| 摘要 |
PROBLEM TO BE SOLVED: To eliminate disorder or pitch nonuniformity of an image in scanning direction while avoiding the resonance between an optical box and a motor or the like housed in it, by changing the natural frequency of the optical box making the part near a motor housing part have a hollow structure. SOLUTION: The optical box 10 is formed by injection molding based on a hollow molding system, its natural frequency is changed and the resonance is avoided by preventing the coincidence with the peculiar natural frequency of motor 5 for rotationally driving a rotary polygon mirror 4, semiconductor laser device, Fθlens and reflection mirror. In a hollow structure 21, the side face or the like of the optical box 10 is provided near the motor 5 for rotationally driving the rotary polygon mirror 4, for example, and when forming the optical box 10, it is formed by pressurizing gas or the like into the optical box 10. Its shape is affected by the pressure of gas, its size is various and the number and position of the hollow structure 21 are determined by the number of gas pressure injections and the position of pressure injection. The mass and density of the optical box 10 are changed by the hollow structure 21 and the natural frequency of the optical box 10 is changed. |
