Developing device and image forming apparatus including the same

A developing device to be installed in an electrophotographic image forming apparatus including a photoconductor drum that is to have an electrostatic latent image formed on a surface thereof, the developing device comprising:

• a developer vessel that accommodates a developer containing a toner and a carrier;
• a toner supply port for supplying the toner into the developer vessel;
• a developing roller that is disposed in the developer vessel and that rotates while carrying the developer to supply the toner onto the surface of the photoconductor drum having the electrostatic latent image formed thereon;
• a developer conveying passage that is disposed between a position in the developer vessel where the toner is supplied and the developing roller;
• and
• a developer conveying helical member and a developer scooping member that are rotatably disposed in the developer conveying passage to convey the developer in the developer conveying passage to the developing roller while agitating the developer, wherein
• the developer conveying passage includes:
• a first developer conveying passage associated with the toner supply port and a second developer conveying passage associated with the developing roller, the first developer conveying passage and the second developer conveying passage being defined by a partitioning plate extending in parallel to an axial direction of the developing roller;
• and a first communicating path and a second communicating path that establish a communication between the first developer conveying passage and the second developer conveying passage at opposite sides in the axial direction,
• the developer conveying helical member includes a first developer conveying helical member disposed in the first developer conveying passage and a second developer conveying helical member disposed in the second developer conveying passage,
• the first developer conveying helical member includes a first rotary shaft rotatably disposed in the first developer conveying passage and a first helical blade fixed to the first rotary shaft,
• the second developer conveying helical member includes a second rotary shaft rotatably disposed in the second developer conveying passage and a second helical blade fixed to the second rotary shaft,
• the developer scooping member includes a first developer scooping member disposed near the first communicating path to send the developer in the first developer conveying passage into the second developer conveying passage, and a second developer scooping member disposed near the second communicating path to send the developer in the second developer conveying passage into the first developer conveying passage,
• the first developer scooping member includes a third rotary shaft rotatably disposed in the first developer conveying passage and near the first communicating path and a first scooping blade fixed to the third rotary shaft so as to avoid any contact with the first and second helical blades, and
• the second developer scooping member includes a fourth rotary shaft rotatably disposed in the second developer conveying passage and near the second communicating path and a second scooping blade fixed to the fourth rotary shaft so as to avoid any contact with the first and second helical blades, and
• the first developer conveying helical member and the second developer conveying helical member convey the developer in directions opposite to each other and the first developer scooping member and the second developer scooping member convey the developer in directions opposite to each other, such that the developer circulates through the first developer conveying passage and the second developer conveying passage.