JPH03171784A - Bimorph element - Google Patents

Abstract

PURPOSE:To acquire enough displacement even if a circumferencial part is completely fixed and to provide a disc bimorph element which can improve mechanical properties such as resonance frequency and generation force by dividing outside electrodes into two parts, respectively in a radius direction and by driving the two divided parts so that their displacements become reverse phase mutually. CONSTITUTION:Main surfaces of piezoelectric plates 11, 12 are bonded through a shim and holding electrode 13. Outside electrodes 14, 15 are bonded to other main surfaces of the piezoelectric plates 11, 12; and the electrodes 14, 15 are divided into two in a radius direction forming peripheral sides 14a, 15a, and central sides 14b, 15b. When the outside electrodes 14, 15 are dirived so that displacement directions thereof are reverse at a boundary of a division part between the outside electrodes 14, 15, rotation element due to displacement is cancelled at a displacement output part of a fixing end of a circumferential part and a circular central part, thereby enabling parallel movement of the displacement output part at a center. Accordingly, displacement of a bimorph element does not lower even if a circumference is fixed completely.

Description

[Detailed description of the invention]

[Object of the Invention] (Industrial Application Field) The present invention relates to a circular bimorph element used as a piezoelectric actuator, and particularly to a bimorph element driven with its circumferential portion fixed. (Prior art) Conventionally, actuators using piezoelectric effects have been small and lightweight. Low power consumption. It is used in a variety of fields because it has many advantages, such as low heat generation, no magnetic field generation and little effect on other electronic components, and easy control because it is driven by voltage. As actuators that utilize such a piezoelectric effect, lateral effect actuators typified by laminated longitudinal effect actuators, sliding effect actuators, and bimorph piezoelectric elements (bimorph elements) have been put into practical use. Among these, if a relatively large amount of displacement is required,
Bimorph elements are often used. As shown in FIG. 3, a bimorph element has a structure in which two piezoelectric elements each having electrodes provided on both main surfaces of a piezoelectric plate are stacked on top of each other. In this case, if a negative potential is applied to the outer atwt electrode 4.5 and a positive potential is applied to the clamping electrode 3 for the piezoelectric plate 1.2 whose polarization direction is in the direction of the arrow in the figure, then the dotted line in the figure The piezoelectric bodies 1 and 2 are curved as shown in FIG. Furthermore, when a potential opposite to the above is applied to the outer electrodes 4, 5 and the clamping electrode 3, the bimorph element curves in the opposite direction. Generally used bimorph elements are rectangular, but when a relatively high resonance frequency or large generated force is required, or when it is necessary to seal around the actuator in applications such as pumps, a circular bimorph element is used. A bimorph element is used. The structure of the conventionally used circular bimorph element*
Shown in Figure 4. Note that Fig. 4(a) is a perspective view, and Fig. 4(a) is a perspective view.
b) is a sectional view taken along the line BB in FIG. Piezoelectric plate 1
, 2 and electrodes 3.4.5 are circular, but the basic configuration is the same as that in FIG. 3. In this circular bimorph element, a predetermined voltage is applied between the clamping electrode 3 and the outer electrodes 4 and 5 to provide a potential that causes the lower piezoelectric plate 2 to contract and the upper piezoelectric plate 1 to expand. Then, as shown by the broken line in FIG. 4(b), it curves convexly upward. When a potential opposite to the above is applied to the electrodes 3 to 5, this bimorph element curves downward in a convex manner. However, this type of bimorph element has the following problems. That is, the circular bimorph element is
Normally, the circumferential portion is fixed and used, but if the circumferential portion is completely fixed at this time, the displacement will be restricted and it will not be displaced. For this reason, a structure is adopted in which the shim material and holding electrode 3 protrudes from the piezoelectric bodies 1 and 2 in the circumferential direction, and the protruding portion is supported by being fixed. On the other hand, in order to improve mechanical properties such as resonance frequency and generated force,
It is possible to change the circumferential portion of the circular bimorph from a support structure to a completely fixed structure, but this structure has the drawback that displacement is restricted as described above. In other words, there was a trade-off relationship between the amount of displacement and mechanical properties. (Three Problems to be Solved by the Invention) As described above, in order to improve the mechanical properties of a circular bimorph element, if an attempt was made to use the circumferential part under a completely fixed condition, the displacement would be restricted. There was a problem that the amount of displacement decreased significantly. The present invention was made in consideration of the above circumstances, and its purpose is to be able to obtain sufficient displacement even when the circumferential portion is completely fixed, and to reduce mechanical problems such as resonance frequency and generated force. An object of the present invention is to provide a circular bimorph element that can improve physical properties.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is to prevent the displacement from being constrained when the circumferential portion is completely fixed. It consists in reversing the . That is, the present invention provides a circular bimorph element in which the main surfaces of two piezoelectric bodies are attached to each other with sandwiching electrodes in between, and outer electrodes are attached to the other main surfaces of each piezoelectric body, respectively. The electrode is divided into two parts in the radial direction, and the two divided parts are driven so that their displacements are in opposite phases. (Function) According to the present invention, by adopting a split electrode structure,
At the fixed end of the circumferential portion and the displacement extraction portion at the center of the circle, the rotational component due to displacement is canceled, and the central displacement extraction portion moves in parallel. Therefore, even if the circumference is completely fixed, the displacement of the bimorph or element will not be reduced. Therefore, even if the circumferential portion is completely fixed, the displacement does not decrease significantly, and it is possible to obtain a sufficient amount of displacement and improve mechanical properties such as resonance frequency and generated force. (Example) Hereinafter, the details of the present invention will be explained by referring to the illustrated example. FIG. 1 shows a schematic configuration of a bimorph element according to an embodiment of the present invention, FIG. 1(a) is a perspective view, and FIG.
b) is a sectional view taken along arrow AA in FIG.゛Figure 1
1.12 is a circular piezoelectric plate made of a piezoelectric material, and the main surfaces of these piezoelectric plates 11.12 are used as shims and clamping electrodes 13.
It is glued through. On the other main surface of the piezoelectric plate 11.12, outer electrodes 14.15 are glued, and these electrodes 14.15 are divided into two parts in the radial direction. The division ratio is determined by the peripheral electrodes 14a. 15a, center side electrode 14b,
The displacements are set to be equal when the same electric field is applied to each of the electrodes 15b. Furthermore, in the center of the circle, there is provided an ineffective part that does not involve the displacement and has no electrodes as a part from which the displacement is taken out. The circumferential portion of the circular bimorph element is completely fixed to the fixed end. FIG. 2 is a schematic diagram for explaining the method of voltage application in the above element. In FIG. 2(a), the piezoelectric plate 1
1. The polarization direction of 12 is the same direction, the clamping electrode 13 is grounded, and the outer electrodes 14 and 15 are connected to the peripheral sides 14a and 15a.
A negative voltage is applied to the center sides 14b and 15b, and a positive voltage is applied to the center sides 14b and 15b. In this case, area A on the peripheral side is displaced convexly downward, and area B on the center side is displaced convexly upward. Therefore, the above-mentioned FIG. 1 (
A displacement as shown in b) is obtained. In FIG. 2(b), the polarization directions of the piezoelectric plates 11 and 12 were reversed between the peripheral side and the center side, and the voltages applied to the outer electrodes were the same. In this case, the clamping electrode 13 is negative, the outer electrode 14.1
By applying a positive voltage to 5, the area A on the peripheral side is displaced convexly downward, and the area B on the center side is displaced convexly upwardly, as shown in FIG. 1(b) above. A displacement like this can be obtained. Furthermore, by using the AC power source 16 as a power source, it is possible to vibrate the bimorph element. As described above, in this embodiment, when the outer electrodes 14 and 15 are driven so that the displacement directions are reversed at the divided portions, the four transitions due to displacement occur at the fixed end of the circumferential portion and the displacement extraction portion of the center portion of the circle. , the central displacement take-out portion moves in parallel. Therefore, even if the circumference is completely fixed, the displacement of the bimorph element will not be reduced. Note that by adopting the divided electrode structure, the displacement becomes approximately 1/2 smaller than that when a bimorph of the same shape with a full electrode structure is driven freely around the circumference. However, in reality, it cannot be used as an actuator if it is free around the circumference, so when compared with a circular bimorph with a circumferential support structure, the overall characteristics are improved. Examples of actual measurements are shown in the table below. A comparison is shown between an embodiment of the present invention and a conventional bimorph having a circumferential support structure, assuming that the materials and shapes used are the same. The division ratio in the embodiment of the present invention is equal division in the radial direction. Table As can be seen from this table, although the amount of displacement in this embodiment is slightly smaller than that in the conventional example, the resonance frequency is significantly higher and high-speed driving is possible. Furthermore, since the circumference is completely fixed, mechanical properties such as resonance frequency and generated force can be improved. Therefore, it can be used in actuators that require a relatively high resonant frequency and a large generated force, and is extremely useful. Note that the present invention is not limited to the embodiments described above. For example, the potentials applied to the clamping electrodes and the outer electrodes are not limited to those shown in FIG. The potential should be such that the phase is the same. Further, in the embodiment, the circumferential portion is fixed and the displacement is taken out at the center of the circle, but conversely, the center of the circle may be fixed and the displacement taken out at the circumferential portion. In addition, various modifications can be made without departing from the gist of the present invention. [Effects of the Invention] As detailed above, according to the present invention, a split electrode structure is adopted and the direction of displacement is reversed between the center side and the peripheral side of the circle, so the circumferential part can be used completely fixed. It is possible to realize a circular bimorph element that can obtain a sufficient displacement even when using a circular bimorph element, and can improve mechanical properties such as resonance frequency and generated force.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a schematic configuration of a circular bimorph element according to an embodiment of the present invention, FIG. 2 is a schematic diagram for explaining a method of driving the bimorph element, and FIG. 3 is a configuration of a strip-shaped bimorph element. FIG. 4 is a diagram showing a schematic configuration of a conventional circular bimorph element. 11... Piezoelectric plate, 12... Piezoelectric plate, 13... Shim and clamping electrode, 14.15... Outer electrode, 14a, 15a... Peripheral electrode, i4b, 15b... Center Side electrode, 16...AC power supply.

Claims (1)

[Claims] The main surfaces of two piezoelectric plates are attached to each other with a sandwiching electrode in between,
1. A circular bimorph element having an outer electrode attached to the other main surface of each piezoelectric plate, wherein each of the outer electrodes is divided into two parts in a radial direction.