Patent ID: 6833855
Filing Date: 2004-12-21
Classification: B41J,G02B

Abstract:
A multi-beam scanning optical system comprising entrance optical means for introducing, to deflecting means, a plurality of light beams emitted from light source means having a plurality of light emitting portions arranged apart from each other at least in a main scan direction; scanning optical means for focusing the plurality of light beams deflected by said deflecting means on a surface to be scanned; and synchronous detection optical means for converging, by a synchronous detection optical element, parts of the plurality of light beams deflected by said deflecting means on a plane of a slit, introducing the parts of the plurality of light beams to a synchronous detection sensor, and controlling timing of scan start positions on said surface to be scanned with respect to the plurality of light beams by using signals from said synchronous detection sensor,wherein, assuming that a focal distance of said scanning optical means is Ff, a focal distance of said synchronous detection optical element is Fb, a focus position shift amount of each light beam introduced to said synchronous detection sensor in a main scan section is &dgr;M1 looking from said slit, a focus position shift amount of each image height is &dgr;X looking from said surface to be scanned, an allowable dot position shift amount of each scanning line is &dgr;Ymax, and a maximum angle difference between incident angles of the light beams upon the slit plane is &thgr;max, Ffâ‰ Fb holds and the following conditional formula is satisfied: |(Fb/Ff)Ã—&dgr;Xâˆ’(Ff/Fb)Ã—&dgr;M1|&lE;&dgr;M1|&lE;&dgr;Ymax/&thgr;max, and wherein said allowable dot position shift amount of each scanning line is not larger than Â½ of resolution in a sub-scan direction.