JP6540934B2 - Piezoelectric element and piezoelectric actuator - Google Patents

Description

  The present invention relates to a piezoelectric element and a piezoelectric actuator for a piezoelectric actuator or a piezoelectric transformer.

  2. Description of the Related Art Conventionally, a piezoelectric actuator in which rectangular piezoelectric elements are stacked to form a main body is known. FIGS. 8A to 8C are a perspective view of the conventional piezoelectric actuator main body 700, a perspective view of the piezoelectric element 710, and a cross-sectional view of the piezoelectric element 710, respectively. The piezoelectric actuator body 700 is formed by stacking integrally sintered laminated piezoelectric elements 710, and the lead electrodes 720 connect the respective external electrodes 715. The piezoelectric element 710 is formed by laminating a piezoelectric layer and an internal electrode. When a voltage is applied, the piezoelectric layer between the electrodes deforms as an active region, but the other inactive regions do not. Therefore, stress is likely to be generated in the vicinity of the boundary of these regions, and in particular, stress is concentrated at the corner C of the internal electrode 712, and breakage is likely to occur.

  On the other hand, a piezoelectric actuator has been developed in which a stress absorbing layer made of lead titanate-based powder is provided to the piezoelectric element so that the piezoelectric layer becomes discontinuous (for example, a patent). It does not change that it is the shape which stress tends to generate in the corner of an internal electrode. On the other hand, a piezoelectric element has been developed in which internal electrodes are provided on the entire surface of the laminated surface and stress concentration is prevented by eliminating the inactive region on the side surface (for example, Patent Document 2).

JP, 2006-286774, A JP 05-003351 A JP, 2000-102272, A Unexamined-Japanese-Patent No. 2000-315828

  However, in the piezoelectric element described in Patent Document 2, since the internal electrode is uniformly exposed on the side surface, it is necessary to form an insulator on the exposed portion of the internal electrode which is not to be connected to the external electrode. I need.

  On the other hand, it is also conceivable to make the piezoelectric element into a disk shape to prevent local stress concentration between the active region and the inactive region. For example, in the case of a piezoelectric transformer, it is known that the shape of the piezoelectric resonator is circular such as a perforated disc, an annular ring, or a cylinder (see Patent Documents 3 and 4). In this case, since there is no corner in the internal electrode, concentration of stress can be prevented. However, the laminated element requires an external electrode which connects the internal electrodes every other layer, and in order to form the external electrode, it is necessary to align the position for fixing the piezoelectric element. For example, when printing an external electrode by screen printing, the θ direction (rotational position around the central axis) of the piezoelectric element is aligned, and the piezoelectric element is fixed so that the printing portion hits the screen mask.

  Moreover, it is difficult to arrange | position each piezoelectric element so that the external electrode between several piezoelectric elements can be connected with a lead wire for piezoelectric actuators, and to stack in multiple stages. In order to avoid this, it is conceivable to form the piezoelectric element in an annular shape and facilitate positioning through the shaft in the through hole, but it takes time and effort to provide external electrodes on each piezoelectric element and connect them .

  In addition, even when the piezoelectric elements are stacked and the external electrodes of the plurality of piezoelectric elements are connected, the positions of the external electrodes need to be aligned. It has been easy to align the positions of the external electrodes of the conventional dice-shaped piezoelectric element, but in the case of the annular shape, it takes time to align.

  The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a piezoelectric element and a piezoelectric actuator which are less likely to concentrate stress locally and which can facilitate work for manufacturing.

  (1) In order to achieve the above object, the piezoelectric element of the present invention is a piezoelectric element for a piezoelectric actuator or a piezoelectric transformer, and is an internal electrode alternately laminated via a piezoelectric layer and the piezoelectric layer. A through-hole formed in the center of the element body, the element body formed in an annular shape, and the external electrode provided on the side surface of the element body and connected to the internal electrode; Is characterized in that it is formed in a shape excluding a perfect circle.

  As described above, since the piezoelectric element of the present invention is formed in an annular shape, the stress is not locally concentrated and the breakage hardly occurs. Then, since the cross section of the through hole is formed in a shape excluding a true circle, the rotational position can be matched using the through hole, and the position of the piezoelectric element can be accurately and easily matched to form the external electrode. Can.

  (2) Further, the piezoelectric element of the present invention includes first and second inner electrodes alternately stacked as the inner electrode, and the first connected to the first inner electrode as the outer electrode. And a second external electrode connected to the second internal electrode, and is used by being stacked in the expansion and contraction direction for a piezoelectric actuator. Thereby, when stacking a plurality of piezoelectric elements, the positions of the respective external electrodes can be aligned accurately and easily.

  (3) Further, the piezoelectric element of the present invention includes at least alternately laminated first and second internal electrodes for input as the internal electrodes, and is connected to the first internal electrodes as the external electrodes. And a second external electrode connected to the second internal electrode, and an external electrode for output, and is used as a piezoelectric transformer. As a result, stress is not concentrated locally because it is formed in an annular shape, and breakage is less likely to occur. Moreover, the operation | work at the time of formation of the external electrode of each element can be simplified.

  (4) Further, the piezoelectric element of the present invention is characterized in that the through hole is formed to have a cross-sectional shape which is less than 2-fold symmetry. As a result, it is not necessary to adjust the positions of the external electrodes by visual observation or the like, and in particular, it becomes easy to adjust the rotational positions using the through holes.

  (5) Further, in the piezoelectric element of the present invention, the first external electrode and the second external electrode are provided at axially symmetrical positions with respect to the central axis of the element body. There is. As a result, even if the direction of the main surface of the piezoelectric element is reversed and used, the position of the external electrode does not change, which facilitates the work.

  (6) Further, the piezoelectric element of the present invention is characterized in that the through hole is formed in a cross-sectional shape without a corner. As a result, stress is not concentrated locally, and breakage is less likely to occur.

  (7) Further, the piezoelectric element of the present invention is characterized in that the through hole is formed in a cross-sectional shape of an oval. As a result, since alignment can be performed with the through holes when forming the external electrodes of the respective elements or when stacking a plurality of elements, the work becomes easy. In addition, manufacturing is easy and local stress around the through hole can be prevented.

  (8) Further, the piezoelectric actuator of the present invention is characterized by including a piezoelectric actuator main body formed by stacking a plurality of the above-mentioned piezoelectric elements on a substantially same central axis in the expansion and contraction direction. As a result, since the piezoelectric actuator is formed in a cylindrical shape, stress is not concentrated locally, and breakage is less likely to occur. In addition, the work burden on manufacturing is reduced.

  According to the present invention, since it is formed in an annular shape, stress is not concentrated locally and breakage is less likely to occur. In addition, the operation at the time of forming the external electrode of the piezoelectric element is facilitated.

(A), (b) is a plan sectional view and a perspective sectional view showing a piezoelectric element according to the first embodiment, and (c) is a plan sectional view showing a shaft. It is a sectional side view which shows the piezoelectric actuator of 1st Embodiment. (A), (b) flat cross section which shows the piezoelectric element of 2nd Embodiment, perspective cross section, (c) It is a plane cross section which shows a shaft. (A), (b) flat cross section which shows the piezoelectric element of 3rd Embodiment, perspective cross section, (c) It is a plane cross section which shows a shaft. (A), (b) is a plan sectional view and a perspective sectional view showing a piezoelectric element according to a fourth embodiment, and (c) is a plan sectional view showing a shaft. (A), (b) flat cross section which shows the piezoelectric element of a comparative example, perspective cross section, (c) It is a plane cross section which shows a shaft. (A), (b) flat cross section which shows the piezoelectric element of a comparative example, perspective cross section, (c) It is a plane cross section which shows a shaft. (A)-(c) It is a perspective view of the conventional piezoelectric actuator main body, the perspective view of a piezoelectric element, and sectional drawing of a piezoelectric element, respectively.

  Next, embodiments of the present invention will be described with reference to the drawings. In order to facilitate understanding of the description, the same reference numerals are given to the same components in the respective drawings, and the overlapping description will be omitted.

First Embodiment
(Configuration of piezoelectric element)
1 (a) and 1 (b) are a plan sectional view and a perspective sectional view showing the piezoelectric element 110, and FIG. 1 (c) is a plan sectional view showing the shaft 120. As shown in FIG. 1 (b) is a cross-sectional view taken along plane 1b shown in FIG. 1 (a), and FIG. 1 (a) is a cross-sectional view taken along plane 1a shown in FIG. 1 (b) (described later) The same applies to FIGS. 3 to 7 (a) and (b)).

  The piezoelectric element 110 is configured of an element body 111 and external electrodes 115 and 116. The element body 111 is formed by laminating the piezoelectric layer 112 and the first and second internal electrode layers 113 and 114 alternately stacked via the piezoelectric layer 112. The element body 111 has a through hole 119 on the central axis C1 penetrating in the stacking direction, and is formed in an annular shape. The outer periphery is circular, and the outer peripheries of the internal electrodes 113 and 114 are also formed in a substantially circular shape, so that the element body 111 does not locally concentrate stress, and breakage is unlikely to occur.

  On the other hand, the through hole 119 is formed in a cross-sectional shape of an oval. An oval means the shape of the locus | trajectory which moved the perfect circle in parallel. By forming the cross section in a shape other than a perfect circle in this manner, the movement of the piezoelectric element 110 can be restrained by the through hole 119, and the piezoelectric element 110 can be fixed in the direction perpendicular to the central axis C1. In addition, movement around the central axis C1 can be fixed. As a result, the rotational position can be aligned using the through holes 119, and the position of the piezoelectric element 110 can be aligned accurately and easily to form the external electrodes 115 and 116. Further, when stacking the plurality of piezoelectric elements 110, the positions of the respective external electrodes 115 and 116 can be aligned accurately and easily.

  The piezoelectric element 110 is used by being stacked in the expansion and contraction direction (stacking direction) for a piezoelectric actuator. The shape of the through hole 119 is effective as long as the position of the external electrode of the element can be determined by the shaft 120 through which the through hole 119 passes. Therefore, for example, in addition to the oval shape, it may have a circular concave shape or a square cross-sectional shape. However, in the case where the cross section of the hole is three or more symmetrical such as a square, the position of the external electrode needs to be aligned by visual observation or the like, so that the cross section of the hole is preferably formed in a shape of two or less symmetry. Moreover, it is preferable that the cross section of the through-hole 119 is formed in the shape without a corner. By making the hole cross section into a cornerless shape, it is possible to prevent local stress concentration on the corner portion.

  In particular, it is preferable that the through holes 119 be formed in an oval cross-sectional shape as shown in FIG. As a result, since alignment can be performed with the through holes when forming the external electrodes of the respective elements or when stacking a plurality of elements, the work becomes easy. In addition, manufacturing is easy and local stress around the through hole 119 can be prevented.

  The first and second outer electrodes 115 and 116 are provided at predetermined positions on the side surface of the element body 111. The first outer electrode 115 is connected to the first inner electrode 113 at the position of the electrode lead-out portion. The second external electrode 116 is connected to the second internal electrode 114 at the position of the electrode lead-out portion. In the example shown in FIG. 1, the first and second outer electrodes 115, 116 are provided at positions intersecting with a plane 1b passing through the central axis C1.

  As described above, it is preferable that the first external electrode 115 and the second external electrode 116 be provided at axially symmetrical positions with respect to the central axis C1 of the element body 111. Thereby, even if the direction of the main surface of the piezoelectric element 110 is reversed and used, the position of the external electrode does not change, and the work becomes easy.

  The shaft 120 is used for alignment of the external electrode through the through hole 119. The shaft 120 is formed in a shape along the inner side surface of the through hole 119, and has an oval cross-sectional shape as shown in FIG. 1 (c).

(Method of manufacturing piezoelectric element)
A method of manufacturing the piezoelectric element 110 configured as described above will be described. First, a predetermined number of internal electrodes are printed on a green sheet, and after laminating a predetermined number of sheets, the green sheet is processed into a laminated body having a rectangular cylinder shape with a rectangular cross section. The profile can be machined by cutting and the through holes can be machined using an end mill. By firing this, it is possible to produce a rectangular cylindrical integral firing type piezoelectric element. The shape of the internal electrode 113 is a shape in which an electrode lead-out portion for connecting to the external electrode is provided in an annular shape along the annular shape of the element cross section. The piezoelectric layer 112 and the internal electrode 113 are stacked, and a layer without the internal electrode 113 is provided at the end on both main surface sides.

  Then, the external electrodes 115 and 116 are formed at predetermined positions on the outer surface of the element main body 111. The printing position of the external electrodes 115 and 116 is aligned by fixing the element main body 111 through a rod having an outer shape that conforms to the inner shape of the through hole 119, the electrode paste is applied by screen printing, and the external electrodes 115 and 116 are printed. Form In this way, it is possible to fabricate a piezoelectric actuator in which the process of forming the external electrode is easy and the stack is easy.

(Configuration of piezoelectric actuator)
FIG. 2 is a cross-sectional view showing an embodiment of the piezoelectric actuator 100. As shown in FIG. As shown in FIG. 2, the piezoelectric actuator 100 includes a piezoelectric actuator main body 105, a shaft 121, spacers 122 and 123, a protrusion 124, lead wires 131 and 132, solders 135 and 136, a fixing portion 150 and a housing 180.

  The piezoelectric actuator main body 105 is formed in a cylindrical shape by stacking a plurality of piezoelectric elements 110 formed in the same annular shape in the expansion and contraction direction on substantially the same central axis C1. By stacking the plurality of piezoelectric elements 110, the piezoelectric actuator 100 can be configured to obtain a large displacement. As a result, since the piezoelectric actuator 100 is formed in a cylindrical shape, stress does not concentrate locally, and breakage is unlikely to occur.

  The inner side surfaces of the through holes 119 are aligned on a common surface, and the outer electrodes 115 and 116 are aligned and connected to the lead wires 131 and 132 by solders 135 and 136. The shaft 121 is formed in a shape (cross-sectional shape of an oval) along the inner side surface of the through hole 119, and inserting the through hole 119 facilitates alignment of the external electrodes 115 and 116. The shaft 121 is inserted into the central through hole 119 of the plurality of stacked piezoelectric elements 110, and fixes the axis of the piezoelectric actuator body 105. By inserting the shaft 121 into the through hole 119, the rotational position of the piezoelectric element 110 can be easily aligned when the piezoelectric element 110 is stacked, and the manufacturing of the piezoelectric actuator 100 can be facilitated.

  The fixing portion 150 fixes one end of the piezoelectric actuator body 105. The fixing portion 150 is coupled to the shaft 121 to fix the position of the shaft 121. The spacers 122 and 123 are provided on both ends of the piezoelectric actuator body 105, respectively. The shaft 121 is slightly shorter than the piezoelectric actuator body 105, and is designed so as not to inhibit the expansion and contraction of the piezoelectric actuator body 105.

  The protrusion 124 is a hemispherical member that transmits the displacement to the outside. The housing 180 is made of metal, for example, and covers the piezoelectric actuator main body 105 and the like. The lead wires 131 and 132 connect the external electrodes 115 and 116 of the respective piezoelectric elements 110 by solders 135 and 136, respectively, and are connected to the outside.

(Method of manufacturing piezoelectric actuator)
A method of manufacturing the piezoelectric actuator 100 configured as described above will be described. A plurality of piezoelectric elements 110 manufactured as described above are used.

  The shaft 121 is inserted into the through hole 119 of the ring-shaped piezoelectric element 110 to align the outer electrodes 115 and 116 of the stacked piezoelectric element 110. In this manner, the positions of the external electrodes when stacking the piezoelectric elements 110 are aligned. Thereby, connection of the external electrodes 115 and 116 becomes easy, and the working efficiency can be improved.

  When the shaft 121 is passed through the through hole, the position on the plane perpendicular to the central axis C1 of the piezoelectric element 110 and the rotational position around the central axis C1 are prevented from shifting, and the spacers 122 and 123 are provided at both ends of the piezoelectric actuator body 105. Deploy. Furthermore, one can be fixed by the fixing portion, the protrusion 124 can be adhered to the other, and the housing 180 can be covered to manufacture the piezoelectric actuator 100.

Second Embodiment
In the above embodiment, the through hole 119 has an oval cross-sectional shape, but may have a rectangular cross-sectional shape. If the through holes have a rectangular cross-sectional shape, the holes can be easily formed using only the corners. 3 (a) and 3 (b) are a plan sectional view and a perspective sectional view showing the piezoelectric element 210, and FIG. 3 (c) is a plan sectional view showing the shaft 220.

  The piezoelectric element 210 is composed of an element body 211 and external electrodes 215 and 216. In the element body 211, a piezoelectric layer 212 and first and second internal electrode layers 213 and 214 alternately stacked via the piezoelectric layer 212 are stacked. The element main body 211 has a through hole 219 on the central axis C2 penetrating in the stacking direction, and is formed in an annular shape. The outer periphery is circular, and the outer peripheries of the internal electrodes 213 and 214 are also formed substantially circular.

  The first and second external electrodes 215 and 216 are provided at predetermined positions on the side surface of the element main body 211. The first outer electrode 215 is connected to the first inner electrode 213 at the position of the electrode lead-out portion. The second external electrode 216 is connected to the second internal electrode 214 at the position of the electrode lead-out portion.

  The shaft 220 is used to align the external electrode through the through hole 219. The shaft 220 is formed in a shape along the inner side surface of the through hole 219, and has a rectangular cross-sectional shape with curved corners as shown in FIG. 3 (c).

Third Embodiment
In the first embodiment, the through hole 119 has a cross-sectional shape of an oval, but may have a cross-sectional shape in which a circular shape is provided with a concave shape of a detent. By forming the through holes in such a shape, the rotational position of the piezoelectric element is uniquely determined. 4A and 4B are a cross-sectional view and a perspective cross-sectional view showing the piezoelectric element 310, and FIG. 4C is a cross-sectional view showing the shaft 320.

  The piezoelectric element 310 is configured of an element main body 311 and external electrodes 315 and 316. In the element body 311, the piezoelectric layer 312 and the first and second internal electrode layers 313 and 314 alternately stacked via the piezoelectric layer 312 are stacked. The element body 311 has a through hole 319 on the central axis C3 penetrating in the stacking direction, and is formed in an annular shape. The outer periphery is circular, and the outer peripheries of the internal electrodes 313 and 314 are also formed substantially circular.

  The first and second external electrodes 315 and 316 are provided at predetermined positions on the side surface of the element body 311. The first outer electrode 315 is connected to the first inner electrode 313 at the position of the electrode lead-out portion. The second external electrode 316 is connected to the second internal electrode 314 at the position of the electrode lead-out portion.

  The shaft 320 is used for alignment of the external electrode through the through hole 319. The shaft 320 is formed in a shape along the inner side surface of the through hole 319, and has a cross-sectional shape in which a convex shape of a rotation stopper is provided in a perfect circle as shown in FIG. 4 (c).

Fourth Embodiment
In the above embodiment, the piezoelectric element is formed in an annular shape for the piezoelectric actuator, but the piezoelectric element may be formed in an annular shape for the piezoelectric transformer. 5 (a) and 5 (b) are a plan sectional view and a perspective sectional view showing the piezoelectric element 410, and FIG. 5 (c) is a plan sectional view showing the shaft 420.

  The piezoelectric element 410 includes an element body 411 and external electrodes 415a, 415b, and 416, and can be divided into an input unit 417a and an output unit 417b in sections in the thickness direction. The external electrodes 415a and 415b are input electrodes, and an input terminal is connected to the external electrode 415a to apply an input voltage, and the external electrode 415b can be grounded. The external electrode 416 is an external electrode for output, and an output voltage can be extracted from the external electrode 416.

  In the element body 411, piezoelectric layers 412 and first to third internal electrode layers 413a, 413b, and 414 alternately stacked via the piezoelectric layers 412 are stacked. In the input portion 417a, the piezoelectric layer 412 and the internal electrode layers 413a and 413b are densely stacked, and in the output portion 417b, the piezoelectric layer 412 is thickly formed, and the internal electrode 414 is provided at an end portion. .

  The element body 411 has a through hole 419 on the central axis C4 penetrating in the stacking direction, and is formed in an annular shape. The outer periphery is circular, and the outer peripheries of the internal electrodes 413a, 413b, and 414 are also formed substantially circular.

  The first to third outer electrodes 415 a, 415 b, and 416 are provided at predetermined positions on the side surface of the element body 411. The first outer electrode 415a is connected to the first inner electrode 413a at the position of the electrode lead-out portion. The second external electrode 415 b is connected to the second internal electrode 413 b at the position of the electrode lead-out portion. The third outer electrode 416 is connected to the first inner electrode 414 at the position of the electrode lead-out portion.

  The shaft 420 is used to align the external electrode through the through hole 419. The shaft 420 is formed in a shape along the inner side surface of the through hole 419, and has an oval cross-sectional shape as shown in FIG. 5 (c). In the piezoelectric element 410 for a cylindrical piezoelectric transformer formed by integrally firing the input part 417a and the output part 417b, the through hole 419 which is not circular is opened at the center, thereby fixing the position in the rotational direction by passing the shaft 420 it can. The cross-sectional shape is preferably an oval, but it may be a rectangular shape or a shape provided with a detent shape of a detent in a round shape.

  As described above, when the piezoelectric element 410 is a laminated element, external electrodes 415a, 415b, 416 connecting the internal electrode layers 413a, 413b, 414 every other layer and connecting to the outside are required. When forming the external electrodes, the positions of the external electrodes must be aligned. For example, in the case of screen printing, it is necessary to align the rotation angle θ direction around the central axis so that the printing portion hits the screen mask.

  As a piezoelectric element for a cylindrical piezoelectric transformer, an integrally fired element having an input part and an output part in one element is usually used. However, when changing the material properties between the input part and the output part, two or more piezoelectric elements may be used by bonding. At this time, it is necessary to adjust the positions of the external electrodes of a plurality of elements, and by using the non-circular hole at the center, it takes less time to align the positions of the external electrodes as compared with the conventional cylindrical shape.

  In the piezoelectric element 410 for the piezoelectric transformer described above, each single input and output section divided in the annular thickness direction is in contact, and an internal electrode for output is provided near the end face on the output section side. It is done. As a result, an inactive layer is provided on both end surfaces, and an external electrode for output is provided on the side surface in addition to the two external electrodes for input. However, various piezoelectric transformers may be considered other than such a form.

  For example, in the above embodiment, another output-side internal electrode may be provided at a position adjacent to the input unit in the output unit, and an inactive layer may be provided between the output unit and the internal electrode of the input unit. Thus, an inactive layer is provided between the input portion and the output portion, and the input circuit and the output circuit can be separated. In this case, two external electrodes are provided on the side of the element body for each of the input and output, and alignment is required at the time of fabrication. In order to provide the external electrodes for input and output on the side surfaces of the element body, alignment by through holes is particularly effective.

  It is also possible to design the form in which the above input circuit and output circuit are separated by the inactive layer to be symmetrical in the thickness direction, and to provide the output parts on both end faces of the input part. In this embodiment, the input part is disposed between two output parts, and an inactive layer is provided between the input part and each output part and on each end face side of the output part, and the total number of inactive layers is four. Layered. Also in this case, two external electrodes are provided on the side of the element body for each of the input and output, and alignment is required at the time of fabrication.

  In the piezoelectric element 410 for a piezoelectric transformer, the internal electrode 414 is provided as an output electrode, but instead of this, an end surface electrode may be provided, and an output external electrode may be provided on the end surface electrode. . In this case, the inactive layer disappears on the end face side of the output part. Also, two external electrodes are provided on the side of the element body for input, and alignment is required at the time of fabrication.

Example, Comparative Example (Piezoelectric Actuator)
The piezoelectric element of Example 1 was manufactured as the piezoelectric element 110 according to the first embodiment described above. On the other hand, as Comparative Example 1, the piezoelectric element 510 shown in FIG. 6 was produced. Then, a plurality of piezoelectric elements were stacked to produce a piezoelectric actuator.

  FIGS. 6A and 6B are a plan sectional view and a perspective sectional view showing the piezoelectric element 510 of the comparative example. FIG. 6C is a plan sectional view showing the shaft 520. As shown in FIG. The piezoelectric element 510 has a through hole 519 having a circular cross-sectional shape on the central axis, and is formed in an annular shape. The element main body 511 is formed by alternately laminating the piezoelectric layers 512 and the internal electrodes 513 and 514. The internal electrodes 513 and 514 are connected to the external electrodes 515 and 516, respectively. With regard to the piezoelectric element 510, the movement around the central axis C5 can not be restrained in a situation where the shaft 520 is inserted into the through hole 519 to align the piezoelectric element 510.

Example 1
As Example 1, a piezoelectric element as shown in FIG. 1 was produced. First, a predetermined number of internal electrodes were printed on a green sheet, and after laminating a predetermined number of sheets, it was processed into a laminate having an outer diameter of 10 mm × 10 mm, a through hole φ2.5 mm × length 3.5 mm, and a cross section oval of 4.5 mm thickness. The outer shape was processed by cutting with a thin blade, and the through holes were processed using an end mill. This was fired to obtain an integral firing-type piezoelectric element having an outer diameter of 7 mm × 7 mm, a through hole of φ2 mm × length of 2.8 mm, and a thickness of 3 mm.

  In the obtained piezoelectric element, 50 layers of 50 μm internal electrode layers were formed per layer, and a layer with no internal electrode was formed 0.25 mm on the upper and lower sides. The piezoelectric element was processed to a thickness of 2.5 mm by surface grinding, and then cylindrically processed to an outer diameter of 6 mm. On the other hand, a shaft was prepared by shaving a cylinder of φ2.5 to a thickness of 1.8 mm. A plurality of produced piezoelectric elements were inserted through a shaft and set in a jig, and an external electrode was formed by screen printing. After removing from the shaft and baking the external electrode, the required number of sheets were stacked through the shaft, and the external electrodes were connected by the lead wires.

(Comparative example 1)
As a comparative example 1, a piezoelectric element as shown in FIG. 6 was produced. First, a predetermined number of internal electrodes were printed on a green sheet, and after laminating a predetermined number of sheets, it was processed into a laminate having an outer diameter of 10 mm × 10 mm, an inner diameter of φ2.5 mm, and a thickness of 4.5 mm. The outer shape was cut with a thin blade, and the inner diameter was a normal drill. The resultant was fired to obtain an integral firing type piezoelectric element having an outer diameter of 7 mm × 7 mm, an inner diameter of φ2 mm, and a thickness of 3 mm. There are 50 electrode layers of 50 μm per one layer, and the layers without internal electrodes on the top and bottom are 0.25 mm.

  This was ground to a thickness of 2.5 mm by surface grinding, and then cylindrically processed to an outer diameter of 6 mm to produce an annular element of φ 6 mm. The internal electrode lead-out portion is designed to be exposed on the surface subjected to the outer shape processing, and the electrode exposed on the outer peripheral surface is visually confirmed and aligned, and the external electrode is formed by screen printing. After baking the external electrodes, they were stacked through the shaft, the external electrodes were visually aligned, temporarily fixed with tape, and the external electrodes were connected to each other by the lead wires.

(inspection result)
In the printing of the external electrode, by using the through hole having a cross-sectional shape of an oval, in the example, processing of 200 times or more that of the comparative example was possible. Further, in the comparative example, it was not possible to completely align, for example, those which were once aligned during visual alignment could be rotated and shifted when aligning the other positions in the case of stacking. The approximate alignment also took 50 times more time than the example.

Example, Comparative Example (Piezoelectric Transformer)
The piezoelectric element of Example 2 was manufactured as a piezoelectric element 410 for a piezoelectric transformer according to the above fourth embodiment. On the other hand, as Comparative Example 2, a piezoelectric element 610 for a piezoelectric transformer shown in FIG. 7 was produced.

  FIGS. 7A and 7B are a plan sectional view and a perspective sectional view showing the piezoelectric element 610 of Comparative Example 2, respectively. FIG. 7C is a plan sectional view showing the shaft 620. The piezoelectric element 610 has a through hole 619 having a circular cross-sectional shape on the central axis, and is formed in an annular shape. The element main body 611 is formed by alternately laminating the piezoelectric layers 612 and the internal electrodes 613a, 613b, and 614. The internal electrodes 613a, 613b, 614 are connected to the external electrodes 615a, 615b, 616, respectively. With regard to the piezoelectric element 610, the movement around the central axis C6 can not be restrained in a situation where the shaft 620 is inserted into the through hole 619 to align the piezoelectric element 610.

(Example 2)
As Example 2, a piezoelectric element as shown in FIG. 5 was produced. A predetermined number of electrodes were printed on a green sheet, stacked in a predetermined number, and crimped, and then processed into an outer diameter of 20 mm × 20 mm, an inner hole φ2.5 mm × length 3.5 mm, an oblong hole, and a thickness 6 mm. The external shape used a thin blade for cutting, and used an end mill for processing the inner hole. This was fired to obtain an integral firing type piezoelectric element having an outer diameter of 16 mm × 16 mm, an inner hole of φ2 mm × 2.8 mm, and a thickness of 4.8 mm.

  This was processed to a thickness of 2.5 mm by double-side polishing. The outer diameter was cylindrically processed to 15 mm using the shaft which shaved the cylinder of (phi) 2.5 prepared to thickness 1.8 mm prepared separately. The structure of the finished device is such that the electrode spacing is 120 μm per layer, the total of 16 layers including the input portion, the output layer having an electrode spacing of 1.9 mm, and the inactive layers at the top and bottom of 0.1 mm. The internal electrode lead-out portion is designed to be exposed on the surface subjected to the outer processing. A plurality of elements produced were set on a shaft having the same shape as the shaft prepared for cylindrical processing, and set in a jig to form external electrodes by screen printing. Thereafter, it was removed from the shaft and the external electrode was baked to obtain a piezoelectric element for a piezoelectric transformer.

(Comparative example 2)
As Comparative Example 1, a piezoelectric element as shown in FIG. 7 was produced. After printing predetermined electrodes on a green sheet and laminating a predetermined number of sheets, after pressure bonding, they were processed into an outer diameter of 20 mm × 20 mm, an inner diameter of φ2.5 mm, and a thickness of 6 mm. The outer shape was cut with a thin blade, and the inner diameter was a normal drill. This was fired to obtain an integral firing type piezoelectric element having an outer diameter of 16 mm × 16 mm, an inner diameter of 2 mm, and a thickness of 4.8 mm.

  This was processed into a thickness of 2.5 mm by double-side polishing and then processed into a cylinder. The structure of the finished device is such that the electrode spacing is 120 μm per layer, the total of 16 layers including the input portion, the output layer having an electrode spacing of 1.9 mm, and the inactive layers at the top and bottom of 0.1 mm. The internal electrode lead-out portion is designed to be exposed on the surface subjected to the outer processing. The electrodes exposed on the outer peripheral surface were visually confirmed and aligned, and external electrodes were formed by screen printing. Thereafter, the external electrode was baked.

(inspection result)
In the printing of the external electrode, by using the oval inner hole, in Example 2, processing of 200 times or more that of Comparative Example 2 was possible. The shape of the inner hole is not limited as long as the position of the external electrode of the piezoelectric element can be determined by the shaft through which the inner hole is passed. In the case of the piezoelectric transformer, there are at least three or more external electrode formation locations, and the roles are determined, respectively. Therefore, in the case of three-fold symmetry or more, it is necessary to match the external electrode positions by visual observation. Therefore, a shape of 2-fold symmetry or less is preferable.

100 Piezoelectric actuator 105 Piezoelectric actuator body 110 Piezoelectric element 111 Element body 112 Piezoelectric layers 113, 114 Internal electrode layer (internal electrode)
115, 116 external electrode 119 through hole 120 shaft C1 central axis 121 shaft 122, 123 spacer 124 protrusion 131, 132 lead wire 135, 136 solder 150 fixing portion 180 body 210 piezoelectric element 211 element body 212 piezoelectric layer 213, 214 internal electrode Layer (internal electrode)
215, 216 external electrode 219 through hole 220 shaft C2 central axis 310 piezoelectric element 311 element main body 312 piezoelectric layer 313, 314 internal electrode layer (internal electrode)
315, 316 External electrode 319 Through hole 320 Shaft C3 Central axis C4 Central axis 410 Piezoelectric element 411 Element body 412 Piezoelectric layers 413a, 413b, 414 Internal electrode layer (internal electrode)
415a, 415b, 416 external electrode 417a input portion 417b output portion 419 through hole 420 shaft

Claims (5)

A piezoelectric element for a piezoelectric actuator or a piezoelectric transformer,
An element body formed in an annular shape, having a piezoelectric layer and internal electrodes alternately stacked via the piezoelectric layer;
Provided on the outer side surface of the element body, and an external electrode connected to the internal electrode,
The through hole provided at the center of the element body is formed in a shape in which the cross section is a true circle and only one concave shape of the detent is provided .
The piezoelectric element characterized in that the concave shape is a shape without corners . The first and second inner electrodes stacked alternately are provided as the inner electrodes,
The external electrode includes a first external electrode connected to the first internal electrode, and a second external electrode connected to the second internal electrode.
2. The piezoelectric element according to claim 1, wherein the piezoelectric element is stacked in the expansion / contraction direction and used for the piezoelectric actuator. As the internal electrodes, at least alternately laminated first and second internal electrodes for input are provided,
The external electrode includes a first external electrode connected to the first internal electrode, a second external electrode connected to the second internal electrode, and an external electrode for output.
The piezoelectric element according to claim 1, wherein the piezoelectric element is used for a piezoelectric transformer.   The piezoelectric element according to claim 2 or 3, wherein the first external electrode and the second external electrode are provided at axially symmetrical positions with respect to a central axis of the element body. .   A piezoelectric actuator comprising a piezoelectric actuator main body formed by stacking a plurality of the piezoelectric elements according to claim 2 on a substantially same central axis in the expansion and contraction direction.

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