| 摘要 |
PROBLEM TO BE SOLVED: To enhance compatibility of scanner unit by previously adjusting the fixing position of a BD unit such that a scanning light for obtaining an image writing reference signal impinges on the center of effective detection part of the BD unit. SOLUTION: A part of scanning light deflected by a rotary polygon mirror 3 is separated by a BD mirror 6 disposed on the outside of an optical box 10 and introduced into a BD unit 11 thence transmitted, as an image writing reference signal, to a semiconductor laser 1. In order to eliminate the possibility that the BD unit 11 can not receive the light due to unit tolerance of the optical box 10 or assembling error of reflectors 5a-5c when a scanner unit is replaced, the BD unit 11 is moved up and down using the emboss 31a of a body side plate 31 as a slide guide and the fixing position of the BD unit 11 is adjusted such that the scanning light impinges on the center of the light receiving plane of the BD unit 11 before the BD unit 11 is secured by means of screws 32.
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