JPS6018227B2 - Ultrasonic generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic generator that operates at maximum efficiency by tracking the oscillation frequency of an oscillation device that drives an ultrasonic transducer to the resonance frequency of the ultrasonic transducer. It is something.

Generally, an ultrasonic transducer used in an ultrasonic application device has mechanical resonance characteristics, and is preferably driven at that resonance frequency in order to increase its electro-mechanical conversion efficiency.

However, its resonance characteristics have a high Q, and in particular, the more the vibration amplitude is expanded using a horn, the higher the Q and the sharper the resonance characteristics. The resonant frequency changes depending on temperature, drive level, load level, etc., or if a tool with a horn at the tip of a processing machine needs to be replaced. must be tracked. Conventionally, for this purpose, a vibration velocity signal is extracted from an ultrasonic transducer using a vibration detector such as a tortoise strain element attached to the vibration system, and this is fed back as an input signal to a drive amplifier to convert the ultrasonic wave. Vibration feedback oscillators that oscillate by tracking the resonance frequency of a device are widely used.

Since the ultrasonic transducer has many sub-resonant frequencies in addition to its basic resonant frequency, a bandpass filter is built into the feedback loop to prevent feedback oscillation at these unnecessary sub-resonant frequencies. , so that it is configured to oscillate only at the fundamental resonant frequency. However, with this method, when the resonance frequency of the ultrasonic transducer changes due to external conditions, the tracking characteristics deteriorate due to a phase shift in the feedback loop due to the bandpass filter. There is a drawback that lowering the Q of the pass filter causes abnormal oscillation at the sub-resonant frequency of the ultrasonic transducer. As another method, a phase comparator detects the amount of phase shift from a predetermined phase difference between the drive voltage or drive current of the ultrasonic transducer and the vibration velocity signal, and the output of the phase comparator is used to control the vibration velocity signal. There is a system in which a voltage controlled oscillator is provided and the output signal of the voltage controlled oscillator is input to a drive amplifier to track the resonant frequency of the ultrasonic transducer and change the oscillation frequency of the oscillator. In the case of this method, integrated circuit element ICs for phase-locked loop PLLs have recently become easily available, making it considerably simpler and easier to manufacture, but the overall configuration requires various accessory functional elements. necessary, complex and costly. Furthermore, when a switching amplifier is used as a driving amplifier for an ultrasonic transducer, the output voltage becomes a rectangular wave, and when driving a commonly used tortoise-distortion transducer, the harmonic components of the rectangular wave act as dampers of the transducer. Since a large amount of current flows through the capacitor, the output current does not become a sine wave, but becomes a rapid current like a motorcycle, which may destroy switching elements such as transistors when driven at high power. Therefore, in such a case, it is necessary to take measures such as inserting a harmonic attenuation filter on the output side of the drive amplifier or driving the drive amplifier with a sine wave. However, if a frequency-dependent resonant circuit consisting of a fixed coil or a capacitor is inserted on the output side of the drive amplifier, when the drive frequency changes to track the conversion resonance frequency, the output voltage and output current of the drive amplifier will be out of phase. This not only reduces the efficiency of the output drive element but also tends to cause destruction. Therefore, it is necessary to avoid using such filter elements as much as possible. Therefore, considering these points, it is naturally preferable to drive the drive amplifier with a sine wave.
Its input signal must also be driven with a sine wave, but
Generally, the output of a voltage controlled oscillator is a rectangular wave, and in practice, the output of the oscillator is waveform-shaped into a sine wave and then input to the drive amplifier. However, such a waveform shaping circuit generally integrates a rectangular wave to create a triangular wave, and then integrates it to create a sine wave, making the circuit complex.Furthermore, the integration circuit becomes more complex as the frequency increases due to frequency dependence. Since the output amplitude decreases, if the range in which the tracking frequency changes is wide, the output voltage will not be constant, causing a problem. The present invention has been made in view of these points, and an object of the present invention is to obtain an ultrasonic generator that can change the oscillation frequency by tracking the resonant frequency of an ultrasonic transducer by simplifying the overall configuration. That is.

The present invention provides a phase comparator that detects the amount of phase shift from a predetermined phase difference between the drive voltage or drive current of the ultrasonic transducer and the vibration velocity signal, and controls by the output of this phase comparator. A voltage-controlled bandpass filter is provided in the feedback loop from the vibration velocity signal to the input of the drive amplifier of the ultrasonic transducer.

Therefore, by feeding back the vibration velocity signal through a voltage-controlled bandpass filter to the input of the drive amplifier of the ultrasonic transducer, the resonant frequency of the ultrasonic transducer can be tracked and the oscillation frequency can be changed, and the oscillation frequency can also be controlled by voltage control. The range of change in the resonant frequency of the bandpass filter is predetermined to cover changes in the resonant frequency due to external conditions of the ultrasonic transducer, and its Q can also be set high to prevent abnormal oscillation at the sub-resonant frequency. The structure is such that it is sufficiently stable and can achieve performance with very little tracking error. Embodiments of the present invention will be described based on the drawings.

First, what is shown in Figure 1 is a block diagram showing the principle of driving a constant voltage drive converter, generally a magnetostrictive resonator. 1 is a voltage controlled band pass filter; The output of the filter 1 is amplified by a driving amplifier 2 and input to an ultrasonic transducer 3 driven by the driving amplifier 2. This ultrasonic transducer 3 generates mechanical vibration, and its vibration velocity signal 4 is used as an input signal to the voltage-controlled bandpass filter 1. Further, a phase comparator 6 is provided which receives the drive voltage or drive current 5 of the ultrasonic transducer 3 and the vibration velocity signal 4 as input, and the phase comparator 6 receives the drive voltage or drive current 5 of the ultrasonic transducer 3 and the vibration velocity signal 4 as input, and the phase comparator 6 receives the drive voltage or the drive current 5 of the ultrasonic transducer 3 and the vibration velocity signal 4 as inputs. The resonant frequency of the voltage-controlled bandpass filter 1 is controlled by the DC output voltage 7 from the phase comparator 6. Therefore, the driving voltage or driving current 5 of the ultrasonic transducer 3
In order to control the phase in the feedback loop by controlling the resonance frequency of the voltage-controlled bandpass filter 1 so that the phase difference between the signal and the vibration velocity signal 4 becomes a predetermined value, the ultrasonic transducer 3 It is driven by Here, the ultrasonic transducer 3 is not limited to a magnetostrictive vibrator, but can be similarly applied to an electrostrictive vibrator if the ultrasonic transducer 3 is driven using its parallel resonance frequency.

The vibration velocity signal 4 may be obtained using a conventionally known method, for example, by attaching a vibration detection element such as a dew strain element to a mechanical vibration system.
The current flowing through the ultrasonic transducer 3 may be extracted or detected using an electric circuit, and the phase comparator 6 may be used as appropriate for a quadrature type comparator, etc. that requires a phase difference of 900° between its two inputs. A phase shift circuit is inserted on one input side. Then, the output of the phase comparator 6 is passed through a DC amplifier and a low-pass filter as necessary, and then is used to control the voltage-controlled band-pass filter 1. Furthermore, a phase shift circuit is appropriately inserted into the feedback loop so that the loop phase becomes zero at the resonance frequency of the ultrasonic transducer 3. Also, Figure 2 is a block diagram showing the case of driving a constant current drive type converter, generally a tortoise strain oscillator.
In FIG. 1, a voltage-current conversion circuit 8, that is, an impedance inversion circuit that converts a constant-voltage drive power source into a constant-current drive power source, is inserted between the drive amplifier 2 and the ultrasonic converter 3. When the device 3 is driven at the series resonance frequency of the Kasumi strain oscillator, constant speed control is performed when the load fluctuates.

Here, the voltage-current conversion circuit 8 includes the drive amplifier 2, and may be controlled by other known means as long as it is a constant current drive power source, such as by controlling the amplification degree of the drive amplifier 2 so that the vibration speed is constant, or by using a switching amplifier. The same operation can be achieved by controlling the output pulse width using a switching amplifier or by controlling the power supply voltage using a switching amplifier.

Next, a specific example of driving a fleas strain vibrator will be described with reference to FIG.

First, a bridged T filter is used as the voltage controlled bandpass filter 1, and its resonance frequency is set by the resistor 9.1.
0, capacitors 11 and 12, and the internal resistance of field effect transistor 13, which operates as a variable resistor and is controlled by its gate bias voltage. That is, the resonant frequency of the voltage-controlled bandpass filter 1 is controlled by the gate bias voltage of the field effect transistor 13. Further, the output of the voltage-controlled bandpass filter 1 is input to a drive amplifier 2, amplified, and then input to a voltage-current conversion circuit 8. The output voltage of the drive amplifier 2 is then applied to the primary coil 1 of the output transformer 14.
5, the voltages generated in the secondary coil 16 whose center tap is grounded are extracted as voltages with different phases of 180 degrees, and are applied to the coil 17 and the capacitor 18.
After passing through the circuit, the output current is synthesized into a constant current output current. Here, the coil 17 and the capacitor 18 are tuned at the resonant frequency of the haze distortion oscillator 3a, and the coil 17
The constant current output current taken out from the connection point between the capacitor 18 and the capacitor 18 becomes a constant current proportional to the output voltage of the drive amplifier 2, which flows differentially between the two primary coils of the vibration speed detection transformer 19 and the electrostrictive vibrator 3a. The current flows into the electrostrictive elements 23 and 24 from the positive electrode plates 21 and 22, and the current flows into the negative terminal 2.
5 and returns to the center tap of the secondary coil 16 of the output transformer 14. In addition, the Kasumi strain vibrator 3a has a positive electrode plate 21 and a Kasumi strain element 23 and 24 sandwiched between an elastic vibrating body 26 in the shape of an exponential step and the other elastic vibrating body 27.
The insulator 28 is sandwiched between two insulators 22, and these are fastened, for example, with bolts at the center.

Here, since the dew strain elements 23 and 24 are arranged at positions where the axial resonance vibration stress of the electrostrictive vibrator 3a is different from each other, the force currents flowing through the dew strain elements 23 and 24 are different, and the respective electric currents are different. Since the currents flowing into the braking capacities of the strain elements 23 and 24 have the same value, the difference between the currents flowing into the respective box strain elements 23 and 24 is detected by the vibration speed detection transformer 19, and the secondary coil 29 is The resulting drive voltage becomes the vibration velocity signal 4. Further, a coil 30 is connected in parallel to the electrostrictive vibrator 3a to co-match the braking capacity of the electrostrictive vibrator 3a and cancel the braking current. The amplitude of the vibration velocity signal 4 is limited by a diode, and then converted into a rectangular wave by a comparator 31, and further phase-shifted by an integrator 32 by 900 degrees so that both inputs of a phase comparator 6 have a phase difference of 90 degrees. is used as one input of the phase comparator 6. Further, the driving voltage 5 is amplitude limited by a resistor and a diode, and then converted into a rectangular wave by a comparator 33, which is then inputted to the other input of a phase comparator 6. Furthermore, the vibration velocity signal 4 taken out as a rectangular wave by the comparator 31 is adjusted to a suitable zero level by a variable resistor 34, and is then input to the voltage-controlled band-pass filter 1. Then, an output proportional to the amount of phase shift from 900, which is a predetermined phase difference between the vibration velocity signal 4 and the drive voltage 5, is extracted by the phase comparator 6, and after being amplified to an appropriate level by the DC amplifier 35, The amplitude is limited by the amplitude limiter 36 so that the variation range of the resonant frequency of the voltage-controlled band-pass filter does not reach the sub-resonant frequency of the haze distortion oscillator 3a, and the field-effect transistor 3 controls the resonant frequency of the voltage-controlled band-pass filter. It has been entered.

In such a configuration, the vibrator drive current becomes a constant current according to the input voltage of the voltage-controlled bandpass filter, that is, the value set by the variable resistor 34 due to the action of the voltage-current converter 8, and thereby the tortoise distortion vibration The child 3a performs constant amplitude operation regardless of the magnitude of the load. Then, the output voltage of the phase comparator 16 controls the resonant frequency of the voltage-controlled bandpass filter 1 through a DC amplifier 35 and an amplitude limiter 36 so that the phase difference between the drive voltage 5 and the vibration velocity signal 4 becomes zero. The oscillation frequency generated by the feedback loop to the input of the drive amplifier 2, voltage-current converter 8, tortoise distortion oscillator 3a, vibration velocity signal 4, comparator 31, and voltage-controlled bandpass filter always becomes the resonant frequency of the tortoise distortion oscillator 3a. It works like that.

Here, if the amplification degree of the comparator 31 is set to be sufficiently large so that the saturated output level is achieved even with a small input signal level, the oscillation will not stop even when the box strain oscillator 3a is heavily loaded. Moreover, the rise of oscillation is good even under heavy loads, and sufficient functionality can be obtained for practical use.

As described above, in the ultrasonic generator of the present invention, the voltage-controlled bandpass filter 1 is inserted into the feedback loop as an oscillation frequency determining element, and the driving voltage or driving current 5 of the ultrasonic transducer 3 and the vibration velocity signal 4 are By controlling the resonant frequency of the voltage-controlled bandpass filter 1 so that the phase difference approaches the set value, the ultrasonic transducer can be driven stably with very little tracking error.

Furthermore, even if a signal such as a rectangular wave or a triangular wave is directly input as an input to a voltage-controlled bandpass filter, the output voltage will be a sine wave with little distortion because it has frequency selection characteristics, and the waveform shaping circuit will This becomes unnecessary and the overall configuration becomes simple. Incidentally, as the voltage-current conversion circuit 8, a more well-known impedance inversion circuit shown in FIG. 4 may be used. In this case, if the series resonance frequency of the coil 37 and the capacitor 38 is approximately tuned to the resonance frequency of the tortoise strain vibrator 3c, and the dew strain vibrator 3a is connected in parallel to the capacitor 38, the working current flowing through the electrostrictive vibrator 3a is constant. It becomes a current and performs a constant amplitude operation, and can be applied as the voltage-current conversion circuit 8 in FIG. 3. As described above, the present invention inserts a voltage-controlled bandpass filter into the feedback loop as an oscillation frequency determining element, so that the phase difference between the drive voltage or drive current of the ultrasonic transducer and the vibration velocity signal approaches a set value. By controlling the resonant frequency of the voltage-controlled bandpass filter in this way, the overall configuration can be simplified and the ultrasonic transducer can be driven stably with very little tracking error. Since a voltage-current converter is inserted between the ultrasonic transducer and the ultrasonic converter, it is possible to operate the ultrasonic transducer well even when the ultrasonic transducer is used as a lightning distortion vibrator.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention; FIGS. 1 and 2 are principle block diagrams, FIG. 3 is a specific circuit diagram,
FIG. 4 is a circuit diagram showing a partial modification thereof. 1... Voltage control band pass filter, 2... Drive amplifier, 3... Ultrasonic transducer, 3a...
... Electrostrictive vibrator (ultrasonic transducer), 4 ... Vibration speed detection signal, 5 ... Drive voltage (or drive current), 6 ... Phase comparator, 8・・・・・・Voltage-current conversion circuit. Hiroyuki's younger brother Izu Figure 3 Figure 4

Claims (1)

[Claims] 1. A phase comparator is provided to detect the amount of phase shift from a predetermined phase difference between the drive voltage or drive current of the ultrasonic transducer and the vibration velocity signal, and An ultrasonic generator characterized in that a voltage-controlled bandpass filter controlled by the output is provided in the feedback loop from the vibration velocity signal to the input of the drive amplifier of the ultrasonic transducer. 2. The ultrasonic generator according to claim 1, wherein the voltage-controlled bandpass filter is a bridged T filter. 3 A phase comparator is provided to detect the amount of phase shift from a predetermined phase difference between the drive voltage or drive current of the ultrasonic transducer and the vibration velocity signal, and the voltage controlled by the output of this phase comparator is provided. A control bandpass filter is provided in a feedback loop from the vibration velocity signal to the input of a drive amplifier of the ultrasonic transducer, and a voltage-current conversion circuit is inserted between the ultrasonic transducer and the drive amplifier. Ultrasonic generator. 4. The ultrasonic generator according to claim 3, wherein the voltage-controlled bandpass filter is a bridged T filter. 5. The ultrasonic generator according to claim 3 or 4, characterized in that the ultrasonic transducer is an electrostrictive vibrator.