JPH06164009A - Multilayer piezoelectric actuator - Google Patents

Abstract

(57) [Abstract] [Purpose] To prevent a crack from being generated in a piezoelectric layer and to obtain a laminated piezoelectric actuator in which failure due to insulation failure is unlikely to occur. [Configuration] (T _A / Y _A ) + (T _C / Y _C )> 3.4 × 10
^-11 · T _C where, T _A: adhesive layer 4 further Thickness (m) Y _A: Young's modulus of the adhesive layer ^{4 (N / m 2) T} C: piezoelectric layers 1 layer of thickness (m) Y _C : A predetermined piezoelectric material (piezoelectric actuator element) 3 is bonded and laminated using a predetermined adhesive 4 so that the Young's modulus (N / m ² ) of the piezoelectric layer 1 is satisfied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric actuator, more specifically, electrodes (internal electrodes) on both sides of a piezoelectric layer.
The present invention relates to a laminated piezoelectric actuator in which a plurality of piezoelectric actuator elements are laminated by adhering a piezoelectric actuator element in which the above are arranged with an adhesive.

[0002]

Prior Art and Problems to be Solved by the Invention FIG.
FIG. 4 is a diagram showing an example of a laminated piezoelectric actuator,
(A) is a plane sectional view and (b) is a side view. Further, FIG. 2 is an enlarged cross-sectional view of the main part thereof.

This laminated piezoelectric actuator is shown in FIG.
As shown in FIG. 2, a plurality of piezoelectric actuator elements 3 (FIG. 2) having electrodes (internal electrodes) 2 disposed on both main surfaces of a piezoelectric layer 1 made of piezoelectric ceramic are adhered with an adhesive 4 to form a plurality of sheets. It is formed by stacking the above piezoelectric actuator elements 3. In each piezoelectric actuator element 3, the internal electrodes 2 arranged on both main surfaces of the piezoelectric layer 1 are drawn out to the ends on different sides.

External thin-film electrodes 6 are formed on opposite side surfaces of the laminated body 5 in which the piezoelectric actuator elements 3 are laminated (side surfaces from which the internal electrodes 2 are drawn out). Further, a thin metal plate 7 is arranged on the outer thin film electrode 6, and a lead wire 8 is connected to the thin metal plate 7. Further, the laminated body 5 thus formed is coated on its entire side surface with the coating agent 9 for exterior.

In the laminated piezoelectric actuator constructed as described above, the internal electrodes 2 of each piezoelectric actuator element 3 are drawn out to the ends on different sides, and at the center of the piezoelectric layer 1. Since the internal electrodes 2 are opposed to each other, when a voltage is applied to the internal electrodes 2, the central portion 11 except for the end portions 10 on both sides of the laminated body 5 mainly expands and contracts (displaces).

Therefore, a stress is applied to the boundary between the central portion 11 that expands and contracts (displaces) and the end portion 10 that does not expand and contract (displace), and cracks 1a occur in the piezoelectric layer 1 to cause insulation failure. is there.

The present invention solves the above problems and prevents cracks from occurring in the piezoelectric layer,
An object of the present invention is to provide a laminated piezoelectric actuator that does not cause a failure due to poor insulation.

[0008]

In order to achieve the above object, the laminated piezoelectric actuator of the present invention comprises a piezoelectric actuator element having electrodes arranged on both surfaces of a piezoelectric layer, which are bonded by an adhesive agent. , (T _A / Y _A ) + (T _C / Y _C )> 3.4 × 10 ⁻¹¹ · T _C ...... (a) However, in a laminated piezoelectric actuator in which a plurality of piezoelectric actuator elements are laminated, , T _a: adhesive Soisso thickness (m) Y _a: Young's modulus of the adhesive layer _{^{(N / m 2) T C}} : piezoelectric Soisso thickness (m) Y _C: Young's modulus of the piezoelectric layer ( N / m ² ) is satisfied.

That is, the present invention has been completed by various studies, assuming a model as described below.

For example, when considering a model in which each of the piezoelectric layer made of piezoelectric ceramics and the adhesive layer is one layer, it can be treated as a model as shown in FIG. In addition,
In order to facilitate understanding, description will be given with reference to each part of the laminated piezoelectric actuator as shown in FIG.

That is, in the model shown in FIG.
The displacement δ (m) of both the piezoelectric layer and the adhesive layer is expressed by the following equation. δ = d ₃₃ · V, where d ₃₃ : piezoelectric constant (m / V) V: applied voltage (V)

Then, the gap area of the above model, that is, the area of the end portions 10, 10 of one piezoelectric actuator element 3 in the laminated piezoelectric actuator of FIG. 4 is S (m ² ), the piezoelectric layer 1 and the adhesive. When the spring constants of the layer 4 are K _C and K _A (N / m), respectively, K _C = (Y _C · S) / T _C …… K _A = (Y _A · S) / T _A …… .

Further, the tensile force when the F (N), a _{δ = δ C + δ A ......} δ C = F / K C ...... δ A = F / K A .......

Then, by substituting ,,, into, δ = {(T _C / Y _C ) + (T _A / Y _A )} · (F / S).

The stress T is T = F / S (N / m ² ).
And from the equation, T = δ / {(T _C / Y _C ) + (T _A / Y _A )}.

Since δ is a strain, it is proportional to T _C.
Therefore, if the formula is modified, (T _C / Y _C ) + (T _A / Y _A ) = δ / T = KT _C.

Therefore, the conditions represented by the above formula (a) were found by examining various conditions preferable as the adhesive from this formula.

That is, the piezoelectric actuator element is prepared by using an adhesive satisfying the above formula (a): (T _A / Y _A ) + (T _C / Y _C )> 3.4 × 10 ⁻¹¹ · T _C. Internal electrodes 2 and 2 by adhering and stacking (Fig. 4)
Also in the laminated piezoelectric actuator configured such that the central portion 11 of the laminated body 5 excluding both end portions 10 expands and contracts (displaces) when a voltage is applied between the central portion 11 and the central part 11 that expands and contracts (displaces). It is possible to prevent the occurrence of cracks at the boundaries between both ends 10 that are not (displaced), and suppress the occurrence of failures due to insulation failure.

[0019]

EXAMPLES The features of the present invention will be described in more detail below with reference to examples of the present invention.

Example 1 A piezoelectric layer having a thickness of 150 μm and a Young's modulus of 5.3 × 10 ¹⁰ N / m ² (for example, lead zirconate titanate (Pb (Zr _{1 -X}
A piezoelectric actuator element in which electrodes (internal electrodes) are formed on both surfaces of a Ti _x ) O ₃ ) -based piezoelectric ceramic layer) is prepared by using an epoxy adhesive having a Young's modulus of 2.95 × 10 ⁹ N / m ^2. By laminating and bonding, a laminated piezoelectric actuator having 63 laminated layers was prepared as a sample. The thickness of the adhesive layer was changed within the range shown in Table 1.

Then, using the above sample, a direct current of 200
A durability test was performed by applying a voltage of V. In the durability test, when the insulation resistance decreased to 1/100, it was determined that the failure occurred.

The results of the above durability test are shown in the graph of FIG. 5, and Table 1 shows the above formula, that is, (T _C / Y _C ).
The value of K at + (T _A / Y _A ) = δ / T = KT _C is shown. Table 1 also shows theoretical values of internal stress applied to the piezoelectric layer (piezoelectric ceramic layer) when a voltage is applied under the above conditions. When obtaining the value of the internal stress, as the value of δ, the d ₃₃ constant (603 ×
A value obtained by multiplying 10 ⁻¹² m / V) by an applied voltage of 200 V (1.
21 × 10 ⁻⁷ m) was used.

[0023]

[Table 1]

From Table 1 and FIG. 5, the thickness of the adhesive layer is 7 μm.
m or more, that is, the value of K in the above equation is 3.47.
It can be seen that when the density is × 10 ^-11 or more, the internal stress decreases and the value of the failure occurrence time (MTTF) remarkably increases.

Example 2 The same piezoelectric layer (piezoelectric ceramic layer) as in Example 1 was used, the thickness of the adhesive layer was kept constant at 6 μm, and the Young's modulus of the adhesive (epoxy adhesive) was in the range shown in Table 2. A laminated piezoelectric actuator (sample) similar to that of the above-mentioned Example 1 was prepared by changing it, and a durability test was conducted under the same conditions as in the above-mentioned Example 1. The results are shown in the graph of FIG. 6 and the value of K in the above equation is shown in Table 2. Table 2 also shows theoretical values of internal stress applied to the piezoelectric layer (piezoelectric ceramic layer) when a voltage is applied under the above conditions.

[0026]

[Table 2]

From Table 2 and FIG. 6, Young's modulus is 2.55 ×
10 ⁹ N / m ² or more, i.e., when the value of K in the equation is 3.46 × 10 ^-11 or more, it can be seen that the value of the failure occurrence time (MTTF) with an internal stress is decreased becomes remarkably large.

From the above Examples 1 and 2, the thickness of the adhesive layer, the Young's modulus, the value of K, and the failure occurrence time (MTT).
From the relationship of F), it is recognized that the value of the failure occurrence time remarkably increases when K = 3.4 × 10 ⁻¹¹ or more, so K =
The condition of 3.4 × 10 ^-11 or more is defined as the scope of claims.

The present invention is not limited to the above-mentioned embodiment, but the thickness and the number of laminated piezoelectric layers, the composition of the material forming the piezoelectric layers, the kind of adhesive, etc. are not limited to the above embodiments. Various applications and modifications can be made within the scope of the gist.

[0030]

As described above, the laminated piezoelectric actuator of the present invention is used.
The quotator is (T_A/ Y_A) + (T C / Y_C)> 3.4
× 10^-11・ T_C To satisfy the relationship of (formula (a)),
Use a specified adhesive (piezoelectric actuator)
The piezoelectric element is attached and laminated.
The inner electrodes face each other in the center of the layer, and a voltage is applied between the inner electrodes.
When added, the center part of the stack excluding both ends expands and contracts.
Laminated piezoelectric actuator configured to (displace)
Even in the case of
Cracks may occur at the boundary between the two ends.
To prevent the occurrence of failures due to poor insulation.
Will be possible.

[Brief description of drawings]

FIG. 1 is a view showing a laminated piezoelectric actuator,
(A) is a plane sectional view and (b) is a side view.

FIG. 2 is an enlarged sectional view of an essential part showing a laminated piezoelectric actuator.

FIG. 3 is a diagram showing a model for explaining the present invention.

FIG. 4 is an enlarged sectional view of an essential part showing a laminated piezoelectric actuator according to the present invention.

FIG. 5 is a graph showing the relationship between the thickness of the adhesive layer and the failure occurrence time (MTTF) in the example of the present invention.

FIG. 6 is a graph showing the relationship between the Young's modulus of the adhesive layer and the failure occurrence time (MTTF) in the example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric layer (piezoelectric ceramic layer) 2 Electrode (internal electrode) 3 Piezoelectric actuator element 4 Adhesive (layer) 5 Laminated body 6 External thin film electrode 7 Metal thin plate 8 Lead wire 9 Coating agent 10 Edge of laminated body 11 Laminated body Central part of

Claims (1)

[Claims] 1. A piezoelectric actuator element having electrodes arranged on both sides of a piezoelectric layer is adhered with an adhesive,
In a laminated piezoelectric actuator formed by laminating a plurality of piezoelectric actuator elements, (T _A / Y _A ) + (T _C / Y _C )> 3.4 × 10 ⁻¹¹ · T _C where T _A : adhesive Soisso thickness (m) Y _a: Young's modulus of the adhesive layer _{^{(N / m 2) T C}} : piezoelectric Soisso thickness (m) Y _C: Young's modulus of the piezoelectric layer (N / m ²⁾ A laminated piezoelectric actuator characterized by satisfying a relationship.