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Take-Off Height using a Piezoelectric Head

IP.com Disclosure Number: IPCOM000115822D
Original Publication Date: 1995-Jun-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 76K

Publishing Venue

IBM

Related People

Flechsig, K: AUTHOR [+4]

Abstract

Disclosed is a method to measure the disk surface roughness that is important for head/disk reliability, directly related to the disk contribution to head/disk clearance. This characteristic has been named Piezoelectric (PZT) takeoff height. The takeoff height is defined as the fly-height of the head at which the head minimum point would just clear the load bearing surface. To make the measurement, the PZT Root Mean Square (RMS), which is sensitive to slider bending resonances, is sampled at fixed head fly-height increments, starting with a fly-height sufficient to ensure the head clears the general disk topography. The RPM (and thus head fly-height) is decreased until the head is making continuous contact with the disk. At this point (i.e.

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Take-Off Height using a Piezoelectric Head

      Disclosed is a method to measure the disk surface roughness
that is important for head/disk reliability, directly related to the
disk contribution to head/disk clearance.  This characteristic has
been named Piezoelectric (PZT) takeoff height.  The takeoff height is
defined as the fly-height of the head at which the head minimum point
would just clear the load bearing surface.  To make the measurement,
the PZT Root Mean Square (RMS), which is sensitive to slider bending
resonances, is sampled at fixed head fly-height increments, starting
with a fly-height sufficient to ensure the head clears the general
disk topography.  The RPM (and thus head fly-height) is decreased
until the head is making continuous contact with the disk.  At this
point (i.e., after landing), the test sequence is reversed, and the
RMS sampled with increasing RPM until the original disk velocity is
reached.

      Fig. 1 shows the landing and takeoff PZT RMS curves of a
thin-film disk, with respect to disk RPM, disk velocity, and PZT head
fly-height.  The inset photographs show the PZT signal at sample
velocities.  Note the effect of "super-burnishing" during the first
landing.  The takeoff height is the fly-height at which the RMS
deviates from the background, or the "knee" of the curve.  Data show
that subsequent landings do not significantly change the takeoff
characteristics of the surface.  This measurement is highly
repeatable, and h...