Dynamic magnetic information storage or retrieval – Monitoring or testing the progress of recording
Reexamination Certificate
2001-02-02
2003-12-30
Holder, Regina N. (Department: 2651)
Dynamic magnetic information storage or retrieval
Monitoring or testing the progress of recording
C360S060000, C360S075000
Reexamination Certificate
active
06671110
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a method for detecting an abnormal fly height of a magnetic head during a write operation in a hard disk drive (HDD) apparatus, a method for using the method for detecting abnormal magnet head fly height to prevent damage to written data, and a hard disk drive apparatus for implementing these methods.
2. Description of the Related Art
In an HDD apparatus, a head slider having a magnetic head is mounted on an end of a suspension arm. The suspension arm is swiveled in a plane parallel to the recording surface of a magnetic disk to move the magnetic head in a substantially radial direction of the magnetic disk to access data at a given position on the magnetic disk.
The head slider flies on an “air bearing” formed by the spinning of the magnetic disk while being elastically held by the suspension arm against the force for lift. Thus the head slider and the magnetic disk are close to each other without coming into contact with each other and a constant distance between them is maintained. The distance between the head slider and the magnetic disk is called “fly height.”
The fly height of the magnetic head can become abnormally high during the operation of the HDD apparatus. This may be caused by a disorder of the air bearing due to a thermal asperity or dust on the magnetic disk, or a shock from outside of the HDD apparatus. If the magnetic head flies abnormally high, the level of a signal reproduced by the magnetic head drops. If a write operation is performed during such a period, data cannot be recorded correctly, even though the write operation is completed with no error being detected. The data recorded incorrectly may not be recovered even if error-correcting capability is used during a read operation.
To prevent such damage to data during a write operation, a method for detecting an abnormal fly height of a magnetic head based on an output waveform of a servo signal has been proposed. If the fly height of the magnetic head becomes abnormally high, the high frequency property of a signal reproduced by the magnetic head and amplified by an amplifier may be degraded. For example, assuming that the amplitude of a servo signal is the same, an output waveform when the flying height is normal as shown in
FIG. 13A
would change into a waveform having an increased width and area as shown in FIG.
13
B. To prevent this, according to a prior-art method, a variation in the fly height of the magnetic head is detected by measuring the peak value (amplitude) and area of the output waveform of a servo signal and calculating a ratio between these values.
However, for the prior-art HDD apparatus in which an abnormal fly height of a magnetic head is detected based on the ratio of the peak value (amplitude) to area of the output waveform of a servo signal as described above, an extra circuit for measuring the peak value of the output waveform as well as a circuit for measuring the area of the output waveform is required, increasing the cost of the apparatus.
SUMMARY OF THE INVENTION
A method for detecting an abnormal fly height of a magnetic head is disclosed. The method includes reproducing a servo signal recorded on a magnetic disk in advance by the magnetic head when a write operation for writing data on the magnetic disk by the magnetic head is initiated. Next, the gain of the servo signal based on the head part of the servo signal reproduced by the magnetic head is determined. The gain of the servo signal is then compared with a reference value to detect an abnormal fly height of the magnetic head. In an advantageous embodiment, the reference value is the gain of a servo signal determined when the fly height of the magnetic head is normal. Alternatively, in other advantageous embodiments, the reference value is based on the gain of a previous servo signal.
In another embodiment of the present invention, the amplitude of the servo signal is determined instead of the gain. The amplitude of the servo signal is then compared to a reference value that, in an advantageous embodiment, is the amplitude of a servo signal determined when the fly height of the magnetic head is normal. Alternatively, in other advantageous embodiments, the reference value is based on the amplitude of a previous servo signal. In a related embodiment, a hard disk drive apparatus utilizes an amplitude detection circuit to determine the amplitude of the servo signal. The amplitude detection circuit includes a full-wave rectifier that converts the servo signal into a DC signal. A sample hold circuit, coupled to the full-wave rectifier, is utilized to sample the converted DC signal to obtain the amplitude of the servo signal. The amplitude detection circuit also includes a capacitor coupled to the sample hold circuit and a reset switch that operates to store a maximum voltage of the servo signal during a certain period of time in the capacitor.
In another aspect of the present invention, a method for writing data on a magnetic disk is disclosed. The method includes reproducing a servo signal recorded on the magnetic disk utilizing a magnetic head in response to an initiation of a write operation. Next, the gain of the servo signal is determined. The gain is then compared with a reference value to detect an abnormal fly height of the magnetic head. It should be noted that in another advantageous embodiment, the amplitude of the servo signal may be alternatively utilized in place of the gain. In response to detecting an abnormal fly height of the magnetic disk, the write operation is terminated. In a related embodiment, the method further includes retrying the write operation after discontinuing the write operation in response to detecting an abnormal fly height.
The foregoing description has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject matter of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
REFERENCES:
patent: 6094318 (2000-07-01), Kim
patent: 6411458 (2002-06-01), Billings et al.
patent: 6483789 (2002-11-01), Kubota et al.
patent: 11298461 (1999-10-01), None
Baba Sachiyo
Fukushima Yukio
Tanka Hidetsugu
Ueda Tetsuo
Bracewell & Patterson L.L.P.
Hitachi Global Storage Technologies - Netherlands B.V.
Holder Regina N.
Martin Robert B.
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