JPH0479003A - Magnetic recorder - Google Patents

Abstract

PURPOSE:To reduce the defect rate of a thin film head by self-degaussing the thin film head while gradually decreasing a recording current on the hysteresis loop of the head >=10 times each time the recording is completed, and starting reproduction within fixed time after self-degaussing is completed. CONSTITUTION:Under the control of a control part 30, a write data 13 synthesizing a degaussing data generated by a degaussing data generation circuit 1 just after a recorded data 12 is sent to a recording amplifier 2 according to the control of a write gate signal 14. A recording current 15 is gradually decreased by operating a gradually current decreasing circuit 3 just after a recording current 18 according to the control of the write gate signal 14, and time for gradually decreasing the current is made coincident to time for the degaussing data. The recording current 15 and the write data 13 are synthesized by the recording amplifier 2, and the recording current flows through a recording / reproducing switching circuit 4 to a thin film head 11. Then, the number of times for gradually decreasing the hysteresis loop of the thin film head is set >=10 times and after self-degaussing is completed, reproduction is started within 50mus. Thus, the data can be reproduced without lowering the error rate of the data.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital magnetic recording device, and particularly to a device using a thin film head.

[Conventional technology]

Thin-film heads have lower head noise and wider bandwidth than ferrite heads, so they can achieve high-speed, high-density magnetic recording, and are essential for high-performance magnetic recording devices.

On the other hand, thin film heads have a unique phenomenon caused by unstable magnetic domain behavior in the magnetic path. Such defective heads may be produced due to a phenomenon in which pulse-like noise is superimposed on the reproduced signal when reproduction is performed immediately after recording.

Such pulse-like noise occurs for about 5 mS immediately after the end of recording, but it tends to occur particularly concentrated during 200 μS immediately after the end of recording.

In disk devices, I
Pulse-like noise will be superimposed on portion D, and if an error occurs at this location, a rotation wait operation will be performed, resulting in a decrease in data throughput. In the worst case, data playback becomes impossible.

In small disk devices, the effect is particularly serious because the interval between the end of data and the ID section is as short as 10 to 20 μs because of the sector system.

In addition, in a disk device that performs sector servo, when pulse-like noise is superimposed on servo information, the S/N of the servo signal decreases, causing head positional deviation and reducing the data error rate. In the worst case, the beam will be zero.

A re-seek operation is required, which again reduces throughput.

[Problem to be solved by the invention]

An object of the present invention is to suppress the pulse noise caused by the defective thin film head, rescue the defective thin film head, and lower the head failure rate.

[Means to solve the problem]

We conducted a failure analysis of the defective thin film head and found that when the thin film head was demagnetized with AC after recording and then played back, the number of pulse-like noises decreased to 1/20, no error occurred in the ID section, and the data of the device was It was found that the error rate was also the same as with a good head.

[Effect]

In order to demagnetize the head after recording is completed, head demagnetization data is added after the recorded data, and the current is gradually reduced within the head demagnetization data period to cause the head to be AC demagnetized.

〔Example〕

An example in which the present invention is implemented in a 5' small magnetic disk device will be described. FIG. 1 is a block diagram of this embodiment, and FIG. 2 is a waveform of each part. Under the control of the control section 30 and under the control of the write gate signal 14, write data 13, which is a combination of the degaussing data 17 generated by the degaussing data generating circuit 1 immediately after the recording data 12, is sent to the recording amplifier 2. The recording data 12 is composed of an ID section 20 and a data section 21. The ID section 20 records cylinder numbers and head numbers in advance, and normally performs only reproduction. The data section 21 normally performs recording and reproduction. A gap 22 is provided between the n sector data 9 section 21 and the n + 1 sector ID section 20' in order to absorb rotational fluctuations of the magnetic disk 4o.

The time of this gap was 10 μS.

The recording current 15 is gradually decreased by operating the current decreasing circuit 3 immediately after the recording current 18 under the control of the write gate signal 14. The current gradual reduction time 19 is made to match the time of the demagnetization data 17. The recording current 15 and the write data 13 are combined by the recording amplifier 2 and sent to the thin film 1 via the recording/reproducing switching circuit 4.
A recording current is applied to 1.

In the case of reproduction, the signal read from the thin film head 11 is amplified by the reproduction amplifier 5 via the recording/reproduction switching circuit 4, the signal S/N is increased by the waveform processing circuit 7, and then converted into pulses by the pulsing circuit 8. Finally, data demodulation is completed in the discrimination circuit 9. Furthermore, the demodulated data is sent to the control section 30 and the quality of the data is checked.

If an error occurs in the ID section, the system waits for rotation, performs playback again, and checks the quality of the data.

Measurement circuit 6 for measuring pulse-like noise that occurs immediately after recording. A pulse count gate 24 was provided.

The control unit 30 controls the pulse count gate 24. The pulse noise measurement conditions are a count time of 100 μs, and measurement is performed immediately after degaussing is completed. Record/playback for 10s
This was repeated to obtain the total number of pulse-like noises. The noise detection level was set to four times the background noise. Data recording frequency is 10M
The demagnetization data was also set to the same frequency in Hz.

Regarding 100 thin-film heads with frequent pulse-like noise,
FIG. 3 shows the effect of gradually reducing the current. If the demagnetization data generation circuit 1 and the current gradual reduction circuit 3 were not canceled to gradually reduce the current, the total number of pulse-like noises was 200 on average. Degaussing data generation circuit 1. Using the current gradual reduction circuit 3 and adjusting the current gradual reduction time 19 to change the number of times the thin film head hysteresis loop gradually decreases, the result is 70 in 5 times and 11 in 10 times.
Q. 30 or above was zero. As a result of examining 150 non-defective heads, it was found that the current was zero even if it did not gradually decrease. Figure 4 shows the influence of pulse noise on the quality of reproduced data. After recording n sector day 9 part 21,
When reproducing the n+1 sector, if pulse-like noise occurs frequently, an error occurs in the ID section 20'. If an error occurs in the ID section, the subsequent data section 21' becomes invalid, so the control section 30 waits one revolution before reading the ID section 20'.

The vertical axis in FIG. 4 shows the number of times the ID section was reread due to an error when recording was performed 100 times using a thin film head that generated many pulse-like noises and the immediately following ID section was reproduced. If the current is not gradually reduced, a retry is always required due to an error in the ID section, but it has been found that if the number of times the current is gradually reduced is set to 10, the number of retries becomes zero. The reason for this was that if the pulse-like noise was kept to a small level by gradually decreasing the current, the FCC in the ID section would prevent errors and eliminate the need for retrials. In this case, it was confirmed that the error rate of the data section was 10-11, which was the same as in the case of a non-defective head.

In addition, in this case, increase the rotational accuracy of the disk to increase the gap 2.
It was confirmed that even when 2 was set to 0.1 μS, no ID section error occurred, and there was no problem even if data was reproduced immediately after the current was gradually reduced.

In this way, according to this embodiment, even if a thin film head that generates pulse-like noise is used, the ID section can be read out without rereading.
Moreover, the error rate of the data section can be made the same as that of a non-defective head.

〔Effect of the invention〕

According to the present invention, even when using a thin film head that generates pulse-like noise after recording, the number of times the thin film head hysteresis loop gradually decreases is 1.
If the number is 0 or more, data can be reproduced without re-reading the ID section and without reducing the data error rate, which has the effect that what was conventionally recognized as a defective head can be used as a good head.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a waveform diagram of each part of the block diagram. FIGS. 3 and 4 are graphs showing the effects of the embodiment of the present invention.

Claims (1)

[Claims] 1. In a digital magnetic recording device using a thin film head, each time recording is completed, the recording current is gradually decreased over a hysteresis loop of the thin film head 10 times or more to perform self-demagnetization of the thin film head, and after self-demagnetization is completed. A digital magnetic recording device characterized by starting reproduction within 50 μS. 2. The digital magnetic recording device according to claim 1, wherein the thin film head self-demagnetizing current waveform is a rectangular wave. 3. The digital magnetic recording device according to claim 1, wherein the self-demagnetizing current waveform of the thin film head is a triangular wave. 4. The digital magnetic recording device according to claim 1, wherein the self-demagnetizing current waveform of the thin film head is a sine wave.