Method for determining read/write head position based on phase detection of a servo pattern
A method determines RW head radial position relative to tracks within a magnetic data disc. This involves sensing both a S-burst signal and a P-burst signal with the RW head. The S-burst signal and P-burst signal are associated with a two-burst servo pattern on the magnetic disc. The S-burst pattern has a phase that remains constant radially across tracks within the magnetic disc. The P-burst has a second phase that rotates radially across tracks within the magnetic disc. By determining a phase difference between a sensed S-burst signal and P-burst signal, it is possible to determine the RW head radial position relative to the tracks on the magnetic disc.
1. A method comprising:
sensing a first burst servo pattern on a portion of a track of a rotatable medium used for data storage, wherein the sensed first burst servo pattern is one of a plurality of first burst servo patterns that are disposed radially across the rotatable medium on each half track of each track of the rotatable medium and in which all first burst servo patterns have a same phase relationship;
sensing a second burst servo pattern on the portion of the track of the rotatable medium following the sensed first burst servo pattern, wherein the sensed second burst servo pattern is one of a plurality of second burst servo patterns in which a corresponding second burst servo pattern follows each first burst servo pattern on each half track and in which all second burst servo patterns across two adjacent tracks have different phases;
determining a phase difference between the sensed first burst servo pattern and the sensed second burst servo pattern; and
locating head radial position based on the phase difference between the sensed first burst servo pattern and the sensed second burst servo pattern.
2. The method of claim 1 , wherein the first burst servo pattern is a S-burst pattern and the second burst servo pattern is a P-burst pattern.
3. The method of claim 2 , wherein a servo pattern for the rotatable medium comprises two bursts per servo wedge for each half track, in which the two bursts are obtained from the S-burst pattern and the P-burst pattern.
4. The method of claim 1 , wherein the second burst servo pattern has a phase difference of 90° for each half track of radial displacement.
5. The method of claim 1 , wherein the second burst servo pattern has a phase difference of 45° for each half track of radial displacement.
6. The method of claim 1 wherein the rotatable medium is a magnetic disk.
7. The method of claim 1 , farther comprising repositioning radially a sensing head after locating head radial position.
8. An apparatus comprising:
a sensing head;
a disk controller to control positioning of the sensing head;
a rotatable medium under control of the disk controller in which a first burst servo pattern is disposed radially across the rotatable medium on each half track of each track of the rotatable medium, wherein all first burst servo patterns across tracks of the rotatable medium have a same phase relationship, and in which a corresponding second burst servo pattern is disposed following each first burst servo pattern on each half track of the medium, wherein all second burst servo patterns across two adjacent tracks have different phases, so that a phase difference between a sensed first burst servo pattern and a corresponding sensed second burst servo pattern on a particular half track identifies radial position of the sensing head based on the phase difference between the sensed first burst servo pattern and the sensed second burst servo pattern.
9. The apparatus of claim 8 , wherein the first burst servo pattern is a S-burst pattern and the second burst servo pattern is a P-burst pattern.
10. The apparatus of claim 9 , wherein a servo pattern for the rotatable medium comprises two bursts per servo wedge for each half track, in which the two bursts are obtained from the S-burst pattern and the P-burst pattern.
11. The apparatus of claim 8 , wherein the second burst servo pattern has a phase difference of 90° for each half track of radial displacement.
12. The apparatus of claim 8 , wherein the second burst servo pattern has a phase difference of 45° for each half track of radial displacement.
13. The apparatus of claim 8 wherein the rotatable medium is a magnetic disk.
14. The apparatus of claim 8 , wherein the disk controller to reposition the sensing head after locating head radial position.