Aircraft ablation topography dynamic measurement device and measurement method

Abstract

The application provides a kind of aircraft ablation topography dynamic measuring device and measuring method, including control module, image acquisition module, structured light projection module and coordinate system registration support;Control module controls image acquisition module, structured light projection module work cooperatively, and completes structured light scanning projection, structured light image and mark point image acquisition, and image processing point cloud calculation;The first group binocular vision system in image acquisition module cooperates with structured light projection module, completes the rapid acquisition of aircraft surface three-dimensional point cloud, the second group binocular vision system uses the mark point on the coordinate system registration support, registers the three-dimensional point cloud coordinate system at different time, and corrects the three-dimensional point cloud collected by the first group binocular vision system.The application overcomes the problem of high temperature, high brightness and high frequency vibration on the surface of aircraft topography dynamic measurement, and the high-temperature dynamic ablation topography data obtained has excellent measurement accuracy and point cloud density.

Description

Technical Field

[0001] This invention belongs to the field of hypersonic test measurement technology, and specifically relates to a dynamic measurement device and method for the ablation morphology of aircraft. Background Technology

[0002] During the on-orbit flight of hypersonic vehicles, the structural shape undergoes varying degrees of change under the influence of aerodynamic forces and aerothermal activity. This significantly reduces the structural strength of the heat shield and alters the vehicle's heat insulation performance. Therefore, during the initial design phase, hypersonic vehicles require extensive aerodynamic heating tests in an arc wind tunnel. By measuring the magnitude and trend of changes in the shape of the heat shield, the heat insulation performance, structural mechanics, and aerodynamic properties of the heat shield are analyzed.

[0003] There are many mature methods for measuring the morphology of objects under normal temperature conditions, including coordinate measuring machines and optical profilometry. The dynamic ablation morphology measurement of heat-resistant structures under electric arc wind tunnel conditions mainly faces the following three difficulties: (1) The surface temperature of the object being measured is high. As the high enthalpy gas flows through the surface of the heat-resistant structure at a high Mach number, the surface temperature of the material will rapidly soar to thousands of degrees Celsius, making it difficult to implement the contact-type morphology measurement scheme; (2) The surface illumination conditions of the object being measured are poor. During the electric arc wind tunnel test, there are bright arc light from the electric arc heater, bright shock waves formed by the high-speed airflow and the heat-resistant structure, and high-temperature self-luminescence of the heat-resistant structure itself. These complex high illumination conditions make it difficult for traditional optical morphology measurement methods (binocular vision method, triangulation method, phase measurement method, etc.) to collect clear ablation images. There are few feature points that can be used to calculate three-dimensional point clouds, and the matching error is large; (3) During the test, the test equipment will cause the object being measured to vibrate rapidly. This high-frequency irregular vibration causes the measured morphology point cloud data to have a large error. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the interference of high temperature, high brightness and vibration when measuring the ablation shape of a heat-resistant structure in an electric arc wind tunnel, and to provide a heat-resistant structure shape measurement device and method that can acquire three-dimensional dynamic shape data and has the ability to correct data jitter.

[0005] The technical solution provided by this invention is as follows:

[0006] In a first aspect, a dynamic measurement device for the ablation morphology of an aircraft includes: a control module, an image acquisition module, a structured light projection module, and a coordinate system registration bracket.

[0007] The image acquisition module includes a support pan-tilt unit and a first camera, a second camera, a third camera, and a fourth camera installed sequentially. Each camera is equipped with a lens and a filter. The first and second cameras, as well as the third and fourth cameras, are arranged in pairs on both sides of the support pan-tilt unit. The four cameras converge and focus on the object under test and simultaneously trigger the shooting action. The second and third cameras on the inner side form a first binocular vision system to capture images of the object under test and acquire structured light image pairs. The first and fourth cameras on the outer side form a second binocular vision system to capture images of the coordinate system registration bracket and acquire marker point image pairs.

[0008] The structured light projection module includes an electric slide, a pan-tilt unit, and multiple line lasers. The line lasers are fixedly mounted on the pan-tilt unit, which is fixedly connected to the electric slide. In actual operation, the electric slide drives the pan-tilt unit to perform periodic reciprocating motion, thereby enabling the line lasers to perform periodic rapid scanning of the object under test.

[0009] The coordinate system registration bracket supports the object to be measured and is equipped with marker points.

[0010] The control module stores and processes the images acquired by the image acquisition module, and controls the image acquisition module and the structured light projection module to work together. The processing of the images acquired by the image acquisition module includes: using structured light image pairs to perform a coarse calculation of the topographic point cloud of the object under test; using the transformation relationship of the same marker points in the marker point image pairs to perform the registration of the three-dimensional point cloud coordinate system in the structured light images at different times; and correcting the three-dimensional point cloud obtained using the structured light images to obtain the topographic point cloud of the object under test after coordinate registration.

[0011] In conjunction with the first aspect, the first camera, the second camera, the third camera and the fourth camera are selected as high-speed cameras with a frame rate of more than 200 frames per second.

[0012] In conjunction with the first aspect, the focal lengths of the lenses on the first, second, third, and fourth cameras ensure that the object under test occupies 1 / 2 to 2 / 3 of the field of view.

[0013] In conjunction with the first aspect, the line laser is a short-wavelength laser with a wavelength between 200nm and 600nm, and the actual bandwidth is less than 50nm.

[0014] In conjunction with the first aspect, the transmission wavelength of the filters on the first and fourth cameras is >700nm; the transmission wavelength of the filters on the second and third cameras is comparable to the laser wavelength, with a bandwidth of less than 20nm; the ratio of the distance between the second and third cameras to the distance from the camera to the object under test is between 0.8 and 2.0.

[0015] Secondly, a method for dynamically measuring the ablation morphology of an aircraft, implemented using the dynamic measurement device for the ablation morphology of an aircraft described in the first aspect, includes:

[0016] The internal and external parameters of the first, second, third, and fourth cameras are calibrated.

[0017] Send a single scan command to the motorized slide, record and observe whether multiple laser lines can fully cover the test piece; under the condition that the test piece can be fully covered, assign values ​​to the position and motion parameters of the motorized slide and assign values ​​to the shooting parameters of the four cameras.

[0018] The electric slide is controlled to scan the model under test in a periodic reciprocating manner. In each scanning cycle, the second and third cameras acquire structured light image pairs, and the first and fourth cameras acquire marker point image pairs, which are then saved in an orderly manner.

[0019] The laser beam centerline is extracted, corrected, and matched from the structured light images acquired by the second and third cameras, and the three-dimensional point cloud of the object under test is coarsely calculated by combining the internal and external parameters obtained from the calibration.

[0020] The two-dimensional coordinates of the center of the marker point in the image of the marker point acquired by the first and fourth cameras are extracted, corrected and matched, and the three-dimensional coordinates of the center of the marker point are determined. The rigid body transformation matrix between the current time coordinate system and the initial time coordinate system is calculated using the three-dimensional coordinates of the center of the marker point.

[0021] The obtained rigid body transformation matrix is ​​used to correct the coarsely calculated 3D point cloud data, and the coordinate-registered object topography point cloud is obtained.

[0022] In conjunction with the second aspect, the calibration of the internal and external parameters of the first, second, third, and fourth cameras includes:

[0023] Four cameras are controlled to simultaneously capture multiple sets of images of a two-dimensional target in different poses near the test object, determining the sub-pixel level coordinates of the feature points on the two-dimensional target images. The obtained four sets of feature point coordinates are then paired according to the camera number, and the intrinsic and extrinsic parameters of each pair of binocular cameras are calibrated using the flat panel template calibration method, resulting in the intrinsic parameter matrix of each camera. Lens correction parameters Rigid body transformation matrix between cameras , , and the base matrix of the second and third cameras. ,in i Number the camera i =1~4.

[0024] In conjunction with the second aspect, the coarse calculation of the 3D point cloud of the object under test is completed in the following manner, including:

[0025] S4.1, segment the foreground and background of the structured light image, and extract the center line of the laser light stripe in the structured light image;

[0026] S4.2, using the intrinsic parameter matrix , and correction parameter group , Distortion correction is performed on the center line of the extracted laser stripe;

[0027] S4.3, using the fundamental matrix Determine the center point of the light stripe in the second camera image. Find the epipolar line in the third camera image and search for the point closest to the epipolar line along the center line of the laser beam in the third camera image. ,Will As a matching point, combined with the intrinsic parameter matrix , Rotation matrix Translation vector After obtaining the 3D points, repeat step S4.3 to obtain the 3D point cloud of the object surface in the current frame structured light image pair. ;

[0028] S4.4, repeat S4.1-S4.3, and sequentially complete the matching of all structured light image pairs to obtain a set of three-dimensional point clouds of the surface of the object under test within the current scanning cycle. All point clouds adopt the current three-dimensional coordinate system of the second camera.

[0029] In conjunction with the second aspect, the rigid body transformation matrix between the current time coordinate system and the initial time coordinate system is obtained in the following manner:

[0030] S5.1, the marked point image is processed by binary thresholding, contour extraction, and ellipse center fitting image algorithm to obtain the first... i For the marker image N Two-dimensional coordinates of the center of a circle. N ≥5, i Image sequence number, 0 < i ≤ K ;

[0031] S5.2, using the intrinsic parameter matrix M 1. M 4 and correction parameter group D 1. D 4. Correct the distortion of the center coordinates of the marked points to obtain the corrected two-dimensional coordinates. , j The marker point number, 0 < j ≤ N ;

[0032] S5.3, Corrected two-dimensional coordinate points Combined with intrinsic parameter matrix M 1 and M 4. Rotation Matrix R 14 and translation vector T 14 The coordinates of the center of the marked point in the three-dimensional coordinate system of the first camera are obtained. ;

[0033] S5.4, the coordinates of the center of the marked point in the first camera's three-dimensional coordinate system. By performing two rigid body transformations, the coordinates of the center of the marked point in the second camera's three-dimensional coordinate system are obtained. And obtain the coordinate system registration support. N The center of the circle is in the... i 3D point set in the second camera coordinate system at any given moment ;

[0034] S5.5, calculated using the matrix singular value decomposition method. and coordinate transformation matrix between , For the first i The rotation matrix from the second camera coordinate system at time 0 to the second camera coordinate system at time 0. For the first i The translation vector from the second camera coordinate system at time 0 to the second camera coordinate system at time 0.

[0035] The dynamic measurement device and method for measuring the ablation morphology of an aircraft provided by the present invention have the following advantages:

[0036] (1) The present invention provides a dynamic measurement device and method for ablation morphology of an aircraft, including a control module, an image acquisition module, a structured light projection module and a coordinate system registration bracket; the control module controls the image acquisition module and the structured light projection module to work synchronously, and completes the structured light scanning projection, structured light image and marker point image acquisition, and image processing point cloud computing; the image acquisition module and the structured light projection module are independent in position; the four high-speed cameras in the image acquisition module constitute two sets of binocular vision systems working in concert. The first set of binocular vision systems works with the structured light projection module to complete the rapid acquisition of three-dimensional point clouds on the surface of the aircraft. The second set of binocular vision systems uses the marker points on the coordinate system registration bracket to register the coordinate system of the three-dimensional point cloud at different times, and corrects the three-dimensional point cloud acquired by the first set of binocular vision systems; the present invention overcomes the problems of high temperature, high brightness and high frequency vibration on the surface during dynamic measurement of aircraft morphology, and has the advantages of simple hardware structure and easy implementation. In terms of algorithm, it reduces the image matching difficulty when traditional binocular vision technology is applied to high temperature test objects. The high temperature dynamic ablation morphology data obtained by the present invention has excellent measurement accuracy and point cloud density;

[0037] (2) The present invention provides a dynamic measurement device and method for ablation morphology of aircraft, which adopts a method of active projection of short-wavelength structured light by structured light projection module combined with narrowband filtering imaging, effectively filtering the interference of high temperature and high brightness arc light to obtain a clear image, and can promote the application of binocular vision technology to the field of high temperature measurement.

[0038] (3) The present invention provides a dynamic measurement device and method for ablation morphology of an aircraft. It uses a high-speed camera, which can shorten the scanning time of the entire surface area of ​​the aircraft, reduce the positional deviation of a single morphology point cloud data caused by scanning, and also ensure that the measurement system can obtain denser three-dimensional morphology point cloud data in a single scanning cycle.

[0039] (4) The present invention provides a dynamic measurement device and method for measuring the ablation morphology of an aircraft, which adopts a structured light projection module to implement periodic line laser continuous scanning projection, and designs an identifiable pattern on the surface of the aircraft, which can realize dense coding of discrete points on the surface of the heat-resistant structure object.

[0040] (5) The dynamic measurement device and method for ablation morphology of aircraft provided by the present invention adopts a structure in which the structured light projection equipment and the image acquisition equipment are not fixedly connected, which allows the measurement device to adapt to the special spatial environment in the arc wind tunnel test section;

[0041] (6) The present invention provides a dynamic measurement device and method for measuring the ablation morphology of an aircraft. The coordinate system registration bracket has a special structure with circulating cooling water inside, which can greatly reduce the ablation damage of the marker points caused by the high temperature airflow.

[0042] (7) The dynamic measurement device and method for ablation morphology of an aircraft provided by the present invention adopts a method of two sets of binocular systems working together to perform coordinate system registration on three-dimensional point clouds collected at different times, thereby eliminating the interference caused by equipment vibration during the test.

[0043] (8) The dynamic measurement device and method for ablation morphology of an aircraft provided by the present invention adopts a synchronous triggering mode of control image acquisition module and structured light projection module, which effectively unifies the time synchronization of structured light projection, structured light image acquisition and marker point image acquisition, and ensures the overall accuracy of three-dimensional morphology measurement data. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the structure of a dynamic measurement device for ablation morphology of an aircraft according to the present invention. Detailed Implementation

[0045] The features and advantages of the present invention will become clearer and more apparent from the following detailed description.

[0046] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0047] This invention provides a dynamic measurement device for the ablation morphology of aircraft, such as... Figure 1 As shown, it includes a control module 1, an image acquisition module 2, a structured light projection module 3, and a coordinate system registration bracket 4;

[0048] The control module 1 includes a host computer 11 and a synchronization controller 12. The host computer 11 stores and processes the images acquired by the image acquisition module 2, and controls the image acquisition module 2 and the structured light projection module 3 to work together through the synchronization controller 12. Cooperative work means that after the structured light projection module moves to the correct starting position according to the clock command, the image acquisition module takes pictures under the same clock command. When the structured light projection module moves to the ending position according to the clock command, the image acquisition module stops taking pictures. During the interval between adjacent scanning cycles, the host computer completes the work of storing the images to the hard disk and starts the next scanning and capturing cycle.

[0049] Image acquisition module 2 includes a support pan-tilt head 21, and a first camera 221, a second camera 222, a third camera 223, and a fourth camera 224 installed sequentially. Each camera is equipped with a lens and a filter. The filter is screwed to the front of the four lenses, and the four lenses are screwed to the four cameras. The first camera 221, the second camera 222, the third camera 223, and the fourth camera 224 are arranged in pairs on both sides of the support pan-tilt head 21. The four cameras converge and focus on the object being measured and simultaneously trigger the shooting action. The second camera 222 and the third camera 224 are located on the inner side. 23 forms a first binocular vision system, captures images of the object under test, and acquires structured light image pairs (images displaying images of the object under test with laser light stripes), which are used for the object's topography point cloud computing; the outer first camera 221 and fourth camera 224 form a second binocular vision system, captures images of the coordinate system registration bracket 4, and acquires marker point image pairs (images displaying the coordinate system registration bracket without laser light stripes). The transformation relationship of the same marker points in the marker point image pairs is used to register the three-dimensional point cloud coordinate system in each frame of structured light images, and the coordinate-registered object's topography point cloud is obtained;

[0050] The structured light projection module 3 includes an electric slide 31, a pan-tilt unit 32, and multiple line lasers 33. The line lasers 33 are fixedly mounted on the pan-tilt unit 32 in a uniformly distributed manner, and the pan-tilt unit 32 is fixedly connected to the electric slide 31. In actual operation, the electric slide 31 drives the pan-tilt unit 32 to perform periodic reciprocating motion at a uniform speed, realizing the periodic rapid scanning of the object to be measured by the line lasers 33.

[0051] The coordinate system registration bracket 4 is a steel frame structure with internal circulating cooling water, which supports the object being measured. Multiple equal-diameter circular holes are drilled around the frame, and the holes are filled with metal plugs, such as copper plugs, as marking points. The surface of the metal plugs is smoothed.

[0052] In order to obtain a sufficient number of images, the first camera 221, the second camera 222, the third camera 223 and the fourth camera 224 are high-speed cameras with a frame rate of more than 200 frames per second, preferably high-speed black and white cameras with a frame rate of more than 200 frames per second.

[0053] The first camera 221 is equipped with a first lens 231 and a first filter 241, the second camera 222 is equipped with a second lens 232 and a second filter 242, the third camera 223 is equipped with a third lens 233 and a third filter 243, and the fourth camera 224 is equipped with a fourth lens 234 and a fourth filter 244; the focal lengths of the first lens 231, the second lens 232, the third lens 233, and the fourth lens 234 ensure that the object under test occupies an area between 1 / 2 and 2 / 3 of the field of view.

[0054] The line laser 33 is a short-wavelength laser with a wavelength between 200nm and 600nm, and an actual bandwidth of less than 50nm. The laser shape is a line or a crosshair. Correspondingly, the transmission wavelengths of the first filter 241 and the fourth filter 244 are >700nm, and no laser stripes are displayed in the acquired marked point image. The transmission wavelengths of the second filter 242 and the third filter 243 are comparable to the laser wavelength, and the bandwidth is less than 20nm. The acquired structured light image displays an image of the object under test with laser stripes.

[0055] This invention also provides a method for dynamically measuring the ablation morphology of an aircraft, comprising the following steps:

[0056] S1, the dynamic measurement device for the ablation morphology of the heat-resistant structure enters the vision system calibration mode. In this mode, the calibration calculation of the internal and external parameters of the vision system is completed.

[0057] Specifically: Under room temperature conditions, four cameras simultaneously capture images of multiple sets of two-dimensional targets (checkerboard or marker circles) in different poses near the test object (within a distance of no more than 50mm). The sub-pixel coordinates of the marker points (checkerboard points or marker circle centers) on the two-dimensional target images are determined. The obtained four sets of feature point coordinates are then paired according to the camera numbers (first + fourth camera, first + third camera, and second + third camera). The internal and external parameters of each pair of binocular cameras are calibrated using a flat panel template calibration method, resulting in the intrinsic parameter matrix for each camera. Lens correction parameters and the rigid body transformation matrix between cameras , , The basic matrix of the second camera and the third camera ,in i Number the camera i =1~4, Let be the rigid body transformation matrix between the first and fourth cameras. R 14 The rotation matrix between the first and fourth cameras. T 14 Let be the translation vector between the first and fourth cameras. Let be the rigid body transformation matrix between the first and third cameras. R 13 The rotation matrix between the first and third cameras. T 13 Let be the translation vector between the first and third cameras. Let be the rigid body transformation matrix between the second and third cameras. R 23 For the rotation matrix between the second and third cameras, T 23This is the translation vector between the second and third cameras.

[0058] S2, the dynamic measurement device for the ablation morphology of the heat-resistant structure enters the measurement preparation mode. In this mode, the control module 1 sends a single scan command to the electric slide stage 31 to record and observe whether multiple laser lines can cover the test piece throughout the entire process. Under the condition that the test piece can be fully covered, the starting point, ending point, scanning speed and pause interval of the electric slide stage 31 are assigned values, and at the same time, multiple shooting parameters such as aperture, exposure time and acquisition frame rate of the four cameras are assigned values.

[0059] S3, the dynamic measurement device for the ablation morphology of the heat-resistant structure enters the ablation image acquisition mode. In this mode, the electric slide 31 scans the model under test rapidly in a cyclic reciprocating manner. In each scanning cycle, the second and third cameras acquire structured light image pairs, and the first and fourth cameras acquire marker point image pairs, which are then saved in an orderly manner.

[0060] S4, the dynamic measurement device for the ablation morphology of the heat-resistant structure enters the three-dimensional point cloud coarse calculation mode. In this mode, the extraction, correction and matching of the center lines of the laser beams of the structured light image pairs acquired by the second and third cameras are completed, and the three-dimensional point cloud coarse calculation of the object under test is completed in combination with the internal and external parameters calibrated in step S1.

[0061] The second and third cameras on the inner side form the first binocular vision system. The ratio of the distance between the two cameras to the distance from the camera to the object being measured is between 0.8 and 2.0, which is used for three-dimensional topographic point cloud computing. Specifically:

[0062] S4.1, use image preprocessing operations such as binary thresholding to complete the segmentation of the foreground and background of the structured light image, and use the gray-scale centroid method or the Steger method to extract the center line of the laser light stripe in the structured light image;

[0063] S4.2, using the intrinsic parameter matrix , and correction parameter group , Distortion correction is performed on the center line of the extracted laser stripe;

[0064] S4.3, using the fundamental matrix Determine the center point of the light stripe in the second camera image. The epipolar line (located on the center line of the laser beam) in the third camera image (its equation is: , y The dependent variable is the linear equation. x (where the independent variable is a straight line equation), and search for the point closest to the epipolar line in the center line of the laser sliver in the third camera image. ,Will As a matching point, combined with the intrinsic parameter matrix , Rotation matrix Translation vector After obtaining the three-dimensional points, repeat step S4.3 to obtain the three-dimensional point cloud of the object surface at the corresponding time point in the structured light image. ;

[0065] S4.4, repeat S4.1-S4.3, and sequentially complete the matching of all structured light image pairs to obtain a set of three-dimensional point clouds of the surface of the object under test within the current scanning cycle (all point clouds adopt the current three-dimensional coordinate system of the second camera).

[0066] S5, the dynamic measurement device for the ablation morphology of the heat-resistant structure enters the three-dimensional point cloud fine calculation mode. In this mode, the two-dimensional coordinates of the center of the marker point are extracted, corrected and matched in the image of the marker point acquired by the first and fourth cameras, and the three-dimensional coordinates of the center of the marker point are calculated. The rigid body transformation matrix between the coordinate system of the current time (current frame) and the coordinate system of the initial time (first frame) is calculated using the three-dimensional center coordinates.

[0067] The first and fourth cameras on the outer side form a second binocular vision system for coordinate system registration, specifically:

[0068] S5.1, the marked point image is processed by binary thresholding, contour extraction, and ellipse center fitting image algorithm to obtain the first... i For the marker image N Two-dimensional coordinates of the center of a circle. N ≥5, i Image sequence number, 0 < i ≤ K , K The maximum number of images;

[0069] S5.2, using the intrinsic parameter matrix M 1. M 4 and correction parameter group D 1. D 4. Correct the distortion of the center coordinates of the marked points to obtain the corrected two-dimensional coordinates. , j The marker point number, 0 < j ≤ N ;

[0070] S5.3, Corrected two-dimensional coordinate points Combined with intrinsic parameter matrix M 1 and M 4. Rotation Matrix R 14 and translation vector T 14 The coordinates of the center of the marked point in the three-dimensional coordinate system of the first camera are obtained. ;

[0071] S5.4, the coordinates of the center of the marked point in the first camera's three-dimensional coordinate system. By performing two rigid body transformations, the coordinates of the center of the marked point in the second camera's three-dimensional coordinate system are obtained. , And obtain the coordinate system registration support. N The center of the circle is in the... i 3D point set in the second camera coordinate system at any given moment ;

[0072] S5.5, calculated using the matrix singular value decomposition method. and coordinate transformation matrix between , For the first i The rotation matrix from the second camera coordinate system at time 0 to the second camera coordinate system at time 0. For the first i The translation vector from the second camera coordinate system at time 0 to the second camera coordinate system at time 0;

[0073] S6. The rigid body transformation matrix obtained in step S5 is used to correct the 3D point cloud data obtained in step S4. That is, the coordinate transformation matrix obtained from the second binocular vision system is used to correct the 3D point cloud data in the first binocular vision system. The calculation formula is as follows: The first i The 3D point cloud coordinates in the second camera coordinate system at time 0 are converted to the 3D point cloud coordinates in the second camera coordinate system at time 0.

[0074] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0075] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A dynamic measurement device for the ablation morphology of an aircraft, characterized in that, It includes a control module (1), an image acquisition module (2), a structured light projection module (3), and a coordinate system registration bracket (4); The image acquisition module (2) includes a support gimbal (21), a first camera (221), a second camera (222), a third camera (223), and a fourth camera (224) installed in sequence. Each camera is equipped with a lens and a filter. The first camera (221), the second camera (222), the third camera (223), and the fourth camera (224) are arranged in pairs on both sides of the support gimbal (21). The four cameras converge and focus on the object under test and trigger the shooting action simultaneously. The second camera (222) and the third camera (223) on the inner side form a first binocular vision system to capture the object under test and obtain structured light image pairs. The first camera (221) and the fourth camera (224) on the outer side form a second binocular vision system to capture the coordinate system registration bracket (4) and obtain marker point image pairs. The structured light projection module (3) includes an electric slide (31), a gimbal (32) and multiple line lasers (33). The line lasers (33) are fixedly mounted on the gimbal (32). The gimbal (32) is fixedly connected to the electric slide (31). In actual operation, the electric slide (31) drives the gimbal (32) to perform periodic reciprocating motion, and the line lasers (33) perform periodic rapid scanning of the object to be measured. The object to be measured is supported on the coordinate system registration bracket (4) and marked points are installed; The control module (1) stores and processes the images acquired by the image acquisition module (2), and controls the image acquisition module (2) to work in coordination with the structured light projection module (3); The processing of the image acquired by the image acquisition module (2) includes: using structured light image to perform a rough calculation of the point cloud of the morphology of the object under test; The coordinate system of the three-dimensional point cloud in the structured light images at different times is registered by using the transformation relationship of the same marker points in the marker point image pair. The three-dimensional point cloud obtained by the structured light image is then corrected to obtain the coordinate-registered object morphology point cloud.

2. The dynamic measurement device for ablation morphology of aircraft according to claim 1, characterized in that, The first camera (221), the second camera (222), the third camera (223) and the fourth camera (224) are high-speed cameras with a frame rate of more than 200 frames per second.

3. The dynamic measurement device for ablation morphology of aircraft according to claim 1, characterized in that, The focal lengths of the lenses on the first camera (221), the second camera (222), the third camera (223), and the fourth camera (224) ensure that the object under test occupies 1 / 2 to 2 / 3 of the field of view.

4. The dynamic measurement device for ablation morphology of aircraft according to claim 1, characterized in that, The line laser (33) is a short-wavelength laser with a wavelength between 200nm and 600nm and an actual bandwidth of less than 50nm.

5. The dynamic measurement device for ablation morphology of aircraft according to claim 1, characterized in that, The transmission wavelength of the filters on the first camera (221) and the fourth camera (224) is >700nm; The transmission wavelength of the filters on the second camera (222) and the third camera (223) is comparable to the wavelength of the laser, and the bandwidth is less than 20nm.

6. The dynamic measurement device for ablation morphology of aircraft according to claim 1, characterized in that, The ratio of the distance between the second camera (222) and the third camera (223) to the distance from the camera to the object being measured is between 0.8 and 2.

0.

7. A method for dynamically measuring the ablation morphology of an aircraft, characterized in that, The method employs the dynamic measurement device for ablation morphology of an aircraft as described in any one of claims 1 to 6, comprising: The internal and external parameters of the first, second, third, and fourth cameras are calibrated. Send a single scan command to the motorized slide, record and observe whether multiple laser lines can fully cover the test piece; under the condition that the test piece can be fully covered, assign values ​​to the position and motion parameters of the motorized slide and assign values ​​to the shooting parameters of the four cameras. The electric slide is controlled to scan the model under test in a periodic reciprocating manner. In each scanning cycle, the second and third cameras acquire structured light image pairs, and the first and fourth cameras acquire marker point image pairs, which are then saved in an orderly manner. The laser beam centerline is extracted, corrected, and matched from the structured light images acquired by the second and third cameras, and the three-dimensional point cloud of the object under test is coarsely calculated by combining the internal and external parameters obtained from the calibration. The two-dimensional coordinates of the center of the marker point in the image of the marker point acquired by the first and fourth cameras are extracted, corrected and matched, and the three-dimensional coordinates of the center of the marker point are determined. The rigid body transformation matrix between the current time coordinate system and the initial time coordinate system is calculated using the three-dimensional coordinates of the center of the marker point. The obtained rigid body transformation matrix is ​​used to correct the coarsely calculated 3D point cloud data, and the coordinate-registered object topography point cloud is obtained.

8. The method for dynamic measurement of ablation morphology of an aircraft according to claim 7, characterized in that, The calibration of the internal and external parameters of the first, second, third, and fourth cameras includes: Four cameras are controlled to simultaneously capture multiple sets of images of a two-dimensional target in different poses near the test object, determining the sub-pixel level coordinates of the feature points on the two-dimensional target images. The obtained four sets of feature point coordinates are then paired according to the camera number, and the intrinsic and extrinsic parameters of each pair of binocular cameras are calibrated using the flat panel template calibration method, resulting in the intrinsic parameter matrix of each camera. Lens correction parameters Rigid body transformation matrix between cameras , , and the base matrix of the second and third cameras. ,in i Number the camera i =1~4; Let be the rigid body transformation matrix between the first and fourth cameras. R 14 The rotation matrix between the first and fourth cameras. T 14 Let be the translation vector between the first and fourth cameras. Let be the rigid body transformation matrix between the first and third cameras. R 13 The rotation matrix between the first and third cameras. T 13 Let be the translation vector between the first and third cameras. Let be the rigid body transformation matrix between the second and third cameras. R 23 For the rotation matrix between the second and third cameras, T 23 This is the translation vector between the second and third cameras.

9. The method for dynamic measurement of ablation morphology of an aircraft according to claim 8, characterized in that, The coarse calculation of the 3D point cloud of the object under test is completed in the following ways: S4.1, segment the foreground and background of the structured light image, and extract the center line of the laser light stripe in the structured light image; S4.2, using the intrinsic parameter matrix , and correction parameter group , Distortion correction is performed on the center line of the extracted laser stripe; S4.3, using the fundamental matrix Determine the center point of the light stripe in the second camera image. Find the epipolar line in the third camera image and search for the point closest to the epipolar line along the center line of the laser beam in the third camera image. ,Will As a matching point, combined with the intrinsic parameter matrix , Rotation matrix Translation vector Once the three-dimensional points are obtained, repeat step S4.3 to obtain the three-dimensional point cloud of the surface of the object under test in the current frame structured light image. S4.4, repeat S4.1-S4.3, and sequentially complete the matching of all structured light image pairs to obtain a set of three-dimensional point clouds of the surface of the object under test within the current scanning cycle. All point clouds adopt the current three-dimensional coordinate system of the second camera.

10. The method for dynamic measurement of ablation morphology of an aircraft according to claim 9, characterized in that, The rigid body transformation matrix between the current time coordinate system and the initial time coordinate system is obtained in the following ways: S5.1, the marked point image is processed by binary thresholding, contour extraction, and ellipse center fitting image algorithm to obtain the first... i For the marker image N Two-dimensional coordinates of the center of a circle. N ≥5, i Image sequence number, 0 < i ≤ K ; S5.2, using the intrinsic parameter matrix M 1. M 4 and correction parameter group D 1. D 4. Correct the distortion of the center coordinates of the marked points to obtain the corrected two-dimensional coordinates. , j The marker point number, 0 < j ≤ N ; S5.3, Corrected two-dimensional coordinate points Combined with intrinsic parameter matrix M 1 and M 4. Rotation Matrix R 14 and translation vector T 14 The coordinates of the center of the marked point in the three-dimensional coordinate system of the first camera are obtained. ; S5.4, the coordinates of the center of the marked point in the first camera's three-dimensional coordinate system. By performing two rigid body transformations, the coordinates of the center of the marked point in the second camera's three-dimensional coordinate system are obtained. And obtain the coordinate system registration support. N The center of the circle is in the... i 3D point set in the second camera coordinate system at any given moment ; S5.5, calculated using the matrix singular value decomposition method. and coordinate transformation matrix between , For the first i The rotation matrix from the second camera coordinate system at time 0 to the second camera coordinate system at time 0. For the first i The translation vector from the second camera coordinate system at time 0 to the second camera coordinate system at time 0.

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