JP2954104B2 - Barkhausen noise detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to inspection of a magnetic head mounted on a magnetic disk drive, and more particularly to a method for detecting Barkhausen noise.

[0002]

2. Description of the Related Art An inductive type thin-film magnetic head includes a magnetic pole and a coil for applying a magnetic field to the magnetic pole. When a current is applied to the coil, a magnetic field is generated at the magnetic pole, and the magnetic pole faces the magnetic medium facing surface. A magnetic signal is recorded on a magnetic medium by leaking a magnetic flux from a small gap provided. At the time of reproduction, the magnetic flux generated from the magnetization of the magnetic medium is attracted into the magnetic pole through the gap, and current is generated in the coil based on a change in the magnetic flux density, thereby reproducing the magnetization information on the medium. In this recording and reproduction, the magnetization is transmitted by moving the domain wall in the magnetic pole.However, a slight change may be caused in the magnetic domain structure of the magnetic pole at the end of the recording operation. ,
There is a problem of so-called Barkhausen noise.

A conventional method for detecting Barkhausen noise involves recording / reproducing at a frequency at which a reproduced waveform interferes with adjacent bits (the lowest frequency or the highest frequency normally used in a target magnetic disk device, or 1/2 of the highest frequency). Was repeated several times, and the standard deviation divided by the average value of the output voltage of the reproduced waveform was quantified in percent.

This utilizes the fact that when Barkhausen noise occurs, the waveform is distorted, and the output voltage of the reproduced waveform fluctuates.

[0005]

In the above-described conventional detection method, the voltage value of a waveform on which a reproduced signal obtained from each bit recorded on a magnetic medium is superimposed is measured, and when a Barkhausen noise is generated. Since the distorted waveform is superimposed, the output value of the obtained reproduction signal is based on the fact that the output value of the reproduced signal has changed compared to that in a normal state where Barkhausen noise does not occur. It is desirable to set as high as possible so that signals from each bit interfere as much as possible.

However, if the operating frequency is set high, the voltage level of the obtained reproduction signal itself becomes low, so that the measurement is performed in a state where the S / N is low, and the influence of noise (white noise, medium noise, etc.) is reduced. Therefore, there is a disadvantage that the sensitivity to a change in the voltage value when Barkhausen noise occurs is reduced.

[0007] Although Barkhausen noise is originally generated at a low frequency, some heads rarely occur frequently. When such a magnetic head is measured by a conventional method, most of the measurements repeated a plurality of times are performed. Contains Barkhausen noise, the standard deviation is small, and there is a problem that it cannot be detected.

The present invention has been made in view of the above circumstances, and solves the disadvantages of the prior art. In particular, the present invention has a high detection power for Barkhausen noise caused by the instability of the magnetic domain structure of a magnetic head. It is an object of the present invention to provide a magnetic disk device which has a magnetic head with less Barkhausen noise selected by an inspection method having the following.

[0009]

SUMMARY OF THE INVENTION According to the present invention, recording and reproduction are performed in a single pattern at a low recording frequency at which reproduction waveforms obtained from respective bits recorded on a magnetic medium do not interfere with each other. The error rate is measured by the peak detection method using a series of multiple operations, and when the specified number of measurements is completed, the value when the error rate is the highest among all the measurement results is recorded as data. It is configured to be treated as. This aims to achieve the above-mentioned object.

According to the Barkhausen noise detecting method of the present invention, when a reproduced waveform read from a magnetic head includes distortion due to Barkhausen noise, the waveform distortion is also detected as a peak of the waveform. Since the data and the data obtained from the playback signal are different,
The error rate will be higher. On the other hand, when there is no distortion due to Barkhausen noise in the reproduced waveform, the obtained error rate value is low.

[0011]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a conceptual diagram showing the shape of a signal from input data recorded on a magnetic medium to reproduction data.

In FIG. 1, reference numeral 1 denotes input data;
0 is magnetization information recorded on the magnetic medium. 11 is a reproduction signal without Barkhausen noise, and 12 is a detection pulse obtained by differentiating the reproduction signal 11. Reference numeral 13 denotes a synchronization signal, and reference numeral 14 denotes reproduction data obtained from the detection pulse 12 and the synchronization signal 13. Reference numeral 21 denotes a reproduction signal in which Barkhausen noise has occurred, reference numeral 22 denotes a detection pulse obtained by differentiating the reproduction signal 21, and reference numeral 24 denotes reproduction data obtained from the detection pulse 22 and the synchronization signal 13.

FIG. 2 is a flowchart of the detection method according to the present invention. First, the magnetic medium is DC-erased (step 100). At this time, band erasing is performed so that an area in an arbitrarily set range can be erased in order to eliminate the influence of a magnetic field from an adjacent track.

Next, predetermined input data 1 is recorded on the magnetic medium (step 101). As described above, this input data 1 is performed in a single pattern at a low recording frequency such that reproduced waveforms obtained from each bit recorded on the magnetic medium do not interfere with each other.

Next, the magnetization information 10 recorded on the magnetic medium is read.
Is reproduced to obtain a reproduction signal 11 or 21. The reproduction signal 11 or 21 is converted into a detection pulse 12 or 22 by a differentiating circuit, and the detection pulse 12 or 22 is passed through the synchronization signal 13 to obtain reproduction data 14 or 24.

An error rate is calculated from the reproduced data 14 or 24 and the input data 1, and the value of the error rate is stored in the memory X (step 102). At this time, if the number of measurements is the first time (step 103), the value of the memory X is stored in the memory Y (step 104).

Next, a series of operations from the erasing of the magnetic medium to the calculation of the error rate are performed again, and the value of the memory X and the memory Y
(Step 105), and the higher error rate is stored in the memory Y (steps 106 and 10).
7). This operation is performed a set number of times (step 10).
8) Finally, the value stored in the memory Y is treated as the measured data of the magnetic head (step 109).

As shown in FIG. 1, if the reproduction waveform 11 has no Barkhausen noise, the reproduction data 14
Is almost the same as the input data 1, so that the error rate has a low value.

On the other hand, in the case of the reproduced waveform 21 in which Barkhausen noise has occurred, the obtained reproduced data 24 is different from the input data 1 because it contains "error" due to the influence of waveform distortion due to Barkhausen noise. , The error rate becomes a high value.

[0021]

Since the present invention is constructed and functions as described above, according to the present invention, a method of independently determining the Barkhausen noise of the inspected magnetic head for each recording bit is employed, and the method is repeated a plurality of times. Since the worst value among the measurements to be performed is treated as data, it has a high detection power even for Barkhausen noise that occurs infrequently.

Further, since a low frequency is employed for the recording frequency so that the recording bits do not interfere with each other, the output level of the reproduced signal also becomes high, and noises other than Barkhausen noise such as medium noise and white noise are generated. Since the influence can be reduced, it is possible to further enhance the detection power of Barkhausen noise.

Thus, by using the Barkhausen noise detection method of the present invention, it is possible to provide a magnetic disk device in which Barkhausen noise hardly occurs.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a process for obtaining reproduction data from input data when the present invention is implemented.

FIG. 2 is a flowchart of a detection method according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Input data 10 Magnetization information recorded on magnetic medium 11 Reproduction signal without Barkhausen noise 12 Detection pulse obtained by differentiating reproduction signal 11 Synchronization signal 14 Reproduction data obtained from detection pulse 12 and synchronization signal 13 21 Bulk Reproduction signal 22 in which Hausen noise is generated 22 Detection pulse 24 obtained by differentiating reproduction signal 21 Reproduction data obtained from detection pulse 22 and synchronization signal 13 100 to 109 Processing steps

Claims (6)

(57) [Claims] 1. A method for detecting Barkhausen noise of a magnetic head for performing a predetermined magnetic recording / reproducing operation on a magnetic medium, comprising recording magnetic information and measuring a bit error rate of a signal obtained by reproducing the magnetic information a plurality of times. A Barkhausen noise detection method, wherein the highest error rate in each measurement result is repeatedly used as data. 2. The Barkhausen noise detecting method according to claim 1, wherein said magnetic head is an inductive thin film magnetic head. 3. The Barkhausen noise detection method according to claim 1, wherein the measurement of the bit error rate is performed using a peak detection method. 4. The Barkhausen noise detection method according to claim 1, wherein the recording of the magnetization information is performed in a single pattern. 5. The Barkhausen noise detecting method according to claim 1, wherein the recording of the magnetization information is performed at a low recording frequency at which a reproduced signal does not interfere with an adjacent bit. 6. A Barkhausen noise detecting method for an inductive thin-film magnetic head for performing a predetermined magnetic recording / reproducing operation on a magnetic medium, comprising: Input data is recorded on a magnetic medium at a low recording frequency that does not interfere with each other, and in a single pattern, a reproduction signal is obtained by reproducing the magnetization information recorded on the magnetic medium, and the reproduction signal is differentiated by a differentiating circuit. Converting the detection pulse into a detection signal; obtaining the reproduction data by passing the detection pulse through a synchronization signal; calculating an error rate between the reproduction data and the input data; storing the error rate value in a first memory; If the number is the first time, the value in the first memory is stored in the second memory, and a series of operations from the erasing of the magnetic medium to the calculation of the error rate are performed again. Comparing the value of the first memory with the value of the second memory, storing the higher error rate in the second memory, and setting a series of operations from erasing the magnetic medium to calculating the error rate; A method for detecting Barkhausen noise, wherein the method is performed and finally the value stored in the second memory is used as the measured data of the magnetic head.