JP6809845B2 - Piezoelectric actuator - Google Patents

Description

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

A piezoelectric actuator including a piezoelectric element and a metal case having a cylinder and a lid in which the piezoelectric element is housed so as to sandwich the piezoelectric element from above and below is known (see, for example, Patent Documents 1 and 2). This piezoelectric actuator is manufactured, for example, by joining the inner surface near the upper end of the cylinder to the side surface of the lid by laser welding or resistance welding while a compressive load is applied to the piezoelectric element.

Japanese Unexamined Patent Publication No. 2005-124272 Japanese Unexamined Patent Publication No. 2012-174947

In such a piezoelectric actuator, tensile stress is repeatedly applied to the welded portion due to displacement during driving.

Recently, it has been required to further increase the displacement amount of the piezoelectric element, and the load on the welded portion has increased.

Here, when the welded portion of the metal case reaches the resistance limit, cracks occur on the surface of the welded portion. When the crack grows inside the weld, the displacement of the piezoelectric actuator changes. In the worst case, the weld may be damaged.

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 capable of suppressing the growth of cracks in a welded portion and stably obtaining a desired displacement amount for a long period of time.

The piezoelectric actuator of the present disclosure includes a piezoelectric element and a case having a cylinder and a lid in which the piezoelectric element is housed so as to sandwich the piezoelectric element from above and below, and the lid is formed from an opening on one end side of the cylinder. The cylinder body and the lid body are joined by being inserted, and the cylinder body has an inclined portion inclined inward from the outer surface near the upper end to the upper end, and the inclined portion is cut in the vertical direction. when viewed in cross-section, the Ri Mizogaa the outer surface of the inclined portion, characterized that you have bent groove.

According to the piezoelectric actuator of the present disclosure, since there is an inclined portion near the upper end of the tubular body, this portion is easily bent, and the stress applied to the welded portion can be dispersed and reduced. Further, since there is a groove on the outer surface of the inclined portion, the stress applied to the welded portion can be reduced by opening and closing the mouth of the groove. Therefore, it is possible to realize a piezoelectric actuator capable of stably obtaining a desired displacement amount for a long period of time.

It is a schematic perspective view which shows an example of a piezoelectric actuator. It is the schematic sectional drawing of the piezoelectric actuator cut along the line AA shown in FIG. It is a schematic perspective view of the piezoelectric element shown in FIG. It is an enlarged view of an example of region B shown in FIG. It is an enlarged view of another example of region B shown in FIG. It is an enlarged view of another example of region B shown in FIG. It is an enlarged view of another example of region B shown in FIG. It is an enlarged view of another example of region B shown in FIG. It is an enlarged view of another example of region B shown in FIG.

Hereinafter, an example of the piezoelectric actuator of this embodiment will be described with reference to the drawings.

1 is a schematic perspective view showing an example of the piezoelectric actuator, FIG. 2 is a schematic sectional view of the piezoelectric actuator cut along the line AA shown in FIG. 1, FIG. 3 is a schematic perspective view of the piezoelectric element shown in FIG. 2, and FIG. Is an enlarged view of an example of the region B shown in FIG.

The piezoelectric actuator 10 shown in FIGS. 1 to 4 includes a piezoelectric element 1 and a case 2 having a tubular body 21 and a lid 22 that accommodate the piezoelectric element 1 so as to sandwich the piezoelectric element 1 from above and below. The lid 22 is inserted from the opening on one end side, and the tubular body 21 and the lid 22 are joined. The tubular body 21 has an inclined portion 211 inclined inward from the outer surface near the upper end to the upper end, and when the inclined portion 211 is viewed in a vertical cross section, it is on the outer surface of the inclined portion 211. There is a groove 50.

As shown in FIG. 3, the piezoelectric element 1 constituting the piezoelectric actuator 10 is laminated with, for example, an active portion in which a plurality of piezoelectric layer 11 and an internal electrode layer 12 are alternately laminated, and both ends in the stacking direction of the active portion. It is a laminated piezoelectric element provided with a laminated body 13 having an inactive portion composed of the piezoelectric layer 11. Here, the active portion is a portion where the piezoelectric layer 11 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 laminate 13 constituting the piezoelectric element 1 is formed in a rectangular parallelepiped shape having, for example, a length of 4 to 7 mm, a width of 4 to 7 mm, and a height of about 20 to 50 mm. The laminate 13 shown in FIG. 3 has a quadrangular prism shape, but may have, for example, a hexagonal prism shape or an octagonal prism shape.

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 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 are alternately arranged in the stacking direction. A positive electrode is drawn out on one side surface of the laminate 13, and a negative 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 relieving stress and does not function as an internal electrode layer.

An external electrode 14 is provided on each of the pair of facing side surfaces of the laminated body 13 from which the positive electrode or the negative electrode of the internal electrode layer 12 is drawn, and is electrically connected to the drawn 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, both positive and negative electrodes of the internal electrode layer 12 are exposed on the other pair of opposite side surfaces of the laminated body 13, and a coating layer 15 made of an insulator is provided on this side surface, if necessary. .. By providing the coating layer 15, it is possible to prevent creepage discharge between both electrodes that occurs when a high voltage is applied during driving. Examples of the insulator to be the coating layer 15 include a ceramic material, and in particular, it 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 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 when stress is generated and changing in volume. A ceramic material such as Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and at least one selected from Yb. X = 0.01 to 0.3). Alternatively, 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. The coating layer 15 is formed by, for example, forming an ink, applying it to the side surface of the laminate 13 by dipping or screen printing, and sintering it.

Further, the piezoelectric actuator 10 includes a case 2 in which the piezoelectric element 1 is housed so as to sandwich the piezoelectric element 1 from above and below. The case 2 has a tubular body 21 and a lid body 22. More specifically, it includes a base 23, a cylinder 21 having a lower end bonded to the upper surface of the base 23, and a lid 22 joined to the upper end of the cylinder 21. Then, the lower end surface of the piezoelectric element 1 is in contact with the upper surface of the substrate 23, and the upper end surface of the piezoelectric element 1 is in contact with the lower surface of the lid 22.

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

The tubular body 21 has a cylindrical portion extending vertically and a flange portion connected to the lower end of the cylindrical portion. The tubular body 21 is formed into a bellows (bellows) shape by, for example, a seamless pipe having a predetermined shape and then rolling or hydrostatic pressing. The tubular body 21 has a predetermined spring constant so that it can 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, for example, 0.1 to 0.5 mm. The diameter of the tubular body 21 is, for example, 5 to 50 mm.

The tubular portion extending vertically from the tubular body 21 to the one end side opening (upper end side opening) is cylindrical, but the other end side opening (lower end side opening) of the tubular body 21 expands outward in the radial direction. It has a so-called trumpet shape. As described above, the opening on the other end side of the tubular body 21 has a trumpet shape, so that the tubular body 21 has a collar portion.

Further, the outer diameter of the lid 22 is set to be about the same as the inner diameter of the opening on one end side of the tubular body 21. The lid 22 is fitted from one end side opening of the tubular body 21, and its side surface (outer circumference) is joined to the inner wall in the vicinity of the one end side opening of the tubular body 21 by welding. Here, as shown in FIG. 4, the region where the lid 22 and the cylinder 21 are joined is referred to as the welded portion 3. By joining the tubular body 21 to the side surface of the lid 22 by welding, high joining strength can be obtained.

Further, the substrate 23 has a disk shape, and in the example shown in the figure, the peripheral portion is thinner than the other portions. Then, the peripheral edge portion of the substrate 23 and the flange portion of the tubular body 21 are joined by welding, for example, so that a compressive load is applied to the piezoelectric element 1.

The substrate 23 is formed with two through holes through which the lead pins 43 can be inserted, and the lead pins 43 are inserted through the through holes. Then, for example, soft glass 44 is filled in the gap between the through holes, and the lead pin 43 is fixed. Further, a lead wire 41 is connected to the tip of the lead pin 43, and the lead wire 41 is attached to the external electrode 14 with solder 42, and a drive voltage is applied to the piezoelectric element 1 via the lead pin 43 and the lead wire 41. Is to be applied.

Then, as shown in FIG. 4, the tubular body 21 has an inclined portion 211 inclined inward from the outer surface near the upper end to the upper end. Further, when the inclined portion 211 is viewed in a cross section cut in the vertical direction, there is a groove 50 on the outer surface of the inclined portion 211.

Since there is an inclined portion 211 near the upper end of the tubular body 21, this portion is easily bent, and the stress applied to the welded portion can be dispersed and reduced. Further, since the groove 50 is provided on the outer surface of the inclined portion 211, the stress applied to the welded portion 3 can be reduced by opening and closing the mouth of the groove 50. Therefore, it is possible to realize the piezoelectric actuator 10 that can stably obtain a desired displacement amount for a long period of time.

The inclined portion 211 may be pre-processed by chamfering the ridge portion between the upper end and the outer surface near the upper end, and is one of the cylinder 21 by welding the cylinder 21 to the lid 22. The part may be melted. Here, the inclined portion 211 is set to be about the same as or slightly longer than the length of the welded portion 3 from the upper end of the tubular body 21 along the longitudinal direction of the tubular body 21. Further, when the inclined portion 211 is straight when viewed in a cross section obtained by cutting the tubular body 21 in the vertical direction, the inclination angle θ of the inclined portion 211 with respect to the vertical direction of the tubular body 21 is the inclination angle θ of the tubular body 21 at this portion. Considering the balance between deformability and strength, it is set to, for example, 15 ° to 45 °.

Further, the groove 50 has a length (length in the direction along the circumferential direction of the cylinder 21) of, for example, 0.2 to 5 mm, and the length thereof is, for example, 1 to 5 of the length in the circumferential direction of the cylinder 21. %. The maximum width of the opening of the groove 50 (distance in the direction along the longitudinal direction of the tubular body 21) is, for example, 0.05 to 1 mm.

Here, as shown in FIG. 5, when the inclined portion 211 is viewed in a cross section cut in the vertical direction, the inclined portion 211 can be configured to be rounded so as to be convex toward the outside. .. According to this configuration, stress is applied to the groove 50 to facilitate opening and closing, so that a desired displacement amount can be stably obtained for a longer period of time.

Further, as shown in FIG. 6, when the inclined portion 211 is viewed in a cross section cut in the vertical direction, the angle formed by the groove 50 and the outer surface of the inclined portion 211 is within the range of 45 degrees to 135 degrees. Can be. In other words, the direction in the depth direction of the groove 50 (the direction of the line segment connecting the center of the width of the opening and the deepest part) with respect to the tangent T of the inclined portion 211 at the center of the width of the opening of the groove 50. It is located within the range of 45 degrees to 135 degrees. In other words, the direction of the groove 50 in the depth direction is within the range of plus or minus 45 degrees with respect to the perpendicular line P perpendicular to the tangent line T. Within this range, the opening of the groove 50 can be effectively opened and closed, which can contribute to stress relaxation of the welded portion 3.

Further, as shown in FIG. 7, when the inclined portion 211 is viewed in a cross section cut in the vertical direction, the groove 50 can be configured to be curved. The groove 50 is configured to have a certain depth by changing the direction in the middle so that the groove 50 does not approach the boundary between the lid 22 and the cylinder 21, so that the strength around the groove 50 is sufficiently secured. , The opening of the groove 50 can be effectively opened and closed, and the stress of the welded portion 3 can be dispersed. In the figure, the groove 50 is bent downward, but in terms of ensuring sufficient strength around the groove 50, the thickness of the inclined portion 211 is larger than that of the upper side where the thickness of the inclined portion 211 becomes thinner. It should be bent to the lower side where it gets thicker.

Further, as shown in FIG. 8, when the inclined portion 211 is viewed in a cross section cut in the vertical direction, the groove 50 can be configured to be curved in a curved shape. According to this configuration, the opening of the groove 50 can be opened and closed larger than the configuration in which the groove 50 is bent in a straight line while sufficiently ensuring the strength around the groove 50, and the stress of the welded portion can be dispersed. It can contribute further.

Further, in the example shown in FIG. 9, there is a gap between the lid 22 and the cylinder 21 below the welded portion, and there is a groove 51 at the corner on the inner surface side of the cylinder 21 in the vicinity of the welded portion. .. According to this configuration, the stress of the welded portion can be further dispersed.

Next, a method of manufacturing the piezoelectric actuator 10 according to the present embodiment will be described.

First, a ceramic green sheet to be the piezoelectric layer 11 is produced. Specifically, a ceramic slurry is prepared by mixing a calcined powder of piezoelectric ceramics, a binder made of an organic polymer such as acrylic or butyral, and a plasticizer. Then, a ceramic green sheet is produced from this ceramic slurry by using a tape molding method such as a well-known doctor blade method or a calender roll method. As the piezoelectric ceramic, any ceramic having piezoelectric characteristics may be used, and for example, a perovskite-type oxide composed of PbZrO _3- PbTiO ₃ or the like can be used. Further, as the plasticizer, dibutyl phthalate (DBP), dioctyl phthalate (DOP) and the like can be used.

Next, a conductive paste to be the internal electrode layer 12 is produced. Specifically, a conductive paste is prepared by adding and mixing a binder and a plasticizer to a metal powder of a silver-palladium alloy. This conductive paste is printed on the above-mentioned ceramic green sheet by a screen printing method, and then a plurality of ceramic green sheets on which the conductive paste is printed are laminated and conductive pastes are formed on both ends in the lamination direction. A laminated molded body is obtained by laminating a plurality of unprinted ceramic green sheets. The laminated body 13 is obtained by debindering the laminated molded product at a predetermined temperature and then firing it at 900 to 1200 ° C.

Next, if necessary, oxide ink is printed on the pair of side surfaces of the laminated body 13 from which both internal electrode layers (positive electrode and negative electrode) are derived by screen printing, and then fired at 900 to 1200 ° C. , The coating layer 15 is formed. In the oxide ink, the oxide powder is dispersed in a solution of a solvent, a dispersant, a plasticizer, and a binder, and then three rolls are passed several times to crush the agglomeration of the powder. At the same time, it is produced by dispersing the powder.

Next, the external electrode 14 made of the metallized layer is formed. First, a binder is added to silver particles and glass powder to prepare a silver glass-containing conductive paste, and the positive electrode or the negative electrode of the internal electrode layer 12 is printed on a pair of opposite side surfaces of the laminate 13 from which the positive electrode or the negative electrode is derived by a screen printing method. , The baking process is performed at a temperature of about 500 to 800 ° C. As a result, the external electrode 14 made of the metallized layer is formed, and the piezoelectric element 1 is completed.

Next, the external electrode 14 and the lead wire 41 are soldered. Further, a base 23 (lower lid) having a shape as shown in FIG. 2 having through holes formed by hole processing is prepared, and lead pins 43 are inserted into the two through holes formed in the base 23, respectively. At the same time, the gap is filled with soft glass 44 and fixed, and the lower end of the piezoelectric element 1 is adhered to the upper surface of the substrate 23 with an adhesive. Then, the lead wire 41 soldered to the external electrode 14 of the piezoelectric element 1 with solder 42 and the lead pin 43 attached to the substrate 23 are connected by soldering.

Next, for example, a bellows shape is formed on a seamless cylindrical cylinder 21 made of SUS304 by rolling. Here, one end side (upper end side) of the tubular body 21 is open, and a collar portion is formed on the other end side (lower end side). Further, the thickness of the groove and the radius of curvature can be changed by changing the shape of the mold during rolling.

A lid 22 made of SUS304 is fitted into the opening so as to close the opening on one end side (upper end side) of the cylinder 21, and is welded by, for example, laser welding.

Here, in order to configure the tubular body 21 as shown in the figure having an inclined portion 211 inclined inward from the outer surface near the upper end to the upper end, for example, the edge portion of the upper end of the tubular body 21 is chamfered in advance. There is a way to put it. Further, the inclined portion 211 may be formed at the same time as welding by aiming the laser at the vicinity of the edge portion of the upper end of the tubular body 21 from diagonally above the upper end of the tubular body 21.

Then, in order to make the groove 50 in the inclined portion 211, a method of making a slit (cut) with a diamond disc after welding can be mentioned.

Further, when the lid 22 and the cylinder 21 are made of SUS304, a method of welding at a high temperature of about 1100 to 1700 ° C. and then rapidly cooling can also be used. While cooling is usually performed at a cooling rate of 100 to 500 ° C./min, here, the cooling rate from the start of cooling to 100 ° C. is set to 100 to 500 ° C./sec for rapid cooling. The groove 50 can be formed by rapidly cooling from this high temperature state.

Further, the lid 22 and the cylinder 21 may be made of different metal materials and may be rapidly cooled after welding. Since different materials have different coefficients of thermal expansion, the groove 50 can be formed because stress tends to concentrate during cooling in a portion where the two materials are adjacent to each other or mixed with each other.

Next, the tubular body 21 and the lid 22 are placed on the piezoelectric element 1 bonded to the substrate 23, the tubular body 21 is pulled with a predetermined load, and a load is applied to the piezoelectric element 1. In this state, the flange portion of the tubular body 21 and the base 23 are welded by, for example, resistance welding.

Finally, the piezoelectric actuator 10 of the present embodiment is completed by applying a DC electric field of 0.1 to 3 kV / mm to the lead pin 42 attached to the substrate 23 to polarize the laminated body 13.

Then, by connecting the lead pin 43 and the external power source and applying a voltage to the piezoelectric layer 11, each piezoelectric layer 11 can be largely displaced by the inverse piezoelectric effect.

10 ... Piezoelectric actuator 1 ... Piezoelectric element 11 ... Piezoelectric layer 12 ... Internal electrode layer 13 ... Laminated body 14 ... External electrode 15 ... Coating layer 2 ... Case 21 ... Cylinder 211 ... Inclined portion 22 ... Lid 23 ... Base 3 ... Welded portion 41 ... Lead wire 42 ... Solder 43 ... Lead pin 44 ... Soft glass 50, 51 ... Groove

Claims (5)

A piezoelectric element and a case having a cylinder and a lid, which are housed inside so as to sandwich the piezoelectric element from above and below, are provided, and the lid is inserted from an opening on one end side of the cylinder to form the cylinder. The lid body is joined, and the tubular body has an inclined portion inclined inward from the outer surface near the upper end to the upper end, and when the inclined portion is viewed in a cross section cut in the vertical direction, the Mizogaa the outer surface of the inclined portion is, a piezoelectric actuator, characterized that you have bent groove. The piezoelectric actuator according to claim 1, wherein the inclined portion is rounded so as to be convex toward the outside when viewed in a cross section obtained by cutting the inclined portion in the vertical direction. Claim 1 or claim, wherein the angle formed by the groove and the outer surface of the inclined portion is in the range of 45 degrees to 135 degrees when the inclined portion is viewed in a cross section cut in the vertical direction. Item 2
Piezoelectric actuators described in. The piezoelectric actuator according to claim 1, wherein when the inclined portion as seen in cross section cut in the vertical direction, the groove, characterized in that the bent curve. Claims 1 to 1, wherein there is a gap between the lid body and the early cylinder body below the welded portion, and a groove is formed at a corner portion on the inner surface side of the cylinder body in the vicinity of the welded portion. The piezoelectric actuator according to any one of claims 4.

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