JP2585322B2 - Piezo actuator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a piezoelectric actuator for obtaining a large displacement and a generated force with a minimum applied electric field.

[Conventional technology]

FIGS. 1 and 2 both show an example of a conventional piezoelectric actuator to which the present invention is applied.

FIG. 1 is a perspective view showing a unimorph type piezoelectric actuator, 1 is an entire piezoelectric element, 2 is a plate-shaped piezoelectric ceramic, 3 is an electrode, 4 is a power source, and a piezoelectric ceramic 2 is provided through the electrode 3. An electric field E is applied. P indicates the polarization direction of the piezoelectric ceramic 2. 11 is the electrode 3
Is a support member made of a bendable metal plate bonded to one side surface of the piezoelectric ceramics 2 via a. An arrow D indicates a direction in which the piezoelectric ceramic 2 contracts due to the application of the electric field E, and an arrow B indicates a direction in which the piezoelectric ceramic 2 expands. In this way, as the piezoelectric element 1, one sheet having a thickness of 10
A support member 11 is attached to one side of a plate-shaped piezoelectric ceramic 2 having a thickness of 0 to 500 μm.
By applying an electric field E in the same direction as the polarization direction P of
It is bent in the direction of arrow C by utilizing the lateral effect of contracting in the direction perpendicular to the thickness direction.

FIG. 2 is a perspective view showing a bimorph type piezoelectric actuator. 1, the same reference numerals as those in FIG. 1 denote the same parts, 2A and 2B denote piezoelectric ceramics, 5 denotes a lateral effect type piezoelectric element, and 6 denotes a fixing base for fixing the piezoelectric element 5.

In this example, the piezoelectric element 5 has a thickness of 100 to 500 μ per sheet.
m plate-shaped piezoelectric ceramics 2A and 2B are directly joined,
An electric field E is applied to one of the piezoelectric ceramics 2A in the direction opposite to the polarization direction P, and the other piezoelectric ceramics 2B is bent in the direction of the arrow C by applying an electric field E in the same direction as the polarization direction P.

[Problems to be solved by the invention]

Incidentally, the unimorph type piezoelectric actuator shown in FIG. 1 is usually used as a vibrator such as a piezoelectric buzzer,
The design method as a vibrator has been almost established. However, when resonance of an actuator or the like is not used, or when low-frequency driving is performed, a method of optimally designing the thickness of the piezoelectric body and the bending member and the like in order to simultaneously obtain a large displacement and a generated force is disclosed. Absent. On the other hand, for a bimorph type piezoelectric actuator having a two-layer structure (without an intermediate plate) as shown in FIG. 3, two piezoelectric ceramics 2A and 2B of the same material and the same dimensions (thickness) are usually bonded together. However, there has not yet been disclosed any device which can obtain a large displacement and generated force in this case.

An object of the present invention is to solve such a problem.
It is an object of the present invention to provide a piezoelectric actuator capable of simultaneously obtaining a large displacement and a generated force in a bending type piezoelectric actuator and further minimizing an applied electric field intensity required for the displacement.

[Means for solving the problem]

The piezoelectric actuator according to the present invention includes a non-piezoelectric bendable plate-shaped support member or the piezoelectric ceramics for restraining the expansion and contraction of the plate-shaped piezoelectric ceramics depending on whether an electric field is applied or not. In a piezoelectric actuator in which support members made of a plate-shaped piezoelectric ceramic having different expansion and contraction directions are directly bonded to each other, the respective Young's moduli of the piezoelectric ceramic and the support member bonded to each other are set to Y ₂ , Y ₁ , and the thickness. Where t ₂ and t ₁ , and the ratio of the two Young's moduli is p, the range of the thickness t ₂ of the piezoelectric ceramic satisfies the following relational expression (I), and the thickness t _{1 of the} support member is the following relational expression. It satisfies (II).

0.8 × A ≦ t ₂ ≦ 1.2 × A (I) F: Force generated as an actuator (N) δ: Displacement (m) required as an actuator l: Length of actuator (m) b: Width of actuator (m) Y ₂ : Young's modulus of piezoelectric body (N / m) A: Optimum thickness of piezoelectric body (m) t ₁ : thickness of support member (m) t ₂ : thickness of piezoelectric body (m) [Action] In the present invention, the applied electric field is low and required. The displacement amount and the generated force can be obtained.

〔Example〕

The present invention provides a unimorph-type or bimorph-type piezoelectric actuator comprising a piezoelectric ceramic and a non-piezoelectric bendable plate-shaped support member or a plate-shaped piezoelectric ceramics support member bonded thereto.
When the material to be used and the required characteristics, ie, the displacement and the generated force, are determined, an optimum combination of thicknesses that minimizes the required applied electric field strength has been found. That is, assuming that the respective Young's moduli of the _two members to be bonded, that is, the piezoelectric ceramic and the support member are Y ₂ and Y ₁ and their thicknesses are t ₂ and t ₁ , respectively, the Young's modulus ratio p and the thickness each ratio q is _{p = Y 2 / Y 1 q} = t 2 / t 1 next, the relationship between the two In this case, it was found that the applied electric field intensity was minimal. At this time, t ₂ is Determines the optimal point.

Here, F: generated force required for the actuator, δ: displacement required for the actuator, l: length of the actuator, b: width of the actuator. In addition, the influence of the electrode or the adhesive layer is usually very small as compared with the thickness of the piezoelectric ceramic or the supporting member, and can be ignored.

Therefore, if it is possible to apply a larger electric field, a larger generated force and larger displacement can be obtained.

The above conditions of t ₁ and t ₂ are optimal values, but in general, the thickness t ₂ of the piezoelectric ceramic is given by the following formula (I), and the thickness t _{1 of the} support member is given by the following formula (II). You only have to be satisfied.

0.8 × A ≦ t ₂ ≦ 1.2 × A (I) The present invention can be applied not only to the conventional unimorph type and bimorph type piezoelectric actuators shown in FIGS. 1 and 2, but also to the previously proposed piezoelectric actuator of FIG.

That is, FIG. 3 is a view for explaining the principle of a piezoelectric actuator disclosed in Japanese Patent Application No. 61-228426, in which a longitudinal effect type laminated piezoelectric element (hereinafter simply referred to as a piezoelectric element) 7 and a support member 11 are combined. That is, a support member 11 made of a metal plate is attached to one side in the longitudinal direction of the piezoelectric element 1 with the piezoelectric element 7 with an insulating adhesive such as an epoxy resin, and is bonded.
An insulating layer 12 is formed.

When manufacturing the piezoelectric element 7, for example, a raw material powder of lead zirconate titanate (PZT) as the piezoelectric ceramic 2 and an organic binder, a plasticizer, a solvent, and the like are kneaded, a slurry is prepared, and a sheet is formed by a doctor blade or the like. After molding and drying, a required electrode 3 is formed by screen printing, and then laminated and heated and pressed to obtain a monolithic molded body.

Since the thickness of the piezoelectric ceramics 2 corresponds to the length of the piezoelectric element 7, the number of layers is determined so that the required element length is obtained. This is cut in a direction perpendicular to the direction of the electrodes 3, that is, cut so that the thickness of the piezoelectric element 7 becomes about several hundred μm, baked, and polished to a required thickness to thereby form a piezoelectric element laminated in the longitudinal direction. A body ceramic 2 is obtained.

Also, firing the molded body without cutting it, then
The same can be obtained by cutting and polishing. Then, a connecting electrode is baked, a lead wire is attached, and a polarization process is performed.

Next, if a unimorph type piezoelectric actuator is to be used, for example, an epoxy resin serving as an insulating material and an adhesive is applied to a pointing member 11 made of a metal plate of a Fe-Ni alloy having a thickness of 90 μm to form an insulating layer 12. Then, the piezoelectric element 7 is bonded.

In the case of a bimorph type piezoelectric actuator,
After sintering the lateral effect type laminated or single-phase piezoelectric element, processing it into a predetermined shape, and performing polarization processing, the insulating layer 12 is formed and the piezoelectric element 7 is bonded as in the unimorph type shown in FIG. .

Although not shown, the direction in which the electric field E is applied, the polarization direction P, the contraction direction D, and the extension direction B are the same as those of the piezoelectric element 1 in FIG.

With such a configuration, when applied to a unimorph-type piezoelectric actuator, the piezoelectric strain is 2-3 times larger than that of the conventional unimorph-type piezoelectric element 1 (d ₃₃ 2-3).
3 × d ₃₁ ). Therefore, both the displacement amount δ and the generated force F are two to three times larger than those of the lateral effect type unimorph type having the same shape.

The following examples all use the above-described vertical effect type laminated piezoelectric element, and use alumina, zirconia or a lateral effect type laminated piezoelectric element having different expansion and contraction directions as a support member. The element width is 5 mm and the element length is 15 mm.

(Example 1) Model: Unimorph Supporting member: Alumina Piezoelectric material: PZT-based ceramics (d ₃₃ = 720 × 10 ⁻¹² m / v) p: 0.1778 [(Y ₂ = 5.9 × 10 ¹⁰ N / m ² ) / ( Y ₁ = 3.3 × 10 ¹¹ N /
m ² )] q: 2.365 (t ₂ = 200 μm / t ₁ = 85 μm) Applied electric field strength: 1.17 kV / mm FIG. 4 shows the applied electric field strength and the amount of displacement, and FIG. 5 shows the measured values representing the relationship between the amount of displacement and the generated force.

(Example 2) Type: unimorph support member: zirconia piezoelectric: PZT ceramics ^{_{(d 33 = 720 × 10 -12}} m / v) p: 0.2810 ^{_{[(Y 2 = 5.9 × 10 10}} N / m 2) / ( Y ₁ = 2.1 × 10 ¹¹ N /
m ² )] q: 1.887 (t ₂ = 195 μm / t ₁ = 104 μm) Applied electric field strength: 1.25 kV / mm Piezoelectric constant d ₃₃ : 720 × 10 ^-12 m / V (Example 3) Model: Bimorph Support member: Lateral effect type piezoelectric material: PZT ceramics (d ₃₁ = 2
60 × 10 ⁻¹² m / v) Piezoelectric material: PZT-based ceramics (d ₃₃ = 720 × 10 ⁻¹² m / v) p: 0.8806 [(Y ₂ = 5.9 × 10 ¹⁰ N / m ² ) / (Y ₁ = 6.7 × 10 ¹⁰ N /
m ² )] q: 1.066 (t ₂ = 180 μm / t ₁ = 170) Applied electric field strength: 1.10 kV / mm (Comparative Example) (if t ₁ in combination of the same materials as in Example 1 does not satisfy the relational expression the formula (II)) Model: unimorph support: alumina piezoelectric: PZT ceramic p: 0.1788 (Example 1 Same) q: 1.0 (t ₂ = 140 μm / t ₁ = 140 μm) Applied electric field strength: 1.70 kV / mm As described above, in each of the embodiments of the present invention, it can be seen that a large displacement and a large generated force can be obtained with a smaller applied electric field intensity than the comparative example.

In addition, since the amount of displacement is large, the tip portion is not horizontal, but if this causes a problem, as shown in FIG. 6, two piezoelectric elements 7 are arranged on the support member 11 and displaced from each other. By reversing the direction, as shown by the dotted line after the displacement, the tip can be kept horizontal.

〔The invention's effect〕

As described above, the present invention provides a non-piezoelectric bendable plate-shaped support member or the piezoelectric body for restraining the expansion and contraction of the plate-shaped piezoelectric ceramic in accordance with the presence or absence of an electric field. In a piezoelectric actuator in which a ceramic and a support member made of a plate-shaped piezoelectric ceramic having a different expansion and contraction direction are directly bonded to each other, the Young's modulus of the piezoelectric ceramic and the support member to be bonded to each other are Y ₂ , Y ₁ , and the thickness. Where t ₂ and t ₁ , and the ratio of the two Young's moduli is p, the range of the thickness t ₂ of the piezoelectric ceramic satisfies the following relational expression (I), and the thickness of the support member is
Since t ₁ satisfies the following relational expression (II), if the material to be used, the amount of displacement, and the generated force are determined, the combination of thicknesses that minimizes the required applied electric field can be determined, and thus the generated force, displacement It has the advantage that the amount can be increased over the prior art.

0.8 × A ≦ t ₂ ≦ 1.2 × A (I)

[Brief description of the drawings]

FIGS. 1, 2, and 3 are piezoelectric actuators each showing an example of an object to which the present invention is applied. FIG. 1 is a unimorph type, FIG. 2 is a bimorph type, and FIG. 3 is a longitudinal effect proposed earlier. FIGS. 4 and 5 are diagrams showing measured values representing the relationship between the applied electric field intensity, the amount of displacement and the generated force shown in the first embodiment, and FIGS. The figure is an explanatory view showing a structure in which two unimorphs are arranged in order to level the tip. In the figure, 1, 5 and 7 are piezoelectric elements, 2, 2A and 2B are piezoelectric ceramics, 3 is an electrode, 4 is a power supply, 6 is a fixed base, 11 is a support member,
12 is an insulating layer.

Claims (1)

(57) [Claims] 1. A non-piezoelectric bendable plate-like support member or a direction in which the piezoelectric ceramic expands and contracts in order to restrain the expansion and contraction of the plate-like piezoelectric ceramic in accordance with the presence or absence of an electric field. In a piezoelectric actuator in which support members made of different plate-like piezoelectric ceramics are directly bonded to each other, the respective Young's moduli of the piezoelectric ceramics and the support member bonded to each other are Y ₂ and Y ₁ , and the thickness is t. ₂ , t ₁ , and the ratio of the two Young's moduli is p, the range of the thickness t ₂ of the piezoelectric ceramic satisfies the following relational expression (I), and the thickness t _{1 of the} supporting member is the following relational expression. A piezoelectric actuator characterized by satisfying (II). 0.8 × A ≦ t ₂ ≦ 1.2 × A (I) F: Force generated as an actuator (N) δ: Displacement (m) required as an actuator l: Length of actuator (m) b: Width of actuator (m) Y ₂ : Young's modulus of piezoelectric body (N / m) a: optimum thickness of the piezoelectric (m) t _1: thickness of the support member (m) t _2: piezoelectric thickness (m)