JP2782306B2 - Ultrasonic motor driving method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving an ultrasonic motor for driving a rotor which is in pressure contact with a piezoelectric ceramic by applying an electric signal of a predetermined frequency to the piezoelectric ceramic and vibrating the piezoelectric ceramic.

[0002]

2. Description of the Related Art In general, this type of ultrasonic motor has been rapidly put into practical use in recent years because of its quietness, low-speed large torque and no generation of noise with respect to an electromagnetic motor. In such an ultrasonic motor, an electric signal is applied to a piezoelectric ceramic, which is a piezoelectric element, to generate vibration and rotate a rotor that is in pressure contact with the piezoelectric ceramic. As shown in FIG. 11, when the piezoelectric ceramics are formed into a perforated disk shape and vibrated as shown in FIG.
1) Vibration called mode and non-axial symmetric vibration of the disk, which is called (1, 1) mode, occurs with a time difference.

[0003] That is, the electrode 21 on the piezoelectric ceramic 20
A, a sine wave voltage signal of a predetermined frequency is applied to the electrode 21B.
When a cosine wave voltage signal having the same frequency as that of the above voltage signal and having a phase difference of 90 ° is applied, the disc-shaped piezoelectric ceramics 20 in the horizontal vibration (R, 1) mode and the vertical vibration in FIG. A certain (1,1) mode vibration is generated, and as a result, an elliptic motion is generated at the points X and X ', which is composed of a horizontal vibration component and a vertical vibration component. Therefore, if the rotor is pressed against these points X and X ', the rotor is driven to rotate. Of these vibration modes,
The (R, 1) mode vibration acts as a pressure component on the rotor, and the (1,1) mode vibration acts as a torque component on the rotor.

[0004]

In such an ultrasonic motor, a signal applied to each electrode is a voltage signal such as a sine wave or a cosine wave, and a circuit for generating such a sine wave signal is provided. As a result of the increase in complexity, there is a disadvantage that the device cannot be configured in a small size. For this reason, it is conceivable that the signal applied to each electrode is a pulse signal, but in this case, there is a problem that the driving torque of the motor is reduced. Therefore, an object of the present invention is to obtain a large driving torque when a signal applied to each electrode of an ultrasonic motor is a pulse signal.

[0005]

According to the present invention, two electrodes are formed on a piezoelectric element, and each of the formed electrodes has the same driving frequency having a different phase by 90 degrees. In the ultrasonic motor that drives the rotor pressed against the piezoelectric element by applying an electric signal to vibrate the piezoelectric element, the electric signal is used as a pulse voltage signal .
In addition, the frequency of the maximum vibration amplitude of the piezoelectric element is
As it will be the same frequency, a driving method to give to each electrode set in the duty of the pulse voltage signal to a value other than 50%.

[0006]

When vibrating a piezoelectric element such as a piezoelectric ceramic, the duty of a pulse signal applied to each electrode on the piezoelectric element is set to a duty other than 50%. As a result, the vibration frequency of the piezoelectric element having the largest amplitude value coincides with the above-mentioned drive frequency, so that the drive efficiency of the ultrasonic motor is improved.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of an apparatus to which an ultrasonic motor driving method according to the present invention is applied. This apparatus is an ultrasonic motor for rotating a rotor by the vibration of a piezoelectric ceramic 20 as shown in FIG. A pulse signal is given to the sonic motor to drive it. In FIG. 1, 1 is a CPU, 2 is an oscillator including a resistor and a capacitor, 3
Is an inverter, 4 is a binary counter, 5, 8 and 9 are data selectors, 6 and 7 are shift registers, 10 and 11 are AND circuits, 12 is a driver, and M is an ultrasonic motor. Here, a is a pulse signal having a frequency twice as high as the driving frequency of the ultrasonic motor M, b is a phase difference control signal for controlling the phase difference of the driving pulse signal given to the ultrasonic motor M to 90 degrees, c is a signal for controlling the duty of the drive pulse signal, and φ is a clock signal.

FIG. 2 is a timing chart showing the timing of each part of the ultrasonic motor driving device. The operation of the driving device will be described with reference to this timing chart. A pulse signal a having a predetermined frequency of 50% duty and equal to the ON time and the OFF time is always output from the oscillator 2.
[FIG. 2 (a)] is sent out and given to one terminal of the binary counter 4 and the other terminal of the binary counter 4 is supplied via the inverter 3 to the inverted signal d of the signal a.
[FIG. 2 (b)] is given. When these two pulse signals are input to the binary counter 4, the signals e and f obtained by dividing these signals by two are transmitted to the data selector 4 [FIGS. 2 (c) and 2 (d)]. As a result, in the data selector 5, if the phase difference control signal b from the CPU 1 is at the “H” level, each of the data selectors 5 shown in FIGS.
Pulse signals g and h having a phase difference of 0 ° are output from the two output terminals, and if the phase difference control signal b is at “L” level, as shown in FIGS. 2 (g) and 2 (h). The signals g and h, that is, the signal h is output such that the phase of the signal h advances by 90 ° with respect to the signal g.

The pulse signal g sent from one terminal of the data selector 5 is output to one input terminal of the AND circuit 10 as it is and to the input terminal of the shift register 6. The shift register 6 shifts the input pulse signal g by the clock signal φ from the CPU 1 and sends it to the data selector 8, and the data selector 8 selects one of the shifted pulse signals by the duty control signal c from the CPU 1. Then, a signal i is output to the other input terminal of the AND circuit 10. That is, now, the level of the phase difference control signal b is “H”,
Assuming that a signal g as shown in (e) is input to the shift register 6, the other input terminal of the AND circuit 10 has:
A pulse signal i as shown in FIG. 2 (i) shifted from the signal g by the time δ is transmitted. On the other hand, as described above, one input terminal of the AND circuit 10 is connected to FIG.
The signal g shown in (e) is input as it is. As a result,
From the output terminal of the AND circuit 10, a signal j having a duty different from the drive pulse signal a is formed on the piezoelectric ceramics 20 in the ultrasonic motor M via the driver 12 as shown in FIG. It is sent to one of the electrodes.

On the other hand, a signal transmitted to the other electrode of the piezoelectric ceramic of the ultrasonic motor M is also transmitted to the shift register 7,
The data selector 9 and the AND circuit 11 are pulse signals having the same duty as the signal j, but the pulse signal has a phase difference of 90 degrees from the signal j by the data selector 5 for controlling the phase difference.

[0011] The piezoelectric ceramics 20 are formed as shown in FIG.
As shown in FIG. 5, when this is formed in the shape of a perforated disk and vibrated, (R, 1) mode vibration, which is radial vibration of the disk, and non-axial symmetric vibration of the disk ( The vibration of the (1) mode occurs with a time difference. In this case, (R,
The 1) mode vibration acts as a pressure component on the rotor, and the (1, 1) mode vibration acts as a torque component on the rotor. FIG. 3 is a diagram showing the vibration characteristics of such a piezoelectric ceramic, and shows the relationship between the vibration frequency and admittance. That is, according to the vibration characteristics of the piezoelectric ceramics 20, the point where the value of admittance increases at the time when the vibration frequency is low, that is, the resonance point where the amplitude value of the vibration is the largest is the vibration frequency of the (R, 1) mode. The next resonance point having a large amplitude value is the vibration frequency of the (1,1) mode that is the torque component. Where (1,
1) The vibration frequency of the mode vibration is defined as the driving frequency of the motor M (about 116.1 KHz), and the voltage signals of this driving frequency are different in phase by 90 degrees, respectively.
0 is applied to each electrode.

In this case, the drive voltage signal applied to each electrode is a pulse signal, and the duty of the pulse signal is 50%.
Then, in addition to the vibration that matches the driving frequency, vibration of a higher frequency than the driving frequency occurs on the piezoelectric ceramics 20 as shown in FIGS. In general, when vibrating a piezoelectric ceramic, it is considered that the most efficient operation is performed when the piezoelectric ceramic is vibrated at the same frequency as the driving frequency. When the ultrasonic motor M is driven, the torque of the motor M decreases. Here, in order to investigate a phenomenon in which higher-order vibration occurs on the piezoelectric ceramic, as shown in FIG. 6, a pulse signal having a driving frequency of 116.1 KHz and a duty of 50% is applied to the electrode 21A of the piezoelectric ceramic 20. Vibration is performed, and the result of the vibration is extracted from the electrode 21B as a current waveform signal. FIG. 7 shows the waveform of the pulse voltage signal applied to the electrode 21A and the waveform of the electrode 21B.
This is an example in which the results of current waveforms taken out of the oscilloscope are observed on channels CH1 and CH2 on an oscilloscope, respectively. Here, when the voltage signal applied to the electrode 21A is a sine wave, only a current signal having the same frequency as the frequency of the reference wave (sine wave) is output from the electrode 21B, but as shown in FIG. When a pulse signal is applied to 21A, a current signal three times as large as the reference wave (pulse signal) is observed from the electrode 21B. When the frequency spectrum component of such a current waveform is analyzed, the driving is performed as shown in FIG. It can be seen that the maximum vibration amplitude is shown at a frequency three times the frequency. Therefore, in this case, the driving efficiency of the ultrasonic motor M decreases.

When the duty of the pulse voltage signal applied to the electrode 21A is changed, and the duty is set to 32% as shown in FIG.
The frequency of the current waveform generated from the electrode 21B is the same as the frequency of the applied pulse voltage signal. In this case, analysis of the frequency spectrum component of the current waveform reveals that the vibration frequency of the piezoelectric ceramics 20 having the largest vibration amplitude is substantially equal to the drive frequency as shown in FIG. Therefore, when the duty of the pulse voltage signal applied to the piezoelectric ceramic electrode is 32%, the torque of the ultrasonic motor M increases. The ultrasonic motor M
The duty of the pulse signal for improving the driving efficiency of the device is not only 32% but also 68%, 40% and 60%.
For example, if the value is shifted by more than 50%, the torque similarly increases, so that the driving efficiency of the motor M improves.

As described above, when the phase of the pulse signal of a predetermined frequency applied to each electrode formed on the piezoelectric ceramic 20 is shifted by 90 ° and the duty of these pulse signals is other than 50%, the ultrasonic motor The driving torque of M is the largest.

[0015]

As described above, according to the present invention,
When the piezoelectric element is vibrated at a predetermined driving frequency, the duty of the pulse signal applied to each electrode on the piezoelectric element is 5
Since the duty is set to a duty other than 0%, the vibration frequency having the largest amplitude value of the piezoelectric element becomes the above-described drive frequency. As a result, the drive torque of the ultrasonic motor increases, and the effect of improving the drive efficiency of the motor is obtained. is there.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an apparatus to which an ultrasonic motor driving method according to the present invention is applied.

FIG. 2 is a waveform chart showing timings of respective parts of the device.

FIG. 3 is a diagram showing a relationship between a vibration frequency and admittance of a piezoelectric ceramic constituting the device.

FIG. 4 is a diagram showing a relationship between a vibration frequency and a phase of a piezoelectric ceramic, and a relationship between the vibration frequency and admittance.

FIG. 5 is a diagram illustrating an example of vibration of a piezoelectric ceramic.

FIG. 6 is a diagram schematically illustrating an example in which a pulse signal is applied to one electrode on a piezoelectric ceramic and a current signal is extracted from the other electrode.

FIG. 7 is a diagram showing observed waveforms of the pulse signal and the current signal.

FIG. 8 is a diagram showing a result of a frequency spectrum analysis of the current signal.

FIG. 9 is a diagram showing an observed waveform of a current signal when the duty of the pulse signal is set to 32%.

FIG. 10 is a diagram showing a result of frequency spectrum analysis of a current signal generated on piezoelectric ceramics by application of a pulse signal of 32% duty.

FIG. 11 is a diagram illustrating a driving principle of an ultrasonic motor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 CPU 2 Oscillator 3 Inverter 4 Binary counter 5, 8, 9 Data selector 6, 7 Shift register 10, 11 AND circuit 12 Driver 20 Piezoelectric ceramics 21A, 21B Electrode M Ultrasonic motor a, d-j Pulse voltage signal b Phase difference Control signal c Duty control signal φ Clock signal

Claims (1)

(57) [Claims] 1. Two electrodes are formed on a piezoelectric element, and an electric signal of the same driving frequency having a phase difference of 90 degrees is applied to each of the formed electrodes to cause the piezoelectric element to vibrate. in the ultrasonic motor for driving the rotor is, the Kaminariki signal with a pulse voltage signal, the pressure
The frequency of the maximum vibration amplitude of the element is the same as the drive frequency
The duty of the pulse voltage signal so that the frequency of 5
An ultrasonic motor driving method, wherein the value is set as a value other than 0%.