JPH0317231B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a bimorph device formed by bonding at least a pair of ceramic electrostrictive plates through a shim plate that also serves as a central electron, and is particularly suitable for piezoelectric actuators with large amplitude operation. This relates to bimorph devices. [Prior Art] A bimorph element operates at high speed by applying a voltage, and its power consumption is low. For this reason, actuators that use bimorph elements in their drive parts are
As an actuator that can replace electromagnets, it is attracting attention mainly for communication terminal equipment that is desired to be small and low-power. However, conventional piezoelectric actuators of this type have a small amount of variation and a small amount of generated force, so their field of application is limited. In order to operate a bimorph element with large force and force, a drive circuit that can apply a high voltage while preventing deterioration of polarization and an element structure suitable for large amplitude operation are required. Regarding the former, there is an unbalanced voltage application polarity switching circuit described in Japanese Patent Application No. 59-43881 "Electrostrictive Vibration Device" related to the invention of the present inventor, and the previous two to
It is now possible to obtain three times the amount of mutation and generation power. [Problem to be solved by the invention] However, it has become clear that when such a large amplitude operation is performed at high temperatures, a new problem occurs in the conventional bimorph element: the electrostrictive plate breaks. Ta. [Means for Solving the Problems] The bimorph element of the present invention has been made in view of the above problems, and has a shim plate with a Ni content of 30 to 30.
The metal is a 55% by weight Ni-Fe alloy with a thermal expansion coefficient of 10 ^-7 to 10 ^-5 /°C, and the shim plate and electrostrictive plate have a volume resistivity of 10 ⁶ to ^{10 13} Ωcm. It is bonded with an adhesive made of resin mixed with carbon particles. [Function] Since the thermal expansion coefficient of the shim plate is close to that of the electrostrictive plate, almost no internal stress is generated due to thermal expansion even at high temperatures, and therefore the electrostrictive plate will not break even if it is greatly deformed. It becomes difficult to do. In addition, the adhesive maintains appropriate adhesive performance while also ensuring the necessary electrical conductivity. [Example] Hereinafter, the present invention will be described in detail with reference to Examples. Table 1 is a table showing the linear expansion coefficient and magnetic properties of various materials.

[Table] The inventor of this application speculates that the cause of the phenomenon in which the electrostrictive plate breaks when a bimorph element is operated with large amplitude at high temperatures is the difference in thermal expansion coefficient between the electrostrictive plate (PZT) and the shim plate. did. Therefore, the shim plate of the conventional bimorph element has
Since brass, nickel silver, phosphor bronze, etc. are mainly used because of their good spring properties, the following implementation was carried out. After bonding an electrostrictive plate 201 made of zircon-dispersed lead titanate (PZT) and a brass plate 202 with a hardening adhesive at 100°C, the plate was returned to room temperature and changes in shape were observed. The shapes (length x width x thickness) of the electrostrictive plate 201 and the brass plate 202 are 45 x 12 x
0.15mm and 45×12×0.05mm. As a result, the two plates were largely curved so that the electrostrictive plate 201 side was inward, as shown in the cross-sectional view of FIG. In order to return this to a flat plate shape, it was necessary to apply a force of about F=15 g to the tip with one end fixed. Similar results were obtained when two plates were cured at room temperature and left at elevated temperatures.
However, in this case, it is curved so that the brass plate side is on the inside. Bimorph elements are made of two electrostrictive plates glued together in a sandwich shape through a shim plate, so they do not bend even if left at high temperatures after being glued together at room temperature. The results revealed that an internal stress equivalent to a tip load of approximately 15 g was generated between the shim plate and the electrostrictive plate. Therefore, it has become clear that when operating at high temperatures, in addition to the strain caused by the application of voltage, strain is caused by the thermal expansion of the shim plate. Including PZT, lead titanate, lead niobate,
When the thermal expansion coefficient of piezoelectric ceramics such as barium titanate and sodium ptadium nitrate is measured, as shown in Table 1, it is about 15 to 50 × 10 ^-7 /°C. Ni−Fe
We focused on Ni-Fe-Co alloys. Figure 3 shows the composition and thermal expansion coefficient α of Ni-Fe alloy.
This shows the relationship between As is clear from the figure, when the Ni content of the Ni-Fe alloy is 30 to 55% by weight, α becomes 100×10 ⁻⁷ ° C. or less, and the alloy becomes close to an electrostrictive plate. As a representative example, an experiment similar to that described above was conducted using 36% Ni-Fe with α equal to or slightly smaller than that of the electrostrictive plate and 45% Ni-Fe with α slightly larger than that of the electrostrictive plate. Figure 4 shows 36% Ni-Fe plate 401 (45×12×
0.05 mm) and the same electrostrictive plate 201 used in the experiment described above are bonded together using a 100° C. curing adhesive and are returned to room temperature. As can be seen from the figure, there is no deformation like when brass is used. It was also found that when 45% Ni-Fe was used, there was some curvature, but the degree of curvature was much smaller than in the case of brass. FIG. 1 is a block diagram showing a piezoelectric actuator in which a bimorph element according to an embodiment of the present invention is used as a driver in a drive circuit capable of large amplitude operation. The bimorph element 1 has a shim plate 11 made of 35% Ni-Fe sandwiched between electrostrictive plates 12 and 13 made of PZT, and the polarization directions are in the same direction as shown by arrows A and B. . Note that the shim plate 11 also serves as a center electrode. FIG. 5 is a perspective view showing the structure of this bimorph element 1 in more detail. Electrodes 501 to 504 made of Au, Ag, Ni, etc. are formed on both surfaces of the electrostrictive plates 12 and 13 by baking, respectively.
Electrodes 502 and 503 on the shim plate 11 side are not provided at the end on the fixed part 505 side. The lead wires 507 to 509 are connected to the electrode 501, the shim plate 11, and the electrode 504 on the fixed part 505 side, respectively. After the electrostrictive plates 12 and 13 are polarized,
It is bonded to the shim plate 11. In FIG. 1, the drive circuit includes an unbalanced voltage application drive input circuit 2, a polarity switching 3, a constant current circuit 4, a constant voltage circuit 5, a control circuit 6 for polarity switching, and a logic voltage power supply 7. The drive input circuit 2 includes a Zener diode 21,
22, a constant voltage Vc in the same direction as the polarization direction is applied to one electrostrictive plate of the bimorph element 1, and a constant voltage Vc in the opposite direction to the polarization direction is applied to the other electrostrictive plate. A voltage lower than the operating voltage of the diode 21 or 22 is applied. The polarity switching circuit 3 is constructed by connecting Darlington-connected transistor circuits 31 to 34 in a bridge configuration, and depending on the output signal of the control circuit 6,
Switches the polarity of the output voltage. The constant current circuit 4 is made up of a CRD 41. The constant voltage circuit 5 uses a pnp transistor.
It is an RCC type step-up constant voltage circuit, and its internal configuration is omitted, but the power supply voltage Ec (5V
level) and outputs a constant voltage Vc. The constant voltage Vc is a value obtained by adding the operating voltage V _ZDO of the internal Zener diode ZDo to the power supply voltage Ec, that is, [Ec + V _ZDO ]. The control circuit 6 switches the Darlington transistor circuit 3 of the polarity switching circuit 3 by switching the switch 61.
1 to 34, and when switch 61 is in the state shown in the figure, transistor circuits 31 and 32 are cut off, and transistor circuit 3
3 and 34 are electrically connected. When the switch 61 is reversed, the transistor circuits 33 and 34 are cut off, and the transistor circuits 31 and 32 are turned off.
conducts. Next, the operation of the piezoelectric actuator configured in this way will be briefly explained. Now, if the switch 61 is in the state shown in the figure,
Since the transistor circuits 31 and 32 are cut off and the transistor circuits 33 and 34 are made conductive, the terminal A of the drive input circuit 2 is at the ground level and the terminal B is at the potential Vc. Therefore, the output voltage Vc of the constant voltage circuit 5 is applied to the electrostrictive plate 13 in the polarization direction, Vc-V _ZD1 is applied to the electrostrictive plate 12 in the reverse polarization direction, and the tip of the bimorph element 1 Displaced downward. When the switch 61 is set to the ground level, the transistor circuits 33 and 34 are cut off and the transistor circuits 31 and 32 are made conductive, so that the terminal B of the drive input circuit 2 is set to the ground level and the terminal A is set to the potential.
Becomes Vc. Therefore, the output voltage Vc of the constant voltage circuit 5 is applied to the electrostrictive plate 12 in the polarization direction, Vc-V _ZD2 is applied to the electrostrictive plate 13 in the reverse polarization direction, and the tip of the bimorph element 1 Displace upward. An electrostrictive plate depolarizes when a polarization deterioration voltage Vd or more is applied in the reverse polarization direction, but according to this drive circuit, the polarization deterioration voltage Vd is reduced in the polarization direction without applying a polarization deterioration voltage Vd or more in the reverse polarization direction. Because it is possible to apply a higher voltage (Vc) than
By switching the switch 61, the bimorph element 1 can be caused to vibrate greatly without deteriorating. Furthermore, according to this drive circuit, even if the applied voltage in the reverse polarization direction is greater than the polarization deterioration voltage Vd and causes depolarization in the electrostrictive plate, as long as the voltage is at a level that does not cause polarization breakdown, the polarization The depolarization is restored by applying a high voltage Vc in the direction, making it possible to vibrate even more strongly. Figure 6 shows the temperature at 70°C using the drive circuit shown in Figure 1.
FIG. 3 is a diagram showing the displacement characteristics of a bimorph element when a continuous operation test at 2 Hz is performed at a temperature of . Characteristics A and B relate to the bimorph element according to the present invention; characteristic A uses 36% Ni-Fe for the shim plate, and characteristic B uses 45% Ni-Fe. Further, characteristics C and D relate to a conventional bimorph element using brass for the shim plate. Further, Table 2 shows the rupture characteristics of the bimorph element.

【table】

〔Effect of the invention〕

As explained above, according to the bimorph element of the present invention, the shim plate is made of Ni containing 30 to 55% by weight of Ni.
−It is a Fe-based alloy and has a coefficient of thermal expansion of 10 ^-7 to 10 ^-5 /
℃ metal, and the shim plate and electrostrictive plate have a resistance of 10 ⁶ to 10 ¹³ Ω.
Since it is bonded with an adhesive made of resin that has a volume resistivity of cm and contains carbon particles, almost no internal stress is generated due to thermal expansion even at high temperatures, and the electrostrictive plate remains stable even when operated with a large amplitude. It becomes difficult to break. Further, it has the effect that desired performance can be ensured in terms of adhesiveness and conductivity. Therefore, the reliability of the bimorph element can be significantly improved.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a piezoelectric actuator using a bimorph element, which is an embodiment of the present invention, and Fig. 2 is a diagram for confirming the stress generated in the bonded body of the brass plate and the electrostrictive plate based on the environmental temperature. Figure 3 is a characteristic diagram showing the relationship between Ni content and thermal expansion coefficient in Ni-Fe alloys, Figure 4 shows the relationship between Ni-Fe plate and electrostrictive plate based on environmental temperature. A cross-sectional view to confirm the stress generated in the body, Figure 5 is the first
A perspective view showing the structure of the bimorph device shown in Fig. 6.
The figure shows the displacement characteristics of various bimorph elements when a 2Hz continuous operation test was performed at a temperature of 70°C using the drive circuit shown in Figure 1. Figure 7 shows the composition of the Ni-Co-Fe alloy. Figure 8A is a characteristic diagram showing the relationship between the ratio and thermal expansion coefficient α. Figure 8A is a characteristic diagram showing the relationship between displacement and generated force of the bimorph element shown in Figure B. Figure 8B is a characteristic diagram showing the relationship between the displacement and generated force of the bimorph element shown in Figure B. A cross-sectional view showing the element,
9 and 10 are both partially enlarged sectional views of the bimorph element shown in FIG. 1. 1...Bimorph element, 11...Shim plate, 1
2,13... Electrostrictive plate, 501-504... Electrode.

Claims (1)

[Claims] 1. In a bimorph element in which electrostrictive plates are bonded to both sides of a shim plate that also serves as a central electrode, and electrodes are provided on the outer surface of the electrostrictive plate, the shim plate has a Ni content of 30 to 55% by weight. of Ni−Fe
^{The shim plate and the electrostrictive plate have a volume resistivity of 10 6 to 10 13 Ωcm} and are mixed with carbon particles. A bimorph element characterized by being bonded with an adhesive made of resin.