Sheet feeding apparatus and image forming apparatus

Abstract

An air blowing portion blows air to the end of sheets supported by a lifting and lowering tray. The sheets blown up by the air from the air blowing portion are sucked and conveyed by a sucking and conveying portion. The sheets are preliminarily blown up above the suckable rang. Then, the sheets are lowered to the suckable range before a sucking and conveying operation is started. In the above operation, the tray is lifted, and thereafter the tray is lowered until the sheets reach the suckable range while repeating a step operation of performing a lowering operation and a stop operation based on detection of the upper surface of the sheets by a sheet detecting mechanism.

1 . A sheet feeding apparatus comprising:
 a lifting and lowering tray which supports sheets;   an air blowing portion blowing air to an end of the sheets to blow upward the sheets supported on the tray;   a sucking and conveying portion sucking and conveying a sheet blown upward by the air blown by the air blowing portion;   a sheet detecting mechanism detecting an uppermost sheet of the sheets supported on the tray; and   a controller configured such that when the uppermost sheet blown upward is lowered to a sucking and conveying position based on detection of an upper surface of the sheet by the sheet detecting mechanism before starting a sucking and conveying operation of a sheet by the sucking and conveying portion, the tray is lowered until the uppermost sheet reaches the sucking and conveying position while repeating a step operation in which a lowering operation and a stop operation are performed.   
     
     
         2 . A sheet feeding apparatus according to  claim 1 , wherein the controller is configured such that a lowering operation time period and a stop operation time period in one step of the step operation of performing the lowering operation and the stop operation of the tray are variable. 
     
     
         3 . A sheet feeding apparatus according to  claim 1 , wherein the controller is configured such that after a sucking and conveying operation of a sheet by the sucking and conveying portion has been started, even if the uppermost sheet is positioned above the sucking and conveying position, the tray is not lowered. 
     
     
         4 . An image forming apparatus provided with a sheet feeding apparatus for feeding sheets one by one, comprising:
 a lifting and lowering tray which supports sheets;   an air blowing portion blowing air to an end of the sheets to blow upward the sheets supported on the tray;   a sucking and conveying portion sucking the sheets blown upward by the air blown by the air blowing portion, and feeding a sheet to an image forming portion;   a sheet detecting mechanism for detecting an uppermost sheet of the sheets supported on the tray; and   a controller configured such that when the uppermost sheet blown upward is lowered to a sucking and conveying position based on detection of an upper surface of the sheet by the sheet detecting mechanism before starting a sucking and conveying operation of a sheet by the sucking and conveying portion, the tray is lowered until the uppermost sheet reaches the sucking and conveying position while repeating a step operation in which a lowering operation and a stop operation are performed.   
     
     
         5 . An image forming apparatus according to  claim 4 , wherein the controller is configured such that a lowering operation time period and a stop operation time period in one step of the step operation of performing the lowering operation and the stop operation of the tray is variable. 
     
     
         6 . An image forming apparatus according to  claim 4 , wherein the controller is configured such that after a sucking and conveying operation of a sheet by the sucking and conveying portion has been started, even if the uppermost sheet is positioned above the suckable range, the tray is not lowered.