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Optical Disk Axial Runout Test

IP.com Disclosure Number: IPCOM000106220D
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 4 page(s) / 150K

Publishing Venue

IBM

Related People

Power, RR: AUTHOR [+2]

Abstract

Some optical disks do not seat properly on the spindle surface of an optical drive because of a media defect. The problem generated by the optical disk not seating properly on the drive spindle is manifested in severe wobbling, wobbling which the laser focus servo is eventually unable to compensate for. This wobbling can eventually result in only a portion of the optical disk being useable for data storage. After this failure condition occurs, whatever data is stored on these wobbly disks must usually be migrated to good media, a process which consumes much time.

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Optical Disk Axial Runout Test

      Some optical disks do not seat properly on the spindle surface
of an optical drive because of a media defect.  The problem generated
by the optical disk not seating properly on the drive spindle is
manifested in severe wobbling, wobbling which the laser focus servo
is eventually unable to compensate for.  This wobbling can eventually
result in only a portion of the optical disk being useable for data
storage.  After this failure condition occurs, whatever data is
stored on these wobbly disks must usually be migrated to good media,
a process which consumes much time.

      Such wobble is typically not a problem for a new disk when the
write process begins at the inner radius of the disk, where the
effects of the wobble are the smallest.  The effect of the wobble
grows in a direct proportion with radius along the disk.  As the
amount of data stored on the disk grows, the radius at which writing
occurs grows and, thus, the severity of the impact of the wobble.
Eventually, it is possible that the wobble is so severe that the data
storage process must be terminated before the disk is full of data.

      A solution is to test the optical disk/drive combination when
the disk is first mounted on a drive and to discard immediately those
media showing defects.  In Fig. 1, a flow chart is shown for this
axial runout (wobble) testing.

      In Fig. 1, the AXIAL RUNOUT TEST subroutine is entered each
time a disk is mounted.  However, a user with a priority read request
could bypass this subroutine.  In that case, the AXIAL RUNOUT TEST
would be entered as soon as the disk became inactive, step 10.

      In step 11, the 3 counters are initialized to zero.  These are
the track counter i, the mount retry counter j, and the new drive
counter k.  The number of tracks per side of the disk is declared via
N.

      In step 12, the laser seeks to track i, which is either the
inner most track (i=0) or the outermost track (i=N).  In step 13, if
track i not already written, the algorithm branches to step 14 and
writes the volume I.D.  in each sector of that track.  If track i
already has the volume I.D.  in each sector, then track i is read in
step 15, providing that the maximum number of read tests was not
exceeded in step 23.  If the disk was already tested successfully
for, say, 5 times, then step 23 branches to a normal exit, step 20.

      If actual reading or writing takes place in steps 14 or 15, the
algorithm converges on step 16, where a query is made as to whether
focus errors were encountered.  If no focus errors were encountered,
the algorithm branches to step 17, where the track counter is
incremented by the number of tracks on a side of the disk.  Then, in
step 18, a check is made as to whether both the inner and outer
tracks of the disk were checked.  If both were, the retry counters of
j and k are reset to zero in step 19 and normal exit is made in step
20.

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