JPH0669300B2 - Ultrasonic motor device - Google Patents

Description

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

2. Description of the Related Art In recent years, an ultrasonic motor that rotates, moves linearly or curvedly by exciting ultrasonic vibration using a piezoelectric body such as a piezoelectric ceramic has been announced, and has attracted attention because of its features such as simple structure, small size and light weight. ing.

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

FIG. 3 shows an example of an ultrasonic motor, which is an annular elastic body 1.
Piezoelectric ceramic 2 as a piezoelectric body on one of the toric surfaces of
Are bonded together to form the piezoelectric driving body 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, bending vibration is excited in the circumferential direction of the driving body 3 and becomes a traveling wave, whereby the moving body 6 rotates.

FIG. 4 shows an example of the electrode structure of the piezoelectric ceramic 2 used in the ultrasonic motor of FIG. In the figure, the bending vibration has 9 wavelengths 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. Therefore, the A electrode group and the B electrode group have a phase shift of a quarter wavelength (= 90 degrees). Adjacent small electrode portions in the electrode groups A and 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. 4, 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.

The operation of the ultrasonic motor configured as described above will be described below. V ₀ · si is applied to the electrode group A of the piezoelectric body 2.
When a voltage represented by n (ωt) is applied (where V ₀ is an instantaneous value of voltage, ω is an angular frequency, and t is time), the driving body 3 causes bending vibration in the circumferential direction.

FIG. 5 is a perspective view of a part of the ultrasonic motor of FIG. 3, in which FIG. 5A is when no voltage is applied to the piezoelectric body 2, and FIG. A state when a voltage is applied is shown.

FIG. 6 is an enlarged view of the contact state between the moving body 6 and the driving body 3. In the electrode group A of the piezoelectric body 2, V ₀ · sin (ω
t), the phase of V ₀ · cos (ωt) in the electrode group 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, if the amplitude of a traveling wave is ξ, then ξ = ξ ₀ · cos (ωt−kx) (1) where ξ ₀ : instantaneous value of wave size k: wave number (= 2π / λ) λ: wavelength x : Can be expressed by position. Equation (1) is ξ = ξ ₀ · (cos (ωt) · cos (kx) + sin (ωt) · s
in (kx)) ・ ・ ・ (2) can be rewritten. Equation (2) shows that the traveling wave is cos (ωt) and sin (ωt) with phase shifted by π / 2 in time, and π / 2 in position. It is shown that it can be obtained by the sum of the products of cos (kx) and sin (kx) that are out of phase with each other. From the above description, the piezoelectric bodies 2 are positioned π / 2 (= λ / 4) relative to each other.
Since it has the electrode groups A and B that are out of phase with each other, an AC voltage that is temporally out of phase with π / 2 is generated from the output of the oscillator having a frequency output equal to the resonance frequency of the driving body 3. By applying to the electrode group, a progressive wave of bending vibration can be generated in the driving body 3.

In addition, the figure shows that the point A of the driving body makes an elliptical motion of the long axis 2w and the short axis 2u by the traveling wave, and the moving body 6 placed on the driving body 3 contacts at the apex of the ellipse. , Shows a state of moving at a velocity of v = ωu in the direction opposite to the traveling direction of the wave. That is, the moving body 6 is pressed against the driving body 3 by an arbitrary static pressure and comes into contact with the surface of the driving body 3, and the moving body 6 and the driving body 3
It is driven at a speed v in the direction opposite to the traveling direction of the wave by the frictional force between and. When there is a slip between the two, the speed becomes smaller than v above. The speed v of the ultrasonic motor shown above can be represented by v = ωt∝ωξ ₀ (3) and is proportional to the instantaneous amplitude value ξ ₀ of the bending vibration of the driving body 3. Therefore, the ultrasonic motor is driven at the resonance frequency of the driver 3 in which a large current flows with a small voltage.

Problems to be Solved by the Invention However, the frequency characteristics of the admittance of the driving body 3 are different during start-up and during operation of the ultrasonic motor, as shown in FIG. This is because the driving body 3 is in surface-to-surface contact with the moving body 6 at the time of start-up, but is in linear contact during operation as shown in FIG. In FIG. 7, a is the frequency characteristic of the admittance of the driving body 3 at rest and at start-up, and b is in operation. Also in the figure,
f _r1 is a resonance frequency at the time of operation, and f _r2 is a resonance frequency at the time of starting. In other words, the resonance frequency, which is the optimum drive frequency, varies during startup and operation. Therefore, if the ultrasonic motor is driven at the same frequency during start-up and operation as in the conventional case, stable and efficient driving cannot always be performed.

The present invention has been made in view of the above points, and an object thereof is to provide an ultrasonic motor device that is always efficient and capable of stable operation.

Means for Solving the Problems The present invention is to solve the above problems, and in a separately-excited drive circuit, an oscillator whose oscillation frequency can be changed between start-up and operation and an amplifier whose gain can be changed are provided. , Only the oscillator, or both. Further, in the self-excited system, only the frequency selection circuit whose center frequency is variable and the frequency selection circuit of the amplifier whose gain is variable have both.

For both the separately-excited method and the self-excited method, the drive frequency of the ultrasonic motor is made to match the resonant frequency of the driver at startup and operation, and the impedance change at startup and operation is changed by changing the gain of the amplifier. Absorb. Further, only the drive frequency is always matched with the drive frequency so that efficient and stable operation can always be performed.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the ultrasonic motor device of the present invention. In the figure, 7 is an oscillator and 8
Is an amplifier. The oscillation frequency of the oscillator 7 is determined by the resistors R ₁ , R ₂ and the capacitor C ₁ , and the gain of the amplifier 8 is determined by the resistors R ₃ , R ₄ , R ₅ . When the power supply voltage V _cc is applied, the charging voltage determined by the resistor R ₆ and the capacitor C ₂ is applied to the input of the buffer 9, and immediately after the power supply voltage V _cc is applied, the output of the buffer 9 is at the logic level “L”. When the charging voltage exceeds the threshold voltage of the buffer 9,
The output of the buffer 9 becomes a logic level "H". That is, when the ultrasonic motor is started, the oscillation frequency f of the oscillator 7
_r is Where K is determined by a constant, it keeps equal the oscillation frequency f _r to f _r2 of Figure 7. The gain G of the amplifier 8 is determined by _{G = -R 4 / R 3 ......} (5). The output of the oscillator 7 is amplified by the amplifier 8 to a level sufficient to start the ultrasonic motor. One of the amplified signals is input to the 90 ° phase shifter 11 and then to the power amplifier 12. The other is directly input to the power amplifier 13.
These two drive signals having different 90 ° phases are applied to the piezoelectric ceramic 2 of the driving body 3 of the ultrasonic motor, and the ultrasonic motor is stably activated.

Immediately after starting, the output of the buffer 9 becomes "H", and both the analog switches 10 are closed. Thus the oscillation frequency f _r of the oscillator 7 extracts a drive signal applied to the 2 transformer 16, by passing only a predetermined frequency range after passing through the buffer 15, the oscillation frequency to the resonant frequency of the driver 3 Serves as a match. Without this bandpass filter, it oscillates at any frequency as long as the oscillating conditions are met, so it oscillates in modes other than the mode of interest.

At startup, the input of the inverter 18 has not reached its threshold voltage, so its output becomes "H" and both analog switches 17 are closed. The characteristics of the bandpass filter at this time are However A _r is the amplification factor, f _r is the center frequency, Q is represented by the selectivity of the filter. The center frequency f _r of the set to be equal to f _r2 of FIG. 7, a resistor _{R 7, R 8, R 10} , R 11 (9) to decide the gain of the amplifier from equation (8), (9) determine the Q so that _f r = _{f r2} from the equation.

Then the input of the inverter 18 is Ji through a resistor R ₁₂ capacitor C
₄ exceeds the threshold hold voltage because it is charged from the supply voltage V _cc. From that time, the output becomes "L", both analog switches 17 open, and the characteristics of the bandpass filter are Determined by The center frequency f _r in the same manner as described above and equal to f _r1 of FIG. 7 determines the gain A _r, the selectivity Q by resistor R _7, R _10.

The signal that has passed through the bandpass filter is amplified by the amplifier 19 by a certain amount, and becomes a drive signal for the ultrasonic motor by the 90 ° phase shifter 9 and the power amplifiers 10 and 11.

As described above, the embodiment of FIG. 2 drives the ultrasonic motor at the resonance frequency of the driving body 3 at the time of startup and during operation,
Since a change in impedance is absorbed by adjusting the gain, a stable self-excited drive device is obtained.

In this embodiment, both the driving frequency and the driving voltage are changed at the time of starting and during operation, but changing the driving frequency alone has a sufficient effect.

EFFECTS OF THE INVENTION As described above, according to the present invention, it is possible to always perform efficient and stable driving at the time of starting and operating the ultrasonic motor.

[Brief description of drawings]

FIG. 1 is a block diagram of an ultrasonic motor device according to an embodiment of the present invention, FIG. 2 is a block diagram of an ultrasonic motor device according to another embodiment of the present invention, and FIG. 3 is a sectional view of the ultrasonic motor. FIG. 4 is a plan view showing the shape and electrode structure of the piezoelectric body used in the ultrasonic motor, FIG. 5 is a model diagram showing the vibration state of the driving body portion of the ultrasonic motor, and FIG. 6 is the ultrasonic motor. FIG. 7 is an explanatory diagram of the principle, and FIG. 7 is a frequency characteristic diagram of impedance of a driving body of the ultrasonic motor. 7 ... Oscillator, 8 ... Operational amplifier, 9 ... Buffer, 10
…… Analog switch, 11 …… 90 degree phase shifter, 12,13 ……
Power amplifier, 14 ... Operational amplifier, 15 ... Buffer, 16 ...
… Transformer, 17 …… Analog switch, 18 …… Inverter, 19 …… Amplifier.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hiroshi Ouchi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-60-22480 (JP, A)

Claims (4)

[Claims] 1. An elastic body and a piezoelectric body are combined to form a piezoelectric driving body, and by applying an AC voltage to the piezoelectric of the piezoelectric driving body, elastic vibration is excited in the piezoelectric driving body, and the elasticity is generated. An ultrasonic motor that moves a moving body that comes in contact with the body and that has an oscillator that changes the oscillation frequency during startup and normal operation, and a control that changes the frequency of the oscillator by distinguishing between startup and normal operation. An ultrasonic motor device having a separately-excited drive circuit including a controller for performing the operation. 2. The ultrasonic motor device according to claim 1, further comprising an amplifier whose gain can be changed during starting and during normal operation. 3. A piezoelectric driving body is formed by coupling an elastic body and a piezoelectric body, and an AC voltage is applied to the piezoelectric body of the piezoelectric driving body to excite elastic vibrations in the piezoelectric driving body. An ultrasonic motor that moves a moving body that comes in contact with an elastic body, and uses a frequency selection circuit that changes the center frequency between startup and normal operation, and a frequency selection circuit that distinguishes between startup and normal operation. An ultrasonic motor device having a self-excited drive circuit including a controller that performs control for changing a center frequency. 4. The ultrasonic motor device according to claim 3, further comprising an amplifier whose gain can be changed during starting and during normal operation.