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Glide Test Technique

IP.com Disclosure Number: IPCOM000099632D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 4 page(s) / 103K

Publishing Venue

IBM

Related People

Annis, JW: AUTHOR [+2]

Abstract

Disclosed is a method for using a Harmonic Ratio Fly- height (HRF) analyzer to measure the spacing change between the pole faces on a magnetic recording head and the magnetic disk media in a Direct Access Storage Device (DASD). Using the HRF analyzer, a glide test is performed if the spacing change resulting from an asperity contact is distinct from other sources of spacing modulation.

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Glide Test Technique

       Disclosed is a method for using a Harmonic Ratio Fly-
height (HRF) analyzer to measure the spacing change between the pole
faces on a magnetic recording head and the magnetic disk media in a
Direct Access Storage Device (DASD).  Using the HRF analyzer, a glide
test is performed if the spacing change resulting from an asperity
contact is distinct from other sources of spacing modulation.

      Figs. 1 and 2 show the HRF output voltage change resulting from
an asperity contact.  Fig. 2 is a schematic of the event showing the
relevant times t1, t2, and tp, as well as the peak signal voltage Vp.
 The maximum spacing change resulting from an asperity contact is
calculated by dividing the peak voltage, Vp, by the HRF sensitivity
factor, the latter being expressed as a voltage change per unit
change in spacing (typically 1-10 millivolts per nanometer).  The
exact asperity height is found by further dividing the spacing change
by the slider stiffness coefficients.  This result is in a form that
provides the change in the spacing at the pole faces given a vertical
displacement along the line of asperity contact.

      In Fig. 3, the instrumentation required to perform an HRF glide
test is shown.  A requirement for the HRF analyzer is that a constant
frequency pattern be written on any track used in the glide test.
For some DASD types, such as those employing a sector servo, this
means that the HRF glide test should be performed before the DASD is
servo- written. Another desirable feature for the HRF glide test is
to allow the reduction of the head steady-state spacing by either
reducing the disk speed or by using a foreign gas w...