Three-dimensional deformation structured light measurement calibration method and system

Abstract

This application provides a method and system for calibrating three-dimensional deformation structured light measurement. The system includes a projector, a camera, a checkerboard target, a control device, and a translation stage. The checkerboard target is mounted on the translation stage, with one checkerboard pattern being red and another being magenta. The control device is configured to control the projector to project a preset monochromatic red stripe image or white light onto the checkerboard target when calibrating the in-plane coordinates or height coordinates of a three-dimensional deformation measurement space, and to control the translation stage to move multiple times along the height direction of the checkerboard target, each movement being performed at a preset interval. The control device is also configured to obtain three-dimensional calibration data corresponding to the checkerboard target and determine calibration coefficients in a preset optical path measurement model based on the three-dimensional calibration data. The system of this application achieves high-efficiency and high-precision calibration.

Description

Technical Field

[0001] The present application relates to the field of deformation measurement technology, and in particular to a three-dimensional deformation structured light measurement calibration method and system. Background Art

[0002] Deformation measurement can observe changes in the shape, size, and position of a deformable object under load, and is crucial for measuring the external parameters and monitoring the structural quality of civil engineering, mechanical structures, and other structures. Fourier transform profilometry (FTP), a 3D measurement technique based on structured light projection, can directly reveal the instantaneous, 3D deformation field characteristics of the measured object.

[0003] FTP measurement uses a structured light field to actively illuminate the object being measured. Based on a specific three-dimensional spatial optical path model, 3D topography data is reconstructed from the light field signal carrying deformation information. The accuracy of the optical path model directly affects the quality of 3D deformation measurement. In traditional FTP measurement, the measurement optical path must first meet complex geometric relationship requirements, including that the camera optical axis and the projector optical axis are coplanar, the line connecting the optical centers of the two is parallel to the reference plane, and the distance between the camera and the measured plane is significantly greater than the characteristic length of the measured area. Based on this optical path model, the measurement system needs to calibrate the in-plane coordinates and height coordinates separately. Specifically, existing calibration methods use multiple targets, such as plane targets and height targets, to calibrate the plane and height coordinates separately.

[0004] In the existing calibration method, a plane target and a height target are used to calibrate two types of coordinates respectively, and the calibration efficiency is low. At the same time, since errors are introduced during the process of disassembling and assembling the targets, the calibration accuracy of the measurement system is also low. Summary of the Invention

[0005] The present application provides a three-dimensional deformation structured light measurement calibration method and system to solve the problems of low calibration efficiency and low calibration accuracy in current calibration methods.

[0006] A first aspect of the present application provides a three-dimensional deformation structured light measurement and calibration system, comprising:

[0007] Projector, camera, checkerboard target, control equipment, and translation stage;

[0008] The control device is respectively connected to the projector, the camera, and the displacement stage; the checkerboard target is set on the displacement stage, the color of one checkerboard in the checkerboard target is red, and the color of the other checkerboard is magenta; the checkerboard target is a single piece;

[0009] The projector is used to project a preset monochromatic red light stripe image or illuminating white light onto the checkerboard target, and the projection stripes generated by projecting onto the preset reference plane are parallel to each other;

[0010] The camera is used to capture the projected stripes on the checkerboard target to generate a stripe image; wherein the optical axis of the camera is perpendicular to the reference plane;

[0011] The control device is used to control the projector to project calibration corresponding light onto the checkerboard target when calibrating the in-plane coordinates, i.e., the x and y coordinates, or the height coordinate, i.e., the z coordinate, of the checkerboard target, and to control the translation stage to move multiple times along the z-axis of the checkerboard target, with each movement being a preset interval value; the calibration corresponding light is a monochromatic red light stripe image or an illuminating white light;

[0012] The control device is also used to obtain three-dimensional calibration related data corresponding to the checkerboard target;

[0013] The calibration coefficients in the preset optical path measurement model are determined according to the three-dimensional calibration related data.

[0014] Furthermore, in the system described above, when calibrating the in-plane coordinates, i.e., the x and y coordinates, or the height coordinate, i.e., the z coordinate, of the checkerboard target, the control device controls the projector to project the calibration corresponding light onto the checkerboard target, specifically for:

[0015] When calibrating the x-coordinate and y-coordinate of the checkerboard target, controlling the projector to project illuminating white light onto the checkerboard target;

[0016] When calibrating the z coordinate of the checkerboard target, the projector is controlled to project a monochromatic red light stripe image onto the checkerboard target.

[0017] Furthermore, in the system described above, the three-dimensional calibration related data includes:

[0018] The geometric relationship parameters among the projector, camera and reference plane, the projection fringe data on the reference plane, the fringe image corresponding to the checkerboard target, and the first theoretical three-dimensional data of the checkerboard target.

[0019] Furthermore, in the system described above, when determining the calibration coefficients in the preset optical path measurement model based on the three-dimensional calibration related data, the control device is specifically configured to:

[0020] The algorithm parameters in the preset optical path measurement model are fitted according to the three-dimensional calibration related data to determine the corresponding calibration coefficients.

[0021] Furthermore, in the above-mentioned system, the preset optical path measurement model includes an implicit calibration algorithm between the fringe phase difference and the deformation along the z direction, and the implicit calibration algorithm is specifically as follows:

[0022]

[0023] Where z represents the z-coordinate value corresponding to the checkerboard target, Ψ(x,y) represents the fringe phase difference between the checkerboard target and the reference plane, and C1(x,y), C2(x,y), and C3(x,y) are algorithm parameters.

[0024] Furthermore, in the system described above, the RGB color mode of magenta is that the red component R value is 255, the green component G value is 0, and the blue component B value is 255; the RGB color mode of red is that the red component R value is 255, the green component G value is 0, and the blue component B value is 0.

[0025] Furthermore, in the system as described above, the camera is equipped with a high-pass filter with a cutoff wavelength of 560 nanometers.

[0026] Furthermore, in the system as described above, the reference plane is an initial checkerboard plane of the checkerboard target before the checkerboard target moves along the z-axis direction of the checkerboard target.

[0027] Furthermore, in the system described above, the control device is further configured to obtain three-dimensional verification-related data corresponding to the checkerboard target and second theoretical three-dimensional data of the checkerboard target; the three-dimensional verification-related data includes a fringe phase difference between the checkerboard target and a reference plane;

[0028] Determine the measured three-dimensional data of the checkerboard target based on the three-dimensional verification related data and the calibrated optical path measurement model; the calibrated optical path measurement model is a preset optical path measurement model with a determined calibration coefficient;

[0029] The three-dimensional deformation measurement accuracy data of the calibrated optical path measurement model is determined according to the measured three-dimensional data and the second theoretical three-dimensional data.

[0030] A second aspect of the present application provides a three-dimensional deformation structured light measurement calibration method, based on the three-dimensional deformation structured light measurement calibration system according to any one of the first aspects, the method is applied to a control device, the method comprising:

[0031] When calibrating the x-coordinate, y-coordinate, or z-coordinate of a checkerboard target, controlling the projector to project calibration corresponding light onto the checkerboard target and move it multiple times along the z-axis direction of the checkerboard target, with each movement having a preset interval value; the calibration corresponding light is a monochromatic red light stripe image or illuminating white light;

[0032] Obtain the three-dimensional calibration related data corresponding to the checkerboard target;

[0033] The calibration coefficients in the preset optical path measurement model are determined according to the three-dimensional calibration related data.

[0034] The present application provides a three-dimensional deformation structured light measurement calibration method and system, the three-dimensional deformation structured light measurement calibration system comprising: a projector, a camera, a checkerboard target, a control device, and a displacement stage; the control device is respectively connected to the projector, the camera, and the displacement stage; the checkerboard target is set on the displacement stage, and the color of one checkerboard in the checkerboard target is red, and the color of the other checkerboard is magenta; the projector is used to project a preset monochromatic red light stripe image or illuminating white light onto the checkerboard target, and the projection stripes generated by the projection onto a preset reference plane are parallel to each other; the camera Used to shoot the projected stripes on the checkerboard target and generate a stripe image; wherein the camera optical axis is perpendicular to the reference plane; the control device is used to control the projector to project the calibration corresponding light onto the checkerboard target when calibrating the in-plane coordinates of the checkerboard target, i.e., the x, y coordinates or the height coordinate, i.e., the z coordinate, and to move multiple times along the z-axis direction of the checkerboard target, with each movement having a preset interval value; the calibration corresponding light is a monochromatic red light stripe image or illuminating white light; the control device is also used to obtain the three-dimensional calibration related data corresponding to the checkerboard target; and determine the calibration coefficient in the preset optical path measurement model based on the three-dimensional calibration related data. The three-dimensional deformable structured light measurement calibration system of the present application has simple geometric constraints, which significantly reduces the difficulty of adjusting the calibration system. During the calibration process, the influence of the grayscale difference of the checkerboard target on the height calibration is eliminated, and only one checkerboard target can be used to calibrate the height direction z coordinate and the in-plane direction x coordinate and y coordinate at the same time, thereby improving the calibration accuracy and also improving the calibration efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0036] Figure 1 This is a schematic diagram of the structure of the three-dimensional deformation structured light measurement and calibration system provided in this application;

[0037] Figure 2a A schematic diagram of a stripe image of a checkerboard target provided in this application;

[0038] Figure 2b A schematic diagram of the checkerboard sampling of the checkerboard target provided in this application;

[0039] Figure 3 Schematic diagram of the measurement geometry of the 3D deformation structured light measurement and calibration system provided in this application Figure 1 ;

[0040] Figure 4Schematic diagram 2 of the measurement geometry of the 3D deformation structured light measurement and calibration system provided in this application;

[0041] Figure 5 This is a flow chart of the three-dimensional deformation structured light measurement calibration method provided in this application.

[0042] The above drawings illustrate specific embodiments of the present application, which will be described in more detail below. These drawings and the textual description are not intended to limit the scope of the present application in any way, but rather to illustrate the concepts of the present application to those skilled in the art by reference to specific embodiments. DETAILED DESCRIPTION

[0043] Exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numerals in different figures represent identical or similar elements, unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.

[0044] The technical solution of the present application is described in detail below with specific embodiments. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present application will be described below with reference to the accompanying drawings.

[0045] To clearly understand the technical solution of this application, we first provide a detailed introduction to the existing technology. Three-dimensional deformation measurement technology can observe the three-dimensional changes in the shape, size, and position of a deformable object under load. Specifically, Fourier transform profilometry is a three-dimensional measurement technology based on structured light projection. This technology actively illuminates the object being measured using a structured light field and reconstructs the surface topography from the light field signal carrying deformation information based on a specific three-dimensional measurement optical path model.

[0046] Traditional FTP measurement optical paths must adhere to strict geometrical constraints, including the coplanarity of the camera and projector optical axes, the line connecting their optical centers parallel to a reference plane, and a distance between the camera and the measured surface significantly greater than the characteristic length of the measured area. However, in actual measurement, adjusting the positions of the camera and projector optical axes is difficult, making it difficult to simultaneously meet the requirements of coplanarity and parallelism. Furthermore, the spatial arrangement of the measurement equipment is limited by the experimental site, making it difficult to maintain an infinite distance between the camera and the reference plane. If this traditional optical path model is still used to reconstruct 3D deformations, systematic errors will be introduced into the measurement results.

[0047] On the basis of satisfying the geometric constraints of the optical path, the measurement system also needs to be calibrated for the in-plane coordinates and height coordinates respectively. There are two existing calibration methods. One is to use a plane target to calibrate the in-plane coordinates, and then move the target through a translation stage to calibrate the height coordinates. Plane targets usually use "black-white" checkerboards or "black-white" marking point targets, but the grayscale difference of the "black-white" image will affect the grayscale of the stripes during the height calibration process, thereby affecting the calibration accuracy of the measurement system. Another type of calibration method is to use multiple targets such as plane targets and height targets to calibrate the spatial and height coordinates respectively. However, multiple targets not only reduce the calibration efficiency, but also introduce errors during the disassembly and assembly of the targets, reducing the calibration accuracy.

[0048] Therefore, in order to solve the problems of low calibration efficiency and low calibration accuracy in the existing technology, the inventors found in their research that the color of the checkerboard in the checkerboard target can be changed during the calibration process. At the same time, the projector projects different colors of light when measuring the coordinates in the plane and the height coordinates, eliminating the influence of the grayscale difference of the checkerboard on the height calibration, and realizing the calibration of three-dimensional coordinates with one target.

[0049] Specifically, this embodiment provides a three-dimensional deformation structured light measurement and calibration system, including: a projector, a camera, a checkerboard target, a control device, and a translation stage.

[0050] The control device is communicatively connected to the projector, camera, and translation stage, respectively, and controls the projector, camera, and translation stage. A checkerboard target is mounted on the translation stage, with one checkerboard square being red and another being magenta. Under the control of the control device, the projector projects a monochromatic red stripe image or white light onto the checkerboard target, with the projected stripes generated onto a pre-set reference plane being parallel to each other. The camera is used to capture the projected stripes on the checkerboard target and generate a stripe image. The camera's optical axis is perpendicular to the reference plane. The control device is also used to obtain 3D calibration data corresponding to the checkerboard target. Calibration coefficients in a preset optical path measurement model are determined based on the 3D calibration data. The 3D deformable structured light measurement calibration system of this embodiment simplifies the spatial geometric constraints of the optical path and reduces the difficulty of optical path adjustment in the calibration system. Furthermore, the influence of grayscale differences between checkerboard squares on the quality of the stripe image is eliminated. A single checkerboard target can be used to simultaneously calibrate both in-plane coordinates and height coordinates, improving calibration accuracy and efficiency.

[0051] Based on the above creative findings, the inventor proposed the technical solution of this application.

[0052] The embodiments of the present application are introduced below with reference to the accompanying drawings.

[0053] Figure 1The schematic diagram of the structure of the three-dimensional deformation structured light measurement and calibration system provided in this application is as follows: Figure 1 As shown, in this embodiment, the three-dimensional deformation structured light measurement and calibration system includes:

[0054] Projector 1 , camera 2 , checkerboard target 3 , control device 4 and translation stage 5 .

[0055] The control device 4 is in communication with the projector 1, the camera 2, and the translation stage 5. A checkerboard target 3 is placed on the translation stage 5. One checkerboard pattern of the checkerboard target 3 is red, and the other checkerboard pattern is magenta. The checkerboard target is a single piece.

[0056] The projector 1 is used to project a preset monochromatic red light stripe image or illuminating white light onto the checkerboard target 3 , and the projection stripes generated by projecting onto the preset reference plane are parallel to each other.

[0057] Camera 2 is used to capture the projected stripes on the checkerboard target 3 to generate a stripe image. The optical axis of camera 2 is perpendicular to the reference plane.

[0058] When calibrating the x-, y-, or z-coordinates of checkerboard target 3, control device 4 controls projector 1 to project calibration light onto checkerboard target 3. During calibration, control stage 5 moves multiple times along the z-axis of checkerboard target 3, each movement by a preset interval. The calibration light is a monochromatic red stripe image or white light.

[0059] The control device 4 is further used to obtain three-dimensional calibration related data corresponding to the checkerboard target 3.

[0060] The calibration coefficients in the preset optical path measurement model are determined according to the three-dimensional calibration related data.

[0061] In this embodiment, a reference coordinate system is established based on the reference plane, with the point where the optical axis of projector 1 intersects the reference plane as the coordinate origin. The x-axis of the reference coordinate system is perpendicular to the direction of the projected fringes on the reference plane, the y-axis is parallel to the direction of the projected fringes on the reference plane, and the z-axis is perpendicular to the reference plane.

[0062] Optionally, in this embodiment, when calibrating the x-coordinate, y-coordinate, or z-coordinate of the checkerboard target 3, the control device 4 controls the projector 1 to project the calibration corresponding light onto the checkerboard target 3, specifically for:

[0063] When calibrating the x-coordinate and the y-coordinate of the checkerboard target 3 , the projector 1 is controlled to project the illuminating white light onto the checkerboard target 3 .

[0064] When calibrating the z coordinate of the checkerboard target 3 , the projector 1 is controlled to project a monochromatic red light stripe image onto the checkerboard target 3 .

[0065] When the projector 1 is controlled to project the monochromatic red light stripes onto the checkerboard target 3 , both the red and magenta checkerboards reflect red light. Figure 2a Figure 2 shows the fringe image sampled by camera 2 when reflecting red light. As can be seen, during the calibration process, this embodiment eliminates the impact of grayscale differences on the checkerboard target on height calibration by pairing specific checkerboard colors with specific illumination sources, thereby improving calibration accuracy.

[0066] When the projector 1 is controlled to project the white light onto the checkerboard target 3, the red squares in the checkerboard target 3 reflect mainly red light, while the magenta squares reflect a mixture of red and blue. The grayscale contrast between the two types of checkerboards is obvious. Figure 2b As shown, the dark squares are red squares and the light squares are magenta squares.

[0067] Optionally, in this embodiment, the reference plane is the initial checkerboard plane before the checkerboard target 3 moves along the z-axis direction of the checkerboard target 3. That is, the z value corresponding to the initial checkerboard plane is zero.

[0068] Optionally, in this embodiment, the preset interval value can be set according to actual needs, for example, it can be set to 1 mm, 0.5 mm, etc.

[0069] Optionally, in this embodiment, projector 1 can be a DLP (Digital Light Processing) projector with a resolution of 1920×1080 pixels and a projection light irradiation area of ​​approximately 280mm×160mm. Camera 2 can be a CCD (Charge Coupled Device) camera with a resolution of 2456×2058 pixels and an effective field of view of approximately 250mm×140mm. The displacement stage 5 can be a displacement stage with a displacement accuracy of 1μm (micrometer, a unit of length) to improve displacement accuracy, thereby improving calibration accuracy.

[0070] One checkerboard color of the checkerboard target 3 is red, and the other checkerboard color is magenta. In this embodiment, the RGB color model of magenta is such that the red component R value is 255, the green component G value is 0, and the blue component B value is 255. That is, the RGB values ​​corresponding to red are (255, 0, 0), and the RGB values ​​corresponding to magenta are (255, 0, 255).

[0071] Optionally, in this embodiment, the camera 2 is provided with a high-pass filter with a cutoff wavelength of 560 nanometers, thereby further reducing the blue component in the magenta squares and reducing the impact of the checkerboard background difference on the stripe quality.

[0072] Optionally, in this embodiment, the three-dimensional calibration related data includes:

[0073] The geometric relationship parameters among the projector, camera and reference plane, the projection fringe data on the reference plane, the fringe image corresponding to the checkerboard target, and the first theoretical three-dimensional data of the checkerboard target.

[0074] The first theoretical three-dimensional data is used for calibration, which refers to the real three-dimensional data of the chessboard target during continuous movement.

[0075] The geometric relationship parameters may include different geometric relationship parameters depending on the preset optical path measurement model, such as the distance from the projector optical center to the reference plane, the distance from the projector optical center to the camera optical center, etc.

[0076] If the initial checkerboard plane is selected as the reference plane, the corresponding projection fringe data can be obtained by shooting with camera 2.

[0077] Optionally, in this embodiment, when the control device 4 determines the calibration coefficients in the preset optical path measurement model according to the three-dimensional calibration related data, it is specifically configured to:

[0078] The algorithm parameters in the preset optical path measurement model are fitted according to the three-dimensional calibration related data to determine the corresponding calibration coefficients.

[0079] When the 3D deformable structured light measurement calibration system in this embodiment calibrates the calibration coefficients in different optical path measurement models, the geometric relationship parameters among the projector, camera, and reference plane may not be the same, and the calibration process may also be different.

[0080] Optionally, in this embodiment, the preset optical path measurement model includes an implicit calibration algorithm between the fringe phase difference and the deformation along the z direction. The implicit calibration algorithm is specifically as follows:

[0081]

[0082] Where z represents the z-coordinate value corresponding to the checkerboard target, Ψ(x,y) represents the fringe phase difference between the checkerboard target and the reference plane, and C1(x,y), C2(x,y), and C3(x,y) are algorithm parameters.

[0083] When performing implicit calibration, calibration coefficients are obtained by parameter fitting using a checkerboard target. In this embodiment, when calibrating the calibration coefficients in the implicit calibration algorithm, calibration can be performed using a fitting method of C2(x,y) / C1(x,y) and C3(x,y) / C1(x,y).

[0084] If explicit calibration is performed, the corresponding explicit algorithm based on the implicit calibration algorithm can be used to obtain the calibration coefficients by directly measuring the geometric relationship parameters.

[0085] In this embodiment, the implicit calibration algorithm and its corresponding explicit algorithm are different from those in the prior art and have been improved to a certain extent. To further illustrate the implicit calibration algorithm of this embodiment, the specific derivation process will be described in detail below:

[0086] like Figure 3 As shown in the figure, the surface of the object being measured refers to the surface of the checkerboard target, which in practical applications can also refer to the actual measurement surface. The projector optical axis P1O1 intersects the reference plane at point O1, which is the coordinate origin. The xyz directions of the established reference coordinate system are shown in the lower right corner of the figure.

[0087] like Figure 3 As shown, P1 P2 is the line connecting the optical center of the projector and the optical center of the camera, the vertical plane is P1'G O1'O2', and the angle is α.

[0088] The angle between the line connecting the projector's optical center and the camera's optical center and the plane containing the projector's optical axis. The plane containing the projector's optical axis includes the x-axis and z-axis of the reference coordinate system. The plane containing the projector's optical axis is shown as P1P2"O2"O1 in the figure.

[0089] In this embodiment, Figure 3 As shown in the figure, the solid line is within plane P1'O1'O2', the long dashed line is within plane P1P2'O2', and the remaining spatial lines are represented by short dashed lines. P1O1 is the projector optical axis, which makes an angle θ with the vertical. P2O2 is the camera optical axis, which is perpendicular to the reference plane and intersects it at point O2. Figure 3 The plane where the projector optical axis is located is defined as the xz plane, the coordinate origin is located at point O1 in the reference plane, the x direction is perpendicular to the projection stripe direction, the y direction is parallel to the projection stripe direction, and the z direction is perpendicular to the reference plane.

[0090] For sinusoidal projection grating, when the projector optical axis is perpendicular to the projected plane, the spacing of the projected fringes is equal. Figure 3 In the projection method, the projector optical axis has an inclination angle θ, and the projection fringe spacing in the reference plane will change with the x-coordinate position. In order to derive the distribution law of the projection fringe in the reference plane, Figure 4 A partial schematic diagram of the projection optical path is given in , where O1A1 is the reference plane and O1N is perpendicular to the projector optical axis P1O1. The projection fringes are evenly spaced within O1N, and their spatial frequency is assumed to be f. Without loss of generality, take any point A1 within the reference plane and connect the projection light P1A1 and O1N to intersect at point A1'. Since points A1 and A1' are on the same projection light, the phase of the sinusoidal fringes at point A1 is the same as that at point A1', that is, the phase of the sinusoidal fringes is Considering that the two triangles ΔA1A1'N are similar to ΔPA1'O1, the phase of the sinusoidal fringe at A1 can be obtained:

[0091]

[0092] Among them, L p is the distance from the projector optical center P1 to the reference plane O1, and f is the spatial frequency.

[0093] Furthermore, when the above sinusoidal stripes are projected onto the reference plane, the stripe grayscale distribution is:

[0094]

[0095] Where I0 is twice the brightness amplitude of the sinusoidal stripes.

[0096] When the fringes are projected onto the three-dimensional surface of the object being measured, the fringes grayscale distribution algorithm can be obtained:

[0097]

[0098] Where Ψ is the fringe phase difference caused by the three-dimensional topography modulation.

[0099] Now Figure 3 Taking any point B on the surface of the object being measured as an example, the mapping relationship between the fringe phase difference Ψ(B) and the deformation of point B along the z direction is derived. Figure 3 As shown in the figure, P1B is the projection light corresponding to point B. Extending P1B intersects the reference plane at point A, meaning the fringe phase at point A is the same as at point B. P2B is the incident light on the camera corresponding to point B. Extending P2B intersects the reference plane at point C, meaning that when capturing the reference fringe, the fringe phase observed at the pixel corresponding to point B is the fringe phase at point C. Therefore, for the pixel corresponding to point B, the phase difference Ψ(B) is equivalent to the phase difference between points A and C in the reference plane.

[0100] For the convenience of derivation, the camera optical axis P2O2 is translated along the negative direction of the y-axis to y=0 and y=y B At O2"P2" and O2'P2', the projection optical axis is translated along the y direction to y=y B Connect and extend P2'B to intersect O1'O2' at C', and connect and extend P1'B to intersect O1'O2' at A'. It can be proved that CC' and AA' are parallel to the positive direction of the y-axis, that is, the phase at point C is the same as the phase at point C', and the phase at point A is the same as the phase at point A'. The phase difference Ψ is further equivalent to the phase difference between point A' and point C' in the reference plane, that is,

[0101] Ψ(x)=Φ(x B )-Φ(x C )=Φ(xA' )-Φ(x C' )

[0102] because

[0103]

[0104] The geometric sub-algorithm 1 can be obtained:

[0105]

[0106] The following will further deduce through spatial geometric relationships and Through point P1' draw a line P1'G parallel to the x-axis, extend BP2' and intersect P1'G at M. It can be seen that So there is geometric sub-algorithm 2:

[0107]

[0108] in,

[0109]

[0110]

[0111] Where L is the distance from the camera optical center P2 to the reference plane point O2, d is the spatial distance between the projector optical center P1 and the camera optical center P2, β is the angle between the connecting line P1P2 and the xz plane, α is the angle between the projection P1'P2' of P1P2 in the vertical plane and the positive direction of the x-axis, and r is the distance between O1O2".

[0112] Substitute the following two equations of the geometric sub-algorithm 1 into the geometric sub-algorithm 2 to obtain the explicit mapping algorithm as follows:

[0113]

[0114] That is, the explicit mapping relationship between the fringe phase difference Ψ and the deformation along the z direction. Furthermore, based on the explicit mapping algorithm, an implicit calibration function under the measurement geometric relationship conditions can be given. After summarizing and transforming the explicit mapping algorithm, it is as follows:

[0115]

[0116] The projection optical axis of the measurement light path corresponding to the above relationship does not need to be directly opposite the reference plane, and it only requires that the stripes in the reference plane are parallel to each other. In terms of camera arrangement, the optical center of the camera can be arranged arbitrarily, and it only requires that the camera optical axis be perpendicular to the reference plane. It is not required that the camera optical axis and the projection optical axis be coplanar, and the line connecting the optical centers of the two does not need to be parallel to the reference plane. Compared with the existing measurement light path, this light path does not perform any telecentric light path approximation simplification in the derivation, and does not require that the distance from the camera to the measured plane be much larger than the characteristic length of the measured area. It is not only suitable for long-distance measurement, but also for large field of view and close-range measurement. Therefore, the preset light path measurement model of this embodiment simplifies the spatial geometric constraints of the measurement light path, reduces the adjustment difficulty of the calibration system, and improves the applicability of three-dimensional deformation measurement.

[0117] Optionally, in this embodiment, if explicit calibration is performed, the geometric relationship parameters in the explicit mapping algorithm can be obtained by direct measurement.

[0118] Optionally, in this embodiment, the control device is further configured to obtain three-dimensional verification related data corresponding to the checkerboard target and second theoretical three-dimensional data of the checkerboard target. The three-dimensional verification related data includes a fringe phase difference between the checkerboard target and a reference plane.

[0119] The three-dimensional data of the chessboard target is determined based on the three-dimensional calibration data and the calibrated optical path measurement model. The calibrated optical path measurement model is a preset optical path measurement model with a determined calibration coefficient.

[0120] The three-dimensional deformation measurement accuracy data of the calibrated optical path measurement model is determined based on the measured three-dimensional data and the second theoretical three-dimensional data.

[0121] The fringe phase difference can be calculated using the aforementioned fringe brightness distribution algorithm or other algorithms. Once the fringe phase difference is determined, the calculated 3D data can be determined by combining it with the calibrated optical path measurement model. By comparing this 3D data with the second theoretical 3D data, the 3D deformation measurement accuracy can be determined.

[0122] When verifying the calibration measurement accuracy, more refined data can be selected. For example, the second theoretical 3D data can have a finer interval than the first theoretical 3D data. For example, the second theoretical 3D data can be selected from multiple sets of data at intervals of 0.1 mm, while the first theoretical 3D data can be selected from multiple sets of data at intervals of 1 mm.

[0123] In this embodiment, the z coordinate of the interval sampling image is also reconstructed to verify the measurement accuracy of the preset optical path measurement model. The interval sampling range is z = 0.5 ~ 99.5mm, and the sampling step is 1mm. The object to be measured is a checkerboard target, and the absolute position of the checkerboard target is given by the displacement stage, and the control accuracy of the displacement stage is 1μm. In the measurement results, the z coordinate measurement value is consistent with the theoretical value. By comparing the difference between the optical path measurement results and the absolute height position of the target, the height direction measurement error is calculated. The root mean square value of the full-field measurement error does not exceed 0.1‰ of the field of view side length.

[0124] Figure 5 The flowchart of the three-dimensional deformation structured light measurement calibration method provided in this application is as follows: Figure 5 As shown, this embodiment also provides a three-dimensional deformation structured light measurement calibration method. The three-dimensional deformation structured light measurement calibration method of this embodiment is based on the three-dimensional deformation structured light measurement calibration system of the previous embodiment, and the method includes the following steps:

[0125] In step S101, when calibrating the x-, y-, or z-coordinates of a checkerboard target, a projector is controlled to project calibration light onto the checkerboard target, and a translation stage is controlled to move multiple times along the z-axis of the checkerboard target, each movement being a preset interval. The calibration light is a pre-set monochromatic red stripe pattern or white light.

[0126] Step S102, obtaining the three-dimensional calibration data corresponding to the checkerboard target.

[0127] Step S103: determining calibration coefficients in a preset optical path measurement model according to the three-dimensional calibration related data.

[0128] The three-dimensional deformation structured light measurement calibration method provided in this embodiment can achieve Figure 1 The technical solution of the system embodiment shown in the figure has the same implementation principle and technical effect as Figure 1 The system embodiments shown are similar and will not be described in detail here.

[0129] According to an embodiment of the present application, the present application also provides a control device, a computer-readable storage medium, and a computer program product.

[0130] The control device is intended for various forms of digital computers, such as laptop computers, desktop computers, workstations, personal digital assistants, blade servers, mainframe computers, and other suitable computers. The components shown herein, their connections and relationships, and their functions are merely examples and are not intended to limit the implementation of the present application described and / or claimed herein.

[0131] The control device includes a processor, memory, and a communicator. These components are interconnected using various buses and can be mounted on a common motherboard or in other ways as needed. The processor processes instructions executed within the electronic device. The communicator is used to communicate with the projector, camera, and translation stage.

[0132] The memory is the non-transitory computer-readable storage medium provided in this application. The memory stores instructions executable by at least one processor, causing the at least one processor to perform the three-dimensional deformation measurement method provided in this application. The non-transitory computer-readable storage medium provided in this application stores computer instructions for causing a computer to perform the three-dimensional deformation structured light measurement and calibration method provided in this application.

[0133] The memory, as a non-transitory computer-readable storage medium, can be used to store non-transitory software programs, non-transitory computer executable programs, and modules. The processor executes the non-transitory software programs, instructions, and modules stored in the memory to execute various functional applications and data processing of the control device, thereby implementing the three-dimensional deformation structured light measurement calibration method described in the above method embodiment.

[0134] At the same time, this embodiment also provides a computer product. When instructions in the computer product are executed by a processor of a control device, the control device can execute the three-dimensional deformation structured light measurement calibration method of the above embodiment.

[0135] Those skilled in the art will readily conceive of other implementations of the embodiments of the present application after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the embodiments of the present application, which follow the general principles of the embodiments of the present application and include common knowledge or customary technical means in the art not disclosed in the embodiments of the present application.

[0136] It should be understood that the embodiments of the present application are not limited to the precise structures described above and shown in the drawings, and various modifications and changes can be made without departing from the scope thereof. The scope of the embodiments of the present application is limited only by the appended claims.

Claims

1. A three-dimensional deformation structured light measurement and calibration system, characterized in that: include: Projector, camera, checkerboard target, control equipment, and translation stage; The control device is communicatively connected to the projector, the camera, and the displacement stage respectively; The checkerboard target is set on the displacement platform, the color of one checkerboard in the checkerboard target is red, and the color of another checkerboard is magenta; the checkerboard target is a single piece; The projector is used to project a preset monochromatic red light stripe image or illuminating white light onto the checkerboard target, and the projection stripes generated by projecting onto the preset reference plane are parallel to each other; The camera is used to capture the projected stripes on the checkerboard target to generate a stripe image; wherein the optical axis of the camera is perpendicular to the reference plane; The control device is used to control the projector to project white light onto the checkerboard target when calibrating the x- and y-coordinates of the checkerboard target; to control the projector to project a monochromatic red light stripe image onto the checkerboard target when calibrating the z-coordinate of the checkerboard target; and to control the translation stage to move multiple times along the z-axis direction of the checkerboard target, with each movement being a preset interval value; The control device is further configured to obtain three-dimensional calibration-related data corresponding to the checkerboard target, wherein the three-dimensional calibration-related data includes: geometric relationship parameters among the projector, the camera, and the reference plane, projection fringe data on the reference plane, a fringe image corresponding to the checkerboard target, and first theoretical three-dimensional data of the checkerboard target; The calibration coefficients in the preset optical path measurement model are determined according to the three-dimensional calibration related data.

2. The system according to claim 1, wherein: When determining the calibration coefficients in the preset optical path measurement model according to the three-dimensional calibration related data, the control device is specifically used to: The algorithm parameters in the preset optical path measurement model are fitted according to the three-dimensional calibration related data to determine the corresponding calibration coefficients.

3. The system according to claim 2, characterized in that The preset optical path measurement model includes an implicit calibration algorithm between the fringe phase difference and the deformation along the z direction. The implicit calibration algorithm is specifically as follows: ； in, Represents the target on the chessboard Coordinate values, represents the fringe phase difference between the checkerboard target and the reference plane, 、 and are algorithm parameters.

4. The system according to claim 1, wherein: The RGB color mode of magenta is that the red component R value is 255, the green component G value is 0, and the blue component B value is 255; the RGB color mode of red is that the red component R value is 255, the green component G value is 0, and the blue component B value is 0.

5. The system according to claim 4, characterized in that The camera is equipped with a high-pass filter with a cutoff wavelength of 560 nanometers.

6. The system according to claim 5, characterized in that The reference plane is an initial checkerboard plane of the checkerboard target before it moves along the z-axis direction of the checkerboard target.

7. The system according to claim 6, characterized in that The control device is further configured to obtain three-dimensional verification related data corresponding to the checkerboard target and second theoretical three-dimensional data of the checkerboard target; the three-dimensional verification related data includes a fringe phase difference between the checkerboard target and the reference plane; Determine the measured three-dimensional data of the checkerboard target based on the three-dimensional verification related data and the calibrated optical path measurement model; the calibrated optical path measurement model is a preset optical path measurement model with a determined calibration coefficient; The three-dimensional deformation measurement accuracy data of the calibrated optical path measurement model is determined according to the measured three-dimensional data and the second theoretical three-dimensional data.

8. A three-dimensional deformation structured light measurement calibration method, characterized in that: Based on the three-dimensional deformation structured light measurement and calibration system according to any one of claims 1 to 7, the method is applied to a control device, and the method includes: When calibrating the x-coordinate, y-coordinate, or z-coordinate of a checkerboard target, controlling the projector to project calibration corresponding light onto the checkerboard target, and controlling the translation stage to move multiple times along the z-axis direction of the checkerboard target, each movement being a preset interval value; the calibration corresponding light is a preset monochromatic red light stripe image or illuminating white light; Obtain the three-dimensional calibration related data corresponding to the checkerboard target; The calibration coefficients in the preset optical path measurement model are determined according to the three-dimensional calibration related data.

Images