EP1095712A1 - Method for regulating the power for ultrasound converter and generator - Google Patents

Abstract

The voltage supply regulation method allows the voltage to rise over an initial interval to a threshold value for the ultrasound converter voltage (Upzt), with regulation of the amplitude and/or frequency of the voltage (Uo) of an ultrasound generator (2) when the threshold value is reached, for holding the ultrasound converter voltage at or below the threshold value over a second interval, using a digital and/or analogue voltage regulator (3,4). An Independent claim for an ultrasound generator for regulating the voltage of an ultrasound converter is also included.

Description

The invention relates to a method for regulating the voltage supply for a Ultrasonic converter and an ultrasonic generator with the features of the generic term of the independent claims.

Piezoelectric transducer systems are primarily used here because of the capacitive component of the converter in the work area one series and one Have parallel resonance frequency. The same conditions also apply to magnetostrictive transducers, in which only the capacitive component by a is replaced inductive and vice versa.

Narrow-band ultrasound converter, primarily when used in welding systems for Plastics and metals have to be operated exactly at their resonance frequency, to guarantee a constant vibration amplitude and on the other hand for a reliable operation with increasing load the voltage and Keep current values at the converter within limits.

Ultrasonic converters are used in a wide variety of applications. Areas of application are e.g. Welding, cutting, cleaning, screening, sonochemistry and many other applications. The load changes frequently during operation. Through the Coupling the converter to the load becomes the resonant frequency of the converter out of tune during operation and must be readjusted very quickly by means of a regulation become.

With ultrasonic welding e.g. the welding sonotrode with increasing force pressed on the object to be welded, which in turn on an anvil or bracket.

It is known to regulate the voltage supply for an ultrasound converter in such a way that the working frequency f of the ultrasonic generator is the parallel resonance frequency of the converter follows.

The values that limit the performance of the ultrasonic converter are Converter voltage and the converter temperature. Sufficient cooling is usually sufficient is present so that the problem of converter temperature is easier to solve.

In order to damage the ultrasonic converter due to overload (too high voltage / To avoid high temperature), the converter voltage, which strengthens the E-field defined, do not exceed a maximum permissible value.

In known methods, the ultrasonic generator (with increasing load) is operated at the parallel resonance frequency f _p . The generator works together with the converter as a constant current source in order to keep the mechanical vibration amplitude constant with a variable load. This circuit design means that the active power output is proportional to the load resistance when the converter is operated at its own resonances. The ultrasonic transducer is operated with a constant amplitude. As soon as the load on the ultrasound converter is so great that the maximum voltage U _{pzt of} the converter is reached, the load on the ultrasound converter may not be increased further in known control methods in order to avoid destruction of the ultrasound converter, in particular of the piezoelectric disks (PZT).

It is known to frequency with analog phase locked loops based on the phased locked loop (PLL) circuit to regulate. The disadvantage of this circuit is that always a clean phase signal, i.e. there must be clear load conditions.

With different load conditions and especially with high powers, as well as already low non-linear behavior of the components, eg saturation of the compensation inductance L _k or detuned compensation, this cannot be guaranteed properly. The result is working with less than optimal response. This results in an excessive voltage and / or current at the piezoelectric transducer. For safety reasons, the values must be limited, which in practice always leads to operation with reduced power.

In this context, power means active power. Otherwise it is on Scheinoder Reactive power referenced.

Pure digital controllers have also been known since the industrial spread of microcontrollers Frequency controller according to EP 0 662 356, which consists of digitized converter current and voltage, or regulate their phase shift. The content of this application becomes explicit included in the present application. But these systems alone are too slow for regulation because of the averaging, sampling and digitization with rapidly changing loads with high quality of the vibration system (Q) e.g. in Welding and / or cutting applications with high required dynamics.

It is an object of the invention to avoid the disadvantages of the known, in particular thus to create a method for regulating the voltage supply of an ultrasound converter and an ultrasound converter which allow the operation of the ultrasound converter even after the maximum power of the converter has been reached with a further increasing load R _s allow.

The method according to the invention should also be sufficiently fast to achieve a Destruction of the ultrasound converter, to prevent in the event of rapid load changes. A Another object of the present invention is an ultrasonic generator to create that is suitable for performing the inventive method.

According to the invention, these tasks are performed using a method and an ultrasound generator with the features of the characterizing part of the independent claims solved.

In a method for regulating the voltage supply of an ultrasound converter when the load changes, the converter voltage increases in a first time period increasing load. The voltage supply is regulated in this first time period in a manner known per se. A similar procedure could also be used use sensibly with decreasing load. The periods would be reversed i.e. the second period of high load comes before the Period with low load. Rise and fall of the load can of course can also be repeated in the method and generator according to the invention.

According to the invention, after a predeterminable threshold value is reached Converter voltage in a second time period the amplitude of the output voltage of the ultrasonic generator and / or the frequency of the generator changed in such a way that the converter voltage becomes smaller as the load increases or preferably is or remains equal to the threshold.

The method according to the invention makes it possible to further increase the load (R _s ) on the ultrasound converter even when the maximum permissible converter voltage is reached. So that the load on the ultrasound converter can be increased further without the risk of destroying the ultrasound converter, either the mechanical amplitude is reduced by reducing the voltage U _o and / or the operating frequency of the ultrasound generator is shifted to a range in which the converter voltage is lower. than in the parallel resonance frequency (with the same load).

The converter voltage increases as follows: U p = 1 U O = χ 2 + R s Z. O

The normalization impedance Z ₀ : Z. O = L k C. O

The values for χ are 0 for the serial resonance frequency and 0 for the parallel one Resonance frequency equal to 1 (this provided that the compensation on the converter is matched).

The value of the compensation L _k is L k = 1 w 2 , C. O The formula for the converter voltage shows that the converter voltage in the case of the serial resonance frequency (χ = 0) is always lower than in the case of the parallel resonance frequency (χ = 1).

As soon as the maximum permissible converter voltage is reached, the load can continue to increase (R _s ) provided that either the voltage U _{0 is} reduced (the value U ₀ in the formula for the converter voltage is reduced, which reduces the active power) and / or if the value of χ in the above formula is reduced. The reduction in the value of χ corresponds to a shift in the operating frequency of the generator from the parallel resonance frequency in the direction of the serial resonance frequency.

In a preferred exemplary embodiment, the phase shift between the voltage U _o supplied by the ultrasound generator and the output current I _out serves as a controlled variable in the first time period. The setpoint of the phase shift is aimed at a minimum value of the phase shift, ideally 0 °. The greater the phase shift practically achieved, the more reactive power is required, which is undesirable. In practice, values between -15 ° and + 15 ° have proven their worth. In this case, the frequency of the ultrasonic generator is a manipulated variable. Controlling the phase shift to the value 0 ° means that the generator is operated at a frequency which corresponds to the parallel resonance frequency of the converter. An operation in the serial resonance frequency would be preferable in view of the converter voltage. However, this is because of the missing zero crossing of the phase between the voltage U ₀ and the current l _out in the case of serial resonance cannot be realized with previously known controllers.

In a further preferred embodiment, in the second period in the first Range the output power of the generator with increasing load on the ultrasonic converter kept constant. At the same time, the frequency of the ultrasonic generator from the parallel resonance frequency towards the serial resonance frequency changed.

In a further preferred exemplary embodiment, the second period, the converter voltage is kept constant and the frequency of the Ultrasonic generator, for example, with increasing load in the direction of the serial resonance frequency updated.

The phase shift control variable is advantageous in the first area. The setpoint the phase shift follows an adjustable setpoint curve. The setpoint curve is predetermined depending on the circuit, preferably by a microprocessor, Microcontroller or digital signal processor specified.

The second area of the second time period preferably begins when the Frequency of the ultrasound generator approximately the serial resonance frequency of the converter corresponds.

The value of the serial and parallel resonance frequency is preferably determined automatically before a load R _{s is} applied to the ultrasound converter or while the load R _{s is} still relatively low, ie when the resonance circuit has a high quality (Q).

During the frequency scan, it is advantageous to use a resistor in series between the ultrasound generator and the ultrasound converter. This prevents currents and voltages that are too high when the ultrasound converter lacks the load R _s . The resistance is bridged during normal operation of the generator.

The value of the frequency spacing and other parameters determined in this way can stored and used to mark the beginning of the second area in the to determine the second period. If the frequency of the generator is going out from the parallel resonance frequency by the previously determined frequency spacing has changed, the frequency of the generator corresponds approximately to the serial resonance frequency. Since the frequency spacing usually changes with increasing load, in general, however, the generator frequency is not exactly the serial resonance frequency correspond.

In an alternative exemplary embodiment, it is conceivable to keep the converter voltage constant at this value when the threshold value of the converter voltage is reached. For this purpose, the voltage U _{o of} the generator is reduced. At the same time, the phase difference is regulated to a minimum value as defined above, preferably towards zero, so that the frequency of the ultrasound generator roughly follows the parallel resonance frequency. This exemplary embodiment also allows extended operation with a further increasing load, even if the maximum permissible converter voltage has already been reached. In comparison to the first exemplary embodiment, the output power is limited more quickly.

The method according to the invention is advantageously carried out with a combination of a fast analog controller part with a slow digital actuator. The analog controller reacts immediately with every load change, the digital controller only intervenes if the phases, current and voltage values have exceeded a certain limit. If the converter voltage is too high, the microcontroller then shifts the operating frequency to a range in the vicinity of f _s . This allows the system to be typical at the same voltage 2 deliver greater performance. It is necessary to use an analog component in the control so that short reaction times can be achieved. The regulation of the phase shift requires an adjustment of the frequency of the generator serving as the manipulated variable in the range of milliseconds. On the other hand, it is not possible with a purely analog control loop to change the frequency of the generator from the parallel resonance frequency in the direction of the serial resonance frequency. For this reason, the control according to the present invention has an additional digital component. The digital component acts on the analog part of the control, in particular by specifying a changed setpoint for the phase shift.

The proportion of analog and digital control is variably adjustable. The frequency control can work purely analog, as well as purely digital, or depending on the desired proportions. This corresponds to the following formula: Analog share = x% Digital share = 100% - x% Frequency control = x% Analogous + (100% -x%) Digital

The generator assigns circuits for analog signal processing and circuits digital signal processing. The circuits for digital signal processing work advantageous to that of analog signal processing.

Figur 1

Ersatzschaltbild eines piezoelektrischen Ultraschallkonverters (1) mit einem Ultraschallgenerator (2),

Figur 2

Darstellung der Ausgangsleistung in Abhängigkeit der Lastimpedanz gemäss einem ersten Ausführungsbeispiel der Erfindung,

Figur 3

Darstellung der Ausgangsleistung in Abhängigkeit der Lastimpedanz gemäss einem zweiten Ausführungsbeispiel der Erfindung,

Figur 4

schematische Darstellung der Lastimpedanz bei geringer Belastung in Abhängigkeit der Frequenz,

Figur 5

schematische Darstellung einer Sollwertkurve für die Phasenverschiebung,

Figur 6

schematische Darstellung der Regelungsanordnung

Figur 7

schematische Darstellung eines Regelkreises und

Figur 8

Ersatzschaltbild eines alternativen Ausführungsbeispiels des erfindungsgemässen Generators und Konverters.

The terms used above, in particular resonance frequencies and the values shown in the formulas refer to an equivalent circuit diagram of the ultrasound converter. The equivalent circuit diagram is shown in the figures. The invention is explained in more detail below with reference to the drawings and in exemplary embodiments. Show it:

Figure 1

Equivalent circuit diagram of a piezoelectric ultrasound converter (1) with an ultrasound generator (2),

Figure 2

Representation of the output power as a function of the load impedance according to a first exemplary embodiment of the invention,

Figure 3

Representation of the output power as a function of the load impedance according to a second exemplary embodiment of the invention,

Figure 4

schematic representation of the load impedance at low loads depending on the frequency,

Figure 5

schematic representation of a setpoint curve for the phase shift,

Figure 6

schematic representation of the control arrangement

Figure 7

schematic representation of a control loop and

Figure 8

Equivalent circuit diagram of an alternative embodiment of the generator and converter according to the invention.

FIG. 1 shows the equivalent circuit diagram for an ultrasound generator 2 with an ultrasound converter 1.

The generator 2 is operated as a current source and supplies a voltage U ₀ with a frequency f, which leads to a converter _voltage U _pzt and an output current l _out .

L _k denotes an inductive compensation arrangement by means of which the output circuit of the ultrasound generator 2 is matched to the ultrasound converter 1.

l _out denotes the current supplied by the ultrasonic generator 2. U _pzt denotes the converter _voltage . The converter voltage is the voltage that is present at the PZT elements (disks) of the ultrasound converter 1. The load acting on the ultrasound converter 1 is denoted by R _s . The quantities L _s and C _s are the electrical equivalents of the mass and the elasticity of the mechanical vibrating structure.

In Figure 2, the output active power of the generator is shown as a function of Load impedance shown.

Curve 21 denotes the maximum output active power to be achieved when operating the generator in the parallel resonance frequency f _p . The power is limited by the maximum voltage U _{pzt max} that can be applied to the converter. Curve 22 denotes the maximum output power that can be reached when the ultrasound generator 2 is operated in the serial resonance frequency f _s .

The curve 23 shows the profile of the output power of the ultrasound generator 2 in a first embodiment.

In a first time period t ₁ , t ₂ , the voltage U ₀ and thus the mechanical amplitude are kept constant. As the load on converter 1 increases, the output power of generator 2 increases. With increasing load, the value of the parallel resonance frequency f _{p of} the ultrasound converter 1 can change at the same time. The frequency f of the ultrasound generator 2 tracks the changing parallel resonance frequency. The tracking is carried out by regulating the difference in the phase position of the voltage U ₀ and the output current I _out to a value close to 0 °. When the maximum output power of the generator is reached at time t ₂ , the first time period t ₁ , t _{2 is} completed, in which work is carried out with a constant mechanical amplitude.

In a further period t ₂ , t ₃ , the voltage U ₀ the mechanical amplitude is reduced. As a result, the converter _voltage U _{pzt is kept} at the maximum permissible value U _pzt max. The converter _voltage U _pzt is a controlled variable. The setpoint is U _{pzt max} . The manipulated variable is voltage U ₀ . The voltage U ₀ is reduced to a value which corresponds to approximately 50% of the mechanical amplitude in the first partial time period t ₁ , t ₂ .

With the control described in Figure 2, it is possible even after reaching the maximum Output power can be worked without increasing the load that there is a risk of destroying the ultrasound converter 1. The power output but decreases.

An alternative exemplary embodiment is shown in FIG. In contrast to the exemplary embodiment in FIG. 2, the second time period t ₂ , t _{3 is divided} into a first area t ₂ , t _x and a second area t _x , t ₃ . The regulation in the first and in the second area is different. Curve 24 shows the course of the output power in the alternative embodiment.

In the first range t ₂ , t _x , the output power P _{out of} the generator is kept constant at the maximum value of 100% power with increasing load (R _s ), but may also increase. The controlled variable is P _out while the voltage U _{0 is the} manipulated variable. At the same time, the frequency f of the voltage U _{0 is changed} from the value of the parallel resonance frequency f _p in the direction of the serial resonance frequency f _s . The change in frequency f is controlled by regulating the phase difference between voltage U ₀ and output current l _out on a corresponding setpoint curve (FIG. 5). Starting from the previously determined frequency spacing Δf between the parallel resonance frequency f _p and the serial resonance frequency f _s , the frequency is shifted from the parallel resonance frequency f _p by the frequency spacing Δf.

The embodiment shown in Figure 3 is compared to the embodiment advantageous in FIG. 2 in that the area shown hatched in FIG. 3 appropriate performance can also be brought into the system.

In the first period, the phase shift Δϕ is regulated to 0 °. The manipulated variable is the frequency f of the voltage U ₀

In the second period, the output power P _{out is} kept constant. The phase shift Δϕ no longer has a constant setpoint but follows a setpoint curve which is determined by the digital controller part (see FIG. 5). The setpoint for the permissible phase shift Δϕ is determined in the microprocessor on the basis of the values of U ₀ , l _out and U _pzt . The manipulated variables are the frequency f and the voltage value of U _0. A combination of a digital and analog control method is therefore shown schematically in FIG.

After reaching the maximum nominal power (100%) at time t ₂ in FIG. 2 or after reaching the serial resonance frequency at time t _x , the phase shift Δϕ is kept constant. In the exemplary embodiment in FIG. 2, the phase shift is kept constant at the value close to 0 °. In the exemplary embodiment according to FIG. 3, the phase shift is kept at a constant value in the second region t _x , t ₃ . It is thereby achieved that the frequency f of the voltage U ₀ roughly follows the serial resonance frequency which changes as the load increases.

At the same time, the converter _voltage U _{pzt is regulated} to a constant (to the maximum permissible) value in the time period t ₂ , t ₃ according to FIG. 2 or in the second range t _x , t ₃ according to FIG. 3. The manipulated variables are the frequency f and the voltage U _{0 of} the generator 2.

In the case of the exemplary embodiment according to FIG. 2, the digital controller is not absolutely necessary since the phase shift Δϕ is regulated to the value close to 0 °. In the exemplary embodiment according to FIG. 3, the phase shift _.DELTA..phi . _Is regulated to a predetermined value specified by the digital controller and dependent on U ₀ , l _out and U _pzt .

FIG. 4 shows schematically the dependence of the amount of the load impedance Z _L (with a low load) on the frequency f of the voltage U ₀ . If the frequency f corresponds to the parallel resonance frequency f _p , the load impedance Z _{L is} at a maximum. If the frequency corresponds to the serial resonance frequency f _s , the load impedance Z _{L is} minimal.

Before carrying out an operating cycle, for example a welding process, the curve shown in FIG. 4 is determined with a frequency scan. The parallel resonance frequency f _p and the frequency spacing Δf between the parallel resonance frequency f _p and the serial resonance frequency f _s can thus be determined. The measurement of the parallel resonance frequency f _p with small loads (idling) makes it possible to start at the beginning of the process with a frequency f of the generator 2 which is close to or corresponds to the parallel resonance frequency f _p . The frequency spacing Δf allows the generator to be guided from the parallel resonance frequency in the direction of the serial resonance frequency in the region t ₂ , t _x according to FIG. 3.

FIG. 5 shows a possible setpoint curve for the phase shift according to the exemplary embodiment from FIG. 3. In the time period t ₁ , t ₂ , the phase shift Δϕ is constantly regulated to 0 °. This ensures that the frequency f of the voltage U ₀ follows the parallel resonance frequency f _p . In the second time period t ₂ , t ₃ , a change in the phase shift Δϕ is permitted in a first range t ₂ , t _x . The change is specified by the digital controller 3. The phase difference Δϕ is changed so that at time t _x the frequency f of the voltage U _{0 has} changed by approximately the frequency constant Δf compared to the parallel resonance frequency f _p . At time t _x at the beginning of the second range t _x , t ₃ , the frequency f of the voltage U ₀ corresponds approximately to the serial resonance frequency f _s . During the second range tx, t ₃ , the phase shift is kept constant at this value.

FIG. 6 shows schematically the combination of an analog controller 4 with a digital controller 3 shown.

The time-dependent values of the voltage U ₀ , the output current I _out and the converter _voltage U _{pzt are} measured with a measuring arrangement 5. In order to ensure regulation with high dynamics, an analog regulator part 4 is used which regulates the generator 2 in frequency f. With a digital controller 3, the setpoint for the phase shift between the voltage U ₀ and the output current I _{out is} predetermined for the analog controller 4. The digital controller 3 is programmed (in the _exemplary embodiment according to FIG. 3) such that the converter _voltage U _{pzt is specified} as a phase shift close to 0 ° until a threshold value U _pzt max is reached. When the threshold value U _pztmax is reached, the digital controller 3 specifies a phase shift Δ which changes according to FIG. Of course, the increase in the phase shift can also be gradual, progressive, degressive (see dashed curves in FIG. 5). When the phase shift calculated based on the frequency spacing Δf between the parallel resonance frequency f _p and the serial resonance frequency f _s in the state without load is reached, the digital controller 3 again specifies a constant value for the phase shift Δϕ, which is not, however, equal to 0 °. In this time period, the digital controller also specifies a regulation of the output power P _out to the maximum value of 100% nominal power. Thanks to the combination of an analog and a digital control, it is possible to carry out a control process with sufficient dynamics, in which the frequency f of the voltage U _{0 of} the generator 2 can be moved from the parallel resonance frequency f _p in the direction of the serial resonance frequency f _s .

If the analog control loop does not detect a usable phase signal, the takes over digital controller 100% control of the frequency and is calculated from the measured Values the load impedance, which is needed to regulate the frequency.

The digital controller contains algorithms that work with multiple resonances in the work area automatically reduce the control range of both controllers and the optimal working frequency selects.

The digital controller communicates with a bus and / or user interface. All operating states can a superimposed control or computer for control and Logging will be passed.

FIG. 7 shows the schematic block or functional circuit diagram of a control circuit for the ultrasonic generator according to the invention. According to FIG. 7, the proportion is one analog and digital control variably adjustable.

The control circuit has a phase comparator 30 for determining the phase between the feedback variables voltage U ₀ and output current I _out . The phase shift Δϕ determined by the phase comparator 30 _is compared in a setpoint comparator 31 with a setpoint Δϕ setpoint. The setpoint Δϕset _is specified by a setpoint generator 40. A setpoint generator or actuator 33 can specify a variable setpoint. The setpoint value output by the actuator 33 can be determined by a digital signal processing arrangement 34. Various setpoints or setpoint curves are specified on the basis of the measured variables output current, voltage and converter voltage.

A controller 32 changes via a voltage controlled oscillator acting as an actuator 36 the frequency f of the generator 2.

In a first operating mode, a value of zero or close to zero can be specified by the actuator 40 as the setpoint for the phase shift Δϕ. In the first time period t ₁ , t ₂ (see FIGS. 2, 3), this operating mode is used. The control is preferably carried out only by the controller 32 in the manner described and thus 100% analog.

The control loop also has a threshold limiter 38 for a minimum frequency f _min and a maximum frequency f _{max of} the voltage controlled oscillator 36. The frequency range in which the frequency of the oscillator 36 can be adjusted can be determined using the threshold value limiter 38. As a result, the limits of the analog control can also be set by the oscillator 36.

The control circuit also has schematically illustrated means 35 for switching on and off of the analog controller 32.

If the phase signal is not usable (for example if the compensation L _{k is} detuned and the load resistance R _{s of} the resonance circuit is too great and the phase does not cross zero when the system becomes capacitive, for example), the analog controller 32 is switched off. The regulation then takes place exclusively digitally via the digital frequency controller 37. This can be done manually or depending on the operating parameters (especially l _out U _o and U _pzt ) by the switch-off means 35.

The control loop also has a digital frequency controller 37. On the basis of the time signals output current I _out , voltage U ₀ and converter voltage U _pzt , the frequency f of the generator 2 can be _regulated via a circuit 39 for changing (ie increasing or reducing) the frequency.

It is conceivable to carry out the control simultaneously in analog and digital form, with the Share of the analog controller 32 and the share of the digital controller 37 variably set can be.

The proportion is determined by setting the minimum and maximum threshold values f _min and f _max for the voltage controlled oscillator 36. The frequency of the generator 2 is determined both by the frequency controller 37 and the circuit 39 and by the controller 32 and the oscillator 36. In this context, it is conceivable to influence the threshold limiter 38 with a microprocessor which interacts with the digital frequency controller 37.

The working curves of the controllers 32 and 37 as well as the actuator 33 and the setpoint generator 40 can be empirically predetermined and z. B. save and from one Call and process the microprocessor. The goal is maximum output power driving at the various load conditions and destroying the converter to prevent.

The properties of the resonance system can be advantageous before starting operation by operating the arrangement in a partial load range.

FIG. 8 shows an equivalent circuit diagram of an exemplary embodiment in which the properties of the resonance system are determined by a frequency scan. In contrast to the equivalent circuit diagram according to FIG. 1, a resistor R _{m is} inserted in series between the generator 2 and the ultrasound converter 1 in FIG. The resistor R _m makes it possible to exclude the risk of overvoltage or overcurrent during the frequency scan to determine the frequency spacing Δf. The resistor R _{m is} bridged during normal operation. The values for Δf and f _p and f _s determined in this partial load operation can be measured in a known manner by measuring arrangements (not shown) and used for the readjustment of the controllers 37 and 32 as well as the threshold value transmitter 38 and the actuator 33.

This system could also work with ultrasonic generators using a different method operate as the one described above for performing a secure frequency scan be beneficial.

Claims (16)

A method for controlling the power supply for an ultrasonic converter (1) with variable load (R _s), wherein, in a first time period (t _1, t _2), the converter voltage (U _PZT), with increasing load (R _s) increases, characterized in that that above a predeterminable threshold value (U _{pzt max} ) of the converter _voltage (U _pzt ) in a second time period (t ₂ , t ₃ ) the voltage (U ₀ ) of the ultrasonic generator (2) is reduced and / or the frequency (f) of the Voltage (U ₀ ) of the ultrasound generator (2) is changed such that the load (R _s ) increases the converter _voltage (U _pzt ) remains less than or equal to the threshold value (U _{pzt max} ) of the converter _voltage (U _pzt ). A method according to claim 1, characterized in that in the first period (t ₁ , t ₂ ) the phase shift (Δϕ) between the voltage (U ₀ ) and the output current (l ₀ ) of the generator (2) is a controlled variable, the setpoint being the Phase shift (Δϕ) is 0 and the frequency (f) of the voltage (U ₀ ) is manipulated variable. Method according to one of claims 1 or 2, characterized in that in the second time period (t ₂ , t ₃ ) in a first area (t ₂ , t _x ) the output power (P _out ) of the ultrasonic generator (2) with increasing load (R _s ) is kept constant and that the frequency (f) of the voltage (U ₀ ) is changed from the parallel resonance frequency (f _p ) of the ultrasound converter (1) in the direction of the serial resonance frequency (f _s ) of the ultrasound converter (1). A method according to claim 3, characterized in that in a second area (t _x , t ₃ ) of the second period (t ₂ , t ₃ ) the converter _voltage (U _pzt ) is kept constant and the frequency (f) of the voltage (U _o ) is tracked with increasing load (R _s ) in the direction of the serial resonance frequency (f _s ) of the ultrasound converter (1). Method according to one of claims 3 or 4, characterized in that in the first area (t ₂ , t _x ) the phase shift (Δϕ) is a controlled variable, the setpoint of the phase shift (Δϕ) being a predetermined setpoint curve, preferably one from a digital controller ( 3, 33, 34) in the form of a microprocessor,
Microcontroller or digital signal processor follows predetermined setpoint curve. A method according to claim 4, characterized in that the second range (t _x , t ₃ ) starts when the frequency of the voltage (U ₀ ) corresponds approximately to the serial resonance frequency (f _s ). Method in particular according to one of claims 4 to 6, characterized in that to determine the resonant circuit parameters of an ultrasound generator (2) and an ultrasound converter (1) before the ultrasound converter (1) is subjected to a load (R _s ) or at low load (R _s ) by changing the frequency of the generator (2), a frequency scan is carried out to determine the serial and parallel resonance frequency (f _s , f _p ) and the frequency spacing (Δf) between the parallel resonance frequency (f _p ) and the serial resonance frequency (f _s ) to determine. A method according to claim 7, characterized in that a resistor (R _m ) is used in series between the ultrasound generator (2) and the ultrasound converter (1) in order to carry out the frequency _scan at the voltage U _pzt at the converter (1) and / or limit the power consumption of the converter (1) to predeterminable maximum values. Method according to one of claims 7 or 8, characterized in that the second range (t _x , t ₃ ) starts when the frequency (f) of the voltage (U ₀ ) has changed by the frequency spacing (Δf). A method according to claim 1, characterized in that after reaching the threshold value (U _{pzt max} ) of the converter _voltage (U _pzt ), the converter _voltage (U _pzt ) is kept constant at the threshold value (U _{pzt max} ), the value of the voltage (U ₀ ) is reduced and the phase shift (Δϕ) is minimized. Method in particular according to one of claims 1 to 9, characterized in that that the voltage supply is controlled analog and digital, the proportion of analog and digital control preferably is continuously adjustable. Ultrasonic generator (2), in particular for carrying out a method according to one of claims 1 to 11, with a regulation for the voltage supply of an ultrasound converter (1), characterized in that the ultrasound generator (2) Means for analog signal processing (4, 32, 36) and means for digital Signal processing (3, 33, 34). Ultrasonic generator according to claim 12, characterized in that the means (3) for digital signal processing in operative connection with the means (4) for analog signal processing are available. Ultrasonic generator (2) according to claim 12, characterized in that the ultrasonic generator (2) has a series switchable or switched resistor (R _m ) between the ultrasonic generator (2) and the ultrasonic converter (1). Method for regulating the voltage supply of an ultrasound converter (1), characterized in that the ultrasound generator (2) is operated such that the frequency (f) of the voltage (U ₀ ) at least at times the serial resonance frequency (f _s ) of the ultrasound converter (1) corresponds. Ultrasonic generator (2) with a controller for the voltage supply of an ultrasonic converter (1), characterized in that the controller is designed such that the voltage (U ₀ ) of the ultrasonic generator is above a predeterminable threshold value (U _{pzt max} ) of the converter voltage (U _pzt ) (2) is changed such that as the load (R _s ) increases, the converter _voltage (U _pzt ) remains less than or equal to the threshold value (U _{pzt max} ) of the converter _voltage (U _pzt ).

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