JP2000049396A - Laminated piezoelectric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated piezoelectric actuator, wherein the stress concentration on the interface between an inactive block and laminate can be sufficiently relaxed. SOLUTION: In the laminated actuator comprising a laminate 1 of alternately laminated a plurality of piezoelectric plates 11 and a plurality of electrodes 12, 14, and ceramic inactive blocks 18 respectively bonded to the upper and lower sides of the laminate 1 with electrodes 14 mutually electrically connected, annular slits 29 are formed in the peripheries of the inactive blocks 18, and the sectional area S1 of the reduced diameter 18a of the inactive block, at which the slit 29 is formed, is made 25-50% of the area S2 of the electrode 12.

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 Conventionally, there has been known a laminated piezoelectric actuator in which a plurality of piezoelectric plates coated with an internal electrode paste are laminated to form a laminate. In such a laminated piezoelectric actuator, a voltage is applied to the piezoelectric plate to extend the piezoelectric plate by several to several tens of μm by an inverse piezoelectric effect, and is used as a driving force source of the actuator.

[0003] The laminated piezoelectric actuator has a structure in which a piezoelectrically inactive portion (inactive body) is firmly joined to upper and lower ends of a piezoelectrically active portion (laminated body). This inert body has a role of transmitting mechanical energy of the piezoelectric element to the outside and a role of insulating the outside from the outside.

As a conventional laminated piezoelectric actuator using thin electrode plates, a laminated body in which a piezoelectric plate and a thin metal plate are alternately laminated, and a pair of inactive bodies which are respectively bonded to the upper and lower sides of the laminated body by an insulating adhesive. In addition, there is known a configuration in which connection projections formed on a thin metal plate are projected in two directions, and the connection projections projecting in the same direction are electrically connected to each other.

In recent years, high-voltage, high-frequency driving has been performed in order to secure a large displacement amount with a small-sized laminated piezoelectric actuator and to perform driving at a higher speed.

[0006]

However, in the above-described laminated piezoelectric actuator, a high voltage is applied to the laminated piezoelectric actuator because the piezoelectrically active laminated body and the inactive body are firmly joined. When applied at a frequency and driven for a long time, the laminate expands and contracts in the axial direction as well as in the radial direction, causing a large stress concentration at the boundary between the inactive body and the laminate. Alternatively, there is a problem that the piezoelectric plate of the laminate is damaged. As a result, there has been a problem that the inactive body peels off and the multilayer piezoelectric actuator does not operate.

In order to solve such a problem, in recent years, the overlapping area of the internal electrode layers in the vicinity of the uppermost layer and the lowermost inactive layer of the laminate has been reduced. Japanese Patent Application Laid-Open No. 7-3016 discloses a laminated piezoelectric actuator having a smaller size.
No. 5).

In such a laminated piezoelectric actuator, the amount of displacement in the laminate near the inactive body is smaller than that in the center of the laminate, so that the stress transmitted to the inactive body can be reduced to some extent. Although the stress concentration at the boundary with the active body can be reduced to some extent, since the inactive body is joined to the upper and lower surfaces of the laminate, the stress due to the displacement of the laminate is greatly transmitted to the inactive body, and the There is a problem that the stress concentration generated at the boundary of the inert body is still large. As a result, there is a problem that cracks and breaks are apt to occur in the inert body and the laminated body when driven for a long time at a high voltage and a high speed.

The present invention sufficiently alleviates stress concentration at the boundary between the inactive body and the laminated body and prevents stress breakdown at the boundary between the laminated body and the inactive body even when operating at high speed with a high applied voltage. It is an object of the present invention to provide a laminated piezoelectric actuator that can be used.

[0010]

According to the present invention, there is provided a laminated piezoelectric actuator comprising: a laminated body in which a plurality of piezoelectric plates and a plurality of electrodes are alternately laminated; And a laminated piezoelectric actuator in which the electrodes are electrically connected alternately, wherein an annular slit is formed on the outer peripheral surface of the inactive body, and a portion of the portion where the slit is formed is formed. sectional area S ₁ of the inactive form reduced diameter portion is 25 to the area S ₂ of the electrode
It is characterized by being 50%.

Here, it is desirable that the cross-sectional shape of the tip of the slit is an arc shape. Further, it is desirable that the slit be filled with a material having a Young's modulus smaller than that of the inert material.

[0012]

In the laminated piezoelectric actuator of the present invention, an annular slit is formed on the outer peripheral surface of the inert body, and the cross-sectional area S of the reduced diameter portion of the inert body in the portion where the slit is formed
_1, since 25 to 50% of the area S ₂ of the electrode, the Young's modulus of the inert bodies near the slit is reduced by the presence of slits, in inert bodies near the slit, expansion and contraction of the radial direction of the laminate The stress transmitted to the inactive body due to the movement is released, stress concentration at the boundary between the laminate and the inactive body can be suppressed, and damage to the end face of the inactive body or the laminate can be prevented. Thereby, even in the case of high voltage and high speed driving, it is possible to drive for a long time without cracking or breaking.

Conventionally, in order to increase the creepage distance required for electrical insulation from the internal and external electrodes to the end face of the inactive body, a laminated piezoelectric actuator having an uneven surface formed on the surface of the inactive body has been known. Although disclosed in Japanese Unexamined Patent Publication No. Hei 4-259268, the effect of reducing stress concentration at the boundary between the laminate and the inactive body cannot be expected simply by providing slits. In other words, in order to alleviate the stress concentration at the boundary between the laminated body and the inert body, an annular slit is formed on the outer peripheral surface of the inert body, and the inert body in the portion where the slit is formed is formed. the cross-sectional area S ₁ of the reduced diameter portion is necessary to be 25 to 50% of the area S ₂ of the electrode.

In the laminated piezoelectric actuator of the present invention, stress tends to concentrate on the inactive material around the slit tip, but the cross-sectional shape of the slit tip makes the inert shape around the slit tip easy. Stress concentration on the body can be reduced.

Further, by filling the slit with a material having a Young's modulus smaller than that of the inactive material, damage of the inactive material starting from the slit can be prevented.

[0016]

1 and 2 show a laminated piezoelectric actuator according to the present invention. Reference numeral 1 denotes a columnar laminated body. In FIG. 1, the insulating resin covering the surface of the laminate 1 is omitted. The laminate 1 is configured by alternately laminating a disc-shaped piezoelectric plate 11 and disc-shaped metal thin plates 14 joined to both surfaces of the piezoelectric body 11 by a conductive adhesive 12.

That is, a disc-shaped metal thin plate 14 is interposed between the piezoelectric plates 11, and these metal thin plates 14 are joined to the piezoelectric plates 11 provided on both sides by the conductive adhesive 12. I have. In this example, the conductive adhesive 12 in contact with the piezoelectric plate 11 serves as an electrode, and the conductive adhesive 12 and the thin metal plate 14 have the same area.

The piezoelectric material constituting the piezoelectric plate 11 is, for example, a piezoelectric ceramic material containing lead zirconate titanate as a main component, but is not limited thereto. Anything is fine. As the piezoelectric material constituting the piezoelectric plate 11, as the piezoelectric strain constant d ₃₃ is high is preferable.

In particular, Pb, Zr, Ti,
A composite perovskite compound containing Zn, Sb, Ni, Te, and at least one of Sr and Ba, wherein the composition formula based on the molar ratio of these metal elements is Pb
_{1-xy Sr x Ba y (} Zn 1/3 Sb 2/3) a (Ni 1/2
Te _1/2 ) _b Zr _c Ti _1-abc O ₃ ,
When the molar ratio of x, y, a, b, and c is 0 ≦ x ≦ 0.12, 0
≦ y ≦ 0.12, 0 <x + y, 0.05 ≦ a ≦ 0.1
2, with respect to 100 parts by weight of the basic component satisfying 0 ≦ b ≦ 0.015 and 0.43 ≦ c ≦ 0.52, PbO and Nb ₂ O ₅ having an equimolar ratio in a total amount of 0.2 to A piezoelectric ceramic composition containing 1.2 parts by weight is desirable.

The thickness t of the piezoelectric plate 11 is 0.2 to 0.6 mm from the viewpoint of miniaturization and application of a high voltage.
It is desirable that

The conductive adhesive 12 formed on both surfaces of the piezoelectric plate 11 is formed by applying a conductive paste to the piezoelectric plate 11 in a circular shape and baking it at about 400 to 600 ° C. The conductive paste is made of a conductive metal powder such as Ag and a glass component, and is baked on the piezoelectric plate 11 by melting the glass component at a high temperature. The conductive adhesive 12 is, in particular, and 70 to 98 wt% of Ag powder, it is preferably made of a 2-30 wt% glass component consisting _{PbO-SiO 2 -B 2 O 3} .

As shown in FIG. 3, connecting projections 15 are integrally formed on the metal thin plate 14 at opposing positions, and these connecting projections 15 are, as shown in FIG.
The piezoelectric plate 11 protrudes in the radial direction. Further, the metal thin plates 14 are interposed between the piezoelectric plates 11 so that the connection protrusions 15 have an angle of 90 degrees alternately as shown in FIG. These metal thin plates 14 are made into a positive electrode thin metal plate and a negative electrode thin metal plate depending on the position of the connection projection 15.

The connection projections 15 are bent in the stacking direction of the laminate 1, and the positive electrode metal sheets and the negative electrode metal sheets are soldered to each other.
Alternatively, they are electrically connected by joining by welding.

Metal sheet 14 to be used and connection projection 1
Reference numeral 5 denotes a conductive material, for example, a metal such as silver, brass, copper, or stainless steel is preferable. The thickness of the metal sheet 14 is
In order not to contribute to the amount of displacement, it is preferable that the thickness is as thin as possible, for example, 20 to 100 μm.

The metal sheet 14 is desirably smaller than the piezoelectric plate 11 so as not to be exposed on the outer peripheral surface of the laminate 1 in order to prevent a short circuit or discharge with another metal sheet 14.

A cylindrical inert body 18 made of ceramics, which is piezoelectrically inactive and transmits mechanical energy, is glass-bonded to the upper and lower surfaces of the laminate 1 with an insulating adhesive 22. The inert body 18 has the same diameter as the piezoelectric plate 11, and may be, for example, the same material as the piezoelectric body 11, or Al ₂ O ₃ or the like.

The insulating adhesive 22 is formed by applying a glass paste to one side of the inert body 18 in a circular shape, and
It is formed by baking with a degree. This glass paste is made of a glass component PbO—SiO ₂ —B ₂ O _{3 of the} conductive adhesive 12 that is baked on the piezoelectric plate 11.

An annular slit 29 is formed on the outer peripheral surface of the inert body 18, and as shown in FIG.
9 is the cross-sectional area S _{1 of the} reduced diameter portion 18a of the inert body in the portion where
Is 25 to 50% of the area S ₂ of the conductive adhesive 12. This is because if the cross-sectional area S ₁ of the inactive form reduced-diameter portion 18a of the portion forming the slit 29 is less than 25% of the area S ₂ of the conductive adhesive 12, since the Young's modulus of the actuator is reduced, not When a shear load is applied to the active body 18, the active body 18 is easily broken.
This is because the effect of suppressing the stress concentration at the boundary between the stacked body 1 and the inert body 18 is small.

The cross-sectional area S ₁ of the reduced diameter portion 18a of the inert body at the portion where the slit 29 is formed is sufficient to prevent damage when a shear load is applied and stress concentration at the boundary between the laminate 1 and the inert body 18. In terms of suppression, conductive adhesive 1
It is preferable that the area S2 of the _second area is 30 to 40%. Although the conductive adhesive 12 and the thin metal plate 14 are integrated, the area S ₂ of the electrode is the area of the conductive adhesive 12.

The thickness B of the slit 29 is 0.5 mm
It is as follows. This is because when the thickness B of the slit 29 is larger than 0.5 mm, the Young's modulus becomes small, and the inert body 18 is easily broken when a shear load is applied thereto. On the other hand, from the viewpoint of workability. Is 0.1m
m or more is desirable.

Further, the distance L between the slit 29 and the end face of the inert body 18 on the side of the laminate 1 is set to 0.3 mm or more from the viewpoint of preventing the end face of the inert body 18 from the side of the laminate 1. However, from the viewpoint of suppressing stress concentration at the boundary between the laminate 1 and the inactive body 18, it is desirable that the inert body 18 be closer to the end face of the inactive body 18 on the laminate 1 side.

Further, in the laminated piezoelectric actuator of the present invention, as shown in FIG. 2, the cross-sectional shape of the tip of the slit 29 is formed in an arc shape, and the inside of the slit 29 is smaller than that of the inert body 18. A material with a low rate, for example, a resin, is filled. In this example, the same resin as the insulating resin covering the surface of the laminate 1 is used. When the cross-sectional shape of the tip of the slit 29 is arc-shaped, the inactive body 18 at the leading end becomes the inactive body reduced diameter portion 18a.

Then, the piezoelectric plate 11 and the connection projection 15
2 is covered with an insulating resin 17 as shown in FIG. 2, and the insulating resin 17 has no gap in the gap between the outer peripheral surface of the piezoelectric plate 11 and the connection projection 15 as well. So that it is filled. As a filling method, it is necessary to adjust the conditions such as viscosity, and to sufficiently fill the insulating resin 17 in the voids under reduced pressure such as a vacuum removal method. In addition, insulating resin 1
For 7, it is desirable to fill a material having a low Young's modulus. Simultaneously with the coating of the insulating resin 17, the insulating resin 17 may be filled in the slit 29 as described above.

In the multilayer piezoelectric actuator configured as described above, the slit 29
The Young's modulus of the inert body 18 in the vicinity decreases, and the stress transmitted to the inert body 18 due to the radial expansion and contraction movement of the laminate 1 is released by the inert body 18 in the vicinity of the slit 29, and the laminate 1 The concentration of stress at the boundary between the inert body 18 and the inert body 18 can be suppressed, and breakage of the inert body 18 or the end face of the laminate 1 can be prevented. Thereby, even in the case of high voltage and high speed driving, driving can be performed for a long time without cracking or breakage.

In the above example, one slit 29 formed in the inert body 18 has been described.
Of course, two or more may be formed. In this case, when a plurality of slits are formed so that the Young's modulus of the inert body 18 gradually increases toward the side opposite to the stacked body 1, stress concentration can be further suppressed.

[0036]

[Example] _{Pb 1-xy Sr x Ba y} (Zn 1/3 S
_{b 2/3) a (Ni 1/2 Te} 1/2) b Zr c Ti 1-abc
When expressed as O ₃ , x = 0.04, y = 0.02, a =
Pb having an equimolar ratio with respect to 100 parts by weight of the basic component satisfying 0.075, b = 0.005, and c = 0.47.
Both surfaces of a PZT sintered body containing O and Nb ₂ O ₅ in a total amount of 0.5 parts by weight were polished to form a disk-shaped piezoelectric body 11 having a diameter of 20 mm and a thickness of 0.5 mm.

On both main surfaces of the piezoelectric body 11, Ag powder 97
Wt%, the glass 3 wt% of paste mainly composed of _{PbO-SiO 2 -B 2 O 3} , diameter 19 mm, thickness 10μ
m, and then dried at 100 ° C.
Bake at 0 ° C.

An Ag thin plate having a thickness of 25 μm was applied to a metal thin plate 14 having a diameter of 19 mm as shown in FIG.
Was punched out to form the connection projection 15.

Then, the metal thin plate 14 was sandwiched between the piezoelectric plates 11, and 100 layers of the piezoelectric plates 11 were laminated to form a laminate. The connection projections 15 of the metal thin plates 14 were alternately arranged so as to be at the same position every other layer.

The inactive bodies 18 disposed on both end faces of the laminate 1 are made of a PZT sintered body having the same composition as the piezoelectric plate 11, and both sides thereof are polished to have a diameter of 20 mm and a thickness of 5 mm.
Was formed. A glass paste of PbO—SiO ₂ —B ₂ O ₃ was printed on one surface of each of these inert materials 18 so as to have a diameter of 19 mm and a thickness of 10 μm, then dried at 100 ° C., and baked at 520 ° C. Thereafter, L = L from the end face of the inert body 18 with a wire saw.
At a position of 0.5 mm, a slit 29 having a cut depth of 3.3 mm and a thickness B of 0.3 mm was formed. Slit 2
The cross-sectional shape of the tip portion was an arc shape. The cross-sectional area S ₁ of the inert body reduced diameter portion 18a in which the slit 29 is formed.
Was 50% of the area S ₂ of the conductive adhesive 12.

Next, the inert bodies 18 are arranged on both end faces of the laminate 1 and light pressure is applied so as not to cause a displacement, and then a weight of about 5 kg is put on the upper portion of the laminate 1 and 600
C. for 1 hour under pressure.

Next, as shown in FIG. 1, the distal ends of the connection projections 15 protruding in the radial direction of the piezoelectric body 11 are each bent in the axial direction, and the bent distal ends are soldered to the connection projections 15. These were connected to form a positive electrode external electrode and a negative electrode external electrode.

A part of the laminate 1 and a part of the inactive body 18 are covered with the insulating resin 17 made of insulating silicon rubber, and are also filled in the slit 29.
DC electric field of 3 kv / mm in silicone oil
For a minute, polarization was performed to obtain a multilayer piezoelectric actuator of the present invention as shown in FIGS.

50 was added to the obtained laminated piezoelectric actuator.
As a result of applying a DC voltage of 0 V, a displacement of 50 μm was obtained. In addition, 0V to + 500V
As a result of applying the alternating voltage of 50 Hz at a frequency of 50 Hz, no crack or break was observed at the boundary between the laminate and the inactive portion even when the driving was performed up to 1 × 10 ⁹ times.

Further, the cutting depth of the inert material 18 by the wire saw was changed to 5 mm and 4 mm,
9 was formed. The cross-sectional areas S ₁ of the inert reduced diameter portions 18 a in which the slits 29 were formed were 28% and 40% of the area S ₂ of the conductive adhesive 12, respectively. When a DC voltage of 500 V was applied to the obtained laminated piezoelectric actuator, a displacement of 50 μm was obtained. Further, as a result of applying an alternating voltage of 0 V to +500 V to the actuator at a frequency of 50 Hz, no crack or break was observed at the boundary between the laminated body and the inactive portion even when the actuator was driven up to 1 × 10 ⁹ times. Was.

Further, the inert material 18 using a wire saw
Is changed to 7 mm and 1.8 mm, and the cross-sectional area S of the inert body reduced diameter portion 18 a in which the slit 29 is formed is formed.
_1, respectively laminated piezoelectric actuator of the comparative example 1 to 10% of the area S ₂ of the conductive adhesive 12, and 75% in Comparative Example 2 the multilayer piezoelectric actuator prepared. Further, a laminated piezoelectric actuator of Comparative Example 3 in which no slit 29 was formed was manufactured.

When the same evaluation as in the above embodiment was performed,
In the multilayer piezoelectric actuator of Comparative Example 1, the inert body was cracked during the driving test setting, and the driving test became impossible. In Comparative Examples 2 and 3, cracks occurred at the boundary between the inactive material and the laminate after 2 × 10 ⁸ times.

The displacement was measured by fixing the sample on an anti-vibration table, attaching an aluminum foil to the upper surface of the sample, and averaging the values measured at the center and three peripheral portions of the element by a laser displacement meter. The value was evaluated.

[0049]

As described in detail above, in the multilayer piezoelectric actuator of the present invention, a slit is formed in the inactive body joined to the upper and lower sides of the multilayer body, and the inactive body reduced diameter portion in which the slit is formed is formed. the cross-sectional area S _1, 25 to 50 of the electrode area S ₂
%, The stress at the boundary between the stacked body and the inactive body can be reduced, and driving can be performed for a long time without cracking or breaking even at high voltage and high speed driving.

[Brief description of the drawings]

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

FIG. 2 is a partially enlarged cross-sectional view of the multilayer actuator of FIG.

FIG. 3 is a plan view showing the metal sheet of FIG. 1;

FIG. 4 is a sectional view taken along line AA of FIG.

[Explanation of symbols]

1 ... laminate 11 ... piezoelectric plate 12 ... conductive adhesive 14 ... metal thin plate 15 .. connecting projection 18 ... inert body 18a ... inactive form reduced-diameter portion 29 ... slit S ₁ area ... inactive form the reduced diameter portion of the cross-sectional area S ₂ ... conductive adhesive

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Katsuhiko Onizuka, Inventor 1-4, Yamashita-cho, Kokubu-shi, Kagoshima Inside the Kyocera Research Institute (72) Inventor Tomohiro Kawamoto 1-4-4, Yamashita-cho, Kokubu-shi, Kagoshima Kyocera Inside Research Institute, Inc.

Claims (3)

[Claims] 1. A laminate comprising a plurality of piezoelectric plates and a plurality of electrodes alternately laminated, and ceramic inactive bodies respectively joined to upper and lower sides of the laminate, and the electrodes are alternately arranged. An electrically connected laminated piezoelectric actuator, wherein an annular slit is formed on the outer peripheral surface of the inert body, and a cross-sectional area S ₁ of the inert body reduced diameter portion of the portion where the slit is formed is: 25-5 of the area S ₂ of the electrode
A multilayer piezoelectric actuator characterized by being 0%. 2. The laminated piezoelectric actuator according to claim 1, wherein the cross-sectional shape of the slit tip is an arc. 3. The multilayer piezoelectric actuator according to claim 1, wherein the slit is filled with a material having a Young's modulus smaller than that of the inert body.