| 摘要 |
PROBLEM TO BE SOLVED: To make the accuracy of the positional deviation of a beam spot higher and also to realize the high image quality and the quiet sound of a color image forming apparatus by reducing the temperature rise of a scanning lens used in an optical scanner and the temperature deviation of every optical scanner of the color image forming apparatus and reducing the vibration of the optical scanner. SOLUTION: A polygon mirror at an upper stage is shown as 20U, a polygon mirror at a lower stage is shown as 20D, and two fθlenses are shown as 31M and 32M. The material of the lenses 31M and 32M is inexpensive plastic material easily forming aspherical shape. It is better that a plate 33M is made of metal having high heat conductivity, and its thermal expansion coefficient is near to that of the lenses 31M and 32M. By setting such material and constitution, there is no part where the temperature of the lenses 31M and 32M locally gets high due to temperature rise in an optical housing 31 caused by heat generation in a polygon mirror and a fixing unit and temperature distribution (especially, in a main scanning direction) is flattened and the positional deviation of the scanning beam spot is restrained. COPYRIGHT: (C)2004,JPO
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