| 摘要 |
PURPOSE:To perform a stable printing of high quality by comparing by comparing a counted value of a counter and the number of clocks held in a holding device and outputting a coincidence signal when both the numbers coincide. CONSTITUTION:An FF12 is preset by a signal A2 time sharing a synchronizing signal A. When the number of laser beam generated in scanning one line is not normal, since a signal F is not outputted from an AND circuit 11, the FF12 maintains the set state. Accordingly, an AND circuit 13 outputs '1' as an error signal ER at an output timing of a signal A1 time sharing the signal A. Thereafter, the FF12 is set by the signal A2 to recognize the normality of the scanning of the one line. When the scanning of the one is normally carried out, the signal F is outputted from the circuit 11 and the FF12 is reset. Therefore, the circuit 13 does not output the error signal ER. Thereby, the abnormality in a rotation of a polygon mirror or the abnormality in the period for generating a clock is produced with respect to the normal synchronizing signal and it can be detected that the printing of a normal dot density is not carried out.
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