Image forming apparatus and developing unit

An electrophotographic image forming apparatus, including a first print mode in which a binary image is formed and a second print mode in which a grayscale image is formed, the apparatus comprising:

• a developing device including a developer reservoir for accommodating a mixed developer including two types of toner having a generally identical hue and different reflection densities;
• a replenishment device including a first toner container for accommodating toner with a high reflection density and a second toner container for accommodating said toner and a low reflection density toner for replenishing the toners to the developer reservoir;
• a first detector for detecting whether each of the toner containers is completely empty of toner;
• a second detector for detecting whether the developer reservoir is nearly or completely empty of mixed developer;
• and
• a controller for controlling the replenishment device based on the detection result of the first and the second detectors and allows or prohibits a printing operation based on the printing mode.

An electrophotographic image forming apparatus, comprising:

• a developing device including a developer reservoir for accommodating a mixed developer including two types of toner having a generally identical hue and different reflection densities;
• a replenishment device for replenishing the two types of toner to the developer reservoir;
• a unit for determining a mixture ratio of the two types of toner in the developer reservoir;
• a detector for detecting whether the developer reservoir is nearly empty of mixed developer;
• and
• a controller for controlling the replenishment device based on the mixture ratio determined by the unit and the detection result acquired by the detector so that the mixture ratio falls within a predetermined range.

A developing unit, comprising:

• a developing device including a developer reservoir for accommodating a mixed developer including two types of toner having a generally identical hue and different reflection densities;
• a replenishment device for replenishing the two types of toner to the developer reservoir;
• a unit for determining a mixture ratio of the two types of toner in the developer reservoir;
• a detector for detecting whether the developer reservoir is nearly empty of mixed developer;
• and
• a controller for controlling the replenishment device based on the mixture ratio determined by the unit and the detection result acquired by the detector so that the mixture ratio falls within a predetermined range.

An electrophotographic image forming apparatus, comprising:

• a developing device including a developer reservoir to accommodate a mixed developer including a plurality of types of toner having a generally identical hue and different reflection densities;
• and
• a replenishment device to replenish said plurality of types of toner to the developer reservoir, the replenishment device including a first toner container to accommodate at least one type of toner out of said plurality of types of toner, and a second toner container to accommodate at least one other type of toner out of said plurality of types of toner,
• wherein the first toner container accommodates a first toner mixture including said plurality of types of toner mixed with a first mixture ratio and the second toner container accommodates a second toner mixture including said plurality of types of toner mixed with a second mixture ratio.

An electrophotographic image forming apparatus, comprising:

• a developing device including a developer reservoir to accommodate a mixed developer including a plurality of types of toner having a generally identical hue and different reflection densities;
• and
• a replenishment device to replenish said plurality of types of toner to the developer reservoir, the replenishment device including a first toner container to accommodate at least one type of toner out of said plurality of types of toner, and a second toner container to accommodate at least one other type of toner out of said plurality of types of toner,
• wherein the first toner container accommodates only one type of toner out of said plurality of types of toner and the second toner container accommodates a toner mixture including mixed two or more types of toner out of said plurality of types of toner.