An imaging system comprises a stirring-conveyance member to supply developer to a developing roller. The stirring-conveyance member includes a spiral structure to convey the developer and a reverse spiral structure disposed downstream the spiral structure in a conveying direction of the developer. The reverse spiral structure has a maximum outer diameter at an upstream end in the conveying direction and a minimum outer diameter at a downstream end in the conveying direction. The minimum outer diameter is approximately ⅗ or less, of the maximum outer diameter.

A developing device includes a developer container, a developer carrier, and a stirring/conveying member. The developer container stores developer containing toner. The developer carrier carries on its surface the toner in the developer container. The stirring/conveying member includes a rotary shaft rotatably supported on the developer container and a stirring blade formed around the outer circumferential face of the rotary shaft and stirs and conveys the developer in the developer container. The stirring/conveying member to be used can be selected from a plurality of types of stirring/conveying members with rotary shafts with different shaft diameters.

A powder transport apparatus includes a housing and first and second transport members. The housing includes first and second transport paths that are separated by a partition wall extending in one direction. The first and second transport paths are connected by first and second connection ports. The first and second connection ports are separated in the one direction with the partition wall interposed therebetween. The first transport member is provided in the first transport path. The first transport member transports powder. The second transport member is provided in the second transport path. The second transport member transports the powder. A transport force of the second transport member at a portion of the second transport member where the second transport member faces the first connection port is smaller than a transport force of the second transport member at a portion where the second transport member faces the partition wall.

A powder transport apparatus includes a housing and first and second transport members. The housing includes first and second transport paths that are separated by a partition wall extending in one direction. The first and second transport paths are connected by first and second connection ports. The first and second connection ports are separated in the one direction with the partition wall interposed therebetween. The first transport member is provided in the first transport path. The first transport member transports powder. The second transport member is provided in the second transport path. The second transport member transports the powder. A transport force of the second transport member at a portion of the second transport member where the second transport member faces the first connection port is smaller than a transport force of the second transport member at a portion where the second transport member faces the partition wall.

A conveyance mechanism which includes a rotation shaft extending in a direction along a first direction connecting first and second discharge ports that is rotatable with a rotation axis extending in the first direction. Wherein, a first rotation conveyance unit is disposed on the rotation shaft, and is rotatable together with the rotation shaft, conveys developer toward the first discharge port, and a second rotation conveyance unit is disposed on the rotation shaft, and is rotatable together with the rotation shaft, conveys developer toward the second discharge port. The second rotation conveyance unit is configured to provide a larger amount of conveyance than the first rotation conveyance unit.

A developing device includes a first conveyance screw including a first blade portion and a second blade portion, the first blade portion configured to convey the developer in a first direction, the second blade portion being disposed downstream of the first blade portion in the first direction and configured to convey the developer in a second direction, a discharge path through which the developer passes to be discharged through a discharge port, and a magnet. The first conveyance screw includes a third blade portion disposed in the discharge path and configured to convey the developer in the first direction. The discharge port is disposed downstream of an upstream end of the third blade portion in the first direction. The magnet is disposed downstream of an upstream end of the discharge port in the first direction so as to overlap with the discharge port in the first direction.

A developing device includes a developer container, a developer carrier, and a stirring/conveying member. The developer container stores developer containing toner. The developer carrier carries on its surface the toner in the developer container. The stirring/conveying member includes a rotary shaft rotatably supported on the developer container and a stirring blade formed around the outer circumferential face of the rotary shaft and stirs and conveys the developer in the developer container. The stirring/conveying member to be used can be selected from a plurality of types of stirring/conveying members with rotary shafts with different shaft diameters.

A developing device includes a developer bearer and a stirring conveyor. The stirring conveyor includes a first conveying chamber including a conveying member and a second conveying chamber to receive the developer from an end of the first conveying chamber. The conveying member includes a forward winding blade, a reverse winding blade, and a shaft portion on which the forward winding blade and the reverse winding blade are mounted with a space therebetween. A circumferential phase of the conveying member at a start position of the reverse winding blade is different from a circumferential phase of the conveying member at an end position of the forward winding blade. The conveying member is disposed in the first conveying chamber so that the space is opposite a portion at which the second conveying chamber receives the developer from the end of the first conveying chamber.

A developing device includes: a housing having a first transport path through which developer is supplied, a second transport path adjoining the first transport path with a first partition wall therebetween, and a first communication path communicating with the second transport path on a downstream side in a developer transport direction in the first transport path; a first transport member disposed in the first transport path and having an axially rotatable first rotary shaft and a first spiral blade projecting from an outer circumferential surface of the first rotary shaft; a second transport member disposed in the second transport path and having an axially rotatable second rotary shaft and a second spiral blade projecting from an outer circumferential surface of the second rotary shaft; and a first blade member projecting from the outer circumferential surface of the first rotary shaft, at a position facing the first communication path, the blade member discharging the developer onto the second transport path from above the first rotary shaft in the first transport path with the rotation of the first rotary shaft.

A developing device includes a first conveyance screw including a first blade portion and a second blade portion, the first blade portion configured to convey the developer in a first direction, the second blade portion being disposed downstream of the first blade portion in the first direction and configured to convey the developer in a second direction, a discharge path through which the developer passes to be discharged through a discharge port, and a magnet. The first conveyance screw includes a third blade portion disposed in the discharge path and configured to convey the developer in the first direction. The discharge port is disposed downstream of an upstream end of the third blade portion in the first direction. The magnet is disposed downstream of an upstream end of the discharge port in the first direction so as to overlap with the discharge port in the first direction.