JP3191406B2 - Driving method of ultrasonic motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving method of an ultrasonic motor which generates a driving force by exciting a vibrating body with an elastic wave using a piezoelectric body such as a piezoelectric ceramic.

[0002]

2. Description of the Related Art An ultrasonic motor and a conventional driving method thereof will be described below with reference to the drawings.

FIG. 5 is a cutaway perspective view of a ring type ultrasonic motor. A ring type piezoelectric ceramic 2 as a driving piezoelectric body is bonded to one of the ring surfaces of a ring type elastic substrate 1 with an adhesive. The ring-shaped vibrator 3 is configured. 4
Is a friction material made of an abrasion-resistant material, and 5 is an elastic body. The moving body 6 is placed in pressure contact with the vibrating body 3 by a pressing means such as a spring (not shown) via the friction material 4.

FIG. 6 is a structural view of a drive electrode formed on the piezoelectric ceramic 2, in which two sets of drive electrodes A and B which are displaced in position by a quarter wavelength of an elastic traveling wave are formed.
The drive electrodes A and B are each composed of a small electrode group having a length corresponding to a half wavelength. Electrodes C and D are 3 /
Drive electrodes A and B having lengths equivalent to 4 wavelengths and 1/4 wavelength
Is formed in order to create a positional shift equivalent to 1/4 wavelength.

When two AC voltages having phases different from each other by 90 degrees are applied to the drive electrodes A and B (for example, a sine wave and a cosine wave), a traveling wave of bending vibration as shown in FIG. You. Here, FIG. 7A shows a vibration mode of bending vibration, and FIG. 7B shows a radial displacement distribution. For ring type ultrasonic motors, radial primary and circumferential 3
A traveling wave of bending vibration of the next or higher order is excited in the vibrating body 3. Due to the transverse component of the wave front of the traveling wave, the moving body 6 is driven by friction and rotates.

As shown in FIG. 8, the vibrating body of the ultrasonic motor exhibits resonance / anti-resonance characteristics when viewed from the drive terminal, as in the case of the piezoelectric ceramic alone, and has a low impedance near the resonance frequency. If driven near the frequency, an elastic traveling wave can be efficiently excited at a low voltage. However, as shown by the arrow in the figure, the admittance of the vibrator by the sweep direction of the drive frequency indicates a hysteresis characteristic from the frequency f ₁ in the region of the f _2, admittance of the vibration body in this region is not determined uniquely super The operation of the sound wave motor becomes unstable. Therefore, unstable operation regions highly stable operation region than (f region of ₂ from the frequency f ₁ of the drawing) (in the drawing from the frequency f ₂ of f ₃ region) of the drive vibrator of the ultrasonic motor
It is necessary to drive stably within.

[0007]

In the conventional ultrasonic motor, in order to drive the vibrating body near its resonance frequency, the electrode C or the electrode D of the piezoelectric body electrode structure shown in FIG. The sensor electrode is used as a sensor electrode for detecting vibration, and the output of the sensor electrode controls the speed of the moving body, and controls the driving frequency near the resonance frequency of the vibrating body. However, the vibrating body oscillates a large number of high frequency components together with the fundamental frequency component for driving. Therefore, if the output of the sensor electrode is directly converted to direct current and then used for control as in the prior art, high-frequency components that do not contribute to the movement of the moving body are simultaneously converted to a direct current signal, and the control accuracy of the rotational speed of the moving body is simultaneously controlled. And the control accuracy of the drive frequency also deteriorates.

The present invention solves the above-mentioned conventional problems, and accurately detects an output voltage effective for rotation of a moving body of a sensor electrode and controls a moving speed of the moving body and a driving frequency of a vibrating body. It is another object of the present invention to provide a high-efficiency ultrasonic motor with stable operation.

[0009]

Means for Solving the Problems A sensor electrode is formed on a piezoelectric body constituting a vibrating body of an ultrasonic motor together with a driving electrode, and an electric voltage generated on the sensor electrode when the vibrating body is driven.
Unwanted high-frequency components that do not contribute to the movement of the moving object from pressure
And adjust the voltage from which the unnecessary high-frequency components have been removed.
To the DC circuit of the rectifier circuit
Depending on the difference from the set voltage corresponding to the moving speed of the moving object
Rectifying circuit using the signal as a control signal and the control signal
Move the above so that the DC output of
Control body speed. Further, in the above configuration,
Using a low-pass or low-pass filter
Do not contribute to the movement of the moving object from the voltage generated at the sensor electrode.
Remove unnecessary high frequency components. Also in the above configuration
In addition, the DC output of the rectifier circuit is
To the other input terminal of the error circuit.
Input the set voltage corresponding to the moving speed of the target moving object
And amplifies the error between the DC output and the set voltage.
An error signal output from the error amplifier circuit is used as a control signal.
You. In the above configuration, the driving frequency of the vibrating body is further
Than the frequency at which the vibrating body shows the hysteresis characteristic.
Set higher.

[0010]

A sensor electrode is formed on a piezoelectric body constituting a vibrating body of an ultrasonic motor together with a drive electrode. When the vibrating body starts vibrating, the sensor electrode generates a voltage proportional to the magnitude of the vibration by a piezoelectric effect. However, this generated voltage contains a large amount of high-frequency components that do not contribute to the movement of the moving body together with the fundamental frequency of driving. By passing the generated voltage of the sensor electrode through a band-pass filter or a low-pass filter, high-frequency components are removed and then input to the rectifier circuit, and only the components that contribute to the moving speed of the moving object are converted to DC components and used as control signals. By doing so, the moving speed of the moving body and the driving frequency of the vibrating body are stably controlled, so that a highly efficient driving of the ultrasonic motor with constantly stable operation is realized.

[0011]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of an ultrasonic motor drive control circuit which is an embodiment of the ultrasonic motor drive method according to the present invention. In FIG. 1, a voltage control oscillation circuit 7 has a control terminal T capable of changing the oscillation frequency by a voltage, and outputs an oscillation signal having a frequency corresponding to the applied voltage.
The output signal of the voltage controlled oscillation circuit 7 is divided into two, and one signal is phase-shifted by 90 degrees by a 90-degree phase shift circuit 8, and the other signal is left as it is, and two signals having a phase difference of 90 degrees respectively. Is made. These two signals are power-amplified by power amplifier circuits A9 and B10, respectively, to a voltage value sufficient to drive the ultrasonic motor, and applied to drive electrodes A and B of the ultrasonic motor, respectively. . As a result, a traveling wave of elastic vibration is excited in the vibrating body,
The moving body is driven by the frictional force and starts moving at a speed proportional to the amplitude of the traveling wave.

FIG. 2 shows an example of the electrode structure of the piezoelectric body constituting the vibrator used in the embodiment shown in FIG.
Together with the sensor electrode E corresponding to 波長 wavelength. When an elastic traveling wave is excited in the vibrating body, a voltage proportional to the piezoelectric constant and the magnitude of vibration of the vibrating body is generated in the sensor electrode E by a piezoelectric effect.

However, as shown in FIG. 3, since the vibration of the vibrating body contains not only the fundamental frequency of driving but also many high-frequency components that do not contribute to the movement of the moving body, the output voltage of the sensor electrode E is high. The waveform is also a waveform containing many high-frequency components. Therefore, the output voltage of the sensor electrode E is passed through the band-pass filter 13 to remove unnecessary high-frequency components that do not contribute to the movement of the moving body, and then converted into a DC signal by the rectifier circuit 14. Thereby, only the voltage corresponding to the amplitude of the elastic traveling wave of the fundamental frequency of the drive that determines the moving speed of the moving body can be accurately DC-converted.

One input terminal of the error amplification circuit 13 has
A set voltage Vd corresponding to the target moving speed of the moving object is input, and the output of the rectifier circuit 12 is input to the other input terminal. The error amplifying circuit 13 amplifies the error between the voltage corresponding to the moving speed of the moving object and the set voltage Vd and outputs the result. The frequency control circuit 15 sets the DC output of the rectifier circuit equal to the set voltage Vd according to the error signal. The driving frequency of the vibrating body is controlled so as to be as follows.

FIG. 4 shows the frequency characteristic of the moving speed of the moving body of the ultrasonic motor and the output voltage of the sensor electrode, the solid line shows the frequency characteristic of the moving speed of the moving body of the ultrasonic motor, and the dotted line shows the output of the rectifier circuit. It is a frequency characteristic of a voltage. As shown in the figure, the vibrating body of the ultrasonic motor has a hysteresis characteristic with respect to the driving frequency as in the case of the piezoelectric body alone, and the operation becomes unstable in this hysteresis region.

[0017] Thus, the driving of the ultrasonic motor to avoid the hysteresis region, at a frequency region higher than, and stably operating frequency range f ₁ from the f ₂ detected voltage of the sensor electrode is monotonic with respect to the drive frequency In the frequency domain of
By setting the speed setting voltage V _d so as to speed corresponding to the drive frequency f _d of the region, the moving speed (rotational speed) of the ultrasonic motor under the control of the stable rotation speed N _d
Is set to

Here, in order to remove unnecessary high-frequency components which do not contribute to the movement of the moving body of the output voltage of the sensor electrode,
Although a band-pass filter is used, a similar effect can be obtained by using a low-pass filter instead of the band-pass filter. In the above embodiments, the ultrasonic motor is driven by a constant AC voltage. However, when the set speed of the moving body is low, the drive voltage is reduced, and when the set speed of the mobile body is high, the drive voltage is increased. Thus, if the driving voltage is changed according to the speed of the moving body, efficient driving can always be performed.

Further, in the above embodiment, the speed control of the moving body is performed by the frequency while limiting the driving frequency range.
The same effect can be obtained even if the speed control of the moving body is performed by the drive voltage while limiting the drive frequency range.

[0020] As described above, precise control over movement speed of the moving body, by controlling the driving frequency in a stable operation region, the speed control of the stable and mobile realizing the driving accurate ultrasonic motor it can.

[Brief description of the drawings]

FIG. 1 is a block diagram of a circuit of an embodiment embodying a driving method of an ultrasonic motor according to the present invention.

FIG. 2 is a plan view of a drive electrode and a sensor electrode formed on a piezoelectric body in the embodiment.

FIG. 3 is an output voltage waveform diagram in the embodiment.

FIG. 4 is a frequency characteristic diagram of a rotation speed and an output voltage of a sensor electrode in the embodiment.

FIG. 5 is a cutaway perspective view of an annular ultrasonic motor.

FIG. 6 is a diagram showing an electrode structure of an annular piezoelectric body.

FIG. 7 is a diagram showing a vibration displacement diagram in a radial direction of a vibrating body of an annular ultrasonic motor.

FIG. 8 is a frequency characteristic diagram of admittance of a vibrating body.

[Explanation of symbols]

 Reference Signs List 7 voltage controlled oscillation circuit 8 90 degree phase shift circuit 9 power amplification circuit A 10 power amplification circuit B 11 ultrasonic motor 12 band pass filter 13 rectification circuit 14 error amplification circuit 15 frequency control circuit

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Katsu Takeda 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Takashi Nojima 1006 Kadoma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd (72) Inventor Katsumi Imada 1006 Kadoma, Kazuma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-3-22874 (JP, A) JP-A 1-148079 (JP, A) JP-A-4-26382 (JP, A) JP-A-4-79776 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02N 2/00

Claims (4)

(57) [Claims] A vibration member is formed by coupling a piezoelectric body to an elastic substrate, a moving body is placed in pressure contact with the vibration body, and a driving electrode formed on the piezoelectric body has a predetermined position. by applying a driving voltage having a phase difference to excite a traveling wave in the vibrator, the ultrasonic motor for moving the moving body, the driving electrodes with the sensor electrodes in the piezoelectric body is constituted
Is, the vibrator of the unnecessary high frequency components not contributing to the movement of the sensor electrostatic occur electrode pressure or <br/> et the mobile removed during driving, rectified voltage the unnecessary high frequency components are removed Input to the circuit, the DC output of the rectifier circuit and the moving speed of the target moving object.
The signal corresponding to the difference from the set voltage corresponding to the
Then, the DC output of the rectifier circuit is set using the control signal.
A method of driving an ultrasonic motor, comprising controlling a speed of the moving body so as to be equal to a constant voltage . 2. A band-pass filter or a low-pass filter.
Using a filter, the voltage of the
2. An unnecessary high frequency component which does not contribute to movement is removed.
A driving method of the ultrasonic motor according to the above. 3. A DC output of a rectifier circuit is input to one input terminal of an error amplifier circuit, and a set voltage corresponding to a target moving speed of a moving object is input to the other input terminal of the error circuit.
To amplify the error between the DC output and the set voltage
The error signal output from the error amplifier circuit is used as a control signal.
The method for driving an ultrasonic motor according to claim 1, wherein 4. The method of driving an ultrasonic motor according to claim 1, wherein the driving frequency of the vibrating body is set higher than a frequency at which the vibrating body exhibits a hysteresis characteristic.