JP2001068750A - Laminated piezoelectric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated piezoelectric actuator which is capable of generating a constant displacement with the same applied voltage even if it is used in a wide range of temperature and varies in temperature due to self- heat release. SOLUTION: A laminated piezoelectric actuator is equipped with an active body 5 composed of piezoelectric plates 1 and metal plates 3 which are alternately laminated, and inactive bodies 7 which are each provided to each edge face of the active body 5. Provided that the length and linear expansion coefficient of the active body 5 in the direction of lamination and the length and linear expansion coefficient of the inactive body 7 in the direction of lamination are represented by L, α and L1, α1, respectively, are so set s to satisfy a formula, |Lα|≈|2L1α1|, where Lα and 2L1α1 are different from each other in polarity.

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, and is used, for example, as a precision positioning device such as an optical device, a drive element for preventing vibration, a drive element for fuel injection of an automobile engine, and the like. The present invention relates to a multilayer piezoelectric actuator.

[0002]

2. Description of the Related Art Hitherto, a laminated piezoelectric actuator in which piezoelectric plates and electrodes are alternately laminated has been known. In such a laminated piezoelectric actuator, a voltage is applied to a piezoelectric plate and the piezoelectric plate is extended by several to several tens of μm by a reverse piezoelectric effect, and is used as a driving force source of the actuator.

[0003] Such a laminated piezoelectric actuator is
For example, an active body in which piezoelectric plates and electrodes are alternately stacked,
An inert body provided on each of both end faces in the stacking direction of the active body, and the inert body transmits a displacement generated by applying a voltage to the active body to the outside, or , Insulation from the outside was achieved.

Conventionally, the same piezoelectric material as that of the active material has been used for the inactive material (see Japanese Utility Model Application Laid-Open No. 61-1986).
No. 127657). Further, in order to increase the reliability of the bonding interface between the active body and the inactive body, a material having anisotropy in elastic modulus may be used as the inactive body (Japanese Patent Laid-Open No. 3-66).
183), or a material containing silver in a piezoelectric plate material is used to prevent cracking of the active body during driving (see JP-A-63-288074).

In recent years, multilayer piezoelectric actuators have been used at various low temperatures, such as a low temperature of 0 ° C. or lower and a high temperature of about 200 ° C., for the purpose of use. In addition, in order to secure a large displacement with a small laminated piezoelectric actuator and to utilize the high response of the laminated piezoelectric actuator, a higher voltage is input at a higher frequency and driving is performed. When used in such a state, a temperature rise due to self-heating occurs in the laminated piezoelectric actuator, and the generated temperature varies variously depending on use conditions. As described above, the multilayer piezoelectric actuator is placed under various temperature conditions not only due to the use environment but also due to self-heating caused by the use conditions.

[0006]

However, under such a temperature condition, when the laminated piezoelectric actuator disclosed in the above-mentioned publication is used, the initial set due to the temperature change of the use environment and the temperature change by self-heating. From the state, a dimensional change in the stacking direction of the multilayer piezoelectric actuator occurs according to the temperature, and even if a voltage that can obtain a predetermined displacement in the initial set state is applied in a heated state, it is set in the entire multilayer piezoelectric actuator. There is a problem that the initial displacement cannot be obtained. To solve such a problem, it is conceivable to increase the applied voltage according to the heat generation temperature. In this case, however, applying a high voltage easily breaks the piezoelectric plate, and reduces the durability. Has been significantly reduced.

That is, the present inventor has studied the relationship between the temperature of the actuator itself and the length of the actuator in the stacking direction. As a result, the size in the stacking direction shrinks as the temperature rises. It was found that at 100 ° C., it shrank by about 0.01 mm as a reference.

[0008] This phenomenon is caused by the fact that the piezoelectric ceramic used in the laminated piezoelectric actuator is subjected to a polarization treatment,
When a voltage is applied, the piezoelectric ceramic expands due to the reverse piezoelectric effect.However, in the polarized piezoelectric ceramic, the state in which the spontaneous polarization of each domain is aligned by the polarization processing rises to the Curie temperature of the material. It is considered that the direction of spontaneous polarization is generated as it approaches, as it returns to the unpolarized state.

When the laminated piezoelectric actuator itself generates heat, the temperature of the piezoelectric ceramic approaches or exceeds its Curie temperature, and the spontaneous polarization of some or all of the piezoelectric ceramics disappears. Since the length of the multilayer piezoelectric actuator in the stacking direction shrinks, a predetermined displacement cannot be obtained even when a voltage at which a predetermined displacement can be obtained at a low temperature is applied to the multilayer piezoelectric actuator at a high temperature. There was a problem.

It is an object of the present invention to provide a laminated piezoelectric actuator capable of generating the same displacement with the same applied voltage even when used in a wide temperature range or when a temperature change occurs due to self-heating.

[0011]

SUMMARY OF THE INVENTION A laminated piezoelectric actuator according to the present invention.
The heater is an active body in which piezoelectric plates and electrodes are alternately stacked.
And provided on both end surfaces of the active body in the laminating direction.
And a laminated piezoelectric actuator having an inert body.
The length of the active body in the stacking direction is L, and the product of the active bodies is L.
The coefficient of linear expansion in the layer direction is α, and the length of the inert body in the stacking direction is α.
L₁The linear expansion coefficient of the inert body in the laminating direction is α₁
And the value represented by Lα and 2L₁α ₁Value represented by
Have different polarities and their absolute values are almost the same.
It is characterized by.

By adopting such a configuration, a temperature change due to heat generation of the laminated piezoelectric actuator itself due to a change in driving conditions such as an applied voltage, an applied load, a driving frequency, and an ambient temperature change. Even if
The dimensional change in the stacking direction of the multi-layer piezoelectric actuator does not occur. For this reason, the same displacement as in the initial state is generated even when a voltage that causes a predetermined displacement in the initial state incorporated in the device or the like is applied at a predetermined temperature. And a stable displacement amount can be obtained.

Further, since the inert material is formed of ceramics containing any one of Al ₂ O ₃ , ZrO ₂ and Si ₃ N ₄ as a main component, the inert material has a linear expansion coefficient of 3.0 × 10 3. ^-6 / ° C. or higher, and also has appropriate strength and hardness, so that it is not necessary to lengthen the dimension in the laminating direction, the inert body can be thinned, and a compact laminated piezoelectric actuator can be obtained. While being able to
The generated displacement can be transmitted without loss.

[0014]

FIG. 1 shows a laminated piezoelectric actuator of the present invention, and FIG. 2 is an enlarged view of a part of the laminated piezoelectric actuator, in which an active body in which a plurality of piezoelectric plates 1 and a plurality of metal plates 3 are alternately laminated. 5 and inactive bodies 7 provided on both end faces of the active body 5 in the laminating direction.

These piezoelectric plates 1 are made of Pb (ZrTi) O ₃
A sintered body containing (hereinafter abbreviated as PZT) as a main component is used, but is not limited to this, and any ceramic having piezoelectricity may be used. As the piezoelectric material constituting the piezoelectric plate 1, those piezoelectric strain constant d ₃₃ is high is preferable. In particular, Pb, Zr, Ti, Z
Piezoelectric ceramics made of a complex perovskite compound containing n, Sb, Ni, Te and at least one of Sr and Ba are desirable.

The thickness t of the piezoelectric plate 1 is desirably 0.2 to 0.6 mm from the viewpoint of miniaturization and application of a high voltage.

A conductive adhesive layer 8 is interposed between the piezoelectric plate 1 and the metal plate 3, and the conductive adhesive layer 8
And the metal plate 3 are joined. This conductive adhesive layer 8
A conductive paste is applied to the piezoelectric plate 1 and the temperature is 400 to 600 ° C.
It is formed by baking with a degree. This conductive paste is made of a conductive metal powder such as Ag and a glass component. The conductive adhesive layer 8 is baked on the piezoelectric plate 1 by melting the glass component at a high temperature. Metal plate 3
And the conductive adhesive layer 8 constitute an internal electrode.

The conductive paste is, in particular, 90 g of Ag powder.
And 97% by weight, it is preferably made of a 3-10 wt% glass component consisting _{PbO-SiO 2 -B 2 O 3} .

As shown in FIG. 3, a connecting projection 3a is formed on the metal plate 3, and protrudes in the radial direction of the piezoelectric plate 1. The metal plate 3 is interposed between the piezoelectric plates 1 such that the connection projections 3a are alternately turned 180 degrees as shown in FIG. These metal plates 3 are made into an electrode plate for a positive electrode and an electrode plate for a negative electrode depending on the position of the connection projection 3a.

Then, the connection projection 3 of the positive electrode plate is formed.
a is electrically connected by soldering or welding to the connection protrusion 3a of the adjacent positive electrode plate, and the connection protrusion 3a of the negative electrode plate is for connection of the adjacent negative electrode plate. It is electrically connected to the projection 3a by soldering or welding.

The metal plate 3 to be used has conductivity, and is preferably, for example, a metal such as silver, brass, copper, and stainless steel. The thickness of the metal plate 3 is preferably as thin as possible so as not to contribute to the displacement amount, for example, 20 to 100 μm. Further, the metal plate 3 is desirably smaller than the piezoelectric plate 1 so as not to be exposed on the outer peripheral surface of the active body 5 in order to prevent a short circuit or discharge with another metal plate 3 having a different polarity.

In the multilayer piezoelectric actuator of the present invention, as shown in FIG. 1, the length of the active body 5 in the stacking direction is L, the linear expansion coefficient of the active body 5 in the stacking direction is α,
The length of the inert body 7 in the stacking direction is L ₁ , and the inert body 7
When the linear expansion coefficient was alpha ₁ in the stacking direction of, L × alpha
And the polarity of the value indicated by 2 × L ₁ × α ₁ are different, and their absolute values are almost the same. Here, the absolute values are substantially the same, the value represented by L × α and 2 × L ₁
It is desirable that the absolute value of the value represented by × α ₁ is the same, but substantially the same effect is obtained even in the range of L × α = (2 × L ₁ × α ₁ ) ± 0.5 × 10 ^-6. Having.

The inert body 7 preferably has a suitable strength and hardness for transmitting the generated displacement without loss, and is preferably made of ceramics for insulating the active body 5 from the outside. Further, in order to reduce the dimension of the laminated piezoelectric actuator in the laminating direction, the linear expansion coefficient is set to 3.0 × 10
^-6 / ° C. or higher, Al ₂ O ₃ , Si ₃ N ₄ ,
Ceramics such as ZrO ₂ are preferred. In particular, Al ₂ O ₃ having a linear expansion coefficient of 6.0 × 10 ⁻⁶ / ° C. or more is desirable.

A glass paste is applied to one end surface of the inactive body 7 to be glass-bonded to the active body 5 and 400 to 600
A glass layer baked at about ° C is formed. This glass paste is composed of a glass component PbO—SiO ₂ —B ₂ O _{3 of a} conductive paste that is baked on the piezoelectric plate 1, and the inactive body 7 is joined to the active body 5 via a glass layer. The outer peripheral surface of the active body 5 is covered with an insulating resin 9. In FIG. 2, the insulating resin 9 is omitted.

It should be noted that the inactive body 7 above and below the active body 5 may be made of different materials. In this case, the length of the active body 5 is L, the coefficient of linear expansion is α, the length of one inactive body is L _1a , the coefficient of linear expansion is α _1a , and the length of the other inactive body is L _1b. If the linear expansion coefficient is α _1b , Lα and L _1a α _1a +
It is necessary that L _1b α _1b have a different polarity and have substantially the same absolute value.

[0026]

Example: Both sides of a PZT sintered body were polished to a diameter of 20 m.
A disk-shaped piezoelectric plate 1 having a thickness of 0.1 mm and a thickness of 0.1 mm was formed. 97% by weight of Ag powder, PbO-
A conductive paste of 3% by weight of glass containing SiO ₂ —B ₂ O ₃ as a main component was printed to a thickness of 10 μm, dried at 100 ° C., and baked at 520 ° C.

An Ag plate having a thickness of 15 μm is slid to a 19 mm diameter having a protrusion 3 a of 2 mm × 2 mm as shown in FIG.
The metal plate 3 was punched out into a circle, and the metal plate 3 was sandwiched between the piezoelectric plates 1, and 100 layers of the piezoelectric plates 1 were laminated to form a laminated piezoelectric body. The connecting projections 3a of the metal plate 3 were alternately arranged so as to be at the same position every other layer.

As shown in Table 1, the inert bodies 7 disposed on both end faces of the metal plate 3 are made of Al ₂ O ₃ , Si ₃ N ₄
And ZrO ₂ , and the same material (unpolarized) as the piezoelectric plate 1. Table 1 shows the coefficient of linear expansion in the laminating direction and the length in the laminating direction from −20 to 200 ° C.

Both sides of the inert body 7 were polished to form the inert body 7 having a diameter of 20 mm. After printing a glass paste of PbO—SiO ₂ —B ₂ O _{3 on} one end surface of these inert bodies 7 to a thickness of 10 μm,
Dried at 0 ° C and baked at 520 ° C. The inert body 7 is arranged above and below the laminated piezoelectric body, and a slight pressure is applied so as not to cause a displacement.
g was put thereon and pressure-bonded at 600 ° C. for 1 hour.

Next, as shown in FIG. 2, the distal ends of the connecting projections 3a protruding in the radial direction of the piezoelectric plate 1 were each bent in the axial direction, and the bent distal ends were connected with solder. Also,
The outer peripheral surface of the active body 5 was coated with an insulating resin 9 made of a silicon-based resin.

[0031] 2kv in silicon oil at 80 ° C
/ Mm DC voltage was applied for 30 minutes to perform polarization processing. 20 to these obtained laminated piezoelectric actuators.
As a result of applying a DC voltage of 0 V, displacement amounts of 20 μm were all obtained.

As a comparative example, a piezoelectric actuator in which the same material as the piezoelectric plate 1 is used for the inactive body 7 and the dimension L _{1 of} which is 8.2 mm, which is the same as the inactive body 7 made of Si ₃ N _4. Also, as a result of applying a DC voltage of 200 V, a displacement amount of 20 μm was obtained.

Further, these actuators were put into a furnace, and the atmosphere temperature was set to -20 to 200 ° C. at an applied voltage of 0 V.
And the dimensional change of the laminated piezoelectric actuator in the laminating direction was measured. FIG. 4 shows the results.

The length L ₁ of the inactive substance 7 is determined by the No. 1 in Table 1.
As shown in 1-3, the temperature range in the case where the linear expansion coefficient α of the active body 5 in the present embodiment is −5.0 × 10 ⁻⁶ / ° C. and the length of the active body 5 in the stacking direction is 11.515 mm− 20-20
Assuming that Lα at 0 ° C., the linear expansion coefficient of the inert body 7 in the stacking direction is α ₁ , and the length in the stacking direction is L ₁ , 2L ₁ α ₁
Are set so that the polarities of the values indicated by are different and their absolute values are almost the same.

Further, the linear expansion coefficient α of the activated body 5 in the laminating direction from -20 to 200 ° C. was measured. Activator 5 was prepared in the same manner as above, that is, piezoelectric plate 1 and metal plate 3
Are bonded via a conductive paste, and the piezoelectric plate 1 is
2kv in 80 ℃ silicone oil
/ Mm DC voltage is applied for 30 minutes to perform polarization processing.
The linear expansion coefficient α was measured. As a result, -20 of Activator 5
The linear expansion coefficient α in the laminating direction up to 200 ° C. is −5.0 ×
It was 10 ^-6 / ° C.

[0036]

[Table 1]

The laminated piezoelectric actuator of the present invention (FIG. 4)
Although the dimensional changes of (b) to (d)) hardly occur at -20 to 200 ° C., the laminated piezoelectric actuator (FIG. 4A) manufactured as a comparison increases with temperature.
It can be seen that the dimensions are shrinking.

Further, these actuators are provided with 0 to +2
As a result of applying a DC electric field of 00V and measuring the amount of displacement at each temperature, the laminated piezoelectric actuator of the present invention has a small dimensional change at each temperature, so that a stable amount of displacement at each temperature can be obtained. It turns out that it is. It can be seen that the variation width of the displacement amount at −20 to 200 ° C. is within 0.005 mm, while in the comparative example, it varies by about 0.01 mm.

The linear expansion coefficient of the piezoelectric plate 1 is completely different from that of the inactive body 7 using the same material. This is because the piezoelectric plate 1 is polarized and the inactive body 7 is unpolarized. Because it is.

The displacement was measured by fixing the sample on a vibration isolator, attaching an aluminum foil to the upper surface of the sample, and using a laser displacement meter.

[0041]

As described above in detail, in the multilayer piezoelectric actuator of the present invention, the change in ambient temperature, the applied voltage,
Even when a temperature change occurs due to heat generation of the laminated piezoelectric actuator itself due to a change in driving conditions such as an applied load and a driving frequency, a dimensional change in a laminating direction does not occur from an initial state incorporated in a device or the like. Below,
A stable displacement can be obtained. In addition, since the inert material is made of ceramics containing Al ₂ O ₃ , ZrO ₂ , and Si ₃ N ₄ as main components, it is not necessary to lengthen the dimension in the stacking direction. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual sectional view of a laminated piezoelectric actuator of the present invention.

FIG. 2 is an enlarged sectional view showing a part of FIG. 1;

FIG. 3 is a plan view in which connection projections are provided on a metal plate.

FIG. 4 is a diagram showing a relationship between an ambient temperature, a dimensional change in a stacking direction of a stacked piezoelectric actuator, and a displacement amount.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Piezoelectric plate 3 ... Metal plate 5 ... Active body 7 ... Inactive body 8 ... Conductive adhesive layer

Claims (2)

[Claims] 1. A laminated piezoelectric actuator comprising: an active body in which piezoelectric plates and electrodes are alternately stacked; and inactive bodies provided on both end faces in the stacking direction of the active body, respectively.
The length of the active body in the stacking direction is L, the linear expansion coefficient of the active body in the stacking direction is α, the length of the inert body in the stacking direction is L ₁ , the linear expansion coefficient of the inert body in the stacking direction when was the alpha _1, the value represented by the values and 2L ₁ alpha _1, represented by L [alpha,
A laminated piezoelectric actuator having different polarities and substantially the same absolute value. 2. An inert substance comprising Al ₂ O ₃ , ZrO ₂ and S
2. The multilayer piezoelectric actuator according to claim 1, wherein the multilayer piezoelectric actuator is made of a ceramic containing any one of i ₃ N ₄ as a main component.