JPH0777014B2 - Measuring method of friction coefficient between disk heads - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A. Industrial fields of use B. Overview of the invention C. Prior art [Figs. 2 and 3] D. Problems to be solved by the invention E. Means for solving the problems F. Action G. Example [FIG. 1] H. Effect of the invention (A. Field of industrial application) The present invention is a method for measuring a friction coefficient between disk heads, and particularly a disk and a head or a head holding the same without using a complicated measuring device. The present invention relates to a method for measuring a coefficient of friction between disk heads capable of measuring a coefficient of friction with a holder.

(B. SUMMARY OF THE INVENTION) The present invention provides a method for measuring a friction coefficient between disk heads, in order to enable the friction coefficient to be measured easily and accurately without using a complicated measuring device. The rate of change of the rotational angular velocity when the rotation is freely rotated is measured in a state where friction is not generated between the head or the head holder and the disk and a state where friction is generated between them.
The friction coefficient is determined from the comparison of the change rates of the rotational angular velocities. Therefore, the friction coefficient can be measured by an ordinary disk driver without using a complicated special measuring device.

(C. Prior art) [Figs. 2 and 3] Devices such as computers and Japanese word processors that use hard disks as recording media are increasing. Such a device has a built-in hard disk driver. As shown in FIG. 2, the driver rotates a magnetic head held by a floating head slider a, which is not shown in the drawing, by a flexure (leaf spring) b to rotate a hard disk c.
It is designed to scan the top.

In such a hard disk driver, when the hard disk c is stationary, the floating head slider a is in contact with the hard disk c due to its own weight or the like. Then, when the hard disk c is rotated, friction occurs between the floating head slider a and the hard disk c. This friction is greatest at the beginning of the rotation of the hard disk c, and when the number of rotations increases, an air film is generated between the floating head slider a and the hard disk c accordingly, so that the floating head slider a floats and the friction becomes small. , And the specified speed (eg 3600 rpm)
Then, an appropriate space is generated between the floating head slider a and the hard disk c. Therefore, if the number of rotations of the hard disk c reaches a predetermined value, friction will not occur.

However, until the number of rotations of the hard disk c rises to a predetermined value after the rotation of the hard disk c is started, friction is generated between the hard disk c and the floating head slider a when the rotation of the hard disk c is stopped. Therefore, if the hard disk c is repeatedly rotated and stopped, the hard disk c and the floating head slider a will be worn and eventually become unusable. Therefore, it is necessary to reduce the friction, and various attempts have been made to reduce the friction. For example, it is an attempt to make the surface of the hard disk a mirror surface or apply a lubricant.

By the way, it is necessary to reduce the friction as described above, but it is more important to accurately grasp the friction before that. Otherwise, the floating head slider a of the device
This is because it is not possible to grasp how the friction between the hard disk c and the hard disk c changes by the repeated start and stop, and how successful the attempt made to reduce the friction is. Therefore, contact start stop (hereinafter referred to as “CSS”) of contacting the floating head slider a to the hard disk c to start the rotation of the hard disk c and then stopping the rotation is repeated, and the CSS is repeated. It is also very important to test how the above coefficient of friction changes.

Conventionally, the magnitude of friction, that is, the measurement of the friction coefficient
It was done according to the ANSI method. Third
Figures (A) and (B) are for explaining the ANSI method. This ANSI method uses floating head slider a
Is removed from the flexure b, the weight d is placed on the flexure b, the thread e is tied to the floating head slider b or the weight d, and the tension applied to the thread e when the hard disk c is rotated is measured by the strain gauge f. Is a method of measuring. Reference numeral h is a metal plate that restricts the radial movement of the hard disk c on which the floating head slider 2 rotates, has a hole h at the tip, and the weight d is loosely fitted in the hole h.

(D. Problems to be Solved by the Invention) By the way, according to the above-described method of ANSI, the friction coefficient cannot be measured unless a special device including the strain gauge f is used. . Moreover, the floating head slider a is purposely flexed to the flexure b.
It is also a big problem that it has to be detached and attached to the weight d.

The most important problem is that the friction coefficient between the hard disk c and the floating head slider a when actually set in the disk player cannot be measured. This is because the ANSI method creates a state in which the hard disk c and the floating head slider a are in contact with each other using a pseudo weight d having a constant weight. The contact state is the hard disk c and the floating head in the disk driver. This is completely different from the actual contact state with the slider a. In particular, in a high-performance hard disk driver, a special condition such as a place where the hard disk c is stored is kept extremely clean. Therefore, for the actual disk driver, the floating head slider a
It is impossible to grasp what is the actual friction coefficient between the hard disk c and the hard disk c, and what is the change in the friction coefficient due to repeated start and stop. This is AN
It can be said that this is the biggest drawback of the SI method.

Further, according to the ANSI method, when the friction coefficient with the floating head slider a at a certain distance from the rotation center of the hard disk c, that is, at a certain tracking position is measured, the very initial friction coefficient is accurate. Although it can be measured, the friction coefficient after that cannot be measured accurately. This is because the floating head slider b is displaced in the radial direction of the hard disk c as soon as the hard disk c starts to rotate.
However, the displacement of the floating head slider b is set within a certain range by using the metal plate g, but it is necessary to prevent the floating head slider b from moving in the radial direction at all in order to obtain an accurate friction coefficient. It is not allowed because it makes measurement impossible. Therefore, the deviation of the floating head slider b in the radial direction of the hard disk c must be allowed to some extent. Therefore, as described above, as soon as the hard disk c starts to rotate, the floating head slider b shifts in the radial direction of the head disk c, so that the measurement target position of the friction coefficient slightly deviates, and the friction coefficient of the same portion is changed. It is not possible to get an accurate picture of the change or the duration of the effect of the lubricant. That is, there is no guarantee that the floating head slider b is always in contact with the exact same position of the hard disk c even if the change in friction coefficient is measured by repeating start and stop tens of thousands of times.
This is also a problem.

The present invention has been made to solve such a problem, and a disk driver or a device similar to that actually drives the disk without using a complicated measuring device can easily and accurately perform the operation of the disk and head. The purpose is to be able to measure the coefficient of friction between them.

(E. Means for Solving Problems) In order to solve the above-mentioned problems, the method for measuring a friction coefficient between disk heads of the present invention is directed to a rotational angular velocity when the disk is rotated at a predetermined speed and then freely rotated. Change rate is measured twice in a state where friction is not generated between the head or a head holder that holds the head and the disc, and a state where friction is generated between the two, and changes in the two rotational angular velocities. The coefficient of friction is calculated from the ratio and the moment of inertia of the disk rotating portion.

(F. Action) According to the method for measuring the coefficient of friction between disk heads of the present invention, the larger the coefficient of friction, the greater the rate of change of the rotational angular velocity when the disk is freely rotated. The friction between the head or head holder disk and the rate of change of the rotational angular velocity when the rotation of the hard disk that rotates at a predetermined rotational angular velocity is set to free rotation with no friction between them. The friction coefficient can be accurately measured from the result of comparison with that in the above state and the intrinsic moment of inertia of the hard disk rotating part.

(G. Example) [FIG. 1] The method for measuring the friction coefficient between disk heads of the present invention will be described in detail below with reference to the illustrated example.

FIG. 1 schematically shows the configuration of a hard disk driver used as a measuring device for measuring the friction coefficient between a floating head slider that supports the head and the hard disk.

In the figure, reference numeral 1 is a signal processing circuit, which outputs a signal to be written in a hard disk to a magnetic head described later, and a signal read from the hard disk by the magnetic head is input to the signal processing circuit 1. It 2 is a system control circuit.

Reference numeral 3 is an amplifier for amplifying the signal output from the signal circuit 1, 4 is a write / read change-over switch, one change-over terminal is connected to the output terminal of the above-mentioned amplifier 3, and the other change-over terminal is a signal read out from the hard disk. It is connected to the input terminal of the amplifier 5 for amplification, and the common terminal is connected to the magnetic head 7 provided on the floating head slider 6. The floating head slider 6 provided with the magnetic head 7 is attached to the tip of a flexure 8 and is moved by a motor 9 in the radial direction of the hard disk 10. A motor drive circuit 11 drives the motor 9 and is controlled by the system control circuit 2.

A motor 12 rotates the hard disk 10 and is driven by a motor drive circuit 13. And the motor drive circuit
13 is controlled by the system control circuit 2.
A pulse generator 15 detects the number of rotations (rotational angular velocity) of the hard disk 10, and generates a rotation detection signal of one pulse each time the hard disk 10 makes one rotation. The rotation detection signal is amplified by the amplifier 16 and input to the system control circuit 2.

Next, how to measure the friction coefficient using such a hard disk driver will be described.

First, the polar moment of inertia I [g
・ Cm · sec ² ] is measured in advance. The hard disk rotating unit includes a hard disk 10, a disk mounting flange (not shown), and a motor 12. That is, when the hard disk is rotated by the motor, the entire body that rotates together with the hard disk is the hard disk rotating unit.

Next, the floating head slider 6 is removed from the flexure 8 so that friction does not occur between the floating head slider 6 and the hard disk 10.
The hard disk 10 is rotated at a certain angular velocity ω [rad / se
c] to rotate. Then, when the hard disk 10 is rotating at the rotational angular velocity ω, the drive by the motor 12 is stopped to make the rotation of the hard disk 10 (or rather the hard disk rotating part) free rotation. If the disk driver has an electromagnetic braking mechanism, that mechanism must not be activated. Then, the change rate (dω / dt) ₂ [rad / sec ² ] of the rotational angular velocity of the hard disk 10 is measured. This rotation angular velocity change rate is measured by counting the pulses of the rotation detection signal output from the pulse generator 15, graphing the transition of the count value per unit time, and determining the slope of the line indicating the transition of the count value. It can be done easily. The rotation detection signal can be easily extracted via the system control circuit 2, for example. Then, the rotation detection signal thus taken out can be processed by a computer to easily calculate the rate of change of the rotational angular velocity and the like.

Next, the floating head slider 6 is attached to the flexure 8 and is tracked to a predetermined position in a state where friction can occur between the floating head slider 6 and the hard disk 10 (normal use state). In that state, the motor 12 rotates the hard disk 10 to the above rotational angular velocity ω [rad / sec].
Rotate at the same speed as. This rotational angular velocity ω [rad /
sec] needs to be set to a value such that the floating head slider 6 does not float from the hard disk 10 and causes friction with the hard disk 10. Therefore, this rotational angular velocity ω must not be too fast.

Then, when the hard disk 10 is rotating at the rotational angular velocity ω, the drive by the motor 12 is stopped to make the rotation of the hard disk 10 (or rather the hard disk rotating part) free rotation. Then, the rate of change (dω / dt) ₁ [rad / sec ² ] of the rotational angular velocity of the hard disk 10 is measured. The change rate of the rotational angular velocity can also be easily measured by the method described above.

Then, the friction coefficient μ is calculated by the following arithmetic expression.

μ = I {(dω / dt) ₂ − (dω / dt) ₁ } / (Nr) where N is the head load [g] and r is the radial position (tracking position) for CSS (contact start stop) test. Distance from the center of rotation).

Next, how the arithmetic expression for calculating the friction coefficient μ is derived will be described.

The following equation (1) is an equation of angular motion of the disk rotating part when friction is generated between the floating head slider 6 and the hard disk 10.

I (dω / dt) ₁ = −M (ω) −μ · N · r (1) In addition, M is a resistance moment other than friction with the floating head slider 6 of the disk rotating part, and the unit is g · cm. Is.

The following equation (2) is an equation of angular motion of the disk rotating portion when friction is prevented from occurring between the floating head slider 6 and the hard disk 10 (the floating head slider 6 is removed from the flexure 8).

I (dω / dt) ₂ = −M (ω) (2) If the above equation (1) is subtracted from the above equation (2), the following equation (3) is obtained.

(Dω / dt) ₂ − (dω / dt) ₁ = μ · N · r / I ...
(3) Then, by multiplying both sides of the above equation (3) by I / N · r, the above equation for obtaining the friction coefficient μ is obtained.

In addition, in order to calculate an accurate value of the friction coefficient μ, it is necessary to obtain the polar moment of inertia I of the disk rotating portion accurately in advance. However, since the disk rotating part of the hard disk driver has a complicated structure unlike an ordinary flywheel, the polar moment of inertia I should be calculated by a simple formula such as I = mR ² (where m is mass and R is radius). I can't. Therefore, the rotational angular velocity change rate (dω / dt) is measured using a hard disk whose friction coefficient has been previously measured by the ANSI method (the very initial friction coefficient can be measured by the ANSI method as described above). ) ₁ and (dω / dt) ₂ are measured. Then, the polar inertia moment I is obtained by substituting the two rotational angular velocity change rates into the above equation (3). In order to obtain the polar moment of inertia I, r and N must be known as a premise, but the measurement of the values is easy.

The polar moment of inertia I obtained once can be used for measuring the friction coefficient of hard disks having the same weight, and it is not necessary to obtain I for each hard disk having the same weight. However, it cannot be used to measure the friction coefficient of hard disks having completely different weights (for example, plastics, aluminum, or ceramics having completely different weights). Therefore, when measuring the friction coefficient of hard disks having different weights, it is necessary to re-determine the polar moment of inertia I.

It can be said that the method of measuring the coefficient of friction between disk heads described above effectively utilizes the principle of the rotational speed damping method. The rotational speed damping method uses a device in which a ring test piece and a flywheel are mounted on the same rotary shaft, and the rotary shaft on which the flywheel and the ring test piece are mounted is rotated by a motor via a clutch. Then, by rotating the rotary shaft with a motor and releasing the clutch when the steady rotation is reached, the rotation is made free rotation, and the pin test is performed to measure the decay rate of the number of rotations (rotational angular velocity) after free rotation. With a load applied to the ring test piece by a piece (a state where friction is generated) and a state where a load is not applied to the ring test piece by a pin test piece (a state where friction is not generated) 2 times. Then, the friction coefficient μ is obtained from the two rotational speed attenuation rates (in other words, the rotational angular velocity change rate) by the above-described arithmetic expression for calculating the friction coefficient μ.

By the way, the general method of decaying the rotational speed is performed with a device that is troublesome to measure by rotating or stopping the rotation, so CSS
It can be said that it is not suitable for repeating the friction coefficient intermittently without interruption. However, the hard disk driver used to measure the coefficient of friction between the hard disk and the floating head slider is essentially a mechanism that can be easily started and stopped repeatedly, and is therefore the best CSS test.

Incidentally, the hard disk driver is generally designed to be abruptly stopped by an electromagnetic brake when it is stopped, but in such a case, free rotation cannot be obtained and the friction coefficient cannot be measured. Therefore, it is necessary to prevent the electromagnetic brake from being applied to the hard disk driver having the electrode braking function. If this point is taken into consideration, the friction coefficient between the disk and the floating head slider can be measured by any type of hard disk driver.

A method for measuring a friction coefficient between a hard disk and a floating head slider by the above-mentioned hard disk driver,
That is, comparing this friction coefficient measuring method with the conventional ANSI method, the ANSI method can be measured only by using a complicated special measuring device equipped with a strain gauge or the like. According to the friction coefficient measuring method, the friction coefficient can be measured by using the hard disk driver as a measuring device. Therefore, no special device is required to measure the coefficient of friction. Moreover, there is no need to take the trouble of removing the floating head slider from the flexure of the hard disk driver and setting the weight on a special measuring device.

Since the friction coefficient can be measured by the hard disk driver, it is not the friction coefficient between the floating head slider and the hard disk in the simulated contact state like ANSI, but the actual hard disk and floating head slider in the hard disk driver. The coefficient of friction in the actual contact state with can be measured. That is, non-destructive measurement in a state suitable for the substance can be performed.

Moreover, the hard disk driver has a tracking mechanism as shown in Fig. 1. By the function of this tracking mechanism, the CSS test can be performed with the tracking position fixed at a fixed position, and the floating head slider is moved to the hard disk during the CSS test. There is no risk of shifting in the radial direction. Therefore, it is possible to accurately grasp the degree of wear of the hard disk, the durability, the durability of the effect of the lubricant, and the like.

The present invention can also be applied to the measurement of the friction coefficient when the head directly contacts the disk without using the floating head slider.

(H. Effect of the Invention) As described above, the method for measuring the coefficient of friction between the disk heads of the present invention provides the disk with a predetermined friction coefficient in a state in which no friction occurs between the disk and the head holder that holds the disk. Rotate to a predetermined speed with friction occurring between the rate of change of the rotational angular velocity of the disk when the disk is rotated at a desired speed and then free rotation, and the head or the head holder that holds it. After that, the rate of change of the rotational angular velocity of the disk when the rotation is freely rotated,
The friction coefficient is calculated based on the moment of inertia of the disk rotating portion.

Therefore, according to the method for measuring the coefficient of friction between disk heads of the present invention, the larger the coefficient of friction, the greater the rate of change of the rotational angular velocity when the hard disk is freely rotated. When the hard disk is changed from a state of rotating at a predetermined rotation angular speed to a state of free rotation in the case of preventing the occurrence of The friction coefficient can be accurately measured from the result of comparison with the ratio) and the moment of inertia of the rotating portion of the hard disk.

Since it is not necessary to measure the tension for measuring the friction coefficient, and the friction coefficient can be measured only by detecting the rotational angular velocity (or the number of rotations), a strain gauge or the like is further provided to hold the pseudo weight on the head. It is not necessary to use a special measuring device having a mechanism for mounting on a tool or a head. Therefore, it can be measured by using the disk driver. This is because the disk driver has a mechanism for detecting the rotation of the hard disk, and it is easy to grasp the rotation angular velocity change rate using the mechanism.

Then, by measuring the friction coefficient using the disk driver, it is possible to grasp the friction coefficient in the actual contact state between the hard disk and the head or the holder thereof in the actual disk driver.

Also, since the disk driver has a tracking mechanism, by making full use of the tracking mechanism, the friction coefficient can be continuously measured while fixing the head tracking position to the same position under the same conditions as in the actual practical state. You can Therefore, it is possible to accurately grasp the degree of wear of the disk and the duration of the effect of the lubricant due to repeated start and stop.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing the outline of the configuration of a measuring device (disk driver) used in one embodiment of the method for measuring the friction coefficient between disk heads of the present invention, and FIG. 2 shows a disk and a head slider (head holder). 3A and 3B are views for explaining a conventional example of the method for measuring the friction coefficient between disk heads, and FIG. 3A is a plan view of the measuring device and FIG. FIG. 4B is a sectional view taken along the line BB of FIG. Explanation of symbols 6 ... Head holder, 7 ... Head, 10 ... Disk, 12 ... Disk rotation motor.

Claims (1)

[Claims] 1. A change in the angular velocity of rotation of a disk when the disk is rotated at a predetermined speed in a state where friction is not generated between the disk and a head holder for holding the disk and then the rotation is freely rotated. Rate, the change rate of the rotational angular velocity of the disk when the disk is rotated at the above-mentioned predetermined speed in a state where friction is generated between the disk and the head or the head holder, and the disk is rotated freely. Method of measuring friction coefficient between disk heads, characterized in that the friction coefficient is calculated based on