JPH01245571A - Piezoelectric actuator - Google Patents

Abstract

PURPOSE:To obtain a piezoelectric actuator capable of obtaining a large displacement and a large generating force using a longitudinal effect type laminated piezoelectric element by a method wherein a tensile stress or a compressive stress, which is generated in the surface part of the piezoelectric element, is reduced within a range of a specified value or lower. CONSTITUTION:If a piezoelectric actuator is designed in such a way that a stress, which is generated in the piezoelectric actuator at the time of flex displacement, in particular a tensile stress, which is generated in the surface part of a longitudinal effect type laminated piezoelectric element 1, is reduced or a compressive stress, which is generated in the surface part, is applied, a breakdown of the element can be prevented because the strength of this surface part is lowest. That is, the respective thicknesses of the element 1, intermediate supporting plates and a transverse effect type laminated piezoelectric element 7 are changed, a stress, which is generated in the interior of the element 1 of the weakest strength, is reduced so as to be within a range of a stress of a rapture strength or lower, that is, within a range of 0.5kg/cm<2> or less as a tensile stress or within a range of 5kg/cm<2> or less as a compressive force and moreover, with such the whole flexural rigidity as this flex type piezoelectric actuator can be obtained a prescribed amount of displacement and a prescribed generating force and a necessary applying field intensity, each plate thickness is decided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a bending type piezoelectric actuator such as a bimorph or unimorph, and particularly to a bending type piezoelectric actuator using a longitudinal effect type laminated piezoelectric element.

[Conventional technology]

3 to 5 all show conventional piezoelectric actuators.

FIG. 3 is a perspective view showing a longitudinal effect type laminated piezoelectric actuator, in which 1 shows the entire longitudinal effect type laminated piezoelectric element (hereinafter simply referred to as a piezoelectric element unless otherwise required), 2 a plate-shaped piezoelectric ceramic, 3 is an electrode, and 4 is a power source, which applies an electric field E to each piezoelectric ceramic 2 through the electrode 3. P
indicates the polarization direction of each piezoelectric ceramic 2. Arrow A indicates the direction in which the piezoelectric ceramic 2 contracts due to the application of the electric field E, and arrow B indicates the direction in which the piezoelectric ceramic 2 expands.

In this way, the piezoelectric element 1 is made by laminating several hundred layers of piezoelectric ceramics 2 having a thickness of about 50 to 100 μm per layer in the thickness direction, and the polarization direction P of the piezoelectric ceramics 2 is
By applying an electric field E in the same direction as , the longitudinal effect is utilized to extend the entire body in the thickness direction.

Figure 4 is a perspective view showing a transverse effect type piezoelectric actuator.
It is called a unimorph type. In this figure, the same reference numerals as in FIG. 3 indicate the same parts, and 5 is a transverse effect type piezoelectric element (hereinafter simply referred to as piezoelectric element unless otherwise required);
6 is a piezoelectric ceramic, and 11 is a bendable metal plate bonded to one side of the piezoelectric ceramic 6 via the electrode 3.

In this way, the piezoelectric element 5 has a thickness of 100 to 5
A metal plate 11 is bonded to one side of a 00 μm plate-shaped piezoelectric ceramic 6, and by applying an electric field E in a direction opposite to the polarization direction P of the piezoelectric ceramic 6, a lateral effect is utilized to elongate it in the longitudinal direction. This type is bent in the direction of arrow C.

Figure 5 is a perspective view showing a transverse effect type piezoelectric actuator.
This is called a bimorph type. In this figure, the same reference numerals as in FIG. 4 indicate the same parts, 6A and 6B are piezoelectric ceramics, 8 is a transverse effect type piezoelectric element (hereinafter simply referred to as a piezoelectric element), and 9 is a fixing base for fixing the piezoelectric element 8. It is.

In this example, each piezoelectric element 8 has a thickness of 100 to 50
0 μm plate-shaped piezoelectric ceramics 6A and 6B are formed either directly or by bonding them together with a metallic intermediate electrode plate in between to facilitate electrode removal. in the opposite direction to the polarization direction P, and in the same direction as the polarization direction P to the other piezoelectric ceramic 6B.
They are of a type in which an electric field E is applied to bend them in the direction of arrow C.

The above bimorph type piezoelectric actuator has a displacement of several 1
The main feature is that it can be relatively large at 0.00 μm, but in order to meet the ever-increasing demands for large displacements and large generated forces, it is better to use the longitudinal effect than the transverse effect to develop new materials. There is an advantage that the amount of displacement can be obtained 2 to 3 times as much as when using the lateral effect without any development.

In other words, Figure 1 shows the piezoelectric actuator (
(See Japanese Patent Application No. 61-228426). The same reference numerals as in FIGS. It is a combination of 7). Note that the insulating layer 1
A metal plate 11 shown in FIG. 4 may be interposed between the piezoelectric element 2 and the piezoelectric element 7.

When manufacturing the piezoelectric actuator shown in Fig. 1, for example, raw material powder of lead zirconate titanate (PZT) as piezoelectric ceramic 2.6B is kneaded with an organic binder, a plasticizer, a solvent, etc., a slurry is prepared, and a doctor blade, etc. After drying, necessary electrodes 3 are formed by screen printing, and then laminated and heated and pressed to obtain a monolithic molded body.

Since the thickness of the piezoelectric ceramic 2 corresponds to the length of the piezoelectric element 1, the number of laminated layers is determined so as to obtain the required element length. This is cut in a direction perpendicular to the direction of the electrodes 3, that is, so that the length of the piezoelectric element 1 is about several 100 μm, and then fired and polished to the required thickness, so that the plates are laminated in the longitudinal direction. A piezoelectric ceramic 2 is obtained.

Alternatively, the same result can be obtained by firing the molded body as it is without cutting it, and then cutting and polishing it. A contact electrode is baked onto this, a lead wire is attached, and polarization is performed.

Next, the piezoelectric ceramic 6B is fired and processed into a predetermined shape, and after polarization treatment is performed, the insulating layer 12 is formed and the piezoelectric element 1 is bonded. Further, in order to facilitate the electrode extraction, a bendable metal plate may be simultaneously bonded between the piezoelectric ceramic 6B and the insulating layer 12 as an intermediate electrode.

In this manner, in order to drive at a low voltage, the longitudinal effect type laminated piezoelectric element 1 laminated in the longitudinal direction of the element is bonded together with the metal plate 11 or another piezoelectric ceramic 6B with the metal plate 11 interposed therebetween.

In particular, when used with the transverse effect type laminated piezoelectric element 7 that utilizes the transverse effect, since the polarization direction and the electric field direction match, a large electric field can be applied without depolarization, making it a preferable structure for large displacements. Further, it is more preferable that the transverse effect type multilayer piezoelectric element 7 is also formed into a multilayer structure as described above in order to lower the voltage.

[Problem to be solved by the invention]

Longitudinal effect type laminated piezoelectric element 1 in bending type piezoelectric actuator
When using, this longitudinal effect type laminated piezoelectric element 1 expands,
Bending occurs by restraining its expansion at a position perpendicular to its direction of expansion, but in this case, the problem is that repeated use will cause cracks in the longitudinal effect type laminated piezoelectric element 1, resulting in destruction of the element. was there.

The reason for this is that in the longitudinal effect type laminated piezoelectric element 1, the internal electrode is in a state where the notch is just inside the piezoelectric ceramic 2, and when tensile stress is applied in the lamination direction, its strength becomes extremely low. It is. When the bending strength is actually measured, the piezoelectric ceramic 2 alone has a bending strength of approximately 10 to 15
However, when the bending strength of the longitudinal effect type laminated piezoelectric element 1 is measured by the bending strength measuring device 13 as shown in FIG. 2, it is approximately 4 to 6 Kg/mm2, which is less than half. In addition, when calculating the stress generated inside the bending piezoelectric actuator using the longitudinal effect type multilayer piezoelectric element 1, it is found that the stress generated inside the bending type piezoelectric actuator using the longitudinal effect type multilayer piezoelectric element 1 is approximately 2.
It was found that a large tensile stress of K g/mm2 was generated. Usually, tensile strength is 1 part of bending strength.
/2 to 1/3, so approximately 2 K generated on the surface
It was found that a tensile stress of g/mm2 destroys the device.

This invention was made to solve the above problems, and aims to provide a piezoelectric actuator that can obtain large displacement and large generated force using longitudinal effect type laminated piezoelectric elements. .

(Means for Solving the Problems) A piezoelectric actuator according to the present invention has plate-shaped piezoelectric ceramics laminated in the thickness direction to form a longitudinal effect type laminated piezoelectric element. In a piezoelectric actuator in which a means for restraining the extension is provided on one side of the piezoelectric actuator, the tensile stress generated on the surface of the longitudinal effect type laminated piezoelectric element is 0.5 Kg/mm2 or less, or the compressive stress is 5K/m2 or less. It is designed to be within the range.

[Effect]

In this invention, the tensile stress generated on the surface of the longitudinal effect type laminated piezoelectric element is set to be within the range of 0.5 Kg/mm2 or less, or the compressive stress is set within the range of 5 K/mm2 or less, so that the piezoelectric actuator Will not be damaged.

〔Example〕

If the stress generated in the piezoelectric actuator during bending displacement, especially the tensile stress generated on the surface of the longitudinal effect type laminated piezoelectric element 1, is reduced or designed to apply compressive stress, the strength of this area is the lowest, so the element destruction can be prevented. That is, longitudinal effect type multilayer piezoelectric element 1. By changing the respective thicknesses of the intermediate support plate and the transverse effect type laminated piezoelectric element 7,
The stress generated inside the longitudinal effect type laminated piezoelectric element 1, which has the weakest strength, is the stress below the breaking strength, that is, the tensile stress is 0.5 Kg/mm' or less, or the compressive stress is 5 Kg/mm' or less.
In addition, the thickness of each plate should be adjusted so that the bending type piezoelectric actuator has the overall bending rigidity and the necessary applied electric field strength so that the bending type piezoelectric actuator can obtain the predetermined amount of displacement and generated force. All you have to do is decide.

Although it is preferable to use a laminate for the transverse effect type laminated piezoelectric element 7 in order to reduce the working voltage, the longitudinal effect type laminated piezoelectric element 1
The thickness of each layer laminated together can be determined from the voltage used and the required electric field strength.

In the following examples, specific plate thicknesses of the elements and element shapes (length, width) are shown so as to obtain several examples of predetermined displacement amounts and generated forces, but other predetermined displacement amounts are possible.

Since the generated force and the element shape can be manufactured based on the above-mentioned method, the present invention is not limited to the examples described below.

The piezoelectric strain constant of the piezoelectric material used in the following examples and comparative examples is d 33" 720 X 10-" m/Vd 3I
= 350 x 10-” m/V.

(Example 1) In a bimorph with an effective element length of 30 mm and width of 15 mm, the force generated per predetermined displacement amount is 600 μm.
Bimorphs were prepared with the following plate thicknesses so as to obtain m and IKgf.

Longitudinal effect type laminated piezoelectric element 400μm intermediate support plate (
Zirconia family) 220μm20μm transverse effect type stacker
Further, since the applied voltage was 120 μm and the required applied electric field strength was about 1.2 KV/mm, the thickness of each layer of the laminate was 100 μm. That is, the longitudinal effect type laminated piezoelectric element 1 has approximately 300 layers, and the transverse effect type laminated piezoelectric element 7 has six layers.

When the displacement amount and generated force were measured when 120V was applied, they were 630 μm and 9503f, respectively.

In addition, in order to measure the stress generated on the surface of the longitudinal effect type laminated piezoelectric element 1, a strain gauge was attached to the element surface.
When the stress was determined by measuring the actual amount of strain, it was found to be 0.1Kg.
It was confirmed that a tensile stress of /mm2 was acting.

However, the stress obtained using a strain gauge is (amount of strain on the element surface when 120V is applied and bent) - (strain i when 120μ is applied to longitudinal effect type multilayer piezoelectric element 1 alone without bending) ) multiplied by the Young's modulus of the piezoelectric material. Furthermore, when a durability test was conducted under no load by repeatedly applying a voltage, durability over 105 cycles or more was confirmed.

(Example 2) In a bimorph with the same effective element length of 30 mm and width of 15 mm as in Example 1, the plate thickness of the two piezoelectric elements was changed without using an intermediate support plate so that a predetermined displacement amount of 600 μm1 generated force IKgf was obtained. was produced as follows.

Longitudinal effect type laminated piezoelectric element 400 μm 00 μm Lateral effect type stacker 800 μm The thickness and applied voltage of each layer of the laminate were the same as in Example 1. When 120 V was applied, the amount of displacement, the generated force, and the stress generated on the surface of the longitudinal effect type laminated piezoelectric element 1 were 620 μm and 980 gf, respectively.

The tensile stress was 0.05 Kg/mm2. Similar to Example 1, the repetition durability was 105 times or more.

(Comparative Example 1) In order to obtain the same displacement amount 1 generation force as in Example 1.2, a bimorph was produced with all dimensions the same except for each plate thickness. The thickness of the piezoelectric body was as follows: Longitudinal effect type multilayer piezoelectric element: 600 μm Transverse effect type stacker: 6008 m In order to obtain the same amount of displacement and generated force as in Examples 1 and 2, a voltage of 100 V was applied. That is, the predetermined amount of displacement and generated force were obtained by applying a voltage 20V lower.

In addition, the stress obtained by the strain gauge was 2.1K g/
It was mm2. A repeated durability test was conducted in the same manner as in Example 1 by repeatedly applying 100V.
The device was destroyed after 102 cycles or less.

(Example 3) Effective element length 25mm, width 8.5mm.

Bimorphs were manufactured with various plate thicknesses as follows so as to obtain a predetermined maximum displacement of 1 mm and a generated force of 100 gf.

Longitudinal effect type laminated piezoelectric element 165μm intermediate support plate (
Made of alumina) 75μm transverse effect type laminated piezoelectric element
240μm, and the applied voltage is 140V, and
Since the required electric field strength was 1.15 KV/mm, the thickness of each layer of the laminate was 120 μm. Displacement amount 1 when applying 140V
The generated force and the stress generated in the longitudinal effect type laminated piezoelectric element 1 are 1.01mm, 993f, and 0.05Kg, respectively.
The compressive stress was /mm2. In a repeated durability test in which 140V was repeatedly applied, durability was confirmed for about 106 times.

Note that whether compressive stress or tensile stress is applied as in this embodiment is determined by the relationship between the elongation of each piezoelectric element due to voltage application and external force.

(Comparative Example 2) In order to obtain the same displacement amount 7 generated force as in Example 3, a bimorph was produced with the same dimensions except for each plate thickness. however,
A phosphor bronze plate was used as the intermediate support plate.

Longitudinal effect type laminated piezoelectric element 230μm intermediate support plate (
(made of phosphor bronze) 20μm transverse effect type laminated piezoelectric element
The voltage applied for 230 μm was 120V. 12
The measured displacement and generated force when applying 0■ are respectively i.

2 mm and 98 gf, but the stress generated on the surface of the longitudinal effect type laminated piezoelectric element 1 was a tensile stress of 1.8 Kg/mm2. When a durability test was conducted by repeatedly applying 120V, it broke after approximately 250 cycles.

(Example 4) A unimorph type piezoelectric actuator was fabricated with each plate thickness as follows so as to obtain a predetermined maximum displacement of 450 μm and a generated force of 45 gf with an effective element length of 15 mm and a width of 5 mm.

Longitudinal effect type laminated piezoelectric element 145μm support plate (made of alumina) 135μm Applied voltage is 125V
Since the required applied electric field strength is 1.25 KV/mm, the thickness of each layer of the laminate is 100 μm. The amount of displacement and generated force when applying 125V, and the stress on the surface of the longitudinal effect type laminated piezoelectric element 1 are 460μm44gf and 0°1K, respectively.
The compressive stress was g/mm2. In a repeated durability test in which 125V was repeatedly applied, durability of approximately 105 times or more was obtained.

(Comparative Example 3) In order to obtain the same displacement amount 1 generation force as in Example 4, a unimorph was produced with all dimensions the same except for each plate thickness.

Longitudinal effect type laminated piezoelectric element 200 μm support plate (made of alumina) 85 μm The applied voltage was 105 V. The amount of displacement and generated force when applying 105V are each 46
It was 5 μm and 43 gf. Further, the stress on the surface of the longitudinal effect type laminated piezoelectric element 1 was a tensile stress of about 1.8 Kg/mm'. Further, when a repeated durability test was conducted by repeatedly applying 1 osv, the device was destroyed after approximately 150 cycles.

〔Effect of the invention〕

As explained above, the present invention has the advantage that the tensile stress generated on the surface of the longitudinal effect type laminated piezoelectric element is 0. 5K g/m
m” or less or the compressive stress is 5 K/mm2
It was set to the following range, so it was a big change.

When a longitudinal effect type laminated piezoelectric element is used in a bending type piezoelectric actuator to obtain a large generated force, the tensile stress generated on the element surface of the longitudinal effect type laminated piezoelectric element is reduced, and even under large displacement,
This has the advantage that the element is not destroyed and durability is greatly improved.

[Brief explanation of the drawing]

Figure 1 is a perspective view of a bimorph piezoelectric actuator using a longitudinal effect type laminated piezoelectric element and a transverse effect type laminated piezoelectric element to which the present invention is applied, and Figure 2 is a measurement of the bending strength of the longitudinal effect type laminated piezoelectric element. Fig. 3 is a perspective view showing a conventional longitudinal effect type multilayer piezoelectric actuator, Fig. 4 is a perspective view showing a unimorph transverse effect piezoelectric actuator, and Fig. 5 is a perspective view showing a bimorph transverse effect piezoelectric actuator. FIG. 2 is a perspective view showing an effect type piezoelectric actuator. In the figure, 1 is a longitudinal effect type laminated piezoelectric element, 2 and 6B are piezoelectric ceramics, 3 is an electrode, 4 is a power supply, 7 is a transverse effect type laminated piezoelectric element, 9 is a fixing table, and 13 is a bending strength measuring device. . Fig. 1 Fig. 2 13 Bending forgery detection device Fig. 3 Fig. 4 Fig. 5

Claims (1)

[Claims] A piezoelectric actuator in which plate-shaped piezoelectric ceramics are laminated in the thickness direction to form a longitudinal effect type laminated piezoelectric element, and a means for restraining the expansion is provided on one longitudinal side of the longitudinal effect type laminated piezoelectric element, The tensile stress generated on the surface of the longitudinal effect type laminated piezoelectric element is 0.5 Kg/mm^2
A piezoelectric actuator characterized in that it has a configuration in which the compressive stress is in the range of 5 Kg/mm^2 or less.