A harness terminal virtual soldering detection method and device

Abstract

The embodiment of the application provides a kind of wire harness terminal false welding detection method and device, it is related to wire harness processing quality detection technical field, method includes: to wire harness assembly loop applies pulse current;The thermal image sequence of welding point area is collected by infrared thermal imager;Extract the initial slope of temperature rise of welding point as characteristic parameter;Characteristic value is compared with pre-set threshold value, it is judged whether there is false welding defect.The device includes fixed clamp, probe clamp, pulse current source, infrared thermal imager and controller.The application has the effect of high detection rate and single detection time is small.

Description

Technical Field

[0001] This invention relates to the field of wire harness processing quality inspection technology, and in particular to a method and apparatus for detecting poor solder joints in wire harness terminals. Background Technology

[0002] The welding quality of wire harnesses and terminals directly affects the operational safety of the entire equipment. Among them, poor welding is the most common and most difficult type of defect to detect.

[0003] Currently, the main methods for detecting cold solder joint defects in the industry are as follows: visual inspection, which can only detect surface defects and cannot determine the internal connection status of the solder joint, resulting in an extremely low detection rate for cold solder joints; contact resistance measurement, which has a certain detection capability for severe cold solder joints but is not sensitive to minor cold solder joints; X-ray inspection, which can see through the internal structure of the solder joint and has high detection accuracy, but the equipment is expensive, poses radiation safety hazards, and has a slow detection speed, making it difficult to achieve full online inspection; and vibration characteristic detection, which has high detection sensitivity but requires specialized excitation and sensing equipment and has high requirements for installation accuracy.

[0004] To address the aforementioned issues, there is an urgent need for an online detection method that is fast, cost-effective, and sensitive to poor solder joints. Summary of the Invention

[0005] To address the aforementioned issues, this application provides a method and apparatus for detecting poor solder joints in wire harness terminals.

[0006] The method and apparatus for detecting poor solder joints in wire harness terminals provided in this application adopt the following technical solution: A method for detecting poor solder joints in wire harness terminals includes the following steps: S1. Fix the wire harness assembly to be inspected at the inspection station so that the connection between the terminal and the wire harness is exposed to the field of view of the infrared thermal imager. S2. By contacting the terminals and the wire harness with a conductive probe, a pulse current is applied to the wire harness assembly circuit. The amplitude of the pulse current is 1-10A and the pulse width is 0.1-1.0 seconds. S3. During the application of pulsed current, infrared thermal image sequences of the welding point area are continuously acquired by an infrared thermal imager, with a sampling frequency of not less than 30 frames / second. S4. Analyze the acquired thermal image sequence, extract the temperature change curve of the welding point area over time, and calculate the temperature rise rate characteristic value, wherein the temperature rise rate characteristic value is the temperature rise rate within the first 0.1 seconds after the pulse current is applied. S5. Compare the calculated temperature rise rate characteristic value with the preset qualified threshold range. If the temperature rise rate characteristic value falls within the qualified threshold range, the welding quality is deemed qualified; otherwise, it is deemed that there is a false welding defect.

[0007] Optionally, the specific method for calculating the temperature rise rate characteristic value in step S4 is as follows: take the average temperature of the 5 thermal images before the pulse current is applied as the initial temperature T0, and take the average temperature of the 3 thermal images near the moment 0.1 seconds after the application as T0. 0.1 According to the formula k = (T) 0.1 - T0) / 0.1 Calculate the initial slope k of the temperature rise.

[0008] Optionally, the preset qualified threshold range in step S5 is pre-calibrated by the following method: take at least 50 known qualified products and 50 known defective products with poor soldering, execute steps S1 to S4 respectively, collect the temperature rise rate characteristic value, determine the optimal discrimination threshold k0 with ROC curve, and set the qualified threshold range as [k0 - δ, k0 + δ], where δ is set according to the actual detection accuracy requirements.

[0009] A device for detecting poor solder joints at wire harness terminals, comprising: The machine base is equipped with a testing station; A fixing fixture, mounted on the machine base, is used to fix the wire harness assembly to the testing station; A probe holder, positioned above the inspection station, includes a first probe and a second probe, used to contact terminals and wire harnesses respectively. The probe holder is connected to a lifting drive mechanism, which can move up and down to achieve contact and separation between the probe and the workpiece. A pulsed current source is electrically connected to the first probe and the second probe to output a pulsed current. An infrared thermal imager is installed above the inspection station, with its lens aimed at the welding point area of ​​the wire harness assembly, to continuously acquire a sequence of infrared thermal images of the welding point area. The controller is electrically connected to the pulse current source, the infrared thermal imager, and the lifting drive mechanism, and includes an image acquisition module, a temperature analysis module, a feature extraction module, and a judgment module. The image acquisition module is used to receive the thermal image sequence acquired by the infrared thermal imager and convert it into a digital signal; The temperature analysis module is used to extract data on the temperature change over time in the welding point area from the thermal image sequence. The feature extraction module is used to calculate the temperature rise rate feature value based on the temperature change data; The judgment module is used to compare the temperature rise rate characteristic value with a preset qualified threshold range and output a qualified or unqualified judgment result.

[0010] Optionally, the probe tip of the probe holder is provided with an elastic contact to buffer the contact pressure.

[0011] In summary, this application includes at least one of the following beneficial technical effects: Utilizing the physical principle that slightly higher contact resistance at poorly soldered joints results in more Joule heating after energization, a minute resistance difference is amplified into a detectable temperature difference by applying a pulsed current. The detection speed is fast, suitable for online full inspection, with a single inspection process requiring only 1.5-2 seconds, far faster than X-ray inspection. It can be embedded in automated production lines to achieve online full inspection, meeting the needs of large-scale production. The infrared thermal imager is a non-contact measurement, causing no damage to the workpiece; inspected products can directly proceed to subsequent processes. The extracted initial slope of temperature rise, used as a characteristic parameter, is insensitive to changes in ambient temperature and surface emissivity, exhibiting high detection stability. Attached Figure Description

[0012] Figure 1 This is the overall flowchart of this method. Detailed Implementation

[0013] The terminology used in the following embodiments is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. As used in the specification and appended claims of this application, the singular expressions “a,” “an,” “the,” “the,” “the,” and “this” are intended to also include expressions such as “one or more,” unless the context clearly indicates otherwise. It should also be understood that in the following embodiments of this application, “at least one” and “one or more” refer to one, two, or more than two. The term “and / or” is used to describe the relationship between related objects, indicating that three relationships may exist; for example, A and / or B can indicate: A alone, A and B simultaneously, or B alone, where A and B can be singular or plural. The character “ / ” generally indicates that the preceding and following related objects are in an “or” relationship.

[0014] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0015] The following is in conjunction with the appendix Figure 1 The present invention will be described in further detail below.

[0016] This embodiment provides a device for detecting poor solder joints at wire harness terminals, including a base, a fixing fixture, a probe holder, a pulse current source, an infrared thermal imager, a controller, and a display module. The base is an aluminum alloy frame structure with a detection station. The fixing fixture is mounted on the base to fix the wire harness assembly at the detection station, including wire harness grippers and terminal grippers, each driven by an independent cylinder. The wire harness grippers are made of soft silicone material, and the gripping surface has a V-groove to accommodate wire harnesses of different diameters. The terminal grippers are designed with a contour-following structure to ensure reliable terminal positioning. A gantry frame is mounted on the base, and the probe holder is positioned above the detection station and mounted on the gantry frame via a lifting cylinder. The probe holder includes a first probe and a second probe. The probes are made of beryllium copper with a gold-plated surface, providing excellent conductivity and wear resistance. Each probe has a spring-loaded contact at its tip, with a compression stroke of 3mm and adjustable contact pressure. The first probe contacts the terminal, and the second probe contacts the conductor portion of the wire harness. The pulse current source is a programmable constant current source with an output range of 0-10A, an adjustable pulse width of 0.1-2 seconds, and a current accuracy of ±0.1%. The positive and negative terminals of the pulse current source are connected to the first and second probes, respectively. An infrared thermal imager is mounted above the gantry frame of the base, with its lens pointing vertically downwards at the welding point area. The working distance between the infrared thermal imager and the welding point is 150mm, and the field of view is 30mm × 22mm, completely covering the welding area. The controller is an industrial computer with a built-in image acquisition card and processing software. It includes an image acquisition module, a temperature analysis module, a feature extraction module, and a judgment module. The image acquisition module receives thermal image sequences output by an infrared thermal imager at a sampling rate of 50 frames per second. The temperature analysis module processes the thermal images, extracts the temperature values ​​of the welding point area, and eliminates background interference. The feature extraction module calculates the initial slope and / or steady-state temperature rise based on temperature-time data. The judgment module compares the feature values ​​with preset thresholds and outputs the judgment result. The display module is an industrial touch screen that displays the temperature change curve of the welding point, test results, and statistical data in real time.

[0017] like Figure 1 As shown, the detection method includes the following steps: S1. Fix the wire harness assembly. Place the welded wire harness assembly at the inspection station. Use the fixing clamp to clamp and position the wire harness and terminals respectively, ensuring that the welding point is in the center of the infrared thermal imager's field of view. Use elastic clamping during fixing to avoid rigid clamping damaging the wire harness insulation layer.

[0018] S2. Apply a pulse current and drive the probe holder to descend via the lifting cylinder, so that the first probe contacts the terminal and the second probe contacts the conductor part of the wire harness. The probe front end is provided with an elastic contact, and the contact pressure is controlled at 1-2N to ensure reliable electrical contact and no damage to the workpiece. Subsequently, the pulse current source outputs a preset pulse current. In this embodiment, the pulse current amplitude is 5A and the pulse width is 0.5 seconds.

[0019] S3. Acquire thermal image sequence. During the application of pulse current, the infrared thermal imager continuously acquires infrared thermal images of the welding point area. The sampling frequency is set to 50 frames / second. The infrared thermal imager uses an uncooled focal plane detector with a resolution of 640×480 pixels and a thermal sensitivity better than 0.05℃, which can accurately capture minute temperature changes.

[0020] S4. Extract the temperature rise rate feature value, analyze the acquired thermal image sequence, and extract the temperature change data of the welding point area over time. There is a significant difference in the temperature rise curve between qualified products and defective products with poor welding. In this embodiment, the extracted temperature rise rate feature value is the initial slope of the temperature rise, that is, the rate of temperature rise in the first 0.1 seconds after the pulse current is applied.

[0021] The specific calculation method is as follows: Extract the initial temperature T0 before the pulse current is applied, and T0 is the average value of the first 5 frames; extract the temperature T0 0.1 seconds after the application. 0.1 T 0.1 Take the average value of 3 frames around 0.1 seconds; according to the formula k = (T 0.1 - T0) / 0.1 Calculate the initial slope of temperature rise; In this embodiment, the initial slope of temperature rise for qualified products is about 8-12℃ / s, and the initial slope of temperature rise for defective products with poor soldering is about 15-25℃ / s.

[0022] S5. Comparison and judgment: The calculated initial temperature rise slope k is compared with the preset qualified threshold range [k_min, k_max]. In this embodiment, after calibration, the qualified threshold range is [7, 13]℃ / s. If the k value falls within this range, the welding quality is judged to be qualified; otherwise, it is judged to have a false weld defect.

[0023] The test results are displayed in real time through the display module, and the controller sends the judgment results to the production line sorting system to realize the automatic rejection of defective products.

[0024] In addition to the initial slope of the temperature rise, the following characteristic parameters can also be used to characterize the welding quality: Steady-state temperature rise method: The temperature rise value ΔT_end at the end of the pulse current application. The contact resistance of the poor solder joint is larger, more Joule heat is generated, and the steady-state temperature rise is also higher. This method is suitable for thick wire diameter bundles where the initial temperature rise is not obvious.

[0025] Temperature rise integral method: Calculate the integral area of ​​the temperature-time curve during the application of the pulse current, i.e., ∫T(t)dt. This characteristic value comprehensively reflects the temperature accumulation effect of the entire energizing process and has good robustness against noise interference.

[0026] Multi-feature fusion method: This method fuses three feature parameters: initial temperature rise slope, steady-state temperature rise, and temperature rise integral. It then uses machine learning methods such as support vector machine or random forest to build a classification model and comprehensively judge the welding quality, which can further improve the detection accuracy.

[0027] Calibration of the acceptable threshold range is a crucial step in ensuring detection accuracy. This embodiment uses the following method for calibration: Sample preparation: Take 100 wire harness assemblies of the same batch and specifications, of which 50 are qualified products produced by normal process and 50 are defective products with poor soldering prepared by process adjustment, such as reducing soldering time and lowering soldering temperature.

[0028] Data acquisition: All samples were tested according to the method in Example 1. The initial slope k value of the temperature rise was collected, and the qualified product group {k_good(i)} and the defective product group {k_bad(j)} were recorded.

[0029] Statistical analysis: The mean μ_good and standard deviation σ_good of the qualified product group were calculated, and the mean μ_bad and standard deviation σ_bad of the defective product group were calculated. In this embodiment, μ_good = 10.2℃ / s, σ_good = 1.5℃ / s; μ_bad = 19.8℃ / s, σ_bad = 2.1℃ / s. The discrimination index d' = |μ_bad - μ_good| / √(σ_good² + σ_bad²) = 3.6, indicating that this characteristic parameter has good discrimination ability.

[0030] Threshold determination: The optimal threshold is determined by the ROC curve. The k values ​​are sorted from smallest to largest, and each k value is used as a candidate threshold. The corresponding true positive rate and false positive rate are calculated, the ROC curve is plotted, and the point with the largest Youden index is selected as the optimal discrimination threshold k0. According to the detection accuracy requirements, the qualified threshold range is set to [k0 - σ, k0 + σ].

[0031] Verification: Take another batch of known samples to verify the threshold and ensure that the detection accuracy is not less than 99%.

[0032] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. Any equivalent modifications or variations made by those skilled in the art based on the content disclosed in the present invention should be included within the scope of protection set forth in the claims.

Claims

1. A method for detecting poor solder joints in wire harness terminals, characterized in that, Includes the following steps: S1. Fix the wire harness assembly to be inspected at the inspection station so that the connection between the terminal and the wire harness is exposed to the field of view of the infrared thermal imager. S2. By contacting the terminals and the wire harness with a conductive probe, a pulse current is applied to the wire harness assembly circuit. The amplitude of the pulse current is 1-10A and the pulse width is 0.1-1.0 seconds. S3. During the application of pulsed current, infrared thermal image sequences of the welding point area are continuously acquired by an infrared thermal imager, with a sampling frequency of not less than 30 frames / second. S4. Analyze the acquired thermal image sequence, extract the temperature change curve of the welding point area over time, and calculate the temperature rise rate characteristic value, wherein the temperature rise rate characteristic value is the temperature rise rate within the first 0.1 seconds after the pulse current is applied. S5. Compare the calculated temperature rise rate characteristic value with the preset qualified threshold range. If the temperature rise rate characteristic value falls within the qualified threshold range, the welding quality is deemed qualified; otherwise, it is deemed that there is a false welding defect.

2. The method for detecting poor solder joints in wire harness terminals according to claim 1, characterized in that: The specific method for calculating the characteristic value of the temperature rise rate in step S4 is as follows: take the average temperature of the 5 thermal images before the pulse current is applied as the initial temperature T0, and take the average temperature of the 3 thermal images near the moment 0.1 seconds after the application as T0. 0.1 According to the formula k = (T) 0.1 - T0) / 0.1 Calculate the initial slope k of the temperature rise.

3. The method for detecting poor solder joints in wire harness terminals according to claim 1, characterized in that: The preset qualified threshold range in step S5 is pre-calibrated by the following method: take at least 50 known qualified products and 50 known defective products with poor soldering, execute steps S1 to S4 respectively, collect the temperature rise rate characteristic value, determine the optimal discrimination threshold k0 with ROC curve, and set the qualified threshold range as [k0 - δ, k0 + δ], where δ is set according to the actual detection accuracy requirements.

4. A device for detecting poor solder joints at wire harness terminals, characterized in that, The method described by any one of claims 1-3 includes: The machine base is equipped with a testing station; A fixing fixture, mounted on the machine base, is used to fix the wire harness assembly to the testing station; A probe holder, positioned above the inspection station, includes a first probe and a second probe, used to contact terminals and wire harnesses respectively. The probe holder is connected to a lifting drive mechanism, which can move up and down to achieve contact and separation between the probe and the workpiece. A pulsed current source is electrically connected to the first probe and the second probe to output a pulsed current. An infrared thermal imager is installed above the inspection station, with its lens aimed at the welding point area of ​​the wire harness assembly, to continuously acquire a sequence of infrared thermal images of the welding point area. The controller is electrically connected to the pulse current source, the infrared thermal imager, and the lifting drive mechanism, and includes an image acquisition module, a temperature analysis module, a feature extraction module, and a judgment module. The image acquisition module is used to receive the thermal image sequence acquired by the infrared thermal imager and convert it into a digital signal; The temperature analysis module is used to extract data on the temperature change over time in the welding point area from the thermal image sequence. The feature extraction module is used to calculate the temperature rise rate feature value based on the temperature change data; The judgment module is used to compare the temperature rise rate characteristic value with a preset qualified threshold range and output a qualified or unqualified judgment result.

5. A wire harness terminal solder joint detection device according to claim 4, characterized in that: The probe holder has an elastic contact at the probe tip to buffer contact pressure.

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