| 摘要 |
PURPOSE:To supply toners by as much as required, by providing a control circuit for discrimination of toner density which controls biasing voltage for development and toner transfer voltage with the output of a toner density sensor and controls the movement of the toner between a toner transfer roll and a developing roll. CONSTITUTION:Development is accomplished by a developing roll 14 which is moved on recording paper 12. The amt. of the toners consumed by the development is detected with a toner density sensor 25, and the output voltage Vx of the magnitude corresponding to the consumed amt. of the toner is fed to a control circuit 26 for discrimination of toner density. Now, when the voltage Vx attains the lower limit voltage V1 indicating the lower limit value of 2wt% toner density in a time t1, a toner transfer roll 16 is rotated by the output signal thereof and the applied voltage VT is changed from -100V to, for example, -70V. Then the toners 23 of a positive polarity stuck on the roll 16 transfer onto the roll 14 applied with -100V, whereby the toners are replenished. The rate of the replenishment is larger as the difference between VT and VB is larger. |
