| 摘要 |
PROBLEM TO BE SOLVED: To detect a positional deviation in the sub-scanning direction of a scanned beam by a simple means and to reliably correct the deviation based on the result of the detection by simple constitution. SOLUTION: When the rotational speed of a polygon motor is stabilized, a beam emitted from an LD and scanner by a polygon scanner is detected by a pair of PDs having thin and long light receiving surfaces crossing in the scanning direction and mutually forming a prescribed angle (S3 and S4). A time interval between two PD detection signals is measured to obtain a deviation from the reference position in the sub-scanning direction of the scanned beam by the obtained value (S6). The adjustment of the height position of the LD corresponding to the deviation quantity is calculated as the number of the steps of a stepping motor 1m (S7). The motor is driven in accordance with the result to adjust the height of the LD to eliminate the deviation in the sub- scanning direction of the scanned beam.
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