JPS61135368A - Piezoelectric actuator - Google Patents

Abstract

PURPOSE:To prevent an electrostrictive plate from deteriorating in its polarization by inserting a voltage limiter to a drive input circuit, and forming it with a pnpn element circuit which is turned ON by the prescribed voltage. CONSTITUTION:A piezoelectric actuator is composed of isogonic polarization type bimorph element 1, a drive input circuit 2, a polarization switching circuit 3, a constant-voltage circuit 4, a controller 5 and a DC power source 6. In this case, voltage limiters 21, 22 are provided, the other ends are commonly connected, connected to one input terminal A of the input circuit 2, and the connecting points of high resistors 23, 24 is connected to the other input terminal B of the input circuit 2. The circuits 21, 22 are formed by connecting in parallel Zener diodes 211, 221 with thyristors 212, 222 of pnpn element, a high voltage is applied to electrostrictive plates H1, H2 when the polarity of the applied voltage is switched, and then gradually lowered. Thus, strong generated force can be obtained at polarity switching time, and sufficient displacement can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a piezoelectric actuator using a bimorph element, particularly a co-polarized bimorph element.

[Conventional technology]

In recent years, with the demand for smaller and lighter terminal devices, bimorph elements using bimorph elements have been attracting attention as small and efficient actuators that can replace electromagnets.

A bimorph element is a stack of electrostrictive plates made of materials such as lead zirconate titanate that are polarized in the thickness direction, and is electrostrictive by applying an appropriate voltage in the thickness direction with one end fixed. The plate is deformed by piezoelectric transverse effect and the free end is displaced.

This type of actuator uses a bimorph element polarized in the same direction, in which the polarization directions of the electrostrictive plates H1 and H2 (direction of arrow A) coincide with each other, as shown in FIG. 11(A).
As shown in the figure (b), the polarization direction of the electrostrictive plates H1 and H2 (
They are broadly classified into those using oppositely polarized bimorph elements in which the directions (in the direction of arrow B) are opposite to each other.

In these two types, if a large displacement is to be obtained with a low voltage, a co-polarized bimorph element is used in which a voltage is simultaneously applied to both electrostrictive plates H1 and H2 (see Fig. 11). (b)) is advantageous.

[Problem that the invention seeks to solve]

However, in the case of the conventional driving method as shown in FIG. As a result, an electrostrictive plate to which a voltage is applied in the opposite direction may be depolarized.

FIG. 12 is a characteristic diagram showing the relationship between the power supply voltage E and the displacement amount δ when the piezoelectric actuator is operated at an operating frequency of 2 Hz.

In the same figure, the curve A indicated by a broken line is shown in Fig. 11 (a).
The present invention relates to a piezoelectric actuator of the type shown in FIG. According to this piezoelectric actuator, the polarization is destroyed at about 8OV, and the displacement amount δ is extremely reduced.

This destruction of polarization occurs when an overvoltage is applied in the opposite direction to the polarization, and in the case of this piezoelectric actuator, the power supply voltage E is directly applied in the opposite polarization direction of the electrostrictive plates H1 and H2, so it cannot be used. It can be seen that the polarization breakdown voltage Vp of the bimorph element is 8OV.

In addition, the practical voltage applied to a bimorph element is limited to about 1/2 to 1/3 of the polarization breakdown voltage Vp, and if it is used at a voltage exceeding this voltage, the polarization will be reduced even if the polarization is not destroyed. Deterioration will occur.

In other words, when a voltage in the opposite direction to the polarization direction is applied to the electrostrictive plate while gradually increasing, the polarization starts to depolarize (degrade) from a certain applied voltage, and the voltage value at this time is called the polarization deterioration voltage Vd. It is called.

In the case of a piezoelectric actuator having the characteristics shown by curve A in Fig. 12, the polarization deterioration voltage Vd of the bimorph element used is about 3OV, and the polarization deterioration voltage Vd directly becomes the limit of the power supply voltage of the piezoelectric actuator. , a displacement amount δ of only about 1n can be obtained.

Additionally, piezoelectric actuators generally require the largest amount of displacement and force when switching polarity, but when high-speed operation is required, the desired amount of displacement may not be obtained due to the effects of hysteresis. . This will be specifically explained using FIG. 13.

That is, FIG. 13(A) is a side view showing the operation of the bimorph element 1, and FIG.
In Figure 13 (a), if we calculate the speed change during the transition from the state shown by the solid line to the state shown by the broken line by switching the polarity and gender, we will get the change in speed as shown in Figure 13 (b). However, after that, the speed decreases rapidly and it takes some time to reach the final position.

Therefore, when vibrating at high speed, the polarity may be reversed before the displacement is sufficiently reached and the displacement amount may become small as shown by the dashed line (displacement amount η). Therefore, the desired amount of displacement cannot be obtained.

[Means for solving problems]

The present invention has been made in view of the above problems, and includes a voltage limiting circuit inserted into the drive input circuit, and the voltage limiting circuit is configured with a pnpn element circuit that is turned on at a constant voltage.

[Effect]

Because a voltage limiting circuit is inserted, when a voltage is applied to the electrostrictive plate in the opposite direction to the polarization direction, the voltage is lower than when a voltage is applied in the same direction as the polarization direction. is applied.

Also, pn turns on the voltage limiting circuit at a constant voltage.
Since it is composed of a pn element circuit, a high voltage is applied at the moment when the polarity of the voltage applied to the electrostrictive plate switches from the same direction as the polarization direction to the opposite direction, and then the applied voltage value gradually decreases. It acts on

〔Example〕

Hereinafter, the present invention will be described in detail along with examples.

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

The piezoelectric actuator is a co-polarized bimorph element 1
．． Drive input circuit 2. Polarity switching circuit 3. Constant voltage circuit 4. It is composed of a control circuit 5 and a DC power supply 6.

The bimorph element 1 includes a drive input circuit 2, a polarity switching circuit 3, and a polarity switching circuit 3. It is connected to a DC power supply 6 via a constant voltage circuit 4.

The bimorph element 1 includes a pair of electrostrictive plates H1 and H2,
These electrostrictive plates H1 and H2 are arranged with the center electrode S in between so that their polarization directions are in the same direction (from top to bottom in the thickness direction in FIG. 1).

Furthermore, electrodes T1. T2 is placed.

One end of the electrostrictive plate H2 on the electrode T2 side is fixed to the base.

The drive input circuit 2 includes a voltage limiting circuit 21 whose cathode side is connected to the electrode T1 of the electrostrictive plate H1, a voltage limiting circuit 22 whose anode side is connected to the electrode T2 of the electrostrictive plate H2, and the electrode T1 and the center electrode S. and a high resistance 24 connected between the electrode T2 and the center electrode S.

In addition, the cathode side and anode side of the voltage limiting circuits 21 and 22 are as follows:
The cathode side and the anode side of Zener diodes 211 and 221, which are internal elements of the respective circuits to be described later, are shown.

The other ends of each of the voltage limiting circuits 21 and 22 are connected in common and then connected to one input terminal A of the drive input circuit 2. Further, the connection point between the high resistances 23 and 24, ie, the center electrode S, is connected to the other input terminal B of the drive input circuit 2.

The voltage limiting circuit 21.22 is characterized in that a Zener diode 211.221 is connected in parallel to a pnpn element circuit including a thyristor 212.222, which is a pnpn element.

In the voltage limiting circuit 21, a Zener diode 21 is connected in parallel to a series body of a resistor 217 and a Zener diode 211.
5 and a series body of thyristor 212 are connected. In this case, the Zener diode 215 is the Zener diode 2
11, the anode side is connected to the terminal A, and the cathode side is connected to the cathode of the thyristor 212. The anode side of this thyristor 212 is connected to the electrode Tl which is in contact with the positive polarization surface of the electrostrictive plate H1 together with the cathode of the Zener diode 211.
It is connected to the.

Further, the connection point between the resistor 214 and the anode of the Zener diode 213 is connected to the gate of the thyristor 212, the other end of the resistor 214 is connected to the cathode of the thyristor 212, and the other end (cathode) of the Zener diode 213 is connected to the anode of the thyristor 212. It is connected.

Furthermore, a diode 216 is connected in parallel to the resistor 217 such that its cathode is connected to the anode side of the Zener diode 211.

Similarly, in the voltage limiting circuit 22, a series body of a Zener diode 225 and a thyristor 222 is connected in parallel with a series body of a resistor 227 and a Zener diode 221.

In this case, the Zener diode 225 has its cathode side connected to the terminal A like the Zener diode 221, and its anode side connected to the cathode of the thyristor 222. The cathode side of this thyristor 222 is connected together with the anode of the Zener diode 221 to an electrode T2 that is in contact with the negative polarization surface of the electrostrictive plate H2.

Further, the connection point between the resistor 224 and the anode of the Zener diode 223 is connected to the gate of the thyristor 222, the other end of the resistor 224 is connected to the cathode of the Zener diode 221, and the other end (cathode) of the Zener diode 223 is connected to the gate of the thyristor 222.
22 anodes. Further, a diode 226 is connected in parallel to the resistor 217 such that its anode is connected to the anode side of the Zener diode 221.

Note that the polarization deterioration voltage of the electrostrictive plates H1 and H2 is Vd
(Hl) and Vd (H2), Zener diode 2
11.221(7) The operating voltage is V (z0211),
V (z0221), the voltage applied between terminals AB is Vc
Then, Vd(Hl), Vd()12)<V c
... (1) V c - Vd (Hl) < V (ZD211) < V c ... (2) is satisfied.

In addition, the Zener diode 211. ．． 221,215.
The operating voltages of 225, 213, and 223 are respectively V (z
0211) , V (Z0221) , V (Z[
)215) , V (ZD225) , V (ZD
213), V (ZD223), and the voltage applied between terminals AB is Vc, then v (zD215) < V (ZD211)
---(4)V(ZD211) -V(ZD215)
< v (20213) < 2 V c −V (z021
5) ...(5) V(ZD225)<V(ZD221)
・ --(6)V(Z0221)
< V (ZD225) < V (ZD223) < 2
V c -V(ZD225)...(7) is satisfied.

The polarity switching circuit 3 includes a pair of pnp transistors 301 whose output side is connected between the terminals A and C and is Darlington-connected, and an output side which is connected between the terminals B and C and which is Darlington-connected. a pnp) transistor pair 302, an npn transistor 303 whose output side is connected between the terminal A and the terminal 1, and an npn) transistor 3 whose output side is connected between the terminal B and the terminal 2;
It has 04.

These transistors are used as polarity changeover switches, and these switches are connected in a bridge configuration. The input side (base) of the transistor pair 301 is connected to the collector of a transistor 306 via a resistor 310, and its emitter is grounded.

Further, the base of the transistor 306 is connected to the output side of the inverter 313 via a resistor 312. The base of a transistor 304 is connected to the output side of this input terminal 313 via a resistor 309.

The input side (base) of the transistor pair 302 is connected to a resistor 30.
7 to the collector of the transistor 305,
The emitter of this transistor 305 is grounded. The base of transistor 305 is connected via resistor 311. connected to the input side of the inverter 313,
Furthermore, it is connected to a control circuit 5.

Further, the base of the transistor 303 is connected to the input side of an inverter 313 via a resistor 308.

The control circuit 5 includes a transistor pair 301 of the polarity switching circuit 3.
and transistor 304 and transistor pair 3
The combination of resistors 501 and 303 is alternately turned on and off to control switching of the polarity of the voltage applied to the bimorph element l. It is composed of a changeover switch 502 and a DC power supply 503 (power supply voltage Ec).

That is, the input side of the inverter 313 in the polarity switching circuit 3 is grounded via the resistor 501, and is also connected to the positive pole of the DC power supply 503 or the ground via the movable end of the changeover switch 502.

The constant voltage circuit 4 is a self-excited oscillation step-up type ringing choke D C/D C using a PNP transistor.
It is a converter.

That is, the constant voltage circuit 4 includes a saturated transformer 41 having three coils 411, 412, and 413 wound in the same direction, a capacitor 404, a resistor 403, 406, and a pn
It is composed of a p-transistor 405, a diode 402, and a Zener diode 401.

The emitter of the transistor 405 is connected to the positive end F of the DC power supply 6 (power supply voltage Ec) together with one end of the coil 412, and the collector is connected to one end of the coil 411. Further, the other end of the coil 412 and one end of the coil 413 are connected in common, and then connected to the base of a transistor 405 via a parallel body of a capacitor 404 and a resistor 403.

The base of the transistor 405 is connected to the ground terminal G together with the other end of the coil 411 via a start resistor 406, and is further connected to the anode of the Zener diode 401. The cathode of the Zener diode 401 is connected to the output terminal E, and a capacitor 407 is connected between the output terminal E and the ground @G.

Further, the cathode of a diode 402 is connected to the cathode of the Zener diode 401, and the anode of this diode 402 is connected to the other end of the coil 413.

Next, the operation of this embodiment will be explained.

First, the operation of the constant voltage circuit 4 will be explained. .

Voltage Ec (
When a voltage of about 5 cm is applied, a current flows through the start resistor of the constant voltage circuit 4 and turns on the transistor 405. When the collector current flows through the coil 411 of the transformer 41, an induced voltage is generated in the coils 412 and 413 as shown by the arrow, so the current flows through the base circuit consisting of the resistor 403 and the capacitor 404, and the transistor 405 is turned on. As it becomes deeper, the collector current becomes even larger.

Eventually, when the magnetic flux of the coil of the transformer 41 is saturated and the collector current stops flowing, the induced voltages of the coils 412 and 413 are reversed. Therefore, the voltage of the coil 413 is applied to the capacitor 407 and charged. When the magnetic flux in the coils 412 and 413 decreases due to this current, the reversed induced voltage becomes low, and current flows again from the DC type a6 to the base circuit of the transistor 405 via the coil 412, so the transistor 405 is turned on and the coil 411 .4
12,413 is re-energized. In this way, the capacitor 407 oscillates and charges are stored in the capacitor 407.

The operating voltage of the Zener diode 401 is V (ZD40
1), the voltage of the capacitor 407 is (Ec+V
(Z0401)) Zener diode 4
Since 01 is conductive, the resistor 403 and capacitor 40
Current no longer flows through the base circuit consisting of 4, and oscillation stops. When the load is connected and the voltage of the capacitor 407 drops, oscillation starts again and the voltage of (Ec+V(z0401)) is maintained.

In this way, in the constant voltage circuit 4, the voltage E of the DC power supply 6
C is boosted to create a constant voltage Vc.

Next, the operations of the polarity switching circuit 3 and the control circuit 5 will be explained.

When the switch 502 in the control circuit 5 is connected as shown in FIG.
01 is also turned on.

Eventually, in the bridge circuit, the switching elements of the transistor pair 301 and the transistor 304 connected in parallel are turned on, so a voltage Vc appears between the terminals A and B such that the terminal A side is positive.

On the other hand, in the control circuit 5, the switch 502
03, transistor pair 301. The base current of the transistor 304 is cut off, so it is turned off.
Transistor pair 302. ) - transistors 304, 305
turns on. Therefore, a voltage Vc appears between terminals A and B such that the terminal B side is positive.

Next, the operation of the drive input circuit 2 and the bimorph element 1 will be explained using the timing chart of FIG. 2. In addition, FIG. 2 (a) and (b) are electrostrictive plates H1 and H, respectively.
2, the direction of the vertical axis (voltage axis) corresponds to the polarization direction. Further, FIG. 1C shows the amount of displacement of the free end of the bimorph element 1, and the positive direction of the vertical axis corresponds to the upward displacement in FIG.

When a voltage Vc is applied between the terminals AB so that the terminal A becomes positive, since the Zener diode 211 is in the forward direction, the voltage Vc is applied to the electrostrictive plate H1 in the same direction as the polarization.

On the other hand, since the Zener diode 221 is in the opposite direction, the electrostrictive plate H
2, V c -V (ZD221) is applied in the opposite direction to the polarization.

Here, when the polarity of the voltage Vc applied between the terminals AB is reversed, and the terminal B becomes positive and the terminal A becomes the ground level, the voltage of the electrode Tl on the upper surface of the electrostrictive plate H1 becomes equal to the voltage of the terminal B. 2 because the voltage Vc that had been charged until then is applied to the strain plate H1.
Becomes Vc. That is, the Zener diode 213,2
A voltage of 2Vc is applied to the 15 series circuits. (5)
From the formula, V(Z0213) +V(ZD215) <
2 V c, a trigger current flows through the gate of thyristor 212, and thyristor 212 turns on.

Here, the resistor 217 is a Zener diode 213.21
It has a resistance value that is sufficiently higher than the impedance of the series circuit of No. 5. With this setting, when 2 VC is applied to the voltage limiting circuit 21, the current mainly flows through the Zener diodes 213 and 215, so that the thyristor 212 can be reliably fired.

Since the charging current to the electrostrictive plate H1 flows through the path of terminal B - electrostrictive plate H1 - thyristor 212 - Zener diode 215 - terminal A, the voltage applied to the electrostrictive plate H1 is V c - in the opposite direction to the polarization. It becomes V (ZD215). The situation at this time is shown in (i) of FIG. 2(a).

After being charged in this manner, since the resistor 23 has a high resistance of several MΩ, only an extremely small current flows through the thyristor 212, and the thyristor 212 returns to its original state. That is, the pnpn element circuit is in a cut-off state.

After that, the electric charge on the electrostrictive plate H1 is changed so that the voltage of the electrostrictive plate H1 is V.
It is discharged through the resistor 23 until it reaches c-V (Z0211). The situation at this time is shown in Figure 2 (a) (
ii).

On the other hand, the time point corresponding to (i) in FIG. 2(a), that is,
Paying attention to the operation of the voltage limiting circuit 22 when the polarity of the voltage Vc applied between the terminals AB is reversed so that the terminal B is at the positive level and the terminal A is at the ground level, the Zener diode 221. Since the diode 226 is in the forward direction, the electrostrictive plate H2
As shown in (i) of FIG. 2(b), Vc is applied in the same direction as the polarization, and thereafter the voltage Vc is maintained until the polarity of the voltage applied between terminals AB is reversed.

Next, when the polarity is reversed again, the electrostrictive plate H2 has a voltage of V c −V (ZD2
25) is applied, and becomes V c-V (z0221) as the thyristor 222 self-recovers. Further, Vc is applied to the electrostrictive plate H1 in the same direction as the polarization, as shown in (iii) of FIG. 2(a).

In this way, the state of voltage application to the electrostrictive plates H1 and H2 changes, so the bimorph element 1 is displaced as shown in FIG. 2(c).

In other words, when a voltage is applied to the electrostrictive plates H1 and H2 in the same direction as the polarization, they tend to contract in the direction perpendicular to the polarization, and when applied in the opposite direction, they tend to extend as shown in C. The free end of 1 is displaced up and down as shown by arrow A.

A high voltage is always applied to each of the electrostrictive plates H1 and H2 in the polarization direction, and a high voltage is applied in the opposite polarization direction only at the time of polarity switching (times (i) and (iii)). After that, the voltage decreases to a level that does not cause deterioration due to self-discharge, and therefore, although it is displaced with a large and strong force at the time of polarity switching (displacement amount ξl, ξ2), no deterioration of characteristics occurs. Furthermore, since the use of this circuit prevents the effect of the hysteresis mentioned above, there is little drop in displacement even during high-speed operation.

Note that in this embodiment, the voltage Vc applied between terminals AB
If the polarization breakdown voltage Vp is lower than the polarization breakdown voltage Vp, the Zener diodes 215 and 225 can be omitted. in this case,
When the thyristors 212 and 222 operate, the electrostrictive plate H1
, H2, a voltage of approximately Vc is applied in the reverse polarization direction of H2, as shown by the dashed lines in FIGS.
As shown by the dashed-dotted line in FIG.

As can be seen from the above operation description, as a driving method, normally a DC voltage is applied to the bimorph element 1, and when the polarity is reversed in a pulsed manner when necessary, Zener in the voltage limiting circuits 21 and 22 Diode 211,2
21 (7) Operating voltage V (Z0211), V (Z02
21) is V c −V d <t/(Z0211), V(Z0
221) < V c . . . (8) must be satisfied.

However, when the polarity is continuously switched and the polarity is vibrated for use, a polarization deterioration voltage Vd or more is applied in the same direction as the polarization, so that the once depolarized polarization is regenerated. Therefore, the operating voltage of the Zener diodes 211 and 221 is lowered to the extent that the above equations (2) and (3) are satisfied, and the electrostrictive plate H
1. Even if a voltage larger than the polarization deterioration voltage Vd is applied in the opposite polarization direction of H2, the polarization does not deteriorate.

FIG. 3 is a characteristic diagram showing the relationship between the displacement amount δ and the operating time in this embodiment.

Size of bimorph element 1 45w1X12 crane WX0.15 size Polarity switching frequency 2Hz Environmental temperature 70℃ under the conditions of Vc=80V.

The solid line A shows the characteristics of this example when V(ZD215) and V(ZD225) are -20V. A solid line B shows the characteristics when the Zener diodes 215° and 225 are removed from this embodiment.

Furthermore, the broken line C shows the characteristics of the conventional device (FIG. 1(a)) operated under the same conditions. However, the applied voltage E of the conventional device is 40V.

As can be seen from this characteristic diagram, the piezoelectric actuator of the present invention can be displaced more than three times as much as the conventional device, and has less deterioration over time.

FIG. 4 is a block diagram showing another embodiment of the present invention,
Components that are the same or corresponding to those in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted.

The drive input circuit 2 in this embodiment includes an electrostrictive plate H1, Hz
This is a circuit for driving a bimorph element with a large displacement, which has a low polarization degradation voltage Vd and cannot apply a voltage in the opposite direction to polarization for a long time.

The drive input circuit 2 is the same as the first embodiment in that it consists of a voltage limiting circuit 21.22 and a high resistance 23.24, but the configuration of the voltage limiting circuit 21.22 is different.

That is, the voltage limiting circuit 21 consists of a thyristor 212 which is a pnpn element whose cathode is connected to the terminal A and whose anode is connected to the electrode T1, and a series body of a Zener diode 218 and a resistor 214 connected in parallel to the thyristor 212. . Note that the cathode of a Zener diode 218 is connected to the anode side of the thyristor 212, and one end of a resistor 214 is connected to the cathode side of the thyristor 212. Also,
The gate of the thyristor 212 is a Zener diode 218
and the connection point between the resistor 214 and the resistor 214 .

The voltage limiting circuit 22 consists of a thyristor 222 whose anode is connected to the terminal A and whose cathode is connected to the electrode T2, and a series body of a Zener diode 228 and a resistor 224 connected in parallel to the thyristor 222. In addition, the thyristor 222
The cathode of a Zener diode 228 is connected to the anode side of the thyristor 222, and one end of a resistor 224 is connected to the cathode side of the thyristor 222. Further, the gate of the thyristor 222 is connected to the connection point between the Zener diode 228 and the resistor 224.

Next, the operation of this embodiment will be explained using the timing chart of FIG. Note that FIGS. 5A and 5B show the voltages applied to the electrostrictive plates H1 and H2, respectively, and the directions of the vertical axes (voltage axes) correspond to the polarization directions, respectively. 4(C) shows the amount of displacement of the free end of the bimorph element 1, and the positive direction of the vertical axis corresponds to the upward displacement in FIG. 4.

When the terminal A is positive, Vc is applied to the electrostrictive plate H1 in the same direction as the polarization through the path of the resistor 214, the Zener diode 218, the electrostrictive plate H1, and the terminal B (FIG. 5(A)).

On the other hand, the operating voltage V of the Zener diodes 218 and 228
(ZD21B), V(Z0228) as V c <V(
20218), V(ZD228) < 2 V c, as shown in FIG. is displaced upward by ξ12. This situation is shown in FIG. 5(c).

Here, if the polarity of the voltage applied between terminals AB is reversed and terminal B is made positive, a voltage of about 2Vc is applied between electrode Tl and terminal A, so Zener diode 218 becomes conductive.
Thyristor 212 turns on. Thyristor 212
When turned on, the electrostrictive plate H1 shows (i) in Fig. 5(a).
), a voltage of about Vc is applied in the opposite direction to the polarization. On the other hand, since the Zener diode 228 is in the forward direction, Vc is applied to the electrostrictive plate H2 in the same direction as the polarization, as shown in (i) of FIG. 5(b).

That is, since the voltage Vc is applied to both the electrostrictive plates H1 and H2, the bimorph element 1 is largely displaced downward (ξ21) as shown in (i) of FIG. 5(C).

Next, when the thyristor 212 self-recovers, the electrostrictive plate H1
Since the electric charge is discharged through the high resistance 23, the displacement of the bimorph element l is only due to the contraction of the electrostrictive Vi, H2, and the amount of displacement is from ξ21 as shown in (ii) of Fig. 5(C). It decreases to ξ22.

Next, when the polarity is reversed again and terminal A becomes positive, the electrostrictive plate H
Since a voltage of Vc is applied to each of 1 and H2, the tip of the bimorph element 1 is largely displaced upward to ξ11, as shown in (iii) of FIG. 5(c).

In addition, if a voltage can be applied for a certain period of time in the polarization direction of the electrostrictive plates H1 and H2, V(ZD218) and V(Z
D228) is set below Vc, and the polarization direction D228) is set to Vc -V.
(ZD218) and Vc-V (ZD228) may be applied.

Further, if terminal A is used and Zener diodes 215 and 225 are connected between terminals A and M, characteristics similar to those shown in the timing chart of FIG. 2 will be exhibited.

FIG. 6 is a block diagram showing still another embodiment of the present invention, and the embodiment shown in FIG.
The only difference is the internal circuit.

The voltage limiting circuit 21 includes a diode 219 whose anode is connected to the terminal A and whose cathode is connected to the electrode TI, and a thyristor 2 whose anode is connected to the electrode T1 and whose cathode is connected to the terminal A.
Contains 12. Further, a series body consisting of a Zener diode 218 and a resistor 214 is connected in parallel to the thyristor 212 so that the anode of the thyristor 212 and the cathode of the Zener diode 218 are connected to form a pnpn element circuit. Note that the gate of the thyristor 212 is connected to a connection point between the Zener diode 218 and the resistor 214.

The voltage limiting circuit 22 includes a diode 229 whose anode is connected to the electrode T2 and whose cathode is connected to the terminal A, and a thyristor 2 whose cathode is connected to the electrode T1 and whose anode is connected to the terminal A.
22, the thyristor 222 includes a series body consisting of a Zener diode 228 and a resistor 224.
The anode of the Zener diode 228 and the cathode of the Zener diode 228 are connected in parallel. In addition, the thyristor 22
The gate of 2 is connected to the connection point between the Zener diode 228 and the resistor 224.

In this embodiment, in the embodiment shown in FIG. 4, the electrostrictive plate H1
, H2, instead of using a series circuit of resistors 214, 224 and Zener diodes 218, 228, a charging-only diode 219°229 is added, and the charging time constant is small, so charging can be done quickly. , the displacement also becomes faster.

FIG. 7 is a block diagram showing still another embodiment of the present invention, and like the embodiment shown in FIG. 6, the internal circuits of the voltage limiting circuits 21 and 22 are different from the embodiment shown in FIG. 3. Only.

The voltage limiting circuit 21 consists of a diode 219 whose anode is connected to the terminal A and whose cathode is connected to the electrode TI, and a Shockley diode 210 whose anode is connected to the electrode T1 and whose cathode is connected to the terminal A. consists of a diode 229 whose anode is connected to the electrode T2 and whose cathode is connected to the terminal A, and a Shockley diode 220 whose cathode is connected to the electrode Tl and whose anode is connected to the terminal A.

In this embodiment, in the embodiment shown in FIG. 6, the thyristor 212. Zener diode 218. A pnpn element circuit consisting of a resistor 214 and a thyristor 222. Zener diode 228. The pnpn element circuit consisting of the resistor 224 is replaced with Shockley diodes 210 and 220, each of which is a pnpn element, and the Shockley diodes 210 and 220 are turned on when a voltage of 2 VC or less is applied in the forward direction. Then, the same operation as the embodiment shown in FIG. 6 is performed.

FIG. 8 is a block diagram showing still another embodiment, and this embodiment is similar to the embodiment shown in FIG.
This is another example when using a bimorph element in which voltage cannot be applied for a long time in the reverse direction.
This circuit is suitable for a driving method in which the polarity is held positive and the polarity is reversed in a pulsed manner as necessary.

The configuration of this embodiment differs from the embodiment shown in FIG. 3 in the internal circuits of the voltage limiting circuits 21 and 22, and in addition
The difference is that has been removed.

Voltage limiting circuit 21 includes a diode 219 whose anode is connected to terminal A and whose cathode is connected to electrode TI. The diode 219 has a thyristor 21 whose anodes are connected to each other.
2 and a Zener diode 215 are connected in parallel such that the anode of the diode 219 and the anode of the Zener diode 215 are connected. Sai! A series body consisting of a Zener diode 213 and a resistor 214 is connected in parallel to the I-star 212 such that one end of the resistor 214 and the cathode of the thyristor 212 are connected. The gate of the thyristor 212 is connected to a Zener diode 213 and a resistor 21.
Connected to 4 connection points.

The voltage limiting circuit 22 consists only of a Zener diode 221 whose cathode is connected to the terminal A and whose anode is connected to the electrode T2.

Next, the operation of this embodiment will be explained using the timing chart of FIG. Note that FIGS. 9A and 9B show the voltages applied to the electrostrictive plates H1 and H2, respectively, and the directions of the vertical axes (voltage axes) correspond to the polarization directions, respectively. 3(C) shows the amount of displacement of the free end of the bimorph element 1, and the positive direction of the vertical axis corresponds to the upward displacement in FIG. 3.

When the terminal B is positive, no voltage is applied to the electrostrictive plate H1 as shown in FIG. 9(a), and Vc is applied only to the electrostrictive plate H2 in the polarization direction as shown in FIG. 9(b). is being applied. Therefore, no deterioration of polarization occurs in this state.

When the polarity is reversed, Vc is applied to the electrostrictive plate H1 in the polarization direction, and Vc-v (Zn22
1) is applied, resulting in a large upward displacement (ξ1)
.

After a short period of time, when the polarity is reversed again, thyristor 2
12 is turned on, V is applied to the electrostrictive plate H1 in the opposite direction.
c-V (Zn215) is applied, and the bimorph element 1
The tip of is displaced downward by ξ2. Thereafter, when the thyristor 212 self-recovers (turns off), the charge on the electrostrictive plate H1 self-discharges, and the applied voltage becomes zero as shown in FIG. 9(a).

On the other hand, since Vc is applied to the electrostrictive plate H2 again, the slight depolarization that had previously occurred due to the application of Vc - V (Zn221) in the polarization direction is canceled out by the amplification effect described above, so there is no deterioration. Does not occur.

FIG. 10 is a block diagram of an embodiment in which a six-layer bimorph element is applied as the bimorph element 1.

Here, the 6-layer bimorph element is composed of a pair of electrostrictive plates [(11 and H21) arranged with the polarization directions in the same direction through a central electrode S, and a pair of electrostrictive plates H12 and H22 that are further polarized. are arranged in the same direction and opposite to the polarizations of the electrostrictive plates H1l and H21, and a pair of electrostrictive plates viH1
3 and H23 are arranged in the same manner.

In each of the embodiments using the two-layer bimorph element described above, when replacing the two-layer bimorph element with a six-layer bimorph element, the voltage limiting circuit 21.
22 should be connected as shown in FIG.

〔Effect of the invention〕

As explained above, according to the piezoelectric actuator of the present invention, a voltage limiting circuit is inserted into the drive input circuit, and the voltage limiting circuit is turned on at a constant voltage.
Since it is configured with an element circuit, when a voltage in the opposite direction to the polarization direction is applied to the electrostrictive plate, a lower voltage is applied than when a voltage in the same direction as the polarization direction is applied.

Therefore, even if the power supply voltage Vc is made several times the polarization deterioration voltage Vd of the electrostrictive plate used in the bimorph element, the electrostrictive plate does not deteriorate. Therefore, it is possible to obtain a displacement several times that of a conventional piezoelectric actuator.

Also, pn turns on the voltage limiting circuit at a constant voltage.
Since it is configured using a pn element circuit, a high voltage is applied at the moment the polarity of the voltage applied to the electrostrictive plate switches from the same direction as the polarization direction to the opposite direction, and after a certain short period of time has passed, the polarization changes. A voltage that does not cause deterioration, or even if it occurs, an applied voltage V that is applied in the same direction at the next polarity reversal.
The applied voltage value gradually decreases to a voltage that is offset by the polarization effect of c.

Therefore, it is possible to obtain strong generated force when switching polarity,
Even when high-speed operation is required, a sufficient amount of displacement can be ensured.

Since the present invention has the above-mentioned effects, it can be applied to coin processing devices, relays, and impact printer heads.

Extremely effective for driving small pumps, etc.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a timing chart showing the operation of the embodiment of FIG. 1, and FIG.
The figure is a characteristic diagram showing the relationship between the displacement amount δ and the operating time of this embodiment, FIG. 4 is a block diagram showing another embodiment of the present invention, and FIG. 5 is a diagram showing the operation of the embodiment of FIG. 4. 6 is a timing chart showing still another embodiment of the present invention, FIG. 7 is a block diagram showing still another embodiment of the present invention, and FIG. 8 is a block diagram showing still another embodiment of the present invention. A block diagram showing the embodiment, FIG. 9 is a timing chart showing the operation of the embodiment of FIG. 8, FIG. 10 is a block diagram showing still another embodiment of the present invention, and FIG. 11 shows a conventional piezoelectric actuator. 12 is a characteristic diagram showing the relationship between power supply voltage E and displacement amount δ when a conventional piezoelectric actuator is operated at an operating frequency of 2 Hz, and FIG. FIG. 2B is a side view showing the operation of the bimorph element 1. FIG. DESCRIPTION OF SYMBOLS 1... Bimorph element, 2... Drive input circuit, 3...
...Polarity switching circuit, 4... Constant voltage circuit, 5... Control circuit, 21.22... Voltage limiting circuit, 210, 220
...Shockley diode, 212, 222...
- Thyristor, Hl, Hz...electrostrictive plate, S...center electrode, Tl, T2...electrode.

Claims (5)

[Claims] (1) Each has at least one electrostrictive plate polarized in the thickness direction on both sides of the central electrode, and each electrostrictive plate has an electrode on the surface facing the central electrode, and is symmetrical with respect to the central electrode. A bimorph element with the polarization direction of the electrostrictive plates arranged in the same position, and an electrode in contact with the positive polarization plane of each electrostrictive plate on the electrostrictive plate side where the negative polarization plane is in contact with the center electrode, respectively. Connect the cathode of the first voltage limiting circuit, and connect the anode of the second voltage limiting circuit to each electrode in contact with the negative polarization surface of each electrostrictive plate on the electrostrictive plate side whose positive polarization surface is in contact with the center electrode. The anode of the first voltage limiting circuit and the cathode of the second voltage limiting circuit are used as one drive input terminal, and the center electrode and the unconnected electrode of the voltage limiting circuit are used as the other drive input terminal. A drive input circuit as a terminal, a constant voltage circuit for applying voltage to the drive input circuit, and a voltage circuit between the constant voltage circuit and the drive input circuit that controls the polarity of the voltage applied to the drive input terminal of the drive input circuit. In the piezoelectric actuator equipped with a switching polarity switching circuit, at least one of the first or second voltage limiting circuit is configured with a pnpn element circuit that turns on at a constant voltage, and the pnp
The anode of the n-element circuit corresponds to the cathode of the constant voltage circuit, pnpn
A piezoelectric actuator characterized in that a cathode of an element circuit is connected to correspond to an anode of a constant voltage circuit. (2) The piezoelectric actuator according to claim 1, wherein the pnpn element circuit comprises a thyristor, which is a pnpn element, and a Zener diode that turns on the thyristor when a certain voltage is applied. (3) A pnpn element circuit includes a thyristor which is a pnpn element, a first Zener diode that turns on the thyristor when a certain voltage is applied, and a second Zener diode connected in series with the thyristor with opposite polarity. A piezoelectric actuator according to claim 1, comprising a Zener diode. (4) The piezoelectric actuator according to claim 1, wherein the pnpn element circuit includes a Zener diode or a diode connected in parallel with the pnpn element with opposite polarity. (5) The supply voltage Vc of the constant voltage circuit is higher than the polarization deterioration voltage Vd of the electrostrictive plate, and the voltage V normally limited by the voltage limiting circuit except when switching polarity is (Vc-Vd)/2<V A piezoelectric actuator according to claim 1, which satisfies <Vc.