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In-Situ DASD Head Flying Height Measurement Using Asperity Disk

IP.com Disclosure Number: IPCOM000100727D
Original Publication Date: 1990-May-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 3 page(s) / 92K

Publishing Venue

IBM

Related People

DeHillerin, CA: AUTHOR [+2]

Abstract

A method is described of measuring absolute slider-to-disk spacing in a direct access storage device (DASD) by quantifing a readback signal modulation resulting from a contact with a disk feature or asperity of known height. The readback signal modulation amplitude resulting from slider spacing changes is an exponential function of the slider-to-disk spacing. By measuring the modulation amplitude during contact with an asperity of known height, and then calculating the spacing change that results, an estimate of the absolute flying height of the slider is provided.

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In-Situ DASD Head Flying Height Measurement Using Asperity Disk

       A method is described of measuring absolute
slider-to-disk spacing in a direct access storage device (DASD) by
quantifing a readback signal modulation resulting from a contact with
a disk feature or asperity of known height. The readback signal
modulation amplitude resulting from slider spacing changes is an
exponential function of the slider-to-disk spacing.  By measuring the
modulation amplitude during contact with an asperity of known height,
and then calculating the spacing change that results, an estimate of
the absolute flying height of the slider is provided.

      An oscilloscope snapshot of readback signal amplitude
modulation during contact with a disk asperity is shown in Fig. 1 and
again schematically in Fig. 2.  The amplitude modulation shows a
head-disk contact producing a change in a readback signal as a
spacing between pole faces (gap) of a read element and a disk media
change.  If the disk asperity is higher than the head flying height,
an easily recognizable readback signal envelope waveform results as
shown.  This contact signature depicts the head sliding over the
asperity and then releasing. The average peak depth of the voltage
modulation is equal to the interference height between the head and
the asperity multiplied by the factor that relates the readback
signal change to the head-disk spacing change.  This factor is
derived from a spacing loss relationship for magn...