JPS6292782A - Ultrasonic motor device - Google Patents

Abstract

PURPOSE:To stabilize low-speed revolution operation by simple circuit constitution by applying a periodic voltage waveform to a control terminal for a VCO, periodically changing the output frequency of the VCO and applying it to a piezoelectric body. CONSTITUTION:An output from a VCO7 is divided into two, one is phase-shifted at 90 deg. by a 90 deg. phase shifter 8, and the other are directly inputted to power amplifiers 9, 9', and amplified up to predetermined levels and applied to a piezoelectric ceramic 3. A control voltage generator 10 transmits a signal, a voltage value thereof periodically changes, over a control terminal for the VCO7. The VCO7 and the control voltage generator 10 are set previously so that there is the resonance frequency of a driver altering by the changes of a temperature and load in the frequency variation region of the VCO7.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an ultrasonic motor device that generates driving force using a piezoelectric body.

Background of the Invention In recent years, ultrasonic motors have been announced that use piezoelectric materials such as piezoelectric ceramics to excite ultrasonic vibrations to generate rotational, linear, or curved motion. Attention has been paid.

Hereinafter, the conventional technology of an ultrasonic motor will be explained with reference to the drawings.

Figure 3 shows an example of an ultrasonic motor, with an annular elastic body 1
An annular piezoelectric ceramic 2 is placed as a piezoelectric body on one of the annular surfaces of the
The piezoelectric drive body 3 is configured by laminating the two. 4 is a slider made of a wear-resistant material, and 5 is an elastic body, which are pasted together 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 this becomes a traveling wave, thereby causing the moving body 6 to rotate.

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 nine wavelengths in the circumferential direction. In the same figure, people and B are electrode groups each consisting of a small area corresponding to a half wavelength, C is an electrode group having a length of three-quarters of a wavelength, and D is an electrode with a length of one-quarter of an e.

Therefore, the position of the electrode group of the person and the electrode group of B is one quarter.
There is a phase shift of wavelength (290 degrees). Adjacent small electrode portions in electrode groups A and B are polarized oppositely to each other in the thickness direction. The adhesive surface of the piezoelectric ceramic 2 with the elastic body 1 is the opposite surface to the surface shown in FIG. 4, and the electrode is a solid electrode. When in use, electrode groups A and B are short-circuited, as indicated by diagonal lines in FIG. 4.

The operation of the ultrasonic motor configured as described above will be described below. −
When a voltage expressed as ground (ωt) is applied (where V is the instantaneous value of the voltage, ω is the angular frequency, and t is the time), the driving body 3 bends and vibrates in the circumferential direction. 3 is a perspective view of a part of the ultrasonic motor of FIG. 3, and FIG. 3 shows the state when no voltage is applied to the piezoelectric body 2;

FIG. 6 is an enlarged depiction of the contact situation between the moving body 6 and the driving body 3. Vo-5In (
ωt) - By applying voltages To -as (ωt )O whose phases are shifted from each other by π/2 to the other electrode group B, a traveling wave for bending imaging can be created in the circumferential direction of the driving body 3. .

Generally speaking, if the amplitude of a traveling wave is ξ, then ξ=ξ.・cDs(ωt
-kx) ・・・・・・・・・ (1) However, ξ
. Instantaneous value of the magnitude of two waves k: Wave number (=2π/λ) λ: Wavelength X: Can be expressed as position. Equation (1) is ξ=ξ.・(House(ωt)・cQg(kx)+5 koku(ωt)
)・sin (kg) )=-= (2) can be rewritten as Equation (2), where the traveling wave has a plate part (ωt) and a coil (ωt) whose phase is shifted by π/2 in time, and positionally. It is shown that it is obtained by the sum of the products of ctls(kX) and sm(kx), which are out of phase by π/2. From the above explanation, the piezoelectric bodies 2 are located at π/2 (=λ/4) relative to each other.
Electrode group A with a phase shift of .

B, from the output of an oscillator with a frequency output equal to the resonant frequency of the driver 3, create an AC voltage with a phase difference of π/2 in time for each, and apply it to the electrode group to drive. A traveling wave of bending vibration can be created in body 3.

Figure 6 shows that point A of the driving body is moving in an ellipse with a major axis 2W and a minor axis 2u due to traveling waves. , it shows how the wave moves at a speed of V=ωU in the opposite direction to the direction of travel of the wave. That is, the moving body 6 is pressed against the driving body 3 with an arbitrary static pressure, contacts the surface of the driving body 3, and is driven at a speed V in the direction opposite to the direction of wave propagation due to the frictional force between the moving body 6 and the driving body 3. Ru. When there is slippage between the two, the velocity becomes smaller than the above V. Further, the speed V of the ultrasonic motor shown above is: (1)=ωuccωξ.・・・・・・・・・
(3), which is the instantaneous amplitude value ξ of the bending vibration of the driving body 3.

is proportional to. Therefore, a large speed can be obtained by driving at the resonant frequency of the driving body 3 through which a large current flows with a small voltage. FIG. 7 shows the relationship between drive frequency and motor rotation speed.

Problems to be Solved by the Invention However, as shown in FIG. 8, the frequency characteristics of the impedance of the driving body 3 differ between when the ultrasonic motor is started and when it is in operation. This is because the driving body 3 is in surface-to-plane contact with the moving body 6 at the time of starting, but during operation, the driving body 3 is in linear contact as shown in FIG. 6. In FIG. 8, a is the frequency characteristic of the impedance of the driving body 3- when it is at rest and when it is started, and b is the frequency characteristic of the impedance of the driving body 3- when it is in operation. Also, in the same figure,
fr+ is the resonant frequency at the time of operation, and fr2 is the resonant frequency at the time of starting. In other words, the resonant frequency, which is the optimum drive frequency, varies between startup and operation. Therefore, if the ultrasonic motor is driven at the same frequency during startup and operation as in the past, efficient driving cannot be achieved at all times.

Therefore, it is necessary to always drive at the resonant frequency of the driver 3, both during startup and during operation. Furthermore, since the resonant frequency changes not only due to load fluctuations but also due to temperature, it is necessary to respond to these changes.0 Also, the speed V of the ultrasonic motor is the instantaneous amplitude value ξ.

is proportional to the instantaneous value ξ. is proportional to the current i flowing through the driving body, so the current i and the speed V are in a proportional relationship.

Therefore, if you want to rotate at a low speed, you only need to reduce the current i. However, as shown in FIG.
and the amplitude value ξ such that minute irregularities on the contact surface of the moving object 6 cannot be ignored. In the vicinity of 10, the operation becomes unstable and the ultrasonic motor eventually stops.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an ultrasonic motor device that has a simple circuit configuration and is capable of stable low-speed rotational operation.

The only way to solve the problem is to add a periodic voltage waveform to the control terminal of the VCO (voltage controlled oscillator) so that the resonant frequency of the driver exists within the variable range, and change the output frequency of the VCO to a period. One of them is changed as is, and the other is amplified after being phase-shifted by 90 and applied to the piezoelectric material.

Since the operating drive frequency changes periodically and the resonant wave number of the driving body is always within the range of change, stable low-speed rotation can be obtained even with changes in temperature and load.

EXAMPLE An example of the present invention will be described below with reference to the drawings. FIG. 1 is a functional block diagram of an ultrasonic motor device according to an embodiment of the present invention. In the same figure, 7 is a VG that generates an AC signal to drive the piezoelectric driver 3 as shown in FIG.
It is a voltage controlled oscillator (voltage controlled oscillator), and the output of the VCO is divided into two parts, one of which is phase-shifted by 90 degrees by a 90 phase shifter 8, and the other is directly input to power amplifiers 9 and 9', respectively.

The power amplifier 9.9' amplifies the AC signal to a level at which the ultrasonic motor operates stably. The two amplified signals having a phase difference of 900° are the electrodes of the piezoelectric ceramic 2 that constitute the piezoelectric driver 3.

B, respectively.

A control voltage generator 10 generates a signal whose voltage value changes periodically. The output of the control voltage generator 10 is the VCO
The VCO7 is input to the control terminal of the control voltage generator 1.
The frequency is changed periodically according to the output voltage of 0.

In this frequency change region, the VC
If O7 and control voltage generator 1o are set, VC
The oscillation frequency of O7 always passes through the resonant frequency of the driver 3. The ultrasonic motor rotates quickly near this frequency and slowly at other frequencies, resulting in a slow average speed. In other words, stable low-speed rotation can be obtained.

To control the rotational speed, if the frequency variable range of VC:07 is increased, the rotational speed will be decreased, and if the variable range is decreased, the rotational speed will be increased. Also, if the driving voltage is increased, the speed will be reduced, and if the driving voltage is decreased, the speed will be reduced.

FIG. 2 is an explanatory diagram of one embodiment of the present invention shown in FIG. As shown in the figure, the output of the control voltage generator 10 uses a triangular wave, and the output frequency of the VCO 7 changes accordingly. The amount of resonance frequency of the driving body 3 is within this frequency range. is set so that it exists. The operation of the motor is shown in a of the same figure, and the output frequency of the VCO 7 is the resonance frequency f of the driver 3.

The motor rotates at a high speed when it passes through , and at other times it stops but rotates at a low speed. Therefore, the average speed becomes low as shown in the figure.

Effect of the invention According to the present invention, temperature can be controlled with an extremely simple configuration.

It is possible to provide an ultrasonic motor device that can provide stable low-speed rotation even when the load changes.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an ultrasonic motor device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of the embodiment of FIG. 1, FIG. 3 is a sectional view of the ultrasonic motor, and FIG. Figure 6 is a plan view showing the shape and electrode structure of the piezoelectric body used in the figure, Figure 6 is a model diagram showing the vibration state of the driver section of the ultrasonic motor, Figure 6 is an explanatory diagram of the principle of the ultrasonic motor, Figure 7 shows drive frequency vs. motor rotation speed 7...VCO (voltage controlled oscillator), 8
...9o0 phase shifter, 9,9'...power amplifier, 10...control voltage generator. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Gin Open Figure 3 Otsu 1 Do Figure 4 3 Figure 5 1 Figure 6 1.7 3 Connecting Choku Sakuranosoft fO9 Co-technical Training Figure 8 Number of L between 2 Figure 9 House Takei

Claims (1)

[Claims] In an ultrasonic motor that moves an object by creating an elastic traveling wave using a piezoelectric body as a driving source, an alternating current is applied to the piezoelectric body, and the resonant frequency of the driving body constituted by the piezoelectric body is within its frequency variable range. A variable oscillator inside the
An ultrasonic motor device comprising: a control circuit that periodically controls the output frequency of the variable oscillator so that it always passes through the resonance frequency.