| 摘要 |
PURPOSE:To maintain the best drum current at all times even if circumference conditions of temperature, etc., are changed so that a drum current can be held at a specific value, to secure the excellent picture quality performance of a copy, and to improve environmental resistance. CONSTITUTION:When the drum current Id increases above a specific value, the potential of a photosensitive drum 30 which is detected by the potential sensor of a voltage control means 22 becomes high. An external control voltage Vc applied with a detection signal corresponding to the potential of the photosensitive drum from the potential sensor 24 becomes high as the potential of the photosensitive drum 30 increases and is applied to a variable constant voltage circuit 12. Then a grid current Ig increases and the drum current Id decreases because of a relation Id=Ih-Ig and returns to its original specific value. When the drum current Id decreases below the specific value, on the other hand, reverse operation is performed and the grid current Ig decreases, so the drum current Id increases and returns to its original specific value. |
