Patent ID: 6256132
Filing Date: 2001-07-03
Classification: G02B,H04N

Abstract:
A multi-beam scanning optical system comprising:a light source having a plurality of light emitting sections arranged at respective positions varying from each other in terms of both the main-scanning direction and the sub-scanning direction perpendicular relative to the main-scanning direction;a rotary polygon mirror having deflection surfaces for deflecting the plurality of light beams emitted respectively from said plurality of light emitting sections;a first optical system arranged on the optical path between said light source and said rotary polygon mirror to transform said plurality of light beams into so many convergent or divergent light beams;a second optical system for focussing said plurality of light beams on a deflection surface of said rotary polygon mirror as so many linear images extending in the main-scanning direction after passing through said first optical system; anda third optical system for focussing the plurality of light beams deflected by said rotary polygon mirror onto a surface to be scanned of a drum having its axis of rotation extending in the main-scanning direction, said third optical system holding said deflection surface and said surface to be scanned in a substantially conjugate relationship in the sub-scanning directionsaid plurality of light beams striking said surface to be scanned being inclined in the sub-scanning direction so as to make their principal rays to show a non-zero angle relative to the normal to the surface to be scanned, thereby producing a positional displacement among the focal points of the light beams on the surface to be scanned in a first direction parallel to the main-scanning direction, said convergent or divergent light beams entering said third optical system producing a relative positional displacement among the focal points thereof on the surface to be scanned in a second direction parallel to the main-scanning direction, said first direction and said second direction being opposite to each other.