JP2002288954A - Head positioning device, fine-adjustable actuator driving device, head positioning control method, head positioning control program, and disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the high speed and accurate positioning of a magnetic head by preventing piezo-electric elements constituting a fine-adjustable actuator from being shorted due to the precipitation of lead, in a two-stage actuator system. SOLUTION: The head positioning device, which controls the position of the magnetic head 2 for accessing to a magnetic disk 1 with a two-stage actuator system consisting of a coarse-adjustable actuator 51 and a fine-adjustable actuator 52, is provided with a positioning control part 6 for the coarse- adjustable actuator 51 and the fine-adjustable actuator 52 constituted by utilizing piezo-electric elements, and with a fine-adjustable part 64 for driving the fine- adjustable actuator 52 and further with a driving signal limiting means 66 for limiting a driving signal level applied to the fine-adjustable part 64 to a threshold value or below, where a change in the characteristic of the piezo-electric elements is caused.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a two-stage actuator system for controlling the position of a head for accessing an information recording / reproducing disk by using a coarse actuator and a fine actuator. The present invention relates to a head positioning device in which an actuator uses a piezoelectric element, and particularly relates to a technique for coping with a short-circuit of a piezoelectric element caused by a high drive voltage.

The preferred embodiment of the head positioning apparatus to which the present invention is applied is one which is mainly mounted on a magnetic disk drive, but is not necessarily limited to this, and may be applied to an optical disk drive. It is.

[0003]

2. Description of the Related Art In recent years, with the development of multimedia, a target position on a magnetic disk is accessed at a high speed (head positioning is performed), and a large amount of video information, audio information, character information, and the like are transferred. There is a strong demand from the market for high-density magnetic disk devices for high-speed recording and reproduction, and various high-speed and high-precision positioning techniques for magnetic heads have been proposed.

In order to realize a higher recording density of a magnetic disk device, a recent magnetic disk device is composed of a reproducing head composed of a GMR head to which a magnetoresistive effect is applied and a recording head composed of an inductive head. A composite magnetic head (head) is adopted.

[0005] The composite type magnetic head comprising the above two types of heads is mounted on the same slider. A slider on which the magnetic head is mounted is mounted on a head support mechanism, and the head support mechanism is configured to be rotatable around an axis mounted on a chassis (rotary actuator). Rotary actuators can reduce the influence of inertia and are resistant to external impacts in the translation direction, so that they are suitable for realizing high-speed access and high-precision positioning.

In order to perform high-speed and high-precision positioning of the magnetic head, it is expected that a future magnetic disk drive will generally be configured to have two driving means, a coarse movement actuator and a fine movement actuator. You.

A coarse actuator such as a voice coil motor (VCM) moves the head support mechanism, slider and magnetic head by rotating the head support mechanism about an axis attached to the chassis. Coarse actuators are primarily used for large movements such as seek / settling and multiple track jumps.

[0008] The fine movement actuator drives a magnetic head or a slider. The fine movement actuator is mainly used for high-speed and fine positioning such as track following and one-track jump. The fine actuator is also called a microactuator (MA).

The reproducing head reads servo information (current position information of the head) recorded on the magnetic disk. By controlling the coarse actuator and the fine actuator based on the servo information, the magnetic head formed on the slider can be accessed (positioned) at an arbitrary position on the magnetic disk.

A mechanism having a coarse actuator and a fine actuator is generally called a piggyback actuator, a two-stage actuator, or a dual-stage actuator. The main drive mechanism is called a coarse movement actuator, and the auxiliary drive mechanism is called a fine movement actuator.

"Conventional example" A conventional control system configured to perform high-speed and high-accuracy positioning using a two-stage actuator will be described below as a conventional example.

Conventional Example 1: JP-A-10-136665 (TDK): Piezoelectric Piggy-Back Microactuat
or for Hard Disk Drive (IEEE TRANSACTIONS ON MAGNE
TICS. VOL.35 NO.2, MARCH 1999) Conventional example 2: Dual-Stage Actuator System for Magnetic
Disk Drive (IEEE TRANSACTIONS ON MAGNETICS. VOL.35
NO.2, MARCH 1999; Fujitsu) Conventional example 3: Japanese Patent Application Laid-Open No. 2001-6305 (NEC) “Conventional configuration and operation” “Conventional example 1” FIGS.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram illustrating a piezo-type piggyback actuator described in Japanese Patent Application Publication No. 65-65, and a block diagram of a servo operation evaluation system of the actuator.

FIG. 12 shows a type II piezoelectric actuator disposed between the flexure portion of the suspension and the head slider. The piezoelectric actuator is driven by a push-pull to swing the head slider. Due to this swinging motion, the magnetic head is minutely driven in the tracking direction. E2 is the beam, E3 is the fixed part, E4
Denotes a movable portion, E5 denotes an electrode layer (piezo element), and E21 denotes a hinge portion.

In this case, a voice coil motor (VC) having a suspension having a magnetic head and a piezo element is used.
M) a coarse positioning control system that drives a fine movement actuator that is a piezo element;
A heavy servo system constitutes a head positioning control system of the magnetic disk drive, and realizes high-precision positioning of the magnetic head.

In FIG. 13, a positioning control system is constituted by only a fine actuator by a suspension including a fine actuator, which is a piezo element, a control unit, a drive unit, and a position detecting unit.

That is, high-precision positioning of the magnetic head is realized by compensating for high-frequency disturbance using the fine movement actuator.

[Conventional Example 2] FIGS. 14 and 15 show the “Dual-S
tage Actuator System for Magnetic Disk Drive ”(IE
EE TRANSACTIONS ON MAGNETICS.VOL.35 NO.2, MARCH 19
FIG. 99 is a perspective view showing a two-stage actuator described in 99) and a block diagram showing a control method in a control system of the two-stage actuator.

In FIG. 14, the microactuator is:
It is composed of a head suspension, a stator plate for attaching to a carriage arm, and a piezo element.

The head suspension is caused to swing by driving the piezo element by push-pull. As a result, the magnetic head mounted on the tip of the slider is finely driven in the tracking direction.

In FIG. 15, the control amount of the fine actuator is calculated based on the position error detected by the magnetic head, the relative displacement of the micro actuator is estimated, and the estimated value is input to the control system of the coarse actuator. Then, the control amount of the coarse actuator is calculated. By controlling and driving each actuator independently, high-precision positioning of the magnetic head is realized.

"Conventional Example 3" FIG.
FIG. 1 is a schematic diagram of a magnetic disk device described in Japanese Patent No. 6305.

A fine movement controller F24 for outputting a control signal for positioning the fine movement part as output data based on a position error signal supplied from the fine movement part of the head moving mechanism F1, and the output data is stored in the movable range of the fine movement actuator. Limiter F that saturates to be within the limits
26, a subtractor F27 and a multiplier F28 for generating data for correcting the output data based on the difference between the output data of the limiter F26 and the output data from the fine movement controller F24.

[0023]

In each of the above-mentioned prior arts, since the driving voltage is high, the piezoelectric element constituting the fine movement actuator may be short-circuited and malfunction may occur.

In Conventional Example 1, controllers are independently designed, each controller independently calculates a control amount based on a position error signal, and controls and drives each actuator to realize high-precision positioning of the head. .

In Conventional Example 1, the piezo-type fine actuator achieves a displacement of 1.2 μm with an offset voltage of 10 V and a command voltage of ± 5 V.

However, in such a control method, when the band of the fine movement actuator is increased to increase the control band, the fine movement actuator has a track pitch of 0.5.
Even in the case of head positioning control in the case of about μm, the command voltage is about ± 9 to 11 V and an offset voltage of 10 V is always applied to the fine actuator.

In the conventional example 2, the characteristics of the piezo-type microactuator are such that the displacement is 0.degree.
Although 81 μm is realized, the block diagram shown in FIG. 15 does not take into account the part that limits the command voltage.

With such a fine movement actuator and such a control system, when the fine movement actuator is made to have a higher band to increase the control band, the fine movement actuator performs head positioning control when the track pitch is about 0.5 μm. However, the command voltage becomes 5 V or more.

The prior art 3 has a limiter for instructing output data whose level of displacement does not exceed the movable range so that the fine movement actuator is controlled and driven within its movable range. However, this is a limiter in the movable range of the fine movement actuator, not a limiter based on the characteristics of the driving element.

On the other hand, in a piezo element, when a voltage is applied to the electrodes on both sides, a lead component in the element causes an electrochemical reaction, and lead is deposited on the electrodes.

As one of the piezo elements, there is a PZT element which is an alloy of lead, zirconia and titanium. This PZT element is not actually composed only of a PZT crystal.
Due to the influence of the process, impurities such as lead oxide and water are always contained.

When a voltage is applied to both ends of the lead oxide and water, an electrochemical reaction is activated, and lead precipitates on the negative electrode side. When this phenomenon progresses, the element is short-circuited, and the piezo element does not generate displacement.

However, when the potential difference is equal to or lower than the decomposition voltage, this phenomenon hardly occurs. When the potential difference exceeds the threshold value, the reaction is exponentially accelerated, and corrosion due to an electrochemical reaction occurs. Deteriorates. And finally, the PZT element is destroyed by the short circuit.

That is, in the conventional two-stage actuator and the control driving system, even in the case of track jump or track following, the voltage applied to the piezo element is a threshold value (decomposition voltage) at which corrosion occurs due to an electrochemical reaction. And the characteristics of the fine movement actuator are deteriorated, so that the position error suppression characteristics are also deteriorated. Therefore, there is a problem that the effect of the two-stage actuator cannot be sufficiently obtained.

In view of the above problem, the present invention is directed to a two-stage actuator having a coarse movement actuator and a fine movement actuator, which prevents a piezoelectric element constituting the fine movement actuator from being short-circuited due to corrosion due to an electrochemical reaction. It is another object of the present invention to provide a high-speed and high-precision positioning of the head by driving the fine movement actuator in a high-bandwidth control, thereby providing a disk device having a high recording density (high track density). .

[0036]

According to the present invention, a head positioning device for solving the above-mentioned problems is provided with a head position for accessing an information recording / reproducing disk as a premise. The control method is a two-stage actuator method in which position control is performed by two actuators, a coarse movement actuator and a fine movement actuator. Further, the above-mentioned fine movement actuator uses a piezoelectric element. The present invention is configured such that in such a head positioning device, the signal level for driving the fine movement actuator using the piezoelectric element is driven by a signal equal to or less than a threshold value at which a characteristic change of the piezoelectric element occurs. It is.

According to the present invention, when driving the piezoelectric element which is a component of the fine movement actuator, the level of the drive signal is limited to a threshold value or less at which the characteristic change of the piezoelectric element occurs. Therefore, it is possible to solve the problem that the piezoelectric element is corroded due to the electrochemical reaction caused by the high drive signal level and the characteristics are degraded, and the function of high-speed and high-precision positioning of the head with respect to the target track is provided. It can last for a long time.
Therefore, high recording density (high track density)
Effectively works to realize the disk device.

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be generally described.

The head positioning device according to the first aspect of the present invention includes:
A two-stage actuator system for controlling the position of a head for accessing an information recording / reproducing disk with a coarse actuator and a fine actuator, wherein the fine actuator is configured using a piezoelectric element In a positioning device, a level of a drive signal of a fine movement actuator using the piezoelectric element is set to be equal to or less than a threshold value at which a characteristic change of the piezoelectric element occurs.

The operation according to the first aspect of the present invention is substantially the same as that described in the above section [Means for Solving the Problems]. In other words, it is possible to solve the problem that the piezoelectric element is corroded due to the electrochemical reaction caused by the high drive signal level and the characteristics are deteriorated, and the high-speed and high-precision positioning function of the head with respect to the target track is extended. Can last for a period of time.

The head positioning device according to the second aspect of the present invention includes:
A coarse actuator and a fine actuator for controlling the position of a head for accessing the information recording / reproducing disk by a two-stage actuator system, and a positioning controller for controlling the coarse actuator and the fine actuator; The fine positioning actuator is configured using a piezoelectric element, the positioning control unit is a head positioning device configured to include at least a fine movement driving unit that drives the fine movement actuator using the piezoelectric element, the fine movement driving unit Drive signal limiting means for limiting the level of the drive signal to be applied to a threshold value or less at which the characteristic change of the piezoelectric element occurs.

The second invention describes the first invention more restrictively. The fine movement drive unit supplies a drive current to drive the fine movement actuator, but in the positioning control unit, the drive signal limiting means sets the level of the drive signal to the fine movement drive unit to be equal to or less than a threshold at which the characteristic change of the piezoelectric element occurs. , Which solves the problem of characteristic deterioration due to corrosion of the piezoelectric element caused by a high drive signal level, and maintains the high-speed, high-precision positioning function of the head with respect to the target track for a long period of time. Can be done.

The head positioning device according to the third invention of the present application is:
In the second aspect, the drive signal limiting means may include a voltage command that changes a current-voltage characteristic of the piezoelectric element in the fine movement actuator and causes a current value flowing through the piezoelectric element to start increasing exponentially with respect to an applied voltage. The driving signal is restricted and output with the value being the threshold value. This describes how the drive signal limiting means determines a threshold as a reference for limiting the drive signal given to the fine movement drive unit.

A head positioning device according to a fourth aspect of the present invention is:
In the first to third inventions, further, a characteristic inspection unit for detecting a relationship between a command drive voltage for the fine movement actuator and a current flowing through the piezoelectric element, and the command drive based on a detection result by the characteristic inspection unit Limiting voltage changing means for changing the threshold value of the voltage.

The operation according to the fourth aspect of the invention is as follows. That is, the current flowing in the piezoelectric element is usually 10
^-7 [A] or less. However, if moisture in the atmosphere enters the element in a high-temperature, high-humidity environment or the like, or moisture enters the element during processing, the order of the current flowing at a decomposition voltage or higher becomes 100 times or more.
The decomposition voltage of the piezoelectric element, which is the threshold value, is theoretically constant depending on the substance, but actually has individual differences including variations in the oxygen overvoltage and variations in the composition of the piezoelectric element.
Therefore, it is necessary to adjust the threshold value of the drive voltage with each fine movement actuator. The characteristic inspection means detects an actual relationship between the command drive voltage and the current flowing through the piezoelectric element, and the limit voltage changing means changes the threshold value for the command drive voltage based on the detection result by the characteristic inspection means. Corresponding. Therefore, control of the head actuator can be performed with high accuracy regardless of individual differences of the piezoelectric elements and changes in the use environment, particularly humidity.

The head positioning device according to the fifth invention of the present application is:
In the first to third inventions, further, a time function for limiting a time during which the drive voltage is continuously output according to the command drive voltage value when the command drive voltage for the fine movement actuator is equal to or higher than a threshold value It has a filter.

The operation according to the fifth invention is as follows. That is, the current flowing through the piezoelectric element increases as the energization time increases. Therefore, in the case of the command drive voltage equal to or higher than the threshold, it is necessary to limit the continuous drive output time. When the command drive voltage is equal to or higher than the threshold, the time function filter limits the continuous drive voltage output time according to the level of the command drive voltage. Therefore, the head actuator can be controlled with high accuracy irrespective of the fluctuation of the command drive voltage.

A head positioning device according to a sixth aspect of the present invention includes:
In the second to fifth inventions, the threshold value in the drive signal restricting means is a decomposition voltage represented by a theoretical decomposition voltage of lead or a sum of a theoretical decomposition voltage of lead and an oxygen overvoltage of lead, or This is the water decomposition voltage.

The operation according to the sixth aspect of the invention is as follows. That is, the cause of the short circuit of the piezoelectric element is that lead is deposited on the electrode. So, in principle,
By setting the theoretical decomposition voltage of lead to the threshold value of the drive signal limiting means, it becomes possible to prevent the precipitation of lead. More practically, the electrolysis proceeds and oxygen is generated at a level obtained by adding a voltage called an oxygen overvoltage to the theoretical decomposition voltage. Up to that point, you can afford.

A head positioning device according to a seventh aspect of the present invention is:
In the first to sixth aspects, the piezoelectric element in the fine movement actuator is a thin-film PZT element made of lead, zirconia, and titanium.

The operation of the seventh aspect is as follows. That is, the PZT element is a typical example of a piezoelectric element having excellent characteristics. However, in reality, the PZT element is not only composed of the PZT crystal but always contains impurities such as lead oxide and water due to the influence of the process. When a voltage is applied to both ends of the lead oxide and water, an electrochemical reaction is activated, and lead precipitates on the negative electrode side. When this phenomenon progresses, the element is short-circuited and the displacement operation cannot be performed. In a head positioning device using such a PZT element for a fine movement actuator, the present invention exhibits the greatest effect.

The above description relates to the invention relating to the head positioning device. However, the eighth to thirteenth inventions relate to the fine actuator driving device. A series of inventions are generally directed to a two-stage actuator type head positioning device including a coarse movement actuator and a fine movement actuator, but more strictly exclude a coarse movement actuator driving device, and It is essentially applied to an actuator drive device.

The fine movement actuator driving apparatus according to the eighth aspect of the present invention is a fine movement actuator driving apparatus including a fine movement actuator using a piezoelectric element for finely positioning the head, and a fine movement driving section for driving the fine movement actuator. And a driving signal restricting means for restricting a level of a driving signal given to the fine movement driving unit to a threshold value or less at which a characteristic change of the piezoelectric element occurs. The operation of this is as described above.

According to a ninth aspect of the present invention, in the fine movement actuator driving device, the drive signal limiting means changes a current-voltage characteristic of the piezoelectric element in the fine movement actuator, and a current value flowing through the element with respect to an applied voltage is an exponential function. The voltage command value that starts to rise gradually is set to the threshold value, and the drive signal is limited and output. The operation of this is as described above.

The fine-movement actuator driving device according to the tenth aspect of the present invention further comprises a characteristic inspection means for detecting a relationship between a command drive voltage for the fine movement actuator and a current flowing through the piezoelectric element, and a detection result obtained by the characteristic inspection means. Limiting voltage changing means for changing a threshold value of the command drive voltage based on the threshold value. The operation of this is as described above.

The fine movement actuator driving device according to the eleventh aspect of the present invention further comprises a time period during which the driving voltage is continuously output according to the command driving voltage value when the command driving voltage for the fine movement actuator is equal to or higher than a threshold value. With a time function filter that limits The operation of this is as described above.

According to a twelfth aspect of the present invention, the threshold value in the drive signal restricting means is represented by a theoretical decomposition voltage of lead or a sum of a theoretical decomposition voltage of lead and an oxygen overvoltage of lead. Is set to the decomposition voltage or the decomposition voltage of water. The operation of this is as described above.

According to a thirteenth aspect of the present invention, in the fine actuator driving device, the piezoelectric element in the fine actuator is a thin film PZT made of lead, zirconia and titanium.
Element. The operation of this is as described above.

The fourteenth invention of the present application relates to a head positioning control method, and has the following steps as preconditions. That is, a step of setting a position error between head position data from servo information on a disk reproduced by the head and target position data for positioning the head at a target position as position error data, and based on the position error data. Generating fine movement control data for controlling the amount of displacement of the fine movement actuator of the head, and outputting a signal based on the fine movement control data to the fine movement actuator as a fine movement drive signal;
Inputting relative displacement data corresponding to the displacement amount of the coarse movement actuator or the fine movement actuator of the head, and generating coarse movement control data for controlling the displacement amount of the coarse movement actuator based on the relative displacement data And outputting a signal based on the coarse movement control data to the coarse movement actuator as a coarse movement drive signal. In the head positioning control method including such a plurality of steps, the present invention further includes the step of outputting a signal based on the fine movement control data to the fine movement actuator, wherein the fine movement control is performed using a threshold value at which a characteristic of the fine movement actuator changes. The method is characterized in that the method includes a step of generating actual fine movement control data in which data is limited, and replacing the actual fine movement control data with the fine movement control data and outputting the data.

According to the head positioning control method of the present invention, it is possible to solve the problem of characteristic deterioration due to corrosion of a piezoelectric element caused by a high drive signal level, and to achieve high-speed and high-precision positioning of a head with respect to a target track. The positioning function can be maintained for a long period of time.
Therefore, high recording density (high track density)
Effectively works to realize the disk device.

In the head positioning control method according to a fifteenth aspect of the present invention, in the fourteenth aspect, the step of generating the actual fine movement control data includes a step of inspecting a change in a displacement characteristic or an electrical resistance characteristic of the fine movement actuator. And changing the threshold value based on the characteristic change. According to the fifteenth aspect, the head actuator can be controlled with high accuracy irrespective of individual differences between the piezoelectric elements and changes in the use environment, particularly humidity.

In the head positioning control method according to a sixteenth aspect of the present invention, in the fourteenth aspect, the step of generating the actual fine movement control data includes continuously outputting a drive voltage to the fine movement actuator based on the fine movement control data. The method has a step of limiting time. According to the sixteenth aspect, it is possible to control the head actuator with high accuracy irrespective of the fluctuation of the command drive voltage.

The seventeenth invention of the present application relates to a head positioning control program, and includes the fourteenth to sixteenth aspects.
It is programmed to execute the head positioning control method of the invention of the invention.

The eighteenth invention of the present application relates to a disk drive, and comprises the head positioning control program of the seventeenth invention.

(Specific Embodiment) Hereinafter, a specific embodiment of a head positioning device according to the present invention will be described with reference to the drawings.

(Embodiment 1) A head positioning apparatus according to Embodiment 1 of the present invention and a magnetic disk drive on which the head positioning apparatus is mounted will be described with reference to FIGS.

[Description of FIG. 1] FIG. 1 is a schematic configuration diagram of a magnetic disk device including a head positioning device according to the first embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a magnetic disk,
Reference numeral 2 denotes a composite magnetic head (hereinafter, referred to as a magnetic head) including a recording head and a reproducing head, 3 a head slider, 4 a head support mechanism, 5 a positioning mechanism, and 51 a voice coil motor (VCM). Coarse movement actuator 52, a fine movement actuator 52 composed of a microactuator (MA) including a piezoelectric element (piezo element, PZT element), 6 a positioning control section, 60 a head position detection section, 61 a relative position estimation detection , 62 is a fine movement control section, 63 is a coarse movement control section, 64 is a fine movement drive section, 65 is a coarse movement drive section, and 66 is a drive signal limiting means as a feature of the present invention.

Here, the magnetic head 2 comprises a reproducing head which is a GMR head to which the magnetoresistance effect is applied and a recording head which is an inductive magnetic head, and is mounted on the head slider 3.

The head support mechanism 4 supports the magnetic head 2 so as to face the magnetic disk 1 via supporting the head slider 3. Coarse motion actuator 51
Drives the head support mechanism 4 about the rotation axis, thereby moving the magnetic head 2 together with the fine movement actuator 52. The fine movement actuator 52 is disposed between the head support mechanism 4 and the head slider 3 and drives the head slider 3 to position the magnetic head 2 at an arbitrary position on the magnetic disk 1.

[Description of FIGS. 2, 3 and 4] FIG. 2 is a block diagram of the servo system of the magnetic disk drive shown in FIG.
FIG. 3 is a detailed block diagram showing the relationship between the fine movement control unit and the MA state estimator in the relative position estimation detection unit. FIG. 4 is a detailed diagram showing the relationship between the coarse movement control unit and the VCM state estimator in the relative position estimation detection unit. It is a block diagram.

Next, the operation sequence of the servo system including the head positioning device in the magnetic disk drive will be described.

The magnetic head 2 includes a coarse actuator 51
The magnetic disk 1 is moved on the magnetic disk 1 by a two-stage actuator composed of an actuator 52 and a fine movement actuator 52. The magnetic head 2 detects a servo pattern as position information written on the magnetic disk 1 and sends a detection signal to the head position detection unit 60. The head position detection unit 60 detects the track position and the inter-track position of the magnetic head 2 from the detection signal from the magnetic head 2, and outputs a position signal Phead representing the current position of the magnetic head 2 to the fine movement control unit 62 for relative position estimation detection. Output to the unit 61.

The control system of the fine movement actuator 52 includes a subtractor 62S, a fine movement control unit 62, and a fine movement actuator 5
And a MA state estimator 612 in the relative position estimation detector 61 which is a second state estimator.

From the head position detecting section 60 to the fine movement controlling section 62
Is supplied to the fine movement control unit 62.
Before being input to the subtractor 62S,
In 2S, the difference between the target position signal R and the head position signal Phead is obtained, and the position error signal Pe is given to the fine movement control unit 62.

The relative position estimation detecting section 61 is constructed as a mathematical model of a coarse actuator 51 composed of VCM and a fine actuator 52 composed of MA. That is, the relative position estimation detection unit 61 uses the VCM state estimator 6
13 and an MA state estimator 612.

The head position signal Phead from the head position detector 60 is also input to the MA state estimator 612 and the VCM state estimator 613 in the relative position estimator 61. The MA state estimator 612 estimates the moving speed of the magnetic head 2 and the amount of disturbance (force disturbance, position disturbance) applied to the magnetic head 2 based on the input head position signal Phead, and estimates the estimated head moving speed signal Ve2 and The disturbance amount signal Fe2 is generated and fed to the fine movement control unit 62 in a feedback manner. In addition, you may comprise so that feed-forward may be provided.

Two signals are input to MA state estimator 612. One is a control amount signal C2 from the fine movement control unit 62.
The other is a compensation signal Pee 'for reducing the estimation error of the MA state estimator 612.

The MA state estimator 612 calculates the estimated head position signal Xe2, the estimated head moving speed signal Ve2, and the estimated disturbance amount signal Fe2 by the fine movement actuator 52,
The estimated head moving speed signal Ve2 and the estimated disturbance amount signal Fe2 are output to the fine movement control unit 62, and the estimated head position signal Xe2 is output to the adder 61A.

The adder 61 A is provided with a fine movement actuator 52.
Head position signal Xe2 and coarse actuator 5
1 is added to the estimated head position signal Xe3, and a total estimated head position signal Xe by the fine movement actuator 52 and the coarse movement actuator 51 is calculated and output to the subtractor 61S.

In the subtracter 61S, an estimated position error signal Pee is generated by subtracting the total estimated head position signal Xe from the head position signal Phead from the head position detector 60. The compensation signal Pee 'is obtained by multiplying the estimated position error signal Pee by the MA state estimator gain 612g.

In fine movement control section 62, position error signal P
e, the estimated head moving speed signal Ve2 and the estimated disturbance amount signal Fe2
1, after multiplication by the velocity feedback gain 622 and the disturbance amount feedforward gain 623, the adder 62A
Is calculated to reduce the position error signal Pe.

The fine movement control section 62 calculates the control amount signal C2 based on the input position error signal Pe, estimated head moving speed signal Ve2 and estimated disturbance amount signal Fe2, and outputs the drive signal limiting means 66 and the MA state estimator 612. Output to

The fine movement control section 62 is configured to generate a control amount signal C2 by multiplying the input position error signal Pe by coefficients of a proportional differentiator (phase lead compensator) and an integrator. You may.

Control amount signal C 2 output from fine movement control section 62
Is not directly applied to the fine movement drive unit 64 but to the drive signal limiting means 66 before that. Fine actuator 5
The level of the control amount signal C2 is limited so as to drive the fine movement actuator 52 below the threshold value at which the characteristic change of the piezoelectric element (PZT element) forming the second element 2 occurs, and the limited control amount signal C2 'is generated to perform the fine movement Output to the unit 64. The fine movement drive unit 64 to which the limited control amount signal C2 'has been input receives the drive signal u2
Is generated and output to the fine movement actuator 52 to control and drive the fine movement actuator 52.

On the other hand, the control system of the coarse actuator 51 includes a subtractor 63S, a coarse motion controller 63, and a relative position estimation detector 61 which is a state estimator of the coarse actuator 51.
And a VCM state estimator 613.

The VCM state estimator 613 in the relative position estimation / detection unit 61 estimates the current position of the magnetic head 2 based on the head position signal Phead input from the head position detection unit 60, and coarsely estimates the estimated head position signal Xe3. Control unit 63
Output to

The coarse motion controller 6 from the VCM state estimator 613
3 is input to the subtractor 63S before being input to the coarse movement controller 63, and the subtractor 63S calculates the difference between the target position signal R and the estimated head position signal Xe3. , The estimated position error signal Pevcm is supplied to the coarse movement control unit 63.

The VCM state estimator 613 in the relative position estimating / detecting section 61 receives the moving speed of the magnetic head 2 and the disturbance (force disturbance, force disturbance) applied to the magnetic head 2 based on the head position signal Phead input from the head position detecting section 60. A position disturbance) amount is estimated, an estimated head moving speed signal Ve3 and an estimated disturbance amount signal Fe3 are generated, and are fed back to the coarse movement control unit 63. In addition, you may comprise so that feed-forward may be provided.

Two signals are input to VCM state estimator 613. One is the control amount signal C from the coarse movement control unit 63.
3, and the other is a compensation signal Pee ″ for reducing the estimation error of the VCM state estimator 613.

The VCM state estimator 613 calculates the estimated head position signal Xe3, estimated head moving speed signal Ve3, and estimated disturbance amount signal Fe3 from the coarse actuator 51, and calculates the estimated head moving speed signal Ve3 and the estimated disturbance amount signal Fe3.
Is output to the coarse movement control unit 63, and the estimated head position signal Xe3 is output to the adder 61A.

The operation of the adder 61A is as described above. That is, the estimated head position signal Xe2 from the fine actuator 52 and the estimated head position signal Xe3 from the coarse actuator 51 are added, and the fine actuator 5
2 and a coarse motion actuator 51 to calculate an overall estimated head position signal Xe and output it to a subtractor 61S.

The operation of the subtractor 61S is as described above. That is, an estimated position error signal Pee is generated by subtracting the total estimated head position signal Xe from the head position signal Phead from the head position detection unit 60. The compensation signal Pee ″ is obtained by multiplying the estimated position error signal Pee by the gain 613 g of the VCM state estimation unit.

In the fine / coarse movement controller 63, the estimated position error signal Pevcm, the estimated head moving speed signal Ve3 and the estimated disturbance amount signal Fe3 are respectively converted into a position error feedback gain 631, a speed feedback gain 632, and a disturbance amount feedforward gain 633. Is multiplied,
A control amount signal C3 that is added by the adder 63A to reduce the estimated position error signal Pevcm is calculated.

The coarse movement control unit 63 calculates a control amount signal C3 based on the input estimated position error signal Pevcm, the estimated head moving speed signal Ve3, and the estimated disturbance amount signal Fe3, and calculates the coarse movement drive unit 65 and the VCM state estimation. Output to the unit 613.

The coarse motion controller 63 multiplies the input estimated position error signal Pevcm by the respective coefficients of a proportional differentiator (phase lead compensator) and an integrator to generate a control amount signal C3. You may comprise.

Coarse drive section 65 to which control amount signal C3 has been input.
Generates a drive signal u3 and outputs it to the coarse actuator 51 to control and drive the coarse actuator 51.

The above is the operation sequence of each actuator control system.

[Description of FIG. 5] FIG. 5 is a configuration diagram of the fine movement actuator 52 composed of a micro actuator (MA).

Here, the fine movement actuator 52 is a piezoelectric element actuator. The two piezoelectric elements are driven by push-pull, and the amount of distortion of the piezoelectric elements is converted into the amount of displacement of the magnetic head by an enlargement mechanism.

The fine movement actuator (piezoelectric element actuator) 52 is composed of a pair of actuator pieces, each of which comprises an upper electrode 521, a piezoelectric element 522, and a lower electrode 523.

[Explanation of FIGS. 6 to 8] Next, corrosion of a piezoelectric element due to an electrochemical reaction will be described with reference to a case where the piezoelectric element is a PZT element.

The PZT element is one of the typical ceramic piezoelectric materials, and the chemical symbol is Pb (Zr, Ti) O ₃ ...... 1) It is represented by This PZT element is generally manufactured by sintering in a powder manufacturing and firing step. Further, the thin PZT element is formed by a sol-gel method, a CVD method (chemical vapor deposition), sputtering, or the like.

Examples of the PZT thin film include {Pb (Zr _0.53 Ti _0.47 )} _0.8 + (PbO) _{0.2 in the} composition formula (2). This is because the Zr: Ti ratio is 53:47,
The element contains PbO in an excess of 20%.

The lead oxide PbO causes an electrochemical reaction due to moisture entering the device during processing or moisture entering the device from the atmosphere during operation. The chemical reaction of lead oxide PbO is as follows.

The hydrogen ion exponent PH in the PZT element: PH
> Time of _{9 PbO + H 2 O → H} + + HPbO 2 - .................................... (3) PH <9 when ^{_{PbO + H 2 O → Pb 2+}} + 2OH - ........................ (4) Therefore, as shown in FIG. 6, lead oxide PbO has PH = 9.
It is most stable in the vicinity, and as it becomes acidic, lead ions P
b ²⁺ occurs.

That is, the lead oxide PbO in the PZT element reacts with the water entering the element to become lead ions.

FIG. 7 is a schematic diagram showing electrolysis (electrochemical reaction) occurring in the PZT element when a voltage is applied to the PZT element.

In FIG. 7, Pt electrodes are arranged on both sides of the PZT element, and a voltage is applied. In this case, the positive electrode side,
The electrochemical reaction including the precipitation of lead on the negative electrode side is represented by the following chemical formula.

[0110] the positive side _{^{4OH - → 2H 2 O + O}} 2 + 4e ................................................ (5) the negative Pb ²⁺ + 2e → Pb .............................. (6) From formula (5), water and oxygen are generated from hydroxide ions on the positive electrode side, and lead is precipitated on the negative electrode side from formula (6). . This reaction is summarized as follows.

2Pb ²⁺ + 4OH ⁻ → 2Pb + 2H ₂ O + O ₂ (7) That is, by applying a voltage to the PZT element to drive the fine movement actuator 52, lead is deposited on the electrode. Eventually, the positive and negative electrodes may be short-circuited by the lead.

Further, the lead Pb component in the PZT element is also converted into lead ions by electrolysis of water when a voltage is applied.

The electrolysis of water (electrochemical reaction) is as follows.

Positive electrode side 2H ₂ O → O ₂ + 4H ⁺ + 4e ……………………… (8) Negative electrode side 2H ⁺ + 2e → H ₂ …………… (9) Oxygen is generated on the positive electrode side, and hydrogen ions are attracted to the negative electrode side to generate hydrogen. Here, PZ near the negative electrode
Since lead in the T element has a higher ionization tendency than hydrogen, the following chemical reaction occurs.

Pb + 2H ⁺ → Pb ²⁺ + H ₂ (10) Pb ²⁺ + 2e → Pb ………………………………… (11) That is, lead is ionized by hydrogen ions generated by electrolysis of water, and the lead ions are further deposited on the negative electrode.

However, chemical reactions such as lead deposition and electrolysis have the characteristic that the reaction is rapidly accelerated beyond a certain voltage threshold.

FIG. 8 is a diagram showing the relationship between the applied voltage (potential difference) and the current flowing through the PZT element in the electrochemical reaction in which lead is deposited. As shown in FIG. 8, the reaction proceeds at the potential difference V1 or more, and the current flowing in the element increases in proportion to the electrolysis. The potential at which this reaction proceeds is called the theoretical decomposition voltage.

The theoretical decomposition voltage is 0.572 V in the reaction of the equations (5) and (6) and 1.229 V in the reaction of the equations (8) and (9).

Further, in order for the electrolysis to actually proceed and oxygen to be generated, it is necessary to add a voltage called an oxygen overvoltage to the theoretical voltage. That is, the electrochemical reaction proceeds by applying a voltage obtained by adding the oxygen overvoltage to the theoretical decomposition voltage.
This oxygen overvoltage is about 0.37 to 0.47V.

In other words, when a voltage is applied to the PZT element to control and drive the fine actuator, which is a microactuator, the voltage at which the reaction of equations (5) and (6) proceeds is 0.527 V + (0. 37 ~ 0.47V) ≒ 0.9 ~
1.0V. The voltage at which the reaction of Equations (8) and (9) proceeds is 1.229 V + (0.37 to 0.47 V) ≒ 1.6 to
It becomes 1.7V.

That is, when the voltage is 1 V or less, the electrochemical reaction for depositing lead hardly proceeds. In addition, if the influence of the atmosphere environment is about 1.7 V or less, the electrochemical reaction for accelerating the electrolysis of water and depositing lead hardly proceeds.

In the case of the fine movement actuator according to the present embodiment, since the polarity of the electrode constantly changes depending on the position of the head, lead Pb is deposited on the electrodes on both sides.
Since the PZT element has a small thickness, a short-circuit (short-circuit) occurs due to the precipitated lead Pb.
The ZT element may be destroyed.

However, as described above, the chemical reaction of lead Pb and water is qualitatively the same as the electrolysis of water, and there is a threshold voltage at which no decomposition reaction occurs (is not accelerated).

In other words, in practice, there is a threshold voltage that falls within the range of the amount of lead Pb deposited and the chemical reaction rate that guarantee the characteristics as a PZT element.

In this embodiment, the drive signal limiting means 66
Thus, the drive of the fine movement actuator 52 composed of the PZT element is controlled at or below the threshold (resolved voltage) or below.

Next, FIG. 9 shows a simulation result of one example of the present embodiment.

The simulation conditions are as follows.

Rotation speed: 12000 r / min Track density: 45000 track / inch Track pitch: 0.56 μm Sampling frequency: 20 kHz Servo band: 1.5 kHz Threshold value of drive signal limiting means: 1.2 V FIGS. d) is a simulation experiment result in the case where the servo loop of the microactuator has the drive signal limiting means 66 under the conditions of the present embodiment.

FIGS. 9A and 9B show simulation results at the time of a track jump. FIG. 9A shows a head position (position error), and FIG. 9B shows a fine movement actuator at that time. 52 shows the drive voltage of the reference numeral 52. FIG.
FIGS. 9C and 9D show simulation results at the time of track following. FIG. 9C shows the head position (position error), and FIG. 9D shows the driving voltage of the fine movement actuator 52 at that time. Is shown.

According to the simulation results, in the magnetic disk drive of this embodiment, when the position error of the head converges to zero in the case of a track jump, the displacement of the fine movement actuator 52 also converges to zero, and FIG. When the threshold voltage is set to 3.6 V, 3.6 V is applied to the fine movement actuator 52 for a duration of 0.4 msec. However, the drive voltage drops thereafter and becomes 1 V or less after 0.7 msec. .

In the case of track following, it is assumed that the position error is on-track at 10% of the track pitch. Although the drive voltage of the fine movement actuator 52 is limited to 0.5 V or less according to FIG. 9D, the positioning is stable.

As described above, the positioning accuracy can be stably maintained while the voltage applied to the fine movement actuator 52 is restricted by the drive signal restricting means 66.

(Embodiment 2) A head positioning apparatus according to Embodiment 2 of the present invention and a magnetic disk drive on which the head positioning apparatus is mounted will be described with reference to FIG.

[Description of FIG. 10] FIG. 10 is a schematic configuration diagram of a magnetic disk drive including a head positioning device according to the second embodiment of the present invention.

Since the mechanical structure of the magnetic disk device is the same as that of the first embodiment, the mechanical description is omitted here. The same components as those in the first embodiment are denoted by the same reference numerals as those in FIG.

In the second embodiment, the characteristic is measured by measuring the relationship between the voltage output from the fine movement driving section 64 to the fine movement actuator 52 and the current flowing through the piezoelectric element of the fine movement actuator 52 to check for the presence or absence of an excessive current. Inspection means 67;
FIG. 1 shows that a limiting voltage changing means 68 for changing a threshold voltage of a driving signal limiting means 66 for limiting a current flowing in a piezoelectric element based on an inspection result of a characteristic inspecting means 67 is added. This is different from the first embodiment.

Normally, the current flowing in the piezoelectric element is Io = 1.
× 10 ^-7 [A] or less. However, when moisture in the atmosphere such as under a high-temperature and high-humidity environment enters the element, or when moisture enters the element during the process, the order of the current flowing at a decomposition voltage or higher becomes 100 times or more.

The decomposition voltage, which is the threshold value, is theoretically constant depending on the substance, but actually has individual differences including variations in the oxygen overvoltage and variations in the composition of the piezoelectric element.

Therefore, it is necessary to adjust the threshold value of the drive voltage for each fine movement actuator.

The characteristic inspection means 67 in FIG. 10 detects a current flowing through the drive circuit as a voltage signal using a detection resistor. A current flowing through the piezoelectric element is derived from the detected voltage value, and when the current is 10 times or more as compared with the value of the current Io in the piezoelectric element, the threshold voltage in the drive signal limiting means 66 is changed to the limited voltage changing means. The voltage is lowered by 0.1 [V] by 68. By repeating this operation, a current 10 times or more the current Io in the piezoelectric element flows in the element, and it is possible to prevent the displacement characteristics of the fine movement actuator 52 from deteriorating due to acceleration of the electrochemical reaction.

As described above, by adding the characteristic inspection means 67 and the limit voltage changing means 68 to the drive signal limiting means 66, the positioning accuracy can be maintained stably even though the voltage applied to the fine movement actuator 52 is limited. Becomes possible.

(Embodiment 3) A head positioning apparatus and a magnetic disk drive according to Embodiment 3 of the present invention will be described.
This will be described with reference to FIG.

[Description of FIG. 11] FIG. 11 is a schematic configuration diagram of a magnetic disk drive including a head positioning device according to the third embodiment of the present invention.

Since the mechanical structure of the magnetic disk drive is the same as that of the first embodiment, the mechanical description is omitted here. The same components as those in the first embodiment are denoted by the same reference numerals as those in FIG. In the present embodiment, when the voltage output from fine movement drive section 64 to fine movement actuator 52 is equal to or less than the threshold value, the voltage is output as it is, and when the voltage is equal to or greater than the threshold value, the time is continuously output according to the drive voltage. Is different from the first embodiment described with reference to FIG.

As described above, the current Io in the piezoelectric element is Io
= 1 × 10 ⁻⁷ [A] or less, but if moisture in the atmosphere such as in a high-temperature and high-humidity environment enters the element, or if moisture enters the element during the process, the current flowing above the decomposition voltage Is 100 times or more.

Further, since the current value increases with the energizing time, it is necessary to limit the continuous driving output time when the driving voltage is higher than the threshold value.

The time function filter 69 shown in FIG. 11 has a drive voltage of 2.2 when the magnetic head 2 is positioned and controlled in the settling mode or the track jump mode.
It operates with a drive voltage of [V] or more.

The simulation result of FIG.
Degree is above threshold. Therefore, in the time function filter 69, when the driving voltage is 4 V or more, 200 μm
400 μsec or less when less than 3 V and less than 4 V,
When the voltage is 2 V or more and less than 3 V, by setting the current to 500 μsec or less, the current flowing in the piezoelectric element rapidly increases.
As a result, it is possible to prevent the piezoelectric element from being broken by electrolysis.

Thus, by repeating this operation, a current 10 times or more the current Io flows into the element, and the displacement characteristics of the fine movement actuator 52 are prevented from deteriorating due to acceleration of the electrochemical reaction.

As described above, by adding the time function filter 69 to the drive signal limiting means 66, the positioning accuracy can be stably maintained while the voltage applied to the fine movement actuator 52 is limited.

In this embodiment, the decomposition voltage, which is the threshold value, is 2.2 V. However, the same effect can be obtained if the threshold value is equal to or lower than the decomposition voltage.

In this embodiment, the time function filter 69 is divided into four stages according to the drive voltage value. However, by limiting the continuous output time, the current flowing in the piezoelectric element is increased. The same effect can be obtained in any number of steps as long as it can be prevented.

Further, in each of the embodiments, the push-pull type in which the micro-actuator of the two-stage actuator is arranged on the suspension is used, but the same effect can be obtained by arranging it on the arm or the slider.

Although the fine actuator 52 and the coarse actuator 51 have independent state estimators, the same effect can be obtained in the case of a multi-input multi-output estimator that models a two-stage actuator. can get.

Although the threshold value of the drive signal limiting means 66 is set to the decomposition voltage, the threshold value may be increased or decreased depending on the performance deterioration rate and the operation time required for reliability.

Further, although the threshold value is described only as a change with time or a change with the characteristics of an individual, a similar effect can be obtained by changing the threshold value every time the operation mode is different, such as a seek operation and a track following operation.

In the optical disk device, tracking is performed by a two-stage actuator including a stepping motor or DC motor for coarse movement positioning and an optical pickup for fine movement positioning. In the case of an optical disk device, in the case of a long stroke seek, coarse movement positioning is performed by a DC motor, and thereafter, an optical pick causes the head to follow a target track. At this time, the DC motor is controlled so that the DC component of the position error during the control of the optical pick becomes zero so that the optical pick does not exceed the operation range. Also,
Here, in track following and one track seek, the position error from the target position of the head is fed back to the MA to control the signal from the head displacement detection signal to zero, and in long seek, the speed is increased. For this purpose, the position error between the head and the target position is fed back to the MA, the amount of head movement by VCM is calculated from the signal from the head displacement detection signal, and the position error between the amount of movement and the target position of the head is fed back. Tracking to a target position exceeding the MA operation range is performed by inputting the target position also to the VCM for speeding up.

The present invention can be applied to such an optical disk device.

[0159]

According to the present invention, in a head positioning apparatus employing a two-stage actuator system for narrowing a track, a driving signal of a driving element for driving a piezoelectric element which is a component of a fine movement actuator is used. To solve the problem of characteristic deterioration due to corrosion of the piezoelectric element caused by high drive signal level because the level is limited to the threshold value or less at which the characteristic change of the piezoelectric element occurs. Thus, the function of high-speed and high-precision positioning of the head with respect to the target track can be maintained for a long period of time. Therefore, it effectively works for realizing a disk device having a high recording density (high track density).

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a magnetic disk drive including a head positioning device according to a first embodiment of the present invention;

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

FIG. 3 is a block diagram illustrating a relationship between a fine movement control unit in a positioning control unit and an MA state estimator in a relative position estimation detection unit according to the first embodiment of the present invention;

FIG. 4 is a block diagram illustrating a relationship between a coarse movement control unit in a positioning control unit and a VCM state estimator in a relative position estimation detection unit according to the first embodiment of the present invention;

FIG. 5 is a configuration diagram of a fine movement actuator according to the first embodiment of the present invention.

FIG. 6 is an explanatory diagram of an electrochemical reaction of lead oxide in a piezoelectric element according to the first embodiment of the present invention.

FIG. 7 is an explanatory diagram of an electrochemical reaction of the piezoelectric element according to the first embodiment of the present invention.

FIG. 8 is an explanatory diagram of a decomposition voltage according to the first embodiment of the present invention.

FIG. 9 is a diagram showing a simulation result according to the first embodiment of the present invention;

FIG. 10 is a schematic configuration diagram of a magnetic disk device including a head positioning device according to a second embodiment of the present invention.

FIG. 11 is a schematic configuration diagram of a magnetic disk drive including a head positioning device according to a third embodiment of the present invention.

FIG. 12 is a configuration diagram showing a piezo-type piggyback actuator in a first conventional example.

FIG. 13 is a block diagram of a servo operation evaluation system of an actuator according to a first conventional example.

FIG. 14 is a perspective view of a two-stage actuator in a second conventional example.

FIG. 15 is a block diagram showing a control method in a control system for a two-stage actuator in a second conventional example.

FIG. 16 is a schematic diagram of a magnetic disk drive in a third conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Magnetic disk 2 Magnetic head 3 Head slider 4 Head support mechanism 5 Positioning mechanism 6 Positioning control part 51 Coarse actuator (voice coil motor: VC
M) 52 Fine actuator (micro actuator:
MA) 60 Head position detection unit 61 Relative position estimation detection unit 62 Fine movement control unit 63 Coarse movement control unit 64 Fine movement drive unit 65 Coarse movement drive unit 66 Drive signal limiting unit 67 Characteristic inspection unit 68 Limit voltage changing unit 69 Time function filter 612 MA state estimator 613 VCM state estimator

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Toshio Inaji 1006 Kazuma Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. F-term (reference) 5D042 LA01 MA15 5D059 AA01 BA01 CA08 CA30 DA19 EA08 5D096 NN03 NN07 RR01 RR12

Claims (18)

[Claims] 1. A two-stage actuator system in which a head for accessing an information recording / reproducing disk is controlled in position by a coarse actuator and a fine actuator, and the fine actuator uses a piezoelectric element. A configured head positioning device,
A head positioning device, wherein a level of a drive signal of the fine movement actuator using the piezoelectric element is set to be equal to or less than a threshold value at which a characteristic change of the piezoelectric element occurs. 2. A coarse movement actuator and a fine movement actuator for controlling the position of a head for accessing an information recording / reproducing disk by a two-stage actuator system, and a positioning control for controlling the coarse movement actuator and the fine movement actuator. A fine positioning actuator configured using a piezoelectric element, wherein the positioning control unit includes at least a fine movement driving unit that drives the fine movement actuator using the piezoelectric element. And a drive signal limiting means for limiting a level of a drive signal given to the fine movement drive unit to a threshold value or less at which a characteristic change of the piezoelectric element occurs. 3. The driving signal restricting means according to claim 1, wherein a current-voltage characteristic of the piezoelectric element in the fine movement actuator changes, and a voltage command value at which a current value flowing through the piezoelectric element starts to rise exponentially with respect to an applied voltage. 3. The head positioning device according to claim 2, wherein the drive signal is limited and output with the threshold value. 4. A characteristic inspecting means for detecting a relationship between a command driving voltage for the fine movement actuator and a current flowing through the piezoelectric element, and a threshold value of the command driving voltage based on a detection result by the characteristic inspecting means. 4. The head positioning device according to claim 1, further comprising a limiting voltage changing unit that changes the head voltage. 5. A time function filter for limiting a time during which the drive voltage is continuously output according to the command drive voltage value when the command drive voltage for the fine movement actuator is equal to or higher than a threshold value. The head positioning device according to any one of claims 1 to 3, wherein: 6. The threshold value of the drive signal limiting means is set to a theoretical decomposition voltage of lead, a decomposition voltage represented by a sum of a theoretical decomposition voltage of lead and an oxygen overvoltage, or a decomposition voltage of water. The head positioning device according to any one of claims 2 to 5, wherein: 7. The piezoelectric element in the fine movement actuator is a thin film PZ made of lead, zirconia and titanium.
7. The head positioning device according to claim 1, wherein the head positioning device is a T element. 8. A fine-movement actuator driving device comprising: a fine-movement actuator using a piezoelectric element for finely positioning the head; and a fine-movement drive section for driving the fine-movement actuator, wherein the fine-movement actuator is provided to the fine-movement drive section. A fine-movement actuator driving device, further comprising a driving signal restricting means for restricting a level of the driving signal to a threshold value or less at which a characteristic change of the piezoelectric element occurs. 9. The drive signal restricting means according to claim 1, wherein said voltage command value is such that a current-voltage characteristic of the piezoelectric element in said fine movement actuator changes and a current value flowing through the element starts to rise exponentially with respect to an applied voltage. 9. The fine-movement actuator driving device according to claim 8, wherein the driving signal is limited and output as a threshold value. 10. A characteristic inspection means for detecting a relationship between a command driving voltage for the fine movement actuator and a current flowing through the piezoelectric element, and a threshold value of the command driving voltage based on a detection result by the characteristic inspection means. 10. The fine-movement actuator driving device according to claim 8, further comprising: a limit voltage changing unit configured to change the threshold voltage. 11. A time function filter for limiting a time during which a drive voltage is continuously output according to a command drive voltage value when a command drive voltage for the fine movement actuator is equal to or higher than a threshold value. The fine movement actuator driving device according to claim 8 or 9, wherein: 12. The driving signal limiting means according to claim 1, wherein the threshold value is a decomposition voltage of lead, a decomposition voltage represented by a sum of a theoretical decomposition voltage of lead and an oxygen overvoltage of lead, or a decomposition voltage of water. The fine movement actuator driving device according to any one of claims 8 to 11, wherein the setting is set. 13. A piezoelectric element in the fine movement actuator, wherein the piezoelectric element is a thin film P composed of lead, zirconia and titanium.
9. The device according to claim 8, wherein the device is a ZT device.
3. The fine-movement actuator driving device according to any one of 2. 14. A position error data, wherein a position error between head position data from servo information on a disk reproduced by the head and target position data for positioning the head at a target position is set as position error data; Generating fine movement control data for controlling the amount of displacement of the fine movement actuator of the head based on the data; outputting a signal based on the fine movement control data to the fine movement actuator as a fine movement drive signal; and coarse movement of the head. Inputting relative displacement data corresponding to the displacement amount of the actuator or the fine movement actuator; generating coarse movement control data for controlling the displacement amount of the coarse movement actuator based on the relative displacement data; A signal based on the control data is used as the coarse drive signal as the coarse drive signal. Outputting a signal based on the fine movement control data to the fine movement actuator, wherein the fine movement control data is limited by a threshold value at which a characteristic of the fine movement actuator changes. A step of generating the actual fine movement control data and replacing the actual fine movement control data with the fine movement control data and outputting the data. 15. The step of generating the actual fine movement control data includes a step of inspecting a change in a displacement characteristic or an electric resistance characteristic of the fine movement actuator, and a step of changing the threshold based on the change in the characteristic. 15. The head positioning control method according to claim 14, wherein: 16. The method according to claim 14, wherein the step of generating the actual fine movement control data includes a step of limiting a time for continuously outputting a drive voltage to the fine movement actuator based on the fine movement control data. Head positioning control method. 17. A head positioning control program which is programmed to execute the head positioning control method according to claim 14. Description: 18. A disk drive comprising the head positioning control program according to claim 17.