Sheet feeding apparatus and image forming apparatus

Abstract

A sheet feeding apparatus having sheet stacking means movable up and down with a plurality of sheets stacked thereon, sheet feeding means for feeding out the sheets stacked on the sheet stacking means and control means for moving the sheet stacking means up and down so that during the supply of the sheets to the sheet stacking means and during the taking-out of the sheets from the sheet stacking means, the upper surface of the sheets stacked on the sheet stacking means may be automatically moved to a sheet supplying position and a sheet taking-out position set between the upper limit position and the lower limit position in the range of the upward and downward movement of the sheet stacking means each time the sheet is supplied and each time the sheet is taken out.

1 . A sheet feeding apparatus comprising: 
 sheet stacking means movable up and down with a plurality of sheets stacked thereon;    sheet feeding means for feeding out the sheets stacked on said sheet stacking means; and    control means for automatically moving an upper surface of sheet stacked on said sheet stacking means to a sheet supplying position each time the sheet is supplied and to a sheet taking-out position each time the sheet is taken out, wherein said sheet supplying position and said sheet taking-out position are respectively set between an upper limit position and a lower limit position in a range of the upward and downward movement of said sheet stacking means.    
     
     
         2 . A sheet feeding apparatus according to  claim 1 , further comprising: 
 position detecting means for detecting the position of the upper surface of the sheets stacked on said sheet stacking means; and    lift means for moving said sheet stacking means up and down;    wherein said control means controls said lift means on the basis of detection by said position detecting means to thereby move said sheet stacking means down so the upper surface of the stacked sheet may be moved to said sheet supplying position when the sheets have been supplied to said sheet stacking means, and move said sheet stacking means up so that the upper surface of the stacked sheets may be moved to said sheet taking-out position when the sheets have been taken out.    
     
     
         3 . A sheet feeding apparatus according to  claim 2 , wherein said position detecting means is provided with two sensors disposed in the direction of upward and downward movement of said sheet stacking means for detecting the position of the upper surface of the sheets stacked on said sheet stacking means, and 
 said control means moves down said upper surface of the sheets stacked on said sheet stacking means to said sheet supplying position on the basis of detection by the upper one of said two sensors when the sheets have been supplied, and    said control means moves up said upper surface of the sheets stacked on said sheet stacking means to sheet taking-out position on the basis of detection by the lower one of said two sensors when the sheets have been taken out.    
     
     
         4 . A sheet feeding apparatus according to  claim 2 , wherein said position detecting means is a sensor extending in the stack direction of the sheets and capable of detecting the position of the upper surface of the stacked sheets, and said control means moves said sheet stacking means up or down so that said upper surface of the sheets may be moved to said sheet supplying position or said sheet taking-out position when any fluctuation in the position of the upper surface of the sheets has occurred.  
     
     
         5 . A sheet feeding apparatus according to  claim 3 , wherein said sheet taking-out position and said sheet supplying position are set so that said sheet taking-out position may be higher than said sheet supplying position.  
     
     
         6 . A sheet feeding apparatus having: 
 a lifter plate provided for upward and downward movement;    a lifter motor for moving said lifter plate up and down;    a pickup roller for feeding out sheets stacked on said lifter plate; and    a controller for controlling said lifter motor to thereby move said lifter plate up and down;    wherein said controller automatically moves an upper surface of sheet stacked on said lifter plate to a sheet supplying position each time the sheet is supplied and to a sheet taking-out position each time the sheet is taken out, wherein said sheet supplying position and said sheet taking-out position are respectively set between an upper limit position and a lower limit position in a range of the upward and downward movement of said lifter plate.    
     
     
         7 . A sheet feeding apparatus according to  claim 6 , further comprising: two sheet surface detection sensors disposed in the direction of upward and downward movement of said lifter plate, and wherein said controller controls the lifter motor in the following manner; 
 when the sheet have been supplied said lifter plate is moved down on the basis of detection by the upper one of said two sheet surface detection sensors so that the upper surface of the sheets stacked on said lifter plate is moved said sheet supplying position, and    when the sheets have been taken out, said lifter plate is moved up on the basis of detection by the upper one of said two sheet surface detection sensors so that the upper surface of the sheets stacked on said lifter plate may be moved to said sheet taking-out position.    
     
     
         8 . A sheet feeding apparatus according to  claim 6  or  7 , wherein said sheet taking-out position and said sheet supplying position are set so that said sheet taking-out position is higher than said sheet supplying position.  
     
     
         9 . An image forming apparatus provided with a sheet feeding apparatus according to any one of  claims 1  to  5 , and an image forming portion for forming an image on a sheet fed from said sheet feeding apparatus.