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Servo Scheme using Capacitive Sensing of Laser Ablated Marks on Magnetic Recording Disks

IP.com Disclosure Number: IPCOM000103824D
Original Publication Date: 1993-Feb-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 4 page(s) / 159K

Publishing Venue

IBM

Related People

Khanna, VD: AUTHOR [+2]

Abstract

Disclosed is a scheme that uses capacitive sensing of laser ablated marks on magnetic recording disks to provide a higher bandwidth active servo, thereby, allowing increased track density. The sector and tracking information is recorded onto the metallic layer magnetic disk by laser ablation during the servo-writing process. A capacitive sensor on the head is used to sense the off-track position by detecting the difference in capacitance between consecutive marks on adjacent data tracks. The off-track signal is used to drive the actuator, thus positioning the R/W head precisely on the data track. The resulting higher servo band width is expected to permit track densities approaching those of typical optical recording.

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Servo Scheme using Capacitive Sensing of Laser Ablated Marks on Magnetic Recording Disks

      Disclosed is a scheme that uses capacitive sensing of laser
ablated marks on magnetic recording disks to provide a higher
bandwidth active servo, thereby, allowing increased track density.
The sector and tracking information is recorded onto the metallic
layer magnetic disk by laser ablation during the servo-writing
process.  A capacitive sensor on the head is used to sense the
off-track position by detecting the difference in capacitance between
consecutive marks on adjacent data tracks.  The off-track signal is
used to drive the actuator, thus positioning the R/W head precisely
on the data track.  The resulting higher servo band width is expected
to permit track densities approaching those of typical optical
recording.

      The track density in magnetic recording is constrained by the
servo.  A typical track pitch on commonly used magnetic disks is
about 10 &mu.m which is an order of magnitude wider than that for
optical recording.  The servo signal is written into a few equispaced
sector areas of the disk during the servo- writing.  The R/W head is
servoed only when it flies over these sector servo areas, but flies
blind in between successive areas.

      To record and read data with a track pitch of a few &mu.m or
less requires more elaborate track servoing and wider servo bandwidth
such that the R/W head can be positioned precisely on the narrower
data tracks.  One way to achieve track positioning at the equivalent
level to that of optical recording is to provide embedded servo
information on the magnetic disks.  It could be in the form of
physical provisions which are sensed, for example, optically by a
laser beam to steer the R/W head precisely on the data tracks.  One
such scheme uses a laser diode and photodetector, mounted side-
by-side to the head on the slider, such that 1.5 &mu.m track pitch
and thus 17 KTPI can be achieved [1].  The scheme requires sample
servo marks formed on glass substrate disks, a laser diode on the
slider, and others components which add complexity to the system.

      In this disclosure, we propose to form micro-marks, for
sectoring and servoing, on the disks using laser ablation as the
process of servo writing.  The dimension of micro-marks is on the
order of 1 &mu.m, and so is the track pitch.  Capacitance sensing is
used to derive sector and servo signals at constant time intervals.
A R/W head with active sample servo is then able to record and read
data with track pitch potentially in the sub-&mu.m regime.

      Sector and servo marks on a proposed magnetic disk are
schematically shown in Fig. 1.  The marks are fabricated during the
servo writing process using laser ablation.  Laser ablation has been
used in write-once optical recording to create physical marks on
optical disks to encode data.  The limitation of mark size depends on
the  optical resolution, typically...