JP2007300798A - Piezoelectric element and ultrasonic actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce power consumption at a part, where only small stress is generated by vibration and to acquire large stretching vibration even if a piezoelectric element is made small while restricting vibration blockage of the piezoelectric element. <P>SOLUTION: An inner electrode layer 5 is composed of a common electrode layer 3 and a power feeding electrode layer 6 alternately arranged through a piezoelectric layer 1 in a laminated direction. The common electrode layer 3 has a common electrode 3a. The power feeding electrode layer 6 has a first power feeding electrode layer 6a, and a second power feeding electrode layer 6b. The first power feeding electrode layer 6a has four separation electrodes 2a-2d, and a first connection electrode 2e for connecting the separation electrodes 2b, 2d with each other. The second power feeding electrode 6b has four separation electrodes 4a-4d, and a second connection electrodes 4e for connecting the separation electrodes 4a, 4c with each other. The common electrode 3a is connected with an outer electrode 7g. The separation electrodes 2b, 2d of the first power feeding electrode layer 6a and the separation electrodes 4b, 4d of the second power feeding electrode layer 6b are connected with outer electrodes 7b, 7d. The separation electrodes 2a, 2c of the first power feeding electrode layer 6a and the separation electrodes 4a, 4c of the second power feeding electrode layer 6b are connected with outer electrodes 7a, 7c. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piezoelectric element and an ultrasonic actuator including the piezoelectric element.

DESCRIPTION OF RELATED ART Conventionally, the ultrasonic actuator provided with the piezoelectric element (electromechanical conversion element) used for various electric equipment etc. is known (for example, refer patent document 1). This piezoelectric element is formed by alternately laminating piezoelectric bodies and electrodes. And in the said ultrasonic actuator, a piezoelectric element is vibrated by applying a voltage to an electrode, and, thereby, a movable body is moved.
Special table 2003-501988 gazette

  Here, this inventor devised what is shown below as an ultrasonic actuator. FIG. 13 is a perspective view of the ultrasonic actuator, FIG. 14 (a) is a perspective view of a piezoelectric element used in the ultrasonic actuator, and FIG. 14 (b) is an exploded perspective view of the piezoelectric element. It is.

  As shown in FIGS. 13 and 14, the piezoelectric element 100 is housed and supported in the case 103 by three support portions 104 </ b> A to 104 </ b> C provided in the case 103. Driving elements 110 and 110 are provided on the end face of the piezoelectric element 100, and these driving elements 110 and 110 support the movable body 111. The drivers 110, 110 are pressed against the movable body 111 by the support portion 104B.

  The piezoelectric element 100 is formed by alternately stacking piezoelectric bodies 101 and internal electrodes 102. The internal electrode 102G is a common electrode (ground electrode) provided over almost the entire main surface of the piezoelectric body 101. The piezoelectric body 101 is polarized in the direction of the arrow shown in FIG.

  The internal electrodes 102A to 102D and 102G are connected to the external electrodes 103A to 103D and 103G, respectively. The external electrodes 103 </ b> A to 103 </ b> D and 103 </ b> G are provided on the end face of the piezoelectric element 100. For example, wires 108 </ b> A to 108 </ b> D and 108 </ b> G are connected to the external electrodes 103 </ b> A to 103 </ b> D and 103 </ b> G via solder 107. And voltage is supplied to each internal electrode 102A-102D, 102G through these wires 108A-108D, 108G.

  By the way, the resonance frequency of stretching vibration and the resonance frequency of bending vibration described later of the piezoelectric element 100 are determined by the material, shape, and the like of the piezoelectric element 100, respectively. The material, shape, and the like of the piezoelectric element 100 are determined so that the resonance frequency of the stretching vibration and the resonance frequency of the bending vibration are approximately the same.

  Hereinafter, the operation of the ultrasonic actuator will be described. 6 to 8 are conceptual diagrams for explaining the vibration modes of the piezoelectric elements.

  The wire 108G is connected to the ground, and a sine wave reference voltage having a specific frequency is applied to the internal electrodes 102A and 102C disposed on one diagonal line of the main surface of the piezoelectric body 101 via the wires 108A and 108C. , 108D, a sinusoidal voltage having substantially the same magnitude and frequency as the reference voltage is applied to the internal electrodes 102B, 102D disposed on the other diagonal line. As a result, a voltage having the same phase is applied to the internal electrodes 102A and 102C, and a voltage having the same phase is applied to the internal electrodes 102B and 102D. When the phase difference between the reference voltage and the voltage applied to the internal electrodes 102B and 102D is 0 °, first-order mode stretching vibration is induced in the piezoelectric element 100 as shown in FIG. On the other hand, when the phase difference is 180 °, second-order mode bending vibration is induced in the piezoelectric element 100 as shown in FIG.

  Further, a reference voltage of a sine wave having a frequency near the resonance frequency substantially matched to the internal electrodes 102A and 102C is added, and a reference voltage whose phase differs from the reference voltage by 90 ° or −90 ° is applied to the internal electrodes 102B and 102D. When a sinusoidal voltage having substantially the same magnitude and frequency is applied, the piezoelectric element 100 is induced harmonically in the first-order stretching vibration and the second-order bending vibration. Thereby, the shape of the piezoelectric element 100 changes in the order as shown in FIGS. As a result, the driver elements 110 and 110 provided in the piezoelectric element 100 move substantially elliptically as viewed from the direction penetrating the paper surface of FIG. That is, the drive elements 110 and 110 move elliptically by the combined vibration of the expansion and contraction vibration and the bending vibration of the piezoelectric element 100. Due to this elliptical movement, the movable body 111 supported by the driver elements 110 and 110 moves relative to the piezoelectric element 100 and moves in the direction of arrow A or arrow B.

  By the way, in the ultrasonic actuator, it is necessary to connect at least five wires 108A to 108D and 108G to the external electrodes 103A to 103D and 103G on the piezoelectric element 100. For this reason, when the piezoelectric element 100 vibrates, the solder 107 as a conductive connection member that connects the wires 108A to 108D and 108G and the wires 108A to 108D and 108G and the external electrodes 103A to 103D and 103G becomes a burden, The vibration of the piezoelectric element 100 is hindered. As a result, the efficiency of the ultrasonic actuator may be reduced.

  In addition, since there is a portion where the internal electrodes 102A to 102D and 102G are not formed in the stress concentration portion where the stress due to vibration is concentrated, when the piezoelectric element 100 is downsized, large stretching vibration cannot be obtained. As a result, the efficiency of the ultrasonic actuator may be further reduced.

  Furthermore, since the internal electrodes 102A to 102D and 102G are formed in portions other than the stress concentration portion, power is consumed even in a portion where stress due to vibration is not generated so much. As a result, the efficiency of the ultrasonic actuator may be further reduced.

  The present invention has been made in view of the above points, and the object of the present invention is to obtain a large stretching vibration even when the piezoelectric element is miniaturized while suppressing the vibration inhibition of the piezoelectric element, and by vibration. The object is to reduce power consumption in a portion where stress is not so much generated.

  In order to achieve the object, the present invention provides a piezoelectric element formed by alternately laminating substantially rectangular piezoelectric layers and internal electrode layers, and the internal electrode layers are arranged in the laminating direction. A common electrode layer and a feeding electrode layer that are alternately arranged via each other, wherein the common electrode layer has a common electrode, and the feeding electrode layer is provided on a main surface of the piezoelectric layer. An electrode layer and a second feeding electrode layer provided on a main surface of a piezoelectric layer different from the piezoelectric layer provided with the first feeding electrode layer on the main surface, wherein the first feeding electrode layer comprises: , Four divided electrodes respectively provided in four regions obtained by dividing the main surface of the piezoelectric layer into two in the longitudinal direction and the short direction, and the main layer of the piezoelectric layer among the four divided electrodes. A pair of divided electrodes provided in two regions facing each other in the first diagonal direction of the surface are connected to each other A first connecting electrode, and the second feeding electrode layer includes four divided electrodes provided in the four regions, and a second diagonal line of the main surface of the piezoelectric layer among the four divided electrodes. A second connection electrode that connects a pair of divided electrodes provided in two regions facing each other in the direction, and the first connection electrode and the second connection electrode are in the longitudinal center of the piezoelectric layer The common electrode is connected to an external electrode provided on the outer surface of the piezoelectric element, and the first feeding electrode layer has the first diagonal direction. A pair of split electrodes provided in two regions facing each other and a pair of split electrodes provided in two regions of the second feeding electrode layer facing each other in the first diagonal direction, the piezoelectric element With external electrodes on the outer surface of A pair of divided electrodes respectively provided in two regions facing the second diagonal direction of the first feeding electrode layer and two facing the second diagonal direction of the second feeding electrode layer The pair of divided electrodes provided in each region are configured to be connected by external electrodes provided on the outer surface of the piezoelectric element.

  According to the present invention, among the four divided electrodes of the first feeding electrode layer, a pair of divided electrodes respectively provided in two regions facing each other in the first diagonal direction of the main surface of the piezoelectric layer are connected to each other first. A pair of divided electrodes provided in two regions facing each other in the second diagonal direction of the main surface of the piezoelectric layer among the four divided electrodes of the second feeding electrode layer are connected to each other by the second connecting electrode. By connecting with, the number of wires and the like can be reduced. As a result, vibration inhibition of the piezoelectric element can be suppressed.

  Further, since the number of connecting steps such as a wire can be reduced, the manufacturing becomes easy. In particular, since the piezoelectric element is weak in mechanical strength, when connecting a wire or the like to an external electrode, the piezoelectric element may be broken due to mechanical stress, but as described above, the connection man-hour of the wire or the like is reduced, The destruction of the piezoelectric element in this connection process can be reduced.

  Furthermore, since the connection point between a wire or the like and the external electrode can be reduced, the reliability is also improved.

  In addition, since the first connection electrode and the second connection electrode are respectively provided at the central portion in the longitudinal direction of the piezoelectric layer, except for the both ends in the short direction, the stress due to the stretching vibration of the primary mode is provided. The area of the electrode of the concentrated stress concentration portion can be increased. Thereby, even when the piezoelectric element is downsized, a large stretching vibration can be realized.

  In addition, with the above-described configuration, the first feeding electrode layer and the second feeding electrode layer are formed in a stress concentration portion where stress due to vibration is concentrated and does not contribute much to vibrations other than the stress concentration portion. It will not be formed in the part. Thereby, power consumption in a portion where stress due to vibration does not occur much can be reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

−Configuration of ultrasonic actuator−
FIG. 1 is a perspective view of an ultrasonic actuator according to this embodiment, FIG. 2 is a perspective view of a piezoelectric element 12 used in the ultrasonic actuator, and FIG. 3 is an exploded perspective view of the piezoelectric element 12. 4 is a plan view of the piezoelectric layer 1, and FIG. 5A is a diagram showing a positional relationship between the first feeding electrode layer 6 a and the common electrode layer 3, and FIG. ) Is a diagram showing the positional relationship between the second feeding electrode layer 6b and the common electrode layer 3. FIG.

  As shown in FIGS. 1 to 3, the ultrasonic actuator includes a piezoelectric element 12. The piezoelectric element 12 includes a pair of main surfaces that face each other, a pair of end surfaces that face each other and extend in the longitudinal direction of the main surface of the piezoelectric element 12, and both the main surface and the end surface. And a pair of side surfaces facing each other and extending in the short direction of the main surface of the piezoelectric element 12. The main surface, the end surface, and the side surface constitute the outer surface of the piezoelectric element 12, and the end surface and the side surface constitute the peripheral surface of the piezoelectric element 12. In this embodiment, a main surface has the largest area among a main surface, an end surface, and a side surface.

  The piezoelectric element 12 is housed and supported by the case 11 (support body) via the three support portions 13a to 13c. Drive elements 8 are provided on one end face of the piezoelectric element 12, and these drive elements 8 support a flat movable body 9. The support portion 13 b on the other end face of the piezoelectric element 12 (the end face opposite to the end face on which the drive elements 8, 8 are provided) presses the drive elements 8, 8 against the movable body 9. Thereby, the frictional force between the tip portions of the driver elements 8 and 8 and the movable body 9 is increased, and the vibration of the piezoelectric element 12 is reliably transmitted to the movable body 9 via the driver elements 8 and 8.

  The piezoelectric element 12 has a substantially rectangular parallelepiped shape in which substantially rectangular piezoelectric layers 1 and internal electrode layers 5 are alternately stacked. The piezoelectric layer 1 is an insulator layer made of a ceramic material such as lead zirconate titanate. The internal electrode layer 5 includes a common electrode layer 3 and a feeding electrode layer 6 that are alternately arranged in the stacking direction (thickness direction of the piezoelectric element 12) via the piezoelectric layers 1. The common electrode layer 3 has a substantially rectangular common electrode 3 a provided over substantially the entire upper main surface of the piezoelectric layer 1. The common electrode 3a is provided with extraction electrodes 3b and 3b extending from the longitudinal center portion toward both end faces of the piezoelectric element 12, respectively. The common electrodes 3a on the different piezoelectric layers 1 are connected to each other by an external electrode 7g for a common electrode through an extraction electrode 3b. The external electrodes 7g are provided on both end faces of the piezoelectric element 12, respectively.

  The feeding electrode layer 6 is a piezoelectric body different from the first feeding electrode layer 6a provided on the upper principal surface of the piezoelectric layer 1 and the piezoelectric layer 1 provided with the first feeding electrode layer 6a on the upper principal surface. It consists of a second feeding electrode layer 6b provided on the upper main surface of the layer 1. That is, on the main surface of the piezoelectric layer 1, any one of the common electrode layer 3, the first feeding electrode layer 6a, and the second feeding electrode layer 6b is printed. Further, the piezoelectric layer 1 is polarized from the first feeding electrode layer 6a or the second feeding electrode layer 6b side to the common electrode layer 3 side, as indicated by an arrow in FIG.

  The first power supply electrode layer 6a is formed in four regions A1 to A4 (see FIG. 4) obtained by dividing the upper main surface of the piezoelectric layer 1 into two in the longitudinal direction L and the short direction S, respectively. The four divided electrodes 2a to 2d and a pair of divided electrodes formed in two regions A2 and A4 of the four divided electrodes 2a to 2d facing the first diagonal direction D1 of the upper main surface of the piezoelectric layer 1 respectively. It has the 1st connection electrode 2e which connects the electrodes 2b and 2d mutually.

  Each of the divided electrodes 2a to 2d is a substantially rectangular electrode and overlaps the common electrode layer 3 when viewed from the stacking direction (see FIG. 5A). That is, the divided electrodes 2 a to 2 d are opposed to each other with the common electrode layer 3 and the piezoelectric layer 1 interposed therebetween. Each of the divided electrodes 2a to 2d is provided with an extraction electrode 2f extending from the longitudinal central portion toward the end face of the piezoelectric element 12. Each extraction electrode 2f does not overlap with the common electrode layer 3 when viewed from the stacking direction (see FIG. 5A). That is, each extraction electrode 2 f does not face the common electrode layer 3. For this reason, an electric field does not arise in the part which opposes each extraction electrode 2f of the piezoelectric material layer 1. FIG. That is, this part becomes a piezoelectrically inactive part. The divided electrodes 2a to 2d are connected to the external electrodes 7a to 7d via the extraction electrodes 2f, respectively. The external electrodes 7c and 7d are provided on one end face of the piezoelectric element 12, and the external electrodes 7a and 7b are provided on the other end face of the piezoelectric element 12, respectively.

  The first connection electrode 2e is provided over almost the entire upper main surface of the portion of the piezoelectric layer 1 in the longitudinal direction excluding both edges in the lateral direction, and is a common electrode layer as viewed from the stacking direction. 3 (see FIG. 5A).

  The second power supply electrode layer 6b includes four divided electrodes 4a formed in four regions A1 to A4 each obtained by dividing the upper main surface of the piezoelectric layer 1 into two in the longitudinal direction L and the short direction S, respectively. To 4d and a pair of divided electrodes 4a and 4c respectively formed in two regions A1 and A3 facing the second diagonal direction D2 of the upper main surface of the piezoelectric layer 1 among the four divided electrodes 4a to 4d. It has the 2nd connection electrode 4e connected mutually.

  Each of the divided electrodes 4a to 4d is a substantially rectangular electrode and overlaps the common electrode layer 3 when viewed from the stacking direction (see FIG. 5B). Each of the divided electrodes 4a to 4d is provided with an extraction electrode 4f extending from the central portion in the longitudinal direction toward the end face of the piezoelectric element 12. Each extraction electrode 4f does not overlap the common electrode layer 3 when viewed from the stacking direction (see FIG. 5B). For this reason, an electric field is not generated in the portion of the piezoelectric layer 1 facing each extraction electrode 4f. The divided electrodes 4a to 4d are connected to the external electrodes 7a to 7d via the extraction electrodes 4f, respectively. Thereby, the divided electrodes 2a to 2d and 4a to 4d facing each other of the first feeding electrode layer 6a and the second feeding electrode layer 6b are connected by the external electrodes 7a to 7d, respectively.

  The second connection electrode 4e is provided over substantially the entire upper main surface of the portion of the piezoelectric layer 1 in the longitudinal direction excluding both lateral edges, and is a common electrode layer as viewed from the stacking direction. 3 (see FIG. 5B).

  As described above, the divided electrodes 2b and 2d of the first feeding electrode layer 6a are connected to each other via the first connection electrode 2e. The divided electrode 2b of the first feeding electrode layer 6a is connected to the divided electrode 4b formed in one of the two regions A2 and A4 of the second feeding electrode layer 6b via the external electrode 7b. The divided electrode 2d of the one feeding electrode layer 6a is connected to the divided electrode 4d formed in the other A4 of the two regions A2 and A4 of the second feeding electrode layer 6b through the external electrode 7d. That is, the divided electrodes 4b and 4d of the second feeding electrode layer 6b on the piezoelectric layer 1 different from the divided electrodes 2b and 2d of the first feeding electrode layer 6a are connected by the external electrodes 7b and 7d. Thus, the divided electrodes 2b and 2d of the first feeding electrode layer 6a and the divided electrodes 4b and 4d of the second feeding electrode layer 6b have the same potential.

  The divided electrodes 4a and 4c of the second power supply electrode layer 6b are connected to each other through the second connection electrode 4e. The divided electrode 4a of the second feeding electrode layer 6b is connected to the divided electrode 2a formed in one A1 of the two regions A1 and A3 of the first feeding electrode layer 6a via the external electrode 7a. The divided electrode 4c of the second feeding electrode layer 6b is connected to the divided electrode 2c formed in the other A3 of the two regions A1 and A3 of the first feeding electrode layer 6a via the external electrode 7c. That is, the divided electrodes 4b and 4d of the second feeding electrode layer 6b on the piezoelectric layer 1 different from the divided electrodes 2b and 2d of the first feeding electrode layer 6a are connected by the external electrodes 7b and 7d. Thereby, the divided electrodes 2a and 2c of the first feeding electrode layer 6a and the divided electrodes 4a and 4c of the second feeding electrode layer 6b have the same potential.

  A wire 10 is connected to each external electrode 7a, 7b, 7g via solder. A voltage for vibrating the piezoelectric element 12 is applied to the internal electrode layer 5 through the wire 10.

  By the way, the resonance frequency of the stretching vibration and the resonance frequency of the bending vibration of the piezoelectric element 12 are determined by the material and shape of the piezoelectric element 12, respectively. The material, shape, and the like of the piezoelectric element 12 are determined so that the resonance frequency of the stretching vibration and the resonance frequency of the bending vibration are approximately the same. In the present embodiment, the material, shape, and the like of the piezoelectric element 12 are determined so that the resonance frequency of the primary mode stretching vibration and the resonance frequency of the secondary mode bending vibration are approximately the same.

  Here, as described above, the external electrodes 7a to 7d need to be formed at a total of four locations, two at each end face of the piezoelectric element 12. However, since only the external electrode 7 on one end face of the piezoelectric element 12 may be connected to the wire 10, the connection part between the piezoelectric element 12 and the wire 10 is connected to one of the external electrodes 7 a and 7 c and the wire 10. Connection (in this embodiment, connection between the external electrode 7a and the wire 10a), connection between one of the external electrodes 7b and 7d and the wire 10, and one connection (in the present embodiment, the external electrode 7b) In total, there are three connections, one for the external electrode 7g for the common electrode and one for the wire 10g. Thereby, the number of the wires 10 which should be connected to the external electrode 7 can be reduced to three. As a result, vibration inhibition of the piezoelectric element 12 can be suppressed, and a decrease in efficiency of the ultrasonic actuator can be suppressed.

  Moreover, since the man-hour for connecting the wire 10 can be reduced, the manufacture of the ultrasonic actuator is facilitated. In particular, since the piezoelectric element 12 is weak in mechanical strength, when the wire 10 is connected to the external electrode 7, the piezoelectric element 12 may be broken due to mechanical stress. However, as described above, the number of connecting steps of the wire 10 is reduced. As a result, the destruction of the piezoelectric element 12 in this connection step can be reduced.

  Furthermore, the connection point between the wire 10 and the external electrode 7 can also be reduced. Thereby, the vibration inhibition by the solder provided in this connection point can be suppressed. In addition, this connection point is an important part in driving the ultrasonic actuator, but since it is easily affected by the external environment such as humidity and temperature change, as described above, by reducing the number of connection points, The reliability of the ultrasonic actuator can be improved.

  By the way, in order to induce the bending vibration of the secondary mode efficiently, it is desirable that the pair of electrodes respectively disposed at the diagonal portions of the upper main surface of the piezoelectric layer 1 have the same potential. Here, as described above, the divided electrodes 2b and 2d of the first power supply electrode layer 6a are electrically connected to the divided electrodes 4b and 4d of the second power supply electrode layer 6b through the external electrodes 7b and 7d to have the same potential. The divided electrodes 4a and 4c of the feeding electrode layer 6b are electrically connected to the divided electrodes 2a and 2c of the first feeding electrode layer 6a through the external electrodes 7a and 7c and have the same potential. As a result, all of the pair of electrodes respectively disposed at the diagonal portions of the upper main surface of the piezoelectric layer 1 can have the same potential.

  External electrodes 7g are formed on both end faces of the piezoelectric element 12, respectively. As a result, the directionality of the piezoelectric element 12 is lost, and when the driver elements 8 are mounted on the piezoelectric element 12, it is not necessary to align the positions. As a result, the mass productivity of the ultrasonic actuator is improved. The external electrode 7g may be formed only on one end face of the piezoelectric element 12.

  Further, the common electrode 3a, the divided electrodes 2a to 2d of the first feeding electrode layer 6a, and the divided electrodes 4a to 4d of the second feeding electrode layer 6b are respectively connected to the external electrodes 7a to 7d via the extraction electrodes 3b, 2f, and 4f. 7g, the common electrode 3a, the divided electrodes 2a to 2d of the first feeding electrode layer 6a, and the divided electrodes 4a to 4d of the second feeding electrode layer 6b are arranged at different positions on the peripheral surface of the piezoelectric element 12. Each can be pulled out. As a result, a sufficient insulation distance can be ensured between the common electrode 3a, the divided electrodes 2a to 2d of the first feeding electrode layer 6a, and the divided electrodes 4a to 4d of the second feeding electrode layer 6b. As described above, in order to obtain a sufficient insulation distance, the extraction electrodes 3b, 2f, 4f of the electrodes 3a, 2a-2d, 4a-4d having different potentials are formed with an interval larger than the thickness of the piezoelectric layer 1. It is desirable.

  In addition, as described above, the common electrode 3a, the divided electrodes 2a to 2d of the first feeding electrode layer 6a, and the divided electrodes 4a to 4d of the second feeding electrode layer 6b are respectively piezoelectrically inactive portions. Since it is connected to the external electrodes 7a to 7d and 7g via the arranged extraction electrodes 3b, 2f and 4f, no extra vibration is generated in the piezoelectric element 12. As a result, the piezoelectric element 12 vibrates with good balance, and the vibration efficiency is improved.

  In addition, as described above, the first connection electrode 2e and the second connection electrode 4e are formed at the central portion in the longitudinal direction of the piezoelectric layer 1 except for the edges in the lateral direction. The area of the electrode at the center portion in the longitudinal direction of 1 can be increased. Here, the central portion in the longitudinal direction of the piezoelectric layer 1 is a node portion of primary mode stretching vibration, that is, a stress concentration portion where stress due to stretching vibration is concentrated. Occur in a concentrated manner. And as mentioned above, even when the piezoelectric element 12 is downsized by increasing the area of the electrode at that portion, a large stretching vibration can be induced. As a result, the efficiency of the ultrasonic actuator can be improved.

  By the way, the larger the electrode area of the first connection electrode 2e and the second connection electrode 4e, the larger the expansion / contraction vibration occurs. However, if the electrode area is too large, the bending vibration of the secondary mode is hindered. Therefore, the widths of the first connection electrode 2e and the second connection electrode 4e are desirably about 5% to 40% of the longitudinal length of the piezoelectric layer 1.

  On the other hand, the first connection electrode 2e and the second connection electrode 4e are ideally formed over almost the entire area in the short direction S of the piezoelectric layer 1, but the first connection electrode 2e and the second connection electrode 4e are formed. If the electrode 4 e is formed up to the edge in the short direction of the piezoelectric layer 1, insulation between the internal electrode layers 5 becomes difficult. Therefore, as described above, the first connection electrode 2e and the second connection electrode 4e are formed on the portion of the piezoelectric layer 1 excluding both edges in the short direction. Specifically, the first connection electrode 2e and the region other than the region where only the length in the thickness direction of the piezoelectric layer 1 enters from the respective edges in the short direction of the piezoelectric layer 1 toward the center in the short direction. It is desirable to form the second connection electrode 4e.

  Hereinafter, the power supply electrode layer 6 and the like will be further described.

  The divided electrodes 2a to 2d of the first power supply electrode layer 6a and the divided electrodes 4a to 4d of the second power supply electrode layer 6b are formed at portions other than the longitudinal end edges of the piezoelectric layer 1. The divided electrodes 2a to 2d and 4a to 4d and the connection electrodes 2e and 4e are portions that overlap the common electrode 3a when viewed from the stacking direction (see FIG. 5). That is, portions of the feeding electrode layer 6 that do not overlap with the common electrode 3a when viewed from the stacking direction are the extraction electrodes 2f and 4f, not the divided electrodes 2a to 2d and 4a to 4d and the connection electrodes 2e and 4e.

  By the way, both ends in the longitudinal direction of the piezoelectric layer 1 are far away from the stress concentration part of the stretching vibration of the primary mode, and the stress is not generated so much. When an electrode is formed in the region where stress is not generated so much, electric power supplied through the electrode is not efficiently converted into vibration, and electrical loss is likely to occur. Therefore, in order to efficiently convert the feed power into vibration, as described above, electrodes are formed in the stress concentration part of the stretching vibration and in the vicinity thereof, so that electrodes are not formed in other parts where stress is not generated so much. ing. Specifically, from each edge in the longitudinal direction of the piezoelectric layer 1 to a region other than a region containing a length corresponding to 10% of the longitudinal length of the piezoelectric layer 1 toward the longitudinal center, It is preferable to form the divided electrodes 2a to 2d of the first feeding electrode layer 6a and the divided electrodes 4a to 4d of the second feeding electrode layer 6b, except for a region that has a length corresponding to 20% of the length in the longitudinal direction. It is more preferable to form in this area. As a result, it is possible to induce a larger first-order expansion / contraction vibration, and to improve the efficiency of the ultrasonic actuator.

  Further, the divided electrodes 2 a to 2 d of the first power supply electrode layer 6 a and the divided electrodes 4 a to 4 d of the second power supply electrode layer 6 b are formed in a portion excluding the central portion in the short side direction of the piezoelectric layer 1.

  By the way, the central portion in the short direction of the piezoelectric layer 1 is far from the stress concentration portion (both edges in the short direction of the piezoelectric layer 1) where stress due to the bending vibration of the secondary mode is concentrated, and the stress is not so much. Does not occur. When an electrode is formed in the region where stress is not generated so much, electric power supplied through the electrode is not efficiently converted into vibration, and electrical loss is likely to occur. Therefore, in order to efficiently convert the feed power into vibration, as described above, electrodes are formed in the stress concentration part of the bending vibration and in the vicinity thereof, and electrodes are not formed in other parts where stress is not generated so much. ing. Specifically, a region other than the region formed by a length corresponding to 10% of the length in the short direction of the piezoelectric layer 1 from the short direction center of the piezoelectric layer 1 toward each edge in the short direction. It is preferable to form the divided electrodes 2a to 2d of the first feeding electrode layer 6a and the divided electrodes 4a to 4d of the second feeding electrode layer 6b in the region, and only a length corresponding to 20% of the length in the short direction. More preferably, it is formed in a region other than the performed region. As a result, a larger second-order bending vibration can be induced, and the efficiency of the ultrasonic actuator can be improved.

  Further, the shape formed by the divided electrodes 2a to 2d and the first connection electrode 2e of the first feeding electrode layer 6a is a point-symmetric shape with respect to the center point M (see FIG. 4) of the upper main surface of the piezoelectric layer 1. is there. Further, the shape formed by the divided electrodes 4 a to 4 d and the second connection electrode 4 e of the second feeding electrode layer 6 b is also a point-symmetric shape with respect to the center point M of the upper main surface of the piezoelectric layer 1. That is, the shape of the first power supply electrode layer 6a excluding (excluding) the extraction electrode 2f and the shape of the second power supply electrode layer 6b excluding the extraction electrode 4f are respectively the first diagonal line on the upper main surface of the piezoelectric layer 1 and the first It is a point-symmetric shape with respect to the intersection of two diagonal lines. In this way, by making the shape of the feeding electrode layer 6 substantially symmetric with respect to the center point M of the upper main surface of the piezoelectric layer 1, vibration of the piezoelectric element 12, particularly bending vibration of the secondary mode is obtained. Symmetry is improved. As a result, excessive vibration does not occur in the piezoelectric element 12, and energy loss is greatly reduced. As a result, the supplied power can be efficiently converted into vibration.

  The shape formed by the divided electrodes 2a to 2d and the first connection electrode 2e of the first power supply electrode layer 6a and the shape formed by the divided electrodes 4a to 4d and the second connection electrode 4e of the second power supply electrode layer 6b are piezoelectric bodies. The shapes are mutually inverted with respect to a center line C (see FIG. 4) extending in the longitudinal direction L of the upper main surface of the layer 1. That is, the shape of the second power supply electrode layer 6b excluding the extraction electrode 4f is a shape obtained by reversing the shape of the first power supply electrode layer 6a excluding the extraction electrode 2f with respect to the center line C. Thus, by making the shape of the first feeding electrode layer 6a and the shape of the second feeding electrode layer 6b substantially opposite to each other with respect to the center line C, vibration of the piezoelectric element 12, particularly the secondary mode. The symmetry of bending vibration is improved. As a result, excessive vibration does not occur in the piezoelectric element 12, and energy loss is greatly reduced. As a result, the supplied power can be efficiently converted into vibration.

  The outermost layer in the stacking direction of the piezoelectric elements 12 is the piezoelectric layer 1. Thereby, the following effects are acquired. That is, when a small ultrasonic actuator (for example, one having a length of about 1 mm to 20 mm) is mounted in a very small space inside the electronic device, the outermost layer of the piezoelectric element 12 is the common electrode layer 3 or the feeding electrode layer 6. In this case, when the metal part in the periphery contacts the main surface of the piezoelectric element 12, the outermost electrode layer may be short-circuited, and the characteristics of the ultrasonic actuator may be significantly deteriorated. Therefore, as described above, the outermost layer in the stacking direction of the piezoelectric elements 12 is the piezoelectric layer 1 that is an insulator, so that no short circuit occurs even when a metal part comes into contact with the main surface of the piezoelectric elements 12. As a result, the reliability of the ultrasonic actuator can be improved.

-Operation of ultrasonic actuator-
Hereinafter, the operation of the ultrasonic actuator will be described. 6 is a displacement diagram of the first-order mode stretching vibration according to the present embodiment, FIG. 7 is a displacement diagram of the second-order mode bending vibration, and FIG. 8 is a conceptual diagram showing the operation of the piezoelectric element 12. It is. 6 to 8, the principal surface of the piezoelectric element 12 is in a positional relationship parallel to the paper surface.

  For example, a reference AC voltage having a frequency in the vicinity of the substantially matched resonance frequency is applied between the common electrode layer 3 and the first feeding electrode layer 6 a via the wire 10, and the common electrode layer 3 is interposed via the wire 10. When the AC voltage having the same magnitude and frequency as the reference AC voltage, the phase of which differs from the reference AC voltage by 90 ° or −90 °, is applied between the piezoelectric element 12 and the second feeding electrode layer 6b. The stretching vibration of the primary mode shown in FIG. 6 and the bending vibration of the secondary mode shown in FIG. 7 are induced harmonically.

  Then, the shape of the piezoelectric element 12 changes in the order as shown in FIGS. As a result, the driver elements 8 provided on the piezoelectric element 12 move substantially elliptically as viewed from the direction penetrating the paper surface of FIG. That is, the driver elements 8 and 8 are elliptically moved by the combined vibration of the expansion / contraction vibration and the bending vibration of the piezoelectric element 12. Due to this elliptical movement, the movable body 9 supported by the driver elements 8 and 8 moves relative to the piezoelectric element 12 and moves in the direction of arrow A or arrow B shown in FIG.

  Here, the expansion / contraction direction of the stretching vibration is the longitudinal direction of the main surface of the piezoelectric element 12, that is, the moving direction of the movable body 9. The vibration direction of the bending vibration is the driver elements 8 and 8 that support the movable body 9. Direction. The stacking direction of the piezoelectric elements 12 is a direction perpendicular to both the stretching direction of stretching vibration and the vibration direction of bending vibration.

(Other embodiments)
In the embodiment, as shown in FIG. 3, the feeding electrode layer 6 may be formed by continuously arranging several layers of the first feeding electrode layer 6 a or the second feeding electrode layer 6 b in the stacking direction, Alternatively, the first feeding electrode layer 6a and the second feeding electrode layer 6b may be randomly arranged, but as shown in FIG. 9, the number of the first feeding electrode layers 6a and the second feeding electrode layer 6b. It is desirable that the number of the power supply electrode layers 6 is the same, and the first power supply electrode layer 6a and the second power supply electrode layer 6b are alternately arranged in the stacking direction.

  Thus, the symmetry of vibration of the piezoelectric element 12 is improved by making the number of the first feeding electrode layers 6a and the number of the second feeding electrode layers 6b the same. As a result, excessive vibration does not occur in the piezoelectric element 12, and energy loss is greatly reduced. As a result, the supplied power can be efficiently converted into vibration.

  Further, the feeding electrode layer 6 is formed by alternately arranging the first feeding electrode layer 6a and the second feeding electrode layer 6b in the stacking direction, so that the symmetry of the vibration of the connection electrodes 2e and 4e of the piezoelectric element 12 is arranged. Will improve. As a result, excessive vibration does not occur in the piezoelectric element 12, and energy loss is greatly reduced. As a result, the supplied power can be efficiently converted into vibration.

  In the embodiment, it is desirable that the external electrode 7 is formed only on the peripheral surface of the piezoelectric element 12 and not formed on the main surface of the piezoelectric element 12. In this case, since the external electrode 7 is not formed on the main surface having the largest area among the outer surfaces of the piezoelectric element 12, a short circuit is less likely to occur even when it comes into contact with a metal part around the outer surface. Furthermore, since no electric field is generated between the external electrode 7 and the common electrode layer 3, no excessive vibration is generated in the piezoelectric element 12, and the efficiency reduction of the ultrasonic actuator can be suppressed.

  In the above-described embodiment, the divided electrodes 2a to 2d and 4a to 4d are substantially rectangular electrodes. However, the present invention is not limited to this, and for example, the divided electrodes 2a to 2d and 4a to 4d may be shaped according to the distribution of stress due to vibration.

  In the above embodiment, the configuration in which the wire 10 is connected to the external electrode 7 by solder has been described. However, other electrical connections such as connection by wire bonding, connection by a conductive adhesive, connection by crimping, connection by contact, etc. A method may be used. As a result, the same effects as those of the above embodiment can be obtained.

  In the above-described embodiment, power supply using the wire 10 has been described. However, other power supply methods such as power supply using conductive rubber, power supply using a flexible substrate, and power supply using a contact pin may be used. As a result, the same effects as those of the above embodiment can be obtained.

  Hereinafter, an example of power feeding using conductive rubber will be described. As shown in FIGS. 10 and 11, each of the support portions 13a, 13b, and 13c is made of conductive rubber in which metal particles are mixed in silicone rubber. In the divided electrode 2d in the region A4 (see FIG. 4) of the first feeding electrode layer 6a, an extraction electrode 2g extending from the divided electrode 2d toward the side surface of the piezoelectric element 43 is provided. In the divided electrode 4c in the region A3 (see FIG. 4) of the second feeding electrode layer 6b, an extraction electrode 4g extending from the divided electrode 4c toward the side surface of the piezoelectric element 43 is provided. External electrodes 7e and 7f are provided on both side surfaces of the piezoelectric element 43, respectively. The common electrode 3a is connected to the support portion 13b through the external electrode 7g. The divided electrodes 2b and 2d of the first feeding electrode layer 6a and the divided electrodes 4b and 4d of the second feeding electrode layer 6b are connected to the support portion 13c via the extraction electrode 2g and the external electrode 7e. The divided electrodes 2a and 2c of the first feeding electrode layer 6a and the divided electrodes 4a and 4c of the second feeding electrode layer 6b are connected to the support portion 13a via the extraction electrode 4g and the external electrode 7f. A voltage is applied to the internal electrode layer 5 through the support portions 13a to 13c and the like. The other points are almost the same as in the above embodiment. As described above, since it is not necessary to provide solder on the piezoelectric element 43, it is possible to suppress the stress caused by vibration from being concentrated on the portion of the piezoelectric element 43 provided with solder and cracking of the piezoelectric element 43.

  Moreover, in the said embodiment, although the movable body 9 driven by the drive force of an ultrasonic actuator is flat form, it is not restricted to this, Arbitrary structures are employ | adopted as a structure of the movable body 9. can do. For example, as shown in FIG. 12, the movable body is a disc body 9 that can rotate about a predetermined axis X, and the driver elements 8 of the ultrasonic actuator are in contact with the side peripheral surface 9 a of the disc body 9. You may be comprised so that it may touch. In such a configuration, when the ultrasonic actuator is driven, the disk body 9 is rotated about the predetermined axis X by the substantially elliptical motion of the driver elements 8.

  In the above-described embodiment, the configuration in which the driver elements 8 are provided on one end face of the piezoelectric element 12 has been described. However, the driver elements 8 may be formed on one side face of the piezoelectric element 12. In this case, the expansion / contraction direction of the primary mode expansion / contraction vibration is the direction in which the driver elements 8 support the movable body 9, and the vibration mode of the secondary mode bending vibration is the movable direction of the movable body 9.

  Moreover, in the said embodiment, although the support body is comprised by the case 11, as long as it has the support part which supports the piezoelectric element 12, you may comprise by what.

(Other)
The piezoelectric element and the ultrasonic actuator described in this specification can also be expressed as follows.

(1) A piezoelectric element formed by alternately laminating substantially rectangular piezoelectric layers and internal electrode layers,
The internal electrode layer is composed of a common electrode layer and a feeding electrode layer alternately arranged in the stacking direction via the piezoelectric layers,
The common electrode layer has a common electrode;
The power supply electrode layer is formed on a main surface of a piezoelectric layer different from the first power supply electrode layer provided on the main surface of the piezoelectric layer and the piezoelectric layer provided with the first power supply electrode layer on the main surface. A second power supply electrode layer provided,
The first feeding electrode layer includes four divided electrodes respectively provided in four regions obtained by dividing the principal surface of the piezoelectric layer into two in the longitudinal direction and the short direction, and the four divided electrodes. A first connection electrode that connects a pair of divided electrodes provided respectively in two regions facing each other in the first diagonal direction of the main surface of the piezoelectric layer;
The second feeding electrode layer includes four divided electrodes respectively provided in the four regions, and two regions of the four divided electrodes that face each other in the second diagonal direction of the main surface of the piezoelectric layer. A second connection electrode that connects a pair of provided split electrodes to each other;
The first connection electrode and the second connection electrode are respectively provided in portions of the central portion in the longitudinal direction of the piezoelectric layer except for both lateral edges.
The common electrode is connected to an external electrode provided on the outer surface of the piezoelectric element,
A pair of split electrodes provided in two regions facing the first diagonal direction of the first feeding electrode layer and two regions facing the first diagonal direction of the second feeding electrode layer, respectively. The pair of divided electrodes provided are connected by external electrodes provided on the outer surface of the piezoelectric element,
A pair of split electrodes provided in two regions facing the second diagonal direction of the first feeding electrode layer and two regions facing the second diagonal direction of the second feeding electrode layer, respectively. A pair of divided electrodes provided is a piezoelectric element connected by an external electrode provided on the outer surface of the piezoelectric element.

(2) The common electrode, the divided electrode of the first feeding electrode layer, and the divided electrode of the second feeding electrode layer are each provided with an extraction electrode,
The piezoelectric element according to (1), wherein the extraction electrode is connected to the external electrode.

  (3) The piezoelectric element according to (2), wherein the common electrode layer, the extraction electrode of the first feeding electrode layer, and the extraction electrode of the second feeding electrode layer do not overlap when viewed from the stacking direction.

  (4) The piezoelectric element according to (1), wherein the divided electrode is provided in a portion excluding both end edges in the longitudinal direction of the piezoelectric layer.

  (5) The piezoelectric element according to (1), wherein the divided electrode is provided in a portion excluding a central portion in a short direction of the piezoelectric layer.

  (6) The piezoelectric element according to (1), wherein a shape formed by the divided electrode and the connection electrode of the feeding electrode layer is a point-symmetric shape with respect to a center point of the main surface of the piezoelectric layer.

  (7) The shape formed by the divided electrode and the first connection electrode of the first power supply electrode layer and the shape formed by the divided electrode and the second connection electrode of the second power supply electrode layer are in the longitudinal direction of the main surface of the piezoelectric layer. The piezoelectric element according to (1), wherein the piezoelectric elements have shapes inverted with respect to the extending center line.

  (8) The piezoelectric element according to (1), wherein the number of first feeding electrode layers and the number of second feeding electrode layers are the same.

  (9) The piezoelectric element according to (1), wherein the power supply electrode layer is formed by alternately arranging the first power supply electrode layer and the second power supply electrode layer in a stacking direction.

  (10) The piezoelectric element according to (1), wherein the outermost layer in the stacking direction of the piezoelectric elements is the piezoelectric layer.

  (11) The piezoelectric element according to (1), wherein the external electrode is provided only on a peripheral surface including an end surface and a side surface of the piezoelectric element.

(12) The piezoelectric element according to (1),
A driver provided on an end surface or a side surface of the piezoelectric element;
A movable body supported by the driver;
By supplying power to the internal electrode layer, the piezoelectric element is caused to vibrate by combining a primary mode stretching vibration and a secondary mode bending vibration, and the movable element is caused to move substantially elliptically by the vibration. An ultrasonic actuator for moving the actuator relative to the piezoelectric element.

(13) It further comprises a support having a support part for supporting the piezoelectric element,
The ultrasonic actuator according to (12), wherein the support portion is made of conductive rubber.

  As described above, the present invention suppresses vibration inhibition of the piezoelectric element by devising the configuration of the feeding electrode layer, and is useful for ultrasonic actuators used in various electronic devices and the like.

1 is a perspective view of an ultrasonic actuator according to an embodiment of the present invention. It is a perspective view of a piezoelectric element. It is a disassembled perspective view of a piezoelectric element. It is a top view of a piezoelectric material layer. (A) is a figure which shows the positional relationship of a 1st feeding electrode layer and a common electrode layer, (b) is a figure which shows the positional relationship of a 2nd feeding electrode layer and a common electrode layer. It is a displacement figure of the expansion-contraction vibration of a primary mode. It is a displacement figure of the bending vibration of a secondary mode. It is a conceptual diagram which shows operation | movement of a piezoelectric element. It is a disassembled perspective view of the modification of a piezoelectric element. It is a perspective view of the modification of an ultrasonic actuator. (A) is a perspective view of a piezoelectric element, (b) is an exploded perspective view of a piezoelectric element. It is a perspective view of the modification of an ultrasonic actuator. It is a perspective view of an ultrasonic actuator. (A) is a perspective view of a piezoelectric element, (b) is an exploded perspective view of a piezoelectric element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric layer 2a-2d Split electrode 2e First connection electrode 2f Lead electrode 3 Common electrode layer 4a-4d Split electrode 4e Second connection electrode 4f Lead electrode 5 Internal electrode layer 6 Feed electrode layer 6a First feed electrode layer 6b First Two feeding electrode layers 7a to 7d External electrode 7g External electrode 8 for common electrode Driver 9 Movable body 10 Wire 11 Case 12, 23, 43 Piezoelectric elements 13a to 13c Support portion

Claims (1)

A piezoelectric element formed by alternately laminating substantially rectangular piezoelectric layers and internal electrode layers,
The internal electrode layer is composed of a common electrode layer and a feeding electrode layer alternately arranged in the stacking direction via the piezoelectric layers,
The common electrode layer has a common electrode;
The power supply electrode layer is formed on a main surface of a piezoelectric layer different from the first power supply electrode layer provided on the main surface of the piezoelectric layer and the piezoelectric layer provided with the first power supply electrode layer on the main surface. A second power supply electrode layer provided,
The first feeding electrode layer includes four divided electrodes respectively provided in four regions obtained by dividing the principal surface of the piezoelectric layer into two in the longitudinal direction and the short direction, and the four divided electrodes. A first connection electrode that connects a pair of divided electrodes provided respectively in two regions facing each other in the first diagonal direction of the main surface of the piezoelectric layer;
The second feeding electrode layer includes four divided electrodes respectively provided in the four regions, and two regions of the four divided electrodes that face each other in the second diagonal direction of the main surface of the piezoelectric layer. A second connection electrode that connects a pair of provided split electrodes to each other;
The common electrode is connected to an external electrode provided on the outer surface of the piezoelectric element,
A pair of divided electrodes provided in two regions facing the first diagonal direction of the first feeding electrode layer and two regions facing the first diagonal direction of the second feeding electrode layer, respectively. The pair of divided electrodes provided are connected by external electrodes provided on the outer surface of the piezoelectric element,
A pair of divided electrodes provided in two regions facing the second diagonal direction of the first feeding electrode layer and two regions facing the second diagonal direction of the second feeding electrode layer, respectively. A pair of divided electrodes provided is a piezoelectric element connected by an external electrode provided on the outer surface of the piezoelectric element.

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