JP2564491B2 - Magnetic disk test method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] A test method for a magnetic disk used in a magnetic disk device, and more particularly to a test method for detecting magnetic foreign matter contained in a magnetic film. For the purpose of detection using the extra pulse error test, a DC erase current is applied to the head coil in both directions during the extra pulse error test to write on the magnetic disk. It is configured to detect the presence or absence of foreign matter.

[Industrial applications]

The present invention relates to a test method for a magnetic disk used in a magnetic disk device, and more particularly to a test method for detecting a magnetic foreign substance such as a permanent magnet contained in a magnetic film.

A magnetic disk is generally a disk-shaped substrate on which a coating of a magnetic material is formed by sputtering or the like, and information is directly magnetized and written on this magnetic film by a head. Therefore, the molding state of the magnetic film directly affects information storage, and therefore is strictly controlled at the manufacturing stage of materials, film formation, etc., and after manufacturing. Here, as product management after manufacturing, there is a test in a state where the magnetic disk is actually used.

[Conventional technology]

Therefore, as a conventional magnetic disk test, there is an extra pulse error test, for example, as a track test for examining the state of a magnetic film. This is mainly for detecting pinholes generated in the magnetic film, and either positive or negative DC erase current is applied to the head to write in one direction magnetized to the magnetic film, and then read by the head. In, in the case where there is a pinhole, since the portion of the pinhole is not magnetized at the time of writing, the read waveform changes between positive and negative at both ends of the pinhole.
A pinhole is detected by observing the lead waveform.

[Problems to be solved by the invention]

On the other hand, although the material of the magnetic film is strictly controlled, it is not possible to completely prevent the contamination of foreign matter, and the foreign matter that is deficient in information storage can only be detected by a final test. As the defective foreign material, it is considered that a magnetic foreign material magnetized in one direction in advance is mixed. If this magnetic foreign substance is included in the magnetic film, a read error will inevitably occur.
It is desired to detect. When trying to detect this magnetic foreign substance by the above-mentioned extra pulse error test,
If the erase direction and the magnetizing direction of the magnet are the same, the peak value of the reproduction output pulse may be low and detection may not be possible.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a magnetic disk test method capable of detecting a magnetic foreign substance mixed in a magnetic film of a magnetic disk by using an extra pulse error test.

[Means for solving problems]

In order to achieve the above object, the test method of the present invention, in the case of a magnetic foreign substance, is magnetized in one direction in advance, so if erased in both directions in the extra pulse error test, the magnetization is clearly reversed in the foreign substance portion. We pay attention to the fact that it can be detected.

Therefore, an erasing current in one direction is applied to the head coil in the extra pulse error test to write in one direction on the magnetic film of the formula head, and then read. Next, the erase current is reversed in the opposite direction for writing and reading, and the presence or absence of magnetic foreign matter is detected from the read waveforms of both.

[Action]

According to the above-mentioned test method, when the magnetic foreign matter is mixed, the read waveform is largely changed at the foreign matter portion when the magnetization direction of the foreign matter and the writing magnetization direction are different in one of the two-way erase, so that the foreign matter is detected.

In this way, according to the present invention, it is possible to clearly detect the magnetic foreign substance by using the extra pulse error test.

〔Example〕

Examples of the test method of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 is a magnetic disk, which is formed by forming a magnetic film 3 on the surface of a disk-shaped substrate 2.

Reference numeral 10 denotes an extra pulse error testing device, which is a writing / reading head 11 arranged close to the magnetic disk 1.
The head 11 is provided with a coil 12 and a gap 13. The middle of the coil 12 is grounded and one end is 2
Is connected to one output side of the flip-flop 17 via the transistors 14a and 15a and the diode 16a, and the coil 12
Similarly, the other ends of the transistors 14b, 15b and the diode 16b
Connected by. Then, a positive direction erase signal is input to the set side of the flip-flop 17, and a negative direction erase signal is input to the reset side.

Therefore, while the magnetic disk 1 is rotated in the extra pulse error test, the forward erase signal "1" is first input. Then, the flip-flop 17 is set, and the output signal of the flip-flop 17 turns on the transistors 14a and 15a to turn on the coil 12.
As shown by the solid line, a DC erase current flows, and a magnetic flux is generated in the head 11 in a direction corresponding to this. Then, the leakage magnetic flux from the gap 13 magnetizes the magnetic film 3 in one direction as shown in FIG. After that, reading is performed by the head 11 and the read waveform in this case is checked. At this time, the pinhole is detected from the change state of the read waveform. On the other hand, when the magnetic foreign substance A is mixed as shown in FIG. 2 (a) and the magnetization direction of the foreign substance A is the same as the writing, the read waveform is slightly different as shown in FIG. 2 (b) due to the difference in magnetic flux level. I can't judge because I am disturbed.

Next, flip the negative erase signal “1”
Input to the reset side of 17 to reset. Then, the transistors 14b and 15b are turned on, a DC erase current flows in the coil 12 of the head 11 in the opposite direction, and the leakage flux in the gap 13 is also reversed, and is written as shown in FIG. 2 (a '). Then, after this, the read waveform is checked and the read waveform is checked. In this case, since the magnetism is clearly reversed in the portion of the foreign substance A, the read waveform largely changes as shown in FIG. A is detected.

It should be noted that when there is no foreign substance A, the read waveform does not change in both cases of erasing in both directions, and this can be judged.

Although the present invention is intended for magnetic disks, it is also applicable to magnetic tapes and the like.

〔The invention's effect〕

As described above, according to the present invention, since the presence or absence of magnetic foreign matter in the magnetic film of the magnetic disk is checked, the read error is eliminated and the quality is improved.

Since it is a method of erasing in both directions using the extra pulse error test, the test is easy and the detection accuracy is high.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a magnetic disk testing method of the present invention, and FIGS. 2 (a), (b), (c), and (d) are diagrams showing a magnetization state and a read waveform. In the figure, 1 is a magnetic disk, 3 is a magnetic film, 10 is an extra pulse error testing device, 11 is a head, 12 is a coil, and A is a magnetic particle.

Claims (1)

(57) [Claims] 1. A magnetic eraser is present on a magnetic disk (1) by applying a DC erase current to a head coil (12) in both directions during an extra pulse error test, and magnetic foreign matter mixed in a magnetic film (3) is read from both read waveforms in this case. A magnetic disk test method for detecting the presence or absence of (A).