Patent Publication Number: US-2012038100-A1

Title: Sheet feeding apparatus with buffer function and method thereof

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sheet feeding apparatus for feeding sheets discharged from an image forming device, such as a printer or a copy machine, to a reprocessing device, such as a stapler, or a tray. 
     More particularly, the present invention relates to a sheet feeding apparatus having a sheet buffer function (temporal storage function), which has a simple structure without a buffer drum and can feed a present sheet and a subsequent sheet by stacking the present sheet and the subsequent sheet. 2. Description of the Related Art 
     In general, as shown in  FIG. 1 , an image processing system includes a sheet feeding apparatus  2  for feeding sheets discharged from an image forming device  1 , and a sheet processing apparatus  3  for reprocessing (finishing) the sheets fed from the sheet feeding apparatus  2  or stacking the sheets onto a tray. 
     The sheet processing apparatus  3  can be configured to perform various reprocessing works, such as punching, bookbinding, or stapling. The sheet processing apparatus  3  including a tray  4  and a stapler  5  is illustrated in  FIG. 1 . 
     The sheet feeding apparatus  2  is disposed between the image forming device  1  and the sheet processing apparatus  3 . Such a sheet feeding apparatus is disclosed in Korean Patent Registration No. 514,285, and U.S. Pat. No. 6,283,470. 
     The sheet feeding apparatus  2  according to the related art has the drum structure, so the structure of the sheet feeding apparatus  2  is complicated and the size of the sheet feeding apparatus  2  is enlarged. 
     In addition, since the sheet feeding apparatus  2  has the drum structure, it is difficult to arrange the sheets when the sheets are fed and the jam of the sheets may frequently occur. 
     SUMMARY 
     The present invention has been made to solve the problems occurring in the prior art, and the present invention provides a sheet feeding apparatus having a buffer function, in which a cam is installed in a pair of discharge rollers without a drum-type buffer and a second feeding path and a branch flap are branched from a first feeding path connected to the discharge rollers to temporally buffer previous sheets. 
     An object of the present invention is to provide the sheet feeding apparatus having a buffer function, which is installed on a sheet feeding path with a simple structure. 
     Another object of the present invention is to provide a sheet feeding apparatus having a buffer function, which may not cause the jam of the sheets and can improve the reliability. 
     In order to accomplish the above objects, the present invention provides a sheet feeding apparatus having a buffer function. The sheet feeding apparatus includes a pair of discharge rollers including a driving roller and an idle roller, a first feeding path connected to the discharge rollers, a second feeding path located at a rear of the first feeding path while being branched from the first feeding path, a branch flap installed at a branch part of the first and second feeding paths, a sheet detecting sensor installed on the first feeding path between the branch flap and the discharge rollers, a cam holder for rotatably supporting both ends of a rotating shaft of the driving roller, and a cam for moving the cam holder up and down to allow the driving roller to selectively engage with the idle roller. 
     The rotating shaft of the driving roller is connected to a reversible motor. 
     The cam holder has a substantially rectangular ring shape having a stepped top surface, the cam is installed in an internal cavity of the cam holder, and the cam selectively makes contact with a stepped inner surface of the cam holder. 
     In addition, the present invention provides a method for feeding sheets. The method includes the steps of discharging a first sheet outward through the pair of discharge rollers until a rear end of the first sheet is detected by the sheet detecting sensor as the first sheet is fed along the first feeding path, reversely driving the pair of discharge rollers as the sheet detecting sensor detects the rear end of the first sheet and moving back the first sheet by guiding the rear end of the first sheet to the second feeding path using the branch flap, driving the cam such that the driving roller and the idle roller of the discharge rollers are spaced part from each other, and returning the branch flap to an initial position thereof to allow a second sheet to be fed along the first feeding path, and allowing the driving roller and the idle roller of the discharge rollers to make contact with each other when a predetermined time has elapsed after a front end of the second sheet has passed through the sheet detecting sensor and rotating the driving roller and the idle roller of the discharge rollers in a forward direction such that the first and second sheets are simultaneously discharged out of the pair of the discharge rollers. 
     According to the present invention, the sheets can be discharged at the high speed without remarkably changing the structure of the sheet feeding apparatus by discharging the sheets through the steps of discharging a first sheet outward through the pair of discharge rollers until a rear end of the first sheet is detected by the sheet detecting sensor as the first sheet is fed along the first feeding path, reversely driving the pair of discharge rollers as the sheet detecting sensor detects the rear end of the first sheet and moving back the first sheet by guiding the rear end of the first sheet to the second feeding path using the branch flap, driving the cam such that the driving roller and the idle roller of the discharge rollers are spaced part from each other, and returning the branch flap to an initial position thereof to allow a second sheet to be fed along the first feeding path, and allowing the driving roller and the idle roller of the discharge rollers to make contact with each other when a predetermined time has elapsed after a front end of the second sheet has passed through the sheet detecting sensor and rotating the driving roller and the idle roller of the discharge rollers in a forward direction such that the first and second sheets are simultaneously discharged out of the pair of the discharge rollers. 
     In addition, the sheet feeding apparatus having the buffer function can be simply installed on the sheet feeding path. 
     Further, the sheet feeding apparatus may have the stable buffer function without causing the jam of the sheets. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a view illustrating the structure of a sheet processing apparatus of an image processing system according to the related art; 
         FIG. 2  is a perspective view of a sheet feeding apparatus having a buffer function according to the present invention; 
         FIG. 3  is an exploded perspective view of a sheet feeding apparatus having a buffer function according to the present invention; 
         FIG. 4  is a sectional view of a sheet feeding apparatus having a buffer function according to the present invention before a cam is driven; 
         FIG. 5  is a sectional view of a sheet feeding apparatus having a buffer function according to the present invention when a cam has been driven; and 
         FIGS. 6A to 6H  are sectional views illustrating the operation of a sheet feeding apparatus having a buffer function according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, the configuration and operation of the sheet feeding apparatus having the buffer function according to the present invention will be described in detail with reference to  FIGS. 2 to 5 . 
     The sheet feeding apparatus  100  includes a pair of discharge rollers  60  including a driving roller  20  and an idle roller  30 , upper and lower guides  31  and  32  installed at upper and lower ends of the discharge rollers  60  to form a sheet discharge path, a sheet support guide  35  installed at a rear of the lower guide  32 , and a pair of branch flaps  81  and  82  installed at a rear end of the paper support guide  35 . 
     The branch flaps  81  and  82  form a first feeding path  40  to discharge sheets through the discharge rollers  60  or open/close a second feeding path  50  which branches rearward from an outlet of the first feeding path  40 . As the discharge rollers  60  are reversely driven, the sheet is moved back and the second feeding path  50  serves as a passage for the sheet to guide the rear end of the sheet being moved back. The second feeding path  50  may be open or closed through the operation of the branch flaps  81  and  82 . 
     A sheet detecting sensor  33  is installed at an upper portion of a rear end of the upper guide  31  in order to detect the rear end of the sheet moving along the sheet support guide  35 . The sheet detecting sensor  33  can be installed on a bracket  34  fixed to the rear end of the upper guide  31 . 
     Meanwhile, both ends of a rotating shaft  21  of the driving roller  20  are fixed to lower portions of cam holders  25  having a substantially rectangular shape. 
     A stepped section  26  making contact with a cam  70  is formed at an inner surface of an upper portion of each cam holder  25 . 
     The cams  70  are fixed to both ends of the rotating shafts  71  in the cam holders  25  having the substantially rectangular shape. 
     If the cams  70  are not driven, as shown in  FIG. 4 , the stepped section  26  formed at an upper inner portion of the cam holder  25  may not make contact with the cam  70 , so the idle roller  30  is engaged with the driving roller  20 . However, as shown in  FIG. 5 , if the cams  70  are driven, the cams  70  make contact with the stepped section  26  formed at the upper inner portion of the cam holder  25 , so the rotating shaft  21  of the driving roller  20  is lift up together with the cam holders  25 . Thus, the idle roller  30  is spaced apart from the driving roller  20 . 
     The rotating shaft  21  of the driving roller  20  is operated by a reversible motor (not shown), and the rotating shaft  71  of the cam  70  is operated by a separate motor (not shown), which is not interworking with the rotating shaft  21  of the driving roller  20 . 
     Hereinafter, the method for buffering and feeding sheets using the sheet feeding apparatus  100  having the above structure will be described with reference to  FIGS. 6A to 6H . 
     First, in a state that the cams  70  do not make contact with the cam holders  25 , the branch flaps  81  and  82  close the second feeding path  50  and open the first feeding path  40  as shown in  FIG. 6A , thereby allowing a first sheet  90  to be discharged through the first feeding path  40 . 
     Then, as shown in  FIG. 6B , if the sheet detecting sensor  33  detects the rear end of the first sheet  90  moving along the first feeding path  40 , the branch flaps  81  and  82  are operated so that the second feeding path  50  is open as shown in  FIG. 6C . At the same time, the discharge rollers  60  are reversely operated so that the rear end of the first sheet  90  is moved back by a predetermined distance along the second feeding path  50 . 
     Even though the first sheet  90  has been moved back, the front end of the first sheet  90  must be positioned between the driving roller  20  and the idle roller  30 . 
     Then, as shown in  FIG. 6D , in a state that the rear end of the first sheet  90  has been moved back by the predetermined distance along the second feeding path  50 , the cams  70  are driven to lift up the cam holders  25 . Thus, the driving roller  20  is spaced apart from the idle roller  30 , so that the feeding of the first sheet  90  is stopped. 
     After that, as shown in  FIGS. 6E and 6F , the branch flaps  81  and  82  are operated such that a second sheet  91  can be fed toward the first feeding path  40 . In this case, the driving roller  20  is spaced apart from the idle roller  30  until the front end of the second sheet  91  passes through the discharge rollers  60  along the surface of the first sheet  90  by passing through branch flaps  81  and  82 . The entry of the second sheet  91  can be detected by the sheet detecting sensor  33  or an additional sheet detecting sensor (not shown). 
     Then, as shown in  FIG. 6G , the cams  70  are driven such that the cams  70  can be spaced apart from the cam holders  25 . Thus, the driving roller  20  makes contact with the idle roller  30  due to the tare thereof. 
     The cams  70  maybe spaced apart from the cam holders  25  in proper time by taking the distance between the sheet detecting sensor and the discharge rollers  60  and the sheet feeding speed into consideration after the entry of the second sheet  91  has been detected. 
     In a state that the driving roller  20  makes contact with the idle roller  30 , if the driving roller  20  is normally driven (counterclockwise direction), the first and second sheets  90  and  91  can be simultaneously discharged. 
     Although it has been described that the two sheets are safely buffered and simultaneously discharged through the procedure shown in  FIGS. 6A to 6H  without causing the jam or the change of the discharge order, the present invention is not limited thereto. It will be understood to those skilled in the art that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.