JP5825656B2 - Piezoelectric actuator and coupled piezoelectric actuator - Google Patents

Description

  The present invention relates to a stacked piezoelectric actuator and a connected piezoelectric actuator that are connected in series along a stacking direction.

  A laminated piezoelectric actuator has alternating layers of piezoelectric bodies and internal electrodes, and includes an active layer that deforms when a voltage is applied and a protective layer that contacts the active layer and does not deform when a voltage is applied. It is known that stress is generated. Since this stress adversely affects the durability of the multilayer piezoelectric actuator, a technique has been proposed to relieve the stress by changing the active layer close to the interface with the protective layer to a layer having a small displacement (for example, (See Patent Document 1 and Patent Document 2).

  The electrostrictive effect element described in Patent Document 1 is an electrostrictive material in which an electrostrictive effect layer and internal electrodes having substantially the same contact area are alternately laminated, and the internal contact electrodes at both ends thereof have substantially the same contact area. A protective layer made of is contacted, and an electric field is applied to the electrostrictive effect layer by an internal electrode. An electrostrictive effect element is disclosed in which the thickness of the electrostrictive effect layer at the center is minimized, and the electrostrictive material layer closer to the protective layer is thicker. As a result, the concentration of shear stress is eased, and the lifetime reliability is increased.

  The multilayer piezoelectric actuator described in Patent Document 2 includes a multilayer body that actually expands and contracts and a ceramic body that is provided on both end surfaces in the stacking direction and does not expand and contract. And about the some piezoelectric material in the stress relaxation part formed in the both sides of the laminated body center part, the generated stress per unit length is gradually reduced toward the ceramic body side, and it designs so that it may disperse | distribute as a whole. In this way, the stress between the laminated body and the ceramic body is relaxed.

Japanese Patent Publication No. 63-10596 Japanese Patent No. 3881484

  In the prior art as described above, the stress generated at the interface between the protective layer and the active layer is relaxed. FIG. 5A is a side view of a conventional piezoelectric actuator 500 to which no voltage is applied. FIG. 5B is a side view of a conventional piezoelectric actuator 500 to which a voltage is applied. The piezoelectric actuator 500 has an active layer 510 and a protective layer 520, and stress is generated at the interface A in the piezoelectric actuator 500 as shown in FIG.

  However, in a product configured by connecting piezoelectric actuators such as positioners, the piezoelectric actuators are bonded to each other at the end surfaces, and the stress further adds to the conventional stress at the interface between the protective layer 520 and the active layer 510 by the bonding. Large stress is generated. 6A is a displacement diagram when it is assumed that the conventional piezoelectric actuators 500 are stacked without being bonded, and FIG. 6B is a conventional connected piezoelectric actuator in which the piezoelectric actuators 500 are bonded and connected. FIG.

  When the piezoelectric actuators 500 are not bonded to each other, the respective piezoelectric actuators 500 are displaced in a drum shape as shown in FIG. In this state, each end surface 530 can be freely displaced while drawing an arc. However, the actual piezoelectric actuator 500 is bonded and used as the coupled piezoelectric actuator 600, and is displaced while keeping the bonding surface 610 parallel as shown in FIG. 6B.

  The state of the conventional coupled piezoelectric actuator 600 shown in FIG. 6B is that the respective end surfaces 530 that can be freely displaced in an arc when the bonding is not performed are constrained in parallel as the bonding surfaces 610 and deformed. The piezoelectric actuators 500 are in tension with each other. In this state, at the interface between the protective layer 520 and the active layer 510, in addition to the stress generated when the piezoelectric actuator 500 is displaced alone, it is further added to generate a tensile stress.

  In the above prior art, the stress generated at the interface between the protective layer and the active layer in the piezoelectric actuator is relieved, but when a plurality of piezoelectric actuators are connected and bonded together, the interface between the protective layer and the active layer is reduced. The tensile stress generated by the addition cannot be relaxed.

  The present invention has been made in view of such circumstances, and a piezoelectric actuator capable of relieving a tensile stress generated by adding a plurality of piezoelectric actuators on the interface between a protective layer and an active layer when bonded and bonded, and It is an object of the present invention to provide a coupled piezoelectric actuator.

  (1) In order to achieve the above object, the piezoelectric actuator of the present invention is a stacked piezoelectric actuator that is connected in series along the stacking direction, in which polarized piezoelectric layers and internal electrodes alternate. An active layer formed by laminating and a protective layer provided at both ends of the active layer in the stacking direction and formed by an unpolarized piezoelectric layer. The electrode is characterized by having a hole in the center.

  As described above, in the piezoelectric actuator of the present invention, since the internal electrode near the protective layer has a hole in the center, when the piezoelectric actuator is about to be displaced like a drum by driving, the deformation of the end face is flattened, The adhesive surface can be displaced while being kept parallel, and the tensile stress can be relaxed. Since both end surfaces become flat with respect to the displacement at the time of voltage application in this way, when the piezoelectric actuator is connected and used, it is possible to relieve the tensile stress generated by being added to the interface between the protective layer and the active layer.

  (2) Moreover, the piezoelectric actuator of the present invention is characterized in that the hole of the internal electrode is circular. Thereby, it is possible to avoid stress concentration on a part of the hole of the internal electrode.

  (3) Moreover, the piezoelectric actuator of the present invention is characterized in that the internal electrodes from the internal electrode closest to the protective layer to the number of layers larger than 1 and smaller than 1/10 of the total number have a hole in the center. . Thus, the effect which relieve | moderates a tensile stress is maintainable by having a hole to the internal electrode to the number of layers larger than one. Further, by providing the holes up to 1/10 or less of the total number of internal electrodes, the stress can be relaxed without impairing the original drive performance of the piezoelectric actuator.

  (4) Further, the piezoelectric actuator of the present invention is characterized in that the hole of the internal electrode is larger than 1/3 of the size of the internal electrode and smaller than the size of the internal electrode. Thereby, stress can be relieved enough, maintaining the drive property of the expansion-contraction of a piezoelectric actuator.

  (5) Further, the piezoelectric actuator of the present invention is characterized in that the hole of the internal electrode is larger as the internal electrode is closer to the protective layer. As a result, the stress can be relaxed step by step, so that there is no sudden change in the stress in the expansion / contraction direction, and the failure probability can be reduced.

  (6) Moreover, the connection type piezoelectric actuator of the present invention is characterized in that a plurality of the above piezoelectric actuators are connected in series by bonding end faces in the stacking direction. Thereby, the connection type piezoelectric actuator can relieve the tensile stress generated by being added to the interface between the protective layer and the active layer of each piezoelectric actuator. As a result, the defective product rate can be reduced.

  ADVANTAGE OF THE INVENTION According to this invention, it can displace, keeping the adhesion surface of the connected piezoelectric actuator in parallel, and can relieve a tensile stress.

(A)-(c) It is a side sectional view, a plane sectional view, and a plane sectional view showing a piezoelectric actuator concerning the present invention, respectively. (A), (b) It is a side view which shows the voltage unapplied state and voltage applied state of the piezoelectric actuator which concerns on this invention, respectively. It is a side view which shows the connection type piezoelectric actuator which concerns on this invention. (A), (b) is the schematic which shows the conventional piezoelectric actuator and the piezoelectric actuator of this invention, respectively. (A), (b) is a side view which shows the conventional piezoelectric actuator. (A), (b) is a side view which shows the conventional piezoelectric actuator.

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

(Configuration of piezoelectric actuator)
FIGS. 1A to 1C are a side sectional view, a plan sectional view, and a plan sectional view showing the piezoelectric actuator 100, respectively. The piezoelectric actuator 100 is a stacked piezoelectric actuator 100 that is connected in series along the stacking direction. In series connection, it is mainly connected in the direction of expansion and contraction. The connected piezoelectric actuator 200 formed by connecting the piezoelectric actuator 100 will be described later.

  The piezoelectric actuator 100 includes an active layer 110 and a protective layer 120. The active layer 110 is formed by alternately laminating polarized piezoelectric layers 111 and internal electrodes 117, and is deformed by application of a voltage. Among the internal electrodes 117, the internal electrode 117b near the protective layer 120 has a hole 118 in the center, and the internal electrode 117a near the center away from the protective layer 120 is uniformly formed and has no hole. The protective layers 120 are provided at both ends of the active layer 110 in the stacking direction, and are formed of unpolarized piezoelectric layers 121.

  As described above, in the piezoelectric actuator 100, the internal electrode 117b in the vicinity of the protective layer 120 has the hole 118 in the center, and both end surfaces 130 of the internal electrode 117 are evenly flat when displaced when a voltage is applied. When the piezoelectric actuator 100 is about to be displaced like a drum by driving, the deformation of the end face 130 can be flattened, and the adhesive surface 210 between the piezoelectric actuators 100 can be displaced while being kept parallel to alleviate the tensile stress. In this way, the tensile stress generated by the bonding surface 210 connecting the piezoelectric actuator 100 can be relaxed.

  The hole 118 of the internal electrode 117b is preferably circular. Thereby, it is possible to avoid stress concentration in a part of the hole of the internal electrode 117b. Further, even-numbered squares close to a circle such as hexagons and octagons are also preferable. In addition, although stress relaxation can be expected even with a square hole, the stress is concentrated at the corners, so the circular hole is superior in stress relaxation. However, even with a square shape such as a square, significant stress relaxation can be expected if the shape is similar to the cross-sectional outer shape of the internal electrode 117b in a cross section perpendicular to the stacking direction.

  A plurality of internal electrodes 117b having holes 118 are preferably provided. In particular, it is preferable that the internal electrode 117b from the internal electrode 117b closest to the protective layer 120 to the number of layers larger than 1 and smaller than 1/10 of the total number has a hole 118 in the center. Thus, by having the holes 118 up to the internal electrodes 117b up to the number of layers greater than 1, the effect of relaxing the tensile stress can be maintained. Further, by having the holes 118 up to the internal electrode 117b that is 1/10 or less of the total number, the stress can be relieved without impairing the original drivability of the piezoelectric actuator 100.

  The hole 118 of the internal electrode 117b is preferably larger than 1/3 of the size of the internal electrode 117b and smaller than the size of the internal electrode 117b. If the size of the hole 118 is about the length of one side of the internal electrode, the generated force can be greatly reduced. Moreover, if the length of the hole 118 is set to 1/3 or less of the length of one side, the effect of stress relaxation becomes thin. By making the hole 118 larger than 1/3 of the size of the internal electrode 117b and smaller than the size of the internal electrode 117b, the tensile stress can be sufficiently relaxed while maintaining the drive of expansion and contraction of the piezoelectric actuator 100.

  The size of the internal electrode 117b indicates the length of one side when the external shape of the internal electrode 117b is rectangular, and the length of the diameter when the external shape is circular. The size of the hole 118 indicates the length of one side when the shape of the hole 118 is rectangular, and indicates the length of the diameter when the shape of the hole 118 is a circle. In particular, when the external shape of the internal electrode 117b is a square and the hole 118 is a circle, the diameter of the hole 118 is preferably about ½ of the length of one side of the external shape of the internal electrode 117b.

  For example, when the cross-sectional shape of the piezoelectric actuator 100 is 6 mm long × 6 mm wide, the diameter of the hole 118 can be set to 3.0 mm. If the hole has a diameter of about 3.0 mm, it can be easily produced by screen printing, and a sufficient displacement can be expected.

  Further, the piezoelectric actuator 100 is formed from the protective layer 120 side so that the hole 118 is directed toward the center of the active layer 110, for example, the size of the first layer> the size of the second layer> the size of the third layer. You can make it smaller in steps as you go to the center. That is, the hole 118 of the internal electrode 117b is larger as it is closer to the protective layer 120. With such a configuration, the stress relaxation amount can be designed to change stepwise with respect to the expansion / contraction direction. As a result, a rapid stress change can be prevented and the fracture probability can be reduced.

(Method for manufacturing piezoelectric actuator)
First, a green sheet of piezoelectric ceramic is prepared. And electrode paste, such as Ag and Ag / Pd, is screen-printed. At that time, printing is performed while avoiding the shape of a hole such as a circle using a screen with an adjusted shape. And the obtained sheet | seat is laminated | stacked according to design, crimped | bonded, and baked. Furthermore, the piezoelectric actuator 100 can be obtained by forming an external electrode connected to the internal electrode and performing polarization treatment.

(Operation of piezoelectric actuator)
2A and 2B are side views showing the voltage unapplied state and the voltage applied state of the piezoelectric actuator 100, respectively. As shown in FIG. 2A, the piezoelectric actuator 100 is rectangular when no voltage is applied. When a voltage is applied to the piezoelectric actuator 100, the piezoelectric actuator 100 expands and contracts. As shown in FIG. 2B, when the piezoelectric actuator 100 is displaced so as to extend in the stacking direction, the internal electrode 117b in the vicinity of the protective layer 120 has a hole 118. Get smaller. Therefore, the piezoelectric actuator 100 is reduced in width and length and deformed in a drum shape, but its end face 130 is maintained flat.

(Connected piezoelectric actuator)
FIG. 3 is a side view showing the coupled piezoelectric actuator 200. The connection type piezoelectric actuator 200 is formed by connecting a plurality of piezoelectric actuators 100 in series by bonding end faces 130 in the stacking direction. Thereby, the coupled piezoelectric actuator 200 can relieve the tensile stress generated at the interface between the protective layer 120 and the active layer 110 of each piezoelectric actuator 100. As a result, the defective product rate can be reduced. Such a coupled piezoelectric actuator 200 is used for a positioner or the like.

(Contrast)
A comparison of the tensile stress between the coupled piezoelectric actuator 200 configured as described above and the conventional coupled actuator 600 will be described. 4A and 4B are schematic views showing a conventional piezoelectric actuator 500 and the piezoelectric actuator 100 of the present invention, respectively. As shown in FIG. 4A, if the individual piezoelectric actuators 500 constituting the conventional coupled piezoelectric actuator 600 are not bonded, they are greatly deformed into a drum shape. Therefore, when these are bonded and connected at the end surfaces, a large tensile stress is generated due to deformation of expansion and contraction.

  On the other hand, as shown in FIG. 4 (b), even if the individual piezoelectric actuators 100 constituting the coupled piezoelectric actuator 200 are not bonded, the deformation is limited, and particularly, both end surfaces are kept flat. Is done. Therefore, even when these are bonded and connected at the end surfaces, the tensile stress generated by the deformation of expansion and contraction is small. As described above, the piezoelectric actuator 100 according to the present invention can relieve the tensile stress due to the displacement because the both end surfaces are flat when deformed, as compared with the conventional piezoelectric actuator 500 in which the internal electrodes near the protective layer are formed on the entire surface.

(simulation)
Further, an FEM analysis was performed on the coupled piezoelectric actuator 200 in which the two piezoelectric actuators 100 were coupled in the stacking direction. A circular hole 118 having a diameter of 3.0 mm was formed in the three layers of internal electrodes 117b in the vicinity of the protective layer 120, and the tensile stress at the interface between the protective layer 120 and the active layer 110 was calculated during displacement. In addition, as a conventional structure, FEM analysis was also performed on a coupled piezoelectric actuator 600 in which two piezoelectric actuators 500 having the same dimensions and no internal electrode having circular holes were coupled in the stacking direction. As a result, it was confirmed that the stress generated in the coupled piezoelectric actuator 200 was relaxed to 2/3 of the stress generated in the conventional structure. It can be said that it is effective in reducing the destruction probability of the piezoelectric actuator.

DESCRIPTION OF SYMBOLS 100 Piezoelectric actuator 110 Active layer 111 Piezoelectric layer 117 Internal electrode 117a Internal electrode 117b Internal electrode 118 Hole 120 Protective layer 121 Piezoelectric layer 130 End surface 200 Connection type piezoelectric actuator 210 Adhesive surface

Claims (4)

An active layer formed by alternately laminating polarized piezoelectric layers and internal electrodes, and a protective layer provided at both ends in the laminating direction of the active layer and formed by an unpolarized piezoelectric layer, and Among the internal electrodes, a laminated piezoelectric actuator in which internal electrodes ranging from the internal electrode closest to the protective layer to the number of layers larger than 1 and smaller than 1/10 of the total number of internal electrodes (greater than 10) have a hole in the center. Are connected in series along the stacking direction by adhering the end faces of the piezoelectric actuators to each other.   The connected piezoelectric actuator according to claim 1, wherein the hole of the internal electrode is circular.   3. The coupled piezoelectric actuator according to claim 1, wherein the hole of the internal electrode is larger than 1/3 of the size of the internal electrode and smaller than the size of the internal electrode.   The connected piezoelectric actuator according to claim 1, wherein the hole of the internal electrode is larger as the internal electrode is closer to the protective layer.

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