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Non-invasive Measurement of Circumferential (Theta) Recording Head Motion in Disk Drive

IP.com Disclosure Number: IPCOM000108001D
Original Publication Date: 1992-Apr-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 3 page(s) / 90K

Publishing Venue

IBM

Related People

Chainer, TJ: AUTHOR [+3]

Abstract

Disclosed is a method of measuring the motion of a magnetic recording head in the direction of the recorded track non-invasively by using the readback signal. Motion of the magnetic recording head in the theta direction affects the accuracy with which servo patterns can be written onto the disk surface. The patterns are read and demodulated to produce a radial position, which is input to a servo loop to maintain the head at a fixed radial position. Inaccuracy in the servo pattern contributes to track following error which in turn limits track density.

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Non-invasive Measurement of Circumferential (Theta) Recording Head Motion in Disk Drive

       Disclosed is a method of measuring the motion of a
magnetic recording head in the direction of the recorded track
non-invasively by using the readback signal.  Motion of the magnetic
recording head in the theta direction affects the accuracy with which
servo patterns can be written onto the disk surface.  The patterns
are read and demodulated to produce a radial position, which is input
to a servo loop to maintain the head at a fixed radial position.
Inaccuracy in the servo pattern contributes to track following error
which in turn limits track density.

      In this proposed method, a 2.5 MHz pattern is read by a data
head and detected to yield a digital signal output shown as "Head 1"
in Fig. 1. This signal is used as the clock source to  write a
replica of the first track with a different recording head on the
same disk stack (Head 2). The clock is generated with a phase-locked
loop, allowing the second track to be written 90 degrees out of phase
from Head 1.  The two detected signals are input to an "AND" gate
whose output pulse width is proportional to the phase or relative
timing between the two signals.  Relative motion of the two heads
will vary the pulse width and therefore the duty cycle. When the two
signals are in phase, the "ANDED" signal has a 50% duty cycle, and
when 180o out of phase, the duty cycle is 0%.  The "ANDED" signal is
averaged by an RC lo...