Sheet feeding apparatus and image forming apparatus

Abstract

A middle plate for piling a sheet bundle is provided elevatably. A duct opened to the side surface of the upper part of the sheet stack supported on the middle plate. A vacuuming belt for vacuuming and feeding the uppermost sheet of the sheet stack supported on the middle plate is provided. A first height detecting means for detecting the uppermost part of the sheet stack supported on the middle plate reaching a first position and a second height detecting means for detecting the uppermost part of the sheet stack supported on the middle plate reaching a second position higher than the first position are provided. At the time the uppermost surface of the sheet stack supported on the middle plate is detected by the first height detecting means, the controller stops the middle plate and commands the air blowing operation from the duct opening, and then at the time the uppermost surface of the sheet bundle is detected by the second height detecting means according to the middle plate raising operation, it commands the vacuuming and feeding operation of the uppermost sheet by the vacuuming belt.

1 . A sheet feeding apparatus comprising: 
 sheet supporting means for moving the uppermost surface of a sheet stack to a predetermined position,    air blowing means having a duct for blowing the air from a direction substantially perpendicular to the side surface of the uppermost part of the sheet stack supported on the sheet supporting means, and    sheet feeding means for vacuuming and feeding the uppermost sheet of the sheet stack supported on the sheet supporting means by vacuuming the air,    wherein the air blowing means blows the air to the uppermost part of the sheet stack supported on the sheet supporting means at a first position which the uppermost sheet of the sheet stack is faced to an opening of the all blowing means, and the uppermost sheet is vacuumed and fed by the sheet feeding means at a second position above the first position.    
   
   
       2 . The sheet feeding apparatus according to  claim 1 , wherein the feeding operation is stopped temporarily after the continuous feeding operation of a predetermined number of sheets at the second position for moving the uppermost sheet of the sheet stack to the first position, and after operating the air blowing means for a predetermined time, the uppermost sheet is moved again to the second position for resuming the feeding operation.  
   
   
       3 . The sheet feeding apparatus according to  claim 1 , further comprising an air blowing speed varying means for changing the air blowing speed blown out from the air blowing means.  
   
   
       4 . The sheet feeding apparatus according to  claim 3 , wherein the sheet feeding means is operated for vacuuming and feeding the uppermost sheet after moving from the first position to the second position after operating the air blowing means and the air speed varying means at the first position for a predetermined time.  
   
   
       5 . The sheet feeding apparatus according to  claim 4 , wherein the feeding operation is stopped temporarily after the continuous feeding operation of a predetermined number of sheets at the second position for moving the uppermost sheet of the sheet stack to the first position, and after operating the air blowing means and the air blowing speed varying means for a predetermined time, the uppermost sheet is moved again to the second position for resuming the feeding operation.  
   
   
       6 . The sheet feeding apparatus according to  claim 3 , wherein the air blowing means and the air blowing speed varying means can be operated also at the time the uppermost sheet of the sheet stack supported on the sheet supporting means is between the first position and the second position.  
   
   
       7 . The sheet feeding apparatus according to  claim 3 , wherein the air blowing speed varying means is a channel moving means for moving the air channel blown out from the air blowing means in the substantially vertical direction in the vicinity of the sheet stack side surface.  
   
   
       8 . The sheet feeding apparatus according to  claim 3 , wherein the air blowing speed varying means increases or reduces the air supply from the air supply source of the air blowing means.  
   
   
       9 . The sheet feeding apparatus according to  claim 3 , wherein the air blowing speed varying means is an air blocking means for blocking or opening the air channel from the air blowing means.  
   
   
       10 . The sheet feeding apparatus according to  claim 1 , further comprising an air orientation varying means for changing the air orientation blown out from the air blowing means.  
   
   
       11 . The sheet feeding apparatus according to  claim 10 , wherein the sheet feeding means is operated at the second position above the first position for vacuuming and feeding the uppermost sheet after operating the air blowing means and the air orientation varying means for a predetermined time at the first position.  
   
   
       12 . The sheet feeding apparatus according to  claim 11 , wherein the feeding operation is stopped temporarily after the continuous feeding operation of a predetermined number of sheets at the second position for moving the uppermost sheet of the sheet stack to the first position, and after operating the air blowing means and the air orientation varying means for a predetermined time, the uppermost sheet is moved again to the second position for resuming the feeding operation.  
   
   
       13 . A sheet feeding apparatus comprising: 
 a middle plate provided elevatably which supports sheet stack,    a duct opened to the side surface of a upper part of the sheet stack supported on the middle plate, and said duct blows out the air from a opening of the duct to the side surface of a upper part of the sheet stack,    a vacuuming belt for vacuuming and feeding a uppermost sheet of the sheet stack supported on the middle plate by vacuuming the air,    first height detecting means for detecting the uppermost sheet of the sheet stack supported on the middle plate reaching a first position,    second height detecting means for detecting the uppermost sheet of the sheet stack supported on the middle plate reaching a second position higher than the first position, and    a controller for commanding the execution of the air blowing operation of the duct when the uppermost surface of the sheet stack supported on the middle plate is detected by the first height detecting means, and commanding the execution of the feeding operation of the vacuuming belt when the uppermost surface of the sheet stack raised by the elevation of the middle plate is detected by the second height detecting means.    
   
   
       14 . The sheet feeding apparatus according to  claim 13 , further comprising a shutter having a slit, vertically movably between the duct opening and the sheet stack such that the shutter is controlled by the controller so as to be moved vertically at the time the air is blown out from the duct opening.  
   
   
       15 . The sheet feeding apparatus according to  claim 13 , further comprising a swing nozzle to be rotated vertically in the duct such that the air is blown out from the swing nozzle at the time the uppermost surface of the sheet stack is detected by the first height detecting means.  
   
   
       16 . An image forming apparatus comprising: 
 an image forming unit for forming an image on a sheet, and    the sheet feeding apparatus according to any of  claims 1  to  15 , for separating and feeding sheets one by one to the image forming unit.