To directly measure the electrified amount of a powder on a powder- holding rotary body and also measure the electrified amount every revolution number of the rotary body correctly by tracking even the rotary body of a high rotation speed.
After the weight of a developing device 11 is measured by a weight-measuring device 27, a first solenoid valve 23 is closed and a second solenoid valve 25 is opened, and a sucking device 21 is actuated. A developing roller 14 is further rotated. The first solenoid valve 23 is opened and the second solenoid valve 25 is closed for one rotation of the developing roller, and a powder toner 13 is sucked. Then, the first solenoid valve 23 is closed and the second solenoid valve 25 is opened for M rotations of the developing roller 14 so as not to suck the powder toner. The process is repeated by a predetermined number of times and, the sucking device 21 and a motor are stopped. Electric charges escaping from the developing roller 14 are measured by an electrometer 18. The weight of the developing device 11 is measured again. The electrified amount of the powder toner 13 is obtained from the measured results.
OTAKA YOSHIMITSU
SATO KATSUTOSHI
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