Patent ID: 7119824
Filing Date: 2006-10-10
Classification: B41J

Abstract:
1. A multi-beam optical scanning apparatus comprising: a light source unit having at least three light emitting portions disposed with being spaced from each other in a main-scanning direction; a first optical system for changing conditions of at least three divergent light beams emitted from the light source unit; a stop for restricting widths of the at least three light beams transmitted through the first optical system at least in the main-scanning direction; a deflecting unit for reflecting the at least three light beams transmitted through the stop; a second optical system for forming images of the at least three light beams reflected by the deflecting unit on a surface to be scanned; and a detecting unit for detecting a writing start position synchronous signal for controlling timing of a scanning start position on the surface to be scanned, the writing start position synchronous signal detecting unit including a detecting device for detecting the writing start position synchronous signal, and a slit member disposed in an optical path between the writing start position synchronous signal detecting device and the deflecting unit, and the writing start position synchronous signal detecting unit being adapted to control the timing of the scanning start position on the surface to be scanned by using a light beam reflected by the deflecting unit and transmitted through the slit member; wherein a condition given by is satisfied, where Si is the spacing in the main-scanning direction between light emitting portions at opposite ends in the at least three light emitting portions, f 1 is the focal length of the first optical system, L 1 is the distance between the stop and a deflecting facet of the deflecting unit, f 2 is the focal length of the second optical system in the main-scanning direction, α is an average of angles formed between principal rays of the at least three light beams incident on the surface to be scanned and a normal to the surface to be scanned in a sub-scanning section, β is an average of angles formed between the principal rays of the at least three light beams incident at any scanning location on the surface to be scanned and the normal to the surface to be scanned in a main-scanning section, δM (β) is the main-scanning focus displacement amount at the scanning location of the average β, δM (BD) is the main-scanning focus displacement amount at a scanning location whereat the at least three light beams pass through the slit member, N M is the number of pixels per inch in the main-scanning direction which is determined from a resolution in the main-scanning direction on the surface to be scanned, and P is the spacing in the sub-scanning direction between image spots of light beams emitted from light emitting portions at opposite ends in the at least three light emitting portions on the surface to be scanned.