JP2020017703A - Piezoelectric actuator - Google Patents

Abstract

To provide a piezoelectric actuator that further reduces noise during drive.SOLUTION: A piezoelectric actuator of the present disclosure comprises a piezoelectric device 1, and comprises a case that accommodates therein the piezoelectric device 1 and includes a cylinder 21, a lid body 22 arranged to close an opening on one end of the cylinder 21, and a bottom body 23 arranged to close an opening on the other end of the cylinder 21. The lid body 22 is partially inserted into the opening on one end of the cylinder 21 and coupled with the cylinder 21, and when the lid body 22 is viewed in an axial direction of the cylinder 21 from the outside of the case 2, a center of the lid body 22 is fixed offset from a center of the cylinder 21.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a piezoelectric actuator used for a mass flow controller, an XY table precision positioning device, and the like.

  Piezoelectric element, a cylindrical body containing the piezoelectric element therein, a lid body arranged to close one end side opening of the cylindrical body, and a bottom arranged so as to close the other end side opening of the cylindrical body 2. Description of the Related Art A piezoelectric actuator including a case including a body is known (for example, see Patent Document 1).

Japanese Patent No. 2844711

  In a conventional piezoelectric actuator, for example, a lid is inserted into a cylindrical body and welded between the side surface of the lid and the cylindrical body. There is almost no gap between them, and when the lid is viewed from the outside of the case in the axial direction of the cylindrical body, the center of the cylindrical body coincides with the center of the lid, and along the axial direction of the cylindrical body. When viewed from the cross section, the lid had a symmetrical structure.

  When a piezoelectric actuator having such a structure is driven by a rectangular wave, the piezoelectric actuator resonates and generates sound. In addition, resonance occurs in the internal space of the case, and this resonance sound leaks to the outside and is annoying. there were.

  The use of a piezoelectric actuator in a quiet environment is increasing, and there is an increasing demand for an improvement in reducing noise when the piezoelectric actuator is driven.

  The present disclosure has been made in view of the above circumstances, and has as its object to provide a piezoelectric actuator in which noise during driving is reduced.

  A piezoelectric actuator according to an embodiment of the present disclosure includes a piezoelectric element, a cylinder housing the piezoelectric element therein, a lid disposed to close an opening on one end of the cylinder, and an opening on the other end of the cylinder. And a case including a bottom body arranged to close the portion, wherein the lid is partially inserted into the one end side opening of the cylinder and joined to the cylinder, and the lid is When the lid is viewed from the outside in the axial direction of the cylinder, the center of the lid is fixed to be shifted from the center of the cylinder.

  According to the piezoelectric actuator of the present disclosure, noise during driving can be reduced.

FIG. 2 is a schematic longitudinal sectional view illustrating an example of a piezoelectric actuator. FIG. 9 is a schematic vertical sectional view showing another example of the piezoelectric actuator. FIG. 9 is a schematic vertical sectional view showing another example of the piezoelectric actuator. FIG. 9 is a schematic vertical sectional view showing another example of the piezoelectric actuator. FIG. 9 is a schematic vertical sectional view showing another example of the piezoelectric actuator.

  Hereinafter, embodiments of a piezoelectric actuator will be described in detail with reference to the accompanying drawings. The present invention is not limited by the embodiments described below.

  A piezoelectric actuator 10 shown in FIG. 1 includes a piezoelectric element 1 and a cylindrical body 21 containing the piezoelectric element 1 therein, and a lid 22 arranged to close an opening on one end side of the cylindrical body 21. , And a case including a bottom body 23 arranged to close the other end side opening of the cylindrical body 21.

  The piezoelectric element 1 constituting the piezoelectric actuator 10 includes, for example, an active portion in which a plurality of piezoelectric layers 11 and internal electrode layers 12 are alternately stacked, and the piezoelectric layers 11 stacked on both ends of the active portion in the stacking direction. This is a stacked piezoelectric element including a stacked body 13 having an inactive portion. Here, the active portion is a portion where the piezoelectric layer expands or contracts in the stacking direction when driven, and the inactive portion is a portion where the piezoelectric layer 11 does not expand or contract in the stacking direction when driven. . The piezoelectric element 1 is housed inside a case 2.

  The laminated body 13 forming the piezoelectric element 1 is formed in a rectangular parallelepiped shape having a length of about 4 mm to 7 mm, a width of 4 mm to 7 mm, and a height of about 20 mm to 50 mm. Note that the laminate 13 may have a hexagonal prism shape, an octagonal prism shape, or the like.

The piezoelectric layer 11 constituting the laminate 13 is made of piezoelectric ceramics having piezoelectric characteristics, and the piezoelectric ceramics have an average particle size of, for example, 1.6 μm to 2.8 μm. As the piezoelectric ceramics, for example, perovskite-type oxide made of lead zirconate titanate _{(PbZrO 3} -PbTiO 3), lithium niobate (LiNbO _3), lithium tantalate (LiTaO ₃₎ or the like can be used.

  The internal electrode layer 12 constituting the laminate 13 is mainly composed of a metal such as silver, silver-palladium, silver-platinum, or copper. For example, a positive electrode and a negative electrode (or a ground electrode) are alternately arranged in the laminating direction. The positive electrode is drawn out on one side of the laminate 13, and the negative electrode (or ground electrode) is drawn out on the other side. With this configuration, it is possible to apply a drive voltage to the piezoelectric layer 11 sandwiched between the internal electrode layers 12 adjacent in the stacking direction in the active portion. Note that the laminate 13 may include a metal layer or the like which is a layer for relaxing stress and does not function as an internal electrode layer.

  External electrodes 14 are provided on a pair of opposing side surfaces of the stacked body 13 from which the positive electrode or the negative electrode of the internal electrode layer 12 is drawn out, respectively, and are electrically connected to the drawn out internal electrode layer 12. The external electrode 14 is a metallized layer made of, for example, a sintered body of silver and glass.

On the other hand, on the other pair of opposite side surfaces of the laminate 13, for example, both the positive electrode and the negative electrode (or the ground electrode) of the internal electrode layer 12 are exposed. Is provided. By providing the coating layer, it is possible to prevent creeping discharge between the two electrodes that occurs when a high voltage is applied during driving. The insulator serving as the coating layer is, for example, a ceramic material. In particular, the insulator can follow the drive deformation (expansion and contraction) of the laminate 13 when the piezoelectric actuator 10 is driven, and the coating layer 15 is peeled off to generate creeping discharge. A material that can be deformed by stress can be used without fear. Specifically, stress occurs when locally phase transformation to volume change to deformable partially stabilized _{zirconia, Ln 1-X Si X AlO} 3 + 0.5X (Ln is, Sn, Y, La, Ce, Pr, Nd, Pm, Sm, Eu
, Gd, Tb, Dy, Ho, Er, Tm, and Yb. x = 0.01 to 0.3), or a piezoelectric material such as barium titanate and lead zirconate titanate in which the distance between ions in the crystal lattice changes to relieve the generated stress. Can be

  The case 2 constituting the piezoelectric actuator 10 is disposed so as to close the cylindrical body 21, the lid 22 arranged to close one end side opening of the cylindrical body 21, and the other end side opening of the cylindrical body 21. A bottom body 23 is included. The upper surface of the piezoelectric element 1 is in contact with the lower surface of the lid 22, and the lower surface of the piezoelectric element 1 is in contact with the upper surface of the bottom 23.

  The cylinder 21, the lid 22, and the bottom 23 are made of a metal such as SUS304 or SUS316L.

  The cylindrical body 21 is, for example, formed into a cylindrical shape having a plurality of grooves (dents) by rolling or isostatic pressing after producing a seamless tube in a predetermined shape, so-called bellows shape. is there. The cylindrical body 21 has a predetermined spring constant so as to follow the expansion and contraction of the piezoelectric element 1 (laminated body 13), and the spring constant is adjusted by the thickness, the groove shape and the number of grooves. For example, the thickness of the cylindrical body 21 is set to 0.1 mm to 0.5 mm. Here, the cylindrical body 21 shown in the figure is a cylindrical body extending straight from one end side opening (upper side opening) to the other end side opening (lower side opening) except for a plurality of grooves (dents). The other end side opening (lower end side opening) of the body 21 may have a so-called trumpet shape (a shape having a flange portion) spreading radially outward.

  The lid 22 is a plate-shaped body or a crown-shaped body whose outer diameter is slightly shorter than the inner diameter of the opening on one end side of the cylindrical body 21. The lid 22 has a part of the cylindrical body 21 inserted through an opening on one end side, and a side surface (outer periphery) of the cylindrical body 21 welded to an inner wall of the opening on one end side.

  The bottom body 23 has, for example, a disk shape, and is joined to the other end side opening of the cylindrical body 22 by welding or the like. Two through holes through which the lead member 3 can be inserted are formed in the bottom body 23, and the lead member 3 is inserted through this through hole. The gap between the through holes is filled with, for example, soft glass, and the lead member 3 is fixed. The tip of the lead member 3 is connected to the external electrode 14 directly or via a lead wire, so that a drive voltage is applied to the piezoelectric element 1.

  When the lid 22 is partially inserted into the opening on one end side of the cylindrical body 21 and joined to the cylindrical body 21, when the lid 22 is viewed from the outside of the case 2 in the axial direction of the cylindrical body 21. In addition, the center of the lid 22 is fixed to be shifted from the center of the cylindrical body 21. Here, the center of the lid 22 is the center of the outer peripheral shape (circle) when the lid 22 is viewed in the axial direction (when viewed in a plan view) when the lid 22 is disk-shaped. When the body 22 has a polygonal plate shape, it means the center of gravity of the outer peripheral shape when viewed in the axial direction (when viewed in plan). Further, the center of the cylindrical body 21 is defined as the center of the cylindrical body 21 when the cylindrical body 21 is viewed in the axial direction (when viewed in a horizontal cross section) when the inner peripheral shape of the cylindrical body 21 is circular. This is the center of the circumferential shape (circle), and when the inner circumferential shape of the cross section of the cylindrical body 21 is a polygonal shape, the inside of the cylindrical body 21 when the cylindrical body 21 is viewed in the axial direction (when viewed in cross section). It means the center of gravity of the peripheral shape (polygonal shape).

With such a configuration, the left-right symmetry of the structure of the piezoelectric actuator 10 is broken. Therefore, another mode resonance appears near the main resonance point, the peak of the main resonance becomes small, and the generated noise can be reduced. Further, since a gap is formed between the cylindrical body 21 and the lid 22, a place having a different length of the internal space of the case 2 is generated (a place having the same distance is divided). Is generated, the peak of the main resonance is reduced, and noise can be reduced.

  The gap between the lid 22 and the cylindrical body 21 is such that when viewed in a section along the axial direction of the cylindrical body 21, the distance w2 of the wider gap is, for example, 1. It is set to 2 to 20 times.

  Here, as shown in FIG. 2, a ridge portion of a portion of the lid 22 that is inserted into the opening on one end side of the cylindrical body 21 may be a tapered portion 221. By providing the tapered portion 221, a part of the vibration wave (sound wave) transmitted through the lid 22 is reflected and scattered, so that the main resonance peak (resonance sound) can be reduced. In addition, since the tapered portion 221 has a portion where the length of the internal space of the case 2 in the axial direction (up and down direction in the drawing) gradually changes, the generation of a plurality of resonance sounds can also reduce the main resonance sound. Is achieved.

  Further, as shown in FIG. 3, the lid 22 is viewed from the outside of the case 2 through a center when the lid 22 is viewed in the axial direction of the cylindrical body 21 and in a cross section along the axial direction of the cylindrical body 21. In this case, the tapered portion 221 is two inclined portions 2211 and 2212 provided at both ends in the direction perpendicular to the axial direction, and the two inclined portions 2211 and 2212 have different inclination angles θ1 and θ2. Is also good. For example, one inclination angle θ1 is 5 to 85 degrees and the other inclination angle θ2 is less than 90 degrees, and the difference (θ2−θ1) between one inclination angle θ1 and the other inclination angle θ2 is positive. It is set in the range of 3 to 20 degrees or minus 3 to 20 degrees.

  Since the inclination angles θ1 and θ2 of the two inclined portions 2211 and 2212 are different, the length of the internal space of the case 2 in the axial direction (up and down direction in the drawing) becomes diversified. , And the main resonance peak (resonance sound) can be reduced.

  Further, as shown in FIG. 4, the cover 22 is viewed from the outside of the case 2 through a center when the cover 22 is viewed in the axial direction of the cylindrical body 21 and in a cross section along the axial direction of the cylindrical body 21. In this case, the tapered portion 221 includes two inclined portions 2211 and 2212 provided at both ends in a direction orthogonal to the axial direction, and the height of the two inclined portions 2211 and 2212 in the direction along the axial direction. The heights h1 and h2 may be different. For example, one height h1 is set to, for example, 0.1 mm to 10 mm, and the other height h2 is set to a range of 1.2 to 20 times the height h1.

  Even when the heights of the two inclined portions 2211 and 2212 along the axial direction are different, the length of the internal space of the case 2 in the axial direction (vertical direction in the drawing) is varied, and the internal space of the case 2 is large. , And the main resonance peak (resonance sound) can be reduced.

  The one end (upper end in the figure) of the cylindrical body 21 is shown to be bent inward at a right angle. May be formed by melting one end of the cylindrical body 21. Further, the configuration is not limited to the configuration in which the corner at one end of the cylindrical body 21 is angular as shown in FIGS. May be carried. Thereby, stress concentration on the corners can be suppressed.

DESCRIPTION OF SYMBOLS 10 Piezoelectric actuator 1 Piezoelectric element 11 Piezoelectric layer 12 Internal electrode layer 13 Stacked body 14 External electrode 2 Case 21 Cylindrical body 22 Cover body 221 Tapered parts 2211, 2122 Inclined part 23 Bottom body 3 Lead member

Claims (4)

A piezoelectric element,
The piezoelectric element is housed inside, a cylindrical body, a lid arranged to close one end side opening of the cylindrical body, and a bottom body arranged to close the other end side opening of the cylindrical body. A part including the lid is partially inserted into the one end side opening of the cylinder and joined to the cylinder, and the lid is attached to the axis of the cylinder from outside the case. A piezoelectric actuator, wherein a center of the lid is fixed to be shifted from a center of the cylindrical body when viewed in a direction.   2. The piezoelectric actuator according to claim 1, wherein a ridge at a portion inserted into the one end side opening of the lid is a tapered portion. 3.   When the lid is viewed from the outside of the case through a center when the lid is viewed in the axial direction of the cylindrical body, and when the lid is viewed in a cross section along the axial direction of the cylindrical body, the tapered portion is 3. The piezoelectric actuator according to claim 2, wherein the two inclined portions are provided at both ends in a direction perpendicular to the axial direction, and the two inclined portions have different inclination angles. When the lid is viewed from the outside of the case through a center when the lid is viewed in the axial direction of the cylindrical body, and when the lid is viewed in a cross section along the axial direction of the cylindrical body, the tapered portion is The two inclined portions provided at both ends in a direction orthogonal to the axial direction, wherein the two inclined portions have different heights in a direction along the axial direction. Piezoelectric actuator.

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