JPH07134098A - Hard disc evaluation testing method - Google Patents

Abstract

PURPOSE:To make possible the evaluation of endurance of a lubricant layer correctly based on information on the intensity of collision by rotating a disc substrate with a head contacting the disc substrate to measure the intensity of the collision. CONSTITUTION:A command for a low rotation speed inputted is provided to a motor 2. A head slider 8 fails to float at the rotation speed and instead, with the slider 3 contacting a hard disc substrate HD1, the HD1 rotates. After a fixed time passes from the rotation of the HD1, an AE signal is measured for a specified time. When the signal is outputted. the time of generating the AE signal and an AE output value are stored. With a head contacting the HD1, the HD1 is driven to rotate at a low rotation speed to measure the AE signal between the head and the HD1. Then, the endurance of the lubricant layer is evaluated based on the time at which the AE signal beings thereby making possible the evaluation of the endurance of the lubricant layer in an actual use of the hard disc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hard disk evaluation test method.

[0002]

2. Description of the Related Art A hard disk (hereinafter referred to as HD) is, for example, a magnetic recording medium capable of large-capacity recording and high-speed signal reading / writing in which a magnetic film is formed on an aluminum disc-shaped disk (substrate). , The disk is rotated at high speed (currently around 3600RPM) to obtain high-speed reading and writing of signals. Further, both the disk and the head are formed of a hard solid, and when they come into contact with each other, both are damaged. Therefore, in a hard disk, while the disk is spinning,
The head is levitated by the flow of air generated by the rotation of the disk. This flying height is currently about 0.2 μm.

However, in recent HDs, when the disk is stopped, the head is landed on the disk surface, for example, at the innermost circumference of the disk where no signal is read or written, and the motor orbits. The head and disk make contact and take off when landing and when stopping.
At this time, if abrasion powder is generated due to abrasion, the disk will be fatally damaged by the abrasion powder when the head moves to a place where signals are read and written while getting in between the head and the disk. A protective film layer, a lubricant layer, etc. are formed so as not to wear.

The durability of the lubricant layer is a very important issue for the durability of HD, and it is necessary to correctly evaluate the durability of the lubricant layer.

[0005]

There are currently two methods for examining the durability of such HD, one of which is called the CSS method and the other is called the DRAG method. . FIG. 4 is a diagram showing an evaluation method by the CSS method, and this method is a method in which the motor is repeatedly turned on and off at fixed time intervals and tested. That is, the rotation speed of the disk is 0 → 3600 in 12 to 20 seconds.
→ It is set to 0 rpm and this is repeated as one cycle, and the durability of the disk is evaluated by using the number of cycles when the friction coefficient becomes a predetermined value or more as the limit value of the durability. Although it has an advantage that it is similar to the operation of, the disadvantage is that it usually takes about 3 to 4 days to give a test result, and a lot of time is required for the durability test.

On the other hand, FIG. 5 is a diagram showing an evaluation method by the DRAG method, which is a constant low speed (100 rpm to 200 rp) with the head and the disk always in contact with each other.
This is a method of testing durability in m). In this method, the operation of HD at the time of testing is different from the actual operation, but CSS
Compared with the method, there is an advantage that the result can be obtained in a short time.

At present, the CSS method is the mainstream, but in the future,
To check the durability of many discs in a short time, D
The RAG method is considered to be advantageous. However, in any case, this is an evaluation test in which the frictional condition between the disk and the head is measured to judge the frictional condition, and it is difficult to obtain a correlation between both equations by focusing only on the frictional coefficient.

The present invention has been made in view of such conventional problems, and an object thereof is to provide a hard disk evaluation test method capable of correctly evaluating the durability of a lubricant layer.

[0009]

Therefore, the present invention improves the durability of the lubricant layer formed on the disc substrate so that the disc substrate is not damaged when the head for signal recording / reading collides with the disc substrate. In the evaluation, while the head is brought into contact with the disk substrate through the lubricant layer to rotate the disk substrate, the collision strength between the head and the disk substrate is measured, and based on the information of the collision strength. The durability of the lubricant layer was evaluated.

[0010]

According to the above construction, when the head is brought into contact with the disc substrate and the disc substrate is rotated, the collision strength changes if the head comes into contact with the disc substrate. Therefore, it is possible to correctly evaluate the durability of the lubricant layer and the hard disk from the information on the collision strength.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In this embodiment, the collision strength between the head and the disk substrate is measured using the AE signal. AE
(Acoustic emssion) signal means when a solid is destroyed,
As a sign of this, it is a signal by an elastic wave generated when a small crack occurs in the solid, and it should be possible to know the information on the collision strength between the head and the disk substrate by this AE signal.

FIG. 1 shows a hard disk substrate (hereinafter referred to as HD
1) shows a hard disk evaluation test device of this example for evaluating the durability of the first example. This device
The durability of the HD1 and the durability of the lubricant layer are determined by paying attention to the above-mentioned AE signal.
According to the present invention, the DR that can obtain the result in a short time
The durability will be evaluated using the AG method.

In FIG. 1, an HD 1 to be evaluated is a disc type disk substrate which is formed of, for example, aluminum or the like and has a magnetic film layer, a protective film layer, a lubricant layer, etc. formed on the surface thereof. It is a readable large-capacity magnetic recording medium. This lubricant layer is HD even if the head contacts HD1.
No. 1 is a layer coated with a lubricant so as not to be damaged. In this example, it is considered that the film thickness of the lubricant affects the durability of the lubricant layer. Decided to investigate the relationship.

A spindle motor (hereinafter simply referred to as a motor) 2 is a motor for rotating the HD 1. The motor 2 is equipped with a rotary encoder (not shown) for obtaining angle information during rotation and an origin signal. The head slider 3 is made of ceramics such as Al ₂ O ₃ .TiC, has a head in contact with the HD 1, and is carried by a head arm 4 so as to be fixed at a predetermined radial position on the disk. It

The AE sensor 5 is a sensor for detecting the collision strength between the head and the HD 1 via the head arm 4 as an AE signal, and the AE signal is amplified by the preamplifier 6. The AD converter 8 includes a sample hold circuit 7
The AE signal from the AE sensor 5 is input via the, and the angle information and the origin signal are input from the rotary encoder. These pieces of information are digitized by the AD converter 8. When measuring, the AD converter 8
If the sampling frequency is fast, the number of data becomes so large that processing cannot be performed. Therefore, the AD converter 8 of the present embodiment has a slow sampling frequency. Further, if the sampling frequency of the AD converter 8 is low, the peak hold circuit 7 cannot capture all the AE signals, causing data to be missed. Therefore, the peak hold circuit 7 holds the peak value of the AE signal only within a predetermined time. This is the circuit interposed in the previous stage.

The AE signal from the AE sensor 5, the angle information from the rotary encoder, and the origin signal are also input to the digital oscilloscope 9. And, for example, the origin (0
(°: origin output of the rotary encoder) The detailed waveform of the AE signal is displayed on the digital oscilloscope 9. Incidentally, since it is said that the AE signal generated at the time of destruction has a frequency component of about 1 MHz,
A digital oscilloscope 9 having a high sampling frequency is used so that the waveform of the AE signal can be captured as it is.

The computer 10 controls the rotation speed of the motor 2, head movement control, etc., and digitizes the angle information from the AD converter 8, the origin signal, the AE signal data for one rotation, and the digital oscilloscope 9.
Is a device for evaluating whether the durability of the HD1 is good or bad by alternately inputting the data in the vicinity of the origin from the. Computer
10 and the digital oscilloscope 9 are connected via, for example, a GPIB interface. An external storage device for recording input data is connected to the computer 10, a screen for displaying the input data and the like is provided, and the input data is stored, and the durability of the disk is evaluated based on the input data. It has a built-in memory that stores software.

Next, the processing of the durability evaluation test of this disk will be described in detail with reference to the flow chart of FIG. still,
The test is performed by changing the film thickness of the lubricant layer, and this treatment is performed for each film thickness. In step (denoted as "S" in the drawing, the same applies hereinafter) 1, for example, measurement conditions such as the total measurement time, the low speed rotation speed of the motor 2, and parameters are input. In this embodiment, the measurement time and the low-speed rotation speed of the motor 2 are set to 200 rpm for 1 to 8 hours, respectively.

In step 2, the head is moved to the origin position of a stage (not shown) that regulates the position of the arm.
In step 3, the motor 2 is instructed for the low speed rotation speed of 200 rpm input in step 1. At this rotation speed, the head slider 3 does not float, and the HD1 rotates while the head slider 3 is in contact with the HD1.

When a certain time has elapsed after the HD 1 has rotated, the process proceeds to steps 4 to 5 to measure the AE signal for a predetermined time. When the AE signal is output, the AE signal generation time and the AE output value are stored in step 6. Since a rotary encoder is attached to the motor 2, it is possible to obtain angle information during rotation, and the HD 1 can be obtained from this angle information.
It is possible to obtain what kind of AE signal is being output at an angular position in the circumferential direction with a constant radius of.

This measurement is performed until the measurement time input in step 1 elapses. When the measurement time is over, the process proceeds to step 7 → 8 to stop the motor. In step 9, off-line statistical processing is performed based on the measured AE signal generation time and the AE output value, and this routine ends. The AE signal is generated when the head, which is a hard solid, and the HD 1 collide with each other, and the growth and the attenuation are repeated several times. In particular, we focused on the time when the AE signal started to appear after the measurement was started.

FIG. 3 is a diagram showing the relationship between the time when the AE signal starts to be generated (vertical axis) and the film thickness of the lubricant (horizontal axis). The time when the AE signal starts to appear is the film thickness of the lubricant. It can be seen that as the thickness increases, it will be delayed. In other words, the lubricant is HD
It can be seen that it plays a role of preventing the initiation of direct contact between 1 and the head. In particular, it can be seen that the time at which the AE signal is generated greatly differs depending on the film thickness t ₁ , and the durability of the lubricant layer greatly differs. From this result, the lubricant layer may be set to a predetermined thickness.

If a strain gauge is attached to the support of the head slicer 3, the friction coefficient can be measured and the correlation with the AE signal can be obtained. With this configuration, the HD1 is rotationally driven at a low rotation speed while the head is in contact with the HD1, and the AE signal between the head and the HD1 is measured,
By evaluating the durability of the lubricant layer based on the time when a signal starts to appear, the durability of the lubricant layer can be correctly evaluated in the actual use condition of the hard disk, and the evaluation device has a simple structure. It is possible and practical.

[0024]

As described above, according to the present invention, the collision strength is measured by rotating the disk substrate while keeping the head in contact with the disk substrate, and the lubricant layer of the lubricant layer is measured based on the collision strength information. The durability can be evaluated correctly.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a hard disk evaluation test apparatus according to an embodiment of the present invention.

FIG. 2 is a flowchart showing the operation of FIG.

FIG. 3 is a diagram showing a relationship between a time when an AE signal starts to be generated and a film thickness of a lubricant.

FIG. 4 is an explanatory diagram of a conventional CSS method of measurement.

FIG. 5 is an explanatory diagram of a conventional measuring method by the DRAG method.

[Explanation of symbols]

 1 hard disk substrate (HD) 2 (spindle) motor 3 head slider 5 AE (acoustic emssion) sensor 10 computer

Claims (1)

[Claims] 1. When evaluating the durability of a lubricant layer formed on a disk substrate so that the disk substrate is not damaged when the head for signal recording / reading collides with the disk substrate, the head is used as a lubricant layer. The disk substrate is brought into contact with the disk substrate via the disk to rotate the disk substrate, the collision strength between the head and the disk substrate is measured, and the durability of the lubricant layer is evaluated based on the collision strength information. A hard disk evaluation test method characterized by the above.