JP2005318725A - Circuit and method for driving piezoelectric bimorph element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To get large displacement by preventing deterioration caused by the polarization inversion of a piezoelectric bimorph element. <P>SOLUTION: In a driving circuit 30 for the piezoelectric bimorph element 10 where one piezoelectric element and the other piezoelectric element are arranged across a middle electrode 4c so that directions of their polarizations P may be the same, a drive input circuit 20 is composed of: one rectifying diode 3a which is connected in the direction of applying a current in the direction of the polarization of one piezoelectric element to one piezoelectric element; one capacitor 2a which is connected in parallel with one rectifier diode; the other rectifier diode 3b which is connected in the direction of applying a current in the direction of the polarization of the other piezoelectric element; the other capacitor 2b which is connected in the direction of applying a current in the direction of the polarization of the other piezoelectric element; a common joining terminal 5a which connects in common one connection end between one rectifier diode and one capacitor not connected to one piezoelectric element and the other connection end between the other rectifier diode and the other capacitor not connected to the other piezoelectric element; and a middle joining terminal 5c. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an actuator using a piezoelectric bimorph element, and belongs to a technical field related to a driving circuit and a driving method for a piezoelectric bimorph element.

  Piezoelectric bimorph elements are a type of actuator that uses the reverse piezoelectric effect of generating a strain proportional to the applied electric field of piezoelectric ceramics. In recent years, piezoelectric bimorph elements have been used in consumer equipment as control of minute displacements and output terminal devices. Yes.

  A piezoelectric bimorph element using two piezoelectric elements is conventionally known, and its structure is described, for example, in FIG. 2 of JP-A-61-30974. The piezoelectric element used for the piezoelectric bimorph is previously polarized. However, when the voltage exceeding the polarization degradation voltage Vec corresponding to the coercive electric field is applied in the opposite direction to the polarization direction of the piezoelectric element, the polarization direction P is reversed. It becomes unusable.

  A voltage higher than the polarization degradation voltage can be applied in the forward direction, but since the same voltage is applied in the forward and reverse directions on the circuit, the piezoelectric element used for the piezoelectric bimorph exceeds the polarization degradation voltage Vec. Had to be used with no range. As an improved technique of this technique, a technique for applying a voltage only in the forward direction by using a rectifier diode is disclosed in FIG. 9 of JP-A-9-65669.

  A technique for controlling the voltage applied in the reverse direction to be equal to or lower than the polarization degradation voltage using a constant voltage diode is disclosed in FIG.

Hereinafter, a conventional driving circuit will be described.
(1) Prior art 1 (FIG. 6 of the present application)
FIG. 2 (2) and Japanese Patent Laid-Open No. 61-30974 (Patent Document 1) Prior Art 2 (FIG. 8 of the present application)
FIG. 9 of Japanese Patent Laid-Open No. 9-65669 (Patent Document 2)
(3) Prior art 3
FIG. 1 of Japanese Patent Application Laid-Open No. 61-30974 (Patent Document 1) The symbols and names described in the gazette are indicated by (), and then the symbols and names in this application are indicated in [].

(1) Drive Circuit of Conventional Technology 1 FIG. 6 is a drive circuit diagram of Prior Art 1. Prior art 1 will be described with reference to FIG.

  In FIG. 6, a piezoelectric actuator (10) [30] has two electrostrictive plates (15), (16) [piezoelectric elements 1a, 1b] bonded together with a central electrode (17) [4c] interposed therebetween. Is formed by. Electrodes (18), (19) [surface-side electrodes 4a, 4b] are provided on one end face of the electrostrictive plates (15), (16), and are interposed between the electrostrictive plates (15), (16). A central electrode (17) [intermediate electrode 4c] is provided.

(2) Drive Circuit of Conventional Technology 2 FIG. 8 is a drive circuit diagram of Conventional Technology 2. Prior art 2 will be described with reference to FIG.

  In FIG. 8, a drive voltage is applied to the electrodes (2a), (3a) [surface-side electrodes 4a, 4b] from the external power supply via the diodes (6), (7) [rectifier diodes 3a, 3b]. In addition, the common electrode (5) [intermediate electrode 4c] is grounded.

  In this piezoelectric bimorph drive circuit, the voltage is applied only in the forward direction with respect to the polarization direction P by using the rectifier diode (6) and the rectifier diode (7) [rectifier diodes 3a, 3b]. In the circuit of FIG. 8, since no voltage is applied in the direction opposite to the polarization direction P, there is no possibility that the polarization direction P is reversed. In this prior art 2, the two piezoelectric plates (2), (3) [piezoelectric elements 1a, 1b] are each driven by unimorph, and are switched and driven by the sign of the electric field. In this circuit, a voltage can be applied to the piezoelectric element without being restricted by the polarization deterioration voltage Vec, and as a result, a displacement larger than that of the prior art 1 can be obtained.

(3) Driving circuit of prior art 3 Prior art 3 will be described with reference to FIG. 1 of Japanese Patent Laid-Open No. 61-30974. The piezoelectric bimorph type piezoelectric actuator (10) of the prior art 3 has a cathode of a constant voltage diode (ZD1) connected to an electrode (18) having a positive polarization, and is connected to an electrode (19) having a negative polarization. A drive input circuit (12a) formed by a terminal connected to the anode of another constant voltage diode (ZD2) and having the other ends of both constant voltage diodes shared, and a central electrode (17), and this drive input Drive circuit (13a) for supplying a constant voltage to the circuit (12a), and the voltage supplied to the electrostrictive plates (15) and (16) [piezoelectric elements 1a, 1b] is equal to or lower than the polarization degradation voltage Vec. Thus, it is the piezoelectric actuator (10) which set the limiting voltage (Vzd1) and (Vzd2) of the constant voltage diodes (ZD1) and (ZD2). It is disclosed in Patent Document 1 that a displacement larger than that of the prior art 1 can be obtained by this circuit.

The patent documents are as follows.
JP 61-30974 A JP-A-9-65669

(1) Problems of conventional technique 2 Problems of conventional technique 2 are as follows. In the piezoelectric bimorph drive circuit of the prior art 2, the two piezoelectric plates (2) and (3) [piezoelectric elements 1a and 1b] are substantially unimorph driven by the drive circuit described above. In addition, there is a problem that a high voltage in the forward direction and a low voltage not exceeding the polarization degradation voltage in the reverse direction cannot be applied at the same time to maximize the performance of the piezoelectric body.

(2) Problems of Conventional Technology 3 Problems of Conventional Technology 3 are as follows. In the configuration diagram of this prior art 3, when the limiting voltages (Vzd1) and (Vzd2) of the constant voltage diodes (ZD1) and (ZD2) connected in series to the electrostrictive plate (15) or (16) are reduced, the voltage is applied. There is a problem that the maximum value of the drive voltage that can be generated is reduced and the maximum displacement is limited.

  On the contrary, if the limiting voltages (Vzd1) and (Vzd2) of the constant voltage diode are increased, it is possible to obtain a larger displacement than that of the prior art 1. However, when the driving voltage is lower than the limiting voltage, the voltage is applied to the constant voltage diode. Therefore, even if the limit voltage is increased too much, the effect of improving the displacement is small. In addition, as the drive voltage (Vd) increases, the voltage applied to the electrostrictive plate (15) or (16) becomes substantially non-linear and it is difficult to control the displacement linearly. Has occurred.

  Furthermore, when the constant voltage diodes (ZD1) and (ZD2) and the electrostrictive plate (15) or (16) are connected in series, when the drive voltage exceeds the limit voltages (Vzd1) and (Vzd2), A current flows into the electrostrictive plate (15) or (16), and a voltage greater than the difference between the drive voltage (Vd) and the limiting voltages (Vzd1) and (Vzd2) is greater than the electrostrictive plate (15) or (16 ). For this reason, the subject that the voltage more than a polarization degradation voltage is applied to a piezoelectric element, and the electrostrictive plate (15) or (16) is depolarized also arises.

Means for solving the problems are as follows. FIG. 1 is a drive circuit of a piezoelectric bimorph element having the configuration of the present invention. In the figure, a piezoelectric bimorph element 10 formed of one piezoelectric element 1a and the other piezoelectric element 1b arranged so that the polarization direction P is the same across the intermediate electrode 4c, and driven by the piezoelectric bimorph element 10 In the drive circuit 30 of the piezoelectric bimorph element formed from the drive input circuit 20 that applies the drive voltage supplied from the power source,
The drive input circuit 20 is
One rectifier diode 3a connected to one piezoelectric element 1a in a direction of energizing in the forward direction with the polarization direction P of one piezoelectric element 1a;
One capacitor 2a connected in parallel to one rectifier diode 3a;
The other rectifier diode 3b connected to the other piezoelectric element 1b in a direction of energizing in the forward direction with the polarization direction P of the other piezoelectric element 1b;
The other capacitor 2b connected in parallel to the other rectifier diode 3b;
One connection end of one rectifier diode 3a and one capacitor 2a not connected to one piezoelectric element 1a and the other connection of the other rectifier diode 3b and the other capacitor 2b not connected to the other piezoelectric element 1b A common connection terminal 5a having a common end;
It is a drive circuit of the piezoelectric bimorph element formed from the intermediate electrode connection terminal 5c connected to the intermediate electrode 4c.

The effects of the invention are compared with the prior art as follows. (See Fig. 1 and Fig. 2)
In the piezoelectric bimorph drive circuit of the prior art 2, as described above, a high voltage in the forward direction and a low voltage not exceeding the polarization degradation voltage are simultaneously applied in the reverse direction to maximize the performance of the piezoelectric plate. I can't.

  On the other hand, according to the present invention, firstly, one piezoelectric element 1a and the other piezoelectric element 1b are connected in parallel to a driving power source, and both positive and negative half waves of the AC power supply voltage are simultaneously applied to both piezoelectric elements. Applied. Therefore, a large displacement can be obtained if the driving voltage is the same as in the prior art 2, and conversely, if the displacement is the same, the driving voltage can be lowered.

  In the drive circuit of the piezoelectric bimorph element of the prior art 3, the limiting voltages (Vzd1) and (Vzd2) of the constant voltage diodes (ZD1) and (ZD2) connected in series to the electrostrictive plate (15) or (16) are reduced. Then, the maximum value of the drive voltage that can be applied is reduced and the maximum displacement is limited. Conversely, the effect of improving the displacement is reduced even if the limit voltage is increased too much.

  On the other hand, since the present invention does not use a constant voltage diode, it is not affected by the limiting voltage, and polarization is applied by applying a polarization forward drive voltage in the forward direction and the polarization direction P to one piezoelectric element 1a. Simultaneously with the forward driving, it is possible to drive the piezoelectric bimorph by simultaneously applying the reverse polarization driving voltage in the opposite direction to the polarization direction P of the other piezoelectric element 1b, so that a larger distortion rate can be generated.

  Similarly, in the drive circuit of the piezoelectric bimorph element of the prior art 3, even when the limiting voltages (Vzd1) and (Vzd2) of the constant voltage diode are appropriately increased, the electrostrictive plate (substantially) with respect to the increase of the drive voltage ( The voltage applied to 15) or (16) becomes nonlinear and it is difficult to control the displacement linearly.

  On the other hand, since the present invention does not use a constant voltage diode, the displacement can be controlled linearly.

The best mode for carrying out the invention is as follows. A piezoelectric bimorph element formed from one piezoelectric element 1a and the other piezoelectric element 1b disposed so that the polarization direction P is the same across the intermediate electrode 4c by the above-described drive circuit for the piezoelectric bimorph element in FIG. In the method of driving
One rectifier diode 3a is connected to one piezoelectric element 1a in the forward direction with the polarization direction P of one piezoelectric element,
One capacitor 2a is connected in parallel to one rectifier diode 3a,
The other rectifier diode 3c is connected to the other piezoelectric element 1b in the forward direction with the polarization direction P of the other piezoelectric element,
The other capacitor 2b is connected in parallel to the other rectifier diode 3b,
One connection end of one rectifier diode 3a and one capacitor 2a not connected to one piezoelectric element 1a and the other connection of the other rectifier diode 3b and the other capacitor 2b not connected to the other piezoelectric element 1b Connect the common end to the common connection terminal 5a,
The intermediate electrode 4c is connected to the intermediate electrode connection terminal 5c,
A drive voltage is applied between the common connection terminal 5a and the intermediate electrode connection terminal 5c,
The absolute value of the drive voltage | Vd | and the piezoelectric element 1a, the electrostatic capacitance Cs and capacitor 2a of 1b, Vec a polarization degradation voltage Vec of the electrostatic capacitance _{C 2} and the piezoelectric element _{2b> | Vd | * C 2} / (Cs + C ₂ )
This is a driving method of the piezoelectric bimorph element set in the relationship.

  FIG. 1 is a circuit diagram of a piezoelectric bimorph element drive circuit 30 including a piezoelectric bimorph element 10 and a drive input circuit 20 according to the present invention. 2A to 2C are respectively a waveform diagram of a drive voltage inputted from the outside to the drive circuit 30 of the piezoelectric bimorph element according to the present invention, a waveform diagram of a voltage applied to one piezoelectric element, and the other. It is a wave form diagram of the voltage applied to the piezoelectric element. In FIG. 2, Vd indicates a driving voltage, and t indicates an elapsed time.

[Explanation of FIG. 1]
In FIG. 1, a drive circuit 30 for a piezoelectric bimorph element includes a piezoelectric bimorph element formed from one piezoelectric element 1a and the other piezoelectric element 1b arranged so that the polarization direction P is the same across the intermediate electrode 4c. 10 and a drive input circuit 20 for applying a drive voltage supplied from a drive power source to the piezoelectric bimorph element 10.

  Surface electrodes 4a and 4b are respectively disposed on the surfaces of the piezoelectric elements 1a and 1b opposite to the surface on which the intermediate electrode 4c is provided. Although not shown, it is desirable that the intermediate electrode 4c sandwiches an elastic plate that prevents damage when the piezoelectric bimorph element is greatly displaced, or holds the elasticity.

  The drive input circuit 20 includes one rectifier diode 3a connected in a direction of energizing one piezoelectric element 1a in the polarization direction, one capacitor 2a connected in parallel to the one rectifier diode 3a, and the other The other rectifier diode 3b is connected to the piezoelectric element 1b in the direction of energization in the polarization direction, and the other capacitor 2b is connected in parallel to the other rectifier diode 3b.

  One connection end of one rectifier diode 3a and one capacitor 2a not connected to one piezoelectric element 1a and the other connection of the other rectifier diode 3b and the other capacitor 2b not connected to the other piezoelectric element 1b The end is connected to a common connection terminal 5a, and the intermediate electrode 4c is connected to the intermediate electrode connection terminal 5c. The connection is made between the common connection terminal 5a and the intermediate electrode connection terminal 5c (hereinafter referred to as drive voltage input terminal 5).

  The drive circuit 30 for the piezoelectric bimorph element drives the piezoelectric bimorph element 10 by applying an external drive voltage (not shown) between the drive voltage input terminals 5 of the drive input circuit 20.

  An external drive voltage is applied to the drive circuit 30 of the piezoelectric bimorph element, but the voltage actually applied to the piezoelectric elements 1a and 1b differs depending on the polarities of the rectifier diodes 3a and 3b. For example, when the polarity of the drive voltage is the energization direction of one rectifier diode 3a, the resistance value of the rectifier diode 3a is almost zero, and one capacitor 2a connected in parallel to the one rectifier diode 3a. Does not share voltage. Therefore, an external driving voltage is applied to one piezoelectric element 1a as it is.

As described above, when the polarity of the drive voltage is the energization direction of one rectifier diode 3a, the polarity of the drive voltage is opposite to the energization direction of the other rectifier diode 3b, and the other rectifier diode 3b is high. It becomes a resistance and cuts off current. Therefore, the drive voltage is shared by the other piezoelectric element 1b and the other capacitor 2b and applied to the other piezoelectric element 1b. Proportion of sharing is determined by the electrostatic capacitance C ₂ of the other piezoelectric element 1b of the capacitance Cs and the other capacitor 2b, the voltage applied to the other piezoelectric element 1b driving voltage Vd and the capacitance ratio C ₂ / (Cs + C ₂ ). The polarity of the driving voltage of the next half wave is opposite to the energizing direction of one rectifier diode 3a, and the same function as described above also works when the polarity is the energizing direction of the other rectifier diode 3b.

As described above, since the energization direction of the rectifier diodes 3a and 3b and the polarization direction of the piezoelectric elements 1a and 1b are matched, when the polarity of the drive voltage matches the polarization direction, the drive voltage remains as it is. , 1b and in the direction opposite to the polarization direction, a part of the drive voltage is applied to the capacitors 2a, 2b, so that the voltage applied to the piezoelectric elements 1a, 1b is derived from the drive voltage from the outside. capacitor 2a, a voltage obtained by subtracting the voltage applied to 2b, that is, _{Vd * C 2 / (Cs +} C 2).

  Further, since the piezoelectric elements 1a and 1b are arranged so that the polarization directions are the same with the intermediate electrode 4c interposed therebetween, the piezoelectric elements 1a and 1b are electrically connected in the opposite direction. Therefore, when a voltage in the polarization direction and in the forward direction (the drive voltage from the outside as it is) is applied to one piezoelectric element 1a, simultaneously, a voltage in the direction opposite to the polarization direction (a drive voltage from the outside) is applied to the other piezoelectric element 1b. (The voltage obtained by subtracting the voltage applied to the capacitor 2b).

[Explanation of FIG. 2]
The waveform diagram of FIG. 2 will be described with reference to the drive circuit 30 of the piezoelectric bimorph element of FIG.

  When the drive voltage Vd having the waveform shown in FIG. 2A is input between the drive voltage input terminals 5 of the drive circuit 30 of the piezoelectric bimorph element according to the present invention, the waveform shown in FIG. The voltage of the waveform shown in FIG. 2C is applied to the other piezoelectric element 1b.

  The first half-wave in FIG. 2 shows a case where a voltage in the polarization direction and the forward direction is applied to one piezoelectric element 1a, and a voltage in the direction opposite to the polarization direction is applied to the other piezoelectric element 1b. As shown in the figure, the drive voltage Vd is applied as it is to one piezoelectric element 1a, and a lower voltage is applied to the other piezoelectric element 1b.

  The next half wave in FIG. 2 shows a case where a voltage in the direction opposite to the polarization direction is applied to one piezoelectric element 1a and a voltage in the direction of polarization and forward is applied to the other piezoelectric element 1b. As shown, a voltage lower than the drive voltage Vd is applied to one piezoelectric element 1a, and the drive voltage Vd is applied to the other piezoelectric element 1b as it is.

Here, for example, when the piezoelectric element 1a, the electrostatic capacitance Cs and capacitor 2a of 1b, and the capacitance _{C 2} of 2b same, piezoelectric elements 1a, 1b and the capacitors 2a, the polarization direction is applied to 2b Since the voltages in the opposite directions are the same, the voltage applied to each is ½ of the drive voltage.

  The fact that the voltage applied to the piezoelectric elements 1a and 1b in the direction opposite to the polarization direction is ½ of the drive voltage Vd means that the drive voltage Vd is a voltage (polarization) that depolarizes the polarization of the piezoelectric elements 1a and 1b. This means that the voltage in the direction opposite to the polarization direction applied to the piezoelectric elements 1a and 1b does not exceed the polarization degradation voltage even if it is set to twice the degradation voltage Vec).

Above example, a piezoelectric element 1a, the electrostatic capacitance Cs and capacitor 2a of 1b, was the case of the electrostatic capacity C ₂ of 2b in the same, the piezoelectric element 1a, the piezoelectric element so 1b is not depolarized 1a, the voltage of the polarization direction opposite to the direction applied to 1b does not exceed the polarization degradation voltage, the drive voltage Vd and the capacitor 2a, 2b and a capacitance C ₂ of to meet the following expressions Should be set.

Vec> | Vd | * C ₂ / (Cs + C ₂ )
As described above, in the present invention, the voltage applied in the reverse direction to the piezoelectric element, so determined by the partial pressure of the capacitance Cs of the capacitance C ₂ and the piezoelectric element of the capacitor, unlike the prior art 3 The voltage in the reverse direction can control the displacement of the piezoelectric bimorph element linearly with respect to the driving electric field in proportion to the driving voltage.

  In this embodiment, a triangular wave has been described as an input waveform. However, the input waveform is not limited to these waveforms, and may be another waveform such as a sine wave or a rectangular wave, or a complex waveform such as voice. However, it may be a waveform with no regularity. Further, the drive voltage Vd here is not a value indicating a value uniquely determined from a waveform such as an effective value or a rated value, but an instantaneous value (instantaneous value).

Normally, rectifier diodes 3a, the inter-terminal capacitances C ₃ in the reverse voltage 3b can be ignored because the capacitance Cs and the capacitor 2a of the piezoelectric element is smaller than the capacitance C ₂ of 2b . However, the rectifier diode 3a, if the inter-terminal capacitance C ₃ becomes larger as can not be ignored in the reverse voltage 3b, capacitor 2a, since the 2b connected in parallel, the capacitance of the capacitor 2a, 2b it is necessary to apply the replacement of C ₂ to _{(C 2} ten _{C 3)} formula.

[Explanation of Table 1 and FIGS. 3 to 5]
Table 1 shows an experimental example No. 1 according to the prior art. 1 to Experimental Example No. 3 and Experimental Example No. 4 to Experimental Example No. 6 is a table comparing experimental examples. In this experimental example comparison table, Experimental Example No. 1 and Experimental Example No. 1 2 is an experimental example of the circuit of prior art 1 (FIG. 6). 1 and Experimental Example No. 1 2 is different from the maximum value of the drive voltage.

Experimental Example No. 3 is an experimental example of the circuit of prior art 2 (FIG. 8). Experimental Example No. 4 to No. 6 is an experimental example of the circuit (Fig. 1) according to the present invention, a capacitor 2a in each experimental example, the capacitance C ₂ of 2b different.

  Experimental Example No. FIG. 7 shows waveforms of voltages applied to the piezoelectric elements 1a and 1b in FIG. In this figure, the sign of voltage is positive in the polarization direction and forward direction, and negative in the reverse direction. Similarly, Experimental Example No. 3 is shown in FIG. 4 is shown in FIG. 5 is shown in FIG. The waveform of 6 is shown in FIG.

  The composition, outer shape, and experimental conditions of the piezoelectric elements 1a and 1b used in these experiments are as follows.

The composition of the piezoelectric element is
Ba _0.925 Ca _0.075 TiO ₃
Its relative dielectric constant is 1280,
The electromechanical constant (kp) is 35.5%,
The coercive electric field (Ec) is 370 V / mm,
The piezoelectric constant (−d31) is 140 pm / V as a value when the electric field strength is 1000 V / mm.

  Although a barium titanate-based piezoelectric element is used here, lead zirconate titanate (PZT) having a large piezoelectric constant may be used.

  The external dimensions of the piezoelectric bimorph element 10 in which two piezoelectric elements are bonded together are 30 * 5 * 0.2 mm, the polarization deterioration voltage (Vec) in this shape is 74 V, and the capacitance (Cs) is 8.50 nF. It is.

  The drive signal used in the experiment was a triangular wave with a frequency of 0.1 Hz, and the voltage was +200 V to −200 V (only Experimental Example 2 was 60 V to −60 V).

  Experimental Example No. 1, a driving voltage having a maximum triangular wave of 200 V is input between the driving voltage input terminals 5, and a driving voltage exceeding the polarization degradation voltage 74 V is applied to the piezoelectric elements 1 a and 1 b in the forward direction and the reverse direction as they are. For this reason, the piezoelectric elements 1a and 1b are reversed in polarity and do not function as piezoelectric bimorphs.

  Experimental Example No. 2, since the drive voltage was limited to a maximum of 60 V of a triangular wave so as not to exceed the polarization degradation voltage 74 V, polarization inversion does not occur, but the displacement is 283 μm at the maximum, which is smaller than the experimental example according to the present invention described later. Became value.

  Experimental Example No. 3, the rectifier diodes 3 a and 3 b are connected in a direction in which the piezoelectric elements 1 a and 1 b are energized in the polarization direction. Since no voltage in the opposite direction to the polarization direction was applied to 1a and 1b, no polarization inversion occurred. However, the maximum displacement was 473 μm, which was a smaller value than the experimental example according to the present invention described later.

Experimental Example No. In 4, a experimental example of a circuit according to the present invention, are set capacitors 2a, the capacitance _{C 2} of 2b to 1.0 nF. In this case, the voltage applied to the piezoelectric elements 1a and 1b in the direction opposite to the polarization direction is limited to about 10.5% (1.00 / (8.50 + 1.00)) of the drive voltage.

  In this Experimental Example No. 4, even when a driving voltage of a maximum of 200 V in a triangular wave is applied between the driving voltage input terminals 5, the piezoelectric elements 1a and 1b have a maximum voltage in the direction opposite to the polarization direction of 21 V (because the reverse direction in Table 1 − 21V), which is less than the polarization degradation voltage 74V, so that no polarization inversion occurs. In this Experimental Example No. In No. 4, the maximum displacement was 524 μm, which was larger than that of the conventional technique (Experimental Example No. 2 and Experimental Example No. 3) in which no capacitor was used.

Experimental Example No. 5 even experimental example of a circuit according to the present invention, are set capacitors 2a, the capacitance _{C 2} of 2b to 3.64NF. In this case, the voltage applied to the piezoelectric elements 1a and 1b in the direction opposite to the polarization direction is limited to about 30.0% (3.64 / (8.50 + 3.64)) of the drive voltage.

  In this Experimental Example No. 5, even if a driving voltage of a maximum of 200 V of a triangular wave is applied between the driving voltage input terminals 5, the piezoelectric element 1 a, 1 b has a maximum voltage of 60 V in the opposite direction to the polarization direction (because it is in the opposite direction in Table 1 − Since the polarization degradation voltage is less than 74V, polarization inversion does not occur. In this Experimental Example No. 5, the maximum displacement is 631 μm. Compared to 4, it was a large value. This is a result of increasing the voltage in the direction opposite to the polarization direction applied to the piezoelectric elements 1a and 1b to about 80% (60/74) of the polarization degradation voltage, and effectively demonstrating the capabilities of the piezoelectric elements 1a and 1b. is there.

Experimental Example No. 6 is also an experimental example of the circuit according to the present invention. Setting the capacitance _{C 2} of capacitor 5.7NF, about 40.0% of the voltage is the driving voltage applied to the opposite direction to the polarization direction of the piezoelectric element (5.70 / (8.50 + 5.70)) It becomes.

  In this Experimental Example No. 6, when a driving voltage of a maximum of 200 V of a triangular wave is applied between the driving voltage input terminals 5, a voltage of a maximum of 80 V of a triangular wave is applied to the piezoelectric elements 1 a and 1 b in the direction opposite to the polarization direction. Has been exceeded. As a result, the polarization of the piezoelectric elements 1a and 1b was reversed, and the function of the piezoelectric bimorph element was stopped. The driving method in which such polarization inversion occurs is not the best embodiment of the piezoelectric bimorph drive circuit according to the present invention.

  However, even if the voltage in the direction opposite to the polarization direction applied to the piezoelectric elements 1a and 1b exceeds the polarization deterioration voltage Vec, the function as the piezoelectric bimorph element may be maintained. This will be described.

  The polarization degradation voltage Vec and the coercive electric field Ec are described together with the method of experimenting and calculating. As a method for obtaining the polarization deterioration voltage Vec and the coercive electric field Ec, a method for obtaining from the electric field-strain curve and a method for obtaining from the electric field-polarization curve are general.

  In the former, when an electric field opposite to the polarization direction is applied, an electric field in which the contraction behavior in the polarization axis direction changes to the extension behavior is defined as Ec. In the latter, Ec is an electric field where the magnitude of polarization is zero. In any of the methods, the value of Ec may vary depending on the measurement conditions. Therefore, it is desirable that the polarization degradation voltage is a value measured under conditions actually used (waveform, frequency, etc.).

  When a voltage equal to or higher than the polarization degradation voltage obtained in this way is applied, the piezoelectric element starts to reverse the polarization. However, the effect of the present invention can be sustained as long as the voltage is short enough for polarization reversal not to be completed or for a short time.

  Furthermore, even if a voltage exceeding the polarization degradation voltage obtained from the electric field-strain curve is applied to the piezoelectric elements 1a and 1b unintentionally due to a malfunction of the drive power supply, etc., this is a single and instantaneous phenomenon. If there is a polarization reversal, once a voltage having an opposite sign (the same direction as the polarization direction) and an absolute value greater than or equal to the polarization degradation voltage is input, the polarization reversal occurs again. As a result, it returns to its original state and functions as a piezoelectric bimorph.

  According to the configuration of the present invention, even in such an undesirable state, the voltage applied in the direction opposite to the polarization direction is set to be lower than the voltage applied in the forward direction, so that the original normal state is restored. I can expect that.

  In the prior art 1, since the voltage applied to the piezoelectric elements 1a and 1b in the polarization direction and the forward direction are approximately equal to the voltage applied in the reverse direction, it is difficult to expect the above phenomenon to occur. In the prior art 2, since no voltage is applied to the piezoelectric elements 1a and 1b in the direction opposite to the polarization direction, the above phenomenon is irrelevant.

  In the present invention, in order to apply a driving voltage to the piezoelectric element 1 as it is in the polarization direction and the forward direction and to apply a lower voltage in the reverse direction, as shown in FIG. 1, the rectifier diodes 3a and 3b And a drive input circuit 20 in which capacitors 2a and 2b are connected in parallel.

  The present invention also includes various modifications based on the parallel connection of the rectifier diodes 3a and 3b and the capacitors 2a and 2b. For example, two parallel or serially connected capacitors are parallel to the rectifier diode. Drive voltage in reverse direction by connecting, connecting resistor and capacitor in parallel or in series and connecting in parallel to rectifier diode, or connecting capacitor, resistor or a combination of these in parallel to rectifier diode Can be shared by both ends of the rectifier diode.

  Further, instead of the drive input circuit 20 in which the rectifier diodes 3a and 3b and the capacitors 2a and 2b are connected in parallel, parts other than these parts, for example, a Zener diode, a thyristor, with a control pole or without a control pole A circuit having the same effect as that of the drive input circuit 20 according to the present invention can be formed by a non-linear element, a combination thereof, or the like. On the other hand, the present invention can form a simple circuit to achieve the above-described effects, and is superior in this respect to a circuit formed by combining other components.

  The embodiments disclosed herein are illustrative and non-restrictive in every respect, and the scope of the present invention is shown not by the above description but by the scope of claims, and is equivalent to the scope of claims. Includes all changes within the meaning and scope.

  The effects of the present invention described above do not have to be all at the same time, but only have one or more effects of the present invention.

  Since the present invention has many unique effects compared to conventional piezoelectric bimorph drive circuits and has excellent productivity without increasing costs, it can be expected to be put to practical use.

1 is a circuit diagram of a piezoelectric bimorph element drive circuit 30 including a piezoelectric bimorph element 10 and a drive input circuit 20 according to the present invention. FIG. 2A to 2C are respectively a waveform diagram of a drive voltage input from the outside to the drive circuit according to the present invention, a voltage applied to one piezoelectric element, and a voltage applied to the other piezoelectric element. FIG. Experimental example No. in the comparison table of experimental examples in Table 1 FIG. 6 is a waveform diagram of a voltage applied to a piezoelectric element used in Experiment 4; Experimental example No. in the experimental table comparison table of Table 1. 6 is a waveform diagram of a voltage applied to a piezoelectric element used in an experiment of No. 5. FIG. Experimental example No. in the experimental table comparison table of Table 1. 6 is a waveform diagram of a voltage applied to a piezoelectric element used in an experiment of No. 6. FIG. 3 is a piezoelectric bimorph drive circuit according to Prior Art 2. Experimental example No. in the experimental table comparison table of Table 1. It is a wave form diagram of the voltage applied to the piezoelectric element used in 1 experiment. 3 is a piezoelectric bimorph drive circuit according to Prior Art 2. Experimental example No. in the experimental table comparison table of Table 1. FIG. 6 is a waveform diagram of a voltage applied to a piezoelectric element used in Experiment 3;

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Piezoelectric bimorph element 20 Drive input circuit 30 Piezoelectric bimorph element drive circuit 1a, 1b Piezoelectric element 1a One piezoelectric element 1b The other piezoelectric element 2a, 2b Capacitor 2a One capacitor 2b The other capacitor 3a, 3b Rectifier diode 3a Rectifier diode 3b Other rectifier diodes 4a, 4b Surface side electrode 4c Intermediate electrode P Polarization direction 5 Drive voltage input terminal 5a Common connection terminal 5c Intermediate electrode connection terminal C ₂ Capacitance C of capacitors 2a, 2b C ₃ Rectifier diodes 3a, 3b The inter-terminal capacitance Cs at the reverse voltage of the capacitance Vec polarization degradation voltage of the piezoelectric elements 1a and 1b.

Claims (3)

A piezoelectric bimorph element formed from one piezoelectric element and the other piezoelectric element arranged so that the polarization direction is the same across the intermediate electrode, and a driving voltage supplied from a driving power source is applied to the piezoelectric bimorph element In the drive circuit of the piezoelectric bimorph element formed from the drive input circuit
The drive input circuit is
One rectifier diode connected to the one piezoelectric element in a direction of energizing in the polarization direction of the one piezoelectric element;
One capacitor connected in parallel to the one rectifier diode;
The other rectifier diode connected to the other piezoelectric element in a direction of energizing in the polarization direction of the other piezoelectric element;
The other capacitor connected in parallel to the other rectifier diode;
One connection end of one rectifier diode and one capacitor not connected to the one piezoelectric element is shared with the other connection end of the other rectifier diode and the other capacitor not connected to the other piezoelectric element. Common connection terminals
A drive circuit for a piezoelectric bimorph element formed from an intermediate electrode connection terminal connected to the intermediate electrode. In the driving method of the piezoelectric bimorph element formed from one piezoelectric element and the other piezoelectric element arranged so that the polarization direction is the same direction across the intermediate electrode,
One rectifier diode is connected to the one piezoelectric element in the forward direction and the polarization direction of the one piezoelectric element,
One capacitor is connected in parallel to the one rectifier diode,
The other rectifier diode is connected to the other piezoelectric element in the forward direction and the polarization direction of the other piezoelectric element,
Connecting the other capacitor in parallel to the other rectifier diode;
One connection end of one rectifier diode and one capacitor not connected to the one piezoelectric element is shared with the other connection end of the other rectifier diode and the other capacitor not connected to the other piezoelectric element. As a common connection terminal,
Connecting the intermediate electrode to an intermediate electrode connection terminal;
By applying a driving voltage between the common connection terminal and the intermediate electrode connection terminal,
A driving method of a piezoelectric bimorph element in which a voltage applied to the piezoelectric element in a direction opposite to a polarization direction is limited to less than a polarization deterioration voltage. The absolute value of the common connection terminal and the driving voltage applied between the intermediate electrode connecting terminal according to claim 2 | Vd | a, and the capacitance Cs of the piezoelectric element, the capacitance C ₂ of the capacitor, a piezoelectric element The polarization degradation voltage Vec corresponding to the coercive electric field of Vec> | Vd | * C ₂ / (Cs + C ₂ )
The driving method of the piezoelectric bimorph element set to the relationship.

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