JPH04145874A - Driving circuit for vibrator type actuator - Google Patents

Abstract

PURPOSE:To enable the title drive circuit to follow the variation of the resonance frequency of a piezoelectric vibrator in real time and to change the direction of vibratory displacement in a moment by constituting the drive circuit of a bias circuit, drive circuit, the first and second switching elements, the piezoelectric vibrator, current detector, and filter. CONSTITUTION:This drive circuit for vibrator type actuators is constituted of two switching elements 11 and 12, a current detector 13, a band-pass filter 14, a DC power source 15, a bias circuit 16, a waveform transformer 17, and a drive circuit 18 and applies an AC voltage across a piezoelectric vibrator 40. The drive circuit 18 controls the turning on/off of the circuits of the switching elements composed of transistors, etc., and the elements 11 and 12 are alternately turned on/off. When the element 11 is turned on, an electric current flows from the DC power source 15 to the power source 15 through the element 11, piezoelectric vibrator 40, and current detector 13. When the electric current flows through the element 11, the other switching elements 12 is turned off.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a drive circuit for a vibrator-type actuator that uses a piezoelectric vibrator, which is an electro-mechanical transducer, as a drive source.

(Prior Art) Conventionally, as shown in FIG. 4, a piezoelectric vibrator used as a drive source of a vibrator-type actuator has an electric conductor on one of both end faces perpendicular to the polarization axis 45 of a ceramic piezoelectric body 41. There are two electrodes 42, 43 separated from each other, and the other end face is provided with an electrode 'If!'. 44 is provided. When an alternating current voltage is applied between the electrodes 42 and 43 of the piezoelectric vibrator 40, a double vibration displacement occurs in the piezoelectric vibrator 40c'. This vibrational displacement becomes maximum when the frequency of the applied alternating current voltage is equal to the resonant frequency of the piezoelectric vibrator 40. FIG. 6 shows the frequency-admittance/phase angle characteristics for applied load of the piezoelectric vibrator 4o.

In FIG. 6, the resonance point of the piezoelectric vibrator 4o is the point where the phase angle θ is 0°, so the piezoelectric vibrator 4° has two resonance frequencies f + = 138.5 kH7-f 2 =
It has 145.2 kllZ. When an AC voltage of frequency f1 is applied between the electrodes 42 and 44 of this piezoelectric vibrator 40, vibration displacement occurs in the direction of the arrow in FIGS. 4(a) and 5(a), and the AC voltage of frequency f2 is generated. When applied, vibration displacement occurs in the direction of the arrow in Fig. 4(b).Furthermore, when an AC voltage of frequency f1 is applied between voltages 143 and 44 of the piezoelectric vibrator 4o, the vibration displacement occurs in the direction of the arrow in Fig. 5(b). Therefore, a vibrator-type actuator that uses this piezoelectric vibrator 40 as a driving source,
Vibration displacement generated by applying an AC voltage of frequency f1 to f2 to the piezoelectric vibrator 4o.
Drive the driven member that contacts 0.

FIG. 3 shows a drive circuit for a conventional vibrator type actuator. The drive circuit for this conventional vibrator type actuator is
An alternating current voltage is supplied between the electrodes 42 and 44 of the piezoelectric vibrator 4o by alternately turning on and off two switching elements 31 and 32 composed of transistors, etc., and the frequency of the alternating voltage is determined by a frequency generator 36. It is determined.

The operation will be explained below.

When the switching element 31 is turned ON, the switching element 3I, the piezoelectric vibrator 40, and the DC power supply 3 are connected to the DC power supply 37.
Current flows to 7. At this time, the switching element 32
is in the OFF state. On the other hand, the switching element 32 is
When N, the piezoelectric vibrator 40 to the switching element 32
, the piezoelectric vibrator 4 in the opposite direction to the piezoelectric vibrator 40.
Current flows through 0. This is because the piezoelectric vibrator 40 performs charging and discharging as a capacitor, and at this time the switching element 31 is in the OF state. This switching element 31
．． ．． AC voltage is supplied to the piezoelectric vibrator 40 by the switching operation of 32. The phase comparator 33 extracts the voltage applied to the piezoelectric vibrator 40 and the current flowing therein as a voltage signal 301 and a current signal 302, respectively, detects a phase difference between these two signals, and outputs the detected phase difference as a phase difference signal.

The frequency control circuit 35 inputs the phase difference signal output from the phase comparator 33 via the filter 34 and converts the voltage signal 3
The oscillation frequency of the frequency generator 36 is controlled so that the phase difference between 01 and the current signal 302 becomes 0.

The frequency generator 36 has its oscillation frequency controlled by the frequency control circuit 35 and outputs a signal to the drive circuit 38. The drive circuit 38 alternately turns on the switching elements 31 and 32 at the frequency of the signal supplied from the frequency generator 36.
N/OFF'. Here, the oscillation frequency of the frequency generator 36 is fl or f which is the resonance frequency of the piezoelectric vibrator 40.
However, as shown in FIG. 7, the resonant frequency of the piezoelectric vibrator 40 changes due to temperature changes and
Since the zero vibration displacement changes, it is necessary to make the oscillation frequency of the frequency generator 36 follow the resonance frequency of the piezoelectric vibrator 40. Therefore, the phase comparator 33 detects the frequency difference between the resonant frequency of the piezoelectric vibrator 40 and the oscillation frequency of the frequency generator 36 and feeds it back to the 1-frequency generator 36. The phase comparator 33, filter 34, frequency control circuit 35, and frequency generator 36 that form this feedback loop are generally called PLI-.

In this way, the conventional drive circuit for a vibrator type actuator uses a feedback loop using a PLL.

(Problems to be Solved by the Invention) However, in the drive circuit of the conventional vibrator type 7' Since the oscillation frequency is changed to follow the changing resonance frequency of the piezoelectric vibrator 40, it takes a certain amount of time for the frequencies to match, and the vibrator type actuator cannot be operated efficiently. In addition, the piezoelectric vibrator 40
In order to reverse the direction of vibration displacement, as shown in FIG. There is a method of switching from f2 to f1, but the former method requires switching time, and the latter method requires a variable frequency generator, which requires a phase comparator 33, a filter 34, and a frequency control circuit 35.
and a control circuit (PL
L) becomes complicated and the number of parts increases. Furthermore, without providing a changeover switch to the piezoelectric vibrator 40, drive circuits are provided between the electrodes 42, 44 and the electrodes 4, 3, and 44 of the piezoelectric vibrator 40 to start, operate, and stop the respective drive circuits. There is also a method of changing the direction of vibration displacement of the piezoelectric vibrator 40, but in this case the circuit becomes very large.

Therefore, an object of the present invention is to provide a drive circuit for a vibrator-type actuator that can follow changes in the resonant frequency of a piezoelectric vibrator in real time, can instantly change the direction of vibration displacement of a piezoelectric vibrator, and has a simple circuit configuration. It's about doing.

(Means for Solving the Problems) The present invention comprises a columnar ceramic piezoelectric body having a polarization axis in a direction parallel to the side surface, and a pair of electrodes provided on both end faces of the ceramic piezoelectric body perpendicular to the polarization axis. A drive circuit for a vibrator-type actuator whose drive source is a piezoelectric vibrator that generates vibrational displacement by an alternating voltage applied between the electrodes, wherein a second terminal is connected to one electrode of the piezoelectric vibrator. a first switching element that turns on/off a current path from the first terminal to the second terminal according to a signal input to the control terminal; and a first terminal connected to one electrode of the piezoelectric vibrator. The current path from the first terminal to the second terminal is controlled by the signal input to the control terminal.
A second switching element is connected between the other electrode of the piezoelectric vibrator and a second terminal of the second switching element, and the current flowing through the piezoelectric vibrator is converted into a voltage signal. a DC power supply having a positive electrode connected to a first terminal of the first switching element and a negative electrode connected to a second terminal of the second switching element; An Oki wave device that converts the AC voltage signal output from the device into a sine wave and outputs it,
a bias circuit that biases a sinusoidal voltage signal output from the filter to a certain voltage value; and a waveform converter that converts the 1F sinusoidal voltage signal output from the bias circuit into a square wave voltage signal. , receiving a square wave voltage signal output from the waveform converter and outputting a control signal to the control terminals of the first and second switching elements to control the first and second switching elements according to the voltage signal. and a drive circuit that alternately turns ON10FF depending on the frequency to apply an AC voltage between the electrodes of the piezoelectric vibrator.

(Function) In the drive circuit of the vibrator type actuator of the present invention, a loop composed of a bias circuit, a drive circuit, first and second switching elements, a piezoelectric vibrator, a current detector, and a filter is a piezoelectric vibrator. The piezoelectric vibrator self-oscillates at one of two resonance frequencies, and the first and second switching elements alternately switch based on the self-oscillation frequency to apply an alternating current voltage to the piezoelectric vibrator.

(Example) Next, the present invention will be explained by giving examples.

FIG. 1 is a diagram that does not show one embodiment of the present invention. This embodiment includes two switching elements 11 and 12 and a current detector 1.
3, a band pass filter 14, a DC power supply 15, a bias circuit 16, a waveform converter 17, and a drive circuit 18, and applies an AC voltage to the piezoelectric vibrator 40. Switching element 11.1 consisting of a transistor etc.
2 is ON10 F F of the circuit by the drive circuit 18
is controlled, and these two switching elements 11 and 12 are alternately turned ON10FF. switching element 11
is in the ON state, the DC power supply 17, the switching element 11, the piezoelectric vibrator 40, the current detector 13, and the DC power supply 1
Current flows to 7. At this time, the switching element 12 is in an OFF state. On the other hand, the switching element 12 is turned on.
When the switching element 1 is in the state, the piezoelectric vibrator 40
2. Current flows to the current detector 13 and the piezoelectric vibrator 40, but this is because the piezoelectric vibrator 40 is charged and discharged as a capacitor. At this time, the switching element 11 is in the OF state. Due to the switching operation of these two switching elements 11 and 12, the electrodes 42 and 44 of the piezoelectric vibrator 40
An alternating current voltage is applied between them. The current detector 13 extracts the current flowing through the piezoelectric vibrator 40 as a voltage, and outputs the voltage signal to the band pass filter 14.

The circuit configuration of the band pass filter 14 is shown in FIG. This band pass filter 14 is a filter using an amplifier 20, and functions as a band pass filter with a center frequency of 146 kHz when the switch SW is ON, and functions as a simple buffer when the switch SW is OFF. do. This center frequency f. is the resonant frequency of the interface L and the capacitor C. The voltage signal that has passed through the band pass filter 14 is input to the bias circuit j6, and is biased to a voltage value obtained by dividing the output voltage of the DC power supply 15 by two resistors R, and then is applied to the waveform converter 1.
7 is output. Here, the voltage signal until input to the waveform converter 17 is a sine wave. The waveform converter 17 is composed of a comparator, and compares the sinusoidal voltage signal biased by the bias circuit 16 with a reference voltage that is the same as the bias value of the bias circuit 16 to convert it into a square wave voltage signal. The drive circuit 18 inputs a square wave voltage signal and turns the switching elements 11 and 12 on and off alternately according to the voltage signal.
F and supplies AC voltage to the piezoelectric vibrator 40. Since the piezoelectric vibrator 40 used in this embodiment is the same as that shown in FIG. 4, its resonance frequency is f , =138.
5kHz and f2=145.2kHz.

Next, time 1 of the circuit of this embodiment is investigated by inputting a signal from point B in FIG. 1 and measuring the signal appearing at point A. Figure 8 shows switch S of band pass fill 14.
FIG. 7 is a diagram showing the frequency-gain/phase difference characteristics of the applied voltage when W is in the ON state and operates as a band pass filter. Here, the gain is the gain of the output signal at point A with respect to the input signal at point B, and the phase difference is the phase difference between the input signal at point B and the output signal at point A. In this embodiment, points A and B are separated to form an open loop, and when a signal is input from point B and a signal is taken out from point A, the gain is 068 in the frequency characteristics of the input-to-output gain and phase difference.
As described above, when there is a frequency f with a phase difference of 0°, when points A and B are connected to form a closed loop, self-oscillation occurs at that frequency f. As f in FIG. 8, there are resonance frequencies fI and f2 of the piezoelectric vibrator 40. Therefore, when the switch SW of the band pass filter 14 is closed to function as a band pass filter,
As is clear from FIG. 8, in this embodiment, self-oscillation occurs at the resonance frequency of the piezoelectric vibrator 40 having a large gain among the frequencies f of 2. FIG. 9 shows the frequency-gain/phase difference characteristics of the applied voltage between points B and A when the switch SW of the band-pass filter 14 is set to 0FF and the band-pass filter 14 functions as a buffer. shows. In Figure 9, the phase difference is 0 when the gain is 068 or more.
The frequency of ° is approximately the resonant frequency f+ of the piezoelectric vibrator 40. Therefore, in this embodiment, the band pass filter 14
The band pass filter 14 is opened by opening the switch SW.
When the piezoelectric vibrator 40 functions as a buffer, the piezoelectric vibrator 40
It self-oscillates at a resonant frequency f1.

In this way, in this embodiment, the resonant frequency f1 of the piezoelectric vibrator 40 is
Alternatively, by self-oscillating at f2 and applying an AC voltage to the piezoelectric vibrator 40, it functions as a drive circuit for a vibrator-type actuator that does not require a frequency generator. In this embodiment as well, the resonant frequencies f+ and f of the piezoelectric vibration 40 depend on the temperature.
2 changes, or the circuit itself always follows the frequency fluctuation in real time, so the resonance frequency f1.2 of the AC voltage applied to the piezoelectric vibrator 40 changes. The time required for frequency matching to f2 is 0, allowing efficient operation of the vibrator type actuator. In addition, the band pass filter 14
By turning ON/OFF the switch SW of the piezoelectric vibrator 4, the oscillation frequency changes instantaneously between fl and f2.
The circuit of this embodiment is capable of instantly changing the direction of the vibration displacement of the piezoelectric vibrator 40, and the direction of motion of the driven member driven by the piezoelectric vibrator 40 is completely independent of the difference in resonance frequency of the piezoelectric vibrator. It won't affect me, so F! It is possible to accommodate piezoelectric vibrators having different resonance frequencies without changing the configuration or circuit constants at all.

(Effects of the Invention) As explained in detail above, according to the present invention, a self-excited vibrator type actuator that self-oscillates at the resonant frequency of a piezoelectric vibrator and applies an AC voltage at that frequency to the piezoelectric vibrator. A drive circuit can be realized, and since this drive circuit follows fluctuations in the resonant frequency of the piezoelectric vibrator in real time, the vibrator type actuator can be operated efficiently. In addition, since the frequency of the AC voltage applied to the piezoelectric vibrator can be changed instantaneously, the direction of the vibration displacement of the piezoelectric vibrator can be instantly changed, and the direction of motion of the vibrator type actuator can be immediately changed. Moreover, since the circuit configuration is simple and the number of parts is small, the circuit can be realized at low cost.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an embodiment of the present invention, and Fig. 2 is a diagram showing an embodiment of the present invention.
FIG. 3 is a diagram showing the configuration of the pass filter 14, FIG. 3 is a diagram showing a drive circuit for a conventional vibrator type actuator, and FIGS. 4 and 5 are piezoelectric vibrators used as a drive source for the vibrator type actuator. 6 is a diagram showing the frequency-admittance/phase angle characteristics of the applied voltage to the piezoelectric vibrator 40, FIG. 7 is a diagram showing the temperature characteristic of the resonant frequency of the piezoelectric vibrator, and FIG. 8 is a diagram showing the temperature characteristics of the resonant frequency of the piezoelectric vibrator 40. Band pass filter 1
FIG. 9 is a diagram showing the frequency-gain/phase difference characteristics of the applied voltage between point B and point A when switch SW 4 is closed.
FIG. 3 is a diagram showing the frequency-gain/phase difference characteristics of the applied voltage between point B and point A when the switch SW of 1 is opened. 11 12.31. '32...Switching element, 1
3... Current detector, 14... Band pass filter, 15.37... DC power supply, 17... Waveform converter, 18.38... Drive circuit, 20... Amplifier 1
, 33... Phase comparator, 34... Filter, 35...
...Frequency control circuit, 36...Frequency generator, 40.
...Piezoelectric vibrator, 41...Ceramic piezoelectric body, 42,
43, 4.4... Electrode, 45... Polarization axis. Agent Patent Attorney Honjo Broker (a) (b) (a) Figure (b)

Claims (2)

[Claims] (1) Consisting of a columnar ceramic piezoelectric body having a polarization axis parallel to the side surface and a pair of electrodes provided on both end faces of the ceramic piezoelectric body perpendicular to the polarization axis, an alternating current voltage is applied between the electrodes. In a drive circuit for a vibrator-type actuator whose drive source is a piezoelectric vibrator that generates vibrational displacement, a second terminal is connected to one electrode of the piezoelectric vibrator, and a signal input to a control terminal causes the first A first switch that turns on/off the current path in the direction from the terminal to the second terminal.
A switching element and a first terminal are connected to one electrode of the piezoelectric vibrator, and a signal input to the control terminal turns on/off a current path from the first terminal to the second terminal.
A second switching element that is turned off is connected between the other electrode of the piezoelectric vibrator and a second terminal of the second switching element, and a current flowing through the piezoelectric vibrator is detected as a voltage signal. a DC power supply having a positive electrode connected to a first terminal of the first switching element and a negative electrode connected to a second terminal of the second switching element; A filter that converts the output AC voltage signal into a sine wave and outputs it, a bias circuit that biases the sine wave voltage signal output from the filter to a certain voltage value, and an output from the bias circuit. a waveform converter for converting a sinusoidal voltage signal into a square wave voltage signal; and a drive circuit that outputs a control signal to alternately turn on and off the first and second switching elements according to the frequency of the voltage signal to apply an alternating voltage between the electrodes of the piezoelectric vibrator. A drive circuit for a vibrator-type actuator. (2) The filter has a switch for switching between a function of functioning as a bandpass filter and a function of functioning as a buffer, and includes the piezoelectric vibrator, the current detector, the filter, the bias circuit, and the drive. A closed loop consisting of the circuit and the first and second switching elements forms a circuit that self-oscillates at the two resonance frequencies of the piezoelectric vibrator, and by switching the switch to change the function of the filter. 2. The drive circuit for a vibrator type actuator according to claim 1, wherein the oscillation frequency of the oscillation circuit is set to one of the two resonance frequencies to switch the direction of vibration displacement of the piezoelectric vibrator.