JPH0632783B2 - Oscillator excitation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a vibrator excitation circuit capable of highly efficiently driving a piezoelectric vibrator for generating ultrasonic vibration and finely adjusting the driving power of the piezoelectric vibrator. Regarding

(Summary of the Invention) The present invention relates to a vibrator excitation circuit that drives a piezoelectric vibrator for generating ultrasonic vibration, and a frequency to a voltage controlled oscillator circuit controlled to follow the resonance frequency of the piezoelectric vibrator. The control signal can be finely adjusted, and the drive power of the piezoelectric vibrator can be finely changed.

(Prior Art and Problems) When performing ultrasonic processing, atomization of liquid using ultrasonic vibration, etc., a piezoelectric vibrator in which a piezoelectric element is integrated with a mechanical structure such as a horn is used. .

In such a piezoelectric vibrator, when the load applied to the mechanical structure such as a horn changes, the resonance frequency (resonance point) also changes. Therefore, frequency tracking is required to drive such a piezoelectric vibrator. However, highly accurate driving cannot be performed without driving using a self-excited oscillation circuit or a PLL. Particularly in a bolted Langevin-type piezoelectric vibrator which has a high Q and requires excitation of a large amount of power, it is very difficult to perform power variation while tracking frequency.

The most basic idea for adjusting the power of a bolted Langevin type piezoelectric vibrator is to use an A
Although there is a configuration in which a class-A or class-B power amplifier circuit is adopted and its input is controlled, the efficiency is low due to the large power loss of the transistor of the power amplifier circuit, and it is being used at present.

On the other hand, the oscillator excitation circuit that drives the transistor of the power amplification circuit in class C or drives with a pulse waveform uses the transistor for switching, and thus the power loss is reduced. However, in this case, it is necessary to devise a variable power.
For example, when driving a transistor of a power amplifier circuit with a pulse waveform, it has been proposed to control the width of the ON period or the OFF period of the drive pulse signal to vary the power. If the pulse width is changed too much, the frequency component of the drive pulse signal may change, which may deviate from the resonance frequency of the piezoelectric vibrator. If the above is required, this variable power is not sufficient in consideration of variations in the piezoelectric vibrator.

Furthermore, the applicant of the present invention detects the output current (emitter current of the output transistor) of the power amplifier circuit which is approximately proportional to the driving power of the piezoelectric vibrator, and adjusts the resonance frequency of the piezoelectric vibrator so that this output current becomes a constant value. A method of driving a piezoelectric vibrator that executes frequency tracking in response to changes is disclosed in Japanese Patent Laid-Open No. 61-14490.
No. 1 has been proposed, but when such a drive system is adopted, if the power supply voltage of the power amplifier circuit is changed and power control is executed, the output current also fluctuates, and frequency tracking is lost. Cause

In view of the above problems, the present invention provides a vibrator excitation circuit that can drive a piezoelectric vibrator for generating ultrasonic vibration with high efficiency in the vicinity of its resonance frequency, and that can finely adjust the driving power of the piezoelectric vibrator. The purpose is to provide.

(Means for Solving Problems) According to the present invention, an oscillation output of a voltage controlled oscillator circuit is amplified by a power amplifier circuit to drive a piezoelectric vibrator, and a voltage value substantially proportional to an output current of the power amplifier circuit. And a reference voltage value are compared with each other, and a frequency control signal corresponding to the difference between the two voltage values is fed back to the voltage controlled oscillator circuit. The frequency control signal is made variable by using the narrow frequency fine adjustment pulse signal, and the problems of the prior art are solved by such means.

(Operation) Since the oscillator excitation circuit of the present invention can finely change the frequency control signal of the voltage controlled oscillation circuit by using the frequency fine adjustment pulse signal having a pulse width narrower than the repetition period, it is possible to reduce load fluctuation. The input power to the piezoelectric vibrator can be finely adjusted by allowing the oscillation frequency of the voltage controlled oscillator circuit to follow the change in the resonance frequency of the piezoelectric vibrator, and by making the oscillation frequency slightly shift from the resonance frequency. can do.

(Embodiment) An embodiment of a vibrator excitation circuit according to the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment, and FIG. 2 is a circuit diagram for explaining the details.

As shown in these figures, the vibrator excitation circuit includes a voltage controlled oscillator circuit 1, a pulse width variable unit 2, a drive circuit (buffer amplification circuit) 3, and an output of the drive circuit 3 between the interstage transformers T _1.
It has a power amplification circuit 4 which receives via the. The output of the power amplifier circuit 4 is supplied to the piezoelectric vibrator TD via the output transformer T ₂ .

Here, the piezoelectric vibrator TD is a piezoelectric element integrated with a mechanical structure such as a horn, and is, for example, a Langevin type piezoelectric vibrator.

Further, the voltage controlled oscillator circuit 1 is composed of, for example, an astable multivibrator, and the pulse width variable unit 2 uses the light receiving element PR ₁ of the photocoupler PC ₁ to adjust the pulse width of the voltage controlled oscillator circuit 1 as shown in FIG. This is a configuration for changing related circuit constants.

Further, the oscillation frequency of the voltage controlled oscillator circuit 1 is set to the piezoelectric vibrator T
In order to follow the change of the resonance frequency (resonance point) of D,
A detection control circuit 5 is provided. The detection control circuit 5
Is composed of a smoothing circuit 6, a reference voltage generator 7 and a comparator 8. A resistor R ₁ is inserted on the emitter side of the transistor Q ₁ of the power amplification circuit 4, and the voltage across the resistor R ₁ which becomes a voltage substantially proportional to the output current of the power amplification circuit 4 is smoothed by the smoothing circuit 6. Is smoothed by and is applied to one input of the comparator 8. The reference voltage value Vref of the reference voltage generator 7 is applied to the other input of the comparator 8.

Here, the comparator 8 is the operational amplifier OP ₁ as shown in FIG.
The smoothing circuit 6 includes resistors R ₂ and R ₂ .
₃ and the capacitor C ₁ . The reference voltage generator 7 has a variable resistor VR ₁ , and the voltage across the variable resistor VR ₁ becomes the reference voltage value Vref.

The output signal of the detection control circuit 5 is sent to the voltage controlled oscillation circuit 1 via the voltage variable section 9 and the frequency control voltage S ₁
Will be returned as. The voltage generator 9 includes a pulse generator 1
A variable pulse signal S ₂ for power adjustment from 0 is applied.

Here, as shown in FIG. 2, the voltage variable unit 9 includes a transistor Q ₂ for applying the frequency control voltage S ₁ to the voltage controlled oscillator circuit 1 and an emitter follower including resistors R ₄ and R ₅ . It has a transistor Q ₃ and a capacitor C ₂ which are inserted in the base circuit of the transistor Q ₂ , an n-gate thyristor (also called PUT) SC ₁ for frequency sweeping, and resistors R ₆ , R ₇ and R _8. There is. Then, a photocoupler PC ₂ is provided to couple the detection control circuit 5 and the voltage variable unit 9. That is, the light emitting element PT ₂ of photocoupler PC ₂ is an operational amplifier OP ₁
The light receiving element PR ₂ is connected to the transistor Q ₃ of the voltage variable unit 9 in parallel. The variable pulse signal S ₂ of the pulse generating circuit 10 is a transistor Q ₃
Applied to the base of.

The variable pulse signal S ₂ has an extremely short pulse width as compared with the pulse repetition period as shown in FIG. 3, and the pulse generation circuit 10 can change either the pulse repetition period or the pulse width. Has become.

The low-voltage power supply voltage Vct of the voltage controlled oscillator circuit 1, the pulse width varying unit 2 and the voltage varying unit 9 is stabilized at a constant value.

Further, a drive pulse width control circuit 11 is provided in order to compensate for output power fluctuations due to voltage fluctuations of the high-voltage power supply voltage B + of the power amplification circuit 4. The drive pulse width control circuit 11 includes a voltage dividing unit 12 that detects a voltage proportional to the high-voltage power supply voltage B +, and a drive pulse width detecting unit 13 that detects a pulse width of a drive pulse on the base side of the transistor Q _1.
And a comparator 14, and the output signal controls the pulse width varying section 2. That is, as shown in FIG. 2, the comparator 14 includes an operational amplifier OP.
_{2 is applied} to one input of the operational amplifier OP ₂ and the voltage obtained by dividing the high-voltage power supply voltage B + by the voltage dividing unit 12 having the resistors R ₉ , R ₁₀ and the variable resistor VR ₂ is applied. To be done. Further, the drive pulse width detection unit 13 amplifies the voltage on the secondary side of the interstage transformer T ₁ with the transistor Q ₄ , rectifies it with the diode D ₁ , and smoothes it with the capacitors C ₃ , C ₄ and the choke L _1. applying a DC voltage proportional to the drive pulse width to the other input of the operational amplifier OP _2. Then, the light emitting element PT ₁ of the photocoupler PC ₁ on the output side of the operational amplifier OP ₂ is caused to emit light to drive the light receiving element PR _{1 serving} as the pulse variable unit 2.

The operational amplifiers OP ₁ and OP ₂ and the reference voltage generator 7
The power supply voltage is also stabilized at a constant value.

Next, the operation of the above embodiment will be described.

First, the frequency sweep operation of the voltage controlled oscillator circuit 1 will be described assuming that there is no variable pulse signal S ₂ from the pulse generation circuit 10 and no detection control signal 5 is output. Now, when the power is turned on, the emitter current of the transistor Q ₂ increases as the capacitor C ₂ of the voltage variable unit 9 is charged, and the voltage across the resistor R ₄ , that is, the frequency control voltage S ₁ increases. Go. As a result, the voltage controlled oscillator circuit 1
The CR time constant is controlled so that it becomes equivalently smaller with the lapse of time, and the oscillation frequency of the oscillator excitation circuit 1 is swept in a direction from a low state to a high state. Capacitor C ₂
When the charging voltage of ₁ is going to exceed the gate potential of the n-gate thyristor SC ₁ , the n-gate thyristor SC ₁ becomes conductive, the voltage of the capacitor C ₂ returns to zero, and the above operation is repeated again. Therefore, the voltage controlled oscillator circuit 1 is repeatedly swept from the low oscillation frequency to the high oscillation frequency.

Frequency-following operation of the voltage controlled oscillator circuit 1 with respect to changes in the resonance frequency due to load fluctuations of the piezoelectric vibrator TD (provided that there is no variable pulse signal S ₂ for power adjustment)
Outputs the output signal of the detection control circuit 5 to the photocoupler PC ₂
It is performed by feeding back to the voltage variable unit 9 at. As is clear from the frequency characteristics of the impedance of the piezoelectric vibrator TD shown by the curve (a) in FIG. 4, the impedance decreases as the resonance frequency r of the piezoelectric vibrator approaches, so the oscillation of the voltage controlled oscillator circuit 1 When the frequency is swept from the lower side toward the higher side, the input power of the piezoelectric vibrator increases near the resonance frequency r, and the voltage value across the resistor R ₁ of the power amplification circuit 4 also increases. Therefore, if the reference voltage value Vref of the reference voltage generator 7 is made to match the input power of the piezoelectric vibrator, that is, the output voltage value of the smoothing circuit 6 when the driving power is almost maximum, the input power of the piezoelectric vibrator is set. The light emitting element PT ₂ on the output side of the operational amplifier OP ₁ emits light at a frequency extremely close to the resonance frequency r at which the photocoupler PC ₂
The light receiving element PR ₂ constituting the element has a low resistance. As a result,
The sweep of the oscillation frequency of the voltage controlled oscillator circuit 1 is performed by the light receiving element P.
When the resistance of R ₂ becomes low, the voltage-controlled oscillation circuit 1 continues to oscillate at a frequency very close to the resonance frequency r at which the input power of the piezoelectric vibrator is almost maximum (this is the drive frequency), This is amplified by the drive circuit 3,
Further, the power is amplified by the power amplifier circuit 4, and the piezoelectric vibrator TD
Added to.

The curve (b) in FIG. 4 shows the relationship between the atomization amount per unit time and the frequency for driving the piezoelectric vibrator when the liquid is atomized by the ultrasonic vibration of the piezoelectric vibrator TD. When the drive frequency of the piezoelectric vibrator matches the resonance frequency r of the piezoelectric vibrator,
It can be seen that the amount of atomization is maximum and the amount of atomization decreases rapidly as it deviates from the resonance frequency r.

Now, in order to keep the work of the piezoelectric vibrator TD, for example, the above-mentioned atomization amount substantially at the maximum, the detection control circuit 5 is arranged so that the voltage controlled oscillation circuit 1 oscillates at a frequency extremely close to the resonance frequency r. However, there are cases where it is desired to change the input power of the piezoelectric vibrator to change the work amount. Therefore, the variable pulse signal S ₂ for power adjustment from the pulse generation circuit 10 is supplied to the voltage variable unit 9. Now, as shown in FIG. 3 (A), when a pulse signal having a waveform whose pulse width is extremely short compared to the pulse repetition period is applied to the base of the transistor Q ₃ of the voltage variable unit 9, the transistor Q _3
3 has low resistance during a very short period corresponding to the pulse width,
As a result, (due to a large capacitance of the capacitor C _2, an abrupt change does not occur.) Terminal voltage of the capacitor C ₂ is to be slightly lowered Namely, when a pulse signal is applied S ₂ to the voltage variable section 9, the pulse applied prior to A voltage value smoothed by subtracting the voltage waveform proportional to the pulse signal S ₂ from the terminal voltage of the capacitor C ₂ is obtained between the base of the transistor Q ₂ and the ground. Then, by changing the pulse width as shown in FIG. 3 (B) or the pulse repetition period as shown in FIG. 3 (C), the voltage value between the base of the transistor Q ₂ and ground is made fine. It can be variably adjusted, and by changing the frequency control voltage S ₁ minutely, the frequency _{1 of} FIG.
The oscillation frequency of the voltage controlled oscillator circuit 1 can be arbitrarily adjusted in the range W ₁ of up to r, and the input power of the piezoelectric vibrator TD can be finely changed. For example, the resonance frequency r
Is 35 kHz, the frequency can be changed within a range of about 0.1%. For example, at r: 35 kHz, W ₁ has a width of about 50 to 80 Hz.

The drive pulse width control circuit 11 uses the high power supply voltage B +
To compensate for fluctuations in the input power of the piezoelectric vibrator TD due to fluctuations in the pulse width of the voltage controlled oscillator circuit 1 via the photocoupler PC ₁ when the high-voltage power supply voltage B + becomes higher than a predetermined value. The width is narrowed and the conduction period of the transistor Q ₁ of the power amplifier circuit 4 is controlled to be short.

In the above embodiment, the voltage controlled oscillator circuit 1 is swept from a low frequency to a high frequency.
_Although the oscillation frequency of the voltage controlled oscillator circuit 1 is set within the range W _{1 of} 1 to r, the voltage controlled oscillator circuit 1 is swept from a high frequency to a low frequency, and the frequency r
It may be set the oscillation frequency of the voltage controlled oscillation circuit 1 to ₂ range W _2.

Further, in the variable voltage unit 9, the smoothing the voltage value of the transistor Q ₂ based by subtracting the voltage waveform that is proportional to the pulse signal S _2, but is obtained between ground and the pulse signal S ₂
It is also possible to add a voltage waveform proportional to the above to obtain a smoothed voltage value.

(Effect of the Invention) As described above, according to the vibrator excitation circuit of the present invention, the resonance frequency of the piezoelectric vibrator is tracked by using the pulse signal having the waveform whose pulse width is extremely shorter than the pulse repetition period. It is possible to finely adjust the frequency control signal to the voltage controlled oscillation circuit controlled as described above, and to finely and substantially linearly adjust the driving power of the piezoelectric vibrator.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a vibrator excitation circuit according to the present invention, FIG. 2 is the same circuit diagram, FIG. 3 is a waveform diagram of a variable pulse signal S ₂ for power adjustment, and FIG. It is a graph which shows the impedance of a vibrator, and the frequency characteristic of the amount of atomization. 1 ... Voltage controlled oscillator circuit, 2 ... Pulse width variable section, 3 ...
... drive circuit, 4 ... power amplification circuit, 5 ... detection control circuit, 6 ... smoothing circuit, 7 ... reference voltage generation unit, 8, 1
4 ... Comparator, 9 ... Voltage variable section, 10 ... Pulse generation circuit, 11 ... Drive pulse width control circuit, 12 ... Voltage dividing section, 13 ... Drive pulse width detection section.

Claims (2)

[Claims] 1. A piezoelectric vibrator is driven by amplifying an oscillation output of a voltage controlled oscillator circuit by a power amplifier circuit, and a voltage value substantially proportional to an output current of the power amplifier circuit is compared with a reference voltage value. In a resonator excitation circuit provided with a detection control circuit that feeds back a frequency control signal according to the difference between the two voltage values to the voltage controlled oscillation circuit, a frequency fine adjustment pulse signal with a narrower pulse width than the repetition period is used. The oscillator excitation circuit is characterized in that the frequency control signal is varied. 2. The oscillator excitation circuit according to claim 1, wherein the pulse signal is one in which the repetition period or the pulse width changes.