JP3023206B2 - Servo writer head positioning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo writer head positioning device for writing a servo pattern on a magnetic disk.

[0002]

2. Description of the Related Art In a magnetic disk device, particularly a hard disk device, it is necessary to position a magnetic head on a target track in order to write / read information. A servo pattern is written on the disk in advance for positioning the head. When writing / reading information, the head drive system is controlled based on position information obtained by reading this pattern.

An apparatus for writing a servo pattern on a magnetic disk is called a servo writer. In this servo writer, a magnetic head for writing a servo pattern is fixed to a carriage rotatably supported around an axis parallel to the rotation axis of the disk, and is driven by a voice coil motor.

[0004] Servo writers are classified into two types according to a servo pattern writing head and a head positioning mechanism. One method uses a head and a head carriage of the magnetic disk device itself, and performs head positioning by physically connecting a carriage driving mechanism provided in a servo writer that can be positioned with high precision to the head carriage. is there. The other is a system using a head and a head positioning mechanism similarly provided in the servo writer, and the servo writer of the present invention also belongs to this system. In either method, the servo pattern is written on the disk while being fixed to the spindle motor of the magnetic disk itself.

In the conventional hard disk drive, the rotating shaft of the spindle motor is supported by a bearing using a ball bearing, so that there is a so-called shaft runout. The shaft runout of the spindle motor is divided into axial runout (runout in the same direction as the rotating shaft) and radial shaft runout (axial runout in the direction perpendicular to the rotary shaft) depending on the direction. These shaft runouts are further divided into components synchronized with rotation and components not synchronized with rotation. Of these, the component that affects the accuracy of the servo pattern written by the servo writer is a component of the radial shaft runout that is not synchronized with the rotation (hereinafter, this is simply referred to as shaft runout).

The magnitude of shaft runout in a spindle motor used in a current small hard disk drive (disk diameter of 2.5 inches, 3.5 inches, etc.) is about 0.3 μm, and the frequency component is as large as about 400 Hz. appear.
For this reason, even if the head is accurately positioned by the servo writer, the servo pattern written on the disk causes a runout of about 0.3 μm. In the current hard disk device, the track density is generally about 2,000 TPI, and the runout of the servo pattern caused by the runout of the axis is not so much a problem. However, the track density is increasing, and if the track density becomes 5,000 TPI or more in the future, the deflection of the servo pattern becomes a problem.

In a servo writer, in order to eliminate the servo pattern vibration, it is necessary to detect the disk vibration due to the axial vibration and to position the head so as to cancel it. FIG. 8 shows a conventional servo writer head positioning device. The head 101 is a head carriage 102
The carriage 102 is rotatably supported on a shaft parallel to the rotation shaft 105 of the disk 104 via a bearing bearing using a ball bearing (not shown), and is driven by a voice coil motor (VCM) 106. You. A corner cube 107 that reflects a laser beam is fixed to the head carriage 102, and the position of the head 101 is measured by a laser length measuring device 108. The position information obtained from the laser length measuring device 108 is supplied to the VCM driving unit 110 via the control circuit 109.
With such a head positioning servo system, the head 101
Is positioned.

However, in such a configuration, a mechanical resonance point of about 2 kHz appears due to the rigidity of a bearing for supporting the head carriage 102 and the like. Therefore,
When a head positioning servo system that follows the shaft runout of the spindle motor is configured by the positioning mechanism as shown in FIG. 8, the control band of the servo must be arranged below this mechanical resonance point. ~ 400
Hz. In such a control band, it is difficult to eliminate the deviation of the servo pattern to such an extent that there is no problem even at a high track density of 5,000 TPI or more.

[0009]

As described above, in the conventional servo writer positioning apparatus, since the control band of the head positioning servo is limited because the mechanical resonance point is low, the servo due to the shaft runout of the spindle motor is restricted. It is difficult to suppress the fluctuation of the pattern sufficiently, which has been a problem when the track density is high.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem. The mechanical resonance point of the head positioning mechanism can be increased to widen the control band of the head positioning servo, and the shaft runout of the spindle motor can be improved. It is an object of the present invention to provide a servo writer head positioning device capable of sufficiently reducing the deflection of a servo pattern due to the above.

[0011]

In order to solve the above-mentioned problems, a head positioning device for a servo writer according to the present invention comprises: a coarse movement mechanism for moving a magnetic head for writing a servo pattern in a radial direction of a magnetic disk; A fine movement mechanism for moving the head in the radial direction of the disk by at least one track pitch, an elastic support member for supporting the head with respect to the coarse movement mechanism and elastically deforming with the operation of the fine movement mechanism, a coarse movement mechanism and a fine movement mechanism The first control means controls the magnetic head to move to a desired track position, and the second control means controls the fine movement mechanism according to the shaft runout of the spindle motor.

[0012]

The head positioning mechanism for the servo pattern writing head is composed of a coarse movement mechanism, a fine movement mechanism, and an elastic support member for elastically supporting the head with respect to the coarse movement mechanism. It is much higher than a conventional head positioning mechanism using a voice coil motor and a bearing. As a result, the control band of the head positioning servo is widened, and the vibration of the servo pattern due to the shaft vibration of the spindle motor for rotating the disk can be sufficiently suppressed.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of a head positioning mechanism and a control system in a head positioning device of a servo writer according to one 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 3 having a rotating shaft connected to a center hub 2. The magnetic head 4 is fixed to the distal end of a head arm 5, and the base end of the head arm 5 is fixed on a disk-shaped rotary stage 8, which is a coarse movement mechanism, by a fixed block 7 via an elastic support member 6. . Elastic support member 6
Is itself made of a leaf spring made of a material having high rigidity, such as steel, and is provided substantially perpendicular to the surface of the rotary stage 8. The rotary stage 8 is driven to rotate by a stepping motor (not shown), whereby the head 4 is moved in the radial direction of the disk 1.

On the other hand, one end of a piezoelectric actuator 9 is in close contact with the side end of the head arm 5. The piezoelectric actuator 9 is composed of a laminated piezoelectric element in which a plurality of piezoelectric elements displaced in the thickness direction are laminated, and the other end is a fixed block 1.
0 is fixed on the rotary stage 8. The piezoelectric actuator 9 moves the head 4 in the radial direction of the disk 1 by at least one track pitch.
That is, the piezoelectric actuator 9 expands and contracts in the direction of arrow A as shown in FIG. As a result, the elastic support member 6 is elastically deformed, the head arm 5 rotates from the position shown by the broken line to the position shown by the solid line, and the head 4 is moved in the radial direction of the disk 1.

Although the displacement of the piezoelectric actuator 9 is highly accurate, the displacement is very small, and the head 4
Is at most several tens of μm. Therefore, the piezoelectric actuator 9 is used as a fine movement mechanism,
In this case, the head 4 can be accurately positioned in the radial direction of the disk 1 over all track positions.

A corner cube 11 as a reflecting mirror is fixed to the head arm 5. A laser length measuring device 12 is arranged facing the corner cube 11.
As shown in FIG. 5, the laser length measuring device 12 includes a laser head 51, an interferometer 52, a receiver 53, and a position detecting circuit 5.
The distance between the corner cube 11 and the interferometer 52 is measured with a resolution of about 2.5 nm, and is output from the position detection circuit 54 as position information of the head 4.

In this case, as shown in FIG. 3, the distance L1 from the support point of the head arm 5 (the center of the elastic support member 6) to the corner cube 11 is made larger than the distance L2 from the support point to the head 4. The moving distance of the corner cube 11 depends on the ratio of L1 / L2.
Larger than the moving distance of This makes it possible to measure the position of the head 4 with higher accuracy than the position measurement resolution of the laser length measuring device 12.

A control signal is generated by a control circuit 13 based on the head position information from the laser length measuring device 12, and a stepping motor for rotating the rotary stage 8 is driven by a motor drive circuit 14 in accordance with the control signal. , The rotating stage 8 is rotated. The control signal output from the control circuit 13 is also supplied to the actuator drive circuit 16 via the adder 15, and the piezoelectric actuator 9 is displaced by the actuator drive circuit 16. Thus, the head 4 is positioned at the target position on the disk 1 set by the control circuit 13 by the rotary stage 8 and the piezoelectric actuator 9.

On the other hand, the piezoelectric actuator 9 is further controlled according to the shaft runout of the spindle motor 3. Hereinafter, the shaft runout measuring system of the spindle 3 will be described. In this embodiment, in order to measure the shaft runout of the spindle motor 3, a position signal for shaft runout measurement is previously written at a specific position on the disk 1, for example, the outermost or innermost circumference. A dedicated magnetic head 17 is provided for writing / reading the position signal for shaft shake measurement. The head 17 is moved in the radial direction of the disk 1 by a piezoelectric actuator 18 as a fine movement mechanism and a moving stage 19 as a coarse movement mechanism, like the head 4 for writing a servo pattern.
The read output of the head 17 is input to the position signal reproducing circuit 21 via the amplifier 20.

As shown in FIG. 4, for example, the position signal reproducing circuit 21 includes a frequency separating circuit 41 for separating and extracting the frequency component of the position signal, and a full-wave rectifying circuit for converting the output of the frequency separating circuit 41 into DC. A sample and hold circuit 43 for sampling and holding the output of the full-wave rectifier circuit 42 at a sampling frequency sufficiently higher than the frequency band of the shaft vibration of the spindle motor 3 reproduces the position signal for shaft vibration measurement. For example, if the rotation speed of the spindle motor 3 is 3,600 rpm, the spindle motor 3
Is about 600 Hz, the sampling frequency in the sample and hold circuit 43 is selected to be about 10 kHz.

The position signal for shaft shake measurement reproduced by the position signal reproducing circuit 21 is input to the control circuit 22. The control circuit 22 generates a control signal by calculation from the input position signal. This control signal is transmitted to the actuator
3, the piezoelectric actuator 18 is driven by being supplied to the piezoelectric actuator 18, and the head 17 is positioned so that the head 17 correctly reads the position signal for measuring the axial runout, that is, the head 17 accurately follows the axial runout. Is done. The axial runout tracking band of the head 17 is 1 kHz.
Set to about.

On the other hand, a reflecting mirror 24 is attached to the piezoelectric actuator 18, and the position of the reflecting mirror 24 is measured by a laser length measuring device 25. Laser length measuring device 25
Is configured as shown in FIG. The movement of the piezoelectric actuator 18 is a movement in the radial direction (radial direction of the disk 1) of the position signal for shaft vibration recorded on the disk 1, and the movement of the spindle motor 3 in the radial direction (asynchronous component). Reflects. Since this axis runout is generally about 0.3 μmp-p, the measurement resolution of the laser length measuring device 25 (about 2.5 nm)
Can be measured sufficiently.

The measurement data of the laser length measuring device 25 is stored in a CPU.
(Microcomputer) 26. The radial movement of the position information of the reflecting mirror 24 measured by the laser length measuring device 25 is determined by the fact that the shaft runout of the spindle motor 3 at the time of recording the shaft runout measurement signal and the current shaft runout overlap. Become. Therefore, the CPU 26 samples and stores the measurement data from the laser length measuring device 25 in synchronization with an index signal generated once per rotation from the spindle motor 3 by a rotary encoder or the like.
The average value is obtained and stored. The same operation is repeatedly performed while gradually changing the generation phase of the index signal.
That is, the measurement data is sampled for each rotation position of the disk 1 at a predetermined angular interval, an average value is obtained and stored. The average value thus stored represents the shaft runout (synchronous component) of the spindle motor 3 when the shaft runout measurement position signal is written to the disk 1 because the random asynchronous component is removed by averaging. I have.

Next, the CPU 26 samples and stores the measurement data of the laser length measuring device 25 representing the current position fluctuation of the reflecting mirror 24 for each rotation position, and stores the average value, That is, the synchronous component of the position information is subtracted. As a result, of the axial runout of the spindle motor 3 at each sampling point, the synchronous component is removed, and only the asynchronous component is measured.

The shaft runout measurement signal thus obtained by the CPU 26 is added to the control signal output from the control circuit 13 by the adder 15 and then added to the actuator drive circuit 1.
6. Thereby, the head 4 is positioned so as to cancel the shaft runout of the spindle motor 3.

The shaft runout measurement position signal is written to an appropriate track on the disk 1 by the following procedure.
As shown in FIG. 6, first, the magnetic head is set at the position indicated by the solid line 61, and a continuous signal of the frequency f1 is written on a certain track by the head. Next, the head is moved to 3/3 of the track width.
It is moved by about 4 in the track width direction and set at the position indicated by the broken line 62, and a continuous signal of frequency f2 is written. Thereafter, the head is moved to the center of the position where the signals f1 and f2 overlap. Thus, the signal reproduced by the head 17 is f
The components of 1 and f2 are almost half each, and the ratio varies depending on the shaft runout of the spindle motor 3.

As described above, in this embodiment, the head 4 for writing the servo pattern is positioned at the target track position on the disk 1 by using both the coarse movement mechanism by the rotary stage 8 and the fine movement mechanism by the piezoelectric actuator 9. And the piezoelectric actuator 9 is connected to the spindle motor 3.
By controlling the position of the head 4 in accordance with the shaft runout, the servo pattern can be written with a small runout.

Further, by using the piezoelectric actuator 9 for the fine movement mechanism, the head carriage is supported by the bearings and there is no backlash in the bearings as seen in the conventional head positioning mechanism driven by the voice coil motor. Accurate positioning becomes possible.

Further, since the head arm 5 itself is supported by the elastic support member 6 made of a material having high rigidity, the mechanical resonance point of the head positioning mechanism is increased to about 5 to 6 kHz. The band is as wide as about 1 kHz or more. As a result, the vibration of the servo pattern due to the shaft vibration of the spindle motor 3 can be sufficiently suppressed, and it is possible to sufficiently cope with a high track density such as 5,000 TPI.

FIG. 7 shows another embodiment of the present invention. In this embodiment, the shaft runout of the spindle motor 3 is measured by a capacitance meter 71.
The control signal corresponding to the shaft runout is generated by inputting the detection output to the control circuit 73 via the amplifier 72. This control signal is supplied to the actuator drive circuit 16 via the adder 15, and the head 4 is controlled so as to cancel the shaft runout of the spindle 3 as in the previous embodiment.
Control the position of. Therefore, this embodiment can provide the same effect as the previous embodiment.

In the embodiment, the piezoelectric actuator is used for the fine movement mechanism. However, a magnetostrictive actuator, an electromagnetic actuator, or the like may be used. Further, although the laser length measuring device is used for measuring the position of the head positioning mechanism, a high-resolution optical scale sensor or other scale sensors may be used. In addition, the present invention can be variously modified and implemented without departing from the gist.

[0033]

According to the present invention, by increasing the mechanical resonance point of the head positioning mechanism of the servo writer, the control band of the head positioning servo for writing the servo pattern can be widened, and the spindle motor The vibration of the servo pattern due to the shaft vibration can be reduced to a level that does not substantially cause a problem even at a high track density.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a head positioning device of a servo writer according to an embodiment of the present invention.

FIG. 2 is an enlarged plan view showing a main part of FIG. 1;

FIG. 3 is an enlarged plan view showing a main part of FIG. 1;

FIG. 4 is a block diagram showing a configuration of a position signal reproducing circuit in FIG. 1;

FIG. 5 is a block diagram showing a configuration of a laser length measuring device in FIG. 1;

FIG. 6 is a diagram showing a position signal for axial vibration measurement written in advance on a disk in the embodiment.

FIG. 7 is a configuration diagram of a head positioning device for a servo writer according to another embodiment of the present invention.

FIG. 8 is a configuration diagram of a conventional servo writer head positioning device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magnetic disk 3 ... Spindle motor 4 ... Magnetic head 5 ... Head arm 6 ... Elastic support member 8 ... Rotation stage 9 ... Piezoelectric actuator 12 ... Laser length measuring device 13 ... Control circuit 14 ... Motor drive circuit 16 ... Actuator drive circuit 17 ... Magnetic head 18 ... Piezoelectric actuator 19 ... Moving stage 21 ... Position signal reproducing circuit 22 ... Control circuit 25 ... Laser measuring device 26 ... CPU 71 ... Capacitance meter 73 ... Control circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-64-48276 (JP, A) JP-A-59-168976 (JP, A) JP-A-60-32168 (JP, A) 272067 (JP, A) Actually open 63-153360 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 21/10

Claims (1)

(57) [Claims] 1. A servo writer for writing a servo pattern by a magnetic head on a magnetic disk rotated and driven by a spindle motor, comprising: a coarse movement mechanism for moving the magnetic head in a radial direction of the magnetic disk; A fine movement mechanism for moving at least one track pitch in the radial direction of the disk, an elastic support member supporting the magnetic head with respect to the coarse movement mechanism, and elastically deforming with the operation of the fine movement mechanism; First control means for controlling the fine movement mechanism to move the magnetic head to a desired track position; and second control means for controlling the fine movement mechanism in accordance with the shaft runout of the spindle motor.
A servo writer head positioning apparatus, comprising: