Method for correcting measurement signals of an electric motor transmission unit and method for detecting wear and / or damage of said unit using said method

Abstract

The present invention relates to a method for correcting a time-dependent measurement signal generated by an electric machine coupled to a transmission on the output side for the influence of a variable output load and a variable speed, the method comprising: a) acquiring a measurement signal that is dependent on the torque of the electric machine-transmission unit; b) generating a useful signal without a DC component from the measurement signal; c) determining an effective value from the measurement signal at intervals; d) generating a load-corrected useful signal by dividing the useful signal without a DC component by an interval-specific effective value at intervals; e) determining the rotational frequency of the electric machine from the measurement signal in a time-resolved manner; f) scaling the load-corrected useful signal to an average rotational frequency to generate a corrected measurement signal; and g) using the corrected measurement signal for fault detection of the electric machine-transmission unit. The present invention also relates to a method for detecting wear and / or damage to the electric machine-transmission unit using the method.

Description

Technical Field

[0001] The present invention relates to a method for correcting a time-dependent measurement signal generated by an electric machine, in particular an electric motor, coupled to a transmission on the output side. The time-dependent measurement signal is corrected for the influence of variable output load and variable speed, thereby making the measurement signals comparable in different operating states. The present invention also relates to a method for detecting wear and / or damage in an electric machine-transmission unit having an electric machine and a transmission coupled to the electric machine on the output side using the correction method. Background Art

[0002] Electromechanical drives consisting of an electric motor and an output-side transmission are becoming increasingly important, particularly as components of large units such as vehicles or production plants.

[0003] For such applications, error-free operation is desirable. Mechanical damage to such electromechanical drives leads to malfunctions and undesirable repair costs. To avoid these disadvantages, component damage in such electromechanical drives should be detected early, for example based on time-dependent condition monitoring.

[0004] Such a method is known, for example, from DE 10 2016 222 660 A1, which carries out the following method steps for detecting damage and / or wear on a translatory moving component of an electromechanical drive:

[0005] - measuring the current supplied to the electric drive;

[0006] -Perform time-frequency analysis;

[0007] - comparing the frequency spectrum of the measured current determined from the time-frequency analysis with a predetermined frequency spectrum; and

[0008] - When a deviation of a predetermined size is determined from the comparison of the two spectra, an error signal is triggered.

[0009] Furthermore, US Pat. No. 4,965,513 A describes a method for monitoring the operating state of an electrically actuated valve by analyzing the motor current. To this end, various frequency analysis methods are applied to the motor current to create a noise signature that is designed to identify wear and abnormal operating conditions. Based on the noise signature, it is possible to determine different characteristic operating states of the electrically actuated valve. In particular, the sum of all mechanical load variations, as manifested in the frequency spectrum and amplitude, can be detected. If this noise signature is created at different time intervals during operation, it is possible to detect aging and wear or abnormal operating conditions.

[0010] However, it has been shown in this prior art that processing of the motor current signal is not sufficient to make reliable statements about wear and damage in changing operating states of a motor-transmission unit having an electric motor and a transmission connected to the electric motor on the output side. Summary of the Invention

[0011] The object of the present invention is therefore to provide a method for correcting a time-dependent measurement signal generated by an electric machine coupled to a transmission on the output side, so that an analysis of the corrected measurement signal for wear and / or damage leads to better results compared to the prior art.

[0012] A further object of the present invention is to provide, based on the calibration method, a method for detecting wear and / or damage of an electric motor / transmission unit having an electric motor and a transmission coupled to the electric motor on the output side.

[0013] The first-mentioned object is achieved by a method according to the invention.

[0014] In this method for correcting a time-dependent measurement signal generated by an electric machine coupled to a transmission on the output side for the influence of a variable output load and a variable speed, the following method steps are performed:

[0015] a) acquiring a torque-dependent measurement signal (M) of the motor-transmission unit;

[0016] b) generating a useful signal (N1) without a DC component from the measurement signal (M);

[0017] c) determining effective values ​​from the measurement signal (M) at intervals;

[0018] d) generating a load-corrected useful signal (N2) by dividing the useful signal (N1) without a DC component in intervals by an interval-specific effective value;

[0019] e) determining the rotational frequency (f) of the electric machine (1) from the measurement signal (M) in a time-resolved manner;

[0020] f) scaling, in particular normalizing, the load-corrected useful signal (N2) to the average rotational frequency to generate a corrected measurement signal (M corr );as well as

[0021] g) Using the corrected measurement signal for fault detection of the motor-transmission unit.

[0022] This correction method results in improved signal quality, in particular an improved signal-to-noise ratio and better comparability of the corrected measurement signals under different load conditions, so that the analysis method applied to the corrected measurement signals results in reliable, better-quality results with respect to wear and / or damage to the motor-transmission unit.

[0023] Using this corrected measurement signal, various analysis methods in the frequency domain, such as FFT (Fast Fourier) analysis or envelope analysis, can be performed. Suitable analysis methods in the time domain include, for example, determining kurtosis, minimum, maximum, RMS, standard deviation, mean value, etc.

[0024] As measurement signal, the motor current, for example, can be evaluated, but also the torque or any other torque-dependent signal, for example.

[0025] The second-mentioned object is achieved by a further method according to the invention for detecting wear and / or damage of an electric motor-transmission unit.

[0026] In this method for detecting wear and / or damage of an electric motor / transmission unit having an electric motor and a transmission coupled to the electric motor on the output side, the following method steps are performed:

[0027] - generating a time-dependent measurement signal by means of the motor-transmission unit;

[0028] - generating a corrected measurement signal according to the method according to the invention as described above;

[0029] - determining a frequency spectrum from the corrected measurement signal by means of an FFT (Fast Fourier Transform) analysis;

[0030] - providing a reference spectrum, which is generated by means of an FFT analysis from a corrected measurement signal of a wear-free and / or damage-free electric motor-transmission unit;

[0031] - comparing the spectrum of the corrected measurement signal with the reference spectrum; and

[0032] - Determining wear-indicative and / or damage-indicative features from a comparison of the frequency spectrum of the corrected measurement signal with the reference frequency spectrum.

[0033] By analyzing the corrected measurement signal in the frequency domain by means of an FFT analysis, component-specific features of the electric motor / transmission unit, whose properties differ due to wear and / or damage, can be identified.

[0034] Therefore, according to the improvement plan,

[0035] - assigning a component-specific characteristic of the motor-transmission unit to each frequency line of the frequency spectrum generated from the corrected measurement signal by means of an FFT analysis; and

[0036] To determine the wear-indicative and / or damage-indicative features, the amplitudes and / or spectral integrals of identical frequency lines of the spectrum of the corrected measurement signal and of the spectrum of a reference spectrum are compared.

[0037] Thus, analysis methods applied to the corrected measurement signals can be performed in an automated manner.

[0038] According to an advantageous refinement of the present invention, method step a) is performed by determining a DC component of the measurement signal and subtracting it from the measurement signal. Preferably, the measurement signal is low-pass filtered to determine the DC component of the measurement signal. By eliminating the DC component, the frequency analysis of the measurement signal results in improved signal quality.

[0039] According to another preferred design of the present invention, method steps b) and c) are performed in the following manner:

[0040] - subdividing the measurement signal into time-continuous time segments smaller than a predetermined time value;

[0041] - determining the interval-specific effective value of the measurement signal for each time period; and

[0042] In order to generate the load-corrected useful signal in each time segment, the useful signal without a DC component is divided by the interval-specific effective value.

[0043] The time value of the time period is determined as a function of the determined drive-side rotational frequency and the time length and / or the number of sampling points of the measured time-dependent measurement signal and is, for example, 0.2 s.

[0044] For the calibration method according to the above and for the evaluation method described, it has proven particularly advantageous to generate a motor current signal as the measurement signal, which is indicative of the motor current of the electric motor of the electric motor-transmission unit.

[0045] If, according to a further development, a brushless DC motor is used as the motor, method step d) can be carried out in a particularly simple manner by:

[0046] - determining the maximum value of the motor current signal and its time value;

[0047] - approximately determining the rotation frequency or brush frequency from the interval of the maximum value of the motor current signal, the number of slots and the number of brushes of the brush DC motor;

[0048] - performing band-pass filtering on the motor current signal within the range of an approximately determined rotation frequency or brush frequency;

[0049] - determining the maximum value from the bandpass filtered motor current signal and its time value; and

[0050] - determining the rotational frequency of the brush DC motor from the intervals of the maximum values ​​of the bandpass filtered motor current signal, the number of slots and the number of brushes. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The present invention will be described in detail below based on embodiments with reference to the accompanying drawings. In the accompanying drawings:

[0052] Figure 1 A schematic diagram showing an example of a system for identifying wear and / or damage of components of a motor-transmission unit;

[0053] Figure 2 Schematic time-current diagrams showing motor current signals of a motor-transmission unit in a new state and a motor-transmission unit with wear;

[0054] Figure 3 Shown according to Figure 2 Schematic diagram of the motor current signal in the frequency range;

[0055] Figure 4 Schematic diagram showing motor current signals with and without a DC component;

[0056] Figure 5 Shown according to Figure 4 Schematic diagram of the motor current signal in the frequency range;

[0057] Figure 6 A time-current or torque diagram is shown with the time profile of the motor current signal, its DC component and the torque;

[0058] Figure 7 shows a time-current diagram with a time-resolved DC-component-free and load-corrected useful signal;

[0059] Figure 8 A diagram showing the time profile of a bandpass filtered motor current signal;

[0060] Figure 9 Shown with Figure 8 Time-frequency diagram of the determined brush frequency and the time profile of the calculated brush frequency based on the measured values;

[0061] Figure 10 shows the measured signal M with correctioncorr A time-current diagram of the time curve of the uncorrected measurement signal M;

[0062] Figure 11 Shown Figure 10 The measurement signal M shown in corr and the spectrum of M;

[0063] Figure 12a shows the corrected measurement signal M of a motor-transmission unit with tooth damage corr and a fragment of the FFT spectrum of the corrected measurement signal of the intact motor-transmission element used as a reference; and

[0064] Figure 12b Shows something like Figure 12a , but without correction of the measured signal. DETAILED DESCRIPTION

[0065] Figure 1 An example of a system or device for detecting wear and / or damage to components of a motor-transmission unit 1 is schematically shown. The motor-transmission unit 1 comprises a motor 1.1 and a transmission 1.2 connected to the motor 1.1 on the output side. The motor 1.1 is preferably an electric motor with a given number of slots and a given number of brushes. The transmission 1.2 has an output shaft 1.20.

[0066] During operation of the motor-transmission unit 1 , in the present case, current measurement is performed by means of a current measuring unit 2 , which supplies a time-resolved motor current signal M of the motor current I supplied to the electric motor 1 . 1 . Motor As the measurement signal M.

[0067] Figure 2 Two examples of the time profile of a time-dependent motor current signal of the motor-transmission unit 1 in different operating states are schematically shown.

[0068] Curve K1 (solid line) shows the motor current signal of the motor-transmission unit 1 in the time domain in a new state, ie, in such a motor-transmission unit 1 , both the motor 1 . 1 and the transmission 1 . 2 are neither damaged nor worn.

[0069] Curve K2 (dashed line) shows the motor current signal in the time domain of a motor / transmission unit 1 whose components, namely the motor 1 . 1 and / or the transmission 1 . 2 , are subject to wear and / or damage.

[0070] The different temporal profiles of the two motor current signals, according to curves K1 and K2, reveal different operating states of the motor / transmission unit 1: namely, an operating state of the motor / transmission unit 1 in a new state and an operating state of the motor / transmission unit 1 exhibiting wear and / or damage. Frequency analysis of these time-dependent motor current signals allows identification of wear- and / or damage-specific features and, therefore, predictive maintenance of the motor / transmission unit 1. However, this presupposes that the values ​​of the frequency analysis are comparable in different operating states of the motor / transmission unit 1, with varying output loads and speeds.

[0071] In order to ensure the comparability of the time-dependent measurement signals in different operating states of the motor-transmission unit 1, the motor current signal M as the time-dependent measurement signal M is subjected to a frequency analysis of the measurement signal Mcorr corrected in this way, for example, by an FFT (Fast Fourier Transformation). Motor Execute the calibration method.

[0072] Here, Figure 1 Basic blocks 3 to 6 are shown as a method for performing a time-dependent measurement of the motor current signal M. Motor The method steps of the correction method of FIG. 3 are described in detail below, wherein the measurement signal M is provided by means of a measuring unit 2 for measuring the motor current I of the electric motor 1 .

[0073] Using the corrected measurement signal M generated according to the method step of block 6 corr is supplied to block 7 for FFT frequency analysis and for generating the spectrum. Figure 3 Such a spectrum is shown by way of example with frequency lines F1 (solid line) and F2 (dashed line), Figure 3 is schematically generated from the motor current signal according to curves K1 and K2 .

[0074] therefore, Figure 3 Five spectral lines f1 to f5 are shown, wherein the frequencies of the spectral lines f1 to f4 are identical for the two motor current signals according to curves K1 and K2 , but have different amplitude characteristics, while the spectral line f5 is assigned to the motor current signal according to curve K2 .

[0075] Each of these spectral lines f1 to f4 can be assigned to a specific mechanical characteristic of the motor-transmission unit 1, where the amplitude value and / or spectral integral represents the operating state. Thus, the F1 spectral lines f1 to f4 indicate the operating state of the motor-transmission unit 1, i.e., that the motor-transmission unit 1 is neither wear-resistant nor damaged. The F2 spectral line f5 indicates damage to the motor-transmission unit 1. For example, f1 can represent the output frequency, f2 can represent the rotational speed of the higher-stage planetary gears, f3 can represent the first-stage planetary gears, f4 can represent the drive frequency, and f5 can represent the fault rollover frequency of the first-stage planetary gears.

[0076] from Figure 3 It can also be seen that the spectrum of the corrected measurement signal Mcorr of the measurement signal according to curve K1 can be compared with the spectrum of the corrected measurement signal according to curve K2, and the current operating state of the motor-transmission unit 1 with respect to wear and damage can be derived from the comparison result. Furthermore, trend curves of wear-specific and / or damage-specific characteristics can also be determined by creating such a spectrum during temporally consecutive operating intervals.

[0077] In the following, according to blocks 3 to 6 (see Figure 1 ) corresponds to the motor current signal M as the measurement signal M Motor The correction method is described below, and then the motor current signal M Motor Provided to block 7 for frequency analysis and creation of spectrum.

[0078] In order to ensure comparability of the frequency spectra of the motor-transmission unit 1 in different operating states, the influence of the changing output load of the motor 1 . 1 and the changing rotational speed of the motor 1 . 1 must be eliminated.

[0079] First, we need to correct the effect of the changing output load on the motor current signal M. Motor impact.

[0080] Due to the fluctuating output load at the motor during the measurement process, the motor current signal M Motor The DC component of Figure 4 Without the correction method according to the invention, the frequency analysis results in Figure 5 The spectrum F2, where the low frequency range is heavily overlapped by the exponentially decreasing signal. For comparison, Figure 5 shows the motor current signal M Motor The spectrum F1 is a spectrum in which the DC component is eliminated, corresponding to the curve K4. In the case of this spectrum F1, the spectral lines are clearly visible, while the spectrum F2 cannot be evaluated in the low-frequency range. Therefore, from the motor current signal M Motor Eliminating the DC component is crucial for FFT analysis.

[0081] Therefore, in accordance with block 3 (see Figure 1 ) in the first method step, the motor current signal M is first determined by the following method Motor The DC component of the motor current signal M is first filtered using a low-pass filter with a cut-off frequency less than 1 Hz. Motor The signal S generated in this way is low-pass filtered. Gleich Corresponding to Figure 6 Curve K5, which approximately corresponds to the motor current signal M Motor The DC component of the motor current signal M Motor For comparison, curve K7 represents the time-resolved output torque of the motor-transmission unit.

[0082] Using the signal S generated in this way gleich , by taking the motor current signal M Motor Subtract the signal S by vector gleich , from the motor current signal M Motor Determine the useful signal N1 without DC component.

[0083] According to the signal S gleich The DC component follows the corresponding Figure 6 The output torque or load torque curve K7 shows the curve trend of the output torque or load torque applied. Due to the changing output load, the motor current signal M Motor The amplitude of the current fluctuations also varies, which is determined by the rotation of the various transmission components, such as according to Figure 1 It can be seen from the curve K3.

[0084] In order to eliminate the motor current signal M Motor These amplitude fluctuations are used to normalize the useful signal N1 without DC component to an effective value (see Figure 1 , block 4).

[0085] To this end, the time-resolved, DC-free useful signal N1 is subdivided into short, continuous time segments with predetermined time values, for example less than 0.2 s, and interval-specific effective values ​​are calculated for these time segments. For this purpose, the signal is divided into individual segments of sufficient length (approximately 0.05 s-0.2 s, fixed but freely selectable values), for example. The smoothing line is adapted to the individual effective values, which also results in a resampling of the number vector of effective values ​​(the same number of samples as the measurement signal). The two number vectors are then divided point by point. Using these interval-specific effective values, each time segment of the DC-free useful signal N1 is divided by the associated interval-specific effective value. The signal amplitude is normalized using the load-corrected useful signal N2 obtained in this way, thereby ensuring that the various motor current signals M Motor comparability.

[0086] according to Figure 7 The time-resolved useful signal N2 shows neither a DC component nor an effective value deviation.

[0087] As mentioned above, in addition to the output load, the drive speed, that is, the rotational speed of the motor 1.1, also affects the motor current signal M Motor signal quality and signal characteristics.

[0088] Therefore, in the next method step, the time curve of the rotational speed of the electric motor 1.1 is determined (see Figure 1 To do this, first the motor current signal M Motor The maximum values ​​and the associated time values ​​are determined. The time difference between these absolute maxima corresponds to the reverse brush frequency in the case of a DC motor. This results in the time points of the local maxima of the time-resolved motor current signal being determined. A frequency value is calculated from the respective reverse time intervals of two consecutive maxima. The approximate brush frequency is obtained from the average value of all these frequency values, provided (as is usually the case) that the brushes cause the maximum values ​​in the time signal. From this approximate brush frequency, the approximate speed can then be determined using the number of brushes and slots. However, this step is not necessary, since the speed normalization of the signal can also be performed using the brush frequency.

[0089] In order to determine the actual speed d or actual rotational frequency f of the motor 1.1, the useful signal N2 (see Figure 7 ) is bandpass filtered. Here, the cutoff frequency is approximately +-15% of the brush frequency. The useful signal N2 after bandpass filtering shows Figure 8 The curve K8 shown. According to the absolute maximum value of the curve K8 (at Figure 8 The actual brush frequency is calculated from the time intervals (circular symbols in the figure). Dividing the number of brushes by the number of slots yields the rotational frequency f or the actual speed d. To do this, a vector of values ​​is generated, consisting of the time intervals of the maximum values. Using an adaptive spline or similar method and resampling to the same number of samples as the measured signal, a function curve is generated, which is used to scale the time axis of the measured signal, in particular, to normalize it. Figure 9 Curve K9 (solid line) shows the temporal profile of the brush frequency calculated from the time intervals of the absolute maximum of curve K8. In contrast, the brush frequency calculated from the measured rotational frequency is shown as curve K10 (dashed line). Both curves K9 and K10 show a high degree of agreement. It should be noted that the rotational frequency can also be determined without a pre-determined brush frequency. To this end, bandpass filtering is performed directly within the range of the previously roughly determined rotational frequency.

[0090] With the determined time-dependent rotation frequency f (see Figure 9 ),Will Figure 7 The time axis normalization or scaling of the load-corrected useful signal N2 shown to the mean rotational frequency is performed in the method step according to block 6 (see Figure 1 ) is performed. Individual periods of the useful signal N2 with a higher frequency are stretched, while periods with a lower rotational frequency are compressed. Using this normalization step or scaling step, a corrected motor current signal, i.e., a corrected measurement signal M, is generated from the load-corrected useful signal N2. corr , the measurement signal M corr Provided according to Figure 1 Block 7 generates a spectrum with the aid of FFT frequency analysis. Figure 10 shows the corrected measurement signal M corr The uncorrected motor current signal M is shown as curve K11 (solid line) and compared thereto. Motor Or curve K12 of the measurement signal M (dashed line).

[0091] As already explained several times, the corrected measurement signal M corr It undergoes FFT frequency analysis and generates an FFT spectrum F3 (see Figure 11 , solid line). In contrast, Figure 11 The FFT spectrum F4 of the uncorrected measurement signal M is shown (dashed line).

[0092] Corrected measurement signal M corr The FFT spectrum F3 shows clearly visible maxima that can be unambiguously assigned to the maximum values ​​of individual transmission and / or motor characteristics and thus serve as a basis for determining damage and wear. These clearly visible maxima, represented as spectral lines, can be clearly distinguished from the noise background. Spectrum F3 shows five spectral lines f1 to f5, which are unambiguously assigned to the following transmission or motor characteristics: the rotational frequency of individual gears, the fault rollover frequency, the input and output rotational frequencies, etc. In other words, each visible spectral line f1 to f5 can be assigned to a distinct motor or transmission component or its behavior.

[0093] If such an FFT spectrum F3 is generated after different operating hours, the respective amplitudes and / or spectral integrals are comparable despite different output loads of transmission 1 . 2 and different rotational speeds of electric machine 1 . 1 of electric machine / transmission unit 1 .

[0094] If it will be based on Figure 11 The FFT spectrum F4 of the uncorrected measurement signal M is the same as the FFT spectrum F4 of the corrected measurement signal M corrComparing the FFT spectra of the transmission 1.2 with the FFT spectra of the motor 1.1 reveals that due to the varying output load of transmission 1.2 and the varying speed of motor 1.1, no clear maximum values ​​can be identified. More precisely, weakly visible features are lost in the background noise. Furthermore, strongly visible features are heavily smeared due to speed fluctuations, making clear frequency assignment impossible and component-specific feature identification impossible.

[0095] Figure 12a The signal of tooth damage on the planetary gears of the transmission 1 . 2 of the motor-transmission unit 1 in the frequency domain is shown as a corrected measurement signal M. corr A fragment of the FFT spectrum F5 of the corrected motor current signal of FIG. The damage-specific features can be identified as the spectral line f6 that appears between line L1 and line L2. For reference, the dashed line F6 shows the corrected signal of an intact motor-transmission unit.

[0096] In contrast, Figure 12b The motor current signal in an uncorrected state according to a previously known method is compared with a reference of an intact motor-transmission unit. Figure 12b The damaged transmission is shown under variable load and speed conditions within the range of the fault rollover frequency of the planetary gear stage. Both the range of this frequency (black dashed line) and the amplitude are strongly smeared, preventing a meaningful comparison. The dotted line represents Figure 11 The uncorrected signal of is used here as a reference. Figure 12a The correction according to the present method is shown.

[0097] With this calibration method according to the invention, not only is the signal-to-noise ratio significantly improved, but the bandwidth over which the wear- and / or damage-specific characteristics extend is also significantly reduced. These two positive properties make the calibration method according to the invention particularly suitable for practical applications in motor-transmission units under diverse environmental requirements.

[0098] In the above embodiment, the measurement signal M is the motor current signal M Motor The curve of the motor current I of the motor 1.1 of the motor-transmission unit 1 is detected (see Figure 1 The measurement signal M can also be generated in another way, for example as an audio signal, by means of a microphone, by means of an acceleration sensor arranged on the motor-transmission unit 1 , a torque sensor, etc.

[0099] The present invention encompasses the possibility of detecting any wear or damage to the motor-transmission unit by evaluating measurement signals, particularly the motor current, for example. This can be used to indicate the remaining possible service life of the motor-transmission unit on a display device, until the motor-transmission unit can still operate largely without any problems. Furthermore, a warning signal can also be output via the display device as soon as specific signs of wear are detected based on the acquired measurement signals.

[0100] The method according to the invention can be used, for example, in actuators of motor vehicles, production machines, robots or the like.

Claims

1. A method for correcting a time-dependent measurement signal (M) generated by an electric machine (1.1) coupled on the output side to a transmission (1.2) for the influence of a variable output load and a variable speed, the method comprising the following method steps: a) acquiring a measurement signal (M) which is dependent on the torque of the motor-transmission unit (1); b) generating a useful signal (N1) without a DC component from the measurement signal (M); c) determining effective values ​​from the measurement signal (M) at intervals; d) generating a load-corrected useful signal (N2) by dividing the useful signal (N1) without a DC component in intervals by an interval-specific effective value; e) determining the rotational frequency (f) of the electric machine (1) from the measurement signal (M) in a time-resolved manner; f) scaling the load-corrected useful signal (N2) to the average rotational frequency to generate a corrected measurement signal (M corr );as well as g) Using the corrected measurement signal for fault detection of the motor-transmission unit.

2. The method according to claim 1, wherein Method step a) is performed by: - determining a DC component of said measurement signal (M); and - Subtracting said DC component from said measurement signal (M).

3. The method according to claim 2, wherein: The measurement signal is low-pass filtered to determine the DC component of the measurement signal.

4. The method according to claim 1, wherein Method steps b) and c) are performed by: - subdividing the measurement signal (M) into time-continuous time segments smaller than a predetermined time value; - determining the interval-specific effective value of the measurement signal (M) for each time period; and In order to generate the load-corrected useful signal (N2) in each time segment, the useful signal (N2) without a DC component is divided by the interval-specific effective value.

5. The method according to claim 1, wherein Generates a motor current signal (M) indicative of a motor current (I) of the motor (1.1) of the motor-transmission unit (1) Motor ) as the time-dependent measurement signal (M).

6. The method according to claim 5, wherein: Method step e) is performed by: - Determine the motor current signal (M Motor ) and its time value; - From the motor current signal (M Motor ) the interval of the maximum value, the number of slots and the number of brushes of the brush DC motor approximately determine the rotation frequency (f0) or the brush frequency; - The motor current signal (M Motor ) bandpass filtering within the range of an approximately determined rotation frequency (f0) or brush frequency; - determining the maximum value from the bandpass filtered motor current signal and its time value; as well as - determining the rotational frequency (f) of the brush DC motor from the intervals of the maximum values ​​of the bandpass filtered motor current signal, the number of slots and the number of brushes.

7. A method for detecting wear and / or damage of a motor-transmission unit (1) comprising an electric motor (1.1) and a transmission (1.2) coupled to the electric motor (1.1) on the output side, the method comprising: - generating a time-dependent measurement signal (M) by means of the motor-transmission unit (1); - Generating a corrected measurement signal (M) according to the method of claim 1 corr ); - from the corrected measurement signal (M corr ) determine the spectrum (F3, F5); - providing a reference spectrum, which is generated by means of an FFT analysis from a corrected measurement signal of a wear-free and / or damage-free electric motor-transmission unit; - The corrected measurement signal (M corr ) is compared with the reference spectrum; as well as - determining wear-indicating and / or damage-indicating features from a comparison of the frequency spectrum (F3, F5) of the corrected measurement signal with the reference frequency spectrum, signaling newly occurring wear or newly occurring damage.

8. The method according to claim 7, wherein: - assigning a component-specific characteristic of the motor-transmission unit to each frequency line of the frequency spectrum generated from the corrected measurement signal by means of an FFT analysis; and To determine the wear-indicative and / or damage-indicative features, the amplitudes and / or spectral integrals of identical frequency lines of the spectrum of the corrected measurement signal and of the spectrum of a reference spectrum are compared.

9. A device for detecting wear and / or damage of an electric motor-transmission unit (1), comprising a processing device, by means of which the method steps according to any one of claims 7 to 8 can be carried out.

Images