| 摘要 |
PURPOSE:To arrange a photosensor in the vicinity of a halogen lamp and to detect original document density accurately by making the quantity of light of the halogen lamp slightly less when the density of the original document is detected. CONSTITUTION:When the density of the original document is detected by prescanning, the halogen lamp 1 is turned on with a voltage which is as low as possible, and then a temperature rise is suppressed and this is advantageous to the life as well. Consequently, the temperature rise is suppressed even during continuous use, the photosensor 6 can be arranged in the vicinity of the halogen lamp 1, and the original density is detected more accurately. In this case, the photocurrent output of the photosensor 6 decreases owing to low-voltage lighting and this is disadvantageous to the S/N, but this is dealt with by setting the circuit constant of an amplifier 8. |
