Sheet feeder and image forming apparatus incorporating the same

Abstract

A sheet feeder includes a stacker to stack sheets and a separation and conveyance device to separate one sheet from the sheets fed from the stacker and convey the sheets one by one. The separation and conveyance device includes a feed roller that rotates in a direction to feed the sheet and a separation roller to press against the feed roller via the sheet. The separation roller has an apparent hardness different from an apparent hardness of the feed roller and is configured to form an indentation in the feed roller.

What is claimed is: 
     
         1 . A sheet feeder comprising:
 a stacker to stack sheets; and   a separation and conveyance device to separate one sheet from the sheets fed from the stacker and convey the sheets one by one,   the separation and conveyance device including:
 a feed roller that rotates in a direction to feed the sheet; and 
 a separation roller to press against the feed roller via the sheet, 
 the separation roller having an apparent hardness different from an apparent hardness of the feed roller and configured to form an indentation in the feed roller. 
   
     
     
         2 . The sheet feeder according to  claim 1 ,
 wherein each of the feed roller and the separation roller includes:   a rotational shaft;   a cylindrical hub supported on the rotational shaft; and   a cylindrical elastic layer fitted to an outer peripheral surface of the hub, and   wherein a thickness of the elastic layer of the feed roller is thicker than a thickness of the elastic layer of the separation roller to cause a difference in the apparent hardness between the feed roller and the separation roller.   
     
     
         3 . The sheet feeder according to  claim 1 ,
 wherein each of the feed roller and the separation roller includes:   a rotational shaft;   a cylindrical hub supported on the rotational shaft; and   a cylindrical elastic layer fitted to an outer peripheral surface of the hub and having a concavo-convex portion on an outer peripheral surface of the elastic layer, and   wherein a height of the concavo-convex portion of the feed roller is higher than a height of the concavo-convex portion of the separation roller to cause a difference in the apparent hardness between the feed roller and the separation roller.   
     
     
         4 . The sheet feeder according to  claim 1 ,
 wherein each of the feed roller and the separation roller includes:   a rotational shaft;   a cylindrical hub supported on the rotational shaft; and   a cylindrical elastic layer fitted to an outer peripheral surface of the hub, and   wherein the feed roller has a concavo-convex portion on an outer peripheral surface of the elastic layer to cause a difference in the apparent hardness between the feed roller and the separation roller.   
     
     
         5 . The sheet feeder according to  claim 1 ,
 wherein each of the feed roller and the separation roller includes:   a rotational shaft;   a cylindrical hub supported on the rotational shaft; and   a cylindrical elastic layer fitted to an outer peripheral surface of the hub and having a concavo-convex portion on an inner peripheral surface of the elastic layer, and   wherein a height of the concavo-convex portion of the feed roller is higher than a height of the concavo-convex portion of the separation roller to cause a difference in the apparent hardness between the feed roller and the separation roller.   
     
     
         6 . The sheet feeder according to  claim 1 ,
 wherein each of the feed roller and the separation roller includes:   a rotational shaft;   a cylindrical hub supported on the rotational shaft; and   a cylindrical elastic layer fitted to an outer peripheral surface of the hub, and   wherein the feed roller has a concavo-convex portion on an inner peripheral surface of the elastic layer to cause a difference in the apparent hardness between the feed roller and the separation roller.   
     
     
         7 . The sheet feeder according to  claim 1 ,
 wherein each of the feed roller and the separation roller includes:   a rotational shaft;   a cylindrical hub supported on the rotational shaft; and having a concavo-convex portion on an outer peripheral surface of the hub, and   a cylindrical elastic layer fitted to the outer peripheral surface of the hub, and   wherein a height of the concavo-convex portion of the feed roller is higher than a height of the concavo-convex portion of the separation roller to cause a difference in the apparent hardness between the feed roller and the separation roller.   
     
     
         8 . The sheet feeder according to  claim 1 ,
 wherein each of the feed roller and the separation roller includes:   a rotational shaft;   a cylindrical hub supported on the rotational shaft; and   a cylindrical elastic layer fitted to an outer peripheral surface of the hub, and   wherein the feed roller has a concavo-convex portion on the outer peripheral surface of the hub to cause a difference in the apparent hardness between the feed roller and the separation roller.   
     
     
         9 . The sheet feeder according to  claim 1 ,
 wherein each of the feed roller and the separation roller includes:   a rotational shaft;   a cylindrical hub supported on the rotational shaft; and   a cylindrical elastic layer fitted to an outer peripheral surface of the hub, and   wherein the elastic layer of the feed roller is a foamed elastic layer to cause a difference in the apparent hardness between the feed roller and the separation roller.   
     
     
         10 . The sheet feeder according to  claim 1 ,
 wherein each of the feed roller and the separation roller includes:   a rotational shaft;   a cylindrical hub supported on the rotational shaft; and   a cylindrical foamed elastic layer fitted to an outer peripheral surface of the hub, and   wherein an expansion ratio of the foamed elastic layer of the feed roller is larger than an expansion ratio of the foamed elastic layer of the separation roller to cause a difference in the apparent hardness between the feed roller and the separation roller.   
     
     
         11 . The sheet feeder according to  claim 1 ,
 wherein each of the feed roller and the separation roller includes:   a rotational shaft;   a cylindrical hub supported on the rotational shaft; and   a cylindrical elastic layer fitted to an outer peripheral surface of the hub, and   wherein at least one of the feed roller and the separation roller has a concavo-convex portion on at least one of the hub and the elastic layer, and   
       the concavo-convex portion has a plurality of convex ridges and a plurality of concave streaks that extend in a direction of the rotational shaft of the at least one of the feed roller and the separation roller. 
     
     
         12 . The sheet feeder according to  claim 1 ,
 wherein each of the feed roller and the separation roller includes:
 a rotational shaft; 
 a cylindrical hub supported on the rotational shaft; and 
 a cylindrical elastic layer fitted to an outer peripheral surface of the hub, and 
   wherein at least one of the feed roller and the separation roller has a concavo-convex portion on at least one of the hub and the elastic layer, and   
       the concavo-convex portion has a plurality of convex ridges and a plurality of concave streaks that extend in a circumferential direction of the at least one of the feed roller and the separation roller. 
     
     
         13 . The sheet feeder according to  claim 1 ,
 wherein each of the feed roller and the separation roller includes:   a rotational shaft;   a cylindrical hub supported on the rotational shaft; and   a cylindrical elastic layer fitted to an outer peripheral surface of the hub, and   wherein at least one of the feed roller and the separation roller has a concavo-convex portion on at least one of the hub and the elastic layer, and   
       the concavo-convex portion has a plurality of projections formed in a scattered pattern. 
     
     
         14 . The sheet feeder according to  claim 1 ,
 wherein each of the feed roller and the separation roller includes:   a rotational shaft;   a cylindrical hub supported on a rotational shaft; and   a cylindrical elastic layer fitted to an outer peripheral surface of the hub, and   wherein at least one of the feed roller and the separation roller has a concavo-convex portion on at least one of the hub and the elastic layer, and   
       the concavo-convex portion has a plurality of depressions formed in a scattered pattern. 
     
     
         15 . The sheet feeder according to  claim 1 ,
 wherein the feed roller and the separation roller are made of a same material.   
     
     
         16 . The sheet feeder according to  claim 1 ,
 wherein the feed roller and the separation roller have a same diameter.   
     
     
         17 . An image forming apparatus comprising:
 the sheet feeder according to  claim 1 , and   an image forming device to form an image on the sheet sent from the sheet feeder.   
     
     
         18 . A sheet feeder comprising:
 a stacker to stack sheets; and   a separation and conveyance device to separate one sheet from the sheets fed from the stacker and convey the sheets one by one, the separation and conveyance device including:   a feed roller that rotates in a direction to feed the sheet; and   a separation roller to press against the feed roller via the sheet,   the separation roller having an apparent hardness harder than an apparent hardness of the feed roller.