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Servo Pattern for Hard Disk Drives with High Track Density

IP.com Disclosure Number: IPCOM000114617D
Original Publication Date: 1995-Jan-01
Included in the Prior Art Database: 2005-Mar-29
Document File: 2 page(s) / 82K

Publishing Venue

IBM

Related People

Semba, T: AUTHOR

Abstract

Disclosed is a method of achieving high track density in a hard disk drive by using a novel servo pattern when the read and write heads are different. The track pitch of the servo pattern and the data pattern are chosen independently. The track pitch of the servo pattern can be chosen so that the best linearity of the position error signal as a function of the radial position is obtained. The track pitch of the data pattern can be chosen so that the best signal-to-noise ratio is obtained under the constraints of the capacity. A DC offset is always applied to the position error signal in order to follow the data track. The amount of the offset is easily calculated by the servo controller.

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Servo Pattern for Hard Disk Drives with High Track Density

      Disclosed is a method of achieving high track density in a hard
disk drive by using a novel servo pattern when the read and write
heads are different.  The track pitch of the servo pattern and the
data pattern are chosen independently.  The track pitch of the servo
pattern can be chosen so that the best linearity of the position
error signal as a function of the radial position is obtained.  The
track pitch of the data pattern can be chosen so that the best
signal-to-noise ratio is obtained under the constraints of the
capacity.  A DC offset is always applied to the position error signal
in order to follow the data track.  The amount of the offset is
easily calculated by the servo controller.

      In conventional hard disk drives, the track pitch of the servo
patterns and that of the data patterns are the same.  However, this
does not mean that the servo performance and the read-back data
quality are optimized at the same time.  In order to preserve the
alignment of the servo patterns and the data patterns in drives with
rotary actuator systems, we had to apply a DC offset to the servo
tracking position during the writing of data, because the center of
the write head and that of the read head are different.  This also
means that the linearity of the position error signal as a function
of the radial position is very important for stable following of the
tracks.

      The Figure shows the new servo patterns, data patterns, and
position error signals of the new method.  The four waveforms show
the amplitude of the read signal at times C and A as functions of the
radial position, and the position error signals calculated from them.
The shaded regions show the servo patterns.  The head moves
vertically in the Figure.  Since the width of the servo pattern is
chosen to be equal to the width of the read head and the pitch of the
servo pattern to be twice the width, the position error signals have
maximum linear range.  In other words, the servo pattern can be
chosen to have...