Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-02-03
2001-08-14
Edun, Muhammad (Department: 2753)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044280, C369S053130, C369S032010
Reexamination Certificate
active
06275455
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to memory systems and more particularly to a system and method for generating position error signals within a magneto-optical computer memory device.
2. Description of the Background Art
Efficient and economic storage of digital information is an important consideration of manufacturers, designers and users of computing systems. In magneto-optical storage devices, digital data is typically stored in tracks located on rotating disks of MO storage media. Close positioning of the adjacent disk tracks maximizes the amount of stored data on a storage disk, thus providing significant economic benefits to system manufacturers and users. Therefore, system designers frequently seek new and improved methods of. reducing track pitch to permit greater storage capacity on the storage media.
Referring now to FIG.
1
(
a
), a plan view of a front surface
112
of a magneto-optical storage media
110
is shown. In magneto-optical storage devices, digital data is typically written into and read from a series of concentric or spiral tracks
114
located within a plurality of data wedges
177
on the surface
112
of storage media
110
. In practice, the digital data is read from the front surface
112
of storage media
110
by projecting a laser-generated light spot from a flying read/write head onto a selected track
114
while storage media
110
is rotating, and then sensing the polarization of light reflected back from storage media
110
.
The read/write head must be accurately positioned above track
114
of rotating storage media
110
during a read/write operation on that track. Many factors (for example, imperfections in track symmetry) may cause the read/write head to be positioned slightly off the center of track
114
, thus requiring position correction of the head for acceptable performance during a read/write operation. One prior art position correction method utilizes a diffraction pattern to generate a position error signal from grooves that are positioned between tracks on the media. Another correction technique is the use of pre-patterned media with position marks embossed on the tracks within a plurality of servo sectors
178
to generate a position error signal (PES). The PES may then provide feedback to compensate for position errors by adjusting the radial position of the read/write head.
Referring now to FIG.
1
(
b
), a diagram of position marks on sample storage media tracks within a servo sector is shown. FIG.
1
(
b
) includes sample tracks 1 (
120
) through 5 (
128
). In FIG.
1
(
b
), five tracks are presented for purposes of illustration, however storage media
110
typically contains a significantly larger number of tracks. Furthermore, FIG.
1
(
b
) depicts track 1 (
120
) through track 5 (
128
) as being straight, whereas in practice they are typically circular. As shown in FIG.
1
(
b
), each track 1 (
120
) through 5 (
128
) has three associated position marks which may be repeated at selected intervals along their corresponding track. The position marks are formed by depressions in the surface
112
of storage media
110
and effectively reduce the reflectivity of surface
112
to thereby attenuate light reflected back to the read/write head from within a full width half maximum diameter of an optical spot
154
formed by an impinging beam of light. Since the operation of each track is similar, track 5 (
128
) will be used in conjunction with FIG.
1
(
c
) to describe the function of respective position marks
140
,
142
and
144
.
Referring now to FIG.
1
(
c
), a drawing of a reflectivity waveform corresponding to position marks
140
,
142
and
144
(FIG.
1
(
b
)) is shown. During a read/write operation on track 5 (
128
), the read/write head is positioned over track 5 (
128
) as media
110
rotates at a selected rate of speed. The read/write head initially encounters position mark
140
which is centered on track 5 (
128
) and which then generates a sync pulse
162
at time
164
.
Next, the flying head encounters position mark
142
which is positioned at a specified perpendicular distance “D” off-center of track 5 (
128
), in the direction of track 4 (
126
). Position mark
142
then generates a pulse “A”
166
at time
168
. The amplitude of pulse A
166
is relatively less than the amplitude of sync pulse
162
. Then, the read/write head encounters position mark
144
which is positioned at the same specified perpendicular distance “D” off-center of track 5 (
128
), but in the opposite direction of position mark
142
. Position mark
144
then generates a pulse “B”
170
at time
172
. The amplitude of pulse B
170
is also relatively less than the amplitude of sync pulse
162
. The radial position error signal (PES) for the read/write head may thus be obtained by taking the difference of the peak reflectivity amplitudes of pulse A
166
and pulse B
170
. The separation of the edges of position marks
142
and
144
determines the linearity of the PES.
In prior art storage systems, the optimal diameter of position marks is equivalent to the full width half maximum (FWHM) value with an optical spot formed by an impinging read/write laser beam, and the distance between adjacent tracks is typically two times this FWHM diameter. FIG.
1
(
b
) illustrates an intensity profile
159
of the light spot and the width
156
of the light spot at the FWHM value. In the prior art, spacing between adjacent tracks is also limited by the size and pattern of the position marks. The limit on increased spacing between adjacent tracks reduces the maximum data density available from the storage media. What is needed, therefore, is an improved system and method that overcomes the aforementioned limitations of the prior art.
SUMMARY OF THE INVENTION
In accordance with the present invention, a system and method are disclosed to generate position error signals within a magneto-optical memory device that implements very narrow track pitches relative to the prior art. In one embodiment of the present invention, narrow track pitches are enabled through the use of a magnetic super resolution storage media that utilizes an aperture within an optical spot. In the preferred embodiment, the track pitch is approximately the full width half maximum (FWHM) diameter of the optical spot. In the preferred embodiment of the present invention, tracks on the magnetic super resolution storage media are pre-patterned with position marks using a manufacturing process. The position marks preferably include a synchronization mark centered on each track followed by sequential “A” and “B” position error marks which are perpendicularly offset on the opposite sides of each track by a selected distance.
In the preferred embodiment, the tracks are sequentially numbered with whole numbers and include sequential pairs of adjacent odd-numbered tracks and even-numbered tracks. The odd-numbered tracks sequentially include an odd synchronization mark centered directly on the track, an odd “A” errbr mark positioned a selected perpendicular distance from the center of the track in a first direction, and an odd “B” error mark positioned the same selected perpendicular distance from the center of the track, but in a second opposite direction.
The even-numbered tracks sequentially include an even synchronization mark centered directly on the track adjacent to the odd synchronization mark, an even “B” error mark positioned the same selected perpendicular distance from the center of the track in the above-mentioned second direction, and an even “A” error mark positioned the same selected perpendicular distance from the center of the track, but in the above-mentioned first direction. In the preferred embodiment, the even “B” error mark is perpendicularly adjacent to an odd “A” error mark which is in the above-mentioned second direction. The even “A” error mark is perpendicularly adjacent to an odd “B” error mark which is in the above-mentioned first direction. In the preferred embodiment, the diameter of the error marks is appro
Carr & Ferrell LLP
Edun Muhammad
Katz Charles B.
Koerner Gregory J.
Seagate Technology Inc.
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