JPH0732609B2 - 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 that use elastic vibration as a driving force by exciting elastic vibration in a driving body that uses a piezoelectric body such as piezoelectric ceramic.

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

FIG. 4 is a perspective view of a conventional ultrasonic motor, in which a ring-shaped piezoelectric ceramic 2 is bonded as a piezoelectric body to one of the ring-shaped surfaces of a ring-shaped elastic body 1 to form a piezoelectric driver 3. Reference numeral 4 is a slider 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 driving body 3 via the slider 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 driving body 3 to drive the moving body 6. The arrow in the figure indicates the rotation direction of the moving body 6.

FIG. 5 shows an example of the electrode structure of the piezoelectric ceramic 2 used in the ultrasonic motor of FIG. In the figure, elastic waves of 9 wavelengths are arranged in the circumferential direction. In the figure, A and B are electrodes each consisting of a small region corresponding to a half wavelength, C is a quarter wavelength and D is a quarter wavelength electrode. Therefore, the A electrode and the B electrode have a positional phase shift of ¼ wavelength (= 90 degrees). Electrode A,
Adjacent small electrode portions in B are polarized in the thickness direction opposite to each other. The surface of the piezoelectric ceramic 2 bonded to the elastic body 1 is the surface opposite to the surface shown in FIG. 5, and the electrode is a solid electrode. When used, the electrode groups A and B are short-circuited and used as indicated by the hatched lines in FIG.

The operation of the ultrasonic motor configured as described above will be described below. When a voltage represented by V = V ₁ × sin (ωt) (1) is applied to the electrode A of the piezoelectric body 2 (where V ₁ is an instantaneous value of voltage, ω is an angular frequency, t is time), The driver 3 vibrates flexurally in the circumferential direction.

FIG. 6 is a perspective view when the driving body of the ultrasonic motor of FIG. 4 is linearly approximated. FIG. 6A shows the piezoelectric body 2 when no voltage is applied, and FIG. 6B shows the piezoelectric body. A state when a voltage is applied to the body 2 is shown.

FIG. 7 is an enlarged view of the contact state between the moving body 6 and the driving body 3. V ₁ × sin (ω
t), the phase of V ₁ × cos (ωt) relative to the other electrode B is π /
If a voltage deviated by 2 is applied, a traveling wave of bending vibration can be generated in the circumferential direction of the driving body 3. Generally, when the amplitude of a traveling wave is ξ, ξ = ξ ₁ × cos (ωt−kx) (2) where ξ ₁ : instantaneous value of wave magnitude k: wave number (2π / λ) λ: wavelength x: It can be expressed as a position. Equation (2) can be rewritten as ξ = ξ ₁ × (cos (ωt) × cos (kx) + sin (ωt) × sin (kx)) (3), and in Equation (3), the traveling wave is π in terms of time. Obtained as the sum of the products of waves cos (ωt) and sin (ωt) that are out of phase by / 2, and cos (kx) and sin (kx) that are out of phase by π / 2 It is shown that. From the above description, since the piezoelectric body 2 has the electrode groups A and B which are phase-shifted from each other by π / 2 (= λ / 4), the piezoelectric body 2 has a frequency output equal to the resonance frequency of the driving body 3. From the output of the oscillator, an alternating voltage that is temporally shifted by π / 2 in phase is generated and applied to the electrode group, whereby a progressive wave of bending vibration can be generated in the driving body 3.

Fig. 7 shows that the point A of the driver is excited by a traveling wave
w, showing the elliptical motion of the short axis 2u, the driver 3
It is shown that the moving body 6 placed on top of the ellipse moves at a velocity of v = ω × u in the direction opposite to the traveling direction of the wave when the moving body 6 contacts at the apex of the ellipse. That is, the moving body 6 is pressed against the driving body 3 with an arbitrary static pressure, comes into contact with the surface of the driving body 3, and the frictional force between the moving body 6 and the driving body 3 causes the moving body 6 to move at a velocity v in the direction opposite to the traveling direction of the wave. Driven. When there is a slip between the two, the speed becomes smaller than v above.

Problems to be Solved by the Invention As described above, the conventional ultrasonic motor requires two AC voltages that are temporally different in phase by π / 2 as drive signals.

In the conventional ultrasonic motor that requires two signals for driving, the driving circuit is essentially complicated, and at least three lead wires are taken out from the electrodes of the piezoelectric ceramic for applying an electric signal.
Become a book.

The present invention has been made in view of the above points, and an object thereof is to provide an ultrasonic motor that can be driven by only one AC signal.

Means for Solving the Problems A piezoelectric body forming a driving body is provided with first and second electrodes formed on the surface of the piezoelectric body so as to be shifted by a quarter wavelength relative to each other, and an AC voltage is applied during driving. The first electrode is 2
The second electrode, which is composed of a plurality of small electrodes having a length corresponding to one-half wavelength and to which no AC voltage is applied during driving, has a length of 2 in a small plane having a half wavelength. Small electrodes with a wavelength less than one-half wavelength are formed asymmetrically, and a plurality of the small electrodes are arranged so that the small planes are adjacent to each other.

Operation When an AC voltage is applied as a drive signal to the first drive electrode, the first standing wave is excited in the drive body. Then, the first standing wave excites a charge on the second electrode, which causes a second standing wave that is substantially 90 degrees out of phase with the first standing wave temporally and positionally. Excited by the driver.

Then, the elastic traveling wave is excited in the driving body by the first standing wave and the second standing wave, and the moving body installed on the driving body moves.

That is, by forming the first electrode that applies an AC voltage to the piezoelectric body and the second electrode that does not apply an AC voltage that has the above-described relationship with the first electrode, it is possible to obtain a superposition with only one drive signal. The sonic motor can be driven.

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

FIG. 1 is a plan view of a piezoelectric body that constitutes a driving body of an ultrasonic motor according to an embodiment of the present invention. In the figure, 7 is a piezoelectric body, and electrodes are attached to both surfaces. E is a first electrode composed of a small electrode whose length in the circumferential direction is slightly shorter than one-half wavelength, and applies an AC signal voltage in the vicinity of the resonance frequency of the driver. The polarization direction of the small electrode of the electrode E and the direction of the applied voltage are set to alternate between the same direction and the opposite direction. In the figure, the small electrodes that are adjacent to each other have opposite polarization directions and are short-circuited to each other for driving. That is, the first electrode E corresponds to the electrode A of FIG. 5 which is a conventional example. F has a circumferential length of 2 which is phase-shifted from the electrode E by a quarter wavelength.
The second electrode is a small electrode having a length in the circumferential direction of less than one-half wavelength, which is asymmetrically installed in the plane of one-half wavelength. That is, as the second electrode F, a small electrode having a length in the circumferential direction of less than ½ wavelength is formed asymmetrically in the place where the electrode B of FIG. 5 which is a conventional example is formed. It is a thing. In this embodiment, the length of the small electrode is slightly shorter than the quarter wavelength. In the figure, the direction of polarization in the adjacent small electrode portions is set so that the electric charges induced in the small electrodes of the electrode F by the standing wave excited by driving the electrode E have the same polarity in the adjacent small electrodes. However, it is also possible to use them by opening them by making the polarization directions of adjacent small electrode parts the same. The electrodes G and H have circumferential lengths of 3/4 wavelength and ¼ wavelength, respectively, and the positional phase difference between the electrodes E and F is ¼ wavelength.
I am trying to reach the wavelength. That is, the electrodes G and H may be omitted. The back surface of the piezoelectric body 7 is a solid electrode. The driving body is constructed by bonding the back surface of the piezoelectric body as described above to the elastic body.

FIG. 2 is an operation explanatory view of a driving body using the piezoelectric body shown in FIG. FIG. 6A shows that a standing wave 9 of bending vibration is excited in the driving body when an AC signal voltage V ₁ near the resonance frequency of the driving body is applied to the lead wire 8 taken out from the electrode E. Shows. In the conventional electrode structure, the second electrode is the same as the first electrode, and only its position is shifted by a quarter wavelength. Therefore, the second electrode is excited by the standing wave excited by the first electrode. The charge applied is zero. However, in the present embodiment, the second electrode F is a small electrode having a length in the circumferential direction of less than ½ wavelength and is located at a position where the electrode B of FIG. 5 which is a conventional example is formed. Since it is formed asymmetrically, the standing wave 9 excited by the electrode E induces electric charges in the electrode F, resulting in a positional relationship with the standing wave 8, as shown in FIG. It is possible to excite a standing wave 11 having a quarter wavelength and a temporally different π / 2 phase. However, the lead wire 10 taken out from the electrode F is in an open state. The same figure (c)
FIG. 3 is a model diagram in which a part of the driving body formed of the piezoelectric body of FIG. 1 is linearized. The polarization direction of each part of the electrode E and the electrode F and each positional relationship are shown.

FIG. 3 is an equivalent circuit of a driving body using the piezoelectric body shown in FIG. In the figure, C ₁ and C ₂ are lead wires 8 and 10, respectively.
Capacitance seen, T ₁ and T ₂ are transformers for electro-mechanical conversion by electrodes E and F, Zm is mechanical impedance of driver,
Z ₁ is the mechanical impedance of the moving body installed in contact with the driving body as seen from the driving body. From the figure, AC signal voltage
V ₁ can excite the standing wave 9 to the driving body through the transformer T ₁ , and the standing wave 9 induces electric charge in the electrode F through the transformer T ₂ , and if the lead wire 10 is left open Voltages with different π / 2 phases are induced in. Since the electrodes E and F are out of phase with each other by a quarter wavelength position, an elastic traveling wave can be generated in the driving body according to the formula (3).

EFFECTS OF THE INVENTION According to the present invention, since an elastic traveling wave can be excited in the driving body with only one AC voltage, the driving circuit becomes extremely simple, and two lead wires can be taken out, one for driving and the other for common. Can be simplified and reliability can be improved.

[Brief description of drawings]

FIG. 1 is a plan view of a piezoelectric body which constitutes a driving body of an ultrasonic motor according to an embodiment of the present invention, FIG. 2 is an operation explanatory view of the driving body using the piezoelectric body of FIG. 1, and FIG. 2 is an equivalent circuit diagram of the driving body, FIG. 4 is a perspective view of a conventional ultrasonic motor, FIG. 5 is a plan view showing the shape and electrode structure of the piezoelectric body used in FIG. 4, and FIG. FIG. 7 is a model diagram showing a vibration state of a driving body portion of the ultrasonic motor, and FIG. 7 is an explanatory diagram of the principle of the ultrasonic motor. 7 ... Piezoelectric body, 8,10 ... Lead wire, 9,11 ... Standing wave, E,
F: Electrode.

Claims (1)

[Claims] 1. An ultrasonic motor for moving a moving body, which is installed in contact with the driving body, by exciting an elastic traveling wave into a driving body composed of an elastic body and a piezoelectric body, wherein First and second electrodes are formed on the surface so as to be displaced from each other by a quarter wavelength, and the first electrode to which an AC voltage is applied at the time of driving is
The second electrode, which is composed of a plurality of small electrodes having a length corresponding to one-half wavelength and to which no AC voltage is applied during driving, has a length of 2 in a small plane having a half wavelength. An ultrasonic motor characterized in that a small electrode having a wavelength of less than one-half wavelength is formed asymmetrically, and a plurality of the small electrodes are arranged so that the small planes are adjacent to each other.