JP3067271B2 - Stacked piezoelectric body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated piezoelectric element (piezo stack) used as an actuator for positioning a hydraulic valve, a cutting tool or a stage of a machine tool, or vibration grinding.

[0002]

2. Description of the Related Art In order to operate a laminated piezoelectric element, it is necessary to connect a lead wire to electrodes formed on both front and back surfaces of a large number of piezoelectric elements constituting the piezoelectric element to apply a voltage. As a first prior art, a large number of piezoelectric elements each formed by printing silver paste or the like on the front and back surfaces of a single piezoelectric element to form an electrode are laminated, and a thin metal plate is sandwiched between the joints of the individual piezoelectric elements to form a metal. A part of the plate is put out on the outer peripheral side surface of each piezoelectric element in the form of an ear piece, and these ear pieces are spotted on a band-shaped side electrode made of a thin metal plate common to the same polarity. There has been a method of bridging with each other by joining by welding or the like, and further connecting lead wires to their side electrodes by soldering and drawing them out.

In Japanese Patent Application Laid-Open No. 59-204288, an electrode is formed by printing a silver paste on the surface of each piezoelectric element except for the outer peripheral portion, and a part of the electrode is extended to the outer peripheral portion. The first side surface electrode is provided on a part of the side surface of the piezoelectric element unit by extension, and the second side surface electrode as an extension of the electrode formed on the back surface of each piezoelectric element unit is similarly set to 180 ° of the first side surface electrode. A laminated piezoelectric body is provided on a part of the outer peripheral side surface on the opposite side, and the required number of piezoelectric elements alone are laminated, and the first side electrode and the second side electrode are respectively aligned in the axial direction. A second prior art is described in which the leads are connected to each other by a conductive rubber-like substance (silicon rubber mixed with silver powder).

[0004]

In the first prior art, the connection between the side electrode formed of a thin metal plate and the lead wire should originally be reliably performed by welding, but the lead having a relatively large heat capacity is required. If the wire and the side electrode with a small thickness and small heat capacity are heated at the same time during welding, the side electrode will melt before the surface of the lead wire melts and a hole will be formed, or a lead consisting of many thin wires In the case of wire, strands are frayed, so it is difficult to perform stable welding under certain conditions, there is a risk that the frayed wire may break the insulating tube to be covered later, and the lead wire is welded to the side electrode and joined Since it is difficult to perform the bonding, it is unavoidable to join them by soldering.

[0005] In the case of soldering, only low-strength solder wax serves as a medium to connect the lead wire and the side electrode, and the lead wire and the side electrode are melted and directly connected to each other. However, if the actuator consisting of the laminated piezoelectric material operates at a high temperature and stress is applied to the joint, the strength of the joint decreases over time even at a temperature below the melting point of the solder wax. However, the joint may be broken due to peeling at the joint surface between the side electrode and the solder wax or cracking of the solder wax.

When a stainless steel thin plate is used for the side electrode, it is necessary to use a strong flux for soldering the lead wires. However, the strong flux has conductivity, and It may cause a leak between the electrodes of the product of the laminated piezoelectric material used. Furthermore, the quality of soldering varies greatly depending on the operator and working conditions, and when a solder angle is formed, a short circuit may occur by breaking through the insulating tube, making it difficult to supply a reliable product stably. Also, in terms of man-hours, there is also a problem that the current soldering method requires a large amount of work time and low productivity.

It is also conceivable to caulk the side electrode and connect it to the lead wire. In this case, however, since the side electrode is a thin metal plate (for example, about several tens of μm thick), sufficient caulking strength is obtained. This leads to a problem that the lead wire is easily pulled out. Therefore, when a thick metal plate (for example, 0.2 mm or more) is used for the side electrode, it can be satisfied in terms of caulking strength and can be welded to a lead wire. Since spot welding with a thin metal plate sandwiched between seams of the piezoelectric element itself is also difficult due to a large difference in heat capacity, such measures are also difficult to implement.

[0008] In the second prior art in which connection is made by a conductive rubber-like substance, there are fewer problems than soldering. However, in terms of reliability and the like, welding and caulking with a thick metal plate are still required. Does not reach. Therefore, the present invention makes it possible to reliably and easily connect the side electrodes and the lead wires of the multilayer piezoelectric body by utilizing the advantages of welding or caulking of a metal plate and supplementing the disadvantages without using soldering. , Providing a new connection that is also durable.
It is a solution of the invention.

[0009]

According to the present invention, as a means for solving the above-mentioned problems, a plurality of piezoelectric elements are stacked with respect to electrodes formed on the front and back surfaces of the piezoelectric elements. A part of the side electrode made of a thin conductive metal plate connected to each polarity at a part of the periphery is made of a relatively thick metal terminal and a relatively thick metal terminal. A laminated piezoelectric body is provided, which is sandwiched by a back metal, integrated by welding, and connected by crimping one end of a lead wire to the terminal.

[0010]

The side electrode is made of a thin conductive metal plate, and it is generally difficult to directly weld a lead wire to a part of the side electrode due to a large difference in heat capacity. When welding is performed, the three members can be easily integrated by welding because the terminal and the back metal have the same heat capacity. And since the terminal is made of a relatively thick metal, caulking with a lead wire against this leads to crimping with sufficient strength, and stable electrical connection from the lead wire to the front and back electrodes of the piezoelectric element alone The connection is completed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the embodiment shown in FIGS. 1 and 2, a laminated piezoelectric element 10 is constituted by laminating a plurality of piezoelectric elements 12 alone. Each piezoelectric element unit 12 is made of a sintered body of piezoelectric ceramics, for example, lead zirconate titanate (referred to as PZT) and a small amount of a third component.
It is a thin disk with a thickness of 0.5 mm and a thickness of 0.5 mm. Although not shown in detail because it is a conventionally known material, silver paste is printed on both the front and back surfaces in a circular shape except for the peripheral portion. Thus, an electrode is formed.

When a plurality of piezoelectric elements 12 are stacked,
The electrodes that are to be homopolar are abutted with each other, and a thin interposed metal plate having a size similar to that of the electrodes and having a thickness of several tens of μm is sandwiched between the electrodes. As the material of the thin interposed metal plate, a stainless steel plate, a copper plate, a brass plate, or the like can be used. A part of the interposed metal plate protrudes beyond the periphery of the piezoelectric element unit 12 to the outside in the radial direction, and the protruding end is bent at a right angle to become an ear piece (not shown).

The lugs of the interposed metal plate connected to the same-sex electrodes are aligned in the axial direction, and they are bridged by using the same material (stainless steel plate, copper plate, brass plate, etc.) as the interposed metal plate. ) Band-shaped side electrode 1 of similar thickness
4 are spot welded to each aligned earpiece. The position 16 of the spot weld is indicated by an X in FIG.
Since the lugs of the interposed metal plate and the band-shaped side electrode 14 are of the same material and thickness, their heat capacities are almost the same. It is performed without any trouble, and there is no possibility that one of them will melt first and make a hole during welding. Thus, the side electrode 14
Are formed along the axis on the cylindrical surface of the multilayered piezoelectric body 10, for example, at a position 180 ° away from the partner. Up to such a configuration may be performed in the conventional technology as described above.

In accordance with the features of the present invention, the embodiment shown in FIGS. 1 and 2 employs a special connection structure for lead wires as described below. That is, a terminal 18 made of a thick metal plate and a backing metal 20 of the same material and having the same thickness are prepared, and these terminals are sandwiched with a part of the side electrode 14 therebetween. Are integrated by a method such as spot welding 22. The terminal 18 and the back metal 20 are preferably made of a relatively soft metal such as brass or a cold-rolled steel plate. Terminal 18 and back metal 20
As described above, laser beam welding may be used in addition to spot welding as described above. In any case, the thin side electrode 14 is integrated with them by welding in a state of being sandwiched between the terminal 18 having a sufficient thickness and the back metal 20, so that a hole is formed in the side electrode 14. There is no such thing that welding cannot be done.

Reference numeral 24 denotes a lead wire, the tip of which is peeled off from the insulating coating and crimped to the terminal 18. FIG.
As shown in FIG. 7, the caulking portion 26 of the terminal 18 is opened, and the leading end of the lead wire 24 is held and caulked. The thickness of the terminal 18 is, for example, 0.2 mm or more when the material is brass so as to provide a sufficient caulking strength. Since the tip of the lead wire 24 is held by the caulking portion 26, there is no fear that the element wire of the lead wire 24 is frayed. As described above, the terminal 18 is connected to the back metal 20 by the side electrode 1.
Since the three members are welded integrally with each other, the lead wire 24 is electrically connected to the front or rear electrode of each piezoelectric element unit 12 via the side electrode 14 by this configuration.

In the figure, reference numeral 28 denotes a dummy, and
0 are provided on both end faces. The dummy 28 indicates the backing metal 20 and secures a necessary insulation distance.
It is made of an insulating material such as PZT or alumina. Finally, the whole is covered with a heat-shrinkable insulating tube 30 such as a silicone resin to prevent the stacked piezoelectric elements 12 from collapsing and also to hold down the lead wires 24 to form an integrated laminated piezoelectric element. 10 is completed.

FIGS. 3A and 3B show the main parts of another embodiment of the present invention. In this example, the terminal 18 and the back metal 20 in the embodiment shown in FIGS. 1 and 2 are continuously formed by one sheet metal 32. Portions of the sheet metal 32 corresponding to the terminal 18 and the caulked portion 26 are illustrated as 18 ′ and 26 ′, and a portion corresponding to the back metal 20 is illustrated as 20 ′. In this embodiment, the terminal portion 18 'and the back metal portion 2 formed by bending one sheet metal 32 are used.
Temporary caulking is performed with the side electrode 14 interposed between 0 ′, and then these are integrally fixed by spot welding or the like.

[0018]

According to the present invention, welding and swaging, which are excellent in workability and excellent in reliability, are used in combination, so that the advantages of both can be utilized and the disadvantages thereof can be skillfully compensated. Therefore, the lead wire can be easily and durably connected to the laminated piezoelectric body without soldering, which is problematic, and overcoming the problems of welding and caulking alone. It becomes possible. This connection structure is superior in all respects, such as strength, durability and safety, to the connection structure by soldering, and makes it possible to raise the operating temperature limit of the piezoelectric actuator by 30 ° or more. However, the work time is less than one half, and there is no fear of leakage due to flux or breakage of the insulating tube due to solder angle, so that the number of causes of quality trouble is reduced.

[Brief description of the drawings]

FIG. 1 is a vertical sectional side view showing an embodiment of a laminated piezoelectric body according to the present invention.

FIG. 2 is a front view of the embodiment shown in FIG.

FIGS. 3A and 3B show a main part of another embodiment of the multilayer piezoelectric body according to the present invention, wherein FIG. 3A is a plan view and FIG. 3B is a front view.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Laminated piezoelectric body 12 ... Piezoelectric element unit 14 ... Side electrode 16, 22 ... Spot welding 18 ... Terminal 20 ... Back metal 24 ... Lead wire 26 ... Caulking part 28 ... Dummy 30 ... Insulating tube 32 ... One sheet metal

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tetsushi Hayashi 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Inside Denso Co., Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 41/083

Claims (1)

(57) [Claims] 1. A strip-shaped thin conductive metal plate which is connected to electrodes formed on the front and back surfaces of a plurality of laminated piezoelectric elements by polarity at a part of a peripheral edge of the piezoelectric element. A part of the front and back of the side electrode made of a terminal made of a relatively thick metal and a back metal made of a relatively thick metal as well, and these three members are integrated by welding, with respect to the terminal. Characterized in that they are connected by caulking one end of a lead wire.