Method for exciting piezoelectric transducers and sound-producing arrangement

Abstract

A method for exciting sound-wave producing transducers (7) which have operating frequencies defining a transducer frequency range, in which a generator (9) produces an electrical excitation signal for the transducers (7), these electrical excitation signal being fed to the transducers (7), wherein the generator (9) carries out frequency sweeps in a frequency sweep range between a minimum frequency (f.sub.min) and a maximum frequency (f.sub.max) with an adjustable sweep rate, with a target frequency (f.sub.Ziel) being defined within said frequency sweep range, this method being characterized in that the minimum frequency (f.sub.min), the maximum frequency (f.sub.max) and the target frequency (f.sub.Ziel) are selected in such a way that a first frequency difference (Δf.sub.1) between the minimum frequency (fmin) and the target frequency (f.sub.Ziel) differs in terms of magnitude from a second frequency difference (Δf.sub.2) between the maximum frequency (f.sub.max) and the target frequency (f.sub.Ziel) within a number of frequency sweeps, and wherein the minimum frequency (f.sub.min) and/or the maximum frequency (f.sub.max) and/or the target frequency (f.sub.Ziel) is/are modified after at least one frequency sweep in such a way that an arithmetic mean of the first frequency differences (Δf.sub.1), formed over all frequency sweeps carried out, and an arithmetic mean of the second frequency differences (Δf.sub.2), formed over all frequency sweeps carried out, are substantially the same in terms of magnitude.

Claims

1. A method for the excitation of one or a plurality of transducers (7), said transducers (7) being designed for generation of sound waves and exhibiting operating frequencies that define a transducer frequency range, the method comprising: generating an electrical excitation signal for the transducers (7) with a generator (9) which has an electrical connection (8) to the transducers (7) and a frequency sweep function for the generation of an electrical excitation signal with a variable excitation frequency (1), and supplying said excitation signal to the transducers (7), the generator (9) carrying out an integral number of frequency sweeps at an adjustable sweep rate in a frequency sweep range between a minimum frequency (f.sub.min) and a maximum frequency (f.sub.max), defining a target frequency within the frequency sweep range, selecting the minimum frequency (f.sub.min), the maximum frequency (f.sub.max) and the target frequency (f.sub.Ziel) such that a first frequency difference (Δf.sub.1) between the minimum frequency (f.sub.mm) and the target frequency (f.sub.Ziel) in a first number of frequency sweeps from a total number of frequency sweeps, differs in terms of magnitude from a second frequency difference (Δf.sub.2) between the maximum frequency (f.sub.max) and the target frequency (f.sub.Ziell), and modifying at least one of the minimum frequency (f.sub.min), the maximum frequency (f.sub.max), or the target frequency (f.sub.Ziel) after at least one said frequency sweep in such a way that an arithmetic mean of the first frequency differences (Δf.sub.1) formed over all the frequency sweeps carried out and an arithmetic mean of the second frequency differences (Δf.sub.2) formed over all the frequency sweeps carried out are substantially equal in terms of magnitude.

2. The method as claimed in claim 1, further comprising changing at least one of the minimum frequency (f.sub.min) or the maximum frequency (f.sub.max) after the completion of at least one frequency sweep.

3. The method as claimed in claim 1, further comprising selecting the minimum frequency (f.sub.min), the maximum frequency (f.sub.max) and the target frequency (f.sub.Ziel) such that during a first one of the frequency sweeps, the first frequency difference (Δf.sub.1) has a first magnitude (A), and the second frequency difference (Δf.sub.2) has a second magnitude (B), and wherein, in a subsequent frequency sweep, modifying at least the target frequency as well as at least one of the minimum frequency (f.sub.min) or the maximum frequency (f.sub.max) such that the first frequency difference (Δf.sub.1) has the second magnitude (B) and the second frequency difference (Δf.sub.2) has the first magnitude (A), wherein the first magnitude (A) and the second magnitude (B) differ.

4. The method as claimed in claim 1, wherein the target frequency (f.sub.Ziel) is changed after the completion of at least one said frequency sweep.

5. The method as claimed in claim 1, further comprising, in the course of at least one of the frequency sweeps, varying the excitation frequency (1) of the drive signal in such that the drive signal has the minimum frequency (f.sub.min) at a first point in time (t.sub.1), the target frequency (f.sub.Ziel) at a second point in time (t.sub.2), and the maximum frequency (f.sub.max) at a third point in time (t.sub.3), wherein the second point in time (t.sub.2) lies between the first point in time (t.sub.1) and the third point in time (t.sub.3), and wherein a first time difference (Δt.sub.1) between the first point in time (t.sub.1) and the second point in time (t.sub.2) and a second time difference (Δt.sub.1) between the second point in time (t.sub.2) and the third point in time (t.sub.3) are equal in terms of magnitude.

6. The method as claimed in claim 5, wherein the frequency sweep is selected such that in the course of at least one said frequency sweep, a first derivative of the frequency with respect to time has a constant first derivative magnitude between the first point in time (t.sub.1) and the second point in time (t.sub.2), and has a constant second derivative magnitude between the second point in time (t.sub.2) and the third point in time (t.sub.3).

7. The method as claimed in claim 6, wherein the frequency sweep is selected such that in the course of at least one said frequency sweep, the first derivative magnitude and the second derivative magnitude differ from one another.

8. The method as claimed in claim 1, further comprising during a plurality of, exciting at least one of the transducers (7) at a respective resonant frequency.

9. The method as claimed in claim 8, further comprising during in the course of a plurality of said frequency sweeps, exciting at least one of the transducers (7) at a respective resonant frequency of a same order.

10. The method as claimed in claim 8, further comprising choosing the target frequency to correspond substantially to a resonant frequency of at least one transducer (7).

11. A sound generation arrangement, comprising: at least one transducer (7): and with a generator (9) which has an electrical connection (8) to the transducer (7), said generator (9) being provided for the generation of an electrical excitation signal for the transducer (7) and comprising a frequency sweep function for generation of an electrical excitation signal with a variable excitation frequency (1), said excitation signal being provided for supply to the transducer (7); said generator (9) being configured provided and designed to carry out, with an adjustable sweep rate, an integral number of frequency sweeps in a frequency sweep range between a minimum frequency (f.sub.min) and a maximum frequency (f.sub.max), with a target frequency (f.sub.Ziel) defined within the frequency sweep range; and wherein the minimum frequency (f.sub.min), the maximum frequency (f.sub.max) and the target frequency (f.sub.Ziel) are selected such that a first frequency difference (Δf.sub.1) between the minimum frequency (f.sub.min) and the target frequency (f.sub.Ziel) in a first number of said frequency sweeps from a total number of frequency sweeps, differs in terms of magnitude from a second frequency difference (Δf.sub.2) between the maximum frequency (f.sub.max) and the target frequency (f.sub.Ziel), and wherein at least one of the minimum frequency (f.sub.min), the maximum frequency (f.sub.max), or the target frequency (f.sub.Ziel) is modifiable after at least one frequency sweep such that an arithmetic mean of the first frequency differences (Δf.sub.1) formed over all the frequency sweeps carried out and an arithmetic mean of the second frequency differences (Δf.sub.2) formed over all the frequency sweeps carried out are substantially equal in terms of magnitude.

12. The method as claimed in claim 8, further comprising choosing the target frequency to correspond substantially to corresponding to a frequency in the transducer frequency range corresponding to a frequency that is formed from an arithmetic averaging of more than one off the resonant frequencies in the transducer frequency range.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further preferred features and forms of embodiment of the inventions emerge from the following description of exemplary embodiments with reference to the drawing.

(2) FIG. 1 shows a schematic illustration of sound generation arrangement according to the invention;

(3) FIG. 2 shows a sweep modulation according to the prior art with reference to an impedance-frequency diagram;

(4) FIG. 3 shows the sweep modulation of FIG. 1 with the aid of an associated frequency-time diagram;

(5) FIG. 4 shows a sweep modulation according to the invention with the aid of an impedance-frequency diagram;

(6) FIG. 5 shows the frequency-time diagram of the sweep modulation according to the invention belonging to FIG. 4;

(7) FIG. 6 shows a further aspect of the sweep modulation according to the invention according to FIG. 4 and FIG. 5 with respect to an impedance-frequency diagram;

(8) FIG. 7 shows the frequency-time diagram belonging to FIG. 6;

(9) FIG. 8 shows a flow diagram of a sweep modulation according to the invention;

(10) FIG. 9 shows a sweep modulation according to the invention in an alternative embodiment with the aid of an impedance-frequency diagram;

(11) FIG. 10 shows a further aspect of the sweep modulation of FIG. 9 with the aid of an impedance-frequency diagram; AND

(12) FIG. 11 shows a further sweep modulation according to the invention in a frequency-time diagram.

DETAILED DESCRIPTION

(13) FIG. 1 shows a sound generation arrangement according to the invention on the basis of an exemplary application in which the method according to the invention can be employed, without however being restricted to this application. Two parts 6 that are to be cleaned, and which have contamination, are located in a bath 4 that is filled with water or with another suitable cleaning medium 5. At least one ultrasonic transducer 7 (solid line) is coupled to the bath 4 and to the water (cleaning medium) 5 inside it, and is designed for the generation and output of ultrasonic waves to the medium 5. These ultrasonic waves bring about the cleaning of the parts 6 from the contamination in a manner known per se. It is within the scope of the invention not only to provide one ultrasonic transducer 7, but a plurality of ultrasonic transducers (accordingly suggested in FIG. 1 with dotted lines).

(14) The ultrasonic transducer 7 is effectively connected in an electrical and a signal sense (via a cable 8) to a (frequency) generator 9. The generator 9 comprises 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 and/or the generator 9 via the effective electrical connection 8, for example a signal line, to the ultrasonic transducer 7. The ultrasonic transducer 7 is thus excited to generate (ultrasonic) sound waves, which are accordingly coupled into the medium 5 for cleaning the parts 6.

(15) A method for the modulation of the excitation frequency 1 of the ultrasonic transducer 7 according to the prior art is illustrated schematically in FIG. 2. FIG. 2 shows an impedance curve 3 of the ultrasonic transducer 7 as is usually exhibited by the ultrasonic transducer 7 in the present context. The excitation frequency 1 that is generated by the generator 9 is varied between a minimum frequency f.sub.min and a maximum frequency f.sub.max. A target frequency f.sub.Ziel lies between the minimum frequency f.sub.min and the maximum frequency f.sub.max. In the present example of FIG. 2, the impedance curve 3 exhibits a local maximum 2 in the region of the target frequency f.sub.Ziel. In this context, a resonant frequency of the ultrasonic transducer 7 at the position of the local maximum 2 is also spoken of. The excitation of the ultrasonic transducer 7 in the vicinity of its resonant frequency (or frequencies) increases the amplitude of oscillation for a given excitation power, and thus the effective efficiency of the sound transduction. The excitation of ultrasonic transducers 7 in the neighborhood of their resonant frequency (or frequencies) is known in order to achieve the highest possible efficiency.

(16) A first frequency difference Δf.sub.1 between the minimum frequency f.sub.min and the target frequency f.sub.Ziel in FIG. 2 is the same in terms of magnitude as a second frequency difference Δf.sub.2 between the maximum frequency f.sub.max and the target frequency f.sub.Ziel. It is assumed in the prior art, that such a symmetrical design of equal magnitudes of the minimum frequency f.sub.min and the maximum frequency f.sub.max around the target frequency f.sub.Ziel leads to particularly good results.

(17) FIG. 3 shows a time-dependency of the excitation frequency 1 in a frequency-time diagram. This, similarly to FIG. 2, is taken from the prior art. It can be seen that the first frequency difference Δf.sub.1 and the second frequency difference Δf.sub.2 are equal in terms of magnitude, as in FIG. 2.

(18) A point in time t.sub.Ziel is defined as that point in time at which the excitation frequency 1 corresponds in terms of magnitude to the frequency f.sub.Ziel. A point in time t.sub.min is defined as the point in time at which the excitation frequency 1 corresponds in terms of magnitude to the frequency f.sub.min. A point in time t.sub.max is defined as that point in time at which the excitation frequency 1 corresponds in terms of magnitude to the frequency f.sub.max. A first time difference Δt.sub.1 is calculated from the difference between the point in time t.sub.Ziel and the point in time t.sub.min. A second time difference Δt.sub.2 is calculated from the difference between the point in time t.sub.max and the point in time t.sub.Ziel. In FIG. 3 the first time difference Δt.sub.1 is equal in terms of magnitude to the second time difference Δt.sub.2.

(19) A frequency sweep begins at the point in time t.sub.min and ends at the point in time t.sub.max, or vice versa. In FIG. 3, the excitation frequency 1 therefore has the form of a straight line during a frequency sweep.

(20) Various methods are known from the prior art for carrying out this type of frequency modulation. If the excitation frequency 1 is set to the minimum frequency f.sub.min after the end of a frequency sweep, then we speak of sawtooth modulation. If the excitation frequency 1 is not set to the minimum frequency f.sub.min after the end of a frequency sweep, but instead falls linearly starting from the maximum frequency f.sub.max, then we speak of triangular modulation. The symmetrical configuration of the modulation of the excitation frequency 1 around the target frequency entails in the previously known methods that a first derivative of the excitation frequency 1 is constant in terms of magnitude during a frequency sweep. Under the prior art, the minimum frequency f.sub.min, the maximum frequency f.sub.max and the target frequency f.sub.Ziel are not normally changed after the completion of a frequency sweep. The previously mentioned disadvantages relating to the generator 9, which generator 9 generates the excitation frequency 1 or provides the excitation signal, result in particular from this. These disadvantages consist, amongst other things, in an increased thermal loss created in the generator 9, said loss having a proportional relationship to the frequency swing used for the sweep modulation: a greater frequency swing entails a greater thermal loss.

(21) A method according to the invention for the modulation of the excitation frequency 1 for the operation of the ultrasonic transducer 7 is illustrated in FIG. 4. As explained previously with reference to FIG. 2, the target frequency f.sub.Ziel is located in the present exemplary embodiment in the region of a local maximum 2 of the impedance curve 3 of the ultrasonic transducer 7. The minimum frequency f.sub.min is smaller in terms of magnitude than the target frequency f.sub.Ziel, the maximum frequency f.sub.max is larger in terms of magnitude than the target frequency f.sub.Ziel. The maximum frequency f.sub.max and the minimum frequency f.sub.min are selected in such a way that the first frequency difference Δf.sub.1 is smaller in terms of magnitude than the second frequency difference Δf.sub.2. The target frequency f.sub.Ziel accordingly is not located in the center between f.sub.min and f.sub.max.

(22) The frequency-time diagram belonging to FIG. 4 is illustrated in FIG. 5. The first time difference Δt.sub.1 between the point in time t.sub.Ziel and the point in time t.sub.min and the second time difference Δt.sub.2 between the point in time t.sub.maxand the point in time t.sub.Ziel are equal in terms of magnitude. This means that a first time-derivative of the excitation frequency 1 in the range between t.sub.min and t.sub.Ziel is, at least as an arithmetic mean, smaller than a first time-derivative of the excitation frequency 1 in the range between t.sub.Ziel and t.sub.max. According to FIG. 4, the change in the excitation frequency 1 with time in the region from point in time t.sub.min up to point in time t.sub.Ziel and also in the region from point in time t.sub.Ziel up to point in time t.sub.max each exhibit the form of a straight line. Here in the present case, the gradient of this straight line in the region between t.sub.Ziel and t.sub.maxis larger in terms of magnitude than in the region between t.sub.min and t.sub.Ziel. Expressed in other words, this means that the ultrasonic transducer 7 in the first region between t.sub.min and t.sub.Ziel is excited in the same time over a smaller frequency spectrum than in the region between t.sub.Ziel and t.sub.max. We can also speak of a lower rate of frequency change in the first region between t.sub.min and t.sub.Ziel in comparison with the second region between t.sub.Ziel and t.sub.max.

(23) Since the temporal progression of the drive signal (excitation frequency f(t)) between the first point in time t.sub.min and the second point in time t.sub.Ziel as well as between the second point in time t.sub.Ziel and the third point in time t.sub.max exhibit different gradients from one another, a bend results in the f(t) diagram on a corresponding graphical illustration. According to the embodiment in FIG. 5, the associated bend angle is less than 180°.

(24) FIG. 6 shows the same impedance curve 3 of the ultrasonic transducer 7 on an impedance-frequency diagram like FIG. 4. The target frequency f.sub.Ziel again lies in the region of the local maximum 2 of the impedance curve 3 of the ultrasonic transducer 7. It can be seen that in FIG. 6, unlike FIG. 4, the first frequency difference Δf.sub.1 is larger in terms of magnitude than the second frequency difference Δf.sub.2. This can be seen on the frequency-time diagram in FIG. 7. The two-time differences Δt.sub.1 and Δt.sub.2 are again equal in terms of magnitude. The change in the excitation frequency 1 over time again exhibits the form of a straight line in the first region from t.sub.min to t.sub.Ziel and in the second region from t.sub.Ziel to t.sub.max. Here, however, in contrast to FIG. 5, the first time-derivative of the excitation frequency 1 in the first region between t.sub.min and t.sub.Ziel is larger in terms of magnitude than in the second region between t.sub.Ziel and t.sub.max. Expressed otherwise, the gradient of the straight line in FIG. 7 in the region between t.sub.Ziel and t.sub.max is smaller in terms of magnitude than in the region between t.sub.min and t.sub.Ziel.

(25) Since the temporal progression of the drive signal (excitation frequency f(t)) between the first point in time t.sub.min and the second point in time t.sub.Ziel as well as between the second point in time t.sub.Ziel and the third point in time t.sub.max exhibit different gradients from one another, a bend again results in the f(t) diagram on a corresponding graphical illustration. According to the embodiment in FIG. 7, the associated bend angle is more than 180°.

(26) The relationship illustrated in FIGS. 4 and 5 between the minimum frequency f.sub.min, the maximum frequency f.sub.max and the target frequency f.sub.Ziel, as well as the impedance curve 3 of the ultrasonic transducer, is used on average in about half of all frequency sweeps. In the other approximate half of the frequency sweeps, a combination of the corresponding parameters according to FIG. 6 and FIG. 7 is used.

(27) An exemplary temporal sequence of individual steps of the method according to the invention is illustrated in FIG. 8. First, the minimum frequency f.sub.min, the target frequency f.sub.Ziel and the maximum frequency f.sub.max are selected such that the magnitude of the first frequency difference Δf.sub.1=A and the magnitude of the second frequency difference Δf.sub.2=B. In a first frequency sweep, a drive signal with an excitation frequency 1 equal to the minimum frequency f.sub.min is generated by the signal unit 10 of the generator 9, and transmitted to the ultrasonic transducer 7 (or the ultrasonic transducers). In the course of the first frequency sweep, the excitation frequency 1 is increased up to the maximum frequency f.sub.max. After a first frequency sweep has been completed, the minimum frequency f.sub.min, the target frequency f.sub.Ziel and/or the maximum frequency f.sub.max are varied such that the magnitude of the first frequency difference Δf.sub.1 is now B and the magnitude of the second frequency difference Δf.sub.2 is now A. The excitation frequency 1 is now reduced from the maximum frequency f.sub.max down to the minimum frequency f.sub.min. A triangular progression of the drive signal, or of the excitation frequency 1 of the drive signal, thus results. As previously explained, the progression can, for example, also have a sawtooth form, if the excitation frequency after the end of the first frequency sweep is increased again starting from the minimum frequency f.sub.min.

(28) It is clear that the maximum frequency f.sub.max, or any other frequency within the frequency sweep range, can also be used as the starting point for the modulation of the excitation frequency 1.

(29) After the second frequency sweep has ended, the magnitudes of the two frequency differences are chosen again to be Δf.sub.1=A and Δf.sub.2=B. After the end of the third frequency sweep, correspondingly again to Δf.sub.1=B and Δf.sub.2=A, etc.

(30) Taking an arithmetic mean over all frequency sweeps, the first frequency difference Δf.sub.1 and the second frequency difference Δf.sub.2 are therefore equal in terms of magnitude, each having the magnitude (A+B)/2. In the frequency-time diagram, this means that the first time-derivative of the excitation frequency 1 in the first region between t.sub.min and t.sub.Ziel is on average approximately equal in terms of magnitude as in the second region between t.sub.Ziel and t.sub.max.

(31) The change of the excitation frequency 1 on the frequency-time diagram can not only have the form of a straight line, but can also adopt other kinds of shape or progressions. For example the excitation frequency 1 can change quadratically with time, f=f(t.sup.2).

(32) FIGS. 9 and 10 each show a further method according to the invention for the modulation of the excitation frequency 1 on an impedance-frequency diagram. In contrast to FIGS. 2, 4 and 6, the target frequency f.sub.Ziel is not approximately equal to the local maximum 2 of the impedance curve 3 of the ultrasonic transducer 7. The target frequency f.sub.Ziel, and correspondingly both the minimum frequency f.sub.min and the maximum frequency f.sub.max, can rather be located at arbitrary positions on the impedance curve 3.

(33) A temporal progression of the change in the excitation frequency 1 is illustrated in FIG. 11 for the case in which the first time difference Δt.sub.1 and the second time difference Δt.sub.2 differ from one another in terms of magnitude. It is also possible, with a specific ratio between the first time difference Δt.sub.1 and the second time difference Δt.sub.2, for the temporal progression of the change of the excitation frequency 1 within a frequency sweep to have the form of a straight line without a bend, although the first frequency difference Δf.sub.1 and the second frequency difference Δf.sub.2 differ from one another in terms of magnitude.