JP2001210884A - Stacked type piezoelectric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stacked type piezoelectric actuator, where an external electrode has high elasticity, disconnection of a conductive wire rod can be prevented and concentration of current in the part of an external electrode can be prevented. SOLUTION: In an actuator body 3, formed by alternately stacking a piezoelectric body 1 and an inner electrode 2 and a stacked type piezoelectric actuator provided to a side surface of the actuator body 3, an external electrode 4 is formed by fixing a mesh member 7 formed of a conductive wire rod 6 to the side surface of the actuator body 3 by means of conductive adhesive 9, and a pitch (p) of the conductive wire rod 6 is set 0.5 to 8 times a thickness (t) of the piezoelectric body 1.

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 used for a precision positioning device such as a fuel injection valve for an automobile, an optical device, and a driving element for preventing vibration.

[0002]

2. Description of the Related Art Hitherto, in order to obtain a large displacement using an electrostriction effect, there has been proposed a laminated piezoelectric actuator in which piezoelectric bodies and internal electrodes are alternately laminated. Multi-layer piezoelectric actuators are classified into two types: co-firing type and stack type in which piezoelectric ceramics and internal electrode plates are alternately laminated. Considering lower voltage and lower manufacturing cost, co-firing type Since the multilayer piezoelectric actuator is advantageous for thinning, it is showing its superiority.

Japanese Patent Laid-Open Publication No. Hei 4-237172 discloses a co-fired type laminated piezoelectric actuator. For example, Japanese Patent Application Laid-Open No. 4-237172 discloses a method in which an insulating layer made of glass is coated every other end of an internal electrode exposed on a side surface of an actuator body. In the external electrode, a concave portion is formed at the same pitch as the insulating layer and slightly larger than the cross section of the insulating layer, the insulating layer is accommodated in the concave portion, and the insulating layer is provided on the convex portion between the concave portions. By bonding the end of the internal electrode where no is formed with a conductive adhesive, the electrical connection between the external electrode and one internal electrode is secured, and the insulation type with the other internal electrode is insulated. A piezoelectric actuator "is disclosed.

[0004]

By the way, in recent years, in order to secure a large displacement under a large pressure with a small piezoelectric actuator, a higher electric field is applied and the piezoelectric actuator is driven continuously for a long period of time. However, when driven continuously for a long time under a high electric field and high pressure, separation occurs between the internal electrodes formed between the piezoelectric bodies and the external electrodes for the positive electrode and the negative electrode, and voltage is applied to some piezoelectric bodies. No longer supplied,
There is a problem that the displacement characteristics change during driving.

In the laminated piezoelectric actuator disclosed in Japanese Patent Application Laid-Open No. 4-237172, an insulating layer made of glass is coated every other end of the internal electrode exposed on the side surface of the actuator body. And the piezoelectric bodies on both sides thereof are firmly joined, and this insulating layer is housed in the concave portion of the external electrode to ensure the insulation between the external electrode and the internal electrode, and to prevent the internal layer where the insulating layer is formed from being formed. Since the electrical connection between the end of the electrode and the external electrode is ensured, there is a problem that the internal electrode and the external electrode are disconnected when driven continuously for a long time under a high electric field and high pressure.

Further, a laminated piezoelectric actuator disclosed in Japanese Patent Application Laid-Open No. 63-153870 is known as one using a thin plate-shaped conductive member for an external electrode. In the laminated piezoelectric actuator disclosed in this publication, a thin plate-shaped conductive member is connected as an external electrode to an internal electrode by a conductive adhesive. When the actuator is driven, the thin plate-shaped conductive member cannot follow the expansion and contraction of the actuator body, and there is a problem that the internal electrode and the external electrode are disconnected while the actuator is driven, and the displacement characteristics change. Was.

In order to solve such a problem, the above publication discloses that a mesh-shaped conductive member is used as a thin plate-shaped conductive member to make the external electrode flexible and adversely affect the expansion / contraction operation of the actuator body. However, when the actuator is driven continuously for a long period of time with a large displacement, such as a fuel injection valve for an automobile, the mesh-shaped conductive member can simply follow the expansion and contraction of the actuator body. However, there has been a problem that the internal electrode and the external electrode are disconnected during driving of the actuator, and the displacement characteristics change.

Further, as a device using a mesh, a laminated piezoelectric actuator as disclosed in Japanese Patent Application Laid-Open No. 8-236828 is known. In the actuator described in this publication, each external electrode electrically connected to each internal electrode is provided on the side surface of the piezoelectric plate, and a contact electrode made of a mesh material is applied to the external electrode by a biasing means. Although it is pressed and abutted to prevent poor conduction, when it is driven continuously for a long time with a large displacement such as a fuel injection valve for automobiles, the external electrode and the abutting electrode wear due to frictional shear force, and the external electrode There is a problem that a current is concentrated in a part and locally heated, and a short circuit easily occurs between the external electrode and the contact electrode.

[0009]

According to the present invention, there is provided a laminated piezoelectric actuator comprising: an actuator body formed by alternately stacking a plurality of piezoelectric bodies and a plurality of internal electrodes; A multilayer piezoelectric actuator comprising external electrodes having electrodes alternately connected thereto, wherein the external electrodes are formed by fixing a mesh member made of a conductive wire to a side surface of the actuator body with a conductive adhesive. The pitch of the conductive wire is 0.5 to 8 times the thickness of the piezoelectric body.

By adopting such a configuration, that is, the pitch of the conductive wires is set to be equal to 0.1 with respect to the thickness of the piezoelectric body.
By making it 5 to 8 times, it becomes possible for the external electrode to have high elasticity, and it is possible to prevent disconnection of the conductive wire. A laminated piezoelectric actuator having high durability without disconnection of the electrodes can be provided.

Further, since the mesh member made of a conductive wire is fixed to the side surface of the actuator main body with a conductive adhesive, the mesh member does not slide on the actuator main body, so that the external electrode can be prevented from being worn and the external electrode can be prevented from being worn. Current can be prevented from being concentrated on a part of the.

In the present invention, the diameter of the conductive wire of the mesh member is preferably 0.05 to 2 times the thickness of the piezoelectric body. By adopting such a configuration,
That is, by making the diameter 0.05 to 2 times the thickness of the piezoelectric body, it is possible to further improve the elasticity of the external electrode.

Further, in the present invention, it is desirable that a lead mounting member made of a sheet metal is fixed to the mesh member, and a lead wire is joined to the lead mounting member. By employing such a configuration, that is, by fixing the lead mounting member made of a plate-like metal, the connection strength between the external electrode and the lead wire can be improved.

Further, in the present invention, it is desirable that the conductive wire of the mesh member has an angle of about 45 ° with respect to the lamination direction of the piezoelectric bodies. By adopting such a configuration, the external electrodes can expand and contract sufficiently following the expanding and contracting actuator body.

[0015]

FIG. 1 is a perspective view showing an embodiment of a laminated piezoelectric actuator according to the present invention, and FIG. 2 is a longitudinal sectional view taken along line AA 'of FIG.

As shown in FIGS. 1 and 2, the laminated piezoelectric actuator of the present invention comprises a plurality of piezoelectric bodies 1 and a plurality of internal electrodes 2.
Are alternately laminated to form a quadrangular prism-shaped actuator body 3, and external electrodes 4 are provided on two opposing side surfaces of the actuator body 3, respectively. The internal electrodes 2 are alternately and electrically connected to these external electrodes 4, and are insulated by providing insulators 5 at every other layer at the end of the internal electrodes 2.

The external electrode 4 comprises a mesh member 7 made of a conductive wire 6 and a conductive adhesive 9 as shown in FIG.
The mesh member 7 is fixed to the side surface of the actuator body 3 by embedding the mesh member 7 in the conductive adhesive 9. The thickness of the conductive adhesive 9 only needs to be large enough to embed the mesh member 7.

Although the mesh member 7 is formed by being buried in the conductive adhesive 9, it may not be completely buried or may be partially exposed. Also, the mesh member 7
Need not necessarily be in contact with the actuator body 3.

The conductive adhesive 9 can be formed of, for example, nickel, silver, platinum, gold or the like and an adhesive such as glass, epoxy resin, polyimide resin, or polyamide-imide resin. For this reason, it is desirable to use silver and a polyimide resin.

The pitch p of the conductive wires 6 is 0.5 to 8 times the thickness t of the piezoelectric body 1. That is, FIG.
As shown in the figure, the plurality of conductive wires 6 are woven in a lattice shape, and the pitch p between the conductive wires 6 is set to 0.5 to 8 times the thickness t of the piezoelectric body 1.

Thus, the pitch p of the conductive wire 6 is
The reason for setting the thickness t of the piezoelectric body 1 to 0.5 to 8 times is as follows.
If it is less than 0.5 times, the pitch p is too narrow, so that the mesh member 7 has a small mesh.
This is because the elasticity in the vertical direction is impaired, and the internal electrode 2 and the external electrode 4 are disconnected without being able to withstand the expansion / contraction operation of the laminated piezoelectric actuator.

On the other hand, when the pitch p is wider than eight times the thickness t of the piezoelectric body 1, the pitch p is too wide and the strength of the mesh member 7 is reduced. Then, the external electrode 4 is damaged. The pitch p of the conductive wires 6 is preferably 0.5 to 2 times the thickness t of the piezoelectric body 1 from the viewpoint that the elasticity of the external electrode 4 is secured and the disconnection of the mesh member 7 is prevented.

In the present invention, the diameter R of the conductive wire 6 of the mesh member 7 is 0.05 to 2 times the thickness t of the piezoelectric body 1.
It is doubled. This is because the elasticity of the external electrode 4 can be further improved by making the diameter R of the conductive wire 6 0.05 to 2 times the thickness t of the piezoelectric body 1.

Conversely, the diameter R of the conductive wire 6 is
If the thickness R is smaller than 0.05 times the thickness t, the diameter R is too small and the conductive wire 6 may be broken when the actuator is driven. If it is larger, the diameter R is too large, the elasticity of the mesh member 7 is impaired, and the internal electrode 2 and the external electrode 4 may be disconnected without being able to withstand the expansion and contraction operation of the laminated piezoelectric actuator. . The conductive wire 6 of the mesh member 7 is desirably stainless steel or Kovar because it is a metal that does not oxidize at low temperatures.

Further, in the present invention, the mesh member 7 is arranged such that the conductive wire 6 of the mesh member 7 forms an angle θ of approximately 45 ° with respect to the lamination direction x of the piezoelectric body 1.
By doing so, the external electrode 4 can expand and contract sufficiently following the actuator body 3 that expands and contracts.

A lead wire 13 is connected to the external electrode 4
5 fixed. As shown in FIGS. 4 and 5, a lead mounting member 17 made of an L-shaped plate-like metal is fixed to the external electrode 4, and the lead wire 13 is joined to the lead mounting member 17 with the solder 15. Good. Thereby, the connection strength between the external electrode 4 and the lead wire 13 can be improved.

The piezoelectric body 1 is made of, for example, lead zirconate titanate Pb (Zr, Ti) O ₃ (hereinafter abbreviated as PZT) or a piezoelectric ceramic material mainly containing barium titanate BaTiO _3. However, the present invention is not limited to these, and any ceramics having piezoelectricity may be used. As the piezoelectric material, as the piezoelectric strain constant d ₃₃ it is high is preferable. The thickness t of the piezoelectric body 1, that is, the distance between the internal electrodes 2 is desirably 0.05 to 0.25 mm from the viewpoint of miniaturization and application of a high electric field.

The internal electrodes 2 are exposed on all side surfaces of the actuator body 3, and grooves are formed on two opposing side surfaces to remove the end of the internal electrodes 2 and a part of the piezoelectric body 1. And in this groove, glass, epoxy resin,
An insulator 5 such as a polyimide resin, a polyamideimide resin, or silicone rubber is filled, and the internal electrodes 2 are alternately insulated. The insulator 5 is preferably made of a material having a low Young's modulus, for example, silicone rubber.

As described above, the internal electrodes 2 are alternately insulated every other layer, and the other end face of the non-insulated internal electrodes 2 is embedded with the mesh member 7 in the conductive adhesive 9 applied in advance. In this state, the conductive adhesive 9 is connected to the external electrodes 4 formed by heating and curing the conductive adhesive 9.

The actuator body 3 is mechanically held on both end surfaces of the actuator body 3 in the stacking direction.
An inert body 21 for transmitting the generated force to the outside is laminated and integrated. Further, in the laminated piezoelectric actuator of the present invention, although not shown, the outer peripheral surface is covered with silicone rubber, thereby preventing creeping discharge between the internal electrodes 2 and applying a large voltage to achieve high displacement. It is possible to secure the amount.

The multilayer piezoelectric actuator configured as described above is manufactured by the following process. First,
A slurry is prepared by mixing a calcined powder of a piezoelectric ceramic such as PZT, a binder made of an organic polymer, and a plasticizer, and has a thickness of 50 to 50 mm by a slip casting method.
A ceramic green sheet of 250 μm is prepared.

On one surface of the green sheet, a conductive paste mainly composed of silver-palladium to be the internal electrode 2 is printed to a thickness of 1 to 10 μm by a screen printing method.
After drying the conductive paste, a predetermined number of green sheets to which the conductive paste is applied are laminated by a predetermined number, and green sheets to which the conductive paste is not applied are provided at both ends of the laminate in the laminating direction. Are laminated.

Next, the laminate is pressurized while being heated,
After integrating the laminate and cutting it into a predetermined size,
The binder is removed, and the mixture is baked at 900 to 1200 ° C. for 2 to 5 hours to form an inert body above and below the actuator body. The end of the internal electrode 2 is exposed on all side surfaces of the actuator body.

Thereafter, on the side surface of the actuator body, the end surfaces of the piezoelectric body 1 including the end portions of the internal electrodes 2 are alternately formed on the two side surfaces so as to have a depth of 50 to 200 every other layer.
A groove having a thickness of 500 μm and a width of 50 to 300 μm in the laminating direction is formed, and the groove is filled with an insulator 5 such as silicone rubber.

Next, a thermosetting conductive adhesive 9 is applied to two side surfaces of the actuator body, and the conductive adhesive 9
The external electrode 4 is formed by embedding a mesh member 7 in the substrate and heating and curing the conductive adhesive 9. Thereby, the internal electrodes 2 are alternately insulated every other layer, and are connected to the external electrodes 4 every other layer.

Thereafter, a lead wire 13 is connected to the external electrodes 4 for the positive electrode and the negative electrode by solder 15, and the outer peripheral surface of the actuator is coated with silicone rubber by a method such as dipping, and then 0.1 to 3 kV is applied. The multilayer piezoelectric actuator of the present invention can be obtained by applying a polarization voltage and polarizing the entire multilayer piezoelectric actuator.

In the above example, the shape of the laminated piezoelectric actuator is a quadrangular prism, but in the present invention, a hexagonal prism,
Any column, such as a cylinder, may be used, but a quadrangular column is desirable from the viewpoint of ease of cutting.

[0038]

EXAMPLE 1 First, a slurry was prepared by mixing a calcined powder of a piezoelectric ceramic containing PZT as a main component, a binder made of an organic polymer, and a plasticizer.
A ceramic green sheet having a thickness of 150 μm was produced.

On one surface of this green sheet, a conductive paste mainly composed of silver-palladium which is to be the internal electrode 2 is printed to a thickness of 5 μm by a screen printing method, and the conductive paste is dried. A plurality of the green sheets to which the conductive paste was applied were laminated on both ends of the laminate in the laminating direction, and ten green sheets to which the conductive paste was not applied were laminated.

Next, the laminate was pressurized while being heated at 100 ° C., and the laminate was integrated into a 10 mm × 10 mm
Was cut into a rectangular column having a size of, a binder was removed at 800 ° C for 10 hours, and the resultant was fired at 1130 ° C for 2 hours to obtain a laminated sintered body. The thickness t of the piezoelectric body 1 is 120
μm.

Thereafter, on the two side surfaces of the actuator body 3, the end surfaces of the piezoelectric body 1 including the end portions of the internal electrodes 2 are alternately formed on the two side surfaces so that every other layer has a depth of 100 μm and a width of 50 μm in the stacking direction. Are formed, and these grooves are filled with silicone rubber to form an insulator 5.
The end of the internal electrode 2 was exposed to the side surface of the actuator body 3 every other layer.

Thereafter, on the side surface of the actuator body 3,
A conductive adhesive 9 made of silver and a polyimide resin is applied,
In the conductive adhesive 9, the diameter R is 0.25 times the thickness t of the piezoelectric body 1, and the pitch p of the conductive wires 6 is a ratio of the thickness t of the piezoelectric body 1 to the thickness t of the piezoelectric body 1 as shown in Table 1. Mesh member 7
Of the conductive wire 6 in the stacking direction x of the piezoelectric body 1 is 45
The external electrode 4 was formed by burying the substrate in a proper manner and heating and curing at 200 ° C. in this state.

Thereafter, the lead wire 13 is connected to the positive electrode external electrode and the negative electrode external electrode by solder 15, and the outer peripheral surface of the actuator is coated with silicone rubber by a method such as dipping, and then a polarization voltage of 1 kV is applied. Then, the entire actuator was subjected to a polarization treatment to obtain a laminated piezoelectric actuator of the present invention shown in FIGS.

In the obtained laminated piezoelectric actuator, 20
As a result of applying a DC voltage of 0 V, a displacement of 10 μm was obtained for each actuator. Further, an AC electric field of 0 to +200 V is applied to these laminated piezoelectric actuators at 50 Hz.
And a driving test was performed.

In the driving test, the laminated piezoelectric actuator was driven up to 1 × 10 ⁹ cycles, the displacement was measured, and the variation from the initial displacement was examined. The displacement was measured by fixing the sample on an anti-vibration table, attaching aluminum foil to the upper surface of the sample, and using a laser displacement meter to calculate the average value of the values measured at the center and the periphery of the element. evaluated. Table 1 shows the results.

[0046]

[Table 1]

From Table 1, it can be seen that the pitch p of the conductive wire rod is out of the range of the present invention. In Nos. 1 and 7, heat was locally generated at the external electrode, thereby disconnecting the internal electrode and the external electrode and reducing the displacement to 5 μm or less. On the other hand, the sample Nos. 2 to 6 stacked piezoelectric actuators are 1 × 1
No decrease in displacement was observed after ⁰⁹ cycles.

Embodiment 2 Next, the pitch p of the conductive wire 6 is made equal to the thickness t of the piezoelectric body 1, and the diameter of the conductive wire 6 is set to a value shown in Table 2 with respect to the thickness t of the piezoelectric body 1. Except for the above, an actuator was manufactured in the same manner as in the above example, and a 200 V DC voltage was applied to the obtained laminated piezoelectric actuator. As a result, a displacement of 10 μm was obtained for each actuator. Further, an AC electric field of 0 to +200 V was applied to these laminated piezoelectric actuators at a frequency of 50 Hz, and a driving test was performed.

In the driving test, the laminated piezoelectric actuator was driven up to 1 × 10 ¹⁰ cycles, the displacement was measured, and the variation from the initial displacement was examined. Further, the connection state between the external electrode and the internal electrode at that time was observed. Table 2 shows the results.

[0050]

[Table 2]

From Table 2, all samples were 1 × 10 ¹⁰
No change in the displacement was observed even after the cycle test. In Nos. 8 and 14, heat was generated locally at the external electrodes, and traces of spark generation were observed between the internal electrodes and the external electrodes. On the other hand, the sample No. of the present invention in which the diameter R of the conductive wire was 0.05 to 2 times the thickness t of the piezoelectric body. 9
In Nos. To 13, after the cycle test, the connection state between the external electrode and the internal electrode was good, and no spark was observed at the connection portion.

[0052]

As described above, in the multilayer piezoelectric actuator of the present invention, the external electrode is formed by fixing the mesh member made of the conductive wire to the side surface of the actuator body with the conductive adhesive. Since the pitch is set to 0.5 to 8 times the thickness of the piezoelectric body, the external electrode has high elasticity, and can prevent the conductive wire from being broken. In addition, the external electrode and the internal electrode are not disconnected, and further, the mesh member does not slide on the actuator body, so that the external electrode can be prevented from being worn and the external electrode can be prevented from generating a spark.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of a laminated piezoelectric actuator of the present invention.

FIG. 2 is a longitudinal sectional view taken along line A-A 'of FIG.

FIG. 3 is a perspective view showing a mesh member.

FIG. 4 is a perspective view showing a state in which a lead mounting member made of a plate-like metal is joined to an external electrode.

FIG. 5 is a longitudinal sectional view taken along line B-B 'of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Piezoelectric body 2 ... Internal electrode 3 ... Actuator main body 4 ... External electrode 6 ... Conductive wire 7 ... Mesh member 9 ... Conductive adhesive 13 ... Lead Wire 17: Lead mounting member p: Pitch of conductive wire t: Thickness of piezoelectric body R: Diameter of conductive wire

Claims (4)

[Claims] 1. An actuator body comprising a plurality of piezoelectric bodies and a plurality of internal electrodes alternately stacked, and an external electrode provided on a side surface of the actuator body and connected to the internal electrodes alternately. A multilayer piezoelectric actuator, wherein the external electrodes are formed by fixing a mesh member made of a conductive wire to a side surface of the actuator body with a conductive adhesive, and the pitch of the conductive wire is
A laminated piezoelectric actuator having a thickness of 0.5 to 8 times the thickness of the piezoelectric body. 2. The multilayer piezoelectric actuator according to claim 1, wherein the diameter of the conductive wire of the mesh member is 0.05 to 2 times the thickness of the piezoelectric body. 3. The multilayer piezoelectric actuator according to claim 1, wherein a lead mounting member made of a sheet metal is fixed to the external electrode, and a lead wire is joined to the lead mounting member. 4. The laminated piezoelectric actuator according to claim 1, wherein the conductive wire of the mesh member has an angle of about 45 ° with respect to the laminating direction of the piezoelectric body.