A multi-frequency linear array laser three-dimensional precision scanning method based on metasurface array

Abstract

The present invention discloses a multi-frequency linear array laser three-dimensional precision scanning method based on a metasurface array, including two laser linear array coding measurement modes of multi-frequency discrete and multi-frequency fusion. Based on a multi-frequency laser light source, a rectangular aperture, a filter array and a metasurface array, a refined discrete focus projection or fusion focus projection of a multi-frequency laser linear array on the surface of a target object can be realized. The projected laser linear array on the surface of the target object is imaged through an imaging lens and a photosensitive element, and the surface contour information of the target object is obtained by solving the geometric relationship of triangulation. This method uses a metasurface to replace traditional complex and bulky projection equipment, with a compact structure and strong functionality. It can realize diffraction-limited focus projection of multi-frequency linear array lasers, improve scanning accuracy and measurement resolution, and the coding measurement mode can adapt to the surface of target objects of different materials, taking into account both measurement efficiency and contour reconstruction integrity.

Description

Technical Field

[0001] The present invention belongs to the technical field of three-dimensional precision scanning, and in particular relates to a multi-frequency linear array laser three-dimensional precision scanning method based on a metasurface array. Background Art

[0002] 3D scanning technology is widely used in aerospace, automotive and other fields. It can realize the 3D shape reconstruction of cross-scale parts in complex industrial scenes, and can effectively promote intelligent manufacturing to achieve industrial digitalization. Optical line laser 3D scanning technology uses the principle of triangulation of multi-eye vision to achieve 3D digital reconstruction by imaging the projected laser line. It has the characteristics of light equipment, handheld measurement, and strong adaptability to light environment.

[0003] Although the traditional single-line laser scanning technology has a simple structure and low cost, its scanning speed is very slow, which seriously restricts the improvement of measurement efficiency. The multi-line laser scanning technology generates multiple projected laser lines to form a linear array laser. Different laser lines can be scanned in parallel to improve the scanning efficiency exponentially, but at the same time, it puts forward more complex design goals for its internal optical components, resulting in increased costs and reduced portability of the equipment. In addition, the linear array laser in the above-mentioned line laser scanning technology is usually a point light source generated by a cylindrical lens, Powell prism or traditional DOE diffraction element, which has a large focusing aberration. Therefore, the projected laser line width is relatively large, often more than tens of microns, which greatly limits the scanning accuracy. Summary of the invention

[0004] In view of the defects of the prior art, the present invention provides a multi-frequency linear array laser three-dimensional precision scanning method based on a metasurface array to solve the above-mentioned technical problems.

[0005] The technical solution of the present invention is as follows:

[0006] A multi-frequency linear array laser three-dimensional precision scanning method based on a metasurface array, that is, using a metasurface to achieve an ideal aberration-free focusing technology for a linear array laser, includes the following steps:

[0007] First, select the multi-frequency discrete or multi-frequency fusion linear array laser coding measurement mode according to the surface material distribution characteristics of the target object;

[0008] When the multi-frequency discrete linear array laser coding measurement mode is selected, based on the multi-frequency laser light source (1), the rectangular aperture (2), the filter array (3) and the metasurface array (4), it is possible to achieve refined discrete focusing projection of the multi-frequency linear array laser on the surface of the target object to be measured, and project linear array lasers of different frequencies onto different material areas according to the surface material of the target object to be measured;

[0009] When the multi-frequency fused linear array laser coding measurement mode is selected, based on the multi-frequency laser light source (1), the rectangular aperture (2) and the metasurface array (4), it is possible to achieve refined fused focusing projection of the multi-frequency linear array laser on the surface of the target object to be measured, and the fused linear array laser can be used to measure the target object to be measured with complex surface materials;

[0010] The projected linear array laser imaging of the surface of the target object is performed by calibrating the camera 1 (5) and the camera 2 (6), and the surface contour information of the target object is obtained by solving the triangulation geometric relationship. The camera 1 (5) and the camera 2 (6) are respectively composed of an imaging lens and a photosensitive element.

[0011] Furthermore, the achromatic metasurface is designed to form a metasurface array using the wavefront phase control principle, where the phase distribution of a single metasurface satisfies the following formula:

[0012]

[0013] Where r is the distance from the center of the element, λ is the designed working wavelength of the light, f is the focal length, and C is the reference phase.

[0014] Furthermore, the multi-frequency discrete linear array laser coding measurement mode specifically works as follows: the multi-frequency laser emitted by the multi-frequency laser light source (1) is transformed into a rectangular light spot through a rectangular aperture (2), and the light of the specified wavelength is selected after filtering by the filter array (3) to enter the metasurface array (4), and the metasurface array (4) then focuses the incident light of different frequencies and projects it onto the target object to be measured. By projecting laser lines of up to 6 different frequencies onto different areas on the surface of the target object to be measured, efficient parallel scanning of the surface contour of the target object to be measured can be achieved, and the frequency of the laser line is set according to the material difference of each area.

[0015] Furthermore, the multi-frequency fusion linear array laser coding measurement mode specifically works as follows: the multi-frequency laser emitted by the multi-frequency laser light source (1) is transformed into a rectangular light spot through the rectangular aperture (2), and the multi-frequency laser is fused and focused and projected onto the target object by the metasurface array (4). By projecting laser lines containing up to 6 different frequencies onto the surface of the target object, the projected laser frequency is set according to the surface material of the target object, and scanning data of multiple frequencies can be obtained in a single scan. For target objects with complex and changeable surface materials, scanning data of different frequencies are fused and complemented with each other to obtain a complete high-quality scanning result.

[0016] Furthermore, the metasurface array is composed of a periodic subwavelength dielectric nanounit structure or a metal nanounit structure, and the metasurface array realizes wavefront phase control based on the principle of propagation phase, geometric phase or resonance phase.

[0017] Furthermore, the geometric shape of the nanounit structure in the metasurface array is a rotationally symmetric cylinder or torus, or a column with anisotropic cross-section, such as a rectangle, an ellipse, a polygon, or any combination of the above shapes. The nanounit structure is arranged in a square or hexagonal unit periodicity to form a metasurface.

[0018] Furthermore, the metasurface array can operate in the visible light and near-infrared frequency range by modifying the geometry and arrangement of the nanounit structure according to the surface material characteristics of the target object.

[0019] Furthermore, the metasurface array performs multi-objective optimization design on the geometric shape and arrangement of the nanounit structure to achieve refined discrete focusing and refined fusion focusing of 1 to 6 linear array lasers of different frequencies, thereby obtaining a linear array laser with a line width close to the diffraction limit.

[0020] Furthermore, the imaging lens is composed of traditional optical elements, or is replaced by a metasurface with the same function.

[0021] Furthermore, when the nanounit structure is anisotropic in shape, polarizers and wave plates need to be arranged on both sides of the metasurface to obtain the desired polarized light.

[0022] The beneficial effects of the present invention are:

[0023] 1) Using metasurface arrays to replace traditional large-volume beam shaping elements can achieve linear array laser projection of various frequencies. Its thickness is only less than 1 mm, making the device more compact and easy to use.

[0024] 2) Through precise control of the wavefront phase, the metasurface array can achieve a focusing imaging effect close to the diffraction limit, greatly reducing the width of the projected laser line, thereby improving the measurement resolution of the system.

[0025] 3) Two multi-frequency linear array laser coding measurement modes are proposed: for the case where the surface material boundaries of the target object are clearly divided, the multi-frequency discrete linear array laser coding measurement mode is used to double the scanning efficiency while ensuring the quality of the scanning data; and for the case where the surface material of the target object is complex and changeable, the multi-frequency fusion linear array laser coding measurement mode is used to make the scanning data of different frequencies merge and complement each other, so as to realize the complete reconstruction of the surface contour of the target object and avoid the problem of contour reconstruction failure or loss due to abnormal response of a single frequency light in some material areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the multi-frequency discrete linear array laser encoding three-dimensional scanning measurement of the metasurface array of the present invention.

[0027] Figure 2 This is a schematic diagram of the three-dimensional scanning measurement of the multi-frequency fusion linear array laser encoding of the metasurface array of the present invention.

[0028] Figure 3 This is a schematic diagram of the linear array laser triangulation measurement principle of the present invention.

[0029] Figure 4 Schematic diagram of two linear array laser coding measurement modes of the present invention.

[0030] Figure 5 These are imaging diagrams of projected laser lines of different laser frequencies on different surface materials of the present invention.

[0031] Figure 6 Schematic diagram of the cross-sectional geometry of the supersurface array nanounit structure of the present invention.

[0032] Figure 7 Schematic diagram of the fine focusing of the supersurface linear array laser of the present invention.

[0033] Among them, 1-multi-frequency laser light source, 2-rectangular aperture, 3-filter array, 4-metasurface array, 5-camera one, 6-camera two. DETAILED DESCRIPTION

[0034] To make the purpose, technical solution and advantages of the present invention clearer, the following is further described in detail with reference to the accompanying drawings and embodiments. However, it should be understood that the embodiments specifically described herein are only used to explain the present invention and are not intended to limit the scope of protection of the present invention in any way.

[0035] The present invention discloses a multi-frequency linear array laser three-dimensional precision scanning method based on a metasurface array, that is, utilizing a metasurface to realize an ideal aberration-free focusing technology of a linear array laser, including two linear array laser coding measurement modes: multi-frequency discrete and multi-frequency fusion.

[0036] First, select the multi-frequency discrete or multi-frequency fusion linear array laser coding measurement mode according to the surface material distribution characteristics of the target object;

[0037] When the multi-frequency discrete linear array laser coding measurement mode is selected, based on the multi-frequency laser light source 1, the rectangular aperture 2, the filter array 3 and the metasurface array 4, it is possible to achieve refined discrete focusing projection of the multi-frequency linear array laser on the surface of the target object to be measured, and project linear array lasers of different frequencies onto different material areas according to the surface material of the target object to be measured;

[0038] When the multi-frequency fused linear array laser coding measurement mode is selected, based on the multi-frequency laser light source 1, the rectangular aperture 2 and the metasurface array 4, the multi-frequency linear array laser on the surface of the target object can be finely fused and focused, and the fused linear array laser can be used to measure the target object with complex surface material;

[0039] The projected linear array laser imaging of the surface of the target object is performed by calibrated camera 1 5 and camera 2 6, and the surface contour information of the target object is obtained according to the triangulation geometric relationship. The camera 1 5 and camera 2 6 are respectively composed of an imaging lens and a photosensitive element.

[0040] Furthermore, the achromatic metasurface is designed to form a metasurface array using the wavefront phase control principle, where the phase distribution of a single metasurface satisfies the following formula:

[0041]

[0042] Where r is the distance from the center of the element, λ is the designed working wavelength of the light, f is the focal length, and C is the reference phase.

[0043] Furthermore, the specific working method of the multi-frequency discrete linear array laser coding measurement mode is as follows: the multi-frequency laser emitted by the multi-frequency laser light source 1 is transformed into a rectangular light spot through the rectangular aperture 2, and the light of the specified wavelength is selected after filtering by the filter array 3 to enter the metasurface array 4, and the metasurface array 4 then focuses the incident light of different frequencies and projects it onto the target object to be measured. By projecting up to 6 laser lines of different frequencies onto different areas on the surface of the target object to be measured, efficient parallel scanning of the surface contour of the target object to be measured can be achieved, and the frequency of the laser line is set according to the material difference of each area.

[0044] Furthermore, the specific working method of the multi-frequency fusion linear array laser coding measurement mode is as follows: the multi-frequency laser emitted by the multi-frequency laser light source 1 is transformed into a rectangular light spot through the rectangular aperture 2, and the multi-frequency laser is fused and focused and projected onto the target object by the metasurface array 4. By projecting laser lines containing up to 6 different frequencies onto the surface of the target object, the projected laser frequency is set according to the surface material of the target object, and scanning data of multiple frequencies can be obtained in a single scan. For target objects with complex and changeable surface materials, scanning data of different frequencies are fused and complemented with each other to obtain a complete high-quality scanning result.

[0045] Furthermore, the metasurface array is composed of a periodic subwavelength dielectric nanounit structure or a metal nanounit structure, and the metasurface array realizes wavefront phase control based on the principle of propagation phase, geometric phase or resonance phase.

[0046] Furthermore, the geometric shape of the nanounit structure in the metasurface array is a rotationally symmetric cylinder or torus, or a column with anisotropic cross-section, such as a rectangle, an ellipse, a polygon, or any combination of the above shapes. The nanounit structure is arranged in a square or hexagonal unit periodicity to form a metasurface.

[0047] Furthermore, the metasurface array can operate in the visible light and near-infrared frequency range by modifying the geometry and arrangement of the nanounit structure according to the surface material characteristics of the target object.

[0048] Furthermore, the metasurface array performs multi-objective optimization design on the geometric shape and arrangement of the nanounit structure to achieve refined discrete focusing and refined fusion focusing of 1 to 6 linear array lasers of different frequencies, thereby obtaining a linear array laser with a line width close to the diffraction limit.

[0049] Furthermore, the imaging lens in the camera is composed of traditional optical elements, or is replaced by a metasurface with the same function.

[0050] Furthermore, when the nanounit structure is anisotropic in shape, polarizers and wave plates need to be arranged on both sides of the metasurface to obtain the desired polarized light.

[0051] It should be noted that Figure 1 and Figure 2 The distance between the projected laser lines can be adjusted by changing the size of each filter and metasurface in the filter array 3 and the metasurface array 4.

[0052] Before the actual scanning measurement, the camera and the projected laser plane need to be calibrated. The camera (including camera 1 5 and camera 2 6) is calibrated by shooting a target composed of reflective points, shooting multi-angle variable distance images and optimizing the camera internal and external parameters; the calibration is completed by fitting the plane equation with the spatial laser line coordinates calculated by projecting multi-frequency laser on a white plane. Figure 3 As shown, in the subsequent 3D scanning measurement process, the linear array laser projection moves and scans the target object, and the camera records the corresponding scanning process image, completes the laser line matching and numbering of the binocular camera image, and according to the relative posture and other parameters of the camera and the laser line in the process, the camera imaging model and the laser plane equation are combined, and the 3D spatial coordinates of the current measuring point can be obtained by calculation, thereby reconstructing the 3D contour of the target object.

[0053] The achromatic metasurface is designed based on the wavefront phase control principle to form a metasurface array, where the phase distribution of a single metasurface satisfies the following formula:

[0054]

[0055] Where r is the distance from the center of the element, λ is the designed working wavelength of the light, f is the focal length, and C is the reference phase.

[0056] like Figure 4As shown in (a), the multi-frequency discrete linear array laser coding measurement mode can realize efficient parallel scanning of the surface contour of the target object by projecting three laser lines of different frequencies onto different areas on the surface of the target object. The corresponding frequency of laser lines can be set for each area according to the material difference to obtain high-quality scanning results.

[0057] like Figure 4 As shown in (b), the multi-frequency fusion linear array laser coding measurement mode projects laser lines containing three different frequencies onto the surface of the target object. A single scan can obtain scanning data of multiple frequencies. For target objects with complex and changeable surface materials, the scanning data of different frequencies can be fused and complemented to obtain a complete high-quality scanning result.

[0058] The metasurface array 4 is composed of a periodic sub-wavelength dielectric or metal nano-unit structure, and realizes wavefront phase control based on the principle of propagation phase, geometric phase or resonance phase.

[0059] like Figure 5 As shown in the figure, in the above two linear array laser coding measurement modes, the projection laser lines of different frequencies have significant differences in imaging effects on target objects with different surface materials, which has a huge impact on the final 3D reconstruction accuracy. Among them, the reflection imaging of the red frequency laser line is more obvious on the surface of plastic materials, so the reconstruction effect is better; while the surface of metal materials needs to be under the blue frequency laser line to obtain better imaging and reconstruction effects. Therefore, when the target object has a combination of multiple surface materials or the surface material is complex and changeable, the use of multi-frequency linear array laser for scanning measurement can obtain a complete and high-precision 3D profile of the target object.

[0060] like Figure 6 As shown, the geometric shape of the nano-unit structure in the supersurface array 4 can be designed as a rotationally symmetric cylinder or torus, or can be designed as a column with anisotropic cross-section, such as a rectangle, an ellipse, a polygon, or any combination of the above shapes. The nano-unit structure is arranged and combined into a supersurface with a square or hexagon as a unit periodicity.

[0061] The metasurface array 4 can operate in the visible light and near-infrared bands by modifying the basic parameters of the nanounit structure according to application requirements.

[0062] like Figure 7 As shown, the metasurface array 4 can achieve refined discrete focusing and refined fusion focusing of 1 to 6 linear array lasers of different frequencies by performing multi-objective optimization design on the geometric shape and arrangement of the nanounit structure, and obtain a linear array laser with a line width close to the diffraction limit.

[0063] For the problem that traditional diffraction elements have a certain aberration and the focal line width is too large to distinguish the small microstructure features on the surface, the use of metasurfaces to obtain diffraction-limited focused linear array lasers can improve the resolution of scanning measurements and achieve refined reconstruction of surface microstructures.

[0064] The multi-objective optimization design method is further explained below.

[0065] The reference phase C(λ) in the above-mentioned metasurface phase distribution formula is used as the optimization variable, and the particle swarm optimization algorithm is applied to take the C(λ) value at different frequencies as the position of the particle, and the number of projection frequencies as the optimization dimension. The difference between the actual phase and the ideal phase achieved by the initial metasurface (i.e., the wave phase difference) is calculated as the fitness of the evaluation function, and the designed metasurface wave phase difference is continuously iterated by optimizing the reference phase with the minimum wave phase difference as the goal. Among them, the initial metasurface is: a metasurface composed of the geometric shape and arrangement of the initial nanounit structure generated according to the initial reference phase C0 with the ideal phase as the goal. With the continuous iteration of the reference phase C(λ), the geometric shape and arrangement of the corresponding nanounit structure are also continuously updated to achieve the optimization of the wave phase difference of the metasurface. During the optimization process, the genetic algorithm is combined to accelerate the convergence speed of the algorithm by introducing the crossover and mutation process of particles with high fitness. When the wave phase difference of the metasurface is less than the set minimum wave phase difference, the iteration process ends, and the optimization design of the metasurface is completed.

[0066] As a preferred implementation, the multi-objective optimization design methods that can be used also include simulated annealing, firefly algorithm, ant colony optimization algorithm and neural network optimization method.

[0067] The imaging lens in the camera can be composed of traditional optical components or replaced by a metasurface with the same function.

[0068] When the nano unit structure is anisotropic in shape, polarizers and wave plates need to be arranged on both sides of the metasurface to obtain the required polarized light.

[0069] The above embodiments are preferred implementations of the present invention, and are only used to illustrate the technical concept and features of the present invention. The purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and it cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A multi-frequency linear array laser three-dimensional precision scanning method based on a metasurface array, characterized in that: The steps include: First, select the multi-frequency discrete or multi-frequency fusion linear array laser coding measurement mode according to the surface material distribution characteristics of the target object; When the multi-frequency discrete linear array laser coding measurement mode is selected, based on the multi-frequency laser light source (1), the rectangular aperture (2), the filter array (3) and the metasurface array (4), it is possible to achieve refined discrete focusing projection of the multi-frequency linear array laser on the surface of the target object to be measured, and project linear array lasers of different frequencies onto different material areas according to the surface material of the target object to be measured; When the multi-frequency fused linear array laser coding measurement mode is selected, based on the multi-frequency laser light source (1), the rectangular aperture (2) and the metasurface array (4), it is possible to achieve refined fused focusing projection of the multi-frequency linear array laser on the surface of the target object to be measured, and the fused linear array laser can be used to measure the target object to be measured with complex surface materials; The projected linear array laser imaging of the surface of the target object is performed by pre-set camera 1 (5) and camera 2 (6), and the surface contour information of the target object is obtained by solving the triangulation geometric relationship; the camera 1 (5) and camera 2 (6) are respectively composed of an imaging lens and a photosensitive element.

2. The method of three-dimensional precision scanning of multi-frequency linear laser based on metasurface array according to claim 1, characterized in that: The achromatic metasurface is designed based on the wavefront phase control principle to form a metasurface array, where the phase distribution of a single metasurface satisfies the following formula: Where r is the distance from the center of the element, λ is the designed working wavelength of the light, f is the focal length, and C is the reference phase.

3. The method of three-dimensional precision scanning of multi-frequency linear array laser based on metasurface array according to claim 1, characterized in that: The multi-frequency discrete linear array laser coding measurement mode specifically works as follows: the multi-frequency laser light emitted by the multi-frequency laser light source (1) is transformed into a rectangular light spot through a rectangular aperture (2), and the light of the specified wavelength is selected after filtering by the filter array (3) to enter the metasurface array (4), and the metasurface array (4) then focuses the incident light of different frequencies and projects it onto the target object to be measured. By projecting laser lines of up to 6 different frequencies onto different areas on the surface of the target object to be measured, efficient parallel scanning of the surface contour of the target object to be measured can be achieved, and the frequency of the laser line is set according to the material difference of each area.

4. The method of multi-frequency linear array laser three-dimensional precision scanning based on metasurface array according to claim 1, characterized in that: The multi-frequency fusion linear array laser coding measurement mode specifically works as follows: the multi-frequency laser emitted by the multi-frequency laser light source (1) is transformed into a rectangular light spot through a rectangular aperture (2), and the multi-frequency laser is fused and focused and projected onto the target object by the metasurface array (4). By projecting laser lines containing up to 6 different frequencies onto the surface of the target object, the projected laser frequency is set according to the surface material of the target object, and scanning data of multiple frequencies can be obtained in a single scan. For target objects with complex and changeable surface materials, scanning data of different frequencies are fused and complemented with each other to obtain a complete high-quality scanning result.

5. The method for three-dimensional precision scanning of multi-frequency linear array laser based on metasurface array according to claim 1 or 2, characterized in that: The metasurface array is composed of a periodic sub-wavelength dielectric nano-unit structure or a metal nano-unit structure, and the metasurface array realizes wavefront phase control based on the principle of propagation phase, geometric phase or resonance phase.

6. The method of three-dimensional precision scanning of multi-frequency linear array laser based on metasurface array according to claim 5, characterized in that: The nano-unit structure in the metasurface array has a rotationally symmetric cylinder or torus, or a rectangular, elliptical, polygonal or any combination of the above shapes with anisotropic cross-section. The nano-unit structure is arranged in a square or hexagonal unit periodicity to form a metasurface.

7. The method of three-dimensional precision scanning of multi-frequency linear array laser based on metasurface array according to claim 6, characterized in that: The metasurface array can operate in the visible light and near-infrared frequency range by modifying the geometric shape and arrangement of the nanounit structure according to the surface material characteristics of the target object.

8. The method of multi-frequency linear array laser three-dimensional precision scanning based on metasurface array according to claim 6, characterized in that: The metasurface array achieves refined discrete focusing and refined fusion focusing of 1 to 6 linear array lasers with different frequencies by performing multi-objective optimization design on the geometric shape and arrangement of the nanounit structure, thereby obtaining a linear array laser with a line width close to the diffraction limit.

9. The method of claim 1 for three-dimensional precision scanning of multi-frequency linear laser based on metasurface array, characterized in that: The imaging lens in the camera is composed of traditional optical elements, or is replaced by a metasurface with the same function.

10. A multi-frequency linear array laser three-dimensional precision scanning method based on a metasurface array according to any one of claims 6 to 8, characterized in that: When the nano unit structure is anisotropic in shape, polarizers and wave plates need to be arranged on both sides of the metasurface to obtain the required polarized light.

Images