JPH08242024A - Piezoelectric actuator - Google Patents

Abstract

PURPOSE: To provide a low-cost moistwre-proof piezoelectric actuator in which internal stress is decreased and large generation-displacement is obtained. CONSTITUTION: A plurality of piezoelectric element plates are formed with an internal electrode on a surface of a piezoelectric seat and stacked to form a piezoelectric element 22. The plurality of piezoelectric elements are stacked by using elastic adhesives 23. Thus, a binding force at expansion and contraction driving is reduced to obtain large generation-displacements.

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 in a positioning mechanism for an XY stage, an ultrasonic motor, a mass flow controller and the like.

[0002]

2. Description of the Related Art Generally, a piezoelectric element formed by alternately laminating a piezoelectric ceramic material and a thin film electrode is known as a minute displacement element used as an actuator for an XY stage positioning mechanism, an ultrasonic motor, a mass flow controller and the like. The piezoelectric ceramic material is used as an actuator for a portion requiring a large load with a small stroke by utilizing the effect that the piezoelectric ceramic material expands and contracts due to an electric field. Since this element is incorporated into the main parts of the manufacturing line, long-term reliability is required, and thus high mechanical strength and high humidity resistance are required.

The structure of a conventional piezoelectric element of this type will be described with reference to FIG. FIG. 11 shows a perspective view of a conventional piezoelectric actuator of the full-surface electrode type. This piezoelectric actuator comprises a piezoelectric sheet 2 made of a ceramic material such as titanate / lead zirconate (PZT) and a thin film of platinum or silver-palladium. The internal electrodes 4 are alternately laminated in a large number, for example, about 100 layers. The end of the internal electrode 4 is exposed to the outside over the entire circumference.
Since it is necessary to alternately apply voltages having different polarities, insulating layers 6 and 8 are formed by coating on two orthogonal side surfaces of the block-shaped piezoelectric element in order to form the applied electrodes. In the insulating layer 6, the edge portions of the internal electrodes are exposed again by dicing along the edges of the internal electrodes 4 every other layer, and in the other insulating layer 8, the internal electrodes 4 of the alternate layer different from the above. Similarly, the edges of the internal electrodes are exposed again by shaving with a dicer along the edges.

Then, external electrodes 10 and 12 made of silver paste or the like are formed by coating on the insulating layers 6 and 8, and the exposed internal electrodes 4 are electrically connected every other layer. Therefore, one external electrode 10 is commonly connected to internal electrodes every other layer, and the other external electrode 12 is commonly connected to internal electrodes every other layer different from the above. It is possible to apply an electric field to each piezoelectric sheet 2 by applying a DC voltage between the first and second electrodes 12, thereby producing an electrostrictive effect.

By the way, the thickness of each piezoelectric sheet 2 is about 1
Since it is as thin as 00 μm, even if a small amount of water adheres to the side surface of the element, the adjacent internal electrodes 4 are easily short-circuited to become unusable, or the internal electrode 4 is less expensive than platinum. -When palladium is used, it causes migration to grow a needle-shaped crystal in a tree shape, which reaches the internal electrode 4 adjacent to the same and causes a short circuit phenomenon in the same manner. . Therefore, in order to improve the moisture resistance, a technique in which the entire piezoelectric element is housed in an expandable and contractible sealed stainless steel can to improve the moisture resistance, and JP-A-3-27008.
An alternating electrode type piezoelectric actuator as shown in Japanese Patent No. 5 has been developed. FIG. 12 is a perspective view showing a conventional piezoelectric actuator of an alternating electrode type, and FIG. 13 is a view showing a surface state and a laminated state of each piezoelectric sheet of the piezoelectric actuator shown in FIG.

This alternating electrode type piezoelectric actuator is
Unlike the full-electrode-type piezoelectric element actuator shown in FIG. 11 in which internal electrodes are formed on the entire surface of the piezoelectric sheet, the piezoelectric sheet 2 of the piezoelectric sheet 2 is formed except that the electrode lead-out portion 14 reaching the end side of the piezoelectric sheet 2 is formed on only a part thereof. No internal electrode is formed on the peripheral portion of the surface, and the internal electrode 4 is formed at a slight distance from the edge of the sheet. Then, as shown in FIG. 13, the piezoelectric sheets 2 thus formed are laminated so that the electrode lead-out portions 14 of the internal electrodes are alternately arranged in the opposite direction as shown in FIG. Since it is exposed to the outside, the external electrodes 10 and 12 are applied here to electrically connect the internal electrodes of every other layer.

[0007]

By the way, in the former structure in which the whole piezoelectric element is housed in a closed stainless steel can, the moisture resistance can be improved, but since the closed can is used, the element is large. However, there is a problem in that the cost is increased due to the necessity of using extra parts in addition to the reduction in space saving. Also, in the latter case of the alternate electrode type piezoelectric actuator, the exposed portion of the internal electrode was small and the moisture resistance could be improved, and the number of steps was small, which contributed to cost reduction, but the portion where the internal electrode was embedded was Between the non-embedded part and
A large stress is generated during operation, which causes a new problem that not only the amount of generated displacement is reduced and a sufficient expansion / contraction stroke cannot be obtained, but also cracks are easily generated. This will be described in detail with reference to FIGS. 14 and 15.

FIG. 14 is a cross-sectional view of the alternate electrode type piezoelectric actuator shown in FIG. 13, and FIG. 15 is a diagram schematically showing a deformed state of the piezoelectric actuator when it is driven by a voltage application and vertically expanded. is there. In the figure, 30 and 32 are external electrodes electrically connected to the internal electrodes of every other layer. A piezoelectric element formed by stacking a large number of piezoelectric sheets is adjacent to a piezoelectric active portion 16 which is a portion in which vertically adjacent internal electrodes 4 are overlapped with each other via sheets to contribute to expansion and contraction in the vertical direction in the drawing. The internal electrode is divided into a piezoelectric inactive portion 18, which is a portion that does not overlap and does not contribute to expansion and contraction. When this piezoelectric element is driven, the piezoelectric active portion 16 expands and contracts due to the electrostrictive effect, whereas the piezoelectric inactive portion 18 does not expand or contract at all, so that the expansion and contraction operation is constrained. As a result of the constraint force thus acting, the entire piezoelectric actuator is largely deformed into a drum shape as shown in FIG. FIG.
5, the modified mode is emphasized and described. . As a result,
The expansion stroke of the entire piezoelectric actuator is suppressed so that the amount of generated displacement cannot be sufficiently obtained, and also a large stress acts mainly on the boundary portion 20 between the piezoelectric active portion 16 and the piezoelectric inactive portion 18 to cause a crack. There was a problem that it became easier to do.

In order to reduce such restraint force, in the latter case, a subunit formed by laminating about 23 thin ceramic layers is formed, and only the piezoelectric inactive portions are bonded to each other to form a large unit. Although an actuator is manufactured, a considerable amount of internal stress is generated even in the subunit, and the present situation is that the occurrence of cracks and the like cannot be sufficiently suppressed. In particular, in a field requiring extremely precise control of a minute displacement amount such as a mass flow controller used for controlling a gas flow rate of a semiconductor manufacturing apparatus, a displacement amount difference of about several μm has a great influence. . Further, in this latter technique, since the adhesive is applied only to the piezoelectric active portion, the adhesive strength is weak and there is a possibility that the adhesive may be peeled off by repeated use.

As a related technique, Japanese Patent Laid-Open No. 3-179.
As shown in Japanese Unexamined Patent Publication No. 228, when a single-piece piezoelectric ceramic as a sensor is attached to a support plate, an elastic adhesive is used to absorb stress caused by a difference in thermal expansion coefficient between the support plate and the ceramic. However, this is not to use an elastic adhesive to increase the displacement of the piezoelectric ceramic, but to simply absorb the stress due to the difference in thermal expansion,
It does not have a direct relationship with the present invention. The present invention has been made to pay attention to the above problems and to solve them effectively. An object of the present invention is to provide a piezoelectric actuator that is inexpensive, has high humidity resistance, has a small internal stress, and can obtain a large amount of generated displacement.

[0011]

In order to solve the above problems, the present invention forms a piezoelectric element by laminating a plurality of piezoelectric element plates each having an internal electrode formed on the surface of a piezoelectric sheet.
A plurality of the piezoelectric elements are connected to each other in the thickness direction by using an elastic adhesive.

[0012]

Since the present invention is configured as described above, the piezoelectric elements are bonded by the elastic adhesive having elasticity even when the displacement amount generated in the piezoelectric elements varies in the thickness direction when the actuator is driven. Therefore, it is possible to absorb the difference in the generated displacement amount. Therefore, it is possible to obtain a sufficiently large generated displacement amount without restraining the expansion and contraction operation of the piezoelectric element. As this elastic adhesive, a relatively soft adhesive such as a vinyl adhesive or a silicone adhesive can be used. When the piezoelectric element has the piezoelectric inactive portion on the peripheral edge thereof, the restraining force against the expansion and contraction operation of the piezoelectric active portion tends to increase, but even in this case, the elastic adhesive absorbs the difference in displacement amount. Because you can
A sufficiently large amount of generated displacement can be obtained, and an increase in internal stress can be prevented.

Further, when the contraction rate matching thin film is formed on the piezoelectric inactive portion, it is possible to reduce the difference in the contraction rate between the piezoelectric active portion and the piezoelectric inactive portion during firing of the piezoelectric element. It is possible to reduce the residual stress inherent in the piezoelectric element itself and increase the amount of displacement generated as a whole. Furthermore, in a piezoelectric element having a piezoelectrically inactive portion, when a polarized piezoelectric element is joined, a flat protrusion is generated at the center of the upper and lower surfaces of the element due to remanent polarization. By mainly interposing an elastic adhesive between the piezoelectric inactive part and the element, this absorbs the difference in the generated displacement amount, and it becomes possible to obtain a sufficiently large generated displacement amount, and at the same time, the generated stress difference is also absorbed. Therefore, it is possible to prevent the occurrence of internal cracks.

[0014]

EXAMPLE An example of the piezoelectric actuator according to the present invention will be described in detail below. 1 to 8 are views showing a manufacturing process of a piezoelectric actuator of the present invention, FIG. 1 is a plan view showing a piezoelectric element plate in which an internal electrode and a contraction rate matching thin film are provided on a piezoelectric sheet, and FIG. FIG. 3 is an enlarged view showing the portion of the shrinkage factor matching thin film of the piezoelectric element plate shown in FIG. 3, FIG. 3 is a view showing a laminated state of the piezoelectric element plates shown in FIG. 1, and FIG. 4 is a perspective view showing a piezoelectric element formed by laminating piezoelectric element plates. FIG. 5, FIG. 5 is a side view of the piezoelectric element plate shown in FIG. 4, FIG. 6 is a perspective view showing a state after polarization of the piezoelectric element shown in FIG. 4, and FIG. 7 is formed by stacking and connecting piezoelectric elements. FIG. 8 is a perspective view showing the piezoelectric actuator of the present invention, and FIG. 8 is an enlarged view showing a connection state between the piezoelectric elements shown in FIG. The same parts as those of the conventional device described above are designated by the same reference numerals.

An important point of the present invention is that, as shown in FIG. 8, an elastic adhesive 23 is used to connect the piezoelectric elements 22 to each other, which has a strong adhesive force, but has a relatively soft material property even after the bonding. The point is that the restraint force during driving was absorbed and released. First, steps required to form the piezoelectric element 22 as shown in FIG. 4 will be described. As shown in FIG. 1, for example, silver-palladium or the like is provided on the surface of a thin plate-shaped piezoelectric sheet 2 made of a ceramic material such as PZT and having a thickness of about 100 μm and a length and width of about 25 mm at a predetermined distance D from its end 2A. Is formed, and the thin film metal of the internal electrode 4 is partially extended only to a part of the edge 2B to expose the electrode from the edge 2B. The part 14 is formed. As a result, the piezoelectric element plate 21 is formed. The thin plate formation of the piezoelectric sheet is performed by, for example, the doctor blade method,
The internal electrodes 4 are formed by screen printing or the like.

In this case, an electric field is applied to a region formed in a U-shape so as to surround the internal electrode 4 other than the electrode lead-out portion 14, that is, a region on the piezoelectric sheet where the internal electrode 4 is not formed, as described later. Since the region is not applied and does not contribute to the piezoelectric effect, the piezoelectric inactive region 24 is formed.
On the other hand, the region where the internal electrode 4 is formed becomes the piezoelectric active region 26.

Then, a contraction rate matching thin film 28 is formed in the substantially U-shaped piezoelectric inactive region 24 by using screen printing or the like like the internal electrodes. In this case, the matching thin film 28
Is formed of a thin metal film as thin as the internal electrode 4,
The piezoelectric sheet 2 is formed slightly inside the respective edges 2A and 2B, and at the same time, is formed so as to be slightly separated from the internal electrode 4 as well, and becomes electrically floating when laminated as described later. To set. Width D of piezoelectric inactive region
However, the width of the matching thin film 28 is set to about 0.5 mm.

The matching thin film 28 may be formed as a solid metal thin film on the entire surface, but in consideration of the adhesion between the piezoelectric sheets at the time of stacking, for example, a fine circular shape as shown in the enlarged view of FIG. It is preferable to form the matching thin films 28 so as to be densely arranged and scattered in, for example, a polka dot pattern. This is because the strength after firing between the piezoelectric sheets and the electrodes is weaker than the strength after firing between the piezoelectric sheets, and considering the strength of the entire piezoelectric element, it is necessary to increase the adhesion between the piezoelectric sheets as much as possible. is there. In FIG. 2, the distance between the circular matching thin films 28 is shown large for ease of description, but is actually very small, for example, 0.06 to
It is set to about 0.15 mm.

When the matching thin films are provided in a scattered manner, each shape is not limited to a circular shape, and may be any shape such as an elliptical shape, a rectangular shape, and a triangular shape. The matching thin film 24 may be made of the same material as the internal electrodes, for example, silver-palladium. In that case, the matching thin film 28 can be formed at the same time when the internal electrodes are formed by screen printing or the like. There is no need to increase the number of steps. However, the material may not be the same as the material of the internal electrodes as long as the same effect for matching the contraction rate can be obtained. As described above, when the internal electrodes 4 and the matching thin film 28 are formed on the piezoelectric sheet 2 to complete the formation of the piezoelectric element plates 21, a plurality of piezoelectric element plates 21 formed in the same manner, for example, 25 sheets, Laminate as shown in FIG. 3, and cold isostatic pressing (CIP: Cold Isostatic Pres)
While being pressed by s), pressure bonding is performed at a temperature of about 120 ° C., and this is sintered at a high temperature of about 1075 ° C. to form a single piezoelectric element 22 as shown in FIG.

When stacking the piezoelectric element plates 21, the piezoelectric element plates 21 that are vertically adjacent to each other are bonded so that the electrode lead-out portions 14 between the piezoelectric element plates 21 are positioned opposite to each other. Therefore, the electrode lead-out portions 14 are arranged in the same direction in every other layer of the piezoelectric sheet 2. As a result, the end portions of the electrode lead-out portions 14 are exposed to the outside every other layer on the side wall of the piezoelectric element after sintering, as shown in FIG. As shown in FIG. 4, when the piezoelectric element is sintered, irregularities are formed on the surface of the piezoelectric element, though very slight. Therefore, the upper and lower surfaces of the piezoelectric element are ground to secure flatness before stacking them. Good to do. In this case, in order to prevent the internal electrodes from being exposed by the surface polishing, as shown in FIG. 5, the upper and lower surfaces of the piezoelectric element 22 have a thickness (about 300 μm) corresponding to about three layers of the piezoelectric sheet,
It is preferable that only the piezoelectric sheets on which the internal electrodes and the matching thin film are not formed are stacked as a dummy. By this surface polishing, for example, the piezoelectric element, which had a height of about 2.7 mm at the time of sintering, was ground and set to about 2.5 mm.

The reason why the piezoelectric element 22 is formed by stacking about 25 piezoelectric element plates as described above is that the number of layers is 30 or less in the material and size of the piezoelectric sheet as described above. This is because, when the number is preferably about 25, the internal stress can be reduced without reducing the number of layers too much. This will be described based on the simulation result shown in FIG. FIG. 10 is a graph showing simulation results of the relationship between the distance from the center of the piezoelectric element and the stress in the stacking direction when the number of laminated piezoelectric sheets is variously changed, and the corresponding portion of the piezoelectric element is shown above the graph. .

The thickness of one PZT piezoelectric sheet was 0.09 mm, the length of the piezoelectric inactive portion (piezoelectric inactive region) was set to 0.6 mm, and a DC voltage of 150 V was applied. The result of time is shown. In the figure, the origin of the horizontal axis indicates the center of the element, and the maximum value of 2.5 mm indicates the surface of the element. As is clear from the graph, as the number of laminated sheets increases, the stress at the interface between the piezoelectric inactive portion and the piezoelectric active portion increases, and in particular, the tensile stress, which is the largest cause of cracking, depends on the number of laminated sheets. To increase. Therefore, the tensile stress can be reduced by reducing the number of laminated layers, but unfortunately the tensile stress is always generated at the interface between the piezoelectric active portion and the piezoelectric inactive portion. However, when considering improvement of the moisture resistance of the element, it is desirable to prevent cracks on the surface of the element, considering that the main purpose is to cut off the moisture invasion route, and to minimize the occurrence of cracks in that part. It can be said that it should be suppressed to the limit. This simulation result revealed that the stress on the surface of the device acts on the compression side when the number of laminated layers is 30 or less. Therefore, by setting the number of laminated layers to about 25, it becomes possible to form a piezoelectric subunit in which cracks are less likely to occur on the element surface. If the number of laminated layers is too small, the production efficiency will decrease, which is not preferable.
Here, the results of this simulation use, as a model, an ideal sintered body in which the state of close contact between the piezoelectric sheet and the internal electrode is good and there is no residual stress inside. Therefore, as described above, when the thin film for achieving the contraction rate matching during sintering is not formed, the adhesion strength in the element is reduced, and for example, due to the tensile stress generated in the vicinity of the piezoelectric active portion and the piezoelectric inactive portion, A fatal crack that reaches the side surface of the device is generated. By forming a large number of piezoelectric sheets 2 (the number of which is based on the result of the simulation) of the contraction rate matching thin film 28 in the piezoelectric inactive region 24 in which the internal electrodes 4 are not formed as described above, a piezoelectric element is formed. , The contraction rates of the ceramic material in the piezoelectric inactive region 24 and the piezoelectric active region 26 during the sintering of the element become substantially the same,
It is possible to provide an element that does not cause residual stress, has high adhesion strength, and is unlikely to cause cracks.

In this case, by forming the matching thin films scattered in a polka dot pattern, for example, as described above, the deterioration of the adhesion strength between the piezoelectric sheets is reduced and cracks can be further prevented. In addition, as described above, by setting the number of laminated piezoelectric sheets to a maximum of about 25, it is possible to obtain a piezoelectric actuator having a large strength against cracks without increasing the number of stacked elements at the time of manufacturing the piezoelectric actuator as will be described later. You can Then, silver-paste or the like is applied along the two side surfaces where the electrode lead-out portion 14 of the piezoelectric element is exposed, for example, 700 ° C.
The first and second external electrodes 3 are formed by firing at a certain degree.
0 and 32 are formed. Then, the external electrodes 30, 32
By applying a DC voltage to, the ceramic material of the piezoelectric sheet is polarized to complete the piezoelectric element.

Due to the polarization effect of the piezoelectric element 22, residual polarization remains even after the voltage application is stopped.
As shown in FIG. 3, the rectangular piezoelectric active portion 16 corresponding to the portion where the internal electrodes are embedded protrudes in the vertical direction to form the flat protrusion 36, and conversely, the peripheral portion thereof, that is, the matching thin film is embedded. Piezoelectric inactive portion 18 corresponding to the portion
Is in the original state because no electric field is applied. In the illustrated example, since it is a perspective view, only the upper flat protruding portion 36 is shown, and the lower flat protruding portion is not shown. In this case, when the thickness of the piezoelectric element 22 is about 2.5 mm, the amount of protrusion of the flat protrusion 36 is about 1.
It is about 0 μm. As described above, generally, the expansion / contraction stroke of the piezoelectric element is very small. For example, the expansion / contraction amount obtained by applying a DC voltage of about 150 V to a piezoelectric sheet having a thickness of about 0.1 mm is about 0.1 μm.
To obtain the amount of expansion and contraction corresponding to the required stroke, a plurality of these piezoelectric elements are connected in series. Therefore, as shown in FIG. 7, a plurality of piezoelectric elements 22 after polarization, which are formed as shown in FIG. 6, are piled up, eight in the illustrated example, and bonded by an elastic adhesive 23 as a feature of the present invention. The piezoelectric actuator 34 is completed. In this way, the internal electrodes can be electrically connected in common every other layer, and by supplying a DC voltage between the external electrodes 30 and 32, an electric field can be applied to the piezoelectric sheet.

The size of the piezoelectric actuator 34 is, for example, 5.5 mm in length and width, and eight piezoelectric elements 22 each having a thickness of about 2.5 mm are stacked in series in the thickness direction and connected, so that the total length is about 20 mm. Becomes In this case, the elastic adhesive 23 has a certain degree of flexibility or softness even after the bonding and solidification, and when the actuator 34 is driven, it follows the expansion of the piezoelectric active portion 16 and the piezoelectric inactive portion. Any adhesive may be used as long as 18 is soft enough to stretch.
As the elastic adhesive 23 of this type, for example, a vinyl adhesive, a silicon adhesive, a polyimide adhesive, or an epoxy adhesive can be used. For example, as shown in FIG. 9, when an epoxy adhesive 38 having low elasticity is used as an adhesive for adhering the piezoelectric element, when the piezoelectric active portion 16 expands as indicated by the arrow 40 when the actuator is driven, the piezoelectric Since the inactive portion 18 is firmly joined so as not to move in the vertical direction in the figure, it cannot follow the extension of the piezoelectric inactive portion 16, and therefore, the restraining force acts on the piezoelectric active portion 16 and the actuator is actuated. The amount of displacement generated as a whole is suppressed and reduced, and a sufficient stroke cannot be earned.

Further, such a restraining force is exerted by the piezoelectric active portion 16
Between the piezoelectric element 18 and the piezoelectric inactive portion 18, the internal stress causes internal fracture or crack inside the piezoelectric element, or the outer peripheral portion of the piezoelectric element generates stress as shown by the arrow 42. Will cause surface cracks. On the other hand, if the elastic adhesive 23 is used to bond the piezoelectric elements 22 to each other as in the piezoelectric actuator of the present invention, the piezoelectric inactive portions 18 are adjacent to each other by following the expansion of the piezoelectric active portions 16. The elastic adhesive 23 interposed between the two expands, and the minute movement of the piezoelectric inactive portion 18 is allowed. Therefore, since almost no restraint force acts on the piezoelectric active portion 16, the amount of displacement generated in the entire actuator can be increased, and at the same time, almost no internal stress is generated. It also becomes possible to prevent the occurrence of cracks.

Further, when the piezoelectric elements 22 are joined to each other, the elastic adhesive 23 is applied to the entire surface of the piezoelectric elements 22 and pressed so as to be pressed from both upper and lower sides of the elements, so that the flat protruding portions 36 are formed. The adhesive 23 between the piezoelectric active portions 36 is removed to the side more than this, and almost remains slightly, so that the adhesive 23 is interposed only between the piezoelectric inactive portions 18. As a result, since the adhesive 23 is hardly present between the piezoelectric active portions 36, it is possible to perform highly accurate minute stroke control without adversely affecting the generated pressing force and the generated displacement amount when the actuator is driven.

Regarding this point, the above-mentioned Japanese Patent Laid-Open No. 3-
In the technology of Japanese Patent No. 270085, first, since the shrinkage-matching thin film is not used, internal stress is accumulated in the subunit (piezoelectric element) itself, and not only is there a cause of cracks or internal fracture. Since the adhesive is provided only in the piezoelectric active portion, the adhesive in this portion may adversely affect the generated displacement amount and the pressing force when the actuator is driven. Actually, the size is 5.5 mm x 5.5 m
A piezoelectric actuator of the present invention in which eight piezoelectric elements each having an m-square and a thickness of 2.5 mm are connected in series with an elastic adhesive to have a length of 20 mm, and a piezoelectric having a size of 5.5 mm × 5.5 mm square. A large number of element plates were laminated with a relatively hard adhesive (epoxy adhesive) and joined together to form a piezoelectric actuator having a length of 20 mm, and the characteristics were compared.

When the performance was compared by applying a DC voltage of 150 V, the piezoelectric actuator of the present invention produced a displacement of 16 μm, whereas the piezoelectric actuator of the comparative example obtained a displacement of 13 μm. . Only 3
Although it is a stroke difference of μm, it is a large stroke difference in the field of controlling a minute amount such as a mass flow controller or an XY moving stage in which this type of actuator is used. Further, in the piezoelectric actuator of the present invention, it was not possible to find a crack or chip on the side surface, but in the comparative example, a crack is generated on the side surface, and the piezoelectric actuator of the present invention is durable. Also proved to be excellent. In this embodiment, the vinyl adhesive or the silicon adhesive is used as the elastic adhesive, but the elastic adhesive is not limited to this, and the elastic adhesive has a softness enough to allow the binding force between the piezoelectric elements. Then, any adhesive may be used. Further, in the above-mentioned embodiment, the piezoelectric element is polarized and then joined, but it is also possible to perform the polarization treatment after the piezoelectric element is joined.

[0030]

As described above, according to the piezoelectric actuator of the present invention, the following excellent operational effects can be exhibited. Since the piezoelectric elements are bonded to each other by using the elastic adhesive, the expansion operation is hardly restrained during the expansion drive, and thus the generated displacement amount can be sufficiently increased. Further, since the internal restraining force can be reduced, it is possible to suppress the internal breakage and cracking of the piezoelectric element, and it is possible to significantly improve the durability and the moisture resistance. In particular, when applied to a piezoelectric element having a piezoelectric active portion and a piezoelectric inactive portion, the extension operation is not restricted during extension drive,
Therefore, not only the generated displacement amount can be further increased, but also the internal restraining force can be reduced to further suppress the occurrence of internal breakage and cracks. Further, when the piezoelectric elements after the polarization treatment are joined, the elastic adhesive is mainly interposed only between the piezoelectric inactive portions, so that not only the above-described function and effect are exhibited but also between the piezoelectric active portions. Has almost no adhesive, so it does not adversely affect the pressing force or the displacement generated when the actuator is driven.
Highly precise minute stroke control can be performed.

[Brief description of drawings]

FIG. 1 is a plan view showing a piezoelectric element plate in which internal electrodes and a shrinkage ratio matching thin film are provided on a piezoelectric sheet.

FIG. 2 is an enlarged view showing a portion of a shrinkage factor matching thin film of the piezoelectric element plate shown in FIG.

FIG. 3 is a diagram showing a laminated state of the piezoelectric element plates shown in FIG.

FIG. 4 is a perspective view showing a piezoelectric element formed by stacking piezoelectric element plates.

5 is a side view of the piezoelectric element shown in FIG.

6 is a perspective view showing a state after the piezoelectric element shown in FIG. 4 is polarized.

FIG. 7 is a perspective view showing a piezoelectric actuator of the present invention formed by stacking and connecting piezoelectric elements.

FIG. 8 is an enlarged view showing a connection state between the piezoelectric elements shown in FIG.

FIG. 9 is a diagram showing a driving state of a piezoelectric element when bonded using a hard adhesive.

FIG. 10 is a graph showing simulation results showing the relationship between the distance from the center of the piezoelectric element and the stress in the stacking direction when the number of stacked piezoelectric sheets is variously changed.

FIG. 11 is a perspective view showing a conventional full-surface electrode type piezoelectric actuator.

FIG. 12 is a perspective view showing a conventional alternating electrode type piezoelectric actuator.

13 is an explanatory diagram for explaining a surface state and a laminated state of a piezoelectric sheet of the actuator shown in FIG.

14 is a side view of the actuator shown in FIG.

FIG. 15 is an explanatory diagram for explaining a driving state of a conventional piezoelectric actuator.

[Explanation of symbols]

 2 Piezoelectric Sheet 4 Internal Electrodes 6 and 8 Insulating Layer 14 Electrode Extraction Section 16 Piezoelectric Active Section 18 Piezoelectric Inactive Section 21 Piezoelectric Element Plate 22 Piezoelectric Element 23 Elastic Adhesive 24 Piezoelectric Inactive Area 26 Piezoelectric Active Area 28 Shrinkage Ratio Matching Thin Film 30 First external electrode 32 Second external electrode 34 Piezoelectric actuator 36 Flat protrusion

Claims (6)

[Claims] 1. A piezoelectric element is formed by laminating a plurality of piezoelectric element plates each having an internal electrode formed on the surface of a piezoelectric sheet, and a plurality of the piezoelectric elements are formed in the thickness direction using an elastic adhesive. A piezoelectric actuator, which is configured to be connected. 2. The piezoelectric element is an alternating electrode type piezoelectric element having a piezoelectric active portion that contributes to electrostrictive displacement and a piezoelectric inactive portion that does not contribute to electrostrictive displacement in a peripheral portion thereof. Item 2. The piezoelectric actuator according to Item 1. 3. The piezoelectric inactive portion is formed with a contraction rate matching thin film on the piezoelectric sheet for reducing a contraction difference at the time of forming the piezoelectric element. 2. The piezoelectric actuator according to item 2. 4. The piezoelectric actuator according to claim 1, wherein the piezoelectric element is polarized before connection. 5. The elastic adhesive is configured to be mainly interposed between the piezoelectric inactive portions of the piezoelectric elements that are adjacently connected to each other, according to any one of claims 1 to 4. The piezoelectric actuator described. 6. The piezoelectric actuator according to claim 1, wherein the elastic adhesive is one of a vinyl adhesive and a silicon adhesive.