JPH0799945B2 - Piezoelectric elliptical motion oscillator - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small motor used in electronic equipment, and more particularly to a piezoelectric elliptical motion oscillator used in a small ultrasonic motor having a small rotor diameter.

[Prior Art] Generally, an ultrasonic motor is
It has advantages such as high torque at low rotation, stop holding force, and little electromagnetic noise, and is used for autofocus of cameras and power motors for automobiles.

FIG. 7 is a schematic view showing the structure of a conventional piezoelectric elliptical motion oscillator used in a compact ultrasonic motor, that is, a prismatic oscillator 10, on two adjacent faces of a metal prism 120 having a substantially square cross section. Electrodes are respectively formed on the piezoelectric ceramic thin plates 121a and 121b, which are polarized in the thickness direction.

The lead terminals 122a and 122b are drawn out from the surface electrodes of the piezoelectric ceramic thin plates 121a and 121b, and the common ground terminal 123 is drawn out from the metal prism 120. Since the cross-sectional shape of the metal prism 120 is substantially square, the metal prism 120 flexurally vibrates in a direction orthogonal to each other at substantially the same resonance frequency.

Therefore, the lead terminals 122a-123 and 122b-123 each have a frequency equal to the resonance frequency and different phases (preferably
When an AC voltage having 90 °) is applied, both ends of the metal prism 120 vibrate circularly or elliptically.

FIG. 8 is a diagram showing a configuration example of an ultrasonic motor using the prismatic vibrator 10 shown in FIG.

In this figure, the discs 124a and
b is attached, and further support pins 125a and 125b are formed at the vibration nodes of the prismatic oscillator 10, and the prismatic oscillator 100 is stably supported by the support pins 125a and 125b. Prismatic vibrator 1
Discs 124a, 124b provided at both ends of 00 are inserted into the hollow portions of the cup-shaped rotary rollers 126a, 126b rotatably supported by the rotary shaft, and are in pressure contact with the inner walls of the hollow portions.

Therefore, when the end of the prismatic vibrator 100 vibrates circularly or elliptically, the cup-shaped rotating rollers 126a and 126b are rotated.

[Problems to be Solved by the Invention] However, in the conventional prismatic elliptical motion oscillator as shown in FIG. 7, since the oscillator is a prism having a square cross section, the resonance frequencies of bending modes in directions orthogonal to each other. The machining accuracy of the prism must be strictly controlled in order to accurately match the above.

In addition, when the piezoelectric ceramic thin plate is bonded to the metal prism, the bonding state varies widely.

Further, in the case of constructing the ultrasonic motor having the structure as shown in FIG. 8, it is necessary to add a disc or the like to both ends of the metal prism in order to improve the contact state with the cup-shaped rotating roller. It had the drawback of being.

Therefore, a technical object of the present invention is to provide a piezoelectric elliptical motion oscillator which does not require a contact member such as a disk and which has relatively low processing accuracy and is easy to manufacture.

[Means for Solving the Problems] According to the present invention, a piezoelectric ellipse having a piezoelectric ceramic having an outer peripheral surface surrounding a central axis and a plurality of interdigital electrodes arranged on the outer peripheral surface and spaced apart from each other. In the motion oscillator, the plurality of interdigital electrodes extend on the outer peripheral surface in the circumferential direction and electrically connect the plurality of circumferential electrodes arranged in parallel to each other. A piezoelectric elliptical motion oscillator is obtained, which has connection electrodes, respectively, and the peripheral electrodes between the plurality of interdigitated finger electrodes adjacent to each other are formed to face each other in the central axis direction. .

[Operation] In the piezoelectric elliptical motion oscillator of the present invention, the piezoelectric ceramic has an outer peripheral surface surrounding the central axis. The plurality of interdigital electrodes are arranged apart from each other in the circumferential direction of the outer peripheral surface of the piezoelectric ceramic.

The plurality of interdigitated electrodes respectively include a plurality of peripheral electrodes extending in the circumferential direction on the outer peripheral surface and arranged in parallel with each other, and a connection electrode electrically connecting the plurality of peripheral electrodes to each other. Have

In addition, the peripheral electrodes between the plurality of intersecting finger electrodes adjacent to each other are formed to face each other in the central axis direction.

When these piezoelectric elements are used to polarize the piezoelectric ceramic in the direction along the central axis, and when an alternating voltage is applied between the pair of the interdigital electrodes, when the polarity of this alternating voltage is the same as the polarity at the time of polarization. In the piezoelectric ceramics, extension strain occurs in a direction perpendicular to the length direction of the peripheral electrode, and when the polarity is opposite to the polarity of the alternating voltage, contraction strain occurs in a direction perpendicular to the length direction of the peripheral electrode.

Therefore, the first pair of electrodes having the first phase on one pair of interdigital electrodes.
At least one of the crossing finger electrode pair is different from the crossing finger electrode pair of the crossing finger electrode pair, and another crossing finger electrode pair that is not symmetrical with respect to the central axis has a second phase different from the first phase. When a second AC voltage having a phase of
The bending vibrations having different phases are excited in the directions intersecting with each other, and the ends of the piezoelectric ceramics make elliptical vibrations in the plane intersecting with the central axis.

Embodiments Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of a piezoelectric elliptical motion oscillator according to an embodiment of the present invention.

In this figure, the outer peripheral surface of the pipe-shaped piezoelectric ceramics 50 is parallel to the circumferential direction, and the peripheral electrodes 101 to 111, 201 to 211, 301 to 3 are composed of a plurality of strip electrodes shorter than 1/4 of the circumference.
11 and 401 to 411 are applied to almost the entire length of the pipe-shaped piezoelectric ceramic 50 to form a peripheral electrode group, and four peripheral electrode groups are formed symmetrically in the circumferential direction, and between the peripheral electrode groups. ,
4 parallel to the length direction of this pipe-shaped piezoelectric ceramic
Connection electrodes 100, 200, 300 and 4 consisting of two strip electrodes
00 is formed and each of these four connection electrodes is connected to every other peripheral electrode in the peripheral electrode group on both sides of each of these four connection electrodes so as not to be electrically connected to each other.

Every other one from above, the peripheral electrodes adjacent to each other are electrically connected to the connection electrodes 100, 200, 300 and 400 to form the first, second, and
Third and fourth interdigital electrodes 1, 2, 3, 4 are formed, respectively.

Therefore, the first and second interdigital electrodes 1, 2, the second and third interdigital electrodes 2, 3, the third and fourth interdigital electrodes adjacent to each other
The circumferential electrodes of the third, fourth, fourth, and first interdigital electrodes 4,1, the interdigital electrodes have shapes facing each other along the central axis direction.

FIG. 2 is a view for explaining the structure of the outer peripheral surface electrode of the piezoelectric elliptical motion oscillator of the present invention, in which the electrode on the upper outer peripheral surface is appropriately expanded in a plane.

Therefore, the connection electrodes shown by the broken lines in FIG. 2 represent the same connection electrode 400.

3 to 5 are diagrams for explaining the operation principle of the piezoelectric elliptical motion oscillator of the present invention.

In FIG. 3, the connecting electrodes 10 in the longitudinal direction facing each other are shown.
0 and 300 and connection electrodes 200 and 400 are connected by connection lines 51 and 52, respectively, to form two terminals 51 'and 52'.
When a high DC voltage is applied between 52 'as shown in the figure, the peripheral electrodes of the first interdigital electrode 1 to the peripheral electrodes of the second and fourth interdigital electrodes, and the peripheral electrodes of the third interdigital electrode are It is polarized toward the peripheral electrodes of the first and fourth interdigital electrodes, that is, in the direction of the arrow 53 shown by the broken line in the drawing.

Pipe-shaped piezoelectric ceramics 50 polarized as shown in FIG.
On the other hand, as shown in FIG. 4, adjacent connecting electrodes 100 and 400 and 200 and 300 in the direction of the central axis are connected by connecting lines 54 and 55, respectively, to form two terminals 54 'and 55'. 54 'and
When a DC voltage is applied between 55 ′ as shown in the figure, the peripheral electrode of the second interdigital electrode 2 is changed from the peripheral electrode of the second interdigital electrode 2 to the peripheral electrode of the third interdigital electrode 3 An electric field is applied to each of the circumferential electrodes of the interdigital electrodes, that is, in the direction indicated by the broken arrow 56 in the figure.

As can be seen from FIG. 4, the first and second interdigital electrodes 1
In the portions of the peripheral electrode groups 201 to 211 facing each other, the polarization direction indicated by the broken arrow 53 and the electric field direction indicated by the solid arrow 56 are opposite to each other. Shrinkage distortion occurs in the vertical direction, and the portions of the peripheral electrode groups 401 to 411 of the third and fourth interdigital electrodes that face each other are indicated by broken line arrows.
The direction of polarization indicated by 53 and the direction of the electric field indicated by the solid arrow 57 are the same, and at this portion, elongation strain occurs in the longitudinal direction.

As a result, the pipe-shaped piezoelectric ceramic 50 is
Bent from the portion of ˜411 to the portion of the peripheral electrode groups 201 to 211.

Therefore, when a first AC voltage having a first phase at a frequency equal to the resonance frequency of the pipe-shaped piezoelectric ceramics 50 is applied between the two terminals 54 'and 55', the pipe-shaped connection is made between the two terminals 54 'and 55'. The piezoelectric ceramic 50 undergoes the first bending vibration.

Further, as shown in FIG. 5, adjacent connecting electrodes 100 and 200 in the central axis direction and connecting electrodes 300 and 400 which are adjacent to each other are connected by connecting lines 58 and 59, respectively, to form two terminals 58 'and 59'. Terminal 5
When a DC voltage is applied between 8'and 59 'as shown in the figure, from the peripheral electrode of the fourth interdigital electrode 4 to the peripheral electrode 1 of the first interdigital electrode, to the peripheral electrode of the second interdigital electrode 2. From this, an electric field is applied toward the peripheral electrodes of the third interdigital electrode 3, that is, in the directions shown by solid arrows 60 and 61 in the figure.

As can be seen from FIG. 5, the second and third interdigital electrodes 2
In the portions of the peripheral electrode groups 301 to 311 facing each other of 3 and 3, the polarization direction and the electric field direction are opposite to each other, and in this portion, contraction strain occurs in the length direction, and the first and fourth intersection fingers. The portions of the peripheral electrode groups 101 to 111 of the electrodes facing each other have the same polarization direction and the same electric field direction, and this portion has elongation strain in the length direction.

As a result, the pipe-shaped piezoelectric ceramic 50 has the peripheral electrode 101.
Bent from the portion of 111 to the portion of the peripheral electrode groups 301 to 311.

Therefore, when a second AC voltage having a second phase different from the first phase at a frequency equal to the resonance frequency of the pipe-shaped piezoelectric ceramic 50 is applied between the two terminals 58 'and 59', the two terminals 58 'and 59' are applied. During this period, the pipe-shaped piezoelectric ceramic 50 undergoes the second bending vibration.

The vibrating surface of the second bending vibration is in a direction including the central axis and at a right angle to the case of the first bending vibration in FIG.

From the above, the elliptical vibration is generated at both ends of the pipe-shaped piezoelectric ceramics by shifting the first and second phases of the first and second AC drive voltages for driving each bending vibration by 90 °. Can be made.

FIG. 6 shows an example of a circuit for driving the piezoelectric elliptical motion oscillator of the present invention.

In this figure, two transformers having one circuit on the input side and two circuits on the output side are used. The input ends 21 and 22 are on the input side of the first transformer 20, and the output ends 25 and 26 are on the output side.
And output terminals 27 and 28 are provided. Similarly, the second transformer 20 'is also provided with input terminals 23 and 24 on the input side, output terminals 29 and 30 on the output side, and output terminals 31 and 32.

The output terminals 25 and 29, 26 and 31, 27 and 30, 28 and 32 are connected to each other to connect the connecting electrodes 100, 200, 200 of the ceramic 50.
It is connected to 300 and 400 respectively.

90 ° to each other between input terminals 21 and 22 and between input terminals 23 and 25
First and second transformer input voltages having different phases, V ₀ sin
When ωt, V ₀ cos ωt is applied, the output voltage between the output terminals 25 and 26, the output terminals 27 and 28, the output terminals 29 and 3 and the output terminals 31 and 32 is 180 degrees from the first and second transformer input voltages. ° Voltages with different phases, −V ₁ sin ωt, −V ₁ cos ωt, are generated.

Therefore, the first transformer output voltage is applied in the same direction between the electrodes 100 and 400 and between the electrodes 200 and 300 so as to face each other.
V ₁ sin ωt is applied, between electrodes 100 and 200, electrodes 400 and
During 300, the second transformer output voltage V ₁ cos ωt is applied.

With such a circuit configuration, two bending vibrations can be simultaneously excited in the piezoelectric ceramics 50 in the directions perpendicular to each other.

Therefore, as described above, the elliptic vibrations can be excited by applying the voltages 90 ° out of phase, V ₀ sin ωt and V ₀ cos ωt, as the respective transformer input voltages.

It should be noted that, as the crossing finger electrodes facing each other are provided at positions where the circumference is divided into n (n is a natural number of 2 or more), they are polarized in a staggered manner along the central axis direction and are mutually polarized in the central axis direction as in the embodiment. A first AC drive voltage is applied to each of a pair of opposing interdigital electrodes, and a first alternating current is applied between the interdigital electrodes that are not symmetrical with respect to the central axis, unlike the pair of interdigital electrodes. It is apparent that similar elliptical vibration can be obtained by applying the second AC drive voltage having a phase different from the phase of the drive voltage.

[Effects of the Invention] As described above, in the piezoelectric elliptical motion oscillator of the present invention, since the oscillator has a simple shape, and in particular, the outer shape is circular, high-precision machining is easy and It is easy to match two resonance frequencies in the orthogonal direction. Further, the circular cross-sectional outer shape makes it possible to obtain a stable motor because the contact state with the cup-shaped rotating roller is good when the ultrasonic motor as shown in the conventional example is constructed.

Further, in the piezoelectric elliptic motion oscillator of the present invention, since no adhesive is used, the variation in characteristics due to adhesion is small, and the effect is practically large.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a piezoelectric elliptical motion oscillator according to an embodiment of the present invention, and FIG. 2 illustrates a structure of electrodes of a piezoelectric elliptical motion oscillator according to an embodiment of the present invention. Figure 3 to 5
FIG. 6 is a diagram for explaining the operation principle of the piezoelectric elliptical motion oscillator according to the embodiment of the present invention, and FIG. 6 is a diagram showing an example of a circuit for driving the piezoelectric elliptical motion oscillator according to the embodiment of the present invention. FIG. 7 is a perspective view showing the operating principle of a piezoelectric elliptical motion oscillator according to a conventional example, and FIG. 8 is a perspective view showing the configuration of an ultrasonic motor using the piezoelectric elliptical motion oscillator according to the conventional example. In the figure, 1,2,3,4 are interdigital electrodes, 10 is a prismatic vibrator, 50 is a pipe-shaped piezoelectric ceramic, 101-111, 201-211, 301-31
1,401 to 411 are peripheral electrode groups, 100,200,300,400 are connection electrodes, 1
20 is a metal prism, 121a and 121b are piezoelectric ceramic thin plates, 122
a, 122b, 123 are lead terminals, 124a, 124b are discs, 125a, 125b
Are support pins, and 126a and 126b are cup-shaped rotating rollers.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 62-264543 (JP, A) Proceedings of the Acoustical Society of Japan, October 1988, p. 867 (1-P- ▲ 4 ▼)

Claims (1)

[Claims] 1. A piezoelectric elliptical motion oscillator comprising: a piezoelectric ceramic having an outer peripheral surface surrounding a central axis; and a plurality of interdigitated finger electrodes arranged on the outer peripheral surface so as to be spaced apart from each other. The electrodes each have a plurality of peripheral electrodes that extend in the circumferential direction on the outer peripheral surface and are arranged in parallel with each other, and connection electrodes that electrically connect the plurality of peripheral electrodes to each other, and are adjacent to each other. The piezoelectric elliptical motion oscillator, wherein the circumferential electrodes between the plurality of interdigitated electrode electrodes are formed to face each other in the central axis direction.