Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data clocking
Reexamination Certificate
2001-08-31
2004-09-28
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data clocking
C360S048000
Reexamination Certificate
active
06798592
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method for writing servo tracks to a disk drive to reduce the sensitivity of the disk drive to sources of position error signal (PES).
2. Description of the Related Art
Disk drives generally have one or more rigid disks on which information can be permanently stored in the form of magnetic transitions written onto and read from the disks. These transitions are written onto and read from a plurality of generally concentric data tracks that are located on the disk. The reading and writing is performed by a head that is positioned over the disk surface by a rotary actuator. A servo system is provided on the disks to enable the head to access, or to seek, a particular track. One such servo system is an embedded servo system, where the servo information is written into servo sectors, i.e., arcuate portions of the concentric tracks reserved for the servo information. The servo sectors are located between data zones, i.e., acurate portion of the concentric tracks reserved for user data. Servo information is written into servo sectors in a process called servowriting.
Servowriting is performed during manufacturing in a device called a servo track writer. The servo track writer is configured to receive a disk drive sub-assembly, called a head disk assembly (HDA), that comprises one or more disks rotatably mounted on a spindle motor, a dedicated head mounted on a head actuator for each disk, and electronics designed to control the spindle motor, the head actuator, and the head. Once positioned in the servo track writer, the servo information can be written to the disks. The servo writing process also establishes the radial density of the tracks, which is typically measured in tracks per inch (“TPI”). More specifically, the servo track writer employs a push pin which is inserted into the HDA to engage the actuator arm. A head positioner circuit actuates the push pin by constant increments to position the heads radially over the disk while writing the servo information into the servo sectors. The HDA electronics biases the actuator arm against the push pin to facilitate precise positioning of the heads.
As mentioned above, the head is positioned over the disk on a rotary actuator and moved by constant increments by the push pin during servowriting. One consequence of the rotary motion of the head over the disk surface is that the head approaches the data zones at varying angles from the inner portion of the disk to the outer portion. At some point in the middle of the disk, a longitudinal axis through the head and a tangent line to the track rotating beneath the head are parallel. This is called the zero skew angle position. By contrast, at points on either side of the zero skew position, there is a skew angle between the longitudinal axis of the head and the tangent to the track. The skew angle increases as the head moves closer to the outer circumference. As a result, the tracks written near the outer circumference of the disk are narrower and closer together (i.e., have a higher track density) than the tracks written near the zero skew position.
Another result of higher skew angle at the outer diameter and the constant incrementing of the actuator by the push pin is that the TPI of tracks near the outer diameter is higher than the TPI near the zero skew position. Increased track density at the outer diameter has been considered a benefit because outer diameter tracks contain a higher proportion of bits than other tracks on the disk. However, track following is much more difficult at the outer diameter tracks for several reasons. The heads are subjected to more turbulence than at other parts of the disk. Also, the disk itself is less stable because vibrations induced in the disk, known as flutter, are greatest at the outer diameter. These and other factors make track following more difficult at the outer diameter compared to other positions in the range of motion of the actuator. This phenomenon can be observed as increased position error signal at the outer diameter tracks compared to other tracks in the drive.
SUMMARY OF THE INVENTION
A need exists for an apparatus and method to reduce the sensitivity of the servo system, as measured by position error signal, to turbulence and other physical stresses at the outer diameter. Further, there is a need to provide more servo margin at the disk outer diameter while at the same time increasing overall track density.
One aspect of the present invention is a method for reducing position error signal in a disk drive. The disk drive comprises a recording head, a rotary actuator, a spindle motor, and a storage medium mounted on the spindle motor. The storage medium comprises an inner circumference, an outer circumference, and a magnetic-storage portion between the inner circumference and the outer circumference. The magnetic-storage portion has a radial width. The magnetic-storage portion comprises a first radial band proximate the outer circumference that includes about one-third of the radial width. The magnetic-storage portion comprises a second radial band proximate the inner circumference that includes about one-third the radial width. The magnetic-storage portion also comprises a third radial band between the first radial band and the second radial band that includes about one-third the radial width. The method comprises writing a first plurality of generally concentric servo tracks to the storage medium in the first radial band at a first average servo track density. The method further comprises writing a second plurality of generally concentric servo tracks to the storage medium in the second radial band at a second average servo track density. The method further comprises writing a third plurality of generally concentric servo tracks to the storage medium in the third radial band at a third average servo track density. The first average servo track density is no greater than the second average servo track density. The first average servo track density is no greater than the third average servo track density.
Another aspect of the present invention is a disk drive that comprises a rotary actuator, a recording head mounted on the rotary actuator, a spindle motor, and a storage medium mounted on the spindle motor. The storage medium comprises an inner circumference, an outer circumference, and a magnetic-storage portion between the inner circumference and the outer circumference. The magnetic-storage portion has a radial width. The magnetic-storage portion comprises a first radial band proximate the outer circumference that includes about one-third of the radial width. The first radial band includes a first plurality of generally concentric servo tracks. The first plurality of concentric servo tracks are written at a first average servo track density. The magnetic-storage portion comprises a second radial band proximate the inner circumference that includes about one-third the radial width. The second radial band includes a second plurality of generally concentric servo tracks. The second plurality of servo tracks are written at a second average servo track density. The magnetic-storage portion further comprises a third radial band between the first radial band and the second radial band. The third radial band includes about one-third the radial width. The third radial band also includes a third plurality of generally concentric servo tracks. The third plurality of servo tracks are written at a third average servo track density. The first average servo track density is no greater than the second average servo track density. The first average servo track density is no greater than the third average servo track density.
Another aspect of the present invention is a servo track writer that writes servo tracks on a storage medium of a head-disk assembly. The head-disk assembly includes at least one recording head mounted on an actuator. The storage medium comprises an inner circumference, an outer circumference, and a magnetic-storage portion
Codilian Raffi
Viglione Joseph M.
Hudspeth David
Kapadia Varsha A.
Knobbe Martens Olson & Bear
Shara, Esq. Milad G.
Western Digital Technologies Inc.
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