| 摘要 |
<p>PROBLEM TO BE SOLVED: To prevent the divergence of focus by thermally expanding a holding member which is arranged between an image forming body and a supporting member and for holding an image forming element, to set the center of the image forming element in the middle position between the image forming body and the supporting member. SOLUTION: A metallic casing 12d and the holding member 12c provided in an exposure unit 12, the supporting member 20 for the exposure unit 12, the substrate of a photoreceptor drum 10 as the image forming body, etc., are thermally expanded by the generation of heat by the LED 121 as a light emitting element of the exposure unit 12. When the linear expansion coefficients of the prism of the supporting member 20, the holding member 12c and the substrate of the photoreceptor drum 10 are defined asα11,α12 andα13, andα13 is >=α11,α12 is >=α11. Thus, even if variation in temp. caused by the generation of the heat from an exposure element occurs, the divergence of the focus of the image forming element hardly occurs.</p> |
