JP6983732B2 - Piezoelectric actuator - Google Patents

Description

The present disclosure relates to piezoelectric actuators used in, for example, mass flow controllers, precision positioning devices for XY tables, and the like.

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

Japanese Patent No. 2844711

In the conventional piezoelectric actuator, for example, the lid is inserted into the cylinder and welded between the side surface of the lid and the cylinder, but the cylinder and the lid located around the welded portion 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 cylinder, the center of the cylinder and the center of the lid are aligned and along the axial direction of the cylinder. When the lid was viewed in cross section, it had a symmetrical structure.

When a piezoelectric actuator with such a structure is driven by a square wave, the piezoelectric actuator resonates to generate sound, and at the same time, resonance occurs in the internal space of the case, and this resonance sound leaks to the outside, causing annoyance to the ears. there were.

The use of the piezoelectric actuator in a quiet environment is increasing, and the demand for improvement to reduce the noise when driving the piezoelectric actuator is also increasing.

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

The piezoelectric actuator of the present disclosure includes a piezoelectric element, a cylinder in which the piezoelectric element is housed, a lid arranged so as to close an opening on one end side of the cylinder, and an opening on the other end of the cylinder. A case including a bottom body arranged so as to close the portion is provided, and the lid body is partially inserted into the one end side opening of the cylinder body and joined to the cylinder body to be joined to the cylinder body. When the lid is viewed from the outside in the axial direction of the cylinder, the center of the lid is offset from the center of the cylinder and fixed.

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

It is a schematic vertical sectional view which shows an example of a piezoelectric actuator. It is a schematic vertical sectional view which shows the other example of a piezoelectric actuator. It is a schematic vertical sectional view which shows the other example of a piezoelectric actuator. It is a schematic vertical sectional view which shows the other example of a piezoelectric actuator. It is a schematic vertical sectional view which shows the other example of a piezoelectric actuator.

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

The piezoelectric actuator 10 shown in FIG. 1 includes a piezoelectric element 1, and also has a tubular body 21 containing the piezoelectric element 1 inside, and a lid 22 arranged so as to close an opening on one end side of the tubular body 21. , And a case including a bottom body 23 arranged so as to close the other end side opening of the tubular body 21.

The piezoelectric element 1 constituting the piezoelectric actuator 10 is composed of, for example, an active portion in which a plurality of piezoelectric layers 11 and internal electrode layers 12 are alternately laminated, and a piezoelectric layer 11 laminated at both ends in the stacking direction of the active portions. It is a laminated type piezoelectric element provided with a laminated body 13 having an inactive portion. Here, the active portion is a portion where the piezoelectric layer expands or contracts in the stacking direction during driving, and the inactive portion is a portion where the piezoelectric layer 11 does not expand or contract in the stacking direction during driving. .. The piezoelectric element 1 is housed inside the case 2.

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

The piezoelectric layer 11 constituting the laminated body 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, a perovskite-type oxide made of _{lead zirconate titanate (PbZrO 3-} PbTIO _{3 ), lithium niobate (LiNbO 3} ), lithium tantalate (LiTaO ₃ ) and the like can be used.

Further, the internal electrode layer 12 constituting the laminated body 13 is mainly composed of a metal such as silver, silver-palladium, silver-platinum, or copper. For example, the positive electrode and the negative electrode (or the ground electrode) are alternately arranged in the stacking direction. A positive electrode is drawn out on one side surface of the laminated body 13, and a negative electrode (or a ground electrode) is drawn out on the other side surface. With this configuration, in the active portion, a driving voltage can be applied to the piezoelectric layer 11 sandwiched between the internal electrode layers 12 adjacent to each other in the stacking direction. The laminated body 13 may include a metal layer or the like that is a layer for relaxing stress and does not function as an internal electrode layer.

An external electrode 14 is provided on each of the pair of opposite side surfaces of the laminated body 13 from which the positive electrode or the negative electrode is drawn out of the internal electrode layer 12, and is 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 laminated body 13, for example, both positive and negative electrodes (or ground electrodes) of the internal electrode layer 12 are exposed, and a coating layer made of an insulator is required on these side surfaces. Is provided. By providing the coating layer, it is possible to prevent creeping discharge between both electrodes that occurs when a high voltage is applied during driving. Examples of the insulator serving as the coating layer include ceramic materials, and in particular, the insulating material can follow the drive deformation (expansion and contraction) of the laminated body 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 so as not to be afraid. _{Specifically, partially stabilized zirconia, Ln 1-X} Si _X AlO _{3 + 0.5X} (Ln is Sn, Y, La, Ce, which can be deformed by locally undergoing phase transformation and volume change when stress is generated. Pr, Nd, Pm, Sm, Eu
, Gd, Tb, Dy, Ho, Er, Tm and Yb. Ceramic materials such as x = 0.01 to 0.3) or piezoelectric materials such as barium titanate and lead zirconate titanate in which the distance between ions in the crystal lattice changes so as to relieve the generated stress can be mentioned. Be done.

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

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

The tubular body 21 is formed into a cylindrical shape having a plurality of grooves (dents), a so-called bellows (bellows) shape, for example, by forming a seamless pipe having a predetermined shape and then rolling or hydrostatic pressing. be. The tubular body 21 has a predetermined spring constant so as to be able to follow the expansion and contraction of the piezoelectric element 1 (laminated body 13), and the spring constant is adjusted according to the thickness, the groove shape, and the number of grooves. For example, the thickness of the tubular body 21 is 0.1 mm to 0.5 mm. Here, the tubular body 21 shown in the figure is a cylindrical one that extends straight from one end side opening (upper end side opening) to the other end side opening (lower end 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 (shape having a flange portion) extending outward in the radial direction.

The lid 22 is a plate-shaped body or a coronal body whose outer diameter is slightly shorter than the inner diameter of the one-end side opening of the tubular body 21. A part of the tubular body 21 is inserted from the one end side opening of the lid body 22, and the side surface (outer circumference) thereof is joined to the inner wall of the one end side opening of the tubular body 21 by welding.

The bottom body 23 has, for example, a disk shape, and is joined to the opening on the other end side of the tubular body 22 by welding or the like. The bottom body 23 is formed with two through holes through which the lead member 3 can be inserted, and the lead member 3 is inserted through the through holes. Then, for example, soft glass is filled in the gap of the through hole, and the lead member 3 is fixed. Further, the tip of the lead member 3 is connected to the external electrode 14 directly or via a lead wire, whereby a driving voltage is applied to the piezoelectric element 1.

When the lid 22 is partially inserted into the opening on one end side of the cylinder 21 and joined to the cylinder 21, and the lid 22 is viewed from the outside of the case 2 in the axial direction of the cylinder 21. In addition, the center of the lid 22 is deviated from the center of the cylinder 21 and fixed. 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 plane) when the lid 22 has a disk shape. 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 a plane). Further, the center of the cylinder 21 is the inside of the cylinder 21 when the inner circumference of the cross section of the cylinder 21 is circular and the cylinder 21 is viewed in the axial direction (when viewed in the cross section). It is the center of the circumferential shape (circle), and when the inner peripheral shape of the cross section of the tubular body 21 is a polygonal shape, the inside of the tubular body 21 when the tubular body 21 is viewed in the axial direction (when viewed in the cross section). It means the center of gravity of the circumferential shape (polygonal shape).

With such a configuration, the left-right symmetry of the structure of the piezoelectric actuator 10 is broken. Therefore, another mode of resonance appears near the main resonance point, the peak of the main resonance becomes smaller, and the generated noise can be reduced. Further, since a gap is created between the cylinder 21 and the lid 22 to create a place where the length of the internal space of the case 2 is different (the place of the same distance is divided), a plurality of places are formed in the internal space of the case 2. Resonance occurs, the peak of the main resonance becomes smaller, and the noise can be reduced.

As for the gap between the lid 22 and the cylinder 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, the ridge portion in the portion of the lid body 22 inserted through the one end side opening of the tubular body 21 may be the tapered portion 221. By providing the tapered portion 221, a part of the vibration wave (sound wave) propagating in the lid 22 is reflected and scattered, and the peak of the main resonance (resonance sound) can be reduced. Further, since the tapered portion 221 has a portion in which the length of the internal space of the case 2 in the axial direction (vertical direction in the figure) gradually changes, even if a plurality of resonance sounds are generated, the main resonance sound is generated. Will have the effect of reducing the size.

Further, as shown in FIG. 3, the lid 22 is viewed from the outside of the case 2 through the center when the lid 22 is viewed in the axial direction of the cylinder 21 and in a cross section along the axial direction of the cylinder 21. At that time, the tapered portions 221 are two inclined portions 2211 and 2212 provided at both ends in the direction orthogonal to the axial direction, and the inclined portions θ1 and θ2 of the two inclined portions 2211 and 2212 are different. May be good. For example, one tilt angle θ1 is 5 to 85 degrees, the other tilt angle θ2 is within the range of less than 90 degrees, and the difference (θ2-θ1) between one tilt angle θ1 and the other tilt 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 212 are different, the lengths of the internal space of the case 2 in the axial direction (vertical direction in the figure) are various, so that the internal space of the case 2 is often used. Resonance sound is generated, and the peak of the main resonance (resonance sound) can be made smaller.

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

Even if the heights of the two inclined portions 2211 and 2212 along the axial direction are different, the lengths of the internal space of the case 2 in the axial direction (vertical direction in the figure) are various, and there are many in the internal space of the case 2. Resonance sound is generated, and the peak of the main resonance (resonance sound) can be made smaller.

It should be noted that although one end portion (upper end portion in the figure) of the tubular body 21 is shown to be formed by being bent at a right angle inward, it is not limited to those pre-processed into such a shape and is welded. It may be formed by melting one end of the cylinder 21. Further, the configuration is not limited to the configuration in which the corners of one side end of the cylinder 21 are angular as shown in FIGS. 1 to 4, and the corners of one side end of the cylinder 21 are rounded as shown in FIG. It may be tinged with. As a result, stress concentration on the corners can be suppressed.

10 Piezoelectric actuator 1 Piezoelectric element 11 Piezoelectric layer 12 Internal electrode layer 13 Laminated body 14 External electrode 2 Case 21 Cylindrical body 22 Lid body 221 Tapered part 2211 and 2212 Inclined part 23 Bottom body 3 Lead member

Claims (4)

Piezoelectric element and
A cylinder in which the piezoelectric element is housed, a lid arranged so as to close one end side opening of the cylinder, and a bottom body arranged so as to close the other end side opening of the cylinder. The lid body includes a case, and the lid body is partially inserted into the one end side opening of the cylinder body and joined to the cylinder body, and the lid body is attached to the shaft of the cylinder body from the outside of the case. A piezoelectric actuator characterized in that the center of the lid is deviated from the center of the cylinder and fixed when viewed in a direction. The piezoelectric actuator according to claim 1, wherein the ridge portion of the portion inserted through the one end side opening of the lid body is a tapered portion. When the lid is viewed from the outside of the case through the center when the lid is viewed in the axial direction of the cylinder and in a cross section along the axial direction of the cylinder, the tapered portion is said to be the tapered portion. The piezoelectric actuator according to claim 2, wherein the piezoelectric actuators are provided at both ends in a direction orthogonal to the axial direction, and the inclination angles of the two inclined portions are different. When the lid is viewed from the outside of the case through the center when the lid is viewed in the axial direction of the cylinder and in a cross section along the axial direction of the cylinder, the tapered portion is said to be the tapered portion. The second aspect of claim 2, wherein the two inclined portions are provided at both ends in a direction orthogonal to the axial direction, and the heights of the two inclined portions in the axial direction are different. Piezoelectric actuator.

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