Browse Prior Art Database

Method for Identifying Genuine Head-Disk Clearance Changes

IP.com Disclosure Number: IPCOM000118262D
Original Publication Date: 1996-Nov-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Easton, MC: AUTHOR

Abstract

Disclosed is a method known as dual-wavelength for measuring changes in the magnetic spacing of a readback element over a disk of a rotating storage device as described in (*). This method uses signals written at two different wavelengths. The average amplitude at each wavelength is measured and the ratio of these two numbers computed. At a later time, the calculation is repeated. The change in spacing between the two measurement times can then be estimated. However, the results may be incorrect if the readback element has suffered a change in state that alters its gain vs. frequency characteristic. In particular, a head state change may lead to the false conclusion that there has been a change in spacing.

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Method for Identifying Genuine Head-Disk Clearance Changes

      Disclosed is a method known as dual-wavelength for measuring
changes in the magnetic spacing of a readback element over a disk of
a rotating storage device as described in (*).  This method uses
signals written at two different wavelengths.  The average amplitude
at each wavelength is measured and the ratio of these two numbers
computed. At  a later time, the calculation is repeated.  The change
in spacing between  the two measurement times can then be estimated.
However, the results  may be incorrect if the readback element has
suffered a change in state  that alters its gain vs. frequency
characteristic.  In particular, a head state change may lead to the
false conclusion that there has been a  change in spacing.

      This invention introduces the use of an additional signal
written at a third wavelength to eliminate such false conclusions
when using the dual-wavelength technique.  With three signal
amplitudes available, the dual-wavelength method is applied to each
of the three distinct pairs of ratios, and three different estimates
are obtained of the change in spacing.  If these three estimates are
in good agreement, then it is likely that an actual clearance change
has taken place.  If the estimates disagree, then a quantitative
method is proposed for determining whether to accept that a spacing
change has taken place.

      Practical application of the method requires data tak...