JPS63220782A - Piezoelectric element - Google Patents

Abstract

PURPOSE:To improve efficiency by forming boundary sections with groove- shaped notch sections in the thickness direction so that a piezoelectric element body is partitioned for each specific region. CONSTITUTION:A metal such as silver is applied onto the surface and rear of a ring-shaped piezoelectric body 20 manufactured by molding piezoelectric ceramics to a ring shape and cutting and polishing the piezoelectric ceramics in specified size through a means such as baking, and electrodes 21, 22 are shaped, thus constituting a piezoelectric element body. Partition boundary sections with groove-shaped notch sections 31-40 notched up to the depth of approximately half the thickness direction of a piezoelectric element body are formed to the surface of the piezoelectric element body so as to partition the surface of the element body for each specific region (eight regions of (a)-(d) and (e)-(h), holding a quarter lambda section M and a three quarter lambda section N). Accordingly, since the partition boundary sections with the groove-shaped notch sections 31-40 are shaped between the adjacent electrodes 21, 22, each polarization section 41-42 is easily brought to the state of saturated polarization accurately, thus inhibiting the generation of cracking due to polarization strain.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a piezoelectric element used in an ultrasonic motor.
In particular, it relates to the configuration of the polarization section.

[Conventional technology]

Recently, ultrasonic motors have been attracting attention as a new motor to replace electromagnetic motors. This ultrasonic motor is not only new in principle, but also has the following advantages over conventional electromagnetic motors.

■Does not require a central axis.

■Thin and lightweight.

■There is no exchange of magnetic influence.

■The component structure is simple and highly reliable.

■Low speed and high torque can be obtained without gears.

[Phase] No backlash and high positioning accuracy.

■Starts up and stops quickly.

■The rotor rotates and chucks against the stator.

It can take on three states: floating.

Thus, in order to take advantage of these advantages, research is underway on various applied technologies for cameras and other devices.

Figure 5 is from Applied Physics, Volume 54, No. 6 (1985)
,P. 589-590" is a schematic diagram of a typical conventional rotary ultrasonic motor disclosed in Japanese Patent No. 589-590. In the figure, 1 is a mounting base, 2 is felt, 3 is a piezoelectric element, 4 is a diaphragm made of an elastic metal material, 5 is a slider, 6 is a rotating body, and 7 is a rotating shaft. Note that the piezoelectric element 3 and the diaphragm 4 constitute a stator, and the rotating body 6 and the rotating shaft 7 constitute a rotor. The principle of this ultrasonic motor is that a metal donut-shaped diaphragm 4 is integrated with an annular piezoelectric cord 3.
In this method, a traveling plate wave is excited by the inverse piezoelectric effect, and the rotor is rotated by being suppressed and placed so as to contact the apex of the backward elliptical trajectory of the surface mass point generated by this.

FIG. 6 is a diagram showing the polarization state of the piezoelectric element 3.

For each polarization section, a ring-shaped piezoelectric body is polarized so that the polarization directions are alternately reversed like 10-+-, or a plurality of divided piezoelectric elements are polarized so that the polarization directions are opposite to each other. It can be obtained by arranging it so that In such a polarization arrangement, one set of adjacent polarization directions opposite to each other corresponds to one wavelength λ. And 180
3/4λ and 1/4λ unpolarized parts (shaded parts) are arranged at different positions, respectively, and nλ polarized parts are arranged symmetrically with respect to the center line connecting these parts. However, the polarization direction is continuously arranged so that the polarization direction is alternately opposite in the circumferential direction.

In this polarization arrangement, the left half of the surface that is not in contact with the diaphragm, with unpolarized parts of 3/4λ and 1/4λ length sandwiched between them, is covered with one electrode, and one side of this is covered with the a electrode. Then, cover the surface of the right half that is not in contact with the diaphragm with another electrode,
This is used as the other side common electrode. Then, the electrode on the diaphragm 4 side is electrically connected to the diaphragm 4, and is shared as a ground-side electrode for all piezoelectric elements.

The electrical signal input terminals in the above structure include three terminals Vl, V2. It becomes E. This kind of polarization arrangement.

When driving a structure having an electrode arrangement, the terminal Vl
There is a phase difference of π/2 between -E and terminal V2 and -E, and the inner and outer diameters and thickness of the λ2 ring.

Average elastic constants and densities of piezoelectric ceramics and diaphragms.

What is necessary is to input an electric signal having a natural frequency ω determined by, etc.

FIG. 7 is a partially cutaway side view of the stator.

Now, when the AC voltage is applied between the diaphragm 4 and the electrodes of the two piezoelectric elements 3, a bending vibration wave is excited in the diaphragm 4, but as shown in FIG. A bending vibration wave expressed by the following equation is generated in one of the adjacent polarized parts.

yl −As in (ωt−2yrp/λ)+As
in (ωt+2πp/λ)· (1) Furthermore, in the other polarized portion, a bending vibration wave expressed by the following equation whose phase difference angle is shifted by ψ from the equation (1) is generated.

y2 attack Bs1n (ωt-2π/λ (p+a)+ψ) +Bs1n (ωt+2π/λ(p+a)+ψ)...(2) Here -2π　a/λ　+ψ−ψ1　.

+2π a/λ+ψ廟ψ2, equation (2) becomes y2−Bsln (ωt−2πp/λ+ψ1) +Bs1n (ωt+2πp/λ+ψ2) (3). The bending vibration waves excited in the above two polarized parts are expressed by equation (1) and (
3), that is, y″y1+y2.The condition for only the traveling wave to exist among this composite bending vibration wave is ψ1−mπ(m−0,±2. ±4...).

ψ2-nπ (n-±1.±3.±5...).

ψ1−−2πa/λ+ψ−mπ2 ψ2−+2πa/λ+ψ−nπ Because it is, a-λ(n-m)/4(n≠m)...(4).

ψ−π(n+m)/2 (5). When the conditions of equations (4) and (5) are satisfied, the composite bending vibration wave is y-As in (ωt-2πp/λ)+As in
(ωt+2yrp/λ)+Bs1n 1ωt-2πp/λ+mπ) +Bs1n (ωt+2πp/λ+nπ) = (A0B) s i n (ωt-2πp/λ)+
(A-B) s in (ωt+2πp/λ)...(
6) It becomes. Therefore, in order for only traveling waves to exist, A-B
... (7) is another condition.

Among the conditions for the existence of only traveling waves mentioned above, (
Equations 4) and (5) can almost be realized by adjusting the electrode shape of the piezoelectric cable 3 and the voltage application means. However, it is quite difficult to completely satisfy the condition of formula 7). That is, even if the piezoelectric cord 3 is subjected to polarization treatment so that a polarized portion as shown in FIG. 6 is generated, non-uniformity occurs in the polarized state.

The reason for this is that since the total area of the piezoelectric cord 3 is large, the material before polarization is uneven due to uneven firing of ceramics, etc., and the polarization is alternate polarization and the polarization process is performed twice. There is a difference in the polarization state in the and (-) direction,
etc.

On the other hand, as shown in FIG. 7, the piezoelectric cord 3 is bonded to the diaphragm 4 using an adhesive 8, but it is not easy to uniformly bond the piezoelectric cable 3 over the entire area. Moreover, the piezoelectric element 3 and the diaphragm 4 originally have dimensional variations.

For this reason, it is extremely difficult to completely satisfy the condition of equation (7).

Therefore, there is variation in the flexural vibration waves, and the parts where large vibration waves are generated come into contact with the rotor, but the parts where vibration waves with small amplitude are generated do not come into contact with the rotor. As a result, a difference occurs in the frequency components of each vibration wave, increasing internal friction and reducing the efficiency of the ultrasonic motor.

Conventionally, the following three methods have been considered as means for solving the above drawbacks.

(1) The electrodes provided on one side of the piezoelectric cable 3 are m electrodes corresponding to each polarized portion, and the polarization state of each polarized portion located under each separated electrode portion is alternately changed. The polarization state is set in the opposite direction, and variations in this polarization state and capacitance are reduced.

(2) The polarization directions of all polarized parts are set in the same direction, and the applied electric fields are set in opposite directions for adjacent polarized parts.

(3) A plurality of individually polarized piezoelectric pieces are arranged so that adjacent polarization directions are opposite to each other.

[Problem that the invention seeks to solve]

In order to confirm the improvement effects achieved by each of the first to third means described above, the present inventors conducted an experiment by creating a piezoelectric element with the same dimensions and structure except for the mounting method of the piezoelectric element and lead wire. I tried it. As a result, it was found that each of the first to third means had a certain degree of improvement effect, but at the same time, each of them had problems as described below.

FIG. 8 and FIGS. 9(a) and 9(b) are diagrams showing an experimental example regarding the first means. PZT (zircon lead titanate) piezoelectric ceramics is formed into a ring shape, cut and polished to a specified size to obtain a ring-shaped piezoelectric body 10, and a separation electrode 11 that can obtain a specified vibration frequency is attached to one side of the ring-shaped piezoelectric body 10. A ground side common electrode 12 was provided on the back surface. As shown in FIG. 9(a), adjacent separated electrodes 11a.

Polarization was performed so that the polarization states under 11b were opposite to each other, and a driving experiment was conducted by applying a voltage as shown in FIG. 9(b).

In the first means, a large polarization distortion occurs at the boundary between adjacent poles 11. For this reason, if an attempt is made to achieve a saturated polarization state, cracks may occur at the boundary, resulting in a decrease in yield. Also, when it is in an unsaturated polarized state,
The electro-mechanical conversion coefficient and the quality factor Qm are both deteriorated, and variations in these constants and capacitance between polarized parts become large, making it difficult to satisfy the above-mentioned condition A-B.

FIG. 10 and FIGS. 11(a) and 11(b) are diagrams showing experimental examples regarding the second means. Similarly to the first means, a ring-shaped piezoelectric body 10, a separation electrode 11, and a ground side common electrode 12 were provided. Then, as shown in FIG. 11(a), a separation electrode 11a is formed.

After polarization treatment is performed so that the polarization directions of all the polarized parts under 11b are in the same direction, the connection 13 as shown in FIG. 10 is applied, and as shown in FIG. A driving experiment was conducted by applying voltage in the opposite direction.

In the second means, the variation in the polarization state is smaller than in the first means, but polarization occurs in the direction along the surface during polarization, resulting in bending displacement.

This makes it impossible to efficiently generate lateral displacement of the piezoelectric element. Further, as can be seen from the terminal structure, twice the applied voltage is required, and even if a transformer is used, a large transformer with a high secondary output voltage is required. Therefore, it cannot be installed in a compact device such as a camera.

Further, as can be seen from the above terminal structure, the metal plate (diaphragm) electrically connected to the back electrode 12 of the ring-shaped piezoelectric body 10 made of piezoelectric ceramics does not have a zero potential. Therefore, it is necessary to create a structure that takes into account the influence of stray capacity and the leakage Tti current, and the configuration becomes complicated.Furthermore, even if the back electrode 12 and the metal plate (diaphragm) are insulated, this Forming a uniform insulation state is extremely difficult in terms of processing and assembly, and in the case of alternating current, current flows through the insulation layer.

FIG. 12 is a diagram showing an experimental example regarding the third means. A plurality of divided piezoelectric pieces 14 made of piezoelectric ceramics similar to the first means are individually polarized, arranged so that the directions of polarization are opposite to each other, and bonded to a ring-shaped metal plate 15. A driving experiment was conducted by applying voltage in the same manner as in method 1.

In the third means, since each piezoelectric piece 4 is individually polarized, each polarized portion can be brought into a saturated polarized state without any problem. However, the work of arranging these piezoelectric pieces 14 so that their polarization directions are opposite to each other and bonding them to the ring-shaped metal plate 15 is extremely complicated, and it is difficult to bond all the piezoelectric pieces 14 uniformly. It is extremely difficult to achieve this condition. Furthermore, it is of course true that if the positioning is not performed with high precision, but even if the positioning is performed with high precision, it has been confirmed that it is impossible to obtain a clean vibration mode like the second method etc. . Furthermore, since each piezoelectric piece 14 is individually bonded, each piezoelectric piece 1
Warping occurs due to the difference in thermal expansion coefficient with a period of element length of 1. A new drawback was identified that did not appear in the second method.

Each of the drawbacks of the three means described above is a problem in practice, and unless these are resolved, it will be difficult to put the method into practical use. By the way, the first means among the first to third means is a means that can obtain a piezoelectric element with an ideal structure as long as a saturated polarization state can be achieved even in the polarization state and variations in the polarization state can be eliminated. It is thought that. Moreover, the second. Compared to the third method, it can be said that the possibility of resolving the drawbacks is relatively high.

Therefore, the present invention improves the first means so that the polarization state of each polarized portion can be easily and accurately brought to a saturated polarization state, and the variation in the polarized state of each polarized portion is extremely small. It is an object of the present invention to provide a piezoelectric element that can satisfy the conditions A-B and realize a highly efficient ultrasonic motor.

[Means for solving problems]

The present invention takes the following measures to solve the above-mentioned problems and achieve the objectives. That is, at least a part of the piezoelectric element main body in the thickness direction (that is, a part of the piezoelectric element main body in the thickness direction may be However, a partition boundary portion having a groove-shaped notch is provided in the partition boundary portion, and in each of the regions partitioned by the partition boundary portion, the polarization directions of adjacent regions are opposite to each other. Multiple polarization parts can be installed.

Note that the partition boundary portion may be a groove-shaped notch filled with an insulating material such as epoxy resin or glass.

[Effect]

By combining such means, the following effects are achieved. In other words, a partition boundary having a groove-shaped notch is formed between adjacent electrodes, so that the polarization electric field does not leak during polarization.

As a result, it is possible to easily and accurately bring each polarized portion into a saturated polarization state, and furthermore, it is possible to suppress the occurrence of cracks due to polarization distortion.

〔Example〕

FIG. 1 is a perspective view showing the appearance of a first embodiment of the present invention. 20 in Figure 1 is PZT (zircon lead titanate), which has a large mechanical quality factor Qm with an electromechanical conversion constant of 31.
This is a ring-shaped piezoelectric body made by molding piezoelectric ceramics into a ring shape, cutting and polishing it to specified dimensions. Electrodes 21 and 22 are provided on the front and back surfaces of the ring-shaped piezoelectric body 20 by baking or depositing a metal such as silver using a vapor tube, sputtering, or other means. The ring-shaped piezoelectric body 20 and the electrodes 21 and 22 constitute a piezoelectric element body. The surface of this piezoelectric element body is covered with a specific area (1/4 in this example).
Approximately 1/2 of the thickness direction of the piezoelectric element body is partitioned into 8 areas (a, b, c, d, e, f, g, h) with the λ part M and the 3/4 λ part N in between. A partition boundary portion having groove-like notches 31, 32 to 40 cut to a certain depth is provided. Said groove-shaped notch 31°32~4
0 means, for example, when a device such as a dicing saw is used, and the blade thickness is 0.
It shall be applied with a cutting blade of 5 mm to 1 ml. For each of the areas a, b, c, d, e, f, g, h partitioned by the partition boundary, for example, a-d and e-
Eight polarized portions 41, 42 to 48 are provided in which the polarization directions of adjacent regions are alternately reversed as shown by arrows by performing polarization processing alternately in the order of h. . This polarization treatment is performed at, for example, 120°C.

The test is carried out in silicone oil under the conditions of 5KV/fin for 60 minutes, and then withering treatment is performed at 150°C for 1 hour.

FIGS. 2(a) and 2(b) are diagrams for explaining the effects of this embodiment having the above configuration, and FIG. 2(a) is a cross-sectional view showing the piezoelectric element of this embodiment, and FIG. ) is a sectional view of a conventional example shown for comparison.

As shown in FIG. 2(a), adjacent electrodes 21a,
Since the partition boundary portion having the groove-shaped notches 31, 32 is provided between 21b and 21b, the polarization electric field does not leak during polarization. As a result, each of the polarized portions 41, 42 to 41 can be easily and accurately brought into a saturated polarized state, and the occurrence of cracks due to polarization distortion can be suppressed.

In order to experimentally confirm that the above polarization state is a saturated polarization state, resonance and 31', Qm, Cx by resonance method
I compared the piezoelectric constants of As a result, there was no significant difference. Also a, C.

A similar effect was obtained by simultaneously polarizing the 3/4λ parts N, f, and h in the positive direction, and then polarizing the 3/4λ parts N, f, and h in the opposite direction simultaneously. Furthermore, a, C,
Terminals connecting 3/4λ parts N, f, h, b, d, e,
Similar results were obtained when a voltage twice the polarization voltage of the previous two polarization methods was applied between the terminal to which the 1/4λ portion M was coupled and polarization and depletion were performed.

On the other hand, if the structure is as in the embodiment, the notches 31 and 32
It is possible to increase the adhesive strength when bonding a metal plate to a surface coated with ~. Therefore, it is possible to provide a stable and highly reliable plate wave vibrator.

Thus, when an ultrasonic motor is constructed using such a vibrator as a stator element, an ultrasonic motor that is extremely efficient compared to conventional ones can be obtained.

The depth of the notches 31, 32 is set to approximately half the thickness H (approximately 0.5 mm) of the ring-shaped piezoelectric body 20 made of piezoelectric ceramics, that is, approximately 1/2H (approximately 0.25 m+s). Therefore, the above-mentioned improvement effect is well exhibited.

That is, if the depth of the notches 31° 32 is too deep, warping will occur during adhesion as in the third method described above, and if it is too shallow, the problem will be improved as in the first method described above. It will not be done.

In addition, as the partition boundary part, as shown by the broken line part in FIG. 2(a), the groove-shaped cutout part may be filled with an insulating member S such as epoxy resin or glass. Even when such an insulating member S is filled, the same effects as described above can be achieved, and even if the depth of the notches 31, 32 is too deep, the occurrence of warping as described above can be prevented. There are advantages that can be achieved.

On the other hand, in the conventional example, as shown in FIG. 2(b), the polarized parts V arranged every other time are first polarized,
Next, since the adjacent polarized portion W portion is polarized in the opposite direction,
In the X portion where no electrode exists, leakage of the polarization state occurs. Moreover, this leakage polarization is in opposite directions between adjacent devices. Therefore, if the width of the X part where no electrode is present is wide enough, the leakage polarization from adjacent polarized parts will be zero near the center of the X part, and no shear stress will occur in the thickness direction of the piezoelectric element at the center. . However, in reality, the width of the X section is often not so wide. Therefore, the internal stress caused by the leakage polarization is large, and in some cases, this internal stress may cause destruction of the piezoelectric ceramic at the X portion. Furthermore, even if the state is stopped on the verge of destruction, if the driving power is large, the distortion caused by the driving power will be superimposed.
There is a risk of destruction of piezoelectric ceramics. Therefore, in order to avoid such a situation, normally the polarization is kept in an unsaturated state, but if the polarization is in an unsaturated state, it is impossible to avoid large variations in the polarization state, and electrical signals cannot be changed mechanically. The ability to convert into physical vibration becomes smaller.

The reason why a large shear stress occurs in the above X part is that the X part is also made of the same ceramic as the electrode forming part, and is made of a material with almost the same elastic constant. It is thought that this is to wake up the child.

However, in this embodiment, as described above, the notch 31.3
2 to 2 are provided to create a structure in which the internal stress cannot seep out, so there is no drawback of the conventional example described above.

FIGS. 3(a) and 3(b) are diagrams showing a second embodiment of the present invention. This embodiment differs from the first embodiment in its manufacturing method. That is, in this example, a piezoelectric ceramic 50 having the same characteristics as in the first example is punched in a green sheet state to a size that takes into account the shrinkage rate during sintering, and then the piezoelectric ceramic 50 is punched out in a size that takes into account the shrinkage rate during sintering. Similarly, groove-shaped notches 61 and 62 are formed using a blade mold and then sintered, and then, as shown in FIG. and electrodes 52 are printed and baked on the back side, respectively, and polarized portions 81, 82-- are provided. This embodiment also has the advantage of being easy to manufacture, as well as having the same effects as the first embodiment.

FIG. 4 is a diagram showing a third embodiment of the present invention.

This embodiment differs from the first embodiment in the manufacturing method and the structure of the notch. That is, in this embodiment, a hollow rod-shaped piezoelectric ceramic cylinder 90 whose inner diameter and outer diameter have a slight margin compared to the final inner and outer diameter dimensions,
Cut grooves 91 corresponding to the number of polarized parts in the length direction,
9.2~ is prepared and set in an insulating material pouring jig (not shown), then epoxy resin or low melting point glass is poured into the cut grooves 91.92~, and after hardening, the final thickness is It is cut into rounds with the blade 101 so that it becomes thicker by the amount of polishing, and then both sides are polished. Then, an electrode (not shown) is applied to a predetermined part on one side of this ring-shaped ceramic using a mask and a means such as a vacuum steam tube, and after applying an electrode to the entire surface of the other side, the adjacent sides are polarized in opposite directions. Process.

In this embodiment, the cutout portions obtained by the cut grooves 91, 92, and so on extend over the entire thickness of the piezoelectric ceramic. Compared to the second embodiment, adjacent polarized parts are completely separated.

Moreover, since both the resin and the glass that are filled are non-piezoelectric, no polarization distribution occurs in that part. Therefore, there is an advantage that a completely saturated polarization state can be realized.

Note that the present invention is not limited to the embodiments described above, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

〔Effect of the invention〕

According to the present invention, at least a portion of the piezoelectric element body in the thickness direction (
In other words, a partition boundary is provided to form a groove-like cutout (this may be a part or all of the thickness),
Each region partitioned by the partition boundary is provided with a plurality of polarized portions in which the polarization directions of adjacent regions are opposite to each other, so that the polarization state of each polarized portion can be easily and accurately determined. It can be made into a saturated polarization state, and the variation in the polarization state of each polarization part is extremely small, and A-B
It is possible to create a piezoelectric element that can satisfy the following conditions and realize a highly efficient ultrasonic motor.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing the appearance of the first embodiment of the present invention;
FIGS. 3(a) and 3(b) are sectional views for explaining the operation of the second embodiment, and FIGS. 3(a) and 3(b) are an overall perspective view and a partial perspective view showing the configuration of the second embodiment of the present invention, FIG. 4 is a perspective view showing the configuration of a third embodiment of the present invention. FIG. 5 to FIG. 12 are diagrams showing the prior art. 20... Ring-shaped piezoelectric body made of PZT (zircon lead titanate) piezoelectric ceramics, 21.22... Electrode, M-1/4λ part, N-3/4λ part, a, b. c, d and e, f, g, h... each divided area,
31.32~...Groove-shaped notch, 41.42~...
Polarized part, S...insulating member. Applicant's agent Patent attorney Tsuboi 4 Figure 1 Figure 2 Figure 5 Figure 6 Figure 7 Figure 8 Figure 10 Figure 9 Figure 11

Claims (2)

[Claims] (1) A partition boundary portion having a groove-shaped notch in at least a part of the thickness direction of the piezoelectric element body so as to partition the piezoelectric element body having electrode plates on the front and back surfaces of the piezoelectric ceramic into specific areas. A piezoelectric element, characterized in that each region partitioned by the partition boundary portion is provided with a plurality of polarization portions in which polarization directions of adjacent regions are opposite to each other. (2) The piezoelectric element according to claim 1, wherein the partition boundary is a groove-shaped notch filled with an insulating material such as epoxy resin or glass.