JP2571802B2 - Piezo actuator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a piezoelectric actuator for obtaining a large displacement and a generated force.

[Prior Art] FIG. 1 shows 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 each of the piezoelectric ceramics 2. Reference numeral 11 denotes a support member made of a bendable metal plate bonded to one side surface of the piezoelectric ceramic 2 via the electrode 3. An arrow A indicates a direction in which the piezoelectric ceramics 2 contracts when an electric field E is applied, and an arrow B indicates a direction in which the piezoelectric ceramics 2 expands.

As described above, as the piezoelectric element 1, one sheet having a thickness of 100 to 500
A support member is provided on one side surface of
11 are bonded together and bent in the direction of arrow C by utilizing a transverse effect of applying an electric field E in the same direction as the polarization direction P of the piezoelectric ceramics 2 to cause contraction in the direction perpendicular to the thickness direction. .

[Problems to be solved by the invention]

By the way, the unimorph type piezoelectric actuator shown in FIG. 1 is usually used as a vibrator such as a piezoelectric buzzer, and a design method of the 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.

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

[Means for solving the problem]

In the piezoelectric actuator according to the present invention, a non-piezoelectric bendable plate-shaped support member is directly bonded to a plate-shaped piezoelectric ceramic which expands and contracts according to the presence or absence of an electric field, in order to restrain the expansion and contraction deformation. In the piezoelectric actuator, the Young's modulus of the support is 2.5 times the Young's modulus of the piezoelectric ceramics bonded to each other.
More than twice, and the thickness t ₂ μm of the piezoelectric body is 100 μm ≦ t ₂ ≦ 5000
μm, and the ratio t ₂ / t ₁ of the thickness t _{2 of the} piezoelectric body to the thickness t ₁ of the support member is 1.6 or more.

[Action]

In the present invention, the required displacement amount and generated force can be obtained with a low applied electric field.

〔Example〕

The present invention relates to a unimorph type piezoelectric actuator composed of a piezoelectric ceramic and a non-piezoelectric bendable plate-like support member bonded thereto, in which the material to be used and the required characteristics such as displacement and generated force are reduced. When determined, the piezoelectric ceramics bonded to each other have a Young's modulus of 2.5 times or more with respect to the Young's modulus, and the thickness t _{2 of the} piezoelectric body.
a 100 [mu] m ≦ t ₂ ≦ 5000 .mu.m to [mu] m, and increasing the thickness t ₂ the ratio t ₂ / t ₁ is the applied field strength required the use of 1.6 or more support members in the thickness t ₁ of the support member of the piezoelectric It has been found that it can be reduced. That is, when the yanking rates of the _two members to be bonded, that is, the piezoelectric ceramics and the support member are Y ₂ and Y ₁ , respectively, Y ₁ ≧ 2.5Y ₂ . The reason that the Young's modulus of the supporting member is limited to 2.5 times or more of the Young's modulus of the piezoelectric body is that if the ratio is smaller than 2.5 times, the reduction of the applied electric field strength is small and the effect is small, and the ratio of the thickness of the piezoelectric body to the supporting member is 1.6 or more. The reason for this is that if the value is smaller than 1.6, the reduction of the applied electric field intensity is not only small, but conversely, the use of a high Young's modulus supporting member requires a high applied electric field intensity, which is inconvenient.

FIG. 3 shows the relationship between the Young's modulus Y ₁ (× 10 ¹⁰ N / m ² ) of the support member 11 and the electric field strength (kV / mm) at the target displacement and the generated force.

The Young's modulus Y ₂ of the piezoelectric element 7 is Y ₂ = 5.9 × 10 ¹⁰ N / m ^{2 and} the thickness of the supporting member is 60 μm. The thickness of the piezoelectric body is 210 μm. The width of the element is 5 mm (that is, the thickness ratio is 3.5). The length of each was fixed at 15 mm.

Curves I, II and III are all unimorph type,
The case of 500 μm / 50 gf, 500 μm / 30 gf, and 250 μm / 25 gf is shown.

FIG As can be seen from the use of support members 11 of a material having a large Young's modulus Y _1, a predetermined amount of displacement in the amount required distortion amount (dE) is small and the force is obtained.

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

Also the amount of work (δ: displacement, F: generated force), the effect of Young's modulus on the reduction of required strain increases. In other words, it is advantageous to use a material having a higher Young's modulus as the work becomes larger.

The present invention can be applied to the conventional unimorph type piezoelectric actuator shown in FIG.
It can be applied to the piezoelectric actuator shown in the figure.

That is, FIG. 2 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 bonded to one side surface of the piezoelectric element 1 in the longitudinal direction with a piezoelectric element 7 made of an insulating adhesive such as an epoxy resin.
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 the 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 be laminated in the longitudinal direction of the plate. The obtained piezoelectric ceramics 2 is obtained.

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

Next, an insulating layer 12 is formed by applying an epoxy resin serving as an insulating material and an adhesive to a supporting member 11 made of, for example, a 90-μm-thick Fe—Ni alloy metal plate, and the piezoelectric element 7 is bonded.

Although not shown, the application direction of the electric field E, the polarization direction P, the contraction direction A, 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 having the same shape.

In each of the following examples, the above-mentioned vertical effect type laminated piezoelectric ceramics are used, and zirconia, alumina, and tungsten carbide are used as the supporting members. In addition, SiC, Si
_{3 N 4, AlN, B 4} C, non-oxide ceramics such as TiC, MgAl
Oxide ceramics such as ₂ O ₄ , mullite, beryllia, and cordierite are listed. The element width is 5 mm, the element length is 15 mm, the thickness of the piezoelectric body is 210 μm, the thickness of the support member is 60 μm, and the Young's modulus of the piezoelectric body is 5.9 × 10 ¹⁰ N / m ² . As a comparative example, a case where phosphor bronze is used for the support member and a case where the thickness ratio between the piezoelectric body and the support member is smaller than 1.6 are shown as examples where Y ₁ / Y ₂ <2.5. The dimensions of the element and the piezoelectric material used are the same as in the embodiment.

(Example 1) support: Zirconia piezoelectric: PZT ceramics ^{_{(d 33 = 720 × 10 -6}} m / v) (Y 1 = 2.1 × 10 11 N / m 2) Y 1 / Y 2 = 3.6 applied field Strength: 1.35kV / mm (Example 2) Supporting member: Alumina Piezoelectric material: PZT-based ceramics (d ₃₃ = 720 × 10 ⁻¹² m / v) (Y ₁ = 3.3 × 10 ¹¹ N / m ² ) Y ₁ / Y ₂ = 5.6 Applied electric field Strength: 1.20kV / mm (Example 3) Supporting member: tungsten carbide (Y ₁ = 6.9 × 10 ¹¹ N / m ² ) Y ₁ / Y ₂ = 11.7 Applied electric field strength: 1.10 kV / mm Piezoelectric constant d ₃₃ : 720 × 10 ^-12 m / V Piezoelectric constant d ₃₁ : 260 × 10 ^-12 m / V (Comparative Example 1) Supporting member: phosphor bronze (Y ₁ = 1.2 × 10 ¹¹ N / m ² ) Y ₁ / Y ₂ = 2.0 Applied electric field strength: 1.54 kV / mm Thickness of support member, thickness of piezoelectric material: same as in each embodiment 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.

(Comparative Example 2) Supporting member: alumina (Y ₁ = 3.3 × 10 ¹¹ N / m ² ) Piezoelectric material: PZT-based ceramics (Y ₂ = 5.9 × 10 ¹⁰ N / m ² ) Thickness of the supporting member: 140 μm (Y ₁ / Y ₂ = 5.6) Thickness of piezoelectric body: 140 μm (t ₂ / t ₂ = 1.0) Applied voltage strength: 1.70 kV / mm As shown in this example, a higher electric field strength is required than in Example 1 (using zirconia) using a Young's modulus lower than alumina, and a higher electric field is required than in the case of phosphor bronze shown in Comparative Example 1. Is inconvenient.

[Effects of the Invention] As described above, the present invention provides a non-piezoelectric bendable plate-shaped support for restricting the expansion and contraction of the plate-shaped piezoelectric ceramics depending on the presence or absence of an electric field. in the piezoelectric actuator formed by bonding a member directly respectively, Y ₂ each Young's modulus of the piezoelectric ceramic and the support member, Y ₁ is Y ₁ ≧ 2.5Y _2, and the thickness t ₂ of the piezoelectric body is 100μm to bond to each other ≦ t ₂ ≦ 5000 μm, and the ratio t ₂ / t ₁ between the thickness t _{2 of the} piezoelectric body and the thickness t ₁ of the support member is 1.6 or more, so that the required applied electric field can be greatly reduced,
As a result, the generated force and the displacement can be increased as compared with the conventional case.

[Brief description of the drawings]

1 and 2 show piezoelectric actuators each showing an example of an object to which the present invention is applied. FIG. 1 shows a unimorph type, and FIG. 2 shows a unimorph type using a longitudinal effect type laminated piezoelectric ceramics proposed earlier. FIG. 3 is an explanatory diagram, and FIG. 3 is a measured value showing the relationship between the applied electric field strength and the Young's modulus of the embodiment of the present invention. 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 piezoelectric device in which a non-piezoelectric bendable plate-shaped support member is directly bonded to a plate-shaped piezoelectric ceramic which expands and contracts in accordance with the presence or absence of an electric field, in order to restrain the expansion and contraction deformation. in the actuator, the Young's modulus of the support 2.5 times or more relative to the Young's modulus of the piezoelectric ceramic bonded to each other, and the thickness t ₂ of the piezoelectric body 1
A piezoelectric actuator, characterized in that 00 μm ≦ t ₂ ≦ 5000 μm and a ratio t ₂ / t ₁ of the thickness t _{2 of the} piezoelectric body to the thickness t ₁ of the support member is 1.6 or more.