CN111798477B - Molten pool monitoring method based on visual technology - Google Patents
Molten pool monitoring method based on visual technology Download PDFInfo
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- CN111798477B CN111798477B CN202010582043.0A CN202010582043A CN111798477B CN 111798477 B CN111798477 B CN 111798477B CN 202010582043 A CN202010582043 A CN 202010582043A CN 111798477 B CN111798477 B CN 111798477B
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T7/00—Image analysis
- G06T7/10—Segmentation; Edge detection
- G06T7/13—Edge detection
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K9/00—Arc welding or cutting
- B23K9/32—Accessories
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T7/00—Image analysis
- G06T7/60—Analysis of geometric attributes
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T7/00—Image analysis
- G06T7/80—Analysis of captured images to determine intrinsic or extrinsic camera parameters, i.e. camera calibration
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T2207/00—Indexing scheme for image analysis or image enhancement
- G06T2207/10—Image acquisition modality
- G06T2207/10048—Infrared image
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/25—Process efficiency
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Abstract
The invention relates to a molten pool monitoring method in additive manufacturing, which aims to solve the technical problems that the prior art cannot accurately obtain molten pool size data or does not further discuss the acquisition of actual size information represented by image characteristics when arc fuse additive manufacturing is carried out, and provides a molten pool monitoring method based on a visual technology, comprising the following steps: s1, acquiring a travel track of a molten pool, and presetting a plurality of monitoring points on the travel track; s2, arranging a camera and an infrared laser light source beside the molten pool, wherein the camera and the infrared laser light source are respectively arranged on two six-degree-of-freedom motion platforms; s3, presetting working angles of the camera and the infrared laser light source at each monitoring point, so that an incident angle optical axis of the camera and an emergent direction optical axis of the infrared laser light source at each monitoring point are intersected at the monitoring point; s4, calibrating the camera at each monitoring point; s5, collecting a molten pool image, processing the molten pool image to obtain the size of the molten pool at each monitoring point, and adjusting the additive manufacturing path in real time.
Description
Technical Field
The invention relates to a molten pool monitoring method in additive manufacturing, in particular to a visual technology-based molten pool monitoring method.
Background
When the arc fuse material is added to manufacture a solid structure, the transition mode from a liquid droplet formed at the end of a wire to a molten pool has important influence on the stability and the forming quality of the forming process of the solid structure, when the droplet forms a fine droplet transition or a jet transition, an arc can be stably burnt, but once large particle transition is formed, or the wire feeding speed is too high, the problems of unstable manufacturing process, poor surface flatness of a fused lamination layer and the like are caused, the next layer is accumulated, and the surface fluctuation degree is further increased.
In the chinese patent with application number of cn201710837757.X, "a device and a method for monitoring a molten pool in an additive manufacturing process based on multiband coupling", a set of optical units composed of lenses is disclosed, and the radiation light and the reflected illumination light of the molten pool are sequentially transmitted through a multi-wavelength refraction-diffraction hybrid focusing mirror, a scanning galvanometer, a dichroic mirror and a spectroscope reverse optical path, the monitoring method proposed in the patent can monitor the size of the molten pool, but the device mentioned in the patent performs optical conversion on the optical performance of the molten pool, although the evolution process of the molten pool can be obtained, the exact data of the size of the molten pool is not explicitly pointed out, and furthermore, a more complicated optical lens unit is used for optical treatment of the molten pool.
In addition, in the research on the size detection and control of a molten pool by laser cladding in the university of the combined fertilizer industry published by the university of the combined fertilizer industry in 2019, a device for monitoring the molten pool by utilizing a CCD camera is introduced, and the device is characterized in that the camera is coaxially arranged with a laser light source, so that the condition that the camera needs to be adjusted along with the change of the movement direction of the molten pool when shooting at the side surface of the molten pool is avoided, but the work of an author only stays in acquiring the outline of the size image of the molten pool, and further discussion on how to acquire the actual size information represented by the image characteristics is not performed, and in practical application, the size width of the molten pool is a parameter with guiding significance.
Disclosure of Invention
The invention provides a molten pool monitoring method based on a visual technology, which aims to solve the technical problems that the prior art cannot accurately obtain the molten pool size data when arc fuse additive manufacturing is performed, and the acquisition of actual size information represented by image characteristics is not further discussed even if the contour of a molten pool size image is obtained.
In order to achieve the above purpose, the present invention provides the following technical solutions:
the molten pool monitoring method based on the visual technology is characterized by comprising the following steps of:
s1, acquiring a travel track of a molten pool, and presetting a plurality of monitoring points on the travel track;
s2, arranging a camera and an infrared laser light source beside the molten pool, wherein the camera and the infrared laser light source are respectively arranged on two six-degree-of-freedom motion platforms;
s3, presetting working angles of the camera and the infrared laser light source at each monitoring point according to the monitoring points preset in the step S1, so that an optical axis of the camera and an optical axis of the infrared laser light source intersect at the monitoring point;
s4, calibrating the camera at each monitoring point
S4.1, placing the calibration plates at each monitoring point in sequence, shooting the calibration plates by using a camera, and collecting a plurality of images at each monitoring point, wherein the images can cover the field of view of the camera;
s4.2, acquiring a group of projection radiation transformation matrixes at each monitoring point according to the images with different angles acquired at each monitoring point in the step S4.1 and hardware parameters of a camera, and taking the projection radiation transformation matrixes as reference data at each monitoring point;
s5, in the additive manufacturing process, acquiring molten pool images at each monitoring point through a camera and an infrared laser light source, processing the molten pool images to obtain the size of the molten pool at each monitoring point, and adjusting the additive manufacturing path in real time according to the reference data at each monitoring point obtained in the step S4.2.
Further, in step S5, the image of the molten pool is collected at each monitoring point, specifically, the image of the molten pool is collected at each monitoring point, the image of the molten pool collected by the camera enters the memory of the upper computer in the form of an image queue through one thread, and the image in the image queue is continuously read from the memory through the other thread.
Further, in step S5, the processing is performed on the molten pool image, specifically, a welding wire is extracted according to a gray value and a shape feature of the molten pool image, the shape of the molten pool is set to be elliptical, a detection frame is drawn below the welding wire, a central area of the molten pool is extracted according to the gray feature in the detection frame, a contour line of the molten pool is extracted, the lowest point of the contour line is taken as the center, protruding portions on two sides are respectively taken as an image processing area, the highest point of the contour line is respectively found in each image processing area, and the pixel distance between the two highest points is the width of the molten pool.
Further, in step S3, the included angle between the plane where the optical axis of the camera and the optical axis of the infrared laser light source are located and the plane where the molten pool is located is 30-60 °.
Further, in step S5, the puddle image is acquired at each monitoring point, specifically, at a speed of 500 frames.
Further, the camera is a wide dynamic high-speed video camera, and a lens of the camera is provided with an optical filter, and the allowed passing wavelength of the optical filter is 808nm.
Further, the outer contour of the calibration plate is rectangular, a plurality of circular marks are arranged on the surface of the calibration plate, the circular marks are arranged in a 7*7 matrix, and the diameter of each circular mark is one half of the center distance of the adjacent circular marks.
Further, the step S4.1 is specifically that the calibration plates are placed at each monitoring point in sequence, at each monitoring point, the calibration plates are placed on the plane where the monitoring point is located, so that the calibration plates are respectively located at the center of the camera view, at four corners and at the center of each side, and then the calibration plates are placed at an included angle of 20 degrees with the plane where the monitoring point is located, and 5 images are acquired at any position where the calibration plates are located in the camera view.
Further, the six-degree-of-freedom motion platform is a six-degree-of-freedom robot.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the molten pool monitoring method based on the visual technology, the cameras are calibrated at each monitoring point, so that when the installation angle of the camera relative to the surface of the molten pool changes, the image of the molten pool can still be accurately acquired, and the accurate size of the molten pool is further obtained; in the invention, a camera and an infrared laser light source are adopted to acquire the image of the molten pool and the size of the molten pool in real time in the additive manufacturing welding process, so that the additive manufacturing path is adjusted in real time, the manufacturing process is controllable, the manufacturing quality is effectively improved, and the welding result is higher in consistency with the preset one.
2. The acquisition and processing of the images are completed through two threads, so that the requirement on the memory of an upper computer for acquiring and processing the molten pool images is reduced, and the acquisition and processing speed and efficiency are increased.
3. According to the invention, the oval outline of the molten pool is extracted to obtain the endpoints of the left and right edges of the molten pool, and the width of the molten pool is obtained, so that the outline and the size of the molten pool are objectively and accurately extracted, and the additive manufacturing process can be controlled more accurately.
4. The invention collects the molten pool image at the speed of 500 frames, not only can dynamically and accurately acquire the size image of the molten pool in real time, but also can collect the image of the molten pool at a reasonable speed, and the use cost of a camera is not excessively increased.
5. The six-degree-of-freedom motion platform adopted in the invention is a six-degree-of-freedom robot, is flexible to operate, and is convenient for adjusting the infrared laser light source and the camera, so that the infrared laser light source and the camera can irradiate and photograph in the optimal posture.
Drawings
FIG. 1 is a flow chart of additive manufacturing using an embodiment of a vision-based bath monitoring method of the present invention;
FIG. 2 is a schematic diagram of the arrangement of a camera and an infrared laser source according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a calibration plate according to an embodiment of the present invention.
Wherein, the device comprises a 1-camera, a 2-infrared laser light source and a 3-molten pool.
Detailed Description
The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention and the accompanying drawings, and it is apparent that the described embodiments do not limit the present invention.
The invention provides a molten pool monitoring method based on a visual technology. Referring to fig. 1, the method for monitoring a molten pool of the present invention comprises the following steps:
before the additive manufacturing printing is carried out, firstly slicing and path planning are carried out on the whole printing object, after the path planning is known, the travel track of a molten pool can be obtained, a plurality of monitoring points are arranged on the travel track of the molten pool, a camera and an infrared laser light source are arranged beside the molten pool, the camera and the infrared laser light source are respectively arranged on two six-degree-of-freedom motion platforms, and the erection position and the angle of the camera and the infrared laser light source at each monitoring point can be set in advance. As shown in fig. 2, the working angles of the camera 1 and the infrared laser light source 2 at each monitoring point are preset, so that the incident angle optical axis of the camera 1 and the outgoing direction optical axis of the infrared laser light source 2 intersect at the monitoring point of the molten pool 3. The incidence angle optical axis of the infrared laser light source and the camera optical axis are intersected at the monitoring point of the molten pool, a plane is determined by the intersection of the incidence angle optical axis of the infrared laser light source and the camera optical axis, the incidence angle optical axis of the infrared laser light source and the camera optical axis are mutually perpendicular in the intersected plane, and the included angle between the plane determined by the intersection of the incidence angle optical axis of the infrared laser light source and the camera optical axis and the plane of the molten pool is controlled within the range of 30-60 degrees, so that the light supplementing effect of the light source can be optimized, and the follow-up extraction of the size of the molten pool is facilitated.
When the six-degree-of-freedom robot performs the additive manufacturing welding process, the six-degree-of-freedom robot ensures that the welding wire at the tail end of the welding equipment and the plane where the molten pool is positioned do not change relative pose, in practical application, a camera and the welding wire can be loaded by the same six-degree-of-freedom robot, a specific tool is arranged at the tail end of the six-degree-of-freedom robot flange, the tool ensures that the relative position relationship between the camera and the welding wire is always constant, and in the additive manufacturing welding process, the welding wire is always vertical to the surface of the molten pool only once to be calibrated.
In order to realize accurate measurement of the size of the molten pool, a camera needs to be calibrated on each molten pool monitoring point in advance, and the calibrated camera can accurately obtain size data through an image algorithm. The camera calibration link can be completed quickly by using a special calibration plate, the calibration plate is placed on each monitoring point, the camera is used for shooting the calibration plate, the camera is used for ordinary illumination, 14 images of the calibration plate are collected, 9 images of the 14 images are horizontally placed on the plane where the monitoring point is located, are parallel to the plane where the monitoring point is located, are respectively located at the right center of a visual field, four corners of the image are abutted against the middle position of the edge of the image, and the rest 5 images are inclined included angles between the plane where the calibration plate is located and the plane where the monitoring point is located, wherein the inclined angles between the planes where the calibration plate is located and the plane where the monitoring point is located are not more than 20 degrees, so that the image profile on the calibration plate is clear, and the 5 images can be randomly distributed in the visual field, so that strict requirements are not made in number. After the image is acquired, a group of projection radiation transformation matrixes can be output at each monitoring point by using special calibration software according to hardware parameters of the camera, and the projection radiation transformation matrixes can be used as reference data at each monitoring point and can be used as input data for measuring the size of a molten pool subsequently.
The calibration plate occupies 1/3-1/2 of the camera field of view, the basic shape is shown in figure 3, the outside is surrounded by a square frame, the surface is composed of a 7*7 solid circle, the diameter of the solid circle is 1/2 of the distance between the centers of the solid circles, and one corner of the square frame is provided with a special mark. The internal parameters and the external parameters of the camera can be calibrated through the calibration plate. The internal parameters of the camera comprise pixel size, distortion coefficient, pixel value and the like of the camera, and the external parameters are mainly the pose relationship between the camera and the plane of the calibration plate.
In the additive manufacturing process, a molten pool image is acquired at each monitoring point through a camera and an infrared laser light source and stored in an upper computer, the upper computer processes the molten pool image to obtain the size of the molten pool at each monitoring point, and the additive manufacturing path is adjusted in real time according to the obtained reference data at each monitoring point.
In the process of material increase manufacturing, a camera collects molten pool images at the speed of 500 frames, in the process of collection, an image buffer of one thread camera is buffered in a PC memory in a mode of an image queue, and another thread in the program continuously takes out the image buffer from the image queue for size measurement and image data storage.
When the molten pool image is processed, firstly, a welding wire is extracted according to gray values and shape characteristics, the position of the molten pool is located below the welding wire, the molten pool is in a form similar to an ellipse in theory, because a camera is obliquely shot, the welding wire is perpendicular to a plane where the ellipse is located, part of the contour of the molten pool is shielded by strong light emitted by the welding wire and the welding wire, a detection frame is drawn below the welding wire, a region in the center of the molten pool is extracted according to gray characteristics in the detection frame, a contour line is firstly extracted according to characteristics of the ellipse shape, a position where a left half part and a right half part are provided with bulges is divided into two image processing regions by taking the lowest point of the contour line as the center, and the highest point of the contour is found in each image processing region, namely, the left edge and the right edge of the ellipse, and the pixel distance between the edges is the width of the molten pool.
The invention can adopt a wide dynamic high-speed camera, a special 808 infrared laser light source is used as illumination equipment, a filter which can only pass 808nm wavelength infrared waves is correspondingly used, and the functions of high-speed monitoring of the molten drop transition process are realized by combining means of optimizing exposure parameters, digital signal processing, picture recombination and the like, introducing image processing algorithms such as low-pass filtering, binarization, edge extraction and the like.
The camera can adopt a camera with the resolution ratio of 1280 x 1024, the highest acquisition speed of 506 frames per second can be realized, the camera is provided with a micro-distance lens, the focal length of 100mm and the aperture of 2.8, and a light filter which can only pass 808nm wavelength light rays is used in front of the lens; the wavelength of the infrared laser light source is 808nm. The camera can be connected to the upper computer by means of camera link, and the upper computer stores a large number of molten pool images, so that the memory of 16G can be configured and a disk array mode is used.
The foregoing description is only illustrative of the present invention and is not intended to limit the scope of the invention, and all equivalent structural changes made by the present invention and the accompanying drawings, or direct or indirect application in other related technical fields, are included in the scope of the present invention.
Claims (7)
1. The molten pool monitoring method based on the visual technology is characterized by comprising the following steps of:
s1, acquiring a travel track of a molten pool, and presetting a plurality of monitoring points on the travel track;
s2, arranging a camera and an infrared laser light source beside the molten pool, wherein the camera and the infrared laser light source are respectively arranged on two six-degree-of-freedom motion platforms;
s3, presetting working angles of the camera and the infrared laser light source at each monitoring point according to the monitoring points preset in the step S1, so that an optical axis of the camera and an optical axis of the infrared laser light source intersect at the monitoring point;
s4, calibrating the camera at each monitoring point
S4.1, placing the calibration plates at each monitoring point in sequence, shooting the calibration plates by using a camera, and collecting a plurality of images at each monitoring point, wherein the images can cover the field of view of the camera;
s4.2, acquiring a group of projection radiation transformation matrixes at each monitoring point according to the images with different angles acquired at each monitoring point in the step S4.1 and hardware parameters of a camera, and taking the projection radiation transformation matrixes as reference data at each monitoring point;
s5, in the additive manufacturing process, acquiring molten pool images at each monitoring point through a camera and an infrared laser light source, processing the molten pool images to obtain the size of the molten pool at each monitoring point, and adjusting the additive manufacturing path in real time according to the reference data at each monitoring point obtained in the step S4.2;
in step S5, the image of the molten pool is collected at each monitoring point, specifically, the image of the molten pool is collected at each monitoring point, the image of the molten pool collected by the camera enters the memory of the upper computer in an image queue mode through one thread, and the image in the image queue is continuously read from the memory through the other thread;
in step S5, the molten pool image is processed, specifically, a welding wire is extracted according to a gray value and a shape feature of the molten pool image, the shape of the molten pool is set to be elliptical, a detection frame is drawn below the welding wire, a central region of the molten pool is extracted according to the gray feature in the detection frame, a contour line of the molten pool is extracted, the lowest point of the contour line is taken as the center, protruding portions on two sides are respectively taken as an image processing region, the highest point of the contour line is respectively found in each image processing region, and the pixel distance between the two highest points is the width of the molten pool.
2. The method for monitoring a molten pool according to claim 1, wherein the method comprises the steps of: in the step S3, the included angle between the plane where the optical axis of the camera and the optical axis of the infrared laser light source are positioned and the plane where the molten pool is positioned is 30-60 degrees.
3. A method for monitoring a molten bath based on visual technology as claimed in claim 2, wherein: in step S5, the image of the molten pool is acquired at each monitoring point, specifically, the image of the molten pool is acquired at a speed of 500 frames at each monitoring point.
4. A method of monitoring a molten bath based on visual technology as claimed in claim 3, wherein: the camera is a wide dynamic high-speed video camera, and a light filter is mounted on a lens of the camera, and the allowed passing wavelength of the light filter is 808nm.
5. The method for monitoring a molten pool according to claim 4, wherein the method comprises the steps of: the outer contour of the calibration plate is rectangular, a plurality of circular marks are arranged on the surface of the calibration plate, the circular marks are arranged in a 7*7 matrix, and the diameter of each circular mark is one half of the circle center distance of each adjacent circular mark.
6. The method for monitoring a molten pool according to claim 5, wherein the method comprises the steps of: the step S4.1 is specifically that the calibration plates are placed at each monitoring point in sequence, at each monitoring point, the calibration plates are firstly placed horizontally on the plane where the monitoring point is located, the calibration plates are respectively located at the center of the camera view, at four corners and at the center of each side, then the calibration plates are placed at an included angle of 20 degrees with the plane where the monitoring point is located, and 5 images are acquired at any position where the calibration plates are located in the camera view.
7. The method for monitoring a molten pool according to claim 6, wherein the method comprises the steps of: the six-degree-of-freedom motion platform is a six-degree-of-freedom robot.
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| CN112828311B (en) * | 2021-01-03 | 2022-05-24 | 苏州星祥益精密制造有限公司 | Metal additive manufacturing online track adjusting method based on real-time three-dimensional detection |
| CN113732312A (en) * | 2021-08-13 | 2021-12-03 | 西安交通大学 | Molten pool monitoring method and device in laser powder bed melting additive manufacturing process |
| CN114289945B (en) * | 2021-12-31 | 2024-07-05 | 北京博清科技有限公司 | Welding equipment, control method thereof and welding system |
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| US10914677B2 (en) * | 2018-04-24 | 2021-02-09 | General Electric Company | System and method for calibrating a melt pool monitoring system of an additive manufacturing machine |
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| CN107796328A (en) * | 2017-09-21 | 2018-03-13 | 西南交通大学 | Metal increasing material manufacturing Pool three-dimensional visual sensor and detection method |
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