JPH04360065A - Measuring device for magnetic disk device - Google Patents

Abstract

PURPOSE:To accurately measure the asynchronous vibration of a magnetic disk caused by the asynchronous shaft vibration of a spindle motor by controlling a head positioning mechanism so as to follow up a position information prerecorded on a magnetic disk. CONSTITUTION:By controlling the head positioning mechanism 4 so as to follow up the position information prerecorded on the magnetic disk 1, the asynchronous shaft vibration of the motor 2 in a state in which the disk 1 is attached to the spindle motor 2 is reproduced as the positional change of the mechanism 4. Then, the positional change of the mechanism 4 is detected, and based on the positional change, the asynchronous vibration of the disk 1 caused by the asynchronous shaft vibration of the motor 2 is measured. In that case, the measuring accuracy is improved by using a laser measuring device 12 for the detection of the positional change of the mechanism 4. And, a processing henceforth is performed by the digital calculation of CPU 13.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring device for a magnetic disk drive, and more particularly to a measuring device for measuring radial runout of a disk in a magnetic disk drive.

0002

2. Description of the Related Art In a magnetic disk drive, data is recorded and reproduced while a head accurately follows a target track. Radial vibration of the disk, especially vibration that is asynchronous to its rotation, will affect the head's tracking ability, so it is important to accurately understand how this vibration is occurring. becomes.

The radial runout of the disk is mainly caused by the axial runout of a spindle motor for rotating the disk. So, for example, literature: AN INVES
TIGATION OFNON-REPEATABLE
SPINDLE RUNOUT: IEEE TRA
NSACTION ON MAGNETICS, VOL
．． MAG-23, NO. 5, 1987, the axial runout of a spindle motor is measured with a capacitance displacement meter, and the characteristics of the axial runout are analyzed to provide guidelines for designing a head positioning system for a magnetic disk drive. In general, the measurement limit of a capacitive displacement meter is about 0.02 μm, whereas the asynchronous runout in the radial direction of a high-precision spindle motor is about 0.3 μmp-p, and the measurement accuracy of a capacitive displacement meter is I can't say it's good enough.

Furthermore, in the method described in the above-mentioned literature, changes in the surface condition of the spindle motor shaft become observation noise when measuring shaft runout, so careful handling is required. Furthermore, since the motor shaft is not a perfect circle, shaft runout that is synchronized with rotation will naturally be observed at the same time. The magnitude of the synchronous component of this shaft runout usually reaches several tens of micrometers. This means that dynamic range and resolution are required at the same time, which is a strict requirement for a measuring device. For this reason, it is quite difficult to simply measure the axial runout of a spindle motor in an actual magnetic disk device.

On the other hand, as another method for measuring shaft runout, there is a method in which the shaft of a spindle motor is mirror-finished and the shaft runout is measured using a laser length measuring device. However, this method is complicated, such as requiring machining of the motor shaft and aligning the optical axis of the laser beam with high precision. Furthermore, considering the inclination of the motor shaft, only a single beam interferometer can be used as a laser length measuring device, and its measurement resolution is limited to about 0.016 μm. Therefore, like the method using the capacitance displacement meter described above, this method is not sufficient as a method for measuring the shaft runout of a spindle motor in a magnetic disk drive.

[0006]

[Problems to be Solved by the Invention] As mentioned above, with the conventional shaft runout measurement technology using a capacitance displacement meter or a laser length measuring device, it is difficult to measure the asynchronous runout in the radial direction of a magnetic disk with sufficient accuracy. The problem was that it was difficult. SUMMARY OF THE INVENTION An object of the present invention is to provide a measuring device for a magnetic disk device that can measure asynchronous runout in the radial direction in a magnetic disk device with high precision.

[0007]

[Means for Solving the Problems] In order to solve the above problems, a measuring device for a magnetic disk device of the present invention includes a magnetic head for reading information recorded on a magnetic disk, and a magnetic head that reads information recorded on a magnetic disk. a head positioning mechanism for positioning the head at a predetermined position on the magnetic disk; a means for reproducing positional information previously recorded on the magnetic disk via the magnetic head; The head positioning mechanism has a means for controlling the head positioning mechanism so as to follow the positional information of the head positioning mechanism, and a measuring means for measuring the deflection of the magnetic disk in the radial direction from the positional fluctuation of the head positioning mechanism.

The measuring means includes, for example, a detecting means for detecting the positional fluctuation of the head positioning mechanism for each rotational position of the magnetic disk, a means for storing the positional fluctuation detected by this means, and a means for storing the positional fluctuation detected by this means. means for averaging the fluctuations for each rotational position; means for storing the positional fluctuations averaged by this means; and means for updating the positional fluctuations for each rotational position averaged by the means, and means for determining the radial deflection of the magnetic disk by subtracting it from the positional fluctuation detected at each current rotational position. The positional fluctuation of the head positioning mechanism itself is detected by a laser length measuring device or the like, and subsequent processing is performed by digital calculation by, for example, a CPU.

[0009]

[Operation] In this way, in the measuring device of the present invention, the head positioning mechanism is controlled so as to follow the positional information recorded in advance on the magnetic disk, so that the spindle can be adjusted with the magnetic disk attached to the spindle motor. The asynchronous shaft runout of the motor is reproduced as a positional fluctuation of the head positioning mechanism. Then, the positional fluctuation of this head positioning mechanism is detected, and the asynchronous runout of the magnetic disk caused by the asynchronous shaft runout of the spindle motor is measured based on the positional fluctuation.

In this case, unlike the method of directly measuring the axial runout of the spindle, a position detector with high accuracy and excellent noise characteristics, such as a linear interferometer, is used as a means for detecting the position fluctuation of the head positioning mechanism. Since a laser length measuring device can be used, it becomes possible to measure asynchronous runout of a magnetic disk with sufficient accuracy.

[0011]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of a measuring device for a magnetic disk device according to an embodiment of the present invention.

In FIG. 1, a magnetic disk 1 is, for example, a hard disk or a floppy disk, and is rotated by a spindle motor 2. As shown in FIG. The magnetic head 3 is provided for measurement and is attached to a head positioning mechanism 4. The head positioning mechanism 4 includes a piezoelectric actuator 5 and a coarse movement stage 6 that moves the piezoelectric actuator 5 in the radial direction, that is, in the radial direction of the disk 1. The piezoelectric actuator 5 is made of, for example, a laminated piezoelectric element in which a plurality of piezoelectric elements are laminated to be displaced in the thickness direction, and is used as a fine movement mechanism for precisely positioning the head 3. The coarse movement stage 6 is composed of, for example, a linear motor, and is used to move the head 3 to an appropriate position on the disk 1.

[0013] Position information, which will be described later, is recorded in advance at a specific position on the disc 1, for example, at the outermost circumference or the innermost circumference. This position information is read by the head 3 and input to the position signal reproducing circuit 8 via the amplifier 7.

The position signal reproducing circuit 8 includes, for example, as shown in FIG. 2, a frequency separation circuit 21 for separating and extracting frequency components of position information, and a full-wave rectification circuit for converting the output of the frequency separation circuit 21 into direct current. 22 and the full wave rectifier circuit 2
The sample and hold circuit 23 samples and holds the output of the spindle motor 2 at a sampling frequency sufficiently higher than the frequency band of shaft runout of the spindle motor 2, and outputs a position signal according to position information. For example, if the rotation speed of the spindle motor 2 is 3,600 rpm, the spindle motor 2
Since the axial runout of is about 600Hz or less, the sampling frequency in the sample hold circuit 23 is 10kHz.
Selected around z.

The position signal output from the position signal reproducing circuit 8 is input to the control circuit 9. The control circuit 9 generates a control signal by calculation from the input position signal. When this control signal is supplied to the piezoelectric actuator 5 via the actuator drive circuit 10, the piezoelectric actuator 5 is driven so that the head 3 follows the position information on the disk 1, that is, the axial runout of the spindle motor 2. It is positioned so that it follows and moves. The tracking band at this time is set to about 1 kHz.

On the other hand, a reflecting mirror 11 is attached to the back side of the piezoelectric actuator 5, and the position of this reflecting mirror 11 is measured by a laser length measuring device 12 placed opposite to the reflecting mirror 11. For example, as shown in FIG. 3, the laser length measuring device 12 includes a laser head 31, an interferometer 32, and a receiver 33.
and a position detection circuit 34. By measuring the moving distance of the reflecting mirror 11, the position detection circuit 34 outputs measurement data representing position information of the head positioning mechanism 4.

This laser length measuring device 12 uses a linear interferometer using two laser beams, and its measurement resolution is about 2.5 nm. This is a capacitance displacement meter used in conventional technology to measure shaft runout,
It has much higher resolution than a laser length measuring device using a single beam interferometer. When directly measuring the shaft runout of a spindle motor as in the conventional technology,
Although it is virtually impossible to use such a laser length measuring device using two beams, in the present invention, the head positioning mechanism 4
Such a laser length measuring device 12 is used to measure the position of
can be used. Further, in this case, it is not necessary to mirror-finish the axis of the spindle motor 2 or to align the optical axis of the laser beam with the axis of the spindle motor 2 with high precision, so it is easy to implement.

The movement of the piezoelectric actuator 5 is the movement in the radial direction of the position information recorded on the disk 1, and this is caused by the radial axial runout of the spindle motor 2 (
(asynchronous component). This shaft runout is generally 0.
Since it is about 3 μmp-p, it is possible to measure it with sufficient accuracy using the measurement resolution (about 2.5 nm) of the laser length measuring device 12.

The measurement data of the laser length measuring device 12 is sent to the CPU
(microcomputer) 13. The movement in the radial direction of the position information of the head positioning mechanism 4 measured by the laser length measuring device 12 is a combination of the shaft runout of the spindle motor 2 at the time the position information was recorded and the current shaft runout. Therefore, the CPU 13 samples and stores the measurement data from the laser length measuring device 12 in synchronization with an index signal generated from the spindle motor 2 once per rotation by a rotary encoder, etc., and then calculates the average value of the data. memorize it. The same operation is repeated by changing the generation phase of the index signal little by little. That is, measurement data is sampled at each rotational position of the disk 1 at predetermined angular intervals, and the average value is determined and stored. The average value stored in this way represents the shaft runout itself (synchronous component) of the spindle motor 2 when the position information is written on the disk 1, since the random asynchronous component is removed by averaging.

Next, the CPU 13 outputs a laser length measuring device 12 that indicates the current positional fluctuation of the head positioning mechanism 4.
Measured data is sampled and stored for each rotational position, and the above average value, that is, the synchronous component of the position information, is subtracted from these positional fluctuations. As a result, the synchronous component of the radial shaft runout of the spindle motor 2 at each sampling time point is removed, and only the asynchronous component is measured.

[0021] The position information previously recorded on the disc 1 is written to an appropriate track on the disc 1 by the following procedure. As shown in FIG. 4, the magnetic head 3 is first set at the position indicated by the solid line 41, and a continuous signal of frequency f1 is written on a certain track by the head. Next, the head 3 is moved in the track width direction by about 3/4 of the track width and set at the position indicated by the broken line 42, and a continuous signal of frequency f2 is written. Thereafter, the head 3 is moved to the center of the position where the signals of f1 and f2 overlap. As a result, head 3
The signal reproduced at 1 includes approximately half of the f1 and f2 components, and the ratio changes depending on the shaft runout of the spindle motor 2.

In the above embodiment, the piezoelectric actuator 5 is used as the fine movement mechanism, but a magnetostrictive actuator, an electromagnetic actuator, etc. may also be used. Further, the head positioning mechanism does not necessarily have to be a combination of a fine movement mechanism and a coarse movement mechanism. Further, although the laser length measuring device 12 is used to measure the position of the head positioning mechanism 4, a high-resolution optical scale sensor or other scale sensor may also be used. In addition, the present invention can be implemented with various modifications without departing from the scope.

[0023]

According to the present invention, by controlling the head positioning mechanism to follow the position information recorded in advance on the magnetic disk, the spindle motor can be de-synchronized when the magnetic disk is attached to the spindle motor. To accurately measure the asynchronous runout of a magnetic disk caused by the asynchronous shaft runout of a spindle motor by reproducing the axial runout of the head positioning mechanism as a positional variation of the head positioning mechanism, and detecting this positional variation with a high-precision laser length measuring device, etc. Can be done.

In addition, the measurement system including the magnetic head, head positioning mechanism, and control system for controlling the positioning mechanism is close to the state assembled as an actual device (magnetic disk device), and can be measured in a state close to the actual device. Since the measurement settings are simpler than the previous technology, it is possible to easily determine shaft runout with high accuracy. Therefore, it can be easily applied as a measuring device for quality control of spindle motors, etc.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a measuring device for a magnetic disk device according to an embodiment of the present invention.

[Fig. 2] Block diagram showing the configuration of the position signal reproducing circuit in Fig. 1

[Figure 3] Block diagram showing the configuration of the laser length measuring device in Figure 1

FIG. 4 is a diagram showing position information written in advance on a disc in the same embodiment.

[Explanation of symbols]

1...Magnetic disk
2...Spindle motor 3...Magnetic head
4...Head positioning mechanism 5...Piezoelectric actuator
6...Coarse movement stage

Claims (2)

[Claims] 1. A magnetic head for reading information recorded on a magnetic disk in a measuring device for a magnetic disk device used in a magnetic disk device that records and reproduces data while rotating the magnetic disk by a spindle motor. a head positioning mechanism for positioning the magnetic head at a predetermined position on the magnetic disk; means for reproducing positional information previously recorded on the magnetic disk via the magnetic head; means for controlling the head positioning mechanism so that the magnetic head follows positional information on the magnetic disk according to positional information provided by the magnetic head; and measuring radial deflection of the magnetic disk from positional fluctuations of the head positioning mechanism. 1. A measuring device for a magnetic disk device, comprising: measuring means. 2. The measuring means includes: a detecting means for detecting a positional variation of the head positioning mechanism for each rotational position of the magnetic disk; a means for storing the positional variation detected by the means; means for averaging the stored positional fluctuations for each rotational position; means for storing the positional fluctuations averaged by the means; and means for averaging the positional fluctuations for each rotational position stored by the means. 2. The magnetic disk device according to claim 1, further comprising means for determining the radial deflection of the magnetic disk by subtracting it from the positional fluctuation for each current rotational position newly detected by the detecting means. Measuring device for