JPH0732896B2 - Piezoelectric vibrator drive - Google Patents

Description

TECHNICAL FIELD The present invention relates to driving a piezoelectric vibrator for efficiently driving a piezoelectric vibrator in which a piezoelectric element is mounted on a mechanical structure for performing ultrasonic processing or the like. Regarding the device.

(Prior Art) When performing ultrasonic processing or the like, for example, as shown in FIG. 3, a piezoelectric vibrator in which a piezoelectric element TD is integrated with a mechanical structure 1 such as a horn is used.

FIG. 4 shows the basic resonance characteristic A of the piezoelectric element TD itself and the resonance characteristic (no load B, load time line C) of the piezoelectric vibrator including the mechanical structure. As you can see from this figure,
The resonance characteristic of the piezoelectric vibrator exists in the frequency band lower than A,
If the piezoelectric vibrator is made to work and a mechanical load is applied,
The resonance characteristic C is lower than the resonance characteristic B under no load.
Appears. Each resonance characteristic A, B, C has two resonance points at the lowest impedance point fr and the highest impedance point far.

FIG. 5 shows the frequency characteristics of the impedance of the piezoelectric vibrator, the electric current, and the working force of the piezoelectric vibrator, which the inventors of the present invention obtained through experiments. The frequency characteristics of the impedance in the upper part of Fig. 5 show that the solid line is no load, the one-dot chain line is the medium mechanical load, and the dotted line is the heavy load. It can be seen that the impedance point fr and the maximum impedance point far shift in the lower direction. Also, in the current in the middle part of FIG. 5, the solid line shows no load, the one-dot chain line shows a medium mechanical load, and the dotted line shows a heavy load, respectively. It is shown to spread to lower frequencies. Further, it has been newly found that the working force of the piezoelectric vibrator shown in the lower part of FIG. 5 has a maximum point at a frequency lower than the lowest impedance point fr, and the current value is slightly lower than the maximum value. .

(Problems to be Solved by the Invention) By the way, the conventional driving method of the piezoelectric vibrator has a constant value within the frequency range D in FIG. 5 between the lowest impedance point fr and the highest impedance point far when there is no load. The piezoelectric vibrator was driven at the frequency. Then, the change in the resonance point due to the change in the mechanical load of the piezoelectric vibrator is ignored, and the decrease in efficiency when the resonance point changes is solved by providing the drive power with an excess capacity. However, providing the drive power with a surplus capacity leads to an increase in the size of the device, and also tends to increase the heat loss of the piezoelectric vibrator.

(Means for Solving Problems) In view of the above points, the present invention provides a highly efficient piezoelectric vibrator driving device that can always drive a piezoelectric vibrator under optimum driving conditions according to a mechanical load state. Is what you are trying to do.

A piezoelectric vibrator driving device of the present invention includes a voltage control oscillation circuit that can vary the oscillation frequency by a control voltage that controls the oscillation frequency, and an amplifier circuit that amplifies the oscillation output of the voltage control oscillation circuit and drives the piezoelectric vibrator. And detecting the output current of the amplifier circuit, outputting the control voltage across the capacitor via a resistor in accordance with the difference between the voltage proportional to the output current and the reference voltage, and performing frequency tracking to the amplifier circuit. A detection control circuit that forms a feedback loop that controls the output current of the PUT to a substantially constant value, a PUT is connected in parallel to the capacitor, and a constant gate voltage is applied to the gate of the PUT, and the control voltage is the gate voltage. When the set level reaches a certain level, the PUT becomes conductive to set the control voltage to zero, and the oscillation frequency of the voltage controlled oscillator circuit is swept from the lower limit set frequency to the upper set frequency. And a frequency sweep circuit for limiting the sweep frequency range of the frequency sweep circuit to a range having one lowest impedance point when the piezoelectric vibrator has a load, and the upper limit set value frequency is the piezoelectric vibrator. It is characterized in that it is set below the minimum impedance point when there is no load.

(Operation) In the present invention, the working force E of the piezoelectric vibrator shown in FIG.
In order to set the operating point within a range F including this range, an amplifier circuit that drives the piezoelectric oscillator with an optimum oscillation frequency in a specific load state (within the range F) of the piezoelectric oscillator The optimum output current is set in advance, and the oscillation frequency is set to follow the change of the minimum impedance point fr of the piezoelectric vibrator so that the output current is maintained at a substantially constant value with respect to changes in the load state. Control. As a result,
The amplifier circuit that drives the piezoelectric vibrator does not require an extra capacitance, and can be made compact and lightweight. Further, since the piezoelectric vibrator is driven under the optimum condition, heat loss is small.

(Embodiment) An embodiment of a piezoelectric vibration driving device according to the present invention will be described below with reference to the drawings.

In Fig. 1, the power supply voltage Vcc is applied between the + terminal and the-terminal.
Is applied, and the power supply voltage Vcc is a voltage controlled oscillation circuit (VCD).
5, the output voltage adjusting voltage variable circuit 6
Is supplied to the drive amplifier circuit 7 via.

The voltage controlled oscillator circuit 5 can change the oscillation frequency by changing the control voltage S. The drive amplifier circuit 7 amplifies the oscillation output of the oscillator circuit 5 and drives the piezoelectric element TD via the output transformer 8. A mechanical structure (actuator) 1 is integrated with the piezoelectric element TD to form a piezoelectric vibrator 2 as a whole.

The detection control circuit 9 forming a feedback loop for controlling the output current of the amplifier circuit 7 (which may be considered as a current flowing through the primary side of the output transformer 8) to a substantially constant value is a transistor Q.
It has a differential amplifier composed of 1, Q2, resistors R1 to R6, and a capacitor C1. The negative voltage obtained by rectifying and smoothing the secondary voltage of the output transistor 8 with the diode D1 and the capacitor C2 is applied to the emitters of the transistors Q1 and Q2 of the differential amplifier via the resistor R5. This is because the operating range of the differential amplifier is set to be wide, and the desired operation is possible even when the voltage supplied to the voltage variable circuit 6 and the amplifier circuit 7 is lowered. A reference voltage Vst obtained by dividing the voltage supplied to the amplifier 7 by the resistors R1 and R2 is applied to the base of the transistor Q2, and the voltage of the resistor R4 (proportional to the output current Iout of the amplifier circuit 7 is applied to the base of the transistor Q1. Applied voltage) is applied through resistor R3. The capacitor C1 removes the high frequency component superposed on the output current Iout. The differential output of the differential amplifier is taken out by resistor R7 and added to capacitor C3. Then, the voltage of the capacitor C3 becomes the control voltage S for controlling the oscillation frequency of the voltage controlled oscillator circuit 5. Here, when the control voltage S is zero, the oscillation frequency becomes the lower limit set value frequency f _L.

The frequency sweep circuit consists of PUT10, resistors R8 and R9, the capacitor
It is composed of C3 and resistor R7.
A PUT10 is connected in parallel, and a resistor R is connected to the gate of the PUT10.
A voltage obtained by dividing the power supply voltage Vcc is given by 8, R9, and a frequency sweep circuit is configured by these PUT10 and resistors R8, R9. Then, when the control voltage S tries to exceed the gate voltage of the PUT 10, the PUT 10 becomes conductive. PUT
The oscillation frequency corresponding to the value of the control voltage S immediately before conduction of 10 is the upper limit set value frequency f _H. After the PUT 10 is turned on, the oscillation frequency of the voltage controlled oscillator circuit 5 is swept from f _L to f _H due to the rise of the terminal voltage accompanying the charging of the capacitor C3.

Next, the operation of the above embodiment will be described with reference to FIG. Second
The curve in FIG. 2A is the frequency characteristic of the impedance when the piezoelectric vibrator 2 is unloaded, and the curve in FIG. 2B is the frequency characteristic of the impedance when the piezoelectric vibrator 2 is loaded.
Sweep range of the oscillation frequency of the voltage controlled oscillator circuit 5 (f _{L to}
f _H ) is set within a range that has only one minimum impedance point under load (when no load, it may be set not to include the minimum impedance point as described later). Since large range E of the working force of the piezoelectric vibrator from FIG. 5 to be in the frequency range of the capacitive impedance of the left side of the lowest impedance point fr of the piezoelectric vibrator no load is found, the upper limit set frequency f _H Is unloaded fr
And the point on the left side. Further, the lower limit set value frequency f _L is set to a point further to the left of fr under load, at which the working force of the piezoelectric vibrator does not decrease so much.

Now, considering a state in which a mechanical load is applied to the piezoelectric vibrator 2, the oscillation frequency of the voltage controlled oscillator circuit 5 at this time is assumed to be fo. When the load becomes heavy in this state, fr of the piezoelectric vibrator moves further to the left, and as a result, the output current Iout of the amplifier circuit 7 driving the piezoelectric vibrator increases (fifth
Refer to the frequency characteristics of the current in the middle row of the figure). Therefore, the terminal voltage of the resistor R4 of the detection control circuit 9 increases, the collector voltage of the transistor Q1 decreases, and the control voltage S also decreases. Therefore, the oscillating frequency of the voltage controlled oscillator circuit 5 decreases, following the decrease of fr of the piezoelectric vibrator, and the decrease of the oscillating frequency compensates for the increase of the output current Iout (direction of decreasing the current). The operating point of the amplifier circuit 7 will be changed.

When the load is lightened when the oscillation frequency of the voltage controlled oscillator circuit 5 is fo, the fr of the piezoelectric vibrator moves to the right,
The output current Iout of the amplifier circuit 7 driving the piezoelectric vibrator decreases (see the frequency characteristic of the current in the middle part of FIG. 5). Therefore, the terminal voltage of the resistor R4 of the detection control circuit 9 decreases, the collector voltage of the transistor Q1 increases, and the control voltage S also increases. Therefore, the oscillating frequency of the voltage controlled oscillator circuit 5 becomes high, following the rise of fr of the piezoelectric vibrator, and
The increase in the oscillation frequency changes the operating point of the amplifier circuit 7 in a direction to compensate for the decrease in the output current Iout (direction to increase the current).

In this way, the oscillation frequency of the voltage controlled oscillator circuit 5 follows the change of the lowest impedance point fr due to the load variation of the piezoelectric vibrator 2, so that the output current Iout of the amplifier circuit 7 that drives the piezoelectric vibrator 2 is almost the same. It will be kept constant.

When the mechanical load of the piezoelectric vibrator 2 is completely removed or when the tracking of the lowest impedance point fr is lost, the output current Iout of the amplifier circuit 7 is further reduced and the control voltage S becomes higher than the gate voltage of the PUT10. , PUT10 becomes conductive and the control voltage S is once set to zero, and then from the lower limit set value frequency f _L of the oscillation frequency of the voltage controlled oscillator circuit 5 to the upper limit set value frequency f _H according to the rise of the terminal voltage of the capacitor C3 To sweep. Then, it operates at the differential output of the differential amplifier of the detection control circuit 9, that is, at the oscillation frequency corresponding to the control voltage S obtained again.

(Effects of the Invention) As described above, according to the piezoelectric vibrator driving apparatus of the present invention, the voltage controlled oscillator circuit 5 that can vary the oscillation frequency by the control voltage S that controls the oscillation frequency, and the voltage controlled oscillator circuit. An amplifier circuit for amplifying the oscillation output of No. 5 to drive the piezoelectric vibrator, an output current of the amplifier circuit is detected, and a capacitor is provided via a resistor R7 according to a difference between a voltage proportional to the output current and a reference voltage. A detection control circuit that outputs the control voltage S to both ends of C3, a PUT10 connected in parallel to the capacitor C3, and a constant gate voltage is applied to the gate of the PUT10 so that the control voltage S is determined by the gate voltage. When the level is reached, the PU
A frequency sweep circuit for sweeping the oscillation frequency of the voltage controlled oscillator circuit 5 from the lower limit set value frequency toward the upper limit set value frequency by setting the control voltage S to zero by the conduction of T10 is provided. By configuring a feedback loop that controls the output current of the amplifier circuit to a substantially constant value, the piezoelectric vibrator can always be driven under optimum driving conditions according to the mechanical load state, and therefore, high efficiency operation can be realized. It is possible. In this case, the output current of the amplifier circuit is proportionally controlled in proportion to the current of the piezoelectric vibrator, and the circuit configuration is simple. Also, if the frequency tracking due to the output current constant control of the amplifier circuit is lost for some reason, the oscillation frequency of the voltage controlled oscillator circuit is swept within the range between the lower limit set value frequency and the upper limit set value frequency by the frequency sweep circuit. , A new frequency tracking point can be easily found. Furthermore, the frequency sweep circuit can be realized by an extremely simple circuit using PUT. As described above, according to the present invention, it is possible to realize a piezoelectric vibrator driving device capable of following the fluctuation of the resonance point of the piezoelectric vibrator with a simple and inexpensive circuit configuration.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a piezoelectric vibrator driving device according to the present invention, FIG. 2 is an explanatory view for explaining the operation of the embodiment, and FIG. 3 is a piezoelectric element in which a mechanical structure is integrated. FIG. 4 is a front view showing an example of a piezo-electric vibrator that has been made into a structure, FIG. 4 is an explanatory view showing the resonance characteristic of the piezoelectric element itself and the resonance characteristic of the piezoelectric vibrator in which a mechanical structure is integrated, and FIG. It is explanatory drawing which shows the frequency characteristic of an electric current and a working force. 1 ... Mechanical structure, 2 ... Piezoelectric vibrator, 5 ... Voltage controlled oscillation circuit, 7 ... Drive amplification circuit, 8 ... Output transformer, 9 ... Detection control circuit, 10 ... PUT, TD ... …Piezoelectric element.

Claims (2)

[Claims] 1. A voltage controlled oscillator circuit (5) capable of varying the oscillation frequency by a control voltage (S) for controlling the oscillation frequency, and an oscillation output of the voltage controlled oscillator circuit (5) is amplified to drive a piezoelectric vibrator. And an output current of the amplifier circuit, and the control voltage (S3) is applied across a capacitor (C3) via a resistor (R7) according to a difference between a voltage proportional to the output current and a reference voltage. ) Is output,
Detection control circuit (9) forming a feedback loop for controlling the output current of the amplification circuit to a substantially constant value by frequency tracking
And a PUT (10) is connected in parallel to the capacitor (C3) and a constant gate voltage is applied to the gate of the PUT (10), and the control voltage (S) reaches a set level determined by the gate voltage. When the PUT (10) is turned on, the control voltage (S) is set to zero, and the oscillation frequency of the voltage controlled oscillator circuit (5) is swept from the lower limit set value frequency toward the upper limit set value frequency. Circuit, limiting the range of the sweep frequency of the frequency sweep circuit to a range having one lowest impedance point when the piezoelectric vibrator has a load, and setting the upper limit set value frequency to the no-load of the piezoelectric vibrator. The drive device for the piezoelectric vibrator, which is set to be equal to or lower than the lowest impedance point (fr) at the time. 2. The detection control circuit comprises a differential amplifier having one input end to which a voltage proportional to the output current of the amplification circuit is input and the other input end set to the reference voltage. The differential output of the differential amplifier to the resistor (R7)
The control voltage (S) across the capacitor (C3) via
The drive device for a piezoelectric vibrator according to claim 1, wherein