| 摘要 |
PURPOSE:To facilitate setting the read timing, by comparing the detection value of a reflection density detecting pattern with a reference value and generating a pulse having a certain width when the part of the highest density of an image is the reference value or less and detecting whether this pulse exists or not. CONSTITUTION:The density in the center of a density detecting pattern 2' on a photoreceptor 9 becomes lower according as a developer is degraded. Therefore, it is necessary that the edge part of the pattern is read to obtain a proper toner density, but setting of the read timing is difficult. Then, an electric conversion output ES from an optical density detecting sensor 12 is compared with a preliminarily set reference value ER, and the output of a comparator 20 is level ''L'' for ES>ER and is level ''H'' for ES<ER, and a pulse having a certain width t0 is generated from a delay circuit 23 when the output is switched from level ''L'' to level ''H'', and this pulse is read at a proper time T2 by a microcomputer 22, and a toner supply circuit 21 is controlled in accordance with existence of the read value. |
