JPS63167686A - Ultrasonic motor - Google Patents

Abstract

PURPOSE:To improve driving efficiency, by a method wherein an annular stator is supported by the node of mode (non-displacement point) of traveling wave, which exists along the line of average radius of the ring of the stator. CONSTITUTION:A stator 10 is constituted of an annular vibration plate 11 and an annular piezoelectric element 12, connected to the vibration plate 11 integrally. The piezoelectric elements 12 are arranged and polarized in respective areas, which are divided into two parts by the line L of the average radius of the ring of the vibration plate 11, while a traveling wave, whose node of mode exists on the line L, is excited by impressing an AC voltage, whose phase is deviated by pi/2 with respect to the phase of the piezoelectric elements 12, on the elements 12. The stator 10 is supported by a L-shape supporting member 13, whose tip end is abutted against the line L of the side of the elements 12. The supporting member 13 is fixed to a base 15 by screws 14. According to this method, the supporting member 13 supports the part of the line L of the average radius, on which the mode node of the traveling wave exists, therefore, the supporting member 13 will never obstruct the vibration of the stator 10.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention excites a bending traveling wave in a stator consisting of an annular piezoelectric element and a diaphragm, and causes the bending traveling wave to reach the apex of an elliptical locus on the stator surface. The present invention relates to an ultrasonic motor that rotates a rotor by touching the rotor.

[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.

■Small, 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.

■There is no backlash and positioning is easy.

■The rotor rotates and chucks against the stator.

It can take on three states: floating.

In order to take advantage of these advantages, various applied techniques are being researched.

FIG. 6 is a schematic diagram of a typical conventional rotary ultrasonic motor. The principle of this ultrasonic motor is that an annular piezoelectric element 1
By exciting a traveling wave through bending vibration caused by the inverse piezoelectric effect in the metal donut-shaped diaphragm 2 integrated with the metal donut-shaped diaphragm 2, and by suppressing and arranging the rotor 3 so as to be in contact with the apex of the backward elliptical motion locus of the surface mass point generated by this. , the rotor 3 is rotated in the direction of arrow A. The above traveling wave excitation method will be explained below.

FIG. 7 is a diagram showing a polarization state diagram of the piezoelectric element 1 constituting a general ultrasonic motor, and corresponds to the diagram seen from below in FIG. 6. Polarize the ring-shaped piezoelectric material so that the polarization directions are alternately opposite, such as +-11, or arrange multiple divided piezoelectric elements so that the polarization directions are opposite to each other. do.

In such an arrangement, one set of adjacent polarization directions opposite to each other corresponds to one wavelength λ. and,
Unpolarized portions 1a and lb having a length of 3/4λ and 1/4λ are arranged at positions different from each other by 180°, and polarized bodies of 02 pieces each are arranged symmetrically with respect to the center line connecting these parts. However, the directions of polarization are arranged continuously in the circumferential direction so that the directions of polarization are alternately opposite to each other.

Of this polarization arrangement, the left half of the surface that is not in contact with the diaphragm, with the 3/4λ and 1/4λ unpolarized parts 1a and 1b sandwiched between them, is covered with one electrode, and this is connected as shown in Figure 8. One side of the electrode is made a common electrode 4a, and the right half surface not in contact with the diaphragm is covered with another electrode, and this is made the other side common electrode 4b as shown in FIG. The electrode 4C on the diaphragm 2 side is electrically connected to the diaphragm 2, and is shared as a ground-side electrode for all piezoelectric elements.

The electrical signal input terminal to the above-mentioned structure has a structure having three terminals a, b, and c as shown in FIG. When driving a structure having such a polarization arrangement and electrode arrangement, a 90° phase shifter 5 is interposed between terminals a and c and between terminals b and c, as shown in FIG. By doing so, the inner and outer diameters of the ring have a phase difference of π/2, and the wavelength is 21.
Thickness.

・I' uniform elastic constant and density of piezoelectric ceramics and diaphragm.

An electric signal having a natural frequency ω determined by the following equation is manually generated.

Now, as shown in FIG. 9, the diaphragm 2 and the electrode 4 on the piezoelectric element
When an AC voltage of frequency ω is applied from the AC power supply 6 between the diaphragm a or 4b, a bending standing wave is excited in the diaphragm 2. When a 1-distribution alternating current voltage is applied to the left part of the piezoelectric cable 1 in FIG. A standing wave with . Furthermore, when an AC voltage with a frequency ω whose phase is shifted by π/2 from the above AC voltage is applied to the right part of the piezoelectric element 1 in FIG. i n2yr/λ
(p-λ/4)s in (ωt-π/2)
A standing wave with a displacement of -(2) is excited.

Therefore, when the AC voltages shown in equations (1) and (2) above are simultaneously applied to the right and left halves of the piezoelectric cord 1, Y-"!!1+)'2-As in (2πp/ A traveling wave with a displacement of λ-ωt)...(3) is obtained.A surface traveling wave with the same phase as the neutral axis is also excited on the surface of the diaphragm 2.The bending traveling wave of such a plate In this case, the mass point on the surface moves backward in an ellipse with respect to the direction of wave propagation, as shown in FIG. 9.Therefore, as shown in FIG. When pressed and placed with a certain pressure, the diaphragm 2
The rotor 3 rotates in a direction opposite to the direction of wave propagation due to the frictional force between the wave and the wave.

[Problem that the invention seeks to solve]

When a bending traveling wave is excited in the diaphragm 2 as described in I,
A mode of vibration (displacement) as shown in FIG. 10 occurs on the surface of the stator. The broken line 7 in FIG. 10 shows the displacement in the resting state, and the solid line shows the displacement in the excited state. As can be seen from FIG. 10, in the above mode, all mass points of the ring are vibrating. In such a vibration mode, the driving efficiency may be significantly reduced depending on how the stator is supported. Conventionally, in order not to impede the above-mentioned vibrations, a vibration isolating rubber or the like has been placed on the side of the stator opposite to the rotor contact side, and the stator has been held via the vibration isolating rubber or the like. However, if the stator is held via a vibration-proofing rubber or the like, vibrations of the stator will leak to the vibration-proofing rubber or the like.

As a result, there has been a problem that energy loss is large and the drive efficiency of the ultrasonic motor is significantly reduced, causing various practical problems. Japanese Patent Application Laid-Open No. 61-49671 discloses a technique in which a support pin is provided at the node of a standing wave and the stator is supported by the support pin, but there are various practical problems.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an ultrasonic motor that does not impede the vibration of the stator, does not leak vibrations, and can drive the rotor extremely efficiently, causing no problems in practice.

[Means for solving problems]

In order to solve the above-mentioned problems and achieve the object, the present invention takes the following measures. In other words, by pressing the rotor against the annular stator in which surface traveling waves are excited,
In the ultrasonic motor configured such that the rotor rotates relative to the stator, a piezoelectric element is polarized and arranged in each region of the annular stator divided into two by an average radius line on the annular ring, so that the mode node is The traveling wave existing on the line is excited, and the stator is supported on the 1-th average radius line.

[Effect]

By taking such measures, the annular stator is supported at the mode node of the traveling wave existing along the average radius line of the annular ring, that is, at the non-displacement point, so that the generated vibration is prevented by the support member. There is no fear, and furthermore, the vibrations do not leak to other places. Therefore, drive efficiency is high.

〔Example〕

Figures 1 to 3 are diagrams showing a first embodiment of the present invention.
The figure is a perspective view showing the appearance of the stator 10. As shown in FIG. 1, this stator 10 has the same external appearance as the conventional one, with an annular piezoelectric cord 12 integrally joined to an annular diaphragm 11 by adhesive or other means. There is.

FIGS. 2(a) and 2(b) are diagrams showing the polarization arrangement of the piezoelectric elements 12 in the stator 10 and stator supporting means. As shown in FIG. 2A, the piezoelectric cords 12 are polarized in each region of the annular stator 10, which is divided into two by an average radius line on the annular ring. The 8-part electrode on the right half is connected to one terminal (
(not shown), and the 8-divided electrode on the left half is also connected in the same way. Thus, as in the case of FIG. 7, by applying an AC voltage with a phase shift of π/2 to the piezoelectric cable 12, the traveling wave whose mode node is on the 1st period line L'- is excited. It has become so. Also, the same figure (b)
As shown, the stator 10 is supported by an L-shaped support member 13 whose tip is in contact with the average radius line L on the piezoelectric element 12 side. The support member 13 is fixed onto a base 15 with screws 14.

In this embodiment, when an AC voltage with a phase shift of π/2 is applied to the piezoelectric element 12, a traveling wave in a vibration mode as shown in FIG. 3 is excited. That is, this traveling wave is a traveling wave in which the mode node C exists on the average radius line L. Outside this traveling wave or in part B, surface mass points are performing backward elliptical motion in the same direction. Therefore, the rotor (not shown) pressed against the surface of the stator 10,
Rotates due to frictional force with the stator surface.

In the above operation, the stator 10 operates at the mode node C of the traveling wave.
Since the support member 13 is supported at the part of the average radius line L where the stator 10 exists, the support member 13 does not impede the vibration of the stator 10, and there is a risk that the vibration energy of the stator 10 may leak to the outside via the support member 13. Nor. Therefore, efficient rotor drive can be performed.

FIGS. 4(a) and 4(b) are diagrams showing a second embodiment of the present invention. This embodiment differs from the first embodiment in the same figure (a).
), a belt-shaped zone R is provided on the average radius line L''- of the stator 20, and the piezoelectric element 22 is polarized and arranged while avoiding this zone R. The supporting member 23 is made to protrude and its protruding end is fixed onto the base 25 with screws 24.

According to this embodiment, since the diaphragm 21 and the support member 23 are integrally provided, they can be easily obtained by bending the same plate material.

Therefore, it has the advantage of being simple in structure and easy to manufacture.

FIG. 5 is a diagram showing a third embodiment of the present invention.

This embodiment differs from the first and second embodiments in that the stator 30 is provided with a piezoelectric element which is diagonally cut and polarized as shown in the figure. It has been experimentally confirmed that even if the piezoelectric element is provided with the polarized piezoelectric elements as described above, the same effects as those of the above embodiment can be achieved.

Note that the present invention is not limited to the above embodiments. For example, the piezoelectric element 12 shown in FIGS. 2(a) and 4(a).
The polarization direction inside 22 may be opposite to that shown. However, in this case, the four right inner electrodes and the four left outer electrodes are driven by the same AC power supply, and the four right outer electrodes and the four left inner electrodes are It is necessary to drive it with a shifted AC power supply. Further, even if the polarization direction is completely reversed from the illustrated state throughout the diagram, there will be no problem in answering the question.

Further, the shape of the diaphragm is not limited to the shape shown in the embodiment, but may be of any shape. The present invention is also applicable to ultrasonic motors that have amplitude in the radial direction. It goes without saying that various other modifications may be made without departing from the spirit of the present invention.

〔Effect of the invention〕

According to the present invention, a piezoelectric element is polarized and arranged in each region divided into two by the average radius line of the annular ring in the annular stator, and the mode node excites the traveling wave existing on the line L. Since the stator is supported on the average radius line, the ultrasonic motor does not interfere with the vibration of the stator, does not leak vibration, and can drive the rotor extremely efficiently. Can be provided.

[Brief explanation of the drawing]

Figures 1 to 3 are diagrams showing a first embodiment of the present invention.
The figure is a perspective view showing the appearance of the stator, Figures 2(a) and 2(b) are diagrams showing the polarization arrangement of piezoelectric elements in the stator and the stator support means, and Figure 3 shows that mode nodes exist on the average radius line of the stator. It is a figure which shows the surface displacement state of a traveling wave. FIGS. 4(a) and 4(b) are diagrams showing a second embodiment of the present invention, and FIG. 5 is a diagram showing a third embodiment of the present invention. 6th
Figures 1 to 10 are diagrams showing the prior art. Figure 6 is a schematic diagram of an ultrasonic motor, Figures 7 and 8 are diagrams showing the configuration of a piezoelectric element, and Figure 9 is a diagram showing the principle of rotation. , FIG. 10 is a diagram showing the surface displacement state of a traveling wave. 10.20.30... Stator, 11.21... Vibration plate, 12.22... Piezoelectric element, 13.23... Support member, 14.24... Screw, 15.25... - Base, L... Average radius line of the ring, R... Zone. Applicant's representative Patent attorney Jun Tsuboi Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 @ Figure 7 Figure 8 Figure 9 Figure 10

Claims (1)

[Claims] In an ultrasonic motor configured such that the rotor rotates with respect to the stator by pressing the rotor against the annular stator in which a surface traveling wave is excited, the mean radius line on the annular ring of the annular stator is A piezoelectric element is polarized and arranged in each divided region so that the mode node excites the traveling wave existing on the line and supports the stator on the average radius line. sonic motor.