Dynamic measurement method and device for morphology of light foldable structure

Abstract

The invention relates to a dynamic measurement method and device for the morphology of a light extensible and retractable structure. The method comprises the steps that a dynamic measurement system for the morphology of the light extensible and retractable structure is built; placing a multi-view three-dimensional calibration block in the center of the measured area, and performing calibration; generating a projection speckle pattern according to the set environmental parameters; a special target ball is placed in the center of the measured area, the laser speckle projection device is started, and a speckle pattern is projected to the surface of the special target ball; measuring the morphology of the special target ball by a multi-view DIC detector, and calculating a deviation value; if the deviation value exceeds the allowable value, finely adjusting the object distance or the projection area photographed by the camera, and repeating the process until the requirement is met; the light foldable structure is placed, the roller shutter type product unfolding and folding mechanism is started, and the DIC detector synchronously measures the whole-field morphology of the light foldable structure; and carrying out data processing on the image processing industrial personal computer to obtain a full-field three-dimensional appearance of the light foldable structure at each time point, and finally generating a three-dimensional appearance dynamic evolution graph of the supporting structure in the unfolding and folding process.

Description

Technical Field

[0001] This invention relates to a method and apparatus for dynamic measurement of the morphology of a lightweight, expandable structure, belonging to the field of geometric dimension measurement. Background Technology

[0002] Lightweight deployable structures are key components in the aerospace field. Their advantages, such as lightweight design, high strength, and corrosion resistance, significantly improve performance and reduce launch costs. Monitoring the dynamic changes in the deployment and retraction morphology of lightweight deployable structures is crucial. This verifies their deployment accuracy, motion stability, and structural reliability, preventing jamming, deformation, or failure, ensuring the success of spacecraft missions in orbit, and providing critical data support for optimized design. Existing methods for monitoring the dynamic changes in the deployment and retraction morphology of lightweight deployable structures mainly include monitoring the meshing of clamping roller groups, mechanical feedback from the winding shaft, and multi-point strain gauge measurements. For example, using multi-stage clamping roller groups to monitor the deployment and retraction morphology of ultra-long thin-walled structures is effective, but this method relies on mechanical contact, easily introducing additional frictional interference, and is difficult to capture local micro-deformations. Other solutions use toothed meshing to transfer interlayer shear force, which can reduce delamination and loosening, but cannot quantify strain distribution in real time, and has high structural complexity. Traditional strain gauge methods are limited by discrete point placement, making it difficult to globally characterize nonlinear deformation, susceptible to electromagnetic interference, and unable to meet the requirements of some products that do not allow for the attachment of extraneous materials. Summary of the Invention

[0003] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a method and device for dynamic measurement of the morphology of lightweight, expandable and retractable structures. This solves the problems of friction interference introduced by mechanical contact, difficulty in capturing the microscopic deformation of lightweight flexible products across the entire field, and inability to quantify dynamic changes in morphology in real time by traditional methods.

[0004] The technical solution of this invention is: a lightweight, deployable, and retractable structural morphology dynamic measurement device, comprising a DIC laser speckle projection detection device, a multi-view stereo calibration block, a target sphere, a roller shutter-type product deployment and retraction mechanism, and an image processing industrial control computer; wherein,

[0005] The DIC laser speckle projection inspection device is a combination of a binocular DIC detector and a laser speckle projector, used to inspect the morphology of lightweight, expandable structures.

[0006] A roller shutter-type product unfolding and retracting mechanism is used to fix the lightweight unfolding and retracting structural component to be measured and drive its movement to produce unfolding and retracting shape changes;

[0007] Multi-view stereo calibration block, used to calibrate DIC laser speckle projection detection device;

[0008] The target ball is used to verify the measurement accuracy of the DIC laser speckle projection detection device and to determine the ready status of the DIC laser speckle projection detection device.

[0009] An image processing industrial control computer is used to drive the DIC laser speckle projection detection device and the roller shutter-type product unfolding and retracting mechanism to work together to complete the projection, calculate the appearance, and finally output a measurement report.

[0010] There are three sets of DIC laser speckle projection detection devices, and the three sets of DIC laser speckle projection detection devices are evenly placed around the area to be measured, with an angle of 120° between them.

[0011] The multi-view stereo calibration block is a triangular prism with a carbon fiber structure, and its size is the size of the measured area × (0.7~1.0). Multiple circular markers are randomly attached to the side of each prism.

[0012] The target ball is a target ball with a base, and its material is aluminum alloy with a coefficient of thermal expansion of 23.4 × 10⁻⁶. -6 / K, with a control precision of 1µm, and the surface is treated with a frosted coating.

[0013] A method for dynamically measuring the morphology of a lightweight, deployable structure using the aforementioned device, comprising:

[0014] 1) Place a multi-view stereo calibration block in the area to be measured, and perform single-view calibration of the binocular DIC detector in a single set of DIC laser speckle projection detection devices and stereo calibration of the binocular DIC detector in three sets of DIC laser speckle projection detection devices to determine the coordinate transformation relationship between the three sets of binocular DIC detectors.

[0015] 2) Generate a projected speckle map based on the set environmental parameters;

[0016] 3) Place the target sphere in the center of the area to be measured, turn on the laser speckle projection device, and project the generated speckle pattern onto the surface of the target sphere;

[0017] 4) The morphology of the target sphere is measured by three sets of DIC detectors, and the diameter of the target sphere is fitted. The deviation is then obtained by subtracting the nominal diameter of the target sphere from the morphology.

[0018] 5) Judge the obtained deviation. If the deviation exceeds the allowable value, adjust the environmental parameters of the camera and repeat steps 2) to 4) until the deviation is less than the allowable value, then proceed to step 6).

[0019] 6) Place the lightweight, retractable structure to be measured in the center of the area to be measured, open the roller shutter-type product retraction mechanism, and use three sets of DIC detectors to simultaneously measure the overall morphology of the area to obtain morphological images of the lightweight, retractable structure from various perspectives.

[0020] 7) The obtained topographic images of the lightweight retractable structure from various perspectives are processed on the image processing industrial control computer to obtain the full-field three-dimensional appearance of the lightweight retractable structure at each time point, and finally a three-dimensional dynamic evolution diagram of the support structure's retraction process is generated.

[0021] The step of generating a projected speckle map based on set environmental parameters includes: constructing a mathematical model for the collaborative optimization of speckle size, density, and imaging resolution, and generating an initial projected speckle map based on the model; the environmental parameters include: the object distance for camera photography, the size of the projected area, the pixel size of speckle particles in the speckle map captured by the camera, the speckle coverage, and the speckle contrast threshold adjustment coefficient.

[0022] The construction of a mathematical model for the coordinated optimization of speckle size, density, and imaging resolution, and the generation of an initial projected speckle map based on this model, includes:

[0023] Based on the pixel size of the speckle particles, the pixel size of the speckle particles in the projected speckle image, the number of speckles n in the projected speckle image, and the speckle contrast threshold ξ in the projected speckle image are calculated. k ;

[0024] Based on the number of speckles n and the speckle contrast threshold ξ k The projected speckle map is generated using a two-dimensional Gaussian function.

[0025] The pixel size of the speckle particles in the projected speckle pattern Where d img p is the pixel size of the speckle grains, k is the pixel size of the speckle grains in the speckle image captured by the DIC camera, and p cam Where N is the pixel size of the DIC camera, f is the focal length of the DIC camera, d is the object distance for the DIC camera, and N is the distance between the pixels and the image. proj-piels For the horizontal pixels of the projector, W screen The physical width of the projection area.

[0026] The number of speckles in the projected speckle map Where n is the number of speckles in the projected speckle map, and c r S represents the speckle coverage. proj-pixels This refers to the resolution of the projector.

[0027] The formula for the speckle contrast threshold in the projected speckle map is: k = 1, 2, ..., n, where ξ k For the k-th speckle contrast threshold, The background gray level is measured for the k-th speckle pattern, and α1 and α2 are adjustment coefficients.

[0028] The two-dimensional Gaussian function is: Among them, (x k ,y k ) represents the image coordinates of the speckle pattern, A k The grayscale amplitude is related to ξ. k Equal, σ k To control the speckle size and meet the requirements

[0029] During the opening of the roller shutter-type product unfolding and retracting mechanism, the unfolding and retracting speed of the tested part is controlled by the roller shutter-type product unfolding and retracting mechanism, with a speed range of 10mm / s to 50mm / s.

[0030] The beneficial effects of this invention are: This invention uses a digital projector to dynamically generate adjustable speckle patterns, combined with a high-speed camera for measurement, to achieve non-contact full-field measurement of the unfolding morphology of lightweight flexible structures. It can capture structural deformation in real time and accurately identify nonlinear behaviors such as local buckling, providing key data support for optimizing product process design. It is suitable for ground testing and on-orbit monitoring of deployable structures in spacecraft. Attached Figure Description

[0031] Figure 1 The flowchart illustrates a method for dynamically measuring the morphology of a lightweight, expandable structure according to the present invention.

[0032] Figure 2 A schematic diagram illustrating the structure of a method and apparatus for dynamically measuring the morphology of a lightweight, expandable, and retractable structure. Detailed Implementation

[0033] This invention provides a lightweight, deployable, and retractable structural morphology dynamic measurement device, comprising a DIC laser speckle projection detection device, a multi-view stereo calibration block, a target sphere, a roller shutter-type product deployment and retraction mechanism, and an image processing industrial control computer; wherein,

[0034] The DIC laser speckle projection inspection device is a combination of a binocular DIC detector and a laser speckle projector, used to inspect the morphology of lightweight, expandable structures.

[0035] A roller shutter-type product unfolding and retracting mechanism is used to fix the lightweight unfolding and retracting structural component to be measured and drive its movement to produce unfolding and retracting shape changes;

[0036] Multi-view stereo calibration block, used to calibrate DIC laser speckle projection detection device;

[0037] The target ball is used to verify the measurement accuracy of the DIC laser speckle projection detection device and to determine the ready status of the DIC laser speckle projection detection device.

[0038] An image processing industrial control computer is used to drive the DIC laser speckle projection detection device and the roller shutter-type product unfolding and retracting mechanism to work together to complete the projection, calculate the appearance, and finally output a measurement report.

[0039] This invention also relates to a method for dynamically measuring the morphology of a lightweight, expandable structure, comprising the following steps:

[0040] a. Construct a lightweight, deployable, and retractable structural morphology dynamic measurement device. This includes 3 sets of DIC laser speckle projection detection devices, 1 multi-view stereo calibration block, 1 dedicated target ball, 1 roller shutter-type product deployment and retraction mechanism, 1 image processing industrial control computer, and the lightweight, deployable, and retractable structural component. The lightweight, deployable, and retractable structural component is the object being measured; the roller shutter-type product deployment and retraction mechanism is used to fix the lightweight, deployable, and retractable structural component and drive its movement to produce morphological changes during deployment and retraction; the multi-view stereo calibration block is used to calibrate the 3 sets of DIC laser speckle projection detection devices; the dedicated target ball is used to verify the system's measurement accuracy and determine the system's readiness status; the image processing industrial control computer is used to drive the DIC laser speckle projection detection device system and the roller shutter-type product deployment and retraction mechanism to work collaboratively, completing projection, image acquisition, morphology calculation, and outputting a measurement report; the 3 sets of DIC laser speckle projection detection devices are evenly placed around the measured area, with an angle of 120° between them.

[0041] b. Place a multi-eye stereo calibration block in the area to be measured and perform single-group DIC calibration and three-group DIC stereo calibration.

[0042] c. Design the projected speckle map based on environmental configuration parameters. Construct a collaborative optimization mathematical model of "speckle size-density-imaging resolution," and generate an initial projected speckle map based on this model. The main parameters include: object distance for camera capture, projection area size, pixel size of speckle particles in the speckle map captured by the camera, speckle coverage, and speckle contrast threshold adjustment coefficient. The specific steps are as follows:

[0043] 1) Calculate the pixel size of the speckle grains in the projected speckle map. Calculation formula: Where d img p represents the pixel size of the speckle grains, k is the pixel size of the speckle grains in the speckle image captured by the DIC camera (default 3~5), and p cam Where N is the pixel size of the DIC camera, f is the focal length of the DIC camera, d is the object distance for the DIC camera, and N is the distance between the pixels and the image. proj-piels For the horizontal pixels of the projector, W screen The physical width of the projection area.

[0044] 2) Calculate the number of speckles in the projected speckle map. Calculation formula: Where n is the number of speckles in the projected speckle map, and c r S represents the speckle coverage (default 30%–50%). proj-pixel This refers to the resolution of the projector.

[0045] 3) Calculate the speckle contrast threshold in the projected speckle map. Calculation formula: k = 1, 2, ..., n, where ξ k For the k-th speckle contrast threshold, The background gray level is measured for the k-th speckle pattern, and α1 and α2 are adjustment coefficients (it is recommended that ξ be between 140 and 200).

[0046] 4) Based on the number of speckles n and the speckle contrast threshold ξ k The projected speckle map is generated using a two-dimensional Gaussian function. The function formula is: (x k ,y k ) represents the image coordinates of the speckle pattern, A k grayscale amplitude (and ξ) k (same numerical value) σ k To control the speckle size (satisfy) ).

[0047] d. Place a special target ball at the center of the area to be measured, turn on the laser speckle projection device, and project a speckle pattern onto the surface of the special target ball;

[0048] e. Measure the morphology of the special target sphere using a multi-view DIC detector, fit the sphere diameter, and calculate the deviation.

[0049] f. If the deviation exceeds the allowable value (0.05 pixels), fine-tune the object distance or projection area of ​​the camera and repeat steps c to e until the deviation is less than the allowable value.

[0050] g. Place a lightweight, retractable structure in the center of the area to be tested, open the roller shutter-type product unfolding mechanism, and use a multi-eye DIC detector to simultaneously measure the overall morphology of the field.

[0051] h. Data processing is performed on an image processing industrial control computer to obtain the full-field three-dimensional appearance of the lightweight retractable structure at each time point, and finally a three-dimensional dynamic evolution diagram of the support structure's retraction process is generated.

[0052] The DIC laser speckle projection detection device is a combination of a binocular DIC detector and a laser speckle projector, such as Figure 1 As shown.

[0053] The multi-view stereo calibration block is a triangular prism with a carbon fiber structure, its size being the size of the measured area × (0.7~1.0), with at least 10~15 random marking points (inner circle diameter 6mm) on each side. Figure 1 As shown.

[0054] The specialized target ball is a high-precision target ball with a base, made of aluminum alloy, with a diameter of 90mm and a coefficient of thermal expansion of 23.4×10⁻⁶. -6 / K, control accuracy 1µm, surface frosted coating treatment;

[0055] The specific operation of generating the projected speckle map based on environmental configuration (or adjustment) parameters involves constructing a collaborative optimization mathematical model of "speckle size-density-imaging resolution," and generating an initial projected speckle map based on this model. The parameters mainly include: the object distance for camera capture, the size of the projected area, the pixel size of the speckle particles in the speckle map captured by the camera, the speckle coverage, and the speckle contrast threshold adjustment coefficient. The specific steps are as follows:

[0056] 1) Calculate the pixel size of the speckle grains in the projected speckle map. Calculation formula: Where d img p represents the pixel size of the speckle grains, k is the pixel size of the speckle grains in the speckle image captured by the DIC camera (default 3~5), and p cam Where N is the pixel size of the DIC camera, f is the focal length of the DIC camera, d is the object distance for the DIC camera, and N is the distance between the pixels and the image. proj-piels For the horizontal pixels of the projector, W screen The physical width of the projection area.

[0057] For example: a DIC camera has a resolution of 2448×2048, a pixel size of 0.0055mm, a focal length of 50mm, and an object distance of 1000mm; a projector has a resolution of 1920×1080 and a projection area of ​​400mm×300mm.

[0058] 2) Calculate the number of speckles in the projected speckle map. Calculation formula: Where n is the number of speckles in the projected speckle map, and c r S represents the speckle coverage (default 30%–50%). proj-pixel This refers to the resolution of the projector.

[0059] 3) Calculate the speckle contrast threshold in the projected speckle map. Calculation formula: k = 1, 2, ..., n, where ξ k For the k-th speckle contrast threshold, The background gray level is measured for the k-th speckle pattern, and α1 and α2 are adjustment coefficients (it is recommended that ξ be between 140 and 200).

[0060] 4) Based on the above parameters, generate a projected speckle map using a two-dimensional Gaussian function. Function formula: (x k ,y k ) represents the image coordinates of the speckle pattern, A k grayscale amplitude (and ξ) k (same numerical value) σ k To control the speckle size (satisfy) ).

[0061] The product unfolding and retracting mechanism can control the unfolding and retracting speed of the tested part, with a speed range of 10mm / s to 50mm / s.

Claims

1. A lightweight deployable structure morphing dynamic measurement device, characterized in that, The device comprises a DIC laser speckle projection detection device, a multi-view stereo calibration block, a target ball, a rolling shutter product deployment mechanism and an image processing industrial computer. The DIC laser speckle projection detection device is a combination of a binocular DIC detector and a laser speckle projector, which is used to detect the appearance of a lightweight deployable structure. The rolling shutter product deployment mechanism is used to fix the lightweight deployable structure to be measured and drive the movement of the lightweight deployable structure to generate the morphological changes of deployment. The multi-view stereo calibration block is used to calibrate the DIC laser speckle projection detection device. The target ball is used to verify the measurement accuracy of the DIC laser speckle projection detection device and determine the readiness of the DIC laser speckle projection detection device. The image processing industrial computer is used to drive the DIC laser speckle projection detection device and the rolling shutter product deployment mechanism to work together, complete the projection and appearance calculation and finally obtain the measurement results.

2. The apparatus of claim 1, wherein, The DIC laser speckle projection detection device has three sets, and the three sets of DIC laser speckle projection detection devices are uniformly placed around the measured area with an angle of 120° between each other.

3. The apparatus of claim 1, wherein, The multi-view stereo calibration block is a carbon fiber structure triangular prism with a size of (0.7-1.0) times the size of the measured area, and a plurality of circular marker points are randomly attached to each side of the prism.

4. The apparatus of claim 1, wherein, The target ball is a base-equipped target ball, which is made of aluminum alloy, has a thermal expansion coefficient of 23.4x10 -6 / K, a control precision of 1um, and a surface sanding coating treatment.

5. A method for dynamic measurement of the shape of a lightweight deployable structure using the apparatus of claim 2, characterized in that, The device comprises: 1) Place the multi-view stereo calibration block in the measured area, and perform single-view angle calibration of the binocular DIC detector in the single-set DIC laser speckle projection detection device and stereo calibration of the binocular DIC detector in the three-set DIC laser speckle projection detection device, respectively, to determine the coordinate conversion relationship between the three sets of binocular DIC detectors. 2) Generate a projection speckle pattern according to the set environmental parameters. 3) Place the target ball in the center of the measured area, turn on the laser speckle projection device, and project the generated projection speckle pattern onto the surface of the target ball. 4) Measure the appearance of the target ball by the three sets of DIC detectors, fit the diameter of the target ball appearance, and then subtract the nominal diameter of the target ball to obtain the deviation. 5) If the deviation exceeds the allowable value, adjust the environmental parameters for camera shooting, and repeat steps 2) to 4) until the deviation is less than the allowable value, and then proceed to step 6). 6) Place the lightweight deployable structure to be measured in the center of the measured area, turn on the rolling shutter product deployment mechanism, and measure the full-field appearance of the lightweight deployable structure at each view by the three sets of DIC detectors. 7) Process the obtained appearance of the lightweight deployable structure at each view on the image processing industrial computer to obtain the full-field three-dimensional appearance of the lightweight deployable structure at each time point, and finally generate a three-dimensional appearance dynamic evolution diagram of the support structure deployment process.

6. The method of claim 5, wherein, The generation of the projection speckle pattern according to the set environmental parameters comprises constructing a speckle size-density-imaging resolution collaborative optimization mathematical model and generating an initial projection speckle pattern according to the model.

7. The method of claim 6, wherein, The construction of the speckle size-density-imaging resolution collaborative optimization mathematical model and the generation of the initial projection speckle pattern according to the model comprise: According to the pixel size of the speckle particles, the pixel size of the speckle particles in the projected speckle pattern, the number n of speckles in the projected speckle pattern and the speckle contrast threshold ξ in the projected speckle pattern are calculated k ; According to the speckle number n and the speckle contrast threshold ξ k The projected speckle pattern is generated using a two-dimensional Gaussian function.

8. The method of claim 6, wherein, Pixel size of speckle grains in the projected speckle pattern where d img is the pixel size of speckle grains, k is the pixel size of speckle grains in the speckle pattern captured by the DIC camera, p cam is the pixel size of the DIC camera, f is the focal length of the DIC camera, d is the object distance at which the DIC camera is taking the picture, N proj-piels is the number of horizontal pixels of the projector, W screen is the physical width of the projection area.

9. The method of claim 8, wherein, the number of speckles in the projected speckle pattern where n is the number of speckles in the projected speckle pattern, c r is the speckle coverage, S proj-pixels is the resolution of the projector.

10. The method of claim 9, wherein, The speckle contrast threshold formula in the projection speckle pattern is: Wherein ξ k is the kth speckle contrast threshold, is the kth speckle measurement background gray, and α1 and α2 are adjustment coefficients.

11. The method of claim 10, wherein, The two-dimensional Gaussian function is: wherein (x k ,y k ) is the image coordinate of the speckle, A k is the gray amplitude, the numerical value is equal to ξ k , and σ k is the control speckle size, and satisfies 12. The method of claim 6, wherein, During the opening process of the roller shutter product display and collection mechanism, the roller shutter product display and collection mechanism controls the display and collection movement speed of the measured piece, and the speed range is 10mm / s~50mm / s. During the opening process of the roller shutter product display and collection mechanism, the roller shutter product display and collection mechanism controls the display and collection movement speed of the measured piece, and the speed range

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