JPH08167746A - Layered piezoelectric actuator - Google Patents

Abstract

PURPOSE: To provide a layered piezoelectric actuator that prevents cracks that cause its breakdown and has a long life when driven repeatedly by suppressing the concentration of stress when it is driven. CONSTITUTION: A pillar shaped layer body 1 is formed by stacking piezoelectric ceramic layers 2 and internal electrode layers alternately, internal electrodes that hold the piezoelectric ceramic layer in between comprise first internal electrode layers 3a and second internal electode layers 3b, and each of a first external electrode that connects the first internal electrodes and a second external electrode that connects the second internal electrodes are formed on the outer surface of the pillar type layer body 1 spirally.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated piezoelectric actuator, for example, a laminated piezoelectric actuator used for precise position control or high-speed position control of an XY stage or the like.

[0002]

2. Description of the Related Art Conventionally, as a structure of a laminated piezoelectric actuator, there is known a structure in which an internal electrode similar to a laminated ceramic capacitor is used as a partial electrode. FIG. 5 shows a perspective view of such a conventional laminated piezoelectric actuator, and reference numeral 1 denotes a columnar laminated body. This columnar laminated body 1 is configured by alternately laminating a plurality of piezoelectric ceramic layers 2 and a plurality of internal electrode layers, and the internal electrode layers sandwiching the piezoelectric ceramic layers 2 are the first internal electrode layer 3a and the first internal electrode layer 3a. 2 internal electrode layers 3b. The first internal electrode layers 3a and the second internal electrode layers 3b are alternately formed in the axial direction of the columnar laminate 1.

The first internal electrode layers 3a are electrically connected to each other by a first external electrode 6 formed on the outer peripheral surface of the columnar laminated body 1, and the second internal electrode layers 3b are columnar laminated. It is electrically connected by the second external electrode 7 formed on the outer peripheral surface of the body 1. Further, the first internal electrode layer 3 a and the second internal electrode layer 3 b are not formed on a part of the surface of the piezoelectric ceramic layer 2 and serve as an electrodeless portion 9.
The first internal electrode layer 3a and the second internal electrode layer 3b have a portion (active portion A) facing each other and a portion (inactive portion B) not facing each other.
It is displaced when a voltage is applied to a and 3b. The first external electrode 6 and the second external electrode 7 are linearly formed in the stacking direction of the columnar stacked body 1.

In such a laminated piezoelectric actuator, since the internal electrodes 3a, 3b and the external electrodes 6, 7 can be connected layer by layer, the electrode forming step is extremely small and the manufacturing cost can be reduced.

[0005]

However, in the above-mentioned laminated piezoelectric actuator, as shown in FIG. 6, when a voltage is applied, the active portion A is displaced,
Since the inactive portion B does not generate displacement and the inactive portion B suppresses the displacement of the active portion A, there is a drawback in that repeated application of a voltage causes mechanical deflection, stress concentration, and easy destruction. .

Further, in the conventional laminated piezoelectric actuator, the displacement direction coincides with the formation direction of the external electrodes 6 and 7. Therefore, if the number of laminated layers is increased in order to obtain a large displacement, the central portion of the columnar laminated body 1 There has been a problem that stress concentration is significantly increased toward both ends in the stacking direction, and both ends are easily damaged by peeling or the like. Therefore, there is a problem that the number of stacked layers is limited and it is difficult to obtain a large displacement.

In view of the above-mentioned conventional problems, the present invention prevents the generation of cracks that cause breakage by suppressing the stress concentration generated during driving to a minimum, and further, a slight tensile force during driving. It is an object of the present invention to provide a laminated piezoelectric actuator that has a long life and does not break even when subjected to bending moment or bending moment.

[0008]

In the laminated piezoelectric actuator of the present invention, a plurality of piezoelectric ceramic layers and a plurality of internal electrode layers are alternately laminated to form a columnar laminated body, and the piezoelectric ceramic layers are sandwiched. First internal electrode layer
A first external electrode composed of an internal electrode layer and a second internal electrode layer, electrically connecting the first internal electrode layers to each other, and a second external electrode electrically connecting the second internal electrode layers to each other. Each of the columnar laminated bodies is formed in a spiral shape on the outer peripheral surface thereof.

[0009]

In the laminated piezoelectric actuator of the present invention, since the external electrode for electrically connecting the internal electrode is formed in a spiral shape on the outer peripheral surface of the columnar laminated body, the displacement direction of the laminated piezoelectric actuator and the external electrode are In addition, the non-electrode portion in which one end of the internal electrode is not exposed to the outer peripheral surface of the columnar laminate is spirally formed on the outer peripheral surface of the columnar laminate (non-parallel to the stacking direction). Thus, the generated stress can be dispersed, and a large stress concentration does not occur in one place unlike the conventional structure.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The laminated piezoelectric actuator of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an embodiment of a cylindrical laminated piezoelectric actuator of the present invention, in which reference numeral 1 indicates a columnar laminated body. This columnar laminated body 1 is configured by alternately laminating a plurality of piezoelectric ceramic layers 2 and a plurality of internal electrode layers, and the internal electrode layers sandwiching the piezoelectric ceramic layers 2 are the first internal electrode layer 3a and the first internal electrode layer 3a. 2 Internal electrode layer 3
b and. These first internal electrode layers 3a
The second internal electrode layers 3b are alternately formed in the axial direction of the columnar stacked body 1.

The piezoelectric ceramic layer 2 is made of, for example, PZT ceramics, and the internal electrode layers 3a and 3b are made of, for example, silver.

The first internal electrode layers 3a are electrically connected to each other by the first external electrode 6 formed on the outer peripheral surface of the columnar laminate 1, and the second internal electrode layers 3b are columnar laminated. It is electrically connected by the second external electrode 7 formed on the outer peripheral surface of the body 1. The first external electrode 6 and the second external electrode 7 are spirally formed (non-parallel to the stacking direction) on the outer peripheral surface of the columnar stack 1.

That is, the first internal electrode layer 3a and the second internal electrode layer 3b are not formed on a part of the surface of the piezoelectric ceramic layer 2 and serve as an electrodeless portion 9. The electrodeless portion 9 Will be formed in a spiral shape. In other words, the connecting portions between the internal electrodes 3a and 3b and the external electrodes 6 and 7 are formed in a spiral shape (non-parallel to the stacking direction) on the outer peripheral surface of the columnar stacked body 1 by gradually changing positions. .

Such a laminated piezoelectric actuator is
On one surface of the piezoelectric ceramic layer 2, the electrodeless portion 9 which is not exposed at the end surface portion thereof and the silver electrode material are baked to form the internal electrode layer 3
a and 3b are formed, and thereafter, the electrodeless portions 9 are spirally rotated by 180 degrees for each layer, and the piezoelectric ceramic layers 2 are laminated with a glass paste layer interposed therebetween, and pressed at a temperature at which the glass melts. Heat treatment is performed to form the columnar laminated body 1.

Then, a conductive epoxy paste is spirally applied to the outer peripheral surface of the columnar laminate 1 in which the internal electrodes 3a and 3b are exposed for each layer, and the internal electrode 3 is heat-treated.
External electrodes 6 and 7 for electrically connecting a and 3b layer by layer electrically in parallel
Is formed, and then, polarization treatment is performed to obtain the laminated piezoelectric actuator of the present invention.

In the laminated piezoelectric actuator configured as described above, the external electrodes 6 and 7 for electrically connecting the internal electrodes 3a and 3b are spirally formed on the outer peripheral surface of the columnar laminated body 1. One end of each of the internal electrodes 3a and 3b has no electrode portion 9 exposed to the outer peripheral surface of the columnar laminate 1, and the electrodeless portion 9 is the columnar laminate 1.
Since each layer is formed in a spiral shape on the outer peripheral surface, the displacement direction of the laminated piezoelectric actuator is different from the formation direction of the external electrodes 6 and 7, and the generated stress can be dispersed. It does not lead to a large stress concentration in one place.

FIG. 2 shows a schematic diagram of displacement that occurs when a voltage is applied to the laminated piezoelectric actuator of the present invention. As can be seen from FIG. 2, it can be seen that the stress is not concentrated but dispersed as compared with the conventional example shown in FIG.

Further, since the piezoelectric ceramic layers 2 are entirely bonded with the glass paste, the piezoelectric ceramic layers 2 are not broken even against a weak tensile force or a bending moment generated at the time of driving, and the reliability is dramatically improved.

FIG. 3 shows the results of analyzing the maximum principal stress with respect to the number of laminated layers of the laminated piezoelectric actuator of the present invention shown in FIG. 1 and the conventional laminated piezoelectric actuator shown in FIG. 5 using the finite element method. Show. According to FIG. 3, in the conventional actuator, the larger the number of laminated layers is, the larger the maximum principal stress during driving becomes, and the more easily it breaks. In contrast, in the actuator of the present invention, even if the number of laminated layers is increased. It can be seen that the increase in the maximum principal stress is very small, it is difficult to break and a long-life piezoelectric actuator can be obtained. That is, as shown in FIG. 2, by changing the state of mechanical deflection to make it smaller, the concentration of stress that becomes a fracture source can also be made smaller.

It is also possible to stack a plurality of units of the laminated piezoelectric actuator of the present invention in the axial direction and bond and fix these units over the entire contact interface.

The present inventors conducted experiments to confirm the effects of the present invention.

Experimental Example 1 First, a piezoelectric ceramic made of lead zirconate titanate Pb (ZrTi) O ₃ system was used, having a diameter of 18 mm and a plate thickness of 0.35.
mm-shaped disc, and an electrode-free portion not exposed at the end face portion and a silver electrode material were baked on one surface thereof to form an internal electrode. Then, the piezoelectric ceramics are laminated via the glass paste layer so that the electrodeless portion is spirally rotated by 180 degrees for each layer from 1 layer to 140 layers, and the glass is melted at a temperature of 550 ° C. for about 20 minutes, Pressure heat treatment 140
A columnar stack of layers was obtained.

Conductive epoxy paste is applied to the outer peripheral surface of the columnar laminate in which the internal electrodes are exposed for each layer, and 1
An external electrode was formed which was cured under the condition of 80 ° C. for 1 hour, and an internal electrode was electrically connected in parallel to each other, and thereafter, a polarization treatment was performed.

When a pressure of 10 kPa was applied in the axial direction of the obtained laminated piezoelectric actuator and a voltage of DC 300 V was applied, a displacement of 48 μm was obtained. Under the above conditions, continuous driving with a triangular wave having a frequency of 0 to 300 V and a frequency of 20 Hz resulted in no characteristic deterioration of the generated displacement even at 10 ⁸ times.

On the other hand, using the above-mentioned piezoelectric ceramic layer, a 140-layer laminated piezoelectric actuator having a conventional structure shown in FIG. 1 was produced. An experiment was conducted in the same manner as above using this conventional laminated piezoelectric actuator. D
Although a displacement of 48 μm was obtained when a voltage of C300 V was applied, the displacement drastically decreased about 10 ⁴ to 10 ⁶ times in continuous driving, leading to destruction.

Therefore, in this embodiment, it is understood that the reliability for continuous driving is greatly improved as compared with the conventional structure.

Experimental Example 2 Piezoelectric ceramics made of lead zirconate titanate Pb (ZrTi) O ₃ system was made into a 10 mm square and 0.35 mm thick plate, and an electrode-free part which was not exposed on the end face was formed on one side. The silver electrodes were baked to form internal electrodes. The electrodeless portion is spirally formed for each layer, that is, the position of each layer is offset so as to be formed on a diagonal line on the side surface of the laminate,
The same electrodeless portion is spirally formed on each of the opposite side surfaces.

A 70-layer columnar laminate having such a structure was produced, and an external electrode was formed in a spiral shape in a portion where the internal electrode was exposed for each layer, and the internal electrodes were electrically connected in parallel for each layer. Two such laminated piezoelectric actuators of 70 layers were produced, two of these were laminated in the axial direction by glass, and the external electrodes of the two laminated piezoelectric actuators were electrically connected, and then polarization treatment was performed. Was applied.

An explanatory view of this state is shown in FIG. This Figure 4
In the figure, reference numeral 13 indicates a laminated piezoelectric actuator of one unit, and these laminated piezoelectric actuators 13 are joined by glass.

When a pressure of 10 kPa was applied in the axial direction of the obtained laminated piezoelectric actuator and a voltage of DC 300 V was applied, a displacement of 47 μm was obtained. Under the above conditions, continuous driving with a triangular wave having a frequency of 0 to 300 V and a frequency of 20 Hz resulted in no characteristic deterioration of the generated displacement even at 10 ⁸ times.

[0031]

As described above, according to the present invention, the external electrodes for electrically connecting the internal electrodes are spirally formed on the outer peripheral surface of the columnar laminated body. The forming direction of the electrodes is different, and an electrode-free part, in which one end of the internal electrode is not exposed on the outer peripheral surface of the columnar laminate, is spirally formed on the outer peripheral surface of the columnar laminate. The generated stress can be dispersed, the large stress concentration does not occur in one place unlike the conventional structure, and the stress concentration generated at the time of driving can be suppressed to the minimum. It can be greatly improved. Therefore, it is possible to provide a highly reliable laminated piezoelectric actuator.

[Brief description of drawings]

FIG. 1 is a perspective view for explaining a cylindrical laminated piezoelectric actuator of the present invention.

FIG. 2 is a schematic diagram of displacement that occurs when a voltage is applied to the cylindrical laminated piezoelectric actuator of FIG.

FIG. 3 is a graph showing the relationship between the maximum principal stress and the number of laminated layers in the laminated piezoelectric actuator of the present invention and the conventional laminated piezoelectric actuator.

FIG. 4 is a perspective view illustrating a quadrangular prism-shaped laminated piezoelectric actuator according to another embodiment of the present invention.

FIG. 5 is a perspective view for explaining a conventional cylindrical laminated piezoelectric actuator.

FIG. 6 is a schematic diagram of a displacement that occurs when a voltage is applied to the cylindrical laminated piezoelectric actuator of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Columnar laminated body 2 ... Piezoelectric ceramic layer 3a ... 1st internal electrode layer 3b ... 2nd internal electrode layer 6, 7 ... External electrode 9 ... Electrode-free part 13 ...・ Layered piezoelectric actuator

Claims (1)

[Claims] 1. A columnar laminate is formed by alternately laminating a plurality of piezoelectric ceramic layers and a plurality of internal electrode layers, and
An internal electrode layer sandwiching the piezoelectric ceramic layer is composed of a first internal electrode layer and a second internal electrode layer, and a first external electrode and the second internal electrode electrically connecting the first internal electrode layers to each other. A laminated piezoelectric actuator, characterized in that second external electrodes for electrically connecting the layers are formed spirally on the outer peripheral surface of the columnar laminated body.