| 摘要 |
In a disk medium, as servo patterns for offset detection, a pattern which is offset to the inner side, a pattern which is offset to the outer side, and a polarity pattern of a size exceeding a width of pattern as necessary are recorded in the track direction at specific cylinder positions of each data surface. In the case where only one of the read signals of the patterns which are offset to the inner side and outer side is obtained, the head is returned in such a direction as to eliminate the offset, and an offset measuring section measures the offset again. In this case, the offset measurement value is set to the total value of the head return amount and the last offset amount obtained from the read signals V1 and V2. When both of the two pattern read signals V1 and V2 are not obtained, the presence or absence of the read signal of the polarity pattern is judged. When the read signal of the polarity pattern exists, the head is offset to the side opposite to the polarity pattern by a predetermined amount and the offset is again measured. When the read signal of the polarity pattern doesn't exist, the head is offset by only the predetermined amount to the side on which the polarity pattern is not recorded and the offset is subsequently measured again.
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