JP2002063774A - Positioning control device - Google Patents

Abstract

(57) Abstract: When a plurality of mechanical resonances exist in a positioning control system such as a magnetic disk drive, an optimal stabilizing method is selected for each resonance. A main resonance stabilized by a phase compensator is selected from a plurality of mechanical resonances, and main resonances other than the main resonance are classified into an "in-phase mode" and an "out-of-phase mode". next,
A notch filter in which the center frequency is set to the resonance frequency of the antiphase mode is inserted, and the antiphase vibration included in the position signal is not fed back to the actuator. Thereafter, a phase compensator for stabilizing the main resonance and the common mode is inserted into the control unit. This phase compensator has an open-loop phase characteristic in which a phase compensator is coupled to a transmission characteristic in which a notch filter and a control target are coupled. ° ~ 1
(When standardized at 80 °).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a head positioning control device for a magnetic disk drive, and more particularly to an operation for causing a magnetic head to follow a target track.

[0002]

2. Description of the Related Art In a head positioning control system such as a magnetic disk drive, a plurality of mechanical resonances of an actuator exist at a frequency higher than a control band. Conventionally, for such resonance, instability has been avoided by lowering the gain of the control system at the resonance frequency using a notch filter or the like. However, the stabilization method using gain reduction using a notch filter is difficult to cope with variations in the resonance frequency between individuals or due to temperature changes.In addition, phase lag occurs, which reduces the phase margin of the control system and improves positioning accuracy. May cause deterioration.

To solve such a problem, Japanese Patent Application Laid-Open No. 11-9 / 1999
Japanese Patent No. 6704 discloses a method of selecting an optimal notch filter when mechanical resonance of a plurality of frequencies exists. This method is a method in which two types of different notch filters are separately inserted into a positioning control system, and an optimum notch filter is selected based on an open loop gain characteristic.

[0004]

According to the method disclosed in the above publication,
Since the method of selecting a notch filter focuses only on the gain characteristic, the notch filter is also selected for resonance that can be stabilized by the phase characteristic. In such a case, an unnecessary notch filter deteriorates the phase margin. In addition, when the gain at the resonance frequency is reduced by the notch filter, the vibration of the resonance cannot be suppressed only by avoiding the excitation.

According to the present invention, in a device for performing positioning control of an object to be controlled by an actuator or the like, when a plurality of mechanical resonances exist at a frequency higher than a control band, a phase characteristic in a frequency response of each resonance is measured and selected. It is an object of the present invention to obtain a control method for selecting an optimal stabilization method for each resonance based on the obtained phase characteristic data.

[0006]

A solution to the above-mentioned problem has the following configuration. First, the frequency characteristics of the control target are measured. Next, resonance stabilized by the phase compensator from the plurality of resonance vibrations existing in the mechanical system (main resonance)
To determine. Next, from the obtained frequency characteristics, the resonance (in-phase mode) having the same phase condition as the main resonance and the phase condition being 180
° Separate into opposite resonance (reverse phase mode). Here, the vibration in the opposite phase mode is compressed by a notch filter or the phase is delayed by 180 ° by a phase inversion filter, and the vibration in the same mode as the main resonance is stabilized by the phase compensator. As a result, it is possible to prevent the notch filter from being inserted into the stabilizable resonance and to suppress the vibration.

[0007]

FIG. 1 is a configuration diagram of a head positioning control system of a magnetic disk drive for explaining an embodiment of a positioning control method according to the present invention. Spindle motor 6
, A magnetic disk 5 as a recording medium is fixed, and rotates at a predetermined rotation speed. A pivot bearing 3 is provided in the side direction of the magnetic disk 5 held by the spindle motor 6 so as to be parallel to the spindle motor axis. The carriage 4 is swingably fixed to the pivot bearing 3. The magnetic head 1 is fixed to a tip of a carriage 4. Power for moving the magnetic head 1 is generated by a voice coil motor (VCM) 2. The magnetic head 1 can detect the position signal recorded in the servo sector 7 on the magnetic disk to know the current position. The position signal detected by the magnetic head is amplified by the head signal amplifier 8 and demodulated by the servo signal demodulator 9. The demodulated servo signal 19 becomes a position signal 20 via the AD converter 10 and is taken into the MPU 16 via the bus 13. The position signal thus obtained is processed by the MPU 16 and V
A CM control signal 21 is generated.

The MPU 16 is connected to the R via the bus 13.
An OM 15 and a RAM 14 are provided. The ROM 15 has M
Various control programs including the present invention executed by the PU 16 are stored, and parameters necessary for various controls are also stored.

An interface controller 17 is connected to the MPU 16 via a bus 13, and issues a read / write access request to the MPU 16 in response to a command from the host controller 18. When a command requesting data read / write is issued, the MPU 16
Executes the positioning method recorded in the ROM 15 and generates an optimum VCM control signal 21 according to the distance from the current head position 20 to the target position. The generated VCM control signal 21 becomes a power amplifier control signal 22 via the DA converter 11 as shown in FIG. 1, is converted into a current 23 via the power amplifier 12, and is applied to the VCM2. VC
M generates the driving force of the head actuator and positions the head at a target position. The operation method of the positioning control device of the present invention has been described above. The present invention relates to a positioning method for generating a VCM control signal 21 based on the difference between the current position and the target position.

Next, the details of the positioning control method of the present invention will be described below.

FIG. 2 is a block diagram of the position control system of the present invention. Here, the control target in FIG. 1 indicates from the VCM control signal 21 calculated by the MPU 16 to the position signal 20 generated so that the processing by the MPU 16 can be performed. This is the transfer function of the object 24. The control unit 25 controls the position signal 20 and the target position 2
6 shows the process from calculating the VCM control signal 21 from the PES 27 which is the difference of 6 to outputting the VCM control signal 21 to the DA converter.

FIG. 3 shows a head drive mechanism comprising a head 1, a VCM 2, a pivot bearing 3, a carriage 4, and the like. The head drive mechanism rotates the pivot bearing center, and the coordinate system of the positioning control system is the rotation coordinate system of the pivot bearing center. It is known that various mechanical resonance vibrations (resonance frequencies) exist in the transfer characteristic from the VCM control input to the head position.
In the present invention, only the mechanical resonance having a large gain and possibly affecting the control system is dealt with among these mechanical resonance vibrations.

FIG. 4 shows a measurement example of the frequency response (gain characteristic 41 and phase characteristic 42) of the transfer characteristic 40 from the VCM control input to the head position in the head drive mechanism. The phase characteristic 42 is a value normalized from -306 ° to 0 ° (for example, -540 ° becomes -180 °) by removing a phase delay due to a dead time or a sampler / hold.

The transfer characteristic 40 comprises a rigid mode and a plurality of vibration modes. The resonance 44 near 4 kHz is a vibration mode called a main resonance frequency, and the control band is limited by the main resonance frequency. In addition, a plurality of resonance vibrations (higher-order resonance frequencies) exist at frequencies higher than the main resonance frequency, and these also affect the stability of the control system. It can be seen from the phase characteristic 42 that the phase of the main resonance lags between −180 ° and −360 °. At the higher-order resonance frequency, the phase lags between −180 ° and −360 ° similarly to the main resonance frequency, and the phase lags from 0 ° to −
It is divided into those that are delayed by 180 ° (shifted by 180 ° from the main resonance frequency). Therefore, in the present invention, among the higher-order resonance frequencies, those whose phase is delayed in the same manner as the main resonance frequency (between -180 ° and -360 ° in this embodiment) are referred to as “in-phase mode”. Are different from each other by 180 ° (in the present embodiment, between 0 ° and −180 °) and the phase is delayed. Therefore, in FIG. 4, the resonance 45 is in the common mode,
Is the reverse phase mode.

FIG. 5 shows an example of a resonance mode shape in the head drive mechanism. FIG. 5A shows a butterfly primary mode that is the main resonance. This mode diagram is VCM
And the head vibrate in the same direction (the opposite direction in the rotating coordinate system). FIG. 5B shows a butterfly secondary mode as an example of the in-phase mode. This mode is 5-7kHz
Near the resonance point, the VCM and the head vibrate in the same direction, but the pivot bearing vibrates in the opposite direction. FIG. 5C shows an S-shaped mode as an example of the reverse phase mode. This mode is
It has a resonance point in the vicinity of 〜１０10 kHz, and the VCM and the head vibrate in opposite directions. In other words, the main resonance and the above-described in-phase mode are modes in which the VCM and the head vibrate in the same direction (the opposite direction in the rotating coordinate system). Direction). From this, it can be seen that, as far as the relationship between the VCM and the head position is concerned, the main resonance and the in-phase mode make the same movement, and the main resonance and the anti-phase mode make the opposite movement.

Next, a method for stabilizing a plurality of mechanical resonances according to the present invention will be described. First, the frequency response of the control target is measured. From this frequency response, the main resonance stabilized by the phase compensator is selected, and the main resonances other than the main resonance are classified into “in-phase mode” and “reverse-phase mode”.
Next, a notch filter in which the center frequency is set to the resonance frequency of the reverse phase mode is inserted, and the vibration of the reverse phase mode included in the position signal is not fed back to the actuator. Thereby, it is possible to prevent the excitation in the reverse phase mode. Thereafter, a phase compensator for stabilizing the main resonance and the common mode is inserted into the control unit. This phase compensator has an open-loop phase characteristic in which a phase compensator is coupled to a transfer characteristic in which a notch filter and a control target are coupled, and has a 360 ° × n (n is an integer) at a resonance frequency of a main resonance and an in-phase mode.
Are designed so as to have a phase characteristic within a range of ± 90 ° with respect to (in the case of standardization at −180 ° to 180 °, a range of −90 ° to 90 °). Thereby, a signal of a phase condition for canceling the vibration in the same mode as the main resonance is output from the control unit to the actuator, and the vibration is suppressed. In particular, as the open-loop phase characteristic approaches 0 °, the damping effect increases. Here, even when the resonance in the common mode has a large gain (for example, -3 dB or more) in the open loop gain characteristic, the stability of the control system is maintained, and the control system becomes unstable or the vibration at the resonance frequency is suppressed. There is no excitation. This can be confirmed by the vector locus of the open loop characteristic using the Nyquist diagram and the sensitivity function characteristic.

A design example of the control unit 25 using the present invention will be described. In this case, the head drive mechanism section has the transfer characteristic 40 shown in FIG.
Is designed for a head positioning control system having First, a notch filter whose center frequency is set to 7.5 kHz, which is the resonance frequency of the reverse phase mode, is inserted into the control unit 25. FIG. 6 shows the frequency response (gain characteristic 49 and phase characteristic 50) of the transfer characteristic 48 obtained by combining the control target and the notch filter.
Is shown. The transfer characteristic 48 is 4 which is the resonance frequency of the main resonance.
The phase at 5 kHz is 15 °, and the phase at 6 kHz which is the resonance frequency of the common mode is −29 °. Accordingly, the phase characteristic of the phase compensator is −105 ° to 75 ° at 45 kHz,
Hz may be in the range of -61 ° to 119 °. Also,
In order to secure a phase margin of the control system, it is necessary to advance the phase at a frequency at which the open loop gain characteristic becomes 0 dB. The phase compensator that satisfies these conditions is
Insert into 5. FIG. 7 shows the frequency characteristics of the control unit 25 designed to satisfy the above specifications, and the open loop characteristics (gain characteristics 51 and phase characteristics 52) of the control unit 25.
Is shown in FIG.

The effects of applying the present invention will be shown using the results of the above design example. In the open loop gain characteristic 51 shown in FIG. 8, the gain at 7.5 kHz at which the reverse phase mode exists is lowered by the notch filter, and it can be confirmed that the present control system does not excite the reverse phase mode. FIG.
FIG. 5 shows a vector locus 53 of the open loop characteristic in the above design example using a Nyquist diagram. In the vector locus 53, the frequency at which the main resonance 44 exists is stabilized by the control unit 25, and is a stable vector locus. Similarly, since the signal passes through a stable vector locus even at the frequency where the resonance 45 in the common mode exists, it is understood that the control system is stable. FIG. 10 shows the gain characteristic 54 of the sensitivity function in the above design example. 6 where the common mode exists
At kHz, the gain characteristic 54 of the sensitivity function is compressed to 0 dB or less, and it can be seen that the vibration due to the resonance 45 is damped.

Since the second embodiment is almost the same as the first embodiment, only different points will be described, and the same components will be denoted by the same reference numerals and description thereof will be omitted. In the first embodiment, a control system in which a notch filter is inserted in order to prevent the excitation in the reverse phase mode and the vibration in the reverse phase mode included in the position signal is not fed back to the actuator. Therefore, in the second embodiment, the phase is set to 180 at the resonance frequency in the opposite phase mode.
° Insert a phase inversion filter Fi (s) 61 to delay,
A method of damping the vibration in the opposite phase mode will be described.

The anti-phase mode oscillation oscillates under a phase condition opposite to the main resonance. Therefore, when the anti-phase mode vibration included in the position signal is input to the phase compensator for stabilizing the main resonance vibration, a signal for exciting the anti-phase mode vibration is output from the phase compensator to the actuator. However, when the anti-phase mode vibration included in the position signal is input to the phase compensator with the phase delayed by 180 °, a signal for damping the vibration is output from the phase compensator to the actuator. Therefore, a phase inversion filter Fi (s) for delaying the phase of the anti-phase mode vibration included in the position signal by 180 ° is coupled to the phase compensator. Here, the phase inversion filter Fi (s) is a secondary filter represented by Expression 1.

[0021]

(Equation 1)

The manner of giving the coefficients ζ and ω of Equation 1 will be described below. ω
Is set to the resonance frequency of the reverse phase mode. Thereby, a phase characteristic of delaying the phase by 180 ° at the resonance frequency in the opposite phase mode is realized. ζ determines the width of the frequency for changing the phase, and is usually selected from 0.05 to 0.5.

In this embodiment, a design method of the control unit 25 to which the present invention is applied will be described. Here, the head drive mechanism is designed for a head positioning control system having the transfer characteristic 40 shown in FIG. The control unit 25 includes a phase inversion filter Fi (s) 61 for delaying the phase by 180 ° at 7.5 kHz, which is the resonance frequency of the opposite phase mode, and a phase compensator having a phase condition for stabilizing the in-phase mode with the main resonance. It is composed by combining. FIG. 11 shows the frequency response of the phase inversion filter Fi (s) 61.

In the present embodiment, the effect when the present invention is applied will be described. FIG. 12 shows a vector locus 63 of the open loop characteristic using the Nyquist diagram in the present embodiment.
The vector locus 63 is a stable vector locus because it is stabilized by the control unit 25 at the frequency where the main resonance 44 exists. Similarly, at a frequency where the resonance 45 which is the in-phase mode and the resonance 46 which is the anti-phase mode exist, the control system is stable because it passes through a stable vector locus.

FIG. 13 shows a gain characteristic 64 of the sensitivity function in this embodiment. At 6 kHz where the in-phase mode exists and at 7.5 kHz where the anti-phase mode exists, the gain characteristic 64 of the sensitivity function is compressed to 0 dB or less, and it can be seen that the vibration caused by the resonance 45 and the resonance 46 is damped.

Since the third embodiment is almost the same as the first and second embodiments, only different points will be described, and the same components will be denoted by the same reference numerals and description thereof will be omitted. In the first and second embodiments, the head drive mechanism has the VCM as the only actuator. In the third embodiment, the head drive mechanism has a configuration in which a VCM is provided as a coarse movement actuator and a fine movement actuator is provided in addition. That is, it is a two-stage actuator drive system. In this embodiment, two piezo elements are mounted on a suspension connecting a carriage and a head as fine movement actuators.

FIG. 14 shows a fine movement actuator mechanism control unit including the head 1, the carriage 4, the suspension 105, the piezo element 106, the piezo element 107, and the piezo element control unit 108. The fine movement actuator is controlled by the piezo element control input 109 to control the piezo element 10.
6. The head 1 is moved by expanding and contracting 107. There are various mechanical resonance vibrations in the transfer characteristics from the piezo element control input 109 to the head position 20.

FIG. 15 shows an example of the frequency response (gain characteristic 141 and phase characteristic 142) of the transfer characteristic from the piezo element control input 109 to the head position 20. Here, the resonance 144 near 6 kHz is regarded as the main resonance in the piezoelectric element control system, and is stabilized by the phase compensator. From the phase characteristics 142, it can be seen that the phase of the main resonance lags between 0 ° and -180 °. Therefore, in the present embodiment, the resonance in which the phase lags between 0 ° and −180 ° as in the main resonance is “in-phase mode”, and the phase is −180 °.
Resonance that lags between 0 ° and −360 ° is the “reverse-phase mode”. Thus, in FIG. 15, resonance 145 is in the in-phase mode and resonance 146 is in the anti-phase mode.

[0029]

According to the positioning control system of the magnetic disk drive, when the control object has a plurality of mechanical resonances, an unnecessary notch filter is removed by selecting a stabilizing method according to a phase characteristic of each resonance. In addition, it is possible to suppress stabilizable vibration. Thereby, the positioning accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a head positioning control system of a magnetic disk drive according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a positioning control method according to the first embodiment of the present invention.

FIG. 3 is a view showing a head drive mechanism according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating a gain characteristic and a phase characteristic from a VCM control input to a head position in a head driving mechanism unit according to the first embodiment of the present invention.

FIG. 5 is a mode diagram of a vibration mode in the head drive mechanism according to the first embodiment of the present invention.

FIG. 6 is a diagram illustrating a transfer characteristic in which a notch filter according to the first embodiment of the present invention and a control target are combined.

FIG. 7 is a diagram showing a transfer characteristic of a control unit when the present invention is applied, showing the first embodiment of the present invention.

FIG. 8 is a diagram showing open-loop characteristics of a control system when the first embodiment of the present invention is applied.

FIG. 9 is a Nyquist diagram showing a vector locus of a control system when the first embodiment of the present invention is applied.

FIG. 10 is a diagram showing a sensitivity function gain characteristic of a control system when the first embodiment of the present invention is applied.

FIG. 11 is a diagram showing gain characteristics and phase characteristics of a phase inversion filter Fi (s) according to a second embodiment of the present invention.

FIG. 12 is a Nyquist diagram showing a vector locus of a control system when the second embodiment of the present invention is applied.

FIG. 13 is a diagram showing sensitivity function gain characteristics of a control system when the second embodiment of the present invention is applied.

FIG. 14 is a diagram of a head drive mechanism control unit using a fine movement actuator according to a third embodiment of the present invention.

FIG. 15 is a diagram showing a gain characteristic and a phase characteristic from a piezo element control input to a head position in a head driving mechanism according to a third embodiment of the present invention.

[Explanation of symbols]

1: magnetic head, 2: voice coil motor (VCM), 4:
Carriage, 20 position signal, 21 VCM control signal, 4
2 ... Phase characteristic from VCM control input to head position in the first embodiment of the present invention, 44 ... Main resonance in the first embodiment of the present invention, 45 ... In the first embodiment of the present invention In-phase mode, 46... Inverse-phase mode in the first embodiment of the present invention, 54
... Sensitivity function gain characteristics in the first embodiment of the present invention, 64
... sensitivity function gain characteristics in the second embodiment of the present invention, 10
5: suspension, 106: piezo element, 107: piezo element.

Continued on the front page (72) Inventor Toshihiko Shimizu 502, Kandatecho, Tsuchiura-shi, Ibaraki Pref. Machinery Research Laboratories, Hitachi, Ltd. (72) Inventor Masaki Otai 502 Kandachi-cho, Tsuchiura-shi, Ibaraki F-term in Machine Research Laboratory, Hitachi Ltd. 5D042 LA01 MA15 5D096 NN03 NN07 RR01 RR03 RR05 RR18

Claims (6)

[Claims] An information recording / reproducing medium; a head for recording / reproducing information while moving relative to the information recording / reproducing medium; an actuator supporting the head and movable in response to a command; A control unit that controls movement by giving a command to the actuator based on a signal reproduced by a head, wherein the actuator has a plurality of mechanical resonance frequencies. The control unit is configured to control the positioning control device at a certain first resonance frequency and at least one second resonance resonance frequency having substantially the same phase characteristic as the first resonance frequency among the mechanical resonance frequencies. The phase of the open loop characteristic is set to a value within ± 90 ° around 360 ° × n (n is an integer), and the phase of the open loop characteristic at the second resonance frequency is obtained. Positioning control apparatus which is characterized in that the emission and higher -3 dB. 2. The positioning control device according to claim 1, wherein at least one third resonance frequency having a phase characteristic different from the first resonance frequency by about 180 ° exists among the mechanical resonance frequencies. In this case, the control unit includes a notch filter in which a center frequency is set to the third resonance frequency. 3. The positioning control device according to claim 1, wherein at least one third resonance frequency having a phase characteristic different from the first resonance frequency by about 180 ° exists among the mechanical resonance frequencies. In this case, the control unit includes a second-order filter that delays the phase of the third resonance frequency by about 180 °. 4. An information recording / reproducing medium, a head for recording / reproducing information while moving relative to the information recording / reproducing medium, and a first actuator which supports the head and is movable in accordance with a command. A first control unit for controlling the driving of the first actuator, a second actuator movable in response to a command, and giving a command to the second actuator based on a signal reproduced by the head. A second control unit that controls the movement of the second actuator, wherein the second actuator has a plurality of mechanical resonance frequencies, a first resonance frequency that is one of the mechanical resonance frequencies, In one or more second resonance frequencies having substantially the same phase characteristics as the first resonance frequency in mechanical resonance, the second control unit may control the open loop characteristics of the positioning control device. A phase control value within ± 90 ° around 360 ° × n (n is an integer), and a gain of the open loop characteristic at the second resonance frequency is −3 dB or more. . 5. The positioning control device according to claim 4, wherein at least one third resonance frequency having a phase characteristic different from the first resonance frequency by about 180 ° exists among the mechanical resonance frequencies. In this case, the second control unit includes a notch filter in which a center frequency is set to the third resonance frequency. 6. The positioning control device according to claim 4, wherein at least one third resonance frequency having a phase characteristic different from the first resonance frequency by about 180 ° exists among the mechanical resonance frequencies. In this case, the second control unit includes a second-order filter that delays a phase by about 180 ° at the third resonance frequency.