Image forming apparatus and curl detecting method

Abstract

An image forming apparatus includes a first sensor lever which rotates between a standby position where the first sensor lever crosses a sheet conveyance path obliquely from a first rotation shaft to a sheet conveyance direction downstream side of the first rotation shaft and a first sensor is turned one of ON and OFF and a retract position where the first sensor lever is retracted from the sheet conveyance path and the first sensor is turned the other of ON and OFF, and a second sensor lever which rotates between a standby position where the second sensor lever crosses the sheet conveyance path obliquely from a second rotation shaft to the sheet conveyance direction downstream side of the second rotation shaft and a second sensor is turned one of ON and OFF and a retract position where the second sensor lever is retracted from the sheet conveyance path and the second sensor is turned the other of ON and OFF.

1 . An image forming apparatus comprising:
 a sheet conveyance path to guide a sheet in a sheet conveyance direction;   a first sensor;   a first sensor lever which rotates around a first rotation shaft substantially parallel to a surface perpendicular to the sheet conveyance direction and substantially parallel to a surface of the sheet conveyed in the sheet conveyance path, and rotates between a standby position where the first sensor lever crosses the sheet conveyance path obliquely from the first rotation shaft to a sheet conveyance direction downstream side of the first rotation shaft and the first sensor is turned one of ON and OFF and a retract position where the first sensor lever is retracted from the sheet conveyance path and the first sensor is turned the other of ON and OFF;   a first urging section to urge the first sensor lever from the retract position side to the standby position side;   a second sensor;   a second sensor lever which rotates around a second rotation shaft substantially parallel to the surface perpendicular to the sheet conveyance direction and substantially parallel to the surface of the sheet conveyed in the sheet conveyance path, and rotates between a standby position where the second sensor lever crosses the sheet conveyance path obliquely from the second rotation shaft to the sheet conveyance direction downstream side of the second rotation shaft and the second sensor is turned one of ON and OFF and a retract position where the second sensor lever is retracted from the sheet conveyance path and the second sensor is turned the other of ON and OFF; and   a second urging section to urge the second sensor lever from the retract position side to the standby position side.   
     
     
         2 . The apparatus of  claim 1 , wherein the first sensor lever and the second sensor lever are arranged to be axisymmetric with each other with respect to a sheet conveying locus in the sheet conveyance direction. 
     
     
         3 . The apparatus of  claim 1 , wherein with respect to a gap of a sheet passing space of the sheet conveyance path in a direction perpendicular to the surface of the sheet conveyed in the sheet conveyance path, when viewed in the first rotation shaft direction, the gap in a range from a crossing position of a sheet contact surface of the first sensor lever in the sheet conveyance direction and a sheet contact surface of the second sensor lever to the first rotation shaft is wider than the gap at a position adjacent to a sheet conveyance direction upstream side of the first rotation shaft in the sheet conveyance direction. 
     
     
         4 . The apparatus of  claim 3 , wherein an expanding inner wall surface of the sheet conveyance path has a shape gradually expanding from the sheet conveyance direction upstream side and then gradually narrowing, and
 the sheet contact surfaces of the first and the second sensor levers at the standby position enter the sheet conveyance path from the inner wall surface of the gradually expanding portion.   
     
     
         5 . The apparatus of  claim 3 , wherein with respect to the sheet passing space in the sheet conveyance path, when viewed in the first rotation shaft direction, the gap at leading edge positions of the first and the second sensor levers at the standby position in the sheet conveyance direction is wider than the gap at the position adjacent to the sheet conveyance direction upstream side of the first rotation shaft in the sheet conveyance direction. 
     
     
         6 . The apparatus of  claim 3 , wherein with respect to the sheet passing space in the sheet conveyance path, when viewed in the first rotation shaft direction, the gap at sheet conveyance direction downstream side end positions of the sheet contact surfaces of the first and the second sensor levers at the retract position is wider than the gap at the position adjacent to the sheet conveyance direction upstream side of the first rotation shaft in the sheet conveyance direction. 
     
     
         7 . The apparatus of  claim 1 , wherein with respect to the sheet passing space in the sheet conveyance path, when viewed in the first rotation shaft direction, the gap at a position of the first rotation shaft is wider than the gap at the position adjacent to the sheet conveyance direction upstream side of the first rotation shaft in the sheet conveyance direction. 
     
     
         8 . The apparatus of  claim 1 , further comprising a curl determination section to determine that the sheet is curled to a side of one of the first and the second sensors, in which a change of a detection result from one of ON and OFF to the other is earlier and a change of a detection result from the other to the one is slower. 
     
     
         9 . The apparatus of  claim 8 , wherein the curl determination section determines that a curl amount of the conveyed sheet is large when a time difference between a change timing of a detection result from one of ON and OFF of the first sensor to the other and a change timing of a detection result from one of ON and OFF of the second sensor to the other is large. 
     
     
         10 . The apparatus of  claim 1 , wherein the first and the second sensor are optical sensors. 
     
     
         11 . A curl detecting method of an image forming apparatus including a sheet conveyance path to guide a sheet in a sheet conveyance direction, a first sensor, a first sensor lever which rotates around a first rotation shaft substantially parallel to a surface perpendicular to the sheet conveyance direction and substantially parallel to a surface of the sheet conveyed in the sheet conveyance path, and rotates between a standby position where the first sensor lever crosses the sheet conveyance path obliquely from the first rotation shaft to a sheet conveyance direction downstream side of the first rotation shaft and the first sensor is turned one of ON and OFF and a retract position where the first sensor lever is retracted from the sheet conveyance path and the first sensor is turned the other of ON and OFF, a first urging section to urge the first sensor lever from the retract position side to the standby position side, a second sensor, a second sensor lever which rotates around a second rotation shaft substantially parallel to the surface perpendicular to the sheet conveyance direction and substantially parallel to the surface of the sheet conveyed in the sheet conveyance path, and rotates between a standby position where the second sensor lever crosses the sheet conveyance path obliquely from the second rotation shaft to the sheet conveyance direction downstream side of the second rotation shaft and the second sensor is turned one of ON and OFF and a retract position where the second sensor lever is retracted from the sheet conveyance path and the second sensor is turned the other of ON and OFF, and a second urging section to urge the second sensor lever from the retract position side to the standby position side, the curl detecting method comprising
 determining a curl state of the sheet conveyed in the sheet conveyance path based on detection results of the first sensor and the second sensor.   
     
     
         12 . The method of  claim 11 , wherein the first sensor lever and the second sensor lever are arranged to be axisymmetric with each other with respect to a sheet conveying locus in the sheet conveyance direction. 
     
     
         13 . The method of  claim 11 , wherein with respect to a gap of a sheet passing space of the sheet conveyance path in a direction perpendicular to the surface of the sheet conveyed in the sheet conveyance path, when viewed in the first rotation shaft direction, the gap in a range from a crossing position of a sheet contact surface of the first sensor lever in the sheet conveyance direction and a sheet contact surface of the second sensor lever to the first rotation shaft is wider than the gap at a position adjacent to a sheet conveyance direction upstream side of the first rotation shaft in the sheet conveyance direction. 
     
     
         14 . The method of  claim 13 , wherein an expanding inner wall surface of the sheet conveyance path has a shape gradually expanding from the sheet conveyance direction upstream side and then gradually narrowing, and
 the sheet contact surfaces of the first and the second sensor levers at the standby position enter the sheet conveyance path from the inner wall surface of the gradually expanding portion.   
     
     
         15 . The method of  claim 13 , wherein with respect to the sheet passing space in the sheet conveyance path, when viewed in the first rotation shaft direction, the gap at leading edge positions of the first and the second sensor levers at the standby position in the sheet conveyance direction is wider than the gap at the position adjacent to the sheet conveyance direction upstream side of the first rotation shaft in the sheet conveyance direction. 
     
     
         16 . The method of  claim 13 , wherein with respect to the sheet passing space in the sheet conveyance path, when viewed in the first rotation shaft direction, the gap at sheet conveyance direction downstream side end positions of the sheet contact surfaces of the first and the second sensor levers at the retract position is wider than the gap at the position adjacent to the sheet conveyance direction upstream side of the first rotation shaft in the sheet conveyance direction. 
     
     
         17 . The method of  claim 11 , wherein with respect to the sheet passing space in the sheet conveyance path, when viewed in the first rotation shaft direction, the gap at a position of the first rotation shaft in the sheet conveyance direction is wider than the gap at the position adjacent to the sheet conveyance direction upstream side of the first rotation shaft in the sheet conveyance direction. 
     
     
         18 . The method of  claim 11 , further comprising
 determining that the sheet is curled to a side of one of the first and the second sensors, in which a change of a detection result from one of ON and OFF to the other is earlier and a change of a detection result from the other to the one is slower.   
     
     
         19 . The method of  claim 11 , further comprising
 determining that a curl amount of the conveyed sheet is large when a time difference between a change timing of a detection result from one of ON and OFF of the first sensor to the other and a change timing of a detection result from one of ON and OFF of the second sensor to the other is large.   
     
     
         20 . The method of  claim 11 , wherein the first and the second sensor are optical sensors.