| 摘要 |
PURPOSE:To maintain toner concentration to a proper value even when the thickness of the layer of a magnetic brush is changed by adjusting a doctor blade by providing a very thin toner concentration sensor inside of the doctor blade. CONSTITUTION:A toner concentration sensor 11a is provided on the side of a doctor blade 10 that faces developer 2. The sensor 11a is provided with coils 13, 14 near the center of a non-magnetic substrate 12, and the coils are connected mutually to form a primary coil. A detecting coil 15 is provided on one face of the substrate 12, and a reference coil 16 is provided on another face, and an adjusting member 17 that regulates the degree of coupling is provided between the two coils. The detecting coil 15 and reference coil 16 are connected to become opposite phase to form a secondary coil, and a differential transformer is formed as a primary coil. When toner concentration became less by consumption, induced voltage of the detecting coil 15 becomes large, and a replenishing roll 3 is driven, and toner 4 is replenished to a developer tank 1. Thus, toner concentration of developer 2 is maintained to a proper value. |
