Method of welding a workpiece using a vision-guided welding platform

Abstract

Provided are methods of welding a workpiece using a vision-guided welding platform, the welding platform including a welding tool and a camera for vision-guiding movement of the welding tool from a start point to an end point on the workpiece. The method includes adjusting a focal length of the camera such that a focal plane of the camera is on a surface of the workpiece and the start point and the end point are within a field of view of the camera, and obtaining a surface image of the workpiece within the field of view; determining a current focal length of the camera; determining a corrected pixel length of a pixel in the surface image corresponding to the determined current focal length based on the determined current focal length and a predetermined focal length-corrected pixel length correspondence; determining a number of pixels in the surface image between the start point and the end point of each movement of the welding tool; determining a distance between the start point and the end point based on the determined corrected pixel length and the number of pixels; and guiding the welding tool to move from the start point to the end point based on the determined distance and welding the workpiece.

Description

TECHNICAL FIELD

[0001] Embodiments of the present disclosure generally relate to workpiece welding, and more particularly, to a method of welding a workpiece using a vision-guided welding platform. BACKGROUND

[0002] Welding machines are widely used for welding of various workpieces. In some welding operations, a camera with vision-guiding function is provided to guide the movement of a welding tool between locations on a workpiece to ensure operation precision and welding performance.

[0003] In welding operations on workpieces with different profiles or workpieces clamped in different postures, the working distance of the welding tool to the surface of the workpiece varies, which requires the camera for vision-guiding to change its focal length to focus on different workpiece surfaces according to the change of the working distance. The size of the field of view of the camera changes with the change of its focal length, so the pixel size in the image of the surface of the workpiece within the field of view obtained by the camera is variable, resulting in that the distance between the start point and the end point of the movement of the welding tool on the workpiece cannot be accurately obtained according to the image of the surface of the workpiece obtained by the camera. SUMMARY

[0004] To overcome at least one of the above and other problems and drawbacks existing in the prior art, the present disclosure is proposed.

[0005] According to an aspect of the present disclosure, there is provided a method of welding a workpiece using a vision-guided welding platform, the welding platform comprising a welding tool and a camera for vision-guiding the movement of the welding tool from a start point to an end point on the workpiece, the method comprising: adjusting the focal length of the camera such that the focal plane of the camera is located on the surface of the workpiece and the start point and the end point are located within the field of view of the camera, and obtaining a surface image of the workpiece within the field of view of the camera; determining the current focal length of the camera; determining the modified pixel length of a pixel in the surface image corresponding to the determined current focal length based on the determined current focal length and a predetermined focal length-modified pixel length correspondence; determining the number of pixels in the surface image between the start point and the end point of each movement of the welding tool; determining the distance between the start point and the end point based on the determined modified pixel length and the number of pixels; and guiding the welding tool to move from the start point to the end point based on the determined distance, and welding the workpiece.

[0006] In some embodiments, the focal length-modified pixel length correspondence comprises a modified pixel length corresponding to each focal length of the camera.

[0007] In some embodiments, the focal length-modified pixel length correspondence comprises a mapping table characterizing the correspondence between each focal length of the camera and the modified pixel length.

[0008] In some embodiments, the corrected pixel lengths corresponding to the respective focal lengths of the camera are different from each other.

[0009] In some embodiments, the method further comprises determining the focal length-corrected pixel length correspondence in advance at least before visually guiding the movement of the welding tool from a start point to an end point on the workpiece.

[0010] In some embodiments, determining the focal length-corrected pixel length correspondence in advance comprises: providing a calibration sample on which a calibration ruler is disposed, the calibration ruler having two calibration points with a known spacing; adjusting the focal length of the camera so that the camera focuses on a surface of the calibration sample at a plurality of different focal lengths and the two calibration points are located within a field of view of the camera, and acquiring a surface image of the calibration sample within the field of view of the camera; determining a pixel length of a pixel in the surface image of the calibration sample at each focal length based on the spacing between the two calibration points of the calibration ruler; and establishing the focal length-corrected pixel length correspondence with the determined pixel length as the corrected pixel length corresponding to each focal length.

[0011] In some embodiments, determining the pixel length of the pixel in the surface image of the calibration sample at each focal length comprises: determining a number of pixels of the surface image of the calibration sample between the two calibration points; and determining the pixel length based on the spacing and the determined number of pixels of the surface image of the calibration sample between the two calibration points.

[0012] In some embodiments, establishing the focal length-corrected pixel length correspondence comprises:

[0013] performing curve fitting on the corresponding pixel lengths determined at the plurality of discrete focal lengths of the camera to obtain a fitting curve or a polynomial characterizing the focal length-corrected pixel length correspondence.

[0014] In some embodiments, the corrected pixel length is a polynomial function of the focal length.

[0015] In some embodiments, a spacing between a center line of the field of view of the camera and a beam center line of the welding tool in a movement direction of the welding tool is preset or adjustable. BRIEF DESCRIPTION OF DRAWINGS

[0016] The above and other aspects, features, and advantages of the embodiments of the present disclosure will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0017] Figure 1 is a schematic diagram showing a configuration of a visual guidance type welding platform according to an exemplary embodiment of the present disclosure;

[0018] Figure 2 FIG. 1 is a graph schematically illustrating a focal length-corrected pixel length correspondence provided according to one example embodiment of the present disclosure;

[0019] Figure 3 FIG. 2 is a flowchart schematically illustrating a method of welding a workpiece using a vision-guided welding platform according to one example embodiment of the present disclosure; and

[0020] Figure 4 FIG. 3 is a flowchart schematically illustrating a method of pre-calibrating a camera to obtain a focal length-corrected pixel length correspondence according to one example embodiment of the present disclosure. DETAILED DESCRIPTION

[0021] Embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. In the description of the embodiments of the present disclosure, the same or similar components are designated by the same or similar reference numerals. The following description of the embodiments of the present disclosure with reference to the accompanying drawings is intended to explain the general scope of the present disclosure and should not be understood as one kind of limitation.

[0022] Further, in the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present disclosure. However, it will be apparent to one of ordinary skill in the art that one or more embodiments can be practiced without these specific details. In other instances, well-known structures and devices are not described in detail in order to simplify the drawings.

[0023] A method of welding a workpiece using a vision-guided welding platform is provided according to embodiments of the present disclosure. As Figure 1 As schematically shown, the vision-guided welding platform includes a welding tool 120 and a camera 130, which can be mounted to a frame 110, and the distance between the welding tool 120 or the camera 130 and the surface of the workpiece can be adjusted by an adjustment mechanism 101. The welding tool 120 has a welding head or nozzle 121 that emits a light beam (e.g., a laser) to weld the workpiece, and the camera 130, which can be a zoom camera, is used to visually guide the movement of the welding tool 120 from a start point to an end point on the workpiece. For example, the camera is used to acquire an image of the surface of the workpiece, and based on the image (e.g., by analyzing or processing the image), the distance or length between the start point and the end point on the workpiece where the welding tool will move is determined. As an example, such a welding platform can perform a spot welding operation on the workpiece, and the movement of the welding tool from one spot (start point) to another spot (end point) on the workpiece is visually guided by the camera.

[0024] In some examples, the distance between the center line of the field of view FOV of the camera 130 and the center line of the beam of the welding tool 120 in the moving direction of the welding tool is preset or adjustable, so as to determine or determine the distance between the starting point and the ending point of the actual movement of the welding tool on the workpiece, and in turn accurately guide the movement of the welding tool on the workpiece.

[0025] As shown in Figure 1 , since the distances from the surfaces of different workpieces to the camera lens are different, the camera 130 needs to focus on the workpiece surfaces at different focal lengths to obtain clear images, that is, the focal planes FP1, FP2 of the camera when focusing on different workpiece surfaces can be different, which leads to the fact that the field of view size of the camera 130 on the workpiece surface is variable. When the camera obtains the surface images of the workpiece surfaces falling within its field of view at different focal lengths, the pixel size (hereinafter, described by taking the pixel length as an example) in the surface images of each workpiece is variable or offset, rather than fixed. In conventional welding technology, no matter how the camera focuses on the workpiece surface to obtain the workpiece surface image, the distance between the starting point and the ending point of the movement of the welding tool is usually calculated in a fixed pixel length (such as the pixel length PL 固定 shown in Figure 2 , which is inaccurate and cannot reflect the pixel size offset in the images obtained on the surfaces of different workpieces.

[0026] Embodiments of the present disclosure provide a method for welding workpieces using a vision-guided welding platform, which can correct such pixel size offset. When the camera focuses on the workpiece surface at different focal lengths FL, the distance or length between the starting point and the ending point of the movement of the welding tool is determined or calculated using the corrected pixel length PL (see the curve in Figure 2 corresponding to the focal length FL, so as to more accurately guide the movement of the welding tool between different positions (such as different welding points) of the workpiece.

[0027] In some embodiments, as shown in Figure 3 , the method for welding workpieces using a vision-guided welding platform mainly includes the following steps:

[0028] Step S101 : Adjust the focal length FL of the camera 130 so that the camera 130 focuses on the surface of the workpiece, i.e. so that the focal plane (FP1, FP2) of the camera is located on or coincides with the surface of the workpiece, and at least the start and end points of the movement of the welding tool 120 on the workpiece are located within the field of view FOV of the camera 130, and acquire a surface image of the workpiece within the field of view FOV of the camera 120. In some examples, the start or end point of the movement of the welding tool on the workpiece can be a site or a welding point on the workpiece where welding will be performed, or a point between these sites or welding points. In some other examples, the impingement position of the beam (e.g. laser beam) of the welding tool on the surface of the workpiece can also be located within the field of view of the camera.

[0029] Step S102: Determine the current focal length of the camera. The current focal length of the camera can be detected by a sensor or acquired from the camera itself, which is not limited in the present disclosure.

[0030] Step S103: Based on the determined current focal length and the predetermined focal length- corrected pixel length correspondence (e.g. as shown in Figure 2 Step S103: Based on the determined current focal length and the predetermined focal length- corrected pixel length correspondence (e.g. as shown in

[0031] Unlike the conventional techniques in which a fixed pixel length is used to calculate the movement distance of the welding tool at various camera focal lengths, according to the embodiments of the present disclosure, the focal length- corrected pixel length correspondence includes a one-to-one correspondence between each focal length of the camera and a corrected pixel length, and the corrected pixel length corresponding to each focal length can be different from each other. For example, the focal length- corrected pixel length correspondence can be reflected by various graphs, expressions, etc. representing the correspondence between each focal length of the camera and the corrected pixel length, such as the curve graph as shown in Figure 2

[0032] Step S104: Determine the number of pixels in the workpiece surface image between the start and end points of each movement of the welding tool. This can be achieved by a suitable image processor or tool, e.g. digitizing or pixelizing the workpiece surface image.

[0033] Step S105: Based on the determined corrected pixel length PL and the number of pixels N, determine the distance or length between the start and end points of the movement of the welding tool. For example, the distance or length P between the start and end points of the movement of the welding tool can be calculated by the following formula:

[0034] P = N x PL, or

[0035] where PL i ​pixel length of each pixel between the start point and the end point of the movement of the welding tool.

[0036] Step S106: based on the determined distance, guiding or controlling the welding tool to move from the start point to the end point and welding the workpiece.

[0037] The above steps can be repeated when welding the next or subsequent position or welding point on the workpiece.

[0038] According to embodiments of the present disclosure, the camera can be calibrated or calibrated before the welding operation is performed, such as at least before the visual guidance of the movement of the welding tool from the start point to the end point on the workpiece, to determine the focal length- corrected pixel length correspondence in advance.

[0039] Figure 4 The method of pre-calibrating or calibrating the camera to obtain the focal length- corrected pixel length correspondence according to one exemplary embodiment of the present disclosure is schematically shown. As shown, the method comprises:

[0040] Step S10: providing a calibration sample, a calibration ruler (such as a scale) is provided on the calibration sample, and the calibration ruler has two calibration points with known spacing;

[0041] Step S11: adjusting the focal length of the camera so that the camera focuses on the surface of the calibration sample at a plurality of different focal lengths and the two calibration points are located within the field of view of the camera, and acquiring a surface image of the calibration sample within the field of view of the camera;

[0042] Step S12: based on the known spacing between the two calibration points of the calibration ruler, determining the actual pixel length of the pixels in the surface image of the calibration sample at each focal length of the camera;

[0043] Step S13: taking the determined pixel length as the corrected pixel length corresponding to each focal length, establishing the focal length- corrected pixel length correspondence. As Figure 3 and 4 As indicated in A of, the established focal length- corrected pixel length correspondence is subsequently used to guide the welding of the welding tool on different workpieces or different points on the workpiece.

[0044] As an example, determining the pixel length of the pixels in the surface image of the calibration sample at each focal length comprises:

[0045] determining the number of pixels between the two calibration points in the surface image of the calibration sample; and

[0046] Based on the distance and the number of pixels between the two calibration points in the determined surface image of the calibration sample, the pixel length is determined; for example, the actual length of each pixel can be calculated as the distance divided by the number of pixels between the two calibration points.

[0047] The focal length - corrected pixel length correspondence can be established in various ways, in some examples, for example, the determined individual pixel lengths and corresponding focal lengths are stored or recorded in a map or table. In some other examples, a fitting method can be employed to establish the focal length - corrected pixel length correspondence, for example, a curve fitting can be performed on the corresponding pixel lengths determined at a plurality of discrete focal lengths during the calibration or calibration of the camera to obtain a fitting curve or polynomial characterizing the focal length - corrected pixel length correspondence. Illustratively, the determined corrected pixel length can be a polynomial function of the focal length of the camera.

[0048] Although embodiments of the present disclosure have been shown and described, it is to be understood that for the purpose of the present disclosure, the embodiments can be changed or modified without departing from the principles and spirit of the present disclosure, the scope of protection of the present disclosure being defined by the appended claims and their equivalents. Furthermore, it should be noted that the use of the words "including", "containing", "having" and "with" herein does not exclude other elements or steps unless otherwise specified. In addition, any element of the claims should not be understood as limiting the scope of protection of the present disclosure.

Claims

1. A method for welding a workpiece using a vision-guided welding platform, the welding platform including a welding tool (120) and a camera (130) for visually guiding the movement of the welding tool from a starting point to an end point on the workpiece, the method comprising: Before the welding tool moves from the starting point to the ending point to weld the workpiece, the camera's focal length is adjusted so that the camera's focal plane coincides with the surface of the workpiece, and the starting point and the ending point are within the camera's field of view, and a surface image of the workpiece within the camera's field of view is acquired. Determine the current focal length of the camera when the camera's focal plane coincides with the surface of the workpiece and the start and end points are within the camera's field of view; Based on the determined current focal length and the predetermined focal length-corrected pixel length correspondence, the corrected pixel length of the pixels in the surface image corresponding to the determined current focal length is determined. Determine the number of pixels in the surface image between the start point and the end point of each movement of the welding tool; Before the welding tool moves from the starting point to the ending point to weld the workpiece, the distance between the starting point and the ending point is determined based on the determined corrected pixel length and the number of pixels; as well as Based on the determined distance, the welding tool is guided to move from the starting point to the ending point, and the workpiece is welded.

2. The method according to claim 1, wherein the focal length-corrected pixel length correspondence includes corrected pixel lengths that correspond one-to-one with each focal length of the camera.

3. The method according to claim 2, wherein the focal length-corrected pixel length correspondence includes a mapping chart characterizing the correspondence between the various focal lengths of the camera and the corrected pixel lengths.

4. The method of claim 2, wherein the corrected pixel lengths corresponding to the various focal lengths of the camera are different from each other.

5. The method according to any one of claims 1-4, further comprising, at least before visually guiding the movement of the welding tool from a starting point to an end point on the workpiece, pre-determining the focal length-corrected pixel length correspondence.

6. The method according to claim 5, wherein pre-determining the focal length-corrected pixel length correspondence comprises: A calibration sample is provided, on which a calibration ruler is set, the calibration ruler having two calibration points with a known spacing; Adjust the focal length of the camera so that the camera focuses on the surface of the calibration sample at multiple different focal lengths and the two calibration points are located within the field of view of the camera, and acquire the surface image of the calibration sample within the field of view of the camera. Based on the distance between the two calibration points on the calibration ruler, the pixel length of each pixel in the surface image of the calibration sample at each focal length is determined; as well as The determined pixel length is used as the corrected pixel length corresponding to each focal length to establish the correspondence between focal length and corrected pixel length.

7. The method of claim 6, wherein determining the pixel length of a pixel in the surface image of the calibration sample at each focal length comprises: Determine the number of pixels in the surface image of the calibration sample between the two calibration points; as well as The pixel length is determined based on the spacing and the number of pixels in the surface image of the determined calibration sample between the two calibration points.

8. The method according to claim 6, wherein establishing the focal length-corrected pixel length correspondence comprises: Curve fitting is performed on the corresponding pixel lengths determined at multiple discrete focal lengths of the camera to obtain a fitted curve or polynomial characterizing the focal length-corrected pixel length correspondence.

9. The method according to any one of claims 1-4 and 6-8, wherein the distance between the center line of the camera's field of view and the beam center line of the welding tool in the direction of movement of the welding tool is preset or adjustable.

Images