Sheet feeding unit

Abstract

A sheet feeding unit including a feeding system, a controlling system to control the feeding system, and a detecting system, which is provided in between the target position and the feeding system and is adapted to detect a predetermined position of the recording sheet at a detecting position, is provided. The controlling system controls the feeding system to carry the recording sheet at a second feeding speed, at a third feeding speed, and at a first feeding speed, so that a period in which the predetermined position of the recording sheet being carried at the first feeding speed changed from the third feeding speed is carried from the detecting position to the target position is equivalent to a period in which the predetermined position of the recording sheet being carried constantly at the first feeding speed is carried from the detecting position to the target position.

1 . A sheet feeding unit, comprising; 
 a feeding system, which is adapted to carry a recording sheet to a target position on a feeding path of the recording sheet,    a controlling system, which is adapted to control the feeding system so that the recording sheet is carried at a first feeding speed, at a second feeding speed being slower than the first feeding speed, and at a third feeding speed being faster than the first feeding speed, and    a detecting system, which is provided in between the target position and the feeding system and is adapted to detect a predetermined position of the recording sheet at a detecting position,    wherein the controlling system controls the feeding system to carry the recording sheet at the second feeding speed until the detecting system detects the predetermined position of the recording sheet, at the third feeding speed changed from the second feeding speed, and at the first feeding speed changed from the third feeding speed, so that a period in which the predetermined position of the recording sheet being carried at the first feeding speed changed from the third feeding speed is carried from the detecting position to the target position is equivalent to a period in which the predetermined position of the recording sheet being carried constantly at the first feeding speed is carried from the detecting position to the target position.    
   
   
       2 . The sheet feeding unit according to  claim 1 , wherein the feeding system is adapted to carry the recording sheet by a force provided from a motor.  
   
   
       3 . The sheet feeding unit according to  claim 2 , wherein the motor is a stepping motor.  
   
   
       4 . The sheet feeding unit according to  claim 3 , wherein the second feeding speed is caused by torque within a pull-in torque range of the stepping motor.  
   
   
       5 . The sheet feeding unit according to  claim 1 , wherein the predetermined position of the recording sheet includes a front end of the recording sheet.  
   
   
       6 . The sheet feeding unit according to  claim 1 , wherein a reflectance of the predetermined position of the recording sheet is different from a reflectance of the other area of the recording sheet excluding the predetermined position.  
   
   
       7 . The sheet feeding unit according to  claim 1 , wherein a transmittance of the predetermined position of the recording sheet is different from a transmittance of the other area of the recording sheet excluding the predetermined position.  
   
   
       8 . The sheet feeding unit according to  claim 1 , wherein the recording sheet is carried at the first feeding speed when the recording sheet is at the target position on the feeding path.  
   
   
       9 . An image forming apparatus, comprising; 
 a sheet feeding unit, which is adapted to carry a recording sheet and to guide the recording sheet in a target position on a feeding path in the image forming apparatus, and    an image forming unit, which is adapted to form an image on the recording sheet at the target position on the feeding path,    wherein the sheet feeding unit includes a feeding system, which is adapted to carry the recording sheet to the target position on the feeding path of the recording sheet, a controlling system, which is adapted to control the feeding system so that the recording sheet is carried at a first feeding speed, at a second feeding speed being slower than the first feeding speed, and at a third feeding speed being faster than the first feeding speed, and a detecting system, which is provided in between the target position and the feeding system and is adapted to detect a predetermined position of the recording sheet at a detecting position,    wherein the controlling system controls the feeding system to carry the recording sheet at the second feeding speed until the detecting system detects the predetermined position of the recording sheet, at the third feeding speed changed from the second feeding speed, and at the first feeding speed changed from the third feeding speed, so that a period in which the predetermined position of the recording sheet being carried at the first feeding speed changed from the third feeding speed is carried from the detecting position to the target position is equivalent to a period in which the predetermined position of the recording sheet being carried constantly at the first feeding speed is carried from the detecting position to the target position.    
   
   
       10 . A sheet feeding unit comprising; 
 a feed roller, which is adapted to carry a recording sheet to a predetermined location on a feeding path,    a stepping motor, which is adapted to rotate the feed roller,    a controlling system, which is adapted to control a feeding speed of the recording sheet being carried by the feed roller,    a detecting system, which is adapted to detect a predetermined position of the recording sheet,    a retainer system, which is adapted to retain the recording sheet at an upstream side of the recording sheet from the feed roller with respect to a normal feeding direction of the recording sheet, and    a load adjusting system, which is provided on the feeding path in between the feed roller and the retainer system so that a load applied on the feed roller to carry the recording sheet is adjusted,    wherein the controlling system is adapted to switch the feeding speed of the recording sheet from a first feeding speed to a second feeding speed before the predetermined position of the recording sheet is detected by the detecting system, the first feeding speed corresponding to a rotation frequency that is within a pull-in torque range of the stepping motor, the second feeding speed being faster than the first feeding speed and corresponding to a rotation speed that is out of the pull-in torque range of the stepping motor, and    wherein the load adjusting system is adapted to reduce the load applied on the feed roller to carry the recording sheet when the feeding speed of the recording sheet is switched from the first feeding speed to the second feeding speed.    
   
   
       11 . The sheet feeding unit according to  claim 10 , wherein a part of the feeding path between the feed roller and the retainer system is shortened so that the load applied on the feed roller to carry the recording sheet is reduced.  
   
   
       12 . The sheet feeding unit according to  claim 10 , 
 wherein the load adjusting system is provided with a guide roller to guide the recording sheet in the feeding path, and    wherein the guide roller is adapted to be shifted so that the part of the feeding path between the feed roller and the retainer system is shortened when the feeding speed of the recording sheet is switched from the first feeding speed to the second feeding speed.    
   
   
       13 . The sheet feeding unit according to  claim 12 , 
 wherein the load adjusting system includes a supporting member, which rotatably supports the guide roller and swingably rotates about an axis, and    wherein the supporting member is attracted in a direction so that the part of the feeding path between the feed roller and the retainer system is elongated by the attraction.    
   
   
       14 . The sheet feeding unit according to  claim 9 , wherein the recording sheet is in a continuous form, and wherein the retainer system retains the recording sheet by rolling the recording sheet around the retainer system.  
   
   
       15 . An image forming apparatus, comprising; 
 a sheet feeding unit, which is adapted to carry a recording sheet and to guide the recording sheet to a predetermined location on a feeding path in the image forming apparatus, and    an image forming unit, which is adapted to form an image on the recording sheet at the predetermined location on the feeding path,    wherein the sheet feeding unit includes a feed roller, which is adapted to carry the recording sheet to the predetermined location on the feeding path, a stepping motor, which is adapted to rotate the feed roller, a controlling system, which is adapted to control a feeding speed of the recording sheet being carried by the feed roller, a detecting system, which is adapted to detect a predetermined position of the recording sheet, a retainer system, which is adapted to retain the recording sheet at an upstream side of the recording sheet from the feed roller with respect to a normal feeding direction of the recording sheet, and a load adjusting system, which is provided on the feeding path in between the feed roller and the retainer system so that a load applied on the feed roller to carry the recording sheet is adjusted,    wherein the controlling system is adapted to switch the feeding speed of the recording sheet from a first feeding speed to a second feeding speed before the predetermined position of the recording sheet is detected by the detecting system, the first feeding speed corresponding to a rotation frequency that is within a pull-in torque range of the stepping motor, the second feeding speed being faster than the first feeding speed and corresponding to a rotation speed that is out of the pull-in torque range of the stepping motor, and    wherein the load adjusting system is adapted to reduce the load applied on the feed roller to carry the recording sheet when the feeding speed of the recording sheet is switched from the first feeding speed to the second feeding speed.