| 摘要 |
PURPOSE:To scan a light beam once and to easily detecting scan abnormality by providing a slit member with a scan abnormality detection part for the light beam. CONSTITUTION:When the output of a beam detector 10 is scanned normally, the output is sent out as the inverse of BD signal 11 to a counter 20 and counter by seven, so that it is sent out to a magnitude comparator 22. The magnitude comparator 22 is set to a set value 7, so the comparator coincides with a counter 20 and its error output 24 is still '0', so that no error is outputted. The output with a voltage waveform BP when a scan is made abnormally is sent out to the counter 20 and counted by nine, and the output of the counter 20 is inputted to the magnitude comparator 22; and the magnitude comparator 22 is set previously to the set value 7, so its output does not coincide with the output of the counter 20, so that the error output 25 is '1'. Consequently, when the laser beam 3 is scanned slantingly, the can abnormality of the laser beam 3 is easily detected.
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