Part positioning device for welding machine tool

Abstract

The invention relates to the technical field of welding positioning and machine vision, in particular to a part positioning device for a welding machine tool, which comprises a protection window, an objective lens, a quarter-wave plate, a polarization splitting prism and an imaging unit positioned at the transmission end of the polarization splitting prism, the laser emitting unit is connected with the side end of the polarization splitting prism; the resolving and outputting unit is electrically connected with the imaging unit; wherein the laser emitting unit emits linear polarization near-infrared laser, and the linear polarization near-infrared laser is reflected by the polarization splitting prism and then is irradiated to the surface of a workpiece through the quarter-wave plate and the objective lens in sequence along the main optical axis; the return light from the workpiece sequentially passes through the objective lens and the quarter-wave plate along the main optical axis; according to the method, emission and imaging share the same primary optical axis and are naturally aligned with the movement direction of a machine tool, shielding and blind areas are remarkably reduced, optical crosstalk and ghost images are effectively inhibited, and accurate positioning of a welding seam path is completed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of welding positioning and machine vision, in particular to a part positioning device for a welding machine tool. BACKGROUND

[0002] In the welding of complex sheet metal parts, pipe parts or special-shaped parts, the precise path and pose of the weld, including the tangential, normal and defocusing amount, are the key factors that determine the welding quality. The traditional methods include: relying on manual positioning by operators; using off-axis camera lighting or imaging, and then converting through spatial calibration; using white light or visible laser stripe projection.

[0003] The above-mentioned solutions have problems such as occlusion sensitivity, large light interference, long coordinate conversion link, insufficient robustness to high-reflectivity / dark surfaces, etc. Especially in the welding site, spatter, smoke and strong arc light can easily reduce the signal-to-noise ratio, and the off-axis structure is prone to failure in concave or blind areas, which seriously affects the accuracy of welding routing. SUMMARY

[0004] The present application provides a part positioning device for a welding machine tool, which emits and images along the same main optical axis, naturally aligns with the machine tool motion direction, significantly reduces occlusion and blind area, and effectively suppresses cross light and ghost images, thereby achieving precise positioning of the weld path.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical solutions: The part positioning device for a welding machine tool comprises: A protective window, an objective lens, a quarter-wave plate, a polarization beam splitter prism and an imaging unit located at the transmission end of the polarization beam splitter prism are arranged in sequence along the same main optical axis.

[0006] Further comprising: A laser emission unit connected to the side end of the polarization beam splitter prism.

[0007] Further comprising: A calculation and output unit electrically connected to the imaging unit; wherein: the linearly polarized near-infrared laser emitted by the laser emission unit is reflected by the polarization beam splitter prism and then irradiated to the workpiece surface along the main optical axis through the quarter-wave plate and the objective lens in sequence; the return light from the workpiece passes through the objective lens and the quarter-wave plate in sequence along the main optical axis, and its polarization state becomes orthogonal linear polarization relative to the incident laser light, and then enters the imaging unit through the polarization beam splitter prism; the calculation and output unit is configured to extract the weld path features based on the images obtained by the imaging unit, establish the extrinsic relationship between the imaging coordinate system and the machine tool coordinate system, and output the three-dimensional coordinate sequence or pose sequence of the weld path in the machine tool coordinate system.

[0008] Optionally, the laser emitting unit includes a near-infrared laser module, a polarizer, and a half-wave plate; and an extinction cavity disposed on the other side port of the polarization beam splitter. The extinction cavity is designed as a labyrinthine folding cavity, which is used to absorb stray light from the non-working side port of the polarization beam splitter to suppress optical feedback.

[0009] Optionally, the polarized near-infrared laser emitted from the laser emitting unit is incident along the reflection channel of the polarizing beam splitter, and the polarizer and half-wave plate are used to align the linear polarization direction incident on the polarizing beam splitter with its reflection axis.

[0010] Optionally, the center wavelength of the near-infrared laser module is one of 808nm, 850nm, or 940nm.

[0011] Optionally, the calculation and output unit is configured to binarize, skeletonize, and curve-fit the bright lines formed by laser irradiation on the workpiece surface to obtain the centerline of the weld path; and transform the centerline coordinates to the machine tool coordinate system through pre-calibrated homography transformation or extrinsic parameters. The calculation and output unit further outputs the tangential, normal, and defocusing amounts corresponding to the path points to form a continuous sequence of weld head poses.

[0012] Optionally, the protective window is a replaceable structure of quartz or borosilicate glass and is installed below the objective lens.

[0013] Optionally, the imaging unit includes a camera filter and a camera and sensor structure surface. The camera filter is a narrowband bandpass filter that matches the laser wavelength. Neutral density attenuation can be superimposed during the welding stage to suppress strong light interference.

[0014] Optionally, a reflective guiding layer is set on the surface of the workpiece splicing weld. The reflective guiding layer is a washable high reflective white coating containing a water-soluble film-forming agent and a high-reflectivity white pigment, which is suitable for improving the contrast of the reflected signal of the target path in the pre-scanning stage. The high-reflectivity white pigment is titanium dioxide, aluminum oxide or barium sulfate; the water-soluble film-forming agent is polyvinyl alcohol or carboxymethyl cellulose.

[0015] This invention provides a part positioning device for welding machine tools, which has the following advantages compared to the prior art: By designing a coaxial optical path, errors caused by parallax, occlusion, and workpiece geometry can be minimized. Furthermore, polarization separation allows emission and imaging to proceed on the same path without interference, and emission and imaging share the same optical axis. The objective lens is responsible for both focusing or collimating the emitted beam and imaging the returned light. Compared to off-axis solutions, there is no geometric parallax, and the sensitivity to occlusion from complex geometries such as grooves and folds is significantly reduced, enabling precise positioning and acquisition of the weld path. Attached Figure Description

[0016] Fig. 1 This is a three-dimensional structural diagram of the present invention; Fig. 2 This is an exploded three-dimensional structural view of the present invention.

[0017] In the diagram: 2. Protective window; 3. Objective lens; 4. Quarter-wave plate; 5. Polarizing beam splitter; 6. Camera filter; 7. Camera; 8. Sensor structure surface; 9. Near-infrared laser module; 10. Polarizer; 11. Half-wave plate; 12. Extinction cavity. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Please see Figs. 1-2 The present invention provides a technical solution: a part positioning device for welding machine tools, comprising: The protective window 2, objective lens 3, quarter-wave plate 4, polarizing beam splitter 5, and imaging unit located at the transmission end of polarizing beam splitter 5 are arranged sequentially along the same principal optical axis.

[0020] Also includes: A laser emitting unit connected to the side of polarizing beam splitter 5.

[0021] Also includes: The calculation and output unit is electrically connected to the imaging unit; wherein: the laser emitting unit emits linearly polarized near-infrared laser light, which is reflected by the polarizing beam splitter 5 and then sequentially passes through the quarter-wave plate 4 and the objective lens 3 along the main optical axis to illuminate the workpiece surface; the return light from the workpiece passes sequentially through the objective lens 3 and the quarter-wave plate 4 along the main optical axis, and its polarization state becomes orthogonal to the incident laser linearly polarized, and is transmitted through the polarizing beam splitter 5 into the imaging unit; the calculation and output unit is configured to extract weld path features based on the image obtained by the imaging unit, establish the external parameter relationship between the imaging coordinate system and the machine tool coordinate system, and output the three-dimensional coordinate sequence or pose sequence of the weld path in the machine tool coordinate system.

[0022] In existing technologies, traditional methods can confirm the welding path, but they rely heavily on interference-free environments. However, the welding workshop environment can generate interference information due to the welding process, affecting the accurate acquisition of the weld path. In this invention, the most important improvement is the design of a coaxial optical path. The coaxial optical path can minimize errors caused by parallax, occlusion, and workpiece geometry. Furthermore, polarization separation allows emission and imaging to be on the same path without interference, and emission and imaging share the same optical axis. The objective lens 3 is responsible for both focusing or collimating the emitted beam and imaging the returned light. Compared with off-axis solutions, there is no geometric parallax, and the sensitivity to occlusion of complex geometries such as grooves and folds is significantly reduced. The path is naturally aligned with the machine tool movement direction, reducing systematic conversion errors.

[0023] Secondly, polarization decoupling is achieved, and the return optical path is cleanly separated. Specifically, through the cooperation of a quarter-wave plate 4 and a polarizing beam splitter 5, the linearly polarized near-infrared laser is reflected into the axis by the polarizing beam splitter 5 and becomes circularly polarized by the quarter-wave plate 4. After being reflected by the workpiece, the chirality is reversed, and the return path is again converted to linear polarization orthogonal to the incident light by the quarter-wave plate 4, thus passing through the polarizing beam splitter 5 and entering the imaging unit. This can realize "the emission goes through the reflection channel and the return goes through the transmission channel", which greatly suppresses crosstalk and ghost images, ensures that the return signal only enters the camera link, and has low background and good stability.

[0024] Specific structural design, such as Figs. 1-2 As shown, from bottom to top along the main optical axis are a protective window 2, an objective lens 3, a quarter-wave plate 4, and a polarizing beam splitter 5. The transmission end of the polarizing beam splitter 5 is the imaging unit, and the side end of the polarizing beam splitter 5 is connected to the laser emission unit. The whole assembly is installed in an integrated lens barrel or camera module. The stacking scheme is reliable. The front end of the lens barrel is equipped with a replaceable protective window pressure ring and a sealing ring to adapt to the welding spatter environment. This is the preferred assembly scheme.

[0025] In a preferred embodiment, the laser emitting unit includes a near-infrared laser module 9, a polarizer 10, and a half-wave plate 11; and an extinction cavity 12 disposed on the other side port of the polarization beam splitter 5. The extinction cavity 12 is designed as a labyrinthine folding cavity. The extinction cavity 12 is used to absorb stray light from the non-working port of the polarization beam splitter 5 to suppress optical feedback. In this embodiment, the laser must be incident with the reflected polarization of the polarization beam splitter 5 in order to be efficiently coupled into the main optical axis. If the non-working port of the polarization beam splitter 5 is not processed, stray light will form a ghost image and generate coherent feedback. The extinction cavity 12 is concentrically mounted with the side opening of the polarization beam splitter 5. The labyrinthine return cavity includes multiple baffles, and the inner wall is blackened with a low-fluorescence extinction coating. The bottom is tilted with an end absorber and has good thermal conductivity with the outer shell, which makes the laser coupling efficiency high and the point position stable. The extinction cavity 12 suppresses ghost images and feedback, and improves the measurement SNR and the stability of the laser source.

[0026] Based on the embodiment of the laser emitting unit, the polarized near-infrared laser emitted by the laser emitting unit is incident along the reflection channel of the polarizing beam splitter 5. The polarizer 10 and the half-wave plate 11 are used to align the linear polarization direction incident on the polarizing beam splitter 5 with its reflection axis. If the polarization direction is inconsistent with the reflection axis of the polarizing beam splitter 5, partial transmission, energy instability and crosstalk will occur.

[0027] Based on the embodiment of the laser emitting unit, the center wavelength of the near-infrared laser module 9 is one of 808nm, 850nm or 940nm. In actual implementation, 808, 850 and 940nm are suitable for industrial devices with mature supply chains, low cost and convenient safety management of visible light and invisible light. The near-infrared laser module 9 can select any of the above center wavelengths, and has strong resistance to ambient light and arc light after filtering.

[0028] In a preferred embodiment, the calculation and output unit is configured to binarize, skeletonize, and curve-fit the bright lines formed by laser irradiation on the workpiece surface to obtain the centerline of the weld path; and transform the centerline coordinates to the machine tool coordinate system through pre-calibrated homography transformation or extrinsic parameters. The calculation and output unit further outputs the tangential, normal, and defocus amounts corresponding to the path points to form a continuous sequence of weld head poses. In this embodiment, weld tracking requires not only a geometric path but also pose, i.e., tangential, normal, and defocus amounts, to drive the welding torch attitude and power. The specific algorithm flow is as follows: First, the narrowband image is processed to an adaptive threshold such as Sa. The path is then refined or skeletonized using either uvola or Otsu. Spline segments are then fitted to the centerline to obtain curvature and tangency. The defocus amount is estimated using the objective depth of focus and defocus model, or by multi-frame or multi-aperture methods. Extrinsic parameters, such as calibration plates, homography transformation, and height compensation, are used to transform the path points from imaging coordinates to machine tool coordinates, outputting three-dimensional coordinates and pose sequences. Introduction and exit segments are automatically generated at the beginning and end of the path, and speed and power labels are applied to areas with high curvature and hole edges. The final effect is to provide a trajectory and attitude that can directly drive the machine tool controller, reducing secondary development; and to significantly improve welding consistency in difficult sections such as corners and edges.

[0029] In a preferred embodiment, the protective window 2 is a replaceable structure made of quartz or borosilicate glass and is installed below the objective lens 3. In a welding workshop environment, welding spatter and fumes can contaminate the front-end optics. The decoupling of the vulnerable component from the expensive objective lens reduces maintenance costs. The protective window 2 can be replaced with an outer frame spring or threaded retainer without disassembling the objective lens. A disposable consumable pack can be selected to enable quick maintenance, keep the optical surface clean, and ensure stable measurement.

[0030] In summary, the imaging unit further includes a camera filter 6, a camera 7, and a sensor structure surface 8. The camera filter 6 is a narrow-band bandpass filter that matches the laser wavelength. During the welding stage, neutral density attenuation can be superimposed to suppress strong light interference. In this embodiment, the arc light and thermal radiation during the welding stage are extremely strong, so it is necessary to ensure that the camera works within the dynamic range and suppress parasitic light. Through design, the camera filter 6 adopts a narrow-band bandpass filter that matches the near-infrared laser module 9. The filter is superimposed during the welding stage, and the sensor structure surface 8 is matched with the back focal plane of the objective lens to obtain the required field of view and resolution, so as to maintain a high SNR under strong light and avoid overexposure and motion blur.

[0031] Furthermore, a reflective guiding layer is set on the surface of the workpiece splice weld. The reflective guiding layer is a washable high-reflectivity white coating containing a water-soluble film-forming agent and a high-reflectivity white pigment, which is suitable for improving the contrast of the reflected signal of the target path during the pre-scanning stage. The high-reflectivity white pigment is titanium dioxide, aluminum oxide, or barium sulfate; the water-soluble film-forming agent is polyvinyl alcohol or carboxymethyl cellulose. This embodiment is a more important part of this case. In the prior art, for low-reflectivity, black, rough, or oily surfaces, their echoes are weak and the contrast is poor. If the contrast can be temporarily improved before welding, the pre-scanning will be faster and more accurate. Directly scanning the splice weld between workpieces is difficult and the imaging is inaccurate. However, by designing a reflective guiding coating, it can be quickly applied to the splice area to simulate the weld path, significantly improving the contrast of the reflected signal during the pre-scanning stage and making the tracking more stable. It can also be completely removed before welding without affecting the welding quality.

[0032] Specific assembly and adjustment steps: The assembly and adjustment process is as follows: S1: Mechanical concentricity: The objective lens 3, polarizing beam splitter 5, and camera 7 are installed in the same lens tube, and the optical axis is corrected for concentricity using a coaxiality tester or collimating telescope.

[0033] S2: Polarization calibration: Add a polarizer 10 to the input side of the polarization beam splitter 5 and adjust the angle of the half-wave plate 11 to maximize the coupling efficiency of the laser through the reflection channel of the polarization beam splitter 5.

[0034] S3: Waveplate angle: Adjust the quarter-wave plate 4 so that its fast axis makes a polarization angle of ±45 degrees with the incident ray, and use the analyzer to verify the polarization orthogonality of the echo.

[0035] S4: Focal length and field of view: Place the calibration target at the working distance, and adjust the focal length of objective lens 3 and the distance between the camera 7 to make the image clear and cover the target's field of view.

[0036] S5: Aperture and Filter: Select camera filter 6, set fixed exposure and gain to ensure that the echo is not overexposed and the grayscale distribution is centered.

[0037] S6: Extinction Verification: Check the other side of the polarizing beam splitter 5 to confirm that the extinction cavity 12 effectively absorbs stray light and there is no obvious ghosting.

[0038] By utilizing the above-mentioned structures, emission and imaging share the same main optical axis, naturally aligning with the machine tool's movement direction, significantly reducing obstruction and blind spots, and achieving emission via reflection and return via transmission, effectively suppressing crosstalk and ghost images, resulting in low background and good stability.

[0039] This invention is applicable to pre-welding positioning and in-situ tracking of various welding machine tools such as arc welding, laser welding, and brazing. It can provide high-precision, low-latency path and pose information, especially in environments with reflective metals, black coatings, complex assemblies, and strong light interference.

[0040] The standard parts used in this embodiment can be purchased directly from the market, and the non-standard structural parts described in the specification and drawings can also be processed without any doubt based on existing technical common sense. At the same time, the connection methods of each component adopt mature conventional methods in the existing technology, and the machinery, parts and equipment all adopt conventional models in the existing technology, so they will not be described in detail here.

[0041] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art 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 appended claims and their equivalents.

Claims

1. A part positioning device for welding machine tools, characterized in that: include: The protective window (2), objective lens (3), quarter-wave plate (4), polarizing beam splitter (5) and imaging unit located at the transmission end of polarizing beam splitter (5) are arranged sequentially along the same principal optical axis. Also includes: A laser emitting unit connected to the side end of the polarization beam splitter (5); Also includes: A calculation and output unit electrically connected to the imaging unit; Wherein: the laser emitting unit emits linearly polarized near-infrared laser, which is reflected by the polarizing beam splitter (5) and then sequentially passes through the quarter-wave plate (4) and the objective lens (3) along the main optical axis to irradiate the surface of the workpiece; the return light from the workpiece passes through the objective lens (3) and the quarter-wave plate (4) along the main optical axis, and its polarization state becomes orthogonal to the incident laser linearly polarized, and is transmitted into the imaging unit through the polarizing beam splitter (5); The calculation and output unit is configured to extract weld path features based on the image obtained by the imaging unit, establish the external parameter relationship between the imaging coordinate system and the machine tool coordinate system, and output the three-dimensional coordinate sequence or pose sequence of the weld path in the machine tool coordinate system.

2. The part positioning device for welding machine tools according to claim 1, characterized in that: The laser emitting unit includes a near-infrared laser module (9), a polarizer (10), and a half-wave plate (11); and an extinction cavity (12) located on the other side of the polarization beam splitter (5). The extinction cavity (12) is designed as a labyrinthine folding cavity. The extinction cavity (12) is used to absorb stray light from the non-working side port of the polarization beam splitter (5) to suppress optical feedback.

3. The part positioning device for welding machine tools according to claim 2, characterized in that: The polarized near-infrared laser emitted from the laser emitting unit is incident along the reflection channel of the polarizing beam splitter (5). The polarizer (10) and the half-wave plate (11) are used to align the linear polarization direction incident on the polarizing beam splitter (5) with its reflection axis.

4. The part positioning device for welding machine tools according to claim 2, characterized in that: The center wavelength of the near-infrared laser module (9) is one of 808nm, 850nm or 940nm.

5. The part positioning device for welding machine tools according to claim 1, characterized in that: The calculation and output unit is configured to binarize, skeletonize, and curve-fit the bright lines formed by laser irradiation on the workpiece surface to obtain the center line of the weld path; and transform the center line coordinates to the machine tool coordinate system through pre-calibrated homography transformation or extrinsic parameters. The calculation and output unit further outputs the tangential, normal, and defocusing amounts corresponding to the path points to form a continuous sequence of weld head poses.

6. The part positioning device for welding machine tools according to claim 1, characterized in that: The protective window (2) is a replaceable structure of quartz or borosilicate glass and is installed below the objective lens (3).

7. The part positioning device for welding machine tools according to any one of claims 1-6, characterized in that: The imaging unit includes a camera filter (6), a camera (7), and a sensor structure surface (8). The camera filter (6) is a narrow bandpass filter that matches the laser band. Neutral density attenuation can be superimposed during the welding stage to suppress strong light interference.

8. The part positioning device for welding machine tools according to claim 7, characterized in that: A reflective guiding layer is applied to the surface of the weld seam of the workpiece. The reflective guiding layer is a washable high reflective white coating containing a water-soluble film-forming agent and a high reflective white pigment. It is suitable for improving the contrast of the reflected signal of the target path during the pre-scanning stage. The high reflective white pigment is titanium dioxide, aluminum oxide, or barium sulfate. The water-soluble film-forming agent is polyvinyl alcohol or carboxymethyl cellulose.

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