Sheet feeding device and image forming apparatus

Abstract

A sheet feeding device includes a sheet accommodating portion for accommodating a sheet, a feeding roller for feeding the sheet by rotation thereof in a state in which the feeding roller contacts an uppermost sheet accommodated in the sheet accommodating portion, a detecting portion for detecting a surface property of the sheet accommodated in the sheet accommodating portion, a changing means for changing contact pressure of the feeding roller to the uppermost sheet, and a controller for controlling the changing means so as to change the contact pressure on the basis of a result of the surface property of the sheet detected by the detecting portion.

What is claimed is: 
     
         1 . A sheet feeding device comprising:
 a sheet accommodating portion configured to accommodate a sheet;   a feeding roller configured to feed the sheet by rotation thereof in a state in which said feeding roller contacts an uppermost sheet accommodated in said sheet accommodating portion;   detecting means configured to detect a surface property of the sheet accommodated in said sheet accommodating portion;   changing means configured to change contact pressure of said feeding roller to the uppermost sheet; and   a controller configured to control said changing means so as to change the contact pressure on the basis of a result of the surface property of the sheet detected by said detecting means.   
     
     
         2 . A sheet feeding device according to  claim 1 , wherein the sheet has surface roughness including first roughness and second roughness larger than the first roughness, and
 wherein after said changing means changes the contact pressure, the contact pressure of said feeding roller when the surface roughness is the second roughness is contact pressure larger than the contact pressure of said feeding roller when the surface roughness is the first roughness.   
     
     
         3 . A sheet feeding device according to  claim 1 , further comprising urging means configured to urge said feeding roller toward the uppermost sheet accommodated in said sheet accommodating portion,
 wherein said changing means changes a force for urging said feeding roller by said urging means.   
     
     
         4 . A sheet feeding device according to  claim 1 , wherein said controller calculates feeding efficiency which is a sheet feeding distance per unit rotation amount by a detection result of the surface property of the sheet and changes the contact pressure by said changing means so that the feeding efficiency is a predetermined value or more. 
     
     
         5 . A sheet feeding device according to  claim 1 , further comprising separating means including a separation nip in which sheets fed by said feeding roller are separated one by one,
 wherein a feeding force generated by the contact pressure of said feeding roller is smaller than a sheet separating force generated in the separation nip.   
     
     
         6 . A sheet feeding device according to  claim 1 , wherein surface roughness of the sheet includes a first parameter indicating a difference between a highest point and a lowest point with respect to a height direction in a contour curve of a surface of the sheet, and is first roughness when the first parameter is a first value and is second roughness when the first parameter is a second value smaller than the first value. 
     
     
         7 . A sheet feeding device according to  claim 6 , wherein the surface roughness includes a second parameter indicating an interval of unevenness with respect to a horizontal direction in the contour curve of the surface of the sheet and is the first roughness when the second parameter is a third value and is the second roughness when the second parameter is a fourth value smaller than the third value. 
     
     
         8 . A sheet feeding device according to  claim 1 , wherein said controller is capable of controlling a rotational speed of said feeding roller, and
 wherein the rotational speed is a first speed when surface roughness of the sheet is first roughness and is a second speed higher than the first speed when the surface roughness is second roughness.   
     
     
         9 . A sheet feeding device according to  claim 1 , wherein said controller controls said changing means so that pressure obtained by adding pressure of a margin with variation in surface property on a surface of the sheet to pressure of a threshold at which a sheet feeding distance per unit rotation amount of said feeding roller is a predetermined distance is the contact pressure of said feeding roller. 
     
     
         10 . A sheet feeding device according to  claim 1 , wherein said detecting means includes a confocal laser optical element configured to laser-scan a surface of the sheet and a light receiving element configured to receive reflected light from the surface of the sheet laser-scanned by said confocal laser optical element, and outputs a signal depending on the surface property. 
     
     
         11 . A sheet feeding device according to  claim 1 , wherein said detecting means is disposed inside said sheet accommodating portion. 
     
     
         12 . A sheet feeding device according to  claim 1 , wherein said changing means includes a spring for generating the contact pressure by pressing said feeding roller, a stepping motor, and a moving member for expanding and contracting said spring by drive of said stepping motor. 
     
     
         13 . An image forming apparatus comprising:
 a sheet feeding device according to  claim 1 ; and   image forming means configured to form an image on the sheet fed by said sheet feeding device.