JPH0680557B2 - Abnormal head contact detection device for magnetic disk device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] A detection signal from an AE sensor that is mounted on a magnetic head and detects an elastic wave generated by the contact between the magnetic head and a magnetic disk is amplified by an amplifier, and then the slider of the magnetic head is An abnormal head contact detection device for a magnetic disk device, which has improved S / N by deriving it through a narrow band pass filter having a cutoff frequency corresponding to the shape and material.

[Industrial application field]

The present invention relates to a magnetic head abnormality detection device for a magnetic disk device, and more specifically, in a state in which a signal detected by an AE sensor when the magnetic disk and the magnetic head are in contact with each other has an improved S / N ratio. The present invention relates to a signal detection configuration from an AE sensor to be taken out.

A magnetic head consisting of a slider provided with an electromagnetic conversion element,
It is placed on a magnetic disk having a magnetic film formed on its surface, and this magnetic disk is rotated at a high speed to generate an air flow between the slider and the magnetic disk, which causes the magnetic head to float above the magnetic disk. A magnetic disk device that records and reproduces information by a leakage magnetic field between a gap layer of a magnetic head and a magnetic film of a magnetic disk is well known.

In such a magnetic disk device, it is necessary to detect in advance a head crash phenomenon in which the magnetic disk and the magnetic head are continuously in contact with each other and damaged.

[Conventional technology]

Here, a general magnetic disk device will be described with reference to the schematic view of FIG. 5, the plan view of the main part of FIG. 5 shown in FIG. 6, and the side view of FIG. 5 shown in FIG.

As shown in FIG. 5, a large number of magnetic disks 3 are stacked and arranged at a predetermined interval on a rotary shaft 2 rotated by a spindle motor 1, and an arrow A is formed on the magnetic disk 3. A magnetic head 6 is installed on an arm 5 extending from a carriage 4 that moves in the left and right directions shown. As shown in FIGS. 6 and 7, the magnetic head 6 is installed on a gimbal structure 7 made of a thin plate member made of elastic steel, and is constituted by a slider 8 having a core. The gimbal structure 7 is installed on a spring plate 9 extending from the arm 5.

A small amount of dust or the like may adhere to the magnetic disk 3, and the slider (magnetic head) 8 comes into contact with the dust so that the magnetic head 8 and the magnetic disk 3 come into contact with each other, and this contact is repeated many times. Then, the magnetic disk 3 and the magnetic head 8
A head crash phenomenon occurs in which both are damaged.

When this head crash phenomenon occurs, it is necessary to replace the entire apparatus. Therefore, as shown in FIG. 7, the AE sensor is provided on the rear side of the surface of the slider 8 facing the magnetic disk 3.
A method of fixing 10 and detecting contact between the magnetic disk and the magnetic head has been considered.

The AE of the AE sensor 10 is an abbreviation for Acoustic Emission, which means the emission of sound, and is a phenomenon in which the strain energy released when a solid material is deformed or destroyed becomes a sound as an elastic wave and is emitted. is there. The frequency of AE is several 10KH
It is often an elastic wave (so-called ultrasonic wave) extending from z to several MHz, and an AE sensor for detecting such an AE wave uses a piezoelectric element such as lead titanate (PbTiO ₃ ).

[Problems to be solved by the invention]

By the way, such an AE sensor 10 is usually hermetically shielded in a metal case, and a signal line for deriving a detection signal of the AE sensor is also amplified by a low noise amplifier in a shielded line such as a coaxial cable.

However, since the AE sensor 10 mounted on the magnetic head needs to be small and lightweight, it is difficult to store it in the container, and since the signal line is attached to the arm 5 of the magnetic head, it has flexibility. There is a need. Therefore, there is a problem in that it is difficult to fix the gimbal structure 7 or the arm 5 on the gimbal structure 7 or the arm 5 completely by using a metal foil or the like, and it is easy to pick up electrical noise.

Further, mechanical noise generated from the gimbal structure 7 is also large. For this reason, 100KHz ~
Although the noise was removed using a band pass filter with a wide band of 1.2 MHz, the detection signal from the AE sensor 10 can be obtained only in a state where the S / N ratio is bad due to the reason described above, and therefore the AE sensor It was difficult to detect only the signal from the AE sensor resulting from the contact between the magnetic head 8 and the magnetic disk 3 among the signals obtained from FIG.

[Means for solving problems]

FIG. 1 is a circuit block diagram showing a signal processing configuration of a head abnormal contact detection device for a magnetic disk device of the present invention. As shown in the figure, signals detected by an AE sensor 21 are collected on a flexible printed circuit board 23, and It is introduced into the amplifier 25 via the printed circuit board 24. Further, this detection signal is taken out to the outside in a state where the S / N ratio of the signal is increased by the bandpass filter 26 having a cutoff frequency corresponding to the shape and material of the slider of the magnetic head.

[Action]

That is, in the signal processing of the head abnormal contact detection device of the magnetic disk device of the present invention, there is generally a phenomenon that electrical noise decreases as the band of the filter used is narrowed, and the machine generated by the gimbal structure 8 or the like. The dynamic noise uses a phenomenon that occurs in a narrow frequency band in which the gain becomes large in the frequency band of 200 KHz or less and the gain sharply decreases when the frequency exceeds 200 KHz.

It also occurs when the magnetic head and magnetic disk come into contact
The signal from the AE sensor has a wide band from the low frequency band to the high frequency band, and a peak occurs at a specific frequency depending on the shape and material of the slider on which the AE sensor is mounted. As a result, the S / N ratio of the detection signal from the AE sensor is improved by using an ultra-narrow bandpass filter that matches the peak of a specific frequency to correspond to the shape and material of the slider of the magnetic head used. Then, the contact phenomenon between the magnetic head and the magnetic disk can be easily detected.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing a main part of a head abnormal contact detection device of a magnetic disk device of the present invention, and FIG. 2 is a schematic view of an abnormal contact detection part of the head.

As shown in FIG. 1 and FIG. 2, the signal derived from the electrodes of the AE sensor 21 mounted on a large number of magnetic heads 20 is derived in the form of parallel connection, and the arm of the magnetic head that is a movable part. It is led out to the flexible printed circuit board 23 installed in 22. The signal derived from the flexible printed circuit board 23 is derived in the form of parallel connection, and the printed circuit board is installed in the non-movable part of the magnetic disk device.
Introduced in 24.

A signal derived from the printed board 24 is guided to an amplifier 25, and further a bandpass filter having a cutoff frequency corresponding to the shape and material of the slider of the magnetic head 20, for example, a bandpass filter 26 having a cutoff frequency of 400 KHz. Through the outside.

As described above, the cutoff frequency of the bandpass filter 26 needs to be changed depending on the shape and material of the slider of the magnetic head.

For example, 5.6mm (length) x 4.0mm (width) x 2.0mm (thickness)
With the ferrite slider of, the cutoff frequency of the bandpass filter 26 is 200 KHz, and the AE with a large S / N ratio.
A detection signal from the sensor is obtained.

Furthermore, for example, 4.6 mm (length) x 3.2 mm (width) x 1.6 mm
It has been experimentally confirmed that with a (thickness) ferrite slider, if the cutoff frequency of the bandpass filter 26 is 400 KHz, the detection signal from the AE sensor can be obtained with a large S / N ratio.

Here, FIG. 3 shows a signal waveform of the abnormal contact detecting apparatus for a head of the present invention in which a bandpass filter having a cutoff frequency of 400 KHz is inserted into 15 AE sensors corresponding to the number of 15 magnetic heads installed.

For comparison with FIG. 3, the detection signal waveform of the AE sensor by the conventional device is shown in FIG.

As shown in FIG. 3, the noise level value N is significantly smaller than the noise level N ′ shown in FIG. 4, and the detected signal from the AE sensor has a large S / N ratio. It was confirmed experimentally that the peak value P of the detection signal from the AE sensor is more prominent than the noise level. Therefore, the signal when the magnetic disk and the magnetic head are in contact with each other can be clearly determined with high reliability. It turns out that it can be detected.

On the contrary, as shown in FIG. 4, it is difficult to distinguish the noise level N'from the peak value P'of the detection signal from the AE sensor in the conventional configuration.

〔The invention's effect〕

As described above, according to the head abnormal contact detection device of the magnetic disk device of the present invention, the shape and material of the slider of the magnetic head are checked in advance, and the cutoff frequency of the bandpass filter is experimentally determined from the shape and material. By setting a bandpass filter with an ultra-narrow band just after the amplifier or in the middle stage, the S / N ratio of the detection signal derived from the AE sensor is significantly improved.

[Brief description of drawings]

FIG. 1 is a circuit block diagram used in a head abnormal contact detection device of a magnetic disk device of the present invention, FIG. 2 is a schematic diagram showing the device configuration of the present invention, and FIG. 3 is a diagram showing an AE detection signal waveform according to the present invention, FIG. 4 is a diagram showing an AE detection signal waveform by a conventional device, FIG. 5 is a schematic diagram of a general magnetic disk device, FIG. 6 is a plan view showing an essential part of FIG. 5, and FIG. It is a side view which shows the principal part of FIG. 1 to 3, 20 is a magnetic head, 21 is an AE sensor, 22 is an arm, 23 is a flexible printed circuit board, 24 is a printed circuit board, 25 is an amplifier, 26 is a band pass filter, and N is a noise level. , P indicates the peak value of the signal.

Claims (2)

[Claims] 1. An AE sensor (21) mounted on a magnetic head detects an elastic wave generated by contact between a magnetic head and a magnetic disk, amplifies the detected signal, and then detects the shape of a slider of the magnetic head and An abnormal head contact detection device for a magnetic disk device, which is derived through a bandpass filter (26) having a cutoff frequency corresponding to a material and detects an abnormal contact between a magnetic head and a magnetic disk. 2. The bandpass filter (26) according to claim 1, wherein the bandpass filter (26) is a narrowband bandpass filter having a constant cutoff frequency on the high-pass side and a constant on the low-pass side. An abnormal head contact detection device for a magnetic disk device according to item 1.