| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical scanner capable of accurately setting a start position of scanning of a photoreceptor with luminous flux in each optical system although only one optical sensor which detects the luminous flux is used.SOLUTION: The number of respective reflection surfaces 42a of a polygon mirror is set to 4×k (k: an integer of 1, 2, 3, ...), and an angle γ of incidence pieces L1-L4 of luminous flux on the reflection surfaces 42a when the centers of effective scanning areas H1, H2 are scanned with the pieces L1-L4 of luminous flux reflected by the reflection surfaces 42a of the polygon mirror 42 is set to 45°. Then when the time from a point ta1 of time of detection of the piece L1 of luminous flux by a BD sensor 72 to a point ta2 of time of a start of main scanning on the effective area H1 by the pieces L1, L2 of luminous flux is denoted as &Dgr;t, and a rotating speed of the polygon mirror 42 is denoted as N turns/second, a point ta4 of time of a start of main scanning on the effective scanning area H2 by the pieces L3, L4 of luminous flux is set to a point of time which is a time &Dgr;T=&Dgr;t+(1/N)/4 after the point ta1 of detection of the piece L1 of luminous flux. |
