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Servo Gain Correction Method at Offset Position Using Mr Head

IP.com Disclosure Number: IPCOM000112488D
Original Publication Date: 1994-May-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 6 page(s) / 113K

Publishing Venue

IBM

Related People

Matsui, T: AUTHOR [+3]

Abstract

This article describes the method to adjust the servo gain for a hard disk drive using read/write head which has the offset between read and write head elements such as Magneto Resistive head.

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This is the abbreviated version, containing approximately 52% of the total text.

Servo Gain Correction Method at Offset Position Using Mr Head

      This article describes the method to adjust the servo gain for
a hard disk drive using read/write head which has the offset between
read and write head elements such as Magneto Resistive head.

      After writing data (4) by write head (2) of such head (Fig. 1),
the read element (1) should follow at the offset position (3) to read
the written data (4) (Fig. 2).  This offset is based on the
misalignment between the read and write head elements.

      When servo positioning error signal is produced from four burst
patterns (Fig. 3), a positioning error signal is expressed as
equation (A) as a function of a displacement d from track center
(Fig. 4).  In the Fig. 3 (a) and (b), the values A', B', C' and D'
mean the read head paths over respective servo patterns A, B, C and
D.  These A', B', C' and D' depend on the offset value d.  They also
depend on read head width, track pitch, etc.

      The read/write head has to follow on a track with an optimum
servo gain to minimize track positioning error signal even following
at the offset position.  But the servo gain is not constant within 1
track (Fig. 4).  As a result, positioning accuracy is worse according
to the gain variance.

      In this method, servo gain adjustment factor is expressed as a
function of the offset value d and other geometric parameter.  This
factor is based on the Positioning Error Signal (PES) and gain value.
These are expressed as a function of various geometric parameters.

      Positioning error signal = PES(d, read width, track width,
etc.)

         Gain value        = differential of PES by d
                      = Gain(d, read width, track width, etc.)

         Adjustment factor = Gain(0)/Gain(d, read width, track width,
etc.)
                      = Adjust(d, read width, track width, etc.)
...(A)

      If other parameters a...