| 摘要 |
PURPOSE:To obtain stable image quality even when the electrostatic charge quantity of toner is fluctuated according to the using state of a copying machine. CONSTITUTION:By a mode set control means 1, one among the image forming modes such as a continuous running mode and plural low duty modes is selected based on the temperature of a fixing roller at the turning off/on time of the copying machine, the rising time of the heater 4 of a fixing roller or the set time of a preheating mode so as to set the optimum developing bias voltage impressed on a developing sleeve from a developing bias power source 6. It is good that one among the image forming modes is selected based on the copying amount (CV) of the copying machine per one month scheduled in the past or the future, a value(Cth) obtained by dividing the number of all the copied sheets by the total turning-on time of the copying machine from a new state or a value(Crh(H)) obtained by dividing the number of copied sheets within a concerned time by H hours last before a present time. |
