JPH05143168A - Ultrasonic wave generator - Google Patents

Abstract

PURPOSE:To obtain a compact and highly efficient ultrasonic wave generator without stopping oscillation even in the case of heavy load in respect to an ultrasonic wave generator for an ultrasonic welder. CONSTITUTION:A voltage control oscillator 1 oscillates a signal with frequency to be changed in accordance with a control signal vc and a driving circuit 2 amplifies the output of the oscillator 1. An output resonance circuit 4 supplies the output of the circuit 2 to an ultrasonic vibrator 3 and a current detection part 5 detects an output current from the circuit 4. The detection part 5 compares the phase of its current detection signal with that of an output voltage signal from the oscillator 1, a control circuit 7 generates a PWM signal with pulse width to be changed in accordance with the detected phase difference and an integrating circuit 8 integrates the PWM signal and generates a control signal vc to control frequency based upon the control of the pulse width by the circuit 7 so that the driving frequency of vibrator 3 coincides with oscillation frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic generator for an ultrasonic welding machine or the like, and more particularly to a small and highly efficient ultrasonic generator which does not stop oscillation even under heavy load.

Ultrasonic welding machines are used for applications such as welding of plastic materials, and with the increasing use of plastic materials in the automobile industry and the like, they have been widely used.

An ultrasonic generator used in such an ultrasonic welding machine is desired to be small in size, highly efficient, and low in cost without causing troubles such as oscillation stop even under heavy load. To be done.

[0004]

2. Description of the Related Art A conventional ultrasonic wave generator includes a condenser bridge incorporated in a final stage circuit, which is an ultrasonic transducer for applying an ultrasonic wave to a work (workpiece) connected to the final stage circuit. The oscillation frequency is detected and fed back to the oscillation circuit to stabilize the oscillation operation.

[0005]

SUMMARY OF THE INVENTION In an ultrasonic welding machine, an ultrasonic vibrator is pressed against a work and vibrated to heat a joint part of a work such as plastic to partially melt the work. However, when the load on the vibrator becomes heavy due to the working condition, the feedback to the oscillation circuit decreases, so that the oscillation cannot be continued and the operation is stopped. That is, the conventional ultrasonic generator is weak against pressure oscillation.

In this case, in order to prevent the oscillation from stopping even if a heavy load is driven, there is no other method than increasing the output itself of the oscillator, and therefore an oscillator which is excessive compared with the work is required.

Further, although the vibration frequency of the ultrasonic vibrator changes in a heavy load state, the frequency automatic tracking of the oscillator circuit against this changes is not perfect, so that the loss of the power circuit increases. Therefore, there is a problem in the power circuit that it is necessary to take measures against heat radiation, which seems to be excessive.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art as described above, and in an ultrasonic welding machine, automatic frequency tracking is performed to stabilize the oscillation, thereby generating an excessive output. It is an object of the present invention to provide an ultrasonic generator that is small in size, highly efficient, and low in cost because it does not require it and does not require excessive heat dissipation measures.

[0009]

An ultrasonic generator of the present invention comprises a voltage controlled oscillator 1 that oscillates at a frequency that changes according to a control signal v _c , and a drive circuit 2 that amplifies the output of the voltage controlled oscillator 1. An output resonance circuit 4 that supplies the output of the drive circuit 2 to the ultrasonic transducer 3, a current detection unit 5 that detects an output current in the output resonance circuit 4, the current detection signal, and the output voltage signal of the voltage controlled oscillator 1. , A phase comparator 6 for comparing the phases of the PWM signal, a control circuit 7 for generating a PWM signal having a pulse width that changes according to the detected phase difference, and an integration for integrating the PWM signal to generate a control signal v _c. The circuit 8 is provided, and is controlled so that the drive frequency and the vibration frequency of the ultrasonic transducer 3 match based on the control of the pulse width in the control circuit 7.

[0010]

4A and 4B show examples of the amplitude response characteristics of the ultrasonic transducer with respect to the driving frequency. FIG. 4A shows the state when no pressure is applied and FIG. 4B shows the state when pressure is applied.

When no pressure is applied, as shown in FIG. 4 (a), the driving frequency of the ultrasonic vibrator matches the vibration frequency f ₀₁ , and the amplitude response becomes maximum. On the other hand, during pressurization,
As shown in (b), the vibration frequency of the ultrasonic transducer changes to f ₀₂ . Therefore, in this state, f
If it is ₀₁ , the amplitude response of the ultrasonic transducer will decrease, so
The drive frequency must be quickly and correctly changed to f ₀₂ .

In the ultrasonic generator of the present invention, the phase comparator detects the voltage corresponding to the phase difference between the voltage and the current of the output circuit, converts the voltage into an analog-digital (A / D) signal, and converts it into a micro computer. The VCO oscillation frequency is always adjusted to the best state by reading and by controlling the pulse width input by the microcomputer to the VCO to minimize the phase difference between the voltage and current of the output circuit. is there.

At first glance, it seems that this method cannot feed back the vibration state of the mechanical system.
Is sufficiently smaller than Q of the mechanical system, and therefore the phase difference between the voltage and current fed back is considered to be purely mechanical.

FIG. 1 is a schematic view showing the principle configuration of an ultrasonic wave generator of the present invention. Reference numeral 1 is a voltage controlled oscillator (V
CO), reference numeral 2 is a drive circuit for amplifying the output of the VCO 1,
Reference numeral 3 is an ultrasonic transducer, reference numeral 4 is an output resonance circuit for supplying the output of the drive circuit 2 to the ultrasonic transducer 3, reference numeral 5 is a current detection unit for detecting an output current in the output resonance circuit 4, and reference numeral 6 Is a phase comparator that compares the phase of the current and voltage of the ultrasonic output, reference numeral 7 is a control circuit that generates a PWM signal with a pulse width that changes according to the phase difference, and reference numeral 8 is a control for the VCO 1 by integrating the PWM signal. It is an integrator circuit that generates a signal.

In the control circuit 7, reference numeral 11 is an analog-digital (A / D) converter for converting an analog signal into a digital signal, reference numeral 12 is a microcomputer (MPU),
Reference numeral 13 is an input / output circuit (I / O) that generates a PWM signal according to a signal from the microcomputer 12. In the drive circuit 2, reference numeral 14 is an inverter, reference numerals 15 and 16 are field effect transistors (FETs), reference numeral 17 is a coupling capacitor,
Reference numeral 18 is an output transformer. In the output resonance circuit 4, reference numeral 19 is a resonance coil and reference numeral 20 is a resonance capacitor. In the current detector 5, reference numeral 21 is a current detecting transformer.

The VCO 1 oscillates at an ultrasonic frequency determined in accordance with the control signal v _c , and its output and the output obtained by inverting it through the inverter 14 result in FETs 15 and 16 being provided.
Is operated by push-pull. The ultrasonic output extracted from the connection point of both FETs 15 and 16 is the coupling capacitor 1
7 to be supplied to the output transformer 18, and the secondary side output thereof is supplied to the ultrasonic transducer 3 via the output resonance circuit 4 including the resonance coil 19 and the resonance capacitor 20 to vibrate it.

The current detecting transformer 21 detects the output current of the output resonance circuit 4, and the detected current signal is applied to one input of the phase comparator 6. The voltage signal of the output of the VCO 1 is applied to the other input of the phase comparator 6, and the phase comparator 6 generates an analog output according to the phase difference between these two inputs. The A / D converter 11 converts this analog signal into a digital signal.

The microcomputer 12 operates as a pulse width modulator, generates a signal having a pulse width that changes according to an input digital signal, and the input / output circuit 13 responds to this signal by PW.
Output M signal. The PWM signal is smoothed through the integrating circuit 8 to generate the control signal v _c .
The VCO 1 has its oscillation frequency controlled according to the control signal v _c .

In the ultrasonic wave generator shown in FIG. 1, the ultrasonic wave frequency generated by the VCO 1 is controlled so that the phase difference between the voltage and the current of the ultrasonic wave output to the ultrasonic vibrator 3 is always minimized. The oscillation frequency is controlled so that the drive frequency always matches the vibration frequency of the ultrasonic transducer. Therefore, the output circuit can always be operated in the state of maximum efficiency to supply the maximum output to the ultrasonic transducer, and the oscillation can be stably operated without stopping even in a heavy load state. Moreover, since the output circuit is efficient, no excessive heat dissipation measures are required.

[0020]

2 shows an embodiment of the present invention, in which the same components as those in FIG. 1 are designated by the same reference numerals, and reference numeral 25 is a driver for supplying the output of the VCO 1 to the FET 15, Reference numerals 26 and 27 are comparators, and reference numeral 28 is an integrating circuit. The inverter 14 phase-inverts the excitation signal having the same amplitude as that of the driver 25 and supplies the excitation signal to the FET 16. The resonance coil 19 and the resonance capacitor 20 form an output resonance circuit 4, and perform an action of supplying the ultrasonic output from the output transformer 18 to the ultrasonic transducer 3 with impedance matching in a resonance state.

Further, FIG. 3 is a time chart showing signal waveforms of respective parts in the ultrasonic wave generator shown in FIG.
The drive frequency and the vibration frequency of the signal of each part are both 28k.
It is shown separately in case (a) of coincidence in Hz and case (b) in which the driving frequency (28 kHz) and the vibration frequency (27.9 kHz) are deviated. The operation of this embodiment will be described below with reference to FIGS.

The comparator 26 includes a FET of a driving circuit.
A voltage signal from the VCO 1 that excites 15 and 16 is input, and a current signal from the current detection transformer 21 that detects the resonance current of the output resonance circuit that drives the ultrasonic transducer 3 is input to the comparator 27. .. Both comparators 26 and 27 compare the input signal with a constant input (ground potential) and generate outputs respectively.

The phase comparator 6 compares the phases of both signals and generates an output indicated by, which is 0 or 5 when the drive frequency and the vibration frequency match.
V, which is indefinite. When the drive frequency and the vibration frequency are deviated, the pulse has an amplitude of 5V. This output is averaged through the integrating circuit 28 to generate the output shown in. When a deviation occurs between the drive frequency and the vibration frequency as shown by A, the average value increases as the tracking progresses, and becomes a constant value at the completion of tracking shown by B.

The A / D converter 11 converts the output of the integrating circuit 28 into a digital signal and inputs it to the microcomputer 12. The microcomputer 12 outputs a PWM signal having a pulse width that changes according to the magnitude of the phase difference. This signal is smoothed through the integrator circuit 8 to produce the VCO control input shown at, which causes VCO 1 to change its output frequency. That is, the oscillation frequency of the VCO 1 is constant at 28 kHz when the drive frequency and the vibration frequency match, but is 28 kHz when the drive frequency and the vibration frequency deviate.
Since it changes from kHz to 27.9 kHz and stabilizes, the drive frequency is always automatically tracked to the vibration frequency of the articulator.

[0025]

As described above, according to the present invention, in the ultrasonic generator of the ultrasonic welding machine or the like, the drive frequency is automatically tracked to the vibration frequency of the ultrasonic vibrator, so that the heavy load state However, the welding work can be stably performed without stopping the oscillation. Also, since the ultrasonic generator can always be operated in a state of maximum efficiency, the same work can be performed with a small-sized and small-output oscillator compared with the conventional product, and the loss of the output stage is small,
It is possible to reduce the size of the radiator.

[Brief description of drawings]

FIG. 1 is a diagram showing a principle configuration of the present invention.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a time chart showing signal waveforms of respective parts.

FIG. 4 is a diagram illustrating an amplitude response characteristic of an ultrasonic transducer.

[Explanation of symbols]

 1 Voltage Controlled Oscillator 2 Drive Circuit 3 Ultrasonic Transducer 4 Output Resonance Circuit 5 Current Detector 6 Phase Comparator 7 Control Circuit 8 Integration Circuit

Claims (1)

[Claims] 1. A voltage-controlled oscillator that oscillates at a frequency that changes according to a control signal, a drive circuit that amplifies the output of the voltage-controlled oscillator, and an output resonance circuit that supplies the output of the drive circuit to an ultrasonic transducer. A current detection unit that detects an output current in the output resonance circuit, a phase comparator that compares the phase of the current detection signal with an output voltage signal of the voltage controlled oscillator, and a phase comparator that detects the phase difference according to the detected phase difference. The ultrasonic transducer includes a control circuit that generates a PWM signal with a varying pulse width and an integration circuit that integrates the PWM signal to generate the control signal, and based on the control of the pulse width in the control circuit. An ultrasonic generator characterized in that the driving frequency and the vibration frequency are controlled so as to match with each other.