A Structured Light Three-Dimensional Topography Measurement Method and Device Based on Natural Phase Shifting

Abstract

The present invention relates to a method and device for three-dimensional shape measurement of structured light based on natural phase shift. The method includes: calibrating each parameter of the system, solving to obtain the corresponding formula between phase and height, and then moving the sample to be measured; projecting a fixed fringe structured light image onto the surface of the sample to be measured through a projector, collecting the fringe light intensity distribution on the surface of the sample to be measured during movement through a camera, and using a structured light phase solving algorithm based on natural phase shift to solve the corresponding phase distribution; according to the corresponding formula between phase and height, converting the solved phase distribution into height values, so as to extract the three-dimensional shape information of the object. Compared with the prior art, the present invention allows the object to move freely during the measurement process without being fixed in position, thus realizing true in-situ measurement and broadening the application range of three-dimensional shape measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of three-dimensional reconstruction of industrial object morphology, and particularly to a method and device for three-dimensional morphology measurement of structured light based on natural phase shift. Background Art

[0002] The surface structured light measurement technology for three-dimensional morphology measurement of objects has important applications in fields such as the semiconductor industry, the automotive industry, and the aerospace industry. The surface structured light measurement technology accurately encodes the position information of each point on the object surface by projecting structured light information with strong texture features on the object surface, then uses a camera to image the structured light projected onto the object surface, performs phase calculation on the past fringe images, and finally decodes the position information of each point on the object surface through the triangulation ray tracing technology to obtain the three-dimensional morphology information of the object surface, having advantages such as high precision, high resolution, non-contact, strong robustness, and high speed.

[0003] Traditional structured light three-dimensional imaging technology requires phase shift of the projected fringe images during the measurement process, takes multiple projected fringe images at different initial phases, and uses the known initial phase differences of the fringe images to restore the phase information of the fringes at each point on the surface, so as to calculate the accurate phase information of the fringes at each point on the surface. However, this traditional technology requires the object to remain stationary during the phase shift process, otherwise it will lead to failure of the final phase calculation. Therefore, traditional structured light three-dimensional contour systems face great challenges when detecting moving objects. Summary of the Invention

[0004] The purpose of the present invention is to provide a method and device for three-dimensional morphology measurement of structured light based on natural phase shift to overcome the defect that the above-mentioned prior art requires the object to remain stationary during the phase shift process.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A method for three-dimensional morphology measurement of structured light based on natural phase shift includes the following steps:

[0007] Place the sample to be measured on the loading plane, set a projector for projecting fringe structured light images for imaging, set a monocular camera for collecting actual light intensity information and the distribution of fringe structured light, and set a loading platform for adjusting the actual position of the object to achieve free movement of the sample during the measurement process. When the object moves on the loading platform, a relative displacement occurs between the object and the fringe structured light, thereby producing the effect of natural phase shift;

[0008] After calibrating the parameters of the system and solving the corresponding formula between the phase and the height, move the sample to be measured; project a fixed structured light image onto the surface of the sample to be measured through a projector, collect several pictures of the intensity distribution of the fringe structured light on the surface of the sample to be measured during movement through a camera, and use the structured light phase solving algorithm based on natural phase shifting to solve the corresponding phase distribution; according to the corresponding formula between the phase and the height, convert the solved phase distribution into height values, so as to extract the three-dimensional shape information of the object.

[0009] Further, the process of calibrating the parameters of the system and solving the corresponding formula between the phase and the height is specifically as follows:

[0010] Set a projector and a camera above the object plane, and calibrate the system parameters of the projector and the camera; use the projector to project a fixed fringe structured light onto the background, and the camera captures the fringe light intensity on the background to obtain a fringe structured light image, and solve the fringe structured light period through Fourier transform, and combine the system parameters to obtain the corresponding formula between the phase and the height; change the phase of the projected fringe structured light image and solve the change of the background light intensity with the spatial position.

[0011] Further, the process of calibrating the system parameters of the projector and the camera is specifically as follows:

[0012] Place a checkerboard calibration plate on the object plane, project complementary Gray code pictures onto the checkerboard calibration plate through the projector, change the pose of the checkerboard calibration plate multiple times, and take pictures of the imaging results projected on the checkerboard calibration plate each time;

[0013] Construct the imaging models of both the projector and the camera as pinhole camera imaging models, identify the corner points of the checkerboard on each captured photo, and calculate the corresponding complete Gray code encoding sequence; calculate the local homology matrix corresponding to each corner point, and convert the coordinates of each corner point under the camera imaging plane to the coordinates under the projector imaging plane through the local homology matrix to realize the internal and external parameter calibration of the imaging models of the projector and the camera.

[0014] Further, the process of obtaining the corresponding formula between the phase and the height is specifically as follows:

[0015] Compress the obtained fringe structured light image signal into a one-dimensional signal, perform Fourier transform on the one-dimensional signal, solve the fringe structured light period, and combine the system parameters of the projector and the camera to obtain the corresponding formula between the phase and the height.

[0016] Further, the transformation expression for performing Fourier transform on the one-dimensional signal is:

[0017]

[0018] Wherein, X(f) is the one-dimensional signal after Fourier transform, x(t) is the one-dimensional signal obtained after image compression, L is the length of the one-dimensional signal, f is the frequency, and t is the time;

[0019] The solution expression for the period of the fringe structured light is:

[0020]

[0021]

[0022] Wherein, P1(f) is the unilateral amplitude, T is the period of the fringe structured light, is the frequency corresponding to the highest point of the unilateral amplitude, that is, the fringe structured light frequency;

[0023] The corresponding formula between the phase and the height is:

[0024]

[0025] Wherein, h is the height of the object, l is the distance between the camera and the projector, d is the height from the projector to the load plane, p is the period of the fringe structured light, is the modulation phase of the object.

[0026] Further, the specific method for changing the phase of the projected fringe structured light image and solving the change of the background light intensity with the spatial position is as follows:

[0027] Change the phase of the generated fringe structured light image to and And project them onto the load plane through the projector respectively, capture the background light intensity through the camera, and obtain the change of the background light intensity with the spatial position after superposition.

[0028] Further, the method adopts a structured light phase solving algorithm based on natural phase shifting. According to the fringe structured light intensity distribution images on the surface of several samples to be measured during movement captured by the camera, and the change of the background light intensity with the spatial position, the phase is solved, and then the unwrapping algorithm is used to obtain the unwrapped phase to obtain the phase distribution.

[0029] Further, the structured light phase solving algorithm based on natural phase shifting is specifically as follows:

[0030] Solution steps: Divide the fringe structured light intensity distribution on the surface of the sample to be measured during movement by the background light intensity to determine the initial position p of the sample to be measured in the pixel coordinates i, so as to translate the sample to be measured in each frame image obtained during the movement of the sample to be measured to the same spatial position, regard the background light intensity and contrast as constant between frames, estimate the fringe phase, solve the object modulation phase using the least squares method, and then calculate the harmonic coefficient by combining the Fourier transform to update the fringe light intensity distribution, and further solve the updated fringe structured light phase and the initial position of the object through the updated fringe structured light intensity distribution and the object modulation phase;

[0031] Iterative step: Repeat the above-mentioned solving steps for multiple rounds to calculate the object modulation phase, fringe structured light phase and harmonic coefficient until the object modulation phase converges to a preset ideal accuracy.

[0032] Furthermore, the expression of the fringe structured light intensity distribution on the surface of the sample to be measured after movement is:

[0033]

[0034] In the formula, I i (x, y) is the fringe structured light intensity distribution on the surface of the sample to be measured after movement, A'(x, y) is the background light intensity, B'(x, y) is the contrast, B k is the harmonic coefficient, is the object modulation phase, i is the number of image frames, δ i ' is the projected fringe phase;

[0035] The calculation expression of the estimated value of the fringe phase is:

[0036]

[0037] In the formula, δ i ' is the estimated value of the fringe phase, p i is the initial position of the sample to be measured in pixel coordinates, and p is the fringe width;

[0038] The expression for solving the object modulation phase using the least squares method is:

[0039]

[0040] In the formula, is the solved object modulation phase;

[0041] The expression for calculating the harmonic coefficient by combining the Fourier transform is:

[0042]

[0043] In the formula, F{} is the Fourier transform, (x m , y m ) is the coordinate of the spectral peak point;

[0044] The update expression for the initial position of the object is as follows:

[0045] p i ←p i +Wrap(Δδ i ')*p

[0046] where Δδ i ' is the phase difference of the fringe structured light before and after the update.

[0047] The present invention also provides a structured light three-dimensional shape measurement device for implementing the structured light three-dimensional shape measurement method based on natural phase shift described above, which is used for three-dimensional shape reconstruction of a sample to be measured, and includes: a camera, a projector, and a sample stage; the sample to be measured is placed on the sample stage; the projector projects a fringe structured light image vertically downward, the sample stage is placed horizontally, the sample to be measured can be movably placed on the sample stage, and the camera captures the imaging result obliquely.

[0048] Compared with the prior art, the present invention has the following advantages:

[0049] (1) Compared with the traditional structured light active phase shift method, the structured light three-dimensional shape measurement method based on natural phase shift proposed by the present invention captures the natural phase shift process of an object under specific illumination conditions, based on the natural phase shift algorithm, uses the intra-frame and inter-frame phase differences to calculate the true phase, and according to the pre-calculated correspondence formula between the phase and the height, converts the phase value into a height value to reconstruct the three-dimensional shape of the naturally moving object, allowing the sample to move freely during the measurement without being fixed in position. Thus, on the one hand, it realizes true in-situ measurement, improves the real-time performance and versatility of the method, breaks through the technical bottleneck that the traditional structured light method requires projection stripe transformation, broadens the application range of three-dimensional shape measurement, and on the other hand, eliminates the complex control device and mechanical structure, reducing the complexity and cost of the system.

[0050] (2) The Fourier transform fitting algorithm proposed by the present invention realizes the calculation of high-order harmonics, solves the problem that errors are introduced due to factors such as the nonlinearity of light intensity, the deviation of object position estimation, and the axial jitter of the measurement plane during the measurement process, resulting in inaccurate solution of the modulation phase of the object, and further improves the accuracy and reliability of the structured light three-dimensional shape measurement method. Description of the Drawings

[0051] Figure 1 It is a schematic structural diagram of a structured light three-dimensional shape measurement device provided in an embodiment of the present invention;

[0052] Figure 2 It is a schematic composition diagram of a structured light three-dimensional shape measurement device provided in an embodiment of the present invention;

[0053] Figure 3 It is a schematic flowchart of a structured light three-dimensional shape measurement method based on natural phase shift provided in an embodiment of the present invention;

[0054] Figure 4 It is a schematic diagram of the state of a structured light three-dimensional shape measurement device based on natural phase shift provided in an embodiment of the present invention for measuring a sphere to be measured;

[0055] Figure 5 It is a comparison diagram of experimental results of using the structured light three-dimensional shape measurement method based on natural phase shift of the present invention and the traditional structured light three-dimensional shape measurement method based on active phase shift under Matlab simulation in an embodiment of the present invention;

[0056] Figure 6 It is a schematic diagram of the state of realizing the fringe projection of a projector on an object to be measured and the imaging of a camera through ray tracing in a Matlab simulation environment provided in an embodiment of the present invention;

[0057] Figure 7 It is a comparison diagram of simulation effects of using the structured light three-dimensional shape measurement method based on natural phase shift of the present invention and the traditional structured light three-dimensional shape measurement method based on active phase shift under Matlab simulation in an embodiment of the present invention. Specific embodiments

[0058] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and illustrated herein can be arranged and designed in various different configurations.

[0059] Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0060] It should be noted that: similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0061] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the invention product is usually placed during use. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0062] It should be noted that the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application, "a plurality" means two or more, unless otherwise specifically defined.

[0063] In addition, terms such as "horizontal" and "vertical" do not mean that the components are required to be absolutely horizontal or hanging, but may be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but may be slightly inclined.

[0064] Embodiment 1

[0065] As Figure 3 shown, this embodiment provides a method for measuring three-dimensional topography of structured light based on natural phase shift, including the following steps:

[0066] Place the sample to be measured on the load plane, set a projector for projecting a fringe structured light image for imaging, set a monocular camera for collecting actual light intensity information and the distribution of the fringe structured light, and set a load platform for adjusting the actual position of the object to achieve free movement of the sample during the measurement process. When the object moves on the load platform, a relative displacement occurs between the object and the fringe structured light, thus producing the effect of natural phase shift;

[0067] After calibrating the parameters of the system and solving the corresponding formula between the phase and the height, move the sample to be measured; project a fixed structured light image onto the surface of the sample to be measured through the projector, collect several pictures of the light intensity distribution of the fringe structured light on the surface of the sample to be measured during movement through the camera, and use the structured light phase solving algorithm based on natural phase shift to solve the corresponding phase distribution; according to the corresponding formula between the phase and the height, convert the solved phase distribution into a height value, thereby extracting the three-dimensional topography information of the object.

[0068] The process of calibrating the system parameters and solving the corresponding formula between phase and height is as follows: Set up a projector and a camera above the object plane, and calibrate the system parameters of the projector and the camera; Use the projector to project a fixed fringe structured light onto the background, and the camera captures the fringe light intensity on the background to obtain the fringe structured light image, and solve the fringe structured light period through Fourier transform, and combine the system parameters to obtain the corresponding formula between phase and height; Change the phase of the projected fringe structured light image and solve the change of the background light intensity with the spatial position.

[0069] Equivalently, the above method includes the following steps:

[0070] S1: Set up a projector and a camera above the object plane, and calibrate the system parameters of the projector and the camera;

[0071] Specifically: Place the sample to be measured on the object plane, set up the projector to project the fringe structured light image for imaging, set up the camera to collect the actual light intensity information and the fringe structured light distribution, the camera can be a monocular camera, and set up the object platform to adjust the actual position of the object to achieve the free movement of the sample during the measurement process;

[0072] The process of calibrating the system parameters of the monocular camera and the projector specifically includes:

[0073] Place a checkerboard calibration board on the object platform, project complementary Gray code pictures onto the checkerboard calibration board through the projector, and the number of Gray code pictures needs to ensure that each point on the imaging plane of the projector can be fully encoded. Change the pose of the checkerboard calibration board multiple times, and take pictures of the imaging results projected on the checkerboard calibration board each time.

[0074] Establish the imaging models of the projector and the camera as the pinhole camera imaging model, identify the corner points of the checkerboard captured in each photo and solve the corresponding complete Gray code encoding sequence, calculate the local homologous matrix corresponding to each corner point, and convert the coordinates of each corner point under the camera imaging plane to the coordinates under the projector imaging plane through the local homologous matrix, so as to realize the calibration of the internal and external parameters of the pinhole imaging models of the projector and the camera.

[0075] S2: Project the fringe structured light image on the surface of the object plane through the projector, and collect the light intensity information and the fringe distribution on the surface of the object plane through the camera to obtain the fringe light intensity, that is, the fringe structured light image;

[0076] S3: Use Fourier transform to solve the fringe structured light period, and combine the system parameters of the projector and the camera to obtain the corresponding formula between phase and height;

[0077] Steps S2 and S3 are specifically as follows:

[0078] The projector projects fixed cosine fringes onto the background. After the camera captures the fringe structured light image signal, the image signal is compressed into a one-dimensional signal, and the fringe period is obtained through Fourier transform. According to the system parameters and geometric relationships, the calculation formula between the object phase and height is obtained.

[0079] The expression of the fringe structured light image captured by the camera is:

[0080] I i (x, y) = A(x, y) + B(x, y)cos[φ i (x, y) + δ]

[0081] In the formula, I i (x, y) is the actual light intensity of the image, A(x, y) is the background light intensity, B(x, y) is the contrast, φ i is the object modulation phase, i is the number of image frames, and δ is the projected fringe phase.

[0082] The image transformation formula for compressing the fringe structured light image signal captured by the camera into a one-dimensional signal and obtaining the fringe period through Fourier transform is:

[0083]

[0084] In the formula, W is the image width, and img is the captured background fringe image.

[0085] The transformation formula for performing Fourier transform on the one-dimensional fringe signal is:

[0086]

[0087] In the formula, X(f) is the one-dimensional signal after Fourier transform, x(t) is the one-dimensional signal obtained after image compression, L is the length of the signal (i.e., the height of the image), and f is the frequency.

[0088] The solution formula for the fringe signal period is:

[0089]

[0090]

[0091] In the formula, P1(f) is the single-sided amplitude, and T is the fringe signal period.

[0092] The calculation formula between the object phase and height is:

[0093]

[0094] Where h is the height of the object, l is the distance between the camera and the projector, d is the height from the projector to the load plane, p is the fringe period, and φ is the object modulation phase. When the imaging distance is far, φ and h can be approximately regarded as a linear relationship.

[0095] S4: By changing the phase of the projected fringe structured light image, solve the variation of the background light intensity with spatial position;

[0096] The fringes can be subjected to four-step phase shifting to solve the variation of the background light intensity with spatial position. The specific process is as follows:

[0097] Change the phases of the generated cosine fringe images to be and project them onto the stage through the projector respectively. Capture the background light intensity through the camera, and after superimposition, obtain the variation of the background light intensity with spatial position.

[0098] S5: Place the sample to be measured on the load plane and move it; project a fringe structured light image onto the surface of the sample to be measured through the projector;

[0099] S6: Collect the fringe light intensity distribution on the surface of the sample to be measured during movement through the camera;

[0100] S7: Solve the corresponding phase distribution according to the variation of the background light intensity with spatial position;

[0101] Adopt a structured light phase solving algorithm based on natural phase shifting. According to the fringe light intensity distribution on the surface of the sample to be measured during movement and the variation of the background light intensity with spatial position, solve the phase, and then obtain the unwrapped phase through an unwrapping algorithm to get the phase distribution.

[0102] The structured light phase solving algorithm based on natural phase shifting is specifically as follows:

[0103] Solving steps: Divide the fringe light intensity distribution on the surface of the sample to be measured during movement by the background light intensity to determine the initial position p of the sample to be measured in pixel coordinates i , thereby translating the sample to be measured in each frame image obtained during the movement of the sample to be measured to the same spatial position, regarding the background light intensity and contrast as constant between frames, estimating the fringe phase, using the least squares method to solve the object modulation phase, thereby calculating the harmonic coefficient in combination with the Fourier transform to update the fringe light intensity distribution, and further solving and updating the fringe phase and the initial position of the object through the updated fringe light intensity distribution and the object modulation phase;

[0104] Iterative steps: Repeat the solving steps for multiple rounds to calculate the object modulation phase, fringe phase, and harmonic coefficient until the object modulation phase converges to a preset ideal accuracy.

[0105] It is equivalent to the natural phase-shifting solution algorithm that solves the phase through iteration. First, divide I i by the background light intensity to compensate for the influence caused by uneven light intensity. Determine the initial position p of the object in pixel coordinates through optical flow method or markers i , and translate the object to be measured in each frame of image to the same spatial position. Consider the background light intensity and contrast as constant between frames, estimate the fringe phase, use the least-squares solution formula combined with Fourier transform to iteratively solve the object modulation phase and update the fringe light intensity. Then, further calculate and update the fringe phase and the initial position of the object through the updated light intensity and the object modulation phase. Repeat the above steps for multiple rounds to calculate the physical modulation phase, fringe phase, and harmonic terms until convergence to the ideal accuracy, and finally obtain the object modulation phase at the ideal accuracy.

[0106] The expression of the fringe light intensity image after the object to be measured moves is:

[0107]

[0108] In the formula, I i '(x, y) is the actual light intensity of the image, A'(x, y) is the background light intensity, B'(x, y) is the contrast, B k is the harmonic coefficient, φ‘(x, y) is the object modulation phase, i is the image frame number, δ i ' is the projected fringe phase;

[0109] The expression of the estimated value of the fringe phase is:

[0110]

[0111] In the formula, δ i ' is the projected fringe phase, p i is the initial position of the object in pixel coordinates, p i is the fringe width;

[0112] The formula for solving the object modulation phase by least squares is:

[0113]

[0114] In the formula, φ j ' is the object modulation phase estimated in each round;

[0115] The formula for calculating the harmonic coefficient by Fourier transform is:

[0116] F{B'(x m , y m )cos[kφ'(x m , y m ) + kδ i ']}B k =F{Ii '(x m ,y m )}

[0117] Wherein, F{} is the Fourier transform, and (x m ,y m ) are the coordinates of the spectral peak point;

[0118] The formula for updating the fringe intensity with the harmonic coefficient obtained by calculation is:

[0119]

[0120] The further position quantity calculation and update expression is:

[0121] p i ←p i +Wrap(Δδ i ')*p

[0122] Wherein, Δδ i ' is the difference in fringe phase before and after update;

[0123] Finally, the above steps are iterated multiple times until the object modulation phase converges to the desired accuracy, and the object modulation phase under the final ideal accuracy is obtained.

[0124] S8: According to the corresponding formula between the phase and the height, the solved phase distribution is converted into height values, so as to extract the three-dimensional topography information of the object.

[0125] Embodiment 2

[0126] As Figure 1 and Figure 2 shown, this embodiment provides a three-dimensional topography measurement device for implementing a three-dimensional topography measurement method based on natural phase shift as in Embodiment 1, which is used to perform three-dimensional topography measurement on a sample to be measured, including a camera 1, a projector 2 and a carrier platform 4; the sample to be measured 3 is placed on the carrier platform 4: the projector 2 projects a fringe structured light image vertically downward, the carrier platform 4 is placed horizontally, the sample to be measured 3 is placed on the carrier platform 4 and moves freely on the carrier platform 4, and the camera 1 captures the imaging result obliquely.

[0127] As Figure 4As shown in the figure, the three-dimensional shape measurement device for structured light three-dimensional shape measurement based on natural phase shift in this embodiment measures regular geometric bodies, specifically spheres. The measurement process is as follows: calibrate the system parameters of the monocular camera and the projector in the device, use the projector to project a fixed fringe structured light image onto the background, the camera captures the fringe light intensity on the background, and solves the fringe period through Fourier transform. Combine the system parameters to obtain the corresponding formula between phase and height, and then perform four-step phase shift on the fringes to solve the variation of the background light intensity with spatial position; then, the object to be measured is installed on the loading platform and placed at the initial position. The projector projects a fringe structured light image with fixed fringes onto the surface of the object to be measured. During the process of the object moving on the loading platform, use the camera to record the light intensity when the object moves on the loading plane, and solve the phase through the natural phase shift solution algorithm. Further, obtain the unwrapped phase through the unwrapping algorithm, and thus convert the phase value into a height value according to the corresponding formula between phase and height, and finally realize the three-dimensional reconstruction of the surface of the sample to be measured.

[0128] As Figure 5 shown in the figure, it is a comparison chart of the effects of using the structured light three-dimensional shape measurement method based on natural phase shift of the present invention and the traditional structured light three-dimensional shape measurement method based on active phase shift in the actual experimental environment. The measurement effect of the natural phase shift method of the present invention is almost the same as that of the traditional method, meeting the requirements of high-precision dynamic measurement.

[0129] Example 3

[0130] As Figure 6 shown in the figure, this embodiment is generally the same as Embodiment 2. The difference is that this embodiment is carried out in the Matlab simulation environment. The fringe projection of the projector on the object to be measured and the imaging of the camera are realized through the ray tracing method. The object to be measured is a Zernike surface with a relatively complex surface shape; the simulation program is used to simulate the calculation effects of the traditional active phase shift method and the passive phase shift method involved in the present invention.

[0131] As Figure 7 shown in the figure, it is a comparison chart of the effects of using the structured light three-dimensional shape measurement method based on natural phase shift of the present invention and the traditional structured light three-dimensional shape measurement method based on active phase shift under Matlab simulation. The measurement effect of the natural phase shift method of the present invention for complex surface shapes is also almost the same as that of the traditional method, meeting the requirements of high-precision dynamic measurement.

[0132] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations according to the concept of the present invention without creative labor. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the existing technology should be within the protection scope determined by the claims.

Claims

1. A structured light three-dimensional shape measurement method based on natural phase shift, characterized in that: The following steps are involved: The sample to be measured is placed on a loading plane, a projector is set to project a stripe structured light image for imaging, a monocular camera is set to collect actual light intensity information and stripe structured light distribution, and a loading platform is set to adjust the actual position of the object to achieve free movement of the sample during the measurement process. When the object moves on the loading platform, a relative displacement occurs between the object and the stripe structured light, thereby producing a natural phase shift effect; After calibrating the system parameters and solving the corresponding formula between phase and height, move the sample to be tested; A fixed structured light image is projected onto the surface of the sample to be tested by a projector, and a number of pictures of the intensity distribution of the stripe structured light on the surface of the sample to be tested when it is moving are collected by a camera. The corresponding phase distribution is solved by a structured light phase solving algorithm based on natural phase shifting. According to the corresponding formula between phase and height, the solved phase distribution is converted into a height value, thereby extracting the three-dimensional morphology information of the object.

2. The method for measuring three-dimensional shape based on structured light of claim 1, characterized in that: The specific process of calibrating the system parameters and solving the corresponding formula between phase and height is as follows: A projector and a camera are set above the object plane, and the system parameters of the projector and the camera are calibrated; a fixed stripe structured light is projected onto the background by the projector, and the camera captures the stripe light intensity on the background to obtain a stripe structured light image, and the stripe structured light period is solved by Fourier transform, and the corresponding formula between phase and height is obtained in combination with the system parameters; The phase of the projected stripe structured light image is changed to solve the variation of background light intensity with spatial position.

3. The method for measuring three-dimensional shape based on structured light of claim 2, characterized in that: The system parameter calibration process of the projector and camera is specifically as follows: A checkerboard calibration plate is placed on the object plane, and a complementary Gray code image is projected onto the checkerboard calibration plate by a projector. The position of the checkerboard calibration plate is changed multiple times, and the imaging result projected onto the checkerboard calibration plate each time is photographed; The imaging models of the projector and the camera are both constructed as pinhole camera imaging models. The corner points of the chessboard on each photo taken are identified, and the corresponding complete Gray code encoding sequence is calculated. The local homology matrix corresponding to each corner point is calculated, and the coordinates of each corner point under the camera imaging plane are converted into coordinates under the projector imaging plane through the local homology matrix, so as to realize the internal and external parameter calibration of the imaging models of the projector and the camera.

4. The method for measuring three-dimensional shape based on structured light of claim 2, characterized in that: The specific process of obtaining the corresponding formula between phase and height is: The acquired stripe structured light image signal is compressed into a one-dimensional signal, and the one-dimensional signal is Fourier transformed to obtain the stripe structured light period. Combined with the system parameters of the projector and camera, the corresponding formula between phase and height is obtained.

5. The method for measuring three-dimensional shape based on structured light of claim 4, characterized in that: The transformation expression for performing Fourier transform on a one-dimensional signal is: Where X(f) is the one-dimensional signal after Fourier transform, x(t) is the one-dimensional signal obtained after image compression, L is the length of the one-dimensional signal, f is the frequency, and t is the time; The solution expression of the stripe structure light period is: Where P1(f) is the single-side amplitude, T is the light period of the stripe structure, is the frequency corresponding to the highest single-side amplitude, i.e., the frequency of the fringe structure light; The corresponding formula between the phase and the height is: Where h is the height of the object, l is the distance between the camera and the projector, d is the height from the projector to the object plane, and p is the period of the fringe structure light. Modulate the phase of the object.

6. The method for measuring three-dimensional shape based on structured light of claim 2, characterized in that: The phase of the projected stripe structured light image is changed to solve the variation of the background light intensity with the spatial position as follows: Change the phase of the generated stripe structured light image to 0, π and The light is projected onto the object plane through a projector, and the background light intensity is captured by a camera. The change of background light intensity with spatial position is obtained after superposition.

7. The method for measuring three-dimensional shape based on structured light of claim 1, characterized in that: The method adopts a structured light phase solution algorithm based on natural phase shifting, solves the phase according to a number of stripe structured light intensity distribution images of the surface of the sample to be tested when it moves, captured by the camera, and the change of background light intensity with spatial position, and then obtains the unfolded phase through an unwrapping algorithm to obtain the phase distribution.

8. The method for measuring three-dimensional shape based on structured light of claim 7, characterized in that: The structured light phase solution algorithm based on natural phase shift is specifically: Solution steps: Divide the intensity distribution of the stripe structured light on the surface of the sample to be tested by the background light intensity when it is moving to determine the initial position p of the sample to be tested in pixel coordinates. i , so that the sample to be tested in each frame image obtained when the sample to be tested is moved is translated to the same spatial position, the background light intensity and contrast are considered to be constant between frames, the fringe phase is estimated, the object modulation phase is solved by least squares, and the harmonic coefficients are calculated in combination with Fourier transform to update the fringe light intensity distribution, and further the fringe structured light phase and the initial position of the object are updated by solving the updated fringe structured light intensity distribution and the object modulation phase; Iteration step: Repeat the solution step for multiple rounds to calculate the object modulation phase, stripe structure light phase and harmonic coefficients until the object modulation phase converges to a preset ideal accuracy.

9. The method for measuring three-dimensional shape based on structured light of claim 8, characterized in that: The expression of the intensity distribution of the stripe structured light on the surface of the sample to be tested after moving is: In the formula, I i (x, y) is the intensity distribution of the stripe structured light on the surface of the sample to be tested after it moves, A'(x, y) is the background light intensity, B'(x, y) is the contrast, B k is the harmonic coefficient, is the object modulation phase, i is the image frame number, δ i ' is the projection fringe phase; The calculation expression of the estimated value of the fringe phase is: In the formula, δ i ' is the estimated value of the fringe phase, p i is the initial position of the sample to be tested in pixel coordinates, and p is the stripe width; The expression for solving the object modulation phase using least squares is: In the formula, Modulate the phase of the object obtained by solving; The expression for calculating the harmonic coefficients in combination with Fourier transform is: Where F{} is the Fourier transform, (x m ,y m ) is the coordinate of the spectrum peak point; The update expression of the initial position of the object is: p i ←p i +Wrap(Dδ i ')*p In the formula, Δδ′ i is the phase difference of the stripe structured light before and after updating.

10. A structured light three-dimensional shape measurement device implementing the structured light three-dimensional shape measurement method based on natural phase shift as claimed in any one of claims 1 to 9, used for reconstructing the three-dimensional shape of a sample (3) to be measured, characterized in that: include: A camera (1), a projector (2) and a loading platform (4); the sample to be tested (3) is placed on the loading platform (4); the projector (2) projects a stripe structured light image vertically downward, the loading platform (4) is placed horizontally, the sample to be tested (3) can be movably placed on the loading platform (4), and the camera (1) collects imaging results at an angle.

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