JPH0350511B2 - - Google Patents

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 devices 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 tyranate 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 the piezoelectric transverse effect to displace the free end.

This type of actuator uses a co-polarized bimorph element in which the polarization directions of the electrostrictive plates H1 and H2 (in the direction of arrow A) coincide with each other, as shown in FIG. Electrostrictive plate H as shown
1 and H2 polarization directions (direction of arrow B) are opposite to each other, and are broadly classified into those using oppositely polarized bimorph elements.

In these two types, if you want to obtain a large displacement with a low voltage, use a co-polarized bimorph device in which voltage is applied to both electrostrictive plates H1 and H2 at the same time (Fig. 11). ) is advantageous.

[Problem that the invention seeks to solve]

However, in the case of the conventional driving method as shown in FIG. 11A, one electrostrictive plate has a
Since the power supply voltage E is applied to the other electrostrictive plate in the opposite direction to the polarization direction, the electrostrictive plate to which the voltage is applied in the opposite direction may be depolarized.

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

In the same figure, the curve A indicated by the broken line is the 11th
This relates to a piezoelectric actuator of the type shown in Figure A. According to this piezoelectric actuator,
At about 80V, the polarization is destroyed and the displacement 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 to the electrostrictive plates H1 and H2 in the opposite polarization direction, so it cannot be used. The polarization breakdown voltage Vp of the bimorph device is
It turns out that it is 80V.

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 not be destroyed, but the polarization will be reduced. 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) at a certain applied voltage.
The voltage value at this time is called a polarization deterioration voltage Vd.

In the case of a piezoelectric actuator with the characteristics shown by curve A in Figure 12, the polarization deterioration voltage Vd of the bimorph element used is about 30V, and the polarization deterioration voltage Vd directly becomes the limit of the power supply voltage of the piezoelectric actuator. , a displacement δ of only about 1 mm can be obtained.

Additionally, piezoelectric actuators are generally required to have 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. 13A is a side view showing the operation of the bimorph element 1, and FIG. If we calculate the change in speed during the transition from the state shown by the solid line to the state shown by the broken line after switching the polarity, it will be as shown in Figure 13 (b), where it will quickly displace to a certain position, but after that the speed will rapidly slow down. , it has the characteristic that it takes time to reach the final position.

Therefore, when vibrating at high speed, the polarity may be reversed before the displacement is sufficiently tight, and the amount of displacement 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 that connects a polarized electrostrictive plate to a polarized electrostrictive plate.
In a piezoelectric actuator that supplies a voltage higher than the polarization deterioration voltage while alternating polarity, the voltage limiting circuit does not limit the voltage supplied to the electrostrictive plate when it is in the same direction as the polarization, but when it is in the opposite direction. It has a characteristic that the voltage decreases according to a predetermined time constant until the voltage is below the polarization deterioration 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. applied.

In addition, since the voltage limiting circuit is configured with a pnpn element circuit that turns on at a constant voltage, 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.
Thereafter, the applied voltage value gradually decreases.

〔Example〕

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

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

The piezoelectric actuator includes a co-polarized bimorph element 1, a drive input circuit 2, a polarity switching circuit 3, a constant voltage circuit 4, a control circuit 5, and a DC power supply 6.

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

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

Furthermore, electrodes T1 and T2 are arranged on the sides of these electrostrictive plates H1 and H2 that face the center electrode S.
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. Note that the cathode side and anode side of the voltage limiting circuits 21 and 22 refer to the cathode side and anode side of Zener diodes 211 and 221, which are internal elements of the respective circuits to be described later.

The other ends of each of the voltage limiting circuits 21 and 22 are
After being connected in common, they are 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 circuits 21 and 22 are characterized by Zener diodes 211 and 221 being connected in parallel to a pnpn element circuit including thyristors 212 and 222 which are pnpn elements.

In the voltage limiting circuit 21, a series body of a Zener diode 215 and a thyristor 212 is connected in parallel with a series body of a resistor 217 and a Zener diode 211. In this case, the Zener diode 21
5, the anode side is connected to the terminal A like the Zener diode 211, and the cathode side is connected to the thyristor 212.
connected to the cathode of The anode side of this thyristor 212 is connected together with the cathode of the Zener diode 211 to an electrode T1 in contact with the positive polarization surface of the electrostrictive plate H1.

In addition, a resistor 214 is connected to the gate of the thyristor 212.
and the anode of the Zener diode 213 are connected, and the other end of the resistor 214 is connected to the thyristor 212.
The other end (cathode) of the Zener diode 213 is connected to the cathode of the thyristor 212 . Furthermore, a diode 216 is connected in parallel to a resistor 217 such that its cathode is connected to the anode side of the Zener diode 211.

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

In addition, a resistor 224 is connected to the gate of the thyristor 222.
and the anode of the Zener diode 223 are connected, 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 anode of the thyristor 222. Furthermore, the anode is a Zener diode 2
Diode 2 is connected to the anode side of 21.
26 is connected in parallel to the resistor 217.

Note that the polarization deterioration voltages of the electrostrictive plates H1 and H2 are vd (H1) and vd (H2), and the operating voltages of the Zener diodes 211 and 221 are V (ZD211) and V
(ZD221), and the voltage applied between terminals AB is Vc, Vd (H1), Vd (H2) < Vc ... (1) Vc - Vd (H1) / 2 < V (ZD211) < Vc ... (2) ) Vc−Vd(H2)/2<V(ZD221)<Vc...(3) is satisfied.

In addition, Zener diodes 211, 221, 2
The operating voltages of 15, 225, 213, and 223 are V (ZD211), V (ZD221), V (ZD215), and V, respectively.
(ZD225), V (ZD213), V (ZD223), and the terminal
If the voltage applied between AB is Vc, then V(ZD215)<V(ZD211)...(4) V(ZD211)-V(ZD215)<V(ZD213)<2Vc-
V(ZD215)……(5) V(ZD225)＜V(ZD211)……(6) V(ZD221)−V(ZD225)＜V(ZD223)＜2Vc−
V (ZD225)... satisfies the relationship (7).

The output side of the polarity switching circuit 3 is connected between the forward air terminal A and the terminal C, and is connected in a Darlington manner.
a pair of pnp transistors 301, a pair of pnp transistors 302 whose output sides are connected between the terminals B and C and are Darlington connected, an npn transistor 303 whose output side is connected between the terminals A and D, and It has an npn transistor 304 whose output side is connected between terminals B and D.

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

Further, the base of the transistor 306 is connected to the resistor 31.
2 to the output side of the inverter 313. The base of a transistor 304 is connected to the output side of this inverter 313 via a resistor 309.

The input side (base) of the transistor pair 302 is connected to the collector of a transistor 305 via a resistor 307, and 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, and further connected to the control circuit 5
It is connected to the.

Furthermore, the base of the transistor 303 is connected to the resistor 30.
8 to the input side of the inverter 313.

The control circuit 5 controls switching of the polarity of the voltage applied to the bimorph element 1 by alternately turning on and off the combination of the transistor pair 301 and the transistor 304 and the combination of the transistor pair 302 and the transistor 303 of the polarity switching circuit 3. , resistance 50
1. Selector switch 502 and 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 of a self-excited oscillation step-up type.
Ringing chain using pnp transistor
It is a DC/DC converter.

That is, the constant voltage circuit 4 includes a saturation type transformer 41 having three coils 411, 412, 413 wound in the same direction, a capacitor 404, resistors 403, 406, a pnp transistor 405, a diode 402, and a zener diode 401. It is structured accordingly.

The emitter of the transistor 405 is connected to the coil 41
The collector is connected to one end of the coil 411, together with one end of the coil 411, to the positive end F of the DC power supply 6 (power supply voltage Ec). Further, after the other end of the coil 412 and one end of the coil 413 are connected in common,
It is 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 the start resistor 4
06 to the ground terminal G along with the other end of the coil 411, and further connects the Zener diode 401
connected to the anode of zener diode 4
The cathode of 01 is connected to the output terminal E, and this output terminal E
A capacitor 407 is connected between the terminal G and the ground terminal 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.

When a voltage Ec (actually about 5 V) is applied from the DC power supply 6 by a switch (not shown), a current flows through the start resistor of the constant voltage circuit 4 and turns on the transistor 405. Collector current is transformer 41
When the voltage flows through the coil 411 of growing.

Eventually, when the magnetic flux of the coil of the transformer 41 is saturated and the collector current stops flowing, the coils 412,
The induced voltage of 413 is inverted. Therefore, the voltage of the coil 413 is applied to the capacitor 407 and charged. This current causes the coils 412, 413 to
When the magnetic flux decreases, the reversed induced voltage becomes low, and current flows again from the DC power supply 6 to the base circuit of the transistor 405 via the coil 412, so the transistor 405 turns on and the coil 41
1,412,413 are 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
(ZD401), when the voltage of the capacitor 407 reaches [Ec+V(ZD401)], the Zener diode 401 becomes conductive, so no current flows through the base circuit consisting of the resistor 403 and the capacitor 404, and oscillation stops. When the load is connected and the voltage of capacitor 407 decreases, oscillation starts again and [EC
+V (ZD401)] voltage is maintained.

In this way, in the constant voltage circuit 4, the DC power supply 6
The voltage Ec 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. 1, the output of the inverter 313 becomes Ec, so the transistor 304 is turned on, and since the transistor 306 is also turned on, the Darlington transistor pair 301 is also turned on. Become. Eventually, in the bridge circuit, the switch elements of transistor pair 301 and transistor 304 connected in parallel are turned on, so that terminal A is connected between terminals A and B.
The voltage Vc appears so that the side is positive.

On the other hand, when the switch 502 is connected to the DC power supply 503 in the control circuit 5, the transistor pair
301, the base current of the transistor 304 is cut off, so it is turned off, and the transistor pair 302, transistors 304 and 305 are turned 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. Note that FIG. 2A and B 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. In addition, C in the same figure shows the amount of displacement of the free end of the bimorph element 1, and the positive direction of the vertical axis is the first
This corresponds to the upward displacement in the figure.

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, 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 H2 has Vc-V (ZD221) in the opposite direction to the polarization.
is applied.

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 T1 on the upper surface of the electrostrictive plate H1 becomes equal to the voltage of the terminal B. The voltage Vc that had been charged up to that point is applied to the strain plate H1, so the voltage becomes 2Vc. That is,
A voltage of 2Vc is applied to the series circuit of Zener diodes 213 and 215. From equation (5), V
(ZD213)+V(ZD215)<2Vc, so thyristor 2
A trigger current flows through the gate of thyristor 212, turning on thyristor 212.

Here, the resistor 217 is the Zener diode 21
The resistance value is sufficiently higher than the impedance of the 3,215 series circuit. With this setting, when 2Vc is applied to the voltage limiting circuit 21, the current mainly flows through the Zener diode 213,
215 and can therefore ensure that thyristor 212 is fired.

The charging current to the electrostrictive plate H1 is from terminal B to electrostrictive plate H.
1-thyristor 212-zener diode 21
Since the voltage flows through the path of 5-terminal A, the voltage applied to the electrostrictive plate H1 is Vc-V in the opposite direction to the polarization.
(ZD215). The situation at this time is shown in Figure 2A.

After being charged in this way, since the resistor 23 has a high resistance of several MΩ, the thyristor 2
Only an extremely small amount of current flows through the thyristor 212, and the thyristor 212 self-resets. That is, the pnpn element circuit is in a cut-off state.

Thereafter, the charge on the electrostrictive plate H1 is discharged through the resistor 23 until the voltage on the electrostrictive plate H1 becomes Vc-V (ZD211). The second scene shows what happened at this time.
This is a diagram.

On the other hand, the time point corresponding to 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.
Since the Zener diode 221 and the diode 226 are in the forward direction, Vc is applied to the electrostrictive plate H2 in the same direction as the polarization as shown in FIG.
Voltage Vc is maintained until the polarity of the voltage applied between AB is reversed.

Next, when the polarity is reversed again, a voltage of Vc-V (ZD225) is applied to the electrostrictive plate H2 as shown in Figure 2 (b), and as the thyristor 222 self-recovers, it becomes Vc-V (ZD221). . In addition, electrostrictive plate H
1, in the same direction as the polarization as shown in Figure 2 A.
Vc is applied.

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. 2C.

That is, 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 expand, so the bimorph element 1 The free end of 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 (time point, ). Since the voltage decreases to a level that does not cause deterioration due to the electric current, displacement occurs with a large and strong force when switching polarity (displacement amount ξ1, ξ
2) However, 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.

In this embodiment, if the voltage Vc applied between the terminals AB 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 opposite polarization directions of the electrostrictive plates H1 and H2 are approximately as shown by the dashed lines in FIG.
Since the voltage Vc is applied, a larger displacement can be achieved (displacement amounts ξ3, ξ4) as shown by the dashed line in FIG. 2C.

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 is used. Operating voltage V of diodes 211 and 221
(ZD211) and V(ZD221) must satisfy Vc-Vd<V(ZD211), V(ZD221)<Vc (8).

However, if the polarity is continuously switched and used with vibration, the polarization degradation voltage will occur in the same direction as the polarization.
Since a voltage higher than Vd is applied, the once depolarized polarization is regenerated. Therefore, even if the operating voltage of the Zener diodes 211 and 221 is lowered to such an extent that the above equations (2) and (3) are satisfied, a voltage greater than the polarization deterioration voltage Vd is applied in the opposite polarization direction of the electrostrictive plates H1 and H2. Does not cause deterioration of polarization.

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

Bimorph element 1 size: 45 mm 1 x 12 mmw x 0.15 mmt Polarity switching frequency: 2 Hz Under the conditions of environmental temperature of 70°C, the characteristics of this example when VC = 80V V(ZD215), V(ZD225) = 20V Indicated by solid line A. The solid line B indicates the Zener diode 215,
This shows the characteristics when 225 is removed.

Furthermore, the broken line C shows the characteristics of the conventional device (FIG. 1A) 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, and the same or corresponding parts as 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 H
This is a circuit for driving a bimorph element with a large displacement, in which the polarization deterioration voltage Vd of 1.H2 is low and a voltage cannot be applied for a long time in the opposite direction to the polarization.

The drive input circuit 2 is the same as the first embodiment in that it includes voltage limiting circuits 21, 22 and high resistances 23, 24, but the configurations of the voltage limiting circuits 21, 22 are different.

That is, in the voltage limiting circuit 21, the cathode is connected to the terminal A.
The anode is connected to the electrode T1.
Thyristor 212, which is a pnpn element, and Zener diode 2 connected in parallel to thyristor 212
18 and a resistor 214 in series. Furthermore, a Zener diode 2 is connected to the anode side of the thyristor 212.
18 cathodes are connected, and one end of a resistor 214 is connected to the cathode side of the thyristor 212. Further, the gate of the thyristor 212 is connected to the connection point between the Zener diode 218 and the resistor 214.

The voltage limiting circuit 22 includes a thyristor 22 whose anode is connected to the terminal A and whose cathode is connected to the electrode T2.
2, a Zener diode 228 connected in parallel to the thyristor 222, and a resistor 224 in series. Note that 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 shown in 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 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 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. 5A).

On the other hand, if the operating voltages V(ZD218) and V(ZD228) of the Zener diodes 218 and 228 are Vc<V(ZD218) and V(ZD228)<2Vc, as shown in FIG. Since no voltage is applied, the tip of the bimorph element 1 moves upward ξ only by the contraction of the electrostrictive plate H1.
Displaced by 12. This situation is shown in FIG. 5C.

Here, if the polarity of the voltage applied between terminals AB is reversed and terminal B is made positive, approximately
Since a voltage of 2Vc is applied, the Zener diode 218 becomes conductive and the thyristor 212 is turned on. When the thyristor 212 is turned on, a voltage of about Vc is applied to the electrostrictive plate H1 in the opposite direction to the polarization, as shown in FIG. 5A. On the other hand, since the Zener diode 228 is in the forward direction, the electrostrictive plate H2 has Vc in the same direction as the polarization, as shown in FIG.
is applied.

That is, voltage Vc is applied to both electrostrictive plates H1 and H2.
is applied, the bimorph element 1 is largely displaced downward as shown in Fig. 5C (ξ1
2).

Next, when the thyristor 212 self-recovers, the charge on the electrostrictive plate H1 is discharged through the high resistance 23, so the displacement of the bimorph element 1 is only due to the contraction of the electrostrictive plate H2, and the amount of displacement is as shown in FIG. As shown in (C), it decreases from ξ21 to ξ22.

Next, when the polarity is reversed again and terminal A becomes positive,
Since a voltage of Vc is applied to each of the electrostrictive plates H1 and H2, the tip of the bimorph element 1 is largely displaced upward to ξ11, as shown in FIG. 5C.

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

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

FIG. 6 is a block diagram showing still another embodiment of the present invention, which differs from the embodiment shown in FIG. 4 only in the internal circuits of voltage limiting circuits 21 and 22.

Voltage limiting circuit 21 includes a diode 219 whose anode is connected to terminal A and whose cathode is connected to electrode T1, and a thyristor 212 whose anode is connected to electrode T1 and whose cathode is connected to terminal A. Further, a series body consisting of a Zener diode 218 and a resistor 214 is connected in parallel to the thyristor 212 such that the anode of the thyristor 212 is connected to the cathode of the Zener diode 218 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 222 whose cathode is connected to the electrode T1 and whose anode is connected to the terminal A.
22, a Zener diode 228 and a resistor 22
4 are connected in parallel such that the anode of the thyristor 222 and the anode of the Zener diode 228 are connected. In addition, the thyristor 22
The gate of 2 is a Zener diode 228 and a resistor 2.
Connects to 24 connection points.

This embodiment avoids using the series circuit of resistors 214, 224 and Zener diodes 218, 228 for charging the electrostrictive plates H1, H2 in the embodiment shown in FIG.
229 is added, and the charging time constant becomes smaller, so charging is faster and displacement is 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 T1, and a Schottley diode 210 whose anode is connected to the electrode T1 and whose cathode is connected to the terminal A. is a diode 229 whose anode is connected to electrode T2 and whose cathode is connected to terminal A.
and a Schottley diode 220 whose cathode is connected to electrode T1 and whose anode is connected to terminal A.

This embodiment is based on the embodiment shown in FIG.
The pnpn element circuit consisting of pnpn elements 2 and 2 is replaced with pnpn elements, ie, pnpn elements, 210 and 220, respectively.
10 and 220 are assumed to be turned on when a voltage of 2 Vc or less is applied in the forward direction, and operate in the same manner as the embodiment shown in FIG.

FIG. 8 is a block diagram showing still another embodiment. Similar to the embodiment shown in FIG. This is another embodiment in which the terminal B is normally held positive, and the circuit is suitable for a driving method in which the polarity is reversed in a pulsed manner as necessary.

The configuration of this embodiment differs from the embodiment shown in FIG. 3 in that the internal circuits of the voltage limiting circuits 21 and 22 are different, and the high resistance 24 is removed.

Voltage limiting circuit 21 includes a diode 219 whose anode is connected to terminal A and whose cathode is connected to electrode T1. The diode 219 includes a thyristor 212 and a Zener diode 21 whose anodes are connected to each other.
5 are connected in parallel such that the anode of the diode 219 and the anode of the Zener diode 215 are connected. A series body consisting of a Zener diode 213 and a resistor 214 is connected in parallel to the thyristor 212 such that one end of the resistor 214 and the cathode of the thyristor 212 are connected. and,
The gate of the thyristor 212 is connected to the connection point between the Zener diode 213 and the resistor 214.

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 shown in 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 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 terminal B is positive, no voltage is applied to the electrostrictive plate H1 as shown in Figure 9A, and Vc is applied only to the electrostrictive plate H2 in the polarization direction as shown in Figure 9B. . Therefore, no deterioration of polarization occurs in this state.

When the polarity is reversed, the electrostrictive plate H1 has a polarization direction
Vc is applied to the electrostrictive plate H2 in the opposite direction.
(ZD221) is applied, so there is a large upward displacement (ξ1).

After a short period of time, when the polarity is reversed again, the thyristor 212 turns on, so the electrostrictive plate H1
Vc-V (ZD215) is applied in the opposite direction, and the tip of the bimorph element 1 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. 9A.

On the other hand, since Vc is again applied to the electrostrictive plate H2, the slight depolarization that had previously occurred due to the application of Vc - V (ZD221) in the opposite polarization direction is canceled out by the amplification effect described above. Therefore, no deterioration occurs.

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

Here, the 6-layer bimorph element means that the central electrode S
A pair of electrostrictive plates H11 and H21 are arranged so that their polarization directions are in the same direction, and a pair of electrostrictive plates H12 and H22 are arranged so that their polarization directions are in the same direction. It is arranged so as to face the polarization, and furthermore, a pair of electrostrictive plates H13 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 circuits 21 and 22 in the drive input circuit 2 are connected as shown in FIG. It shows good things.

〔Effect of the invention〕

As explained above, according to the piezoelectric actuator of the present invention, the piezoelectric actuator supplies a voltage higher than the polarization deterioration voltage to the polarized electrostrictive plate through the voltage limiting circuit while alternating the polarity. The circuit has a characteristic that when the voltage supplied to the electrostrictive plate is in the same direction as the polarization, it is not restricted, but when it is in the opposite direction, it decreases according to a predetermined time constant to a voltage below the polarization deterioration voltage. 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 after a certain short period of time has passed, the voltage is increased to such an extent that no deterioration of polarization occurs, or even if it occurs. The applied voltage value gradually decreases to a voltage that is offset by the polarization action of the applied voltage Vc applied in the same direction at the next polarity reversal.

Therefore, a strong generated force can be obtained during polarity switching, and even when high-speed operation is required, a sufficient amount of displacement can be ensured.

Since the present invention has the above effects, it can be used in coin processing devices, relays, 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 shown in FIG. 1, FIG. 3 is a characteristic diagram showing the relationship between displacement δ and operating time in this embodiment, and FIG. 4 is another embodiment of the present invention. 5 is a timing chart showing the operation of the embodiment of FIG. 4, FIG. 6 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, FIG. 9 is a timing chart showing the operation of the embodiment of FIG. 8, and FIG. Fig. 10 is a block diagram showing still another embodiment of the present invention, Fig. 11 is a schematic configuration diagram showing a conventional piezoelectric actuator, and Fig. 12 shows the power supply voltage when the conventional piezoelectric actuator is operated at an operating frequency of 2 Hz. A characteristic diagram showing the relationship between E and the amount of displacement δ, FIG. 13A is a side view showing the operation of the bimorph element 1, and FIG. It is a characteristic diagram. 1... Bimorph element, 2... Drive input circuit,
3... Polarity switching circuit, 4... Constant voltage circuit, 5...
Control circuit, 21, 22... Voltage limiting circuit, 21
0,220...Shockley diode, 21
2,222...thyristor, H1, H2...electrostrictive plate, S...center electrode, T1, T2...electrode.

Claims (1)

[Scope of Claims] 1. A piezoelectric actuator that supplies a voltage higher than a polarization deterioration voltage to a polarized electrostrictive plate H1 via a voltage limiting circuit 21 while alternating its polarity, the voltage limiting circuit comprising: first voltage supply means 217, 2 for supplying the supply voltage to the electrostrictive plate without reducing the supply voltage when the polarity is the same as the polarization direction of the electrostrictive plate;
11, when the polarity of the supply voltage is opposite to the polarization direction of the electrostrictive plate, the voltage applied to the electrostrictive plate is lower than twice the supply voltage and higher than the polarization deterioration voltage; a second voltage supply means 212, 215 that temporarily sets the voltage so that the electrostrictive plate is switched, and cuts off the voltage when the current flowing through the electrostrictive plate at the time of polarity switching becomes smaller than a predetermined value; third voltage supply means 211, 217 for limiting the supply voltage to a value equal to or less than the polarization deterioration voltage at the time when the current flowing in the current becomes smaller than the predetermined value;
A piezoelectric actuator comprising the above, wherein the time from the polarity switching point until the polarization degradation voltage becomes lower than or equal to the polarization deterioration voltage is longer than the displacement time of the actuator.