JPH04313369A - Ultrasonic actuator driving circuit - Google Patents

Abstract

PURPOSE:To vibrate a self-excited oscillating circuit with only the specified frequency f1 between the frequencies f1 and f2 of a piezoelectric vibrator by forming a circuit for supplying an excitation AC signal to the columnar piezoelectric vibrator with the self-excited oscillating circuit. CONSTITUTION:Electrodes A1 and A2 are provided on one end face of a columnar piezoelectric vibrator 4, an excitation AC signal is impressed between the electrode A1 and an electrode B, and the electrode A2 and the electrode B are connected through a resistance R5. The current flowing through the vibrator 4 is detected by the resistance R5, a voltage proportional to the current is positively fed back to comparators 21 and 22, and a self-excited oscillating circuit is formed with the feedback loop for driving switches Q1 and Q2 through a switch driver 3.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit that supplies drive power to a vibrator type actuator that uses a piezoelectric vibrator as an electro-mechanical transducer.

0002

2. Description of the Related Art FIG. 11 is a perspective view of a piezoelectric vibrator described in Japanese Patent Application No. 129122/1982. In this piezoelectric vibrator 4, two electrodes A1 and A2, which are electrically separated from each other, are provided on one end surface perpendicular to the polarization axis 45 of a cylindrical piezoelectric ceramic 41, and an electrode is provided on the other end surface. B
is provided. Electrode A1 and electrode A2 of this piezoelectric vibrator 4
When an alternating current voltage is applied between the piezoelectric vibrator 4 and the piezoelectric vibrator 4, vibration displacement occurs on the side surface of the piezoelectric vibrator 4. This vibrational displacement becomes maximum when the frequency of the applied alternating current voltage is equal to the resonant frequency of the piezoelectric vibrator 4. FIG. 2 shows the frequency-admittance/phase angle characteristics of the applied voltage to the piezoelectric vibrator 4. In FIG. 2, the resonance point of the piezoelectric vibrator 4 is the point where the phase angle θ is 0°,
The piezoelectric vibrator 4 has two resonance frequencies f1 and f2. Frequency f1 between electrodes A1 and B of this piezoelectric vibrator 4
When an AC voltage of f2 is applied, a vibrational displacement occurs in the direction of the arrow shown in FIG. 11(a), and when an AC voltage of frequency f2 is applied, a vibrational displacement is generated in the direction of the arrow shown in FIG. 11(b).

FIG. 12 shows a piezoelectric vibrator 4 having the same structure as FIG. 11.
Terminal a2 is provided on electrode A2, and terminal a of electrode A1 is
1 is a diagram illustrating a main part of a vibrator-type actuator in which alternating current voltage of a power source can be switched and applied between terminal a2 of electrode A2 and terminal a2 of electrode A2. The piezoelectric vibrator 4 in FIG. 12 has a frequency f
When an alternating current voltage of 1 is applied as shown in FIG. 4(a), a vibrational displacement appears in the same direction as the polarization axis 45, and when applied as shown in FIG. Furthermore, when an AC voltage with a frequency f2 is applied as shown in the figure (a), vibration displacement occurs in the direction opposite to the polarization axis 45, and when applied as shown in the figure (b), the vibration displacement occurs in the same direction as the polarization axis 45. A displacement occurs. Therefore, a vibrator-type actuator that uses this piezoelectric vibrator 4 as a drive source for mechanical motion uses the vibration displacement generated on the side surface of the piezoelectric vibrator 4 by applying an alternating current voltage of frequency f1 or f2 to the piezoelectric vibrator 4. , drives a driven member that contacts the side surface of the piezoelectric vibrator 4.

FIG. 13 shows a conventional drive circuit for a vibrator type actuator. This conventional drive circuit for a vibrator-type actuator supplies alternating current voltage between electrodes a1 and a2 of a piezoelectric vibrator 4 by alternately turning on and off two switching elements 31 and 32 composed of transistors and the like. , the frequency of the alternating voltage is determined by a frequency generator 36. The operation will be explained below.

When the switching element 31 is turned on, the switching element 31, the piezoelectric vibrator 4,
A current flows to the DC power supply 37. At this time, the switching element 32 is in an OFF state. On the other hand, when the switching element 32 is turned on, a current flows through the piezoelectric vibrator 4 from the piezoelectric vibrator 4 to the switching element 32 to the piezoelectric vibrator 4 in the opposite direction. This is because the piezoelectric vibrator 4 performs charging and discharging as a capacitor, and at this time the switching element 31 is in the OFF state. This switching element 3
AC voltage is supplied to the piezoelectric vibrator 4 by the switching operations of 1 and 32. The phase comparator 33 is connected to the piezoelectric vibrator 4
The voltage applied to and the flowing current are each expressed as a voltage signal 3.
01, as a current signal 302, detect the phase difference between these two signals, and output as a phase difference signal 303. The frequency control circuit 35 inputs the phase difference signal 303 output from the phase comparator 33 as a phase difference signal 304 via the filter 34, and outputs the voltage signal 301 and current signal 302.
A frequency control signal 305 is generated to control the oscillation frequency of the oscillator 36 so that the phase difference between the oscillator 36 and the oscillator 36 is zero. The oscillator 36 has its oscillation frequency controlled by a frequency control signal 305 and outputs a high frequency alternating current signal 306 to the drive circuit 38 . The drive circuit 38 alternately turns on and off the switching elements 31 and 32 at the frequency of the AC signal 306. Here, the oscillation frequency of the oscillator 36 is set to f1 or f2, which is the resonance frequency of the piezoelectric vibrator 4, but since the resonance frequency of the piezoelectric vibrator 4 fluctuates due to temperature changes, the oscillation frequency of the oscillator 36 is set to f1 or f2, which is the resonance frequency of the piezoelectric vibrator 4. It is necessary to follow the resonance frequency of the child 4. Therefore, the phase comparator 33 detects the frequency difference between the resonance frequency of the piezoelectric vibrator 4 and the oscillation frequency of the oscillator 36 and feeds it back to the oscillator 36. A feedback loop including the phase comparator 33, filter 34, frequency control circuit 35, and oscillator 36 is generally called a PLL. In this way, the conventional drive circuit for a vibrator type actuator uses a feedback loop using a PLL.

[0006]

[Problems to be Solved by the Invention] However, in the conventional drive circuit for a vibrator type actuator, the frequency of the AC voltage applied to the piezoelectric vibrator 4 is varied by changing the oscillation frequency of the oscillator 36 using a feedback loop using a PLL. Since the resonant frequency of the piezoelectric vibrator 4 is followed, it takes a certain amount of time for the frequencies to match, and the vibrator type actuator cannot be operated efficiently. Also,
When reversing the direction of vibration displacement of the piezoelectric vibrator 4, Fig. 1
2, there is a method in which a changeover switch is provided on the piezoelectric vibrator 4 to switch the electrode to which AC voltage is applied, and a method in which the oscillation frequency of the oscillator 36 is switched from f1 → f2 or f2 → f1, but the former method Switch switching time is required, and the latter method requires a PLL that can change the oscillation frequency discontinuously, and requires a phase comparator 33, a filter 34, a frequency control circuit 35, and a frequency generator 36.
The control circuit (PLL) made up of the above becomes complex and the number of parts increases. Furthermore, without providing a changeover switch in the piezoelectric vibrator 4, drive circuits are provided between the electrodes A1 and B and between the electrodes A2 and B of the piezoelectric vibrator 4, and the respective drive circuits are started and stopped. There is also a method of changing the direction of the vibration displacement, but in this case the circuit would become very large.

As shown in FIG. 2, the admittances of the piezoelectric vibrators at the resonance frequencies f1 and f2 are very close values, so when the piezoelectric vibrator 4 is used as a resonant circuit in the PLL, the Generally, it is not easy to determine which of the frequencies the PLL oscillates at. In addition, in a normal PLL, oscillation can be easily stopped by grounding the AC signal 306 in FIG. 13 with a switch, but once a PLL has stopped, it may not start immediately just by opening the switch. . Therefore, the conventional circuit shown in FIG. 13 is not suitable for driving a vibrator type actuator that frequently starts and stops.

Accordingly, a first object of the present invention is to provide a vibrator-type actuator drive circuit that stably supplies an alternating current signal at one of the resonant frequencies of a piezoelectric vibrator. A second object of the present invention is to provide an ultrasonic actuator drive circuit that can quickly and reliably start and stop an alternating current signal that drives a piezoelectric vibrator.

[0009]

[Means for Solving the Problems] The means provided by the present invention to solve the above-mentioned problems are as follows: (1) Electrodes A and B are provided on both end faces of a columnar piezoelectric ceramic, respectively.
a piezoelectric vibrator, the piezoelectric vibrator having a polarization axis perpendicular to both end surfaces, and a piezoelectric vibrator that is in direct contact with a side surface of the piezoelectric ceramic or in contact with a coating placed on the side surface. Among the electrodes A and B, at least the electrode A is an electrode A1 and A2 which are insulated from each other.
A circuit for driving the ultrasonic actuator by applying a resonant frequency of the piezoelectric ceramic between the electrode B and the electrode A1 or A2 in the ultrasonic actuator that is divided into A resistor is connected between one of them and the electrode B, and the electrode A1
Alternatively, an oscillation circuit is provided in which a reactance component between the electrode B and the electrode on the side of A2 to which the resistor is not connected is used as the reactance of the resonant circuit.

(2) In the ultrasonic actuator drive circuit of (1) above, the oscillation circuit includes current detection means for generating a voltage according to the current flowing in the resonant circuit, and the voltage is inputted as a positive feedback voltage. It is preferable that there be provided an amplifying means for amplifying the amplified voltage and applying it to the resonant circuit, and a starting means for supplying a signal having an amplitude smaller than the amplitude of the positive feedback voltage to an input terminal of the amplifying means.

(3) In the ultrasonic actuator drive circuit of (2) above, the amplifying means generates a voltage at a binary logic level depending on whether the input voltage exceeds a threshold voltage. a second comparator that generates a binary logic level voltage of opposite logic to that of the first comparator depending on whether the input voltage exceeds the threshold voltage; the first amplifying the outputs of the two comparators, respectively;
and a second switch driver, and first and second switching elements driven by the outputs of the first and second switch drivers, respectively, the first and second switching elements being connected in series to a DC power supply. It is desirable that the resonant circuit be connected between a connection point between the first and second switching elements and one terminal of the DC power supply.

(4) In the ultrasonic actuator drive circuit of (3) above, the activation means includes a third comparator whose threshold voltage is the same as the threshold voltages of the first and second comparators; a fourth comparator having the same threshold voltage as the third comparator and receiving the output of the third comparator;
first and second resistance elements connected in series between the input terminal and the output terminal of the comparator, and the connection point of these first and second resistance elements and the output of the fourth comparator. It is preferable that the input terminal of the third comparator is connected to the input terminal of the amplifying means.

[0013]

[Operation] The ultrasonic actuator targeted by the ultrasonic actuator drive circuit of the present invention has electrodes A and B on both end faces of a columnar piezoelectric ceramic, and at least electrode A is divided into electrodes A1 and A2 that are insulated from each other. A piezoelectric vibrator is used as an electromechanical transducer, and a moving object is brought into contact with a side surface of the piezoelectric vibrator or a coating placed on the side surface of the piezoelectric vibrator. An example of the frequency characteristics of this type of piezoelectric vibrator is shown in FIG. FIG. 2(a) shows the frequency characteristic of the absolute value of admittance, and FIG. 2(b) shows the frequency characteristic of the phase angle of admittance.

As shown in FIGS. 2(a) and 2(b), the piezoelectric vibrator has two resonance points at frequencies f1 and f2, and the admittance at both resonance frequencies is approximately equal. At these resonance frequencies, the phase of the current with respect to the applied voltage (drive voltage) is 0. Resonant frequency f1
FIG. 3 shows the temperature characteristics of admittance at and f2. As is clear from this figure, both admittances are 10℃
They intersect once nearby. Therefore, if a self-excited oscillation circuit in which the reactance component of the piezoelectric vibrator is used as the reactance of the resonant circuit is used as an ultrasonic actuator drive circuit, it is determined whether the oscillation circuit oscillates at the frequency f1 or f2 depending on the piezoelectric vibration. Depends on the child's temperature. In an ultrasonic actuator using this type of piezoelectric vibrator, the direction of movement of the object to be moved changes depending on the frequency of the drive voltage supplied from the drive circuit, as disclosed in Japanese Patent Application No. 1-261084 by the same inventor as the present application. It is shown in FIG. Therefore, it is necessary to determine which of the resonant frequencies f1 and f2 to drive the piezoelectric vibrator to specify the moving direction of the moving object.

[0015] As shown in FIG. 4, the present inventor has discovered that by connecting the resistor R5 between one of the electrodes A1 and A2, which are formed by dividing the electrode A into two, and the electrode B, , the frequency characteristics of the resonant circuit seen between electrode A1 and electrode B on the side to which resistor R5 is not connected are shown in FIG. 5 from the characteristics in FIG. 2.
We have discovered that it is possible to change the characteristics shown in When a resistor R5 is connected as shown in Fig. 4 and the value of the resistor R5 is changed, the electrode A1
The admittance between and B changes as shown in FIG. Further, when R5=68KΩ, the relationship between the temperature of the piezoelectric vibrator 4 and its admittance is as shown in FIG. As is clear from FIG. 7, according to the circuit configuration of FIG. 4, the admittance at frequency f1 is greater than the admittance at frequency f2 regardless of temperature. Therefore, in the drive circuit of the present invention, the oscillation frequency of the oscillation circuit is always f regardless of the temperature of the piezoelectric vibrator.
1, and thus the moving direction of the object to be moved in the ultrasonic actuator can be determined in advance.

[0016]

EXAMPLES Next, the present invention will be explained in more detail with reference to Examples. FIG. 1 is a circuit diagram showing a first embodiment of the present invention. This embodiment includes a DC power supply E1, a bias circuit 1,
A waveform conversion section 2, a switch driver 3, switches Q1 and Q2 made up of FETs, a piezoelectric vibrator 4, a current detector 5 made up of a resistor R4, a coupling capacitor C1 for DC cutoff, a resistor R3, and a resistor. It consists of R5. The bias circuit 1 consists of resistors R1 and R2 connected in series between both ends of a DC power source E1.

The waveform converter 2 includes comparators 21 and 22 constructed of MOS ICs. The comparator 21 compares the input voltage (the voltage at the node N1) with an internally held threshold voltage, and when the input voltage is greater than the threshold voltage, the comparator 21 takes a logical value of "1".
”, and when the input voltage is smaller than the threshold voltage, outputs 0V as a voltage level corresponding to the logical value “0”. The comparator 22 has the opposite logic to the comparator 21. That is, the comparator 22 generates a binary logic level voltage of the input voltage (voltage of node NI)
When the input voltage is larger than the threshold voltage, 0V is outputted as a voltage at a level corresponding to a logical value "0", and when the input voltage is smaller than the threshold voltage, +5V is outputted as a voltage at a level corresponding to a logical value "1".

The switch driver 3 has comparators 21 and 2
2 and amplifies it to a voltage sufficient to drive switches Q1 and Q2. Switch Q1 and Q2
are connected in series between both ends of the DC power supply E1, and are driven by the output voltage of the switch driver 3. The switch driver 3 turns off the switch Q2 when the switch Q1 is on, and turns on the switch Q2 when the switch Q1 is off, depending on the output of the waveform converter 2. When the switch Q1 is conductive and the switch Q2 is disconnected, a current flows through a path from the positive terminal of the DC power source E1 to the switch Q1, the piezoelectric vibrator 4, the resistor R4, and the negative terminal of the DC power source E1. Next, when the switch Q1 is turned off and the switch Q2 is turned on, the charges accumulated in the piezoelectric vibrator 4 are discharged through the switch Q2 and the resistor R4. The voltage appearing across resistor R4 passes through capacitor C1 and resistor R3 to node N1.
and is input to comparison circuits 21 and 22. Resistors R1 and R2 divide the voltage of DC power supply E1 and supply bias voltage to comparators 21 and 22. This bias voltage is set to the threshold voltage of the comparators 21 and 22.

In the circuit of FIG. 1, if the potential of the node N1 is now higher than the threshold voltage of the comparators 21 and 22, the output of the comparator 21 is at a high potential, the output of the comparator 22 is at a low potential, and the switch Q1 is conductive. , switch Q2 is cut off, piezoelectric vibrator 4
The direction of the current flowing through the resistor R4 is from A1 to B, and the direction of the current flowing through the resistor R4 is from the top to the bottom of the diagram. (The switch driver 3 will be described in detail later with reference to FIGS. 14 and 15.) Therefore, a voltage that further increases the potential at this point is fed back to the node N1 from the current detector 5. Moreover, when the potential of the node N1 is lower than the threshold voltage of the comparators 21 and 22, all the states are reversed to the above case, and the node N
A voltage that further lowers the potential of 1 is fed back from the current detector 5. Therefore, the circuit shown in FIG. 1 is a positive feedback circuit that includes comparators 21 and 22 and a switch driver 3 as amplifying means and a piezoelectric vibrator 4 as a resonant circuit, and constitutes an oscillation circuit. The reactance in the resonant circuit is a reactance component of the piezoelectric vibrator 4. Therefore, the oscillation circuit is a self-excited oscillation circuit that oscillates automatically following the resonance frequency of the piezoelectric vibrator 4.

In the embodiment shown in FIG. 1, since the resistor R5 is connected between the electrodes A2 and B of the piezoelectric vibrator 4, as explained with reference to FIG. and B
The admittance seen between the two shows the frequency characteristics shown in FIG. 5(a). Therefore, the piezoelectric vibrator 4 is stably excited at the frequency f1 regardless of the temperature, and the object to be moved that is in contact with the side surface of the piezoelectric vibrator 4 is moved in the direction of the polarization axis 45 as shown in FIG. 12(a).

FIG. 8 is a circuit diagram showing a second embodiment of the present invention. This second embodiment includes a starting circuit 6 in place of the bias circuit 1 in the first embodiment shown in FIG.
Furthermore, it has a switch S1. FIG. 9 is a circuit diagram of the starting circuit 6 and a diagram showing signal waveforms at nodes N4 and N5 on this circuit. The starting circuit 6 includes comparators 61, 62,
It is a self-excited oscillator consisting of resistors R6, R7 and capacitor C2. Comparators 61 and 62 are the same as comparator 22. As shown in FIG. 9, the potential of node N4 is
2 pulsates with a small amplitude around the threshold value of the comparator 61, and the frequency of the pulsation is determined by the capacitor C2 and the resistor R7.

The switch S1 is a start/stop switch for an oscillation circuit forming the ultrasonic actuator drive circuit shown in FIG. When switch S1 is closed, the signal is passed to comparator 21,
22, the drive circuit stops oscillation. When the switch S1 is opened, a small amplitude signal at the node N4 is input from the self-oscillating starting circuit 6, and the drive circuit starts operating with the output of the starting circuit 6. Then, a current flows through the piezoelectric vibrator 4, and the current detector 5 feeds back a voltage proportional to the current to the node N1 of the waveform converter 2 via the capacitor C1 and the resistor R3. Since the capacitor C1 is provided, the only signal fed back to the node N1 is an AC signal. The feedback AC signal and the small amplitude signal of the starting circuit 6 are at the node N
1 and are superimposed. The amplitude of the feedback AC signal is determined by the starting circuit 6.
much larger than the amplitude of the small amplitude signal. Since the drive circuit oscillates with a signal that increases the amplitude at the node N1, the oscillation frequency of the drive circuit gradually shifts from the frequency of the output of the starting circuit 6 to the resonant frequency f1 of the piezoelectric vibrator 4,
It becomes stable at that frequency f1.

As mentioned above, the small amplitude signal output from the node N4 of the starting circuit 6 oscillates around the threshold values of the comparators 61 and 62. The comparators 61, 62 are the comparators 21, 62,
It is made of the same MOS IC as 22, and the threshold voltage is also the same as comparator 2.
1 and 22, the output of the starting circuit 6 will oscillate around the threshold values of the comparators 21 and 22. Since the comparators 61 and 62 are placed in the same temperature environment as the comparators 21 and 22, the starting circuit 6
Even if the threshold value of 2 changes, a bias voltage that automatically follows the threshold value is generated. Therefore, starting circuit 6
is also an automatic bias adjustment circuit.

In the embodiment shown in FIG. 8, as described above, by providing the starting circuit 6, the piezoelectric vibrator 4 can be rapidly excited when the switch S1 is opened, and even if the threshold voltage of the waveform converter 2 fluctuates, the activation circuit 6 is provided. The bias voltage can automatically follow its threshold voltage. When the switch S1 is provided in the embodiment of FIG. 1, there is no guarantee that the switch S1 can be activated immediately even if the switch S1 is changed from the closed state to the open state, but the embodiment of FIG. 8 has improved this point. Furthermore, in the embodiment shown in FIG. 1, since the bias circuit 1 is composed of only resistors, the bias voltage cannot follow the fluctuations in the threshold voltage of the waveform converter 2;
This point has also been improved in the embodiment. In this way, Figure 2
This embodiment can be applied to an ultrasonic actuator that is frequently interrupted because it can reliably start the ultrasonic actuator by providing the starting circuit 6, and it can be applied to an ultrasonic actuator that is frequently interrupted, and because it automatically adjusts the bias voltage according to temperature fluctuations. It can operate efficiently and stably.

FIG. 10 is a diagram showing a peripheral circuit of a piezoelectric vibrator in a third embodiment of the present invention. This third embodiment is constructed by replacing the circuit between nodes N2 and N3 in the first embodiment of FIG. 1 and the second embodiment of FIG. 8 with that of FIG. 10. The circuit of FIG. 10 is provided with a switch S2, and the movable contact pieces 11 and 12 are interlocked. switch S2
When the driving voltage is introduced to the electrode A1, the resistor R5 is connected to the electrode A2, and when the resistor R5 is connected to the electrode A1, the driving voltage is introduced to the electrode A2. Therefore, in this third embodiment, the piezoelectric vibrator 4 is used as in the first and second embodiments.
can be stably excited at the frequency f1, and the moving direction of the moving object can be arbitrarily selected by switching the switch 2.

FIG. 14 is a circuit diagram showing a specific example of the switch driver 3 in the embodiments of FIGS. 1 and 8, and FIG. 15 is a diagram showing input and output waveforms of the switch driver 3. This switch driver 3 consists of a step-up transformer. The number of primary windings of the step-up transformer is Wp, and the number of windings of the two secondary windings are WS1 and WS2, respectively, and WS1=WS2. The voltage applied between the source and gate of switch Q1 by winding WS1 is VGS1, and the voltage applied between the source and gate of switch Q2 by winding WS2 is VGS2. As shown in Figure 15,
VP and VGS2 are voltages based on the ground potential GND, and VGS1 is based on the voltage VDS between the source and drain of the switch Q2. In this way, the switch driver 3 is a circuit that amplifies the output voltage VP of the waveform converter 2, generates two AC voltages VGS1 and VGS2 having different reference potentials, and drives the switches Q1 and Q2.

Note that if the output voltage of the waveform converter 2 is large enough to drive the switches Q1 and Q2, the switch driver 3 does not need to have a step-up function, but even in this case, the switch driver 3 is It is necessary to generate two alternating current voltages with different potentials. Also, Figure 14
shows a switch driver configured with a transformer, but the switch driver can also be configured with an integrated circuit. When configured with an integrated circuit, the output of the comparator 22 can be set to VGS2 with the reference potential of GND unchanged, but the output of the comparator 21 can be set to VGS1 by raising the reference potential from GND to VDS. There is a need to.

[0028]

[Effects of the Invention] As described above in detail with reference to the embodiments, the ultrasonic actuator drive circuit of the present invention can stably supply an alternating current signal at one of the resonant frequencies of the piezoelectric vibrator. , the AC signal can be started and stopped quickly and reliably.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing the frequency characteristics of admittance of a cylindrical piezoelectric vibrator.

FIG. 3 is a diagram showing temperature-admittance characteristics of a cylindrical piezoelectric vibrator.

FIG. 4 is a diagram showing a basic circuit of the present invention for changing the frequency characteristics of a cylindrical piezoelectric vibrator.

FIG. 5 is a diagram showing the frequency characteristics of admittance of the circuit in FIG. 4;

FIG. 6 is a diagram showing the relationship between resistance and admittance in the circuit of FIG. 4;

FIG. 7 is a diagram showing the temperature-admittance characteristics of the circuit in FIG. 4;

FIG. 8 is a circuit diagram showing a second embodiment of the present invention.

FIG. 9 is a diagram showing a starting circuit and signal waveforms of each part thereof in the embodiment of FIG. 8;

FIG. 10 is a diagram showing a drive direction switching circuit in a third embodiment of the present invention.

FIG. 11 is a diagram showing an example of a cylindrical piezoelectric vibrator.

FIG. 12 is a diagram showing an example of a cylindrical piezoelectric vibrator with a drive direction switch.

FIG. 13 is a block circuit diagram showing a conventional ultrasonic actuator drive circuit.

14 is a circuit diagram showing a specific example of the switch driver 3 in the embodiments of FIGS. 1 and 8. FIG.

FIG. 15 is a diagram showing input and output waveforms in the circuit of FIG. 14;

[Explanation of symbols]

1 Bias circuit 2 Waveform conversion section 3 Switch driver 4 Piezoelectric vibrator 5 Current detector 41 Cylindrical piezoelectric ceramic A1, A2, B　　Electrode a1, a2, b terminal

Claims (4)

[Claims] 1. A piezoelectric vibrator comprising electrodes A and B provided on both end surfaces of a columnar piezoelectric ceramic, the polarization axis of the piezoelectric ceramic being perpendicular to both end surfaces, and a piezoelectric vibrator that is directly attached to the side surface of the piezoelectric ceramic. or a moving object that is in contact with a coating placed on the side surface, and of the electrodes A and B, at least electrode A is insulated from each other.
In the circuit for driving the ultrasonic actuator by applying the resonant frequency of the piezoelectric ceramic between the electrode B and the electrode A1 or A2 in the ultrasonic actuator that is divided into A resistor is connected between one of the electrodes A1 and the electrode B, and a reactance component between the electrode B and the electrode A1 or A2 to which the resistor is not connected is connected to a resonance circuit. An ultrasonic actuator drive circuit characterized by being provided with an oscillation circuit having a reactance of . 2. The oscillation circuit includes current detection means that generates a voltage according to the current flowing through the resonant circuit, and amplification means that inputs the voltage as a positive feedback voltage, amplifies it, and applies it to the resonant circuit. 2. The ultrasonic actuator drive circuit according to claim 1, further comprising activation means for supplying a signal with an amplitude smaller than the amplitude of the positive feedback voltage to an input terminal of the amplification means. 3. The amplifying means includes a first comparator that generates a binary logic level voltage depending on whether the input voltage exceeds the threshold voltage; a second comparator that generates a binary logic level voltage with a logic opposite to that of the first comparator depending on whether the A second switch driver, and first and second switching elements driven by the outputs of the first and second switch drivers, respectively, the first and second switching elements being connected in series to a DC power supply. 4. The ultrasonic wave generator according to claim 3, wherein the resonant circuit is connected between a connection point between the first and second switching elements and one terminal of the DC power source. Actuator drive circuit. 4. The activation means has a threshold voltage of the first
and a third comparator having the same threshold voltage as the second comparator; and a fourth comparator having the same threshold voltage as the third comparator and receiving the output of the third comparator. first and second resistance elements connected in series between the input end and the output end of the third comparator, a connection point between these first and second resistance elements, and the fourth comparison and a capacitive element connected between the output terminal of the third comparator and the output terminal of the third comparator, and the input terminal of the third comparator is connected to the input terminal of the amplifying means. Ultrasonic actuator drive circuit.