EP0254237A2 - Method for phase controlled power- and frequency adjustement of an ultrasonic transducer and apparatus for application of the method - Google Patents

Method for phase controlled power- and frequency adjustement of an ultrasonic transducer and apparatus for application of the method Download PDF

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Publication number
EP0254237A2
EP0254237A2 EP87110425A EP87110425A EP0254237A2 EP 0254237 A2 EP0254237 A2 EP 0254237A2 EP 87110425 A EP87110425 A EP 87110425A EP 87110425 A EP87110425 A EP 87110425A EP 0254237 A2 EP0254237 A2 EP 0254237A2
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EP
European Patent Office
Prior art keywords
frequency
phase
converter
transducer
locked loop
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EP87110425A
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German (de)
French (fr)
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EP0254237B1 (en
EP0254237A3 (en
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Herbert Gässler
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
    • B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
    • B06B1/0207—Driving circuits
    • B06B1/0223—Driving circuits for generating signals continuous in time
    • B06B1/0238—Driving circuits for generating signals continuous in time of a single frequency, e.g. a sine-wave
    • B06B1/0246—Driving circuits for generating signals continuous in time of a single frequency, e.g. a sine-wave with a feedback signal
    • B06B1/0253—Driving circuits for generating signals continuous in time of a single frequency, e.g. a sine-wave with a feedback signal taken directly from the generator circuit
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B2201/00—Indexing scheme associated with B06B1/0207 for details covered by B06B1/0207 but not provided for in any of its subgroups
    • B06B2201/50—Application to a particular transducer type
    • B06B2201/55—Piezoelectric transducer
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S323/00—Electricity: power supply or regulation systems
    • Y10S323/901—Starting circuits

Definitions

  • the invention relates to a method for phase-controlled power and frequency control of an ultrasound transducer, which is fed by the frequency-variable oscillator of a phase-locked loop with voltage pulses amplified by a driver stage, the frequency of the oscillator initially being varied by a wobbler to find the resonance of the ultrasound transducer and the wobbler after locking the phase-locked loop to the resonant frequency of the converter is locked.
  • the invention further relates to a device for performing this method.
  • the swinging of the Transducer with great damping for example if there is a residual drop of liquid on the converter or if non-atomized liquid flows along the converter even before it starts to vibrate. Then the available excitation energy is often not sufficient to allow the transducer to vibrate.
  • a general increase in the excitation power would have the disadvantage of uneconomical operation and would entail the risk of overloading the converter.
  • the vibration amplitude influenced by the transducer power also determines the droplet size, which is generally determined by the intended use, so that for this reason alone there are limits to the free variation of the excitation power.
  • care must also be taken to operate the ultrasonic transducer with a constant oscillation amplitude in order to obtain a uniform droplet spectrum during liquid atomization.
  • the invention has for its object to improve a method of the type mentioned so that a swinging of the transducer is guaranteed even with high initial damping and breaking of the vibration is reliably avoided even with strong changes in damping.
  • This object is achieved according to the invention in that after the ultrasonic transducer has started to vibrate A capacitive phase angle between the current and voltage in the converter is set and maintained in operation in the region of its series resonance frequency, so that the operating frequency of the oscillator is reduced compared to the series resonance frequency of the converter by the phase control of the phase-locked loop, with a change in the phase angle due to a mechanical load on the converter an increase in the operating frequency of the oscillator and thus leads to a shift towards the series resonance frequency of the converter.
  • the progress achieved by the invention essentially consists in the fact that, in contrast to the previously known method, the ultrasound transducer is not operated in resonance, but in a quasi-forced oscillation just below its resonance frequency. Although this requires, due to the significantly higher transducer impedance outside the resonance frequency, a higher transducer voltage than would be necessary when operating in resonance, however, the excitation power in the transducer can be significantly increased due to the strong change in impedance in the region of the resonance frequency, even through lower frequency changes.
  • the method is ideally suited to automatically supply the converter with the power required for optimal atomization for all operating cases. In particular, this also prevents the vibration from breaking off when the liquid throughput is too great.
  • the converter output also adjusts itself accordingly to different liquid densities and viscosities of the liquids to be atomized.
  • the capacitive phase angle between current and voltage in the converter is preferably in the range between -30 ° and -85 °.
  • phase steepness in the frequency range below the series resonance frequency is set by an additional impedance in the converter circuit so that the converter power, which rises over the falling converter impedance when the operating frequency is shifted toward the series resonance frequency, essentially compensates the damping of the converter .
  • the converter is supplied with the power required for this in each of its operating states.
  • the transducer Since the excitation of the transducer takes place in pulse form due to the desired high efficiency, but the transducer would then continue to oscillate at its natural frequency, which is different from that, it is recommended that the transducer be supplied with two voltage pulses of opposite polarity per oscillation period, each time by half the period of oscillation are offset. This prevents the phase-locked loop, particularly when there is a large deviation between the natural resonance of the transducer and the excitation frequency, from disengaging.
  • the duration of the voltage pulses be less than a quarter of the period of the transducer vibration.
  • the duration of the two voltage pulses per oscillation period are compared by integration and the duration of at least one of the two voltage pulses is regulated to ensure that the two voltage pulses are identical.
  • the wobbler provided for locating the resonance frequency starts up at a frequency below the resonance frequency of the converter.
  • the wobble process should be about 5. 103 periods of the resonance frequency oscillation extend. It is also recommended that the wobble range is limited to a frequency range that has no further secondary resonances of the transducer, so that it is ensured that the phase-locked loop can only lock onto the series resonance frequency of the transducer.
  • the invention further relates to a device for carrying out the method, in particular for operating a piezoelectric ultrasound transducer, with an oscillator controlled by a phase-locked loop for generation, a driver stage for amplification and a transformer for transmitting the excitation pulses for the transducer, this influencing the phase-locked loop required synchronization signal is tapped on a winding of the transformer, as well as with a wobbler, which initially varies the oscillator frequency in order to find the resonance frequency of the converter and is locked to the resonance frequency after the phase-locked loop has engaged.
  • the object on which the invention is based is achieved in that the phase detector of the phase-locked loop is preceded by an adjustable phase-shifting element, the phase-rotation angle of which is set such that when the phase rule is engaged a capacitive phase angle between current and voltage is maintained in the converter.
  • an additional impedance is expediently provided in the converter circuit, which reduces the frequency-dependent phase steepness below the series resonant frequency of the converter.
  • this additional impedance is formed by a capacitor connected in parallel with the converter.
  • the capacitor forming the additional impedance and the other capacitances, which are not caused by the transducer each amount to approximately one third of the low capacitance measured by the transducer.
  • the inductance of the secondary winding of the transformer is then dimensioned according to the Thompson formula, taking into account all capacitances of the converter circuit and a frequency which is about a factor of 1.3 higher than the converter series resonant frequency.
  • the driver stage is expediently designed as a push-pull driver, so that two voltage pulses of opposite polyarity are fed to the converter during each oscillation period.
  • the driver stage Expediently upstream of a symmetry stage which integrates the two voltage pulses of the push-pull driver and compares them with one another by means of a comparator which, in the case of asymmetry, adjusts the operating point of one of the push-pull drivers.
  • the operating voltage of the driver stage can be variably adjustable by the wobbler and / or the latching signal of the phase locked loop.
  • the operating voltage is regulated by a clocked power supply, the clock frequency of which corresponds to the oscillator frequency of the phase locked loop. In this way, disturbances in the phase-locked loop otherwise caused by clocked power supplies can be largely avoided.
  • the circuit arrangement shown in FIG. 1 serves in particular to operate a piezoelectric ultrasound transducer 1.
  • an oscillator controlled by a conventional phase-locked loop 2 and not shown in detail in the drawing is provided, the output frequency of which is from a driver stage 3, 4 is amplified, which feeds the converter 1 via a transformer 5.
  • the synchronization signal required to influence the phase locked loop 2 is tapped at a winding 6 of the transformer 5.
  • a wobbler 7 is provided, which initially varies the oscillator frequency in a forced manner to find the series resonance frequency of the converter 1 denoted by 1.1 in FIG. 2 and is locked to the resonance frequency after the phase-locked loop 2 has latched.
  • An adjustable phase shifter 8 which carries out a phase shift of the synchronization signal, is connected upstream of the phase detector of the phase locked loop 2.
  • the phase angle is set so that when the phase-locked loop 2 is engaged, a capacitive phase angle between current and span voltage in the converter.
  • the phase-locked loop 2 as can be seen from the mutually assigned phase and impedance curve in FIG. 2a, must reduce the excitation frequency, so that the converter is operated in a quasi-forced oscillation below its resonance frequency.
  • FIG. 2a even small changes in the phase position lead to a likewise relatively small change in frequency, which, however, then results in a relatively strong change in the converter impedance.
  • phase angle in the converter 1 undergoes a slight shift due to a stronger damping of the converter 1, as shown in FIG. 3a, this results in an increase in frequency, which results in a reduction in the converter impedance and thus an increase in the power supplied pulls itself.
  • I L the current through the secondary winding 5.1 of the transformer 5
  • I C the current through an additional impedance 9 to be described below
  • I W the converter current and with 11 the voltage at the converter 1.
  • an additional impedance 9 which is formed by a capacitor connected in parallel with the converter 1, is provided in the converter circuit and reduces the phase steepness of the converter 1.
  • Both the capacitor forming the additional impedance 9 and the other capacities, which are not caused by the converter 1, and also the cable capacitance, are dimensioned such that they each amount to approximately one third of the basic capacitance of the converter 1 measured at low frequency.
  • the inductance of the secondary winding 5.1 of the transformer 5 is then determined according to the Thompson formula, taking into account all capacitances of the converter circuit and on the basis of a frequency which is about a factor of 1.3 higher than the converter series resonant frequency.
  • 2c shows the phase and impedance curve assigned to one another when the electrical resonance frequency is shifted to lower frequencies as a result of an LC element connected in parallel with the converter, that is to say it lies below the mechanical resonance frequency which is unchanged in terms of position. In this case it must be ensured that the electrical resonance frequency is so far away from the mechanical resonance frequency that the capacitive branch in turn has the necessary steepness.
  • the driver stage 3, 4 is designed in particular as a push-pull driver, as a result of which the converter 1 receives an excitation pulse during each half-period. This ensures that the transducer 1, which oscillates freely outside the excitation pulses and is otherwise operated in a forced oscillation, cannot run from the excitation frequency to the extent that disengagement of the phase locked loop 2 would have to be feared.
  • the driver stage 3, 4 is preceded by a balancing stage 10, which integrates the two voltage pulses of the push-pull driver and compares them with one another by means of a comparator. In the event of an asymmetry of the two voltage pulses, the operating point of one of the two push-pull drivers is adjusted accordingly by the balancing stage.
  • the operating voltage of the voltage regulator 11 for the driver stage 3, 4 can be variably adjusted by the wobbler 7 or possibly also by the latching signal of the phase locked loop 2, as is indicated in the drawing by the line 12.
  • To start the voltage regulator 11 can therefore initially provide its maximum output voltage, which is reduced to the intended operating value after the start of the oscillation.
  • the converter 1 always starts to oscillate with maximum power, since the phase-locked loop 2 initially engages at the series resonance frequency of the converter 1, where it has its minimum impedance and therefore consumes the maximum possible power. The frequency is lowered and the excitation power is reduced as a result of the rise in impedance as a result of this after the oscillation has started.
  • the operating voltage can also be regulated by a clocked power supply, the clock frequency of which advantageously corresponds to the oscillator frequency of the phase-locked loop, so that faults in the control loop are avoided.
  • a separate voltage regulator 13 is provided for the phase locked loop itself.
  • an overload protection 14 is provided, with the aid of which the primary-side current through the transformer 5 is monitored and, if necessary, the modulation is limited.
  • the liquid supply to the converter 1 can be delayed via a liquid valve 16 actuated by a timing element 15.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Apparatuses For Generation Of Mechanical Vibrations (AREA)

Abstract

Das Verfahren dient zur phasengesteuerten Leistungsund Frequenzregelung eines Ultraschallwandlers (1), der von dem frequenzveränderlichen Oszillator eines Phasenregelkreises (2) mit durch eine Treiberstufe (3, 4) verstärkten Spannungspulsen gespeist wird. Dabei wird zunächst die Frequenz des Oszillators zum Auffinden der Resonanz (1.1) des Ultraschallwandlers (1) von einem Wobbler (7) zwangsgeführt variiert und der Wobbler (7) nach Einrasten des Phasenregelkreises (2) auf die Resonanzfrequenz (1.1) des Wandlers (1) gesperrt. Nach dem Anschwingen des Ultraschallwandlers im Bereich seiner Serienresonanzfrequenz wird ein kapazitiver Phasenwinkel zwischen Strom und Spannung im Wandler eingestellt und betriebsmäßig aufrecht erhalten, so daß durch die Phasenregelung des Phasenregelkreises (2) die Betriebsfrequenz des Oszillators gegenüber der Serienresonanzfrequenz (1.1) des Wandlers (1) verringert wird. Eine Änderung des Phasenwinkels infolge einer mechanischen Belastung des Wandlers führt dann zu einer Erhöhung der Betriebsfrequenz in Richtung zur Serienresonanzfrequenz des Wandlers.The method is used for phase-controlled power and frequency control of an ultrasonic transducer (1), which is fed by the frequency-variable oscillator of a phase-locked loop (2) with voltage pulses amplified by a driver stage (3, 4). First, the frequency of the oscillator to find the resonance (1.1) of the ultrasonic transducer (1) is varied in a forced manner by a wobbler (7) and the wobbler (7) after the phase-locked loop (2) has snapped onto the resonance frequency (1.1) of the transducer (1 ) blocked. After the ultrasonic transducer has started to vibrate in the range of its series resonance frequency, a capacitive phase angle between current and voltage in the transducer is set and maintained operationally, so that the operating frequency of the oscillator is compared to the series resonance frequency (1.1) of the transducer (1) by the phase control of the phase locked loop (2). is reduced. A change in the phase angle due to a mechanical load on the transducer then leads to an increase in the operating frequency in the direction of the series resonance frequency of the transducer.

Description

Die Erfindung betrifft ein Verfahren zur phasenge­steuerten Leistungs- und Frequenzregelung eines Ul­traschallwandlers, der von dem frequenzveränderli­chen Oszillator eines Phasenregelkreises mit durch eine Treiberstufe verstärkten Spannungspulsen ge­speist wird, wobei zunächst die Frequenz des Oszil­lators zum Auffinden der Resonanz des Ultraschall­wandlers von einem Wobbler zwangsgeführt variiert und der Wobbler nach Einrasten des Phasenregel­kreises auf die Resonanzfrequenz des Wandlers ge­sperrt wird. Weiter betrifft die Erfindung eine Vorrichtung zur Durchführung dieses Verfahrens.The invention relates to a method for phase-controlled power and frequency control of an ultrasound transducer, which is fed by the frequency-variable oscillator of a phase-locked loop with voltage pulses amplified by a driver stage, the frequency of the oscillator initially being varied by a wobbler to find the resonance of the ultrasound transducer and the wobbler after locking the phase-locked loop to the resonant frequency of the converter is locked. The invention further relates to a device for performing this method.

Aus der DE-PS 34 01 735 ist bereits eine Vorrich­tung bekannt, die eine Durchführung des oben genann­ten Verfahrens ermöglicht. Diese Vorrichtung hat sich in der Praxis bewährt, zumal sie zahlreiche der früher beim Betrieb von Ultraschallwandlern bestandenen Probleme und Schwierigkeiten beseitigt hat. Bekanntlich muß bei der Verwendung von Ultra­schallwandlern zur Flüssigkeitszerstäubung oder zu Schweißzwecken der die Anregungsfrequenz für den Wandler liefernde Oszillator sich auf zahlreiche sich ändernde Betriebseigenschaften des piezoelek­trischen oder magnetostriktiven Wandlers einstellen können. So können zunächst Änderungen der Resonanz­frequenz des Wandlers auftreten, die von der Last am Wandler, von der Temperatur, sowie dem Alterungs­grad der Piezokeramik bzw. des magnetostriktiven Materials abhängig sind. Ferner treten Impedanz­änderungen des Wandlers auf, die eine Abhängigkeit von der Frequenz, der Last, der Amplitude sowie der Temperatur zeigen. Diese Impedanzänderungen können darüber hinaus von den spezifischen Eigenschaften des Wandlerwerkstoffes, insbes. der physikalischen Eigenschaften der Piezoscheiben verursacht sein. Schließlich teten auch noch Änderungen des Phasen­winkels zwischen Strom und Spannung um Wandler auf, die ebenfalls von der Anregungsfrequenz, der Last, der Amplitude sowie der Temperatur abhängig sind. Diese genannten Erscheinungen treten in der prak­tischen Anwendung gemeinsam auf, so daß sich der Oszillator auf die sich daraus ergebenden Ände­rungen der Betriebsbedingungen einstellen können muß. Bei der Vorrichtung aus der DE-PS 34 01 735 gelingt dies insbes. durch die Verwendung eines Phasenregelkreises bereits weitgehend. Schwierigkei­ten bereitet jedoch nach wie vor das Anschwingen des Wandlers unter großer Bedämpfung, wenn sich also bei­spielsweise ein restlicher Flüssigkeitstropfen auf dem Wandler befindet oder bereits vor dem Anschwingen nicht zerstäubte Flüssigkeit an dem Wandler entlang strömt. Dann reicht nämlich häufig die zur Verfügung stehende Anregungsenergie nicht aus, um den Wandler anschwingen zu lassen. Eine generelle Erhöhung der An­regungsleistung hätte dagegen den Nachteil eines un­wirtschaftlichen Betriebs und würde die Gefahr einer Überlastung des Wandlers in sich bergen. Im übrigen bestimmt die von der Wandlerleistung beeinflußte Schwingungsamplitude auch die Tröpfchengröße, die sich in der Regel aus dem Anwendungszweck bestimmt, so daß schon aus diesem Grund der freien Variation der Anregungsleistung Grenzen gesetzt sind. Schließ­lich ist auch auf einen Betrieb des Ultraschallwand­lers mit konstanter Schwingungsamplitude zu achten, um bei der Flüssigkeitszerstäubung ein gleichmäßiges Tröpfchenspektrum zu erhalten.From DE-PS 34 01 735 a device is already known which enables the above-mentioned method to be carried out. This device has proven itself in practice, especially since it eliminates many of the problems and difficulties that previously existed in the operation of ultrasonic transducers Has. As is known, when using ultrasonic transducers for liquid atomization or for welding purposes, the oscillator providing the excitation frequency for the transducer must be able to adjust to numerous changing operating properties of the piezoelectric or magnetostrictive transducer. For example, changes in the resonant frequency of the transducer can occur, which are dependent on the load on the transducer, the temperature and the degree of aging of the piezoceramic or the magnetostrictive material. Furthermore, impedance changes of the converter occur, which show a dependence on the frequency, the load, the amplitude and the temperature. These changes in impedance can moreover be caused by the specific properties of the transducer material, in particular the physical properties of the piezo disks. Finally, changes in the phase angle between current and voltage around converters also occurred, which are also dependent on the excitation frequency, the load, the amplitude and the temperature. These phenomena mentioned occur together in practical use, so that the oscillator must be able to adjust to the resulting changes in the operating conditions. In the device from DE-PS 34 01 735, this is largely achieved by using a phase-locked loop. However, the swinging of the Transducer with great damping, for example if there is a residual drop of liquid on the converter or if non-atomized liquid flows along the converter even before it starts to vibrate. Then the available excitation energy is often not sufficient to allow the transducer to vibrate. A general increase in the excitation power, on the other hand, would have the disadvantage of uneconomical operation and would entail the risk of overloading the converter. In addition, the vibration amplitude influenced by the transducer power also determines the droplet size, which is generally determined by the intended use, so that for this reason alone there are limits to the free variation of the excitation power. Finally, care must also be taken to operate the ultrasonic transducer with a constant oscillation amplitude in order to obtain a uniform droplet spectrum during liquid atomization.

Der Erfindung liegt die Aufgabe zugrunde, ein Ver­fahren der eingangs genannten Art so zu verbessern, daß ein Anschwingen des Wandlers auch bei hoher An­fangsbedämpfung sicher gewährleistet ist und auch bei starken Bedämpfungsänderungen ein Abreißen der Schwingung sicher vermieden wird.The invention has for its object to improve a method of the type mentioned so that a swinging of the transducer is guaranteed even with high initial damping and breaking of the vibration is reliably avoided even with strong changes in damping.

Diese Aufgabe wird nach der Erfindung dadurch gelöst, daß nach dem Anschwingen des Ultraschallwandlers im Bereich seiner Serienresonanzfrequenz ein kapaziti­ver Phasenwinkel zwischen Strom und Spannung im Wandler eingestellt und betriebsmäßig aufrecht er­halten wird, so daß durch die Phasenregelung des Phasenregelkreises die Betriebsfrequenz des Oszilla­tors gegenüber der Serienresonanzfrequenz des Wand­lers verringert wird, wobei eine Änderung des Pha­senwinkels infolge einer mechanischen Belastung des Wandlers zu einer Erhöhung der Betriebsfrequenz des Oszillators und damit zu einer Verschiebung in Richtung zur Serienresonanzfrequenz des Wandlers führt.This object is achieved according to the invention in that after the ultrasonic transducer has started to vibrate A capacitive phase angle between the current and voltage in the converter is set and maintained in operation in the region of its series resonance frequency, so that the operating frequency of the oscillator is reduced compared to the series resonance frequency of the converter by the phase control of the phase-locked loop, with a change in the phase angle due to a mechanical load on the converter an increase in the operating frequency of the oscillator and thus leads to a shift towards the series resonance frequency of the converter.

Der durch die Erfindung erreichte Fortschritt be­steht im wesentlichen darin, daß der Ultraschall­wandler im Gegensatz zu dem bisher bekannten Ver­fahren nicht in Resonanz, sondern knapp unterhalb seiner Resonanzfrequenz in einer quasi-erzwungenen Schwingung betrieben wird. Dies bedingt zwar, wegen der deutlich höheren Wandlerimpedanz außerhalb der Resonanzfrequenz, eine höhere Wandlerspannung als sie bei Betrieb in Resonanz nötig wäre, dafür kann jedoch wegen der starken Impedanzänderung im Bereich der Resonanzfrequenz schon durch geringere Frequenz­änderungen die Anregungsleistung im Wandler wesent­lich erhöht werden. Da ferner in der Nähe der Resonanz­frequenz des Wandlers die Phasensteilheit der Phasen­winkeländerung zwischen Strom und Spannung im Wandler in Abhängigkeit von der Frequenz sehr groß ist, führen durch die Bedämpfung des Wandlers verursachte Pha­senwinkeländerungen zu einer Frequenzänderung in Richtung zur Resonanzfrequenz, die dann die be­schriebene Erhöhung der Wandlerleistung zur Folge hat. Auf diese Weise ist das Verfahren hervorragend geeignet, dem Wandler für alle Betriebsfälle auto­matisch die zum optimalen Zerstäuben notwendige Leistung zuzuführen. Dadurch wird insbes. auch ein Abreißen der Schwingung bei zu großem Flüssigkeits­durchsatz verhindert, darüber hinaus stellt sich die Wandlerleistung auch verschiedenen Flüssigkeitsdich­ten und Viskositäten der zu zerstäubenden Flüssig­keiten entsprechend ein.The progress achieved by the invention essentially consists in the fact that, in contrast to the previously known method, the ultrasound transducer is not operated in resonance, but in a quasi-forced oscillation just below its resonance frequency. Although this requires, due to the significantly higher transducer impedance outside the resonance frequency, a higher transducer voltage than would be necessary when operating in resonance, however, the excitation power in the transducer can be significantly increased due to the strong change in impedance in the region of the resonance frequency, even through lower frequency changes. Furthermore, since the phase steepness of the phase angle change between current and voltage in the converter as a function of the frequency is very large in the vicinity of the resonant frequency of the converter phase angle changes caused by the damping of the converter lead to a frequency change in the direction of the resonance frequency, which then results in the described increase in converter power. In this way, the method is ideally suited to automatically supply the converter with the power required for optimal atomization for all operating cases. In particular, this also prevents the vibration from breaking off when the liquid throughput is too great. In addition, the converter output also adjusts itself accordingly to different liquid densities and viscosities of the liquids to be atomized.

Der kapazitive Phasenwinkel zwischen Strom und Span­nung im Wandler liegt dabei vorzugsweise im Bereich zwischen -30° ind -85°.The capacitive phase angle between current and voltage in the converter is preferably in the range between -30 ° and -85 °.

Weiter empfiehlt es sich im Rahmen der Erfindung, daß die Phasensteilheit in dem unterhalb der Serienreso­nanzfrequenz liegenden Frequenzbereich durch eine Zu­satzimpedanz im Wandlerkreis so eingestellt ist, daß die über die sinkende Wandlerimpedanz bei Verschie­bung der Betriebsfrequenz hin zur Serienresonanzfre­quenz ansteigende Wandlerleistung die Bedämpfung des Wandlers im wesentlichen kompensiert. Dadurch wird dem Wandler in jedem seiner Betriebszustände gerade etwa die hierfür erforderliche Leistung zugeführt.It is also recommended within the scope of the invention that the phase steepness in the frequency range below the series resonance frequency is set by an additional impedance in the converter circuit so that the converter power, which rises over the falling converter impedance when the operating frequency is shifted toward the series resonance frequency, essentially compensates the damping of the converter . As a result, the converter is supplied with the power required for this in each of its operating states.

Da wegen des angestrebten hohen Wirkungsgrades die Anregung des Wandlers pulsförmig erfolgt, der Wandler jedoch anschließend mit seiner demgegenüber abweichenden Eigenfrequenz weiterschwingen würde, empfiehlt es sich, daß dem Wandler pro Schwingungs­periode zwei Spannungsimpulse jeweils entgegen ge­setzter Polarität zugeführt werden, die zeitlich um die halbe Schwingungsdauer gegeneinander versetzt sind. Dadurch wird verhindert, daß die Phasenregel­schleife insbes. bei größerer Abweichung zwischen Eigenresonanz des Wandlers und Anregungsfrequenz ausrastet.Since the excitation of the transducer takes place in pulse form due to the desired high efficiency, but the transducer would then continue to oscillate at its natural frequency, which is different from that, it is recommended that the transducer be supplied with two voltage pulses of opposite polarity per oscillation period, each time by half the period of oscillation are offset. This prevents the phase-locked loop, particularly when there is a large deviation between the natural resonance of the transducer and the excitation frequency, from disengaging.

Um die Eigenschwingung des Wandlers andererseits nicht zu stark zu stören, empfiehlt es sich, daß die Dauer der Spannungspulse kleiner ist als ein Viertel der Periodendauer der Wandlerschwingung. Um eine unsymmetrische Schwingungsform zu vermeiden, empfiehlt es sich weiter, daß die Dauer der beiden Spannungspulse pro Schwingungsperiode durch Inte­gration miteinander verglichen werden und die Dauer zumindest eines der beiden Spannungspulse auf Gleich­heit der Beiden Spannungspulse geregelt wird.On the other hand, in order not to disturb the natural vibration of the transducer too much, it is recommended that the duration of the voltage pulses be less than a quarter of the period of the transducer vibration. In order to avoid an asymmetrical form of oscillation, it is further recommended that the duration of the two voltage pulses per oscillation period are compared by integration and the duration of at least one of the two voltage pulses is regulated to ensure that the two voltage pulses are identical.

Um ein schnelles und sicheres Einrasten der Phasen­regelschleife zu erreichen, ist es weiter zweckmäßig, wenn der zum Auffinden der Resonanzfrequenz vorge­sehene Wobbler bei einer unterhalb der Resonanzfre­quenz des Wandlers liegenden Frequenz anläuft. Um dabei das sichere Einrasten des Phasenregelkreises zu erreichen, sollte sich der Wobbelvorgang etwa über 5 . 10³ Periodendauern der Resonanzfrequenz­schwingung erstrecken. Weiter empfiehlt es sich, daß der Wobbelbereich auf einen keine weiteren Ne­benresonanzen des Wandlers aufweisenden Frequenz­bereich beschränkt ist, so daß sichergestellt ist, daß der Phasenregelkreis allein auf die Serienreso­nanzfrequenz des Wandlers einrasten kann.In order to achieve a quick and secure locking of the phase-locked loop, it is further expedient if the wobbler provided for locating the resonance frequency starts up at a frequency below the resonance frequency of the converter. To ensure that the phase-locked loop snaps into place to achieve, the wobble process should be about 5. 10³ periods of the resonance frequency oscillation extend. It is also recommended that the wobble range is limited to a frequency range that has no further secondary resonances of the transducer, so that it is ensured that the phase-locked loop can only lock onto the series resonance frequency of the transducer.

Weiter betrifft die Erfindung eine Vorrichtung zur Durchführung des Verfahrens, insbes. zum Betrieb eines piezoelektrischen Ultraschallwandlers, mit einem von einem Phasenregelkreis gesteuerten Oszilla­tor zur Erzeugung, einer Treiberstufe zur Verstär­kung und einem Transformator zur Übertragung der An­regungspulse für den Wandler, wobei das zur Beein­flussung des Phasenregelkreises benötigte Synchroni­sationssignal an einer Wicklung des Transformators abgegriffen wird, sowie mit einem Wobbler, der zu­nächst zum Auffinden der Resonanzfrequenz des Wand­lers die Oszillatorfrequenz zwangsgeführt variiert und nach Einrasten des Phasenregelkreises auf die Resonanzfrequenz gesperrt wird.The invention further relates to a device for carrying out the method, in particular for operating a piezoelectric ultrasound transducer, with an oscillator controlled by a phase-locked loop for generation, a driver stage for amplification and a transformer for transmitting the excitation pulses for the transducer, this influencing the phase-locked loop required synchronization signal is tapped on a winding of the transformer, as well as with a wobbler, which initially varies the oscillator frequency in order to find the resonance frequency of the converter and is locked to the resonance frequency after the phase-locked loop has engaged.

Vorrichtungsmäßig wird die der Erfindung zugrunde liegende Aufgabe dadurch gelöst, daß dem Phasendetek­tor des Phasenregelkreises ein einstellbares Phasen­drehglied vorgeschaltet ist, dessen Phasendrehwinkel so eingestellt ist, daß bei eingerastetem Phasenregel­ kreis ein kapazitiver Phasenwinkel zwischen Strom und Spannung im Wandler aufrecht erhalten wird. Um bei einer Belastungserhöhung des Wandlers eine angepaßte Leistungserhöhung zu erreichen, ist im Wandlerkreis zweckmäßigerweise eine Zusatzimpedanz vorgesehen, die die frequenzabhängige Phasensteilheit unterhalb der Serienresonanzfrequenz des Wandlers verringert. Diese Zusatzimpedanz ist in bevorzugter Ausführungs­form von einem dem Wandler parallel geschalteten Kondensator gebildet. Eine besonders zweckmäßige Anpassung ergibt sich dabei dann, wenn der die Zu­satzimpedanz bildende Kondensator und die übrigen, nicht durch den Wandler bedingten Kapazitäten je­weils etwa ein Drittel der niederfrequent gemessenen Grundkapazität des Wandlers betragen. In weiter bevor­zugter Ausführungsform der Erfindung ist dann die Induktivität der Sekundärwicklung des Transforma­tors nach der Thompson-Formel unter Berücksichti­gung aller Kapazitäten des Wandlerkreises und einer um etwa einen Faktor von 1,3 höheren Frequenz als der Wandlerserienresonanzfrequenz bemessen.In terms of the device, the object on which the invention is based is achieved in that the phase detector of the phase-locked loop is preceded by an adjustable phase-shifting element, the phase-rotation angle of which is set such that when the phase rule is engaged a capacitive phase angle between current and voltage is maintained in the converter. In order to achieve an adapted increase in power when the converter is subjected to an increase in load, an additional impedance is expediently provided in the converter circuit, which reduces the frequency-dependent phase steepness below the series resonant frequency of the converter. In a preferred embodiment, this additional impedance is formed by a capacitor connected in parallel with the converter. A particularly expedient adaptation arises if the capacitor forming the additional impedance and the other capacitances, which are not caused by the transducer, each amount to approximately one third of the low capacitance measured by the transducer. In a further preferred embodiment of the invention, the inductance of the secondary winding of the transformer is then dimensioned according to the Thompson formula, taking into account all capacitances of the converter circuit and a frequency which is about a factor of 1.3 higher than the converter series resonant frequency.

Um trotz der erzwungenen Schwingung eine gleich­mäßige Anregung zu erreichen und ein Ausrasten des Phasenregelkreises zu verhindern, ist die Treiber­stufe zweckmäßigerweise als Gegentakttreiber aus­gebildet, so daß während jeder Schwingungsperiode dem Wandler jeweils zwei Spannungspulse entgegen gesetzter Polyarität zugeführt werden. Dabei ist der Treiberstufe zweckmäßigerweise eine Symmetriestufe vorgeschaltet, die die beiden Spannungspulse des Gegentakttreibers integriert und durch einen Komparator miteinander vergleicht, der bei Unsymmetrie den Arbeitspunkt eines der Gegentakttreiber verstellt.In order to achieve uniform excitation despite the forced oscillation and to prevent the phase-locked loop from disengaging, the driver stage is expediently designed as a push-pull driver, so that two voltage pulses of opposite polyarity are fed to the converter during each oscillation period. Here is the driver stage Expediently upstream of a symmetry stage which integrates the two voltage pulses of the push-pull driver and compares them with one another by means of a comparator which, in the case of asymmetry, adjusts the operating point of one of the push-pull drivers.

Um eine noch weiterreichende Anpassung der Anregungs­leistung zu erzielen, kann die Betriebsspannung der Treiberstufe durch den Wobbler und/oder das Rastsig­nal des Phasenregelkreises veränderlich einstellbar sein. Schließlich kann es sich auch zur Erzielung eines besonders günstigen Wirkungsgrades empfehlen, daß die Regelung der Betriebsspannung durch eine ge­taktete Stromversorgung erfolgt, wobei deren Takt­frequenz der Oszillatorfrequenz des Phasenregelkrei­ses entspricht. Dadurch können sonst von getakteten Stromversorgungen hervorgerufene Störungen im Phasen­regelkreis weitgehend vermieden werden.In order to achieve an even more extensive adaptation of the excitation power, the operating voltage of the driver stage can be variably adjustable by the wobbler and / or the latching signal of the phase locked loop. Finally, it can also be recommended to achieve a particularly favorable efficiency that the operating voltage is regulated by a clocked power supply, the clock frequency of which corresponds to the oscillator frequency of the phase locked loop. In this way, disturbances in the phase-locked loop otherwise caused by clocked power supplies can be largely avoided.

Im folgenden wird die Erfindung an einem in der Zeich­nung dargestellten Ausführungsbeispiel näher erläutert; es zeigen:

  • Fig. 1 eine Vorrichtung nach der Erfindung in einem schematischen Blockschaltbild,
  • Fig. 2 den Frequenzgang und die Phasenlage eines Ul­traschallwandlers im Resonanzbereich, wobei die Teilfigur 2b im wesentlichen der Teilfigur 2a entspricht und Fig. 2c die Dämpfung und Phasen­lage bei dem Wandler parallelgeschaltetem LC-Glied zeigt,
  • Fig. 3 in den Teilfiguren a) und b) ein Vektordia­gramm für einen Ultraschallwandler bei ge­ringer bzw. bei hoher Belastung für den in Teilfigur c) dargestellten Sekundärkreis.
The invention is explained in more detail below using an exemplary embodiment shown in the drawing; show it:
  • 1 shows a device according to the invention in a schematic block diagram,
  • 2 shows the frequency response and the phase position of an ultrasound transducer in the resonance range, the sub-figure 2b essentially corresponds to the sub-figure 2a and FIG. 2c shows the attenuation and phase position in the converter with an LC element connected in parallel,
  • Fig. 3 in the sub-figures a) and b) a vector diagram for an ultrasonic transducer at low or high load for the secondary circuit shown in sub-figure c).

Die in Fig. 1 der Zeichnung dargestellte Schaltungs­anordnung dient insbes. zum Betrieb eines piezoelek­trischen Ultraschallwandlers 1. Zur Erzeugung der Anregungsfrequenz ist ein von einem üblichen Phasen­regelkreis 2 gesteuerter, in der Zeichnung nicht im einzelnen dargestellter Oszillator vorgesehen, dessen Ausgangsfrequenz von einer Treiberstufe 3, 4 verstärkt wird, die über einen Transformator 5 den Wandler 1 speist. Das zur Beeinflussung des Phasenregelkreises 2 benötigte Synchronisationssignal wird an einer Wicklung 6 des Transformators 5 abgegriffen. Ferner ist ein Wobbler 7 vorgesehen, der zunächst zum Auf­finden der in Fig. 2 mit 1.1 bezeichneten Serien­resonanzfrequenz des Wandlers 1 die Oszillator­frequenz zwangsgeführt variiert und nach Einrasten des Phasenregelkreises 2 auf die Resonanzfrequenz ge­sperrt wird.The circuit arrangement shown in FIG. 1 serves in particular to operate a piezoelectric ultrasound transducer 1. To generate the excitation frequency, an oscillator controlled by a conventional phase-locked loop 2 and not shown in detail in the drawing is provided, the output frequency of which is from a driver stage 3, 4 is amplified, which feeds the converter 1 via a transformer 5. The synchronization signal required to influence the phase locked loop 2 is tapped at a winding 6 of the transformer 5. Furthermore, a wobbler 7 is provided, which initially varies the oscillator frequency in a forced manner to find the series resonance frequency of the converter 1 denoted by 1.1 in FIG. 2 and is locked to the resonance frequency after the phase-locked loop 2 has latched.

Dem Phasendetektor des Phasenregelkreises 2 ist ein einstellbares Phasendrehglied 8 vorgeschaltet, das eine Phasenverschiebung des Synchronisationssignals vornimmt. Dabei ist dessen Phasenwinkel so einge­stellt, daß bei eingerastetem Phasenregelkreis 2 ein kapazitiver Phasenwinkel zwischen Strom und Span­ nung im Wandler besteht. Um diese Phasenbedingung aufrecht erhalten zu können, muß der Phasenregel­kreis 2, wie sich aus dem einander zugeordneten Pha­sen- und Impedanzverlauf in Fig.2a ergibt, die Anre­gungsfrequenz verringern, so daß der Wandler in einer quasi erzwungenen Schwingung unterhalb seiner Reso­nanzfrequenz betrieben wird. Wie sich dabei der Fig. 2a weiter entnehmen läßt, führen bereits geringe Ver­änderungen der Phasenlage zu einer ebenfalls verhält­nismäßig geringen Frequenzänderung, die allerdings dann eine relativ starke Änderung der Wandlerimpe­danz zur Folge hat. Wenn daher durch eine stärkere Bedämpfung des Wandlers 1, wie dies in Fig. 3a ge­zeigt ist, der Phasenwinkel im Wandler 1 eine gering­fügige Verschiebung erfährt, so hat dies eine Fre­quenzerhöhung zur Folge, die eine Verringerung der Wandlerimpedanz und damit eine Erhöhung der zuge­führten Leistung nach sich zieht. Im übringen ist in Fig. 3 mit IL der Strom durch die Sekundärwicklung 5.1 des Transformators 5, mit IC der Strom durch eine im folgenden noch zu beschreibende Zusatzimpedanz 9, mit IW der Wandlerstrom und mit 11 die Spannung am Wandler 1 bezeichnet. Der Phasenwinkel φ gibt die Phasenbeziehung zwischen dem Gesamtstrom Iges und der Spannung 11 an, wobei die sich bei Belastung des Wandlers 1 einstellende Phasenwinkeländerung Δφ = φ₁ - φ₂ von dem Phasenregelkreis ausgewertet wird.An adjustable phase shifter 8, which carries out a phase shift of the synchronization signal, is connected upstream of the phase detector of the phase locked loop 2. The phase angle is set so that when the phase-locked loop 2 is engaged, a capacitive phase angle between current and span voltage in the converter. In order to be able to maintain this phase condition, the phase-locked loop 2, as can be seen from the mutually assigned phase and impedance curve in FIG. 2a, must reduce the excitation frequency, so that the converter is operated in a quasi-forced oscillation below its resonance frequency. As can further be seen from FIG. 2a, even small changes in the phase position lead to a likewise relatively small change in frequency, which, however, then results in a relatively strong change in the converter impedance. Therefore, if the phase angle in the converter 1 undergoes a slight shift due to a stronger damping of the converter 1, as shown in FIG. 3a, this results in an increase in frequency, which results in a reduction in the converter impedance and thus an increase in the power supplied pulls itself. In Fig. 3 with I L the current through the secondary winding 5.1 of the transformer 5, with I C the current through an additional impedance 9 to be described below, with I W the converter current and with 11 the voltage at the converter 1. The phase angle φ indicates the phase relationship between the total current I tot and the voltage 11, the phase angle change Δφ = φ₁ - φ₂ occurring when the converter 1 is loaded being evaluated by the phase locked loop.

Um bei einer Erhöhung der Wandlerbelastung die richti­ge Nachregelung der Leistung zu erreichen, ist es er­forderlich, die Phasensteilheit im Bereich unterhalb der Serienresonanzfrequenz des Wandlers entsprechend einzustellen. Hierzu ist im Wandlerkreis eine von einem dem Wandler 1 parallel geschalteten Kondensa­tor gebildete Zusatzimpedanz 9 vorgesehen, die die Phasensteilheit des Wandlers 1 verringert. Sowohl der die Zusatzimpedanz 9 bildende Kondensator als auch die übrigen, nicht durch den Wandler 1 bedingten Kapazitäten wie etwa auch die Kabelkapazität sind da­bei so bemessen, daß sie jeweils etwa ein Drittel der niederfrequent gemessenen Grundkapazität des Wandlers 1 betragen. Die Induktivität der Sekundärwicklung 5.1 des Transformators 5 bestimmt sich dann nach der Thompson-Formel unter Berücksichtigung aller Kapazi­täten des Wandlerkreises und unter Zugrundelegung einer um etwa einen Faktor von 1,3 höheren Frequenz als der Wandlerserienresonanzfrequenz.In order to achieve the correct readjustment of the power when the transducer load is increased, it is necessary to adjust the phase steepness in the range below the series resonance frequency of the transducer accordingly. For this purpose, an additional impedance 9, which is formed by a capacitor connected in parallel with the converter 1, is provided in the converter circuit and reduces the phase steepness of the converter 1. Both the capacitor forming the additional impedance 9 and the other capacities, which are not caused by the converter 1, and also the cable capacitance, are dimensioned such that they each amount to approximately one third of the basic capacitance of the converter 1 measured at low frequency. The inductance of the secondary winding 5.1 of the transformer 5 is then determined according to the Thompson formula, taking into account all capacitances of the converter circuit and on the basis of a frequency which is about a factor of 1.3 higher than the converter series resonant frequency.

In Fig. 2c ist der einander zugeordnete Phasen- und Impedanzverlauf gezeigt, wenn die elektrische Resonanz­frequenz infolge eines zum Wandler parallel geschalte­ten LC-Gliedes zu tieferen Frequenzen hin verschoben ist, also unterhalb der - lagemäßig unveränderten - mechanischen Resonanzfrequenz zu liegen kommt. In diesem Fall muß dafür gesorgt werden, daß die elek­trische von der mechanischen Resonanzfrequenz so weit entfernt liegt, daß der kapazitive Zweig wiederum die nötige Steilheit aufweist.2c shows the phase and impedance curve assigned to one another when the electrical resonance frequency is shifted to lower frequencies as a result of an LC element connected in parallel with the converter, that is to say it lies below the mechanical resonance frequency which is unchanged in terms of position. In this case it must be ensured that the electrical resonance frequency is so far away from the mechanical resonance frequency that the capacitive branch in turn has the necessary steepness.

Die Treiberstufe 3, 4 ist im einzelnen als Gegentakt­treiber ausgebildet, wodurch der Wandler 1 während jeder Halbperiode einen Anregungspuls erhält. Dadurch ist sichergestellt, daß der außerhalb der Anregungs­pulse frei schwingende, im übrigen in erzwungener Schwingung betriebene Wandler 1 nicht soweit aus der Anregungsfrequenz laufen kann, daß ein Ausrasten des Phasenregelkreises 2 zu befürchten wäre. Um eine mög­lichst unverzerrte Schwingungsform des Wandlers 1 zu erhalten, die auch im Hinblick auf ein gleichmäßiges Tröpfchenspektrum wünschenswert ist, ist der Trei­berstufe 3, 4 eine Symmetrierstufe 10 vorgeschaltet, die die beiden Spannungspulse des Gegentakttreibers integriert und durch einen Komparator miteinander vergleicht. Bei einer Unsymmetrie der beiden Span­nungspulse wird dann der Arbeitspunkt eines der bei­den Gegentakttreiber durch die Symmetrierstufe ent­sprechend verstellt.The driver stage 3, 4 is designed in particular as a push-pull driver, as a result of which the converter 1 receives an excitation pulse during each half-period. This ensures that the transducer 1, which oscillates freely outside the excitation pulses and is otherwise operated in a forced oscillation, cannot run from the excitation frequency to the extent that disengagement of the phase locked loop 2 would have to be feared. In order to obtain an undistorted form of oscillation of the transducer 1 which is also in view of a uniform one Droplet spectrum is desirable, the driver stage 3, 4 is preceded by a balancing stage 10, which integrates the two voltage pulses of the push-pull driver and compares them with one another by means of a comparator. In the event of an asymmetry of the two voltage pulses, the operating point of one of the two push-pull drivers is adjusted accordingly by the balancing stage.

Um eine weitere Leistungsregelung zu erreichen, ist die Betriebsspannung des Spannungsreglers 11 für die Treiberstufe 3, 4 durch den Wobbler 7 bzw. gegebenen­falls auch durch das Rastsignal des Phasenregelkrei­ses 2 veränderlich einstellbar, wie dies in der Zeich­nung durch die Leitung 12 angedeutet ist. Zum An­schwingen kann daher der Spannungsregler 11 zunächst seine maximale Ausgangsspannung zur Verfügung stellen, die nach erfolgtem Anschwingen auf den vorgesehenen Betriebswert reduziert wird. Aber auch ohne diese zusätzliche Spannungsregelung erfolgt das Anschwingen des Wandlers 1 stets mit maximaler Leistung, da der Phasenregelkreis 2 zunächst auf der Serienresonanz­frequenz des Wandlers 1 einrastet, wo dieser seine minimale Impedanz besitzt und daher die maximal mög­liche Leistung aufnimmt. Erst nach deem Anschwingen erfolgt dann über die Regelung der Phasenlage ein Absenken der Frequenz und infolge des dadurch beding­ten Impedanzanstiegs eine Verringerung der Anregungs­leistung.In order to achieve a further power control, the operating voltage of the voltage regulator 11 for the driver stage 3, 4 can be variably adjusted by the wobbler 7 or possibly also by the latching signal of the phase locked loop 2, as is indicated in the drawing by the line 12. To start the voltage regulator 11 can therefore initially provide its maximum output voltage, which is reduced to the intended operating value after the start of the oscillation. But even without this additional voltage control, the converter 1 always starts to oscillate with maximum power, since the phase-locked loop 2 initially engages at the series resonance frequency of the converter 1, where it has its minimum impedance and therefore consumes the maximum possible power. The frequency is lowered and the excitation power is reduced as a result of the rise in impedance as a result of this after the oscillation has started.

Die Regelung der Betriebsspannung kann im übrigen durch eine getaktete Stromversorgung erfolgen, wo­bei deren Taktfrequenz vorteilhafterweise der Oszil­latorfrequenz des Phasenregelkreises entspricht, so daß Störungen im Regelkreis vermieden werden. Für den Phasenregelkreis selbst ist dabei ein eigener Spannungsregler 13 vorgesehen.The operating voltage can also be regulated by a clocked power supply, the clock frequency of which advantageously corresponds to the oscillator frequency of the phase-locked loop, so that faults in the control loop are avoided. A separate voltage regulator 13 is provided for the phase locked loop itself.

Um eine Überlastung der Treiberstufe 3, 4 und/oder des Wandlers 1 zu vermeiden, ist ein Überlastschutz 14 vorgesehen, mit dessen Hilfe der primärseitige Strom durch den Transformator 5 überwacht und ge­gebenenfalls die Aussteuerung begrenzt wird.In order to avoid overloading the driver stage 3, 4 and / or the converter 1, an overload protection 14 is provided, with the aid of which the primary-side current through the transformer 5 is monitored and, if necessary, the modulation is limited.

Zur weiteren Verbesserung des Anschwingverhaltens kann die Flüssigkeitszufuhr zum Wandler 1 über ein durch ein Zeitglied 15 betätigtes Flüssigkeits­ventil 16 verzögert erfolgen.To further improve the start-up behavior, the liquid supply to the converter 1 can be delayed via a liquid valve 16 actuated by a timing element 15.

Claims (18)

1. Verfahren zur phasengesteuerten Leistungs- und Frequenzregelung eines Ultraschallwandlers, der von dem frequenzveränderlichen Oszillator eines Phasenregelkreises mit durch eine Treiberstufe verstärkten Spannungspulsen gespeist wird, wobei zunächst die Frequenz des Oszillators zum Auffin­den der Resonanz des Ultraschallwandlers von einem Wobbler zwangsgeführt variiert und der Wobbler nach Einrasten des Phasenregelkreises auf die Resonanzfrequenz des Wandlers gesperrt wird, dadurch gekennzeichnet, daß nach dem Anschwingen des Ultraschallwandlers (1) im Bereich seiner Serienresonanzfrequenz (1.1) ein kapazitiver Phasenwinkel zwischen Strom und Spannung im Wandler (1) eingestellt und betriebsmäßig auf­recht erhalten wird, so daß durch die Phasenrege­lung des Phasenregelkreises (2) die Betriebsfre­quenz des Oszillators gegenüber der Serienresonanz­frequenz (1.1) des Wandlers (1) verringert wird, wobei eine Änderung des Phasenwinkels infolge einer mechanischen Belastung des Wandlers (1) zu einer Erhöhung der Betriebsfrequenz des Oszil­lators und damit zu einer Verschiebung in Rich­tung zur Serienresonanzfrequenz (1.1) des Wand­lers führt.1. A method for phase-controlled power and frequency control of an ultrasound transducer, which is fed by the frequency-variable oscillator of a phase-locked loop with voltage pulses amplified by a driver stage, the frequency of the oscillator initially being varied by a wobbler to find the resonance of the ultrasound transducer and the wobbler after latching of the phase locked loop is locked to the resonant frequency of the transducer, characterized in that after the ultrasonic transducer (1) has started to vibrate, a capacitive phase angle between the current and voltage in the transducer (1) is set and maintained in operation in the region of its series resonant frequency (1.1), so that by the phase control of the phase locked loop (2), the operating frequency of the oscillator compared to the series resonance frequency (1.1) of the converter (1) is reduced, with a change in the phase angle due to a mechanical load on the converter (1) z u An increase in the operating frequency of the oscillator and thus a shift towards the series resonance frequency (1.1) of the converter. 2. Verfahren nach Anspruch 1, dadurch gekennzeich­net, daß der kapazitive Phasenwinkel zwischen Strom und Spannung im Wandler (1) im Bereich zwischen -30° und -85° liegt.2. The method according to claim 1, characterized in that the capacitive phase angle between current and voltage in the converter (1) is in the range between -30 ° and -85 °. 3. Verfahren nach Anspruch 1 oder 2, dadurch gekenn­zeichnet, daß die Phasensteilheit in dem unter­halb der Serienresonanzfrequenz (1.1) liegenden Frequenzbereich durch eine Zusatzimpedanz (9) im Wandlerkreis so eingestellt ist, daß die über die sinkende Wandlerimpedanz bei Verschiebung der Be­triebsfrequenz hin zur Serienresonanzfrequenz (1.1) ansteigende Wandlerleistung die Bedämpfung des Wandlers im wesentlichen kompensiert.3. The method according to claim 1 or 2, characterized in that the phase steepness in the frequency range below the series resonance frequency (1.1) is set by an additional impedance (9) in the converter circuit so that the falling converter impedance when the operating frequency is shifted towards the series resonance frequency (1.1) increasing converter power essentially compensates for the damping of the converter. 4. Verfahren nach den Ansprüchen 1 bis 3, dadurch gekennzeichnet, daß dem Wandler (1) pro Schwingungs­periode zwei Spannungspulse jeweils entgegengesetzter Polarität zugeführt werden, die zeitlich um die halbe Schwingungsdauer gegeneinander versetzt sind.4. The method according to claims 1 to 3, characterized in that the converter (1) per voltage period, two voltage pulses each of opposite polarity are supplied, which are offset in time by half the period of oscillation. 5. Verfahren nach den Ansprüchen 1 bis 5, dadurch ge­kennzeichnet, daß die Dauer der Spannungspulse kleiner ist als ein Viertel der Periodendauer der Wandlerschwingung.5. The method according to claims 1 to 5, characterized in that the duration of the voltage pulses is less than a quarter of the period of the transducer vibration. 6. Verfahren nach den Ansprüchen 4 und 5, dadurch ge­kennzeichnet, daß die Dauer der beiden Spannungs­impulse pro Schwingungsperiode durch Integration miteinander verglichen wird und die Dauer zumindest eines der beiden Spannungspulse auf Gleichheit der beiden Spannungspulse geregelt wird.6. The method according to claims 4 and 5, characterized in that the duration of the two voltage pulses per oscillation period is compared by integration with one another and the duration of at least one of the two voltage pulses is controlled for equality of the two voltage pulses. 7. Verfahren nach den Ansprüchen 1 bis 6, dadurch ge­ kennzeichnet, daß der zum Auffinden der Resonanz­frequenz (1.1) vorgesehene Wobbler (7) bei einer unterhalb der Resonanzfrequenz (1.1) des Wandlers (1) liegenden Frequenz anläuft.7. The method according to claims 1 to 6, characterized ge indicates that the wobbler (7) provided to find the resonance frequency (1.1) starts at a frequency below the resonance frequency (1.1) of the transducer (1). 8. Verfahren nach Anspruch 1 oder 8, dadurch gekenn­zeichnet, daß der Wobbelvorgang sich etwa über 5 . 10³ Periodendauern der Resonanzfrequenzschwingung er­streckt.8. The method according to claim 1 or 8, characterized in that the wobbling process is about 5. 10³ periods of the resonance frequency oscillation extends. 9. Verfahren nach den Ansprüchen 1 und 7 oder 8, da­durch gekennzeichnet, daß der Wobbelbereich auf einen keine weiteren Nebenresonanzen des Wandlers (1) aufweisenden Frequenzbereich beschränkt ist.9. The method according to claims 1 and 7 or 8, characterized in that the wobble range is limited to a frequency range having no further secondary resonances of the transducer (1). 10. Vorrichtung zur Durchführung des Verfahrens nach Anspruch 1, insbes. zum Betrieb eines piezoelektri­schen Ultraschallwandlers, mit einem von einem Phasenregelkreis (2) gesteuerten Oszillator zur Er­zeugung, einer Treiberstufe (3, 4) zur Verstärkung und einem Transformator (5) zur Übertragung der Anregungspulse für den Wandler (1), wobei das zur Beeinflussung des Phasenregelkreises (2) benötigte Synchronisationssignal an einer Wicklung (6) des Transformators (5) abgegriffen wird, sowie mit einem Wobbler (7), der zunächst zum Auffinden der Reso­nanzfrequenz (1.1) des Wandlers (1) die Oszilla­torfrequenz zwangsgeführt variiert und nach Ein­rasten des Phasenregelkreises (2) auf die Resonanz­ frequenz (1.1) gesperrt wird, dadurch gekenn­zeichnet, daß dem Phasendetektor des Phasenregel­kreises (2) ein einstellbares Phasendrehglied (8) vorgeschaltet ist, dessen Phasendrehwinkel so ein­gestellt ist, daß bei eingerastetem Phasenregel­kreis (2) ein kapazitiver Phasenwinkel zwischen Strom und Spannung im Wandler (1) aufrecht erhal­ten wird.10. The device for carrying out the method according to claim 1, in particular for operating a piezoelectric ultrasound transducer, with an oscillator controlled by a phase-locked loop (2) for generation, a driver stage (3, 4) for amplification and a transformer (5) for transmitting the Excitation pulses for the converter (1), the synchronization signal required to influence the phase-locked loop (2) being tapped at a winding (6) of the transformer (5), and with a wobbler (7) which is initially used to find the resonance frequency (1.1) of the converter (1) the oscillator frequency varies in a positively driven manner and after the phase-locked loop (2) has snapped onto the resonance frequency (1.1) is blocked, characterized in that the phase detector of the phase-locked loop (2) is preceded by an adjustable phase-shifting element (8), the phase rotation angle of which is set such that when the phase-locked loop (2) is engaged, a capacitive phase angle between current and voltage in the converter ( 1) is maintained. 11. Vorrichtung nach Anspruch 10, dadurch gekennzeich­net, daß im Wandlerkreis eine Zusatzimpedanz (9) vorgesehen ist, die die frequenzabhängige Phasen­steilheit unterhalb der Serienresonanzfrequenz (1.1) des Wandlers (1) verringert.11. The device according to claim 10, characterized in that an additional impedance (9) is provided in the converter circuit, which reduces the frequency-dependent phase steepness below the series resonance frequency (1.1) of the converter (1). 12. Vorrichtung nach Anspruch 11, dadurch gekennzeich­net, daß die Zusatzimpedanz (9) von einem dem Wand­ler (1) parallel geschalteten Kondensator gebildet ist.12. The apparatus according to claim 11, characterized in that the additional impedance (9) is formed by a capacitor connected in parallel with the converter (1). 13. Vorrichtung nach Anspruch 12, dadurch gekennzeich­net, daß der die Zusatzimpedanz (9) bildende Konden­sator und die übrigen, nicht durch den Wandler (1) bedingten Kapazitäten jeweils etwa ein Drittel der niederfrequent gemessenen Grundkapazität des Wand­lers (1) betragen.13. The apparatus according to claim 12, characterized in that the additional impedance (9) forming capacitor and the other, not caused by the converter (1) capacities are each about a third of the low-frequency measured basic capacitance of the converter (1). 14. Vorrichtung nach den Ansprüchen 10 bis 13, dadurch gekennzeichnet, daß die Induktivität der Sekundär­ wicklung (5.1) des Transformators (5) nach der Thompson-Formel unter Berücksichtigung aller Kapa­zitäten des Wandlerkreises und einer um etwa einen Faktor von 1,3 höheren Frequenz als der Wandler­serienresonanzfrequenz (1.1) bemessen ist.14. Device according to claims 10 to 13, characterized in that the inductance of the secondary winding (5.1) of the transformer (5) according to the Thompson formula, taking into account all capacitances of the converter circuit and a frequency which is about a factor of 1.3 higher than the converter series resonant frequency (1.1). 15. Vorrichtung nach den Ansprüchen 10 bis 14, da­durch gekennzeichnet, daß die Treiberstufe (3, 4) als Gegentakttreiber ausgebildet ist.15. Device according to claims 10 to 14, characterized in that the driver stage (3, 4) is designed as a push-pull driver. 16. Vorrichtung nach Anspruch 15, dadurch gekennzeich­net, daß der Treiberstufe (3, 4) eine Symmetrier­stufe (10) vorgeschaltet ist, die die beiden Spannungspulse des Gegentakttreibers integriert und durch einen Komparator miteinander vergleicht, der bei Unsymmetrie den Arbeitspunkt eines der Gegentakttreiber verstellt.16. The apparatus according to claim 15, characterized in that the driver stage (3, 4) is preceded by a balancing stage (10) which integrates the two voltage pulses of the push-pull driver and compares them with one another by a comparator which adjusts the operating point of one of the push-pull drivers in the case of asymmetry. 17. Vorrichtung nach den Ansprüchen 1 bis 16, dadurch gekennzeichnet, daß die Betriebsspannung der Trei­berstufe (3, 4) durch den Wobbler (7) und/oder das Rastsignal des Phasenregelkreises (2) veränderlich einstellbar ist.17. The device according to claims 1 to 16, characterized in that the operating voltage of the driver stage (3, 4) by the wobbler (7) and / or the latching signal of the phase locked loop (2) is variably adjustable. 18. Vorrichtung nach Anspruch 17, dadurch gekennzeichnet, daß die Regelung der Betriebssspannung der Treiber­stufe (3, 4) durch eine getaktete Stromversorgung erfolgt, wobei deren Taktfrequenz der Oszillator­frequenz des Phasenregelkreises (2) entspricht.18. The apparatus according to claim 17, characterized in that the regulation of the operating voltage of the driver stage (3, 4) is carried out by a clocked power supply, the clock frequency of which corresponds to the oscillator frequency of the phase locked loop (2).
EP87110425A 1986-07-25 1987-07-18 Method for phase controlled power- and frequency adjustement of an ultrasonic transducer and apparatus for application of the method Expired - Lifetime EP0254237B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE3625149 1986-07-25
DE19863625149 DE3625149A1 (en) 1986-07-25 1986-07-25 METHOD FOR PHASE-CONTROLLED POWER AND FREQUENCY CONTROL OF AN ULTRASONIC TRANSDUCER, AND DEVICE FOR IMPLEMENTING THE METHOD

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EP0254237A2 true EP0254237A2 (en) 1988-01-27
EP0254237A3 EP0254237A3 (en) 1989-07-05
EP0254237B1 EP0254237B1 (en) 1994-09-21

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Also Published As

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DE3625149A1 (en) 1988-02-04
DE3750560D1 (en) 1994-10-27
EP0254237B1 (en) 1994-09-21
US4849872A (en) 1989-07-18
EP0254237A3 (en) 1989-07-05

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