Optical scanner and image forming apparatus

Abstract

An optical scanner includes a single deflector to optically scan a plurality of target surfaces. The deflector is shared by all the beams from a plurality of light sources. The optical scanner includes photodetectors arranged to receive the deflected beams deflected. The beams traveling toward the deflector have an open angle in a deflecting rotation plane. A plurality of scanning optical systems are arranged to guide the deflected beams to different target surfaces. Each of the scanning optical systems includes at least two identical scanning lenses. At least one specific scanning lens in the scanning optical system is at a position rotated 180 degrees from a corresponding specific scanning lens in another scanning optical system. The specific scanning lens has a sub scan curvature on at least one surface with a shape asymmetrically varying from an optical axis toward both peripheries in the main scan direction.

1 . An optical scanner comprising: 
 a plurality of light sources;    a coupling optical system arranged to couple beams emitted from the light sources;    a line image focusing optical system arranged to focus the beams coupled through the coupling optical system to a line image extending longer in a main scan direction;    a deflector that has deflecting reflective surfaces in the vicinity of focused positions of the line image and arranged to deflect the beams from the line image focusing optical system; and    a plurality of scanning optical systems arranged to guide the beams deflected at the deflector to different target surfaces to form focused light spots, wherein    the deflector has a common rotary axis for deflecting reflective surfaces,    the beams entering a common deflecting reflective surface of the deflector to travel toward different target surfaces has an open angle θ in a deflecting rotation plane,    each of the scanning optical systems includes at least two scanning lenses and corresponding scanning lenses in the scanning optical systems are identical, and    wherein at least one specific scanning lens in the scanning optical systems arranged to guide the beams deflected at the common deflecting reflective surface to different target surfaces is located at a position 180 degrees rotated about an optical axis from a corresponding specific scanning lens in another scanning optical system, and    wherein the specific scanning lens has a sub scan curvature on at least one surface with a shape asymmetrically varying gradually from an optical axis toward both peripheries in the main scan direction.    
   
   
       2 . The optical scanner according to  claim 1 , wherein the specific scanning lens arranged in the scanning optical systems having the minimum angle between an incident beam to the deflector and the optical axis of the scanning lens is determined to have a power in the sub scan direction at incident beam side proximate to a periphery lower than a power in the sub scan direction at opposite side proximate to the periphery.  
   
   
       3 . The optical scanner according to  claim 1 , wherein at least one scanning lens other than the specific scanning lens has a sub scan curvature on at least one surface asymmetrically varying gradually from an optical axis toward both peripheries in the main scan direction.  
   
   
       4 . The optical scanner according to  claim 3 , wherein the scanning lens other than the specific scanning lens is determined to have a power in the sub scan direction at incident beam side proximate to periphery higher than a power in the sub scan direction at opposite side proximate to the periphery.  
   
   
       5 . An image forming apparatus for multicolor, comprising 
 an optical scanner that includes 
 a plurality of light sources;  
 a coupling optical system arranged to couple beams emitted from the light sources;  
 a line image focusing optical system arranged to focus the beams coupled through the coupling optical system to a line image extending longer in a main scan direction;  
 a deflector that has deflecting reflective surfaces in the vicinity of focused positions of the line image and arranged to deflect the beams from the line image focusing optical system; and  
 a plurality of scanning optical systems arranged to guide the beams deflected at the deflector to different photosensitive objects to form focused light spots, wherein  
   the deflector has a common rotary axis for deflecting reflective surfaces,    the beams entering a common deflecting reflective surface of the deflector to travel toward different photosensitive objects has an open angle θ in a deflecting rotation plane,    each of the scanning optical systems includes at least two scanning lenses and corresponding scanning lenses in the scanning optical systems are identical, and    wherein at least one specific scanning lens in the scanning optical systems arranged to guide the beams deflected at the common deflecting reflective surface to different photosensitive objects is located at a position 180 degrees rotated about an optical axis from a corresponding specific scanning lens in another scanning optical system, and    wherein the specific scanning lens has a sub scan curvature on at least one surface with a shape asymmetrically varying gradually from an optical axis toward both peripheries in the main scan direction.