| 摘要 |
PURPOSE:To prevent the over-control of image density and to prevent the excessive decrease in the density of a copied image, by keeping the range for automatic control of image density within a specified width and maintaining the image density determined by the preset conditions for regulation when out of said range. CONSTITUTION:When the reflection density of an original is high, the holding voltage Valpha of an integrator decreases and voltage drop i1XR6 decreases as well. When the reflection density of the original is low, the holding voltage V increases and the voltage drop i1XR6 increases. Therefore, the voltage applied on a lamp 21 for illuminating the original, such as a halogen lamp via CVR, is changed by the varying degrees of the voltage drop iXR6. On the other hand, when the voltage Valpha of the integrator drops down to a limit value VRef or below, a switch SW3 is changed over from a terminal NC to NO by a comparator Q2 which detects the same. As the switch is changed over, the input voltage V1 of CVR is changed to V1=ValphaXR5/(R5+R6). The output voltage of the CVR in accordance with the voltage V1 is supplied and applied on the lamp 21 whereby the excessive automatic control of the image density is prevented. |
