| 摘要 |
PROBLEM TO BE SOLVED: To provide a developing device which has both functions of toner density control and toner residual quantity control by using a permeability sensor and maintains a stable and high-quality copy image until toner residual quantity is detected. SOLUTION: A large-diameter screw 25a mounted on the outside of the axis of a part opposite a toner density sensor 8, a toner supply port 21 located in the upstream in the developer conveyance direction of a first agitating roller 3 in which a plate-like agitating blade 24 is mounted in the upstream and the toner density sensor 8 located upstream of the central part in the longitudinal direction of the first agitating roller 3 are provided. The lowest value of an output value delivered from the toner density sensor during a fixed period of time including a time when a supplied toner passes over the toner density sensor is compared with the largest value of an output value delivered during a fixed period of time precedent thereto, and when the difference is less than a predetermined value, it is decided that a toner residue does not exist. Therefore, the decision that a toner residue does not exist is made before a toner supply is completely run out and at the same time toner density can be controlled. |
