| 摘要 |
PROBLEM TO BE SOLVED: To detect periodical defects accurately. SOLUTION: The photoelectric conversion signal of a light receiver 12 is binarized by an AGC circuit 28 and a binarization circuit 29. The binarization signal is counted based on a clock from a reference clock generation circuit 35, thus judging whether the defect is a width defect having length in a width direction or not. A periodical defect detection section 27 judges whether the width defect occurs periodically or not. First, the width defect is detected, and then its periodicity is judged, thus excluding noise due to fine defects and accurately judging periodical width defects. |
