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Browse Prior Art Database

Maintaining Tracking in the Presence of Optical Disk Surface Debris

IP.com Disclosure Number: IPCOM000113605D
Original Publication Date: 1994-Sep-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Bui, NX: AUTHOR [+2]

Abstract

Debris or large defects on the surface of a disk used for optical storage can disturb the ability of a disk drive to maintain the focus and position of the laser beam. Reducing the focus and tracking servo bandwidths when in the region of disk defects can allow the drive to recover previously written data and write adjacent sectors.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 100% of the total text.

Maintaining Tracking in the Presence of Optical Disk Surface Debris

      Debris or large defects on the surface of a disk used for
optical storage can disturb the ability of a disk drive to maintain
the focus and position of the laser beam.  Reducing the focus and
tracking servo bandwidths when in the region of disk defects can
allow the drive to recover previously written data and write adjacent
sectors.

      The bandwidth of the focus and tracking servo loops must be
kept high to accurately follow the surface of the disk in the
presence of shock and vibration.  Thus small excursions of the focus
and tracking error signals result in large corrective forces applied
to the actuators, to reduce the errors as quickly as possible.  When
the servo signals are corrupted due to the beam passing over disk
debris, the servos respond to the inaccuracies, exacerbating the
errors.

      Momentarily reducing the bandwidth of the focus and tracking
loops (Fig. 1) when debris is known to exist at a location on the
disk prevents the servos from executing a false reaction, but still
allows focus and tracking to be maintained unless shock and vibration
levels are continuous and large.  The beam is therefore able to pass
over the opaque area while maintaining tracking and focus, allowing
data to be transferred from the rest of the track.

The application of the bandwidth reduction is implemented under
microcode control.