JP2689425B2 - Ultrasonic motor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic motor that generates a driving force using a piezoelectric body. 2. Description of the Related Art In recent years, an ultrasonic motor that excites elastic vibrations in a vibrating body using a piezoelectric body such as a piezoelectric ceramic and uses this as a driving force has attracted attention. Hereinafter, a conventional technique of an ultrasonic motor will be described with reference to the drawings. FIG. 6 is a perspective view of a conventional annular ultrasonic motor,
A vibrating body 3 is formed by bonding an annular piezoelectric ceramic 2 as a piezoelectric body to one of the annular surfaces of an annular elastic body 1. Reference numeral 4 denotes a friction material made of an abrasion-resistant material, and reference numeral 5 denotes an elastic body. The moving body 6 is in contact with the vibrating body 3 via the friction material 4. When an electric field is applied to the piezoelectric body 2, a traveling wave of bending vibration is excited in the circumferential direction of the vibrating body 3 to drive the moving body 6. Note that the arrow in the figure indicates the rotation direction of the moving body 6. FIG. 7 shows an example of the electrode structure of the piezoelectric ceramic 2 used in the ultrasonic motor of FIG. In the figure, 9 waves of elastic liquid are spread in the circumferential direction. In the figure, A and B are electrode groups each composed of a small area corresponding to a half wavelength, C is an electrode having a length of 3/4 wavelength, and D is an electrode having a length of a quarter wavelength. The electrodes C and D form a phase difference of a quarter wavelength (= 90 degrees) between the electrode groups A and B in position. The adjacent small electrode portions in the electrodes A and B are polarized in the thickness direction opposite to each other. The bonding surface of the piezoelectric body 2 to the elastic body 1 is a surface opposite to the surface shown in FIG. 7, and the electrodes are solid electrodes. In use, the electrode groups A and B are
As shown by hatching in the figure, each is used after being short-circuited. V ₁ = V ₀ × sin (ωt) (1) V ₂ = V ₀ × cos (ωt) (2) on the electrodes A and B of the piezoelectric body 2 of the ultrasonic motor configured as described above. However, if V ₀ : instantaneous value of voltage ω: voltage V ₁ and V ₂ represented by angular frequency t: time are respectively applied, ξ = ξ ₀ × (cos (ωt) × cos (Kx) + sin (ωt) × sin (kx)) = ξ ₀ × cos (ωt−kx) (3) where, ξ: bending vibration amplitude value ξ ₀ : bending vibration instantaneous value k: wave number (2π / Λ) λ: Wavelength x: A traveling wave of bending vibration that advances in the circumferential direction, which can be represented by a position, is excited. FIG. 8 shows that the point A on the surface of the vibrating body 3 performs an elliptical motion of the long axis 2w and the short axis 2u by the excitation of the traveling wave, and the moving body 6 pressurized on the vibrating body 3 has an elliptical shape. By contact near the vertex, frictional force causes v
= Ω x u. Problems to be Solved by the Invention In order to increase the output of the ultrasonic motor, the kinetic energy of the vibrator may be increased. Since the kinetic energy is proportional to the square of the mass and velocity of the oscillator,
The output can be increased by increasing the mass or speed of the vibrator.
Once the outer shape of the ultrasonic motor is determined, the size of the hole in the vibrator can be reduced to increase the mass, and the amplitude of the vibration can be increased to increase the speed. However, the amplitude of the vibration is limited by the allowable distortion of the piezoelectric body. In addition, since the conventional ultrasonic motor uses the circular bending vibration of the first-order radial direction and the third-order circumferential direction or more, the amplitude value suddenly decreases near the inner circumference as shown in FIG. , Even if the hole of the vibrating body is made small, the kinetic energy does not become so large. Therefore, there is a problem that the output cannot be increased in the conventional ultrasonic motor using the ring-shaped bending vibration of the primary direction in the radial direction and the tertiary direction in the circumferential direction as in the related art. The present invention has been made in view of the above, and an object of the present invention is to provide an efficient ultrasonic motor capable of increasing the output with the same volume. Means for Solving the Problems A disk-shaped vibrating body is used as a vibrating body, and bending vibrations of a radial second order, a circumferential third order or more are used as a vibration mode, and as a driving electrode of a piezoelectric body forming the vibrating body. Two sets of drive electrodes are concentrically formed with a circle where the sign of the electric charge induced in the piezoelectric body due to bending vibration changes in the radial direction of the vibrator. Operation With the above configuration, the inside of the vibrating body is effectively contributed to the kinetic energy of the vibrating body to increase the output, and the sign of the charge induced in the piezoelectric body vibrates. By configuring two sets of drive electrodes concentrically with a circle that changes in the radial direction of the body as a boundary, the sign of the charge in the same electrode group becomes the same, and the charges do not cancel each other out in the same electrode group. Since the vibration of the vibrating body is efficiently excited, it is possible to provide an efficient ultrasonic motor. Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cutaway perspective view showing the outline of the configuration of the ultrasonic motor of the present invention. A vibrating body 9 is formed by attaching a disc-shaped piezoelectric ceramic 8 as a piezoelectric body to one of the main surfaces of the disc-shaped elastic body 7. On the other main surface of the elastic body 7, a projection 10 for taking out mechanical output is formed.
Numeral 11 denotes a friction material made of an abrasion-resistant material, and 12 denotes an elastic body. The moving body 13 is in pressure contact with the protrusion 10 provided on the vibrating body 9 via the friction material 11. When an electric field is applied to the piezoelectric body 8, a traveling wave of bending vibration is excited in the circumferential direction of the moving body 9 and the moving body 13 is driven by a frictional force. The moving body 13 starts rotating motion around the rotation axis 14. FIG. 2 is a vibration distribution state and a radial displacement distribution diagram of the vibrating body 9 when the secondary vibration in the radial direction and the bending vibration in the tertiary direction in the circumferential direction are excited. Unlike when using the radial primary vibration mode,
The displacement does not decrease suddenly even at the inner circumference. Therefore,
When the ultrasonic motor occupies the same volume, the kinetic energy of the vibrating body 9 can be made larger than that in the case where the first-order radial vibration mode is used, and the ultrasonic motor capable of obtaining a large output can be realized. FIG. 3 is a plan view showing an example of a disk-shaped piezoelectric ceramic used in a disk-shaped ultrasonic motor when a traveling wave of bending vibration of radial second order and circumferential fourth order is used. In the figure,
(A) is the displacement distribution in the radial direction, and since the secondary vibration mode in the radial direction is used, there is a vibration node other than the center of the piezoelectric ceramic, and the node is a circle surrounded by this node. It is shown that the displacement direction of vibration is opposite to the thickness direction on the inner circumference side and the outer circumference side of the circle. (B) is the radial distribution of the electric charges induced by the vibration excited in the piezoelectric ceramic. Like the vibration excited in the piezoelectric ceramic has nodal circles, r _{0 in} FIG. It is shown that the polarities of the induced charges are changed on the inner circumference side and the outer circumference side of a circle having a radius of. (C) is an electrode structure diagram of a piezoelectric ceramic in the case where electrodes are formed inside a circle in which the polarity of charges induced by vibration changes. The electrode group E ₁ and the electrode group F ₁ have a radius r _{0 in} which the positive and negative polarities of the electric charges induced by the secondary bending vibration in the radial direction change in the radial direction.
Is an electrode group composed of small electrode portions arranged concentrically within the circle, each having a length corresponding to one-half wavelength in the circumferential direction, and the polarization directions of the adjacent electrode portions being opposite to the thickness direction. . The electrode groups E ₁ and F ₁ have a quarter phase in the circumferential direction.
It is constructed by shifting the wavelength (90 degrees). Therefore, if the electrode groups E ₁ and F ₁ are short-circuited and a voltage with a 90 ° phase difference with respect to time is applied to the solid electrode on the back surface, the polarities of the radial charges induced by vibration are the same. Therefore, a progressive wave of bending vibration of radial second order and circumferential fourth order is excited in the vibrating body 9. FIG. 4 is a plan view showing another example of a disk-shaped piezoelectric ceramic used in a disk-shaped ultrasonic motor when traveling waves of bending vibration of radial second order and circumferential fourth order are used. In the same figure, (a) is a radial displacement distribution, and as in FIG. 3 (a), the displacement direction of vibration is opposite to the thickness direction on the inner circumference side and the outer circumference side of the node circle. It has become. (B) is the radial distribution of the electric charges induced by the vibration excited in the piezoelectric ceramic. As in FIG. 3 (b), on the inner and outer circumference sides of a circle with radius r ₀ , It shows that the polarity of the induced charges has changed. (C) is an electrode structure diagram of the piezoelectric ceramic in the case where an electrode is configured with a circle where the polarity of charge induced by vibration changes as a boundary. Electrode group E ₂ is outside the circle of radius r _{0 in} which the positive and negative polarities of electric charges induced by radial secondary bending vibration change, and electrode group F ₂ is inside the circle of changing electric charge polarity. Is a group of concentric circles, each of which has a length corresponding to a half wavelength in the circumferential direction, and the polarization direction of the adjacent electrode portions is opposite to the thickness direction. And the electrode group
E ₂ and F ₂ have a phase equivalent to a quarter wavelength in the circumferential direction (90 degrees)
It is composed by shifting. Therefore, if the electrode groups E ₂ and F ₂ are short-circuited and a voltage with a 90 ° phase difference with time is applied to the solid electrode on the back surface, the polarity of the radial electric charge induced by vibration will change. Because it ’s inside and outside,
The traveling waves of the bending vibration of the radial second order and the circumferential direction fourth order are excited in the vibrating body 9 without canceling out the induced charges. FIG. 5 is a plan view showing another example of a disk-shaped piezoelectric ceramic used in a disk-shaped ultrasonic motor when a traveling wave of bending vibration of radial second order and circumferential direction fourth order is used. . In the same figure, (a) is a radial displacement distribution, and similarly to FIGS. 3 (a) and 4 (a), the displacement of vibration on the inner circumference side and the outer circumference side of the node circle is It indicates that the direction is opposite to the thickness direction. (B) is the radial distribution of the electric charges induced by the vibration excited in the piezoelectric ceramic, and as in FIGS. 3 (b) and 4 (b), a circle with a radius of r ₀ It shows that the polarities of the induced charges are changed between the inner circumference side and the outer circumference side. (C) is an electrode structure diagram of the piezoelectric ceramic in the case where an electrode is configured with a circle where the polarity of charge induced by vibration changes as a boundary. In the electrode group E ₃ , charges induced by the secondary bending vibration in the radial direction are outside the circle of radius r ₀ where the positive and negative polarities change in the radial direction, and the electrode group E ₄ and the electrode group F ₃ Concentric circles are formed inside the circle whose polarity changes, and the circumference direction is half each.
It is an electrode group composed of small electrode portions having a length corresponding to the wavelength, and the polarization directions of the electrode portions adjacent to each other are opposite to the thickness direction. In consideration of the fact that the radial electric charges induced by the vibrations have opposite signs, the electrode groups E ₃ and E ₄ have polarization directions of the small electrode portions constituting the electrode groups E ₃ adjacent in the radial direction. And the polarization direction of the small electrode portion that configures the electrode group E ₄ is opposite to the thickness direction, the electrode groups E ₃ and E ₄ are configured in the opposite phase in the circumferential direction, and the electrode group F 4 ₃ and E ₃ and E ₄ have a phase of 4 in the circumferential direction.
It is constructed by shifting by one-half wavelength (90 degrees). Therefore, if the electrode groups E ₃ and E ₄ are short-circuited to form one drive electrode, the electrode group F ₃ is short-circuited, and a voltage that is 90 degrees out of phase with the solid electrode on the back side is applied, Since the polarities of the radial electric charges induced by the electric field are inside and outside the circle, the induced electric charges do not cancel each other out in the same manner as in the case of FIG. Direction 4
The traveling wave of the next bending vibration is excited. As described above, if the drive electrodes are configured, the radial electric charges have the same sign in the same electrode group, the radial electric charges are not canceled out in the same electrode group, and the vibration of the vibrating body is efficient. Well excited According to the present invention, it is possible to provide an efficient ultrasonic motor having a large output. EFFECTS OF THE INVENTION According to the present invention, bending vibration of radial second order and circumferential third order or higher is used as a vibration mode, and a circle where the sign of the electric charge induced in the radial direction of the piezoelectric body by the bending vibration changes is defined as a boundary. As described above, by configuring two sets of drive electrodes concentrically, it is possible to provide an efficient ultrasonic motor with a large output.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cutaway perspective view of a disc type ultrasonic motor of the present invention, and FIG. 2 is a case where bending vibration of radial second order and circumferential third order is used as a vibration mode. The vibration state of the vibrating body and the displacement distribution diagram in the radial direction. Fig. 3 shows the disc type ultrasonic motor.
Fig. 4 is a plan view of an example piezoelectric ceramic, Fig. 4 is a plan view of another piezoelectric ceramic used in a disc type ultrasonic motor, and Fig. 5 is another piezoelectric used in a disc type ultrasonic motor. FIG. 6 is a plan view of the ceramic, FIG. 6 is a cutaway perspective view of the annular ultrasonic motor, FIG. 7 is a plan view showing the shape and electrode structure of the piezoelectric body used in the ultrasonic motor of FIG. 6, and FIG. FIG. 9 is an explanatory diagram of the operation principle of the ultrasonic motor, and FIG. 9 is a vibration distribution state and radial displacement distribution diagram of the vibrating body when the bending vibration of the first-order radial direction and the eighth-order circumferential direction is used as the vibration mode. 7 ... elastic body, 8 ... piezoelectric body, 9 ... vibrating body, 10 ... projection body, 11 ... friction material, 12 ... elastic body, 13 ... moving body, 14
……Axis of rotation.

Claims (1)

(57) [Claims] The piezoelectric body is driven by an alternating voltage, so that the disc-shaped vibrating body composed of the piezoelectric body and the elastic body is radially secondary and circumferentially 3
In an ultrasonic motor that excites a traveling wave of a bending vibration equal to or more than the following to move a moving body that is installed in contact with the vibrating body, the sign of the charge induced in the piezoelectric body by the bending vibration is An ultrasonic motor, wherein two sets of drive electrodes are concentrically formed with a circle that changes in the radial direction of the vibrating body as a boundary. 2. The ultrasonic motor according to claim 1, wherein two sets of drive electrodes are concentrically formed in a circle in which the sign of the electric charge induced in the piezoelectric body changes in the radial direction of the vibrating body. 3. Claims are characterized in that two sets of drive electrodes are concentrically arranged, one set inside a circle in which the sign of the electric charge induced in the piezoelectric body changes in the radial direction of the vibrating body, one set outside the circle. The ultrasonic motor according to claim 1. 4. Two sets of concentric drive electrodes are provided in a circle in which the sign of the electric charge induced in the piezoelectric body changes in the radial direction of the vibrating body, and one set of concentric drive electrodes is provided outside the circle. Claim 1 characterized in that one set of the above is a new set of drive electrodes, and another set within the circle is a total of two sets of drive electrodes.
The ultrasonic motor according to the item.