Dynamic magnetic information storage or retrieval – Checking record characteristics or modifying recording...
Reexamination Certificate
1997-10-16
2001-01-23
Kim, W. Chris (Department: 2753)
Dynamic magnetic information storage or retrieval
Checking record characteristics or modifying recording...
C360S046000, C360S053000
Reexamination Certificate
active
06178053
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a storage apparatus for magnetically recording and reproducing information to/from a disk medium and, more particularly, to a storage apparatus for reducing a read error caused by a thermal asperity of an MR head.
In association with an increase in information amount in an information-oriented society dealing with multimedia data in recent years, an increase in storage capacity of a magnetic disk apparatus as a peripheral apparatus of a computer is requested. In order to increase the storage capacity, it is necessary to increase a density on a medium recording surface by improving a bit density BPI or a track density TPI per unit length. In order to increase the bit density BPI on the medium recording surface, it is necessary to improve frequency characteristics of a magnetic head or medium, and to improve a magnetic head or a medium such that an output of the head is not dropped even at a high frequency and high frequency noises are not increased.
At present, the magnetic head is divided into a reproducing head and a recording head in order to efficiently reproduce data written in a medium. An MR (Magneto-Resistive) head is used as a reproducing head. The MR head converts a recorded magnetic field change into a resistance value change. The resistance value change is further converted into a voltage change by a preamplifier provided for a head IC, thereby reproducing recording data. When the MR head is used, a thermal asperity (called “TA” hereinbelow) phenomenon becomes a problem. The TA phenomenon is a phenomenon such that a resistance value is rapidly changed by heat generated when an MR device comes into contact with a medium scratch or dust on the medium and a base line of a reproduction waveform is shifted, so that data cannot be reproduced. Especially, since a head floating amount tends to be decreased more and more in order to efficiently reproduce data, there is a tendency such that the TA phenomenon often occurs due to a reduction in medium clearance of the MR head.
In a conventional magnetic disk apparatus, when a read error of data or a read error of servo information occurs by external noises, a shock, or the like, the error is recovered by re-reading the data. That is, the external noises and shock are temporary phenomena and the error can be usually avoided by the re-reading operation. On the contrary, the error due to the TA phenomenon is a fixed error that is caused by a scratch of the medium or the like, so that the error cannot be avoided by the re-reading operation. Usually, the error is regarded as a medium defect and an alternating process is executed. In the conventional magnetic disk apparatus, however, whether the read error is caused by the external noises or the TA phenomenon cannot be distinguished, the re-reading operation is executed in spite of a fact that the error is the unrecoverable error caused by the TA phenomenon. The number of times of the re-reading operations is generally determined to be, for example, 100 times. Consequently, with respect to the read error caused by the TA phenomenon, only after the re-reading operation was performed 100 times, the error is decided to be the unrecoverable read error and a message indicating that the operation was finished as an abnormality is reported to an upper apparatus. Consequently, it takes a long time for a process when the read error occurs due to the TA phenomenon and there is a problem such that an accessing performance of the magnetic disk apparatus largely deteriorates.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a storage apparatus such as a magnetic disk apparatus or the like in which a TA phenomenon is detected and an error avoiding process is properly executed, thereby raising accessibility.
A storage apparatus of the invention comprises: a fault detecting unit for setting a predetermined threshold level (hereinbelow, simply called a “threshold”) for a reproduction waveform signal into a read demodulating unit for demodulating read data and servo data which is used for head positioning from the reproduction waveform signal of an MR head serving as a read head and for outputting a fault signal when the reproduction waveform signal exceeds the threshold; and an error avoiding unit which is provided for the read demodulating unit and operates so as to avoid a read error when the fault signal is generated. The fault detecting unit detects an abnormal fluctuation of the reproduction waveform signal caused by the TA (Thermal Asperity) when the MR head is used as a read head and generates the fault signal. The error avoiding unit operates so as to promptly recover the abnormal fluctuation of the reproduction waveform signal due to the TA when the MR head is used as a read head. The error avoiding unit operates so as to promptly recover the abnormal fluctuation of the reproduction waveform signal for a predetermined time T in which the abnormal fluctuation of the reproduction waveform signal caused by the TA continues from a time point when the fault signal is obtained. The time T of the avoiding operation is set to a time within a time that is several times as long as the time of the abnormality fluctuation of the reproduction waveform signal due to the TA. The error avoiding unit raises a cut-off frequency of a high pass filter provided for the read demodulating unit when the fault signal is obtained, thereby promptly recovering the abnormal fluctuation of the reproduction waveform signal due to the TA. When the cut-off frequency of the high pass filter is raised, a frequency band of low frequency components which can be attenuated when a base line of the reproduction waveform signal due to the TA phenomenon rises like a pulse is widened and a fluctuation amount and a period of the base line are reduced. For example, with respect to the read data, a data lost length can be suppressed to a range where errors can be corrected by an ECC. When the fault signal is obtained, the error avoiding unit holds a gain of an AGC (Automatic Gain Control) amplifier provided for the read demodulating unit to a value at a time point when the fault signal is obtained, thereby suppressing an AGC loop from being disturbed by the abnormal fluctuation of the reproduction waveform signal due to the TA. Further, when the fault signal is obtained, the error avoiding unit holds a loop gain of a PLL which is provided for the read demodulating unit and is used for generating a read clock to the value at the time point when the fault signal is obtained, thereby suppressing the PLL loop from being disturbed by the abnormal fluctuation of the reproduction waveform signal due to the TA.
Further, according to the present invention, the fault detecting unit has a threshold setting unit for setting an optimum threshold for detecting the TA fault. The threshold setting unit monitors the presence or absence of an output of the fault signal while decreasing the threshold of the fault detecting unit in a state where the MR head is positioned to a predetermined position of the disk medium and a reproducing operation is executed. The threshold setting unit detects the threshold to discriminate the presence or absence of the generation of the fault signal and sets the threshold to an amplitude value AM of the reproduction waveform signal. A value (&agr;·AM) obtained by multiplying the detected amplitude value AM with a predetermined coefficient &agr; (for example, &agr;=2) is set as a threshold TH into the fault detecting unit. The threshold setting unit positions the head into a servo region of the disk medium and detects an amplitude value of the reproduction waveform signal. It is also possible to position the head into a data region of the disk medium and to detect the amplitude value of the reproduction waveform signal. The threshold setting unit also sequentially designates and positions the head (head number HH) every cylinder (cylinder number CC) of the disk medium, detects the amplitude value of the reproduction signal at w
Fujitsu Limited
Kim W. Chris
Neal Regina Y.
Staas & Halsey , LLP
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