Patent ID: 8077370
Filing Date: 2011-12-13
Classification: G02B

Abstract:
1. A scanning optical apparatus comprising: a light source; a first optical element configured to convert light emitted from the light source into a beam of light; a second optical element configured to convert the beam of light having passed through the first optical element into a linear image extending in a main scanning direction; a polygon minor configured to deflect the beam of light having passed through the second optical element in the main scanning direction; a third optical element configured to convert the beam of light having been deflected by the polygon mirror into a spot-like image to be focused on a scanned surface, the third optical element being a single lens having a pair of opposite incident-side and exit-side lens surfaces having first and second optical axes, respectively, each of the pair of opposite lens surfaces being aspheric in a main scanning direction, and having a curvature in a sub-scanning direction varying continuously and symmetrically from a position corresponding to the optical axis thereof outward in a main scanning direction, each of the pair of lens surfaces having a shape symmetric in the main scanning direction with respect to a sub-scanning plane containing the optical axis thereof; and a synchronization detection beam path configured such that the beam of light travels therethrough from the polygon minor to a position that is opposite to the light source across the optical axes of the pair of lens surfaces, to be directed to a sensing element producing a signal for synchronization at a start-of-scan position, wherein a distance h between a center of rotation of the polygon mirror and a center of the beam of light incident on the polygon mirror fulfills the following conditions: where R indicates a radius of an inscribed circle of the polygon mirror, N indicates the number of specular surfaces of the polygon mirror, a indicates an angle [rad] formed by the beam of light incident on the polygon mirror with a reference line extending in a direction of travel of the beam of light to be incident on the scanned surface at right angles after being reflected off the polygon mirror, θ bd indicates an angle [rad] formed by the beam of light traveling from the polygon mirror along the synchronization detection beam path with the reference line, θ eos indicates an angle [rad] formed by the beam of light reflected off the polygon mirror at an end-of-scan position with the reference line, and b eos and b bd indicate breadths of the beam of light in the main scanning direction on each of the specular surfaces of the polygon mirror at the end-of-scan position and at a position in which the beam of light reflected off the polygon mirror travels along the synchronization detection beam path, respectively; and wherein the following condition is satisfied: where β 2 indicates an angle [deg] formed in a main scanning plane between the first optical axis and the second optical axis of the third optical element, and wherein at least one of the following conditions is satisfied: where β 1 indicates an angle [deg] formed in the main scanning plane between the first optical axis and the reference line, and D 2 indicates an amount of shift [mm] in the main scanning plane, of a point of intersection between the second optical axis and the exit-side lens surface, from the first optical axis.