| 摘要 |
PURPOSE:To obtain proper density even after numbers of copies are taken through an electrophotographic copying machine which decides on the amount of exposure automatically according to original density, by increasing the amount of exposure as the number of copies increases. CONSTITUTION:A photosensitive drum 114 is rotated by the length of an original 109 to measure the potential of a photosensitive surface corresponding to the original density by a sensor 123 in a preliminary scanning process. An image exposing circuit 122 controls a lighting circuit 124 on the basis of the mean original density value obtained by integrating the sensor output in the scanning time to decide on the brightness of an original lighting lamp 108. Copying operation for the 1st sheet is carried out on the basis of original density information in the preliminary scanning, but the lamp illuminance value corresponding to the original density is increased by one rank after 20 copies are taken to compensate a decrease in copy density with the number of copies. Then, the illuminance is increased at intervals of 20 copies. |
