Method for detecting welding quality by adopting visual detection technology

Abstract

The invention discloses a method for detecting welding quality by adopting a visual inspection technology. The method comprises the following steps of: acquiring three-dimensional images of a welding wire, a welding flux at the periphery of the welding wire and a welding surface by utilizing an industrial camera; acquiring the contour edge of the image by using the three-dimensional image, and constructing a sectional view comprising a welding surface, a welding wire and a welding flux; determining the highest point of the sectional view as a vertex, calculating the height from the vertex to the welding plane, and fitting the contour line of the welding wire by using a point of 1 / 2 height below the height as a circle center; according to the contour line, fitted in the previous step, of the welding wire, the graph of the welding wire is removed from the sectional view obtained in the second step, images of the welding surface and the welding flux are left, the height and the contact angle of the welding flux are calculated, and whether the set qualified standard is met or not is judged.

Description

[0001] The present application relates to the technical field of measurement, in particular to a method for detecting welding quality by using visual detection technology.

[0002] In the industrial field, the welding quality is usually detected by using visual detection technology, that is, an industrial camera is used to collect images of the fillets and the solder around the fillets, and then an edge detection algorithm is used to determine whether the solder around each fillet is connected to prevent short circuit, or whether there is solder around the fillet to determine whether there is a lack of solder, or further determine whether there is a cavity in the solder, but the morphology of the solder is not comprehensively detected and determined. In particular, when the lead and the pad of the circuit board are welded, not only the welding stability of the solder and the pad needs to be considered, but also the welding stability of the solder and the lead needs to be considered. In particular, the industry usually uses the Hot-bar method to weld the lead and the pad of the circuit board. The main principle of Hot-bar welding is that the Hot-bar machine converts the grid voltage into low voltage and high current through the transformer of the pulse power supply, and uses the current passing through the jig head to generate resistance heat to heat the pressure head for welding. During the welding process, the input energy of the joint is controlled by controlling the pressure and the power-on time of the Hot-bar, to ensure the reliable connection of the joint. In the cable manufacturing industry, it is a mature welding process with unique advantages over other welding processes, such as fast heating and cooling, no damage to components near the welding joint, etc., and it is increasingly favored by the industry.

[0003] The main features of Hot-bar welding are: 1. Fast heating and cooling, no damage to components near the welding joint; 2. By controlling the pulse current amplitude and the power-on time, the heating temperature of the welding joint and the heating and welding time can be accurately controlled to achieve the effect of process control of the welding part from preheating-welding-reflow; 3. The welding height can be accurately controlled, especially suitable for soft wire (FPC, FFC, etc.) processing.

[0004] How to detect the welding quality is a problem that needs to be solved by the industry, so it is necessary to develop a method for detecting the welding quality by using visual detection technology.

[0005] The present application aims to provide a method for detecting welding quality by using visual detection technology, to solve the problem that the welding quality cannot be judged by using visual detection technology when the lead and the circuit board are welded by using the Hot-bar method.

[0006] ​​​To achieve the above object, the method for detecting welding quality by using visual detection technology according to the present application comprises the following steps:

[0007] Step 1: collecting three-dimensional images of the welding wire, the solder outside the welding wire and the welding surface by using an industrial camera;

[0008] Step 2: obtaining the contour edge of the above-mentioned images by using the three-dimensional images, and constructing a cross-sectional view including the welding surface, the welding wire and the solder;

[0009] Step 3: confirming the highest point of the cross-sectional view as a vertex, and then calculating the height of the vertex to the welding plane, and using the point 1 / 2 height below the height as the center of the circle to fit the contour line of the welding wire;

[0010] Step 4: removing the image of the welding wire from the cross-sectional view obtained in Step 2 according to the contour line of the welding wire fitted in the above step, and leaving the image of the welding surface and the solder;

[0011] Step 5: calculating the height of the solder and the contact angle, and judging whether the set qualified standard is reached.

[0012] According to the above main features, in the step of fitting the contour line of the welding wire in Step 3, the step of removing 10% of the points far away is further included, which specifically comprises the following steps: firstly, all the qualified points are fitted into a circle by using the least square method, wherein the qualified points are the points whose distance to the center of the circle minus the radius to obtain the difference value △d; then, 10% of the points with the largest absolute value of the difference value △d are removed, and the remaining 90% of the points are the qualified points.

[0013] According to the above main features, when the image of the welding wire is removed from the cross-sectional view obtained in Step 2 in Step 4, the difference value △d is obtained by subtracting the radius from the distance between the contour point and the center of the circle, and the point is removed if the absolute value of the difference value △d is less than the set threshold value.

[0014] According to the above main features, in Step 5, the height of the solder is detected, and compared with the diameter of the cable, and the solder height is greater than 50% of the diameter of the cable and less than 75% of the diameter of the cable, which is qualified.

[0015] According to the above main features, in Step 5, the judgment of the contact angle is specifically as follows: firstly, a straight line is fitted by using a set number of contour points of the solder starting from the contact point of the solder and the cable; then, the distance between the new contour point and the fitted straight line is calculated every time a new contour point is added, and if the distance is less than the threshold value, the new contour point is added to the previous contour point to fit the straight line again; the above process is repeated until the distance between the newly collected contour point and the straight line exceeds the set threshold value, and at this time, the angle between the fitted straight line and the vertical line of the welding surface is defined as the contact angle, and if the contact angle is less than 90 degrees, the welding quality is qualified.

[0016] Compared with the prior art, the application detects the welding quality by using visual detection technology, so that the image processing technology is used to analyze the shape of the solder to determine whether it meets the set qualified standard. [DETAILED DESCRIPTION]

[0017] Figure 1 Cross-sectional view of the soldering wire, the solder surrounding the soldering wire and the soldering surface.

[0018] Figures 2A to 2C Schematic diagram for calculating the contact angle between the solder and the soldering surface.

[0019] Figure 3 Schematic diagram of the profile of the fitted soldering wire, the solder surrounding the soldering wire and the soldering surface.

[0020] Figure 4 Flowchart of the method for detecting the welding quality by using visual detection technology according to the application. [DETAILED DESCRIPTION]

[0021] For the welding quality judgment of the Hot-bar (hot-bar soldering or pulse hot-bar soldering) method for welding the wire and the pad of the circuit board, the technical solution of the application evaluates the soldering height and the contact angle, as shown in Figure 1 , for the soldering height, the reference plane (such as the soldering surface) is taken as the reference, the height h of the highest point of the solder is detected, and the height h is compared with the cable diameter D. The height h needs to be greater than 50% of the cable diameter D and less than 75% of the cable diameter D to be the acceptable height. If the height h of the highest point of the solder is lower than 25% of the cable diameter D, it is considered as a false soldering, and if the height h of the highest point of the solder is higher than 75% of the cable diameter D, it is considered as too much solder paste.

[0022] For the contact angle, as shown in Figure 2A , Figure 2B and Figure 2C , taking the left solder as an example, a straight line is fitted from the set number (such as 5) of profile points of the solder starting from the contact point of the solder and the cable. Then, the distance from the new profile point to the above fitted straight line is calculated every time a new profile point is added. If the distance is less than the threshold value, the new profile point is added to the previous profile point to fit a straight line again. This is repeated until the distance from the newly collected profile point to the straight line exceeds the above set threshold value. At this time, the angle between the fitted straight line and the vertical line (perpendicular to the reference plane) is defined as the contact angle. It is considered that the welding quality is qualified if the contact angle is less than 90 degrees.

[0023] Please refer to Figure 4As shown, it is a flowchart of the method for detecting the welding quality by using the visual detection technology for implementing the present application. The method for detecting the welding quality by using the visual detection technology for implementing the present application comprises the following steps:

[0024] Step one: collecting the three-dimensional images of the welding wire, the solder outside the welding wire and the welding surface by using the industrial camera;

[0025] Step two: obtaining the contour edge of the above-mentioned image by using the above-mentioned three-dimensional image, and constructing the cross-sectional view comprising the welding surface, the welding wire and the solder;

[0026] Step three: confirming the highest point of the cross-sectional view as the vertex, and then calculating the height of the vertex to the welding plane, and using the point of 1 / 2 height of the height downward as the center of the circle to fit the contour line of the welding wire;

[0027] Step four: removing the image of the welding wire from the cross-sectional view obtained in step two according to the contour line of the welding wire fitted in the above step, and leaving the image of the welding surface and the solder, as shown by the dashed line in Figure 3

[0028] Step five: calculating the height of the solder and the contact angle, and judging whether the set qualified standard is reached.

[0029] In the specific implementation, the step of fitting the contour line of the welding wire in step three further comprises the step of removing 10% of the points away from the center. Here, removing 10% of the points away from the center is set by the user according to the production situation of the material, and the purpose is to remove the interference of the solder on the fitted circle. Specifically, first, all the points meeting the conditions are fitted into a circle by using the least square method, wherein the points meeting the conditions are the points whose difference △d obtained by subtracting the radius from the distance of each point to the center of the circle is the absolute value, and then 10% of the points with the largest absolute value of the difference △d are removed, and the remaining 90% of the points are the points meeting the conditions, and the circle fitted by using the above-mentioned points meeting the conditions in step three is used as the contour line of the welding wire.

[0030] In addition, in the specific implementation, when the image of the welding wire is removed from the cross-sectional view obtained in step two in step four, the difference △d obtained by subtracting the radius from the distance between the contour point and the center of the circle is removed if the absolute value of the difference △d is less than the set threshold value.

[0031] Compared with the prior art, the welding quality is detected by using the visual detection technology, so that the image processing technology is used to analyze the shape of the solder to judge whether the set qualified standard is met.

[0032] It can be understood that the technical solution and the inventive concept of the present application can be replaced or changed by those skilled in the art, and all these changes or replacements shall belong to the protection scope of the claims attached to the present application.​

Claims

1. A method for detecting the quality of a weld using a vision detection technique, characterized in that The method comprises the following steps: Step one: using an industrial camera to collect a three-dimensional image of the soldering wire, the solder outside the soldering wire, and the soldering surface; Step two: using the three-dimensional image to obtain the contour edge of the image, and constructing a cross-sectional view including the soldering surface, the soldering wire, and the solder; Step three: confirming the highest point of the cross-sectional view as the vertex, and then calculating the height of the vertex to the soldering plane, using the point 1 / 2 height below the height as the center of the circle to fit the contour line of the soldering wire; Step four: removing the image of the soldering wire from the cross-sectional view obtained in step two according to the contour line of the soldering wire fitted in the previous step, and leaving the image of the soldering surface and the solder; Step five: calculating the height and contact angle of the solder, and determining whether the set standard is met.

2. The method of claim 1, wherein the method further comprises: In step three, the step of fitting the contour line of the soldering wire further comprises a step of removing 10% of the points farthest away, specifically, first fitting a circle to all the points meeting the conditions by the least square method, wherein the points meeting the conditions are points whose absolute value of the difference △d obtained by subtracting the radius from the distance of each point to the center of the circle, and then removing 10% of the points with the largest absolute value of the difference △d, and the remaining 90% of the points are the points meeting the conditions. ​ 3. The method of claim 1, wherein the method further comprises: determining a location of the weld joint on the workpiece; and determining a location of the camera on the workpiece. In step four, when removing the image of the soldering wire from the cross-sectional view obtained in step two, the difference △d is obtained by subtracting the radius from the distance between the contour point and the center of the circle, and if the absolute value of the difference △d is less than the set threshold, the point is removed.

4. The method of claim 1, wherein the method further comprises: determining a location of the defect on the workpiece based on the captured image. In step five, the height of the highest solder point is compared with the diameter of the cable, and if the height of the highest solder point is greater than 50% of the diameter of the cable and less than 75% of the diameter of the cable, the soldering quality is qualified.

5. The method of claim 1, wherein the method further comprises: determining a location of the weld joint on the workpiece; and determining a location of the camera on the workpiece. In step five, the judgment of the contact angle is specifically as follows: starting from the contact point of the solder and the cable, a certain number of contour points of the solder are collected to fit a straight line, then for each new contour point, the distance between the new contour point and the fitted straight line is calculated, if the distance is less than a threshold, the new contour point is added to the previous contour points to fit a new straight line, and the process is repeated until the distance between the newly collected contour point and the straight line exceeds the set threshold, at this time, the angle between the fitted straight line and the vertical line of the soldering surface is defined as the contact angle, and if the contact angle is less than 90 degrees, the soldering quality is qualified.

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