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Browse Prior Art Database

8-Track-Type Phase Modulated Servo Pattern

IP.com Disclosure Number: IPCOM000112842D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 81K

Publishing Venue

IBM

Related People

Anderson, TB: AUTHOR [+3]

Abstract

A servo pattern for a hard disk drive is disclosed. This technique allows the use of a phase modulated servo pattern at seek velocities previously unobtainable without loss of signal to noise while following the track center. The improved seek performance is obtained by using a dedicated servo scheme that has twice the number of servo samples required to control the actuator. Even position samples are used to track follow. Odd samples used during actuator moves. The odd samples are written such that the position information covers twice the radial displacement of the even samples. By alternately changing the phase of each frequency burst in the servo pattern, the odd samples can be written without requiring higher servowriting clock frequencies.

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8-Track-Type Phase Modulated Servo Pattern

      A servo pattern for a hard disk drive is disclosed.  This
technique allows the use of a phase modulated servo pattern at seek
velocities previously unobtainable without loss of signal to noise
while following the track center.  The improved seek performance is
obtained by using a dedicated servo scheme that has twice the number
of servo samples required to control the actuator.  Even position
samples are used to track follow.  Odd samples used during actuator
moves.  The odd samples are written such that the position
information covers twice the radial displacement of the even samples.
By alternately changing the phase of each frequency burst in the
servo pattern, the odd samples can be written without requiring
higher servowriting clock frequencies.

      A phase modulated servo positioning system uses the relative
phase of two fields written on the disk to determine actuator radial
position.  These fields are written such that the magnetic
transitions of one burst advance in phase and the other burst retards
in phase on each successive servo track.  At the completion of the
servowrite process, the servo pattern looks like a series of chevrons
extending from the disk inner diameter to the disk outer diameter.
The angle of the chevrons relative to the circumferential tracks
defines the amount of phase shift that occurs as the servo head is
moved radially.  When the actuator is seeking, the servo head is
moving diagonally across the pattern.  The angle of the chevron
pattern relative to the trajectory of the servo head defines the
amount of phase shift seen.

      The phase demodulator circuits determine phase by measuring the
phase of the servo head signal between three servo fields as the head
is moved radially.  The phase of the first and third field change in
unison, the second field changes in an opposing fashion.  While
seeking, the servo head traverses the servo pattern diagonally.  This
causes the phase of the signal to change f...