Rotor bar fault detection system and method based on asymmetric dual-frequency eddy current array

Abstract

This invention belongs to the field of rotor fault classification and assessment technology, specifically involving a rotor guide bar fault detection system and method based on an asymmetric dual-frequency eddy current array. The inner layer excitation coil of the probe corresponds to the distribution of the guide bars, while the outer layer receiving coil has a higher density and covers the guide bars and gap areas, adapting to the rotor's curved surface. A dual-frequency excitation module applies low-frequency and high-frequency signals in a time-division manner, forming a gradient eddy current field inside the rotor. An angle synchronization drive module achieves precise synchronization between the response signal and the rotor position. A signal conditioning and acquisition module performs lift-off compensation and phase correction. A feature identification and processing module extracts the dual-frequency amplitude ratio, phase difference, and impedance change values, and identifies the fault type, location, and severity based on a multi-dimensional feature threshold matrix. This invention uses an asymmetric array structure to eliminate blind spots in guide bar gap detection and distinguishes between surface and internal defects through a dual-frequency collaborative mechanism. It can adapt to rotor rotation conditions, and the detection results are less affected by mechanical vibration and lift-off fluctuations.

Description

Technical Field

[0001] This invention belongs to the field of rotor fault classification and assessment technology, specifically relating to a rotor bar fault detection system and method based on an asymmetric dual-frequency eddy current array. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the manufacturing quality and operational reliability of drive motors, as core power components, have attracted much attention. Motor rotor bars are typically formed using die-casting, which can easily lead to defects such as broken bars, thin bars, porosity, and looseness during actual production, severely affecting motor efficiency and lifespan. Eddy current testing technology, due to its advantages of non-contact operation, high sensitivity, and fast response, is widely used in the field of defect detection in metal components. Existing research has seen scholars apply arrayed eddy current probes to defect detection in planar or simple curved structures such as pipes and plates. By designing flexible probes adapted to curved structures, and combining finite element simulation analysis, the impact of defects on coil impedance has been studied. Other researchers have introduced deep learning-assisted recognition methods, constructing feature extraction networks to achieve automatic defect classification, significantly improving detection accuracy.

[0003] However, existing eddy current testing technologies still have significant limitations when applied to fault detection of motor rotor bars. First, traditional array eddy current probes often employ symmetrical coil arrangements, such as matrix or linear arrangements, primarily suitable for continuous surface structures. In contrast, motor rotor bars are distributed in a circumferential arc-shaped pattern, with bars and gaps alternating. Traditional probes struggle to achieve full coverage detection of both the bar body and the gap area, resulting in blind spots. Second, existing excitation modes are mostly single-frequency excitation or simple multi-frequency superposition, only optimizing detection sensitivity for defects of a single depth. They cannot effectively distinguish between surface defects such as cracks and fractures on the rotor bar surface and deep defects such as internal porosity and air bubbles. Furthermore, while deep learning-based recognition methods offer high accuracy, they suffer from high model complexity, stringent hardware requirements, and reliance on a large number of labeled samples. This leads to poor robustness in dynamic industrial testing scenarios, making it difficult to effectively address interference factors such as phase shifts caused by rotor rotation and lift-off fluctuations due to mechanical errors. Summary of the Invention

[0004] The purpose of this invention is to provide a rotor bar fault detection system and method based on an asymmetric dual-frequency eddy current array to solve the problems mentioned in the background art.

[0005] The present invention achieves the above objectives through the following technical solutions:

[0006] This invention proposes a rotor bar fault detection system based on an asymmetric dual-frequency eddy current array, applicable to motor rotors with multiple bars and bar gaps, including:

[0007] An asymmetric double-layer eddy current array probe includes an inner ring excitation coil array and an outer ring receiving coil array; the arrangement of the inner ring excitation coil array corresponds to the distribution of the guide bars; the arrangement density of the outer ring receiving coil array is greater than that of the inner ring excitation coil array, and its detection area covers the guide bars and the gaps between the guide bars; the probe has an arc-shaped structure adapted to the rotor surface;

[0008] The dual-frequency excitation module is used to apply low-frequency and high-frequency excitation signals to the inner ring excitation coil array in a time-division manner to form eddy current fields of different depths inside the rotor bars.

[0009] The rotation angle synchronization drive module is used to drive the rotor to rotate at a constant speed and to collect the rotor rotation angle signal in real time to generate a synchronization trigger signal.

[0010] The signal conditioning and acquisition module is used to synchronously acquire the response signal of the outer receiving coil according to the synchronous trigger signal, and to perform signal compensation and correction.

[0011] The feature recognition and processing module is used to extract feature parameters of low-frequency and high-frequency response signals, and identify the type, location and severity of rotor bar faults based on preset fault judgment criteria.

[0012] As a further preferred embodiment, the outer ring receiving coil array has more coils than the inner ring excitation coil array, and each receiving coil is arranged circumferentially in the gap area between adjacent inner ring excitation coils.

[0013] As a further preferred embodiment, the dual-frequency excitation module outputs low-frequency and high-frequency excitation signals using a time-division multiplexing mode. The low-frequency excitation signal is used to detect surface cracks and fracture defects in the guide bar, while the high-frequency excitation signal is used to detect internal porosity, air holes, and inclusion defects in the guide bar. The switching cycle of the dual-frequency excitation module is less than the rotor rotation cycle, so that the same detection position can obtain response signals under low-frequency and high-frequency excitation in a single scan cycle.

[0014] As a further preferred embodiment, the dual-frequency excitation module uses a DDS signal generator, with a low-frequency detection signal band of 100kHz–500kHz and a high-frequency detection signal band of 2MHz–5MHz.

[0015] As a further preferred embodiment, the asymmetric double-layer eddy current array probe is encapsulated with an elastic substrate and has an elastic support structure, which is used to adaptively adjust the fit between the probe and the rotor surface during rotor rotation and suppress lift-off distance fluctuations.

[0016] As a further preferred embodiment, the signal conditioning and acquisition module includes a lift-off effect compensation unit and a phase correction unit;

[0017] The lift-off effect compensation unit compensates for the amplitude of the response signal based on a preset compensation coefficient and the actual lift-off deviation, as shown in the following formula:

[0018]

[0019] In the formula, U comp The compensated signal amplitude; U meas This represents the actual measured signal amplitude. α Δ is the compensation coefficient; h This represents the difference between the actual lift-off and the benchmark lift-off.

[0020] The phase correction unit establishes a mapping relationship between phase offset and rotational speed based on the rotor angle signal, and corrects the signal phase offset caused by rotor rotation, as shown in the following formula:

[0021]

[0022] In the formula, This is the phase offset. oh This refers to the actual rotational speed of the rotor. k This is the proportionality coefficient; b This is the initial phase offset.

[0023] As a further preferred embodiment, the feature parameters extracted by the feature identification processing module include the dual-frequency amplitude ratio. K With dual-frequency phase difference Δ i ,in:

[0024] The dual-frequency amplitude ratio K It is the ratio of the amplitude change of the response signal in the high-frequency band to that in the low-frequency band.

[0025] The dual-frequency phase difference Δ i This represents the difference in phase offset between the high-frequency and low-frequency response signals.

[0026] The feature recognition and processing module also extracts the impedance change value Δ. Z The severity of the fault is quantified based on the magnitude of the impedance change; the impedance change is determined by the change in resistance Δ of the receiving coil. R With the change in inductive resistance Δ X The calculation yields the following formula:

[0027] .

[0028] As a further preferred embodiment, the preset fault discrimination criterion is a multi-dimensional feature threshold matrix, which includes feature threshold ranges for different fault types and different severity levels; the fault diagnosis module determines the fault based on the dual-frequency amplitude ratio. KWith dual-frequency phase difference Δ i Determine the fault type and based on the impedance change value Δ Z The severity level of the fault is determined by comparing the result with the preset grading threshold.

[0029] The fault types include surface defects, internal defects, and mixed defects; the discrimination criterion for surface defects is the dual-frequency amplitude ratio. K Less than the first threshold and the dual-frequency phase difference Δ i The absolute value is greater than the second threshold; the discrimination condition corresponding to the internal defect is the dual-frequency amplitude ratio. K Greater than the third threshold and the dual-frequency phase difference Δ i The absolute value is less than the fourth threshold; the discrimination condition corresponding to the mixed defect is the dual-frequency amplitude ratio. K It lies between the first threshold and the third threshold.

[0030] This invention also proposes a rotor guide bar fault detection method based on an asymmetric dual-frequency eddy current array, applied to the aforementioned rotor guide bar fault detection system based on an asymmetric dual-frequency eddy current array, comprising the following steps:

[0031] S1: The asymmetric double-layer eddy current array probe is attached to the cylindrical curved surface of the rotor, so that the arrangement of the inner ring excitation coil array corresponds to the distribution of the rotor guide bars, and the detection area of ​​the outer ring receiving coil array covers the guide bars and the gaps between the guide bars.

[0032] S2: Low-frequency and high-frequency excitation signals are applied to the inner ring excitation coil array in a time-division manner through the dual-frequency excitation module, forming gradient eddy current fields of different depths inside the rotor guide bars;

[0033] S3: Drives the rotor to rotate at a constant speed through the rotation angle synchronous drive module, and collects the rotor rotation angle signal in real time and generates a synchronous trigger signal;

[0034] S4: Based on the synchronous trigger signal, the response signal of the outer receiving coil under the excitation of the low-frequency band and the high-frequency band is synchronously acquired through the signal conditioning and acquisition module, and signal compensation and correction are performed.

[0035] S5: The feature recognition processing module extracts the feature parameters of the low-frequency and high-frequency response signals, and identifies the fault type, location and severity of the rotor bar based on the preset fault judgment criteria.

[0036] The beneficial effects of this invention are as follows:

[0037] (1) The probe adopts an inner and outer double-layer asymmetric design. The inner ring excitation coil corresponds one-to-one with the rotor guide bar, and the outer ring receiving coil is staggered and has a higher density, which can cover the gap area between the guide bars. This solves the problem of the detection blind zone in the gap of the guide bar of the traditional symmetrical probe and improves the detection capability of small defects in the gap area.

[0038] (2) The excitation method of time-division switching between low frequency and high frequency is adopted. The low frequency signal is used to detect cracks and fractures on the surface of the guide bar, and the high frequency signal is used to detect porosity and air holes inside the guide bar. This realizes the distinction and identification of surface and internal defects and overcomes the limitation that single frequency excitation can only detect defects of a single depth.

[0039] (3) The probe adopts an elastic packaging structure, which can adaptively fit the rotor surface, reducing the lift-off fluctuations caused by mechanical vibration and installation errors; at the same time, it combines the rotation angle signal to correct the phase shift caused by rotation in real time, reducing the interference of rotor dynamic conditions on the detection results and improving the stability and repeatability of the detection data.

[0040] (4) By extracting the amplitude ratio, phase difference and impedance change values ​​of the dual frequency, and comparing them with the characteristic threshold matrix calibrated in the experiment, fault judgment is made. It does not require a large number of samples to train the deep learning model. It has low computational cost and simple deployment. It has good practicality and scalability in industrial field environment. Attached Figure Description

[0041] Figure 1 This is a system block diagram of the rotor bar fault detection system of the present invention;

[0042] Figure 2 This is a schematic diagram of the asymmetric double-layer eddy current array probe structure of the present invention;

[0043] Figure 3 This is a timing diagram of the dual-frequency cooperative excitation signal of the present invention;

[0044] Figure 4 This is a schematic diagram of the signal transmission of the laser positioning sensor of the present invention. Detailed Implementation

[0045] The following description provides specific application scenarios and requirements for this specification, intended to enable those skilled in the art to make and use the contents of this specification. Various partial modifications to the disclosed embodiments will be apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments and applications without departing from the spirit and scope of this specification. Therefore, this specification is not limited to the embodiments shown, but rather to the widest scope consistent with the claims.

[0046] The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not restrictive. For example, unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the” used herein may also include the plural forms. When used in this specification, the terms “comprising,” “including,” and / or “containing” mean that the associated integers, steps, operations, elements, and / or components are present, but do not exclude the presence of one or more other features, integers, steps, operations, elements, components, and / or groups, or that other features, integers, steps, operations, elements, components, and / or groups may be added to the system / method.

[0047] Considering the following description, these and other features of this specification, as well as the operation and function of the related components of the structure, and the economy of assembly and manufacture of the parts, can be significantly improved. All of these form part of this specification with reference to the accompanying drawings. However, it should be clearly understood that the drawings are for illustrative and descriptive purposes only and are not intended to limit the scope of this specification. It should also be understood that the drawings are not drawn to scale.

[0048] The flowcharts used in this specification illustrate operations implemented according to some embodiments of this specification. It should be clearly understood that the operations in the flowcharts may not be implemented in a sequential order. Instead, the operations may be implemented in reverse order or simultaneously. Furthermore, one or more additional operations may be added to the flowcharts. One or more operations may be removed from the flowcharts.

[0049] Example 1

[0050] like Figure 1 As shown, the rotor guide bar fault detection system based on an asymmetric dual-frequency eddy current array of the present invention is applied to a motor rotor with multiple guide bars and guide bar gaps. It mainly includes an asymmetric dual-layer eddy current array probe, a dual-frequency excitation module, a rotation angle synchronous drive module, a signal conditioning and acquisition module, and a feature identification and processing module. The structure, connection relationships, and functions of each component are described in detail below with reference to the accompanying drawings.

[0051] I. Asymmetric Double-Layer Eddy Current Array Probe

[0052] like Figure 1 and Figure 2 As shown, the asymmetric dual-layer eddy current array probe includes an inner ring excitation coil array and an outer ring receiving coil array. (From the attached...) Figure 2As can be seen, the probe adopts a double-layer annular asymmetric structure. The inner ring excitation coil array is equidistantly arranged along the rotor circumference, and its number is consistent with the number of rotor bars, ensuring that each bar corresponds to one excitation coil, so that the excitation magnetic field can accurately act on the surface of each bar. The outer ring receiving coil array has a higher density than the inner ring excitation coil array. In this embodiment, the number of outer ring receiving coils is 1.5 times the number of inner ring excitation coils, and each receiving coil is staggered along the circumference and directly above the gap area between adjacent inner ring excitation coils, with the coil spacing being half the bar spacing. The probe as a whole is encapsulated with a flexible substrate, prefabricated into an arc-shaped structure consistent with the rotor curvature, and equipped with an elastic support structure. This embodiment is specifically adapted to cast copper rotors with 24 bars. During installation, the elastic probe structure ensures that the eddy current probe fits tightly against the rotor's arc-shaped surface, making it suitable for rotor cylindrical curved surface structures.

[0053] The advantage of this asymmetric double-layer arrangement design is that the inner ring excitation coil corresponds one-to-one with the guide bar, ensuring effective coverage of the excitation magnetic field in the guide bar area; the outer ring receiving coil has a higher density and is staggered, so that its detection area not only covers the guide bar body, but also covers the gap area between the guide bars, thereby eliminating the detection blind zone that exists in the gap between the guide bars in traditional symmetrical probes.

[0054] II. Dual-frequency excitation module

[0055] The dual-frequency excitation module is electrically connected to the inner excitation coil array and is used to apply low-frequency and high-frequency excitation signals to the inner excitation coil array in a time-division multiplexing manner. In this embodiment, the dual-frequency excitation module uses a DDS (Direct Digital Synthesis) signal generator, with the low-frequency detection signal bandwidth set to 300kHz, the high-frequency detection signal bandwidth set to 3MHz, and the excitation signal amplitude set to 5Vpp. The dual-frequency signals are output in time-division multiplexing mode, amplified by a power amplifier, and then input to the inner excitation coil group. The timing diagram of the dual-frequency coordinated excitation signal is shown below. Figure 3 As shown. The dual-frequency signal switching period is set to 1ms, which is one-tenth of the rotor rotation period, ensuring that the response signals under low-frequency and high-frequency excitation can be obtained sequentially at the same detection position within a single scan cycle.

[0056] The mechanism of dual-frequency time-division multiplexing excitation is as follows: low-frequency signals (100kHz~500kHz) have a shallow skin depth and mainly act on the surface of the conductor bar, making them sensitive to surface defects such as surface cracks and fractures; high-frequency signals (2MHz~5MHz) have strong penetrating power and can reach the interior of the conductor bar, making them sensitive to internal defects such as porosity and air bubbles. In this embodiment, 300kHz and 3MHz are selected as typical low-frequency and high-frequency operating frequencies, respectively, which can cover the detection requirements of most cast copper rotor conductor bars. By applying excitation signals of two frequencies in a time-division manner, two sets of response signals carrying defect information of different depths can be obtained at the same detection location, providing a data basis for subsequent differentiation between surface and internal defects.

[0057] III. Angle Synchronization Drive Module

[0058] The rotation angle synchronization drive module includes a servo motor and a laser positioning sensor. The servo motor drives the rotor to rotate at a constant speed within the range of 800~1600 r / min; in this embodiment, the servo motor drives the rotor to rotate at a constant speed of 1200 r / min. The laser positioning sensor is installed next to the elastic support of the asymmetric annular eddy current array probe (close to the probe body), and its detection end is precisely aligned with the positioning mark on the side of the rotor (the arc-shaped outer surface where the guide bar is located), used to collect the rotor rotation angle signal in real time and generate a synchronization trigger signal. In this embodiment, the sampling frequency of the laser positioning sensor is set to 10kHz, which can meet the precise positioning requirements under high-speed rotation. The sampling rate of the high-speed data acquisition card is set to 1MHz, synchronously acquiring the response signal characteristic values ​​of all outer ring receiving coils, including the amplitude change Δ. U Phase offset and impedance change value Δ Z After data acquisition, the data is transmitted to the signal processing unit. The signal transmission process between the laser positioning sensor and other modules is as follows: Figure 4 As shown.

[0059] The function of the rotational synchronization mechanism is as follows: as the rotor rotates, each guide bar passes through the probe's detection area sequentially. The rotational angle signal collected by the laser positioning sensor can accurately determine the current position of the guide bar below the probe, thus achieving a one-to-one correspondence between the response signal and the guide bar position. This not only eliminates the signal aliasing problem caused by rotor rotation but also provides a reference for subsequent phase correction.

[0060] IV. Signal Conditioning and Acquisition Module

[0061] The signal conditioning and acquisition module is connected to the corner synchronization drive module and the outer ring receiving coil array. It is used to synchronously acquire the response signal of the outer ring receiving coil according to the synchronization trigger signal and perform signal compensation and correction. The signal conditioning and acquisition module includes a lift-off effect compensation unit and a phase correction unit.

[0062] (a) Lift-off effect compensation unit

[0063] Due to mechanical vibrations or installation errors during rotor rotation, the lift-off distance between the probe and the rotor surface fluctuates, causing changes in the amplitude of the response signal. To suppress this interference, this embodiment employs an elastic probe structure combined with a lift-off effect compensation algorithm. Figure 2 As shown, by utilizing the telescopic function of the micro-spring in the elastic probe structure, when the rotor rotation causes mechanical vibration or installation errors lead to fluctuations in the lift-off distance, the elastic structure can adaptively adjust the fit between the probe and the rotor surface, controlling the lift-off fluctuation within the range of ±0.1mm.

[0064] Based on this, the lift-off effect compensation unit further compensates for the amplitude of the response signal in the following manner:

[0065]

[0066] In the formula, U comp The compensated signal amplitude; U meas This represents the actual measured signal amplitude. α Δ is the compensation coefficient; h This represents the difference between the actual lift-off and the benchmark lift-off.

[0067] compensation coefficient α The following experimental calibration was used to determine the following: For example, using a cast copper rotor with a rated speed of 1500 r / min as the test object, under the condition of a 1 mm lift-off from the reference point, the corresponding measured amplitude was collected by adjusting the lift-off distance, and the compensation coefficient was calibrated by least squares fitting. α =0.081 / mm. This compensation coefficient can be used as the initial parameter for rotors of the same specification, and can be recalibrated for rotors of different models. Through the dual suppression of elastic structure and compensation algorithm, the signal error caused by lift-off fluctuation can be effectively controlled, effectively avoiding misjudgment of faults caused by lift-off changes.

[0068] (ii) Phase correction unit

[0069] The rotation of the rotor causes a continuous change in the relative position of the detection coil and the guide bar, resulting in a phase shift in the response signal related to the rotational speed. To eliminate this interference, the phase correction unit establishes a mapping relationship between the phase shift and the rotational speed based on the rotational angle signal acquired by the laser positioning sensor, and corrects the signal phase shift caused by the rotor rotation in the following manner:

[0070]

[0071] In the formula, This is the phase offset. oh This refers to the actual rotational speed of the rotor. kThis is the proportionality coefficient; b This is the initial phase offset.

[0072] proportionality coefficient k and initial phase offset b Calibration experiments determined that, consistent with the lift-off compensation calibration object, the probe lift-off distance was fixed at 1 mm, the excitation parameters remained unchanged, and measurements were performed using a laser positioning sensor (sampling frequency 10 kHz) and a high-speed data acquisition card (sampling rate 1 MHz). The experimental environment was a room temperature of 25℃, free from strong electromagnetic interference, and with no significant rotor vibration. Within the range of 800–1600 r / min, five calibration speeds (800 r / min, 1000 r / min, 1200 r / min, 1400 r / min, and 1600 r / min) were selected with a step size of 200 r / min. The response signal of the health guide bar was collected, and the phase offset was extracted. Linear regression fitting was performed with speed as the abscissa and phase offset as the ordinate to obtain… k =0.025°·s / rad, b =1.2°. This set of calibration values ​​can be used as initial parameters for fault detection of the guide bars of cast copper rotors of the same specification. Different models of rotors can be recalibrated based on this. The phase correction unit calculates the phase offset in real time according to the current speed and compensates it to the response signal, making the phase data collected at different speeds comparable and laying the foundation for subsequent phase feature extraction.

[0073] (III) Signal Preprocessing Procedure

[0074] In this embodiment, the signal conditioning and acquisition module performs complete signal preprocessing on the acquired dual-frequency signals. First, a bandpass filter is used for frequency domain filtering to remove power frequency interference and environmental noise. Second, the amplitude of the dual-frequency signals is normalized to eliminate the influence of signal amplitude fluctuations. Then, lift-off compensation and phase correction are performed by a lift-off effect compensation unit and a phase correction unit, respectively. Finally, the dual-frequency amplitude ratio feature and dual-frequency phase difference feature are extracted to provide input data for subsequent fault diagnosis.

[0075] V. Feature Recognition and Processing Module

[0076] The feature identification and processing module is connected to the signal conditioning and acquisition module. It is used to extract feature parameters of low-frequency and high-frequency response signals and identify the type, location and severity of rotor bar faults based on preset fault judgment criteria.

[0077] (I) Feature parameter extraction

[0078] The feature parameters extracted in this embodiment include the dual-frequency amplitude ratio. K Dual-frequency phase difference Δ i and impedance change value Δ Z The specific definition is as follows:

[0079] Dual-frequency amplitude ratio K This is the ratio of the amplitude changes in the high-frequency band to the low-frequency band response signal. ;Δ U 1 represents the amplitude variation (in mV) of a high-frequency band signal (2MHz–5MHz); Δ U 2 represents the amplitude variation (unit: mV) of low-frequency band signals (100kHz–500kHz). K The smaller the value, the more significant the surface defects of the rotor components, such as broken bars and surface cracks; K The higher the value, the more prominent the internal defects of the rotor components, such as porosity and air holes. Quantitative analysis is as follows:

[0080] K A value <0.3 is considered a surface defect, such as broken stripes or surface cracks. Low-frequency signals are more sensitive to surface defects, leading to Δ U 2 increases significantly, while the high-frequency signal Δ U The response is weak, therefore the ratio is low. K Too small;

[0081] 0.3 ≤ K A ratio <0.7 is considered a mixed defect, such as fine streaks or shallow porosity. These defects affect both the surface and interior layers simultaneously, and the response levels of high and low frequency signals are similar; therefore, the ratio... K It is in the middle range.

[0082] K A value ≥ 0.7 is considered an internal defect, such as porosity or air pockets. High-frequency signals are more sensitive to internal defects, leading to Δ U 1 increases significantly, while the low-frequency signal Δ U 2 has a weaker response, therefore the ratio K Too large.

[0083] Dual-frequency phase difference Δ i This is the difference in phase offset between the high-frequency and low-frequency response signals. ;Δ i The phase difference between the two frequencies (unit: °); This represents the phase shift in the high-frequency band (unit: °). The phase shift (unit: °) is for the low-frequency band. Broken bar faults cause abrupt phase changes, while internal porosity has a smaller impact on the phase. For example, broken bar faults not only satisfy... K A value less than 0.3 will also lead to a phase abrupt change, satisfying |Δ i |>45°; while the internal looseness satisfies K ≥ 0.7 and |Δ i |<20°.

[0084] The impedance change ΔZ is determined by the change in resistance Δ of the receiving coil. R With the change in inductive resistance Δ X The calculation yielded: ;Δ Z Δ represents the change in the total impedance of the coil (unit: Ω). R Δ represents the change in resistance (unit: Ω). X This represents the change in inductive reactance (unit: Ω).

[0085] Among them, the dual-frequency amplitude ratio K This reflects the depth and location of the defect. Surface defects cause significant changes in the amplitude of low-frequency signals, leading to... K The value is too small; internal defects cause significant changes in the amplitude of high-frequency signals, leading to... K The value is too large. Dual-frequency phase difference Δ i This reflects the influence of defects on the phase of the electromagnetic field. Severe defects such as broken bars can cause abrupt phase changes, Δ. i The absolute value increases. The impedance change Δ Z This reflects the degree to which the defect obstructs the eddy current path; the larger the defect volume and the more severe the cross-sectional loss, the greater the Δ. Z The larger the value.

[0086] (II) Fault Diagnosis Criteria

[0087] The preset fault discrimination criterion is a multi-dimensional feature threshold matrix, which is obtained through experimental calibration of standard test pieces with different fault types. The calibration process includes: fabricating standard test pieces with the same material and size as the rotor to be tested; artificially creating fault types such as broken bars, thin bars, looseness, and porosity; and setting different severity levels such as mild, moderate, and severe; performing repeated tests on each standard test piece under uniform testing conditions; and collecting and recording the dual-frequency amplitude ratio. K Dual-frequency phase difference Δ i Impedance change value Δ Z Cluster analysis was performed on the collected data to determine the characteristic threshold boundaries for different fault types and severity levels.

[0088] In this embodiment, the fault type determination rule is as follows: when the dual-frequency amplitude ratio K Less than the first threshold (e.g., 0.3) and the dual-frequency phase difference Δ i When the absolute value is greater than the second threshold (e.g., 45°), it is judged as a surface defect (fracture, surface crack); when the dual-frequency amplitude ratio K Greater than the third threshold (e.g., 0.7) and the dual-frequency phase difference Δ i When the absolute value is less than the fourth threshold (e.g., 20°), it is judged as an internal defect (porosity, pores); when the dual-frequency amplitude ratio K When the defect falls between the first and third thresholds, it is classified as a mixed defect (fine stripes, shallow porosity).

[0089] The severity classification rules for faults are as follows: based on the impedance change value Δ Z The severity level of the fault is determined by comparing the result with a preset grading threshold. Preset grading threshold Z 1. Z 2. Obtained through calibration using standard test specimens, of which Z 1 is the dividing point between minor and moderate faults. Z 2 is the dividing point between moderate and severe faults. When Δ Z < Z At time 1, it was determined to be a minor fault (5%~15% loss of conductor cross-section). Z 1≤ Δ Z < Z At time 2, it is determined to be a moderate fault (15%~30% loss of conductor cross-section). When Δ Z ≥ Z At time 2, it was determined to be a severe fault (the conductor strip cross-section loss is more than 30%).

[0090] Through the aforementioned multi-dimensional feature threshold matrix, this system can accurately identify the type, location, and severity of rotor bar faults. The detection results are unaffected by speed fluctuations and lift-off changes, demonstrating good robustness in dynamic detection scenarios in industrial settings.

[0091] Example 2

[0092] Based on the above system, the present invention also provides a rotor bar fault detection method based on an asymmetric dual-frequency eddy current array, comprising the following steps:

[0093] S1: Probe Installation and Positioning

[0094] An asymmetric dual-layer eddy current array probe is attached to the cylindrical curved surface of the rotor, ensuring that the arrangement of the inner ring excitation coil array corresponds to the distribution of the rotor guide bars, while the detection area of ​​the outer ring receiving coil array covers the guide bars and the gaps between them. An elastic support structure is used to adjust the fit between the probe and the rotor, ensuring that the lift-off distance remains stable near a reference value.

[0095] S2: Dual-frequency excitation applied

[0096] A dual-frequency excitation module applies low-frequency and high-frequency excitation signals to the inner excitation coil array in a time-division manner. In this embodiment, the low-frequency signal frequency is set to 300kHz, the high-frequency signal frequency is set to 3MHz, and the switching period is 1ms (corresponding to one-tenth of the rotor rotation period). The dual-frequency signals create gradient eddy current fields of different depths inside the rotor guide bars.

[0097] S3: Angle Synchronization and Signal Acquisition

[0098] The rotor is driven to rotate at a constant speed of 1200 r / min by the rotation angle synchronization drive module. The laser positioning sensor collects the rotor rotation angle signal in real time and generates a synchronization trigger signal. Based on the synchronization trigger signal, the signal conditioning and acquisition module synchronously acquires the response signals of the outer ring receiving coil under the excitation of the low-frequency and high-frequency bands at a sampling rate of 1 MHz.

[0099] S4: Signal Compensation and Correction

[0100] The signal conditioning and acquisition module performs lift-off compensation and phase correction on the acquired response signal. The lift-off compensation unit is configured as follows: Compensate for signal amplitude; the phase correction unit according to Calculate the phase offset and compensate it to the response signal.

[0101] S5: Feature Extraction and Fault Diagnosis

[0102] The feature recognition and processing module extracts the amplitude ratio of the low-frequency and high-frequency response signals. K Dual-frequency phase difference Δ i and impedance change value Δ Z Based on the multi-dimensional feature threshold matrix, firstly through... K Value and Δ i The value determines the fault type, and then through Δ Z The severity level of the fault is determined by comparing the value with the preset grading threshold, and the fault location and diagnosis result are finally output.

[0103] Through the above steps, this method can realize online detection of guide bar faults under the condition of rotor uniform rotation. The single detection cycle only takes a few seconds, which is suitable for batch detection scenarios in industrial production sites.

[0104] The above description is merely a preferred embodiment of this disclosure and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of this disclosure is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-described concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features disclosed in this disclosure that have similar functions.

[0105] Furthermore, while the operations are described in a specific order, this should not be construed as requiring these operations to be performed in the specific order shown or in a sequential order. In certain environments, multitasking and parallel processing may be advantageous. Similarly, while several specific implementation details are included in the above discussion, these should not be construed as limiting the scope of this disclosure. Certain features described in the context of individual embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented individually or in any suitable sub-combination in multiple embodiments.

[0106] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A rotor bar fault detection system based on an asymmetric dual-frequency eddy current array, applied to a motor rotor with multiple bars and bar gaps, characterized in that, include: An asymmetric double-layer eddy current array probe includes an inner ring excitation coil array and an outer ring receiving coil array; the arrangement of the inner ring excitation coil array corresponds to the distribution of the guide bars; the arrangement density of the outer ring receiving coil array is greater than that of the inner ring excitation coil array, and its detection area covers the guide bars and the gaps between the guide bars; the probe has an arc-shaped structure adapted to the rotor surface; The dual-frequency excitation module is used to apply low-frequency and high-frequency excitation signals to the inner ring excitation coil array in a time-division manner to form eddy current fields of different depths inside the rotor bars. The rotation angle synchronization drive module is used to drive the rotor to rotate at a constant speed and to collect the rotor rotation angle signal in real time to generate a synchronization trigger signal. The signal conditioning and acquisition module is used to synchronously acquire the response signal of the outer receiving coil according to the synchronous trigger signal, and to perform signal compensation and correction. The feature recognition and processing module is used to extract feature parameters of low-frequency and high-frequency response signals, and identify the type, location and severity of rotor bar faults based on preset fault judgment criteria. The outer ring receiving coil array has more coils than the inner ring excitation coil array, and each receiving coil is staggered in the gap area between adjacent inner ring excitation coils along the circumferential direction. The dual-frequency excitation module outputs low-frequency and high-frequency excitation signals using a time-division multiplexing mode. The low-frequency excitation signal is used to detect surface cracks and fracture defects in the guide bar, while the high-frequency excitation signal is used to detect internal porosity, air holes, and inclusion defects in the guide bar. The switching cycle of the dual-frequency excitation module is less than the rotor rotation cycle, so that the response signals under low-frequency and high-frequency excitation can be obtained sequentially at the same detection position within a single scan cycle. The signal conditioning and acquisition module includes a lift-off effect compensation unit and a phase correction unit; The lift-off effect compensation unit compensates for the amplitude of the response signal based on a preset compensation coefficient and the actual lift-off deviation, as shown in the following formula: ； In the formula, U comp The compensated signal amplitude; U meas α is the actual measured signal amplitude; α is the compensation coefficient; Δh is the difference between the actual lift-off and the reference lift-off. The phase correction unit establishes a mapping relationship between phase offset and rotational speed based on the rotor angle signal, and corrects the signal phase offset caused by rotor rotation, as shown in the following formula: ； In the formula, ω is the phase offset; k is the actual rotor speed; b is the proportional coefficient; and b is the initial phase offset.

2. The rotor guide bar fault detection system based on an asymmetric dual-frequency eddy current array according to claim 1, characterized in that, The dual-frequency excitation module uses a DDS signal generator, with a low-frequency detection signal band of 100kHz–500kHz and a high-frequency detection signal band of 2MHz–5MHz.

3. The rotor bar fault detection system based on an asymmetric dual-frequency eddy current array according to claim 1, characterized in that, The asymmetric double-layer eddy current array probe is encapsulated with an elastic substrate and has an elastic support structure, which is used to adaptively adjust the fit between the probe and the rotor surface during rotor rotation and suppress lift-off distance fluctuations.

4. The rotor guide bar fault detection system based on an asymmetric dual-frequency eddy current array according to claim 1, characterized in that, The feature parameters extracted by the feature identification processing module include the dual-frequency amplitude ratio K and the dual-frequency phase difference Δθ, where: The dual-frequency amplitude ratio K is the ratio of the amplitude changes of the high-frequency band and the low-frequency band response signal; The dual-frequency phase difference Δθ is the difference in phase offset between the high-frequency band and the low-frequency band response signal. The feature identification processing module also extracts the impedance change value ΔZ, and quantifies the severity of the fault based on the magnitude of the impedance change value; the impedance change value is calculated from the resistance change ΔR and the inductive reactance change ΔX of the receiving coil, as shown in the following formula: 。 5. The rotor guide bar fault detection system based on an asymmetric dual-frequency eddy current array according to claim 4, characterized in that, The preset fault discrimination criterion is a multi-dimensional feature threshold matrix, which includes feature threshold ranges for different fault types and different severity levels. The fault diagnosis module determines the fault type based on the dual-frequency amplitude ratio K and the dual-frequency phase difference Δθ, and determines the fault severity level based on the comparison result of the impedance change value ΔZ and the preset grading threshold. The fault types include surface defects, internal defects, and mixed defects; the discrimination condition for surface defects is that the dual-frequency amplitude ratio K is less than a first threshold and the absolute value of the dual-frequency phase difference Δθ is greater than a second threshold; the discrimination condition for internal defects is that the dual-frequency amplitude ratio K is greater than a third threshold and the absolute value of the dual-frequency phase difference Δθ is less than a fourth threshold; the discrimination condition for mixed defects is that the dual-frequency amplitude ratio K is between the first threshold and the third threshold.

6. A rotor bar fault detection method based on an asymmetric dual-frequency eddy current array, applied to the rotor bar fault detection system based on an asymmetric dual-frequency eddy current array as described in any one of claims 1-5, characterized in that, Includes the following steps: S1: The asymmetric double-layer eddy current array probe is attached to the cylindrical curved surface of the rotor, so that the arrangement of the inner ring excitation coil array corresponds to the distribution of the rotor guide bars, and the detection area of ​​the outer ring receiving coil array covers the guide bars and the gaps between the guide bars. S2: Low-frequency and high-frequency excitation signals are applied to the inner ring excitation coil array in a time-division manner through the dual-frequency excitation module, forming gradient eddy current fields of different depths inside the rotor guide bars; S3: Drives the rotor to rotate at a constant speed through the rotation angle synchronous drive module, and collects the rotor rotation angle signal in real time and generates a synchronous trigger signal; S4: Based on the synchronous trigger signal, the response signal of the outer receiving coil under the excitation of the low-frequency band and the high-frequency band is synchronously acquired through the signal conditioning and acquisition module, and signal compensation and correction are performed. S5: The feature recognition processing module extracts the feature parameters of the low-frequency and high-frequency response signals, and identifies the fault type, location and severity of the rotor bar based on the preset fault judgment criteria.

Images