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Magnetic Field Modulation Coil Arrangement for Downward Compatibility with Magneto-Optic Media

IP.com Disclosure Number: IPCOM000116547D
Original Publication Date: 1995-Oct-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 122K

Publishing Venue

IBM

Related People

Demura, M: AUTHOR [+5]

Abstract

A method for enabling a Magnetic Field Modulation (MFM) optical drive to maintain backward compatability with existing Magneto-Optic (MO) media. A second actuator system is employed opposite the objective lens of the drive containing a magnet configuration.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Magnetic Field Modulation Coil Arrangement for Downward Compatibility
with Magneto-Optic Media

      A method for enabling a Magnetic Field Modulation (MFM) optical
drive to maintain backward compatability with existing Magneto-Optic
(MO) media.  A second actuator system is employed opposite the
objective lens of the drive containing a magnet configuration.

      The problem relates to bias magnets used in Optical Storage
Devices.  It is most easily explained through the use of figures.
Fig. 1 displays the typical bias coil arrangement used throughout the
MO rewritable Optical Drive Industry.  On one side of the media there
is the moving actuator.  On the other side of the media there is a
fixed magnet.  The fixed magnet is either an electromagnet type or a
rotatable permanent magnet type.  Drive's employing this technique
require at least 2 revolutions to write data: one pass to erase and
one pass to write.  Also note that the bias magnet need not be so
close to the media (typically a millimeter or so), allowing for
double-sided media and the according capacity benefits.

      During the last year several companies have introduced Optical
Storage products that can write and rewrite customer data in a single
pass.  They make use of a method called MFM which enables Direct Over
Write (DOW).  Fig. 2 shows the bias arrangement used by the Sony
MiniDisc and by Canon's 3.5" MFM DOW drive.  Again, the moving
actuator is on one side of the media.  On the other side of the media
is an electromagnet.  This electromagnet must be very close to the
media (within microns) because of fast field switching requirements.
This has two implications.  First, the magnet must either be flown
over the media (as in the DASD world) or be in contact with the
media.  The latter is what Sony and Canon are doing and is displayed
in Fig. 2.  Second, the media must be single-sided.  Notice also that
the electromagnet (called the slider head) is connected through a
suspension arm and a joint arm back to the moving actuator on the
other side of the media.  When the actuator moves to a desired track
location, the slider head is always directly opposing.  Note also
that seek times are limited by this bulky actua...