| 摘要 |
PROBLEM TO BE SOLVED: To provide a low-cost optical scanner which can detect an image formation state independently in both horizontal and vertical scanning directions without providing any synchronization detecting device and can accurately detect the size of a beam spot even if an output signal includes noise. SOLUTION: A detecting means 10 has a triangular opening on a PD, etc., and differentiates the output signals of both the horizontal and vertical scanning directions to find the size of the beam spot. Paying attention to the fact that the signal waveform of even a signal having noise added to the original ideal signal does not vary so much, this device predetermines the signal variation between a low voltage level Va and a high voltage level Vb and measures the time ts of the variation of the signal voltage from Va to Vb. The length of the time ts corresponds to the size of the beam spot. The time ts is measured by counting clock signals having equal intervals from the moment the signal reaches the low level voltage Va to the moment the signal then reaches the high voltage level Vb and multiplying the count number by clock cycles.
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