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Bad Position Error Signal Detection and Correction Scheme

IP.com Disclosure Number: IPCOM000121870D
Original Publication Date: 1991-Oct-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 75K

Publishing Venue

IBM

Related People

Hagen, MD: AUTHOR [+3]

Abstract

This invention offers a method of Position Error Signal (PES) correction to corrupted readings which reduces the likelihood of instability without adding cost to the file. This is achieved by writing twice the number of PES samples on the dedicated servo surface than is required by the servo control algorithm. During a given sample time two PES samples (called even and odd samples) are read. The control algorithm computation begins when an even sample is read. During the sample time before the computation is complete, an odd sample will be read and stored. Normally, the odd sample is not used. If the even sample is judged to be corrupted, then the previously read odd sample is used in its place. The result is a more robust control scheme in the presence of bad PES readings.

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Bad Position Error Signal Detection and Correction Scheme

      This invention offers a method of Position Error Signal
(PES) correction to corrupted readings which reduces the likelihood
of instability without adding cost to the file. This is achieved by
writing twice the number of PES samples on the dedicated servo
surface than is required by the servo control algorithm.  During a
given sample time two PES samples (called even and odd samples) are
read.  The control algorithm computation begins when an even sample
is read. During the sample time before the computation is complete,
an odd sample will be read and stored.  Normally, the odd sample is
not used.  If the even sample is judged to be corrupted, then the
previously read odd sample is used in its place.  The result is a
more robust control scheme in the presence of bad PES readings.

      In some of today's Direct Access Storage Devices (DASDs) data
head positioning is done using a digitally controlled servo system.
Digital servo systems may read position information from a single
disk surface that has been chosen as the servo surface.  This surface
is called the dedicated servo surface.  The other surfaces in the
DASD are used to store the user's data.  Position error information
is read from this dedicated surface once every sample time.  The
sample time is selected to be often enough to properly control the
head position but is limited by how much time it takes the servo CPU
to compute the control algorithm after a sample is read.

      Once the Position Error Signal (PES) is read from the dedicated
surface the servo CPU calculates the control signal needed to hold
the actuator over the desired data track.  If this PES reading is
incorrect due to media defects, electronic noise, or whatever, then
that sample's control signal will be incorrect and caus...