JP4954783B2 - Piezoelectric element and vibration type actuator - Google Patents

Description

  The present invention relates to a piezoelectric element and a vibration type actuator including the piezoelectric element.

2. Description of the Related Art Conventionally, a vibration type actuator including a piezoelectric element (electromechanical conversion element) that is used in various electric devices is known (see, for example, Patent Document 1). This piezoelectric element is formed by alternately laminating piezoelectric bodies and electrodes. In the vibration type actuator, the piezoelectric element is vibrated by applying a voltage to the electrode, thereby moving the movable body.
Special table 2003-501988 gazette

  The vibration type actuator requires a two-phase power source. The piezoelectric element of the vibration actuator usually has a piezoelectric body and a two-phase independent feeding electrode and a common electrode. If this piezoelectric element is of a single plate type having a thickness of several millimeters, with electrodes formed on both surfaces of a single layer of piezoelectric material, several tens of millimeters are required to sufficiently displace the piezoelectric element. An applied voltage of V to several hundred V is required.

  Therefore, in recent years, by alternately laminating piezoelectric bodies and electrodes, the thickness of the piezoelectric bodies between the electrodes is reduced, so that the voltage applied to the piezoelectric bodies per unit length (even with the same power supply voltage) ( The electric field strength) is increased to reduce the driving voltage.

  However, for example, in order to realize 3V driving by a lithium ion power source used as a power source of recent portable devices, the thickness of the piezoelectric body must be reduced to several tens of um or less. If it does so, a piezoelectric constant will deteriorate or the ratio of the electrode with respect to a piezoelectric element will increase, and efficiency will fall.

  By the way, in view of the efficiency and the number of devices used, a half-bridge driving method or a single driving method is generally used as a driving method of the piezoelectric element. In these systems, only a voltage corresponding to the difference between the ground level and the power supply level can be applied to the piezoelectric element.

  If the full-bridge drive method or push-pull drive method is adopted, the voltage of the power supply level and the reverse power supply level can be applied to the piezoelectric element. Can be applied.

  However, a conventional vibration actuator having a common electrode cannot use a power supply circuit that applies a reverse voltage, such as a full bridge circuit or a push-pull circuit.

  On the other hand, it is conceivable to divide the common electrode. However, if the common electrode is simply divided, eight contact points between the external electrode on the outer surface of the element (for example, the peripheral surface of the element) and the wire are required. Degradation of characteristics due to weight occurs.

  Further, when the connection electrode for connecting the external electrodes to each other is formed on the element outer surface (for example, the element main surface) after dividing the common electrode, the number of the contacts can be reduced to four. An electrode must be formed at the edge portion (so-called edge connection), and when the piezoelectric element comes into contact with its peripheral parts, there is a problem in reliability, such as removal of the electrode at the edge portion.

  The present invention has been made in view of this point, and an object of the present invention is to enable full-bridge driving and improve reliability in a piezoelectric element and a vibration type actuator.

  In order to solve the problem, the present invention provides a piezoelectric element in which substantially rectangular piezoelectric layers and internal electrode layers are alternately stacked, and the internal electrode layers are arranged in the stacking direction in the piezoelectric layer. The positive electrode layer includes a first positive electrode layer provided on the main surface of the piezoelectric layer, and the first positive electrode on the main surface. A second positive electrode layer provided on a main surface of the piezoelectric layer different from the piezoelectric layer provided with the layer, and the negative electrode layer is provided on the main surface of the piezoelectric layer. A negative electrode layer and a second negative electrode layer provided on a main surface of a piezoelectric layer different from the piezoelectric layer provided with the first negative electrode layer on the main surface, the first positive electrode layer And the first negative electrode layer has a major surface of the piezoelectric layer and a major surface of the piezoelectric layer, respectively. Four divided electrodes provided in four regions each divided into two in the direction, and provided in two regions of the four divided electrodes facing the first diagonal direction of the main surface of the piezoelectric layer. A connection electrode that connects the pair of divided electrodes to each other, and each of the second positive electrode layer and the second negative electrode layer includes four divided electrodes provided in the four regions, It has a connection electrode for connecting a pair of divided electrodes respectively provided in two regions facing each other in the second diagonal direction of the main surface of the piezoelectric layer among the two divided electrodes.

  According to the present invention, since a reverse voltage can be applied to the piezoelectric element, full-bridge driving is possible. Further, since a plurality of piezoelectric elements can be connected in series, they can be operated in a coordinated manner. Further, the edge connection is unnecessary, and the reliability is improved.

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

(Embodiment 1)
−Configuration of vibration actuator−
As shown in FIGS. 1 and 2, the vibration actuator includes a substantially rectangular parallelepiped piezoelectric element 12 (for example, a length 6.0 mm × width 1.7 mm × thickness 1.0 mm). 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 accommodated and supported by the case 11 via 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 driver element 8 and the movable body 9 are made of a ceramic material whose main component is, for example, zirconia, alumina, or silicon nitride. The support portion 13c on the other end face of the piezoelectric element 12 (the end face opposite to the end face on which the drive elements 8 and 8 are provided) presses the drive elements 8 and 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 is formed by alternately laminating substantially rectangular piezoelectric layers 1 and internal electrode layers 2. The piezoelectric layer 1 is an insulator layer made of a piezoelectric ceramic material mainly composed of lead zirconate titanate, for example.

  The internal electrode layer 2 is an electrode layer made of a metal whose main component is, for example, silver or palladium. The internal electrode layer 2 is divided into four divided electrodes 3, 3,... Divided into a square shape, and one of the upper main surfaces of the piezoelectric layer 1 among these four divided electrodes 3, 3,. The connection electrode 4 connects the pair of divided electrodes 3 and 3 located on one diagonal line to each other, and the extraction electrode 5 pulls the divided electrode 3 to the element end face. The divided electrode 3 drawn to the element end face by the lead electrode 5 is connected to the divided electrode 3 of the same potential on the different internal electrode layers 2 via the external connection electrode (external power feeding electrode) 6. The external connection electrode 6 is an electrode made of a metal whose main component is, for example, silver or palladium. Four external connection electrodes 6 are formed on each of both end faces of the piezoelectric element 12, and it is desirable that the external connection electrodes 6 be arranged with an interval larger than the thickness of the piezoelectric layer 1. The divided electrode 3 is supplied with electric power through the external connection electrode 6, the extraction electrode 5, and the connection electrode 4.

  The internal electrode layer 2 includes a positive electrode layer (feeding electrode layer) 2 a and a negative electrode layer (ground electrode layer) 2 b that are alternately arranged in the stacking direction (thickness direction of the piezoelectric element 12) via the piezoelectric layers 1. . The positive electrode layer 2a and the negative electrode layer 2b are insulated from each other and are not conducted. The positive electrode layer 2a includes a first positive electrode layer 2aa provided on the upper main surface of the piezoelectric layer 1, and a piezoelectric body different from the piezoelectric layer 1 provided with the first positive electrode layer 2aa on the upper main surface. The second positive electrode layer 2ab is provided on the upper main surface of the layer 1. The negative electrode layer 2b is a piezoelectric body different from the first negative electrode layer 2ba provided on the upper main surface of the piezoelectric layer 1 and the piezoelectric layer 1 provided with the first negative electrode layer 2ba on the upper main surface. The second negative electrode layer 2bb provided on the upper main surface of the layer 1. The internal electrode layer 2 has a first plus electrode layer 2aa, a first minus electrode layer 2ba, a second plus electrode layer 2ab, and a second minus electrode layer 2bb repeatedly arranged in this order via the piezoelectric layer 1 in the stacking direction. Being done. The piezoelectric layer 1 is polarized from the positive electrode layer 2a side to the negative electrode layer 2b side.

  Hereinafter, the first positive electrode layer 2aa will be described. The four divided electrodes 3, 3,... Of the first plus electrode layer 2aa are divided into four regions A1 to A4 obtained by dividing the upper main surface of the piezoelectric layer 1 into two in the longitudinal direction L and the lateral direction S, respectively. (See FIG. 3), and the connection electrode 4 is a first diagonal direction of the upper main surface of the piezoelectric layer 1 (the direction in which the first diagonal line extends) among these four divided electrodes 3, 3. ) A pair of divided electrodes 3 and 3 provided in two regions A1 and A3 facing D1 are electrically connected. Each divided electrode 3 is a substantially rectangular electrode, and overlaps with each divided electrode 3 of the minus electrode layer (adjacent electrode layers) 2b when viewed from the stacking direction. That is, each divided electrode 3 of the first plus electrode layer 2aa and each divided electrode 3 of the minus electrode layer 2b are opposed to each other with the piezoelectric layer 1 interposed therebetween. Each divided electrode 3 is provided with an extraction electrode 5 extending toward the end face of the piezoelectric element 12. Each extraction electrode 5 does not overlap with each divided electrode 3 of the negative electrode layer 2b when viewed from the stacking direction. That is, each extraction electrode 5 of the first plus electrode layer 2aa does not face each divided electrode 3 of the minus electrode layer 2b. For this reason, an electric field does not arise in the part facing each extraction electrode 5 of the piezoelectric layer 1. That is, this part becomes a piezoelectrically inactive part.

  Next, the second positive electrode layer 2ab will be described. The four divided electrodes 3, 3,... Of the second plus electrode layer 2ab are also provided in the four regions A1 to A4, respectively, and the connection electrode 4 is one of these four divided electrodes 3, 3,. The pair of divided electrodes 3 and 3 provided in the two regions A2 and A4 respectively facing the second diagonal direction (direction in which the second diagonal extends) D2 of the upper main surface of the piezoelectric layer 1 are electrically connected. Each divided electrode 3 is provided with an extraction electrode 5 extending toward the end face of the piezoelectric element 12. The position where each extraction electrode 5 is extracted is the same as the extraction position of each extraction electrode 5 of the first plus electrode layer 2aa. Then, through the external connection electrodes 6 and 6, the divided electrodes 3 and 3 in the regions A1 and A3 of the first positive electrode layers 2aa and the divided electrodes 3 and 3 in the regions A1 and A3 of the second positive electrode layers 2ab are electrically connected. Through the external connection electrodes 6 and 6, the divided electrodes 3 and 3 in the regions A2 and A4 of each first positive electrode layer 2aa and the divided electrodes 3 and 3 in the regions A2 and A4 of each second positive electrode layer 2ab Is conducting. The other points are substantially the same as those of the first plus electrode layer 2aa.

  Next, the negative electrode layer 2b will be described. The four divided electrodes 3, 3,... Of the first negative electrode layer 2ba are also formed in the four regions A1 to A4, respectively, and the connection electrode 4 is the first diagonal line, like the first positive electrode layer 2aa. A pair of divided electrodes 3 and 3 arranged in two regions A1 and A3 facing each other in the direction D1 are electrically connected. Each divided electrode 3 is provided with an extraction electrode 5 extending toward the end face of the piezoelectric element 12. The four divided electrodes 3, 3,... Of the second negative electrode layer 2bb are also formed in the four regions A1 to A4, respectively, and the connection electrode 4 is the second diagonal line, like the second positive electrode layer 2ab. A pair of divided electrodes 3 and 3 arranged in two regions A2 and A4 facing in the direction D2 are electrically connected. Each divided electrode 3 is provided with an extraction electrode 5 extending toward the end face of the piezoelectric element 12. The position where each extraction electrode 5 is extracted is the same as the extraction position of each extraction electrode 5 of the first negative electrode layer 2ba. The divided electrodes 3 and 3 in the regions A1 and A3 of the first minus electrode layers 2ba and the divided electrodes 3 and 3 in the regions A1 and A3 of the second minus electrode layers 2bb are electrically connected through the external connection electrodes 6 and 6. Through the external connection electrodes 6 and 6, the divided electrodes 3 and 3 in the regions A2 and A4 of the first negative electrode layers 2ba and the divided electrodes 3 in the regions A2 and A4 of the second negative electrode layers 2bb are electrically connected. Has been. The other points are almost the same as those of the plus electrode layer 2a.

  By adopting the electrode configuration as described above, when the four external connection electrodes 6, 6,... On any one end face of the piezoelectric element 12 are fed, the divided electrodes 3 in four independent regions A1 to A4. , 3... Can be supplied with voltages. That is, the external connection electrodes 6 and 6 connected to the divided electrodes 3 and 3 in the regions A1 and A3 of each positive electrode layer 2a are A +, and the divided electrodes 3 and 3 in the regions A2 and A4 of each positive electrode layer 2a. The external connection electrodes 6 and 6 respectively connected to B +, and the external connection electrodes 6 and 6 respectively connected to the divided electrodes 3 and 3 of the regions A1 and A3 of each negative electrode layer 2b are A and If the external connection electrodes 6 and 6 connected to the divided electrodes 3 and 3 in the regions A2 and A4 of the negative electrode layer 2b are B−, the distance between A + and A− on one end face of the piezoelectric element 12 , And by applying a voltage between B + and B−, respectively, an electric field is applied to the piezoelectric layer 1 corresponding to the positions of the regions A1 and A3 and the piezoelectric layer 1 corresponding to the positions of the regions A2 and A4. Can be added.

  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.

  Hereinafter, the internal electrode layer 2 and the like will be further described.

  Each divided electrode 3 is connected to an external connection electrode 6 via an extraction electrode 5 disposed in a piezoelectrically inactive portion. As a result, 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.

  The internal electrode layer 2 includes a first plus electrode layer 2aa, a first minus electrode layer 2ba, a second plus electrode layer 2ab, and a second minus electrode layer 2bb in this order via the piezoelectric layer 1 in the stacking direction. It becomes. Thereby, the symmetry of the vibration of the arrangement part of the connection electrode 4 of the piezoelectric element 12 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.

  Further, the numbers of the first plus electrode layer 2aa, the second plus electrode layer 2ab, the first minus electrode layer 2ba, and the second minus electrode layer 2bb are the same. Thereby, the symmetry of vibration of the piezoelectric element 12 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 vibration type 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 piezoelectric element 12 is piezoelectric when the outermost layer is the internal electrode layer 2. When the metal part in the periphery contacts the main surface of the element 12, the outermost electrode layer may be short-circuited, and the characteristics of the vibration type 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 vibration type actuator can be improved.

−Operation of vibration type actuator−
Hereinafter, the operation of the vibration type actuator will be described. 4 is a displacement diagram of stretching vibration in the primary mode, FIG. 5 is a displacement diagram of bending vibration in the secondary mode, and FIG. 6 is a conceptual diagram showing the operation of the piezoelectric element 12. 4 to 6, the principal surface of the piezoelectric element 12 is in a positional relationship parallel to the paper surface.

  For example, between wires A + and A− via a wire (not shown), that is, the divided electrodes 3 and 3 in the regions A1 and A3 of the positive electrode layer 2a and the divided electrode 3 in the regions A1 and A3 of the negative electrode layer 2b. , 3, a sine wave reference AC voltage (hereinafter referred to as a first voltage) having a frequency in the vicinity of the resonance frequency is applied, and between B + and B−, that is, the region A2, of the positive electrode layer 2a. A sinusoidal AC voltage (hereinafter referred to as the second voltage) having the same magnitude and frequency as the first voltage between the divided electrodes 3 and 3 of A4 and the divided electrodes 3 and 3 of the regions A2 and A4 of the negative electrode layer 2b. Applied). As a result, in-phase voltages are applied to the divided electrodes 3 and 3 in the regions A1 and A3 of the plus electrode layer 2a, and in-phase voltages are applied to the divided electrodes 3 and 3 in the regions A2 and A4 of the plus electrode layer 2a. When the phase difference between the first voltage and the second voltage is 0 degree, the piezoelectric element 12 is induced to expand and contract in the primary mode shown in FIG. On the other hand, when the phase difference is 180 degrees, the piezoelectric element 12 is induced to bend in the second mode shown in FIG.

  Further, a first voltage of a sine wave having a frequency near the resonance frequency is applied between A + and A−, and the phase between B + and B− is different from the first voltage by 90 degrees or −90 degrees. When a second voltage of a sine wave having the same magnitude and frequency as the first voltage is applied, the piezoelectric element 12 is harmonized with the stretching vibration of the primary mode shown in FIG. 4 and the bending vibration of the secondary mode shown in FIG. Induced.

  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 expansion / contraction 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, 8 supporting 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.

-Example-
The full bridge circuit shown in FIG. 7 was driven with a power supply voltage of 3 V (vibration actuator according to the present invention). FET was used as a switching circuit. A voltage of ± 3 V was applied to the piezoelectric element 12 by switching at 270 kHz by the CPU. The FET gate signal applied between A + and A− and the FET gate signal applied between B + and B− have the same frequency and a phase difference of 90 degrees. In this case, the voltage applied to the piezoelectric element 12 was 6 Vpp, and the moving speed of the movable body 9 in the no-load state was 90 mm / s.

  On the other hand, the configuration of the half bridge shown in FIG. 8 was driven under the same conditions (conventional vibration type actuator having a common electrode). In this case, the voltage applied to the piezoelectric element 12 was 3 Vpp, and the moving speed of the movable body 9 in the no-load state was 50 mm / s.

(Embodiment 2)
In the present embodiment, the configuration of the vibration type actuator is different from that of the first embodiment. As shown in FIG. 9, in this embodiment, the driver elements 8 are mounted on one end surface of the piezoelectric element 12 at the antinodes of the bending vibration, and are opposite to the end surface where the driver element 8 is mounted. On the other end surface, conductive rubber as a support portion 13 b is provided via the external connection electrode 6, and this conductive rubber 13 b is electrically connected to a power supply terminal in the case 11. Then, by applying a preload from the lower side of the case 11, a force is applied to the piezoelectric element 12 through the conductive rubber 13 b, and the driver elements 8 are pressed against the movable body 9.

  The conductive rubber 13b has, for example, a laminated structure of a support layer mainly composed of silicone rubber and a conductive layer in which silicone rubber and metal particles such as silver are mixed, and in the lamination direction (left and right direction in FIG. 9) It is insulated and anisotropic. Since there are four external connection electrodes 6 on the other end face of the piezoelectric element 12, it is possible to connect to four terminals by one anisotropic conductive rubber 13b.

  In addition, in order to improve the positional accuracy in the longitudinal direction of the main surface of the piezoelectric element 12, rubber may be provided on each side surface of the piezoelectric element 12 as the support portions 13a and 13c.

(Embodiment 3)
The present embodiment is different from the second embodiment in the configuration of the vibration type actuator. As shown in FIGS. 10 and 11, in this embodiment, two external power supply electrodes 6 are formed on each side surface of the piezoelectric element 12, and two external connection electrodes 6 are formed on both end surfaces. Then, four channels are drawn from both side surfaces of the piezoelectric element 12 by anisotropic conductive rubber as the support portions 13a and 13c (the conductive rubbers 13a and 13c are insulated in the vertical direction in FIG. 10). A preload is applied to the rubber (support portion) 13b on the element bottom surface (element end surface).

  In the second embodiment, the external power supply electrode 6 is formed on the lower end face, and the conductive rubber 13b serves both as a power supply terminal and as a preload. Here, when it is desired to increase the output of the vibration type actuator, it is necessary to apply a large preload, and strictness is required for applying the preload. For this reason, in the second embodiment, the pressure on the conductive rubber 13b necessary for stable conduction may not match the pressure on the conductive rubber 13b necessary for applying the preload.

  In this embodiment, since the external power supply electrode 6 is formed on both side surfaces of the piezoelectric element 12 and power is supplied from each side surface of the element, the role of the power supply terminal can be eliminated from the support portion 13b to which the preload is applied, and the reliability is improved. Can be improved.

  Note that since the element side surface is usually smaller than the element end face, it is difficult to form the two external power supply electrodes 6 with an insulation distance therebetween, but as shown in FIG. Thus, the insulation distance between the two external power supply electrodes 6 can be secured. For this reason, it is desirable that the two external connection electrodes 6 formed on the element end face be formed as far as possible from the element side face.

(Other embodiments)
In each of the embodiments, the internal electrode layer 2 includes the first plus electrode layer 2aa, the first minus electrode layer 2ba, the second plus electrode layer 2ab, and the second minus electrode layer 2bb via the piezoelectric layer 1 in the stacking direction. Although arranged in this order, it is not limited to this. Several layers of the first plus electrode layer 2aa or the second plus electrode layer 2ab may be continuously arranged in the stacking direction, and several layers of the first minus electrode layer 2ba or the second minus electrode layer 2bb are continuously arranged in the stacking direction. May be arranged. Alternatively, the first plus electrode layer 2aa and the second plus electrode layer 2ab may be randomly arranged, and the first minus electrode layer 2ba and the second minus electrode layer 2bb may be randomly arranged.

  In each of the above embodiments, the shape formed by the divided electrode 3 and the connection electrode 4 of the internal electrode layer 2 is a point-symmetric shape with respect to the center point M (see FIG. 3) of the upper main surface of the piezoelectric layer 1. May be. That is, the shape of the internal electrode layer 2 excluding the extraction electrode 5 may be point-symmetric with respect to the intersection of the first diagonal line and the second diagonal line of the upper main surface of the piezoelectric layer 1. Thus, by making the shape of the internal electrode layer 2 substantially symmetric with respect to the center point M of the upper main surface of the piezoelectric layer 1, the vibration of the piezoelectric element 12, particularly the 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.

  In each of the above embodiments, the shape formed by the divided electrode 3 and the connection electrode 4 of the first plus electrode layer 2aa and the shape formed by the divided electrode 3 and the connection electrode 4 of the second plus electrode layer 2ab are divided into piezoelectric layers. The shape of the divided electrode 3 and the connection electrode 4 of the first negative electrode layer 2ba is reversed with respect to the center line C (see FIG. 3) extending in the longitudinal direction L of the upper main surface of the first negative electrode layer 2ba. The shape formed by the divided electrode 3 and the connection electrode 4 of the electrode layer 2bb may be reversed with respect to the center line C. That is, the shapes of the first plus electrode layer 2aa and the first minus electrode layer 2ba excluding the extraction electrode 5 are inverted with respect to the center line C, respectively. The shape of the negative electrode layer 2bb may be used. In this way, the shape of the first plus electrode layer 2aa and the shape of the second plus electrode layer 2ab are substantially inverted with respect to the center line C, and the shape of the first minus electrode layer 2ba and the second minus electrode are By making the shape of the layer 2bb substantially reversed with respect to the center line C, the symmetry of the vibration of the piezoelectric element 12, particularly the bending vibration of the secondary mode 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.

  Further, in each of the above embodiments, as shown in FIG. 12, the overlapping portion of the divided electrode 3 of the plus electrode layer 2a and the divided electrode 3 of the minus electrode layer 2b when viewed from the stacking direction is the piezoelectric layer 1 You may form in the part except a longitudinal direction both-ends edge part.

  By the way, both end portions in the longitudinal direction of the piezoelectric layer 1 are far away from the stress concentration portion of the primary mode stretching vibration, 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 should be formed in the stress concentration part of the stretching vibration and in the vicinity thereof, and electrodes should not be formed in other parts where stress is not generated so much. It is good to do. Specifically, in each region other than the region that includes a length corresponding to 10% of the length in the longitudinal direction of the piezoelectric layer 1 from each edge in the longitudinal direction of the piezoelectric layer 1 toward the center in the longitudinal direction. The overlapping portion is preferably formed, and more preferably formed in a region other than a region that has a length corresponding to 20% of the length in the longitudinal direction. As a result, it is possible to induce a larger first-order stretching vibration and to improve the efficiency of the vibration actuator.

  In each of the above embodiments, the overlapping portion may be formed in a portion excluding the central portion in the lateral 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 to vibration, as described above, electrodes should be formed in the stress concentration part of the bending vibration and in the vicinity thereof, and electrodes should not be formed in other parts where stress is not generated much. It is good to do. 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. The overlapping portion is preferably formed in the region, and more preferably in a region other than the region formed by a length corresponding to 20% of the length in the short direction. As a result, a larger second-order bending vibration can be induced, and the efficiency of the vibration type actuator can be improved.

  Further, in each of the above embodiments, the connection electrode 4 may be provided over almost the entire surface of the piezoelectric layer 1 at the center in the longitudinal direction, excluding both edge portions in the lateral direction. Thereby, the area of the electrode of the longitudinal direction center part of the piezoelectric material layer 1 can be enlarged. 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 vibration type actuator can be improved.

  By the way, as the electrode area of the connection electrode 4 is larger, a larger stretching vibration is generated. However, if the electrode area is too large, the bending vibration of the secondary mode is hindered. Therefore, the width of the connection electrode 4 is desirably about 5% to 40% of the longitudinal length of the piezoelectric layer 1.

  On the other hand, the connection electrode 4 is ideally formed over almost the entire region in the short direction of the piezoelectric layer 1, but the connection electrode 4 is formed up to the edge in the short direction of the piezoelectric layer 1. Then, insulation between the internal electrode layers 2 becomes difficult. Therefore, as described above, the connection electrode 4 is preferably formed on the portion of the piezoelectric layer 1 excluding both lateral edges. Specifically, the connection electrode 4 is formed in a region other than a 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. Is desirable.

  In each of the above embodiments, the divided electrode 3 is a substantially rectangular electrode. However, the present invention is not limited to this, and for example, the divided electrode 3 may have a shape corresponding to the distribution of stress due to vibration.

  In each of the embodiments described above, power supply using a wire has been described. However, other power supply methods such as power supply using a flexible substrate or power supply using a contact pin may be used. As a result, the same effects as those of the above embodiments can be obtained.

  Further, in each of the above embodiments, the movable body 9 driven by the driving force of the vibration type actuator is a flat plate shape, but is not limited to this, and the movable body 9 may have any configuration. Can be adopted. For example, as shown in FIG. 13, the movable body is a disk body 9 that can rotate about a predetermined axis X, and the drive elements 8, 8 of the vibration type actuators contact the side peripheral surface 9 a of the disk body 9. You may be comprised so that it may touch. In the case of such a configuration, when the vibration type actuator is driven, the disk body 9 is rotated about the predetermined axis X by the substantially elliptical motion of the driver elements 8.

  Further, in each of the embodiments, the configuration in which the driver elements 8 are provided on one end face of the piezoelectric element 12 has been described, but 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 moving direction of the movable body 9.

  The present invention is not limited to the embodiments, and can be implemented in various other forms without departing from the spirit or main features thereof.

  As described above, the above-described embodiment is merely an example in all respects and should not be interpreted in a limited manner. The scope of the present invention is defined by the claims, and is not limited by the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  As described above, the piezoelectric element and the vibration type actuator according to the present invention can be applied to an application for enabling full-bridge driving and improving reliability.

It is a perspective view of a vibration type actuator. (A) is a perspective view of a piezoelectric element, and (b) is a plan view of a piezoelectric layer in which an electrode layer is provided on the upper main surface. It is a figure which shows the upper side main surface of a piezoelectric material 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 circuit diagram of the drive circuit of a piezoelectric element. It is a circuit diagram of the drive circuit of a piezoelectric element. It is a front view of a vibration type actuator. It is a front view of a vibration type actuator. (A) is a perspective view of a piezoelectric element, (b) is an exploded perspective view of a piezoelectric element. (A) is a perspective view of a piezoelectric element, and (b) is a plan view of a piezoelectric layer in which an electrode layer is provided on the upper main surface. It is a perspective view of the modification of a vibration type actuator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric layer 2 Internal electrode layer 2a Positive electrode layer 2aa First positive electrode layer 2ab Second positive electrode layer 2b Negative electrode layer 2ba First negative electrode layer 2bb Second negative electrode layer 3 Split electrode 4 Connection electrode 5 Lead electrode 6 External connection electrode 8 Driver 9 Movable body 12 Piezoelectric element

Claims (3)

A piezoelectric element formed by alternately laminating substantially rectangular piezoelectric layers and internal electrode layers,
The internal electrode layer is composed of a positive electrode layer and a negative electrode layer alternately arranged via the piezoelectric layers in the stacking direction,
The positive electrode layer has a first positive electrode layer provided on a main surface of the piezoelectric layer and a main surface of a piezoelectric layer different from the piezoelectric layer provided with the first positive electrode layer on the main surface. A second positive electrode layer provided,
The negative electrode layer is formed on a main surface of a piezoelectric layer different from the first negative electrode layer provided on the main surface of the piezoelectric layer and the piezoelectric layer provided with the first negative electrode layer on the main surface. A second negative electrode layer provided,
Each of the first plus electrode layer and the first minus electrode layer has four divided electrodes provided in four regions obtained by dividing the main surface of the piezoelectric layer into two in the longitudinal direction and the short direction, respectively. And a connection electrode for connecting a pair of divided electrodes respectively provided in two regions facing the first diagonal direction of the main surface of the piezoelectric layer among the four divided electrodes,
Each of the second plus electrode layer and the second minus electrode layer includes four divided electrodes provided in the four regions, and a second diagonal direction of the main surface of the piezoelectric layer among the four divided electrodes. A piezoelectric element comprising a connection electrode for connecting a pair of divided electrodes provided in two regions facing each other to each other. The piezoelectric element according to claim 1, wherein
The internal electrode layer is formed by arranging the first plus electrode layer, the first minus electrode layer, the second plus electrode layer, and the second minus electrode layer in this order via the piezoelectric layer in the stacking direction. A piezoelectric element characterized by that. The piezoelectric element according to claim 1 or 2,
A driver provided in the piezoelectric element;
A movable body supported by the driver;
By supplying power to the piezoelectric element, the piezoelectric element is caused to oscillate in a combination of expansion and contraction vibration and bending vibration, and the movable body is moved by moving the driver by a substantially elliptical motion by the vibration. Type actuator.

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