| 摘要 |
PURPOSE:To prolong the life of the rotary polygon mirror and to reduce the size, weight, and power consumption of a driving motor by providing the rotary polygon mirror consisting of a support which is made of a light-transmissive member and has a polygonal hollow part and reflecting surfaces formed in contact with the polygonal hollow part, and a driving device which rotates the rotary polygon mirror fast. CONSTITUTION:An optical device 10 has a light emitting device 12, the rotary polygon mirror 17 which is rotated fast by the driving motor 16 as a driving device to put a laser beam 13 in deflecting and scanning operation in a main scanning direction or the lengthwise direction of a photosensitive drum 14, and an image forming lens unit 18 which images the laser beam 13 reflected by the rotary polygon mirror 17 on the photosensitive drum 14. Then the rotary polygon mirror 17 consists of the glass-made support 21 which is a columnar light-transmissive support and have a polygonal hollow part or an octagonal columnar hollow part 21a recessed inside, and the reflecting surfaces 22a - 22h formed by vapor-depositing aluminum on the surface of the hollow part 21a. Consequently, the life of the rotary polygon mirror 17 is prolonged, the load, size, and weight of the driving motor 16 are reducible. |
