JP5717869B2 - Piezoelectric actuator - Google Patents

Description

  The present invention relates to a fuel injection device for an automobile engine, a liquid injection device such as an ink jet, a precision positioning device for an XY table, a valve control for adjusting a gas flow rate, a camera autofocus mechanism, a zoom mechanism, a camera shake correction mechanism, and a hard disk drive head. The present invention relates to a piezoelectric actuator used for position control, optical axis adjustment of optical equipment, focus adjustment, mass flow controller, and the like.

  As the piezoelectric actuator, for example, a columnar laminate in which a plurality of piezoelectric layers and internal electrode layers are laminated, and the internal electrode layers are alternately and electrically attached to the side surfaces of the laminate in the lamination direction. There is known one in which a piezoelectric element including a pair of connected external electrodes is enclosed in a metal container (see, for example, Patent Document 1).

JP 2002-58261 A

  In the above piezoelectric actuator, members such as a base and a case are joined via a welded part by laser welding or resistance welding in a state where a compressive load is applied to the piezoelectric element so that the piezoelectric element is always placed under compressive stress. It is enclosed in a metal container.

  In such an actuator, when tensile stress is repeatedly applied to the weld due to displacement due to driving, the case is deformed around the intersection of the weld and the case (inner upper end of the weld) as seen in cross section, and stress is applied to this part. This tends to concentrate and becomes the starting point of cracks, and there is a problem that the interface between the welded part and the case breaks down due to fatigue.

  The present invention has been devised in view of the above-described problems, and an object of the present invention is to provide a piezoelectric actuator capable of suppressing fatigue fracture of a weld due to tensile stress.

The piezoelectric actuator of the present invention includes a piezoelectric element, a base that contacts one end of the piezoelectric element, and a case that has an inner surface that contacts the other end of the piezoelectric element and accommodates the piezoelectric element therein. A piezoelectric actuator in which the base body and the case are joined via a welded portion, wherein the case includes a tubular portion, a curved portion that is curved outward from one end of the tubular portion, An inner side of the welded portion in contact with the case, wherein the welded portion is provided between the bent portion and the base body and between the curved portion and the base body. The upper end is joined to the curved portion, and the inner surface of the welded portion is located in a region on the extension of the tubular portion .

  According to the piezoelectric actuator of the present invention, the portion where the maximum tensile load is applied to the welded portion is closer to the center of the piezoelectric actuator, so that the tensile load applied to the inner welded portion itself is reduced and is not easily deformed against the tensile stress. Become. Therefore, fatigue failure at the interface between the weld and the case due to continuous driving of the piezoelectric actuator can be suppressed, and the piezoelectric actuator can be driven stably for a long period of time.

It is sectional drawing which shows an example of embodiment about the piezoelectric actuator of this invention. It is a schematic perspective view of the piezoelectric element shown in FIG. It is an enlarged view which shows an example of the principal part of the piezoelectric actuator shown in FIG. It is an enlarged view which shows the other example of the principal part of the piezoelectric actuator shown in FIG. It is an enlarged view which shows the other example of the principal part of the piezoelectric actuator shown in FIG. It is a principal part enlarged view of the conventional piezoelectric actuator.

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

  FIG. 1 is a sectional view showing an example of an embodiment of the piezoelectric actuator of the present invention, FIG. 2 is a schematic perspective view of the piezoelectric element shown in FIG. 1, and FIG. 3 is an enlarged view of a main part of the piezoelectric actuator shown in FIG. is there.

  A piezoelectric actuator 1 shown in FIGS. 1 to 3 includes a piezoelectric element 2, a base 5 that contacts one end of the piezoelectric element 2, and an inner surface that contacts the other end of the piezoelectric element 2. The piezoelectric actuator includes a case 3 to be accommodated, and the base body 5 and the case 3 are joined to each other via the welded portion 4. The case 3 includes a cylindrical portion 302 and one end (lower end) of the cylindrical portion 302. A curved portion 303 that is curved and spreads outward, and a flange portion 301 that extends further outward from the curved portion 303, and the welded portion 4 is formed between the curved portion 303 and the base body 5 between the flange portion 301 and the base body 5. It is provided across.

  As shown in FIG. 2, the piezoelectric element 2 includes, for example, an active portion 25 in which a plurality of piezoelectric layers 21 and internal electrode layers 22 are alternately stacked, and a piezoelectric layer that is stacked at both ends in the stacking direction of the active portions 25. The laminated piezoelectric element includes a laminated body 20 having an inactive portion 26 made of 21 (not including the internal electrode layer 22). Here, the active portion 25 is a portion where the piezoelectric layer 21 extends or contracts in the stacking direction during driving, and the inactive portion 26 is a portion where the piezoelectric layer 21 does not extend or contract in the stacking direction during driving.

  The laminated body 20 constituting the piezoelectric element 2 is formed in a rectangular parallelepiped shape having a length of 4 to 7 mm, a width of 4 to 7 mm, and a height of 20 to 50 mm, for example. In addition, although the laminated body 20 shown in FIG. 2 is a quadrangular prism shape, a hexagonal prism shape, an octagonal prism shape, etc. may be sufficient, for example.

The plurality of piezoelectric layers 21 constituting the laminate 20 are made of piezoelectric ceramics (piezoelectric ceramics) having piezoelectric characteristics, and the piezoelectric ceramics are formed with an average particle diameter of, for example, 1.6 to 2.8 μm. . As the piezoelectric ceramic, for example, a perovskite oxide made of PbZrO ₃ —PbTiO ₃ (lead zirconate titanate) or the like, lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), or the like can be used.

  The internal electrode layer 22 is formed of, for example, silver, silver-palladium alloy, silver-platinum, copper, or the like, and a pair of side surfaces on which the positive electrode and the negative electrode (or ground electrode) are opposed to each other in the stacked body 20. Are alternately derived. With this configuration, a driving voltage is applied to the piezoelectric layer 21 sandwiched between the internal electrode layers 22 adjacent in the stacking direction in the active portion 25.

  The stacked body 20 may include a metal layer that is a layer for relaxing stress and does not function as the internal electrode layer 22.

  Then, external electrodes 23 are respectively attached to a pair of opposing side surfaces of the stacked body 20 in which the positive electrode and the negative electrode (or the ground electrode) of the internal electrode layer 22 are alternately derived, and the internal electrode layer 22 thus derived is derived. It is joined with. The external electrode 23 is a conductor layer made of a sintered body of silver and glass, for example, and is electrically connected to the internal electrode layer 22. As shown in FIG. 1, a lead wire 13 is attached to the external electrode 23 by, for example, solder 15, and a driving voltage is applied via the lead wire 13.

On the other hand, both the positive electrode and the negative electrode (or the ground electrode) of the internal electrode layer 22 reach the other pair of opposing side surfaces of the laminate 20, and a coating layer 24 made of, for example, an oxide is formed on this side surface. Has been. Formation of the covering layer 24 can prevent creeping discharge between the two electrodes that occurs when a high voltage is applied during driving. Examples of the oxide forming the coating layer 24 include a ceramic material, and in particular, can follow the driving deformation (expansion / contraction) of the laminate 2 when the piezoelectric actuator is driven, and the coating layer 24 is peeled off to cause creeping discharge. It is preferable that the material be deformable by stress so that it does not occur. 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, A ceramic material such as Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, at least one selected from x = 0.01 to 0.3), Alternatively, piezoelectric materials such as barium titanate and lead zirconate titanate (PZT) in which the distance between ions in the crystal lattice changes so as to relieve the generated stress can be used. The coating layer 24 is formed, for example, by forming it into an ink form, applying it to the side surface of the laminate 20 by dipping or screen printing, and sintering.

  The piezoelectric actuator 1 shown in FIG. 1 has a base body 5 whose upper surface is in contact with one end of the piezoelectric element 2 and an inner surface in contact with the other end of the piezoelectric element 2. And a case 3 to be housed. As shown in FIG. 3, the case 3 has a flange portion 301 that is joined to the base 5, and the upper surface of the base 5 and the case 3 are joined via the welded portion 4.

  Specifically, the base body (lower lid member) 5 is formed in a disk shape with a metal material such as SUS304 or SUS316L, and the shape is not particularly limited. Yes. The base 5 is formed with two through holes through which the lead pins 17 can be inserted. The lead pins 17 electrically connected to the lead wires 13 are inserted into the through holes to electrically connect the external electrode 23 and the outside. Is conducting. The gap between the through holes is filled with soft glass 6 to fix the lead pins 17 and prevent the outside air from entering.

  On the other hand, the case 3 is formed of a metal material such as SUS304 or SUS316L like the base body 5, and the case body 30 and a disk-shaped lid member provided so as to close the opening on one end side of the case body 30. (Upper lid member) 31.

  The case body 30 constituting the case 3 is formed in a bellows shape by rolling or hydrostatic pressing after a seamless tube is produced in a predetermined shape. The case body 30 has a predetermined spring constant so that it can follow the expansion and contraction of the piezoelectric element 2 (laminated body 20) when a voltage is applied to the piezoelectric element 2, and depends on the thickness, groove shape, and number of grooves. The spring constant is adjusted. The opening on the one end side of the case body 30 is formed in a cylindrical shape, but the opening on the other end side of the case body 30 is formed in a so-called trumpet shape that spreads outward in the radial direction. As described above, the opening on the other end side of the case main body 30 has a trumpet shape, so that the case 3 (the case main body 30) has a flange portion 301 to which the base body 5 is bonded.

  The lid member 31 constituting the case 3 is formed so that the outer diameter is the same as the inner diameter of the case main body 30, and is fitted into the opening on one end side of the case main body 30, and is attached to the inner wall near the opening on the one end side. The outer periphery is welded. A recess is formed in the lid member 31, and the other end of the piezoelectric element 2 is in contact with the recess. Here, the insulating material 32 is provided so as to cover the inner peripheral wall surface of the concave portion, thereby preventing a short circuit or the like between the external electrodes 23.

  The case body 30 and the lid member 31 may be formed separately from each other and welded, or may be integrally formed.

  As shown in FIG. 3, the case 3 (the case main body 30) includes a tubular portion 302, a curved portion 303 that curves from one end of the tubular portion and spreads outward, and a flange that spreads further outward from the curved portion 303. Part 301. And the upper surface of the base | substrate 5 and the case 3 are joined via the welding part 4, and the inner side upper end 41 of the welding part 4 is joined to the curved part 303. FIG. That is, the welded portion 4 is provided from between the flange portion 301 and the base 5 to between the curved portion 303 and the base 5. The outer upper end of the welded portion 4 is joined to the flange portion 301.

  At this time, the flange portion 301 of the case 3 and the base 5 are welded in a state where a compressive load is applied to the piezoelectric element 2, and the piezoelectric element 2 is enclosed in a storage space formed by the case 3 and the base 5 together with an inert gas. Thus, the piezoelectric actuator 1 is obtained.

In the conventional structure in which the inner upper end 41 of the welded portion 4 as shown in FIG. 6 is joined to the flange portion 301 of the case 3 (the welded portion 4 is provided only between the flange portion 301 and the base body 5), the drive When repeated tensile stress is applied to the welded part 4 due to the displacement of the case 3, the case 3 is deformed with the intersection (the inner upper end 41 of the welded part 4) between the welded part 4 and the case 3 as a fulcrum. Further, the stress is easily concentrated, and this portion becomes a starting point of the crack, and there is a possibility that the interface between the welded portion 4 and the case 3 (the flange portion 301) may be fatigued. On the other hand, according to the embodiment of the present invention shown in FIG. 3, the portion to which the maximum tensile load of the welded portion 4 is applied is closer to the center, so that the tensile load itself applied to the inner upper end 41 of the welded portion 4 becomes smaller. It becomes difficult to be deformed against tensile stress. Therefore, fatigue failure at the interface between the weld 4 and the case 3 due to continuous driving of the piezoelectric actuator can be suppressed, and the piezoelectric actuator can be driven stably for a long period of time.

  Here, in the said structure, it is preferable that the welding part 4 is provided over the perimeter of the bending part 303, and the inner side upper end 41 of the welding part 4 is joined over the perimeter of the bending part 303. FIG. The curved portion 303 is provided around the lower side of the case 3, but by being joined over the entire circumference of the curved portion 303, the curved portion 303 is less likely to be deformed with respect to tensile stress on the entire circumference. Since the stress can be reduced at the inner upper end 41 of the welded portion 4, it is possible to prevent fatigue fracture that tears the interface due to local stress concentration.

  Also, as shown in FIG. 3, it is preferable that the inner surface formed from the curved portion 303 of the case 3 through the welded portion 4 to the base 5 has at least two bent portions as viewed in cross section.

  Since there are two bent portions, there are two or more stress concentration locations when the piezoelectric actuator 1 is driven, and fatigue fracture at the interface between the welded portion 4 and the case 3 due to tensile stress can be further suppressed. Therefore, the piezoelectric actuator 1 can be driven stably for a long time. Although depending on the material of the welded portion 4, it is effective that the two bent portions are separated by 0.05 mm or more. As the welded portion 4, an annular member in which at least one of the upper surface and the lower surface is welded to the lower surface of the case 3 or the upper surface of the base 5 can be used. In this case, the inner upper end of the welded portion 4 is the curved portion 303 ( What is necessary is just to adjust the position of an annular member so that it may join to the inner side from the starting point of the curved part 303 by the side of the collar part 301. FIG. In addition, when there is no step on the inner surface of the welded portion 4, there are two bent portions as shown in FIG. 3, but by providing a plurality of steps on the inner surface of the welded portion 4, the bent portion is set to two or more locations. Can do.

  Further, as shown in FIG. 4, it is preferable that a part of the welded portion 4 (the inner upper end 41 in contact with the case 3) is located in a region on the extension of the tubular portion 302. In FIG. 4, an area on the extension of the cylindrical portion 302 is shown as an area c. Thereby, since the tensile load applied to the inner upper end 41 in contact with the case 3 of the welded portion 4 is in the axial direction, such an action is not applied at the inner upper end 41, so that the stress applied to this part is reduced, and this part is reduced. The crack in can be further suppressed.

  Moreover, as shown in FIG. 5, it is preferable that the inner upper end 41 which contacts the case 3 of the welding part 4 inclines inward, and the angle which the welding part 4 and the case 3 make is 0 degree-45 degree | times. In particular, it is preferable that the welded portion 4 has a surface that smoothly contacts the curved portion 303 (the inner upper end 41 that contacts the case of the welded portion 4 has a curved shape that smoothly contacts the curved portion 303). Here, the welded portion 4 has a surface that smoothly touches the curved portion 303 (the inner upper end 41 that touches the case of the welded portion 4 has a curved shape that touches the curved portion 303 smoothly). This means that the angle formed by the part 4 and the case 3 is close to 0 degrees. In other words, it means that the angle formed between the inner wall surface in the vicinity of the inner upper end 41 of the welded portion 4 and the tangent line of the curved portion 303 with which the inner upper end 41 contacts is close to 0 degrees. Thereby, since the tensile stress is dispersed on the inner surface of the welded portion 4 and the stress is not concentrated at the inner upper end 41, cracks can be further suppressed at the inner upper end 41. As will be described later, for example, when resistance welding is performed on the annular welded portion 4 formed on a part of the base body 5, the welded portion 4 has a shape having a surface that smoothly contacts the curved portion 303. The above-described effects can be obtained by welding in such a manner. On the other hand, as will be described later, for example, an annular welding portion 4 made of a material (ring) different from the base 5 is prepared, the upper surface of the ring is welded to the flange portion 301, and the lower surface of the ring is welded to the base 5. In this case, it is preferable that the welded portion 4 has a surface that smoothly contacts the curved portion 303 and the base 5.

  Next, a method for manufacturing the piezoelectric actuator 1 according to the present embodiment will be described.

First, a ceramic green sheet to be the piezoelectric layer 21 is produced. Specifically, a ceramic slurry is prepared by mixing a calcined powder of piezoelectric ceramic, a binder made of an organic polymer such as acrylic or butyral, and a plasticizer. And a ceramic green sheet is produced from this ceramic slurry by using tape forming methods, such as a well-known doctor blade method and a calender roll method. As the piezoelectric ceramic, any material having piezoelectric characteristics may be used. For example, a perovskite oxide made of PbZrO ₃ —PbTiO ₃ may be used. As the plasticizer, dibutyl phthalate (DBP), dioctyl phthalate (DOP), or the like can be used.

  Next, a conductive paste to be the internal electrode layer 22 is produced. Specifically, a conductive paste is prepared by adding and mixing a binder and a plasticizer to a silver-palladium alloy metal powder. This conductive paste is printed on the ceramic green sheet using a screen printing method, and then a plurality of ceramic green sheets on which the conductive paste is printed are stacked, and the conductive paste is formed at both ends in the stacking direction. A multilayer molded body is obtained by laminating a plurality of ceramic green sheets that are not printed. The laminated body 20 is obtained by debinding the laminated molded body at a predetermined temperature and then firing at 900 to 1200 ° C.

  Next, ink such as partially stabilized zirconia, lead zirconate titanate, and the same material as the piezoelectric layer is formed on a pair of side surfaces from which both internal electrode layers 22 (positive electrode and negative electrode) are led out of the side surfaces of the laminate 20. Is printed by screen printing, and then fired at 900 to 1200 ° C. to form the coating layer 24.

  In this ink, oxide powder is dispersed in a solution of a solvent, a dispersant, a plasticizer, and a binder, and then the three-roll roll is passed several times to break up the aggregation of the powder. It is produced by dispersing.

  Next, the external electrode 23 is formed. First, a silver glass-containing conductive paste is prepared by adding a binder to silver particles and glass powder, and printing is performed by screen printing on a pair of opposing side surfaces of the laminate 20 from which the positive electrode or negative electrode of the internal electrode layer 22 is derived. The baking process is performed at a temperature of about 500 to 800 ° C. Thereby, the piezoelectric element 2 is completed.

  Next, the external electrode 23 and the lead wire 13 are soldered. Further, a base body (lower lid member) 5 having a shape as shown in FIG. 1 formed by forming an annular welded portion 4 by cutting and forming a through hole by drilling is prepared. The welded portion 4 is positioned so that the inner upper end 41 of the welded portion 4 is joined to the curved portion 303. Then, lead pins 17 are respectively inserted into the two through holes formed in the base body (lower lid member) 5 and the gap is filled with the soft glass 6 and fixed. Further, one end of the piezoelectric element 2 is fixed to the upper surface of the base body 5. Glue the parts with an adhesive. Then, the lead wire 13 soldered to the external electrode 23 of the piezoelectric element 2 with the solder 15 and the lead pin 17 attached to the substrate 5 are connected by solder.

  Next, a bellows shape is formed on the seamless cylindrical case body 30 made of SUS304 by rolling, and a lid member made of SUS304 (upper lid) is formed so as to close the opening on the other end side (upper end side) of the case body 30. The member 3 is welded by laser welding to produce the case 3. A flange 301 is formed on one end side (lower end side) of the case body 30.

  Next, the case 3 is put on the piezoelectric element 2 bonded to the base 5, the case 3 is pulled with a predetermined load, and the load is applied to the piezoelectric element 2. In this state, the case 3 and the upper surface of the annular welded portion 4 provided on the base 5 are welded by resistance welding, and the piezoelectric element 2 is sealed. At this time, the inner upper end 41 of the welded portion 4 is joined to the curved portion 303. In addition, when using the thing different from a base | substrate as the cyclic | annular welding part 4, the ring used as the cyclic | annular welding part 4 is prepared, the upper surface of this ring is welded to the collar part 301, and the lower surface of a ring is made into a base | substrate. 5 may be welded. In addition, the welded portion 4 is welded while being crushed by welding while applying a load so that a load is applied to the entire annular welded portion 4, but the welded portion 4 has a surface that smoothly contacts the curved portion 303 ( In order for the inner upper end 41 in contact with the case of the welded portion 4 to have a curved shape that smoothly touches the curved portion 303), the welded portion 4 has a degree of bulging of the inner welded portion 4 at this time. The weight adjustment may be performed to such a degree that the surface smoothly contacts the curved portion 303 (the inner upper end 41 that contacts the case of the welded portion 4 has a curved shape that smoothly contacts the curved portion 303).

  Next, a hole for inactive gas injection is drilled at a predetermined position of the case 3, and after evacuating in the vacuum chamber to release oxygen in the case (storage space), nitrogen gas is injected into the vacuum chamber Then, nitrogen purge inside the case (storage space) is performed. Thereafter, the hole for filling the inert gas is welded by laser welding to close the hole.

  Finally, the piezoelectric actuator 1 of the present embodiment is completed by applying a direct current electric field of 0.1 to 3 kV / mm to the lead pin 17 attached to the substrate 5 to polarize the laminate 20. Then, by connecting the lead pin 17 and an external power source and applying a voltage to the piezoelectric layer 21, each piezoelectric layer 21 can be largely displaced by the inverse piezoelectric effect. This makes it possible to function as an automobile fuel injection valve that injects and supplies fuel to the engine, for example.

  The piezoelectric actuator according to the present embodiment includes, for example, a fuel injection device for an automobile engine, a liquid injection device such as an ink jet, a precision positioning device for an optical device, a valve control for adjusting a gas flow rate, a camera autofocus mechanism, a zoom mechanism, and a camera shake. It is used as a correction mechanism, hard disk drive head position control, optical axis adjustment of optical equipment, focus adjustment, mass flow controller, and the like.

  A piezoelectric actuator as an example of the embodiment of the present invention was manufactured as follows.

First, a ceramic slurry is prepared by mixing a calcined powder of a piezoelectric ceramic mainly composed of lead zirconate titanate (PbZrO ₃ —PbTiO ₃ ) having an average particle size of 0.4 μm, a binder, and a plasticizer. A ceramic green sheet to be a piezoelectric layer having a thickness of 150 μm was prepared.

  300 ceramic green sheets obtained by printing a conductive paste serving as an internal electrode on one side of the ceramic green sheet by adding a binder to a silver-palladium alloy (silver 95 mass% -palladium 5 mass%) by a screen printing method. A laminated molded body having a laminated structure was produced.

  Next, after cutting the laminated molded body with a dicing saw machine so as to have a predetermined size, the laminated molded body was dried and fired to produce a laminated body. Firing was carried out at 1000 ° C. for 200 minutes after holding the temperature of 800 ° C. for 90 minutes. The laminate had a rectangular parallelepiped shape, and the size thereof was 5 mm in length, 5 mm in width, and 35 mm in height.

  Next, ink of the same material as the piezoelectric layer is prepared, and printed on the side surface of the laminate from which both electrodes of the internal electrode layer are derived by screen printing so that the thickness of the coating layer is 20 μm, Then, it baked at 1000 degreeC and formed the coating layer on the side surface of a laminated body.

  Next, a silver glass-containing conductive paste is prepared by adding a binder to silver particles and glass powder, and this is printed on the side surface of the laminate by a screen printing method and baked at a temperature of about 500 to 800 ° C. After forming the electrode, the lead wire was connected to the external electrode by soldering.

  In addition, a disk-shaped substrate was made of SUS304. Specifically, an annular welded portion was formed by cutting, and a substrate having the shape shown in FIG. 1 in which through holes were formed at two locations was produced. And the lead pin was attached to the through-hole formed in the base | substrate with soft glass. As the specifications of the welded portion, the upper width a and the lower width b of the welded portion shown in FIG. 3 are as shown in Table 1 described later. Moreover, the thickness of the welded part was 50 μm.

  Next, the laminate was fixed to the upper surface of the base with an adhesive, and the lead wire soldered to the external electrode and the lead pin attached to the base were connected by soldering.

  Next, a disk-shaped upper lid member was made of SUS304. In addition, a case made by welding a case main body and an upper lid member formed by a rolling process to a seamless cylinder made of SUS316L by laser welding to a base body (lower lid member) The case was covered with the piezoelectric element, the case was pulled with a predetermined load, a load was applied to the piezoelectric element, and the contact portion between the case and the welded portion of the base was welded by resistance welding to seal the piezoelectric element. In the case, the outer diameter of the flange part is 14 mm, the boundary between the flange part and the curved part is a position of 11 mm, the outer diameter of the cylindrical part is 10 mm, the inner diameter of the cylindrical part is 9.6 mm, The joining position between the inner upper end and the case was φ10.5 mm.

  Next, a hole for inert gas injection is drilled at a predetermined position of the case, and after evacuating in the vacuum chamber to release oxygen in the case (storage space), nitrogen gas is injected into the vacuum chamber. After purging nitrogen inside the case (storage space), the hole for nitrogen purging is welded by laser welding to close the hole, and the nitrogen purging is completed, and the embodiment of the present invention (sample number 1) is obtained. A piezoelectric actuator was fabricated.

  On the other hand, as another example of the embodiment of the present invention, a sample was prepared in which the inner upper end in contact with the case of the welded portion was located in a region on the extension of the cylindrical portion. Specifically, a base body in which the position of the inner upper end of the welded portion was φ9.8 mm was produced, and the contact portion of each member was resistance-welded and sealed.

  Further, as a comparative example, a sample was prepared in which the position of the inner upper end of the welded portion was φ11.7 mm and was located on the flange portion outside the curved portion. Welding was performed.

  Finally, a 3 kV / mm direct current electric field was applied to the two lead pins of these samples for 15 minutes to perform polarization treatment, thereby producing a piezoelectric actuator.

  When a DC voltage of 170 V was applied to the obtained laminate of piezoelectric actuators, a displacement amount was obtained in the lamination direction in all the piezoelectric actuators.

  Further, these piezoelectric actuators were subjected to a continuous drive test that continued to be driven by a rectangular wave having a voltage of 200 V, a frequency of 10 Hz, and a Duty 50 in an environment of 50 ° C. The results are shown in Table 1.

  From Table 1, the piezoelectric actuators (Sample Nos. 1 and 2) of the examples of the present invention have almost no change in the displacement amount after a continuous drive test of 1 million cycles, and maintain the effective displacement amount necessary as a piezoelectric element. In addition, it was found that there was no detachment of the welded part, and a stable displacement could be obtained even after long-term use.

  On the other hand, the piezoelectric actuator (sample number 3) of the comparative example was stopped after 170,000 cycles. When this sample was confirmed, detachment at the interface of the weld was observed. In addition, cracks were observed in the piezoelectric element due to the contact of the load accompanying the disconnection of the weld.

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric actuator 13 ... Lead wire 15 ... Solder 17 ... Lead pin 2 ... Piezoelectric element 20 ... Laminate 21 ... Piezoelectric layer 22 ... Internal electrode layer 23- .... External electrode 24 ... covering layer 25 ... active part 26 ... inactive part 3 ... case 30 ... case body 31 ... lid member 32 ... insulating material 301 ... ３０２ 302 ··· cylindrical portion 303 ··· curved portion 4 ··· weld portion 41 ··· inner upper end 5 ··· base 6 ··· soft glass

Claims (3)

A piezoelectric element;
A base that contacts one end of the piezoelectric element;
A piezoelectric actuator having an inner surface in contact with the other end of the piezoelectric element, and a case for accommodating the piezoelectric element therein, wherein the base and the case are joined via a welded portion;
The case includes a tubular portion, a curved portion that is curved outward from one end of the tubular portion, and a flange that is further outward from the curved portion,
The welded portion is provided between the flange portion and the base and between the curved portion and the base, and an inner upper end that contacts the case of the welded portion is joined to the curved portion, and the welding A piezoelectric actuator characterized in that an inner surface of the portion is located in a region on an extension of the cylindrical portion .   The piezoelectric actuator according to claim 1, wherein the welded portion is provided over the entire circumference of the curved portion. The piezoelectric actuator according to claim 1 or claim 2, wherein the weld has a surface in contact with smooth and the curved portion.

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