METHOD AND APPARATUS FOR DETERMINING AT LEAST ONE MECHANICAL PARAMETER OF A MECHANICAL OBJECT

Abstract

A method is provided including the steps: —first excitation of the object via a multifrequency signal; —detecting a first response signal of the object at one or multiple measuring points at the object; —transforming the first response signal from a time range into a frequency-dependent range; —selecting one or multiple frequencies, based on the frequency-dependent range; —second excitation of the object based on the selected frequencies; —detecting a second response signal of the object at one or multiple measuring points of the object; —ascertaining a mechanical parameter based on the second response signal.

Claims

1-15. (canceled)

16. A method for ascertaining at least one mechanical parameter of a mechanical object, the method comprising the steps of: providing a first excitation the object via a multifrequency signal; detecting a first response signal of the object at at least one measuring point at the object; transforming the first response signal from a time range into a frequency-dependent range; selecting at least one frequency based on the frequency-dependent range; providing a second excitation of the object based on the selected at least one frequency; detecting a second response signal of the object at the at least one measuring point of the object; and ascertaining a mechanical parameter based on the second response signal.

17. The method as recited in claim 16 wherein the object is a blade wheel.

18. The method as recited in claim 17 wherein the object is at least one blade of the blade wheel.

19. The method as recited in claim 17 wherein the blade wheel is an integrally manufactured blade wheel.

20. The method as recited in claim 16 wherein the first excitation takes place using an acoustic signal.

21. The method as recited in claim 16 wherein the multifrequency signal is a sweep signal or a chirp signal.

22. The method as recited in claim 21 wherein a length of the sweep signal or of the chirp signal is shorter than a mechanical settling time of the object.

23. The method as recited in claim 16 wherein the frequency-dependent range into which the first response signal is transformed is a function of time, rotational speed, or position.

24. The method as recited in claim 23 wherein the transformation of the first response signal is carried out via a wavelet transformation or via a chirplet transformation.

25. The method as recited in claim 16 wherein the selection of the at least one frequency based on the frequency-dependent range maximizes a piece of information concerning an amplitude pattern or phase pattern over the frequency-dependent range.

26. The method as recited in claim 16 wherein multiple frequencies of the at least one frequency are selected in such a way that an equation system is determined or overdetermined with regard to the mechanical parameter.

27. The method as recited in claim 16 wherein the second excitation of the object takes place based on at least one sinusoidal excitation signal.

28. The method as recited in claim 16 wherein the ascertainment of the mechanical parameter includes selecting the second response signals, on the basis of which the mechanical parameter being ascertained on the basis of the second response signals.

29. A device for ascertaining at least one mechanical parameter of a mechanical object, and configured to: carry out a first excitation of the object using a multifrequency signal; detect a first response signal of the object at at least one measuring point at the object; transform the first response signal from a time range into a frequency-dependent range; carry out a second excitation of the object based on selected frequencies; detect a second response signal of the object at the at least one measuring point of the object; and ascertain the mechanical parameter based on the second response signal.

30. The device as recited in claim 29 wherein the mechanical object is supported by one or multiple springs having a predefined stiffness.

31. The device as recited in claim 29 wherein the first excitation or the second excitation takes place via a plurality of speakers, each of which excites a portion of the mechanical object and a calibration of a sound level and of a phase takes place in succession for one or multiple speakers.

32. The device as recited in claim 31 wherein a portion of the mechanical object is one of multiple blades of a blade wheel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Further advantages and features result from the following specific embodiments, which refer to the figures. The figures do not always show the specific embodiments true to scale. The dimensions of the various features may in particular be appropriately enlarged or reduced for clarity of the description. Some of the figures are shown in a schematic fashion.

[0059] FIG. 1 shows a coupling diagram;

[0060] FIG. 2 shows a signal representation of a wavelet;

[0061] FIG. 3 shows a frequency response of a mechanical object;

[0062] FIG. 4 shows a coupling diagram;

[0063] FIG. 5 shows a coupling diagram; and

[0064] FIG. 6 shows a block diagram of a method according to one specific embodiment of the disclosure.

DETAILED DESCRIPTION

[0065] In the following descriptions, identical or at least functionally equivalent features are denoted by the same reference numerals.

[0066] In the following detailed description, reference is made to the appended drawings, which constitute part of this description and which show specific aspects for purposes of illustration, and via which the present disclosure may be understood. It is understood that other aspects and/or features may be used, and that functional, structural, or logical changes are possible, without departing from the scope of the present disclosure. The following detailed description is therefore not to be construed in a limiting sense, since the scope of the present invention is defined by the appended claims.

[0067] In general, an explanation of a described method also applies to a corresponding device for carrying out the method, or a corresponding system that includes one or multiple devices, and vice versa. If, for example, a particular method step is described, a corresponding device may have a feature for carrying out the described method step, even if this feature is not explicitly described or illustrated in the figure. On the other hand, if, for example, a particular device is described on the basis of functional units, a corresponding method may include a step that carries out the described functionality, even if such steps are not explicitly described or illustrated in the figures. Likewise, a system may be provided with corresponding device features or with features for carrying out a certain method step. It is understood that features of the various aspects and specific embodiments described above or explained below by way of example may be combined with one another unless expressly stated otherwise.

[0068] FIG. 1 relates to a first excitation of a mechanical object. In this case, the mechanical object is an integrally manufactured blade wheel. The coupling diagram may be utilized for better illustration of the complex oscillation behavior of a blade wheel. The natural frequencies of the blade wheel are plotted as a function of the associated number of node diameter lines. FIG. 1 shows such a coupling diagram 100, and also various node diameter families 102, each of which is characterized by similar natural frequencies. The nonintegral node diameters illustrated in FIG. 1 are interpolations that are used solely to clarify the position of a node diameter family. The natural frequencies under consideration range from 0 kHz to 10 kHz. A total of seven node diameter families are illustrated. A first node diameter family oscillates already below 1 kHz. A second node diameter family oscillates at approximately 2 kHz. Further node diameter families oscillate at natural frequencies between 2 kHz and 8 kHz. A topmost node diameter family oscillates at approximately 9 kHz. The integrally manufactured blade wheel disk under consideration is excited, using the method, for detecting at least one mechanical parameter via a first multifrequency signal. This excitation takes place in that the blade wheel disk is stably supported at rest. Situated beneath each blade of the blade wheel disk is a speaker, as an acoustic actuator, which may emit the multifrequency signal in such a way that it impinges in the same manner on each blade of the blade wheel disk, and shifts it into a first excitation. To emulate a rotation of the blade wheel disk, the speakers are activated via a corresponding phase shift, so that each speaker provides for its blade a corresponding excitation that is phase-shifted, and the corresponding blades are thus likewise excited with phase shifting. The phase-shifted activation is produced by an appropriate control unit which also generates the multifrequency signal. To avoid undesirable coupling effects between the blades or the blade wheel disk and the device for detecting the at least one mechanical parameter of the blade wheel disk, the blade wheel disk is supported by the device on three springs. The springs are designed as coil springs and are situated beneath the blade wheel disk, so that the blade wheel disk is supported with its weight on the three springs. The springs have the same stiffness, which is significantly less than the stiffness of the blade wheel disk, or the stiffness that is expected from the blade wheel disk and its blades. The blade wheel disk is set into oscillations via its blades by the first excitation, using a multifrequency signal 101. In this case, multifrequency signal 101 represents a sweep pulse. The sweep pulse is generated from 3.84*10^6 supporting points in the time range. The sweep signal passes through frequencies which from the lowest frequency to the highest frequency encompass a bandwidth of 10 kHz.

[0069] Alternatively, the method has also been implemented using an excitation signal at 22 s and at a clock rate of 375 kHz clock pulse, using 80 speakers for all blades of a blade wheel. In contrast to the method provided in DE 102009010375 A1, the excitation is implemented not only at individual frequencies, but also with a continuous consecutive series of multiple frequencies as a continuous frequency transit. In addition, the phase activation is no longer achieved using a delay device, but, rather, using a signal output device on which the phase-shifted and calibrated signals are statically stored. The calibration takes place in succession for the sound level and the phase. Furthermore, instead of a single measuring stage, the provided method includes two stages with a first excitation and a second excitation for increasing the accuracy of the detected mechanical parameter.

[0070] FIG. 2 shows a signal pattern 200 of a Mutter wavelet, with the aid of which one or multiple response signals, resulting from the first excitation using a sweep signal, are transformed into a frequency- and time-dependent range. In this case, the Mutter wavelet represents a Morlet wavelet. A wavelet transformation is carried out using same. The Morlet-Mutter wavelet includes a real portion 201 and an imaginary portion 202. An amplitude 203 of the wavelet is marked as an envelope. The signals processed by the wavelet transformation, which as response signals in response to the first excitation via sweep pulse 101 are detected at the individual blades via laser vibrometry, are determined at a plurality of measuring points. The measuring points are situated at an upper tip of each blade. The measuring points are distributed in such a way that node diameter families previously ascertained by simulation may be detected.

[0071] FIG. 3 shows an amplitude response 300, i.e., an amplitude that is plotted as a function of a frequency. Amplitude response 301 represents the oscillation behavior of the third blade of the blade wheel at a rotational speed of 5000 revolutions/min, and exhibits resonance. This rotational speed is achieved during start-up of the blade wheel after a defined operating period, and represents a typical operating state in which the blade wheel operates. In addition to the amplitude response of the third blade of the blade wheel, an ideal amplitude response 302 at the rotational speed in question is illustrated. The mistuning now results, for example, from the difference in the ideal amplitude response from the amplitude response of the blade in question.

[0072] FIG. 3 also shows a selection of multiple frequencies 303, as supporting points, from the measured frequency-dependent range. The selected frequencies are illustrated by vertical lines, each of which ends with a round point on the measured curve. Accordingly, the supporting points are selected for the third blade for a rotational speed of 5000 revolutions/min. Additionally or alternatively, one or multiple supporting points may be selected for other rotational speeds. FIG. 3 shows only the selection of the supporting points for the third blade. In the present example, this step is carried out for all blades of the blade wheel in order to establish the differences between the individual blades with regard to the mechanical parameters, and thus the mistuning of the blade wheel with regard to a node family. In particular, enough supporting points are required for a blade so that the subsequently used equation system from which the mechanical parameters are ascertained is at least determined; i.e., an unambiguous solution is made possible. In the present case, these are two supporting points for each blade and for each node family. In particular, the same supporting points may be used for all blades. Alternatively, even more supporting points, in particular three, four, five, or ten, may be selected so that the equation system is overdetermined. An overdetermined equation system may be solved with respect to the mechanical parameter(s) via the least squares method, for example, in particular using the Moore-Penrose pseudoinverse.

[0073] FIG. 4 shows coupling diagram 100 from FIG. 1. In addition, selected frequencies 303 are now depicted in FIG. 4 along the Y axis. These frequencies are situated in the bottom rectangle at the right edge of the diagram. FIG. 4 also shows yet further mode families that result from further resonances, not illustrated, which in particular may also be represented in each case by at least five supporting points. A second excitation of the integrated blade wheel is carried out at these frequencies. A single multifrequency signal is not used as with the first excitation; instead, the blade wheel or the blades is/are excited via individual monofrequency sinusoidal oscillations that include only the selected frequencies. The type of excitation and the experimental procedure remain the same as for the first excitation of the blade wheel.

[0074] FIG. 5 likewise shows coupling diagram 100 from FIG. 1 or FIG. 4. After the blade wheel has been excited a second time at the selected frequencies via sinusoidal pulses, frequencies or frequency ranges are selected a second time. As shown in FIG. 5, these frequency ranges include individual node diameter families 502. Via the corresponding amplitudes or phases for the selected frequency ranges, a model may now be computed from which the correspondingly desired parameters, in this case the Lehr's damping factor, changes in stiffness, damping properties, and the excitation are determined. A so-called reduced-order code (ROC) may be used as the basis for the equation system.

[0075] FIG. 6 shows an overview of the described method according to one specific embodiment. Identification 601 of various mechanical parameters 602 of a mechanical object is carried out with the aid of a model-based adaptation 605 of corresponding parameters with regard to experimentally ascertained information 603, and is computed with the aid of an ROC 604. Parameter δλ represents a change in the stiffness of a blade, for example relative to an average value or relative to the stiffness of the preceding blade. Parameter ξ represents a damping of a blade, for example according to Lehr's damping factor. Parameter ξ_m_B represents the average damping of the blades. The parameter relates to the average damping of the disk ξ_m_S. Parameter δξ_B indicates a deviation of the damping of a blade from ξ_m_B. Parameter f_B depicts the excitation for one blade or for each blade. A mistuning of the blade wheel may be comprehensively described using a set of parameters for each blade of the blade wheel.

[0076] The equation system thus includes the change in the stiffness of each blade. In addition, the equation system includes the damping properties of the disk and/or of the blades; the damping of each blade may be determined in particular separately and/or as an average value. The equation system also includes the excitation of the blades and/or of the disk corresponding to the excitation during measurement; the excitation may be applied to one or multiple blades, in particular each blade, and/or to the disk.

LIST OF REFERENCE NUMERALS

[0077] 100 coupling diagram [0078] 101 spectrum of the sweep pulse [0079] 102 node diameter family [0080] 200 signal representation: Morlet wavelet [0081] 201 wavelet (real portion) [0082] 202 wavelet (imaginary portion) [0083] 203 wavelet amplitude [0084] 300 frequency-dependent range [0085] 301 measured amplitude response of the third blade [0086] 302 ideal amplitude response of the third blade [0087] 303 selected supporting points of the measured amplitude response [0088] 502 selected frequency ranges for model identification [0089] 600 measuring method [0090] 601 model identification or parameter identification [0091] 602 identified mechanical parameters [0092] 603 measured data [0093] 604 reduced-order model [0094] 605 mechanical model