| 摘要 |
PURPOSE:To converge and focus a light beam on a scanning surface securely by adjusting finely an image formed on the scanning surface by an anamorphic optical system under the control of a means for storing the surface tilt of a rotary polygon mirror. CONSTITUTION:The light beam 2 from a laser light source 1 passes through a cylindrical lens 4 and is incident on the rotary polygon mirror 5 as a vertical linear image, which is reflected there to scan on a scanning surface 8 as a spot image through the anamorphic optical system consisting of an ftheta lens 6 and a cylindrical lens 7. The surface tilt of the polygon mirror from a surface 5a to surfaces 5b and 5c is unevitable, but the shift of the position is stored previously in a ROM 10 to move finely a lens 4 as shown by C under the control of the ROM 10 through the operation of a moving means 9 which responds to the surface tilt. Thus, the surface tilt and axis movement of the polygon mirror 5 are corrected with high accuracy to converge and focus the light beam on the scanning surface all the time. |
