Sheet feeding device and image forming apparatus

Abstract

A sheet feeding device includes a feeding member that rotates and feeds a sheet; a resistance member that contacts the feeding member with the sheet interposed therebetween, the resistance member contacting the sheet fed by the feeding member and applying a resistance against the feeding of the sheet; a holding unit that holds the resistance member so that the resistance member is movable to a position where the resistance member does not contact the feeding member; and an urging unit that urges the resistance member held by the holding unit in a direction opposite to a feeding direction of the sheet.

What is claimed is: 
     
         1 . A sheet feeding device comprising:
 a feeding member that rotates and feeds a sheet;   a resistance member that contacts the feeding member with the sheet interposed therebetween, the resistance member contacting the sheet fed by the feeding member and applying a resistance against the feeding of the sheet;   a holding unit that holds the resistance member so that the resistance member is movable to a position where the resistance member does not contact the feeding member; and   an urging unit that urges the resistance member held by the holding unit in a direction opposite to a feeding direction of the sheet.   
     
     
         2 . The sheet feeding device according to  claim 1 ,
 wherein a surface of the resistance member that faces the feeding member is arc shaped in cross section,   wherein the resistance member is rotatably held by the holding unit, and   wherein the urging unit is a spring that applies a rotational force to the resistance member.   
     
     
         3 . The sheet feeding device according to  claim 1 ,
 wherein the resistance member includes a flat surface that applies the resistance against the feeding of the sheet.   
     
     
         4 . The sheet feeding device according to  claim 2 ,
 wherein the holder member includes a rotation fulcrum, and   wherein the rotation fulcrum is located so that a contact force between the feeding member and the resistance member increases when the resistance member applies the resistance to the sheet.   
     
     
         5 . The sheet feeding device according to  claim 1 ,
 wherein the feeding member and the resistance member are not in contact with each other before the feeding member is rotated.   
     
     
         6 . The sheet feeding device according to  claim 1 ,
 wherein the urging unit is disposed in a central region of the resistance member in a width direction that crosses a movement direction of the resistance member or on each side of the central region in the width direction.   
     
     
         7 . The sheet feeding device according to  claim 1 ,
 wherein, when a single sheet is nipped between the feeding member and the resistance member, the resistance member is moved against an urging force applied by the urging unit to the position where the resistance member does not contact the feeding member.   
     
     
         8 . The sheet feeding device according to  claim 1 ,
 wherein, in the case where a single sheet is nipped between the feeding member and the resistance member, when Np is a pressing force with which the resistance member presses the sheet against the feeding member and μ is a coefficient of friction of the resistance member, a force Fp applied to the resistance member in the feeding direction through the single sheet is Fp=Np×μ, and   wherein, when Fr is an urging force applied to the resistance member by the urging unit in the direction opposite to the feeding direction of the sheet, Fp>Fr is satisfied.   
     
     
         9 . An image forming apparatus comprising:
 the sheet feeding device according to  claim 1 ; and   an image forming unit which forms an image on the sheet fed by the sheet feeding device.