Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
1999-04-23
2002-06-25
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S025000
Reexamination Certificate
active
06411458
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a disk drive. More particularly, the present invention relates to a disk drive employing a method of monitoring transducer fly height to retire a defective data site on recording surface.
2. Description of the Related Art
During manufacturing of a disk drive, a defect discovery procedure is performed to detect sites on a disk surface in the disk drive which are defective and thus likely to subsequently cause unrecoverable errors during user operation of the disk drive. These defective data sites are termed “primary defects.” After locating the defective data sites, the defect discovery procedure marks them out in a table as defective locations on the disk surface which are not available for use during user operation of the disk drive. The defect discovery procedure includes writing a known data pattern to the disk surface with a transducer head and subsequently reading the data pattern from the disk surface. Defective data sites are identified by comparing the data pattern read from the disk surface with the known data pattern.
In order to statistically reduce the chances of encountering a defective data site after the manufacturing process (and thereby reducing unrecoverable errors reported by the disk drive), disk drive manufacturers commonly include data areas which surround or bound the defective data site as also unusable for storing data, a process known as “padding.” It is desirable to pad data sites because a defect (such as a scratch) might cause marginal error performance in data sites close to the defective data sites even though they were not detected during the defect discovery procedure.
Defective data sites which are not identified during manufacturing but encountered during user operation are termed “grown” defects. Many grown defects occur in locations adjacent to defective data sites found during defect discovery. Therefore, padding of the defective data sites also reduces the number of grown defects encountered during user operation, and reduces the chances of reporting an “unrecoverable error” as a result of the grown defect.
Transducer heads in current disk drives are designed to fly at increasingly low flying heights above the disk surface. Despite efforts to improve surface regularity of disk media, tiny irregularities known as anomalies or asperities can remain. These irregularities have a greater effect on a transducer head that is designed to fly closer to the disk surface. For example, anomalies or asparities on the disk surface can cause the transducer head to fly outside of a specified operating fly-height range. When the transducer head flies outside of the specified fly-height range, various problems can occur. For example, data which is being written to the disk surface tends to be unreliable. Furthermore, a high flying transducer head may be affecting or changing data written in adjacent tracks. Although the written data may be subsequently readable, the adjacent tracks may be damaged and unreadable. Also, a read error may occur causing the disk drive to begin a recovery process which can be very time consuming and possibly incapable of recovering the data.
A disadvantage with known defect discovery procedures that are employed during the manufacturing process is that they are not sensitive to a transducer head having a varying flying height which can deviate above the fly-height specification and unreliably write user data during a user operation of the disk drive. For example, although a read signal may appear acceptable during a read operation of the defect discovery procedure, the transducer head may be moving or bouncing around as it passes over a disk anomaly. Notwithstanding such fly-height variations, read channel circuitry in the disk drive may be able to recover the data in the read signal. However, an undetected disk anomaly causing movement (fly-height variations) of the transducer head may subsequently cause the transducer head to unreliably write user data while flying above a high-fly threshold during a user operation of the disk drive.
Various techniques can be used for measuring the flying height of the transducer head. For example, PCT Patent Application No. PCT/US97/19019 to Carlson et al., filed on Oct. 10, 1997, suggests measuring the flying height by using the ratio of the magnitudes of two analog read signal portions having different frequencies. The Carlson PCT patent application further suggests monitoring the flying height by detecting the number of peaks in a read signal to determine whether the head is in a fly-height range during a user write operation of the disk drive. The Carlson PCT patent application discloses postponing the user write operation when the head is detected outside of the fly-height range.
U.S. Pat. No. 4,777,544 to Brown et al. suggests a method and apparatus for in-situ measurement of head/recording medium clearance. A periodic signal is written to the disk surface, and subsequently read back. The flying height of the transducer head is lowered to zero, and a second signal is read back defining a first signal. The first flying height is calculated as a ratio, expressed in decibels, of the first and second signals times the wavelength divided by a constant.
U.S. Pat. No. 5,377,058 to Good et al. suggests fly-height servo control of read/write head suspension. The fly-height of the transducer head is dynamically adjusted to a reference fly-height using a servo loop. The dynamic adjustment of the transducer head fly-height is accomplished using a piezoelectric element.
U.S. Pat. No. 5,410,439 to Egbert et al. suggests a disk file with clearance and glide measurement and early head crash warning. A disk glide test is performed prior to the disk file assembly step in the manufacturing process. The glide test seeks changes in head/disk clearance, reflected by changes in a read back signal. Egbert et al. suggest that such changes may be attributable to irregularities on the disk surface such as aspirates, which can result in catastrophic failure due to head/disk contact. If a glide defect is found, the disk would be replaced due to an almost certain impending head crash.
There is a need for a defect discovery procedure that is sensitive to a transducer head having a varying flying height which can deviate above the fly-height specification and unreliably write user data during a user operation of the disk drive.
SUMMARY OF THE INVENTION
The invention can be regarded as a method of manufacturing a disk drive that includes a transducer means designed to comply with a fly-height specification while flying above a disk. The method includes generating a warning signal representing a condition in which the transducer means is flying outside the fly-height specification as a result of flying above a defect site within a physical sector having a physical sector address. The method includes associating the warning signal with a defect site address that points to the defect site and storing the defect site address in a defect discovery table. The method further includes using the defect discovery table to locate the physical sector address. The method includes storing the physical sector address in a defect management table to retire the physical sector.
The invention can also be regarded as a method of retiring a defective data site on a disk in a disk drive. The disk has a data region for storing data. The disk drive includes a transducer means designed to comply with a fly-height specification while flying above the disk. The method includes reading the data stored in the data region to produce a read signal having a first fly-height varying component and a second fly-height varying component. The method further includes providing a threshold value and generating a warning signal responsive to the first and second fly-height varying components and the threshold value when the transducer means is flying outside the fly-height specification. The method includes retiring the defective data site on the disk in response to the
Billings Russell A.
Shea Michael J.
Shara, Esq. Milad G
Western Digital Technologies Inc.
Wong Kin
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