Sheet conveyance device

Abstract

A sheet conveyance device that is capable of appropriately correcting a position of a sheet in the sheet width direction with respect to an image transferred thereon. A shift mechanism shifts a sheet conveyed in a sheet width direction perpendicular to a sheet conveyance direction. A first sensor detects one side edge of the sheet in the sheet width direction. A second sensor detects the other side edge of the sheet in the sheet width direction. A control unit drives the shift mechanism so that the center of the sheet in the sheet width direction is coincident with a predetermined target position based on the gap of the first and second sensors, detection timing of the one side edge by the first sensor, detection timing of the other side edged by the second sensor, and a predetermined standard value of sheet width.

What is claimed is: 
     
         1 . A sheet conveyance device comprising:
 a shift mechanism configured to shift a sheet conveyed in a sheet width direction perpendicular to a sheet conveyance direction;   a first sensor configured to detect one side edge of the sheet in the sheet width direction;   a second sensor configured to be arranged at a different position from said first sensor in the sheet width direction and to detect the other side edge of the sheet in the sheet width direction; and   a control unit configured to drive said shift mechanism so that the center of the sheet in the sheet width direction is coincident with a predetermined target position based on the gap of said first and second sensors, detection timing of the one side edge by said first sensor during a shift of the sheet in the sheet width direction, and detection timing of the other side edged by said second sensor during the shift of the sheet.   
     
     
         2 . The sheet conveyance device according to  claim 1 , wherein said control unit determines difference between an actual sheet width of the sheet and a standard value of the sheet width based on the detection timing of the one side edge by said first sensor during the shift of the sheet in the sheet width direction, the detection timing of the other side edge by said second sensor during the shift of the sheet, and the standard value of the sheet width, determines a shift distance required for matching the center of the sheet in the sheet width direction with the target position based on the difference and a standard shift distance required for matching a center of a sheet of which width is equal to the standard value with the target position, and shifts the sheet by the shift distance. 
     
     
         3 . The sheet conveyance device according to  claim 2 , further comprising a front end sensor configured to detect the front end of the sheet,
 wherein said control unit performs a preliminary shift for shifting the sheet in the sheet width direction so that said second sensor does not detect the sheet and said first sensor detects the sheet, if said second sensor detects the sheet and said first sensor does not detect the sheet at the time when said front end sensor detects the front end of the sheet, and   wherein said control unit shifts the sheet in a direction opposite to the shift direction of the preliminary shift so that the center of the sheet is coincident with the target position in the sheet width direction after finishing the preliminary shift.   
     
     
         4 . The sheet conveyance device according to  claim 2 , wherein said shift mechanism has a drive mechanism including a motor that shifts a conveyance roller, which conveys the sheet in the sheet conveyance direction, in the sheet width direction, and
 wherein said control unit determines the standard shift distance and the shift distance based on the number of pulses for driving the motor and a shift distance of the conveyance roller per one pulse.   
     
     
         5 . The sheet conveyance device according to  claim 2 , further comprising a distance variation mechanism configured to change the gap of said first and second sensors. 
     
     
         6 . The sheet conveyance device according to  claim 2 , wherein a plurality of pairs of the first and second sensors of which gaps in the sheet width direction are different are arranged. 
     
     
         7 . A sheet conveyance device comprising:
 a shift mechanism configured to shift a sheet in a sheet width direction perpendicular to a sheet conveyance direction;   a side-edge detection unit configured to detect a side edge of the sheet in the sheet width direction;   a difference detection unit configured to detect difference between an actual sheet width of the sheet and a standard value of the sheet width in the sheet width direction; and   a control unit configured to drive said shift mechanism so that the sheet is shifted to a predetermined target position in the sheet width direction based on the side edge of the sheet detected by said side-edge detection unit and the difference detected by said difference detection unit.   
     
     
         8 . The sheet conveyance device according to  claim 7 , further comprising a setting unit configured to set up the size of the sheet, and wherein the standard value is determined based on the size set up by said setting unit. 
     
     
         9 . The sheet conveyance device according to  claim 7 , wherein said side-edge detection unit has a first sensor for detecting one side edge of the sheet and a second sensor for detecting the other side edge of the sheet, and the first and second sensors are aligned in the sheet width direction. 
     
     
         10 . The sheet conveyance device according to  claim 9 , wherein said control unit causes said shift mechanism to shift the sheet so that one of the first and second sensors does not detect the sheet and the other sensor detects the sheet, if the one of the sensors detects the sheet and the other sensor does not detect the sheet at the time when the sheet is conveyed to a predetermined position. 
     
     
         11 . The sheet conveyance device according to  claim 9 , wherein said difference detection unit detects the difference based on the gap of the first and second sensors and a shift distance of the sheet between a position where one of the first and second sensors detects the sheet and the other sensor does not detect the sheet and a position where the one of the sensors does not detect the sheet and the other sensor detects the sheet. 
     
     
         12 . The sheet conveyance device according to  claim 7 , wherein the predetermined target position is determined as a position at which the center of the sheet in the sheet width direction is coincident with a center of an image that is formed by an image forming unit and will be transferred onto the sheet.