JPH05301077A - Ultrasonic wave generator - Google Patents

Abstract

PURPOSE:To securely lock the resonance frequency of an oscillator by analog control with simple circuit configuration. CONSTITUTION:A drive circuit 40 is driven to make an oscillator 23 sweep oscillation by a voltage control oscillator 18 where the oscillation frequency is controlled by bias voltage changing with time of a main integrating condenser 37 changed on the start of operation, and the phase difference between one of drive current and drive voltage of the oscillator 23 and an oscillating speed signal is computed by a phase comparator 25 to integrate the difference by a sub-integrating condenser 27. When the zero cross of the integrated phase difference comparison output is detected by a zero cross detector 28, both the detection of resonance frequency of the oscillator 23 on the start of operation and the follow-up control of resonance frequency of the oscillator during operation are performed with one main integrating condenser 37 by switching the phase difference comparison output of the sub-integrating condenser 27 to the main integrating condenser 37 by a selector switch 29.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic wave generator for driving a vibrator of an ultrasonic wave application device such as an ultrasonic welder or an ultrasonic processing machine at a resonance frequency.

[0002]

2. Description of the Related Art Generally, the sharpness Q of the resonance characteristic of a vibrator of an ultrasonic wave application apparatus has a large value. Therefore, an ultrasonic wave generation apparatus that oscillates this at an ultrasonic frequency is required to increase its operating efficiency. The oscillator is driven at the resonance frequency. However, in such an ultrasonic generator,
When the horn or tool connected to the oscillator is replaced or the temperature or load changes, etc., the resonant frequency of the oscillator changes and becomes out of synchronization with the drive frequency. PLL (Phase Locked Loop)
The automatic tracking circuit of the method controls the tracking to the resonance frequency. The automatic tracking circuit of such an ultrasonic generator is
For example, it is formed by a VCO (Voltage Controlled Oscillator) or the like, which is a voltage controlled oscillator whose oscillation frequency is variable, and the oscillator is arranged so that the relative phase between the detection signal proportional to the oscillation speed of the oscillator and the drive current match. The oscillating frequency of the driving power source is controlled to be tracked.

More specifically, in such an ultrasonic generator, as shown in FIG. 3 (a), the resonance frequency f ₀₁ of the vibrator is located approximately in the center of the control range of the VCO. At relative resonance frequency f ₀₁
The zero cross on the frequency characteristic of 1 and the dip on the frequency characteristic of the drive current It match. In such an ultrasonic generator, the resonance frequency f ₀₁ of the vibrator is changed to the resonance frequency f ₀₁ for tool replacement or the like as illustrated in FIG.
The resonance frequency f ₀₁ may decrease to ₀₂ or may increase to the resonance frequency f ₀₃ as illustrated in FIG. In either case, if the relative phase difference signal φs is “+”, the VCO is controlled to a high frequency, and if the relative phase difference signal φs is “−”, the VCO is controlled to a low frequency. The oscillation frequency of the VCO in the range of _{1 to} f ₂ is controlled to be tracked toward the resonance frequencies of f _{01 to} f ₀₃ , which are points where the zero of the relative phase difference signal φs crosses. In such an ultrasonic wave generator, since there is only one zero cross of the relative phase difference signal φs of the vibrator existing within the control range f _{1 to} f _{2 of} the VCO and the effective range is wide, the oscillation start frequency of the VCO is f ₁ It is possible to track the resonance frequency anywhere in the range from to f ₂ .

However, in the actual ultrasonic wave generator, as shown in FIG.
As illustrated in (a), the zero cross f ₃ , which becomes an obstacle in the vicinity of the resonance frequency f ₀₁ of the oscillator due to the complication of the vibration system,
If f ₄ like is occurring is common, in such a case, the frequency f ₃ ~f ₄ becomes effective range of the tracking control.
It should be noted that FIG. 7B illustrates the relative phase difference signal φs and the drive current It when the resonance frequency f ₀₁ is lowered to f ₀₂ due to the replacement of the vibration system or the tool. Similarly, FIG. The relative phase difference signal φs and the drive current It when the frequency f ₀₁ rises to f ₀₃ are illustrated. Then, such a case where the resonance frequency f in those phase difference characteristics change, the effective range of the phase difference characteristic which satisfies all of these cases is f ₅ ~f ₆
Therefore, it becomes necessary to make VCO drift within this range. In other words, in such an ultrasonic generator, a malfunction occurs at the start of oscillation unless the allowable value of the characteristic variation of the vibrator or VCO is narrowly restricted. Therefore, for example, a machine tool in which a tool connected to the vibrator is exchangeable. However, the versatility is significantly reduced, which is not preferable.

In order to solve such a problem, the ultrasonic generator disclosed by the applicant in Japanese Patent Publication No. Sho 61-10194 has a wider range than the effective range of the tracking control of the PLL circuit at the start of oscillation. Sweep is performed to detect a resonance point, and the sweep frequency of the VCO is locked at this resonance point before tracking control is started. In the ultrasonic generator disclosed in the above publication, the integral capacitor used for sweeping and the integral capacitor used for PLL control are operated separately, so that the integral voltage of the sweep lock is held even during the execution of PLL control. It is supposed to do.

[0006]

In the ultrasonic generator disclosed in the above publication, since the resonance point is locked by the sweep over a wide range and the tracking control is started, the allowable value of the characteristic fluctuation of the oscillator or VCO is set. It can be expanded to improve versatility. However, in this ultrasonic generator, the charge held by the integration capacitor for sweep lock actually decreases over time due to spontaneous discharge, so the voltage value of this integration capacitor deviates from the allowable range and the resonance point Occurs during the oscillation operation.

Therefore, in order to solve the uncertainty of the sweep lock due to the sample hold of the analog value as described above, the applicant of the present invention further discloses the CPU in JP-A-60-34776.
Although it has been proposed that the sweep locking is performed with a digital value by the (Central Processing Unit), this will complicate the circuit structure and hinder the reduction in size and weight and the improvement in productivity.

[0008]

The invention according to claim 1 is
A main integration capacitor that is charged with a bias voltage at the start of operation is provided, and a voltage controlled oscillator that generates a frequency controlled by the bias voltage that changes with time of this main integration capacitor is provided. A phase comparator for providing a circuit, providing a vibrator that oscillates at a drive frequency that changes with time of the drive circuit, and comparing the phase difference between one of the drive current and the drive voltage of the vibrator and the vibration speed signal. And a sub-integration capacitor that integrates the output of this phase comparator to generate a phase-difference comparison output, and a zero-cross detector that detects the zero-cross of the phase-difference comparison output generated by this sub-integration capacitor. When the detector detects zero cross, the phase difference comparison output of the sub integration capacitor is connected to the main integration capacitor. The switch is provided that.

According to a second aspect of the invention, in the first aspect of the invention, the drive current supplied to the drive circuit is limited from the start of operation until at least the changeover switch switches the connection destination of the phase comparator to the main integration capacitor. A protection circuit is provided.

[0010]

According to the invention described in claim 1, both the sweep of the drive frequency for detecting the resonance frequency of the vibrator at the start of operation and the tracking control of the resonance frequency of the vibrator during continuous operation are provided in one main unit. Since it can be performed by the integration capacitor, the resonance frequency swept-locked by the natural discharge of the integration capacitor like the conventional ultrasonic generator that detects the resonance frequency of the oscillator and the tracking control by separate integration capacitors. Since it is not reset, it can contribute to the improvement of the reliability of the ultrasonic generator, and since it is not necessary to perform such sweep lock with a digital value by a computer, its circuit structure is simple and compact. It can contribute to weight reduction and productivity improvement.

According to the second aspect of the invention, even if the resonance point of the vibrator is detected by sweeping a wide range of frequencies, an excessive drive current does not flow into the drive circuit, so that it is possible to prevent damage to each part.

[0012]

Embodiments of the present invention will be described with reference to FIGS. 1 and 2. First, in this ultrasonic generator 1, as illustrated in FIG. 1, an oscillation enable FF (Flip Flop) 4 to which a set switch 2 and a reset switch 3 are connected is provided with first and second differentiators 5, 6 Is connected to the first and second one-shot multis 7 and 8 respectively, and the transistor 9 connected to the first one-shot multi 7 and the oscillation enable FF 4 are connected via a transistor 10 to a photocoupler. 11 is connected. The output terminal of the photocoupler 11 has a MOS (Metal-Oxide-Se)
The gate and the source of the transistor 12 are connected to each other, and the drain and the source of the MOS transistor 12 are connected to the resistor 13 in parallel.
A DC power supply 14 and a power amplifier 15 are connected to both ends of 3. On the other hand, at the other input terminal of the OR gate 16 provided between the second differentiator 6 and the second one-shot multi 8, the output of the DC amplifier 38 connected to the control input of the VCO 18 is connected to the window comparator. The VCO 18 and the oscillation enable FF 4 are connected to each other via the AND gate 19 and the power amplifier 15. The output transformer 20 connected to the power amplifier 15 is connected to both ends of the oscillator 23 via the common matching inductor 21 and the resistor 22, respectively, and the detection sensor connected to the oscillator 23. 24 and one end of the output transformer 20 output the vibration speed signal es and the drive current it, respectively.

Therefore, an integration resistor 26 and a sub-integration capacitor 27 are sequentially connected to the phase comparator 25 to which the vibration speed signal es and the drive current it are fed back, and the sub-integration capacitor 27 detects zero cross. The device 28 and the first analog switch 29, which is a changeover switch, are connected to each other. Also, only the drive current it is A
C / DC (Alternating Current / Direct Curren
t) The current comparator 31 fed back through the converter 30 and the zero-cross detector 28 are AND gates 32.
Is connected to the sweep FF 33 via the, and the second one-shot multi 8 is connected to the other input terminal of the sweep FF 33 via the inverter 34 and the third differentiator 35 in sequence. ..

Here, this second one-shot multi 8
Is connected to a second analog switch 36, and a main integration capacitor 37 is connected to the first and second analog switches 29 and 36, and a DC amplifier 38 is connected.
Via the window comparator 17 and the VCO 1
And 8 are connected. Here, a constant current power supply 39 is also connected to the first analog switch 29, and one of the constant current power supply 39 and the sub integration capacitor 27 is selectively connected to the main integration capacitor 37 by switching. It has become. Since the main integration capacitor 37 is for tracking control and the sub integration capacitor 27 is for sweeping, the sub integration capacitor 27 has a smaller capacity than the main integration capacitor 37 in order to improve responsiveness. .. In addition, this ultrasonic generator 1
Then, the drive circuit 4 for generating the drive voltage of the vibrator 23
0 is formed by a power amplifier 15, an output transformer 20, a common matching inductor 21 and a resistor 22.
A protection circuit 41 that limits the power supply current supplied to the power amplifier 15 from the start of operation until at least the resonance point is detected is formed by the transistor 10, the photocoupler 11, the MOS transistor 12, the resistor 13, and the like. There is.

In the ultrasonic wave generating apparatus 1 having such a structure, for example, an ultrasonic welder or an ultrasonic processing machine in which a plurality of kinds of horns and tools (both not shown) are exchangeably connected to the vibrator 23, etc. Is being used for.
Then, in such an ultrasonic generator 1, when the resonance frequency of the vibrator 23 changes due to replacement of the horn, temperature change, load change, etc., the frequency of the drive voltage of the vibrator 23 is controlled to follow the resonance frequency. It is supposed to do. In addition,
The ultrasonic wave generator 1 of the present embodiment drives the oscillator 23 in parallel resonance point, that is, drives by a constant voltage power supply.

Therefore, the operation of each part when executing the tracking control of the ultrasonic wave generating apparatus 1 will be described in detail below with reference to the time chart of FIG. First, when the user (not shown) turns on the set switch 2 at time T ₀ , the oscillation enable FF 4 is set and the output Q ₁ changes from “0” to “1”. The gate 19 is opened and the oscillation output of the VCO 18 is transmitted to the power amplifier 15. Therefore,
Since the drive circuit 40 including the power amplifier 15 and the common matching inductor 21 drives the oscillator 23 to oscillate,
The oscillator 23 starts ultrasonic vibration at a drive frequency corresponding to the oscillation frequency output by the VCO 18, but in the ultrasonic generator 1, V is generated at the start of oscillation drive.
The resonance frequency of the oscillator 23 is detected by sweeping the oscillation frequency of the CO 18.

That is, the output Q ₁ of the oscillation enable FF 4 when the set switch 2 is turned on is converted into a pulse having a sharp rise by the second differentiator 6 and is also input from the OR gate 16 to the second one-shot multi 8. As a result, the second one-shot multi 8 is triggered and outputs the reset pulse P ₂ . Then, the operation state S _{1 of} the second analog switch 36 is made by the reset pulse P ₂ and the bias voltage V of the main integration capacitor 37 is increased.
_CB is charged to the voltage Es, this voltage Es is amplified by the DC amplifier 38, and the oscillation frequency of the VCO 18 is set to the frequency at the start of the sweep. So this V
The power amplifier 15 to which the oscillation frequency of the CO 18 is transmitted via the AND gate 19 outputs a driving voltage having a frequency corresponding to the oscillation signal. It will be applied to the vibrator 23 through the inductor 21 for.

By doing so, in this ultrasonic generator 1, the set switch 2 is started to start the oscillating operation.
At the time T _{0 when} is input, the oscillator 23 is driven at the frequency at the start of the sweep.

Further, in this ultrasonic generator 1, the reset pulse P ₂ is phase-inverted by the inverter 34 and then differentiated by the third differentiator 35, so that the time elapsed after the oscillation drive of the oscillator 23 is started. At T ₁ , when the reset time by the second one-shot multi 8 is completed and the output of the reset pulse P ₂ is stopped, the sweep FF triggered by the fall edge of the output of the third differentiator 35.
The output Q _{2 of} 33 becomes "1", whereby the operating state S ₂ of the first analog switch 29 is switched to the constant current power supply 39 side. Then, as described above, the bias voltage V _CB of the main integration capacitor 37 is discharged by the output current of the constant current power supply 39 and decreases with time from the voltage Es. Therefore, the oscillation frequency of the VCO 18 corresponds to this voltage decrease. Since it rises, the drive frequency of the oscillator 23 generated by the power amplifier 15 also rises.

By doing so, in the ultrasonic generator 1, the drive frequency of the oscillator 23 oscillated and driven at the frequency at the start of the sweep at the time T ₀ increases with time from the time T _1. Therefore, the drive frequency of the vibrator 23 is swept.

When the driving frequency of the vibrator 23 rises in this way, a current corresponding to the frequency characteristic of the impedance of the vibrator 23 flows, and this is the resistance of the resistor 22.
Is detected as the drive current it by the AC / DC converter 30.
And the vibration speed signal es output from the detection sensor 24 corresponding to the vibration speed of the vibrator 23 is input to the other end of the phase comparator 25. The AC / DC converter 30 to which the drive current it is input outputs a DC signal It having a frequency characteristic proportional to the magnitude of the drive current to the current comparator 31, as shown in the figure. When the DC signal It falls below a preset threshold V, the detection signal P ₃ is output to one end of the AND gate 32. On the other hand, the phase comparator 25 detects the phase difference by comparing the input drive current it with the vibration speed signal es, and this is converted into the phase difference comparison output φs by the integration resistor 26 and the sub-integration capacitor 27. Is input to the zero-cross detector 28. Here, since the zero-cross detector 28 monitors that the phase difference comparison output φs becomes a zero-cross in the falling direction, the output signal of the zero-cross detector 28 which has confirmed the zero-cross at time T ₂ is output to the AND gate 32. To be done. At this time, since the AND gate 32 is opened by the detection signal P ₃ as described above, the sweep FF 33 is reset by the output signal of the AND gate 32 at the time T ₂ , and the first analog switch 29 is initialized. It will return to the state.

By doing so, in this ultrasonic generator 1, the discharge to the main integration capacitor 37 is stopped, the excitation drive of the oscillator 23 is performed at the resonance point, and then the phase comparator 25 outputs. Drive current it
Since the phase difference signal between the vibration speed signal es and the vibration speed signal es is output to the main integration capacitor 37, the drive frequency of the vibrator 23 driven by the VCO 18 and the power amplifier 15 corresponding to the bias voltage V _CB of the main integration capacitor 37. Will be stably tracked to the resonance frequency.

In the ultrasonic generator 1, if the resonance point is not detected due to the sweep of the driving frequency at the times T _{1 to} T ₃ as described above, the main integration capacitor 3
7 continues discharging until time T ₃ , and the limit is detected by the window comparator 17 which monitors the bias voltage V _CB after it is amplified by the DC amplifier 38. Further, when the output from the window comparator 17 to the one-shot multi 8 via the OR gate 16, the one-shot multi 8 is triggered and outputs the reset pulse P ₂ , so that the sweep is restarted by the reset pulse P _2. Then, the resonance point is searched again. In the ultrasonic generator 1, the restart of the sweep as described above causes a trouble such as damage of the vibration system during a normal tracking operation to make tracking impossible or an excessive load causes a phase difference. It is also done in case of extreme increase. Further, the broken line of the time chart illustrated in FIG. 2 shows a state in which the reset function of the sweep FF 33 at the time of detecting the resonance point is stopped so that the resonance point is not detected and the sweep operation is repeated.

Further, in the ultrasonic generator 1, since the resonance point of the vibrator 23 is detected by sweeping a wide range of frequencies as described above, the driving current it of the vibrator 23 is at a frequency near the resonance point. May be too large when compared with the resonance. In this case, the power amplifier 15 and the network may be overloaded by the application of an excessive current, or the vibration of the vibrator 23 or the like may become excessively large, resulting in damage. Therefore, in the ultrasonic generator 1, A protection circuit 41 is provided to prevent such damage.

That is, when the set switch 2 is turned on and the output Q ₁ of the oscillation enable FF 4 becomes "1", this rising signal is differentiated by the first differentiator 5 and then the first one-shot multi 7 is triggered. To do. At this time, the duration of the output pulse P ₁ of the first one-shot multi 7 is set to a time T ₄ longer than the time T ₃ required for the sweep, and the output pulse P ₁ causes the transistor 9 to turn on. Become. That is, since the transistor 12 is in the off state until the time T ₄ after the completion of the sweep, the supply voltage + B to the power amplifier 15 is supplied from the DC power source 14 through the resistor 13, and the power amplifier due to the excessive current flows. It is possible to prevent the destruction of 15 and the network.

Further, in the ultrasonic generator 1, when the detection of the resonance point is completed by the time T ₃ and the tracking control of the PLL system becomes stable, the output pulse P of the first one-shot multi 7 at the time T ₄ . ₁ stops and the transistor 9 is turned off. Then, since the transistor 10 connected to the transistor 9 is turned on and the photocoupler 11 is driven, the operating state Q of the MOS transistor 12 is increased.
₃ turns on. Then, the resistor 13 is short-circuited, so that the DC power supply 14 directly supplies power to the power amplifier 15, and the power amplifier 15 is fully driven under the DC power supply 14.

The protection circuit for preventing overcurrent as described above is a pulse width controlled switching regulator.
It is also possible to use a structure (not shown) to reduce the supply voltage. Further, in this ultrasonic generator 1, when the user operates the reset switch 3, the oscillation enable FF 4
Output Q ₁ of "0" becomes "0", the gate 19 is closed, and the oscillation drive of the vibrator 23 is stopped.

Further, in the ultrasonic generator 1 of the present embodiment, the description has been given by exemplifying that the vibrator 23 is driven at the parallel resonance point by the constant voltage drive power source, but the present invention is not limited to the above-mentioned form. Even when the oscillator 23 is driven at the series resonance point by the constant current drive power source, the same effect can be obtained by changing some circuits. Note that, as such a circuit change, for example, it is possible to use the vibration velocity signal and the vibrator drive voltage as the phase comparison input.

[0029]

According to the first aspect of the present invention, the main control capacitor is provided which is charged with the bias voltage at the start of operation, and the voltage control which generates the frequency controlled by the bias voltage which changes with time of the main control capacitor. An oscillator is provided, a drive circuit driven by this voltage controlled oscillator is provided, and a vibrator that performs sweep oscillation at a drive frequency that changes with time of this drive circuit is provided, and one of the drive current and the drive voltage of this vibrator is provided. A phase comparator that compares the phase difference with the vibration velocity signal is provided, a sub-integration capacitor that integrates the output of this phase comparator to generate a phase difference comparison output, and the phase difference comparison output generated by this sub-integration capacitor A zero-cross detector for detecting the zero-cross of the sub-integration capacitor is provided when the zero-cross detector detects the zero-cross. By providing a changeover switch for connecting the force to the main integration capacitor, the drive frequency sweep for detecting the resonance frequency of the vibrator at the start of operation and the tracking control of the resonance frequency of the vibrator during continuous operation are provided. Both of them can be performed by a single main integration capacitor, so that the natural discharge of the integration capacitor, like the conventional ultrasonic generator that detects the resonance frequency of the oscillator and tracking control by separate integration capacitors. Since the sweep-locked resonance frequency is not reset by this, it can contribute to the improvement of the reliability of the ultrasonic generator, and since it is not necessary to perform such sweep-lock with a digital value by a computer, The circuit structure is simple, and it has effects such as contributing to size reduction and weight reduction and productivity improvement.

According to a second aspect of the present invention, in the first aspect of the invention, the drive current supplied to the drive circuit is limited from the start of operation until at least the changeover switch switches the connection destination of the phase comparator to the main integration capacitor. By providing a protection circuit that prevents the excessive drive current from flowing into the drive circuit even when the resonance point of the oscillator is detected by sweeping a wide range of frequencies, it is possible to prevent damage to each part. Is to have.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a time chart.

FIG. 3 is a characteristic diagram showing a first conventional example.

FIG. 4 is a characteristic diagram showing a second conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ultrasonic generator 23 Transducer 25 Phase comparator 27 Sub-integration capacitor 28 Zero cross detector 29 Changeover switch 37 Main integration capacitor 40 Drive circuit 41 Protection circuit

Claims (2)

[Claims] 1. A main integration capacitor to which a bias voltage is charged at the start of operation, a voltage controlled oscillator that generates a frequency controlled by a bias voltage that changes with time of the main integration capacitor, and a voltage controlled oscillator that drives the voltage. Drive circuit, a vibrator that oscillates at a drive frequency that changes with time of this drive circuit, and a phase comparison that compares the phase difference between one of the drive current and drive voltage of this vibrator and the vibration velocity signal. And a sub-integration capacitor that integrates the output of this phase comparator to generate a phase difference comparison output,
A zero-cross detector that detects a zero-cross of the phase difference comparison output generated by the sub-integration capacitor, and a changeover switch that connects the phase-difference comparison output of the sub-integration capacitor to the main integration capacitor when the zero-cross detector detects a zero-cross. An ultrasonic wave generator comprising: 2. A protection circuit for limiting the drive current supplied to the drive circuit from the start of operation until at least the connection point of the phase comparator is switched to the main integration capacitor by the changeover switch. The ultrasonic generator described.