| 摘要 |
PURPOSE:To reduce wind whistle caused by air flowing out from the cover of a rotary polygon mirror. CONSTITUTION:The rotary polygon mirror 1 has a reflection surface 1a reflecting a laser beam on its outer peripheral surface, and rotates at high speed in a direction shown by an arrow R, so that the laser beam is deflected to perform scanning. The mirror 1 is covered with the nearly cylindrical cover 2, and the cover 2 is provided with a window 3 through which the laser beam is allowed to pass. A guiding piece 4 projecting in a reverse direction to the rotating direction of the mirror 1 at an angle within a range from 20 deg. to 40 deg. to the outside of the tangential plane A of the cylindrical part 2a of the cover 2 is provided on the side edge 3b of the window 3 on a downstream side in the rotating direction of the mirror 1. Since the free end 4a of the piece 4 is largely separated to the outside from the cover 2 in a diameter direction, the air flowing over the cover and flowing out to the outside is decelerated because it wares away from the surface of the mirror 1. Therefore, the loud wind whistle is not produced. |
