Sheet conveyor, image forming apparatus, and sheet conveying method

Abstract

According to one embodiment, a sheet conveyor includes a first roller 62 having a first cam 71 , rotating against the first roller, whose cam diameter simply increases and a second roller 63 having a second cam 72 , rotating against the second roller, whose cam diameter simply increases. The first cam contacts the second cam at their cam surfaces of increased cam diameters when the sheet is conveyed by the first and second rollers. When the rear end of the sheet goes out of the first and second rollers, a delay time is provided by the first and second cams until the first and second rollers directly contact one the other because the first and second cams rotate by the same distance from the contacting cam surfaces of increased cam diameter.

1 . A sheet conveyor comprising:
 a first roller which rotates in a first rotational direction;   a second roller which contacts with the first roller to rotate in a second rotational direction opposite to the first rotational direction, the second roller and the first roller conveying a sheet by holding the sheet therebetween;   a first cam configured to move with the first roller and to rotate against the first roller, the first cam having a cam surface of a first diameter when taking a first cam posture in a state that the sheet is not present between the first and second rollers, and having a cam surface of a second diameter greater than the first diameter when taking a second cam posture in a state that the sheet is present between the first and second rollers;   a second cam configured to move with the first roller and to rotate against the second roller, the second cam having a cam surface of the third diameter when taking a third cam posture in a state that the sheet is not present between the first and second rollers, the cam surface of the fourth diameter of the second cam when taking a fourth cam posture in a state that the sheet is present between the first and second rollers, the cam surface of the third diameter of the second cam contacting the cam surface of the first diameter of the first cam when the first cam takes the first cam posture and the second cam takes the third cam posture, the cam surface of the fourth diameter of the second cam further contacting the cam surface of the second diameter if the first cam when the first cam takes the second cam posture and the second cam takes the fourth cam posture; and   an urging member configured to apply a force to the first cam to rotate the first cam against the first roller from the first cam posture to the second cam posture and also apply a force to the second cam to rotate the second cam against the second roller from the third cam posture to the fourth cam posture.   
     
     
         2 . The sheet conveyor according to  claim 1 , further comprising:
 a second urging member that applies a pressure to the first cam and the second cam to forcibly contact one the other.   
     
     
         3 . The sheet conveyor according to  claim 1 , wherein the first cam has a first gear and the second cam has a second gear meshed with the first gear. 
     
     
         4 . The sheet conveyor according to  claim 3 , wherein the first cam rotates against the first roller and the second cam rotates against the second roller simultaneously as the first gear and the second gear are meshed with one the other. 
     
     
         5 . The sheet conveyor according to  claim 1 , wherein the first cam has a surface distance between the cam surface of the first diameter and the cam surface of the second diameter and the second cam has a surface distance equal to that of the first cam between the cam surface of the third diameter and the cam surface of the fourth diameter. 
     
     
         6 . The sheet conveyor according to  claim 1 , wherein the diameter of the first cam simply increases from the cam surface of the first diameter to the cam surface of the second diameter, the diameter of the second cam also simply increases from the cam surface of the third diameter to the cam surface of the fourth diameter. 
     
     
         7 . The sheet conveyor according to  claim 1 , wherein the urging member includes a first spring which applies the force to the first cam and a second spring which applies the force to the second cam. 
     
     
         8 . The sheet conveyor according to  claim 1 , wherein the first roller and the second roller contact one the other with a delay time after the rear end of the sheet is pressed out from the first roller and the second roller, the delay time being a time interval from the state that the cam surface of the second diameter of the first cam taking the second cam posture contacts the cam surface of the fourth diameter of the second cam taking the fourth cam posture to the state that the cam surface of the first diameter of the first cam taking the first cam posture contacts the cam surface of the third diameter of the second cam taking the third cam posture. 
     
     
         9 . An image forming apparatus comprising:
 a sheet feeding section configured to supply a sheet;   a sheet conveying section, configured to convey the sheet from the sheet feeding section to an image transfer position, which includes   a first roller which rotates in a first rotational direction,   a second roller which contacts with the first roller to rotate in a second rotational direction opposite to the first rotational direction, the second roller and the first roller conveying a sheet by holding the sheet therebetween,   a first cam configured to move with the first roller and to rotate against the first roller, the first cam having a cam surface of a first diameter when taking a first cam posture in a state that the sheet is not present between the first and second rollers, and having a cam surface of a second diameter greater than the first diameter when taking a second cam posture in a state that the sheet is present between the first and second rollers,   a second cam configured to move with the first roller and to rotate against the second roller, the second cam having a cam surface of the third diameter when taking a third cam posture in a state that the sheet is not present between the first and second rollers, the cam surface of the fourth diameter of the second cam when taking a fourth cam posture in a state that the sheet is present between the first and second rollers, the cam surface of the third diameter of the second cam contacting the cam surface of the first diameter of the first cam when the first cam takes the first cam posture and the second cam takes the third cam posture, the cam surface of the fourth diameter of the second cam further contacting the cam surface of the second diameter if the first cam when the first cam takes the second cam posture and the second cam takes the fourth cam posture, and   an urging member configured to apply a force to the first cam to rotate the first cam against the first roller from the first cam posture to the second cam posture and also apply a force to the second cam to rotate the second cam against the second roller from the third cam posture to the fourth cam posture; and   an image forming section which forms an image and transfers the image to the sheet conveyed by the sheet conveying section at the image transfer position.   
     
     
         10 . The image forming apparatus according to  claim 9 , further comprising:
 a second urging member that applies a pressure to the first cam and the second cam to forcibly contact one the other.   
     
     
         11 . The image forming apparatus according to  claim 9 , wherein the first cam has a first gear and the second cam has a second gear meshed with the first gear. 
     
     
         12 . The image forming apparatus according to  claim 11 , wherein the first cam rotates against the first roller and the second cam rotates against the second roller simultaneously as the first gear and the second gear are meshed with one the other. 
     
     
         13 . The image forming apparatus according to  claim 9 , wherein the first cam has a surface distance between the cam surface of the first diameter and the cam surface of the second diameter and the second cam has a surface distance equal to that of the first cam between the cam surface of the third diameter and the cam surface of the fourth diameter. 
     
     
         14 . The image forming apparatus according to  claim 9 , wherein the diameter of the first cam simply increases from the cam surface of the first diameter to the cam surface of the second diameter, and the diameter of the second cam also simply increases from the cam surface of the third diameter to the cam surface of the fourth diameter. 
     
     
         15 . The image forming apparatus according to  claim 9 , wherein the urging member includes a first spring which applies the force to the first cam and a second spring which applies the force to the second cam. 
     
     
         16 . The image forming apparatus according to  claim 9 , wherein the first roller and the second roller contact one the other with a delay time after the rear end of the sheet is pressed out from the first roller and the second roller, delay time being a time interval from the state that the cam surface of the second diameter of the first cam taking the second cam posture contacts the cam surface of the fourth diameter of the second cam taking the fourth cam posture to the state that the cam surface of the first diameter of the first cam taking the first cam posture contacts the cam surface of the third diameter of the second cam taking the third cam posture. 
     
     
         17 . A sheet conveying method which is carried out by a sheet conveyer comprising:
 a first roller which rotates in a first rotational direction;   a second roller which contacts with the first roller to rotate in a second rotational direction opposite to the first rotational direction, the second roller and the first roller conveying a sheet by holding the sheet therebetween;   a first cam configured to move with the first roller and to rotate against the first roller, the first cam having a cam surface of a first diameter when taking a first cam posture in a state that the sheet is not present between the first and second rollers, and having a cam surface of a second diameter greater than the first diameter when taking a second cam posture in a state that the sheet is present between the first and second rollers;   a second cam configured to move with the first roller and to rotate against the second roller, the second cam having a cam surface of the third diameter when taking a third cam posture in a state that the sheet is not present between the first and second rollers, the cam surface of the fourth diameter of the second cam when taking a fourth cam posture in a state that the sheet is present between the first and second rollers, the cam surface of the third diameter of the second cam contacting the cam surface of the first diameter of the first cam when the first cam takes the first cam posture and the second cam takes the third cam posture, the cam surface of the fourth diameter of the second cam further contacting the cam surface of the second diameter if the first cam when the first cam takes the second cam posture and the second cam takes the fourth cam posture; and   an urging member configured to apply a force to the first cam to rotate the first cam against the first roller from the first cam posture to the second cam posture and also apply a force to the second cam to rotate the second cam against the second roller from the third cam posture to the fourth cam posture, the method including,   rotating the first cam against the first roller and the second cam against the second roller so that the cam surface of the second diameter of the first cam comes to contact the cam surface of the fourth diameter of the second cam when the sheet is held between the first roller and the second roller;   conveying the sheet by holding the sheet between the first roller and the second roller; and   providing a delay time by the first cam and the second cam from the state that the cam surface of the second diameter of the first cam contacts the cam surface of the fourth diameter of the second cam until the cam surface of the first diameter of the first cam comes to contact the cam surface of the third diameter of the first cam comes to contact the cam surface of the third diameter of the second cam when the rear end of the sheet is pushed out from the first roller and the second roller.