JPS62247770A - Ultrasonic motor - Google Patents

Abstract

PURPOSE:To improve rotation speed, torque and efficiency significantly, by a method wherein one of contact surfaces between a stator and a rotor is tapered. CONSTITUTION:An ultrasonic motor is provided with a piezoelectric element 1, a vibration element 2 and a rotor 3, and at an opposite surface of the rotor 3 to the vibration plate 2, a taper surface 3a is provided and slanted so that the thickness is gradually decreased towards outside of a circular ring. The taper surface 3a is also formed to match the shape of apex in radial direction in surface travelling wave excited by the vibration plate 2. Thereby the rotor is contacted at any point on the apex of wave when the surface travelling wave is excited. As a result, the rotor 3 can be rotatedat high efficiency.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention excites a bending traveling wave in a stator consisting of an annular piezoelectric element and a diaphragm, and a rotor is formed at the apex of an elliptical locus on the stator surface caused by the bending traveling wave. This 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.

■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. 5 is a schematic diagram of a typical conventional rotary ultrasonic motor. The principle of this ultrasonic motor is that an annular piezoelectric element 1
A traveling wave is excited by the inverse piezoelectric effect in the metal donut-shaped diaphragm 2 integrated with the metal donut-shaped diaphragm 2, and the rotor 3 is pressed and placed so as to be in contact with the apex of the backward elliptical motion locus of the surface mass point generated thereby. 3 in the direction of arrow A. The above traveling wave excitation method will be explained below.

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

In such an arrangement, one set of adjacent polarization directions opposite to each other corresponds to one wavelength λ. and,
Unpolarized portions 1a and 1b having lengths of 37/4λ and 1/4λ are arranged at 1800 different positions, respectively, and polarized bodies 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 7. One side of the electrode is used as a common electrode 4a, and the right half of the electrode is covered with another electrode, which is used as the other side of the 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 structure has three terminals a, b, and c as shown in FIG. When driving a structure having such a polarization arrangement and electrode arrangement, a phase difference of π/2 is established between terminals a and C and between terminals b and c, and the inner and outer diameters of the 22-ring ring are , the thickness, the average elastic constant of the piezoelectric ceramic and the diaphragm, the density 8, etc.

Now, as shown in FIG.
When an AC voltage of 2 is applied, a bending standing wave is excited in the diaphragm 2. The above AC voltage is applied to the piezoelectric element 1 in FIG.
When the voltage is applied to the left side of the diaphragm 2, a standing wave having a displacement of Vt = As t n2π/λ psinωt (1) is excited on the neutral axis of the diaphragm 2 . 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 side portion of the piezoelectric element 1 in FIG. i n27r
/λ(p-λ/4) sin (ωt-, yr/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 half and left half of the piezoelectric element 1, V=Vx +V2 −As in (27rl)/λ−ωt) A traveling wave with a displacement of =13) is obtained. A surface traveling wave having the same phase as the neutral axis is also excited on the surface of the diaphragm 2. In such a bending traveling wave of a plate, as shown in FIG. 8, the mass point on the surface moves backward in an ellipse with respect to the direction of wave travel. Therefore, when the rotor 3 is placed on the surface of the diaphragm 2 by pressing it with a certain pressure as shown in FIG.
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 above,
The amplitude of the surface wave increases as it goes outward in the radial direction.

Figures 9 to 11 are diagrams showing the process, with Figure 9 being a sectional view, Figure 10 being a perspective view of part B in Figure 9, and Figure 11 being a perspective view of part B in Figure 9.
The figure is an enlarged sectional view of part B in FIG. 9. Note that M in FIG. 11 indicates the excited state, and N indicates the non-excited state. As shown in FIGS. 9 to 11, the amplitude of the surface wave, that is, the displacement of the mass point, increases as it moves outward in the radial direction of the diaphragm 2. When the rotor 3 is placed under pressure on the diaphragm 2 in such a state, the diaphragm 2 and the rotor 3 come into contact only at their radially outer edge portions. For this reason, there has been a problem that the efficiency as an ultrasonic motor is significantly reduced, causing various practical problems.

Therefore, the present invention has developed a super 8-wave motor that has the entire rotor in stable contact with the peak of the surface traveling wave excited by the stator's diaphragm, operates extremely efficiently, and has excellent rotation speed and torque. The purpose is to provide.

C. Means for Solving Problems] In order to solve the above problems and achieve the object, the present invention takes the following measures. That is, in an ultrasonic motor configured so that the rotor rotates relative to the stator by pressing the rotor against the stator in which surface traveling waves are excited, at least one of the surfaces where the stator and rotor come into contact is The surface should be inclined. For example, the shape of the surface that contacts the diaphragm of the rotor is made into a tapered surface that matches the radial shape of the apex of the surface traveling wave.

[Effect]

By taking such measures, the rotor comes into contact with the peak of the surface traveling wave excited on the surface of the diaphragm over the entire area.

〔Example〕

FIG. 1 is a diagram showing a first embodiment of the present invention.

Piezoelectric element 1. Vibration plate 2. The rotor 3 has an inner diameter of 45φ.

It has an outer diameter of 60φ. The thickness of diaphragm 2 is 2.5
It is set to s. A tapered surface 3a is provided on the surface of the rotor 3 facing the diaphragm, and the tapered surface 3a is inclined so that the wall thickness gradually decreases toward the outside of the ring. This tapered surface 3a is a tapered surface that matches the shape in the radial direction of the apex of the surface traveling wave excited in the diaphragm 2. The surface traveling wave will be explained below.

When the piezoelectric element 1 expands and contracts, waves of a mode corresponding to its driving frequency are excited in the diaphragm 2.

The natural frequency of each mode and its displacement vector can be analyzed using the finite element method.

FIG. 2 is a diagram showing a surface displacement state obtained by analyzing a mode in which nine waves are formed in the circumferential direction of the annular diaphragm 2. When the wave height value at the top of this wave is examined in detail on a cross section C perpendicular to the direction of travel of the wave, it becomes as shown in Fig. 3. However, the vertical scale in Figure 3 is enlarged. Although the curve in FIG. 3 generally has a complicated shape, it can be approximately approximated by a linear or quadratic function in a small amplitude range. Therefore, as shown in FIG. 1, the surface of the rotor 3 on the diaphragm side is
If it is processed into a shape that matches the above curve, the rotor 3 will come into contact with all points on the crest of the wave when the surface traveling wave is excited.

When experiments were conducted on the ultrasonic motor of this embodiment configured as described above, the following results were obtained. That is, by applying an alternating current voltage having a natural frequency corresponding to the required mode to the piezoelectric element 1, and adjusting the magnitude of the voltage appropriately, the crest of the wave is applied to the rotor 3 over the entire area. I made contact with. As a result, it was possible to avoid a situation in which the rotor 3 contacts only the outer annular portion of the diaphragm 2 as in the conventional case, and it was possible to rotate the rotor 3 with high efficiency. Improvements were also observed in rotational speed and torque.

The shape of the tapered surface 3a may be appropriately set depending on the output (rotation speed, torque) required by the ultrasonic motor.

FIG. 4 is a sectional view showing a second embodiment of the present invention. This embodiment is an example in which a tapered surface 2a as shown in the figure is provided on the surface of the imaging plate 2 that comes into contact with the rotor 3. In other words, when a surface traveling wave is excited in the diaphragm 2, the tapered surface 2a is such that the top of the wave is horizontal in the radial direction.
is provided. In this case, the shape of the rotor 3 may remain the same as before. This embodiment also provides the same effects as the first embodiment.

Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, a tapered surface is formed only on one of the rotor 3 or the diaphragm 2, but if necessary, a tapered surface may be formed on both the rotor 3 and the imaging plate 2. good. It goes without saying that various other modifications can be made without departing from the gist of the present invention.

〔Effect of the invention〕

According to the present invention, while a bending traveling wave is excited in the diaphragm of the stator, the rotor comes into contact with the entire crest of the wave, which greatly improves rotational speed, torque, and efficiency. We can provide sonic motor.

[Brief explanation of drawings]

Figures 1 to 3 are diagrams showing a first embodiment of the present invention.
The figure is a cross-sectional view showing the configuration, Figure 2 is a diagram showing the surface displacement state of waves in various modes depending on the driving frequency, and Figure 3 is a diagram showing the surface displacement state of waves in various modes depending on the driving frequency.
FIG. 3 is a vertical sectional view taken in the direction of wave propagation in the figure. FIG. 4 is a sectional view showing the structure of a second embodiment of the present invention. Fifth
Figures to Figures 11 are diagrams showing the prior art, Figure 5 is a schematic diagram of an ultrasonic motor, Figures 6 and 7 are diagrams showing the configuration of a piezoelectric element, and Figure 8 is a diagram showing the principle of rotation. , FIG. 9 is a sectional view showing the configuration of the motor, and FIGS. 10 and 11 are views showing the state of the 8 portions in FIG. 9 when bending waves are excited. 1... Piezoelectric element, 2... Vibration plate, 3... Rotor,
2a. 3a...Tapered surface. Applicant's representative Patent attorney Jun Tsuboi Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9

Claims (1)

[Claims] In an ultrasonic motor configured such that the rotor rotates relative to the stator by pressing the rotor against the stator in which surface traveling waves are excited, at least one of the surfaces where the stator and rotor come into contact is An ultrasonic motor characterized by having an inclined surface.