| 摘要 |
PURPOSE:To detect accurately toner concentration by providing a developing device with a magnet arranged oppositely to developer and a pressure sensor arranged between the magnet and the developer so that its detecting surface is abutted upon the magnet. CONSTITUTION:The pressure sensor 12 outputs a signal corresponding to attracting force between the developer 22 and the electro-magnet 11, and at the time of detecting the attracting force exceeds a prescribed value, decides the reduction of toner concentration in the developing device 20, so that a toner feeding roller 31 in a toner hopper 30 is rotated. Consequently, toner 32 in the hopper 30 is replenished to the developing device 20 and the toner concentration in the developing device 20 is increased by the replenishment of the toner, so that the magnetized ratio of the developer 22 is reduced and the attracting force between the developer 22 and the electro-magnet 11 is reduced. The pressure sensor 12 detects said status and stops the rotation of the roller 31. Thus, the toner concentration in the developing device 20 is controlled at a prescribed value. |
