Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
1999-06-11
2003-01-14
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
Reexamination Certificate
active
06507450
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to magnetic disk drives (disk drives), and more particularly to an efficient method of using a servo track writer (STW) for continuously recording servo information along one, continuous, single helix spiral.
2. Description of the Related Art
A conventional disk drive has a head disk assembly (HDA) including at a least one disk, a spindle motor for rapidly rotating the disk, and a head stack assembly (HSA) that includes an actuator assembly and a head gimbal assembly (HGA) with a transducer head for reading and writing data. The HSA is part of a servo control system that positions the transducer head over a particular track on the disk to read or write information from that track. The HSA earns its name from the fact that it generally includes a plurality of HGAs that collectively provide a vertical stack of heads called a “head stack.”
The industry presently prefers a “rotary” or “swing-type” actuator assembly that conventionally comprises an actuator body which rotates on a pivot assembly between limited positions, a coil that extends from one side of the actuator body to interact with a pair of permanent magnets to form a voice coil motor (VCM), and an actuator arm that extends from the opposite side of the actuator body to support the HGA.
A disk drive is ultimately used to store user data in one or more “data tracks” on the surface of its disks. Such data tracks are most commonly arranged as a plurality of concentric data tracks, but some disk drives have had a spiral data track as shown, for example, in U.S. Pat. Nos. 4,636,885; 5,583,712; and 5,619,387. In either case, special servo information is recorded on at least one disk surface so that the disk drive's servo control system may control the actuator, via the VCM, to accurately position the transducer head to read or write user data to or from the data tracks. In colloquial terms, the servo information provides the servo control system with the “your head is here” data it needs to attain and then maintain a desired head position. In operation, the disk drive's servo control system intermittently or continuously processes (read only) the pre-recorded servo information just before or while the disk drive processes (reads or writes) user data in the data tracks.
The servo information is factory recorded at the time of manufacture using an expensive and low-throughput manufacturing fixture called a servo track writer (STW). The STW records the servo information in special “servo tracks” on each surface of each disk, or on one dedicated disk, for later use by the servo control system when the drive is in the hands of the user. The servo tracks are generally used throughout the life of the disk drive without modification.
Earlier disk early drives used a “dedicated servo” system where one head and one disk surface provide the servo information for all of the other heads and disk surfaces. As shown in
FIG. 2
, however, the industry presently prefers an “embedded servo” system wherein the servo information is interspersed amongst the data on each surface of each disk. The servo information is contained in servo wedges
300
that are each divided into a plurality of servo sectors
310
. The servo sectors
310
are recorded concentrically in order to provide numerous concentric servo tracks (one entire rotation of servo sectors
310
). The servo wedges
300
precede a corresponding number of data wedges
400
that are ultimately used to record concentric data tracks
10
that are divided into a plurality of data sectors (not shown). Each data wedge
400
may contain a whole or fractional part of one or more data sectors (not shown). Because the servo information is provided in servo sectors
310
, an embedded servo system is sometimes called a “sector servo” system.
In recording the embedded servo information, the STW takes temporary control of the drive's write operation, repeatedly locates the write transducer to a desired radial position, and then writes, erases, or does nothing (remains idle) at specific angular positions between the head and a reference position of the disk as the disk rotates beneath the write transducer. In order to precisely locate the head where needed, a conventional HDA has first and second access ports (later covered with adhesive labels) for allowing the STW to “reach in” and temporarily control the radial position of the actuator and measure the angular position of the disk while recording the servo information. As to the radial position of the actuator, the conventional STW inserts a moveable “push pin” into the first port, commands the HDA's VCM to bias the actuator against the push pin, moves the push pin against the bias to move the actuator and the attached headstack, and measures the position of the push pin with a laser interferometer to control the radial position of the write transducer carried by the pin-guided actuator. As to the angular position of the write transducer relative to an index position of the disk, the conventional STW inserts a stationary “clock head” into the second port, records a “clock track” containing thousands of “clock marks” and one “index mark” (e.g. an extra clock mark or a gap) on a disk surface of one of the disks, and measures the angular position of the write transducer relative to the index mark by detecting the index mark and thereafter tracking (i.e. counting) the intermediate clock marks.
The conventional STW puts an embedded servo pattern onto a disk by recording concentric servo tracks in a plurality of discrete concentric “passes.” Each pass consists of moving the push-pin to “step” the headstack to a desired radial position, allowing the head to “settle,” and during one ensuing revolution of the disk, writing new servo information, erasing overlapping portions of previously written servo information, or remaining idle (neither writing nor erasing). On the first pass, the STW moves the write transducer to an outer diameter of the disk, and then records magnetic transitions at discrete angular intervals to record the servo information including track identification (track ID) data and servo bursts. During the second and each of the thousands of subsequent passes, the STW steps the write transducer inward by a fraction of a data track pitch (e.g. ½), waits for the write transducer to settle (as much as one full revolution), and then records the servo information during another full revolution, writing more magnetic transitions, trimming overlapping portions of previously recorded transitions, or holding idle, as appropriate for the desired servo pattern. In order to record concentric servo tracks, therefore, the STW must repeatedly step, wait, and record.
The conventional method of recording concentric servo tracks creates a manufacturing bottleneck because each HDA must remain in the STW for an extensive amount of time in order to step, wait, and record each pass that collectively make up the required servo information. It takes a relatively long time to make thousands of passes of step, wait, and record. For example, given a disk drive that has a spindle motor that rotates at 4,500 RPM, an actuator with an effective stroke (ES) of one inch, and an intended data track density of 8,000 tracks per inch (TPI), and further assuming that the STW steps the write transducer by ½ a data track pitch per pass, it would take 3.56 minutes to record the servo information, i.e.:
8,000
TPI
*
1
ES
1
/
2
TP
*
4500
RPM
=
3.56
minutes
The 3.56 minutes assumes 100% STW efficiency. In reality, however, there are other overhead times associated with recording the servo information. As noted above, the write transducer must be stepped after ending one pass and before starting another. The pass to pass “seek and settle” time, or time lag before the write transducer is ready to start a new pass, is one of the more costly overhead times associated with
Hudspeth David
Myers Dawes & Andras
Shara, Esq. Milad G.
Slavitt Mitchell
Western Digital Technologies Inc.
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