JP6144577B2 - Piezoelectric actuator - Google Patents

Description

  The present invention relates to a piezoelectric actuator used in 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 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 Documents 1 and 2).

  For example, a configuration including a base and a case joined to the base is adopted as a metal container, and the base and the case are joined by laser welding, resistance welding, brazing, or the like. In the above-described piezoelectric actuator, the upper surface of the substrate is in contact with the end of the piezoelectric element in a state where a compressive load is applied to the piezoelectric element so that the piezoelectric element is always placed under compressive stress, and is opposite to the piezoelectric element. The inner surface of the case is in contact with the end on the side.

JP-A-6-334233 JP 2002-58261 A

  Here, when repeated tensile stress is applied due to deformation caused by driving, there is a problem that a stress load is applied to the joint portion and the joint portion may cause fatigue failure.

  The present invention has been devised in view of the above problems, and an object thereof is to obtain a piezoelectric actuator capable of suppressing a stress load applied to a joint portion due to a tensile stress.

The present invention includes a piezoelectric element, a base body whose upper surface is in contact with the lower end portion of the piezoelectric element, and a case in which the piezoelectric element is housed and whose inner surface is in contact with the upper end portion of the piezoelectric element. A piezoelectric actuator in which the base body and the case are joined via joints, wherein the case includes a cylindrical part in which a plurality of circumferential grooves are provided in the axial direction, and a plurality of circumferential grooves A piezoelectric actuator having a deeper groove than the other groove, and the thickness of the cylindrical portion in the deep groove being smaller than the thickness of the cylindrical portion in the other groove It is.

The piezoelectric actuator of the present invention is characterized in that, in the above configuration, the deep groove has a narrowest or wider maximum width than the other groove . Moreover, the piezoelectric actuator of the present invention is characterized in that, in the above configuration, the deep groove and the other groove are curved surfaces having the same radius of curvature in a sectional view.

The piezoelectric actuator of the present invention includes a piezoelectric element, a base whose upper surface is in contact with the lower end portion of the piezoelectric element, the piezoelectric element accommodated therein, and an inner surface in contact with the upper end portion of the piezoelectric element. A piezoelectric actuator in which the base and the case are bonded via a bonding portion, the case including a cylindrical portion in which a plurality of circumferential grooves are provided in the axial direction, together there are deep grooves of depth than the other grooves in the circumferential direction of the grooves, the deep have grooves is characterized in maximum width narrower Ikoto than the other groove.

The piezoelectric actuator of the present invention includes a piezoelectric element, a base whose upper surface is in contact with the lower end portion of the piezoelectric element, the piezoelectric element accommodated therein, and an inner surface in contact with the upper end portion of the piezoelectric element. A piezoelectric actuator in which the base and the case are bonded via a bonding portion, the case including a cylindrical portion in which a plurality of circumferential grooves are provided in the axial direction, Some circumferential grooves have deeper grooves than the other grooves, and these deep grooves are different from the other grooves.
The maximum width is wider, and the deep groove and the other groove are curved surfaces having the same radius of curvature in a sectional view .

The piezoelectric actuator of the present invention is characterized in that, in the above configuration, a plurality of the circumferential grooves are provided at equal intervals in the axial direction .

  According to the piezoelectric actuator of the present invention, the plurality of circumferential grooves have a deeper groove than the other grooves, so that the deeper groove absorbs vibration more at the joint. Such a load can be reduced.

  Therefore, it is possible to improve the life of the joint portion by continuous driving of the piezoelectric actuator, and it is possible to drive the piezoelectric actuator stably for a long time.

FIG. 1A is a schematic sectional view showing an example of an embodiment of a piezoelectric actuator of the present invention, and FIG. 1B is an enlarged cross-sectional view showing a main part of the piezoelectric actuator shown in FIG. FIG. It is a schematic perspective view of the piezoelectric element in the piezoelectric actuator shown in FIG. It is a principal part expanded sectional view which shows the principal part of the other example of embodiment of the piezoelectric actuator of this invention. It is a principal part expanded sectional view which shows the principal part of the other example of embodiment of the piezoelectric actuator of this invention. It is a principal part expanded sectional view which shows the principal part of the other example of embodiment of the piezoelectric actuator of this invention. It is a principal part expanded sectional view which shows the principal part of the other example of embodiment of the piezoelectric actuator of this invention. It is a principal part expanded sectional view which shows the principal part of the other example of embodiment of the piezoelectric actuator of this invention.

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

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

  A piezoelectric actuator 1 shown in FIG. 1 includes a piezoelectric element 2, a base 3 whose upper surface is in contact with the lower end of the piezoelectric element 2, and the piezoelectric element 2 inside. A piezoelectric actuator comprising a case 4 and a base 3 and a case 4 joined via a joint 5, wherein the case 4 is a cylindrical part provided with a plurality of circumferential grooves 40 in the axial direction. 41 and a plurality of circumferential grooves 40 include grooves 401 deeper than the other grooves 402.

  As shown in FIG. 2, the piezoelectric element 2 includes, for example, an active portion 23 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 of the active portion 23 in the stacking direction. The multilayer piezoelectric element includes a multilayer body 25 having an inactive portion 24 composed of 21. Here, the active portion 23 is a portion where the piezoelectric layer 21 extends or contracts in the stacking direction during driving, and the inactive portion 24 is a portion where the piezoelectric layer 21 does not extend or contract in the stacking direction during driving.

The laminated body 25 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 about 20 to 50 mm, for example. In addition, although the laminated body 25 shown in FIG. 2 is a quadrangular prism shape, for example, a hexagonal prism shape, an octagonal prism shape, etc. may be sufficient.

The plurality of piezoelectric layers 21 constituting the laminate 25 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 laminate 25. Are alternately derived. With this configuration, in the active part 23, a driving voltage is applied to the piezoelectric layer 21 sandwiched between the internal electrode layers 22 adjacent in the stacking direction.

  Note that the stacked body 25 may include a layer (for example, a metal layer) that is a layer for relaxing stress and does not function as the internal electrode layer 22.

  Then, external electrodes 26 are respectively attached to a pair of opposing side surfaces of the stacked body 25 in which the positive electrode and the negative electrode (or the ground electrode) of the internal electrode layer 22 are alternately led out, and the internal electrode layer 22 thus led out. It is joined with. The external electrode 26 is a metallized 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, the lead wire 61 is attached to the external electrode 26 with solder 62 (conductive adhesive), and a driving voltage is applied via the lead wire 61 and the solder 62. ing.

On the other hand, the positive electrode and the negative electrode (or the ground electrode) of the internal electrode layer 22 reach the other pair of side surfaces facing the laminated body 25, and a coating layer 27 made of an oxide is formed on the side surfaces. ing. By forming the covering layer 27, it is possible to prevent creeping discharge between both electrodes that occurs when a high voltage is applied during driving. Examples of the oxide forming the coating layer 27 include a ceramic material. In particular, the oxide can form a creeping discharge because the coating layer 27 peels off and can follow the driving deformation (expansion / contraction) of the laminate 25 when the piezoelectric actuator is driven. A material that can be deformed by stress is preferred so as not to cause 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, 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, in which the distance between ions in the crystal lattice changes so as to relieve the generated stress, can be mentioned. The coating layer 27 is formed, for example, by forming it into an ink form, applying it to the side surface of the laminate 25 by dipping or screen printing, and sintering.

  The piezoelectric actuator shown in FIG. 1 includes a base body 3 whose upper surface is in contact with the lower end portion of the piezoelectric element 2 and a case in which the piezoelectric element 2 is housed inside and the inner surface is in contact with the upper end portion of the piezoelectric element 2. 4 is provided.

Specifically, the base body (lower lid member) 3 is made of a metal material such as SUS304 or SUS316L and has a thin peripheral edge in the drawing. The lower end of the piezoelectric element 2 is in contact with the upper surface of the base 3. The base 3 is formed with two through holes through which the lead pins 63 can be inserted. The lead pins 63 electrically connected to the lead wires 61 are inserted into the through holes to electrically connect the external electrode 26 and the external circuit. Is made conductive. The gap between the through holes is filled with soft glass 64 to fix the lead pins 63 and prevent the outside air from entering.

  On the other hand, the case 4 is made of a metal material such as SUS304 or SUS316L, like the base 3, and has a disc-like shape provided so as to close the cylindrical portion 41 and one end side opening of the cylindrical portion 41. And a lid member (upper lid member) 44. The case 4 is bonded to the base 3 via the bonding portion 5, accommodates the piezoelectric element 2 inside, and has an inner surface in contact with the upper end portion of the piezoelectric element 2.

  The case 4 includes a cylindrical portion 41 in which a plurality of circumferential grooves 40 are provided in the axial direction. Among the plurality of circumferential grooves 40, a groove 401 that is deeper than the other grooves 402. There is.

  Specifically, the case 4 of this example includes a cylindrical tubular portion 41 provided with a plurality of circumferential grooves 40, and a curved portion 42 that curves outward from the lower end of the tubular portion 41. And a flange 43 extending outward from the curved portion 42.

  Specifically, the cylindrical portion 41 is a portion extending linearly in the vertical direction including the circumferential groove 40 in the cross section shown in the figure. The case 4 includes a curved portion 42 and a flange portion 43 that are formed integrally with the cylindrical portion 41 so as to be continuous with the lower end of the cylindrical portion 41 (the lower end of the linearly extending portion). The curved portion 42 is a portion that is curved in the cross section shown in the drawing, and the collar portion 43 is a portion that is continuous with the curved portion 42 and that is linearly extended in the horizontal direction in the cross section shown in the drawing, and these are radial directions. It is formed in a so-called trumpet shape that spreads outward.

  The cylindrical portion 41 constituting the case 4 is formed into a bellows shape by rolling, hydrostatic pressing, drawing, or the like after forming a seamless tube with a predetermined shape, thereby forming a plurality of circumferential grooves 40. ing. The cylindrical portion 41 has a predetermined spring constant so that it can follow the expansion and contraction of the piezoelectric element 2 (laminated body 25) when a voltage is applied to the piezoelectric element 2, and has a thickness, groove shape, and number of grooves. The spring constant is adjusted by. In addition, the cylindrical part 41 shown to a figure is curved and formed inside so that an outer diameter and an internal diameter may become small in the part of the groove | channel 40. FIG. Moreover, although the cross section of the cylindrical part 41 between the groove | channel 40 arrange | positioned adjacently and the groove | channel 40 is linear, it may be the curved shape which bulged outside, for example.

  Further, the lid member 44 constituting the case 4 is formed so that the outer diameter is the same as the inner diameter of the cylindrical portion 41, and is fitted into the one end side opening of the cylindrical portion 41, and in the vicinity of the one end side opening. The outer periphery is welded to the inner wall. The lid member 44 has a recess, and the upper end of the piezoelectric element 2 is in contact with the recess. Here, an insulating material 45 is provided so as to cover the inner peripheral wall surface of the recess, so that the pair of external electrodes 26 of the piezoelectric element 1 do not directly touch the inner surface of the lid member 44. Therefore, it is possible to prevent the external electrodes 26 from being short-circuited.

  The tubular portion 41 and the lid member 44 may be formed separately from each other and welded, or may be formed integrally.

  Then, the flange portion 43 of the case 4 and the base body 2 are joined via the joint portion 4 in a state where a compressive load is applied to the piezoelectric element 2, and the piezoelectric element 2 is not in the storage space formed by the case 4 and the base body 3. Enclosed with active gas.

  Here, in the structure in which the joint portion 5 is provided between the flange portion 43 of the case 4 and the base body 3, when repeated tensile stress is applied to the joint portion 5 due to deformation caused by driving, the stress concentrates on the joint portion 5. There exists a possibility that the junction part 5 may carry out fatigue failure.

Therefore, in the piezoelectric actuator of the present invention, the case 4 includes a cylindrical portion 41 in which a plurality of circumferential grooves 40 are provided in the axial direction, and the plurality of circumferential grooves 40 are more than the other grooves 402. There is a deep groove 401.

  Since the groove 401 having a deeper depth than the other grooves 402 is present in the plurality of circumferential grooves 40, the deep groove 401 absorbs vibration more and reduces the load applied to the joint portion 5. Therefore, the life until fatigue fracture of the joint portion 5 is extended, and the durability can be improved.

  When the depth of the other groove 402 is, for example, 0.5 to 1.5 mm, the depth of the deep groove 401 is 1.01 to 1.2 times the depth of the other groove 402. The depth is effective.

  Further, the figure shows an example in which the number of circumferential grooves 40 is four in total, and the number of deep grooves 401 is one and the number of other grooves 402 is three. The number should be less than half the number of other grooves 402. For example, when there are four circumferential grooves 40, it is preferable that there is one deep groove 401, and when there are five circumferential grooves 40, there are one or two deep grooves 401. Preferably there is. Furthermore, there is no particular limitation on the position where the deep groove 401 is provided.

  Here, as shown in FIG. 3, the thickness t <b> 1 of the tubular portion 41 in the deep groove 401 is preferably thinner than the thickness t <b> 2 of the tubular portion 41 in the other groove 402. By reducing the thickness of the cylindrical portion 41 in the deep groove 401, stress is easily applied to the deep groove 401, and the load applied to the joint portion 5 is further reduced. Elongates and becomes more resistant to fatigue failure, improving durability.

  When the thickness t2 of the tubular portion 41 in the other groove 402 is, for example, 0.05 to 0.3 mm, the thickness t1 of the tubular portion 41 in the deep groove 401 is the thickness t2 of the other groove 402. It is effective that the thickness is 0.70 to 0.99 times as large as.

  In the actuator of the present invention, as shown in FIG. 4, it is preferable that a plurality of circumferential grooves 40 are provided at equal intervals in the axial direction. In other words, it is preferable that the circumferential grooves 40 are provided at the same pitch in the axial direction. By making the interval L0 between the circumferential grooves 40 equal, there is no bias in the stress applied to each groove 40 due to the deviation in the interval. Stress is applied. Accordingly, the life of the joint portion 5 is extended, and fatigue resistance is further reduced, and durability is improved. The drawing shows that the intervals between the grooves 40 and the grooves 40 are all the same interval L0.

  Further, as shown in FIG. 5, it is preferable that the deep groove 401 has a narrower maximum width than the other grooves 402. Here, the maximum width is generally the width at the opening (the outermost portion of the groove 401 and the groove 402) when viewed in a cross section. Since the maximum width L1 of the deep groove 401 is narrower than the maximum width L2 of the other grooves 402, stress is easily applied to the deep groove 401, and the load applied to the joint portion 5 is further reduced. The service life is extended and the durability is improved due to the difficulty of fatigue destruction.

  In order to obtain this effect, when the maximum width L2 of the other groove 402 is 1 to 5 mm, for example, the maximum width L1 of the deep groove 401 is 0.7 to the maximum width of the other groove 402. It is effective that the ratio is 0.9 times.

On the other hand, as shown in FIG. 6, the deep groove 401 may be wider than the other grooves 402. Since the maximum width L1 of the deep groove 401 is wider than the maximum width L2 of the other grooves 402, the deep groove 401
It is possible to suppress the local stress concentration in the layer and to improve the durability.

  In order to obtain this effect, when the maximum width L2 of the other groove 402 is, for example, 1 to 5 mm, the maximum width L1 of the deep groove 401 is 1.1 of the maximum width L2 of the other groove 402. It is effective to be -1.4 times.

  In this case, it is preferable that the deep groove 401 and the other groove 402 have curved surfaces having the same radius of curvature in a cross-sectional view, and the stress distribution in the deep groove 401 can be inclined to further suppress local stress concentration. Further, durability can be improved.

  Here, as a method of measuring the radius of curvature, measurement is performed by measuring curvature from an image using a projector, or by obtaining data using a three-dimensional measuring instrument and then analyzing coordinate data. Can do. Moreover, the method of cut | disconnecting a case and measuring from a cross section may be sufficient, and it does not limit about the measuring method.

  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. After debinding the laminated molded body at a predetermined temperature, the laminated body 25 is obtained by firing at 900 to 1200 ° C.

Next, an ink made of an oxide such as a perovskite oxide made of PbZrO ₃ —PbTiO ₃ is formed on a pair of side faces from which both internal electrode layers 22 (positive electrode and negative electrode) are led out of the side faces of the laminate 25. Is printed by screen printing and then fired at 900 to 1200 ° C. to form the coating layer 27.

  The oxide ink disperses the powder of the oxide in a solution of a solvent, a dispersant, a plasticizer, and a binder, and then pulverizes the powder by passing three rolls several times. It is produced by dispersing powder.

  Next, the external electrode 26 made of a metallized layer 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 25 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 external electrode 26 made of a metallized layer is formed, and the piezoelectric element 2 is completed.

Next, the external electrode 26 and the lead wire 13 are soldered. Further, a base body (lower lid member) 7 having a shape as shown in FIG. 1 formed by forming an annular portion by cutting and forming a through hole by drilling is prepared. The lead pin 17 is inserted into each of the two through holes formed in the member 7, the gap is filled with the soft glass 9 and fixed, and the lower end of the piezoelectric element 2 is bonded to the upper surface of the base 7 with an adhesive. Then, the lead wire 61 soldered to the external electrode 21 of the piezoelectric element 2 with the solder 15 and the lead pin 63 attached to the base 3 are connected by solder.

  Next, a plurality of circumferential grooves 40 having a bellows shape are formed on the seamless cylindrical tubular portion 41 made of SUS316L by rolling. Here, the deep groove 401 and other grooves 402 can be formed by changing the amount of pressing when drawing. Moreover, the cylindrical part 41 from which the maximum width of the groove | channel 40 differs can be produced by changing the diameter of a pressing jig, whenever the groove | channel 40 of the circumferential direction is shape | molded. In addition, a deep groove can also be produced by pressing, and the position of the deep groove can be changed by changing the mold used for the pressing.

  A case 4 is produced by welding a lid member (upper lid member) 44 made of SUS304 by laser welding so as to close an opening on one end side (upper end side) of the cylindrical portion 41. In addition, the other end side (lower end side) of the cylindrical part 41 is formed with a so-called trumpet-shaped curved part 42 and a flange part 43 that spread outward in the radial direction.

  Next, the case 4 is placed on the piezoelectric element 2 bonded to the base 3, the case 4 is pulled with a predetermined load, and a load is applied to the piezoelectric element 2. For example, an annular protrusion is provided on the upper surface of the base 3, and the flange 43 of the case 4 and the annular protrusion provided on the base 3 are welded by resistance welding in a state where the load is applied. The element 2 is sealed. In addition, when using a thing different from the base | substrate 3 as a cyclic | annular protrusion, the ring used as a cyclic | annular protrusion is prepared, the upper surface of this ring is welded to the collar part 43, and the lower surface of a ring is welded to the base | substrate 3. do it.

  In addition, as the junction part 5, if it can join firmly not only by welding, it will not specifically limit.

  Next, a hole for injecting inert gas is drilled at a predetermined position of the case 4 and evacuated in a vacuum chamber to release oxygen in the case (storage space), and then 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 63 attached to the substrate 3 to polarize the laminated body 25. Then, by connecting the lead pin 62 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.

  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.

A ceramic green sheet obtained by printing a conductive paste to be an internal electrode layer produced by adding a binder to a silver-palladium alloy (silver 95% by mass-palladium 5% by mass) on one side of the ceramic green sheet by a screen printing method. A laminated molded body was produced in which 260 sheets were laminated and 20 ceramic green sheets without conductive paste were laminated on the top and bottom.

  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 performed at 1000 ° C. for 200 minutes after holding a 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, an ink made of partially stabilized zirconia, piezoelectric material, the same material as the piezoelectric layer, and lead zirconate titanate is prepared, and screen printing is performed so that the coating layer has a thickness of 20 μm. Then, printing was performed on the side surface of the laminate in which both electrodes of the internal electrode layer were exposed, and then baking was performed at 1000 ° C. to form a coating layer on the side surface of the laminate.

  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, a base having the shape shown in FIG. 1 was prepared in which welds were provided by cutting and through holes were formed at two locations. And the lead pin was attached to the through-hole formed in the base | substrate with soft glass. The base was provided with an annular projection having a thickness of 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. Moreover, the cylindrical part which formed the groove | channel of the circumferential direction which is a bellows shape, the curved part, and the collar part was drawn by drawing in the seamless cylinder made from SUS316L. Here, out of the five circumferential grooves, one deep groove having a diameter of 9 mm and a maximum width of 2 mm is formed, and another groove having a diameter of 0.2 mm larger than the deep groove and a maximum width of 2 mm is set to 4 Prepared are a sample of the example using the cylindrical portion (sample 1) and a sample of a comparative example (sample 2) in which five circumferential grooves having only the same diameter as the other grooves of the sample 1 are formed. did.

  Then, the case formed by welding the cylindrical portion and the upper lid member by laser welding is placed on the piezoelectric element bonded to the base body (lower lid member), the case is pulled with a predetermined load, and the load is applied to the piezoelectric element. After the application, the contact portion between the case and the annular protrusion on the base was welded by resistance welding to seal the piezoelectric element.

  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 in the case (storage space), the hole for nitrogen purge was welded by laser welding to close the hole, and the nitrogen purge was completed.

  Finally, a 2.5 kV / mm direct current electric field was applied to the two lead pins of these samples for 10 minutes for polarization treatment, and a piezoelectric actuator was manufactured.

  When a DC voltage of 120 V was applied to the obtained laminate of piezoelectric actuators, displacement amounts were obtained in the lamination direction in all piezoelectric actuators.

Further, these piezoelectric actuators were subjected to a continuous drive test that continued to be driven with a rectangular wave having a voltage of 150 V, a frequency of 80 Hz, and a Duty 50 in an environment of 60 ° C.

  As a result, the piezoelectric actuator (Sample 1) of the embodiment of the present invention has almost no change in displacement after 10 million cycles of continuous driving test, and maintains the effective displacement necessary for the piezoelectric element. It has been found that there is no disconnection of the joint and that a stable displacement can be obtained even after long-term use.

  In contrast, the piezoelectric actuator of the comparative example (Sample 2) stopped after 2.3 million cycles. When this sample was confirmed, fatigue fracture was observed at the joint. Further, cracks were observed in the piezoelectric element due to the contact of the load accompanying the disconnection of the joint.

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric actuator 2 ... Piezoelectric element 21 ... Piezoelectric layer 22 ... Internal electrode layer 23 ... Active part 24 ... Inactive part 25 ... Laminate 26 ... External Electrode 27 ... Coating layer 3 ... Base 4 ... Case 41 ... Cylindrical part 42 ... Curved part 43 ... Bridge 44 ... Lid member 45 ... Insulating material 40. .... Circumferential groove 401 ... Deep groove 402 ... Other groove 5 ... Joint 61 ... Lead wire 62 ... Solder 63 ... Lead pin 64 ... Soft glass

Claims (7)

A piezoelectric element; a base whose upper surface is in contact with a lower end portion of the piezoelectric element; and a case which accommodates the piezoelectric element therein and whose inner surface is in contact with an upper end portion of the piezoelectric element. The case is a piezoelectric actuator joined to a case via a joint, and the case includes a cylindrical portion in which a plurality of circumferential grooves are provided in the axial direction, and the plurality of circumferential grooves include There is a groove deeper than other grooves, and the thickness of the cylindrical part in the deep groove is thinner than the thickness of the cylindrical part in the other groove . The piezoelectric actuator according to claim 1, wherein the deep groove has a maximum width narrower than that of the other groove . The piezoelectric actuator according to claim 1, wherein the deep groove has a maximum width wider than that of the other groove . The piezoelectric actuator according to claim 3 , wherein the deep groove and the other groove are curved surfaces having the same radius of curvature in a cross-sectional view . A piezoelectric element; a base whose upper surface is in contact with a lower end portion of the piezoelectric element; and a case which accommodates the piezoelectric element therein and whose inner surface is in contact with an upper end portion of the piezoelectric element. The case is a piezoelectric actuator joined to a case via a joint, and the case includes a cylindrical portion in which a plurality of circumferential grooves are provided in the axial direction, and the plurality of circumferential grooves include together there are deep grooves of depth than the other grooves, the deep have grooves pressure electrostatic actuator you wherein the narrower maximum width than said other groove. A piezoelectric element; a base whose upper surface is in contact with a lower end portion of the piezoelectric element; and a case which accommodates the piezoelectric element therein and whose inner surface is in contact with an upper end portion of the piezoelectric element. The case is a piezoelectric actuator joined to a case via a joint, and the case includes a cylindrical portion in which a plurality of circumferential grooves are provided in the axial direction, and the plurality of circumferential grooves include There is a deeper groove than the other groove, and the deeper groove has a maximum width wider than the other groove, and the deep groove and the other groove have curved surfaces with the same radius of curvature in a sectional view. and pressure electrostatic actuator characterized by that.   A plurality of circumferential grooves are provided at equal intervals in the axial direction.
The piezoelectric actuator according to claim 6.

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