Laser triangulation displacement measurement method and device using multi-eye metasurface

Abstract

The present invention discloses a laser triangulation displacement measurement method and device using a multi-eye metasurface. Firstly, based on the metasurface technology, the transmitting lens group, receiving lens group and filter in the traditional laser triangulation displacement sensor are integrated into an integrated multi-eye metasurface module, which can simultaneously realize the collimation of the emitted laser, the imaging of the scattered light spot on the target object to be measured, and the filtering of the non-working wavelength stray light in the environment. While having a very high functional integration, it also reduces the complexity of the system. By building a displacement calibration experimental platform, the target object to be measured is scanned, and the mapping relationship between the displacement of the target object to be measured and the equivalent light spot position is obtained to realize laser triangulation displacement measurement. The laser triangulation displacement measurement device of the present invention has a simple system composition, is easy to assemble, is compact and small as a whole, can be easily integrated on a motion device to achieve high-precision scanning, and is not prone to mechanical interference.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical precision measurement, and in particular relates to a laser triangulation displacement measurement method and device using a multi-eye metasurface. Background Art

[0002] Precision measurement technology plays a vital role in the context of the rapid development of science and technology, and is a necessary condition for promoting the development of high-end manufacturing. At this stage, precision measurement technology is gradually developing towards high precision, high integration, and online detection. The traditional laser triangulation method has been widely used in industrial production for geometric parameter detection and morphology measurement due to its advantages such as non-contact, high precision, and large range.

[0003] However, when the traditional laser triangulation method measures objects with different surface colors, roughness and curvature, the diffuse reflection spot obtained will produce serious distortion, and the intensity of the reflected light will also fluctuate violently, resulting in an increase in the spot positioning error and a reduction in the measurement accuracy. Chinese patent application CN106931888A discloses a dual-path laser displacement sensor, which introduces a left-right symmetrically arranged reflector in the traditional laser triangulation ranging sensor to superimpose the left and right imaging spots, thereby achieving compensation for the center of gravity offset of the spot. Compared with the solution of using two sets of receiving mirrors in the prior art, this method simplifies the system to a certain extent, but additionally introduces a reflector and a spectroscope, which increases the system volume and the complexity of system assembly. In addition, this method can only correct the influence of the center of gravity offset of the spot in the direction of the vertical dual-path symmetry plane. When facing some samples with complex surface curvature changes, when measuring surfaces with large curvature changes in the direction of the dual-path symmetry plane, obvious spot offset will still occur, which increases the measurement error.

[0004] In addition, when facing a measurement environment with strict space constraints, due to the large size of traditional laser triangulation distance measurement sensors, they will face the problem of being unable to measure. Taking deep hole measurement as an example, Chinese patent application CN104776807A proposes an aperture measurement method based on a staggered combination of laser triangulation displacement sensors, using two laser triangulation displacement sensors to be assembled in parallel and staggered to form a measurement system for aperture measurement; Chinese patent application CN113029016A proposes a deep hole measurement system and method based on a triangular radius measurement method, through three laser rangefinders arranged on the same cross section, using a triangle circumscribed circle to calculate the radius of the deep hole. It can be seen that these methods, in the space-constrained measurement environment represented by deep holes, the basic premise for achieving measurement is that the sensor is compact and can penetrate into the corresponding space-constrained measurement environment. However, the above-mentioned Chinese patent application only proposes a measurement method, but does not solve the key problem of implementing the method, that is, how to reduce the volume of the sensor so that it can adapt to the required space-constrained measurement environment. Summary of the invention

[0005] In view of the above-mentioned defects in the prior art, the present invention proposes a laser triangulation displacement measurement method and device using a multi-eye metasurface.

[0006] The technical solution of the present invention is as follows:

[0007] A laser triangulation displacement measurement method using a multi-eye metasurface comprises the following steps:

[0008] Step 1: Design and manufacture a collimating metasurface, fix it on the top of a micro positioning bracket, and use it to collimate and focus the output light of the laser onto the target object. Install an aperture between the laser and the collimating metasurface.

[0009] Step 2: design and manufacture four imaging metasurfaces, fix them in sequence on the circumferential inclined surface of the micro positioning bracket, and set the photosensitive device on the imaging surface behind the micro positioning bracket to realize multi-eye small aberration imaging of the laser spot on the target object.

[0010] Step 3: Build a displacement calibration experimental platform, scan the moving target object, superimpose the multi-eye imaging spots on the photosensitive device, calculate the equivalent spot position, obtain the mapping relationship between the displacement of the target object and the equivalent spot position, and realize laser triangulation displacement measurement.

[0011] Furthermore, in step 1, the method for designing and manufacturing the collimating metasurface is as follows:

[0012] Step 1-1, calculating the target phase profile required for the collimating metasurface according to the distance between the laser and the collimating metasurface, the laser beam diameter and the divergence angle;

[0013] Step 1-2, selecting a sub-wavelength nano-unit structure with a desired target phase response through simulation calculation, arranging the sub-wavelength nano-unit structure according to the target phase profile obtained in step 1-1, and generating a processing file for the collimated metasurface;

[0014] Steps 1-3, using micro-nano processing technology to prepare the aligned metasurface.

[0015] Furthermore, in step 2, the method for designing and manufacturing the imaging metasurface is as follows:

[0016] Step 2-1, based on the generalized Snell's law, establish a ray tracing model for the imaging metasurface, take the minimum imaging aberration as the optimization target, set the distance and inclination constraints between the photosensitive device, the imaging metasurface and the target object, and apply the multi-objective optimization algorithm to optimize the target phase profile of the imaging metasurface to obtain the target phase profile that can achieve small aberration imaging within the range. The target phase profile of the imaging metasurface can be expressed as follows:

[0017]

[0018] Where λ is the operating wavelength, f is the approximate focal length, r is the distance from the center of the imaging metasurface, and a i represents the phase correction coefficient of the i-th order polynomial, where n is the order of the polynomial.

[0019] Step 2-2, selecting a sub-wavelength nano-unit structure with a desired target phase response through simulation calculation, arranging the sub-wavelength nano-unit structure according to the target phase profile obtained in step 2-1, and generating a processing file for an imaging metasurface;

[0020] Step 2-3, using micro-nano processing technology to prepare the imaging metasurface.

[0021] By using the method of optimizing the target phase profile of the imaging metasurface in step 2, the relative tilt angle between the imaging metasurface and the photosensitive device can be reduced to zero, thereby transforming the micro positioning bracket into a planar structure, making the device more compact.

[0022] Furthermore, step 2-1 is specifically implemented as follows:

[0023] First, the distance and inclination constraints among the photosensitive device, the imaging metasurface and the target object are set so that the object-image distances l1 and l2 corresponding to the object-image conjugate points A1 and A2 meet the maximum and minimum value constraints, that is, l min <l1、l2<l max At the same time, the imaging inclination angles α and β also meet the maximum and minimum value constraints, that is, θ min <α、β<θ max The maximum and minimum limits of the above-mentioned object-image distance and imaging inclination angle can be set according to the needs of the actual measurement application process. The larger the ratio of image distance to object distance l2 / l1, the higher the measurement accuracy, but it will also cause the imaging aberration to become larger. The imaging inclination angles α and β respectively determine the scattered light intensity of the target object and the received light intensity of the photosensitive device, affecting the signal-to-noise ratio of the final imaging spot. Subsequently, the secondary phase profile that achieves off-axis near-perfect imaging is used as the initial target phase profile of the imaging metasurface, where the secondary phase profile can be expressed as: According to the established imaging metasurface ray tracing model, the imaging aberration of the imaging metasurface 5 within the measurement range is calculated and used as the optimization objective function, which can be specifically expressed as:

[0024] Finally, taking the minimum imaging aberration as the optimization goal, a multi-objective optimization algorithm is applied to optimize the target phase profile of the imaging metasurface. The object-image distances l1, l2 and the imaging inclination angles α, β are iteratively optimized to obtain the target phase profile that can achieve small aberration imaging within the range.

[0025] Furthermore, in step 3, the method for calculating the equivalent spot position is:

[0026] Taking the intersection of the symmetry axes of the four circumferentially distributed imaging metasurfaces and the photosensitive device as the origin, coordinate axes are established along the symmetry plane directions of the four imaging metasurfaces respectively, and the multi-eye imaging spots distributed on the four coordinate axes are superimposed. The spot estimation algorithm is used to locate the sub-pixel position of the superimposed spot to obtain the equivalent spot position.

[0027] A laser triangulation displacement measurement device using a multi-eye metasurface, comprising a photosensitive device, a laser, an aperture, a collimating metasurface, an imaging metasurface and a micro positioning bracket;

[0028] The micro positioning bracket adopts a bottomless tetrahedral pyramid transparent thin shell structure, the collimating metasurface is arranged at the center position of the top plane of the micro positioning bracket, the imaging metasurfaces are distributed on the inclined surfaces around the micro positioning bracket at equal intervals along the circumferential direction, the photosensitive device is arranged on the imaging surface of the imaging metasurface located behind the micro positioning bracket, the laser and the aperture are arranged between the photosensitive device and the collimating metasurface, wherein the collimating metasurface, the imaging metasurface and the micro positioning bracket together constitute a multi-eye metasurface module.

[0029] Furthermore, the aperture of the aperture is slightly larger than the diameter of the passing laser beam, which can prevent the aperture from reflecting the laser beam and block the backscattered light of the collimated metasurface, thereby eliminating the interference of the outgoing laser beam on the imaging quality of the photosensitive device.

[0030] Furthermore, the sub-wavelength nanostructured unit material on the collimating metasurface and the imaging metasurface is a transparent dielectric with a high refractive index.

[0031] Furthermore, the sub-wavelength nanometer unit structure is a column, and the cross-sectional geometric shape thereof is one or a combination of circular, rectangular, polygonal, and elliptical shapes.

[0032] Furthermore, the basic principle of the subwavelength nanounit structure to achieve phase control is: by changing the geometric size parameters of the subwavelength nanounit structure, the electromagnetic resonance in the high refractive index dielectric subwavelength nanounit structure is simultaneously excited, and the subwavelength nanounit structure is arranged to form a Huygens metasurface, so that it maintains high transmittance at the operating wavelength of the laser, while the transmittance at other wavelengths is close to zero, which can simultaneously play the role of laser beam collimation, imaging and filtering out stray light in other bands in the reflected light.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. Based on the metasurface technology, the present invention integrates the transmitting lens group, receiving lens group and filter in the traditional laser triangulation displacement sensor into an integrated multi-eye metasurface module. The module can simultaneously realize the collimation of the outgoing laser, the imaging of the scattered light spot on the target object, and the filtering of the non-working wavelength stray light in the environment. While having a very high functional integration, it also reduces the complexity of the system.

[0035] 2. The multi-eye metasurface module of the present invention can perform bidirectional compensation for the deviation of scattered light spots on target objects with complex surface curvature changes through four circumferentially symmetrically arranged imaging metasurfaces, breaking the limitation of the traditional method of using two sets of receiving mirrors to achieve only one-way compensation for the center of gravity deviation of light spots. It can truly adapt to the measurement of target objects with surface curvature changes in any direction and improve the displacement measurement accuracy.

[0036] 3. The imaging metasurface in the present invention has a free phase profile, which is different from the traditional hyperbolic phase profile metasurface that will produce significant aberrations when used off-axis. The imaging metasurface optimized for laser triangulation displacement measurement can achieve extremely small aberration imaging within the range, thereby improving the displacement measurement accuracy and measurement sensitivity.

[0037] 4. The laser triangulation displacement measurement device of the present invention has a simple system composition, is easy to assemble, is compact and small in size, can be easily integrated on a motion device to achieve high-precision scanning, and is not prone to mechanical interference. At the same time, with its small size advantage, it can also be used in measurements in environments with extreme space constraints such as deep micro-holes. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of the laser triangulation displacement measurement method using a multi-eye metasurface and the working principle of the device of the present invention.

[0039] Figure 2 Schematic diagram of the optical path principle of laser triangulation displacement imaging of the imaging metasurface of the present invention.

[0040] Figure 3Schematic diagram showing the comparison of ray tracing results when performing laser triangulation displacement imaging between the optimized target phase profile of the imaging metasurface of the present invention and the traditional hyperbolic phase profile.

[0041] Figure 4 This is a flow chart of the optimization method for imaging the target phase profile of the metasurface of the present invention.

[0042] Figure 5 Schematic diagram of the optimized target phase profile result of the imaging metasurface of the present invention and its phase difference with the traditional hyperbolic phase profile.

[0043] Figure 6 It is a schematic diagram of multi-eye imaging spot superposition and equivalent spot position calculation of the present invention.

[0044] Figure 7 Schematic diagram of the three-dimensional structure of the multi-eye metasurface module of the present invention.

[0045] Figure 8 Schematic diagram of the transmittance response curve of the Huygens metasurface of the present invention.

[0046] Among them, 1-photosensitive device, 2-laser, 3-aperture, 4-collimating metasurface, 5-imaging metasurface, 6-micro positioning bracket. DETAILED DESCRIPTION

[0047] 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.

[0048] The present invention discloses a laser triangulation displacement measurement method using a multi-eye metasurface. Figure 1 As shown, it includes the following steps:

[0049] Step 1, design and manufacture a collimating metasurface 4, fix it on the top of a micro positioning bracket 6, and use it to collimate and focus the output light of the laser 2 onto the target object, and install an aperture 3 between the laser 2 and the collimating metasurface 4;

[0050] Step 2, design and manufacture four imaging metasurfaces 5, fix them in sequence on the circumferential inclined surface of the micro positioning bracket 6, and arrange the photosensitive device 1 on the imaging surface behind the micro positioning bracket 6, so as to realize multi-eye small aberration imaging of the laser spot on the target object;

[0051] Step 3, build a displacement calibration experimental platform, scan the moving target object, superimpose the multi-eye imaging spots on the photosensitive device 1, calculate the equivalent spot position, obtain the mapping relationship between the displacement of the target object and the equivalent spot position, and realize laser triangulation displacement measurement.

[0052] Specifically, in step 1, the method for designing and manufacturing the collimating metasurface 4 is as follows:

[0053] Step 1-1, according to the distance between the laser 2 and the collimating metasurface 4, the laser beam diameter and the divergence angle, combined with the output light source model of the laser 2, the wavefront phase profile of the input light of the collimating metasurface 4 can be obtained by importing it into the optical simulation software. Since the ideal wavefront phase profile of the collimated output light is a plane wave, the target phase profile required by the collimating metasurface 4 can be calculated by subtracting the plane wave phase profile from the input light wavefront phase profile obtained by the above simulation;

[0054] Step 1-2, selecting a sub-wavelength nanometer unit structure with a desired target phase response through simulation calculation, arranging the sub-wavelength nanometer unit structure according to the target phase profile obtained in step 1-1, and generating a processing file of the collimated metasurface 4;

[0055] Step 1-3, using micro-nano processing technology to prepare the aligned metasurface 4.

[0056] Specifically, in step 2, the method for designing and manufacturing the imaging metasurface 5 is as follows:

[0057] Step 2-1, based on the generalized Snell's law, a ray tracing model of the imaging metasurface 5 is established, such as Figure 2 As shown. For the target object within the measurement interval, the light spot trajectory on it is distributed along the Z direction and forms an angle α with the optical axis of the imaging metasurface 5, and the corresponding imaging surface on the photosensitive device 1 forms an angle β with the optical axis. The distances l1 and l2 between the object-image conjugate points A1 and A2 on the optical axis that intersect the two (i.e., the Z-direction light spot trajectory and the imaging surface on the photosensitive device 1) and the center point O of the imaging metasurface 5 are the corresponding object-image distances. In this model, the object-image distances l1 and l2 of the imaging metasurface 5 and the imaging inclination angles α and β should approximately meet the Scheimpflug clear imaging conditions.

[0058] However, if Figure 3 (a) shows the ray tracing result of laser triangulation displacement imaging using the traditional hyperbolic phase profile. The horizontal axis in the figure is the direction of the optical axis. It can be seen that there are obvious aberrations in the full measurement range. Therefore, it is necessary to optimize the phase profile of the metasurface to reduce the imaging aberration.

[0059] like Figure 4 The flowchart of the optimization method of the target phase profile of the imaging metasurface 5 is shown. First, the distance and inclination constraints among the photosensitive device 1, the imaging metasurface 5 and the target object are set so that the object-image distances l1 and l2 corresponding to the object-image conjugate points A1 and A2 meet the maximum and minimum value constraints, that is, l min<l1、l2<l max At the same time, the imaging inclination angles α and β also meet the maximum and minimum value constraints, that is, θ min <α、β<θ max The maximum and minimum limits of the above-mentioned object-image distance and imaging inclination angle can be set according to the needs of the actual measurement application process. The larger the ratio of image distance to object distance l2 / l1, the higher the measurement accuracy, but it will also cause the imaging aberration to become larger. The imaging inclination angles α and β respectively determine the scattered light intensity of the target object and the received light intensity of the photosensitive device 1, affecting the signal-to-noise ratio of the imaging spot finally obtained. Subsequently, the secondary phase profile that achieves off-axis near-perfect imaging is used as the initial target phase profile of the imaging metasurface 5, where the secondary phase profile can be expressed as: According to the established imaging metasurface ray tracing model, the imaging aberration of the imaging metasurface 5 within the measurement range is calculated and used as the optimization objective function, which can be specifically expressed as:

[0060] Finally, taking the minimum imaging aberration as the optimization goal, a multi-objective optimization algorithm such as particle swarm optimization or genetic algorithm is applied to optimize the target phase profile of the imaging metasurface 5. The object-image distances l1, l2 and the imaging inclination angles α, β are iteratively optimized to obtain a target phase profile that can achieve small aberration imaging within the range. The target phase profile of the imaging metasurface 5 can be expressed as follows:

[0061]

[0062] Where λ is the operating wavelength, f is the approximate focal length, r is the distance from the center of the imaging metasurface, and a i represents the phase correction coefficient of the i-th order polynomial, where n is the order of the polynomial.

[0063] Figure 5 The target phase profile results of the optimized imaging metasurface are shown ( Figure 5 (a)) and the phase difference between it and the traditional hyperbolic phase profile with the same focal length ( Figure 5 (b) in Figure 2), according to the established ray tracing model, Figure 5 The phase difference shown in (b) will result in Figure 3 The serious imaging aberration shown in (a) in Figure 1. However, the imaging metasurface with optimized target phase profile can significantly reduce the aberration during laser triangulation imaging, as shown in Figure 2. Figure 3 As shown in (b), perfect on-axis imaging and off-axis imaging with small aberrations can be achieved.

[0064] Step 2-2, selecting a sub-wavelength nano-unit structure with a desired target phase response through simulation calculation, arranging the sub-wavelength nano-unit structure according to the target phase profile obtained in step 21, and generating a processing file of the imaging metasurface 5;

[0065] Step 2-3, using micro-nano processing technology to prepare the imaging metasurface 5.

[0066] As a preferred embodiment, the method of optimizing the target phase profile of the imaging metasurface 5 in step 2 can reduce the relative inclination angle between the imaging metasurface 5 and the photosensitive device 1 to zero, thereby transforming the micro-positioning bracket 6 into a planar structure, making the device more compact.

[0067] The following is a supplementary description of the method of building a displacement calibration experimental platform and scanning the target object in step 3: the target object is set on a high-precision linear translation stage, the movement stroke of the high-precision linear translation stage is greater than the small aberration imaging range of the imaging metasurface 5, and the movement direction of the high-precision linear translation stage is consistent with the laser direction output by the laser 2. The high-precision linear translation stage is controlled to move at equal intervals from the starting point to the end point of the stroke, and the multi-eye imaging spot can be obtained on the photosensitive device 1 using the methods in the above steps 1 and 2.

[0068] When measuring a target object with a surface curvature change in any direction, the light spot on the surface of the target object is imaged on the imaging surface of the photosensitive device 1 through the imaging metasurface 5, forming four multi-eye imaging light spots with offset centers of gravity, such as Figure 6 Specifically, in step 3, the method for calculating the equivalent spot position is:

[0069] With the intersection of the central symmetry axis of the four circumferentially distributed imaging metasurfaces 5 and the photosensitive device 1 as the origin, coordinate axes are established along the symmetry plane directions of the four imaging metasurfaces 5. The multi-eye imaging spots distributed on the four coordinate axes have their center of gravity shifted due to the change in the surface curvature of the target object. By merging the four coordinate axes into one coordinate axis and superimposing the spots, an equivalent spot with symmetrical light intensity distribution is obtained. The spot estimation algorithm is used to locate the sub-pixel position of the superimposed spot to obtain the equivalent spot position.

[0070] A laser triangulation displacement measurement device using a multi-eye metasurface, such as Figure 1 As shown, it includes a photosensitive device 1, a laser 2, an aperture 3, a collimating metasurface 4, an imaging metasurface 5 and a micro positioning bracket 6;

[0071] The micro positioning bracket 6 is a transparent thin shell structure of a tetrahedron without a bottom surface. The collimating metasurface 4 is arranged at the center position of the top plane of the micro positioning bracket 6. The imaging metasurfaces 5 are respectively distributed on the inclined surfaces around the micro positioning bracket 6 at equal intervals along the circumferential direction. The photosensitive device 1 is arranged at the imaging surface of the imaging metasurface located behind the micro positioning bracket 6. The laser 2 and the aperture 3 are arranged between the photosensitive device 1 and the collimating metasurface 4. The collimating metasurface 4, the imaging metasurface 5 and the micro positioning bracket 6 together constitute a multi-eye metasurface module, and its three-dimensional structure schematic diagram is shown as follows: Figure 7 shown.

[0072] Preferably, the laser 2 can be selected as an on-chip semiconductor laser so that the overall thickness of the device is kept within ten millimeters.

[0073] The aperture of the aperture 3 is slightly larger than the diameter of the passing laser beam. While preventing the aperture from reflecting the laser beam, it can also block the backscattered light of the collimated metasurface 4 to eliminate the interference of the outgoing laser beam on the imaging quality of the photosensitive device 1.

[0074] The sub-wavelength nanostructured unit material on the collimating metasurface 4 and the imaging metasurface 5 is a transparent dielectric with a high refractive index.

[0075] The sub-wavelength nanometer unit structure is a column, and the cross-sectional geometric shape thereof is one or a combination of a circle, a rectangle, a polygon, and an ellipse.

[0076] The basic principle of the sub-wavelength nano-unit structure to achieve phase control is to change the geometric size parameters of the sub-wavelength nano-unit structure, simultaneously stimulate the electromagnetic resonance in the high refractive index dielectric sub-wavelength nano-unit structure, and form a Huygens metasurface by arranging the sub-wavelength nano-unit structure. The Huygens metasurface has the following characteristics: Figure 8 The transmittance response curve is shown in FIG. 1 , where λ0 is the operating wavelength of the laser 2. The collimating metasurface 4 and the imaging metasurface 5 designed based on the Huygens metasurface principle can maintain high transmittance at the operating wavelength of the laser 2, while the transmittance at other wavelengths is close to zero, and can simultaneously collimate the laser beam, image it, and filter out stray light in other bands in the reflected light.

[0077] 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 laser triangulation displacement measurement method using a multi-eye metasurface, characterized in that: The following steps are involved: Step 1, design and manufacture a collimating metasurface, fix it at the center of the top plane of a micro positioning bracket, and use it to collimate and focus the output light of the laser onto the target object to be measured, and install an aperture between the laser and the collimating metasurface; the micro positioning bracket adopts a bottomless tetrahedral pyramid transparent thin shell structure; Step 2, design and manufacture four imaging metasurfaces, and fix them on the circumferential inclined surface of the micro positioning bracket in turn and at equal intervals along the circumference, and set the photosensitive device on the imaging surface behind the micro positioning bracket to realize multi-eye small aberration imaging of the laser spot on the target object; the collimation metasurface, the imaging metasurface and the micro positioning bracket together constitute a multi-eye metasurface module; Step 3: Build a displacement calibration experimental platform, scan the moving target object, superimpose the multi-image light spots on the photosensitive device, calculate the equivalent light spot position, obtain the mapping relationship between the displacement of the target object and the equivalent light spot position, and realize laser triangulation displacement measurement; The method to calculate the equivalent spot position is: Taking the intersection of the symmetry axes of the four circumferentially distributed imaging metasurfaces and the photosensitive device as the origin, coordinate axes are established along the symmetry plane directions of the four imaging metasurfaces respectively, and the multi-eye imaging spots distributed on the four coordinate axes are superimposed. The spot estimation algorithm is used to locate the sub-pixel position of the superimposed spot to obtain the equivalent spot position.

2. The laser triangulation displacement measurement method using a multi-eye metasurface according to claim 1, characterized in that: In step 1, the method for designing and manufacturing the collimating metasurface is as follows: Step 1-1, calculating the target phase profile required for the collimating metasurface according to the distance between the laser and the collimating metasurface, the laser beam diameter and the divergence angle; Step 1-2, selecting a sub-wavelength nano-unit structure with a desired target phase response through simulation calculation, arranging the sub-wavelength nano-unit structure according to the target phase profile obtained in step 1-1, and generating a processing file for the collimated metasurface; Steps 1-3, using micro-nano processing technology to prepare the aligned metasurface.

3. The laser triangulation displacement measurement method using a multi-eye metasurface according to claim 1, characterized in that: In step 2, the method for designing and manufacturing the imaging metasurface is as follows: Step 2-1, based on the generalized Snell's law, a ray tracing model of the imaging metasurface is established, and the minimum imaging aberration is taken as the optimization target. The distance and inclination constraints among the photosensitive device, the imaging metasurface and the target object are set, and the target phase profile of the imaging metasurface is optimized by applying a multi-objective optimization algorithm to obtain a target phase profile that can achieve small aberration imaging within the range; wherein, the target phase profile of the imaging metasurface can be expressed as follows: Where λ is the operating wavelength, f is the approximate focal length, r is the distance from the center of the imaging metasurface, and a i represents the phase correction coefficient of the i-th order polynomial, n is the order of the polynomial; Step 2-2, selecting a sub-wavelength nano-unit structure with a desired target phase response through simulation calculation, arranging the sub-wavelength nano-unit structure according to the target phase profile obtained in step 2-1, and generating a processing file for an imaging metasurface; Step 2-3, use micro-nano processing technology to prepare the imaging metasurface.

4. The laser triangulation displacement measurement method using a multi-eye metasurface according to claim 3 is characterized in that: Step 2-1 is implemented as follows: First, the distance and inclination constraints among the photosensitive device, the imaging metasurface and the target object are set so that the object-image distances l1 and l2 corresponding to the object-image conjugate points A1 and A2 meet the maximum and minimum value constraints, that is, l min <l1、l2<l max At the same time, the imaging inclination angles α and β also meet the maximum and minimum value constraints, that is, θ min <α、β<θ max ; The maximum and minimum limits of the above-mentioned object-image distance and imaging inclination angle can be set according to the needs of the actual measurement application process. The larger the ratio of image distance to object distance l2 / l1, the higher the measurement accuracy, but it will also cause the imaging aberration to become larger. The imaging inclination angles α and β respectively determine the scattered light intensity of the target object and the received light intensity of the photosensitive device, affecting the signal-to-noise ratio of the imaging spot finally obtained; then, the secondary phase profile that achieves off-axis near-perfect imaging is used as the initial target phase profile of the imaging metasurface, where the secondary phase profile can be expressed as: According to the established imaging metasurface ray tracing model, the imaging aberration of the imaging metasurface within the measurement range is calculated and used as the optimization objective function, which can be specifically expressed as: Finally, taking the minimum imaging aberration as the optimization goal, a multi-objective optimization algorithm is applied to optimize the target phase profile of the imaging metasurface. The object-image distances l1, l2 and the imaging inclination angles α, β are iteratively optimized to obtain the target phase profile that can achieve small aberration imaging within the range.

5. A laser triangulation displacement measurement device using a multi-eye metasurface, which is used to implement the measurement method of claim 1, characterized in that: Including photosensitive devices, lasers, apertures, collimating metasurfaces, imaging metasurfaces and micro positioning brackets; The micro positioning bracket adopts a bottomless tetrahedral pyramid transparent thin shell structure, the collimating metasurface is arranged at the center position of the top plane of the micro positioning bracket, the imaging metasurfaces are distributed on the inclined surfaces around the micro positioning bracket at equal intervals along the circumferential direction, the photosensitive device is arranged on the imaging surface of the imaging metasurface located behind the micro positioning bracket, the laser and the aperture are arranged between the photosensitive device and the collimating metasurface, wherein the collimating metasurface, the imaging metasurface and the micro positioning bracket together constitute a multi-eye metasurface module.

6. The laser triangulation displacement measurement device using a multi-eye metasurface according to claim 5, characterized in that: The aperture of the aperture is slightly larger than the diameter of the laser beam passing therethrough.

7. The laser triangulation displacement measurement device using a multi-eye metasurface according to claim 5, characterized in that: The sub-wavelength nanostructured unit material on the collimating metasurface and the imaging metasurface is a transparent dielectric with a high refractive index.

8. The laser triangulation displacement measurement device using a multi-eye metasurface according to claim 7, characterized in that: The sub-wavelength nanometer unit structure is a column, and the cross-sectional geometric shape thereof is one or a combination of a circle, a rectangle, a polygon, and an ellipse.

9. The laser triangulation displacement measurement device using a multi-eye metasurface according to claim 7, characterized in that: The basic principle of achieving phase control by the subwavelength nanounit structure is: by changing the geometric size parameters of the subwavelength nanounit structure, the electromagnetic resonance in the high refractive index dielectric subwavelength nanounit structure is simultaneously excited, and the subwavelength nanounit structure is arranged to form a Huygens metasurface, so that it maintains high transmittance at the operating wavelength of the laser, while the transmittance at other wavelengths is close to zero, which can simultaneously play the role of laser beam collimation, imaging and filtering out stray light in other bands in the reflected light.

Images