JPH05248814A - Magnetic disk media strength test method - Google Patents

Abstract

(57) [Summary] [Purpose] A test piece is pressed and slid on the surface of a rotating magnetic disk medium to detect vibrations and changes in friction resistance of the test piece.
By the method of determining the medium strength, the partial damage in the initial stage of the medium surface caused by the sliding is accurately detected without overlooking. [Configuration] Output 1 of AE sensor that detects vibration of test piece
6 and the strain gauge output 17 for detecting the frictional resistance are both obtained in synchronization with the rotation of the medium (signal 11). A change in the signal outputs 16 and 17 above a certain level is detected at a certain detection level, and the obtained signal (AE level sensor output 1
9a and the strain gauge level sensor output 19b) appear at the same angular position more than a predetermined number of times (for example, when the angle signal is used to detect a predetermined number of times at the position where the rotation phase is θ °), the reproducibility determination signal is It is output and it is determined that the surface of the medium has been partially damaged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a strength test method for a magnetic disk medium, and more particularly to a strength test method for a magnetic disk medium capable of reliably and accurately detecting a minute damaged and destroyed portion on the magnetic disk medium.

[0002]

2. Description of the Related Art Generally, in a magnetic disk device such as a hard magnetic disk, a magnetic head is levitated or brought into contact with a magnetic disk medium which rotates at a high speed for recording and reproduction, but dust is attached to the surface of the magnetic disk medium. If this happens, it will be sandwiched between the magnetic head and the medium and slide, causing damage to the surface of the magnetic disk. Therefore, when manufacturing a magnetic disk, it is necessary to manufacture a magnetic disk having a high strength with less damage and deterioration due to such sliding in consideration of such an accident. Therefore, the strength of the magnetic disk surface is tested. Is being done.

Conventionally, as a method for testing the strength of the magnetic disk surface, there is a method disclosed in, for example, Japanese Patent Publication No. 60-36012. In this method, a test piece made of the same material as the magnetic head is pressed and slid on the surface of the magnetic disk under test that rotates at a high speed for a certain period of time, and a change in sliding sound, a change in sliding friction torque, and a The change in the amount of dust is measured using a sound pressure gauge, a strain gauge, and a dust counter,
The strength of the magnetic disk surface is determined from these values.

[0004]

In the above-mentioned prior art, a test piece of the same material as the magnetic head is slid on the surface of the magnetic disk under pressure to perform a fixed number of slides (for example, 100K times, 50K times,
The strength of the magnetic surface of the magnetic disk is determined by measuring changes in the sliding noise, sliding friction torque, dust amount, etc. that occur after 30K times), and a general magnetic disk device is used. Although it has the advantage that the test results can be obtained in a relatively short time compared to the one that carries out the durability test such as loading and unloading of the magnetic head, the method of measuring the change of the sliding friction torque by the strain gauge has Due to the difference in frictional force due to the difference or partial decrease in the lubricant due to sliding before the damage occurs, a change in the torque occurs and an erroneous detection is made, which makes it difficult to make an accurate determination. In the method of measuring the change in the dust amount, it is not possible to accurately judge whether the increase in the dust amount is due to the abrasion of the magnetic disk or the abrasion of the test piece when using the easily-eroded test piece. With the method of measuring the change in the sliding noise, it is not possible to accurately obtain the site on the surface of the magnetic disk where the sliding noise occurs. In addition, AE (Ac
A method of detecting damage to the magnetic disk by detecting the vibration of an acoustic emission sensor is also conceivable, but this causes an increase in vibration due to the lubricant and the like that has fallen off the magnetic disk entering between the test piece and the magnetic disk. In some cases, this increase may be erroneously detected as partial damage to the magnetic disk. In actual sliding, the entire sliding part is not uniformly damaged, and partial damage occurs due to uneven lubricant, uneven surface, uneven magnetic film thickness, etc. In spite of the fact that the magnetic film is almost completely destroyed by the growth of the magnetic field, the above-mentioned conventional measuring method does not consider the occurrence of such partial (local) damage. Since only the average change in the characteristics of the entire sliding test position on the sliding surface of the disk surface can be obtained, it is not only possible to reliably and early detect the occurrence of minute scratches (the damage cannot be detected unless the damage increases to a certain extent), It was difficult to eliminate false detection and detect only true damage occurrence. In addition, since the damage state of the disk is determined after a certain number of times of sliding, it is difficult to detect the exact number of times of sliding at which the disk starts to be damaged.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art and to provide a vibration detecting means by an AE sensor,
By using the sliding friction torque detection means with a strain gauge, the angular position where the magnetic disk is damaged is detected by synchronizing with the magnetic disk rotation during the test, and the initial minute damage to the magnetic disk medium is erroneously detected. To detect without.

[0006]

In order to achieve the above object, the present invention provides a test by pressurizing and sliding a test piece to a radial position where the surface of a magnetic disk rotating at a constant rotation speed is tested. In a strength test method of a magnetic disk medium for detecting damage of a magnetic disk medium by measuring a change in vibration of the piece and a change in friction resistance, a change in vibration and a change in friction resistance of the test piece are measured by rotating the magnetic disk. It is characterized in that a partial damage detecting means for detecting partial damage at an arbitrary angular position of the magnetic disk medium is provided by measuring in synchronization with.

Specifically, the partial damage detection means is a frictional force and an ultrasonic wave signal (ultrasonic force) when a test piece is pressed and slid at a radial position (test track) for testing the surface of a magnetic disk medium under a certain condition. Required band, for example, 10 KHz to 300
A medium surface state detection means for detecting a medium surface state (damaged state) such as an acoustic emission signal (having a resonance peak in the frequency characteristic), a light reflectance, or the like, which has a relatively flat frequency characteristic at KHz. , The output of the medium surface state detecting means at the same angular position changes by a certain value or more with respect to the average value at the initial stage of the test, and the medium surface damage occurs when this change repeatedly occurs continuously for a certain number of revolutions or more. And a determination means for determining. Then, the sliding resistance (strength) of the magnetic disk medium is tested by measuring the cumulative number of times until the medium surface is damaged in this way.

Further, one or a plurality of outputs of various medium surface state detecting means for detecting the medium surface state such as the frictional force, the ultrasonic signal, the acoustic emission signal, or the light reflectance are constant. A comparator for detecting the increase above, a number of times recorder for recording the number of times that a change of a certain value or more at the same angular position is repeated repeatedly, and a surface when the number of times exceeds a certain value. It can be configured by a judgment circuit for judging that the damage has occurred.

[0009]

The operation based on the above configuration will be described.

According to the present invention, when a test piece is pressed and slid to a test position on the surface of a rotating magnetic disk and a change in vibration or frictional resistance of the test piece that occurs at that time is detected, In particular, by measuring these changes in synchronization with the rotation of the magnetic disk, partial damage (local damage) at an arbitrary angular position of the magnetic disk medium can be detected. As compared with the detection method in which only the average change in the characteristic value for one rotation is known, it is possible to reliably detect the occurrence of minute scratches without overlooking. Also, when the detection output at the same angular position changes by a certain value or more and the number of times this change is repeated reaches a certain number of times or more, it is judged that the surface of the medium is damaged, and the true damage is determined. The occurrence of can be detected without error.

Further, the sliding resistance of the magnetic disk medium is measured by pressing and sliding a test piece on the surface of the rotating magnetic disk medium under constant conditions and measuring the cumulative number of rotations until the surface is damaged. Intensity) can be determined.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram of the entire measuring system used in the present invention. In FIG. 1, 1 is a magnetic disk to be tested, 2 is a test piece, 3 is an AE sensor, 4 is a strain gauge for measuring a strain amount of a support spring of the test piece 2 due to friction, 5 is a rotation speed and a rotation angle detector. , 6 is a test piece support mechanism, 7 is a spindle motor, and 8 is a disk damage detection circuit.

The details of the disk damage detection circuit 8 are shown in FIG. In FIG. 4, 16 is the output of the AE sensor 3, 17 is the output of the strain gauge 4, 18a and 18b are AGC circuits, 19a and 19b are level sensors, 20 is a phase comparison circuit, 21 is a reproducibility comparison circuit, and 22 is a motor. It is a stop signal.

The AGC circuits 18a and 18b in FIG. 4 are the same, and the details thereof are shown in FIG. In FIG. 2, 9 is AE
Output of sensor 3 or output of strain gauge 4, 10 is AGC
An amplifier, 11 is a rotation index signal obtained from the rotation speed and rotation angle detection circuit 5, 12 is an integrator, 13 is a peak latch circuit, 14 is a reference level signal, and 15 is a level comparator.

The magnetic disk 1 to be tested whose surface has been cleaned is attached to the spindle 7, and the rotational speed of the magnetic disk 1 is set so that the peripheral speed at the test position in the radial direction is 20 m / s. Then, a part of the spherical test piece 2 made of the same material as the head is pressed and slid under the load of a practical magnetic head. The load may be increased or decreased depending on the acceleration test conditions. At this time, the rotation index signal 11 is counted and the frequency band 1 is added to the support mechanism 6 of the test piece.
AE sensor 3 of about ~ 100 KHz and strain gauge 4
Is attached, its output is amplified by an amplifier, and partial damage to the magnetic disk 1 is detected by the detection method described below in synchronization with the rotation speed.

First, the sensitivity of the measurement system is corrected in advance (sensitivity calibration).
As a result, a fixed number of rotation index signals 11 are counted after the test is started, and when the sliding of the test piece 2 and the magnetic disk 1 is stabilized, the gain is adjusted by the AGC circuit shown in FIG.

FIG. 3 is a diagram for explaining the operation of FIG. 2,
The operation principle will be described with reference to FIG. AE sensor output 9 (low output when there is no damage), AGC amplifier 1
It is input to the integrator 12 via 0, and the peak value (output of the peak latch circuit 13) of the integrated output (cleared by the index signal 11 for each rotation of the disk) as a result of this is output from the circuit 13. the output, as shown in the period T ₂ -T _3, the output of the integrator is rising period until reaching the peak value from the time exceeding the level of the last is held in its elevated levels thereafter.) the reference level The gain of the AGC amplifier 10 is controlled by the comparison output with the signal 14. The comparison output of the comparator 15 is 0
(The output of the peak latch circuit 13 becomes the reference level 14
Until the comparison output becomes 0, the gain of the AGC amplifier 12 is latched. In this way, the level is set when there is no damage (initial state). At the same time, the strain gauge output 9 is adjusted similarly. After the sensitivity correction (sensitivity calibration) is completed, the test is continued until a scratch is generated, and the disk damage is detected by the disk damage detection circuit shown in FIG.

FIG. 5 is an explanatory diagram of the operation of FIG. Figure 4,
The operation will be described with reference to FIG. An AE level sensor 19a and a strain gauge level sensor 1 that output a pulse signal when an output equal to or greater than a preset value is detected.
9b, AE sensor output 16 and strain gauge output 1
When 7 detects that the output exceeds the detection level, by comparing the angle (rotation angle of the magnetic disk) at that time with the angle detection signal (timing pulse), each output 16, 17 can detect the angle at which the output exceeds the detection level. (The angle θ in the figure) is detected. The angle detected by the AE sensor (output of the sensor 19a) and the angle detected by the strain gauge (output of the sensor 19b) are compared by the phase comparison circuit 20. As a result, if the angle positions are the same, the reproducibility determination signal 21 is output, and the reproducibility determination signal 21 is counted in synchronization with the rotation of the magnetic disk. When the reproducibility determination signals 21 are output at a plurality of angles at the same time, counting is performed at each angle. N = 1, at the same angle
2, ..., N, the motor stop signal 2 when a certain number of consecutive counts is detected (when there is repetitiveness)
2 is output and the spindle motor is stopped. In this way, the count number of the rotation index signal at the time when the partial damage of the magnetic disk is detected is used as the evaluation result.

As the test piece, the same material as that of the magnetic head and a part of the spherical surface is used as the test piece, but the test piece is not limited to this, and a hard material such as diamond or sapphire, or It is also possible to use a transparent material such as quartz or glass. When a transparent material is used, the test can be performed while observing through the sliding contact. Further, the damage detecting means is not limited to the above-mentioned embodiment, and any means capable of detecting a change due to damage within one rotation of the disk may be used.

The magnitude of the reference level signal 14 can be adjusted according to the magnetic disk under test.

[0022]

As described above in detail, according to the present invention, a change in vibration or a change in friction of a test piece which is pressed and slid on a magnetic disk medium is measured in synchronization with the rotation of the magnetic disk medium. By doing so, it is possible to detect partial damage at an arbitrary angular position of the magnetic disk medium.
There is an effect that it is possible to surely and accurately detect local minute scratches generated in the initial stage of the sliding test without fail. Further, since the detection output is obtained in synchronization with the rotation of the magnetic disk medium, the angular position where the vibration is generated is specified, and there is an effect that the sensitivity of the disk damage detection is improved.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a measuring device used in the present invention.

FIG. 2 is a configuration diagram of an automatic gain control (AGC) circuit.

3 is an explanatory diagram of an operation principle of the automatic gain control circuit of FIG.

FIG. 4 is a detailed configuration diagram of the disk damage detection circuit of FIG.

FIG. 5 is an explanatory diagram of an operation principle of a disk damage detection circuit.

[Explanation of symbols]

 1 magnetic disk medium 2 test piece 3 AE sensor (vibration detector) 4 strain gauge (friction resistance detector) 5 rotation speed and angle detector 6 test piece support mechanism 7 spindle motor 8 disk damage detection circuit 9 AE sensor output 10 Auto Gain Control (AGC) Amplifier 11 Rotation Index Signal 12 Integrator 13 Peak Latch Circuit 14 Reference Level Signal 15 Level Comparator 16 AE Output 17 Strain Gauge Output 18 AGC Circuit 19 Level Sensor 20 Phase Comparison Circuit 21 Reproducibility Judgment Circuit 22 Motor stop signal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tamotsu Sasaki 2880 Kozu, Odawara City, Kanagawa Stock Company Hitachi Ltd. Odawara Factory

Claims (1)

[Claims] 1. A test piece is pressed and slid to a radial position where a surface of a magnetic disk rotating at a constant rotation speed is tested, and a change in vibration and a change in friction resistance of the test piece are measured. In a strength test method for a magnetic disk medium for detecting damage to the magnetic disk medium, by measuring a change in vibration and a change in friction resistance of the test piece in synchronization with rotation of the magnetic disk, A strength test method for a magnetic disk medium, comprising a partial damage detection means for detecting partial damage at an angular position.