JPH06181344A - Piezoelectric element - Google Patents

Abstract

PURPOSE:To enable the elongation of a piezoelectric body to be transmitted to a metal electrode and magnified in displacement by a method wherein the surface roughness of either the piezoelectric body or a surface electrode and a thickness difference between a thickest part and a thinnest part of the piezoelectric body or a drive member are set smaller than specific values respectively. CONSTITUTION:The surface roughness Rmax of either the surface 111 of a piezoelectric body 11 or the surface 121 of a surface electrode 12 is set below 1mum, and a thickness difference (parallelism) between a thickest part and a thinnest part of either the piezoelectric body 11 or a drive member 1 is set smaller than 2mum. Therefore, a load is equally applied onto the piezoelectric body 11, so that the piezoelectric body is lessened in compressive stress. Therefore, the piezoelectric element 11 becomes large in displacement and uniformly elongated. By this setup, the elongation of the piezoelectric body 11 is efficiently and almost totally transmitted to a metal electrode 2, and furthermore the piezoelectric body 11 is enlarged in displacement at driving.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric element that can be used as an actuator or the like.

[0002]

2. Description of the Related Art A piezoelectric element has a structure including a driving member composed of a piezoelectric body and electrodes such as silver attached to both surfaces thereof, and a metal electrode (external electrode) for applying a voltage to the driving member. That is, the voltage is converted into a displacement or a force by utilizing the deformation of the piezoelectric body when a voltage is applied to the piezoelectric body. Due to the above characteristics, this piezoelectric element is used in automobile parts, actuators for precision machine tools, VTRs, ultrasonic motors, and the like.

A piezoelectric element is used as a device element for which control accuracy and response speed are required due to its small displacement. Particularly when it is used as an actuator, several tens of layers are laminated to increase the displacement amount. .

In the case of producing a piezoelectric element, the surface of a piezoelectric body is processed, and a surface electrode of silver or the like is applied to the surface of the piezoelectric body.
A metal electrode is laminated on it. The piezoelectric body is usually processed by a double-sided grinder with diamond abrasive grains # 200 to 60.
It is processed with 0. Therefore, the surface roughness of the piezoelectric body is Rm.
It becomes 3 to 5 μm in ax. Further, the parallelism of the piezoelectric body (difference between maximum and minimum thickness) is 6 to 10 μm. In addition, since the surface electrode is usually attached by screen printing and then firing, the surface roughness of the drive member with the surface electrode attached is 5-8 μm in Rmax.
m, the parallelism on both sides is 10 to 16 μm. This value is the limit because the grain size of the grindstone used in the processing of the piezoelectric body is limited, and because the surface electrode is applied by screen printing and then fired.

[0005]

When the piezoelectric elements produced in this way are laminated and used as an actuator or the like by applying a preload, the surface roughness of the piezoelectric body is large and the parallelism of both sides is poor. Therefore, there is a problem that the contact between the piezoelectric elements becomes non-uniform, stress concentration occurs, and the displacement becomes smaller than the displacement obtained from the piezoelectric constant.

SUMMARY OF THE INVENTION An object of the present invention is to provide a piezoelectric element having a large displacement amount during driving, which has been made in view of the above problems of the prior art.

[0007]

According to the present invention, a driving member comprising a plate-shaped piezoelectric body and a pair of surface electrodes attached to both surfaces of the piezoelectric body, and a driving member arranged so as to sandwich the driving member. In a piezoelectric element including a pair of plate-shaped metal electrodes, the surface roughness of at least one of the piezoelectric body and the surface electrode is Rmax 1 μm or less, and the thickness of at least one of the piezoelectric body and the driving member. The piezoelectric element is characterized in that the difference between the maximum and the minimum is 2 μm or less.

[0008]

The amount of displacement of the piezoelectric element increases as the compressive stress due to the preload decreases (see FIG. 3). In the piezoelectric element of the present invention, at least one of the piezoelectric body and the surface electrode has a small surface roughness, and at least one of the piezoelectric body and the driving member has good parallelism (maximum and minimum thicknesses). Is small), the load applied to the piezoelectric body becomes uniform and the compressive stress becomes small. Therefore, the amount of displacement of the piezoelectric element increases. Further, since the piezoelectric body also has uniform elongation, most of the elongation can be efficiently transmitted to the metal electrode, and the amount of displacement increases.

[0009]

The piezoelectric element of the present invention has a large amount of displacement during driving.

[0010]

EXAMPLES Specific examples of the present invention will be described below.

(Specific Example) As shown in FIG. 1, the piezoelectric element of the present invention includes a driving member 1 having a pair of surface electrodes 12 attached to both surfaces of a plate-shaped piezoelectric body 11, and the driving member 1. It is composed of a pair of plate-shaped metal electrodes 2 arranged so as to be sandwiched.

The surface 111 of the piezoelectric body 11 or the surface electrode 1
The roughness of at least one of the two surfaces 121 is R
The maximum is 1 μm or less, and the difference (parallelism) between the maximum and minimum thicknesses of at least one of the piezoelectric body 11 and the driving member 1 is 2 μm or less. Within this range, the amount of displacement per piezoelectric element when driven can be about 1 μm. It is desirable that both the surface roughness (Rmax) and the parallelism are small.

The above method can be performed by the following method. Granularity # 2 for processing piezoelectric materials
000 or more diamond grindstone is used to grind the piezoelectric body by single-sided grinding, or the surface of the piezoelectric body is further lap-polished so that the surface roughness of the piezoelectric body is Rmax 1μ.
It can be m or less. Further, in the processing of the surface electrode, the surface roughness of the surface electrode is Rm by polishing.
It can be ax 1 μm or less.

Next, the parallelism of the piezoelectric body or the driving member is set to 2
The processing for making it less than or equal to μm is similar to the processing for surface roughness,
It is preferable to use a single-sided grinder or a jig having a good parallelism for lapping.

In the present invention, the surface roughness (Rmax) of the piezoelectric material and the like is a value measured by a surface roughness meter, and the parallelism is a value measured by a thickness tester.

The material of the piezoelectric body may be PZT (lead zirconate titanate), ceramics such as BaTiO _3, or any other material that exhibits a piezoelectric effect.

The piezoelectric body has an outer diameter of 5 to 20 mm and a thickness of 0.
A disc shape with a diameter of 2 to 1.0 mm is preferable.

Examples of the material of the surface electrode include silver. The thickness of the surface electrode is preferably in the range of 3 to 5 μm.

The material of the metal electrode may be SUS or the like. The thickness of the metal electrode is 10 to 30.
The range of μm is preferable.

The piezoelectric element of the present invention can be used for an actuator or the like, and the displacement amount during driving can be increased by stacking a plurality of piezoelectric elements.

Examples of the present invention will be described below.

(Embodiment) A mixture of fine ceramic powder to be a piezoelectric material and a resin is press-molded, and then CIP is performed.
(Cold isostatic pressing) was performed. This was degreased and further baked in an electric furnace at 1200 ° C. for 4 hours. The obtained fired body is processed into an outer diameter of 12 mm and a thickness of 0.5 mm, and the surface is # 3.
000 diamond whetstone to polish the surface roughness
The maximum was 0.8 μm, and the parallelism was 1.6 μm. After that, a surface electrode made of silver was applied to both surfaces of the piezoelectric body by screen printing, and after firing, the surface of the surface electrode was polished to have a surface roughness Rmax of 0.8 μm and a driving member parallelism of 1.6 μm. . A pair of metal electrodes (material SUS304, outer diameter 12 mm, thickness 30 so as to sandwich the driving member).
mm). In this way, the piezoelectric element (Sample No. 1) according to this example was manufactured.

For comparison, in the processing of the piezoelectric body and the driving member, the particle size of the diamond grindstone was increased,
A piezoelectric element of a comparative example was manufactured in the same manner as above except for the above. In the piezoelectric element of the comparative example, the surface roughness of the piezoelectric body and the surface electrode is Rmax 2 μm, the parallelism of the piezoelectric body and the driving member is 4 μm (Sample No. C1), and the surface roughness of the piezoelectric body and the surface electrode is Rmax is 5 μm, and the parallelism between the piezoelectric body and the driving member is 10 μm (Sample No. C
There are two types, 2).

The displacement amounts of the obtained piezoelectric element single plates of this example and comparative example were measured under compressive stress as follows. The measurement was performed by a displacement measuring device using a laser displacement meter. The compressive stress is 20 MPa and the applied voltage is 800 V.
And The measured displacement of the piezoelectric element single plate is shown in FIG.
From FIG. 2, it can be seen that the displacement amount of the piezoelectric element of this example is larger than that of the comparative example.

Also, five piezoelectric elements are laminated (metal electrodes (thickness of the metal electrodes in this case is 30 μm) are alternately laminated with six driving members) to produce a laminated piezoelectric element.
When the displacement amount was measured in the same manner as described above, the displacement amount of the piezoelectric element of this example (Sample No. 1) was larger than that of any of the comparative examples. About 2 compared to C2
It was confirmed to be 0% larger.

Further, with respect to the piezoelectric element single plate of this example, the change in the displacement amount when the compressive stress was changed while the applied voltage was kept constant at 800 V was measured in the same manner as above. The result is shown in FIG. It can be seen from FIG. 3 that the displacement amount of the piezoelectric element increases as the compressive stress decreases.

Next, a change in the displacement amount was measured when the surface roughness of the piezoelectric body and the surface electrode was kept constant and the parallelism of the piezoelectric body and the driving member was changed. The surface roughness of the piezoelectric body and the surface electrode is kept constant at Rmax of 0.8 μm, and the parallelism of the piezoelectric body and the driving member is 1.6 μm (this embodiment), 4 μm.
(Comparative example) and 10 μm (comparative example), the displacement amount of the piezoelectric element single plate was measured in the same manner as above. The result is shown in FIG. From FIG. 4, the displacement amount of this example is larger than that of any comparative example, and the parallelism is 10 μm in particular.
It can be seen that it is about 28% larger than that of.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view of a piezoelectric element according to an embodiment of the present invention.

FIG. 2 is a diagram showing a displacement amount of a piezoelectric element in Examples and Comparative Examples of the present invention.

FIG. 3 is a diagram showing a displacement amount of a piezoelectric element in an example of the present invention.

FIG. 4 is a diagram showing a displacement amount of a piezoelectric element in an example of the present invention and a comparative example.

[Explanation of symbols]

 1 Driving Member 2 Metal Electrode 11 Piezoelectric Body 12 Surface Electrode

Claims (1)

[Claims] 1. A drive member comprising a plate-shaped piezoelectric body and a pair of surface electrodes attached to both surfaces of the piezoelectric body, and a pair of plate-shaped metal electrodes arranged so as to sandwich the drive member. In the piezoelectric element, the surface roughness of at least one of the piezoelectric body and the surface electrode is Rmax 1 μm or less, and the difference between the maximum and the minimum thickness of at least one of the piezoelectric body and the driving member. Is 2 μm or less, a piezoelectric element.