Browse Prior Art Database

IP.com Disclosure Number: IPCOM000112067D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 47K

IBM

## Related People

Suzuki, H: AUTHOR

## Abstract

Disclosed is a technique to compensate the variation of Servo Gain of Hard Disk Drive (HDD) due to head tolerance of the width. This technique is implemented at servo track writing (STW) when servo data is written on the disk surface.

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Disclosed is a technique to compensate the variation of Servo
Gain of Hard Disk Drive (HDD) due to head tolerance of the width.
This technique is implemented at servo track writing (STW) when servo
data is written on the disk surface.

The relationship among head width, servo data, and servo gain
can be explained by Fig.1.  For example, head gap width is 4 &mu.m
and track pitch is 8 &mu.m, then head center is moved 1 &mu.m.

Servo%Gain =<A(V)>over<A(V)+B(V)>=<3> over <3+1>= 0.75

This equation is usually used on servo gain calculation on HDD.
A(v) and B(v) are the voltages read by the head.  The voltage is
proportional to the length of the servo data covered by the head.  In
this case, the lengths over A and B are 3 &mu.m and 1 &mu.m,
respectively.  In the case of a narrower head and a wider head, the
servo gain change is explained on Figs. 2 and 3.

The technique of this disclosure is to measure such variation
of servo gain and to record the results on a certain area of each
disk surface against each head on STW, because the facility of STW
has the capability to move the head by a submicron order and to write
the results.  This technique is useful if the increase of the track
is required without the increase of tolerance of head width due to
the cost point-of-view.

If the same calculation is applied on narrower and wider heads,
servo gain varies.  For example, where narrower...