Sheet conveyance apparatus and image forming apparatus

Abstract

A sheet conveyance apparatus includes a first conveyance unit, a second conveyance unit, a drive source, and a drive transmission unit. When the first conveyance unit conveys a sheet in a second conveyance direction and the second conveyance unit does not convey the sheet, the drive transmission unit enters a second transmission state in such a manner that the first conveyance unit conveys the sheet at a first conveyance speed. The second conveyance unit conveys the sheet at a second conveyance speed higher than the first conveyance speed. From a contact state in which the sheet conveyed in the second conveyance direction is in contact with both the first conveyance unit and the second conveyance unit is caused, until the contact state is released, the drive transmission unit is kept in a non-transmission state.

What is claimed is: 
     
         1 . A sheet conveyance apparatus comprising:
 a first conveyance unit configured to convey a sheet in a first conveyance direction and a second conveyance direction opposite to the first conveyance direction, the first conveyance unit being configured to convey the sheet in the second conveyance direction after conveying the sheet in the first conveyance direction;   a second conveyance unit configured to convey the sheet in the second conveyance direction;   a drive source configured to drive the first conveyance unit; and   a drive transmission unit configured to enter a first transmission state of transmitting drive force of the drive source in such a manner that the first conveyance unit conveys the sheet in the first conveyance direction, a second transmission state of transmitting the drive force in such a manner that the first conveyance unit conveys the sheet in the second conveyance direction, and a non-transmission state in which the drive force is not transmitted to the first conveyance unit,   wherein, when the first conveyance unit conveys the sheet in the second conveyance direction and the second conveyance unit does not convey the sheet, the drive transmission unit enters the second transmission state in such a manner that the first conveyance unit conveys the sheet at a first conveyance speed with the drive force,   wherein the second conveyance unit conveys the sheet at a second conveyance speed higher than the first conveyance speed, and   wherein, from a contact state in which the sheet conveyed in the second conveyance direction is in contact with both the first conveyance unit and the second conveyance unit is caused until the contact state is released, the drive transmission unit is kept in the non-transmission state in such a manner that the first conveyance unit is allowed to be rotated by the sheet conveyed at the second conveyance speed.   
     
     
         2 . The sheet conveyance apparatus according to  claim 1 ,
 wherein the drive transmission unit includes a first member connected to the drive source, and a second member arranged coaxially with the first member and connected to the first conveyance unit,   wherein the first member includes a first to-contact portion and a second to-contact portion,   wherein the second member includes a first to-be-contacted portion to be contacted by the first to-contact portion, and a second to-be-contacted portion to be contacted by the second to-contact portion, and   wherein the drive transmission unit is configured to enter the first transmission state by the first to-contact portion and the first to-be-contacted portion coming into contact with each other, to enter the second transmission state by the second to-contact portion and the second to-be-contacted portion coming into contact with each other, and to enter the non-transmission state by the first to-contact portion and the first to-be-contacted portion being separated from each other and the second top-contact portion and the second to-be-contacted portion being separated from each other.   
     
     
         3 . The sheet conveyance apparatus according to  claim 2 , wherein an amount of relative rotation of the first member and the second member for the drive transmission unit to transition from the second transmission state to the first transmission state is larger than an amount of relative rotation of the first member and the second member in a period in which both the first conveyance unit and the second conveyance unit convey the sheet in the second conveyance direction. 
     
     
         4 . The sheet conveyance apparatus according to  claim 2 ,
 wherein a rotational direction of the first member and the second member that is set when the first conveyance unit conveys the sheet in the first conveyance direction is a first rotational direction, and a rotational direction of the first member and the second member that is set when the first conveyance unit conveys the sheet in the second conveyance direction is a second rotational direction,   wherein the first member includes a protruding portion protruding in a rotational axis direction of the first member and the second member, the first to-contact portion is an end portion of the protruding portion in the first rotational direction, and the second to-contact portion is an end portion of the protruding portion in the second rotational direction,   wherein the second member includes a recess portion that accepts the protruding portion, the first to-be-contacted portion is an end portion of the recess portion in the first rotational direction, and the second to-be-contacted portion is an end portion of the recess portion in the second rotational direction.   
     
     
         5 . The sheet conveyance apparatus according to  claim 4 , wherein a central angle between the first to-contact portion and the second to-contact portion with respect to a rotational axis line of the first member and the second member is smaller than a central angle between the first to-be-contacted portion and the second to-be-contacted portion with respect to the rotational axis line. 
     
     
         6 . The sheet conveyance apparatus according to  claim 4 ,
 wherein the protruding portion is one of a plurality of protruding portions arranged along a circular arc centered on a rotational axis line of the first member and the second member, and   wherein the recess portion is one of a plurality of recess portions arranged along the circular arc each to respectively engage with a protruding portion of the plurality of protruding portions.   
     
     
         7 . The sheet conveyance apparatus according to  claim 2 ,
 wherein a rotational direction of the first member and the second member that is set when the first conveyance unit conveys the sheet in the first conveyance direction is a first rotational direction, and a rotational direction of the first member and the second member that is set when the first conveyance unit conveys the sheet in the second conveyance direction is a second rotational direction,   wherein the second member includes a protruding portion protruding in a rotational axis direction of the first member and the second member, the first to-be-contacted portion is an end portion of the protruding portion in the first rotational direction, and the second to-be-contacted portion is an end portion of the protruding portion in the second rotational direction, and   wherein the first member includes a recess portion that accepts the protruding portion, the first to-contact portion is an end portion of the recess portion in the first rotational direction, and the second to-contact portion is an end portion of the recess portion in the second rotational direction.   
     
     
         8 . The sheet conveyance apparatus according to  claim 2 ,
 wherein a rotational direction of the first member and the second member that is set when the first conveyance unit conveys the sheet in the first conveyance direction is a first rotational direction, and a rotational direction of the first member and the second member that is set when the first conveyance unit conveys the sheet in the second conveyance direction is a second rotational direction, and   wherein, when the contact state is caused, the second to-be-contacted portion gets away from the second to-contact portion toward the second rotational direction.   
     
     
         9 . The sheet conveyance apparatus according to  claim 2 ,
 wherein the first conveyance unit includes a roller configured to rotate by receiving the drive force from the drive transmission unit,   wherein the roller rotates at a first angular speed when the first conveyance unit conveys the sheet at the first conveyance speed,   wherein, when the contact state is caused, the roller rotates at a second angular speed higher than the first angular speed following the sheet conveyed by the second conveyance unit at the second conveyance speed, and   wherein, the roller rotating at the second angular speed rotates the second member relatively relative to the first member, and changes a state of the drive transmission unit from the second transmission state to the non-transmission state.   
     
     
         10 . The sheet conveyance apparatus according to  claim 9 , wherein the first member and the second member rotate around a rotational axis line of the roller. 
     
     
         11 . The sheet conveyance apparatus according to  claim 9 , wherein the first member and the second member rotate around a rotational axis line different from a rotational axis line of the roller. 
     
     
         12 . The sheet conveyance apparatus according to  claim 1 , wherein the second conveyance unit is arranged downstream of the first conveyance unit in the second conveyance direction. 
     
     
         13 . The sheet conveyance apparatus according to  claim 12 , further comprising:
 a first guide that is arranged between the first conveyance unit and the second conveyance unit in the second conveyance direction, and configured to guide the sheet; and   a second guide facing the first guide across space through which the sheet passes,   wherein the first conveyance unit is a first roller pair having a first nip at which the sheet is nipped,   wherein the second conveyance unit is a second roller pair having a second nip at which the sheet is nipped, and   wherein the first guide includes a portion protruding toward the second guide from an imaginary straight line connecting the first nip and the second nip when viewed in a rotational axis direction of the first roller pair.   
     
     
         14 . The sheet conveyance apparatus according to  claim 13 ,
 wherein the first conveyance unit is arranged on a second conveyance path on which the sheet is reversely conveyed to form an image on a second surface of the sheet with an image formed on a first surface while the sheet passes through a first conveyance path,   wherein the second conveyance unit is arranged on a third conveyance path on which the sheet reversely conveyed by the first conveyance unit is conveyed again toward the first conveyance path, and   wherein the first guide is arranged to face the second surface of the sheet conveyed from the first conveyance unit toward the second conveyance unit.   
     
     
         15 . The sheet conveyance apparatus according to  claim 1 , wherein the second conveyance unit is arranged upstream of the first conveyance unit in the second conveyance direction. 
     
     
         16 . An image forming apparatus comprising:
 the sheet conveyance apparatus according to  claim 1 ; and   an image forming unit configured to form an image on the sheet conveyed by the sheet conveyance apparatus.