| 摘要 |
PURPOSE:To correct an uneven scan of a polygon mirror by bringing a lens for constituting a light beam scanning optical system, to a minute displacement in the sub-scanning direction in its main plane. CONSTITUTION:An objective lens L2 is held and supported by a spring 11 on a base 11, and an electrostrictive element 8 and a thermal deformation absorbing member 12 are interposed in the upper and the center parts of a holder 9. A beam B1 of a light source 1 is enlarged to B2 by lenses L1, L2 and reflected by a reflecting surface M of a polygon mirror 3, and a light spot P is formed on a recording surface 6 through a lens 4. In this case, the surface M is inclined by DELTAtheta against a revolving shaft of the polygon mirror 3, therefore, the light spot P is shifted in the direction of 2DELTAtheta from a prescribed scanning track. The shift quantity is held 14 by a signal of a detector 5, a correction quantity d=f2tan(2DELTAtheta) of the lens L2 is calculated and a control signal is outputted 15, and the electrostrictive element 8 is driven 16. In this way, a beam B3 becomes parallel to an optical axis X, and the light spot P is formed on the prescribed scanning track on the recording surface through the lens 4. According to this constitution, an uneven scan caused by a pyramid error of each reflecting surface can be corrected. |
