| 摘要 |
PURPOSE:To obtain a copied image having a high gradient without any fog, by making the frequency of the alternating electric field to be impressed to a toner carrier lower than the frequency in the case in which said frequency is smaller than a predetermined threshold, when the integrated value of the latent image potential on a photosensitive drum is larger than said threshold. CONSTITUTION:The potential of the electrostatic latent image formed on a photosensitive drum 1 according to an original is detected with a potential sensor 11. The detection signal is amplified with an amplifier 12, and is fed to an arithmetic control circuit 13, by which the signal is integrated. The circuit 13 discriminates whether the integrated value is larger or smaller than the threshold stored in the circuit 13. The circuit 13 sends a signal to a biasing power source 14 for developing so as to impress an alternating electric field of a low frequency to a toner carrying body 15 when the integrated value is larger than the threshold and to impress an alternating electric field of a high frequency thereto when the integrated value is small. The copied image having well reproduced medium contrast without any fog up to the high ground density as with a photographic original is thus obtd. from a document original. |
