Sheet feeder and image forming apparatus

Abstract

There is provided a sheet feeder including: a lifting unit that lifts a loading portion having a recording medium loaded thereon; a position detecting unit that detects whether the uppermost surface of the recording medium is disposed at a predetermined first position; a sheet feed mechanism that feeds the recording medium from the loading portion; a thickness detecting unit that detects thickness of the recording medium fed by the sheet feeding mechanism; and a control unit that, when the position detecting unit detects that the uppermost surface of the recording medium is disposed at the first position, controls the lifting unit such that the uppermost surface of the recording medium is lifted up to a second position that is higher than the first position by a distance determined based on cumulative value of the thickness of the recording medium detected by the thickness detecting unit.

1 . A sheet feeder comprising:
 a lifting unit that lifts a loading portion having at least one recording medium loaded thereon;   a position detecting unit that detects whether the uppermost surface of the recording medium loaded on the loading portion is disposed at a predetermined first position;   a sheet feed mechanism that feeds the recording medium from the loading portion;   a thickness detecting unit that detects thickness of the recording medium fed by the sheet feeding mechanism; and   a control unit that, when the position detecting unit detects that the uppermost surface of the recording medium is disposed at the first position, controls the lifting unit such that the uppermost surface of the recording medium is lifted up to a second position that is higher than the first position by a distance determined based on cumulative value of the thickness of the recording medium detected by the thickness detecting unit.   
     
     
         2 . A sheet feeder comprising:
 a lifting unit that lifts a loading portion having at least one recording medium loaded thereon;   a position detecting unit that detects whether the uppermost surface of the recording medium loaded on the loading portion is disposed at a predetermined first position;   a sheet feed mechanism that feeds the recording medium from the loading portion;   a thickness detecting unit that detects thickness of the recording medium fed by the sheet feeding mechanism;   a thickness cumulative value calculating unit that calculates the cumulative value of thickness of the at least one recording medium detected by the thickness detecting unit; and   a control unit that, when the cumulative value calculated by the thickness cumulative value calculating unit is equal to a predetermined threshold value indicating that the uppermost surface of the recording medium loaded on the loading portion is disposed at a second position, controls the lifting unit such that the uppermost surface of the recording medium is lifted up to a predetermined first position higher than the second position.   
     
     
         3 . The sheet feeder of  claim 2 , wherein:
 there are a plurality of sheet feed units comprising the sheet feed mechanism and the lifting unit;   the sheet feeder further comprises a storage unit that stores the threshold value relating to the position of the recording medium of each of the sheet feed units, and   the control unit reads the threshold value for the recording medium fed by any one of the plurality of sheet feed units from the storage unit and uses the read threshold value as the predetermined threshold value.   
     
     
         4 . The sheet feeder of  claim 2 , wherein:
 there are a plurality of sheet feed units comprising the sheet feed mechanism and the lifting unit;   the sheet feeder further comprises a storage unit that stores respective threshold values of each of the sheet feed units, and   the control unit reads a threshold value for the sheet feed mechanism of any one of the plurality of sheet feed units from the storage unit and uses the read threshold value as the predetermined threshold value.   
     
     
         5 . An image forming apparatus comprising:
 a sheet feeder; and   an image forming unit that forms an image on at least one recording medium fed by the sheet feeder,   wherein the sheet feeder includes:   a lifting unit that lifts a loading portion having the recording medium loaded thereon;   a position detecting unit that detects whether the uppermost surface of the recording medium loaded on the loading portion is disposed at a predetermined first position;   a sheet feed mechanism that feeds the recording medium from the loading portion;   a thickness detecting unit that detects thickness of the recording medium fed by the sheet feeding mechanism; and   a control unit that, when the position detecting unit detects that the uppermost surface of the recording medium is disposed at the first position, controls the lifting unit such that the uppermost surface of the recording medium is lifted up to a second position that is higher than the first position by a distance determined based on cumulative value of the thickness of the recording medium detected by the thickness detecting unit.   
     
     
         6 . An image forming apparatus comprising:
 a sheet feeder; and   an image forming unit that forms an image on at least one recording medium fed by the sheet feeder,   wherein the sheet feeder includes:   a lifting unit that lifts a loading portion having the recording medium loaded thereon;   a position detecting unit that detects whether the uppermost surface of the recording medium loaded on the loading portion is disposed at a predetermined first position;   a sheet feed mechanism that feeds the recording medium from the loading portion;   a thickness detecting unit that detects thickness of the recording medium fed by the sheet feeding mechanism;   a thickness cumulative value calculating unit that calculates cumulative value of thickness of the at least one recording medium detected by the thickness detecting unit; and   a control unit that, when the cumulative value calculated by the thickness cumulative value calculating unit is equal to a predetermined threshold value indicating that the uppermost surface of the recording medium loaded on the loading portion is disposed at a second position, controls the lifting unit such that the uppermost surface of the recording medium is lifted up to a predetermined first position higher than the second position.   
     
     
         7 . The image forming apparatus of  claim 6 ,
 wherein there are a plurality of sheet feed units comprising the sheet feed mechanism and the lifting unit;   the sheet feeder further comprises a storage unit that stores the threshold value relating to the position of the recording medium of each of the sheet feed units, and   the control unit reads the threshold value for the recording medium fed by any one of the plurality of sheet feed units from the storage unit and uses the read threshold value as the predetermined threshold value.   
     
     
         8 . The image forming apparatus of  claim 6 ,
 wherein there are a plurality of sheet feed units comprising the sheet feed mechanism and the lifting unit;   the sheet feeder further comprises a storage unit that stores respective threshold values of each of the sheet feed units, and   the control unit reads a threshold value for the sheet feed mechanism of any one of the plurality of sheet feed units from the storage unit and uses the read threshold value as the predetermined threshold value.