| 摘要 |
PROBLEM TO BE SOLVED: To identify a track within the range equivalent to plural tracks and to expand the range of position detecting by having a position area different from a phase difference between plural position areas. SOLUTION: Positional information is identified from a phase difference of a vector between a position area (o1) and a position area (o2) with a servo circuit. When a reference track is expressed by a track Tr0, a phase difference of both o1 and o2 is 0 in the track Tr0, a phase of o1 is -90 deg., a phase of o2 is -135 deg. and a phase difference between a vector o1 and a vector o2 becomes +45 deg. in a track Tr1 which is jumped one track from the reference track Tr0. The phase of o1 is -180 deg., the phase of o2 is -270 deg. and a phase difference between the vectors becomes -90 deg. in a track Tr2 which is jumped two tracks from the reference track Tr0. Therefore, reference tracks of tracks Tr0 to Tr7 are identified from the phase difference between the vector o1 and the vector o2.
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