Browse Prior Art Database

Asperity Knee Detection Using Harmonic Ratio Flyheight

IP.com Disclosure Number: IPCOM000120179D
Original Publication Date: 1991-Mar-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 84K

Publishing Venue

IBM

Related People

Smith, GJ: AUTHOR

Abstract

A method of measuring the clearance between a head and disk in a disk access storage device (DASD) using the readback signal is disclosed. This method measures the true clearance between a head and the disk roughness summits by inferring from the readback signal when contacts first occur during low flying conditions.

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Asperity Knee Detection Using Harmonic Ratio Flyheight

      A method of measuring the clearance between a head and disk in
a disk access storage device (DASD) using the readback signal is
disclosed.  This method measures the true clearance between a head
and the disk roughness summits by inferring from the readback signal
when contacts first occur during low flying conditions.

      To measure the true head/disk clearance using the readback
signal requires that one recognize that the vertical displacement
modulation of a slider caused by intermittent contact with disk
summits is different than that seen during normal head flight.  While
flying, a head attempts to comply with the disk surface and can do so
for modulating frequencies up to a few kilohertz.

      When the head is contacting disk summits, a new regime is
entered where the head displacement modulation is caused by both the
disk curvature and any intermittent contact with the disk.  As the
disk speed is reduced further, the head is forced to comply with the
disk curvature directly as well as a greatly increased number of disk
asperities.  In each of these three regimes, the head modulation is
distinct and, therefore, it can be used as an indicator of
intermittent contact.

      The invention presented requires monitoring the readback signal
from a magnetoresistive (MR) head while the disk speed is reduced and
the head remains on-track.  For inductive heads, the signal/noise is
too low to allow good measurements of the head signal at lower disk
speeds.  If the head flying height is reduced by means that do not
reduce the signal/noise, such as reducing the ambient pressure, then
this method will also work for inductive heads.  For MR heads, the
signal/noise is usually found to improve with lower speeds.  This
makes the MR head more attractive for thi...