Air conditioner frequency conversion plate screw locking detection method

Abstract

The invention relates to the technical field of screw locking detection, and provides an air conditioner frequency conversion board screw locking detection method comprising the following steps: dividing an assembly area into a power module area, a control core area, an electrical interface area and a heat dissipation auxiliary area; according to the physical structure characteristics of the assembly areas, an independent torsion threshold range and expected torsion curve characteristics are configured for each area; on the basis of the physical structure characteristics of the screw holes in different assembly areas, matching corresponding screw types for the areas, and determining a screw tightening rotating speed range according to the matching relationship between the selected screw types and the physical structure characteristics of the screw holes; locking operation is executed within the screw tightening rotating speed range, torque data in the screw locking process are collected, whether the screw is assembled in place or not is judged according to the comparison result of the torque data and a preset torque standard, and the preset torque standard is set based on the selected screw type and the physical structure characteristic of the screw hole; and judging whether the screw and the screw hole are slipped or not.

Description

Technical Field

[0001] This invention relates to the field of screw tightening detection technology, and in particular to a method for detecting the tightening of screws on an air conditioner inverter board. Background Technology

[0002] In the air conditioning manufacturing industry, the tightening quality of the inverter board screws is crucial for the stable operation of the air conditioner.

[0003] Currently, the tightening test of screws on air conditioner inverter boards typically uses a standardized torque threshold. This means that a fixed torque range is set, and when the torque reaches this range, the screw is considered properly assembled. However, the type of screw used in this process is relatively fixed, generally selected based on past experience and common standards, with little consideration given to the physical structural characteristics of different screw holes and assembly areas.

[0004] Existing technologies do not fully consider the differences in physical structural characteristics of different assembly areas of the inverter board, making it impossible to accurately configure the torque threshold and select the appropriate screw type according to the characteristics of different areas. This leads to misjudgments in actual screw tightening tests, affecting the quality and reliability of the air conditioner inverter board. Summary of the Invention

[0005] To address the aforementioned shortcomings, the present invention aims to propose a method for detecting the tightening of screws on an air conditioner inverter board. This method aims to accurately monitor and judge the screw tightening process by configuring torque threshold ranges and expected torque curve characteristics according to the characteristics of different areas of the inverter board, matching suitable screw types and determining tightening speed ranges based on the screw hole structure characteristics, thereby effectively solving the problem of screws not being properly tightened.

[0006] To achieve this objective, the present invention adopts the following technical solution: A method for detecting the tightness of screws on an air conditioner inverter board includes the following steps: S1: Based on the functional characteristics of the frequency converter control board, the assembly area is divided into the power module area, the control core area, the electrical interface area, and the heat dissipation auxiliary area. S2: Based on the physical structural characteristics of the power module area, control core area, electrical interface area and heat dissipation auxiliary area, configure an independent torque threshold range and expected torque curve characteristics for each area; S3: Based on the physical structure characteristics of screw holes in different assembly areas, match the corresponding screw type for each area, and determine the screw tightening speed range according to the compatibility relationship between the selected screw type and the physical structure characteristics of the screw hole. S4: Perform a locking operation within the screw tightening speed range, collect torque data during the screw tightening process in real time, and determine whether the screw is properly assembled based on the comparison result of the torque data and the preset torque standard, wherein the preset torque standard is set based on the selected screw type and the physical structure characteristics of the screw hole. S5: During the screw tightening operation, based on the characteristics of torque data changes, the physical structure of the screw hole, the selected screw type, and the vibration response characteristics during the tightening process, determine whether the screw and screw hole have stripped.

[0007] Preferably, in step S1, based on the functional characteristics of the frequency converter control board, the assembly area is divided into a power module area, a control core area, an electrical interface area, and a heat dissipation auxiliary area, including: Based on board topology analysis, the spatial distribution characteristics of power semiconductor devices and the physical contour characteristics of their heat dissipation substrates are identified. When a cluster distribution of high-current load terminals is detected, and the associated area has a metal substrate heat dissipation structure, the corresponding area is marked as the power module area. When the stacked structure features of the multilayer PCB board and the physical location features of the debugging port are identified, and the temperature sensor interface has a clustered distribution feature in the area, the corresponding area is marked as the control core area. When the conductive structural features of the external load terminal block and the insulating encapsulation features of the communication interface are detected simultaneously, and the electrical isolation structural features of the power input circuit are present, the corresponding area is marked as the electrical interface area. When the mechanical fixing bracket features of the heat dissipation enhancement element and the connection path features of its thermal management wires are identified, and the associated area has vibration-resistant structural reinforcement features, the corresponding area is marked as the heat dissipation auxiliary area.

[0008] Preferably, in step S2, based on the physical structural characteristics of the power module area, control core area, electrical interface area, and heat dissipation auxiliary area, an independent torque threshold range and expected torque curve characteristics are configured for each area, including: To address the high thermal conductivity requirements of the metal substrate in the power module area, a torque curve feature with a steep rising edge and a first threshold range are configured. The lower threshold value of the power module area is used to ensure the minimum contact pressure between the power device and the heat dissipation substrate. To address the overvoltage protection requirements of multilayer PCBs in the control core area, a gently rising torque curve and a second threshold range are configured. The upper limit of the threshold in the control core area is constrained by the shear strength of the interlayer dielectric of the PCB. To address the mixed-material zoning characteristics of the electrical interface area, a stepped torque curve characteristic for the metal terminal area and a linear torque curve characteristic for the plastic housing area are configured respectively. The median threshold value of the metal area is positively correlated with the conductive cross-sectional area of ​​the terminal. To address the vibration resistance requirements of the heat dissipation auxiliary zone, a torsion curve with bimodal characteristics and a high threshold stability range are configured. The threshold tolerance range of the heat dissipation auxiliary zone is inversely proportional to the vibration spectrum energy distribution.

[0009] Preferably, in step S3, matching the corresponding screw type for each region includes: For the through-hole structure features of the metal substrate in the power module area, a mechanical screw type with a full thread structure is matched. The thread engagement depth of the mechanical screw type with a full thread structure is positively correlated with the substrate thickness. For the shallow blind via structure of multilayer PCBs in the control core area, the type of self-tapping screw is matched. The thread lead angle of the self-tapping screw type is negatively correlated with the compressive strength of the PCB layer. For the mixed material hole characteristics of the electrical interface area, distinguish between the mechanical screws in the metal terminal area and the self-tapping screws in the plastic housing area. The screw head diameter in the electrical interface area has a dynamic constraint relationship with the terminal insulation distance. For the deep through-hole vibration-resistant structure characteristics of the heat dissipation auxiliary area, the mechanical screw type with anti-loosening structure is matched. The axial stiffness of the mechanical screw type with anti-loosening structure is proportionally matched with the mass moment of inertia of the reactor.

[0010] Preferably, the screw tightening speed range is determined based on the compatibility between the selected screw type and the physical structural characteristics of the screw hole, including: For the combination of fully threaded mechanical screws and metal through holes in the power module area, a high speed range is set, and the upper limit of the screw tightening speed is constrained by the critical value of the thread friction heat effect. For the combination of self-tapping screws and shallow blind holes in the control core area, a low speed range is set, and the rate of change of the screw tightening speed gradient is negatively correlated with the brittleness coefficient of the glass fiber layer. For the assembly scenario of mixed mechanical screws / self-tapping screws in the electrical interface area, the rotation speed is set differently according to the material zone. The rotation speed in the metal zone is positively correlated with the screw lead angle, while the rotation speed in the plastic zone is inversely proportional to the thermoplastic deformation temperature. For the combination of anti-loosening mechanical screws and deep through holes in the heat dissipation auxiliary area, a medium-to-high speed range is set, and the speed fluctuation amplitude of screw tightening is constrained by the embedding dynamic characteristics of the anti-loosening structure.

[0011] Preferably, determining whether the screw is properly assembled based on the comparison result between the torque data and the preset torque standard includes: Extract the geometric feature parameters of the real-time torque curve, including the location of the extreme point of the rising slope, the number of inflection points of curvature change, and the fluctuation amplitude of the plateau segment; The geometric feature parameters are then matched with the expected torque curve features of the corresponding assembly area. For the power module area, if no steep single-peak characteristic is detected in the torque curve within the preset stroke, and the peak torque is consistently lower than the critical threshold of contact pressure, it is determined that the power device and the heat dissipation substrate have poor assembly contact. For the control core area, if the torque curve does not reach the minimum curvature inflection point number threshold and the amplitude of the platform segment is lower than the preset anti-interference threshold, it is determined that the screw did not penetrate the solder mask layer, resulting in a loose connection. For the metal terminal area of ​​the electrical interface area: if the inflection point of the stepped curve lags behind the conductive cross-sectional area matching range, or the step height is consistently lower than the minimum conductive pressure threshold, then the terminal conductive surface is determined to be improperly assembled. For the plastic housing area of ​​the electrical interface area: if the slope fluctuation of the linear segment exceeds the thermoplastic deformation tolerance coefficient, or the slope direction deviates from the opposite direction of the insulation spacing compression trend, the housing structure assembly is judged to be unstable. When no bimodal feature is detected in the heat dissipation auxiliary area or the peak spacing exceeds the allowable offset, an alarm for vibration-resistant structure failure is triggered.

[0012] Preferably, step S5 includes determining whether the screw hole has experienced stripping: Based on the physical structural characteristics of the screw hole, the area is divided into the front inlet area, the middle meshing area, and the rear bottom hole area. When the torque curve exhibits high-frequency oscillation characteristics in the inlet region and the vibration spectrum shows a resonance peak of thread guide angle mismatch, it is determined that the guide slope in the inlet region is slipping. When the torque data shows asymmetric attenuation characteristics in the middle meshing zone, and the vibration energy migrates to the low frequency band and exceeds the upper limit of the material structure damping, it is determined that the middle thread meshing surface is slipping. When the torque mutation rate in the bottom hole area of ​​the rear section exceeds the preset safety gradient, and the vibration sensor detects the bottom impact spectrum characteristics, it is determined that the bearing surface of the rear section is slipping.

[0013] One of the above technical solutions has the following advantages or beneficial effects: This invention, based on the functional characteristics of the frequency converter control board, divides the assembly area into a power module area, a control core area, an electrical interface area, and a heat dissipation auxiliary area. This enables precise identification and classification of different areas, facilitating targeted processing based on the different physical structural characteristics of each area and improving the accuracy and effectiveness of screw tightening detection. By configuring independent torque threshold ranges and expected torque curve characteristics for each area according to their physical structural characteristics, this invention achieves precise control and judgment of screw tightening torque in different areas, ensuring that the screw tightening degree in each area meets its own structural requirements and improving the reliability of the entire frequency converter control board assembly. Furthermore, by matching corresponding screw types to each area based on the physical structural characteristics of the screw holes in different assembly areas, and determining the screw tightening speed range based on the compatibility relationship between the selected screw type and the physical structural characteristics of the screw holes, this invention further enhances the overall reliability of the frequency converter control board assembly. This system achieves precise matching between the screw and the screw hole, while determining the appropriate tightening speed. This helps reduce wear on the screw and screw hole during subsequent tightening operations, improving tightening quality and efficiency. By performing the tightening operation within the screw tightening speed range, torque data during the screw tightening process is collected in real time. The torque data is compared with the preset torque standard to determine whether the screw is properly assembled, enabling real-time and accurate monitoring of screw assembly. This allows for timely detection and resolution of assembly defects, improving the stability of assembly quality. Furthermore, during the screw tightening operation, based on the characteristics of torque data changes, the physical structure of the screw hole, the selected screw type, and the vibration response characteristics during the tightening process, it determines whether the screw and screw hole have stripped. This enables timely detection and judgment of stripping issues during screw tightening, avoiding problems such as loose assembly caused by stripping, further enhancing the comprehensiveness and reliability of screw tightening detection. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0015] Figure 1 This is a flowchart of the method for detecting the tightening of screws on an air conditioner inverter board provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the system corresponding to the method for detecting the tightening of screws on an air conditioner inverter board provided in this embodiment of the invention; Figure 3 This is a vibration spectrum energy distribution diagram of the heat dissipation auxiliary area of ​​the air conditioning inverter board screw tightening detection method provided in the embodiment of the present invention; Figure 4This is a schematic diagram of the screwdriver vibration energy-threshold tolerance mapping model for the screw tightening detection method of the air conditioner inverter board screw provided in the embodiment of the present invention; Figure 5 This is the torque curve of the power module area of ​​the screw tightening detection method for the air conditioner inverter board provided in this embodiment of the invention; Figure 6 This is the torque curve of the control core area of ​​the air conditioner inverter board screw tightening detection method provided in this embodiment of the invention; Figure 7 This is the torque curve of the metal terminal area of ​​the electrical interface area of ​​the screw tightening detection method for the screws of the air conditioner inverter board provided in this embodiment of the invention; Figure 8 This is the torque curve of the plastic housing area of ​​the electrical interface area of ​​the screw tightening detection method for the air conditioner inverter board provided in this embodiment of the invention; Figure 9 This is the torque curve of the heat dissipation auxiliary area of ​​the air conditioner inverter board screw tightening detection method provided in the embodiment of the present invention. Detailed Implementation

[0016] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0017] In this invention, the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0018] A method for detecting the tightness of screws on an air conditioner inverter board, such as... Figure 1 As shown, a preferred embodiment of the present invention is as follows: Figure 2 To determine its corresponding system module diagram, the following steps are included: S1: Based on the functional characteristics of the frequency converter control board, the assembly area is divided into the power module area, the control core area, the electrical interface area, and the heat dissipation auxiliary area. It should be noted that the "inverter control board" is the core component in an air conditioner used to adjust and control the inverter function, and it contains various functional modules and electrical components. "Functional characteristics" refer to the specific functions performed by different modules, such as power conversion, signal control, electrical connection, and heat dissipation. "Assembly area" refers to the specific location area on the inverter control board where screws need to be installed. The "power module area" is mainly responsible for handling the conversion and transmission of high-power electrical energy, typically including high-current devices and DC compressor terminals. The "control core area" is the control center of the inverter board, including the CPU chip, debugging ports, and sensor interfaces. The "electrical interface area" is used to connect with other external electrical components, such as four-way valves, fan terminals, and communication lines. The "heat dissipation auxiliary area" is mainly responsible for dissipating heat from components that generate heat, such as the mounting points for external reactors. In this step, the technique used is to divide the assembly area according to the layout and characteristics of different functional modules on the inverter control board, so that targeted testing can be performed on each area subsequently.

[0019] Understandably, dividing the inverter control board into different functional areas allows for full consideration of the differences in structure, materials, and stress characteristics of each area. This is because different functional modules have different screw tightening requirements. For example, the power module area requires high torque to ensure tight contact between power devices and the heat sink, while the control core area requires precise torque control to prevent PCB overvoltage cracking. Therefore, dividing the assembly area provides a basis for configuring independent torque thresholds and expected torque curve characteristics for each area, thereby enabling accurate detection of inverter board screw tightening, avoiding misjudgments caused by uniform testing, and improving the quality and reliability of screw assembly.

[0020] Specifically, the topology of the frequency converter control board is first analyzed to identify the spatial distribution and physical contour features of each functional module. Then, for the power module area, the presence of clustered high-current load terminals and their associated metal substrate heat dissipation structures are detected to determine the area's extent. For the control core area, the layering structure of the multi-layer PCB, the physical location of the debugging ports, and the clustered distribution of temperature sensor interfaces are identified to mark this area. When identifying the electrical interface area, the conductive structure of the external load terminals, the insulation encapsulation features of the communication interfaces, and the electrical isolation structure of the power input circuit are simultaneously detected. For the heat dissipation auxiliary area, the mechanical mounting characteristics of the heat dissipation enhancement components and the connection paths of their thermal management wires are identified, and the vibration-resistant structural reinforcement features are considered to determine this area.

[0021] S2: Based on the physical structural characteristics of the power module area, control core area, electrical interface area and heat dissipation auxiliary area, configure an independent torque threshold range and expected torque curve characteristics for each area; It should be noted that "physical structural characteristics" include the material properties, dimensions, and hole types of each region. For example, the thickness of the metal substrate and heat dissipation requirements in the power module area; the number of layers and interlayer dielectric strength in the multilayer PCB board of the control core area; the conductive cross-sectional area of ​​the metal terminals and the insulation spacing of the plastic shell in the electrical interface area; and the vibration-resistant structure of the heat dissipation auxiliary area. "Torque threshold range" refers to the upper and lower limits of the screw tightening torque set for each region, used to determine whether the screw is tightened to the appropriate degree. "Expected torque curve characteristics" refer to the curve shape characteristics of torque changing with time or angle during screw tightening under ideal conditions. Different regions have different torque curve characteristics due to their different physical structures. The technology used in this step is to configure independent torque thresholds and expected torque curve characteristics for each region based on its physical structural characteristics, in order to achieve targeted detection.

[0022] Understandably, the physical structural characteristics of different areas determine their varying requirements for screw tightening torque. For example, the power module area requires higher torque to ensure close contact between power devices and the heat sink to prevent overheating, resulting in a steep peak in the torque curve indicating that the screw has reached the bottom of the substrate. In contrast, the multilayer PCB board in the control core area is more fragile and requires lower torque to prevent cracking, resulting in a torque curve that rises gradually.

[0023] Specifically, for the power module area, based on the high thermal conductivity and thickness of its metal substrate, a torque curve with a steep rising edge and a high torque threshold range are configured, where the lower threshold ensures the minimum contact pressure between the power device and the heat dissipation substrate. For the control core area, based on the shear strength of the interlayer dielectric of the multilayer PCB and the physical structural characteristics such as the layout of the debugging ports and sensor interfaces, a torque curve with a gentle rising edge and a lower upper torque threshold are configured. In the electrical interface area, based on the partitioning characteristics of its mixed materials, the metal terminal area is configured with a stepped torque curve based on the characteristics such as the conductive cross-sectional area of ​​the terminals, while the plastic shell area is configured with a linear torque curve based on the characteristics such as the insulation spacing, and corresponding torque thresholds are determined for each. For the vibration resistance requirements and physical characteristics such as the deep through-hole structure of the heat dissipation auxiliary area, a torque curve with a bimodal characteristic and a high threshold stability range are configured, and its threshold tolerance range is related to the vibration spectrum energy distribution. For example, in the power module area of ​​an air conditioner inverter board, based on the thickness of its aluminum-based heat sink and heat dissipation requirements, the torque threshold range is configured to be 0.8-1.2 N·m, and the expected torque curve is characterized by a steep peak. The control core area is configured with a torque threshold of 0.4-0.6 N·m, and the expected torque curve is expected to rise gently. The metal terminal area of ​​the electrical interface area is configured with a torque threshold of 0.6-0.8 N·m, and the curve is stepped. The plastic shell area is configured with a torque threshold of 0.3-0.5 N·m, and the curve is linear. The heat dissipation auxiliary area is configured with a torque threshold of 1.0-1.5 N·m, and the curve has a bimodal characteristic.

[0024] S3: Based on the physical structure characteristics of screw holes in different assembly areas, match the corresponding screw type for each area, and determine the screw tightening speed range according to the compatibility relationship between the selected screw type and the physical structure characteristics of the screw hole. It should be noted that "screw hole physical structure characteristics" include the type of screw hole (e.g., through hole, blind hole, deep blind hole, etc.), material (metal or plastic), size (diameter, depth, etc.), and hole wall strength. There are various "screw types," such as machine screws and self-tapping screws, and different types of screws differ in thread structure, material, and strength. "Matching relationship" refers to the degree of matching between the selected screw type and the physical structure of the screw hole, including whether the screw thread fits tightly with the screw hole, whether the screw length is suitable for the screw hole depth, and whether the screw strength matches the load-bearing capacity of the screw hole. "Screw tightening speed range" refers to the suitable speed range for screw tightening operations in this assembly area; different screw types and screw hole physical structure characteristics have different speed requirements. In this step, the technique used is to select the appropriate screw type based on the physical structure characteristics of the screw hole and determine the screw tightening speed range based on the matching relationship between the two to ensure that the screw can be tightened correctly and efficiently into the screw hole.

[0025] Understandably, selecting the appropriate screw type and determining the proper tightening speed are crucial for ensuring a good fit between the screw and the screw hole. For example, the through-hole structure of the metal substrate in the power module area requires fully threaded machine screws to ensure sufficient connection strength, and the thread engagement depth must be adapted to the substrate thickness to ensure a locking effect. Conversely, the shallow blind hole structure of the multi-layer PCB in the control core area requires self-tapping screws, whose thread lead angle must match the compressive strength of the PCB layer to avoid damage to the PCB during tightening. Furthermore, different screw and screw hole combinations have different speed requirements. A suitable speed ensures that the screw is evenly stressed, smoothly screwed into the screw hole, and achieves the required torque, avoiding problems such as incomplete tightening or damage to the screw hole due to excessively fast or slow speeds. By matching the screw type to the physical structural characteristics of the screw hole and determining the tightening speed range, the quality and efficiency of screw assembly can be improved, ensuring the stability and reliability of the inverter board.

[0026] Specifically, in the power module area, for its through-hole structure on the metal substrate, machine screws with full threads are selected, and the screw length is determined according to the substrate thickness, so that the thread engagement depth is positively correlated with the substrate thickness. In the control core area, for the shallow blind hole structure of the multi-layer PCB, self-tapping screws are selected, and their thread lead angle is determined according to the compressive strength of the PCB layer, showing a negative correlation. For the mixed material holes in the electrical interface area, machine screws are used in the metal terminal area and self-tapping screws are used in the plastic shell area, and the screw head diameter must match the terminal insulation spacing, showing a dynamic constraint relationship. In the deep through-hole vibration-resistant structure of the heat dissipation auxiliary area, machine screws with anti-loosening structure are selected, and the screw axial stiffness is proportionally matched with the reactor mass moment of inertia. For example, in the power module area of ​​an air conditioner inverter board, M3×8mm full-thread machine screws are used, and their thread engagement depth is adapted to the through-hole structure of the 5mm thick aluminum-based heat sink; in the control core area, M2×5mm self-tapping screws are used, and their lead angle is determined according to the compressive strength of the PCB layer to prevent damage to the PCB during tightening.

[0027] S4: Perform a locking operation within the screw tightening speed range, collect torque data during the screw tightening process in real time, and determine whether the screw is properly assembled based on the comparison result of the torque data and the preset torque standard, wherein the preset torque standard is set based on the selected screw type and the physical structure characteristics of the screw hole. It should be noted that "screw tightening speed range" refers to the speed range suitable for screw tightening operations in this assembly area, determined in step S3. "Tightening operation" refers to the process of tightening the screw using an electric screwdriver or other tightening tool at a set speed. "Torque data" is data collected in real-time during the screw tightening process, reflecting the force on the screw, usually expressed in Newton-meters (N·m). "Preset torque standard" is a torque range or specific value set according to the selected screw type and the physical structure characteristics of the screw hole, used to determine whether the screw is tightened properly. "Comparison result" refers to the result obtained by comparing the real-time collected torque data with the preset torque standard. In this step, the technology used is to perform screw tightening operations within a set speed range, collect torque data in real time, and compare it with the preset torque standard to determine whether the screw is properly assembled.

[0028] Understandably, operating within a predetermined screw tightening speed range ensures even force distribution during tightening, preventing issues like incomplete tightening or damage to the screw hole due to excessively fast or slow speeds. Simultaneously, real-time torque data provides a clear picture of the force between the screw and the screw hole. By comparing this data with a preset torque standard, it's possible to accurately determine if the screw has been tightened to the appropriate level. This is because when the screw is properly tightened, the torque reaches a preset threshold. If this threshold isn't reached, the screw is not tightened properly, affecting the reliability of the connection; if the threshold is exceeded, it can damage the screw hole or cause excessive stress on the component. Therefore, this method allows for timely detection of problems during assembly, improving the quality and reliability of screw assembly.

[0029] Specifically, in the power module area, screws are tightened using an electric screwdriver at a speed of 800-1000 rpm, and torque data is collected in real time and compared with a preset torque standard of 0.8-1.2 N·m. If the torque data reaches this range, the screw is considered to be properly assembled; otherwise, it is considered not properly tightened. In the control core area, screws are tightened at a speed of 600-800 rpm, and the collected torque data is compared with a preset standard of 0.4-0.6 N·m. In the electrical interface area, metal terminals are tightened at a speed of 800-1000 rpm, and the torque data is compared with 0.6-0.8 N·m; plastic housing terminals are tightened at a speed of 400-600 rpm, and the torque data is compared with 0.3-0.5 N·m. In the heat dissipation auxiliary area, screws are tightened at a speed of 1000-1200 rpm, and the torque data is compared with a preset standard of 1.0-1.5 N·m. For example, in the power module area of ​​an air conditioner inverter board, an electric screwdriver tightens a screw at a speed of 900 rpm. The real-time collected torque data is 1.0 N·m. After comparing it with the preset torque standard, it is determined that the screw is properly assembled. If the collected torque data is only 0.6 N·m, it is determined that it is not properly tightened and needs to be retightened.

[0030] S5: During the screw tightening operation, based on the characteristics of torque data changes, the physical structure of the screw hole, the selected screw type, and the vibration response characteristics during the tightening process, determine whether the screw and screw hole have stripped.

[0031] It should be noted that "torque data variation characteristics" include the changes in the shape, slope, fluctuation amplitude, and peak position of the torque curve over time or angle. "Screw hole physical structure characteristics" refer to the physical properties of the screw hole, such as its type, material, size, and wall strength. "Screw type," such as machine screws and self-tapping screws, exhibits different stress and deformation characteristics during tightening. "Vibration response characteristics" refer to the vibration signal characteristics generated during screw tightening due to the interaction between the screw and the screw hole, as well as the influence of the surrounding structure, including vibration frequency, amplitude, and phase. The technique used in this step comprehensively considers torque data variation characteristics, screw hole physical structure characteristics, screw type, and vibration response characteristics, analyzing these factors to determine whether the screw and screw hole have experienced stripping.

[0032] Understandably, if stripping occurs during screw tightening, it reduces the reliability of the connection between the screw and the screw hole, and may even lead to connection failure, thus affecting the stability and reliability of the frequency converter board. The causes of stripping are related to the physical structural characteristics of the screw hole (such as insufficient hole wall strength, excessive hole diameter, etc.), the screw type (such as insufficient thread strength, mismatched thread shape, etc.), and vibrations generated during tightening. Therefore, analyzing the characteristics of torque data changes can reveal the stress on the screw during tightening, identifying any abnormal fluctuations or premature plateauing, indicating stripping. Combining this with the physical structural characteristics of the screw hole can determine whether the screw hole can withstand the tightening force of the screw. The screw type can reveal its stripping characteristics during tightening. Vibration response characteristics reflect the interaction between the screw and the screw hole, as well as the influence of the surrounding structure. By combining this information, it is possible to accurately determine whether stripping has occurred in the screw and screw hole, allowing for timely intervention and ensuring assembly quality.

[0033] Specifically, in the power module area, if abnormal fluctuations occur in the torque curve during tightening, such as failing to reach the preset steep single-peak characteristic, and considering the metal substrate material of the screw hole and the type of mechanical screw, and simultaneously detecting abnormal vibration frequency in the vibration response, stripping can be determined. In the control core area, if the rising slope and curvature of the torque curve do not match expectations, and considering the characteristics of the multilayer PCB shallow blind hole structure and self-tapping screws, as well as specific signals in the vibration response, stripping can be determined. In the electrical interface area, stripping is determined based on the physical structure characteristics of the screw holes in the metal terminal area or plastic housing area, the type of screw used (mechanical screw or self-tapping screw), and the characteristics of torque data changes and vibration response. In the heat dissipation auxiliary area, stripping is determined by considering the deep through-hole anti-vibration structure, the characteristics of mechanical screws with anti-loosening structures, and torque and vibration responses. For example, in the control core area of ​​an air conditioner inverter board, when tightening with self-tapping screws, the upward slope of the torque curve was significantly lower than expected, and abnormal vibration signals were detected in the vibration response. Based on the analysis of the multi-layer PCB shallow blind hole structure and screw type, it was determined that stripping had occurred. This was due to insufficient hole wall strength or a mismatch between the screw lead angle and the PCB compressive strength when the self-tapping screw was screwed into the PCB shallow blind hole.

[0034] It should be noted that "board topology analysis" refers to analyzing the layout and connection relationships of various components and modules on the frequency converter control board to understand its overall structure and functional distribution. This can be achieved by obtaining the board's original design documents beforehand, including schematics and PCB layouts. The schematics detail the electrical connections between components on the board, while the PCB layout shows the component placement and wiring information. By reading and analyzing these documents, the board's topology can be accurately understood. "Spatial distribution characteristics of power semiconductor devices" refers to the location, quantity, and arrangement of power semiconductor devices such as IGBTs and MOSFETs on the board. "Physical contour characteristics of the heat sink substrate" includes the shape, size, material, thickness, and other physical characteristics of the heat sink substrate. "Cluster distribution characteristics of high-current load terminals" refers to the concentrated distribution area of ​​high-current load terminals on the board, which is associated with the power modules. "High-current load terminals" are metal conductive components of a certain size and shape, capable of withstanding large currents without overheating. Their shape may be columnar, sheet-like, or other forms suitable for electrical connection, and their surfaces are usually tin-plated or have other metal plating treatments. "Metal substrate heat dissipation structure characteristics" refers to the metal material used in the heat dissipation substrate and its heat dissipation structure design features, such as through holes and heat sink fins. "Multilayer PCB board stack-up structure characteristics" refers to the number of layers in a multilayer PCB board, the function of each layer, and the connection method. "Physical positioning characteristics of the debugging port" refers to the specific location and physical dimensions of the debugging port on the PCB board. "Clustered distribution characteristics of temperature sensor interfaces" refers to the concentrated distribution area of ​​temperature sensor interfaces on the board, usually arranged in clusters. "Conductive structure characteristics of external load terminals" refers to the structural characteristics of the conductive parts of external load terminals, such as metal material and contact method. External load terminals are generally metal posts or terminal blocks with threaded holes or other forms of fixing structures to facilitate connection with external wires. External load terminals serve as an electrical connection bridge between the inverter board and external load devices (such as solenoid valves, fans, resistive loads, etc.), transmitting the control signals or electrical energy output by the inverter board to the external load to achieve load control and drive. "Insulation and encapsulation characteristics of communication interfaces" refers to the insulation and encapsulation form of the communication interface, such as plastic shells and insulating coatings. "Electrical isolation structure characteristics of the power input circuit" refers to the design features used for electrical isolation in the power input circuit, such as isolation transformers and optocouplers. The power input circuit consists of power input lines (usually L / N lines, i.e., live and neutral wires), input filter circuits, rectifier bridges, and electromagnetic compatibility (EMC) filter circuits. "Mechanical mounting characteristics of heat dissipation enhancement components" refers to the structural characteristics of the mechanical mounting brackets used for heat dissipation enhancement components (such as reactors and cooling fans), such as the shape, material, and fixing method of the brackets. "Connection path characteristics of thermal management leads" refers to the distribution of connection paths for thermal management leads (such as temperature sensing lines and power lines) on the circuit board."Vibration-resistant structural reinforcement features" refers to the vibration-resistant structural design features adopted in the heat dissipation auxiliary area, such as vibration damping pads and reinforced supports. The technology used in this step is to accurately divide the assembly area by analyzing the topology and various features of the circuit board.

[0035] Specifically, firstly, a topology analysis is performed on the frequency converter control board, and the layout diagram of each component and module on the board is drawn. Then, the spatial distribution characteristics of power semiconductor devices and the physical contour characteristics of the heat dissipation substrate are identified. When a cluster of high-current load terminals is found, and the associated area has a metal substrate heat dissipation structure, this area is marked as the power module area. Next, the stack-up structure of the multilayer PCB board and the physical positioning characteristics of the debugging ports are identified, and the presence of a cluster of temperature sensor interfaces in this area is checked. If the conditions are met, it is marked as the control core area. Afterwards, the conductive structure of the external load terminals and the insulation encapsulation characteristics of the communication interface are simultaneously detected, and the presence of an electrical isolation structure for the power input circuit is confirmed. If the conditions are met, it is marked as the electrical interface area. Finally, the mechanical mounting characteristics of the heat dissipation enhancement components and the connection path characteristics of the thermal management wires are identified, and the presence of vibration-resistant structural reinforcement characteristics in the associated area is checked. If the conditions are met, it is marked as the heat dissipation auxiliary area. For example, on a certain air conditioner inverter board, topology analysis revealed that multiple high-current IGBT devices were concentrated on one side, and there was an aluminum heat dissipation substrate. This conforms to the characteristics of high-current load terminal cluster distribution and metal substrate heat dissipation structure, so it was marked as the power module area. In the center of the board, a multi-layer PCB board structure, debugging ports, and clustered temperature sensor interfaces were identified, which meet the characteristic conditions of the control core area, and thus it was marked.

[0036] It should be noted that "high thermal conductivity requirement of metal substrate" refers to the use of a metal substrate in the power module area, which has high thermal conductivity. Screw tightening is necessary to ensure good contact between the power devices and the substrate for effective heat dissipation. "Steep rising torque curve characteristic" refers to the torque curve rapidly rising at a certain point during screw tightening, forming a steep slope, indicating that the screw has reached the bottom of the substrate. "First threshold range" refers to a relatively high torque range set for the power module area to ensure sufficient tightening force. "Lower threshold value" is the minimum torque range experienced by the screwdriver in the power module area, used to ensure minimum contact pressure between the power devices and the substrate, preventing overheating due to poor contact. "Multi-layer PCB overvoltage protection requirement" refers to the fragility of the multi-layer PCB in the control core area, requiring protection against excessive tightening force that could damage the PCB due to overvoltage. "Gentle rising torque curve characteristic" indicates that the torque curve rises slowly during tightening to avoid large impact forces. "Second threshold range" is a lower torque range set for the control core area, below the first threshold range, to protect the PCB. "Threshold Upper Limit" refers to the maximum torque range experienced by the screwdriver in the control core area, limited by the shear strength of the interlayer dielectric of the PCB, to prevent exceeding this strength from causing PCB delamination or damage. "Mixed Material Zone" refers to areas in the electrical interface area where different materials such as metal terminals and plastic shells coexist. "Stepped Torque Curve Characteristic" indicates that in the metal terminal area, the torque curve rises in a stepped manner during tightening, related to the multi-segment connection structure of the metal terminals. "Linear Torque Curve Characteristic" indicates that in the plastic shell area, the torque curve rises linearly, consistent with the stress characteristics of plastic materials. "Median Threshold Value in Metal Area" is the median value of the torque threshold range in the metal terminal area, positively correlated with the conductive cross-sectional area of ​​the terminal; the larger the conductive cross-sectional area, the greater the tightening force required to ensure a good electrical connection. "Vibration Resistance Requirement" refers to the need for the heat dissipation auxiliary area to have good vibration resistance to prevent screws from loosening during vibration. "Bimodal Torque Curve Characteristic" indicates that the torque curve exhibits two distinct peaks during tightening; the first peak corresponds to the screw penetrating components such as anti-loosening washers, and the second peak corresponds to the screw finally tightening onto the substrate. The "high threshold stability range" refers to a region with a wide torque threshold range that remains stable after tightening, meeting vibration resistance requirements. The "threshold tolerance range" is the allowable torque fluctuation range, inversely proportional to the vibration spectrum energy distribution. That is, the wider the vibration energy distribution, the smaller the allowable torque fluctuation range, ensuring the screw maintains a reliable connection under vibration. Vibration spectrum energy refers to the energy distribution of each frequency component of the vibration signal in the frequency domain. It reflects the frequency characteristics and energy distribution features of the vibration signal and is one of the important indicators for analyzing vibration signals. The strength of the vibration signal can be determined by adding a torque threshold range and torque curve characteristics to the screwdriver, based on the physical structural characteristics of each region.

[0037] Understandably, the power module area, due to the high thermal conductivity of its metal substrate, requires ensuring tight contact between the power devices and the heat dissipation substrate. Therefore, a torque curve with a steep rising edge and a high threshold range are configured. This ensures sufficient contact pressure between the power devices and the heat dissipation substrate during the locking process when the torque rapidly rises above the lower threshold, achieving good heat dissipation. The multi-layer PCB board in the control core area is prone to damage from excessive locking force. Therefore, a torque curve with a gentle rising edge and a low threshold range are configured to apply the locking force evenly, avoiding exceeding the shear strength of the interlayer dielectric and preventing PCB delamination or breakage. The metal terminal area of ​​the electrical interface area needs to ensure reliable conductivity. A stepped torque curve and a threshold median value positively correlated with the conductive cross-sectional area are configured to accommodate the multi-segment structure of the metal terminals and ensure tight connections between segments. The plastic housing area, based on its material properties, is configured with a linear torque curve to linearly increase the locking force and avoid damage to the plastic housing. To meet vibration resistance requirements, the heat dissipation auxiliary area is configured with a torsion curve featuring a bimodal characteristic and a high threshold stability range. The first peak ensures effective locking of the anti-loosening structure, while the second peak guarantees reliable final screw fixation. Simultaneously, by controlling the threshold tolerance range (e.g., ... Figure 4 The inverse relationship between the screw connection and the vibration spectrum energy distribution (as shown) ensures the stability of the screw connection under vibration conditions. This configuration, tailored to the physical structural characteristics of each area, precisely meets the locking requirements of different areas, improving the quality and reliability of screw assembly and ensuring the stable operation of the air conditioning inverter board under various operating conditions, such as... Figure 3 This is a vibration spectrum energy distribution diagram of the heat dissipation auxiliary area. Additionally, in one embodiment, based on the above steps, the obtained torque curve of the power module area is as follows: Figure 5 As shown, the obtained torque curve of the control core area is as follows: Figure 6 As shown, the torque curve of the metal terminal area of ​​the electrical interface region is as follows: Figure 7 As shown, the torque curve of the plastic housing area of ​​the electrical interface region is as follows: Figure 8 As shown, the obtained torque curve of the heat dissipation auxiliary zone is as follows: Figure 9 As shown.

[0038] Specifically, in the power module area, based on the thickness of the metal substrate and heat dissipation requirements, the lower limit of the torque required to ensure minimum contact pressure between the power device and the heat dissipation substrate is calculated. Then, combined with actual tightening conditions and material strength, a first threshold range is determined, and a torque curve characteristic with a steep rising edge is configured. For example, in the power module area of ​​an air conditioner inverter board, after calculation and testing, the torque threshold range is determined to be 0.8-1.2 N·m, and the torque curve is expected to show a steep peak when the screw is close to being tightened. In the control core area, based on the interlayer dielectric shear strength of the multilayer PCB, the upper limit of the low threshold range is determined, and a torque curve characteristic with a gradual rise is configured. For example, the torque threshold of a certain control core area is set to 0.4-0.6 N·m, and the curve rises gradually to protect the PCB. In the metal terminal area of ​​the electrical interface zone, the height of each step of the stepped torque curve and the corresponding median threshold are determined according to the size of the conductive cross-sectional area of ​​the terminal. For example, for terminals with larger conductive cross-sectional areas, a higher median threshold is configured to ensure good conductive connection. In the plastic housing area, a linear torque curve is configured based on the characteristics of the plastic material, with a torque threshold range of 0.3-0.5 N·m to ensure uniform application of locking force. In the heat dissipation auxiliary area, a bimodal torque curve is configured based on vibration resistance requirements and actual vibration test data to determine the range of the high threshold stability range. The threshold tolerance range is set according to the vibration spectrum energy distribution. For example, the torque threshold of a certain heat dissipation auxiliary area is set to 1.0-1.5 N·m, with a smaller allowable tolerance range to ensure that the screws do not loosen under vibration.

[0039] It should be noted that "through-hole in metal substrate" refers to a through-hole designed on the metal substrate of the power module area for screw mounting and fixing. "Machine screw with full thread structure" refers to a screw whose shank is entirely threaded, typically used for connecting metal materials, offering high strength and connection reliability. "Thread engagement depth" refers to the depth to which the screw thread engages with the thread in the screw hole. "Positive correlation" indicates that the thread engagement depth increases with the substrate thickness to ensure the screw is securely fixed to the substrate. "Shallow blind via structure feature of multilayer PCB" refers to shallow blind vias designed on the PCB board in the control core area; the depth of the holes is relatively shallow, typically not exceeding the total thickness of the PCB board. "Self-tapping screw" is a screw that can self-tap its threads in plastic or softer materials, suitable for connecting multilayer PCBs. "Thread lead angle" is the rise angle of the screw thread, related to the screw's self-tapping performance and tightening force. "Negative correlation" indicates that the thread lead angle decreases with the compressive strength of the PCB layer to prevent damage to the PCB board during tightening. "Mixed Material Hole Features" refers to the screw holes in the electrical interface area being composed of different materials (metal and plastic). "Screw Head Diameter" refers to the maximum diameter of the screw head. "Terminal Insulation Spacing" refers to the insulation distance between metal terminals; the screw head diameter must match this distance to prevent short circuits caused by an excessively large screw head. "Dynamic Constraint Relationship between Screw Head Diameter and Terminal Insulation Spacing in the Electrical Interface Area" means that the screw head diameter is adjusted according to changes in the terminal insulation spacing to meet insulation requirements. "Deep Through-Hole Vibration-Resistant Structure Features" refers to the screw holes in the heat dissipation auxiliary area being deep through holes, and this area needs to have good vibration resistance. "Machine Screws with Anti-Loosening Structures" refers to screws with special anti-loosening designs, such as spring washers or anti-loosening nuts, which effectively prevent the screw from loosening during vibration. "Screw Axial Stiffness" refers to the screw's resistance to deformation in the axial direction. "Reactor Mass Moment of Inertia" is the product of the reactor's mass and the square of its distance from the rotation axis, reflecting the reactor's inertial characteristics during vibration. "Proportional Matching Relationship" indicates a certain proportional relationship between the screw axial stiffness and the reactor's mass moment of inertia to ensure that the screw maintains a reliable connection under vibration. The technique used in this step is to select the appropriate screw type for each region based on the physical structural characteristics of the screw holes in each region, and to ensure the compatibility between the screw and the screw hole.

[0040] Specifically, in the power module area, appropriately sized fully threaded machine screws are selected based on the diameter and depth of the through-holes in the metal substrate, ensuring the thread engagement depth is compatible with the substrate thickness. For example, for a 5mm thick aluminum-based heat sink through-hole, an M3×8mm fully threaded machine screw is selected, with a thread engagement depth of 5mm, positively correlated with the substrate thickness. In the control core area, suitable self-tapping screws are selected for the diameter and depth of shallow blind holes in multilayer PCBs, and the thread lead angle is adjusted according to the compressive strength of the PCB layer. For example, for a multilayer PCB with a shallow blind hole diameter of 2mm and a depth of 3mm, an M2×5mm self-tapping screw is selected, with a lead angle determined to be 30 degrees based on the compressive strength of the PCB layer to ensure no damage to the PCB during tightening. In the electrical interface area, machine screws are selected for the metal terminal area based on the terminal size and conductivity requirements, while self-tapping screws are selected for the plastic housing area based on the diameter and depth of the plastic holes, ensuring the screw head diameter matches the terminal insulation spacing. For example, M2.5×6mm machine screws are used in the metal terminal area, while M2×4mm self-tapping screws are used in the plastic housing area. The screw head diameter is adjusted within a suitable range according to the terminal insulation spacing to ensure insulation safety. In the heat dissipation auxiliary area, machine screws with anti-loosening structures are selected based on the diameter and depth of the through-hole and the reactor's moment of inertia, and the ratio of their axial stiffness to the reactor's moment of inertia is determined. For example, for a through-hole in a certain heat dissipation auxiliary area, M4×10mm machine screws with anti-loosening structures are selected, and their axial stiffness is calculated to be proportionally matched to the reactor's moment of inertia to meet vibration resistance requirements.

[0041] Preferably, the screw tightening speed range is determined based on the compatibility between the selected screw type and the physical structural characteristics of the screw hole, including: For the combination of fully threaded mechanical screws and metal through holes in the power module area, a high speed range is set, and the upper limit of the screw tightening speed is constrained by the critical value of the thread friction heat effect. For the combination of self-tapping screws and shallow blind holes in the control core area, a low speed range is set, and the rate of change of the screw tightening speed gradient is negatively correlated with the brittleness coefficient of the glass fiber layer. For the assembly scenario of mixed mechanical screws / self-tapping screws in the electrical interface area, the rotation speed is set differently according to the material zone. The rotation speed in the metal zone is positively correlated with the screw lead angle, while the rotation speed in the plastic zone is inversely proportional to the thermoplastic deformation temperature. For the combination of anti-loosening mechanical screws and deep through holes in the heat dissipation auxiliary area, a medium-to-high speed range is set, and the speed fluctuation amplitude of screw tightening is constrained by the embedding dynamic characteristics of the anti-loosening structure.

[0042] It should be noted that "combination of fully threaded mechanical screws and metal through holes" refers to the connection method used in the power module area, where fully threaded mechanical screws are paired with metal through holes. "High speed range" refers to a relatively high screw tightening speed range, typically used for metal connections to improve tightening efficiency. "Critical value of thread frictional heat effect" refers to the point at which the heat generated by thread friction during tightening reaches a certain limit, causing a decrease in the performance of the screw or screw hole; therefore, the upper limit of the speed needs to be constrained by this critical value to prevent overheating. "Combination of self-tapping screws and PCB shallow blind holes" refers to the combination of self-tapping screws and shallow blind holes on the PCB board used in the control core area. "Low speed range" refers to a relatively low screw tightening speed range, suitable for more fragile materials such as multilayer PCBs to avoid damage. "Speed ​​gradient change rate" refers to the rate of change of speed during screw tightening. "Glass fiber layer brittleness coefficient" is a material characteristic parameter of the glass fiber layer in a multilayer PCB, reflecting its brittleness under stress. "Negative correlation" indicates that the rate of change of rotational speed gradient decreases as the brittleness coefficient of the glass fiber layer increases, preventing the glass fiber layer from cracking due to excessively rapid changes in rotational speed during tightening. "Mixed assembly scenario of mechanical screws / self-tapping screws" refers to the assembly of both mechanical screws and self-tapping screws in the electrical interface area. "Differentiated rotational speed settings based on material zones" means setting different rotational speeds for metal and plastic zones based on the material of the screw hole area. "Metal zone rotational speed is positively correlated with screw lead angle" means that in the metal zone, the rotational speed increases appropriately as the screw lead angle increases, because a larger lead angle means the screw advances faster during tightening, requiring a slightly higher rotational speed to ensure tightening efficiency and quality. "Plastic zone rotational speed is inversely proportional to thermoplastic deformation temperature" means that in the plastic zone, the rotational speed decreases as the thermoplastic deformation temperature increases, because plastic is prone to deformation at high temperatures, and a lower rotational speed reduces heat generated by friction, preventing overheating and deformation of the plastic hole wall. "Anti-loosening mechanical screws combined with deep through holes" refers to the use of anti-loosening mechanical screws in the heat dissipation auxiliary area in conjunction with deep through holes. "Medium-high speed range" refers to the speed range between high and low speeds, ensuring both tightening efficiency and meeting the assembly requirements of the anti-loosening structure. "Speed ​​fluctuation amplitude" refers to the magnitude of speed fluctuation during tightening. "Anti-loosening structure embedding dynamic characteristics" involves various dynamic factors affecting the anti-loosening structure during embedding into the screw hole, such as friction and impact forces. The speed fluctuation amplitude needs to be constrained by these factors to ensure the anti-loosening structure can be correctly embedded and perform its anti-loosening function. The technique used in this step is to determine a suitable screw tightening speed range based on the compatibility between the screw type and the physical structural characteristics of the screw hole, ensuring that the screw can be smoothly and reliably tightened into the screw hole.

[0043] It's understandable that the combination of fully threaded mechanical screws and metal through holes in the power module area allows for higher tightening speeds due to the high strength of the metal, thus improving efficiency. However, excessively high speeds can lead to excessive heat generation from thread friction, affecting the performance of the screw and screw hole. Therefore, the upper limit of the speed needs to be constrained by the critical value of the thread frictional heat effect to ensure that overheating does not cause problems during tightening. In the control core area, the combination of self-tapping screws and PCB shallow blind holes requires lower tightening speeds due to the fragility of the PCB, especially when it contains a fiberglass layer. This prevents damage to the fiberglass layer due to excessive speed. Furthermore, the rate of change of the speed gradient is negatively correlated with the brittleness coefficient of the fiberglass layer; that is, for fiberglass layers with a high brittleness coefficient, the speed change should be slower to prevent localized stress concentration and breakage during tightening. In the mixed assembly scenario of the electrical interface area, the mechanical screws in the metal area, due to their high material strength, can have their speed appropriately increased based on the screw lead angle to match the screw's forward speed and ensure tightening efficiency. However, the self-tapping screws in the plastic area require consideration of the thermoplastic deformation temperature, necessitating lower speeds to reduce frictional heat generation and prevent deformation of the plastic hole walls. The anti-loosening mechanical screws in the heat dissipation auxiliary area, combined with the deep through-hole, require tightening at medium to high speeds while ensuring proper insertion of the anti-loosening structure, balancing efficiency and reliability. The speed fluctuation amplitude is constrained by the insertion dynamics of the anti-loosening structure, ensuring its smooth insertion into the screw hole and effective anti-loosening function. By appropriately setting the screw tightening speed range, uniform force is ensured during tightening, facilitating smooth assembly and avoiding various problems caused by improper speed, thus improving the quality and reliability of screw assembly.

[0044] Specifically, in the power module area, for the combination of fully threaded mechanical screws and metal through holes, the high-speed range is determined based on the screw specifications and the thermal conductivity of the metal material. For example, in a certain power module area, an M3×8mm fully threaded mechanical screw is selected, and the tightening speed is set to 1000-1200 rpm. Simultaneously, the temperature during tightening is monitored to ensure it does not exceed the critical value for thread frictional heat effect. In the control core area, for the combination of self-tapping screws and PCB shallow blind holes, the low-speed range is determined based on the number of PCB layers, material, and the brittleness coefficient of the glass fiber layer. For example, in a certain control core area, an M2×5mm self-tapping screw is used, and the tightening speed is set to 400-600 rpm. The rate of change of the speed gradient is controlled within a safe range to avoid damaging the glass fiber layer. In the electrical interface area, for the metal terminal area assembled with mechanical screws, the rotation speed is set according to the screw lead angle. For screws with a larger lead angle, the rotation speed can be appropriately increased to 800-1000 rpm. For the plastic housing area assembled with self-tapping screws, a lower rotation speed is set according to the thermoplastic deformation temperature, such as 300-500 rpm, to prevent overheating and deformation of the plastic hole wall. In the heat dissipation auxiliary area, for the combination of anti-loosening mechanical screws and deep through holes, a medium-to-high rotation speed range of 800-1000 rpm is set according to the type of anti-loosening structure and embedding requirements. The rotation speed fluctuation amplitude is monitored in real time to ensure that the anti-loosening structure is correctly embedded. For example, when the rotation speed fluctuation amplitude exceeds a certain limit, the tightening parameters or equipment are adjusted in time.

[0045] It should be noted that the "real-time torque curve" refers to a curve that reflects the change of torque over time or angle, acquired and plotted in real time during the screw tightening process. "Geometric characteristic parameters" include the location of the extreme points of the rising slope, the number of inflection points of curvature change, and the amplitude of plateau segment fluctuations, used to describe the shape and variation characteristics of the torque curve. The "location of the extreme points of the rising slope" refers to the location of the point where the torque curve has the largest slope during its ascent, typically corresponding to the critical position where the screw contacts the connected component or abuts the substrate. The "number of inflection points of curvature change" reflects the number of curvature changes in the torque curve, which can be used to determine whether the screw has experienced different stress stages during tightening. The "amplitude of plateau segment fluctuations" refers to the fluctuation amplitude of the torque curve near the completion of tightening, which can be used to determine whether the screw is stably tightened. "Similarity matching" compares the real-time acquired torque curve geometric characteristic parameters with the expected torque curve characteristics of the corresponding assembly area, evaluating the degree of similarity to determine whether the screw assembly meets expectations. The "Expected Torque Curve Characteristics of the Power Module Area" includes a steep single-peak characteristic, indicating that the screw has reached the bottom of the heat sink during tightening. Simultaneously, the peak torque should exceed the critical contact pressure threshold to ensure good contact between the power device and the heat sink. The "Critical Contact Pressure Threshold" refers to the minimum torque value required to ensure sufficient contact pressure between the power device and the heat sink. The "Expected Torque Curve Characteristics of the Control Core Area" includes a minimum curvature inflection point threshold and a preset anti-interference threshold for the plateau segment amplitude, used to determine whether the screw has penetrated the solder mask and is stably tightened. The "Minimum Curvature Inflection Point Threshold" is the minimum number of curvature change inflection points the torque curve should reach during tightening, typically corresponding to the stage where the screw passes through each PCB layer. The "Preset Anti-Interference Threshold for Plateau Segment Amplitude" is the minimum allowable value of the plateau segment amplitude of the torque curve nearing completion of tightening, used to determine whether the screw is stably tightened. The "Expected Torque Curve Characteristics of the Electrical Interface Area Metal Terminal Area" includes the relationship between the inflection point position of the stepped curve and the conductive cross-sectional area matching range, as well as the relationship between the step height and the minimum conductive pressure threshold. The "inflection point of the stepped curve" corresponds to the position where the screw connects to different segments of the metal terminal during tightening. The "conductive cross-sectional area matching range" is a torque range determined based on the conductive cross-sectional area of ​​the metal terminal, ensuring the screw is tightened within this range for a good conductive connection. The "step height" refers to the height of each step in the stepped rise of the torque curve, which should be above the minimum conductive pressure threshold to ensure sufficient pressure between the terminal's conductive surface and the screw, achieving reliable conductivity. The "minimum conductive pressure threshold" is the torque value corresponding to the minimum pressure required to ensure good conductivity between the metal terminal and the screw. The "expected torque curve characteristics of the plastic housing area in the electrical interface region" includes the relationship between the slope fluctuation amplitude of the linear segment and the thermoplastic deformation tolerance coefficient, as well as the relationship between the slope direction and the direction of the insulation spacing compression trend. The "linear segment slope fluctuation amplitude" is the fluctuation amplitude of the torque curve in the linear rising segment, reflecting the deformation stability of the plastic material during stress.The "thermoplastic deformation tolerance coefficient" is the deformation fluctuation coefficient of the plastic material within the allowable range. Exceeding this coefficient will lead to damage to the plastic hole wall or excessive deformation. The "relationship between the slope direction and the direction of the insulation spacing compression trend" is used to determine whether the screw has exerted the correct compression effect on the insulation spacing during tightening. If the direction deviates in the opposite direction, it indicates a problem in the assembly process. The "expected torque curve characteristics of the heat dissipation auxiliary area" includes a double-peak feature and the allowable offset of the peak spacing. The double-peak feature indicates that the screw penetrates components such as the anti-loosening washer successively during tightening and is finally locked onto the substrate. The peak spacing should be within the allowable range to ensure the effective embedding of the anti-loosening structure and the reliable fixation of the screw. The "allowable offset of the peak spacing" is the allowable error range of the spacing between the double peaks. Exceeding this range will trigger a vibration-resistant structure failure alarm. The technique used in this step is to extract the geometric feature parameters of the real-time torque curve and perform similarity matching with the expected torque curve characteristics of each region to determine whether the screw is properly assembled.

[0046] Understandably, by acquiring the geometric characteristic parameters of the torque curve in real time, detailed force information of the screw during the tightening process can be obtained. Matching these parameters with the expected torque curve characteristics of each region allows for accurate determination of whether the screw is assembled in the intended manner. For the power module area, if a steep single-peak characteristic is not observed and the peak torque is below the critical contact pressure threshold, it indicates that the screw has not reached the bottom of the heat sink substrate, resulting in poor contact between the power device and the substrate, affecting heat dissipation; therefore, poor assembly contact is determined. If the torque curve of the control core area does not reach the minimum curvature inflection point threshold and the amplitude of the plateau segment is below the preset anti-interference threshold, it indicates that the screw has not penetrated the solder mask layer, resulting in a loose connection and affecting the reliability of the circuit connection. If the step-shaped curve inflection point of the metal terminal area in the electrical interface area is delayed or the step height is insufficient, it means that the screw is not tightened within the correct conductive cross-sectional area, resulting in incomplete assembly of the terminal conductive surface and affecting conductivity. Excessive slope fluctuations or reversed slope direction in the linear segment of the plastic casing area indicate unstable deformation of the plastic material under stress or improper compression of the insulation gap, leading to instability in the casing structure assembly and posing a short-circuit risk. The absence of a double-peak characteristic or peak spacing exceeding the allowable offset in the heat dissipation auxiliary area indicates improper embedding of the anti-loosening structure or screw tightening position deviation, triggering a vibration-resistant structure failure alarm and affecting the reliability of the screws under vibration.

[0047] Specifically, in the power module area, the torque curve is acquired in real time, and geometric feature parameters such as the location of the extreme points of the rising slope, the number of inflection points of curvature change, and the amplitude of plateau segment fluctuations are extracted. These parameters are compared with the expected steep single-peak characteristics and the critical contact pressure threshold. For example, if the torque curve does not show a significant steep single peak within the preset tightening stroke, and the peak torque remains below 0.8 N·m (assuming the torque corresponding to the critical contact pressure threshold is 0.8 N·m), then it is determined that the power device and the heat sink substrate have poor assembly contact. In the control core area, the geometric feature parameters of the torque curve are also extracted to check whether the minimum number of curvature inflection points threshold (e.g., set to 2 inflection points) is reached and whether the amplitude of the plateau segment is higher than the preset anti-interference threshold (e.g., set to 0.3 N·m). If these conditions are not met, it is determined that the screw has not penetrated the solder mask layer, resulting in a loose connection. In the metal terminal area of ​​the electrical interface zone, check whether the inflection point of the stepped curve is within the conductive cross-sectional area matching range (e.g., the torque range determined by the terminal conductive cross-sectional area is 0.5-0.7 N·m), and whether the step height reaches the minimum conductive pressure threshold (e.g., 0.6 N·m). In the plastic housing area, check whether the slope fluctuation amplitude of the linear segment exceeds the thermoplastic deformation tolerance coefficient (e.g., set to ±0.1 N·m), and whether the slope direction is consistent with the insulation spacing compression trend. If they are inconsistent or exceed the tolerance coefficient, the housing structure assembly is determined to be unstable. In the heat dissipation auxiliary area, determine whether the torque curve has a double-peak characteristic, and whether the peak spacing is within the allowable offset range (e.g., set to ±0.2 mm). If not, an anti-vibration structure failure alarm is triggered. For example, in the power module area of ​​an air conditioner inverter board, the actual collected torque curve did not show a steep single peak, and the peak torque was only 0.6 N·m, which is lower than the contact pressure critical threshold of 0.8 N·m. Therefore, it is determined that the assembly contact is poor, and the screws need to be retightened.

[0048] It should be noted that "physical structural characteristics of screw holes" include the type, material, size, thread parameters (such as pitch, thread profile, etc.), and wall strength of the screw hole. The "front entry zone" refers to the part of the screw hole near the opening, usually including a guide ramp to guide the screw into the hole. The "middle engagement zone" is the middle part of the screw hole, mainly responsible for engagement with the screw thread and undertaking the main connection function. The "rear bottom hole zone" is the bottom area of ​​the screw hole; in blind holes, it is the bottom of the hole, and in through holes, it is the area that contacts the connecting component on the other side. "High-frequency oscillation characteristics" refer to the high-frequency, small-amplitude fluctuations appearing in the front entry zone of the torque curve, usually related to thread guide angle mismatch. "Thread guide angle mismatch resonance peak" is a specific frequency peak appearing in vibration spectrum analysis, corresponding to the resonance phenomenon caused by thread guide angle mismatch. "Asymmetric attenuation characteristics" refer to the asymmetric attenuation pattern of the torque curve in the middle engagement zone, indicating unilateral wear or damage to the thread engagement surface. "Vibration energy migration to lower frequency bands" indicates that the energy in the vibration signal gradually shifts to lower frequency ranges, usually related to plastic deformation of materials or thread wear. "Material structural damping upper limit" is the maximum limit that a material structure can absorb and dissipate vibration energy; exceeding this limit leads to structural failure. "Torque mutation rate" refers to the rate at which torque changes in the bottom hole region; exceeding a preset safety gradient indicates poor contact between the screw and the bottom of the screw hole or the presence of impact. "Bottom impact spectrum characteristics" are specific impact vibration spectra detected by the vibration sensor in the bottom region, caused by collision between the screw and the bottom of the screw hole or damage to the bearing surface. The technique used in this step is to divide different regions based on the physical structural characteristics of the screw hole and to determine whether stripping has occurred in each region by analyzing torque curve characteristics and vibration response characteristics, while simultaneously generating corresponding maintenance strategies.

[0049] Understandably, different areas of the screw hole play different roles during the tightening process, and the causes and manifestations of stripping vary accordingly. By dividing the screw hole into the front entry area, the middle engagement area, and the rear bottom hole area, the stripping characteristics of each area can be analyzed specifically. In the front entry area, if high-frequency oscillation characteristics are observed and the vibration spectrum shows a resonance peak due to thread guide angle mismatch, it indicates that there is stripping on the guide slope when the screw enters the screw hole. This is because inaccurate machining or damage to the thread guide angle prevents the screw from entering the thread correctly, causing torque fluctuations and resonance phenomena. In the middle engagement area, if the torque data shows asymmetrical attenuation characteristics and the vibration energy migrates to the low-frequency band exceeding the upper limit of the material's structural damping, it indicates that there is unilateral wear or damage on the thread engagement surface, resulting in poor engagement between the screw and the screw hole, and stripping. At the same time, the migration of vibration energy reflects plastic deformation or wear of the material during the stress process. In the bottom hole area of ​​the later section, if the torque mutation rate exceeds the preset safety gradient and a specific bottom impact spectrum characteristic is detected, it indicates poor contact between the screw and the bottom of the screw hole or damage to the bearing surface, resulting in sudden torque changes and impact vibrations, which can lead to stripping of the screw.

[0050] Specifically, when determining whether a screw hole is stripped, it is first divided into a front inlet area, a middle engagement area, and a rear bottom hole area based on the physical structural characteristics of the screw hole. In the front inlet area, the torque curve is monitored in real time for high-frequency oscillation characteristics, and vibration spectrum analysis is used to check for resonance peaks due to thread guide angle mismatch. For example, using high-precision torque and vibration sensors, if high-frequency oscillations of the torque curve are detected in the front inlet area of ​​a screw hole, and vibration spectrum analysis shows resonance peaks at specific frequencies, consistent with thread guide angle mismatch characteristics, then stripping is determined to have occurred in that area. In the middle engagement area, the torque data is analyzed for asymmetric attenuation characteristics, and the vibration energy migration is monitored to see if it exceeds the upper limit of the material's structural damping. For example, if the torque curve shows significant asymmetric attenuation in the middle section, and the amplitude of vibration energy migration to lower frequencies exceeds the upper limit of the material's structural damping for that screw hole, then stripping is determined to have occurred on the middle thread engagement surface. In the rear bottom hole area, the rate of torque mutation is detected to see if it exceeds a preset safety gradient, and vibration sensors are used to check for bottom impact spectrum characteristics. For example, if the torque mutation rate reaches 0.5 N·m / s (assuming a preset safety gradient of 0.3 N·m / s), and the vibration sensor detects a specific bottom impact spectrum, then the rear bearing surface is determined to be stripped. After determining the stripping location, a tiered maintenance strategy is generated based on the functional correlation of the assembly area. For example, if the stripping location is at a critical connection point in the power module area, affecting heat dissipation and power transmission, then maintenance is prioritized, requiring replacement of screw holes or surrounding components; if the stripping location is in a non-critical housing connection area, simple repair measures can be taken or it can be addressed during the next maintenance.

[0051] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0052] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for detecting the tightness of screws on an air conditioner inverter board, characterized in that, Includes the following steps: S1: Based on the functional characteristics of the frequency converter control board, the assembly area is divided into the power module area, the control core area, the electrical interface area, and the heat dissipation auxiliary area. S2: Based on the physical structural characteristics of the power module area, control core area, electrical interface area and heat dissipation auxiliary area, configure an independent torque threshold range and expected torque curve characteristics for each area; S3: Based on the physical structure characteristics of screw holes in different assembly areas, match the corresponding screw type for each area, and determine the screw tightening speed range according to the compatibility relationship between the selected screw type and the physical structure characteristics of the screw hole. S4: Perform a locking operation within the screw tightening speed range, collect torque data during the screw tightening process in real time, and determine whether the screw is properly assembled based on the comparison result of the torque data and the preset torque standard, wherein the preset torque standard is set based on the selected screw type and the physical structure characteristics of the screw hole. S5: During the screw tightening operation, based on the characteristics of torque data changes, the physical structure of the screw hole, the selected screw type, and the vibration response characteristics during the tightening process, determine whether the screw and screw hole have stripped.

2. The method for detecting the tightening of screws on an air conditioner inverter board according to claim 1, characterized in that, In step S1, based on the functional characteristics of the frequency converter control board, the assembly area is divided into a power module area, a control core area, an electrical interface area, and a heat dissipation auxiliary area, including: Based on board topology analysis, the spatial distribution characteristics of power semiconductor devices and the physical contour characteristics of their heat dissipation substrates are identified. When a cluster distribution of high-current load terminals is detected, and the associated area has a metal substrate heat dissipation structure, the corresponding area is marked as the power module area. When the stacked structure features of the multilayer PCB board and the physical location features of the debugging port are identified, and there are clustered distribution features of temperature sensor interfaces in the area, the corresponding area is marked as the control core area. When the conductive structural features of the external load terminal block and the insulating encapsulation features of the communication interface are detected simultaneously, and the electrical isolation structural features of the power input circuit are present, the corresponding area is marked as the electrical interface area. When the mechanical fixing bracket features of the heat dissipation enhancement element and the connection path features of its thermal management wires are identified, and the associated area has vibration-resistant structural reinforcement features, the corresponding area is marked as the heat dissipation auxiliary area.

3. The method for detecting the tightening of screws on an air conditioner inverter board according to claim 1, characterized in that, In step S2, based on the physical structural characteristics of the power module area, control core area, electrical interface area, and heat dissipation auxiliary area, an independent torque threshold range and expected torque curve characteristics are configured for each area, including: To address the high thermal conductivity requirements of the metal substrate in the power module area, a torque curve feature with a steep rising edge and a first threshold range are configured. The lower threshold value of the power module area is used to ensure the minimum contact pressure between the power device and the heat dissipation substrate. To address the overvoltage protection requirements of multilayer PCBs in the control core area, a gently rising torque curve and a second threshold range are configured. The upper limit of the threshold in the control core area is constrained by the shear strength of the interlayer dielectric of the PCB. To address the mixed-material zoning characteristics of the electrical interface area, a stepped torque curve characteristic for the metal terminal area and a linear torque curve characteristic for the plastic housing area are configured respectively. The median threshold value of the metal area is positively correlated with the conductive cross-sectional area of ​​the terminal. To address the vibration resistance requirements of the heat dissipation auxiliary zone, a torsion curve with bimodal characteristics and a high threshold stability range are configured. The threshold tolerance range of the heat dissipation auxiliary zone is inversely proportional to the vibration spectrum energy distribution.

4. The method for detecting the tightening of screws on an air conditioner inverter board according to claim 1, characterized in that, In step S3, matching the corresponding screw type for each region includes: For the through-hole structure features of the metal substrate in the power module area, a mechanical screw type with a full thread structure is matched. The thread engagement depth of the mechanical screw type with a full thread structure is positively correlated with the substrate thickness. For the shallow blind via structure of multilayer PCBs in the control core area, the type of self-tapping screw is matched. The thread lead angle of the self-tapping screw type is negatively correlated with the compressive strength of the PCB layer. For the mixed material hole characteristics of the electrical interface area, distinguish between the mechanical screws in the metal terminal area and the self-tapping screws in the plastic housing area. The screw head diameter in the electrical interface area has a dynamic constraint relationship with the terminal insulation distance. For the deep through-hole vibration-resistant structure characteristics of the heat dissipation auxiliary area, the mechanical screw type with anti-loosening structure is matched. The axial stiffness of the mechanical screw type with anti-loosening structure is proportionally matched with the mass moment of inertia of the reactor.

5. The method for detecting the tightening of screws on an air conditioner inverter board according to claim 1, characterized in that, Based on the compatibility between the selected screw type and the physical structure of the screw hole, the screw tightening speed range is determined as follows: For the combination of fully threaded mechanical screws and metal through holes in the power module area, a high speed range is set, and the upper limit of the screw tightening speed is constrained by the critical value of the thread friction heat effect. For the combination of self-tapping screws and shallow blind holes in the control core area, a low speed range is set, and the rate of change of the screw tightening speed gradient is negatively correlated with the brittleness coefficient of the glass fiber layer. For the assembly scenario of mixed mechanical screws / self-tapping screws in the electrical interface area, the rotation speed is set differently according to the material zone. The rotation speed in the metal zone is positively correlated with the screw lead angle, while the rotation speed in the plastic zone is inversely proportional to the thermoplastic deformation temperature. For the combination of anti-loosening mechanical screws and deep through holes in the heat dissipation auxiliary area, a medium-to-high speed range is set, and the speed fluctuation amplitude of screw tightening is constrained by the embedding dynamic characteristics of the anti-loosening structure.

6. The method for detecting the tightening of screws on an air conditioner inverter board according to claim 1, characterized in that, Determining whether the screw is properly installed based on the comparison between the torque data and the preset torque standard includes: Extract the geometric feature parameters of the real-time torque curve, including the location of the extreme point of the rising slope, the number of inflection points of curvature change, and the fluctuation amplitude of the plateau segment; The geometric feature parameters are then matched with the expected torque curve features of the corresponding assembly area. For the power module area, if no steep single-peak characteristic is detected in the torque curve within the preset stroke, and the peak torque is consistently lower than the critical threshold of contact pressure, it is determined that the power device and the heat dissipation substrate have poor assembly contact. For the control core area, if the torque curve does not reach the minimum curvature inflection point number threshold and the amplitude of the platform segment is lower than the preset anti-interference threshold, it is determined that the screw did not penetrate the solder mask layer, resulting in a loose connection. For the metal terminal area of ​​the electrical interface area: if the inflection point of the stepped curve lags behind the conductive cross-sectional area matching range, or the step height is consistently lower than the minimum conductive pressure threshold, then the terminal conductive surface is determined to be improperly assembled. For the plastic housing area of ​​the electrical interface area: if the slope fluctuation of the linear segment exceeds the thermoplastic deformation tolerance coefficient, or the slope direction deviates from the opposite direction of the insulation spacing compression trend, the housing structure assembly is judged to be unstable. When no bimodal feature is detected in the heat dissipation auxiliary area or the peak spacing exceeds the allowable offset, an alarm for vibration-resistant structure failure is triggered.

7. The method for detecting the tightening of screws on an air conditioner inverter board according to claim 1, characterized in that, Step S5 includes determining whether the screw hole has experienced stripping: Based on the physical structural characteristics of the screw hole, the area is divided into the front inlet area, the middle meshing area, and the rear bottom hole area. When the torque curve exhibits high-frequency oscillation characteristics in the inlet region and the vibration spectrum shows a resonance peak of thread guide angle mismatch, it is determined that the guide slope in the inlet region is slipping. When the torque data shows asymmetric attenuation characteristics in the middle meshing zone, and the vibration energy migrates to the low frequency band and exceeds the upper limit of the material structure damping, it is determined that the middle thread meshing surface is slipping. When the rear bottom hole area contacts the screw hole, the torque mutation rate exceeds the preset safety gradient. When the vibration sensor detects the bottom impact spectrum characteristics, it is determined that the rear bearing surface is slipping.

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