| 摘要 |
PROBLEM TO BE SOLVED: To detect a failure mode that a quantity of light of a semiconductor laser diode decreases slightly or the like by monitoring the quantity of light of the semiconductor laser diode, judging whether or not the quantity of light is within a specified range, and outputting the judgment result as a logic value signal. SOLUTION: When the image-forming apparatus receives a printing request, a scanner motor 107 and a polygon mirror 108 are rotated and a semiconductor laser diode 121 is driven. At this time, a photodiode 122 feeds back a quantity of light of the semiconductor laser diode 121 to a semiconductor laser diode- driving circuit 102. A quantity of light of a semiconductor laser diode 103 is controlled so that the quantity of light becomes a target value. At the same time, whether or not the quantity of light is within a predetermined range is monitored, and the result is output as a logic value signal. The output logic value signal is fed back to a control part 101, where it is judged whether the quantity of light of the semiconductor laser diode 103 is normally controlled or not.
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