JPS6257265A - Driving piezoelectric element - Google Patents

Abstract

PURPOSE:To increase the displacement amount and the generated power by alternately applying electric fields of specific different waveforms in the same direction and reverse direction of the polarization, and to enable the polarization deteriorated due to application of voltage in the reverse direction of the polarization to be fully restored by applying voltage in the polarization direction. CONSTITUTION:When the withstand electric field strength of a piezoelectric element is Ec, the piezoelectric element is driven by applying, in the reverse polarization direction for time T, an electric field E the maximum value of which is in the range of (1/4)Ec and (9/10)Ec, and then applying an electric field which is equal to or greater than [E+(n/10)Ec] (n=0-10) for 0.5XTX10<-n+1> or longer in the polarization direction. For instance, in order to seek the voltage to be applied in the polarization direction in the case where voltage Vd is applied in the reverse polarization direction for Time To, and then the polarity is switched and voltage is applied in the polarization direction, if n is sought by using To=0.5ToX10<-n+1>, the result is about 0.7. If To= ToX10<-n+1> is used, n is 1. Therefore, it is only needed to apply in the polariza tion direction voltage of [Vd+0.7X(1/10)Vc]-[Vd+(1/10)Vc] or greater.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is capable of producing a piezoelectric element by applying electrolysis of different waveforms alternately in the same direction and in the opposite direction to the polarization to a piezoelectric element in which a ferroelectric material is polarized. This relates to a driving method that distorts the .

[Conventional technology]

In recent years, with the demand for smaller and lighter terminal equipment, piezoelectric elements have attracted attention as small and efficient actuators that can replace electromagnetic drive components. A piezoelectric element is an element in which a high electric field is applied to a ferroelectric material such as lead zirconate titanate to form polarization.

If an electric field is applied to this element in the same direction as the polarization, it will be distorted in proportion to the electric field, and if an electric field is applied in the opposite direction to the polarization, it will be distorted in the opposite direction, so the force generated at this time can be extracted and used as an actuator.

FIG. 2 shows an example of this application, and is a bimorph element in which two piezoelectric elements made by polarizing thinly cut ferroelectric materials are pasted together so that the polarization directions are the same. In the same figure, 1
is a bimorph element, Hl.

Hz is a piezoelectric element with a thickness h=0.1511, 200 is an AC power supply with a maximum voltage ±Vp, and 100 is a bimorph element support portion.

Briefly explain the operation. When point A is positive, Hl is distorted in the shrinking direction because a voltage is applied in the polarization direction, and Hz is distorted in the elongation direction because the same voltage is applied in the opposite direction to the polarization. As a result,
The tip of the bimorph element 1 is displaced upward. When the polarity changes and point A becomes negative, Hl is extended by applying a voltage in the opposite polarization direction, and Hz is contracted by applying the same voltage in the polarization direction, so that the tip of the bimorph element 1 is displaced downward. The voltages applied to Hl and Hz are shown in Figures 3 (a) and (b), respectively. When an alternating current voltage is applied in this way, the tip vibrates.

The results of measuring the tip amplitude δ while increasing the power supply voltage by 1 Vpl are shown in FIG. 4 as a solid line ■. In the figure, the horizontal axis represents the power supply voltage M7pl, and the vertical axis represents the tip amplitude δ. According to the solid line ■, δ increases almost in proportion to Vp, but rapidly decreases near 90V. FIG. 5 shows the results of measuring the elongation strain Δl when a voltage was applied to a piezoelectric element (thickness 1 nm) in the reverse polarization direction while rapidly increasing the power supply voltage. When a high electric field is applied in the direction of opposite polarization, the amount of strain decreases rapidly as shown by the solid line (■) in FIG. 4, but this is because the polarization formed during manufacturing disappears or is reversed. The electric field Ec at which the amount of strain rapidly decreases will be referred to as coercive electric field strength. For the material shown in Figure 5, EC-600V/
It is tm. The piezoelectric element H1°Hz in Fig. 2 is h = 0
．． 15n, so the coercive voltage Vc corresponding to the coercive electric field strength Ec is 9
It becomes 0V. Therefore, when the characteristics shown in FIG. 4 are measured over a short period of time, the voltage at which the tip amplitude δ decreases becomes equal to the coercive voltage Vc.

Even when vibrating at a voltage lower than the coercive voltage Vc, deterioration of the amplitude is observed if the vibrator is operated for a long time. FIG. 6 is a graph showing this situation, with the horizontal axis representing the operating time and the vertical axis representing the amplitude δ. This is a case where the same bimorph element as in FIG. 2 is used, but deterioration is observed when the power supply voltage IVpl is 30 V or more, and the deterioration increases as the voltage increases.

From this figure, it can be seen that when the bimorph element is driven by the circuit of FIG. 2, the allowable voltage is 1/3 to 1/4 of the coercive voltage Vc. Therefore, in order to use it under conditions with little deterioration, conventionally the coercive voltage Vc is applied in the polarization direction and the reverse polarization direction.
A small voltage of 173 to 1/4 or less was applied, and the amplitude and generated force were very small.

In response to this, the inventors of the present application have proposed a drive circuit that can further increase the amplitude and generated force by applying different voltages in the polarization direction and the reverse polarization direction. FIG. 7 is its circuit diagram. The configuration will be briefly explained. A constant voltage diode z is connected to the electrode in contact with the positive polarization surface of one piezoelectric element.
Connect the cathode of D1, connect the anode of a constant voltage diode ZD2 to the electrode in contact with the negative electrode surface of the other piezoelectric element,
The other terminals of the two constant voltage diodes are used in common as one input terminal, and the center electrode S is used as the other input terminal, and a DC voltage is applied therebetween by switching the polarity. In the same figure, 3 is a polarity switch, 4 is a power supply voltage V
DC/D that boosts 1 to Vo (=V1 +VZIIO)
5 is a changeover switch control circuit, and 6 is a constant current circuit.

The operation of this circuit will be briefly explained. When the switch 502 is in the state shown in the figure, VO appears at point A, so approximately vO is applied to the piezoelectric element H1 in the polarization direction, and vo-vzD2 is applied to the piezoelectric element H2 in the opposite polarization direction, resulting in a bimorph. The tip of element 1 is displaced upward. When the polarity changes, H
V o -VZDI is added to l in the opposite polarization direction, and Hz
Approximately 0 is added to the polarization direction, and the tip is displaced downward.

FIGS. 8(a) and 8(b) show the voltages applied to the piezoelectric elements H1 and Hz, respectively. In this circuit, by appropriately selecting the operating voltage VZD of the constant voltage diode according to (1)0, the voltage applied in the reverse polarization direction can be controlled to a constant value or less, so that no deterioration of polarization occurs.

The solid line ■ in FIG. 4 shows the voltage of 2 Hz when the voltage applied in the polarization direction is increased while the voltages V o - VZDI and V o - V2O3 applied in the reverse polarization direction are both set to 30 V using the circuit shown in Fig. 7. These are the results of measuring the amplitude δ of the tip of the bimorph element 1 when driven at .

■It is also possible to increase 0 to 100 V or more, and the amount of displacement in this case increases about three times compared to when 30 V is applied in both the polarization direction and the general polarization direction using the conventional circuit shown in Figure 2. . Furthermore, since the generated force also increases, the amount of displacement multiplied by the generated force increases by about 9 times compared to the conventional circuit.

[Problem that the invention seeks to solve]

As described above, by using the circuit shown in FIG. 7 by the present inventor, it is possible to obtain a considerably larger amount of displacement and generated force than in the conventional circuit shown in FIG. 2.

However, when a piezoelectric element is used as an actuator in place of an electromagnetic drive component, a larger displacement amount and generated force are often required.

[Means for solving problems]

The piezoelectric element driving method of the present invention was made in view of the above problems, and when the coercive electric field strength of the piezoelectric element is EC,
The maximum value in the general polarization direction is (1/4) Ec or more (9/1
0) Apply an electric field E that is less than E c for T time, and then apply an electric field (n = 0 to 10) that is more than ' E + (n/10) E C, J in the polarization direction for 0.5 × T × 10 - n+
1 or more.

[Effect]

In the general polarization direction, the maximum value is (1/4) Ec or more and (9
/10) Since a high electric field of less than E c is applied, the amount of displacement and generated force are large. Further, the polarization deteriorated by applying a voltage in the polarization direction is almost completely restored by applying a voltage in the polarization direction.

〔Example〕

Before going into the description of the embodiments, the basic principle of the present invention will be explained. In FIG. 5, a voltage V is applied to a piezoelectric element having a thickness h, and the length ! When the piezoelectric element expands by Δl, the amount of strain is Δ7! / j! It is expressed as = d(V/h). That is, the amount of strain in the piezoelectric element is proportional to the strength of the electric field applied to the piezoelectric element, and this proportionality constant is the d constant. The change in d constant was measured when a voltage was applied for a long time in the polarization direction to a piezoelectric element that had been polarized by applying a high electric field during manufacturing, and was normalized to the d constant (initial value) at the time of polarization formation. This is the graph shown in Figure 9. In the figure, the horizontal axis shows the application time (logarithmic scale), and the vertical axis shows the change in the d constant. The piezoelectric element used in the experiment was made of the same material as in FIG. 5 and had a thickness of 0.15 nm. Therefore, the coercive voltage Vc is approximately 90
It is V.

Solid lines (■) to (■) indicate the case where voltage is applied in the polarization direction. If a voltage of 1/4 to 1/3 or more of the coercive voltage Vc is applied, the deterioration will be accelerated, and each time the applied voltage increases by about (1/10) Vc, the time required for the d constant to decrease by the same amount from the initial value. becomes about one order of magnitude shorter, as indicated by the intersection of the dashed-dotted lines.

When a high voltage is applied in the same direction as the polarization to the piezoelectric element whose d-constant has been reduced to the initial value of 172 in this way, the polarization is re-formed and the d-constant recovers as shown by the broken lines (2) and (2).

According to the example in the same figure, (1/4)Vc ~ (1/3)V
When c is Vd (30■ in the figure), when 'V d + (3/10) V CJ (-about 57 V) is added in the polarization direction, the d constant decreases to 1/2 in 150 hours, When a similar voltage is applied to this element in the polarization direction, it takes nearly 1500 hours for the d constant to recover (dashed line ■). In this way, it takes 5 to 10 times longer to recover with the same voltage. On the other hand, if the voltage applied in the polarization direction is set to about 66V, which is (1/10) Vc higher than the voltage applied in the polarization direction 'Vd + (3/10) Vcj (=57■), the time required for recovery is the same as that required for deterioration. The time is reduced to about 172 to 1 times the original time (broken line ■).

In this way, (n/
10) When a high voltage of V c (n=o-10) is applied in the polarization direction, the time required for recovery is (1/2)
It will be about Xl0-"' to 10-"'. Based on this experimental result, the following driving method can be considered. In other words, the polarization deteriorated by applying an electric field E in the polarization direction for a time T is changed by applying an electric field of "E+(n/10)EcJ" in the polarization direction to a
This is a driving method that re-forms by adding Tl0-''' (a ~0.5-1) or more, and by repeating this, it stably secures a large displacement while preventing a decrease in the d constant.

For example, let us find the voltage applied in the polarization direction when Vd is applied in the polarization direction for the TO time, and then the polarity is switched and a voltage is applied in the polarization direction.

T o ~0.5 T o ×1Q−n+I to find n, which is approximately 0.7. Also, T o = T o
If XIQ-"' is set, n is 1. Therefore, in the polarization direction, (V d +0.7
c) A voltage of ˜(V d + (1/10)V c) or more may be applied. The timing chart in FIG. 10 illustrates this operation. In the figure, 81 is a region of depolarization, and S2 is a region of re-polarization.

The timing chart in FIG. 11 shows a case where the voltage application time in the polarization direction is 1720, which is the voltage application time in the reverse polarization direction.

From 0.5 x 10-'' = 1/20, since n=2, it is sufficient to add V d + (2/10) V c or more in the polarization direction.

This driving method assumes that depolarization will occur when a voltage is applied in the reverse polarization direction, and is used by applying a high voltage in the polarization direction to recover this, but the voltage applied in the reverse polarization direction is too strong. If depolarization is rapid, even if polarization can be reshaped by switching polarity, the operation will be unstable.

Therefore, the maximum value E ma of the electric field applied in the reverse polarization direction
x is actually (8/10) E c ~ (9/10) B
c is the upper limit.

Also, since depolarization occurs significantly above (1/4) E c , (1/4) E c < Bmax < (9/10
) E c is a particularly effective region for the present invention.

Next, the present invention will be explained in detail together with examples.

FIG. 1 is a timing chart showing one embodiment of the present invention, and shows a driving method when a bimorph element operated by the circuit of FIG. 7 is applied to a coin processing device of a public telephone.

The coin processing actuator must have the characteristics of vibrating once every 5 to 180 seconds, with a displacement of 2 cranes or more, a generated force of 25 g or more, and a reciprocation time of 0.5 seconds or less. This characteristic is 50mL
This driving method becomes indispensable when realizing 15n+WX0.15 with a bimorph element in which piezoelectric elements of a certain size are superimposed. In FIG. 7, taking as an example the case where the tip of the bimorph element 1 is normally displaced downward and moves back and forth once when storing a coin, the potential of J of the changeover switch control circuit 5 is the first
It will look like figure (a). At this time, the voltage applied to the piezoelectric element H1 is as shown in FIG.

Therefore, if we set 0.5 X10-”'=1/360, n
=3.26. Therefore, the voltage vO applied in the polarization direction needs to be higher than the voltage V o −VZDI applied in the opposite polarization direction by 3.26×(1/10) V c or more.

(V o-VZDI l +3.26X(1/10)V
c=V.

Then VZDI = 3.26X (1/10) V
c. When Vc is 90V, V ZDI is 29.3
It is necessary to make it more than V. Therefore, for example, VO=80
When using a power supply of V, the voltage applied in the reverse polarization direction is V.
o -VZDI must be less than or equal to 50.7V.

Actually, for safety reasons, it is desirable to use around 40V.

On the other hand, the voltage applied to the piezoelectric element H2 is as shown in FIG. 1 (c), and the application time in the polarization direction is more than 10 times the application time in the opposite polarization direction. Therefore, 0.5 Xl0-”'=1
If it is set to 0, n=-0,3. Therefore, the voltage applied in the polarization direction is 0.3' from the voltage applied in the opposite polarization direction.
X (1/10) VC is greater than or equal to the value obtained by subtracting CJ. However, in the circuit of FIG. 7, it is not possible to apply a voltage lower in the polarization direction than in the reverse polarization direction, so in reality, V (polarization direction)≧V (reverse polarization direction). Furthermore, ■ (reverse polarization direction) is (8/10) V c ~ (9/
10) Vc or less is desirable, so when Vc is 90V, ■ (reverse polarization direction) is preferably 70V or less. Also, Hl
, the maximum voltage applied to both H2 in the reverse polarization direction is (1/4)
Since the present invention is particularly effective when Vc (approximately 22V) or more, in this example, when vO is 80■, 22V < V
o −VZDI <40V, 22V <V o −
The driving condition range is V2O3<70V.

By the way, the coercive electric field strength EC generally has a negative temperature gradient. Therefore, as the temperature increases, the EC decreases, but in this case, the practical reverse electric field strength also decreases. Therefore, E
It is desirable that C be defined by the upper limit of the operating temperature.

FIG. 12 is a circuit diagram showing an improved example of the circuit shown in FIG. 7.

Moreover, FIG. 13 is the timing chart, and the second
This is an example of the following. In this example, when switching the polarity, a voltage larger than the voltage shown in FIG. This is an example of driving in which polarization is re-formed by inversion.

First, the operation of the circuit will be briefly explained. Assume that the J terminal of the changeover switch control circuit 5 is normally at rhhighJ as shown in FIG. 13(A). In this case, terminal B becomes positive, but the circuit that applies voltage to Hl is a diode 219.
Since the voltage is cut off by , no voltage is applied to Hl as shown in FIG. 13(b).

-4, H2, as shown in FIG. 13(C), Vo is applied in the polarization direction, so the tip is displaced downward.

When the J terminal of the changeover switch control circuit 5 is set to rlowJ, the polarity is reversed and the terminal A becomes positive. VO is added to Hl in the polarization direction, and V o-VZD is added to H2 in the opposite polarization direction.
221 is added and displaced upward.

Next, when the J terminal becomes high J again, the polarity is reversed, and the terminal B becomes positive and the terminal A becomes the ground level. Since Hl had been charged with a charge corresponding to the voltage Vo until then, the potential at the electrode T1 of Hl rises to 2Vo. Kokote, VZD2
When 13 + VZD221 <2 V o, a trigger current flows through the gate of the thyristor 212 and the thyristor 212 is turned on. Therefore, the charging current to Hl flows through the path (terminal B-H1 -> thyristor 212 -> constant voltage diode 215 -> terminal A0), so when charging to Hl is completed, the charging current is limited and the thyristor 212 self-recovers. Since Vo is applied to H2 in the polarization direction, the tip of the bimorph element 1 is largely displaced downward. As time passes, the charge on Hl is discharged through the resistor 23, so the voltage applied in the reverse polarization direction decreases to zero. The discharge time is controlled by a resistor 23.

As described above, in this circuit, the voltage applied to Hl in the reverse polarization direction becomes V o -VZD215 when switching polarity,
After that, it decreases with time and becomes zero after time T3, but during this time, the voltage applied in the polarization direction to re-form the deteriorated polarization is V o -VZ in the opposite polarization direction.
It is assumed that the voltage of D215 continues for a time T3. - For example, if T3 is set to about 5 seconds, the application time in the polarization direction is 1/10 of the application time in the reverse polarization direction.

Therefore, if we set 0.5 Xl0-''=1/10, n is approximately 1.7.

Therefore, the voltage applied in the polarization direction is ■ (reverse polarization direction)
+1.7 X (1/10) V c or more is required. Since the voltage applied in the polarization direction is Vo, Vo > Vo - VZD215 +1.7
10) If V c is set, VZD215 > 1.7 X
(1/10) V c, and if Vc is 90V, V
ZD215 >15.3'V, looking at safety, VZD21
5>18V. Therefore, when Vo is 80cm, the driving condition range of this embodiment is 22V<Vo-VZD215<62V.

In addition, in this example, the tip of the element that was largely displaced during polarity switching (Fig. 13A) returns slightly as the charge of Hl is discharged, but in order to prevent this, a magnet was placed at the tip of the bimorph element. The bimorph element may be held by this suction force.

In addition, in this embodiment, as shown in FIG. 13 (b), since the voltage application time T3 in the reverse polarization direction is determined by the resistor 23,
There is an advantage that the time T2 for which the bimorph element is displaced and held downward can be further lengthened. This is effective when the bimorph element is normally displaced in one direction and is vibrated once largely when necessary.

FIG. 14 shows an example of a circuit for applying a power supply voltage in the polarization direction and a voltage subtracted by a constant voltage from the power supply voltage in the reverse polarization direction, which is another means for realizing the present invention. A constant voltage diode ZDI is connected in series with Hl, and a power supply is connected to this circuit. Then, while the voltage applied to the piezoelectric element is applied in an unrestricted direction, that is, while the anode of the constant voltage diode ZD1 is positive, the constant voltage diode ZD1
A phototransistor PTI that operates to short-circuit is connected in parallel to the constant voltage diode zD1. The phototransistor PTI is operated by light emission from the photodiode L1.

On the other hand, for H2, a constant voltage diode ZD2 is connected in series.
is connected, and power is connected to this circuit. While the voltage applied to the piezoelectric element H2 is applied in an unrestricted direction, that is, while the electrode S is positive, the phototransistor PT2, which operates to short-circuit the constant voltage diode ZD2, is connected in parallel to the constant voltage diode ZD2. It is connected to the. Phototransistor PT2 is operated by light emission from photodiode L2.

The voltages applied to Hl and H2 are shown by solid lines in FIGS. 15(a) and 15(b), respectively.

The operation of the circuit that applies voltage to Hl will be explained using FIG. If there is no phototransistor PTI, and the power supply voltage is as shown by the dashed line, the voltage applied to Hl will be as shown by the broken line. That is, when the power supply voltage increases, the voltage applied in the polarization direction of Hl also increases, but even if the power supply voltage passes tp and begins to decrease, the voltage of H1 does not decrease for a while. This is because ZDI is connected, so the voltage Vp charged to Hl.

This is because the charge charged in Hl is not discharged until the difference from the power supply voltage reaches VZDI. Phototransistor PT
The reason why adding I solves this problem is as follows. While the point A is positive, the photodiode L1 emits light, so the phototransistor PTI is operating. Therefore, when the power supply voltage passes tp and begins to decrease, the charge on Hl is discharged via the phototransistor PTI, so that the same voltage as the power supply voltage is applied to Hl as shown by the solid line. When the polarity changes and point A becomes negative, the phototransistor PTI is turned off. When the voltage at point A becomes less than -VZDI, voltage starts to be applied in the opposite polarization direction, as shown in the figure.

In this way, when this circuit is used, for any given power supply voltage, the power supply voltage is in the polarization direction, and the power supply voltage is V in the reverse polarization direction.
A voltage minus ZDl is applied. Therefore, according to this embodiment, if a voltage of ry-VZDI J is applied for a time TO in the reverse polarization direction, and a voltage V higher than this by VZDl is applied for a time TO in the polarization direction, V Z
DI is 0.7 (1/10) V c ~ (1/10)
V c or more is desirable. - For example, when Vc is 90V, VZDI >9 and Vp is 80V, the practical range is 22V < V p -VZDl <71V.

Note that H2 operates in the same way as Hl, so a description thereof will be omitted.

Figure 16 shows a Darlington transistor II instead of the phototransistor used as a short circuit in Figure 14.
This is an example using TII and DT21. The operation of the circuit that charges Hl will be explained. When the voltage at point A is positive and rising, a forward current flows through ZDI, and Hl is charged in the polarization direction. When the voltage at point A begins to drop, electrode T1
The voltage at point A tends to become higher than that at point A, but since the Darlington transistor DTII is turned on at this time, the charge on H1 is discharged and eventually becomes equal to the voltage at point A. When point A becomes negative, current flows to the base of Darlington transistor DT12, turning it on, so Darlington transistor D
The base voltage of TII becomes equal to the emitter voltage, and the base current is cut off, so Darlington transistor DT
II is turned off. Therefore, a voltage of V - VZDI is applied to H1 in the reverse polarization direction. Here, while the voltage is applied to nl in the reverse polarization direction, the Darlington transistor DT12 is in the on state, so if the resistance R11 is smaller than the old resistance value, the charging current in the reverse polarization direction is 8 points - electrode. 5-Hl-Electrode T1→Resistor R11→Darlington transistor DT12→Point A, and a voltage of V-VZDI is applied to H1 in the opposite polarization direction. The same applies to H2.

FIG. 17 shows another means of realizing the present invention, in which two piezoelectric elements are used.
It uses multimorph elements constructed by stacking two or more layers. In the figure, 10 is a multimorph element;
H is a piezoelectric element, and 1L12 is a one-way voltage limiting circuit.

FIG. 18(A) shows a drive circuit for a laminated piezoelectric actuator using the longitudinal strain effect as shown in the perspective view of FIG. 18(B). 15 is a laminated piezoelectric actuator, 16 is a laminated piezoelectric element, 20 is a piezoelectric element, 18-1 is an internal electrode, 1
8-2 is a connection electrode, and 17 is a displacement amount enlarging mechanism. The laminated piezoelectric element 16 is made by stacking piezoelectric materials and internal electrodes alternately and sintering them, and then cutting and notching them as shown in the figure.
It is obtained by applying a connecting electrode and forming polarization.

The operation when a constant voltage diode is used in the one-way voltage limiting circuit is as follows. 16-1 if point A is positive
Vo is applied to each piezoelectric element 16-2 in the polarization direction and extends as shown in the figure, and vo - is applied to each piezoelectric element 16-2 in the opposite polarization direction.
VZDI is applied and it contracts. This amount of strain is the amount of displacement magnification mechanism 1
7, it is enlarged and its tip is displaced downward. When the polarity is reversed, the tip is similarly displaced upward.

〔Effect of the invention〕

As explained above, the present invention applies a voltage whose maximum voltage exceeds (1/4) Vc in the reverse polarization direction, and then applies an applied voltage in a predetermined range according to the applied voltage and application time in the reverse polarization direction. By giving an application time, the deteriorated polarization is re-formed and driven, so the voltage applied in the reverse polarization direction can be much higher than conventional methods while preventing polarization deterioration, and in addition, an even higher voltage can be applied in the polarization direction. can be applied. Therefore, the amount of displacement and generated force as an actuator.

can be dramatically increased. Polarization deterioration voltage Vd
Compared to the conventional driving method in which the following voltages are applied in the polarization direction and the reverse polarization direction, the amount of displacement multiplied by the generated force exceeds 10 times, and there is little deterioration in the characteristics of the actuator. The present invention can be applied to bimorph elements, unimorph elements, multimorph elements, laminated piezoelectric elements, piezoelectric motors, etc. Furthermore, these actuators can be applied to coin processing devices, impact printers, relays, etc.

[Brief explanation of the drawing]

FIG. 1 is a timing chart showing an embodiment of the present invention;
Fig. 2 is a circuit diagram showing a conventional piezoelectric element drive circuit, Fig. 3 is its timing chart, Fig. 4 is a characteristic diagram showing the relationship between the power supply voltage and the amplitude of the bimorph element 1, and Fig. 5 is a diagram showing the relationship between the applied voltage and the amplitude of the bimorph element 1. A characteristic diagram showing the relationship with the amount of strain of the piezoelectric element, Fig. 6 is a characteristic diagram showing the state of polarization deterioration, Fig. 7 is a circuit diagram showing an example of a piezoelectric element drive circuit, and Fig. 8 is the circuit of Fig. 7. FIG. 9 is a characteristic diagram showing changes in the d constant. FIGS. 10 and 11 are timing charts showing the operating principle of the present invention.
Figure 2 is a diagram showing an example of a circuit for implementing the present invention;
14 is a timing chart showing the operation of the present invention, FIG. 14 is a diagram showing another example of a circuit for implementing the present invention, FIG. 15 is a timing chart showing the operation, and FIGS. It is a figure which shows the other example of a circuit for implementation. 1... Bimorph element, Hl, H2... Piezoelectric element. Patent applicant: Nippon Telegraph and Telephone Corporation Agent: Kazuko Yamakawa (and 1 other person) Figure 2 Figure 4 Figure 5 Push button also ff1 (V) IR (LLILL+) 3% 'ijE'': 1krC
off p

Claims (3)

[Claims] (1) A driving method in which a piezoelectric element is polarized by applying a high electric field to a ferroelectric material, and the piezoelectric element is driven by applying an electric field in the opposite polarization direction to distort the piezoelectric element,
When the coercive electric field strength of the piezoelectric element is Ec, an electric field E whose maximum value is (1/4) Ec or more and (9/10) Ec or less is applied in the reverse polarization direction for T time, and then "E+" is applied in the polarization direction.
(n/10)Ec'' or more (n=0 to 10).
A piezoelectric element driving method characterized by adding 5×T×10^-^n^+^1 or more. (2) The piezoelectric element driving method according to claim 1, wherein Ec is the coercive electric field strength at the upper limit of the piezoelectric element operating temperature. (3) When applying a voltage in the opposite polarization direction to one piezoelectric element group using a plurality of piezoelectric elements, a voltage is applied in the polarization direction to the other piezoelectric element group.
Piezoelectric element driving method described in .