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Browse Prior Art Database

Disk Drive Over-Velocity Detector

IP.com Disclosure Number: IPCOM000118926D
Original Publication Date: 1997-Sep-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Related People

Serrano, LJ: AUTHOR

Abstract

In a closed loop seek, the servo estimates the actuator's velocity by using position information read from the disk. It uses this estimate to drive the actuator velocity to follow a designed velocity profile. In a typical seek, the servo drives the actuator to a "top-of-profile" value, then coasts for a period of time prior to decelerating. While traveling at this top-of-profile velocity, the applied control is zero.

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Disk Drive Over-Velocity Detector

      In a closed loop seek, the servo estimates the actuator's
velocity by using position information read from the disk.  It uses
this estimate to drive the actuator velocity to follow a designed
velocity profile.  In a typical seek, the servo drives the actuator
to a "top-of-profile"  value, then coasts for a period of time prior
to decelerating.  While traveling at this top-of-profile velocity,
the applied control is zero.

      A problem arises when the servo becomes disoriented, and the
estimate of velocity is invalid.  This can occur because of
preemptive seeks, unusual disk defects, or programming deficiencies.
In these cases, the servo may force the actuator to a much higher
velocity than  that defined by the top-of-profile.  The actuator will
then impact the  crash stop at a much higher velocity than that for
which the crash stop was designed.  This is a so called
"over-velocity" situation.

      One technique for preventing this situation is to integrate
the control either in the analog or digital domain.  This value is
approximately proportional to the velocity, though the analog method
does not account for the effects of static windage and the digital
method does not account for power amp saturation.

      Another technique is to use the servo controller to estimate
the velocity from information decoded from the disk.  If the entire
track ID is written each servo sector, it is possible to detect an
over-velocity situation using this information alone.  However, if
the servo is lost, it may fail to make use of this information.

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