| 摘要 |
PURPOSE:To obtain a control signal to be used for emitting a beam light source in a no-picture area, by controlling the start of the irradiation of the light beam in accordance with the rotation of a rotary polygon mirror. CONSTITUTION:A shroud 8 installed around a rotary polygon mirror 2 is provided with a window 81 for optical beam scanning and a fitting hole 82 for a reflecting type photocoupler. The fitting hole 82 is installed to a position, to which an output signal is sent from the reflecting type photocoupler within a period, within which each surface of the rotary polygon mirror 2 faces no- picture areas. An electronic circuit section 6 controls the start of the irradiation of the optical beam of a beam light source 1 based on the output signal of the reflecting type photocoupler and detection signal of a beam detector 5. Therefore, a control signal to emitt the beam light source in a no-picture area can be obtained easily.
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