JP4594069B2 - Driving method of piezoelectric actuator - Google Patents

Description

  The present invention relates to a driving method of a piezoelectric actuator, and in particular, a piezoelectric device characterized by a driving method for suppressing deterioration due to migration of an electrode exposed on a side surface of the piezoelectric actuator using a soft material having a low coercive electric field. The present invention relates to an actuator driving method.

In recent years, miniaturization and refinement of information equipment have progressed, and the demand for actuators that require a minute movement distance has increased.
For example, in a focus correction and tilt angle control of an optical system, a head actuator of an ink jet printer device, a magnetic disk device, etc., a piezoelectric actuator capable of moving and controlling a minute distance is required.

  In particular, in a magnetic disk device, since the control distance required for the piezoelectric actuator is large, the electric field applied to the actuator is considerably large, and the operating environment is severe, and operation in a high temperature and high humidity environment must be guaranteed. Therefore, high reliability is required.

Among the above required characteristics, various piezoelectric actuators are known as satisfying the displacement characteristics (see, for example, Patent Documents 1 to 3). In Patent Document 1, peeling of electrodes is prevented. being mixed ceramics constituting the piezoelectric actuator material in order to increase the reliability has been proposed.

In such a piezoelectric actuator having excellent displacement characteristics, a material having a high piezoelectric constant such as Pb (Ni, Nb) O ₃ -PbTiO ₃ -PbZrO ₃ (PNN-PT-PZ) is used to increase the displacement stroke of the head. Since it is used, a conventional multilayer piezoelectric actuator will now be described with reference to FIG.

See FIG.
FIG. 12 is a schematic perspective view of a conventional multilayer piezoelectric actuator, in which an internal electrode layer 42 such as Au is screen-printed on a green sheet to be a piezoelectric layer 41 such as PNN-PT-PZ, and then on that. A new green sheet is overlaid and the internal electrode layer 42 is screen-printed again, and this process is repeated as many times as necessary to form a piezoelectric block.

  Next, the piezoelectric block is fired in the atmosphere at, for example, 1050 ° C., the piezoelectric block is cut into a predetermined size with a cut-and-sew, Au or the like is evaporated on the side surface, and the exposed internal electrode layers 42 are alternately connected. A surface electrode 43 is provided.

  When driving such a piezoelectric actuator, the piezoelectric material that constitutes a piezoelectric actuator with excellent displacement characteristics has a low coercive electric field, so a voltage is always applied in either positive or negative direction so that polarization does not reverse during driving. Basically, the polarity of the voltage is not reversed.

In order to increase the stroke, an AC voltage may be applied for driving. In this case, the maximum value of the applied voltage is equal to or greater than the positive coercive electric field by adjusting the DC bias voltage. The value is greater than or equal to the negative coercive field, or the maximum value of the applied voltage is less than or equal to the positive coercive field and the minimum value is less than or equal to the negative coercive field. Driving.
JP 2004-308234 A JP 2003-284362 A JP 2003-061370 A

  There is a problem that the deterioration phenomenon that the insulation resistance decreases when the piezoelectric actuator continues to operate under the high voltage and high humidity environment with the voltage application method as described above is extremely fast. It is considered migration due to the exposed electrodes.

  That is, if a direct current voltage is continuously applied to the piezoelectric actuator, migration is particularly likely in an environment of high humidity in which an electrode material is diffused by being attracted by an electric field from one electrode toward the other electrode.

See FIG.
In order to increase the resistance to such migration, it is possible to adopt a configuration in which the electrode is not exposed on the side surface as shown in FIG. 13, but in such a configuration, the wall 44 restricts the displacement amount. As a result, the amount of displacement inherent in the piezoelectric actuator is reduced, and the required displacement characteristics are often not satisfied.
From the above situation, the high performance piezoelectric actuator including the reliability has not been developed yet.

  Accordingly, an object of the present invention is to improve the reliability by suppressing migration caused by the electrodes exposed on the side surfaces.

FIG. 1 is a block diagram showing the principle of the present invention. Means for solving the problems in the present invention will be described with reference to FIG. 1. The upper diagram is a drive circuit diagram of a piezoelectric actuator. Is a drive voltage waveform diagram.
To solve the Figure 1 reference above problems, the present invention is small after applying Kutomo least two periods of the driving waveform, the piezoelectric actuator and applying the driving waveform obtained by inverting the voltage least two periods A driving method, wherein the maximum value of the applied voltage is greater than or equal to a positive coercive field and the minimum value is greater than or equal to a negative coercive field, or the maximum value of the applied voltage is less than or equal to a positive coercive field and the minimum value is The maximum value of the absolute value of the drive waveform that is equal to or less than a negative coercive electric field and is not inverted is equal to the maximum value of the absolute value of the inverted drive waveform .

In this way, after a predetermined time has elapsed, the switch means 2 is used to reverse the polarity of the applied voltage, whereby the diffusion of the electrode exposed on the side surface of the piezoelectric actuator 1 can be suppressed.
In this case, it is desirable to invert at least at an initial period of one hour or longer, but the shortest period is a two-cycle driving waveform.

In this case, the applied voltage may be a peak-to-zero voltage waveform, or the maximum value of the applied voltage is positive using a DC bias power supply 3 and an AC drive power supply 4 as power supplies in order to increase the stroke. A voltage waveform that is greater than or equal to the coercive field and has a minimum value that is greater than or equal to a negative coercive field or that has a maximum applied voltage that is less than or equal to a positive coercive field and that has a minimum value that is less than or equal to a negative coercive field . A voltage waveform in which the maximum absolute value of the drive waveform is equal to the maximum absolute value of the inverted drive waveform is used.

In this case, the inversion period of the applied voltage may be equal, or may be gradually shortened. Since accumulated diffusion atoms increase due to accumulation of operating time, the inversion period is gradually shortened. Migration can be effectively suppressed.
In addition, even if frequent inversion is performed, a decrease in insulation resistance due to migration can be effectively suppressed. However, when the number of inversions increases dramatically, deterioration due to polarization inversion is accelerated.

Further, it is desirable that the voltage change rate when the applied voltage is reversed is 0, which enables smooth inversion driving.
In such a voltage inversion, the driving is slightly unstable in the first pulse immediately after the inversion, but the instability becomes large when the voltage change rate at the inversion is not zero.

  It is desirable to reverse the applied voltage using a timer when the applied voltage is reversed. That is, by counting the operation time by the timer, the applied voltage can be accurately inverted with reference to only the time when the applied voltage is on.

  The above driving method is particularly effective in the multilayer piezoelectric actuator 1 in which the electrodes are exposed on the side surfaces.

The piezoelectric actuator 1 has a low coercive voltage, for example, PbTiO ₃ , Pb (Zr, Ti) O ₃ , PNN, Pb (Ni, Nb) O ₃ —PbTiO ₃ —PbZrO ₃ , Pb of 100 kV / cm or less. This is effective in the case of a piezoelectric body mainly composed of (Mg, Nb) O ₃ or Pb (Mg, Nb) O ₃ —Pb (Zr, Ti) O ₃ .

  The electrode exposed on the side surface of the piezoelectric actuator 1 is preferably a conductive material that can be fired simultaneously with a green sheet such as Ag, Pd, Ag-Pd, Pt, Au, Ir, or Ir oxide.

  Further, in order to improve the adhesion of the electrode to the piezoelectric body, any one of Ag, Pd, Ag-Pd, Pt, Au, Ir, or Ir oxide and ceramics, in particular, the same ceramic as the composition of the piezoelectric actuator 1 is used. It is desirable to use a mixed material consisting of

  Further, by providing a movement control mechanism that controls the movement of the magnetic head by the above-described driving method of the piezoelectric actuator 1, a highly reliable magnetic disk device can be configured.

  The magnetic disk device preferably includes at least one of an operation time storage mechanism for storing operation time on the disk and a timer for determining timing of voltage reversal.

  According to the present invention, a positive or negative voltage is applied, the displacement amount is controlled without reversing the positive and negative voltages, and the migration of the electrode material is suppressed by reversing the applied voltage after a certain time has elapsed. Therefore, a stable operation can be obtained in a high temperature and high humidity environment without reducing the displacement amount of the piezoelectric actuator.

In the present invention, PbTiO ₃ , Pb (Zr, Ti) O ₃ , PNN, Pb (Ni, Nb) O ₃ —PbTiO ₃ —PbZrO ₃ , Pb (Mg, Nb) O ₃ having a low coercive voltage of 100 kV / cm or less. Alternatively, the displacement amount can be controlled by applying a voltage positively or negatively to a laminated piezoelectric actuator made of a piezoelectric material mainly composed of any one of Pb (Mg, Nb) O ₃ —Pb (Zr, Ti) O _3. After a certain period of time, in the shortest case, after applying a drive waveform of 2 cycles, normally, after 1 hour, the polarity of the voltage is reversed to control the amount of displacement, and this voltage reversal is repeated periodically. It is.

Here, with reference to FIG. 2 and FIG. 3, the drive method of the piezoelectric actuator of Example 1 of this invention is demonstrated, First, it demonstrates from the manufacturing method of a piezoelectric actuator.
First, PbO, NiO, Nb ₂ O ₅ , TiO ₂ , and ZrO ₂ raw materials are weighed in predetermined amounts and mixed using a pure water (H ₂ O) or alcohol as a solvent and wet pulverizing with a ball mill. .
Each raw material in this case is in a powder form. For example, when each raw material is mol%, PbO: NiO: Nb ₂ O ₅ : TiO ₂ : ZrO ₂ = 50: 8.3: 16.3: 17 : Weigh to 8

Next, the wet-mixed slurry is taken out of the mill, the balls are separated and removed, and then the solvent water is evaporated in a dryer to dry the powder.
Next, the dried powder is put into an electric furnace and, for example, preliminarily fired at 850 ° C. for 3 hours, from a compound of Pb (Ni, Nb) O ₃ —PbTiO ₃ —PbZrO ₃ (PNN-PT-PZ) having a perovskite structure. A calcined powder is obtained.

Next, a solvent, a binder, a plasticizer, and a dispersant are added to the obtained powder, and wet-kneaded again using a ball mill.
In this case, ethyl alcohol is used as the solvent, polyvinyl butyral is used as the binder, dibutyl phthalate is used as the plasticizer, and Celna 501 (trade name, manufactured by Chukyo Yushi Co., Ltd.) is used as the dispersant, and the mixing ratio is powder. For 100 parts by weight
Ethyl alcohol 35.0 parts by weight Polyvinyl butyral 5.0 parts by weight Dibutyl phthalate 1.9 parts by weight Serna 501 (trade name, manufactured by Chukyo Yushi Co., Ltd.) 1.8 parts by weight.

Next, the kneaded slurry is taken out from the mill, and after the balls are separated and removed, the balls are placed in a defoamer to evaporate ethyl alcohol to adjust the viscosity of the slurry.
Next, the slurry with adjusted viscosity is formed on a mylar sheet by a doctor blade method so that the thickness becomes, for example, 0.1 mm after firing, and dried to obtain a green sheet, followed by drying. The green sheet is cut and punched to a predetermined size.

Next, the green sheet is heat treated at, for example, 500 ° C. for 4 hours to degrease the organic component such as a binder or a plasticizer in the green sheet, and then the degreased green sheet is again washed in the electric furnace at 963 A ceramic having a composition of aPbNi _1/3 Nb _2/3 O ₃ —bPbTiO ₃ —cPbZrO ₃ can be obtained by firing at 900 ° C. or less, for example, 900 ° C. for 6 hours.
In this case, the composition ratios a, b, and c are a≈0.5, b≈0.34, and c≈0.16 in the above-described weighing ratio.

  Next, after processing the obtained fired body to a size of 1 mm × 1 mm, Au is vapor-deposited on both surfaces of the fired body to form electrodes, thereby obtaining a single-layer piezoelectric actuator.

See Figure 2
The sample thus prepared was placed in a high-temperature and high-humidity environment of 80 ° C. and 80%, and an accelerated deterioration test was performed by reversing the voltage of about 225 V every 50 hours as shown in FIG.
As a result, the insulation resistance, which was 502 GΩ before the test, decreased only to 2.85 GΩ after 200 hours.

See Figure 3
On the other hand, another sample prepared at the same time was placed in a high temperature and high humidity environment of 80 ° C. and 80%, and an accelerated deterioration test was conducted by applying a voltage of about 225 V continuously as shown in FIG. The insulation resistance, which was 492 GΩ before, decreased to 0.911 GΩ after 200 hours, and the insulation resistance decreased more than three times compared to when the voltage was inverted.

From this result, it has been found that the effect of suppressing a decrease in the insulation resistance of the piezoelectric actuator by changing the voltage application direction after a certain time has elapsed.
In this case, the decrease in insulation resistance is thought to be due to the accumulation of diffusion electrode material due to migration.Therefore, if the cycle for changing the voltage application direction is made shorter, the accumulation of diffusion electrode material will decrease, so the insulation resistance will decrease further. It can be effectively suppressed.

  By reversing the voltage application direction, the polarization direction of the piezoelectric actuator is also reversed. Therefore, there is a concern about deterioration of the piezoelectric effect due to polarization reversal. Even if the direction of application of the electrode is reversed, the number of polarization reversals is only 100,000 times, and it is considered that the electrodes can be sufficiently put into practical use.

Next, with reference to FIG. 4 and FIG. 5, the driving method of the multilayer piezoelectric actuator according to the second embodiment of the present invention will be described. First, the manufacturing method of the multilayer piezoelectric actuator will be described.
First, a green sheet is prepared by the same method as in the first embodiment. In this case, the thickness after firing is set to 38 μm.

Next, after forming an internal electrode layer on the green sheet by, for example, printing a platinum paste by a screen printing method, four green sheets on which the internal electrode layer is screen-printed are stacked, and nothing is printed on the green sheet. After the sheets are stacked one on top of the other, using a press, for example, uniaxial pressure molding is performed while applying heat at 100 ° C.
The green sheet on which nothing is printed is provided because good firing is not performed when the entire thickness is small, and does not directly affect the element characteristics.

  Thereafter, a fired body was formed by firing after heat degreasing as in Example 1 above, and the fired body thus obtained was cut into a predetermined size and cut out to have four layers of internal electrodes. A laminated piezoelectric actuator having a three-layer structure is obtained.

See Figure 4
FIG. 4 is a drive circuit diagram used in Embodiment 2 of the present invention, in which the polarity of the drive voltage applied to the DC bias power supply 13, the AC drive power supply 14, and the piezoelectric actuator 11 that determines the base of the applied voltage is reversed. Switch means 12 is provided.

See Figure 5
FIG. 5 is a drive voltage waveform diagram according to the second embodiment of the present invention. The DC bias power supply 13 sets the minimum value of the positive drive voltage waveform and the maximum value of the negative drive voltage waveform to 0V. The laminated piezoelectric actuator is placed in a high-temperature and high-humidity environment of 80 ° C. and 80%, and a sine wave voltage of about 57 V is inverted at a frequency of 1 kHz every 50 hours by the AC drive power supply 14.

By the way, when an accelerated deterioration test was performed without voltage reversal under the same conditions, the insulation resistance, which was 411 GΩ before the test, decreased to 4.44 GΩ after 78 hours.
From this result, there was no significant difference in the degree of deterioration between the DC voltage and the sine wave voltage in the single-layer piezoelectric actuator and the multilayer piezoelectric actuator of Example 1.
Therefore, even in a practical multilayer piezoelectric actuator, it is possible to suppress deterioration by reversing the applied voltage after a lapse of a certain time.

  Next, with reference to FIG. 6, the driving method of the piezoelectric actuator according to the third embodiment of the present invention will be described. However, the other configuration is exactly the same as the second embodiment except that the voltage inversion timing is different. Only the drive voltage waveform will be described.

See FIG.
FIG. 6 is an explanatory diagram of a driving voltage waveform in the driving method of the piezoelectric actuator according to the third embodiment of the present invention. Here, a sine wave voltage of about 57 V is applied at a frequency of 1 kHz, but the voltage inversion is sequentially shortened. Is.

  The effect of reverse diffusion of the diffusion electrode component due to voltage reversal diminishes as the storage operation time increases, so by sequentially reducing the voltage reversal, the insulation resistance can be effectively reduced as the storage operation time increases. Can be suppressed.

Next, a magnetic disk device according to a fourth embodiment of the present invention will be described with reference to FIGS.
See FIG.
FIG. 7 is a perspective view showing the main part of the main part of the magnetic disk apparatus according to the fourth embodiment of the present invention, which employs the above-described piezoelectric actuator driving method. The magnetic disk apparatus 20 is a magnetic disk written on the magnetic disk 21. A slider 22 having a magnetic sensor for reading information and writing magnetic information to the magnetic disk 31, a fine movement arm 23 having the slider 22 attached to the tip via a suspension (not shown), and a pair of driving the fine movement arm 23 The piezoelectric actuator 24 and the fine movement arm 23 are swingably supported by a shaft 26, and are configured by a base arm 25 rotatably supported by a chassis (not shown) of the magnetic disk device 20 and an electromagnetic actuator 27 for driving the base arm 25. Is done.
In this case, the upper and lower surfaces of the piezoelectric actuator 24 are bonded and fixed to the rear end portion of the fine movement arm 23 and the front end portion of the base arm 25.

See FIG.
FIG. 8 is a block diagram illustrating functions of the magnetic disk device according to the fourth embodiment of the present invention. The magnetic disk device 20 includes a drive circuit 30 that drives the piezoelectric actuator 24 while inverting the voltage, and the operation of the magnetic disk device 20. A timer 28 for measuring and integrating time is provided, and a control circuit 29 for directly writing the measured and accumulated operating time in the operating time recording area of the magnetic disk 21 is provided.

See FIG.
FIG. 9 is a circuit configuration diagram of the drive circuit, and includes a pair of switch means 31, a DC bias power supply 32, and an AC drive power supply 33 that are linked.

See FIG.
FIG. 10 is an example of a time chart of the driving voltage, and here shows a case where the driving voltage is inverted every 50 hours.
As shown in the figure, by adjusting the DC bias voltage, when the average voltage value is positive, the maximum value V _{+ max} of the applied voltage is not less than the positive coercive electric field + E _c and the minimum value V _{+ min} is When the negative coercive electric field −E _c is set and the voltage is inverted and the average voltage value is negative, the maximum value V _−max of the applied voltage is equal to or less than the positive coercive electric field + E _c and the minimum value V _−. Set _{min to} be equal to or less than the negative coercive electric field −E _c .

By applying such a drive waveform voltage, the stroke can be increased, and when the average voltage value is positive, even if the applied voltage becomes negative, the negative coercive electric field −E _c is not exceeded. When the average voltage value is negative, even if the applied voltage becomes positive, it does not exceed the positive coercive electric field + E _c , so that deterioration due to polarization inversion can be suppressed.

See FIG.
FIG. 11 is a flowchart of the piezoelectric actuator control in a general use state. When the power is turned on, the accumulated operation time directly written on the magnetic disk in the process described later is read to determine the elapsed time.

  If the elapsed time does not exceed the preset value, continue operation, drive the piezoelectric actuator to perform writing / reading, measure the operation time during that time with a timer, add up, write / read When continuing, the elapsed time is sequentially determined.

  If the accumulated operating time exceeds the set value as a result of the determination, the switch means of the drive circuit is operated to reverse the voltage application direction to drive the piezoelectric actuator to perform writing / reading, and to increase the accumulated operating time. After clearing, the elapsed time is sequentially determined.

  To end the use of the magnetic disk, turn on the end button, and automatically write the operating time measured and accumulated by the timer with the ON input directly into the operating time save area of the magnetic disk according to the command of the control circuit. When the save ends, the power is automatically turned off.

  As described above, in Example 4 of the present invention, since the reversal time of the applied voltage is controlled based on the actual operation time, the applied voltage is accurately reflected in the amount of accumulation of the diffusion electrode component accompanying migration. Can be reversed, improving reliability.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the conditions and configurations described in the embodiments, and various modifications are possible. For example, the voltages described in the embodiments The frequency and the frequency are merely examples, and may be changed as appropriate according to the application.

In each of the above embodiments, the piezoelectric material constituting the piezoelectric actuator is PNN-PT-PZ, but is not limited to PNN-PT-PZ, and a soft material having a coercive electric field of 100 kV / cm ² or less. If it is good.

Such soft materials include PbTiO ₃ , Pb (Zr, Ti) O ₃ , Pb (Ni, Nb) O ₃ , Pb (Mg, Nb) O ₃ , or Pb (Mg, Nb) O ₃ —Pb. (Zr, Ti) O _{3 and the} like.

  In each of the above embodiments, the electrode is made of Au, but is not limited to Au, and Ag, Pd, Ag-Pd, Pt, Ir, Ir oxide, or the like may be used. In any case, any conductive material that can be fired together with the green sheet may be used.

  Furthermore, in order to improve the adhesion to the electrode to the piezoelectric body, it is desirable to mix ceramics into an electrode material made of Ag, Pd, Ag-Pd, Pt, Au, Ir, or Ir oxide, When the same ceramic as the composition constituting the piezoelectric actuator is used, there is no need to consider the firing temperature or deterioration of characteristics due to diffusion of undesired components.

  In addition, the inversion period shown in each of the above embodiments is merely an example, and it is desirable to invert at a period of 1 hour or more in consideration of a guarantee of 100,000 hours.

  In the third embodiment, the inversion cycle is continuously shortened. However, the inversion cycle may be performed stepwise. For example, the voltage inversion is performed every 50 hours during the initial operation, and the integrated operation time is obtained. However, it may be performed every 40 hours after 2000 hours, and every 30 hours after 4000 hours have elapsed.

The detailed features of the present invention will be described again with reference to FIG. 1 again.
1 again (Appendix 1) A drive method for a piezoelectric actuator , wherein a drive waveform having an inverted voltage is applied for at least two cycles after a drive waveform of at least two cycles has been applied. The maximum value of the voltage is not less than the positive coercive field and the minimum value is not less than the negative coercive field, or the maximum value of the applied voltage is not more than the positive coercive field and the minimum value is not more than the negative coercive field, A method for driving a piezoelectric actuator, wherein the maximum absolute value of the drive waveform in the non-inverted state is equal to the maximum absolute value of the inverted drive waveform.
(Supplementary Note 2) The inversion of the applied voltage is performed at least once, and the drive method for a piezoelectric actuator according to note 1, wherein the inversion period is equidistant.
(Supplementary note 3 ) The piezoelectric actuator driving method according to supplementary note 1, wherein the applied voltage is inverted at least once and the inversion cycle is gradually shortened.
(Supplementary Note 4 ) The method for driving a piezoelectric actuator according to any one of Supplementary notes 1 to 3 , wherein a rate of voltage change when the applied voltage is inverted is zero.
(Supplementary note 5 ) The method for driving a piezoelectric actuator according to any one of supplementary notes 1 to 4 , wherein when the applied voltage is reversed, the applied voltage is reversed using a timer.
(Supplementary note 6 ) The piezoelectric actuator driving method according to any one of supplementary notes 1 to 5 , wherein the piezoelectric actuator 1 is a stacked piezoelectric actuator 1 with electrodes exposed on the side surfaces.
(Supplementary note 7 ) The piezoelectric actuator driving method according to any one of supplementary notes 1 to 6 , wherein the piezoelectric actuator 1 is a soft material having a coercive voltage of 100 kV / cm or less.
(Supplementary Note 8) The piezoelectric actuator _{1 is, PbTiO 3, Pb (Zr,} Ti) O 3, Pb (Ni, Nb) O 3, Pb (Ni, Nb) O 3 -PbTiO 3 -PbZrO 3, Pb (Mg, The piezoelectric actuator according to appendix 7 , wherein the piezoelectric actuator is composed of a piezoelectric body mainly composed of Nb) O ₃ or Pb (Mg, Nb) O ₃ —Pb (Zr, Ti) O ₃ . Driving method.
(Additional remark 9 ) The electrode exposed to the side surface of the said piezoelectric actuator 1 is either Ag, Pd, Ag-Pd, Pt, Au, Ir, or an Ir oxide, Additional remark 6 thru | or Additional remark 8 characterized by the above-mentioned. The method for driving a piezoelectric actuator according to any one of the above.
Appendix (Supplementary Note 10) The electrode electrode exposed on the side surfaces of the piezoelectric actuator 1, the Ag, Pd, Ag-Pd, Pt, Au, Ir, or characterized by comprising a ceramics either Ir oxide The driving method of the piezoelectric actuator according to any one of 6 to appendix 8 .
(Supplementary note 11 ) The method for driving a piezoelectric actuator according to supplementary note 10, wherein the composition of the ceramic contained in the electrode is the same as that of the piezoelectric actuator 1.
(Supplementary Note 12) A magnetic disk apparatus characterized by comprising a movement control mechanism controlling the movement of the magnetic head by the drive method for a piezoelectric actuator according to any one of Supplementary Notes 1 to Appendix 11.
(Additional remark 13 ) The magnetic disk apparatus of Additional remark 12 provided with the operation time memory | storage mechanism which preserve | saves operation time on a disk.
(Supplementary note 14 ) The magnetic disk device according to supplementary note 12 or 13 , wherein a timer for determining the timing of the voltage reversal is provided.

  As an application example of the present invention, driving of a piezoelectric actuator of a magnetic disk device is typical, but the present invention is not limited to a magnetic disk device, and a driving method of a piezoelectric actuator used for focus correction and tilt angle control of an optical system. Alternatively, the present invention is also applied to a method for driving a piezoelectric actuator of an ink jet printer apparatus.

It is explanatory drawing of the fundamental structure of this invention. It is a drive voltage waveform figure in Example 1 of this invention. It is a drive voltage waveform figure in a comparative example. It is a drive circuit diagram used for Example 2 of the present invention. It is a drive voltage waveform figure in Example 2 of this invention. It is a drive voltage waveform figure in Example 3 of this invention. It is a principal part perspective view which shows the main-body part of the magnetic disc apparatus of Example 4 of this invention. It is a block diagram which shows the function of the magnetic disk apparatus of Example 4 of this invention. It is a circuit block diagram of the drive circuit in Example 4 of this invention. It is a time chart of the drive voltage in Example 4 of this invention. It is a flowchart of the piezoelectric actuator control in the general use condition in Example 4 of this invention. It is a schematic perspective view of the conventional multilayer piezoelectric actuator. It is a schematic perspective view of the multilayer piezoelectric actuator provided with the conventional wall.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric actuator 2 Switch means 3 DC bias power supply 4 AC drive power supply 11 Piezoelectric actuator 12 Switch means 13 DC bias power supply 14 AC drive power supply 20 Magnetic disk apparatus 21 Magnetic disk 22 Slider 23 Fine movement arm 24 Piezoelectric actuator 25 Base arm 26 Shaft 27 Electromagnetic Actuator 28 Timer 29 Control circuit 30 Drive circuit 31 Switch means 32 DC bias power supply 33 AC drive power supply 41 Piezoelectric layer 42 Internal electrode layer 43 Surface electrode 44 Wall

Claims (4)

A method for driving a piezoelectric actuator, comprising: applying a drive waveform having a voltage inverted after applying a drive waveform of at least two cycles ;
The maximum value of the applied voltage is not less than the positive coercive field and the minimum value is not less than the negative coercive field, or the maximum value of the applied voltage is not more than the positive coercive field and the minimum value is not more than the negative coercive field. Yes,
A method for driving a piezoelectric actuator, wherein the maximum absolute value of the drive waveform in the non-inverted state is equal to the maximum absolute value of the inverted drive waveform. 2. The method of controlling a piezoelectric actuator according to claim 1, wherein the applied voltage is inverted at least once and the inversion period is an equal interval. The method for controlling a piezoelectric actuator according to claim 1, wherein the applied voltage is inverted at least once and the inversion cycle is gradually shortened. 4. A magnetic disk apparatus comprising a movement control mechanism for performing movement control of a magnetic head by the method for driving a piezoelectric actuator according to claim 1 .

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