Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2000-06-12
2004-12-28
Le, Kimlien (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S112170
Reexamination Certificate
active
06836451
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention broadly relates to optical servo systems. More particularly, the invention relates to the optical detection system used in an optically assisted disk drive to detect marks on a magnetic disk and thereby precisely locate the magnetic read/write head relative to tracks on the magneto-optical disk.
2. Brief Description of the Prior Art
Since the introduction of the personal computer in the 1970's and the development of the floppy disk, the need for greater and greater amounts of storage space has continued unabated. The original floppy disk could store less than 100 kilobytes and the most commonly used (3.5 inch) floppy disk today, introduced in the late 1980's can store 1.4 megabytes. Although fixed (hard) disks now store many gigabytes, there remains a need for removable storage media with high capacity.
High capacity removable storage media became popular in the 1980's with the advent of desktop publishing (DTP). Relatively large, clumsy, and undependable “cartridges” from Syguest, Iomega, and other companies were used to transport large DTP files that could not fit on a floppy disk, to a printing plant. High capacity storage media is still in demand today for transporting large files when a broadband connection is not available and for transporting confidential information without using the public network.
One high capacity removable media system which is growing in popularity is the “a:drive” from OR Technology Inc. of Campbell, Calif. While its outward appearance is almost indistinguishable from that of a 3.5 inch, 1.44 megabyte floppy disk drive, the “a:drive” provides 120 megabytes of storage on ultra high density disks, known as “LS-120” or “Superdisk” media. At the same time, the “a:drive” product is compatible with current and legacy 3.5 inch technology and can read and write to both 720 kilobyte and 1.44 megabyte disks. As its name implies, the “a:drive” can serve as a bootable drive in any system in which it is installed.
The “a:drive” achieves its high capacity and enhanced accuracy and reliability by using an optical positioning system for accurately guiding a magnetic dual-gap head that accommodates the differing track densities of conventional and ultra high density disks without error or mishap.
Prior art
FIG. 1
shows a dual media disk storage system for reading data from and writing data to the surface
10
of removable magnetic media
12
having an axis of rotation
14
and a plurality of concentric data tracks
16
. Although the disk drive system is capable of handling dual media, in this instance, for the sake of clarity, only one disk is shown, the well known 3.5 high density type that holds 1.44 megabytes when formatted.
A read/write head
18
is guided by an actuator
20
and actuator arm
22
which positions the read/write head
18
over a desired track
16
on the surface
10
of disk
12
. The actuator arm
22
carries a strip having a periodic reflection profile
24
which is used in this instance because the 3.5 disks do not carry any location markings on their surface. In this instance, the periodic reflection profile
24
is a linear encoder. Actuator
20
is under control of a conventional, closed loop servo system
28
which is responsive to a signal from an optical sensor
30
mounted on the underside of sensor housing
28
.
FIG. 2
shows in more detail how a split beam arrangement is used to detect either the reflection profile for a linear encoder when reading/writing 3.5 disks or the markings on the surface of an LS-120 disk when reading/writing it. The sensor system carried on the arm
22
includes, in addition to the light detector
30
, a laser source
32
, a hologram
34
, a lens array
36
and a rooftop mirror
38
. Light from the laser source
32
is diffracted by the hologram
34
and focused by the lens array
36
. The rooftop mirror directs the light and reflections to either the linear encoder
24
or the surface of an LS-120 disk
40
.
It can be appreciated from prior art
FIG. 2
that the sensor system requires multiple passive optical elements, all of which must be aligned during the assembly process. The alignment requires expensive tooling. Each passive element occupies a finite space and additional space must be provided for the alignment tooling. The sizes of the elements also require a large mechanical supporting structure.
In addition, it will be appreciated by those skilled in servo system shown in prior art
FIG. 2
is relatively large and wi a “full height” drive bay to be accommodated.
Additionally those skilled in the art will recognize th servo system for an LS-120 type disk drive requires a quadrature between the adjacent sensors; that the detection of the sensors m synchronous; and that the first stage of the pre-amplifier used in a typical optical servo system would be more effective by amplifying the tangential and radial tracking signals only and not the DC component, thereby allowing for a larger gain and more signal amplitude.
In the prior art, light from a laser is typically focused by passive optical elements to form three highly focused points of light at the plane of the disk. Other passive optical elements gather reflected light from these three points and focus the reflected light onto three separate detectors. The detectors produce track sensing signals that include a low noise pair of sinusoidal signals in exact quadrature indicating the track radial position.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an improved positioning device (referred to hereinafter generically as optical servo systems) that can be used for metrology, optical data storage, or data storage systems that use optical features on the media for tracking purposes.
It is also an object of the invention to provide optical servo systems for data storage devices that do not require alignment of elements during assembly of the data storage devices.
It is another object of the invention to provide an optical servo system for a data storage device that reduces the overall cost of the data storage device.
It is still another object of the invention to provide an optical servo system for a data storage device that is smaller in size than conventional optical pickup systems.
It is also an object of the invention to provide an optical servo system that provides built-in quadrature phase shift.
It is another object of the invention to provide an optical servo system in which the source and detector(s) are fabricated on a single substrate.
It is still another object of the invention to provide an optical servo system in which each of the optical detectors and apertures are small enough and close enough to provide a synchronous detection.
It is also an object of the invention to provide an optical servo system that requires fewer components in the first stage of a signal preamplifier.
It is another object of the invention to provide an optical servo system that operates without lenses.
It is still another object of the invention to provide an optical servo system that has a high signal to noise ratio.
In accord with these objects, which will be discussed in detail below, the present invention provides a lensless optical servo system having an unfocused light source and patterned photodetectors. The unfocused light is reflected by the markings on an LS-120 disk and the reflected light carries the pattern of the markings the considerable distance in its far-field to the photodetectors. The convolution of this light pattern and a mating geometric pattern on the photodetectors causes the photodetectors to generate signals representing the position of the track on the disk.
According to a presently preferred embodiment of the invention, set forth herein to illustrate the principals of the invention, a laser diode and three detectors are formed on the same silicon substrate. Further, according this illustrative preferred embodiment, sinusoidal metalization (a form of aperture) is applied to the detectors in the radial direction (radial
Cook Kirk
Farnsworth Stephen W.
Spaeth Werner
Fish & Richardson P.C.
Infineon - Technologies AG
Le Kimlien
LandOfFree
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