Method for exciting piezoelectric transducers and sound generation arrangement

Abstract

Method for exciting one or more, preferably piezoelectric, transducers (7), which transducers (7) are designed to generate sound waves and have operating frequencies which define a converter frequency range, in which a generator (9) which has an electrical connection (8) to the converters (7) and a frequency sweep function for generating an electrical excitation signal with a variable excitation frequency (1) generates an electrical excitation signal for the converters (7), which excitation signal is supplied to the converters (7), wherein the generator (9) with an adjustable sweep rate performs a total number of frequency sweeps in a frequency sweep range between a minimum frequency (f min ) and a maximum frequency (f max ) carries out, within which frequency sweep range a target frequency (f Ziel ) is defined, characterized by the fact that the minimum frequency (f min ), the maximum frequency (f max ) and the target frequency (f Ziel ) are chosen such that a first frequency difference (Δf1) exists between the minimum frequency (f min ) and the target frequency (f Ziel ) during a first number of frequency sweeps from the total number of frequency sweeps, preferably during substantially all frequency sweeps, in magnitude from a second frequency difference (Δf2) between the maximum frequency (f max ) and the target frequency (f Ziel ) differs, and where the minimum frequency (f min ) and / or the maximum frequency (f max ) and / or the target frequency (f Ziel) is modified after at least one frequency sweep such that an arithmetic mean of the first frequency differences (Δf1) and an arithmetic mean of the second frequency differences (Δf2) formed over all frequency sweeps are essentially equal in magnitude.

Description

[0001] The invention relates to a method for exciting ultrasonic transducers according to the preamble of claim 1. Such a method comprises the excitation of at least one ultrasonic transducer, which is configured to generate sound waves and has operating frequencies that define a transducer frequency range. The method further utilizes a generator which has an electrical connection to the ultrasonic transducer. The generator is configured to generate an electrical drive signal with a variable excitation frequency.

[0002] It is known to use piezoelectric crystals as ultrasonic transducers, or transducers for short. The crystals can be set into vibration by an electrical signal and thereby emit sound waves in the ultrasonic range. These emitted sound waves can be used, for example, to remove contaminants from components. Preferably, the transducers are operated at a specific, design-related resonant frequency. Often, several piezoelectric transducers are used whose resonant frequencies differ to a greater or lesser extent. This is intended, on the one hand, to achieve a wider frequency bandwidth of the transducers in order to remove contaminants of varying sizes – the size of the detached contaminants is related to the resonant frequency of the transducers.On the other hand, the superposition of vibrations from transducers with different resonant frequencies makes the emitted sound wave field more homogeneous overall, which can have a positive effect on the quality of the cleaning.

[0003] It is already known to vary the excitation frequency for operating piezoelectric transducers not statically, but over time. This is called sweep modulation. Previously known applications use sweep modulation with a frequency response that repeats within a fixed, predefined range. Frequency responses are known in which the excitation frequency changes linearly with time. The excitation frequency signal can take the form of a sawtooth wave or a triangle wave.

[0004] EP 1 997 159 B1 discloses a megasound processing device and an associated operating method, which megasound processing device utilizes piezoelectric transducers operated at fundamental resonant frequencies of at least 300 kHz. In the described method, the excitation frequency for operating the piezoelectric transducers is varied within a range encompassing all fundamental resonant frequencies of the piezoelectric transducers used. This sweep modulation range extends above and below a frequency range ("transducer range") defined by the fundamental resonant frequencies of the piezoelectric transducers. Crucially, the transducer range is symmetrically exceeded and fallen below during the sweep modulation of the excitation frequency. This ensures that all fundamental resonant frequencies are excited by the drive signal.In particular, this is intended to take into account the fact that the resonant frequencies of the piezoelectric transducers can change due to temperature or age influences.

[0005] Similar devices and methods are also known from US 2005 / 0003737A1, US 2005 / 0098194A1, and US 7004016B1. These publications describe a sweep modulation that exceeds or falls below the converter frequency range. The exceeding and falling below the converter range is symmetrical in each case.

[0006] A problem with known sweep modulation methods is that sweep modulation exhibits a relatively large frequency deviation to achieve the symmetrical exceeding or falling below the transducer range. However, such a large frequency deviation is associated with increasing losses in the power section of the generator, which provides the necessary drive signals. This results in significant heat loss in the generator, which can limit the maximum achievable frequency deviation for sweep modulation. Furthermore, the mechanical stress on the sound transducers (ultrasonic converters, ultrasonic elements, transducers, or similar components) also increases with increasing frequency deviation. Additionally, narrowband or high-quality systems face the problem that the sweep modulation frequency deviation must not be too large, as this could otherwise excite undesired resonance frequencies or vibration modes.In the worst case scenario, this could damage or destroy the entire system.

[0007] The invention is based on the objective of providing an improved method for exciting ultrasound transducers, which effectively utilizes the advantages of sweep modulation while avoiding the problems described above.

[0008] This problem is solved by a method having the features of claim 1 and by a sound-generating arrangement having the features of claim 11. Advantageous further developments are described in the dependent claims.

[0009] The applicant has recognized that the inventive method for exciting the transducers is particularly advantageous if, during a number of frequency sweeps (sweep modulation), a first frequency difference between a minimum frequency at which the sweep begins and a target frequency differs in magnitude from a second frequency difference between a maximum frequency at which the sweep ends and the target frequency. The target frequency is generally defined as a frequency whose magnitude lies between the minimum and maximum frequencies.The minimum frequency and / or the maximum frequency and / or the target frequency is modified after at least one frequency pass such that an arithmetic mean of the first differences, which is calculated over all frequency passes performed, and an arithmetic mean of the second differences, which is also calculated over all frequency passes performed, are essentially equal in magnitude.

[0010] A frequency sweep of the excitation frequency is performed between the minimum and maximum frequencies, with the excitation frequency exhibiting essentially all values ​​between the minimum and maximum frequencies at least once during the sweep. It is therefore within the scope of the invention if the excitation frequency at the beginning of the sweep is equal in magnitude to the minimum frequency and at the end of the sweep is equal in magnitude to the maximum frequency. The reverse is also possible. It is also within the scope of the invention if the excitation frequency is equal in magnitude to the minimum and / or maximum frequency several times during a single sweep.

[0011] To generate sound waves according to the inventive method, a single transducer, preferably a piezoelectric transducer, can be used. Due to manufacturing processes, this transducer may exhibit irregularities in layer thickness, so that the respective resonant frequencies of transducers of the same type may differ slightly. Furthermore, different areas of a single transducer may be exposed to different temperature influences, which can cause its resonant frequency to split into slightly different partial resonant frequencies. Thus, a single transducer can also define a transducer frequency range or a transducer in the sense described above.

[0012] The frequency deviation of sweep modulation is defined as the difference between the maximum and minimum frequencies. The variation of the minimum, maximum, and / or target frequency during a certain number of frequency sweeps within a total number of sweeps, as described in the invention, offers the advantage that the frequency deviation is smaller in essentially all sweeps than described in the prior art. This minimizes temperature losses in the power-generating generator and simultaneously reduces the probability of converter failure.

[0013] Preferably, after at least one frequency sweep, the minimum frequency and / or the maximum frequency are changed. This allows the frequency sweep to be varied around the target frequency. Changing the minimum or maximum frequency is easy to implement from a control engineering perspective and does not require any additional circuitry.

[0014] According to a preferred embodiment of the method according to the invention, the minimum frequency, the maximum frequency, and the target frequency are selected such that, during a first frequency sweep, the first frequency difference has a first magnitude (A) and the second frequency difference has a second magnitude (B). During a subsequent frequency sweep, at least the target frequency, and preferably also the minimum frequency and the maximum frequency, are modified such that the first frequency difference has the second magnitude (B) and the second frequency difference has the first magnitude (A), wherein preferably the first magnitude and the second magnitude are different (A ≠ B). The applicant considers such an alternatingly symmetrical selection of the frequency differences around the target frequency to be particularly advantageous.The excitation frequency can be increased from the minimum frequency to the maximum frequency after each frequency sweep, resulting in a sawtooth-like time course of the excitation frequency. A sequence of frequency differences over several frequency sweeps could, for example, exhibit the magnitudes (AB-BA-AB-BA-AB-BA). The direction of change in the excitation frequency can also change after each frequency sweep; for example, after reaching the maximum frequency, the excitation frequency can be reduced again, resulting in a triangular time course of the excitation frequency. It is also within the scope of the invention to provide a combination of these two variants or even further variants. The essential point is that the frequency differences during the respective frequency sweeps can exhibit the aforementioned combinations of magnitudes.

[0015] It is particularly preferred that the target frequency be changed after at least one frequency sweep. This form of sweep modulation variation is especially advantageous when the desired target frequency is not precisely known but must be determined during the process or during the frequency sweeps. In this way, a desired operating point of the at least one ultrasonic transducer can be flexibly defined according to the specific requirements.

[0016] According to an alternative embodiment, during at least one frequency sweep, preferably all frequency sweeps, the excitation frequency of the drive signal is varied such that the drive signal has the minimum frequency at a first time (t1), the target frequency at a second time (t2) and the maximum frequency at a third time (t3), wherein the second time lies between the first and the third time, and wherein a first time difference between the first time and the second time and a second time difference between the second time and the third time are equal in magnitude.

[0017] In other words, this means that during a frequency sweep, the target frequency can be reached essentially halfway through the total duration of the sweep. Conversely, this also means that the time course of the drive signal f(t) will have different slopes between the first and second time points, as well as between the second and third time points, if the target frequency is not exactly midway between the minimum and maximum frequencies. While it is not necessary for the first and second time differences to be equal in magnitude within the framework of the inventive method, such equality can be particularly advantageous if the repetition rate of the sweep modulation is generated or triggered by a harmonic carrier signal, for example, a sinusoidal carrier signal.In this case, the first, second and third time points advantageously coincide with characteristic points of the harmonic carrier signal, for example inflection points or extrema.

[0018] The frequency change of the drive signal in the area of ​​the second time point can be continuous (mathematically speaking: differentiable), but it can also be designed in the form of a mathematical jump discontinuity.

[0019] In principle, the excitation frequency can exhibit almost any desired temporal profile during a frequency sweep.

[0020] A particularly advantageous embodiment of the method according to the invention exists when the first and second time differences are equal in magnitude. However, the method according to the invention is by no means limited to this; with a suitable selection of the minimum frequency, the maximum frequency, and the target frequency, the first and second time differences can also be different in magnitude.

[0021] Preferably, the frequency sweep is selected such that, during at least one frequency sweep, and preferably all frequency sweeps, the first derivative of the excitation frequency (or rate of change of the excitation frequency) has a constant value between the first and second time points and a constant value between the second and third time points. From a circuit design perspective, this is simpler to implement than a derivative or rate of change of the excitation frequency that has a non-constant value.

[0022] According to a preferred embodiment, the frequency sweep is selected such that during at least one frequency sweep, preferably all frequency sweeps, the first derivative magnitude and the second derivative magnitude differ from each other.

[0023] If the time course of the drive signal f(t) exhibits different slopes between the first and second time points, and between the second and third time points, a kink may appear in an f(t) diagram when the frequency otherwise has a linear dependence on time. The corresponding kink angle can be less than or greater than 180°.

[0024] Preferably, at least one transducer, preferably several transducers, most preferably all transducers, are excited at a respective resonant frequency during several, preferably all, frequency sweeps. This increases the efficiency of the excitation.

[0025] Particularly preferably, at least one transducer, preferably several transducers, and most preferably all transducers are excited during several, preferably all, frequency sweeps at a respective resonant frequency of the same order, preferably at a respective fundamental resonant frequency. An advantage of this method is that when all transducers are excited at a resonant frequency of the same order, their operating parameters are comparable, thus increasing the homogeneity of the emitted sound wave field. If transducers were excited at resonant frequencies of different orders, resonance patterns with different spectral widths could result, and the superposition of the sound waves emitted by the individual transducers could potentially lead to inhomogeneities in the sound field.

[0026] In a preferred embodiment of the invention, the target frequency is selected essentially according to a resonance frequency, preferably a fundamental resonance frequency, of at least one transducer, and / or according to a frequency in the transducer frequency range, preferably according to a frequency formed by arithmetic averaging at least some, preferably all, resonance frequencies in the transducer frequency range. Such a selection of the target frequency has the advantage that as many resonance frequencies as possible, or all resonance frequencies of a certain order, are covered during a single frequency sweep or during a plurality of frequency sweeps. This, in turn, increases the efficiency of the transducer excitation.

[0027] Further preferred features and embodiments of the inventions will become apparent from the following description of exemplary embodiments with reference to the drawing. Fig. Figure 1 shows a schematic representation of a sound generation arrangement according to the invention; Fig. Figure 2 shows a state-of-the-art sweep modulation using an impedance-frequency diagram; Fig. Figure 3 shows the sweep modulation from Fig. 1. based on an associated frequency-time diagram; Fig. Figure 4 shows a sweep modulation according to the invention using an impedance-frequency diagram; Fig. 5 shows that to Fig. 4. Frequency-time diagram of the sweep modulation according to the invention; Fig. Figure 6 shows another aspect of the sweep modulation according to the invention. Fig. 4 and Fig. 4 using an impedance-frequency diagram; Fig. 7 shows the Fig. 6 related frequency-time diagram; Fig. Figure 8 shows a flowchart of a sweep modulation according to the invention; Fig. Figure 9 shows an alternative embodiment of a sweep modulation according to the invention using an impedance-frequency diagram; Fig. Figure 10 shows another aspect of sweep modulation from Fig. 9 using an impedance-frequency diagram; and Fig. Figure 11 shows another sweep modulation according to the invention in a frequency-time diagram.

[0028] Fig. Figure 1 shows a sound generation arrangement according to the invention using an application example in which the method according to the invention can be used, but is not limited to this application. Parts 6 to be cleaned, which have soiling, are located in a tub 4 filled with water or another suitable cleaning medium 5. At least one ultrasonic transducer 7 (solid line) is coupled to the tub 4 and the water (cleaning medium) 5 contained therein. This transducer is designed to generate and emit ultrasonic waves to the medium 5. These ultrasonic waves clean the parts 6 of the soiling in a manner known per se. It is within the scope of the invention to provide not only one ultrasonic transducer 7, but a plurality of ultrasonic transducers (in Fig. 1 indicated accordingly with dashed lines).

[0029] The ultrasonic transducer 7 is electrically and signal-wise connected (via a line 8) to a (frequency) generator 9. The generator 9 has a signal unit 10, which is designed to generate a high-frequency excitation signal with a variable excitation frequency 1. The excitation signal is transmitted from the signal unit 10, or the generator 9, to the ultrasonic transducer 7 via the electrical connection 8, for example, a signal line. This excites the ultrasonic transducer 7 to generate (ultra)sound waves, which are then coupled into the medium 5 to clean the parts 6.

[0030] In Fig. 2 is a method for modulating the excitation frequency 1 of the ultrasound transducer 7, shown schematically according to the state of the art. Fig. Figure 2 shows an impedance curve 3 of the ultrasonic transducer 7, as it typically exhibits in the present context. The excitation frequency 1, which is generated by the generator 9, is adjusted between a minimum frequency f min and a maximum frequency f max varies. Between the minimum frequency f min and the maximum frequency f max A target frequency f ziel In the present example of the Fig. 2 shows the impedance curve 3 in the region of the target frequency f zieıA local maximum 2 is observed. In this context, one also speaks of a resonance frequency of the ultrasound transducer 7 at the location of the local maximum 2. Exciting the ultrasound transducer 7 near its resonance frequency(ies) increases the vibration amplitude for a given excitation power and thus the efficiency of the sound conversion. It is known to excite ultrasound transducers 7 in the region of their resonance frequency(ies) to achieve the highest possible efficiency.

[0031] A first frequency difference Δf1 between the minimum frequency f min and the target frequency f ziel is in the Fig. 2 equal in magnitude to a second frequency difference Δf2 between the maximum frequency f max and the target frequency f ziel In the prior art, it is assumed that such a symmetrical, equal-magnitude design of the minimum frequency f min and the maximum frequency f maxto achieve the target frequency f zieı around leads to particularly good results.

[0032] Fig. Figure 3 shows the time dependence of the excitation frequency 1 in a frequency-time diagram. This is analogous to Fig. 2 taken from the prior art. It can be seen that the first frequency difference Δf1 and the second frequency difference Δf2, as in Fig. 2, are equal in amount.

[0033] A time t ziel is defined as the point in time at which the excitation frequency 1 is equal in magnitude to the frequency f zieı corresponds to a time t. min is defined as the time at which the excitation frequency 1 is equal in magnitude to the frequency f min corresponds to a time t. max is defined as the time at which the excitation frequency 1 is equal in magnitude to the frequency f max This corresponds to a first time difference Δt1, calculated from the difference between time t. zieland the time t min A second time difference Δt2 is calculated from the difference between time t max and the time t ziel In Fig. 3, the first time difference Δt1 is equal in magnitude to the second time difference Δt2.

[0034] A frequency sweep begins at time t min and ends at time t max , or vice versa. In Fig. 3. Therefore, during a frequency sweep, the excitation frequency 1 has the form of a straight line.

[0035] Several methods for performing this type of frequency modulation are known from the prior art. If the excitation frequency 1 is returned to the minimum frequency f after the end of a frequency sweep, min If the excitation frequency 1 is not set to the minimum frequency f after the end of a frequency sweep, this is called sawtooth modulation. minset, but starting from the maximum frequency f max If the frequency decreases linearly, it is called triangular modulation. The symmetrical design of the modulation of the excitation frequency 1 around the target frequency means that, in previously known methods, the first derivative of the excitation frequency 1 remains constant in magnitude during a frequency sweep. The minimum frequency f min , the maximum frequency f max as well as the target frequency f zielAccording to the current state of the art, the parameters are not regularly changed after completion of a frequency sweep. This results in the aforementioned disadvantages, particularly concerning generator 9, which generates the excitation frequency 1 or provides the excitation signal. These disadvantages include, among other things, increased heat loss generated in generator 9, which is proportional to the frequency deviation of the sweep modulation: a larger frequency deviation results in greater heat loss.

[0036] In Fig. Figure 4 shows a method according to the invention for modulating the excitation frequency 1 for operating the ultrasonic transducer 7. The target frequency f ziel is located, as previously shown by Fig. 2 explained, in the present embodiment in the region of a local maximum 2 of the impedance curve 3 of the ultrasonic transducer 7. The minimum frequency f minis smaller in magnitude than the target frequency f ziel , the maximum frequency f max is greater in magnitude than the target frequency f ziel The maximum frequency f max and the minimum frequency f min are chosen such that the first frequency difference Δf1 is smaller in magnitude than the second frequency difference Δf2. The target frequency f ziel Therefore, it is not midway between f min and f max .

[0037] That to Fig. The corresponding frequency-time diagram is shown in Figure 4. Fig. 5 shown. The first time difference Δt1 between time t ziel and the time t min and the second time difference Δt2 between time t max and the time t ziel are equal in magnitude. This implies that a first time derivative of the excitation frequency 1 in the range between t min and t ziel, at least on the arithmetic mean, is smaller than a first time derivative of the excitation frequency 1 in the range between t ziel and t max According to the Fig. 4 shows the change in the excitation frequency 1 with time in the range from time t min until time t ziel as well as in the area from time t ziel until time t max Each takes the form of a straight line. In this case, the slope of this line in the range between t is ziel and t max greater in magnitude than in the range between t min and t ziel In other words, this means that the ultrasound transducer 7 is in the first range between t min and t ziel is excited over a smaller frequency spectrum in the same time than in the range between t ziel and t max One can also assume a lower frequency change rate in the first range between t min and tziel compared to the second area between t ziel and t max speak.

[0038] Since the time course of the drive signal (excitation frequency f(t)) between the first time t min and the second time point t ziel as well as between the second time point t ziel and the third point in time t max Since the slopes differ from each other, a kink appears in the f(t) diagram when graphically represented accordingly. According to the configuration in Fig. 5, the corresponding bending angle is less than 180°.

[0039] Fig. Figure 6 shows the same impedance curve 3 of the ultrasonic transducer 7 in the impedance-frequency diagram as Fig. 4. The target frequency f zieı This is again located in the region of the local maximum 2 of the impedance curve 3 of the ultrasound transducer 7. It can be seen that in Fig. 6, contrary to Fig. 4, the first frequency difference Δf1 is larger in magnitude than the second frequency difference Δf2. This can be seen in the frequency-time diagram in Fig. 7. Again, the two time differences Δt1 and Δt2 are equal in magnitude. The change in the excitation frequency 1 over time again shows in the first range of t min are ziel and in the second area of ​​t ziel are max the shape of a straight line. However, unlike... Fig. 5, the first time derivative of the excitation frequency 1 in the first region between t min and t ziel greater in magnitude than in the second range between t ziel and t max In other words, is in Fig. 7 the slope of the straight line in the range between t ziel and t max smaller in magnitude than in the range between t min and t ziel .

[0040] Since the time course of the drive signal (excitation frequency f(t)) between the first time t min and the second time point t ziel as well as between the second time point t ziel and the third point in time t max Since the slopes differ from each other, a kink appears in the f(t) diagram when graphically represented accordingly. According to the design in Fig. 7, the corresponding bending angle is greater than 180°.

[0041] The one in the Fig. 4 and Fig. 5. The relationship between the minimum frequency f is shown. min , the maximum frequency f max and the target frequency f zieı The impedance curve 3 of the ultrasound transducer is used on average in approximately half of all frequency sweeps. In the other half of the frequency sweeps, a combination of the corresponding parameters is used according to... Fig. 6 and Fig. 7 used.

[0042] In Fig. Figure 8 shows an exemplary temporal sequence of individual steps of the method according to the invention. First, the minimum frequency f is determined. min , the target frequency f zieı and the maximum frequency f max The frequency difference is chosen such that the magnitude of the first frequency difference Δf1 = A and the magnitude of the second frequency difference Δf2 = B. In a first frequency sweep, a drive signal with an excitation frequency 1 equal to the minimum frequency f is used. min The signal is generated by the signal unit 10 of the generator 9 and transmitted to the ultrasonic transducer 7 (or transducers). During the first frequency sweep, the excitation frequency 1 is increased to the maximum frequency f. max increased. After the end of a first frequency sweep, the minimum frequency f min , the target frequency f zieı and / or the maximum frequency f maxThe values ​​are varied such that the magnitude of the first frequency difference Δf1 is now B and the magnitude of the second frequency difference Δf2 is now A. The excitation frequency 1 is now determined by the maximum frequency f. max up to the minimum frequency f min This reduces the drive signal's behavior, resulting in a triangular waveform or the excitation frequency 1 of the drive signal. As explained previously, the waveform can also be sawtooth-shaped, for example, if the excitation frequency decreases from the minimum frequency f after the first frequency sweep. min The initial increase is increased.

[0043] It is obvious that the maximum frequency f max , or any other frequency within the frequency sweep range, can serve as the starting point for modulating the excitation frequency 1.

[0044] After the second frequency sweep, the magnitudes of the two frequency differences are again chosen to be Δf1 = A and Δf2 = B. After the third frequency sweep, Δf1 = B and Δf2 = A are chosen again, and so on.

[0045] In an arithmetic mean over all frequency sweeps, the first frequency difference Δf1 and the second frequency difference Δf2 are therefore equal in magnitude and each has the magnitude A+B2 In the frequency-time diagram, this means that the first time derivative of the excitation frequency 1 is in the first region between t min and t ziel on average, the amount is approximately the same as in the second range between t ziel and t max .

[0046] The change in excitation frequency 1 in the frequency-time diagram can not only have the form of a straight line, but can also take on other shapes or profiles. For example, the excitation frequency 1 can change quadratically with time, f = f(t). 2 ).

[0047] Fig. 9 and Fig. Figures 10 each show a further method according to the invention for modulating the excitation frequency 1 in an impedance-frequency diagram. In contrast to the Fig. 2, Fig. 4 and Fig. 6 is the target frequency f zieı not approximately equal to the local maximum 2 of the impedance curve 3 of the ultrasound transducer 7. Rather, the target frequency f zieı and accordingly the minimum frequency f min as well as the maximum frequency f max at any point on the impedance curve 3.

[0048] In Fig.Figure 11 shows a time course of the change in the excitation frequency 1 for the case where the first time difference Δt1 and the second time difference Δt2 are different in magnitude. For a specific ratio between the first time difference Δt1 and the second time difference Δt2, it is also possible that the time course of the change in the excitation frequency 1 within a frequency sweep has the form of a straight line without a kink, even though the first frequency difference Δf1 and the second frequency difference Δf2 differ in magnitude.

Claims

[1] Method for exciting one or more, preferably piezoelectric, transducers (7), which transducers (7) are designed to generate sound waves and have operating frequencies which define a converter frequency range, in which a generator (9) which has an electrical connection (8) to the converters (7) and a frequency sweep function for generating an electrical excitation signal with a variable excitation frequency (1) generates an electrical excitation signal for the converters (7), which excitation signal is supplied to the converters (7), wherein the generator (9) with an adjustable sweep rate performs a total number of frequency sweeps in a frequency sweep range between a minimum frequency (f min ) and a maximum frequency (f max ) carries out, within which frequency sweep range a target frequency (f Ziel ) is defined, characterized by, that the minimum frequency (f min ), the maximum frequency (f max ) and the target frequency (f Ziel ) are chosen such that a first frequency difference (Δf1) exists between the minimum frequency (f min ) and the target frequency (f Ziel ) during a first number of frequency sweeps from the total number of frequency sweeps, preferably during substantially all frequency sweeps, in magnitude from a second frequency difference (Δf2) between the maximum frequency (f max ) and the target frequency (f Ziel ) differs, and where the minimum frequency (f min ) and / or the maximum frequency (f max ) and / or the target frequency (f Ziel) is modified after at least one frequency sweep such that an arithmetic mean of the first frequency differences (Δf1) and an arithmetic mean of the second frequency differences (Δf2) formed over all frequency sweeps are essentially equal in magnitude. [2] Method according to claim 1, wherein after completion of at least one frequency sweep the minimum frequency (f min ) and / or the maximum frequency (f max ) is changed. [3] Method according to claim 1 or 2, wherein the minimum frequency (f min ), the maximum frequency (f max ) and the target frequency (f Ziel ) are chosen such that, during a first frequency sweep, the first frequency difference (Δf1) has a first magnitude (A) and the second frequency difference (Δf2) has a second magnitude (B), and in which, in a subsequent frequency sweep, at least the target frequency and preferably also the minimum frequency (f) are determined. min ) and the maximum frequency (f max ) is modified so that the first frequency difference (Δf1) has the second magnitude (B) and the second frequency difference (Δf2) has the first magnitude (A), preferably the first amount (A) and the second amount (B) are different. [4] Method according to any one of claims 1 to 3, wherein the target frequency (f Ziel ) is changed after completion of at least one frequency sweep. [5] Method according to one of the preceding claims, wherein during at least one frequency sweep, preferably all frequency sweeps, the excitation frequency (1) of the drive signal is varied such that the drive signal at a first time (t1) has the minimum frequency (f min ), at a second time point (t2) the target frequency (f Ziel) and at a third time (t3) the maximum frequency (f max ) shows, where the second time point (t2) lies between the first time point (t1) and the third time point (t3), and wherein a first time difference (Δt1) between the first time (t1) and the second time (t2) and a second time difference (Δt1) between the second time (t2) and the third time (t3) are equal in magnitude. [6] Method according to claim 5, wherein the frequency sweep is selected such that during at least one frequency sweep, preferably all frequency sweeps, a first derivative of the frequency with respect to time has a constant first derivative value between the first time (t1) and the second time (t2) and a constant second derivative value between the second time (t2) and the third time (t3). [7] Method according to claim 6, wherein the frequency sweep is selected such that during at least one frequency sweep, preferably all frequency sweeps, the first derivative magnitude and the second derivative magnitude differ from each other. [8] Method according to one of the preceding claims, wherein during several, preferably all, frequency sweeps at least one of the transducers (7), preferably several transducers (7), most preferably all transducers (7), is excited at a respective resonant frequency. [9] Method according to claim 8, wherein during several, preferably all, frequency sweeps at least one of the transducers (7), preferably several transducers (7), most preferably all transducers (7), is excited at a respective resonance frequency of the same order, preferably at a respective fundamental resonance frequency. [10] Method according to claim 8 or 9, wherein the target frequency is selected substantially according to a resonance frequency, preferably a fundamental resonance frequency, of at least one transducer (7), and / or according to a frequency in the transducer frequency range, preferably according to a frequency, which is formed from an arithmetic average of at least some, preferably all, resonance frequencies in the converter frequency range. [11] Sound generation arrangement with at least one, preferably piezoelectric transducer (7) and with a generator (9) which has an electrical connection (8) to the transducer (7), which generator (9) is provided for generating an electrical excitation signal for the transducer (7) and has a frequency sweep function for generating an electrical excitation signal with a variable excitation frequency (1), which excitation signal is provided for supply to the transducer (7), which generator (9) is designed and configured to perform a total number of frequency sweeps in a frequency sweep range between a minimum frequency (f) at an adjustable sweep rate min ) and a maximum frequency (f max ) to determine within which frequency sweep range a target frequency (f Ziel ) definable, where the minimum frequency (f min ), the maximum frequency (f max ) and the target frequency (f Ziel ) are selectable such that a first frequency difference (Δf1) exists between the minimum frequency (f min ) and the target frequency (f Ziel ) during a first number of frequency sweeps from the total number of frequency sweeps, preferably during substantially all frequency sweeps, in magnitude from a second frequency difference (Δf2) between the maximum frequency (f max ) and the target frequency (f Ziel) differs, and where the minimum frequency (f min ) and / or the maximum frequency (f max ) and / or the target frequency (f Ziel ) can be modified after at least one frequency sweep such that an arithmetic mean of the first frequency differences (Δf1) and an arithmetic mean of the second frequency differences (Δf2) formed over all frequency sweeps are essentially equal in magnitude.

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