Abstract: In an image forming apparatus, a developing device is disposed adjacent to a belt-like photosensitive member. A rotary type developing device has a hollow cylindrical casing rotatable around a shaft having a central portion for rotation. The developing device includes a casing which is rotated in a predetermined direction, and four partitions which divide the casing to make four developing units which extend radially outward from the shaft. A toner storing section or hopper is provided on one side of the developing device, i.e., on a front side of the image forming apparatus, and a toner cartridge is detachable from a top of the hopper, and the toner cartridge is exchanged when an end signal of the toner is detected by a sensor in the casing. The toner hopper is filled by new toner from the toner cartridge, and the toner is carried by conveyor members, which control an amount of the toner in the casing, and a supply roller supplies the toner to a developing roller.

Abstract: A developing device capable of obviating the cohesion of toner and reducing the amount of dead toner is disclosed. The device has a developing unit accommodating a first and a second screw therein. The first and second screws extend from the toner hopper to the other longitudinal end of the developing unit in parallel to a developing roller and a supply roller. The first screw feeds toner from a toner hopper to a developing section. The second screw collects toner not contributed to development from the developing section and returns it to the first screw for recirculation. In this configuration, the collected toner and dead toner aggregating in the lower portion of the developing unit are forcibly moved to the developing section. The direction in which the screw portion of the second screw is inclined may be partly reversed to form a reverse transfer portion. Alternatively, a part of a casing adjoining the hopper may be implemented as a slant.

Abstract: In an image forming apparatus, a rotary developing device effects development by revolving a plurality of developing sections around a rotary shaft until any one of them reaches a developing position where it faces an image carrier. Cartridges are respectively mounted to hoppers included in the developing sections. Guides are provided on the inner periphery of each cartridge in order to guide toner, moving due to the revolution or the developing device, toward a toner outlet formed in the cartridge. Even when the amount of toner remaining in the cartridge is small, the entire toner is replenished into the associated hopper and fully consumed.