Sheet discharging device and image forming apparatus including the sheet discharging device

Abstract

In a sheet discharging unit including a pair of sheet discharge rollers which discharges a sheet P, the outer diameter of a sheet discharge drive roller included in the pair of sheet discharge rollers is set so that the outer diameter of a straight portion which is a central portion in the width direction perpendicular to the discharging direction of the sheet P is larger than the outer diameters of both end portions in the width direction. Further, in the sheet discharging unit, the pair of sheet discharge rollers respectively include metal shafts extending in the width direction and elastic layers respectively wound around the metal shafts and continuously formed to be longer in the width direction than the width of a sheet P with a passable maximum size. Further, at least one elastic layer of the pair of sheet discharge rollers is formed of a foamed material.

1 . A sheet discharging device comprising:
 a sheet stacking portion on which sheets are staked; and   a pair of sheet discharge rollers which discharges a sheet, on which a toner image is fixed by heat, onto the sheet stacking portion in a U-shaped curve in a width direction perpendicular to the discharging direction of the pair of sheet discharge rollers, wherein each of the pair of sheet discharge rollers includes a rotating shaft extending in the width direction and an elastic layer is provided on the rotating shaft and continuously formed to be longer in the width direction than the width of a sheet with a passable maximum size, and at least one elastic layer of the pair of sheet discharge rollers is formed of a foamed material.   
     
     
         2 . The sheet discharging device as claimed in  claim 1 , wherein the outer diameter of the central portion in the width direction, of one sheet discharge roller of the pair of sheet discharge rollers, is larger than the outer diameters of the both end portions in the width direction. 
     
     
         3 . The sheet discharging device as claimed in  claim 2 , wherein the one sheet discharge roller is disposed above the other sheet discharge roller of the pair of sheet discharge rollers. 
     
     
         4 . The sheet discharging device as claimed in  claim 2 , wherein the elastic layer of the one sheet discharge roller has, in the central portion in the width direction, a cylindrical portion without a change of the outer diameter, a length L of the cylindrical portion is 0 L ⅓ L 1  with respect to a length L 1  in the width direction of the sheet with a maximum size that allows the sheet to pass between the pair of sheet discharge rollers, and the elastic layer has taper shape from the both ends in the width direction of the cylindrical portion to the both ends in the width direction of the one sheet discharge roller. 
     
     
         5 . The sheet discharging device as claimed in  claim 2 , wherein the elastic layer of the one sheet discharge roller has a crown shape with a maximum outer diameter in the central portion in the width direction of the sheet. 
     
     
         6 . The sheet discharging device as claimed in  claim 2 , wherein the elastic layer of the one sheet discharge roller has a hardness higher than that of the elastic layer of the other sheet discharge roller of the pair of sheet discharge rollers. 
     
     
         7 . The sheet discharging device as claimed in  claim 1 , wherein a tube-like resin film is wound around the outer circumference of at least one of the elastic layers of the pair of sheet discharge rollers disposed on the printed surface side of the sheet. 
     
     
         8 . An image forming apparatus comprising:
 an image forming portion which forms a toner image;   a fixing portion which fixes the toner image on a sheet by heat; and   a sheet discharging device which discharges the sheet, having passed through the fixing portion,   wherein the sheet discharging device includes:
 a sheet stacking portion on which sheets are staked; and 
 a pair of sheet discharge rollers which discharges a sheet, on which a toner image is fixed by heat, onto the sheet stacking portion in a U-shaped curve in a width direction perpendicular to the discharging direction of the pair of sheet discharge rollers, wherein each of the pair of sheet discharge rollers includes a rotating shaft extending in the width direction and an elastic layer is provided on the rotating shaft and continuously formed to be longer in the width direction than the width of a sheet with a passable maximum size, and 
 at least one elastic layer of the pair of sheet discharge rollers is formed of a foamed material. 
   
     
     
         9 . The image forming apparatus as claimed in  claim 8 , wherein the outer diameter of the central portion in the width direction, of one sheet discharge roller of the pair of sheet discharge rollers, is larger than the outer diameters of the both end portions in the width direction. 
     
     
         10 . The image forming apparatus as claimed in  claim 9 , wherein the one sheet discharge roller is disposed above the other sheet discharge roller of the pair of sheet discharge rollers. 
     
     
         11 . The image forming apparatus as claimed in  claim 9 , wherein the elastic layer of the one sheet discharge roller has, in the central portion in the width direction, a cylindrical portion without a change of the outer diameter, a length L of the cylindrical portion is 0 L ⅓ L 1  with respect to a length L 1  in the width direction of the sheet with a maximum size that allows the sheet to pass between the pair of sheet discharge rollers, and the elastic layer has taper shape from the both ends in the width direction of the cylindrical portion to the both ends in the width direction of the one sheet discharge roller. 
     
     
         12 . The image forming apparatus as claimed in  claim 9 , wherein the elastic layer of the one sheet discharge roller has a crown shape with a maximum outer diameter in the central portion in the width direction of the sheet. 
     
     
         13 . The image forming apparatus as claimed in  claim 9 , wherein the elastic layer of the one sheet discharge roller has a hardness higher than that of the elastic layer of the other sheet discharge roller of the pair of sheet discharge rollers. 
     
     
         14 . The image forming apparatus as claimed in  claim 8 , wherein a tube-like resin film is wound around the outer circumference of at least one of the elastic layers of the pair of sheet discharge rollers disposed on the printed surface side of the sheet.