Developing device and image forming apparatus including the same

1. A developing device comprising:

a developing container partitioned into a stirring-transport chamber, a supplying-transport chamber, and a collecting-transport chamber that are arranged substantially in parallel with one another, for storing a two-component developer including a carrier and a toner;

a developer carrying member supported rotatably by the developing container, for carrying developer on a surface thereof;

a supplying-transport member, located within the supplying-transport chamber, for stirring and transporting developer in a transport direction along an axial axis of the developer carrying member and supplying developer stirred and transported thereby to the developer carrying member;

a stirring-transport member located within the stirring-transport chamber, for stirring and transporting developer in a direction reverse to the transport direction of the supplying-transport member;

a collecting-transport member located within the collecting-transport chamber, for stirring and transporting developer collected from the developer carrying member in the same direction as the transport direction of the supplying-transport member;

a first developer passage provided between the supplying-transport chamber and the stirring-transport chamber, for passing developer from the stirring-transport chamber to the supplying-transport chamber;

a second developer passage provided between the supplying-transport chamber and the stirring-transport chamber, for passing developer from the supplying-transport chamber to the stirring-transport chamber; and

a communication portion provided at a downstream end of the collecting-transport chamber and on an upstream side of the second developer passage in the transport direction of the supplying-transport member, for passing developer from the collecting-transport chamber to the supplying-transport chamber,

wherein a developer transporting speed of the collecting-transport member differs from a developer transporting speed of the supplying-transport member,

wherein the collecting-transport member passes developer to the supplying-transport chamber also from a region upstream of the communication portion in the transport direction of the supplying-transport member,

wherein a clearance is provided along a longitudinal direction of the collecting-transport member above a partition wall that partitions between the collecting-transport chamber and the supplying-transport chamber, and

wherein the clearance becomes wider from an upstream side toward a downstream side in the transport direction of the supplying-transport member.

2. A developing device according to claim 1 , wherein the collecting-transport chamber is located in a higher position than the supplying-transport chamber.

3. A developing device according to claim 1 , wherein the developer transporting speed of the collecting-transport member is larger than the developer transporting speed of the supplying-transport member.

4. A developing device according to claim 3 , wherein the collecting-transport member and the supplying-transport member each comprise a rotary shaft and a helical blade formed on an outer peripheral surface of the rotary shaft, the helical blade of the collecting-transport member having an outer diameter smaller than an outer diameter of the helical blade of the supplying-transport member, the collecting-transport member exhibiting a rotational speed faster than the supplying-transport member.

5. A developing device according to claim 1 , wherein the partition wall has a plurality of window-like opening portions along a longitudinal direction of the collecting-transport member.

6. A developing device according to claim 1 , further comprising a developer discharge portion provided at the downstream end of the supplying-transport chamber for discharging surplus developer.

7. An image forming apparatus, comprising the developing device according to claim 1 .