Gear crack internal and external depth detection method and system based on gear coil induction thermal response

Abstract

The present invention provides a method and system for detecting the internal and external depth of a gear crack by inductive thermal response of a tooth-like coil, and relates to the field of image detection. The method adopts a designed tooth-like coil to implement electromagnetic excitation on the gear groove, and forms a relatively uniform induced current with curved surface shape characteristics on the surface and near surface of the gear. The eddy current generates movement in the gear, and when the depth of the defect changes, the movement of the current changes accordingly, so that the temperature around the defect forms a temperature difference with other areas. The thermal cloud map becomes more obvious as the depth of the defect increases, and the temperature characteristic point of the cloud map in the middle of the defect has a high proportional match with the depth. For cracks inside the gear, the defect position and morphology can be obtained when the burial depth is shallow, and within a certain range, the burial depth is quantitatively related to the tooth surface temperature at the defect. The present invention reveals the intrinsic connection between the thermal response of the induced eddy current and the internal and external cracks of the gear, and constructs a characteristic characterization method and parameters for the crack depth, which plays an important role in the field of defect detection of industrial parts.

Description

Technical Field

[0001] The invention relates to the field of image detection, and in particular to a method and system for detecting the internal and external depths of gear cracks by inducing thermal response of a simulated tooth coil. Background Art

[0002] Gears are indispensable mechanical components in modern industry, and they play a vital role in many fields such as industry, transportation, energy, aerospace, etc. The importance of gears is reflected in their core functions in power transmission, speed control, torque conversion, precision motion control, and system integration. During the operation or production process of gears, due to factors such as fatigue, corrosion, and wear, defects such as cracks and wear may occur. If these defects are not discovered and handled in time, they may cause the gears to break and fail, and the failure of the gears may lead to serious consequences. For example, if the gears in the casing of an aircraft engine fail, it will directly cause the aircraft engine to stop running, which will cause major hidden dangers to life safety or cause certain economic losses to the company.

[0003] Regular nondestructive testing of gears is of great significance. It can timely detect defects inside or on the surface of gears, such as cracks and wear, so that corresponding measures can be taken in time to avoid accidents. Regular nondestructive testing of gears can also improve the safety of gears, extend service life, improve product quality, reduce economic losses, etc. At present, there are three main types of nondestructive testing for gears: ultrasonic nondestructive testing, electromagnetic eddy current testing, and magnetic particle testing.

[0004] Ultrasonic nondestructive testing is a method of detecting defects by propagating ultrasonic waves in conductive materials through acoustic coupling media. This method can effectively detect internal defects of gears, but it requires the coupling medium to be applied to the surface in advance during testing, and this method cannot effectively detect defects on the tooth surface.

[0005] The basic principle of electromagnetic eddy current testing is based on the Faraday electromagnetic induction principle, which determines the presence of defects by changing the magnetic field or the impedance of the coil. This method has the advantages of high sensitivity and non-contact, but it cannot effectively determine the depth of gear defects and near-surface defects.

[0006] Magnetic particle testing is a non-destructive testing technology used to detect surface and near-surface defects of ferromagnetic materials. The main advantages of magnetic particle testing are that it is easy to master, visualized, low-cost, and can effectively detect surface defects. However, its disadvantages are also obvious. During the test, magnetic powder or magnetic suspension needs to be applied, and there are certain requirements for the direction and strength of the magnetic field, and it is more dependent on the experience of the operator. Summary of the invention

[0007] In view of the above problems, the present disclosure proposes a method for detecting crack depths on inner and outer surfaces of gears by imitating thermal response of electromagnetic excitation of a tooth-shaped coil.

[0008] In order to solve at least one of the above technical problems, the present disclosure proposes a method for detecting the internal and external depth of a gear crack by using a simulated gear coil to induce thermal response, comprising:

[0009] The gears are electromagnetically excited by the designed tooth-like coils to form induced currents on the gear surface and near the surface. Then, the temperature is detected to obtain a thermal cloud map. The temperature characteristic points of the cloud map are extracted according to the probe points.

[0010] After judging the internal and external cracks according to the thermal cloud map, if it is an internal crack, the hidden depth of the internal crack is tested; if it is an external crack, the depth of the external crack is tested;

[0011] The temperature characteristic point of the cloud map in the middle of the defect is used as the main judgment basis, and other temperature characteristic points of the cloud map are used as auxiliary judgments to realize the detection of the external crack depth;

[0012] Through the quantitative relationship between the defect buried depth and the tooth surface temperature within a certain range, the hidden depth of internal cracks can be detected.

[0013] Furthermore, the tooth-shaped coil structure includes:

[0014] The tooth-shaped coil is an excitation coil composed of multiple triangular arcs coaxial with the curved surfaces of various parts of the gear slot. The radius of the top arc of the tooth-shaped coil is 47mm, the radius of the left and right sides is 18mm, and the radius of the bottom arc is 4mm. The upper and lower height of the tooth-shaped coil is 25mm, the thickness is 12mm, the outer diameter of the coil wire is 1.8mm, the inner diameter is 0.8mm, the material is copper, and the number of turns is 5. During the detection process, the tooth-shaped coil is placed inside the gear slot, and the side surfaces and bottom of the tooth-shaped coil are 2mm away from the side surfaces and bottom of the gear slot.

[0015] Furthermore, electromagnetic excitation of the gear by the designed tooth-shaped coil includes:

[0016] The current applied to the coil is in the form of a sinusoidal AC signal with a maximum oscillation frequency of 50kHz. When the coil is unloaded, the current is 2A. When the coil is placed in the gear slot for heating, the current is 6A. The maximum heating power of the excitation device is 120W.

[0017] Furthermore, the excitation device includes: a capacitor, an inductor, a MOSFET, a diode, a voltage-stabilizing diode, a pull-down resistor, and a current-limiting resistor, and the current is directly loaded onto the gate of the MOSFET through the current-limiting resistor.

[0018] Furthermore, the tooth-shaped coil structure further includes: a tooth-shaped coil auxiliary device:

[0019] The input voltage of the induction heating device is limited to DC5~12V. The power supply is converted into DC5~12V by using auxiliary equipment. The tooth-shaped coil auxiliary device is composed of a transformer, a diode, a voltage regulator, and a voltage stabilizer. It also includes a self-priming pump with a power supply of DC5V. The maximum flow rate of the self-priming pump is 1.6L / min and the maximum lift is 1.5m.

[0020] Furthermore, the temperature characteristic point of the cloud map in the middle of the defect is used as the main judgment basis, and other temperature characteristic points of the cloud map are used as auxiliary judgments to realize the detection of the external crack depth, including:

[0021] Probe points are arranged at both end areas of the defect and in the middle of both sides of the defect.

[0022] Furthermore, the detection of the external crack depth includes: extracting the temperature characteristic points of the cloud map at different depths, using a fourth-order polynomial fitting, and finally obtaining the defect depth and temperature expressions at different probe points:

[0023] Probe point 1 and probe point 4 are located on the same side, and probe point 2 and probe point 3 are located on the same side, and are arranged at the corner points of the defect respectively.

[0024] Probe point 5 and probe point 6 are located in the middle of the defect, 0.5 mm away from the defect edge.

[0025] Coefficient of determination for probe point 1 , the fitting formula is as follows:

[0026]

[0027] Coefficient of determination for probe point 2 , the fitting formula is as follows:

[0028]

[0029] Coefficient of determination for probe point 3 , the fitting formula is as follows:

[0030]

[0031] Coefficient of determination for probe point 4 , the fitting formula is as follows:

[0032]

[0033] Coefficient of determination for probe point 5 , the fitting formula is as follows:

[0034]

[0035] Coefficient of determination for probe point 6 , the fitting formula is as follows:

[0036]

[0037] Probe point 5 and probe point 6 are located in the middle of the defect, 0.5 mm away from the defect edge. x is the defect depth, y It is the temperature characteristic point of the defect cloud map;

[0038] The temperature data of probe point 5 is used as the main basis for judgment, and the data of other positions are used as auxiliary.

[0039] Furthermore, it is characterized in that the detection of the hidden depth of the internal crack is achieved through the quantitative relationship between the defect buried depth and the tooth surface temperature within a certain range, including:

[0040] Through the thermal cloud map, the probe point is arranged in the middle of the highest temperature area, a defect is set in the middle of the tooth surface on one side of the gear groove, namely defect 1, and a defect is set in the middle of the tooth bottom, namely defect 2.

[0041] Furthermore, through the quantitative relationship between the defect buried depth and the tooth surface temperature within a certain range, the detection of the hidden depth of the internal crack is realized, including:

[0042] Determination coefficient of the probe point at defect 1 , the fitting formula is as follows:

[0043]

[0044] Determination coefficient of the probe point at defect 2 , the fitting formula is as follows:

[0045]

[0046] In the formula h is the defect burial depth, y It is the temperature characteristic point of the cloud map.

[0047] In addition, the present invention also provides a gear crack internal and external depth detection system based on a gear-simulating coil induction thermal response, comprising:

[0048] Excitation module: The gear is electromagnetically excited by the designed tooth-shaped coil to form an induced current on the gear surface and near the surface, and then the temperature is detected to obtain a thermal cloud map; and the temperature characteristic points of the cloud map are extracted according to the probe points;

[0049] Excitation module: After judging internal and external cracks according to the thermal cloud map, if it is an internal crack, the hidden depth of the internal crack is detected; if it is an external crack, the depth of the external crack is detected;

[0050] External crack depth detection module: The cloud temperature characteristic point in the middle of the defect is used as the main judgment basis, and other cloud temperature characteristic points are used as auxiliary judgments to realize the detection of external crack depth;

[0051] Internal crack hidden depth detection module: The internal crack hidden depth is detected through the quantitative relationship between the defect buried depth and the tooth surface temperature within a certain range.

[0052] The above technical solution has the following advantages or beneficial effects:

[0053] (1) An excitation coil designed for gear detection based on the tooth slot structure expands the detection coverage area, such as the tooth surfaces on both sides of a single tooth slot and the tooth bottom and root areas, greatly increasing the effective current field area and density. This type of coil structure can display the thermal cloud map after a single excitation, without the need to move the coil multiple times to detect different positions on the tooth surface. In addition, a relatively uniform induced current with curved surface shape characteristics is formed on the gear surface and near the surface, thereby forming a thermal map with obvious resolution effect characteristics;

[0054] (2) The visualization and quantitative detection of gear surface cracks are proposed. This method is not limited by the operator's experience and can achieve accurate quantitative detection of crack depth. The temperature cloud map combined with the probe point fixed temperature has higher detection accuracy, which is conducive to the realization of intelligent upgrades.

[0055] (3) The visualization of gear internal cracks and the quantitative detection of hidden depth are proposed. This method reveals the correlation between gear internal defects and temperature response cloud maps, providing a convenient visualization method for the detection of internal cracks. At the same time, the deep-seated laws between the temperature characteristic points of the cloud map at different positions on the gear surface and the hidden depth of the defects are revealed, and the limit position of the hidden depth is quantified, providing a reference for timely discovery and prediction of hidden faults.

[0056] (4) This method is a non-contact detection method. It does not require direct contact with the gear being tested. It can achieve a comprehensive detection of defects in all positions of the gear at one time, avoiding adverse damage to the gear transmission parts. In addition, it does not require expensive and complex testing equipment, and the measurement accuracy fully meets the needs of fault monitoring.

[0057] The present invention starts from the essence of multi-physical field coupling and interaction, further understands the intrinsic connection between gear surface temperature and gear defects, and explores more effective characteristic characterization methods and parameters for describing gear defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The present invention and its features, configurations and advantages will become more apparent by reading the detailed description of non-limiting embodiments with reference to the following drawings. The same reference numerals indicate the same parts throughout the drawings. The drawings are not drawn to scale, but rather to illustrate the subject matter of the present invention.

[0059] Figure 1 This is a flow chart of the method for detecting the internal and external depth of a gear crack by induction thermal response of a simulated gear coil as described in Example 1;

[0060] Figure 2 This is a block diagram of a gear crack internal and external depth detection system based on the thermal response of a simulated gear coil as described in Example 3;

[0061] Figure 3 This is a schematic diagram of the principle of eddy current induction gear defect depth detection described in Example 4;

[0062] Figure 4 The structure of the excitation coil and the current flow distribution diagram of the fourth embodiment;

[0063] Figure 5 For the crack defect set on the gear surface described in the fourth embodiment, the temperature response cloud map and the probe points arranged at the defect are used to observe the temperature response diagram at the defect;

[0064] Figure 6 The temperature response diagram of the gear surface described in the fourth embodiment;

[0065] Figure 7 The temperature cloud diagram of gear defects at different depths at 0.15s as shown in Example 4;

[0066] Figure 8 The probe point fitting data of defects of different depths described in Example 4;

[0067] Fig. 9 The temperature cloud diagram at different burial depths of the gear defect 1 (tooth surface crack) described in Example 4;

[0068] Fig.10 This is a simulation diagram of different buried depths and surface temperature responses of defect 2 (tooth bottom crack) described in Example 4;

[0069] Fig.11 This is the fitting curve of the temperature characteristic points of the cloud map at different burial depths described in Example 4. DETAILED DESCRIPTION

[0070] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. It should be noted that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application.

[0071] It should be understood that when the terms “include” and / or “comprise” are used in the present specification, they specify the presence of features, steps, operations, devices, components and / or their combinations.

[0072] The terms “first”, “second” and “third” are used for descriptive purposes only and should not be understood as indicating or implying relative importance.

[0073] The technical solutions in the embodiments of the present invention are described below in conjunction with the drawings in the embodiments of the present invention. It is obvious that the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the protection scope of the present invention.

[0074] Embodiment 1:

[0075] This embodiment proposes Figure 1 The gear crack internal and external depth detection method using the induction thermal response of the gear simulation coil includes:

[0076] The gears are electromagnetically excited by the designed tooth-like coils to form induced currents on the gear surface and near the surface. Then, the temperature is detected to obtain a thermal cloud map. The temperature characteristic points of the cloud map are extracted according to the probe points.

[0077] After judging the internal and external cracks according to the thermal cloud map, if it is an internal crack, the hidden depth of the internal crack is tested; if it is an external crack, the depth of the external crack is tested;

[0078] The temperature characteristic point of the cloud map in the middle of the defect is used as the main judgment basis, and other temperature characteristic points of the cloud map are used as auxiliary judgments to realize the detection of the external crack depth;

[0079] Through the quantitative relationship between the defect buried depth and the tooth surface temperature within a certain range, the hidden depth of internal cracks can be detected.

[0080] This embodiment uses an excitation coil designed for gear detection based on the tooth slot structure to expand the detection coverage area, such as the tooth surfaces on both sides of a single tooth slot and the tooth bottom and root areas, greatly increasing the effective current field area and density. This type of coil structure only requires a single excitation to display a thermal cloud map, without the need to move the coil multiple times to detect different positions on the tooth surface. In addition, a relatively uniform induced current with curved surface shape characteristics is formed on the gear surface and near the surface, thereby forming a thermal map with obvious resolution effect characteristics;

[0081] This embodiment proposes visualization of cracks on the gear surface and quantitative detection of their depth, which is not limited by the operator's experience and can achieve accurate quantitative detection of crack depth. The temperature cloud map combined with the probe point fixed temperature has higher detection accuracy, which is conducive to realizing intelligent upgrades.

[0082] This embodiment proposes the visualization of cracks in gears and the quantitative detection of hidden depths. This embodiment reveals the association between defects in gears and temperature response cloud maps, providing a convenient visualization method for detecting internal cracks. At the same time, it reveals the deep laws of cloud map temperature feature points at different positions on the gear surface and the hidden depth of defects, quantifies the limit position of the hidden depth, and provides a reference for timely discovery and prediction of hidden faults.

[0083] This embodiment is a non-contact detection, which does not require direct contact with the gear being tested, and can achieve a comprehensive detection of defects at all positions of the gear at one time, avoiding adverse damage to the gear transmission parts. In addition, there is no need for expensive and complex testing equipment, and the measurement accuracy fully meets the needs of fault monitoring.

[0084] This embodiment starts from the nature of multi-physical field coupling and interaction, further understands the intrinsic connection between gear surface temperature and gear defects, and explores more effective feature characterization methods and parameters for describing gear defects.

[0085] Embodiment 2:

[0086] This embodiment is further disclosed on the basis of the first embodiment:

[0087] Furthermore, the tooth-shaped coil structure includes:

[0088] The tooth-shaped coil is an excitation coil composed of multiple triangular arcs coaxial with the curved surfaces of various parts of the gear slot. The radius of the top arc of the tooth-shaped coil is 47mm, the radius of the left and right sides is 18mm, and the radius of the bottom arc is 4mm. The upper and lower height of the tooth-shaped coil is 25mm, the thickness is 12mm, the outer diameter of the coil wire is 1.8mm, the inner diameter is 0.8mm, the material is copper, and the number of turns is 5. During the detection process, the tooth-shaped coil is placed inside the gear slot, and the side surfaces and bottom of the tooth-shaped coil are 2mm away from the side surfaces and bottom of the gear slot.

[0089] Furthermore, electromagnetic excitation of the gear by the designed tooth-shaped coil includes:

[0090] The current applied to the coil is in the form of a sinusoidal AC signal with a maximum oscillation frequency of 50kHz. When the coil is unloaded, the current is 2A. When the coil is placed in the gear slot for heating, the current is 6A. The maximum heating power of the excitation device is 120W.

[0091] Furthermore, the excitation device includes: a capacitor, an inductor, a MOSFET, a diode, a voltage-stabilizing diode, a pull-down resistor, and a current-limiting resistor, and the current is directly loaded onto the gate of the MOSFET through the current-limiting resistor.

[0092] Furthermore, the tooth-shaped coil structure further includes: a tooth-shaped coil auxiliary device:

[0093] The input voltage of the induction heating device is limited to DC5~12V. The power supply is converted into DC5~12V by using auxiliary equipment. The tooth-shaped coil auxiliary device is composed of a transformer, a diode, a voltage regulator, and a voltage stabilizer. It also includes a self-priming pump with a power supply of DC5V. The maximum flow rate of the self-priming pump is 1.6L / min and the maximum lift is 1.5m.

[0094] Furthermore, the temperature characteristic point of the cloud map in the middle of the defect is used as the main judgment basis, and other temperature characteristic points of the cloud map are used as auxiliary judgments to realize the detection of the external crack depth, including:

[0095] Probe points are arranged at both end areas of the defect and in the middle of both sides of the defect.

[0096] Furthermore, the detection of the external crack depth includes: extracting the temperature characteristic points of the cloud map at different depths, using a fourth-order polynomial fitting, and finally obtaining the defect depth and temperature expressions at different probe points:

[0097] Probe point 1 and probe point 4 are located on the same side, and probe point 2 and probe point 3 are located on the same side, and are arranged at the corner points of the defect respectively.

[0098] Probe point 5 and probe point 6 are located in the middle of the defect, 0.5 mm away from the defect edge.

[0099] Coefficient of determination for probe point 1 , the fitting formula is as follows:

[0100]

[0101] Coefficient of determination for probe point 2 , the fitting formula is as follows:

[0102]

[0103] Coefficient of determination for probe point 3 , the fitting formula is as follows:

[0104]

[0105] Coefficient of determination for probe point 4 , the fitting formula is as follows:

[0106]

[0107] Coefficient of determination for probe point 5 , the fitting formula is as follows:

[0108]

[0109] Coefficient of determination for probe point 6 , the fitting formula is as follows:

[0110]

[0111] Probe point 5 and probe point 6 are located in the middle of the defect, 0.5 mm away from the defect edge. x is the defect depth, y It is the temperature characteristic point of the defect cloud map;

[0112] The temperature data of probe point 5 is used as the main basis for judgment, and the data of other positions are used as auxiliary.

[0113] Furthermore, it is characterized in that the detection of the hidden depth of the internal crack is achieved through the quantitative relationship between the defect buried depth and the tooth surface temperature within a certain range, including:

[0114] Through the thermal cloud map, the probe point is arranged in the middle of the highest temperature area, a defect is set in the middle of the tooth surface on one side of the gear groove, namely defect 1, and a defect is set in the middle of the tooth bottom, namely defect 2.

[0115] Furthermore, through the quantitative relationship between the defect buried depth and the tooth surface temperature within a certain range, the detection of the hidden depth of the internal crack is realized, including:

[0116] Determination coefficient of the probe point at defect 1 , the fitting formula is as follows:

[0117]

[0118] Determination coefficient of the probe point at defect 2 , the fitting formula is as follows:

[0119]

[0120] In the formula h is the defect burial depth, y It is the temperature characteristic point of the cloud map.

[0121] This embodiment uses an excitation coil designed for gear detection based on the tooth slot structure to expand the detection coverage area, such as the tooth surfaces on both sides of a single tooth slot and the tooth bottom and root areas, greatly increasing the effective current field area and density. This type of coil structure only requires a single excitation to display a thermal cloud map, without the need to move the coil multiple times to detect different positions on the tooth surface. In addition, a relatively uniform induced current with curved surface shape characteristics is formed on the gear surface and near the surface, thereby forming a thermal map with obvious resolution effect characteristics;

[0122] This embodiment proposes visualization of cracks on the gear surface and quantitative detection of their depth, which is not limited by the operator's experience and can achieve accurate quantitative detection of crack depth. The temperature cloud map combined with the probe point fixed temperature has higher detection accuracy, which is conducive to realizing intelligent upgrades.

[0123] This embodiment proposes the visualization of cracks in gears and the quantitative detection of hidden depths. This embodiment reveals the association between defects in gears and temperature response cloud maps, providing a convenient visualization method for detecting internal cracks. At the same time, it reveals the deep laws of cloud map temperature feature points at different positions on the gear surface and the hidden depth of defects, quantifies the limit position of the hidden depth, and provides a reference for timely discovery and prediction of hidden faults.

[0124] This embodiment is a non-contact detection, which does not require direct contact with the gear being tested, and can achieve a comprehensive detection of defects at all positions of the gear at one time, avoiding adverse damage to the gear transmission parts. In addition, there is no need for expensive and complex testing equipment, and the measurement accuracy fully meets the needs of fault monitoring.

[0125] This embodiment starts from the nature of multi-physical field coupling and interaction, further understands the intrinsic connection between gear surface temperature and gear defects, and explores more effective feature characterization methods and parameters for describing gear defects.

[0126] Embodiment three:

[0127] This embodiment provides Figure 2 A gear crack internal and external depth detection system based on a gear-simulating coil induction thermal response is shown, comprising:

[0128] Excitation module: The gear is electromagnetically excited by the designed tooth-shaped coil to form an induced current on the gear surface and near the surface, and then the temperature is detected to obtain a thermal cloud map; and the temperature characteristic points of the cloud map are extracted according to the probe points;

[0129] Excitation module: After judging internal and external cracks according to the thermal cloud map, if it is an internal crack, the hidden depth of the internal crack is detected; if it is an external crack, the depth of the external crack is detected;

[0130] External crack depth detection module: The cloud temperature characteristic point in the middle of the defect is used as the main judgment basis, and other cloud temperature characteristic points are used as auxiliary judgments to realize the detection of external crack depth;

[0131] Internal crack hidden depth detection module: The internal crack hidden depth is detected through the quantitative relationship between the defect buried depth and the tooth surface temperature within a certain range.

[0132] This embodiment uses an excitation coil designed for gear detection based on the tooth slot structure to expand the detection coverage area, such as the tooth surfaces on both sides of a single tooth slot and the tooth bottom and root areas, greatly increasing the effective current field area and density. This type of coil structure only requires a single excitation to display a thermal cloud map, without the need to move the coil multiple times to detect different positions on the tooth surface. In addition, a relatively uniform induced current with curved surface shape characteristics is formed on the gear surface and near the surface, thereby forming a thermal map with obvious resolution effect characteristics;

[0133] This embodiment proposes visualization of cracks on the gear surface and quantitative detection of their depth, which is not limited by the operator's experience and can achieve accurate quantitative detection of crack depth. The temperature cloud map combined with the probe point fixed temperature has higher detection accuracy, which is conducive to realizing intelligent upgrades.

[0134] This embodiment proposes the visualization of cracks in gears and the quantitative detection of hidden depths. This embodiment reveals the association between defects in gears and temperature response cloud maps, providing a convenient visualization method for detecting internal cracks. At the same time, it reveals the deep laws of cloud map temperature feature points at different positions on the gear surface and the hidden depth of defects, quantifies the limit position of the hidden depth, and provides a reference for timely discovery and prediction of hidden faults.

[0135] This embodiment is a non-contact detection, which does not require direct contact with the gear being tested, and can achieve a comprehensive detection of defects at all positions of the gear at one time, avoiding adverse damage to the gear transmission parts. In addition, there is no need for expensive and complex testing equipment, and the measurement accuracy fully meets the needs of fault monitoring.

[0136] This embodiment starts from the nature of multi-physical field coupling and interaction, further understands the intrinsic connection between gear surface temperature and gear defects, and explores more effective feature characterization methods and parameters for describing gear defects.

[0137] Embodiment 4:

[0138] This embodiment proposes a thermal response detection technology based on eddy current induction, which is combined with other physical quantities such as solid heat transfer caused by electromagnetic effect, such as Figure 3 The principle diagram of eddy current induction gear defect depth detection is shown in the figure. During the detection, the excitation coil with high-frequency alternating current is brought close to the gear. At this time, induced current and flow are generated on the surface and inside of the material, and hysteresis induces heat. The temperature distribution of the gear is measured using the thermal cloud map. When defects, cracks appear on the surface of the inspected material, or the depth of the surface defect changes, the distribution of the induced current will change. The different density distribution of the induced current will form various temperature distribution areas near the defect. The defect location, size, shape parameters, etc. are determined by comparing the temperature of the non-defective area and the defective area on the gear surface.

[0139] (1) Structural design of excitation coil probe

[0140] The coil structure is crucial to the test results. Different coil structures reflect different parameters. Reasonable design of the excitation coil is crucial to the parameter response under study. By designing different coil structures for comparison, the response of the parameters and the detection efficiency are comprehensively considered, and finally the structure of the excitation coil is determined. Figure 4 It is the structure of the excitation coil and the distribution diagram of the current flow;

[0141] Through the establishment of the model of the above coil, analyze and observe whether the temperature response of the tooth surface meets the required requirements. The coil excitation current is 5A, the frequency is 15kHz, and the excitation time is 0.15s. The materials are copper (excitation coil), iron (gear) and air (air domain) in Table 1.

[0142] Figure 5 A crack defect is set on the gear surface, and the temperature response at the defect is observed by comparing the temperature response cloud map and the probe points arranged at the defect. Figure 6 for Figure 4 The temperature response of the gear surface under the excitation of the tooth-shaped coil shown.

[0143] The optimization design of the excitation coil is mainly reflected in the following aspects: 1) The coil structure should be able to well reflect the location and shape of the defect, and the coil structure should not have a blind spot, which will affect the comprehensiveness of the tooth surface detection; 2) Consider the operability, convenience and function of automatic detection of the actual detection. If only one area can be detected during the detection, when other areas are to be detected, the coil needs to be moved, and the detection efficiency will be greatly reduced; 3) The manufacturing difficulty of the coil structure should not be too complicated; 4) The temperature distribution at the defect has a more obvious advantage, which can well reflect some characteristic information of the defect, and the temperature change at the defect can also meet the resolution of existing equipment.

[0144] By comparing the temperature distribution cloud maps of different forms of coil excitation, it can be seen that the final results are quite different. Taking the above factors into consideration, the tooth-shaped coil structure has a more comprehensive coverage area for the tooth surface. From the temperature cloud map of its excitation response, it can be seen that the temperature distribution changes more obviously at the defect, which can well reflect the location, shape, size and other parameters of the defect. From the changes in the temperature characteristic points of the cloud map at the defect, it can be seen that the temperature change amplitude at the defect is still relatively obvious, which fully and thoroughly displays the shape and position characteristics of the defects of each part of the gear.

[0145] (2) Detection of gear surface crack depth

[0146] In order to study the effect of defect depth on tooth surface temperature, the final temperature response of each defect excitation change was extracted by increasing the defect depth from the initial depth to 4.3 mm, so as to analyze the effect of defect depth on temperature. Figure 7 The temperature cloud map of gear defects at different depths at 0.15s, with temperature characteristic points of the cloud map set at the corner and middle of the defect.

[0147] It can be seen from the temperature response cloud map at different defects that when the defect depth increases, the temperature color at both ends of the defect gradually becomes darker, that is, the temperature at both ends of the defect is gradually rising, and the temperature in the middle area of ​​the defect, that is, the temperature at the position of probe point 5 and probe point 6, is gradually decreasing with the increase of depth. In order to verify the situation found, the temperature at probe points 1 to 6 is extracted at different defect depths, and the temperature data at different depths are fitted. Through the fitted curve, its changing trend can be intuitively seen. First, with the increase of depth, the defect probe points 1, 2, 3, and 4 all show obvious temperature rising trends, and probe points 5 and 6 show obvious downward trends. And as the depth increases, its temperature response begins to stabilize, such as when the defect depth is about 3.7mm, it begins to stabilize.

[0148] The above analysis shows that as the depth of the defect increases, the current that changes direction gradually increases until the depth reaches a certain level, when all the current begins to change and flow to both ends of the defect. At this time, the temperature at the defect will tend to be stable, that is, the temperature will no longer continue to rise with the increase in depth. That is, for the defects at different locations found above, when the depth of the defect increases to a certain stage, its temperature begins to stabilize.

[0149] Based on the above research and analysis, the defect depth is quantitatively analyzed through temperature data. Figure 8 The probe point fitting data of defects at different depths. From the fitting data, the convergence of probe points 5 and 6 is higher than that of other probe points. By comparing the response of the temperature characteristic points of the cloud map, it can be seen that in actual applications, the conversion of the depth by extracting the temperature data in the middle has a higher accuracy. However, due to the influence of the current skin effect, the temperature changes at probe points 1 to 4 will tend to be stable at a certain depth and will not be proportional to the depth. Therefore, in the actual detection process, the temperature data in the middle of the defect can determine the defect depth more accurately, and the temperature characteristic points of the cloud map at other locations can be used as auxiliary judgments.

[0150] (3) Detection of hidden depth of cracks in gears

[0151] Fig. 9The temperature cloud diagram of gear defect 1 (tooth surface crack) at different burial depths is shown in Figure 2. Fig. 9 It can be observed that when defects occur inside the gear, an uneven temperature field will also occur during the heating process. The main reason for this change in the temperature field is the existence of defects, which causes a sudden change in the direction of the current flow, thereby causing a change in Joule heat, which ultimately manifests itself in uneven temperature distribution on the tooth surface.

[0152] From the temperature response cloud map, we can see that on the tooth surface of the defect-free gear, the overall temperature is relatively uniform without temperature mutation. When a defect is buried 0.1mm~2mm below the tooth surface, the temperature field distribution on the tooth surface can be clearly seen. The temperature distribution on the tooth surface is uneven due to the existence of the defect. When the burial depth is shallow, the position and shape of the defect can be clearly seen. However, with the increase of the burial depth and the influence of the current skin effect, the surface temperature distribution at the defect will no longer be obvious, that is, Fig. 9 The burial depth is 1.3mm and thereafter.

[0153] Fig.10 On the right is a simulation diagram of different burial depths and surface temperature responses at defect 2 (tooth bottom crack). It can be seen that its overall change trend is the same as that of defect 1. The location and shape of the defect can be observed through the temperature cloud map, but the temperature cloud map cannot reflect the burial depth of the defect. At this time, because the burial depth of the defect is gradually increasing, most of the current will be concentrated near the surface due to the skin effect of the current. Therefore, the closer the defect is to the surface, the greater the Joule heat it generates, so the higher its surface temperature. When the defect is farther away from the surface, the Joule heat generated at the defect is smaller due to the smaller current density inside the gear. When the Joule heat at the defect is less than the Joule heat generated on the surface, the surface temperature cloud map will no longer clearly reflect the location and shape of the defect.

[0154] Fig.11 Fitting curves for temperature characteristic points of cloud maps at different burial depths can intuitively show the change in the temperature response of the tooth surface at the defect with different burial depths. Within a certain range, the burial depth of the defect is proportional to the temperature of the tooth surface at the defect. However, when the burial depth reaches a certain range, the defect also shows a relatively stable change, and the temperature cloud map cannot reflect the existence of the defect. Fig. 9 1.3mm and Fig.10 When the tooth surface temperature is 1mm, it is impossible to determine whether there are defects through the temperature cloud map distribution of the tooth surface, so it is impossible to perform quantitative analysis of the defects. Fig. 9 as well as Fig.10Other temperature cloud maps that can reflect defects can be used to perform quantitative analysis of the absence by collecting temperature data at the defect site at the end of the excitation, and the fitting formula can be used to perform quantitative analysis of the burial depth of the defect.

[0155] Through the above research and analysis, near-surface cracks caused by heat treatment processes such as quenching and grinding can be effectively detected and identified. By combining the temperature response cloud map of the tooth surface and the temperature data at the defect, the depth of the near-surface crack can be determined, and the closer the crack is to the surface, the clearer and more accurate its temperature cloud map will be. It should be noted that although this method can detect near-surface defects, due to the skin effect of the current, it is determined that this method cannot have a greater depth of detection. However, for near-surface defect detection, this method has a higher sensitivity and can accurately determine the shape, position and depth of the defect.

Claims

1. A method for detecting the internal and external depth of a gear crack by using a gear coil to induce thermal response, characterized in that: include: The gears are electromagnetically excited by the designed tooth-shaped coils, and induced currents are formed on the gear surface and near the surface. Then the temperature is detected to obtain the thermal cloud map. And extract temperature characteristic points of cloud map according to probe points; After judging the internal and external cracks according to the thermal cloud map, if it is an internal crack, the hidden depth of the internal crack is tested; if it is an external crack, the depth of the external crack is tested; The temperature characteristic point of the cloud map in the middle of the defect is used as the main judgment basis, and other temperature characteristic points of the cloud map are used as auxiliary judgments to realize the detection of the external crack depth; specifically, the probe points are arranged in the two end areas of the defect and in the middle of both sides of the defect; after the temperature characteristic points of the cloud map at different depths are extracted, the fourth-order polynomial fitting is used to finally obtain the defect depth and temperature expressions at different probe points; Through the quantitative relationship between the buried depth of defects within the range and the tooth surface temperature, the hidden depth of internal cracks can be detected; The tooth-shaped coil structure includes: The tooth-shaped coil is an excitation coil composed of multiple triangular arcs coaxial with the curved surfaces of various parts of the gear slot. The radius of the top arc of the tooth-shaped coil is 47mm, the radius of the left and right sides is 18mm, and the radius of the bottom arc is 4mm. The upper and lower height of the tooth-shaped coil is 25mm, the thickness is 12mm, the outer diameter of the coil wire is 1.8mm, the inner diameter is 0.8mm, the material is copper, and the number of turns is 5. During the detection process, the tooth-shaped coil is placed inside the gear slot, and the side surfaces and bottom of the tooth-shaped coil are 2mm away from the side surfaces and bottom of the gear slot.

2. The gear crack inner and outer depth detection method based on the induction thermal response of the gear-simulating coil according to claim 1 is characterized in that: Electromagnetic excitation of gears by designed tooth-shaped coils includes: The current applied to the coil is in the form of a sinusoidal AC signal with a maximum oscillation frequency of 50kHz. When the coil is unloaded, the current is 2A. When the coil is placed in the gear slot for heating, the current is 6A. The maximum heating power of the excitation device is 120W.

3. The gear crack inner and outer depth detection method based on the induction thermal response of the gear-simulating coil according to claim 2 is characterized in that: The excitation device includes: a capacitor, an inductor, a MOSFET, a diode, a voltage-stabilizing diode, a pull-down resistor, and a current-limiting resistor, and the current is directly loaded onto the gate of the MOSFET through the current-limiting resistor.

4. The gear crack inner and outer depth detection method based on the induction thermal response of the gear-simulating coil according to claim 1 is characterized in that: The tooth-shaped coil structure also includes: a tooth-shaped coil auxiliary device: The input voltage of the induction heating device is limited to DC5~12V. The power supply is converted into DC5~12V by using auxiliary equipment. The tooth-shaped coil auxiliary device is composed of a transformer, a diode, a voltage regulator, and a voltage stabilizer. It also includes a self-priming pump with a power supply of DC5V. The maximum flow rate of the self-priming pump is 1.6L / min and the maximum lift is 1.5m.

5. The gear crack inner and outer depth detection method based on the induction thermal response of the gear-simulating coil according to claim 1 is characterized in that: The detection of external crack depth includes: extracting temperature characteristic points of cloud map at different depths, fitting with fourth-order polynomial, and finally obtaining the defect depth and temperature expressions at different probe points: Probe point 1 and probe point 4 are located on the same side, and probe point 2 and probe point 3 are located on the same side, and are arranged at the corner points of the defect respectively. Probe point 5 and probe point 6 are located in the middle of the defect, 0.5 mm away from the defect edge. Coefficient of determination for probe point 1 , the fitting formula is as follows: Coefficient of determination for probe point 2 , the fitting formula is as follows: Coefficient of determination for probe point 3 , the fitting formula is as follows: Coefficient of determination for probe point 4 , the fitting formula is as follows: Coefficient of determination for probe point 5 , the fitting formula is as follows: Coefficient of determination for probe point 6 , the fitting formula is as follows: Probe point 5 and probe point 6 are located in the middle of the defect, 0.5 mm away from the defect edge. x is the defect depth, y It is the temperature characteristic point of the defect cloud map; The temperature data of probe point 5 is used as the main basis for judgment, and the data of other positions are used as auxiliary.

6. The gear crack inner and outer depth detection method based on the induction thermal response of the gear-simulating coil according to claim 1 is characterized in that: Through the quantitative relationship between the buried depth of defects within the range and the tooth surface temperature, the hidden depth of internal cracks can be detected, including: Through the thermal cloud map, the probe point is arranged in the middle of the highest temperature area, a defect is set in the middle of the tooth surface on one side of the gear groove, namely defect 1, and a defect is set in the middle of the tooth bottom, namely defect 2.

7. The gear crack inner and outer depth detection method based on the induction thermal response of the gear-simulating coil according to claim 6 is characterized in that: Through the quantitative relationship between the buried depth of defects and the tooth surface temperature within the range, the detection of the hidden depth of internal cracks is realized, including: Determination coefficient of the probe point at defect 1 , the fitting formula is as follows: Determination coefficient of the probe point at defect 2 , the fitting formula is as follows: In the formula h is the defect burial depth, y It is the temperature characteristic point of the cloud map.

8. A gear crack internal and external depth detection system based on the thermal response of a gear coil, characterized in that: include: Excitation module: The gears are electromagnetically excited by the designed tooth-shaped coils to form induced currents on the gear surface and near the surface, and then the temperature is detected to obtain a thermal cloud map; And extract temperature characteristic points of cloud map according to probe points; Excitation module: After judging internal and external cracks according to the thermal cloud map, if it is an internal crack, the hidden depth of the internal crack is detected; if it is an external crack, the depth of the external crack is detected; External crack depth detection module: The cloud map temperature feature point in the middle of the defect is used as the main judgment basis, and other cloud map temperature feature points are used as auxiliary judgments to realize the detection of external crack depth; specifically, the following steps are used: probe points are arranged in the two end areas of the defect and in the middle of both sides of the defect; after extracting the cloud map temperature feature points at different depths, fourth-order polynomial fitting is used to finally obtain the defect depth and temperature expressions at different probe points; Internal crack hidden depth detection module: Through the quantitative relationship between the buried depth of defects within the range and the tooth surface temperature, the internal crack hidden depth can be detected; The tooth-shaped coil is an excitation coil composed of multiple triangular arcs coaxial with the curved surfaces of various parts of the gear slot. The radius of the top arc of the tooth-shaped coil is 47mm, the radius of the left and right sides is 18mm, and the radius of the bottom arc is 4mm. The upper and lower height of the tooth-shaped coil is 25mm, the thickness is 12mm, the outer diameter of the coil wire is 1.8mm, the inner diameter is 0.8mm, the material is copper, and the number of turns is 5. During the detection process, the tooth-shaped coil is placed inside the gear slot, and the side surfaces and bottom of the tooth-shaped coil are 2mm away from the side surfaces and bottom of the gear slot.

Images