Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
1999-09-24
2003-02-11
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
Reexamination Certificate
active
06519107
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to head positioning in magnetic hard disk drives. More specifically, the present invention relates to a method for writing head position reference servo patterns on a magnetic data storage disk by employing a servowriter to record a coarse position reference burst pattern, and then by employing the disk drive servo to self-write a final fine position burst reference pattern based on the coarse position burst reference pattern.
BACKGROUND OF THE INVENTION
Magnetic hard disk drives conventionally employ rotary voice coil head positioners for rapidly moving a data transducer head between concentric data tracks during track seeking operations and for maintaining the head over a selected data track during user data writing or reading operations. The data transducer head is maintained in very close proximity to a rotating magnetic data storage surface by flying on an air bearing at approximately one microinch, or less, above the surface. In this way, lineal data storage densities can be made very high. As lineal recording densities have begun to approach practical limits, another more recent trend for increasing storage capacity has been to make effective head magnetic widths narrower and narrower, in order to reduce track width and thereby increase the number of concentric data tracks that may be defined on a disk storage surface of standard manufacturing size, such as 3.5 inches in diameter.
Dual head structures have been adopted in order to recover discernable flux transition signals recorded on the disk. An inductive write element is used to write flux transitions onto the disk, while a separate read element of magneto-resistive or giant magneto-resistive material is used to read the flux transitions from the disk. It is known to provide a relatively wide write element, and a relatively narrow read element. In fact, narrower read elements are presently preferred because they permit a track to be read even though the head may not be precisely registered with, or maintained at, a track centerline by the head positioner. This relaxed tracking tolerance means that a less complex and expensive head position tracking system (servo) can be employed within the disk drive product. The use of separate write and read elements necessitates different tracking target positions for reading and writing, because of the presence of manufacturing tolerances. When a rotary head positioner is used, the write-to-read offset (the radial separation between the optimum tracking targets for writing and reading on a given track) clearly varies across the stroke of the rotary positioner as a function of the skew angle of the head support structure (air bearing slider body) relative to the recorded track. This offset variation at any particular position is known as the “write-to-read offset”. One drawback of narrow read elements is that such elements make it difficult to obtain a good position error signal (“PES”) at all positions across the radial width of a data track when used with a traditional burst pattern, for example the pattern described in commonly assigned U.S. Pat. No. 5,170,299 to R. Moon, entitled: “Edge Servo for Disk Drive Head Positioner”, the disclosure thereof being incorporated herein by reference. This drawback requires provision and use of a special servo burst pattern that provides a usable PES at virtually all radial head positions, relative to actual center, for each track across the actuator stroke.
The write and read elements of dual head structures can have certain positional offsets, particularly when a rotary voice coil actuator is used to position dual-element heads. With a rotary actuator the positional offsets between the write and read elements vary over the rotational stroke of the actuator and head transducer relative to the disk surface.
Because the data tracks are placed very close together (high track density of 1,000 to 20,000 tracks, or greater, per disk radial inch) a head position servo loop is typically provided as part of the disk drive electronics in order to control the head positioner. In order to provide head position information to the servo loop, each magnetic storage surface typically carries recorded servo information. This information is most frequently “embedded” within each data track as a circumferential series of narrow servo sectors between user data sectors or segments, sometimes referred to as “wedges” or “spokes”. The servo information typically comprises certain phase-coherent digital information used during track seeking and coarse positioning operations, and fine position information typically in the form of burst patterns used for head tracking during reading and writing operations from and to a particular track. Once written during a servowriting step within the disk drive manufacturing process, servo sectors are thereafter protected by disk drive controller logic from overwriting as being denominated “read-only” areas of the disk's storage surface. As the head passes over a servo sector location, coarse and fine position information is sampled by the head, and this sampled information is provided to, and used by, the disk drive's servo control loop for closed loop control of the head positioning apparatus during track seeking and track following operations.
In order to provide precisely written servo information, very precise servowriting instruments, typically employing laser-based interferometer technology, are employed within “clean rooms” of the drive manufacturing facility wherein atmospheric particulate contamination is closely controlled. Clean rooms are required because the disk drive is typically servo-written with its interior exposed to the ambient environment. The laser-interferometer servowriter precisely measures actuator position of the disk drive. Based upon this precisely measured position, a drive head positioner, such as a rotary voice coil actuator, is moved under servowriter control from track to track while each data head in turn writes the servo information to an associated data storage surface. Once the servo pattern is written, it can be tested by a read back procedure while the drive remains at the servowriter station in order to verify that the servo patterns have been effectively and accurately written. It is known to write servo bursts with three passes per track under servowriter control. However, with a high number of tracks on each disk surface, the servo burst writing process can become very time consuming and therefore very expensive.
Representative examples of disk drive servowriters and servowriting techniques are provided in U.S. Pat. No. 5,748,398 to Seo, entitled: “Method for Writing Servo Signals onto a Magnetic Disk and Magnetic Disk Drive Equipped with Magnetic Disk(s) Having Servo Pattern Recorded by the Method”; U.S. Pat. No. 5,726,879 to Sato, entitled: “Control Apparatus, a Stage Apparatus and a Hard Disk Servowriter Apparatus Including a Robust Stabilizing Compensator”; U.S. Pat. No. 5,627,698 to Malek, entitled: “Servo Information Recording Method and Apparatus for an Enclosed Data Storage System”; U.S. Pat. No. 5,339,204 to James et al., entitled: “System and Method for Servowriting a Magnetic Disk Drive”, the disclosures thereof being incorporated herein by reference. One characteristic which is common to servowriters is that they are very complex and expensive items of capital equipment within the disk drive manufacturing process. Servowriter and related clean room costs must be amortized as an incremental cost burden of each disk drive being produced and servowritten.
It has been proposed to write a servo pattern on a surface of a reference disk with a servowriter. Following installation of the reference disk onto a disk drive spindle, the reference servo patterns are used to write embedded servo patterns onto other storage surfaces within the disk drive. Such approach is described by H. Ono, in an article entitled: “Architecture and Performance of the ESPER-2 Hard-Disk Drive Servowriter”,
IBM J. Res. Develop
. Vol. 37, No
Ehrlich Richard M.
Jeppson David B.
Lin Jong
Oki Kenji
Hudspeth David
Maxtor Corporation
Wong K.
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