The following description relates to one or more multi-beam scanning optical systems configured to be incorporated in an image forming device.
Recently, in an image forming device such as a laser copy machine and a laser printer, there has been used for a copying operation or drawing operation, a so-called multi-beam scanning optical system. The multi-beam scanning optical system is configured to deflect a plurality of laser beams emitted by a light source with a deflector so as to scan the laser beams on a drawn surface in a predetermined direction (hereinafter referred to as a main scanning direction), taking on-off control to be synchronized with a modulated signal generated based on drawing data. In such an image forming device, a copying operation or drawing operation for forming a desired image is performed by translating the drawn surface exposed by the multi-beam scanning optical system in a direction perpendicular to the main scanning direction of each laser beam (hereinafter referred to as an auxiliary scanning direction).
In a conventional multi-beam scanning optical system, a polygon mirror provided with a plurality of mirror surfaces is generally employed as a deflector. However, in the multi-beam scanning optical system, the polygon mirror and a motor unit for rotating the polygon mirror occupy a very large space and cause a high cost of the system.
Thus, there has been proposed a multi-beam scanning optical system which employs a micro-mirror device, instead of the polygon mirror, as a deflector. The micro-mirror is fabricated based on a MEMS (Micro Electro Mechanical Systems) Technology that is recently coming into practical use, and is capable of quick response. The multi-beam scanning optical system with the micro-mirror device employed as a deflector can be more downsized at lower cost than the configuration with the polygon mirror employed as a deflector. Such a multi-beam scanning optical system is proposed, for example, in a paragraph 0138 of Japanese Patent Provisional Publication No. 2001-4942 (hereinafter referred to as '942 Publication).
However, in '942 Publication, there is only a general abstract description that a micro-mirror device may be used as substitute for the polygon mirror. Namely, in '942 Publication, there is no disclosure regarding a specific configuration of the multi-beam scanning optical system which provides favorable optical performances in case where the micro-mirror device is actually be used as a deflector.