Sheet conveying apparatus and image forming apparatus

Abstract

In case a belt member of an endless intermediate transfer belt causes an improper running such as a skewed or zigzag movement, the belt member contacts belt contact detecting portions on both ends of a belt control roller and causes friction thereon. A difference in the frictional forces on the belt contact detecting portions causes a pivoting of a rotary axis of the belt control roller about a roller support member formed by a supporting shaft and a bearing at the center, thereby correcting the belt member in running operation to an appropriate position.

1 . A sheet conveying apparatus comprising: 
 an endless belt for conveying a recording medium sheet;    a belt control roller which constitutes at least one of plural rollers supporting the belt and serves to correct an improper running of the belt caused by a skew or zigzag movement thereof;    a roller support member for supporting the belt control roller in an angularly variable manner about a fulcrum at a longitudinal center of the roller; and    first and second belt contact detecting portions provided on both end portions of the belt control roller so as to come into contact with and to be subjected to a friction by the belt itself in case of an improper running thereof;    wherein the belt control roller causes an angular change of a rotary axis thereof about the roller supporting member as a fulcrum according to a difference between the frictional forces of the first and second belt contact detecting portions.    
   
   
       2 . A sheet conveying apparatus according to  claim 1 , wherein the first and second belt contact detecting portions are provided at a same distance with respect to the roller support member.  
   
   
       3 . A sheet conveying apparatus according to  claim 1 , further comprising urging means which urges a rotary axis of the belt control roller toward a base position where the rotary axis becomes parallel to those of the plural rollers.  
   
   
       4 . An image forming apparatus comprising a sheet conveying apparatus according to  claim 1 , and an image forming part for recording an image on a sheet conveyed by the sheet conveying apparatus.  
   
   
       5 . A belt guiding apparatus comprising: 
 a roller maintained in contact with and driven by a moving belt;    a support member for rotatably supporting the roller;    support means which pivotably supports the support member in such a manner that the roller can change a direction of a rotary axis thereof;    a first friction member so provided as to pivot integrally with the support member and receiving, from the belt, a frictional force which becomes larger as the belt is displaced from a predetermined position to a first lateral direction; and    a second friction member so provided as to pivot integrally with the support member and receiving, from the belt, a frictional force which becomes larger as the belt is displaced from the predetermined position to a second lateral direction opposite to the first lateral direction;    wherein the support member pivots together with the first and second friction members, by the frictional force which the first or second friction member receives from the belt, to change the direction of the rotary axis of the roller thereby correcting the displacement of the belt.    
   
   
       6 . A belt guiding apparatus according to  claim 5 , wherein the first and second friction members are unrotatably fixed to the support member.  
   
   
       7 . A belt guiding apparatus according to  claim 5 , wherein the first friction member has a larger contact area with the belt when the belt is displaced from the predetermined position to the first lateral direction.  
   
   
       8 . A belt guiding apparatus according to  claim 5 , wherein the second friction member has a larger contact area with the belt when the belt is displaced from the predetermined position to the second lateral direction.  
   
   
       9 . A belt guiding apparatus according to claim  5 , wherein the first and second friction members are positioned at lateral sides of the roller.  
   
   
       10 . A belt guiding apparatus according to  claim 5 , wherein a rotation center of the support member is positioned at a longitudinal center of the roller.  
   
   
       11 . A belt guiding apparatus according to  claim 5 , wherein a distance from the rotary center of the support member to the first friction member is equal to a distance from the rotary center of the support member to the second friction member.  
   
   
       12 . A belt guiding apparatus according to  claim 5 , wherein a distance from the first friction member to the second friction member is equal to or larger than a width of the belt.  
   
   
       13 . A belt guiding apparatus according to  claim 5 , wherein a distance from the first friction member to the second friction member is equal to or smaller than a width of the belt.  
   
   
       14 . A recording medium conveying apparatus comprising: 
 a belt for conveying a recording medium;    plural rollers for supporting the belt;    a control roller maintained in contact with and driven by the moving belt;    a support member for rotatably supporting the control roller;    support means which pivotably supports the support member in such a manner that the control roller can change a direction of a rotary axis thereof;    a first friction member so provided as to pivot integrally with the support member and receiving, from the belt, a frictional force which becomes larger as the belt is displaced from a predetermined position to a first lateral direction; and    a second friction member so provided as to pivot integrally with the support member and receiving, from the belt, a frictional force which becomes larger as the belt is displaced from the predetermined position to a second lateral direction opposite to the first lateral direction;    wherein the support member pivots together with the first and second friction members, by the frictional force which the first or second friction member receives from the belt, to change the direction of the rotary axis of the roller thereby correcting the displacement of the belt.    
   
   
       15 . An image forming apparatus comprising: 
 a belt for conveying a recording medium;    plural rollers for supporting the belt;    recording means which records an image on the recording medium conveyed by the belt;    a control roller maintained in contact with and driven by the moving belt;    a support member for rotatably supporting the control roller;    support means which pivotably supports the support member in such a manner that the control roller can change a direction of a rotary axis thereof;    a first friction member so provided as to pivot integrally with the support member and receiving, from the belt, a frictional force which becomes larger as the belt is displaced from a predetermined position to a first lateral direction; and    a second friction member so provided as to pivot integrally with the support member and receiving, from the belt, a frictional force which becomes larger as the belt is displaced from the predetermined position to a second lateral direction opposite to the first lateral direction;    wherein the support member pivots together with the first and second friction members, by the frictional force which the first or second friction member receives from the belt, to change the direction of the rotary axis of the roller thereby correcting the displacement of the belt.