JPH02203579A - Laminated displacement element - Google Patents

Abstract

PURPOSE:To improve voltage conversion efficiency and reliability by cutting out the end edge part of an inner electrode every other layer, forming a non- displacement part, and performing the contact with outer electrodes assuredly. CONSTITUTION:By using a mask, an inner electrode 2a is partially cut out, thereby forming a non-displacement part 1a at the end edge part of a thin plate 1. On an inner electrode 1b of the opposite side of the electrode 2a, a non-displacement part 2b is formed. After the thin plate provided with the electrodes 2a, 2b are laminated and bonded with pressure, a lamination body 5 is cut into elements of a specified dimension, to be baked. These non- displacement parts 1a, 1b are arranged in each layer or every several layers in a non-superposed state, and an outer electrode 3a is formed on the rear side surface of the lamination body 5. When the electrodes 2a and 3a are electrically connected and a voltage is applied to the electrode 3a, the lamination body can be driven as a lamination type displacement element, and fluctuation ratio and reliability thereof can be improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an electromechanical transducer used in actuate ultrasonic motors of industrial robots, etc.
In particular, the present invention relates to an improvement in a laminated displacement element in which the amount of displacement is increased by laminating a plurality of thin plates made of an electromechanical conversion material via internal electrodes.

[Conventional technology]

Conventionally, laminated displacement elements used for displacement elements used in X-Y stage positioning mechanisms, brakes, etc. are made by attaching electrodes to a thin plate of piezoelectric ceramic material processed into a predetermined shape, and then polarizing it. , a method of joining using an organic adhesive either directly or via a thin metal is used. However, when stacking layers using adhesive as described above, depending on the usage conditions, the adhesive layer may absorb displacement due to vibration of the piezoelectric element, or the adhesive may deteriorate due to high temperature environment or long-term use. There are drawbacks.

For this reason, recently, multilayer piezoelectric elements having a multilayer chip capacitor structure have been put into practical use. That is, 1. For example, as described in Japanese Patent Publication No. 59-32040, a paste-like piezoelectric ceramic material made by adding a binder to raw material powder and kneading is formed into a thin plate of a predetermined thickness, and one side of this thin plate or Internal electrodes are formed by coating both sides with a conductive material such as silver-palladium. A predetermined number of the above thin plates are laminated and crimped.

Further, after being processed into a predetermined shape, the laminate is made into a ceramic by firing, and external electrodes are formed on both sides of the laminate. The laminated piezoelectric element with the above structure has excellent adhesion between the thin plate made of piezoelectric ceramic material and the internal electrode, and has stable thermal properties, so it can be used satisfactorily even in high-temperature environments, and can be used for long periods of time. It has the advantage of extremely little deterioration over time.

FIG. 3 shows an example of the structure of the laminated piezoelectric element.

This is the so-called alternating electrode type. In FIG. 3, 1 is a thin plate made of piezoelectric ceramic material,
The positive and negative internal electrodes 'la and 2b are alternately sandwiched and stacked. The internal electrodes 2a, ``lb'' are formed such that their negative end edges protrude or are exposed to the outside, and the external electrodes 3a,
Connect to 3b.

With the above configuration, when positive and negative voltages are applied to the external electrodes 3a and 3b, an electric field is generated between the internal electrodes 2a and 2b, and the 'ija plate l is elongated and displaced in the thickness direction due to the longitudinal effect of the piezoelectric ceramic material. will occur.

Next, the one shown in FIG. 4 is an example of another laminated piezoelectric element, which is a so-called full-surface electrode type with improved pressure 1 displacement efficiency (for example, disclosed in Japanese Patent Laid-Open No. 196068/1983). etc.). In FIG. 4, the same parts are indicated by the same reference numerals as in FIG. On the negative side of the laminate 5 formed as described above, coatings 4 made of an insulating material are placed on the edges of the internal electrodes 2a and 2b every other layer (for example, only on the internal electrode 2b).
At the same time, an external electrode 3a (not shown) made of an electrically conductive material is applied to the top 2 of the covering 4.

On the other hand, on the other side of the laminate 5, a coating 4 is provided on the edge of the internal electrode (for example, 2a) that is not provided with the coating 4, and an external electrode (not shown) is placed on top of the coating 4. Let it happen.

Furthermore, as a means for forming an external electrode in the above-mentioned full-surface electrode type, the method shown in FIG.
1-174681), in order to form the external electrodes in FIG. 5, first, as shown in FIG. As shown in Figure 5 (bl), an automatic cutting machine or the like is used to cut the inner
Next, as shown in FIG. 5 (C1), the external electrode 3a is coated and baked.The internal electrode 2b is also coated with the external electrode 3b (not shown). ).

[Problem to be solved by the invention]

First, in the one shown in FIG. 3, the internal electrodes 2a,
The overlapping part of 'lb forms the displacement part a, and the inner electrode 2a is formed around the 5 peripheral part.

Since 2b does not polymerize, it becomes a non-displaced part. Therefore, even if a voltage is applied to the external electrodes 3a and 3b, the electric field strength is large only in the displaced part a, and the electric field strength in the non-displaced part is small, which inhibits the deformation of the entire element and There is a problem in that it is not possible to obtain the displacement specific to the material. Further, since large strain occurs and stress is concentrated at the boundary between the displaced portion a and the non-displaced portion A, there is also the problem that the thin plate 1 or the entire element may crack.

FIG. 6 is an enlarged explanatory view of the main parts of the laminated piezoelectric element shown in FIG. 3, and FIG. 7 is a diagram showing the relationship between lateral position and principal stress, and the same parts have the same reference numbers as in FIG. 3. In the diagrams shown in FIG. 1, it is clear that a large tensile stress is applied to the displaced portion a where the internal electrodes 2a and 2b overlap. Moreover, this tensile stress increases as the number of stacked 9 thin plates 1 increases (the number appended to the curve in Figure 7 indicates the number of stacked layers)
.

The bonding strength between the one-way electrodes 2a, 2b and the thin plate 1 is 5
kgf/mm", and even if the number of layers in the thin plate 1 is 10, the maximum tensile stress in the non-displaced part is 5 kg.
f/mm'' and the number of laminated layers is 201) or more, the value exceeds 5 kgf/1sta''.

For this reason, a crank occurs at the 0 section in FIG.

There is a problem that the function of the element is obstructed and, in extreme cases, it may lead to destruction.

In addition, in the full-surface electrode type having the configuration shown in FIGS. 4 and 5, there is no non-displaced portion as described above, so that no problem occurs due to the action of tensile stress.

However, in the configuration shown in FIG. 4 above,
This is because it is necessary to provide the covering 4 made of an insulating material over the entire width of the edges of the internal electrodes 2a, 2b.

Requires complicated work. In addition, the above-mentioned M4 and the internal electrode 2a,
The center must match with 2b.

For example, there is a problem that the coating 4 cannot be formed at a desired position due to accumulated errors in the thickness of the thin plate 1 and/or the internal electrodes 2a, 2b, resulting in dielectric breakdown. In addition, if the thickness of the thin plate l becomes thinner and becomes less than 100 μm, the peripheral edge or hem of the coating 4 that should be formed on every other layer of the internal electrodes 2a and 2b will inadvertently expand, causing Since the edge of the electrode i2a or 2b is also covered, there are also problems such as not being able to conduct with the external electrodes 3a and 3b.

On the other hand, also in the configuration shown in FIG.

When forming the grooves 6, the difficulty in positioning them is similar to that shown in FIG. 4 above.

In addition, since the internal electrodes 2a and 2b are laminated and crimped together with the thin plate 1, their edges are curved.
The groove 6 may be formed at a location where the groove 2b does not exist, which poses problems such as causing dielectric breakdown when a voltage is applied.

It is an object of the present invention to solve the problems existing in the above-mentioned prior art and to provide a laminated displacement element with high piezoelectric conversion efficiency and high reliability.

[Means to solve the problem]

In order to achieve the above object, there are two aspects of the present invention.

A laminate is formed by alternately stacking a plurality of thin plates made of an electromechanical transducer material and internal electrodes made of a conductive material, which are formed to have substantially the same planar contour and contact area, and the internal electrodes are placed on the side surface of this laminate. In a laminated displacement element having a pair of external electrodes to be connected to every other layer, the end edges of the internal electrodes are partially cut off at every other layer to form non-displaceable parts, and these non-displaceable parts are arranged in a non-polymerized state for each layer or for each plurality of layers, and external electrodes are provided in each of these non-displaced portions. A technical method was adopted.

In the present invention, the external electrodes may be provided on the same side of the laminate or on different sides.

Although it is preferable that the outer 1-it pole is provided non-parallel to the ridgeline of the laminate, a small number of non-displaceable portions may be overlapped to form a stepped field.

[Effect]

With the above configuration, the connection between the internal electrode and the external electrode can be easily and reliably made, and the non-displaced part can be dispersed, and the value of tensile stress generated in the non-displaced part can be significantly reduced. Can be done.

〔Example〕

FIG. 1 (al to fhl are respectively perspective views showing thin plates in embodiments of the present invention, FIG. 1 (1) is a perspective view showing an embodiment of the present invention, and the same parts are shown in FIGS. 3 to 5 above. First of all, FIG.
In 1, for example, P b (Zr, Ti) Ox powder, PVB as an organic binder and BP as a plasticizer.
BG and trichlene as an organic solvent are added and mixed, and this mixed material is made into a 100mm thick film using a doctor blade method.
Next, a silver-palladium paste for forming internal electrodes 2a and 2b is screen printed on the entire surface of the thin plate 1, which is formed on a sheet-like thin plate 1 having a thickness of μm. In this case, the internal electrode 2a is partially removed by masking, for example, to form a non-displaceable part 1a at the edge of the thin plate 1, as shown in FIG. Non-displacement part 1
The formation position of a is slightly shifted for each layer. - As shown in the force cylinder 1 diagrams (bl, (d), frl and (hl), a non-displaceable portion 1b is formed in the internal electrode 2b opposite to the internal electrode 2a.The internal electrode 2 formed as described above
a.

For example, 100 thin plates l having 2b are alternately laminated and crimped, and then cut into a predetermined size and shape to form a laminate, 1
It was baked at 050-1200°C for 1-5 hours.

Next, the external electrode 3a is provided as shown in FIG.
For example, since internal electrodes 2b of the same polarity exist above and below this non-displaceable portion 1a, a conductive material may be coated or screen printed in a band shape on this non-displaceable portion 1a.

Note that an external electrode 3b (not shown) is similarly provided on the back side of the laminate 5.

With the above configuration, the external electrodes 3a, 3b are electrically connected to the internal electrodes 2a, 2b, respectively.

By applying a voltage between the external electrodes 3a and 3b, the stacked body 5 can be driven as a stacked displacement element.

In this case, non-displaceable portions 1a exist in some of the edge parts of the thin plate 1, but these positions are arranged so that they do not overlap in the direction of one layer of the thin plate 1, or so that even if they overlap, only a few of them overlap. Because it is.

It is possible to prevent tensile stress of an unfavorable value from being generated in these parts.

FIG. 1 ft1 Q) I is a perspective view showing other embodiments of the present invention, and since the representation is simplified, individual thin plates,
The edges of the internal electrodes are omitted. First, as shown in FIG.
, 3b. External power FfA3a.

The terminals connected to 3b are concentrated in the same part, so it is preferable to use the thin plate 1 shown in FIG. Regarding polymerization of several layers.

They are stacked one after another with their positions shifted. Therefore, the external electrode 3a is formed in a stepped shape. Note that the same applies to the other external electrode 3b (not shown). The operation of the above structure is similar to that of the embodiment shown in FIG. 1(1).

In the above embodiment, an example was described in which screen printing was used as a means of forming the internal electrodes and external electrodes, but the method is not limited to this, and the same effect can be achieved by other methods such as plating, binding, coating, etc. It is. Furthermore, in the above embodiment, the case where the electromechanical conversion material is a piezoelectric material was described, but since the Curie temperature is lower than room temperature,
Regarding electrostrictive materials that do not require polarization, have large displacement, and have small hysteresis,
Exactly the same effect as above can be expected. Examples of such electrostrictive materials include 1, for example (Pbo, wtw Lao, o*4) (Zr++, i
s Tio, 5s) o, wtw Os T(Pb
o, ss Sro, +s) (Zre, s+ Tio
, sa Zno, ortsNia, osqs W
ho, to) Os + (Pbo, ss Sro,
+s) (Zro, so Tie, so Zn++,
osNio, as Nbo, to) Os, etc. can be used.

〔Effect of the invention〕

Since the present invention has the structure and operation as described above,
You can expect the following effects.

1) Since the structure has dispersed non-displaceable parts, undesired tensile stress is not generated, cracks are prevented from occurring, and reliability can be greatly increased.

(2) When forming external electrodes, there is no need to provide a covering or grooves, reducing the number of processing steps and time, and improving productivity.

(3) Since undesired grooves are not formed in the thin plate portions forming the laminate, dielectric breakdown during voltage application can be prevented, and quality and reliability can be significantly improved.

(4) Since the internal electrode is provided over the entire surface of the thin plate, piezoelectric conversion efficiency is extremely high.

[Brief explanation of the drawing]

1(8) to 1+l are respectively perspective views showing the thin plates in the embodiments of the present invention, FIG. 1(1) is a perspective view showing the embodiments of the present invention, and FIG. FIGS. 3 and 4 are perspective views showing other embodiments of the invention, respectively, and FIGS.
) (03 is an explanatory diagram showing conventional external electrode forming means. FIG. 6 is an enlarged explanatory diagram of main parts of the laminated piezoelectric element shown in FIG. 3, and FIG. 7 is an explanatory diagram showing the relationship between lateral position and principal stress. 1: T?J plate, la, Ib: non-displaced part, 2a, 2b:
Internal electrodes, 3a, 3b: external electrodes.

Claims (5)

[Claims] (1) A laminate is formed by alternately stacking a plurality of thin plates made of an electromechanical transducer material and internal electrodes made of a conductive material, which are formed to have approximately the same planar contour and contact area, and the side surfaces of this laminate are In the laminated displacement element which is provided with a pair of external electrodes to be connected to the internal electrodes at every other layer, the end edges of the internal electrodes are partially cut off at every other layer to form non-displaceable parts, and these 1. A laminated displacement element characterized in that non-displaceable portions are formed in a non-overlapping state for each layer or for each plurality of layers, and external electrodes are provided for each of these non-displaceable portions. (2) The laminated displacement element according to claim (1), wherein the pair of external electrodes are provided on the same side surface of the laminated body. (3) Claim in which the external electrodes are provided on different sides of the laminate (
1) The laminated displacement element described above. (4) The laminated displacement element according to any one of claims (1) to (3), wherein the external electrodes are provided non-parallel to the ridgeline of the laminated body. (5) The laminated displacement element according to any one of claims (1) to (3), wherein the external electrodes are formed in a stepped shape.