Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
1998-06-12
2001-02-20
Nguyen, Hoa T. (Department: 2753)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S075000, C360S078110, C250S23700G
Reexamination Certificate
active
06191911
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a servowriter positioning apparatus for use with a hard disk drive that allows the precise positioning of the servo-pattern writing heads that is required for successful servowriting. The present invention also relates to a track position sensor for providing the track position of read/write heads of a hard disk drive instead of the conventional servo-pattern.
BACKGROUND OF THE INVENTION
As the capacity and performance of hard disks continue to advance, the ability to provide higher resolution track position signals for read/write heads of a hard disk assembly (HDA) is becoming increasingly important. In order to maintain the position of the magnetic head along the center line of a desired track, servo information in the form of a magnetic servo pattern is prerecorded on the disk surfaces during the manufacture of disk drives. The device used to record the magnetic pattern is called a servowriter and of course the accuracy of the servowriter will be critical to the accuracy of the resulting servo-pattern and the accuracy of the position of the read/write heads.
Recently the data density of hard disk drives has grown by 60% per year, and for example a storage density of up to 2.7 GB per square inch with a track density of up to 13,700 TPI (tracks per inch) is commercially available from International Business Machines Corporation. It is likely that in the near future even greater densities will be available, e.g. up to 50,000 TPI. Since when servo-writing a head position accuracy within 1% of the track pitch is required, these ever greater track densities place major demands on the servo-writer accuracy.
PRIOR ART
Conventionally laser-interferometry based position sensing is widely used in current servowriters. U.S. Pat. No. 5,333,140 describes a system using a two-frequency laser interferometer as a position transducer in a servo-writer as shown in FIG.
1
. In this arrangement position of the drive arm carrying the servo write heads
30
is sensed through the movement of a retroreflector
31
that follows its motion. The retroreflector is mounted on an external stage
32
which pushes the servo heads along the radii direction. In this arrangement there is a delicate interface between the external stage and the drive arm, and hence the servo write heads are prone to slippage, warping and vibrations which resulting positioning errors in the servowriting and the resulting servo pattern.
FIG. 2
shows an attempt to improve this system with the retroreflector
31
attached to a rotary actuator
33
carrying the servo write heads
30
. In order to avoid the problems described above with reference to U.S. Pat. No. 5,333,140 the rotary drive arm is directly set in the servo loop. However, attaching a bulky retroreflector to the mid-span of the drive arm reduces the effective position resolution by 30-50% and increases the settling time of the servo write heads.
Furthermore, although the resolution and accuracy of a laser interferometer measurement system are high, such systems are expensive, complicated and large in size. It is hard to minimize the size and costs of servo writers, and because of the long settling time of servo write heads servowriting is a time consuming job—taking about five minutes for each hard disk assembly. As a consequence hard disk manufacturers require a large number of servo writers. There is therefore a clear need for a more accurate, more compact and more economic servowriter.
Since conventional servo writers are extremely expensive and sensitive to vibration, contamination and electromagnetic interference, they must be operated on heavy granite anti-vibration tables in a clean room that is itself protected from vibration and shock. For high-volume production these requirements present considerable problems of cost and quality control. Indeed while a magnetic servo pattern is conventionally used for positioning the read/write heads in a hard disk, the servo pattern occupies up 6-10% of the usable disk space and so it would be preferable to be able to be able to do away with the need for a servo pattern at all, so providing more usable space on the disk and eliminating the need for servo-writing.
SUMMARY OF THE INVENTION
According to the present invention there is provided apparatus for sensing the position and/or movement of a servo write head of a servowriter for a hard disk assembly, comprising: a grating member, an optical read head for reading position information of said grating member, at least one servo write head fixedly connected to said grating member, and an actuator for driving together the grating member and said at least one servo write head.
Preferably the at least one servo write head is supported on an actuator arm and wherein the grating member is fixed to the actuator arm for movement therewith, the actuator arm being rotatably driven by said actuator about an axis.
In a preferred embodiment, to increase the resolution of the apparatus, the grating member has an elongate form with a grating formed at one end thereof, and the at least one servo write head is located at a position approximately midway along the grating member between the axis and the grating.
Preferably the grating member may take the form as described in detail in copending application Ser. No. 08/824,759, that is to say it may comprise two parallel reflection grating sections, each of the two sections having the same pitch but being displaced relative to each other by one eighth of the pitch. The two grating sections may be separated by a smooth section for generating a focus error correction signal. The optical read head preferably includes a laser light source and the grating sections comprise alternating lands and grooves, the grooves having a depth equal to one quarter the wavelength of the laser source.
The optical read head may take a number of forms. Preferably the optical read head comprises a laser light source, means for dividing the laser light source into three beams, means for directing the three beams onto the surface of the grating member, means for detecting the beams reflected from the grating member, and means for outputting intensity-modulated signals corresponding to the motion of the grating member.
The actuator may cause the servo write head(s) to move linearly over the hard disk, for example along a radius, and may cause the grating member to likewise move linearly. Preferably, however, the actuator is a rotary actuator adapted to cause the servo write head and the grating member to rotate about an axis, and wherein the grating sections are arcuate with a centre of curvature corresponding to the axis of rotation of the servo write head and the grating member.
The servo write head(s) may be a specially dedicated head, however preferably the read/write heads of the hard disk assembly themselves are used for writing the servo pattern.
In such a way the present invention provides a more accurate, compact and economical apparatus for the accurate servo-writing of a servo pattern onto a hard disk.
However, the servo pattern still occupies 6-10% of the usable space on a hard disk. By means of the present invention the position and movement of the read/write heads can be accurately sensed and hence controlled without the need for any servo pattern at all.
Hence according to the present invention there is further provided apparatus for sensing the position and/or movement of the read/write heads of a hard disk assembly comprising, a grating member fixedly connected to a said read/write head, an optical read head for reading position information of said grating member, and an actuator for driving together said grating member and said read/write head.
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patent: 6034838 (2000-03-01), Touji e
Cai Lilong
Zhou Weidong
Burns Doane Swecker & Mathis L.L.P.
Davidson Dan I.
Nguyen Hoa T.
The Hong Kong University of Science and Technology
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