JP2523634B2 - Ultrasonic motor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic motor that uses a piezoelectric body to generate a driving force.

2. Description of the Related Art In recent years, attention has been paid to ultrasonic motors which use elastic vibration as a driving force by exciting elastic vibration in a vibrating body using a piezoelectric body such as a piezoelectric ceramic.

Hereinafter, a conventional technique of an ultrasonic motor will be described with reference to the drawings.

FIG. 5 is a perspective view of a conventional annular ultrasonic motor,
A vibrating body 3 is constructed by laminating an annular piezoelectric ceramic 2 as a piezoelectric body on one of the annular surfaces of the annular elastic body 1. Reference numeral 4 is a friction material made of a wear resistant material, and 5 is an elastic body, which are bonded to each other to form a moving body 6. 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. The arrow in the figure indicates the rotation direction of the moving body 6.

FIG. 6 shows an example of the electrode structure of the piezoelectric ceramic 2 used in the ultrasonic motor of FIG. In the figure, nine elastic waves are arranged in the circumferential direction. In the figure, A and B are electrode groups each consisting of a small region corresponding to a half wavelength, C is a quarter wavelength, and D is a quarter wavelength electrode. The electrodes C and D have a phase difference of a quarter wavelength (= 90 degrees) between the electrode groups A and B. 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 with the elastic body 1 is the surface opposite to the surface shown in FIG. 6, and the electrode is a solid electrode. In use, the electrode groups A and B are short-circuited and used as indicated by the hatched lines in FIG.

V ₁ = V _O × sin (ωt) (1) V ₂ = V _O × cos (ωt) (2) on the electrodes A and B of the piezoelectric body 2 of the ultrasonic motor configured as above V _O : Instantaneous voltage value ω: Angular frequency t: By applying voltages V ₁ and V ₂ represented by time, respectively, the vibrating body 3 has ξ = ξ _O × (cos (ωt) × cos (kx) + sin (ωt) × sin ( kx)) = ξ O × cos (ωt-kx) ... (2) where ξ: the amplitude value of the bending vibration ξ _O: bending the instantaneous value k of the vibration wave number (2π / λ) λ: Wavelength x: A traveling wave of bending vibration that propagates in the circumferential direction, which can be represented by a position, is excited.

FIG. 7 shows that the point A on the surface of the vibrating body 3 makes 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 installed by pressing on the vibrating body 3 has an elliptical shape. By contacting in the vicinity of the apex, frictional force causes v in the direction opposite to the traveling direction of the wave.
It shows that the object moves at a speed of ω × u.

Problems to be Solved by the Invention In order to efficiently drive the ultrasonic motor, it is sufficient to increase the kinetic energy of the vibrating body. Since the kinetic energy is proportional to the square of the mass and speed of the vibrating body, the output can be increased by increasing the mass or speed of the vibrating body. When the outer shape of the ultrasonic motor is determined, the size of the hole of the vibrating body may be reduced to increase the mass, and the amplitude of vibration may be increased to increase the speed. However, the vibration amplitude is limited due to the allowable strain of the piezoelectric body. Further, since the conventional ultrasonic motor uses circular bending vibration of radial first order and circumferential third order or higher, 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 in that the output cannot be increased in the ultrasonic motor using the bending vibration of the circular ring of the first order in the radial direction and the third order or more in the circumferential direction as in the related art.

Further, since the entire vibrating body of the annular ultrasonic motor vibrates as shown in FIG. 8, it is difficult to fix the position of the vibrating body. Moreover, mechanical loss is inevitable due to fixing.

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, a bending vibration mode of a radial second order, a circumferential third order or more is used as the traveling wave, and a drive electrode of the piezoelectric body is Inside the circle in which the electric charge induced by the bending vibration is 0, or inside and outside the circle, the electric impedance and the mechanical impedance are set to be equal to each other, and a portion corresponding to a quarter wavelength in the circumferential direction is provided. Only two pairs of electrodes having different phases are formed.

Operation With the above configuration, the inside of the vibrating body is also effectively contributed to the kinetic energy of the vibrating body, and ideal traveling waves can be easily excited without exciting unnecessary standing waves It is possible to realize an ultrasonic motor with high efficiency and high output.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

Example 1 FIG. 1 (a) is a displacement distribution diagram of a vibrating body in a radial vibration secondary mode and a circumferential direction quaternary bending vibration mode of a disk-shaped ultrasonic motor in Example 1 of the present invention, and FIG. Is a charge distribution diagram induced by the vibration of the vibrating body, FIG.
[FIG. 6] is a plan view showing an electrode structure of the disk-shaped piezoelectric body 8 of the example. In the figure, E and F each have a circumferential direction of 2
The electrode group is composed of small electrode portions having a length corresponding to one-half wavelength, and the polarization directions of the electrode portions adjacent to each other are opposite to the thickness direction. The electrode groups E and F are set such that both the electrical impedance and the mechanical impedance are equal to each other inside the boundary circle where the charge amount induced by the bending vibration of the radial second order and the circumferential fourth order is zero. The phase is shifted in the circumferential direction by a quarter wavelength (90 degrees). Therefore, if the electrode groups E and F are short-circuited and driven by the same voltage with a phase difference of 90 degrees with respect to time, the radial direction secondary and circumferential direction 4 are applied to the vibrating body 9 without exciting unnecessary standing waves. The traveling wave of the next bending vibration is excited.

Example 2 FIG. 2 (a) is a displacement distribution diagram of a vibrating body in a radial vibration mode and a circumferential quaternary bending vibration mode of a disk-shaped ultrasonic motor in Example 2 of the present invention, FIG. 2 (b). Is a charge distribution diagram induced by the vibration of the vibrating body, FIG.
[FIG. 6] is a plan view showing an electrode structure of the disk-shaped piezoelectric body 8 of the example. In the figure, each of F and G has a circumferential direction of 2
The electrode group is composed of small electrode portions having a length corresponding to one-half wavelength, and the polarization directions of the electrode portions adjacent to each other are opposite to the thickness direction. The electrode groups F and G are set so that both the electrical impedance and the mechanical impedance are equal to each other inside and outside the boundary circle where the electric charge amount induced by the bending vibration of the quadratic radial direction and the quaternary circumferential direction becomes zero. The phase is shifted by a quarter wavelength (90 degrees) in the circumferential direction.
Therefore, if the electrode groups F and G are short-circuited and driven at the same voltage with a phase difference of 90 degrees with respect to time, the radial direction secondary and circumferential direction 4 are applied to the vibrating body 9 without exciting unnecessary standing waves. The traveling wave of the next bending vibration is excited.

Embodiment 3 FIG. 3 (a) is a displacement distribution diagram of a vibrating body in a radial vibration secondary and circumferential quaternary bending vibration mode of a disk type ultrasonic motor in Embodiment 3 of the present invention, FIG. 3 (b). Is a charge distribution diagram induced by the vibration of the vibrating body, FIG.
[FIG. 6] is a plan view showing an electrode structure of the disk-shaped piezoelectric body 8 of the example. In the figure, E, F, and G are electrode groups each including a small electrode portion having a length corresponding to a half wavelength in the circumferential direction, and the polarization directions of adjacent electrode portions are opposite to the thickness direction. is there. The electrode groups E, F, and G include only the electrode group E and the electrode groups F and G on the inside and outside of the boundary circle where the charge amount induced by the bending vibration of the radial second order and the circumferential fourth order is zero. The electrical impedance and mechanical impedance, which are
They are set to be equal to each other, and the electrode group E and the electrode groups F and G are configured such that their phases are shifted in the circumferential direction by a quarter wavelength (90 degrees). Therefore, the electrode groups E, F, G
, And the electrode groups F and G are further short-circuited, and the electrode group E and the electrode groups F and G are driven with the same voltage which is 90 degrees out of phase with respect to time. Without doing
A traveling wave of bending vibration of radial second order and circumferential fourth order is excited in the vibrating body 9.

FIG. 4 is a cutaway perspective view showing the configuration of the disc type ultrasonic motor used in the first, second and third embodiments. A disk-shaped piezoelectric ceramic 8 as a piezoelectric body is attached to one of the main surfaces of the disk-shaped elastic body 7 to form a vibrator 9.
Is composed. Further, on the other main surface of the elastic body 7, a protrusion 10 for taking out mechanical output is formed. Reference numeral 11 is a friction material made of a wear resistant material, and 12 is an elastic body, which are bonded to each other to form a moving body 13. The moving body 13 is the friction material 11
Through, and is in pressure contact with the protrusion 10 installed on the moving body 9. 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 vibrating 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. Further, since the vibrating body 9 is driven in the bending vibration mode, the vibrating body 9 can be securely fixed without disturbing the vibration at the center portion where the displacement due to the vibration is small or the node portion of the vibration.

EFFECTS OF THE INVENTION As described above, according to the present invention, the output can be increased by using the bending vibration of the secondary radial direction and the cubic tertiary or higher as the vibration mode, and the electric charge induced by the bending vibration is 0. By setting the electrical impedance and the mechanical impedance to be equal to each other inside the circle, or inside and outside, the ideal traveling wave is excited by applying the same voltage to each electrode group, Further, since the loss due to fixing is small, it is possible to realize an ultrasonic motor with good driving efficiency by a simple driving method.

[Brief description of drawings]

FIG. 1 (a) is a displacement distribution diagram of a driving body of a disk type ultrasonic motor in Embodiment 1 of the present invention, and FIG. 1 (b) is a charge distribution diagram induced by the bending vibration of the driving body. FIG. 2 (c) is a plan view showing the piezoelectric ceramic electrode structure of the same embodiment, FIG. 2 (a) is a displacement distribution map of a driving body of a disc type ultrasonic motor in embodiment 2 of the present invention, and FIG. 6A is a charge distribution diagram induced by the bending vibration of the driving body, FIG. 6C is a plan view showing the piezoelectric ceramic electrode structure of the same embodiment, and FIG. 3A is a third embodiment of the present invention. The displacement distribution diagram of the driving body of the disk type ultrasonic motor, the same figure (b) shows the charge distribution diagram induced by the bending vibration of the driving body, and the same figure (c) shows the piezoelectric ceramic electrode structure of the same embodiment. The plan view shown in FIG. 4, FIG. 4 is a cutaway perspective view of the disc type ultrasonic motor, and FIG. 6 is a plan view showing the shape and electrode structure of the piezoelectric body used in the ultrasonic motor of FIG. 5, FIG. 7 is an explanatory view of the operating principle of the ultrasonic motor, and FIG. FIG. 6 is a displacement distribution diagram of a driving body of the disc type ultrasonic motor used in FIG. 1 ... elastic body, 2 ... piezoelectric body, 3 ... vibrating body, 4 ... friction material, 5 ... elastic body, 6 ... moving body, 7 ... elastic body, 8
...... Piezoelectric body, 9 ...... vibration body, 10 ...... projection body, 11 ...... friction material, 12 ...... elastic body, 13 ...... moving body, 14 ...... rotating shaft.

Claims (1)

(57) [Claims] 1. A movement installed in contact with the piezoelectric body by driving the piezoelectric body with an alternating voltage to excite an elastic traveling wave in the vibrating body composed of the piezoelectric body and the elastic body. In an ultrasonic motor for moving a body, a disk-shaped vibrating body is used as the vibrating body, a bending vibration mode of radial second order, circumferential third order or higher is used as the traveling wave, and a drive electrode of the piezoelectric body is used. Is a quarter wavelength in the circumferential direction in which the electric impedance and the mechanical impedance are set to be equal to each other inside or inside and outside the circle where the electric charge induced by the bending vibration is zero. An ultrasonic motor characterized by comprising two pairs of electrode groups whose phases differ by a considerable amount.