| 摘要 |
PROBLEM TO BE SOLVED: To improve accuracy of detecting off-tracking by preventing erroneous detection caused by a noise component when off-tracking is detected, and using a conventionally obtained TE signal without adding new circuitry. SOLUTION: A system controller measures the level of a TE signal (step S11), and determines whether or not a predetermined number or more of TE signals has been detected within a predetermined fixed time (step S12). Thus, if the predetermined number or more of TE signals is detected (Yes in step S12), then whether or not the level of the measured TE signal exceeds a preset threshold value for a preset fixed period is determined (sep S13). Thus, if the level of the TE signal exceeds the threshold value for the fixed period (Yes in step S13), off-tracking is determined (step S14). COPYRIGHT: (C)2008,JPO&INPIT
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