Visual identification method for weld seams in boiler membrane walls

Abstract

This invention relates to a visual recognition method for weld seams in boiler membrane walls. A linear laser emitter emits a linear laser beam that illuminates the workpiece surface and intersects with the weld seam. A camera captures an image of the intersection point of the linear laser and the weld seam. The final weld point location is then deduced based on the relationship between the weld seam and the laser line. This avoids the adverse effects of the welding environment on simple image recognition of the weld point location, while also reducing recognition errors caused by weld slag obscuring the weld seam. Furthermore, as the workpiece moves, a complete and smooth curved weld seam is calculated, effectively improving welding accuracy.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and in particular to a method for visual recognition of weld seams in boiler membrane walls. Background Technology

[0002] In existing technologies, machine vision identification of weld seam locations directly identifies the intersection of a laser line and the weld seam. This method is relatively effective for planar weld seams because weld seams on a plane are relatively straight and easy to predict. Additionally, planes have good reflectivity and a relatively clean environment. A boiler membrane wall is a common boiler wall structure, consisting of a series of parallel, vertically arranged metal tubes that form a membrane wall. High-temperature flue gas from the combustion process inside the boiler transfers heat to the water or steam within these tubes.

[0003] Therefore, in machine vision recognition of workpieces with curved weld seams, such as boiler membrane walls, the weld seams between the flat steel and metal pipes of the boiler membrane wall vary considerably due to the inherent structural features of the membrane wall itself and the precision requirements of its manufacturing. Furthermore, the curved environment also affects visual recognition. Thus, it is difficult to obtain the correct weld seam location using only two-dimensional images. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for visually recognizing weld seams in boiler membrane walls and other workpieces with curved weld seams, which can be calculated using laser weld seam intersection images.

[0005] To achieve the above objectives, the present invention provides a visual recognition method for weld seams in boiler membrane walls. This method uses a linear laser emitter to project a linear laser beam onto the workpiece surface, intersecting with the workpiece weld seam. A camera is used to acquire an image of the intersection point between the linear laser beam and the workpiece weld seam. Weld point recognition is then performed according to the following steps:

[0006] S1: Use a camera to obtain Figure A, showing the position where the linear laser intersects with the weld seam of the workpiece;

[0007] S2: Apply Gaussian filtering to image A and then binarize it to obtain image B;

[0008] S3: The centerline extraction method based on the Hessian matrix is ​​used to refine the B map to obtain the C map;

[0009] S4: Keep the point with pixel value 255 in image C, and obtain The trajectory is recorded as follows, and the point with pixel value 255 is denoted as... ;

[0010] S5: Use Hough test to calculate the longest straight line in graph C. We obtain diagram D, and then find the lowest point along the straight line to find the lower endpoint of the line segment. ;

[0011] S6: For diagram C Each on the trajectory Tangent slope analysis at a point, eliminating points with abrupt slope changes. Line segments formed by points Filter out elliptical segments ;

[0012] S7: Construct the ellipse fitting equation using the least squares method, and use the Lagrange multipliers to solve for the eigenvectors that meet the screening requirements to obtain the E-graph;

[0013] S8: Combined straight lines The intersection point is obtained by fitting the ellipse equation in step S7. In the mathematical model established by the workpiece parameters, the contact point between the flat steel and the metal tube cross-section is the intersection point P. Determine the intersection point... Calculate the distance between the intersection point P and the point P, and take the intersection point. The midpoint of the line connecting the intersection point P and the point of intersection is the final weld point; the intersection point P is the contact point between the flat steel and the metal pipe section in the mathematical model established by the workpiece parameters.

[0014] A further approach is to, in step S5, only take the upper half of diagram C. Points, then use Hough test to calculate the straight line. .

[0015] A further approach is to, in step S6, only take the straight lines in graph C. Below Perform tangent slope analysis at the point.

[0016] A further approach is to perform the following steps in step S6 on diagram C. Each on the trajectory Tangent slope analysis at a point:

[0017] a. Let a certain point on graph C... The slope of the point is abrupt change in slope The x-coordinate of the point is ;

[0018] b. Elimination In the trajectory The arc segments were selected. The arc segment is denoted as the elliptic segment. ,in .

[0019] A further approach is to perform ellipse fitting in step S7 using the following method:

[0020] Establish the equation of the ellipse: ;

[0021] Optimization objective: Let ;

[0022] The optimization objective is:

[0023]

[0024] ;

[0025] Constructing the Lagrange function ;

[0026] Differentiating it yields zero:

[0027]

[0028] Right now, ;

[0029] make, ;

[0030] but, ;

[0031] right Select feature vectors that meet the requirements.

[0032] The visual recognition method for weld seams of boiler membrane walls designed in this invention can calculate the correct weld point position by using laser weld seam intersection images, and can effectively deal with workpieces with curved weld seams, such as boiler membrane walls. Attached Figure Description

[0033] Figure 1 It is a mathematical model established based on known workpiece parameters;

[0034] Figure 2 It is Figure A in Example 1;

[0035] Figure 3 It is Figure B in Example 1;

[0036] Figure 4 It is Figure C in Example 1;

[0037] Figure 5 This is Figure D in Example 1;

[0038] Figure 6 It is Figure E in Example 1;

[0039] Figure 7 This is the mathematical model diagram of Figure C in Example 1;

[0040] Figure 8 This is the fitting effect diagram of E-graph in Example 1. Detailed Implementation

[0041] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0042] Example 1.

[0043] like Figure 1 As shown in this embodiment, the method for visually recognizing weld seams in boiler membrane walls uses a linear laser emitter to emit a linear laser beam that illuminates the workpiece surface and intersects with the workpiece weld seam. A camera is used to acquire an image of the intersection point between the linear laser beam and the workpiece weld seam, and weld point recognition is performed according to the following steps:

[0044] S1: Use a camera to obtain Figure A, which shows the intersection of the linear laser and the weld seam of the workpiece; since the cross-section obtained by the laser plane emitted by the linear laser emitter being tangent to the boiler membrane wall pipe is an ellipse, the top view of the left weld section of the boiler membrane wall is Figure A.

[0045] S2: Apply Gaussian filtering to image A and then binarize it to obtain image B;

[0046] S3: The centerline extraction method based on the Hessian matrix is ​​used to refine the B map to obtain the C map;

[0047] S4: Keep the point with pixel value 255 in image C, and obtain The trajectory is recorded as follows, and the point with pixel value 255 is denoted as... ;

[0048] S5: Use Hough test to calculate the longest straight line in graph C. We obtain diagram D, and then find the lowest point along the straight line to find the lower endpoint of the line segment. The model diagram of diagram C is as follows: Figure 5 As shown, combined with Figure 1 We know that the straight line The upper surface of the flat steel sheet for the boiler membrane wall, end points The edge of the flat steel relative to the metal pipe, i.e., one side of the weld;

[0049] S6: For diagram C Each on the trajectory Tangent slope analysis at a point, eliminating points with abrupt slope changes. Line segments formed by points Filter out elliptical segments Thus, weld seam trajectories can be eliminated through tangent slope analysis. This allows for the extraction of the correct elliptic segment. ;

[0050] S7: Construct the ellipse fitting equation using the least squares method, and use the Lagrange multipliers to solve for the eigenvectors that meet the screening requirements to obtain the E-graph;

[0051] S8: Combined straight lines The intersection point is obtained by fitting the ellipse equation in step S7. In the mathematical model established by the workpiece parameters, the contact point between the flat steel and the metal tube cross-section is the intersection point P. Determine the intersection point... Calculate the distance between the intersection point P and the point P, and take the intersection point. The midpoint of the line connecting the intersection point P and the point of intersection is the final weld point; intersection point P is the contact point between the flat steel and the metal pipe cross-section in the mathematical model established by the workpiece parameters. In this embodiment, the final fitting effect diagram is as follows. Figure 8 As shown, the above method is used to infer the final weld point position by the relationship between the weld seam and the laser line, thereby avoiding the adverse effects of the welding environment on the simple image recognition of the weld point position. At the same time, it also reduces the recognition error caused by the weld slag itself obscuring the weld seam. Furthermore, as the workpiece moves, a complete and smooth curved weld seam is calculated, effectively improving the welding accuracy.

[0052] A further approach is to, in step S5, only take the upper half of diagram C. Points, then use Hough test to calculate the straight line. This reduces the impact of other pixel data outside the straight line, thus improving the accuracy of line calculation.

[0053] A further approach is to, in step S6, only take the straight lines in graph C. Below Perform tangent slope analysis at the point. This reduces the amount of processing required for straight lines. The calculations improve the overall recognition speed of the scheme.

[0054] A further approach is to perform the following steps in step S6 on diagram C. Each on the trajectory Tangent slope analysis at a point:

[0055] a. Let a certain point on graph C... The slope of the point is abrupt change in slope The x-coordinate of the point is ;

[0056] b. Elimination In the trajectory The arc segments were selected. The arc segment is denoted as the elliptic segment. ,in This effectively protects the weld section. and elliptic segment Distinguish, and be able to The point where the slope changes abruptly is obtained from the point. .

[0057] A further approach is to perform ellipse fitting in step S7 using the following method:

[0058] Establish the equation of the ellipse: ;

[0059] Optimization objective: Let ;

[0060] The optimization objective is:

[0061]

[0062] ;

[0063] Constructing the Lagrange function ;

[0064] Differentiating it yields zero:

[0065]

[0066] Right now, ;

[0067] make, ;

[0068] but, ;

[0069] right Select feature vectors that meet the requirements.

[0070] In the description of this invention, it should be noted that the terms "vertical," "upper," "lower," "horizontal," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0071] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0072] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for visually identifying weld seams in boiler membrane walls, characterized in that, A linear laser emitter is used to emit a linear laser beam that illuminates the surface of the workpiece and intersects with the weld seam. A camera is used to capture an image of the intersection point between the linear laser beam and the weld seam, and the weld point is identified according to the following steps: S1: Use a camera to obtain Figure A, showing the position where the linear laser intersects with the weld seam of the workpiece; S2: Apply Gaussian filtering to image A and then binarize it to obtain image B; S3: The centerline extraction method based on the Hessian matrix is ​​used to refine the B map to obtain the C map; S4: Keep the point with pixel value 255 in image C, and obtain The trajectory is recorded as follows, and the point with pixel value 255 is denoted as... ; S5: Use Hough test to calculate the longest straight line in graph C. We obtain diagram D, and then find the lowest point along the straight line to find the lower endpoint of the line segment. ; S6: For diagram C Each on the trajectory Tangent slope analysis at a point, eliminating points with abrupt slope changes. Line segments formed by points Filter out elliptical segments ; S7: Construct the ellipse fitting equation using the least squares method, and use the Lagrange multipliers to solve for the eigenvectors that meet the screening requirements to obtain the E-graph; S8: Combined straight lines The intersection point is obtained by fitting the ellipse equation in step S7. In the mathematical model established by the workpiece parameters, the contact point between the flat steel and the metal tube cross-section is the intersection point P. Determine the intersection point... Calculate the distance between the intersection point P and the point P, and take the intersection point. The midpoint of the line connecting the intersection point P and the point of intersection is the final solder joint; In step S6, the following steps are performed on diagram C. Each on the trajectory Tangent slope analysis at a point: a. Let a certain point on graph C... The slope of the point is abrupt change in slope The x-coordinate of the point is ; b. Elimination In the trajectory The arc segments were selected. The arc segment is denoted as the elliptic segment. ,in .

2. The method for visually identifying weld seams in boiler membrane walls according to claim 1, characterized in that, In step S5, only the upper half of diagram C is taken. Points, then use Hough test to calculate the straight line. .

3. The method for visually identifying weld seams in boiler membrane walls according to claim 1, characterized in that, In step S6, only the straight lines in diagram C are taken. Below Perform tangent slope analysis at the point.

4. The method for visually identifying weld seams in boiler membrane walls according to claim 1, characterized in that, In step S7, ellipse fitting is performed as follows: Establish the equation of the ellipse: ; Optimization objective: Let ; The optimization objective is: ； Constructing the Lagrange function ; Differentiating it yields zero: Right now, ; make, ; but, ; right Select feature vectors that meet the requirements.

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