Magnetic sheet crack detection method and system

Abstract

The invention relates to the technical field of magnetic material detection, in particular to a magnetic sheet crack detection method and system.The method comprises the steps that a to-be-detected magnetic sheet is placed in a uniform magnetic field generating device to be magnetized, and the magnetic field intensity of a magnetic field is selected according to the characteristics of the to-be-detected magnetic sheet; after magnetization is completed, independent Hall effect sensors are placed around the magnetic sheet to be detected, and the magnetic field intensity of the magnetic sheet in all directions is measured at the same time; performing normalization processing on the obtained magnetic field intensity, mapping the magnetic field intensity into a gray value of an image pixel to construct a magnetic field intensity image, calculating a magnetic field gradient, and determining a magnetic field gradient amplitude image according to the calculated magnetic field gradient; and setting a judgment threshold according to the magnetic field gradient amplitude image, marking the part greater than the threshold, determining a crack region, and calculating crack parameters. According to the method, the distribution of the magnetic field of the magnetic sheet and the crack condition of the magnetic sheet are accurately detected through a method of combining data processing with magnetic field characteristics, and the efficiency, precision and automation level of magnetic sheet detection are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic material detection, and in particular to a magnetic sheet crack detection method and system. Background Art

[0002] Magnetic sheets are widely used in many fields such as electronics, electricity, and communications. During the production and use of magnetic sheets, cracks may appear on the surface of the magnetic sheets due to various stresses, temperature changes, mechanical shocks, and other factors. These cracks will seriously affect the performance of the magnetic sheets, such as reducing magnetic permeability, increasing magnetic loss, and may even cause the magnetic sheets to fail, thereby affecting the normal operation of the entire device or system.

[0003] At present, the commonly used methods for detecting cracks in magnetic sheets include visual detection, ultrasonic detection, eddy current detection, etc. The visual detection method is simple and easy, but the detection accuracy is low and it is difficult to detect small cracks; ultrasonic detection requires professional ultrasonic equipment and skilled operators, and the detection speed is slow; eddy current detection has high requirements for the flatness of the detection surface, and the detection effect is not good for magnetic sheets with complex shapes. Therefore, it is necessary to develop a new method for detecting cracks in magnetic sheets to improve the detection accuracy, speed and adaptability. Summary of the invention

[0004] In view of the above-mentioned technical deficiencies, the present invention provides a magnetic sheet crack detection method and system.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for detecting cracks in a magnetic sheet is provided, the method comprising the following steps:

[0007] Step S10: placing the magnetic sheet to be tested in a uniform magnetic field generating device for magnetization, wherein the magnetic field strength is selected according to the characteristics of the magnetic sheet to be tested;

[0008] Step S20: After the magnetization is completed, independent Hall effect sensors are placed around the magnetic piece to be tested to simultaneously measure the magnetic field strength of the magnetic piece in all directions to obtain magnetic field strength data;

[0009] Step S30: normalizing the obtained magnetic field intensity data, calculating the magnetic field gradient, determining the magnetic field gradient amplitude according to the calculated magnetic field gradient, and mapping it to the gray value of the image pixel to construct a magnetic field amplitude image;

[0010] Step S40: setting a determination threshold according to the magnetic field gradient amplitude image, marking the portion greater than the threshold to determine the crack area and calculating the crack parameters;

[0011] Wherein, the magnetic field strength of the magnetic field in step S10 is selected according to the characteristics of the magnetic sheet to be detected, and the selected range is 1000 to 5000 A / m, including 1000 A / m and 5000 A / m;

[0012] In step S20, independent Hall effect sensors are placed around the magnetic sheet to be tested and the magnetic field strength of the magnetic sheet in all directions is measured at the same time. The Hall effect sensors are controlled by a program to start working synchronously, and a rectangular coordinate system is constructed with the magnetic sheet to be tested as the origin, including an x-axis and a y-axis. The magnetic field strength of the magnetic sheet in all directions is measured as the magnetic field strength in the x-axis and y-axis directions.

[0013] Among them, the magnetic sheet crack detection result output in step S40 includes no crack and crack presence; when the magnetic sheet crack detection result is crack presence, the position of the crack area on the magnetic sheet is marked and the calculated crack parameters are displayed.

[0014] Preferably, in step S10, the magnetic sheet to be tested is placed in a uniform magnetic field generating device for magnetization, and the steps include:

[0015] Magnetic sheet material analysis: Analyze the material composition or crystal structure of the magnetic sheet to be tested, determine the material composition to obtain the magnetic characteristic parameters, and determine the magnetic field strength of the magnetizing magnetic field based on the magnetic characteristic parameters;

[0016] Preparation of magnetic field generating device: Select electromagnetic magnetizer as magnetic field generating device, use magnetic field strength measuring instrument to measure and calibrate the magnetic field strength generated by the device, and control the magnetic field error within ±5%;

[0017] Magnetization: Place the magnetic piece to be tested at the center of the magnetic field uniform area of ​​the uniform magnetic field generating device, fix the magnetic piece with a magnetic piece fixing fixture, keep the surface of the magnetic piece to be tested perpendicular to the magnetic field direction, turn on the magnetic field generating device, and make its magnetic field strength reach the magnetic field strength determined in the magnetic piece material analysis, and magnetize the magnetic piece to be tested.

[0018] Preferably, after the magnetization is completed in step S20, the input current of the magnetic field generating device is reduced so that the magnetic field strength drops to 0 A / m, and the reduction rate of the input current is 50 A / m·s. When the magnetic field strength drops to 0 A / m, the power supply of the magnetic field generating device is turned off, the magnetic sheet fixing fixture is moved to take the magnetized magnetic sheet out of the magnetic field generating device, and the magnetic field strength of the magnetic sheet after the magnetization is completed is measured.

[0019] Preferably, the step of normalizing the obtained magnetic field strength in step S30 is:

[0020] The obtained magnetic field strength data are traversed, and the maximum and minimum values ​​in the magnetic field strength data are selected. The normalization formula is shown in formula (1):

[0021]

[0022] Among them, B norm (x, y) is the normalized value of the point (x, y) in the magnetic field intensity data, B(x, y) is the magnetic field intensity at the point (x, y) in the magnetic field intensity data, and B min is the minimum value in the magnetic field strength data, B max is the maximum value in the magnetic field strength data, B norm The value range of (x, y) is between 0 and 1, excluding 0 and 1. All data in the magnetic field intensity data are traversed to complete the normalization operation.

[0023] Preferably, the step of calculating the magnetic field gradient in step S30, determining the magnetic field gradient amplitude according to the calculated magnetic field gradient, and mapping it into grayscale values ​​of image pixels to construct a magnetic field gradient amplitude image comprises:

[0024] Determine the step size: Determine the step size based on the resolution of the Hall effect sensor and the size of the magnetic sheet, with a value range of 0.1 to 1 mm, including 0.1 mm and 1 mm;

[0025] Calculate the magnetic field gradient: Calculate the magnetic field gradient in the x direction and the y direction respectively. The calculation formula of the magnetic field gradient in the x direction is shown in formula (2):

[0026]

[0027] Among them, G x (x, y) is the magnetic field gradient of the point (x, y) in the x direction, Δx is the step length in the x direction, and the gradient of the point in the x direction, i.e. the magnetic field change rate, is obtained by calculating the ratio of the difference in magnetic field intensity between two adjacent points on the x axis to the step length; the calculation formula for the magnetic field gradient in the y direction is shown in formula (3):

[0028]

[0029] Among them, G y (x,y) is the magnetic field gradient of the point (x,y) in the y direction, Δy is the step length in the y direction, and the gradient of the point in the x direction, i.e. the rate of change of the magnetic field, is obtained by calculating the ratio of the difference in magnetic field intensity between two adjacent points on the x-axis to the step length;

[0030] Calculate the gradient amplitude: Calculate the magnetic field gradient amplitude based on the calculated gradients in the x-direction and y-direction. The calculation formula is shown in formula (4):

[0031]

[0032] Among them, G(x,y) is the calculated magnetic field gradient amplitude, which reflects the overall change degree of the magnetic field intensity at that point in the plane;

[0033] Normalization: Normalize the calculated magnetic field gradient amplitude G(x,y), and traverse G(x,y) to determine the minimum magnetic field gradient amplitude G min and the maximum value of the magnetic field gradient amplitude G max , the calculation formula is shown in formula (5):

[0034]

[0035] Among them G norm (x,y) is the normalized magnetic field gradient amplitude at point (x,y);

[0036] Generate amplitude image: According to the calculated G norm (x, y) is used for grayscale value mapping. A linear mapping method is used to set the minimum value of the magnetic field gradient amplitude to correspond to the grayscale value 0, the maximum value to correspond to the grayscale value 255, and the middle is mapped proportionally. The calculation formula is shown in formula (6):

[0037] Gray(x,y)=G norm (x,y)×255 (6)

[0038] Gray(x,y) is the gray value mapped to the point (x,y). All normalized data are traversed to complete the image gray value mapping and obtain the magnetic field amplitude grayscale map.

[0039] Preferably, the step of setting a determination threshold according to the magnetic field gradient amplitude image, marking a portion greater than the threshold to determine a crack area and calculating crack parameters in step S40 includes:

[0040] Judgment threshold setting: According to the maximum and minimum values ​​of the magnetic sheet crack size in the historical detection data and the characteristics of the magnetic sheet to be detected, the judgment threshold T is set, and the pixel point G(x,y)>T is marked as the starting point of the crack area, marked as 1, and the remaining pixel points are marked as 0, where G(x,y) is the calculated magnetic field gradient amplitude;

[0041] Region growing algorithm: Select one starting point from the starting points marked as crack regions as the starting point of region growth, start from the first starting point of the starting points marked as crack regions, and add them to a queue. When performing cyclic growth, select one pixel point from the queue as the current processing pixel point, and for each adjacent pixel point (x n ,y n ), calculate the difference ΔG of the magnetic field gradient amplitude with the current processing pixel point, and the calculation formula is shown in formula (7):

[0042] ΔG=|G(x n ,y n )-G(x,y)| (7)

[0043] Among them, G(x n ,y n ) is the point (x n ,y n ) at the magnetic field gradient amplitude; setting the growth area criterion, that is, setting the threshold of the difference in magnetic field gradient amplitude between adjacent pixel points to ΔT, when ΔG<ΔT, merging the adjacent pixel points into the crack area until no more growth occurs;

[0044] Repeated growth: Select the next starting point from the starting point marked as the crack area, and repeat the regional growth algorithm steps until all the starting points marked as crack areas have completed regional growth, and the determined crack area is obtained;

[0045] Crack parameter calculation: Calculate the crack parameters based on the determined crack area.

[0046] Wherein, the step of calculating crack parameters according to the determined crack area comprises:

[0047] Calculate the crack length: Extract all pixel coordinates (x i ,y i ), i = 1, 2, ..., n, n is the number of pixels in the crack area, and the distance between any two points is calculated as shown in formula (8):

[0048]

[0049] Where d is the point (x i ,y i ) and point (x j ,y j ) and select the maximum value d max as crack length;

[0050] Calculate the crack width: According to the calculated crack length, determine the corresponding straight line direction as the length direction. For each pixel point on the crack area, calculate its vertical distance to the length direction straight line, and take the average value to get the crack width.

[0051] Calculate the crack area: Count the number of pixels N in the crack area, determine the area A corresponding to each pixel in the actual magnetic disk, and calculate the crack area using the formula S=N×A.

[0052] In addition, to achieve the above-mentioned purpose, the present invention also proposes a magnetic sheet crack detection system, the magnetic sheet crack detection system comprising:

[0053] Magnetization module for the magnetic piece to be tested: the magnetic piece to be tested is placed in a uniform magnetic field generating device for magnetization, and the magnetic field strength of the magnetic field is selected according to the characteristics of the magnetic piece to be tested;

[0054] Module for acquiring magnetic field strength of the magnetic piece to be tested: After magnetization is completed, independent Hall effect sensors are placed around the magnetic piece to be tested to simultaneously measure the magnetic field strength of the magnetic piece in all directions to obtain magnetic field strength data;

[0055] The magnetic field strength data preprocessing module of the magnetic sheet to be tested is used to normalize the obtained magnetic field strength data, calculate the magnetic field gradient, determine the magnetic field gradient amplitude according to the calculated magnetic field gradient, and map it to the gray value of the image pixel to construct a magnetic field amplitude image;

[0056] The crack detection and calculation module of the magnetic sheet to be tested: the judgment threshold is set according to the magnetic field gradient amplitude image, the part greater than the threshold is marked to determine the crack area and calculate the crack parameters;

[0057] The magnetic field strength of the magnetic field in the magnetizing module of the magnetic sheet to be tested is selected according to the characteristics of the magnetic sheet to be tested, and the selected range is 1000 to 5000 A / m, including 1000 A / m and 5000 A / m;

[0058] In the magnetic field strength acquisition module of the magnetic piece to be tested, independent Hall effect sensors are placed around the magnetic piece to be tested and the magnetic field strength of the magnetic piece in all directions is measured simultaneously. The Hall effect sensors are controlled by a program to start working synchronously, and a rectangular coordinate system is constructed with the magnetic piece to be tested as the origin, including an x-axis and a y-axis, and the magnetic field strength of the magnetic piece in all directions is measured as the magnetic field strength in the x-axis and y-axis directions;

[0059] The magnetic sheet crack detection and calculation module outputs the magnetic sheet crack detection results including no crack and crack presence; when the magnetic sheet crack detection result is crack presence, the position of the crack area on the magnetic sheet is marked and the calculated crack parameters are displayed.

[0060] In addition, to achieve the above-mentioned purpose, the present invention also proposes a magnetic sheet crack detection device, which includes: a memory, a processor, and programs such as a magnetic sheet crack detection algorithm stored in the memory and run on the processor, and the programs such as the magnetic sheet crack detection algorithm are steps to implement a magnetic sheet crack detection method as described above.

[0061] In addition, to achieve the above-mentioned purpose, the present invention also provides a computer program product, which includes programs such as a magnetic sheet crack detection algorithm. When the magnetic sheet crack detection algorithm and other programs are executed by a processor, a magnetic sheet crack detection method as described above is implemented.

[0062] The advantages and effects of the present invention are:

[0063] The present invention proposes a magnetic sheet crack detection method and system, which uses a method of combining data processing with magnetic field characteristics to quickly and accurately detect cracks on the surface of the magnetic sheet and calculate relevant parameters of the cracks on the surface of the magnetic sheet, and can be widely used in quality inspection and fault diagnosis during the production and use of magnetic sheets. Through automated image processing, no human intervention is required, which greatly saves time and labor costs, shortens the detection time of magnetic sheet surface cracks, and improves detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0065] Figure 1 The present invention is a flow chart of a magnetic sheet crack detection method.

[0066] Figure 2 The figure is a schematic diagram of the structure of a magnetic sheet crack detection system of the present invention.

[0067] Figure 3 The present invention is a schematic block diagram of the structure of a magnetic sheet crack detection electronic device. DETAILED DESCRIPTION

[0068] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0069] The present invention provides a method for detecting cracks in a magnetic sheet, such as Figure 1 As shown, the following steps are included:

[0070] Step S10: placing the magnetic piece to be tested in a uniform magnetic field generating device for magnetization, and the magnetic field strength of the magnetic field is selected according to the characteristics of the magnetic piece to be tested.

[0071] The magnetic field strength of the magnetic field in step S10 is selected according to the characteristics of the magnetic sheet to be detected, and the selected range is 1000 to 5000 A / m, including 1000 A / m and 5000 A / m.

[0072] Specifically, in step S10, the magnetic sheet to be tested is placed in a uniform magnetic field generating device for magnetization, and the steps include:

[0073] Magnetic sheet material analysis: Analyze the material composition or crystal structure of the magnetic sheet to be tested, determine the material composition to obtain the magnetic characteristic parameters, and determine the magnetic field strength of the magnetizing magnetic field based on the magnetic characteristic parameters;

[0074] Preparation of magnetic field generating device: Select electromagnetic magnetizer as magnetic field generating device, use magnetic field strength measuring instrument to measure and calibrate the magnetic field strength generated by the device, and control the magnetic field error within ±5%;

[0075] Magnetization: Place the magnetic piece to be tested at the center of the magnetic field uniform area of ​​the uniform magnetic field generating device, fix the magnetic piece with a magnetic piece fixing fixture, keep the surface of the magnetic piece to be tested perpendicular to the magnetic field direction, turn on the magnetic field generating device, and make its magnetic field strength reach the magnetic field strength determined in the magnetic piece material analysis, and magnetize the magnetic piece to be tested.

[0076] Step S20: After the magnetization is completed, independent Hall effect sensors are placed around the magnetic piece to be detected to simultaneously measure the magnetic field strength of the magnetic piece in all directions to obtain magnetic field strength data.

[0077] Among them, in step S20, independent Hall effect sensors are placed around the magnetic piece to be tested to simultaneously measure the magnetic field strength of the magnetic piece in various directions, the Hall effect sensors are controlled by the program to start working synchronously, and a rectangular coordinate system is constructed with the magnetic piece to be tested as the origin, including the x-axis and the y-axis, and the magnetic field strength of the magnetic piece in various directions is measured as the magnetic field strength in the x-axis and y-axis directions.

[0078] Specifically, after the magnetization is completed in step S20, the input current of the magnetic field generating device is reduced so that the magnetic field strength drops to 0 A / m, and the reduction rate of the input current is 50 A / m·s. When the magnetic field strength drops to 0 A / m, the power of the magnetic field generating device is turned off, the magnetic sheet fixing clamp is moved to take the magnetized magnetic sheet out of the magnetic field generating device, and the magnetic field strength of the magnetic sheet after the magnetization is completed is measured.

[0079] Step S30: normalize the obtained magnetic field intensity data, calculate the magnetic field gradient, determine the magnetic field gradient amplitude according to the calculated magnetic field gradient, and map it to the gray value of the image pixel to construct a magnetic field amplitude image.

[0080] Specifically, the step of normalizing the obtained magnetic field strength in step S30 is:

[0081] The obtained magnetic field strength data are traversed, and the maximum and minimum values ​​in the magnetic field strength data are selected. The normalization formula is shown in formula (1):

[0082]

[0083] Among them, B norm(x, y) is the normalized value of the point (x, y) in the magnetic field intensity data, B(x, y) is the magnetic field intensity at the point (x, y) in the magnetic field intensity data, and B min is the minimum value in the magnetic field strength data, B max is the maximum value in the magnetic field strength data, B norm The value range of (x, y) is between 0 and 1, excluding 0 and 1. All data in the magnetic field intensity data are traversed to complete the normalization operation.

[0084] Specifically, the steps of calculating the magnetic field gradient in step S30, determining the magnetic field gradient amplitude according to the calculated magnetic field gradient, and mapping it to the grayscale value of the image pixel to construct the magnetic field gradient amplitude image include:

[0085] Determine the step size: Determine the step size based on the resolution of the Hall effect sensor and the size of the magnetic sheet, with a value range of 0.1 to 1 mm, including 0.1 mm and 1 mm;

[0086] Calculate the magnetic field gradient: Calculate the magnetic field gradient in the x direction and the y direction respectively. The calculation formula of the magnetic field gradient in the x direction is shown in formula (2):

[0087]

[0088] Among them, G x (x, y) is the magnetic field gradient of the point (x, y) in the x direction, Δx is the step length in the x direction, and the gradient of the point in the x direction, i.e. the magnetic field change rate, is obtained by calculating the ratio of the difference in magnetic field intensity between two adjacent points on the x axis to the step length; the calculation formula for the magnetic field gradient in the y direction is shown in formula (3):

[0089]

[0090] Among them, G y (x,y) is the magnetic field gradient of the point (x,y) in the y direction, Δy is the step length in the y direction, and the gradient of the point in the x direction, i.e. the rate of change of the magnetic field, is obtained by calculating the ratio of the difference in magnetic field intensity between two adjacent points on the x-axis to the step length;

[0091] Calculate the gradient amplitude: Calculate the magnetic field gradient amplitude based on the calculated gradients in the x-direction and y-direction. The calculation formula is shown in formula (4):

[0092]

[0093] Among them, G(x,y) is the calculated magnetic field gradient amplitude, which reflects the overall change degree of the magnetic field intensity at that point in the plane;

[0094] Normalization: Normalize the calculated magnetic field gradient amplitude G(x,y), and traverse G(x,y) to determine the minimum magnetic field gradient amplitude G min and the maximum value of the magnetic field gradient amplitude G max , the calculation formula is shown in formula (5):

[0095]

[0096] Among them G norm (x,y) is the normalized magnetic field gradient amplitude at point (x,y);

[0097] Generate amplitude image: According to the calculated G norm (x, y) is used for grayscale value mapping. A linear mapping method is used to set the minimum value of the magnetic field gradient amplitude to correspond to the grayscale value 0, the maximum value to correspond to the grayscale value 255, and the middle is mapped proportionally. The calculation formula is shown in formula (6):

[0098] Gray(x,y)=G norm (x,y)×255 (6)

[0099] Gray(x,y) is the gray value mapped to the point (x,y). All normalized data are traversed to complete the image gray value mapping and obtain the magnetic field amplitude grayscale map.

[0100] Step S40: setting a determination threshold according to the magnetic field gradient amplitude image, marking the portion greater than the threshold to determine the crack area and calculate the crack parameters.

[0101] In step S40, the magnetic sheet crack detection result output includes no crack and crack presence; when the magnetic sheet crack detection result is crack presence, the position of the crack area on the magnetic sheet is marked and the calculated crack parameters are displayed.

[0102] Specifically, in step S40, the step of setting a determination threshold according to the magnetic field gradient amplitude image, marking a portion greater than the threshold to determine a crack area, and calculating crack parameters includes:

[0103] Judgment threshold setting: According to the maximum and minimum values ​​of the magnetic sheet crack size in the historical detection data and the characteristics of the magnetic sheet to be detected, the judgment threshold T is set, and the pixel point G(x,y)>T is marked as the starting point of the crack area, marked as 1, and the remaining pixel points are marked as 0, where G(x,y) is the calculated magnetic field gradient amplitude;

[0104] Region growing algorithm: Select one starting point from the starting points marked as crack regions as the starting point of region growth, start from the first starting point of the starting points marked as crack regions, and add them to a queue. When performing cyclic growth, select one pixel point from the queue as the current processing pixel point, and for each adjacent pixel point (x n ,y n ), calculate the difference ΔG of the magnetic field gradient amplitude with the current processing pixel point, and the calculation formula is shown in formula (7):

[0105] ΔG=|G(x n ,y n )-G(x,y)| (7)

[0106] Among them, G(x n ,y n ) is the point (x n ,y n ) at the magnetic field gradient amplitude; setting the growth area criterion, that is, setting the threshold of the difference in magnetic field gradient amplitude between adjacent pixel points to ΔT, when ΔG<ΔT, merging the adjacent pixel points into the crack area until no more growth occurs;

[0107] Repeated growth: Select the next starting point from the starting point marked as the crack area, and repeat the regional growth algorithm steps until all the starting points marked as crack areas have completed regional growth, and the determined crack area is obtained;

[0108] Crack parameter calculation: Calculate the crack parameters based on the determined crack area.

[0109] The step of calculating crack parameters according to the determined crack area includes:

[0110] Calculate the crack length: Extract all pixel coordinates (x i ,y i ), i = 1, 2, ..., n, n is the number of pixels in the crack area, and the distance between any two points is calculated as shown in formula (8):

[0111]

[0112] Where d is the point (x i ,y i ) and point (x j ,y j ) and select the maximum value d max as crack length;

[0113] Calculate the crack width: According to the calculated crack length, determine the corresponding straight line direction as the length direction. For each pixel point on the crack area, calculate its vertical distance to the length direction straight line, and take the average value to get the crack width.

[0114] Calculate the crack area: Count the number of pixels N in the crack area, determine the area A corresponding to each pixel in the actual magnetic disk, and calculate the crack area using the formula S=N×A.

[0115] In addition, the present invention also provides a magnetic sheet crack detection system, please refer to Figure 2 , the magnetic sheet crack detection system comprises:

[0116] Magnetization module for the magnetic piece to be tested: the magnetic piece to be tested is placed in a uniform magnetic field generating device for magnetization, and the magnetic field strength of the magnetic field is selected according to the characteristics of the magnetic piece to be tested;

[0117] Module for acquiring magnetic field strength of the magnetic piece to be tested: After magnetization is completed, independent Hall effect sensors are placed around the magnetic piece to be tested to simultaneously measure the magnetic field strength of the magnetic piece in all directions to obtain magnetic field strength data;

[0118] The magnetic field strength data preprocessing module of the magnetic sheet to be tested is used to normalize the obtained magnetic field strength data, calculate the magnetic field gradient, determine the magnetic field gradient amplitude according to the calculated magnetic field gradient, and map it to the gray value of the image pixel to construct a magnetic field amplitude image;

[0119] The crack detection and calculation module of the magnetic sheet to be tested: the judgment threshold is set according to the magnetic field gradient amplitude image, the part greater than the threshold is marked to determine the crack area and calculate the crack parameters;

[0120] Wherein, the magnetic field strength of the magnetic field in the magnetization module of the magnetic sheet to be tested is selected according to the characteristics of the magnetic sheet to be tested, and the selected range is 1000 to 5000 A / m, including 1000 A / m and 5000 A / m;

[0121] In the magnetic field strength acquisition module of the magnetic piece to be tested, independent Hall effect sensors are placed around the magnetic piece to be tested and the magnetic field strength of the magnetic piece in all directions is measured at the same time. The Hall effect sensors are controlled by a program to start working synchronously, and a rectangular coordinate system is constructed with the magnetic piece to be tested as the origin, including an x-axis and a y-axis. The magnetic field strength of the magnetic piece in all directions is measured as the magnetic field strength in the x-axis and y-axis directions.

[0122] Among them, the magnetic sheet crack detection and calculation module outputs the magnetic sheet crack detection results including no crack and crack presence; when the magnetic sheet crack detection result is crack presence, the position of the crack area on the magnetic sheet is marked and the calculated crack parameters are displayed.

[0123] The present application provides a magnetic sheet crack detection system, which adopts a magnetic sheet crack detection method in the above embodiment, and can solve the technical problems of low efficiency and low accuracy of the traditional magnetic sheet crack detection method. Compared with the prior art, the beneficial effects of the magnetic sheet crack detection system provided by the present application are the same as the beneficial effects of the magnetic sheet crack detection method provided by the above embodiment, and the other technical features of the magnetic sheet crack detection system are the same as the features disclosed in the above embodiment method, which will not be repeated here.

[0124] The present application provides a magnetic sheet crack detection device, which includes: at least one processor; and a memory connected to the at least one processor in communication; wherein the memory stores instructions that can be executed by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute a magnetic sheet crack detection method in the above-mentioned embodiment one.

[0125] Reference below Figure 3 , which shows a schematic diagram of the structure of a magnetic sheet crack detection device suitable for implementing the embodiment of the present application. A magnetic sheet crack detection device in the embodiment of the present application may include but is not limited to mobile terminals such as mobile phones, laptop computers, digital broadcast receivers, PDAs (Personal Digital Assistants), PADs (Portable Application Descriptions), PMPs (Portable Media Players), etc., and fixed terminals such as digital TVs, desktop computers, etc. Figure 3 The magnetic sheet crack detection device shown is only an example and should not bring any limitation to the function and scope of use of the embodiments of the present application.

[0126] Figure 3The magnetic sheet crack detection device shown may include a processing system 1001 (e.g., a central processing unit, a graphics processing unit, etc.), which can perform various appropriate actions and processes according to a program stored in a read-only memory (ROM) 1002 or a program loaded from a storage system 1003 to a random access memory (RAM) 1004. Various programs and data required for the operation of a magnetic sheet crack detection device are also stored in RAM 1004. The processing system 1001, ROM 1002, and RAM 1004 are connected to each other via a bus 1005. An input / output (I / O) interface 1006 is also connected to the bus. Typically, the following systems can be connected to the I / O interface 1006: an input system 1007 including, for example, a touch screen, a touchpad, a keyboard, a mouse, an image sensor, a microphone, an accelerometer, a gyroscope, etc.; an output system 1008 including, for example, a liquid crystal display (LCD), a speaker, a vibrator, etc.; a storage system 1003 including, for example, a magnetic tape, a hard disk, etc.; and a communication system 1009. The communication system 1009 can allow a magnetic sheet crack detection device to communicate with other devices wirelessly or by wire to exchange data. Although a magnetic sheet crack detection device with various systems is shown in the figure, it should be understood that it is not required to implement or have all the systems shown. More or fewer systems may be implemented or have instead.

[0127] In particular, according to the embodiments disclosed in the present application, the process described above with reference to the flowchart can be implemented as a computer software program. For example, the embodiments disclosed in the present application include a computer program product, which includes a computer program carried on a computer-readable medium, and the computer program includes a program code for executing the method shown in the flowchart. In such an embodiment, the computer program can be downloaded and installed from a network through a communication system, or installed from a storage system 1003, or installed from a ROM 1002. When the computer program is executed by the processing system 1001, the above-mentioned functions defined in the method of the embodiment disclosed in the present application are executed.

[0128] The present application provides a magnetic sheet crack detection device, which adopts a magnetic sheet crack detection method in the above embodiment, and can solve the technical problems of low efficiency and low accuracy of the traditional magnetic sheet crack detection method. Compared with the prior art, the beneficial effects of the magnetic sheet crack detection device provided by the present application are the same as the beneficial effects of the magnetic sheet crack detection method provided by the above embodiment, and the other technical features of the magnetic sheet crack detection device are the same as the features disclosed in the method of the previous embodiment, which will not be repeated here.

[0129] The various parts disclosed in this application can be implemented by hardware, software, firmware or a combination thereof. In the description of the above embodiments, specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0130] The present application also provides a computer program product, including a computer program, which implements the steps of the magnetic sheet crack detection method as described above when executed by a processor.

[0131] The computer program product provided by the present application can solve the technical problems of low efficiency and low accuracy of the traditional magnetic sheet crack detection method. Compared with the prior art, the beneficial effects of the computer program product provided by the present application are the same as the beneficial effects of the magnetic sheet crack detection method provided by the above embodiment, which will not be repeated here.

[0132] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A magnetic sheet crack detection method, characterized in that: The method comprises the following steps: Step S10: placing the magnetic sheet to be tested in a uniform magnetic field generating device for magnetization, wherein the magnetic field strength is selected according to the characteristics of the magnetic sheet to be tested; Step S20: After the magnetization is completed, independent Hall effect sensors are placed around the magnetic piece to be tested to simultaneously measure the magnetic field strength of the magnetic piece in all directions to obtain magnetic field strength data; Step S30: normalizing the obtained magnetic field intensity data, calculating the magnetic field gradient, determining the magnetic field gradient amplitude according to the calculated magnetic field gradient, and mapping it to the gray value of the image pixel to construct a magnetic field gradient amplitude image; Step S40: setting a determination threshold according to the magnetic field gradient amplitude image, marking the part greater than the threshold to determine the crack area and calculate the crack parameters, and outputting the magnetic sheet crack detection result; The magnetic field strength of the magnetic field in step S10 is selected according to the characteristics of the magnetic sheet to be detected, and the selected range is 1000A / m to 5000A / m, including 1000A / m and 5000A / m; In step S20, independent Hall effect sensors are placed around the magnetic sheet to be tested and the magnetic field strength of the magnetic sheet in various directions is measured at the same time. The Hall effect sensors are controlled by a program to start working synchronously, and a rectangular coordinate system is constructed with the magnetic sheet to be tested as the origin, including an x-axis and a y-axis. The magnetic field strength of the magnetic sheet in various directions is measured as the magnetic field strength in the x-axis and y-axis directions. The magnetic sheet crack detection result output in step S40 includes no crack and crack presence; when the magnetic sheet crack detection result is crack presence, the position of the crack area on the magnetic sheet is marked and the calculated crack parameters are displayed.

2. A magnetic sheet crack detection method according to claim 1, characterized in that: In step S10, the magnetic sheet to be tested is placed in a uniform magnetic field generating device for magnetization, and the steps include: Magnetic sheet material analysis: Analyze the material composition or crystal structure of the magnetic sheet to be tested, determine the material composition to obtain the magnetic characteristic parameters, and determine the magnetic field strength of the magnetizing magnetic field based on the magnetic characteristic parameters; Preparation of magnetic field generating device: Select electromagnetic magnetizer as magnetic field generating device, use magnetic field strength measuring instrument to measure and calibrate the magnetic field strength generated by the device, and control the magnetic field error within ±5%; Magnetization: Place the magnetic piece to be tested at the center of the magnetic field uniform area of ​​the uniform magnetic field generating device, fix the magnetic piece with a magnetic piece fixing fixture, keep the surface of the magnetic piece to be tested perpendicular to the magnetic field direction, turn on the magnetic field generating device, and make its magnetic field strength reach the magnetic field strength determined in the magnetic piece material analysis, and magnetize the magnetic piece to be tested.

3. A magnetic sheet crack detection method according to claim 1, characterized in that: After the magnetization is completed in step S20, the input current of the magnetic field generating device is reduced to reduce the magnetic field strength to 0 A / m, and the reduction rate of the input current is 50 A / m·s. When the magnetic field strength is reduced to 0 A / m, the power supply of the magnetic field generating device is turned off, and the magnetic sheet fixing fixture is moved to take the magnetized magnetic sheet out of the magnetic field generating device, and the magnetic field strength of the magnetic sheet after the magnetization is completed is measured.

4. A magnetic sheet crack detection method according to claim 1, characterized in that: The step of normalizing the obtained magnetic field strength in step S30 is as follows: The obtained magnetic field strength data are traversed, and the maximum and minimum values ​​in the magnetic field strength data are selected. The normalization formula is shown in formula (1): Among them, B norm (x, y) is the normalized value of the point (x, y) in the magnetic field intensity data, B(x, y) is the magnetic field intensity at the point (x, y) in the magnetic field intensity data, and B min is the minimum value in the magnetic field strength data, B max is the maximum value in the magnetic field strength data, B norm The value range of (x, y) is between 0 and 1, excluding 0 and 1. All data in the magnetic field intensity data are traversed to complete the normalization operation.

5. A magnetic sheet crack detection method according to claim 1, characterized in that: The step of calculating the magnetic field gradient in step S30, determining the magnetic field gradient amplitude according to the calculated magnetic field gradient, and mapping it to the gray value of the image pixel to construct the magnetic field gradient amplitude image includes: Determine the step size: Determine the step size based on the resolution of the Hall effect sensor and the size of the magnetic sheet, with a value range of 0.1 to 1 mm, including 0.1 mm and 1 mm; Calculate the magnetic field gradient: Calculate the magnetic field gradient in the x direction and the y direction respectively. The calculation formula of the magnetic field gradient in the x direction is shown in formula (2): Among them, G x (x, y) is the magnetic field gradient of the point (x, y) in the x direction, Δx is the step length in the x direction, and the gradient of the point in the x direction, i.e. the magnetic field change rate, is obtained by calculating the ratio of the difference in magnetic field intensity between two adjacent points on the x axis to the step length; the calculation formula for the magnetic field gradient in the y direction is shown in formula (3): Among them, G y (x,y) is the magnetic field gradient of the point (x,y) in the y direction, Δy is the step length in the y direction, and the gradient of the point in the x direction, i.e. the rate of change of the magnetic field, is obtained by calculating the ratio of the difference in magnetic field intensity between two adjacent points on the x-axis to the step length; Calculate the gradient amplitude: Calculate the magnetic field gradient amplitude based on the calculated gradients in the x-direction and y-direction. The calculation formula is shown in formula (4): Among them, G(x,y) is the calculated magnetic field gradient amplitude, which reflects the overall change degree of the magnetic field intensity at that point in the plane; Normalization: Normalize the calculated magnetic field gradient amplitude G(x,y), and traverse G(x,y) to determine the minimum magnetic field gradient amplitude G min and the maximum value of the magnetic field gradient amplitude G max , the calculation formula is shown in formula (5): Among them G norm (x,y) is the normalized magnetic field gradient amplitude at point (x,y); Generate amplitude image: According to the calculated G norm (x, y) is used for grayscale value mapping. A linear mapping method is used to set the minimum value of the magnetic field gradient amplitude to correspond to the grayscale value 0, the maximum value to correspond to the grayscale value 255, and the middle is mapped proportionally. The calculation formula is shown in formula (6): Gray(x,y)=G norm (x,y)×255 (6) Gray(x,y) is the gray value mapped to the point (x,y). All normalized data are traversed to complete the image gray value mapping and obtain the magnetic field amplitude grayscale map.

6. A magnetic sheet crack detection method according to claim 1, characterized in that: The step of setting a determination threshold according to the magnetic field gradient amplitude image in step S40, marking a portion greater than the threshold to determine a crack area and calculating crack parameters includes: Judgment threshold setting: According to the maximum and minimum values ​​of the magnetic sheet crack size in the historical detection data and the characteristics of the magnetic sheet to be detected, the judgment threshold T is set, and the pixel point G(x,y)>T is marked as the starting point of the crack area, marked as 1, and the remaining pixel points are marked as 0, where G(x,y) is the calculated magnetic field gradient amplitude; Region growing algorithm: Select one starting point from the starting points marked as crack regions as the starting point of region growth, start from the first starting point of the starting points marked as crack regions, and add them to a queue. When performing cyclic growth, select one pixel point from the queue as the current processing pixel point, and for each adjacent pixel point (x n ,y n ), calculate the difference ΔG of the magnetic field gradient amplitude with the current processing pixel point, and the calculation formula is shown in formula (7): ΔG=|G(x n ,y n )-G(x,y)| (7) Among them, G(x n ,y n ) is the point (x n ,y n ) at the magnetic field gradient amplitude; setting the growth area criterion, that is, setting the threshold of the difference in magnetic field gradient amplitude between adjacent pixel points to ΔT, when ΔG<ΔT, merging the adjacent pixel points into the crack area until no more growth occurs; Repeated growth: Select the next starting point from the starting point marked as the crack area, and repeat the regional growth algorithm steps until all the starting points marked as crack areas have completed regional growth, and the determined crack area is obtained; Crack parameter calculation: Calculate the crack parameters based on the determined crack area.

7. A magnetic sheet crack detection method according to claim 6, characterized in that: The step of calculating crack parameters according to the determined crack area comprises: Calculate the crack length: Extract all pixel coordinates (x i ,y i ), i = 1, 2, ..., n, n is the number of pixels in the crack area, and the distance between any two points is calculated as shown in formula (8): Where d is the point (x i ,y i ) and point (x j ,y j ) and select the maximum value d max as crack length; Calculate the crack width: According to the calculated crack length, determine the corresponding straight line direction as the length direction. For each pixel point on the crack area, calculate its vertical distance to the length direction straight line, and take the average value to get the crack width. Calculate the crack area: Count the number of pixels N in the crack area, determine the area A corresponding to each pixel in the actual magnetic disk, and calculate the crack area using the formula S=N×A.

8. A magnetic sheet crack detection system, characterized in that: The magnetic sheet crack detection system comprises: Magnetization module for the magnetic piece to be tested: the magnetic piece to be tested is placed in a uniform magnetic field generating device for magnetization, and the magnetic field strength of the magnetic field is selected according to the characteristics of the magnetic piece to be tested; Module for acquiring magnetic field strength of the magnetic piece to be tested: After magnetization is completed, independent Hall effect sensors are placed around the magnetic piece to be tested to simultaneously measure the magnetic field strength of the magnetic piece in all directions to obtain magnetic field strength data; The magnetic field strength data preprocessing module of the magnetic sheet to be tested is used to normalize the obtained magnetic field strength data, calculate the magnetic field gradient, determine the magnetic field gradient amplitude according to the calculated magnetic field gradient, and map it to the gray value of the image pixel to construct a magnetic field amplitude image; The crack detection and calculation module of the magnetic sheet to be tested: the judgment threshold is set according to the magnetic field gradient amplitude image, the part greater than the threshold is marked to determine the crack area and calculate the crack parameters; The magnetic field strength of the magnetic field in the magnetizing module of the magnetic sheet to be tested is selected according to the characteristics of the magnetic sheet to be tested, and the selected range is 1000 to 5000 A / m, including 1000 A / m and 5000 A / m; In the magnetic field strength acquisition module of the magnetic piece to be tested, independent Hall effect sensors are placed around the magnetic piece to be tested and the magnetic field strength of the magnetic piece in all directions is measured simultaneously. The Hall effect sensors are controlled by a program to start working synchronously, and a rectangular coordinate system is constructed with the magnetic piece to be tested as the origin, including an x-axis and a y-axis, and the magnetic field strength of the magnetic piece in all directions is measured as the magnetic field strength in the x-axis and y-axis directions; The magnetic sheet crack detection and calculation module outputs the magnetic sheet crack detection results including no crack and crack presence; when the magnetic sheet crack detection result is crack presence, the position of the crack area on the magnetic sheet is marked and the calculated crack parameters are displayed.

9. A magnetic sheet crack detection device, characterized in that: The magnetic sheet crack detection device comprises: A memory, a processor, and a magnetic sheet crack detection program stored in the memory and executable on the processor, wherein the magnetic sheet crack detection program, when executed by the processor, implements a magnetic sheet crack detection method as described in any one of claims 1 to 7.

10. A computer program product, characterized in that The computer program product includes a magnetic sheet crack detection program, and when the magnetic sheet crack detection program is executed by a processor, a magnetic sheet crack detection method according to any one of claims 1 to 7 is implemented.

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