Three-dimensional temperature and three-dimensional deformation measurement method based on single multispectral camera

Abstract

The embodiment of the application provides a three-dimensional temperature and three-dimensional deformation measurement method based on a single multispectral camera, which is suitable for additive manufacturing processes of various metal materials, and is suitable for various complex part shapes, different shaped substrates, in addition, the plane mirror assembly is simple to build and has low cost, the measurement process has high repeatability and high efficiency, based on the multispectral camera capable of high-speed measurement, the three-dimensional temperature and three-dimensional deformation in the additive manufacturing process are measured on line and in real time. The method can complete temperature measurement of 1100 DEG C at most, and the three-dimensional deformation and temperature measurement are accurate, suitable for monitoring the three-dimensional temperature and three-dimensional deformation measurement in the additive manufacturing process, and then inverting the process state and part quality.

Description

Technical Field

[0001] The present application relates to the field of additive manufacturing technology, and in particular to a three-dimensional temperature and three-dimensional deformation measurement method based on a single multispectral camera. Background Art

[0002] The quality of products processed during laser additive manufacturing is closely related to the thermal process and deformation during manufacturing. Differences in laser power, scanning speed, incident angle, and material properties can all lead to various defects and residual stresses, thereby reducing the mechanical properties of the product. Analyzing the deformation and thermal processes during printing can support part quality analysis. The real-time status of the printing process can be analyzed based on the three-dimensional deformation and temperature changes at the bottom of the substrate during printing, thereby achieving real-time feedback for additive manufacturing and improving part quality. Therefore, monitoring the three-dimensional deformation and temperature of the bottom of the substrate during additive manufacturing is very important.

[0003] Traditional cameras often capture images within the visible light band (400-780nm), and by expanding their sensitivity range along short and long wavelengths, they become multispectral cameras. Commonly used multispectral cameras have a sensitivity wavelength range of 400-1000nm, and can obtain digital images within each band. Among the multi-band images captured by multispectral cameras, images in the near-infrared and red light bands can be used for colorimetric temperature measurement, and images in the blue band can be used for deformation analysis, meeting the needs of simultaneous monitoring of temperature and deformation in additive manufacturing. However, if three-dimensional temperature is to be obtained, two multispectral cameras are required to monitor from different angles, making the monitoring system large and costly.

[0004] Therefore, how to develop a single-camera three-dimensional temperature and three-dimensional deformation monitoring method for the additive manufacturing process, with accurate measurement results and no interference from complex environments, is a technical problem that technical personnel in this field urgently need to solve. Summary of the Invention

[0005] The present application aims to solve one of the technical problems in the related art at least to a certain extent.

[0006] To this end, the purpose of this application is to propose a three-dimensional temperature and three-dimensional deformation measurement method based on a single multispectral camera. This method uses a multispectral camera to build a plane mirror assembly, and combines colorimetric temperature measurement with binocular vision principle. Based on a single multispectral camera, it can achieve three-dimensional temperature and three-dimensional deformation measurement in the additive manufacturing process.

[0007] To achieve the above objectives, this application proposes a three-dimensional temperature and three-dimensional deformation measurement method based on a single multispectral camera, comprising the following steps:

[0008] A measurement system is built based on a single multispectral camera and calibrated using a ceramic calibration plate. The measurement system includes a multispectral camera and a plane mirror assembly. The position of the plane mirror assembly is adjusted so that the target object of the measurement system can be imaged on both sides of the multispectral camera.

[0009] Using laser etching to prepare a high-temperature grating on the bottom of the cantilever beam substrate of the additive manufacturing device and using the measurement system to monitor the additive manufacturing process and obtain a photographic image including the molten pool temperature;

[0010] The captured image is divided into a left view and a right view, and the left view and the right view are processed as images obtained by different multispectral cameras in the binocular vision principle to complete stereo matching to obtain three-dimensional displacement and deformation information; wherein the blue band, red band and near-infrared band of the multispectral camera are used to respectively perform deformation measurement and colorimetric temperature measurement on the left view and the right view.

[0011] In some embodiments, the plane mirror assembly is a four-way reflector measuring optical path, including a right-angle prism and plane mirrors respectively arranged opposite to the two right-angle sides of the right-angle prism; the two plane mirrors are in the same horizontal plane so that left and right sides are imaged in the multispectral camera.

[0012] In some embodiments, a synchronization trigger is provided on the measurement system to enable simultaneous image acquisition of the color channel and the near-infrared channel in the multispectral camera.

[0013] In some embodiments, a filter component is provided on the measurement system to eliminate interference from strong laser, high temperature radiation and dust splashing in the additive manufacturing process when the multispectral camera captures images.

[0014] In some embodiments, when calibrating the plane mirror assembly using a 3 mm black and white ceramic plate as the ceramic calibration plate, the ceramic calibration plate is photographed in at least ten different postures to obtain the intrinsic and extrinsic parameter matrices of the multispectral camera to complete the parameter calibration of the multispectral camera.

[0015] In some embodiments, after calibrating the multispectral camera using a ceramic calibration plate to complete the calibration of the internal and external parameters of the multispectral camera, the method further includes using an induction eddy current heating device to complete the colorimetric temperature measurement calibration of the multispectral camera to obtain the ratio of multispectral radiation intensity; wherein, in the colorimetric temperature measurement calibration experiment of the multispectral camera, the temperature range is 550-1100°C, and the temperature is increased in increments of 20°C. After each increment is kept warm for 5 minutes, the multispectral camera is used to capture visible light and near-infrared band images at different temperatures.

[0016] In some embodiments, before preparing the high-temperature grating, high-temperature white primer is sprayed on the bottom of the cantilever beam substrate and then kept at 200°C for 30 minutes; when preparing the high-temperature grating, the laser power is 5W and the etching speed is 3000mm / s.

[0017] In some embodiments, the multispectral camera has a maximum measurement frequency of 30 Hz, which can monitor the three-dimensional temperature and three-dimensional deformation of the additive manufacturing process of any specimen shape, and realize in-situ real-time measurement of the three-dimensional temperature and three-dimensional deformation during the additive manufacturing process.

[0018] In some embodiments, when three-dimensional deformation measurement is performed using the blue band in the multispectral camera, the high-temperature grating is used as the deformation carrier, and stereo matching is performed based on the binocular vision principle to obtain the surface morphology and three-dimensional position information of the target object, and provide three-dimensional coordinates for the temperature result in the colorimetric temperature measurement.

[0019] In some embodiments, colorimetric temperature measurement is performed using the red band and near-infrared image in the multispectral camera to obtain accurate temperature values, and three-dimensional temperature field distribution information is obtained in combination with the three-dimensional position information.

[0020] Compared with the prior art, this application has the following advantages:

[0021] This application is applicable to additive manufacturing processes of various metal materials, as well as various complex parts and substrates of varying shapes. Furthermore, the plane mirror assembly is simple and inexpensive to construct, and the measurement process is highly repeatable and efficient. Using a high-speed multispectral camera, this method enables online, real-time measurement of three-dimensional temperature and deformation during additive manufacturing. This method can measure temperatures up to 1100°C, and accurately measures three-dimensional deformation and temperature, making it suitable for monitoring three-dimensional temperature and deformation measurements during additive manufacturing, and for inverting process status and part quality.

[0022] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0024] Figure 1 This is a flow chart of a three-dimensional temperature and three-dimensional deformation measurement method based on a single multispectral camera proposed in one embodiment of the present application;

[0025] Figure 2 is a schematic diagram of a multispectral camera calibration device proposed in one embodiment of the present application;

[0026] Figure 3 This is a schematic diagram of a multi-spectral single-camera 3D temperature and 3D deformation measurement device proposed in one embodiment of the present application;

[0027] Figure 4 This is a schematic diagram of a multi-spectral three-dimensional melt pool temperature measurement device proposed in one embodiment of the present application;

[0028] In the figure, 1. Laser head; 2. High-temperature grating; 3. 45° reflector; 4. Right-angle prism; 5. Plane mirror; 6. Beam splitter; 7. Near-infrared CCD target; 8. Near-infrared light; 9. Color CCD target; 10. Visible light; 11. Molten pool; 12. Cantilever beam substrate. DETAILED DESCRIPTION

[0029] The embodiments of the present application are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present application and are not to be construed as limiting the present application. On the contrary, the embodiments of the present application include all variations, modifications, and equivalents that fall within the spirit and scope of the appended claims.

[0030] To achieve the above purpose, see Figure 1 This application proposes a three-dimensional temperature and three-dimensional deformation measurement method based on a single multispectral camera, which includes the following steps:

[0031] S1: Build a measurement system based on a single multispectral camera and calibrate it using a ceramic calibration plate. The measurement system includes a multispectral camera and a plane mirror assembly. By adjusting the position of the plane mirror assembly, the target object of the measurement system is imaged on both sides of the multispectral camera.

[0032] S2: using laser etching to prepare a high-temperature grating 2 at the bottom of the cantilever beam substrate 12 of the additive manufacturing device and using a measurement system to monitor the additive manufacturing process and obtain a photographic image including the molten pool temperature;

[0033] S3: The captured image is divided into a left view and a right view. The left view and the right view are processed as images obtained by cameras at different angles in the binocular vision principle, and stereo matching is performed to obtain three-dimensional displacement and deformation information. The blue band, red band, and near-infrared band of the multispectral camera are used to perform deformation measurement and colorimetric temperature measurement on the left view and right view, respectively.

[0034] Specifically, in S1, a measurement system is built based on a single multispectral camera, wherein the measurement system includes a multispectral camera and a plane mirror assembly, wherein the single multispectral camera and the plane mirror assembly are arranged in correspondence with each other, and the optical path of the plane mirror assembly is adjusted to ensure that the target object, i.e., the measurement object, is imaged in a suitable position in the multispectral camera. By adjusting the position of the plane mirror assembly, the target object of the measurement system can be presented in images on the left and right sides of the multispectral camera.

[0035] For example, Figure 3 As shown, the plane mirror assembly includes a right-angle prism 4 and two plane mirrors 5, wherein the two plane mirrors 5 are respectively arranged opposite to the two right-angle sides of the right-angle prism 4. In this embodiment, the two plane mirrors 5 can be understood as two GCC-102111 rectangular plane reflectors, which are respectively located above and below the right-angle prism 4 and the two plane mirrors 5 are in the same horizontal plane. The right-angle prism 4 in this embodiment is specifically a GPH11 K9 right-angle prism, which is fixed, and the angles of the two plane mirrors 5 can be adjusted. The light entering the plane mirror assembly is reflected by the two plane mirrors and then projected onto the two right-angle sides of the right-angle prism 4. The light is then reflected by the two right-angle sides of the right-angle prism 4 and becomes two parallel rays of light that are projected onto the multispectral camera to image the measurement object.

[0036] It can be seen that the multispectral camera in this embodiment uses a single-lens multispectral camera for measurement, model AD-130GE, which includes a beam splitter prism 6; a near-infrared CCD target surface 7; and an internal optical path structure of near-infrared light 8 and a color CCD target surface 9. Figure 3 and Figure 4 The multispectral camera contains two photosensitive chips, each with a resolution of 1296×966 pixels, sensitive to the visible light band (400-700nm) and the near-infrared band (730-1000nm), respectively. Light entering the multispectral camera is focused by an optical lens and then enters a beam splitter prism 6, which splits it into two beams, which are then directed onto two target surfaces, forming the left and right images.

[0037] Conventional additive manufacturing devices include a laser head 1 and a cantilever substrate 12. In this embodiment, a high-temperature grating 2 is fabricated at the bottom of the cantilever substrate 12, and a 45-degree reflector 3 is positioned at the bottom of the grating. This transmits an image of the high-temperature grating 2 at the bottom of the cantilever substrate 12 to a multispectral camera via a plane mirror assembly. Monitoring the three-dimensional temperature distribution during additive manufacturing requires the use of two multispectral cameras. Compared to conventional systems, the measurement system of this embodiment can reduce its size and the number of multispectral cameras required, improving the cost-effectiveness of the system and avoiding synchronization issues associated with dual multispectral cameras.

[0038] In some embodiments, when calibrating the plane mirror assembly using a 3 mm black and white ceramic calibration plate, the ceramic calibration plate is photographed in at least ten different postures to obtain the intrinsic and extrinsic parameter matrices of the multispectral camera to complete the parameter calibration of the multispectral camera.

[0039] Specifically, the ceramic calibration plate is a 3mm black and white ceramic plate. When the plane mirror assembly is calibrated using the ceramic calibration plate, the ceramic calibration plate is photographed in at least ten different postures. In other words, in this embodiment, the ceramic calibration plate is used to calibrate the intrinsic and extrinsic parameters of the multispectral camera. In this embodiment, it is necessary to photograph the ceramic calibration plate in at least 10 different postures and complete the multispectral camera calibration based on the Zhang Zhengyou calibration method to obtain the intrinsic and extrinsic parameter matrices of the multispectral camera to complete the calibration of the intrinsic and extrinsic parameters of the multispectral camera, so as to complete the determination of the three-dimensional position in subsequent steps.

[0040] In some embodiments, it also includes temperature measurement calibration of the measurement system, that is, before realizing the measurement of the three-dimensional deformation field of the basic bottom of additive manufacturing, it is necessary to use a ceramic calibration plate to calibrate the intrinsic and extrinsic parameters of the measurement system of the multispectral camera, and before realizing the measurement of the three-dimensional temperature field of the basic bottom of additive manufacturing, it is necessary to use an induction eddy current heating device to complete the colorimetric temperature measurement calibration of the multispectral camera to obtain the ratio of the multispectral radiation intensity; in the colorimetric temperature measurement calibration experiment of the multispectral camera, the temperature range is 550-1100℃, and the temperature is increased in increments of 20℃. After each increment is kept warm for 5 minutes, the multispectral camera is used to capture visible light 10 and near-infrared band images at different temperatures.

[0041] Specific examples include Figure 2 As shown, a nickel-based alloy block is heated to a preset temperature and measured using an infrared spot thermometer. A real-time feedback system regulates the current to stabilize the block's temperature within ±2°C of the preset temperature. After stabilizing the block at 900°C, the aperture size is fixed and images are acquired at different exposure times. For each exposure time, 20 images are acquired at a 2Hz frequency, and the grayscale average is calculated to obtain the color and near-infrared grayscale values ​​for each exposure time. Based on the relationship between exposure time and grayscale value, the multispectral camera's exposure time can be adjusted to accommodate a wider temperature measurement range when overexposure or underexposure occurs. Specifically, when the temperature is too high, the sensor's exposure time is reduced to reduce image grayscale. When the temperature is too low, resulting in low image grayscale, the exposure time can be increased to improve image grayscale, enabling low-temperature measurement.

[0042] Specifically in S2, a high-temperature grating 2 is prepared by laser etching at the bottom of the cantilever beam substrate 12 of the additive manufacturing device, wherein before preparing the high-temperature grating 2, a high-temperature white primer needs to be sprayed on the bottom of the cantilever beam substrate 12, and then the specimen is baked, and then the high-temperature grating 2 is prepared by laser etching. For example, the high-temperature white primer is sprayed on the bottom of the cantilever beam substrate 12 and then kept warm at 200°C for 30 minutes; when preparing the high-temperature grating 2, a laser marking machine is used for etching, wherein the laser power is 5w and the etching speed is 3000mm / s.

[0043] In this embodiment, additive manufacturing is LENS additive manufacturing, in which a measurement system is used to monitor the additive manufacturing process, that is, to measure the laser near-net-shape forming process. During measurement, the position and orientation of the single camera system are adjusted to improve the measurement effect, so that the multispectral camera obtains image data including the temperature of the molten pool 11. The method of using the measurement system to monitor the additive manufacturing process is exemplified as follows: Figure 3 As shown, a measurement system monitors the bottom of the substrate during additive manufacturing (AM) and inspects the LENS laser repair process. The LENS machine used is a Staubli Unimation (RX60). Printing is performed using the illustrated cantilever beam substrate 12 as the substrate. The printing strategy uses serpentine scanning, a laser power of 1100W, and a scanning speed of 10mm / s. The measurement system obtains image information of the molten pool 11 at different viewing angles to perform 3D measurement.

[0044] In some embodiments, a filter component is provided on the measurement system to eliminate interference from strong lasers, high temperature radiation, and dust splashing in the additive manufacturing process when the multispectral camera captures images.

[0045] Specifically, when performing in-process inspection of the LENS additive manufacturing process, a filter assembly is required to eliminate interference from strong laser light, high-temperature radiation, and dust splashing. Specifically, the filter assembly includes an attenuator, a cutoff plate, and a filter assembly to achieve good image quality. The filter assembly is installed on the multispectral lens to improve temperature measurement accuracy. Preferably, a synchronization trigger is also connected to the measurement system to enable simultaneous image acquisition of the color channel and near-infrared channel of the multispectral camera.

[0046] Specifically, in S3, after the measurement system completes the measurement, a computer is used to perform image processing, separating the left and right perspectives of the blue band in the multispectral image into left and right views within the blue band. Specifically, a function is written in MATLAB to separate the left and right views in a single-camera image. The left and right views are processed as sampled moiré images obtained by different multispectral cameras using the binocular vision principle to perform stereo matching. The three-dimensional position information of the substrate surface topography is obtained based on the intrinsic and extrinsic parameters obtained by calibrating the measurement system in step S1, providing the three-dimensional coordinates for the temperature result in the colorimetric temperature measurement.

[0047] The temperature measurement is completed based on the colorimetry principle and calibration results by combining the red band and near-infrared image in the multispectral color image, and the three-dimensional temperature field is obtained by combining the three-dimensional position information. Figure 4 As shown, since the temperature of the molten pool 11 is relatively high, a higher temperature range is selected during calibration to complete the measurement. Then, a computer is used to perform image processing, and the images of the red band and the near-infrared band are separated into left and right perspectives to form left and right views under the red band and the near-infrared band. The left view and the right view are used as images obtained by different multispectral cameras in the binocular vision principle to complete stereo matching. The three-dimensional position information is obtained according to the internal and external parameters obtained by the calibration of the measurement system in step S1. The temperature measurement is completed according to the colorimetric method to obtain accurate temperature values. The three-dimensional temperature field distribution information is obtained in combination with the three-dimensional position information.

[0048] The method in this application is applicable to all printed structures in laser near-net forming and can be used under different printing parameters. By combining the three-dimensional deformation information obtained with the temperature distribution information obtained by the measurement system, the synchronous measurement of the basic bottom three-dimensional temperature field and the three-dimensional deformation field during the additive manufacturing process can be completed based on a single multispectral camera. Therefore, after adjusting the viewing angle and position of the measurement system in this application, the three-dimensional temperature and three-dimensional deformation of the additive manufacturing process of any specimen shape can be monitored. The measurement frequency of the multispectral camera can reach up to 30Hz, which can realize in-situ real-time measurement of three-dimensional temperature and three-dimensional deformation.

[0049] It should be noted that, in the description of this application, the terms "first", "second", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance. In addition, in the description of this application, unless otherwise specified, the meaning of "plurality" is two or more.

[0050] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, segment or portion of code comprising one or more executable instructions for implementing the steps of a specific logical function or process, and the scope of the preferred embodiments of the present application includes alternative implementations in which functions may be performed out of the order shown or discussed, including performing functions in a substantially simultaneous manner or in the reverse order depending on the functions involved, which should be understood by those skilled in the art to which the embodiments of the present application belong.

[0051] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present application. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0052] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A three-dimensional temperature and three-dimensional deformation measurement method based on a single multispectral camera, characterized in that: The following steps are involved: A measurement system is built based on a single multispectral camera and calibrated using a ceramic calibration plate. The measurement system includes a multispectral camera, a plane mirror assembly, and a filter assembly. By adjusting the position of the plane mirror assembly, the target object of the measurement system can be imaged on both sides of the multispectral camera. The filter assembly is used to eliminate interference from strong lasers, high-temperature radiation, and dust splashing during the additive manufacturing process when the multispectral camera captures images. After spraying a primer on the bottom of the cantilever beam substrate of the additive manufacturing device and drying it, a high-temperature grating is prepared by laser etching, and the measurement system is used to monitor the additive manufacturing process to obtain a captured image including the molten pool temperature; The captured image is divided into a left view and a right view, and the left view and the right view are processed as images obtained by cameras at different angles in the binocular vision principle to complete stereo matching to obtain three-dimensional displacement and deformation information; the blue band, red band and near-infrared band of the multispectral camera are used to respectively perform deformation measurement and colorimetric temperature measurement on the left view and the right view.

2. The method according to claim 1, characterized in that The plane mirror assembly is a four-way reflector measuring light path, including a right-angle prism and plane mirrors respectively arranged opposite to the two right-angle sides of the right-angle prism; the two plane mirrors are in the same horizontal plane, so that left and right sides are imaged in the multispectral camera.

3. The method according to claim 2, characterized in that A synchronization trigger is provided on the measurement system to enable simultaneous image acquisition of the color channel and the near-infrared channel of the multispectral camera.

4. The method according to claim 1, wherein When calibrating the plane mirror assembly using a 3mm black and white ceramic plate as the ceramic calibration plate, at least ten shots of the ceramic calibration plate in different postures are taken to obtain the intrinsic and extrinsic parameter matrices of the multispectral camera to complete the parameter calibration of the multispectral camera.

5. The method according to claim 4, characterized in that After calibrating the multispectral camera using a ceramic calibration plate to complete the calibration of the internal and external parameters of the multispectral camera, the method further includes using an induction eddy current heating device to complete the colorimetric temperature measurement calibration of the multispectral camera to obtain the ratio of multispectral radiation intensity; in the colorimetric temperature measurement calibration experiment of the multispectral camera, the temperature range is 550-1100°C, and the temperature is increased in increments of 20°C. After each increment is kept warm for 5 minutes, the multispectral camera is used to capture visible light and near-infrared band images at different temperatures.

6. The method according to claim 1, characterized in that Before preparing the high-temperature grating, high-temperature white primer is sprayed on the bottom of the cantilever beam substrate and then kept at 200° C. for 30 minutes; when preparing the high-temperature grating, the laser power is 5W and the etching speed is 3000mm / s.

7. The method according to claim 1, characterized in that The multispectral camera has a maximum measurement frequency of 30 Hz, and can monitor the three-dimensional temperature and three-dimensional deformation of the additive manufacturing process of any specimen shape, and realize in-situ real-time measurement of the three-dimensional temperature and three-dimensional deformation during the additive manufacturing process.

8. The method according to claim 1, characterized in that When three-dimensional deformation measurement is performed using the blue band in the multispectral camera, the high-temperature grating is used as the deformation carrier, and stereo matching is performed based on the binocular vision principle to obtain the surface morphology and three-dimensional position information of the target object, and provide three-dimensional coordinates for the temperature result in colorimetric temperature measurement.

9. The method according to claim 1, characterized in that Colorimetric temperature measurement is performed using the red band and near-infrared image in the multispectral camera to obtain an accurate temperature value, and three-dimensional temperature field distribution information is obtained in combination with the three-dimensional position information.

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