| 摘要 |
PURPOSE:To correct the amount of surface inclination of a rotary polygon mirror by measuring the time necessary for a scanning beam by each mirror surface of the rotary polygon mirror to pass between two photodetecting elements installed near a body to be scanned. CONSTITUTION:The photodetecting elements 10 and 11 are provided at a side end part of the body to be scanned and arranged on a main scanning line on an original set on the body to be scanned at a scanning start part off the area of the original at an interval. A triangular coating body 11b is placed on the top surface of the photodetection surface 11a of the 2nd photodetecting element 11 at angle alpha to a line orthogonal to the scanning line to shield the photodetection surface 11a partially. The passing time of the scanning beam passing between the two photodetecting elements varies with the extent of surface inclination and the driving frequency of an acoustooptic deflecting element is varied on the basis of the time measured value to correct the amount of surface inclination that each mirror surface has. |
