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Optimizing Access Profiles to Minimize Head Fly Height Loss

IP.com Disclosure Number: IPCOM000102122D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 4 page(s) / 141K

Publishing Venue

IBM

Related People

Berg, L: AUTHOR [+2]

Abstract

Reliability of a disk file depends strongly on maintaining adequate head-to-disk spacing. When the head is changing radial position, the flow field under the head is affected by both the disk rotation and the actuator motion. Some motions of the actuator can cause more flyheight loss than others. In particular, for typical rotary actuator files, outward motions (toward the OD of the disk) cause much greater fly height loss than similar motions inward. It is possible to enhance file performance and reduce flyheight losses by selecting an actuator velocity profile for inward motion that is different from the one used for outward motion. Furthermore, if the file is designed to idle at the outside of the disk, most of the motions will tend to be the faster inward ones, and performance will be enhanced even more.

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Optimizing Access Profiles to Minimize Head Fly Height Loss

       Reliability of a disk file depends strongly on
maintaining adequate head-to-disk spacing.  When the head is changing
radial position, the flow field under the head is affected by both
the disk rotation and the actuator motion.  Some motions of the
actuator can cause more flyheight loss than others.  In particular,
for typical rotary actuator files, outward motions (toward the OD of
the disk) cause much greater fly height loss than similar motions
inward.  It is possible to enhance file performance and reduce
flyheight losses by selecting an actuator velocity profile for inward
motion that is different from the one used for outward motion.
Furthermore, if the file is designed to idle at the outside of the
disk, most of the motions will tend to be the faster inward ones, and
performance will be enhanced even more.

      In a disk file, the spacing between the head and the disk plays
a crucial role in determining the reliability of the file.  This
spacing is determined to a great extent by the nature of the air flow
field between the head and the disk.  In a rotary actuator disk file,
the air entering the air-bearing comes substantially from the leading
edge of the slider, but a significant amount of the air also comes in
from the sides of the slider.  This occurs because the slider is not
aligned with the flow due to the nature of the rotary actuator
geometry.  As the amount of side flow is increased, the flyheight of
the slider tends to drop since the air is not pressurized as
effectively as it would be if all the air entered at the leading edge
taper.

      For maintaining flyheight, and hence enhancing reliability, it
is important that the flow from the sides of the slider be minimized.
While it is not often possible to change the amount of air entering
the air-bearing from the sides during on-track flying, it is possible
to modify the extra amount of side-flow during track access.

      During track access, the head has an added side-on velocity
that draws air under the air-bearing from the sides.  This side flow
tends to bleed off pressurized air, so even though the head-on flow
is not reduced, the total pressure on the slider can be significantly
reduced.  Fig. 1 shows a typical rotary actuator file geometry for
the case when the actuator is moving the head outward on the disk.
The important velocities are the relative velocity of the disk as
seen from the head due to the disk's rotation, and the relative
velocity of the...