not shown). 
     The sheet separating mechanism  22  includes a retard roller  32  with retard surface  40  (see  FIG. 3 ) mounted on the retard roller  32 . The sheet separating mechanism positions the retard surface  40  such that a first portion of the retard surface  40  contacts an edge of the underlying sheet  30 . The sheet separating mechanism is structured to rotate the retard roller  32  after top sheet  26  is fed from the stack  28  to present a next portion of the retard surface  40  for contacting the next underlying sheet. 
     Referring to  FIGS. 2 and 3 , the retard roller  32  is mounted on side plates  34  that are supported by springs  36  in support frame  38 . The retard surface  40  on retard roller  32  can be made of a relatively high friction material and may be made of rubber. One-way clutch  42  allows the retard roller  32  to rotate from the first contact position in a single direction to present the next portion of retard surface  40  to contact the next sheet in the stack  28 . 
       FIG. 4  shows one configuration for driving the rotation of the retard roller  32 . Two outer rolls  44  contact an edge of paper stack  28  or a tray (not shown) containing paper stack  28 . After top sheet  26  is fed from the stack  28 , the stack  28  moves up to present the next sheet for feeding. The movement of the stack  28  causes the retard roller  32  to roll and position a next portion of the retard surface  40  for contacting the next sheet. Rolling of the retard roller  32  occurs because the upward movement of the stack  28  rotates the contacting outer rolls  44  which in turn rotate inner roll  46  which contacts intermediate roll  48 . The inner roll  46  may include a one-way clutch (not shown) to allow the inner roll  46  to rotate in a single direction or the one-way clutch  42  may be built into the sheet separating device  22  as shown in  FIG. 3 . The rotating inner roll  46  rotates the contacting intermediate roll  48  which, in turn, rotates the retard roller  32  by connecting belt  49 . 
     The retard surface  40  contacts an edge of the underlying sheet  30 . Because some printers or copies do not utilize a small outer portion at the border of the sheet surface in their respective printing processes, the retard surface  40  can be positioned to contact a portion at the border of the surface of the next sheet  30  adjacent to the lead edge of next sheet  30 . To avoid smudging, the amount of the surface contacted by the retard surface  40  can be a portion of the surface within about 3 millimeters (mm) from the edge of the sheet  30 . 
       FIG. 5  shows a side elevation view of sheet feeding system  50 . System  50  includes a vacuum sheet feeder  52  that includes vacuum feed head shuttle  54  and shuttle lead plate  56 . While vacuum sheet feeder  52  is shown in  FIG. 5 , other sheet feeding mechanisms are contemplated to be within the scope of this disclosure. System  50  also includes sheet separating mechanism  58  which includes a retard belt  60  that has a relatively high friction surface. 
     Vacuum sheet feeder  52  feeds top sheet  26  from the stack of sheets  28  in a feed direction  64  away from the stack  28 . The sheet separating mechanism  58  is positioned such that the retard belt  60  contacts the edge of the underlying sheet  30 . The surface of the retard belt  60  applies a friction force to the edge of the underlying sheet  30  in a direction generally opposite the feed direction  64 . After the vacuum sheet feeder feeds a top sheet  26 , the retard belt  60  is driven by the retracting shuttle lead plate  56  to travel opposite to the feed direction such that a next portion of the retard belt  60  is positioned to contact the next underlying sheet. 
     Referring to  FIGS. 6-8 , the sheet separating mechanism  58  includes retard belt  60  which can be made from a relatively high friction material such as rubber. Drive cam  66  rotates around drive shaft  68  and alternatingly pushes cam follower  70  up and down against spring  72  which exerts an alternatingly high and low spring force against belt frame  74 . The drive shaft  68  is shown to be driven by drive source gear  76  that engages the drive shaft  68  with bevel gears  78  and  80 . The drive shaft  68  drives the retard belt  60  with O-ring belt  82  connected to the shaft of lower pulley  84 . One-way clutch  69  allows the retard belt  60  to travel in a single direction around lower and upper pulleys  84  and  85 . 
       FIG. 6  shows the sheet separating mechanism  58  in a low force position. Drive cam  66  is positioned on drive shaft  68  to allow the cam follower  70  to be in a lower position thereby allowing the spring  72  to be uncompressed. This low force position of the drive cam  66  occurs when the vacuum sheet feeder  52  is moving in a direction opposite the feed direction  64 , moving back into position to feed a next sheet. 
       FIG. 7  shows the sheet separating mechanism in a high force position. The drive source gear  76  (coupled to the motion of the vacuum sheet feeder  52 ) and the drive shaft  68  are adapted to rotate the drive shaft a half turn as the vacuum sheet feeder  52  moves in the feed direction  64  during feeding of top sheet  26 . The rotation of the drive shaft  68  rotates drive cam  66  through a position that forces the cam follower  70  up against the spring  72  and thereby pushes the belt frame up against the edge of the underlying sheet  30  while the top sheet  26  is being fed. The one-way clutch  69 ′ prevents O-ring belt  82 , shown in  FIG. 8 , from turning retard belt  60  when the drive shaft  68  is driven in this direction. 
     Referring again to  FIGS. 6-8 , upon completion of the feeding motion, the return motion of the vacuum sheet feeder  52  is coupled to the drive shaft  68  and reverses the rotation of the drive shaft  68 . The reversed rotation returns the drive cam  66  to the low force position and the one-way clutch  69 ′ allows the O-ring belt  82  to translate the retard belt  60  to position a next portion of the retard belt  60  to contact the next underlying sheet in the stack. 
     As noted in  FIG. 7 , the sheet separating mechanism  58  can be positioned on the vacuum sheet feeder  52  such that the distance  71  between the drive shaft  68  and the shuttle lead plate  56  remains fixed. 
     The spring  72  allows for tighter control of the retard nip force of the retard belt  60  against the underlying sheet  30  by allowing for the variation in force and for any tolerance stack issues in the assembly. Thus, the next sheet will be contacted during the high force period in a surface area about 3 mm within the leading edge of the underlying sheet  30 , thereby preventing smudging of the underlying sheet  30  by avoiding contact with the active print area of the sheet. Control of the vacuum force of the vacuum sheet feeder  52  can be difficult, therefore, the sheet feeding system  50 , shown in  FIG. 5 , allows for wider latitude in vacuum force by more easily and precisely controlling the retard nip force of the retard belt  60 . 
     At the low force position shown in  FIG. 6 , the retard nip force is predetermined to be below a sheet marking threshold. At the high force position shown in  FIG. 7 , the retard nip force is set for sheet separation, which can be at about 1 pound of force. 
       FIG. 9  shows a perspective depiction of the sheet feeding system  50 . The vacuum feed head shuttle  54  and shuttle lead plate  56  operate to feed a top sheet  26  (see  FIG. 5 ) in a feed direction  64  away from the stack of sheets  28 . A drive pulley  88  mounted on the vacuum feed shuttle drive motor  90  drives bevel gear  80  with O-ring belt  92 . Bevel gear  80  drives bevel gear  78  on drive shaft  68 . Drive shaft  68  rotates drive cam  66  (see  FIGS. 6-7 ) to a high force position when the shuttle drive motor  90  drives vacuum feed head shuttle  54  in the feed direction. When the shuttle drive motor  90  returns the vacuum feed head shuttle  54  in the opposite direction of the feed direction  64 , the drive shaft rotates drive cam  66  to a low force position and drives O-ring belt  82  to move retard  60  around the upper and lower pulleys  85  and  84  in direction  94  such that a next portion of the retard belt  60  is positioned to contact the next underlying sheet  30  during the next feed cycle. By coupling the drive shaft  68  to the shuttle drive motor  90 , the timing of the high and low nip force against the next sheet  30  and the timing of repositioning the belt  60  is coupled to the timing of the feeding of the top sheet  26 . 
     It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.