Dynamic magnetic information storage or retrieval – Monitoring or testing the progress of recording
Reexamination Certificate
2000-12-15
2004-01-27
Holder, Regina N. (Department: 2651)
Dynamic magnetic information storage or retrieval
Monitoring or testing the progress of recording
C360S075000
Reexamination Certificate
active
06683736
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic recording device, and more particularly, to a method detecting a fault such as an open circuit, a short circuit, etc. of a magnetic recording head such as a hard disk, etc.
2. Description of the Related Art
For a conventional magnetic recording device, a fault such as an open circuit, a short circuit, etc. of a magnetic recording head is detected by monitoring its terminal voltage when the magnetic recording head actually writes data.
FIGS. 1A and 1B
are schematic diagrams explaining the conventional fault detecting method. In
FIG. 1A
, a rectangular wave is a voltage representing actual written data, whereas a wave indicated by a curved line is the terminal voltage of a head. Normally, there is a tendency such that a transient change (flyback) such as an overshoot, etc. occurs in the terminal voltage of the head at a time point when data is changed, and settles to a rectangular wave value thereafter.
In
FIGS. 1A and 1B
, levels
1
and
2
are two levels to detect a fault of the head. If the rectangular wave voltage corresponding to the data is equal to or lower than the level
1
, the head is detected to be short-circuited. If the voltage is equal to or higher than the level
2
, the head is detected to be open. In
FIG. 1A
, the voltage at a fault detection time point (
1
) is between the levels
1
and
2
, and it is properly detected that the head is not faulty.
In
FIG. 1B
, the frequency of written data becomes high, so that the time period during which the terminal voltage of the head remains at a rectangular wave voltage becomes very short after an overshoot occurs, and the data is immediately inverted. Accordingly, if the terminal voltage of the head is monitored, for example, at a time point (
2
), the value of the monitored voltage is determined to be equal to or higher than the level
2
although the head actually performs proper operations. As a result, it is determined that a fault occurs in the head, that is, an open circuit of the head is determined to occur. This is because the frequency of written data is higher than that in FIG.
1
A.
A flyback period during which a transient change such as an overshoot occurs in the terminal voltage of a head is determined by the inductance of a write coil of the head. Therefore, the flyback period remains nearly constant regardless of the frequency of written data. Consequently, the time period during which the voltage remains at a certain level of a rectangular wave becomes much shorter than that in
FIG. 1A
after the flyback period elapses, so that it becomes impossible to properly detect a fault of the head.
FIGS. 2A and 2B
explain a problem that the short circuit of a head cannot be properly detected. In
FIG. 2A
, the terminal voltage of the head is almost “0” which indicates a short circuit after the flyback period elapses, and the short circuit of the head can be properly detected by monitoring the voltage at a time point (
3
).
In the meantime, since the frequency of written data becomes higher in
FIG. 2B
, the time period during which the terminal voltage of the head is lower than the level
1
becomes very short. Accordingly, if the voltage is monitored, for example, at a time point (
4
), the short circuit of the head cannot be detected, and fault detection cannot be properly made.
If the margin between the flyback period and the data inversion cycle becomes smaller with an increase in the speed of a magnetic recording device as described above, a fault such as an open or a short circuit of the magnetic recording head cannot be properly detected when a fault is detected by monitoring the terminal voltage of the head, which corresponds to the written data. As a result, the data write operation is determined to be proper, and the data is written, leading to a data loss.
SUMMARY OF THE INVENTION
An object of the present invention is to allow a fault of a magnetic recording head to be properly detected even if the frequency of written data becomes higher with an increase in the speed of a magnetic recording device.
With a method detecting a fault of a magnetic recording head of a magnetic recording device according to the present invention, an electric current for writing low-frequency test data or a direct current is applied to a magnetic recording head at a time point when data is not actually recorded, and a proper/improper operation of the magnetic recording head is detected by determining whether or not the terminal voltage of the magnetic recording head is within a predetermined range.
By performing the process detecting a fault of a magnetic recording head at a time point when data is not actually recorded as described above, a fault can be properly detected even if the data write speed of a magnetic recording device is high.
REFERENCES:
patent: 5982568 (1999-11-01), Yamamoto et al.
patent: 6014282 (2000-01-01), Ito
patent: 6043945 (2000-03-01), Tsuboi et al.
patent: 6069760 (2000-05-01), Yun
patent: 6141162 (2000-10-01), Kotani
patent: 08-55304 (1996-02-01), None
patent: 11-16131 (1999-01-01), None
patent: 11-242836 (1999-09-01), None
Fujitsu Limited
Greer Burns & Crain Ltd.
Holder Regina N.
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