A method for diagnosing a planetary gearbox fault based on a circuit resonator

Abstract

A kind of planetary gearbox fault diagnosis method based on circuit resonator belongs to the field of planetary gearbox fault diagnosis. Including the following steps: piezoelectric sheet is connected in parallel with inductor, and an LC resonant circuit is formed. Then the piezoelectric sensor is pasted on the planetary gearbox shell, so that the piezoelectric sheet and the box are coupled as a whole. The time domain voltage signal between the capacitor ends in the resonant circuit when the planetary gearbox is running is collected, and then it is analyzed by resonance demodulation. No need to locate the resonance band through a series of algorithms, because the resonance frequency of the resonant circuit is known. The envelope order spectrum of the resonance band is obtained, and compared with various fault characteristic frequencies, so as to realize fault diagnosis. It can effectively avoid the interference of corresponding running of fixed shaft gear train and other components, and accurately extract the fault characteristics of planetary gear train.

Description

Technical Field

[0001] This invention belongs to the field of planetary gearbox fault diagnosis, specifically relating to a planetary gearbox fault diagnosis method based on a circuit resonator. Background Technology

[0002] Planetary gearboxes are core components of many rotating machines, widely used in wind turbines, aero engines, and construction machinery. Planetary gearboxes often operate under high loads, fluctuating speeds, and poor lubrication conditions, factors that can lead to tooth cracks, breakage, and other failures. Numerous facts demonstrate that if gear failures are not diagnosed promptly, they can cause serious consequences and significant economic losses. Therefore, condition monitoring and fault diagnosis of gearboxes provide crucial information for equipment operation and maintenance, playing a vital role in preventing serious failures and minimizing economic losses.

[0003] Vibration signal-based fault detection methods are characterized by high sensitivity, low cost, and the ability to perform online monitoring, making them a research hotspot in the field of rotating machinery fault diagnosis. Spectral analysis of the vibration signals from planetary gearboxes is a commonly used method. The unique structure of planetary gear systems determines their distinctive and complex spectral structure. The vibration signal of a healthy planetary gearbox not only contains the meshing frequency and its higher harmonics, but also sidebands on both sides of each meshing frequency. In the case of sequential meshing, the sidebands on both sides of the meshing frequency exhibit asymmetry. Under fault conditions, the distribution of the modulation sidebands becomes even more complex.

[0004] In a planetary gearbox, the planetary gear train operates at low speeds, resulting in weaker vibration signals; conversely, the fixed-axis gear train operates at high speeds, exhibiting stronger vibration signals. Furthermore, the meshing frequency of the fixed-axis gear train may be close to the higher harmonic frequencies of the planetary gear train's meshing frequency. These factors often cause the meshing information of the planetary gear train to be submerged in the vibration response and background noise of the fixed-axis gear train, making fault feature extraction from the planetary gear train difficult. Summary of the Invention

[0005] In view of the above problems, the purpose of this invention is to provide a fault diagnosis method for planetary gearboxes based on circuit resonators. By directly analyzing the resonance response information of the planetary gear system and avoiding interference from the fixed-axis gear system, the method highlights various characteristic frequencies of the planetary gear system, obtains the envelope order spectrum of the resonance band, and compares it with various fault characteristic frequencies, thereby achieving fault diagnosis.

[0006] A fault diagnosis method for planetary gearboxes based on circuit resonators includes the following steps:

[0007] 1) Design an LC resonant circuit and a reasonable resonant frequency;

[0008] 2) Attach the piezoelectric element to the planetary gearbox housing and collect the time-domain voltage signal across the capacitor in the resonant circuit when the planetary gearbox is running;

[0009] 3) Map the time-domain voltage signal to the frequency domain, and filter the frequency-domain signal with the resonant frequency as the center to obtain the envelope order spectrum of the filtering result;

[0010] 4) Calculate various fault characteristic frequencies based on the geometric parameters of the planetary gear system, and compare them with the envelope order spectrum obtained in step 3) to achieve fault diagnosis.

[0011] In step 1), the response model of the LC resonant circuit is:

[0012]

[0013] Where I(t) is the current generated by the piezoelectric element, which is equivalent to the current input of the resonant circuit; u(t) is the voltage output across the capacitor; L is the inductance value; and C is the capacitance value. The pulse excitation for the circuit;

[0014] Resonant frequency:

[0015] In step 2), the piezoelectric element is bonded to the planetary gearbox housing, and the strain of the housing is the strain of the piezoelectric element. During gearbox operation, the vibration of the housing is transmitted to the piezoelectric element, causing it to continuously deform and thus output current. The impact excitation in the planetary gearbox causes a pulse response in the strain at the piezoelectric element, which in turn causes a pulse response in the current output by the strain gauge. The current pulse and its derivative correspond to broadband excitation in the frequency domain. By setting a reasonable resonant frequency, the bandwidth of the circuit pulse excitation covers the resonant frequency, thereby exciting the circuit resonance.

[0016] The current generated by the piezoelectric sensor can be regarded as the input of the LC resonant circuit, and the data acquisition card receives the voltage output across the inductor in the resonant circuit.

[0017] The frequency of gear meshing excitation is consistent with the frequency of the current signal generated by the piezoelectric element.

[0018] The meshing impact excitation and the fault impact excitation caused by local faults in the planetary gearbox correspond to narrow pulses in the time domain. These impact excitations cause the strain at the piezoelectric element to have a pulse response, thereby causing the current I(t) output by the strain gauge to have a pulse response.

[0019] The current pulse and its derivative correspond to broadband excitation in the frequency domain. By setting a reasonable resonant frequency, the circuit can be pulse-excited. The bandwidth covers the resonant frequency, thereby exciting the circuit to resonate.

[0020] In step 3), the frequency domain signal is filtered, and the occurrence frequencies of meshing impact excitation and fault impact excitation in the gearbox are modulated into the resonant frequency band of the voltage signal; the resonant band centered on the circuit resonant frequency is envelope demodulated to directly extract the fault characteristic frequency.

[0021] In step 4), various fault characteristic frequencies are calculated based on the geometric parameters of the planetary gear system, the resonance band centered on the circuit resonant frequency is obtained, and the envelope order spectrum of the time-domain signal corresponding to this resonance band is obtained, thereby extracting the meshing frequency and fault characteristic frequency of the gearbox.

[0022] The technical effects achieved by this invention are:

[0023] 1. This invention utilizes a piezoelectric sensor to convert the vibration signal of the gearbox into an electrical signal, and designs a resonant circuit so that the current output by the piezoelectric element excites the circuit to resonate, thereby modulating the fault characteristic frequency of the planetary gearbox into the resonant band of the circuit.

[0024] 2. This invention allows for customizing the resonant frequency by adjusting the parameters of the resonant circuit, thus avoiding the resonant band search step in traditional resonant demodulation methods and improving the accuracy and efficiency of fault feature extraction. This invention can accurately identify local faults in planetary gearboxes under strong noise interference. Attached Figure Description

[0025] Figure 1 This is a system framework diagram of the present invention.

[0026] Figure 2 This is a schematic diagram of the experimental platform.

[0027] Figure 3 This is a resonant circuit composed of a piezoelectric sensor and an inductor.

[0028] Figure 4 This is the equivalent structure diagram of the resonant circuit.

[0029] Figure 5 This refers to the acquired time-domain voltage signal. Figure 5 In the graph, the horizontal axis represents time, and the vertical axis represents pressure.

[0030] Figure 6 This refers to the frequency domain of the voltage signal. Figure 6 In the diagram, the horizontal axis represents frequency, and the vertical axis represents amplitude.

[0031] Figure 7 This is the filtered voltage signal. Figure 7 In the graph, the horizontal axis represents time, and the vertical axis represents pressure.

[0032] Figure 8This represents the envelope order spectrum of the circuit's resonant frequency band. Figure 8 In the diagram, the horizontal axis represents the carrier order, and the vertical axis represents the amplitude. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the following embodiments will be used in conjunction with the accompanying drawings to further illustrate the invention. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0034] This invention proposes a planetary gearbox fault diagnosis method based on resonance demodulation. Figure 1 This is a system framework diagram of the present invention. Embodiments of the present invention include the following steps:

[0035] 1) Design a resonant circuit and install a piezoelectric sensor on the planetary gearbox housing. Specifically, design an LC resonant circuit, which includes a piezoelectric sensor and an inductor, connecting the piezoelectric element and the inductor in parallel. Install the piezoelectric sensor on the planetary gearbox housing, coupling the piezoelectric element and the housing as a whole, enabling it to sense the vibration of the gearbox during operation. Collect the voltage signal output by the resonant circuit during the operation of the planetary gearbox. The response model of the LC resonant circuit is as follows:

[0036]

[0037] Where I(t) is the current generated by the piezoelectric element, which is equivalent to the current input of the resonant circuit; u(t) is the voltage output across the capacitor; L is the inductance value; and C is the capacitance value of the piezoelectric element. This is the pulse excitation for the circuit.

[0038] Resonant frequency:

[0039] The piezoelectric element is bonded to the planetary gearbox housing, and the strain of the housing corresponds to the strain of the piezoelectric element. During gearbox operation, the vibration of the housing is transmitted to the piezoelectric element, causing it to continuously deform and thus output current. The current generated by the piezoelectric sensor can be considered as the input of an LC resonant circuit, and the data acquisition card receives the voltage output across the inductor in the resonant circuit.

[0040] 2) Acquire the voltage signal output by the resonant circuit during the operation of the planetary gearbox; during the operation of the planetary gearbox, acquire the time-domain voltage signal across the capacitor in the resonant circuit, and then perform resonance demodulation analysis. A data acquisition card can be used to record the output voltage signal of the resonant circuit. These signals reflect the vibration of the planetary gearbox during operation. The frequency of the gear meshing excitation is consistent with the frequency of the current signal generated by the piezoelectric element. The meshing impact excitation and the fault impact excitation caused by local faults in the planetary gearbox correspond to narrow pulses in the time domain. These impact excitations cause a pulse response in the strain at the piezoelectric element, thus causing a pulse response in the current I(t) output by the strain gauge. The current pulse and its derivative correspond to a wideband excitation in the frequency domain. Setting a reasonable resonant frequency allows for pulse excitation of the circuit. The bandwidth covers the resonant frequency, thereby exciting the circuit to resonate.

[0041] 3) Fourier Transform: The acquired time-domain voltage signal is subjected to a Fourier transform, converting it from the time domain to the frequency domain, which is used to identify different frequency components in the signal. The average amplitude of the normalized spectrum is subtracted to reduce the influence of noise and make the main frequency components more prominent.

[0042] 4) Perform bandpass filtering on the frequency domain signal, centered on the resonant frequency. Determine the resonant frequency of the circuit (determined by the inductance and capacitance values), and perform bandpass filtering on the frequency domain signal based on this frequency to obtain the filtered portion containing the circuit's resonant response. The purpose of filtering is to remove irrelevant noise and interference, retaining only the signal within the frequency range relevant to the gearbox fault characteristics. This portion of the signal is closely related to the fault characteristics of the planetary gearbox.

[0043] 5) Obtain the envelope order spectrum of the filtered result; further process the filtered signal to obtain its envelope order spectrum. This step can help identify and extract the characteristic frequencies of various components in the planetary gearbox.

[0044] A Hilbert transform is performed on the filtered time-domain data to extract the signal envelope. Based on the rotational speed data collected by the photoelectric sensor, the rotational frequency of the planetary gear carrier is determined, and the time-domain envelope is resampled accordingly. The resampled data is then transformed again (e.g., by Fourier transform) to obtain the envelope order spectrum. The envelope order spectrum can more clearly display the characteristic frequencies of various components in the planetary gearbox, which helps in the identification and diagnosis of faults.

[0045] 6) Compare the obtained envelope order spectrum with the known fault characteristic frequencies of the planetary gearbox to achieve fault diagnosis. Analyze the comparison to identify abnormal frequency components, thereby determining whether a fault exists in the planetary gearbox and the specific location of the fault.

[0046] This invention utilizes the sensitivity of a circuit resonator to a specific frequency, combined with signal processing technology, to achieve effective diagnosis of planetary gearbox faults.

[0047] Figure 2 A schematic diagram of an experimental platform is provided. This platform is used to collect and analyze the output voltage data of the resonant circuit of a planetary gearbox under different health conditions. The experimental platform includes a computer, a data acquisition card, a resonant circuit, a piezoelectric sensor, a planetary gearbox, a parallel gearbox, a bevel gearbox, a drive motor, and a magnetic powder brake. The piezoelectric sensor is mounted on the outer shell of the planetary gearbox to capture vibration signals. Figure 2 Experiments were conducted on the experimental platform shown to obtain the resonant circuit output voltage data of the planetary gearbox under different health conditions.

[0048] The acquired signal is subjected to FFT transformation, and the average amplitude of the normalized spectrum is subtracted from the spectral value to reduce the influence of noise and highlight the main frequency.

[0049] By performing bandwidth filtering centered on the circuit's resonant frequency, the portion containing the circuit's resonant response is obtained.

[0050] Resonant frequency: Where L is the inductance value and C is the capacitance value.

[0051] A Hilbert transform is performed on the filtered time-domain data to obtain its envelope. Then, based on the rotational speed data collected by the photoelectric sensor, the planetary carrier rotation frequency is calculated. Based on this, the time-domain envelope is resampled, and an FFT transform is performed on the resampled data to obtain the envelope order spectrum.

[0052] In the experiment, the piezoelectric sensor was attached to the planetary gearbox housing, and an inductor was connected in parallel with the piezoelectric sensor to form a resonant circuit, such as... Figure 3 As shown.

[0053] The equivalent structure of a resonant circuit is as follows: Figure 4 As shown. When a piezoelectric sensor is subjected to strain, it generates current, which is equivalent to a current source; the piezoelectric element itself has an internal capacitance, which is connected in parallel with an inductor, and the output signal of the circuit is the voltage across the inductor.

[0054] Before conducting the experiment, the inductance L and the capacitance C of the piezoelectric element were measured, and the formula was used to... Calculate the resonant frequency of the circuit. In this embodiment, f n =7440.6Hz.

[0055] The assembly gear parameters of the planetary gearbox in the experiment are shown in Table 1:

[0056] Table 1. Gear Assembly Parameters for Planetary Gearbox

[0057] Gear parameters numerical values Number of teeth on the gear ring 86 Number of teeth of the sun gear 40 Number of teeth on planetary gears 23 Number of planetary gears 3

[0058] The experimental results were obtained by resampling the planetary carrier frequency and obtaining the envelope order spectrum. The characteristic orders of each component are shown in the table below:

[0059] Table 2 Characteristic frequencies of planetary gearboxes

[0060]

[0061] The experimental signal analysis is as follows:

[0062] Voltage data was collected under planetary gear tooth breakage fault conditions. The signal sampling rate was 51.2KHz, and the motor output frequency was set to 30Hz. In actual operation, the speed may fluctuate slightly.

[0063] Figure 5 The acquired time-domain voltage signal is shown; the waveform of the raw voltage signal acquired from the planetary gearbox in the time domain is displayed. The signal reflects the vibration generated by the planetary gearbox during operation.

[0064] Figure 6 The voltage signal is in the frequency domain; the time-domain signal is converted into a frequency-domain signal through Fourier transform in order to analyze the different frequency components in the signal.

[0065] Figure 7 This is the filtered voltage signal; it shows the voltage signal after bandwidth filtering. The purpose of filtering is to remove noise and other interference signals while retaining frequency components relevant to the fault characteristics of the planetary gearbox.

[0066] Figure 8 This is the envelope order spectrum of the circuit's resonant frequency band. It displays the envelope order spectrum of the processed signal within the circuit's resonant frequency band. The envelope order spectrum allows for a clearer identification of the fault characteristic frequencies of various components in the planetary gearbox.

[0067] Figures 5-8 This refers to the entire process from raw signal acquisition to signal processing and analysis. Figure 5 Acquire time-domain voltage signals, in Figure 6 The resonant frequency band of the circuit can be observed and extracted, and the time-domain waveform is as follows. Figure 7 As shown, a clear impulse response can be observed. Figure 8 The failure frequency and harmonics of the planetary gears can be observed, thereby determining the health status of the planetary gearbox.

[0068] This invention eliminates the need for a series of algorithms to locate the resonance band, as the resonance frequency of the resonant circuit is known. It obtains the envelope order spectrum of the resonance band and compares it with various fault characteristic frequencies, thereby achieving fault diagnosis. This invention effectively avoids interference from the operation of fixed-axis gear trains and other components, accurately extracting fault characteristics of planetary gear trains.

[0069] The above embodiments are merely preferred embodiments of the present invention and should not be considered as limiting the scope of the present invention. All equivalent variations and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A fault diagnosis method for planetary gearboxes based on circuit resonators, characterized in that... Includes the following steps: 1) Design an LC resonant circuit and a reasonable resonant frequency; The response model of the LC resonant circuit is as follows: Where I(t) is the current generated by the piezoelectric element, which is equivalent to the current input of the resonant circuit; u(t) is the voltage output across the capacitor; L is the inductance value; and C is the capacitance value. The pulse excitation for the circuit; Resonant frequency of the circuit 2) Attach the piezoelectric element to the planetary gearbox housing and collect the time-domain voltage signal across the capacitor in the resonant circuit when the planetary gearbox is running; The acquisition card collects the time-domain voltage signal across the capacitor in the resonant circuit when the planetary gearbox is running. The current generated by the piezoelectric sensor is regarded as the input of the LC resonant circuit, and the acquisition card receives the voltage output across the inductor in the resonant circuit. The frequency of gear meshing excitation is consistent with the frequency of the current signal generated by the piezoelectric element; The meshing impact excitation and the fault impact excitation caused by local faults in the planetary gearbox correspond to narrow pulses in the time domain. These impact excitations cause the strain at the piezoelectric element to have a pulse response, which in turn causes the current I(t) output by the strain gauge to have a pulse response. The current pulse and its derivative correspond to broadband excitation in the frequency domain. By setting a reasonable resonant frequency, the pulse excitation of the circuit can be achieved. The bandwidth covers the resonant frequency, thereby exciting the circuit to resonate; 3) Map the time-domain voltage signal to the frequency domain, and filter the frequency-domain signal with the resonant frequency as the center to obtain the envelope order spectrum of the filtering result; The frequency domain signal is filtered, and the frequencies of meshing impact excitation and fault impact excitation in the gearbox are modulated into the resonant frequency band of the voltage signal; the resonant band centered on the circuit resonant frequency is envelope demodulated to directly extract the fault characteristic frequency. 4) Calculate various fault characteristic frequencies based on the geometric parameters of the planetary gear system, and compare them with the envelope order spectrum obtained in step 3) to achieve fault diagnosis. The process involves calculating various fault characteristic frequencies based on the geometric parameters of the planetary gear system, obtaining the resonance band centered on the circuit resonant frequency, and obtaining the envelope order spectrum of the time-domain signal corresponding to this resonance band, thereby extracting the gearbox's meshing frequency and fault characteristic frequency.

2. The planetary gearbox fault diagnosis method based on a circuit resonator as described in claim 1, characterized in that... In step 2), the piezoelectric sheet is bonded to the planetary gearbox housing, and the strain of the housing is the strain of the piezoelectric sheet. During the operation of the gearbox, the vibration of the housing is transmitted to the piezoelectric sheet, causing the piezoelectric sheet to deform continuously, thereby outputting current. The impact excitation in the planetary gearbox causes the strain at the piezoelectric sheet to have a pulse response, thereby causing the current output by the strain gauge to have a pulse response.

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