A method for enhancing eddy current testing features of surface micro-cracks of a spacer

Abstract

The application discloses a kind of vortex detection feature enhancement methods of spacer bar surface micro crack, it is related to vortex detection technical field, for solving the unstable drift characteristics that background response benchmark presents on spatial distribution, by calling the structure boundary position of the spacer bar surface to be measured, along its setting scan path and collecting probe scanning track data, structure boundary is divided into structural response attribution section, and initial vortex sequence is detected according to scan path, and based on structural response attribution section is segmented and marked, generates each section background response benchmark;Collect contour height data and probe real-time spatial position, calculate surface lift fluctuation index, generate compensation background response amount to compensate background response benchmark, according to compensation background response amount, carry out abnormal separation to initial vortex sequence, and combined with structural response attribution section executes enhancement screening, locates crack candidate area, to weaken the interference of vortex detection result to structure boundary and lift change.

Description

Technical Field

[0001] This invention relates to the field of eddy current detection technology, and more specifically, to a method for enhancing the eddy current detection features of microcracks on the surface of a spacer bar. Background Technology

[0002] During the operation and maintenance of power transmission lines, spacers, as key mechanical supports and spacing maintenance components, are subjected to long-term vibration loads, wind-induced swaying, and electromagnetic coupling, making their surface structure prone to early microcracks and other microscopic damage. Because these microcracks are extremely small in their initial stage, propagate discontinuously, and exhibit non-uniform distribution along the surface structure boundaries, they typically require highly sensitive eddy current detection methods for identification and localization.

[0003] The existing technology has the following shortcomings: Currently, existing eddy current detection technologies, when performing continuous scanning analysis on complex curved surface components such as spacer bars, typically treat the entire scanning sequence as a unified processing object. They lack mechanisms for constructing segmented background response benchmarks for different structural boundary sections, and joint processing methods for synchronously compensating for dynamic fluctuations caused by surface contours during probe scanning. This results in unstable and drifting characteristics in the spatial distribution of the background response benchmarks, thereby weakening the prominence and separability of microcrack anomaly signals and reducing the positioning accuracy and identification reliability of crack candidate regions. Therefore, this paper proposes an eddy current detection feature enhancement method for microcracks on the surface of spacer bars.

[0004] The information disclosed in the background section is only intended to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] To overcome the aforementioned deficiencies of the prior art, embodiments of the present invention provide an eddy current detection feature enhancement method for microcracks on the surface of spacers. This method addresses the problems mentioned in the background art by employing structural boundary partitioning modeling and segmented background response benchmark construction, combined with eddy current signal enhancement processing through surface lift-off dynamic compensation, and an anomaly separation and screening collaborative mechanism.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for enhancing the eddy current detection features of microcracks on the surface of a spacer bar, comprising the following steps: Step S1: Retrieve the structural boundary position on the surface of the spacer to be tested, set the scanning path along the surface of the spacer to be tested, collect the probe scanning trajectory data, and divide the structural boundary position into the structural response belonging segment after collecting the probe scanning trajectory data; Step S2: Detect the initial eddy current sequence according to the scanning path, segment and mark the initial eddy current sequence based on the structural response attribution segment, and generate the background response benchmark for each structural response attribution segment by marking the initial eddy current sequence. Step S3: Collect the profile height data of the surface of the spacer bar to be tested, obtain the real-time spatial position of the eddy current probe as it moves along the scanning path, calculate the surface lift-off fluctuation index by combining the profile height data, compensate the background response benchmark by the surface lift-off fluctuation index and generate the compensated background response quantity. Step S4: Perform anomaly separation on the initial eddy current sequence based on the compensation background response, perform enhanced screening processing on the anomaly separation results based on the structural response attribution segment, and locate the crack candidate region after enhanced screening processing.

[0007] In a preferred embodiment, in step S1, the surface of the spacer bar to be tested is unfolded into a scannable area, and the spacing between adjacent scan lines is set according to the effective sensing diameter of the eddy current probe. The area to be scanned is spread out along the surface of the spacer bar to be tested. The spacing between adjacent scanning lines is determined by half the effective sensing diameter of the eddy current probe, and the arc length interval of the sampling points is determined by one-quarter of the effective sensing diameter. The probe scanning trajectory data includes the sampling time and the spatial coordinates of the probe center; The scanning path is represented as a path centerline formed by connecting multiple discrete points in sequence, and each discrete point has corresponding spatial coordinates and arc length coordinates. Calculate the Euclidean distance between the spatial coordinates of the probe center at the current sampling time and the spatial coordinates of each discrete point along the path; Select the discrete point on the path with the smallest Euclidean distance as the corresponding point of the current sampling point on the scanning path; Assign the arc length coordinates of the discrete points on the path to the arc length coordinates of the current sampling point.

[0008] In a preferred embodiment, in step S1, each structural boundary position is mapped to the scanning path, and a set of path points in the scanning path whose distance from the structural boundary position is less than or equal to the half-width of the segment extension is determined. The minimum value of the arc length coordinates corresponding to the path point set is used as the starting arc length coordinate of the boundary, and the maximum value of the arc length coordinates corresponding to the path point set is used as the ending arc length coordinate of the boundary. Based on the starting and ending arc length coordinates of each structural boundary position on the scanning path, the starting arc length coordinates are extended forward and the ending arc length coordinates are extended backward according to the segment expansion half-width. The expanded segment is then limited to the total arc length of the scanning path to obtain the structural response belonging segment.

[0009] In a preferred embodiment, in step S2, the initial eddy current sequence is constructed by sorting the sampling point arc length coordinates as the eddy current probe moves along the scanning path, including the sampling point number, arc length coordinates and response amplitude. The initial eddy current sequence is labeled by comparing the arc length coordinates of each sampling point in the initial eddy current sequence with the starting and ending arc length coordinates of the structural response segment. When the arc length coordinates of a sampling point fall into a certain structural response segment, the sampling point is marked with the corresponding segment number and structural type. Conversely, do not mark the sampling points; Extract the response amplitude corresponding to the structural response segment from the initial eddy current sequence.

[0010] In a preferred embodiment, in step S2, the number of background statistical window sampling points corresponding to the structural response belonging segment is determined based on the effective sensing radius of the probe and the arc length interval between adjacent sampling points. Based on the response amplitude corresponding to the number of background statistical window sampling points, the median is calculated to generate the background amplitude. The background amplitude, corresponding arc length coordinates, segment number, and structure type of each sampling point are rearranged according to the sampling order of the initial eddy current sequence to obtain the background response benchmark.

[0011] In a preferred embodiment, in step S3, the contour height data of the surface of the spacer bar to be measured is collected; Contour height data refers to the surface height information obtained by scanning the surface of the spacer bar to be measured along the scanning path using a laser contour scanning device. Acquire the real-time spatial position of the eddy current probe as it moves along the scanning path; Real-time spatial position refers to the spatial coordinates of the probe center synchronously acquired by the trajectory acquisition component as the eddy current probe moves along the scanning path, including the X-direction coordinates, Y-direction coordinates, and Z-direction coordinates at the corresponding sampling time; The Z-axis coordinate represents the vertical height of the eddy current probe center relative to the mounting reference surface; Read the Z-axis coordinates in the real-time spatial position, retrieve the contour height value of the corresponding arc length coordinates, and calculate the actual lift-off distance.

[0012] In a preferred embodiment, in step S3, the arithmetic mean of the actual lift-off distances of all sampling points within the current scanning path is used as the reference lift-off distance. The liftoff offset corresponding to each sampling point is calculated based on the actual liftoff distance and the reference liftoff distance. The liftoff offset is then normalized to obtain the surface liftoff fluctuation index. Based on the detection data of historical crack-free standard spacers under different lifting conditions, the correspondence between the lifting fluctuation index and the background response change ratio was statistically analyzed, and the lifting compensation gain coefficient was obtained by least squares fitting. The background response benchmark is compensated based on the lift-off compensation gain coefficient and the surface lift-off fluctuation index to generate the compensated background response quantity.

[0013] In a preferred embodiment, in step S4, the abnormal response value is obtained by subtracting the compensation background response value of the corresponding sampling point from the response amplitude in the initial eddy current sequence. For each sampling point, a continuous analysis window is formed by one sampling point before and after it. The average value of the abnormal response within the continuous analysis window is calculated to obtain the local average abnormal response. According to the structural response to the assigned zone, the average absolute value of the local average abnormal response in each zone is calculated, and the abnormal enhancement coefficient of the corresponding sampling point is calculated. The local average anomaly response is enhanced based on the anomaly enhancement coefficient to generate an enhanced anomaly response. The upper quartile and interquartile range of the enhanced abnormal response within each structural response segment are calculated separately, and the enhancement screening threshold is generated based on the upper quartile and interquartile range.

[0014] In a preferred embodiment, in step S4, the enhanced anomaly response quantity corresponding to each sampling point is compared with the enhancement screening threshold of the structural response belonging segment: When the enhanced abnormal response is greater than or equal to the enhanced screening threshold, the corresponding sampling point is marked as a crack candidate point; Otherwise, the corresponding sampling point will not be marked as a crack candidate point; Crack candidate points with continuous arc length coordinates and a distance between adjacent crack candidate points less than or equal to the arc length interval of one sampling point are merged to form the same crack candidate region. The minimum value of the arc length coordinates corresponding to the candidate points of continuous cracks is taken as the starting position of the crack candidate region, and the maximum value of the arc length coordinates corresponding to the candidate points of continuous cracks is taken as the ending position of the crack candidate region, thus completing the crack candidate region localization.

[0015] The technical effects and advantages of this invention are as follows: This invention retrieves the structural boundary position on the surface of the spacer under test, sets a scanning path along the surface of the spacer and collects probe scanning trajectory data, dividing the structural boundary into structural response attribution segments; detects the initial eddy current sequence according to the scanning path, segments and marks the initial eddy current sequence based on the structural response attribution segments, generates background response benchmarks for each segment, collects the contour height data of the surface of the spacer under test and the real-time spatial position of the eddy current probe, calculates the surface lift-off fluctuation index, and compensates the background response benchmarks to generate a compensated background response quantity; performs anomaly separation on the marked initial eddy current sequence based on the compensated background response quantity, and performs enhanced screening processing in conjunction with the structural response attribution segments to locate crack candidate regions, weaken the interference of structural boundary and lift-off changes on eddy current detection results, and improve the prominence and positioning accuracy of microcrack response characteristics on the spacer surface. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the implementation of the eddy current detection feature enhancement method for microcracks on the surface of a spacer bar according to the present invention.

[0017] Figure 2 This is a schematic diagram illustrating the steps of an eddy current detection feature enhancement method for microcracks on the surface of a spacer bar according to the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] This invention retrieves the structural boundary position on the surface of the spacer under test, sets a scanning path along the surface of the spacer under test, and collects probe scanning trajectory data to divide the structural boundary into structural response attribution segments. An initial eddy current sequence is detected according to the scanning path, and the initial eddy current sequence is segmented and marked based on the structural response attribution segments to generate a background response benchmark for each segment. Contour height data of the surface of the spacer under test and the real-time spatial position of the eddy current probe are collected, the surface lift-off fluctuation index is calculated, and the background response benchmark is compensated to generate a compensated background response quantity. Anomalies in the marked initial eddy current sequence are separated based on the compensated background response quantity, and enhanced screening processing is performed in conjunction with the structural response attribution segments to locate crack candidate regions and reduce the interference of structural boundary and lift-off changes on the eddy current detection results.

[0020] Example 1, such as Figures 1 to 2 As shown, a method for enhancing the eddy current detection features of microcracks on the surface of a spacer bar includes the following steps: Step S1: Retrieve the structural boundary position on the surface of the spacer to be tested, set the scanning path along the surface of the spacer to be tested, collect the probe scanning trajectory data, and divide the structural boundary position into the structural response belonging segment after collecting the probe scanning trajectory data; Step S2: Detect the initial eddy current sequence according to the scanning path, segment and mark the initial eddy current sequence based on the structural response attribution segment, and generate the background response benchmark for each structural response attribution segment by marking the initial eddy current sequence. Step S3: Collect the profile height data of the surface of the spacer bar to be tested, obtain the real-time spatial position of the eddy current probe as it moves along the scanning path, calculate the surface lift-off fluctuation index by combining the profile height data, compensate the background response benchmark by the surface lift-off fluctuation index and generate the compensated background response quantity. Step S4: Perform anomaly separation on the initial eddy current sequence based on the compensation background response, perform enhanced screening processing on the anomaly separation results based on the structural response attribution segment, and locate the crack candidate region after enhanced screening processing.

[0021] The specific implementation method is as follows: In step S1, the structural boundary position of the surface of the spacer to be tested is retrieved. The structural boundary position refers to the position data of the edge of the clamping groove, the edge of the bolt hole, the root edge of the connecting rib, and the start and end boundary of the rounded transition in the coordinate system of the surface of the spacer to be tested.

[0022] The location of the structural boundary can be provided by the three-dimensional structural model or surface laser profile scanning data of the spacer bar to be tested, and the set of structural boundary locations is composed of structural type, boundary number and spatial coordinates.

[0023] Set a scanning path along the surface of the spacer bar to be tested, unfold the surface of the spacer bar to be tested into a scannable area, set the spacing between adjacent scanning lines according to the effective sensing diameter of the eddy current probe, and the spacing between scanning lines should not be greater than half of the effective sensing diameter of the eddy current probe, so that the clamping groove, bolt hole, connecting rib and rounded transition are all covered by at least one scanning line. Sampling points are set along each scanning line, and the arc length interval between sampling points is no more than one-quarter of the effective sensing diameter of the probe.

[0024] The probe scanning trajectory data is collected by a trajectory acquisition component installed on the scanning actuator. The probe scanning trajectory data includes the sampling time and the spatial coordinates of the probe center.

[0025] The sampling time is in seconds, and the spatial coordinates of the probe center are in millimeters.

[0026] It should be added that an eddy current probe is a non-contact electromagnetic detection device with an internal excitation coil and an induction coil. It is used to generate an alternating electromagnetic field near the surface of the spacer bar under test and to receive the eddy current response signal caused by the change in the conductivity state of the surface layer of the spacer bar under test. The scanning actuator is used to drive the eddy current probe to move along the scanning path. The trajectory acquisition component includes a position encoder and a synchronous acquisition controller. The position encoder acquires the displacement of the eddy current probe as it moves along the scanning path, and the synchronous acquisition controller records the sampling time and aligns the displacement and the eddy current detection signal in time to obtain the probe scanning trajectory data.

[0027] The scanning path is represented as a centerline formed by connecting multiple discrete points along the path. Each discrete point has corresponding spatial coordinates and arc length coordinates. The Euclidean distance between the probe center spatial coordinates at the current sampling moment and the spatial coordinates of each discrete point is calculated. The discrete point with the smallest Euclidean distance is selected as the corresponding point on the scanning path for the current sampling point, and its arc length coordinate is assigned as the arc length coordinate of the current sampling point. If the two discrete points with the smallest Euclidean distance are adjacent, linear interpolation is performed between the two discrete points according to the distance ratio to obtain the arc length coordinate of the current sampling point.

[0028] Map each structural boundary position onto the scanning path, obtain the path points in the scanning path whose distance to the structural boundary position is less than or equal to the segment expansion half width, take the minimum value of the arc length coordinates corresponding to the path points as the boundary starting arc length coordinates, and take the maximum value of the arc length coordinates corresponding to the path points as the boundary ending arc length coordinates. The section extension half-width is determined by adding the effective sensing radius of the eddy current probe, the trajectory acquisition error, and the structural boundary positioning error.

[0029] The structural response segment is determined according to the following formula: ; in, For the j-th structural response, Let J be the coordinates of the starting arc length of the j-th structural boundary on the scan path. Let be the coordinates of the boundary termination arc of the j-th structural boundary on the scan path.

[0030] The effective sensing radius of the eddy current probe is determined by the half-width of the response when the eddy current probe scans a standard narrow groove on a crack-free calibration block; the trajectory acquisition error is determined by the upper limit of the position deviation acquired when the scanning actuator repeatedly passes through the same calibration point; the structural boundary positioning error is determined by the upper limit of the residual after the structural boundary position and surface contour measurement data are registered.

[0031] Through the above processing, the segment number, structure type, starting arc length coordinates, ending arc length coordinates, and corresponding sampling point number of each structural response segment are obtained, and the structural response segment is passed to step S2.

[0032] In step S2, the initial eddy current sequence is detected according to the scanning path. The initial eddy current sequence refers to the sequence formed by arranging the eddy current detection responses collected at each sampling point according to the arc length coordinate as the eddy current probe moves along the scanning path. The initial eddy current sequence includes the sampling point number, arc length coordinate, and response amplitude. The unit for arc length coordinates is millimeters, and the unit for response amplitude is millivolts.

[0033] The arc length coordinates of each sampling point in the initial eddy current sequence are compared with the starting and ending arc length coordinates of each structural response segment: When the arc length coordinates of a sampling point fall into a certain structural response segment, the sampling point is marked with the corresponding segment number and structural type. If the arc length coordinates of a sampling point do not fall within any structural response segment, the sampling point is not marked.

[0034] This yields the initial eddy current sequence.

[0035] For each structural response segment, the response amplitude belonging to that segment is extracted from the initial eddy current sequence.

[0036] The number of sampling points in the background statistics window is determined based on the effective sensing radius of the probe and the arc length interval of the sampling points.

[0037] in, The number of background statistical window sampling points corresponding to the j-th structural response segment. The effective sensing radius of the probe. The arc length interval between adjacent sampling points. This indicates rounding up to the nearest integer.

[0038] The larger the half-width of the segment extension or the smaller the arc length interval between adjacent sampling points, the more sampling points the background statistics window covers, and the wider the range of geometric background response can be reflected.

[0039] Within each structural response attribution segment, taking the i-th sampling point as the center, select the preceding and following points... The response amplitudes of each sampling point form a local amplitude set, and the median of the local amplitude set is taken as the background amplitude of the i-th sampling point:

[0040] in, Let i be the background amplitude of the i-th sampling point. The response amplitude at the k-th sampling point in the local amplitude set. Let be the set of local amplitudes centered on the i-th sampling point, and median represents the median value.

[0041] The fewer local spikes in the response amplitude, The closer to the structural boundary, the more continuous the background changes; the more concentrated the local peaks, the more obvious the median statistics' suppression effect on the local peaks.

[0042] The background amplitude, corresponding arc length coordinates, segment number, and structure type of each sampling point are rearranged according to the sampling order of the initial eddy current sequence to generate a background response benchmark.

[0043] The background amplitude in the background response reference is in millivolts, maintaining the same dimension as the response amplitude in the initial eddy current sequence; the arc length coordinate in the background response reference is in millimeters, maintaining the same dimension as the probe scanning trajectory data.

[0044] In step S3, the contour height data of the surface of the spacer bar to be tested is collected, the real-time spatial position of the eddy current probe as it moves along the scanning path is obtained, the surface lift-off fluctuation index is calculated by combining the contour height data, the background response benchmark is compensated by the surface lift-off fluctuation index and the compensated background response quantity is generated.

[0045] The contour height data refers to the surface height information obtained by scanning the surface of the spacer under test along the scanning path using a laser contour scanning device. The contour height data includes the arc length coordinates and contour height value corresponding to each sampling position. The contour height value is measured using the mounting reference surface of the spacer under test as a unified reference datum, and is used to characterize the degree of local geometric undulation on the surface of the spacer under test. A larger contour height value indicates a more pronounced convexity of the surface relative to the mounting reference surface at the corresponding position; a smaller contour height value indicates a more pronounced concavity of the surface relative to the mounting reference surface at the corresponding position.

[0046] It should be noted that the laser contour scanning device refers to a non-contact surface contour measurement device installed on the scanning platform. The laser emitting unit projects a laser line onto the surface of the spacer bar to be measured, the imaging receiving unit receives the laser contour image formed by surface reflection, and the displacement calculation unit calculates the contour height value corresponding to each sampling position according to the laser triangulation principle, and outputs contour height data corresponding one-to-one with the arc length coordinates according to the scanning path.

[0047] Real-time spatial position refers to the spatial coordinates of the probe center synchronously acquired by the trajectory acquisition component as the eddy current probe moves along the scanning path. The real-time spatial position includes the X-axis, Y-axis, and Z-axis coordinates at the corresponding sampling moment. The Z-axis coordinate represents the vertical height of the eddy current probe center relative to the mounting reference surface, reflecting the actual spatial relationship between the eddy current probe and the surface of the spacer under test. A larger Z-axis coordinate indicates a higher height of the eddy current probe from the mounting reference surface.

[0048] It should be noted that the trajectory acquisition component refers to the position synchronization measurement module installed on the scanning actuator.

[0049] Subsequently, the actual lift-off distance corresponding to each sampling point is calculated based on the real-time spatial location and contour height data. For each sampling point, the Z-direction coordinate in the real-time spatial location is read, and the contour height value of the corresponding arc length coordinate is retrieved. The actual lift-off distance is then calculated according to the following formula: ; in, This is the actual lift-off distance. This represents the Z-axis coordinate in the real-time spatial location. This represents the contour height value corresponding to the arc length coordinate.

[0050] The actual lift-off distance reflects the true distance between the sensing surface of the eddy current probe and the surface of the spacer under test. The larger the value, the farther the probe is from the surface of the spacer under test, the weaker the electromagnetic coupling ability, and the more obvious the attenuation of the eddy current response caused by the lift-off effect. The smaller the value, the closer the probe is to the surface of the spacer under test, and the stronger the electromagnetic coupling ability.

[0051] To eliminate the influence of differences in installation height between different testing batches on the lift-off calculation results, the arithmetic mean of the actual lift-off distances of all sampling points within the current scanning path is used as the reference lift-off distance. The reference lift-off distance is used to characterize the overall average lift-off state between the eddy current probe and the surface of the spacer under test during this scanning process. The larger the value, the greater the average distance of the probe from the surface during the overall testing process.

[0052] Subsequently, the liftoff offset corresponding to each sampling point is calculated based on the actual liftoff distance and the reference liftoff distance. The calculation expression is as follows: ; in, To lift off offset, This is the actual lift-off distance. For reference lift-off distance.

[0053] The lift-off offset reflects the degree of deviation of the current sampling position from the overall average lift-off state. The larger the absolute value, the more obvious the local lift-off change caused by structures such as clamping grooves, bolt holes, connecting ribs, or rounded transitions; the smaller the absolute value, the more stable the probe lift-off state.

[0054] To uniformly describe the degree of lift-off variation at different locations, the lift-off offset is dimensionlessly normalized to obtain the surface lift-off fluctuation index, whose calculation expression is as follows: ; in, To extract the volatility index from the surface, To lift off offset, For reference lift-off distance, It is a very small constant. This is the index value of the sampling point.

[0055] The surface lift fluctuation index is used to reflect the degree of fluctuation of local lift changes relative to the overall average lift state. The larger the value, the more obvious the lift fluctuation caused by local geometric fluctuations, and the more significant the change in background response caused by the lift effect. The smaller the value, the more stable the local lift state, and the weaker the influence of lift changes on the background response.

[0056] Since the background response benchmark only reflects the geometric background response generated by the structural boundary and does not consider the influence of lift-off variation on the amplitude of the eddy current response, the background response benchmark is compensated according to the surface lift-off fluctuation index.

[0057] First, based on the detection data of historical crack-free standard spacers under different lifting conditions, the correspondence between the lifting fluctuation index and the background response change ratio was statistically analyzed, and the lifting compensation gain coefficient was obtained by least squares fitting.

[0058] The lift-off compensation gain coefficient is used to describe the degree of change in the background response corresponding to a unit lift-off volatility index. The larger the value, the more significant the impact of the lift-off change on the background response.

[0059] It should be noted that least squares fitting is a parameter estimation method that establishes functional relationships between variables based on historical sample data. It constructs an objective function for the sum of squared errors between predicted and actual measured values, and then seeks model parameters that minimize this sum. In this scheme, least squares fitting uses the surface lift-off fluctuation index and the corresponding background response variation ratio obtained from historical crack-free standard spacers under different lift-off conditions as input samples. By calculating the minimum value of the sum of squared errors between the predicted and actual measured values ​​for each group of samples, the lift-off compensation gain coefficient is determined, ensuring that the generated compensated background response is as close as possible to the actual background response.

[0060] Subsequently, the background response benchmark is compensated based on the lift-off compensation gain coefficient and the surface lift-off fluctuation index to generate the compensated background response quantity, the calculation expression of which is as follows: ; in, To compensate for the background response, The background amplitude in the background response benchmark. To lift off the compensation gain coefficient, To extract the volatility index from the surface, This is the index value of the sampling point.

[0061] The compensated background response is used to characterize the estimated background response after considering both the structural geometric background response and the local lift-off changes. The closer the value is to the actual detected background response, the higher the background modeling accuracy. This allows for a more accurate reduction of the background response impact caused by structural abrupt changes such as clamping grooves, bolt holes, connecting ribs, and rounded transitions in subsequent anomaly separation processing, improving the retention capability of local anomaly responses of surface microcracks. The compensated background response is then used for anomaly separation processing.

[0062] In step S4, the initial eddy current sequence is anomaly separated according to the compensation background response amount, and the anomaly separation result is enhanced and screened based on the structural response attribution segment. After the enhanced and screened process, the crack candidate region is located.

[0063] The initial eddy current sequence and the compensation background response have the same sampling order and correspondence, so the corresponding calculation is performed point by point according to the sampling point number.

[0064] First, background response subtraction is performed on each sampling point. The compensation background response of the corresponding sampling point is subtracted from the response amplitude in the initial eddy current sequence to obtain the abnormal response, which is calculated as follows: ; in, This is an abnormal response quantity. To label the response amplitude in the initial eddy current sequence, To compensate for the background response, This is the index value of the sampling point.

[0065] The abnormal response quantity is used to reflect the local residual response after deducting the structural geometric background response and the lift-off effect. The larger its absolute value, the more obvious the deviation of the location from the normal background response, and the higher the possibility of local defect response. The smaller its absolute value, the closer the detection response is to the background response, and the weaker the local abnormal characteristics.

[0066] Since the abnormal response generated by microcracks typically exhibits localized continuous changes, while random noise usually manifests as fluctuations at isolated sampling points, a continuous evaluation of the abnormal response quantity is necessary. For each sampling point, a continuous analysis window is formed by the sampling point before and after it. The average value of the abnormal response quantity within the continuous analysis window is calculated to obtain the local average abnormal response quantity, which is expressed as follows: ; in, This represents the local average abnormal response. , and These represent the abnormal response quantities corresponding to three adjacent sampling points.

[0067] The local average abnormal response quantity is used to reflect the degree of continuous change of the abnormal response within a local range. The larger the value, the better the spatial continuity of the abnormal response, which is more consistent with the response characteristics after the formation of microcracks; the smaller the value, the more the abnormal response mainly comes from random fluctuations.

[0068] Subsequently, based on the structural response attribution zone, the average absolute value of the local average abnormal response within each zone is calculated, and the abnormal enhancement coefficient of the corresponding sampling point is calculated. The calculation expression is as follows: , ; in, The abnormal enhancement coefficient, This represents the local average abnormal response. It is the average of the absolute values ​​of all local average anomalous response quantities within the structural response attribution zone. This represents the total number of sampling points within the structural response's assigned section. This is the sampling point index value. This is the index value of the structural response to the assigned section.

[0069] The anomaly enhancement coefficient is used to reflect the prominence of the current sampling point's abnormal response relative to the overall background level of the segment to which the structural response belongs. The larger the value, the more significantly the current abnormal response is higher than the normal background fluctuation level of the same segment, and the higher the probability that it belongs to a local abnormal response. The closer the value is to 1, the more consistent the current abnormal response is with the overall background change of the segment to which the structural response belongs.

[0070] To further suppress the residual background response still present near the structural boundary, an enhancement process is performed on the local average anomalous response quantity based on the anomalous enhancement coefficient to generate an enhanced anomalous response quantity, the calculation expression of which is as follows: ; in, To enhance the abnormal response quantity, This represents the local average abnormal response. The abnormal enhancement coefficient, This is the index value of the sampling point.

[0071] The enhanced anomaly response value is used to reflect the degree of local anomaly after adaptive enhancement of the structural response to the assigned region. The larger the value, the more prominent the anomaly response of the current sampling point is relative to the structural region, and the more obvious the microcrack features are. The smaller the value, the more the current sampling point is still within the range of structural background changes.

[0072] Subsequently, the upper quartile and interquartile range of the enhanced anomaly response within each structural response segment were calculated. Based on the upper quartile and interquartile range, the enhancement screening threshold for the corresponding segment was generated, and its calculation expression is as follows: ; in, The enhanced filtering threshold corresponding to the segment to which the j-th structural response belongs. Let be the upper quartile of the enhanced anomaly response within the segment to which the j-th structural response belongs. Let be the interquartile range of the enhanced anomaly response within the segment to which the j-th structural response belongs, and , It is the lower quartile.

[0073] The enhanced screening threshold is used to reflect the statistical upper limit of the normal and abnormal fluctuations of the current structural response to the segment. It adopts a robust statistical method based on interquartile range, which can effectively avoid the significant impact of a small number of real crack signals in the segment on the threshold calculation, and ensure that the threshold will not be passively raised in the multi-crack scenario, thereby maintaining a stable crack detection sensitivity.

[0074] Finally, the enhanced anomaly response quantity corresponding to each sampling point is compared with the enhancement screening threshold of the corresponding structural response segment: When the enhanced abnormal response is greater than or equal to the enhanced screening threshold, the corresponding sampling point is marked as a crack candidate point; Otherwise, the corresponding sampling point will not be marked as a crack candidate point.

[0075] Crack candidate points with continuous arc length coordinates and a distance between adjacent crack candidate points less than or equal to the arc length interval of one sampling point are merged to form the same crack candidate region. The minimum value of the arc length coordinates corresponding to the continuous crack candidate points is taken as the starting position of the crack candidate region, and the maximum value of the arc length coordinates corresponding to the continuous crack candidate points is taken as the ending position of the crack candidate region. Finally, the crack candidate region is located and used as the data input for subsequent defect identification and location calibration.

[0076] Finally, it should be noted that in this paper, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0077] Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0078] In this document, the singular forms “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that terms such as “comprising / including” or “having” specify the presence of the stated features, integrals, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, integrals, steps, operations, components, parts, or combinations thereof. Meanwhile, the term “and / or” as used in this specification includes any and all combinations of the associated listed items.

[0079] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can be referred to each other.

[0080] The above description of the disclosed embodiments will enable those skilled in the art to make or use various modifications to these embodiments. It will be readily apparent to those skilled in the art that the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for enhancing the eddy current detection features of microcracks on the surface of a spacer bar, characterized in that: Includes the following steps: Step S1: Retrieve the structural boundary position on the surface of the spacer to be tested, set the scanning path along the surface of the spacer to be tested, collect the probe scanning trajectory data, and divide the structural boundary position into the structural response belonging segment after collecting the probe scanning trajectory data; Step S2: Detect the initial eddy current sequence according to the scanning path, segment and mark the initial eddy current sequence based on the structural response attribution segment, and generate the background response benchmark for each structural response attribution segment by marking the initial eddy current sequence. Step S3: Collect the profile height data of the surface of the spacer bar to be tested, obtain the real-time spatial position of the eddy current probe as it moves along the scanning path, calculate the surface lift-off fluctuation index by combining the profile height data, compensate the background response benchmark by the surface lift-off fluctuation index and generate the compensated background response quantity. Step S4: Perform anomaly separation on the initial eddy current sequence based on the compensation background response, perform enhanced screening processing on the anomaly separation results based on the structural response attribution segment, and locate the crack candidate region after enhanced screening processing.

2. The method for enhancing the eddy current detection features of microcracks on the surface of a spacer bar according to claim 1, characterized in that: In step S1, the area to be scanned is expanded along the surface of the spacer bar to be tested, and the spacing between adjacent scanning lines is determined by half the effective sensing diameter of the eddy current probe, and the arc length interval of the sampling points is determined by one-quarter of the effective sensing diameter. The probe scanning trajectory data includes the sampling time and the spatial coordinates of the probe center; The scanning path is represented as a path centerline formed by connecting multiple discrete points in sequence, and each discrete point has corresponding spatial coordinates and arc length coordinates. Calculate the Euclidean distance between the spatial coordinates of the probe center at the current sampling time and the spatial coordinates of each discrete point along the path; Select the discrete point on the path with the smallest Euclidean distance as the corresponding point of the current sampling point on the scanning path; Assign the arc length coordinates of the discrete points on the path to the arc length coordinates of the current sampling point.

3. The method for enhancing the eddy current detection features of microcracks on the surface of a spacer bar according to claim 2, characterized in that: In step S1, the positions of each structural boundary are mapped to the scanning path, and the set of path points in the scanning path whose distance from the structural boundary position is less than or equal to the half-width of the segment extension is determined. The minimum value of the arc length coordinates corresponding to the path point set is used as the starting arc length coordinate of the boundary, and the maximum value of the arc length coordinates corresponding to the path point set is used as the ending arc length coordinate of the boundary. Based on the starting and ending arc length coordinates of each structural boundary position on the scanning path, the starting arc length coordinates are extended forward and the ending arc length coordinates are extended backward according to the segment expansion half-width. The expanded segment is then limited to the total arc length of the scanning path to obtain the structural response belonging segment.

4. The method for enhancing the eddy current detection features of microcracks on the surface of a spacer bar according to claim 3, characterized in that: In step S2, the initial eddy current sequence is constructed by sorting the sampling point arc length coordinates as the eddy current probe moves along the scanning path, including the sampling point number, arc length coordinates, and response amplitude. The initial eddy current sequence is labeled by comparing the arc length coordinates of each sampling point in the initial eddy current sequence with the starting and ending arc length coordinates of the structural response segment. When the arc length coordinates of a sampling point fall into a certain structural response segment, the sampling point is marked with the corresponding segment number and structural type. Conversely, do not mark the sampling points; Extract the response amplitude corresponding to the structural response segment from the initial eddy current sequence.

5. The method for enhancing the eddy current detection features of microcracks on the surface of a spacer bar according to claim 4, characterized in that: In step S2, the number of background statistical window sampling points corresponding to the structural response belonging to the segment is determined based on the effective sensing radius of the probe and the arc length interval between adjacent sampling points. Based on the response amplitude corresponding to the number of background statistical window sampling points, the median is calculated to generate the background amplitude. The background amplitude, corresponding arc length coordinates, segment number, and structure type of each sampling point are rearranged according to the sampling order of the initial eddy current sequence to obtain the background response benchmark.

6. The method for enhancing the eddy current detection features of microcracks on the surface of a spacer bar according to claim 1, characterized in that: In step S3, the contour height data of the surface of the spacer bar to be tested is collected; Contour height data refers to the surface height information obtained by scanning the surface of the spacer bar to be measured along the scanning path using a laser contour scanning device. Acquire the real-time spatial position of the eddy current probe as it moves along the scanning path; Real-time spatial position refers to the spatial coordinates of the probe center synchronously acquired by the trajectory acquisition component as the eddy current probe moves along the scanning path, including the X-direction coordinates, Y-direction coordinates, and Z-direction coordinates at the corresponding sampling time; The Z-axis coordinate represents the vertical height of the eddy current probe center relative to the mounting reference surface; Read the Z-axis coordinates in the real-time spatial position, retrieve the contour height value of the corresponding arc length coordinates, and calculate the actual lift-off distance.

7. The method for enhancing the eddy current detection features of microcracks on the surface of a spacer bar according to claim 6, characterized in that: In step S3, the arithmetic mean of the actual lift-off distances of all sampling points within the current scanning path is used as the reference lift-off distance; The liftoff offset corresponding to each sampling point is calculated based on the actual liftoff distance and the reference liftoff distance. The liftoff offset is then normalized to obtain the surface liftoff fluctuation index. Based on the detection data of historical crack-free standard spacers under different lifting conditions, the correspondence between the lifting fluctuation index and the background response change ratio was statistically analyzed, and the lifting compensation gain coefficient was obtained by least squares fitting. The background response benchmark is compensated based on the lift-off compensation gain coefficient and the surface lift-off fluctuation index to generate the compensated background response quantity.

8. The method for enhancing the eddy current detection features of microcracks on the surface of a spacer bar according to claim 1, characterized in that: In step S4, the compensation background response value at the corresponding sampling point is subtracted from the response amplitude in the initial eddy current sequence to obtain the abnormal response value; For each sampling point, a continuous analysis window is formed by one sampling point before and after it. The average value of the abnormal response within the continuous analysis window is calculated to obtain the local average abnormal response. According to the structural response to the assigned zone, the average absolute value of the local average abnormal response in each zone is calculated, and the abnormal enhancement coefficient of the corresponding sampling point is calculated. The local average anomaly response is enhanced based on the anomaly enhancement coefficient to generate an enhanced anomaly response. The upper quartile and interquartile range of the enhanced abnormal response within each structural response segment are calculated separately, and the enhancement screening threshold is generated based on the upper quartile and interquartile range.

9. The method for enhancing the eddy current detection features of microcracks on the surface of a spacer bar according to claim 8, characterized in that: In step S4, the enhanced anomaly response quantity corresponding to each sampling point is compared with the enhancement screening threshold of the structural response segment to which it belongs: When the enhanced abnormal response is greater than or equal to the enhanced screening threshold, the corresponding sampling point is marked as a crack candidate point; Otherwise, the corresponding sampling point will not be marked as a crack candidate point; Crack candidate points with continuous arc length coordinates and a distance between adjacent crack candidate points less than or equal to the arc length interval of one sampling point are merged to form the same crack candidate region. The minimum value of the arc length coordinates corresponding to the candidate points of continuous cracks is taken as the starting position of the crack candidate region, and the maximum value of the arc length coordinates corresponding to the candidate points of continuous cracks is taken as the ending position of the crack candidate region, thus completing the crack candidate region localization.

Images