| 摘要 |
PURPOSE:To reduce noises due to the fluctuation of the air by providing wind protecting pipes in a manner allowing three optical axes from a light source to a polygon scanner and an ftheta lens to prism mirrors 5a, 5b to pass therethrough. CONSTITUTION:A light beam L1 generated from a light source 1 is, after passing through a pipe 2a, reflected by a polygon scanner 3. Reflecting lights L2, L3 pass through an ftheta lens 4 and pipes 2b, 2c to be reflected by prism mirrors 5a, 5b and incident upon sensors 6a, 6b; 6c, 6d for a required time, respectively. The time interval from when the powers measured by the sensors 6a, 6b are equal to each other to when the powers measured by the sensors 6c, 6d become equal to each other is measured, so that jitters are calculated. Since there are plastic or metallic pipes 2a-2c in this apparatus, noises of a measured value due to the fluctuation of the air are reduced. If the pipes 2a-2c have wave-like inner shapes in the longitudinal direction, the irregular reflection of the light beam within the pipes 2a-2c can be prevented. |
