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Adaptive Just-In-Time Velocity Profile Algorithm for Power Savings in a Direct Access Storage Device

IP.com Disclosure Number: IPCOM000122972D
Original Publication Date: 1998-Jan-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 4 page(s) / 114K

Publishing Venue

IBM

Related People

Ottesen, HH: AUTHOR [+2]

Abstract

Disclosed is a unique, exceedingly simple and adaptive velocity seek-profile algorithm that is ideally suited for "just-in-time" servo for disk drive actuators. "Just-in-time" reduces the latency time to zero by adjusting the velocity profile. This implies that the selected data sector appears under the recording head "just-in-time". It extends power savings to several disk drive applications, since most power is expended in the acceleration/deceleration phase of the seek. It can also be used for evasive maneuvering of damaging protruding surface defects. For example, power savings from batteries in portable applications and reduction in actuator power dissipation in desk-top or Redundant Array of Independent Disks (RAID) applications.

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Adaptive Just-In-Time Velocity Profile Algorithm for Power Savings
in a Direct Access Storage Device

      Disclosed is a unique, exceedingly simple and adaptive velocity
seek-profile algorithm that is ideally suited for "just-in-time"
servo for disk drive actuators.  "Just-in-time" reduces the latency
time to zero by adjusting the velocity profile.  This implies that
the selected  data sector appears under the recording head
"just-in-time".  It extends  power savings to several disk drive
applications, since most power is expended in the
acceleration/deceleration phase of the seek.  It can also be used for
evasive maneuvering of damaging protruding surface defects.  For
example, power savings from batteries in portable applications and
reduction in actuator power dissipation in desk-top or Redundant
Array of Independent Disks (RAID) applications.  It is ideal  for
multimedia applications, where large amounts of data are transferred
between the system and the disk drives.

      Two common Direct Access Storage Device (DASD)-actuator
seek-velocity profiles are shown in Fig. 1.  The actuator accelerates
during a period T_a to a constant velocity V_max under acceleration
a, then coasts for a period T_c at constant velocity.  Deceleration
from V_max to zero velocity is accomplished over a period of T_d at a
deceleration d.  This minimum time profile is illustrated as profile
1.  The "just-in-time" profile is the dash-dot profile labeled 2.
All the parameters associated with this profile will be primed; i.e.,
T_a',T_c',T_d',a',d',V_max').  Note that the area under both profiles
is identical.

      Referring to Fig. 1, the minimum access-time T_min for a
relatively long seek and the corresponding acceleration time T_a and
deceleration time T_d are given by

      It is well known from engineering dynamics that integration of
the velocity v(t), gives the position x(t), i.e., x(t) = integral of
v(t)dt.  Thus, the area A under the seek-velocity profile, 1, is
equal to the seek length.  This area A can be expressed as

      The "just-in-time" seek-velocity profile, 2, in Fig. 1 can be
cleverly scaled by a factor k from the parameters of the minimum-time
seek-velocity profile, 1, by making the following changes to the
profile

      Substitution of the third Equation into a primed version of the
second Equation shows that the areas under the two velocity profiles
are identical, the third and fourth Equations show that any
mi...