Workpiece defect detection method and device based on pre-magnetization and swept frequency pulse eddy current

Abstract

The present invention discloses a method and device for detecting defects in a workpiece based on pre-magnetization and swept-frequency pulse eddy current, wherein the method comprises: performing local saturation pre-magnetization on the workpiece to be tested by means of a permanent magnet, applying low-frequency and high-frequency swept-frequency pulse signals to the workpiece to be tested that is locally saturated and pre-magnetized respectively, so that the workpiece to be tested generates a response signal; processing and analyzing the response signal, and generating the defect size and defect position of the workpiece to be tested. The method can solve the problem that traditional pulse eddy current can only detect surface and shallow defects in ferromagnetic materials, obtain the defect size by detecting the characteristic quantity of the response signal, and can distinguish whether the defect is located on the upper surface or the lower surface, thereby improving the detection accuracy and detection efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of defect detection, and in particular to a workpiece defect detection method and device based on pre-magnetization and swept-frequency pulse eddy current. Background Art

[0002] In the petroleum, chemical and other industries, storage tanks are important tools for storing crude oil, natural gas and various petrochemical raw materials. Oilfield storage tanks are mostly made of ferromagnetic materials. Due to being in the natural environment for many years, the storage tanks will be affected by various adverse factors during their service, resulting in aging and damage. In particular, corrosion thinning, corrosion perforation, fissure cracks, etc. caused by chemical corrosion and electrochemical corrosion pose serious hidden dangers to the safety of storage tanks. If not handled in time, it may cause leakage accidents. Among them, the bottom of the tank is in a harsh environment and bears the greatest pressure, which is more prone to defects. It is one of the most critical parts in tank defect detection.

[0003] Eddy current testing can generally only be applied to non-ferromagnetic conductive materials, while the Q235 steel commonly used in oil and gas tank bodies is a ferromagnetic material. In ferromagnetic materials, due to the existence of the skin effect, the penetration depth of eddy current in traditional eddy current testing technology is very shallow, and it can only detect shallow defects on the upper surface of the tank bottom plate, and is insensitive to deep defects in the tank bottom plate. The inner wall of the tank bottom plate is prone to electrochemical corrosion caused by sewage and sludge, and the outer wall of the tank bottom plate is in direct contact with the soil and is also susceptible to corrosion and damage. Therefore, increasing the penetration depth of eddy current is a prerequisite for applying eddy current testing technology to tank bottom plate defect detection.

[0004] The use of array technology can improve the spatial resolution of detection, thereby improving detection performance. Traditional eddy current detection mostly uses enameled copper wire to wind coils. The coil parameters are highly random, and it is difficult to ensure the consistency of parameters between each coil, which affects the application of eddy current array technology in actual engineering.

[0005] Both the inner and outer walls of the tank bottom plate are prone to corrosion, resulting in defects. In order to achieve high-definition and efficient automatic detection, it is necessary to process and improve the excitation signal and response signal, overcome the shortcomings of traditional eddy current detection, and strive to detect defects of different sizes on the inner and outer walls of the tank bottom plate at the same time during a single detection process, and obtain defect parameters by detecting characteristic quantities. Summary of the invention

[0006] The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

[0007] To this end, an object of the present invention is to propose a workpiece defect detection method based on pre-magnetization and swept-frequency pulse eddy current, which can solve the problem that traditional pulse eddy current can only detect surface and shallow defects in ferromagnetic materials. The defect size is obtained by detecting characteristic quantities through the response signal, and it can distinguish whether the defect is located on the upper surface or the lower surface, thereby improving the detection accuracy and detection efficiency.

[0008] Another object of the present invention is to provide a workpiece defect detection device based on pre-magnetization and swept-frequency pulse eddy current.

[0009] To achieve the above object, an embodiment of the present invention provides a workpiece defect detection method based on pre-magnetization and swept frequency pulse eddy current, comprising:

[0010] S1, obtaining a workpiece to be measured, performing local saturation pre-magnetization on the workpiece to be measured, and applying low-frequency and high-frequency sweep pulse signals to the workpiece to be measured that has been locally saturated pre-magnetized so that the workpiece to be measured generates a response signal;

[0011] S2, processing and analyzing the response signal to generate the defect size and defect position of the workpiece to be tested.

[0012] The workpiece defect detection method based on pre-magnetization and swept-frequency pulse eddy current of the embodiment of the present invention obtains the workpiece to be tested, performs local saturation pre-magnetization on the workpiece to be tested, applies low-frequency and high-frequency swept-frequency pulse signals to the workpiece to be tested that is locally saturated and pre-magnetized, respectively, so that the workpiece to be tested generates a response signal, and processes and analyzes the response signal to generate the defect size and defect position of the workpiece to be tested. In this way, the problem that traditional pulse eddy current can only detect surface and shallow defects in ferromagnetic materials can be solved, the defect size is obtained by detecting the characteristic quantity of the response signal, and it can be distinguished whether the defect is located on the upper surface or the lower surface, thereby improving the detection accuracy and detection efficiency.

[0013] In addition, the workpiece defect detection method based on pre-magnetization and swept-frequency pulse eddy current according to the above embodiment of the present invention may also have the following additional technical features:

[0014] Furthermore, in one embodiment of the present invention, the swept frequency pulse signal is generated by multiplying a linear frequency modulation signal and a sign function.

[0015] Furthermore, in one embodiment of the present invention, the S2 further comprises:

[0016] Performing signal extension and signal fusion processing on the response signal through a peak detector;

[0017] Extracting detection feature quantity from the processed response signal;

[0018] The detection feature quantity is analyzed to generate defect size information and defect position information of the workpiece to be detected.

[0019] Further, in one embodiment of the present invention, the analyzing the detection feature quantity to generate the defect size information and defect position information of the workpiece to be detected includes:

[0020] The extracted detection feature quantity is the inflection point time and the peak point of the processed response signal. The defect position of the workpiece to be measured is determined according to the inflection point time, and the defect size of the workpiece to be measured is determined according to the peak point.

[0021] Furthermore, in one embodiment of the present invention,

[0022] Performing local saturation pre-magnetization on the workpiece to be measured by means of a permanent magnet;

[0023] The frequency sweep pulse signal is applied to the workpiece to be tested through a detection probe array.

[0024] To achieve the above object, another embodiment of the present invention proposes a workpiece defect detection device based on pre-magnetization and swept-frequency pulse eddy current, comprising: a permanent magnet, a detection probe array, a main control circuit and a host computer;

[0025] The permanent magnet is used to perform local saturation pre-magnetization on the workpiece to be measured;

[0026] The detection probe array is used to successively apply low-frequency and high-frequency sweep pulse signals to the locally saturated pre-magnetized workpiece to be tested so that the workpiece to be tested generates a response signal;

[0027] The main control circuit is used to send the response signal to the host computer;

[0028] The host computer is used to analyze the response signal and generate the defect size and defect position of the workpiece to be tested.

[0029] The workpiece defect detection device based on pre-magnetization and swept-frequency pulse eddy current of the embodiment of the present invention obtains the workpiece to be tested, performs local saturation pre-magnetization on the workpiece to be tested, applies low-frequency and high-frequency swept-frequency pulse signals to the workpiece to be tested that is locally saturated and pre-magnetized, respectively, so that the workpiece to be tested generates a response signal, and processes and analyzes the response signal to generate the defect size and defect position of the workpiece to be tested. In this way, the problem that traditional pulse eddy current can only detect surface and shallow defects in ferromagnetic materials can be solved, the defect size can be obtained by detecting the characteristic quantity of the response signal, and it can be distinguished whether the defect is located on the upper surface or the lower surface, thereby improving the detection accuracy and detection efficiency.

[0030] In addition, the workpiece defect detection device based on pre-magnetization and swept-frequency pulse eddy current according to the above embodiment of the present invention may also have the following additional technical features:

[0031] Furthermore, in one embodiment of the present invention, the swept frequency pulse signal is generated by multiplying a linear frequency modulation signal and a sign function.

[0032] Furthermore, in one embodiment of the present invention, the detection probe array is also used to perform signal extension and signal fusion processing on the response signal through a peak detector;

[0033] The host computer is specifically used to extract detection feature quantities from the processed response signal, and analyze the detection feature quantities to generate defect size information and defect position information of the workpiece to be detected.

[0034] Further, in one embodiment of the present invention, the analyzing the detection feature quantity to generate the defect size information and defect position information of the workpiece to be detected includes:

[0035] The extracted detection feature quantity is the inflection point time and the peak point of the processed response signal. The defect position of the workpiece to be measured is determined according to the inflection point time, and the defect size of the workpiece to be measured is determined according to the peak point.

[0036] Furthermore, in one embodiment of the present invention, the main control circuit is also used to control the coordinated operation of the detection probe array.

[0037] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0039] Figure 1 A flow chart of a workpiece defect detection method based on pre-magnetization and swept-frequency pulse eddy current according to an embodiment of the present invention;

[0040] Figure 2 A schematic diagram of the structure of a device for implementing a workpiece defect detection method based on pre-magnetization and swept-frequency pulse eddy current according to an embodiment of the present invention;

[0041] Figure 3 A schematic diagram of a permanent magnet structure according to an embodiment of the present invention;

[0042] Figure 4 is a schematic diagram of a main control circuit according to an embodiment of the present invention;

[0043] Figure 5 is a principle diagram of a detection probe array according to an embodiment of the present invention;

[0044] Figure 6 A schematic diagram of a linear frequency modulation signal and a swept frequency pulse excitation according to an embodiment of the present invention;

[0045] Figure 7 is a waveform diagram of a saturated frequency swept pulse eddy current defect detection signal according to an embodiment of the present invention;

[0046] Figure 8 Schematic diagram of characteristic quantities of saturated frequency swept pulse eddy current detection signals according to an embodiment of the present invention;

[0047] Fig. 9 is a graph showing the relationship between the peak value of a saturated frequency swept pulse eddy current detection signal and the defect diameter according to an embodiment of the present invention;

[0048] Fig.10 The figure is a schematic structural diagram of a workpiece defect detection device based on pre-magnetization and swept-frequency pulse eddy current according to an embodiment of the present invention. DETAILED DESCRIPTION

[0049] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0050] The following describes a workpiece defect detection method and device based on pre-magnetization and swept-frequency pulse eddy current according to an embodiment of the present invention with reference to the accompanying drawings.

[0051] First, a workpiece defect detection method based on pre-magnetization and swept-frequency pulse eddy current proposed according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0052] Figure 1 The present invention is a flow chart of a workpiece defect detection method based on pre-magnetization and swept-frequency pulse eddy current according to an embodiment of the present invention.

[0053] like Figure 1 As shown, the workpiece defect detection method based on pre-magnetization and swept frequency pulse eddy current includes the following steps:

[0054] Step S1, obtaining a workpiece to be measured, performing local saturation pre-magnetization on the workpiece to be measured, and applying low-frequency and high-frequency sweep pulse signals to the workpiece to be measured that has been locally saturated pre-magnetized to make the workpiece to be measured generate a response signal.

[0055] Specifically, the workpiece to be tested may be a variety of ferromagnetic materials. As one of the workpieces to be tested, a tank bottom plate is used as the workpiece to be tested, and defect detection is performed on the tank bottom plate.

[0056] like Figure 2 As shown, the tank bottom plate is firstly locally saturated and pre-magnetized by a permanent magnet to reduce the magnetic permeability of the material so as to increase the eddy current penetration depth.

[0057] Specifically, the bottom plate of a storage tank is generally made of ferromagnetic materials such as carbon steel, and its magnetic permeability is much higher than that of non-ferromagnetic materials. The skin depth of eddy current is negatively correlated with the magnetic permeability of the material to be tested, so the skin depth of eddy current in ferromagnetic materials is extremely small. Permanent magnets are used to locally pre-magnetize the bottom plate of the storage tank so that the material reaches a saturated or near-saturated state, reducing the magnetic permeability of the material to increase the penetration depth of the eddy current. When traditional eddy current technology is applied to ferromagnetic materials, it can only detect shallow defects in the test piece, while saturated eddy current can detect deep defects.

[0058] like Figure 3 The figure shows the structure of the permanent magnet. According to the actual engineering requirements, the permanent magnet is designed to be two identical magnets placed side by side, and the effective magnetization area is the area between the two permanent magnets. The material used for the corner part of the magnet is 10# steel, and the other parts of the magnet are made of neodymium iron boron NdFe30 material.

[0059] After the workpiece to be measured is locally saturated and pre-magnetized by a permanent magnet, low-frequency and high-frequency sweep pulse signals are applied to the workpiece to be measured in sequence.

[0060] In an embodiment of the present invention, a new sweep frequency pulse signal is used as an excitation signal, which is characterized in that the frequency of the excitation signal changes linearly with time, and the eddy current penetration depths generated by excitation signals of different frequencies are different. The low-frequency component emitted first is sensitive to deep defects and defects with larger sizes, and the high-frequency component emitted later is sensitive to shallow defects and defects with smaller sizes, thereby achieving the purpose of simultaneously detecting defects of different sizes in shallow and deep layers.

[0061] The swept frequency pulse excitation is derived from the linear frequency modulation signal in the signal detection theory, which is characterized by that the instantaneous frequency changes linearly with time, and the frequency components of the signal are uniform within the corresponding bandwidth. The standard linear frequency modulation signal is very complex in hardware implementation, so in the embodiment of the present invention, the linear frequency modulation signal is used as a reference, and then the linear frequency modulation signal and the sign function are multiplied to obtain the corresponding swept frequency pulse excitation.

[0062] Furthermore, by applying low-frequency and high-frequency sweep pulse signals to the workpiece to be tested through the detection probe array, defects of different sizes in shallow and deep layers can be detected simultaneously in one sweep process. By further processing and analyzing the response signal, the size and position information of various defects in the workpiece to be tested can be obtained.

[0063] Step S2, processing and analyzing the response signal to generate the defect size and defect position of the workpiece to be tested.

[0064] Furthermore, step S2 further comprises:

[0065] The response signal is extended and fused by a peak detector;

[0066] Extracting detection feature quantity from the processed response signal;

[0067] The detection feature quantity is analyzed to generate the defect size information and defect position information of the workpiece to be tested.

[0068] Furthermore, the detection feature quantity is analyzed to generate defect size information and defect position information of the workpiece to be detected, including:

[0069] The extracted detection feature quantities are the inflection point time and the peak point of the processed response signal. The defect position of the workpiece to be tested is determined according to the inflection point time, and the defect size of the workpiece to be tested is determined according to the peak point.

[0070] Specifically, the traditional pulse eddy current detection only collects the response signal after a single pulse, and the signal decays very quickly. In the embodiment of the present invention, the response after each pulse in the swept frequency pulse excitation is regarded as a complete full-process signal for processing, and the duration of a single pulse eddy current response signal is extended by a peak detector, so that the response signal of the swept frequency pulse eddy current detection is fused into a whole. The fused response signal is continuously collected from the start time of the excitation.

[0071] It should be noted that the peak detector can be implemented by a peak detection module arranged in the detection probe array.

[0072] After the response signal is extended and fused in the detection probe array, it is transmitted to the main control circuit through the communication module for aggregation and fusion. The main control circuit then sends the aggregated and fused response signal to the host computer, which processes and analyzes the response signal. The host computer not only analyzes and processes the detection data and extracts the detection feature quantity, but also can display the detection data in real time.

[0073] The main control circuit can also store the corresponding signal in a storage module such as an SD card for subsequent analysis.

[0074] Among them, as a defect detection method, the host computer extracts the detection feature quantity from the response signal, and generates the defect position information and defect size information of the workpiece to be tested by analyzing the detection feature quantity. The detection feature quantity is the inflection point time and peak point of the response signal. The defect position of the workpiece to be tested is determined according to the inflection point time, and the defect size of the workpiece to be tested is determined according to the peak point.

[0075] There are three inflection points in the response signal, among which the time of the first inflection point can be used to distinguish whether the defect is located on the upper or lower surface of the tank bottom plate. The lower frequency excitation signal has a greater penetration depth and can reach the location of the defect on the lower surface, while the low-frequency excitation signal is located at the front end of the swept frequency excitation, so the inflection point of the lower surface appears earlier than that of the upper surface. The inflection point time difference between the upper and lower surfaces is obvious, which can be used as a characteristic quantity to determine the location of the defect. The third inflection point is the peak point of the response signal. The peak value of the differential response signal appears at the end of the excitation signal. It is the sum of the responses generated by each excitation frequency in the swept frequency excitation, which represents the overview of the defect size. Therefore, the peak value is used to judge the defect radius. The combination of the two characteristic quantities can obtain the size information and location information of the defect.

[0076] In summary, the detection method of the embodiment of the present invention first uses a magnet to perform local saturation pre-magnetization on the bottom plate of the storage tank to reduce the magnetic permeability of the material to increase the penetration depth of the eddy current. At the same time, a new sweep pulse excitation is proposed, which is characterized in that the frequency of the excitation signal changes linearly with time, and the eddy current penetration depth generated by the excitation signals of different frequencies is different. The low-frequency component emitted first is sensitive to deep defects and defects with larger sizes, and the high-frequency component emitted later is sensitive to shallow defects and defects with smaller sizes, so as to achieve the purpose of simultaneously detecting defects of different sizes in shallow and deep layers. For the detection response signal, since the signal attenuation speed is extremely fast, the signal extension and signal fusion are performed by the peak detector. Fifteen detection probes are arranged in an array form in the central area of ​​the magnet, and each probe is equipped with an excitation coil and a receiving coil for eddy current detection. The main control circuit in the system controls all probes to work together, collects and organizes the detection data of each probe, and saves the data to a storage card or directly displays it in real time on the host computer. Finally, the host computer performs data processing, extracts two characteristic quantities of inflection point time and peak size, and obtains the size information and position information of the defect. The method and device of the present invention can solve the problem that traditional pulse eddy current can only detect surface and shallow defects in ferromagnetic materials. The defect size is obtained by detecting characteristic quantities of the response signal, and it can be distinguished whether the defect is located on the upper surface or the lower surface, thereby improving detection accuracy and detection efficiency.

[0077] Specifically, Figure 2As shown, in the detection device, the workpiece to be tested is brought into a saturated or near-saturated state by a permanent magnet to improve the eddy current detection performance. A staggered array of 15 detection probes is arranged in the effective magnetization area of ​​the permanent magnet to improve the detection accuracy. Each probe is equipped with a set of eddy current excitation coils and two sets of receiving coils to realize sweep pulse eddy current detection, and signal conditioning and data acquisition modules are provided to perform preliminary processing on the detection signal. The processed digital signal is transmitted from the bottom detection probe to the upper main control circuit via RS485 communication, and the main control circuit realizes the overall control of the detection system and the summary and collation of the detection data. The defect detection data can be displayed and analyzed in real time by a computer, or imported into a memory card for subsequent further analysis, so as to obtain relevant information on the defects of the tank bottom plate.

[0078] Specifically, the main control circuit is used to control the coordinated work of multiple probes, collect and organize the detection data of each probe. The data can be transmitted to the host computer in real time for processing and display, and the data can also be directly stored in the storage device for subsequent analysis.

[0079] In this embodiment, the main control circuit is used as the control core of the detection device, and its principle block diagram is as follows: Figure 4 As shown. The main control circuit is based on a dual-chip core board, adopts a dual-core structure of FPGA and DSP working together, and has the timing processing capability of FPGA and the powerful computing capability of DSP. FPGA and DSP communicate through uPP. The main control circuit exchanges data with the underlying 15-way probes through the communication module. The processed data can be transmitted to the host computer in real time through the RS485 communication module for processing and display. At the same time, the data can also be directly stored in storage modules such as SD cards for subsequent analysis. The circuit is equipped with a power management module to uniformly manage the power supply voltages at all levels on the entire main control circuit.

[0080] In the detection probe array, the detection probe is the basic detection unit. Multiple detection probes are arranged in an array with good array consistency to improve detection performance. The detection probe is equipped with an eddy current detection excitation coil and a receiving coil, and is equipped with a signal conditioning circuit to perform preliminary processing on the detection signal. Each probe can independently complete the basic function of swept frequency pulse eddy current detection. In order to improve the spatial resolution of defect detection, each probe is very small and arranged in an array. The principle block diagram of a single detection probe is shown in the figure. Figure 5 The detection probe is based on CPLD and is equipped with a power management module to uniformly manage the power supply voltages at all levels on the probe. It also includes two main parts: excitation signal generation and detection signal reception.

[0081] The eddy current detection coil on the probe is completed by densely winding on the circuit board to improve the detection accuracy and ensure the consistency between each probe. The inner diameter of the excitation coil is 16.8mm, the outer diameter is 20mm, the number of turns is 34, and the inductance value is 34.2μH; the inner diameter of the receiving coil is 2.8mm, the outer diameter is 7.8, the number of turns is 52, and the inductance value is 4.5μH.

[0082] The excitation signal generation part adopts the CSD series N-channel enhancement MOSFET produced by TI, which can meet the control requirements of the excitation coil. Through MOSFET, the voltage and power of the CPLD sweep logic signal are amplified to generate a high jump speed and stable pulse amplitude sweep pulse excitation, which is applied to the excitation coil, realizing the requirements of the swept pulse eddy current detection for generating a primary field. The response signal on the receiving coil is converted into a digital signal after being processed by the signal follower module, peak detection module, signal conditioning module and AD sampling module, and input into the CPLD chip to complete the detection of a saturated swept pulse eddy current signal.

[0083] In this embodiment, a peak detector based on a Schottky diode is used to fuse the response signal of the swept frequency pulse eddy current. The rate of change of the induced voltage on the receiving coil is very high and the duration is extremely short. The function of the peak detector is to memorize and maintain the maximum value of the positive amplitude of the received fluctuation signal, so that the pulse eddy current response signal, which originally decays very quickly, becomes a waveform with a longer duration and is convenient for signal acquisition. After applying the peak detector, the response signal after a single excitation pulse in the swept frequency excitation will be fused into an overall signal. Starting from the start time of the excitation, the fused response signal is continuously collected, and the signal in the entire time window is treated as a whole for processing and analysis.

[0084] In this embodiment, the sweep pulse excitation is derived from a linear frequency modulation signal (Chirp signal). The pulse signal is approximated based on the linear frequency modulation signal to achieve the sweep pulse excitation in the time domain and frequency domain. Taking the cutoff frequency of 1MHz as an example, the signal bandwidth is set to obtain the corresponding linear frequency modulation signal as shown in the figure. Figure 6 As shown in the lower middle graph, the approximate sweep pulse signal is obtained by calculating the symbol function as follows Figure 5 As shown in the upper middle graph, the standard linear frequency modulation signal is very complex in hardware implementation, so the present invention uses the linear frequency modulation signal as a reference, and then multiplies the linear frequency modulation signal and the sign function to obtain the corresponding swept frequency pulse excitation.

[0085] In this embodiment, an artificial defect is set, and the defect parameters are given in Table 1. The differential response signals obtained by the detection experiment of defects with different radii are as follows: Figure 7 shown.

[0086] Table 1 Defect parameters

[0087]

[0088] It can be seen that the overall differential response signal increases with the increase of the defect radius, and this trend can be characterized by the peak value. In addition, the differential response signal has three obvious inflection points, of which the last inflection point is the peak point of the differential response signal. The blue in the figure (the upper broken line in the figure) is the upper surface defect detection signal, and the red (the lower broken line in the figure) is the lower surface defect detection signal. For upper surface defects, the first inflection point of the response signal appears at around 60us; and for lower surface defects, the first inflection point of the response signal appears at around 40us. According to the time when the first inflection point of the differential detection signal appears, the location of the defect can be distinguished. Extract the detection feature quantity of the differential response signal, and the feature quantity is shown as follows Figure 8 The above two features are extracted and the obtained data are sorted in Table 2.

[0089] Table 2 Detection feature data

[0090]

[0091] Observe the data in the table. For the upper surface defects, the inflection time fluctuates within the range of 60μs+ / -5μs, and for the lower surface defects, the inflection time fluctuates within the range of 40μs+ / -5μs. Therefore, the defects on the upper and lower surfaces can be easily distinguished by the inflection time. This is because the lower frequency excitation signal has a greater penetration depth and can reach the location of the lower surface defects, while the low-frequency excitation signal is located at the front end of the swept frequency excitation, so the inflection point of the lower surface appears earlier than that of the upper surface. The inflection time difference between the upper and lower surfaces is obvious, so the discrimination threshold can be simply set to 50μs. If the inflection time is less than the threshold time, it is determined that the detected defect is located on the lower surface of the specimen; if the inflection time is greater than the threshold time, it is determined that the detected defect is located on the upper surface of the specimen. The above experiments prove that the inflection time is an effective feature quantity for distinguishing defects on the upper and lower surfaces.

[0092] The detection data of the peak value of the upper and lower surface defect response signals are plotted, and the results are as follows: Fig. 9 As shown, the upper broken line is the upper surface defect, and the lower broken line is the lower surface defect. The peak value of the differential response signal appears at the end of the excitation signal, which is the sum of the responses generated by each excitation frequency in the swept frequency excitation, and represents the profile of the defect size. For the upper surface defect, the linear relationship between the peak value of the response signal and the defect diameter is good. For the upper surface defect, the linear relationship between the amplitude of the response signal and the defect diameter is good, and its goodness of fit R1 2 =0.9879, it can be considered that the signal amplitude is linearly related to the defect diameter; the linear relationship between the amplitude of the defect on the lower surface and the defect diameter is slightly worse than that on the upper surface, and its goodness of fit R2 2=0.9179.

[0093] According to the workpiece defect detection method based on pre-magnetization and swept-frequency pulse eddy current proposed in an embodiment of the present invention, by acquiring the workpiece to be tested, the workpiece to be tested is locally saturated pre-magnetized, and low-frequency and high-frequency swept-frequency pulse signals are applied to the locally saturated pre-magnetized workpiece to be tested respectively to make the workpiece to be tested generate a response signal, and the response signal is processed and analyzed to generate the defect size and defect position of the workpiece to be tested. In this way, the problem that traditional pulse eddy current can only detect surface and shallow defects in ferromagnetic materials can be solved, the defect size is obtained by detecting the characteristic quantity of the response signal, and it can be distinguished whether the defect is located on the upper surface or the lower surface, thereby improving the detection accuracy and detection efficiency.

[0094] Next, a workpiece defect detection device based on pre-magnetization and swept-frequency pulse eddy current proposed in accordance with an embodiment of the present invention will be described with reference to the accompanying drawings.

[0095] Fig.10 The figure is a schematic structural diagram of a workpiece defect detection device based on pre-magnetization and swept-frequency pulse eddy current according to an embodiment of the present invention.

[0096] like Fig.10 As shown, it includes: a permanent magnet, a detection probe array, a main control circuit and a host computer.

[0097] The permanent magnet is used to perform local saturation pre-magnetization on the workpiece to be tested;

[0098] The detection probe array is used to successively apply low-frequency and high-frequency sweep pulse signals to the workpiece to be tested which is partially saturated and pre-magnetized so that the workpiece to be tested generates a response signal;

[0099] The main control circuit is used to send the response signal to the host computer;

[0100] The host computer is used to analyze the response signal and generate the defect size and defect position of the workpiece to be tested.

[0101] Furthermore, in one embodiment of the present invention, a swept frequency pulse signal is generated by multiplying a linear frequency modulation signal and a sign function.

[0102] Furthermore, in one embodiment of the present invention, the detection probe array is also used to perform signal extension and signal fusion processing on the response signal through a peak detector;

[0103] The host computer is specifically used to extract the detection feature quantity from the processed response signal, and analyze the detection feature quantity to generate defect size information and defect position information of the workpiece to be tested.

[0104] Furthermore, in one embodiment of the present invention, the defect size information and defect position information of the workpiece to be tested are generated by analyzing the detection feature quantity, including:

[0105] The extracted detection feature quantities are the inflection point time and peak point of the processed response signal. The defect position of the workpiece to be tested is determined according to the inflection point time, and the defect size of the workpiece to be tested is determined according to the peak point.

[0106] Furthermore, in one embodiment of the present invention, the main control circuit is also used to control the coordinated operation of the detection probe array.

[0107] It should be noted that the aforementioned explanation of the embodiment of the workpiece defect detection method based on pre-magnetization and swept-frequency pulse eddy current is also applicable to the device of this embodiment and will not be repeated here.

[0108] According to the workpiece defect detection device based on pre-magnetization and swept-frequency pulse eddy current proposed in the embodiment of the present invention, by acquiring the workpiece to be tested, the workpiece to be tested is locally saturated pre-magnetized, and low-frequency and high-frequency swept-frequency pulse signals are applied to the locally saturated pre-magnetized workpiece to be tested respectively to make the workpiece to be tested generate a response signal, and the response signal is processed and analyzed to generate the defect size and defect position of the workpiece to be tested. In this way, the problem that traditional pulse eddy current can only detect surface and shallow defects in ferromagnetic materials can be solved, the defect size is obtained by detecting the characteristic quantity of the response signal, and it can be distinguished whether the defect is located on the upper surface or the lower surface, thereby improving the detection accuracy and detection efficiency.

[0109] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0110] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0111] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A workpiece defect detection method based on pre-magnetization and swept frequency pulse eddy current, characterized in that: The following steps are involved: S1, obtaining a workpiece to be measured, performing local saturation pre-magnetization on the workpiece to be measured, and applying low-frequency and high-frequency sweep pulse signals to the workpiece to be measured that has been locally saturated pre-magnetized so that the workpiece to be measured generates a response signal; S2, processing and analyzing the response signal to generate the defect size and defect position of the workpiece to be tested; Generate the frequency sweep pulse signal by multiplying the linear frequency modulation signal and the sign function; Said S2 further comprises: Performing signal extension and signal fusion processing on the response signal through a peak detector; Extracting detection feature quantity from the processed response signal; Analyzing the detection feature quantity to generate defect size information and defect position information of the workpiece to be detected; The step of analyzing the detection feature quantity to generate defect size information and defect position information of the workpiece to be detected includes: The extracted detection feature quantity is the inflection point time and the peak point of the processed response signal. The defect position of the workpiece to be measured is determined according to the inflection point time, and the defect size of the workpiece to be measured is determined according to the peak point.

2. The method according to claim 1, characterized in that Performing local saturation pre-magnetization on the workpiece to be measured by means of a permanent magnet; The frequency sweep pulse signal is applied to the workpiece to be tested through a detection probe array.

3. A workpiece defect detection device based on pre-magnetization and swept frequency pulse eddy current for implementing the method as claimed in any one of claims 1 to 2, characterized in that: include: Permanent magnet, detection probe array, main control circuit and host computer; The permanent magnet is used to perform local saturation pre-magnetization on the workpiece to be measured; The detection probe array is used to successively apply low-frequency and high-frequency sweep pulse signals to the locally saturated pre-magnetized workpiece to be tested so that the workpiece to be tested generates a response signal; The main control circuit is used to send the response signal to the host computer; The host computer is used to analyze the response signal to generate the defect size and defect position of the workpiece to be tested; Generate the frequency sweep pulse signal by multiplying the linear frequency modulation signal and the sign function; The detection probe array is also used to perform signal extension and signal fusion processing on the response signal through a peak detector; The host computer is specifically used to extract the detection feature quantity from the processed response signal, and analyze the detection feature quantity to generate the defect size information and defect position information of the workpiece to be tested; The step of analyzing the detection feature quantity to generate defect size information and defect position information of the workpiece to be detected includes: The extracted detection feature quantity is the inflection point time and the peak point of the processed response signal. The defect position of the workpiece to be measured is determined according to the inflection point time, and the defect size of the workpiece to be measured is determined according to the peak point.

4. The device according to claim 3, characterized in that The main control circuit is also used to control the coordinated work of the detection probe array.

Images