| 摘要 |
PURPOSE: To keep the density of a gray level picture element almost fixed regardless of the change of a development density by controlling the on-time of a laser and the size of the gray level picture element concerning the gray level picture element. CONSTITUTION: The lamp signal of a lamp generating circuit 527 is transmitted to a comparator 525. The comparator 525 compares the lamp signal with a light gray analog voltages VLG outputted from D/A converters 520 and 522, which are adjusted by the present value of the DC component of a developer bias, and with a dark gray analog voltage VDG. When the present light gray voltage is equal to below a nominal setting value of the D/A converter 520, the pulse width of a light beam control signal LG outputted from the comparator 525 is enlarged so that the on-time of a laser beam becomes long. Therefore, the width of the light gray picture element formed in a photosensitive body is increased. Thus, the density of the gray level picture element is kept to be fixed. |
