Structured light three-dimensional shape measurement method and device based on natural phase shift

Abstract

The invention relates to a structured light three-dimensional shape measurement method and device based on natural phase shift, and the method comprises the steps: calibrating all parameters of a system, solving a corresponding formula between the phase and the height, and moving a to-be-measured sample; the method comprises the following steps: projecting a fixed stripe structured light image to the surface of a to-be-detected sample through a projector, collecting stripe light intensity distribution of the surface of the to-be-detected sample during movement through a camera, and solving corresponding phase distribution by adopting a structured light phase solving algorithm based on natural phase shift; and converting the solved phase distribution into a height value according to a corresponding formula between the phase and the height so as to extract the three-dimensional shape information of the object. Compared with the prior art, an object is allowed to move freely in the measurement process and does not need to be fixed, so that real in-situ measurement is realized, and the application range of three-dimensional shape measurement is widened.

Description

Technical Field

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

[0002] Surface structured light measurement technology for measuring the three-dimensional shape of objects has important applications in the semiconductor industry, automobile industry, aerospace industry and other fields. Surface structured light measurement technology accurately encodes the position information of each point on the surface of an object by projecting structured light information with strong texture features on the surface of the object, then uses a camera to image the structured light projected onto the surface of the object, performs phase resolution on the past fringe image, and then decodes the position information of each point on the surface of the object through triangular ray tracing technology to obtain the surface three-dimensional shape information of the object. It has the advantages of high precision and high resolution, non-contact, strong robustness and high speed.

[0003] Traditional structured light 3D imaging technology requires phase shifting of the projected fringe image during the measurement process, taking multiple projected fringe images at different initial phases, and using the known initial phase difference of the fringe image to restore the phase information of the fringe at each point on the surface, so as to accurately calculate the phase information of the fringe at each point on the surface. However, this traditional technology requires the object to remain stationary during the phase shifting process, otherwise the final phase solution will fail. Therefore, traditional structured light 3D profiling systems face huge challenges when detecting moving objects. Summary of the invention

[0004] The purpose of the present invention is to provide a structured light three-dimensional shape measurement method and device based on natural phase shifting in order to overcome the defect of the prior art that the object must remain stationary during the phase shifting process.

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

[0006] A structured light three-dimensional shape measurement method based on natural phase shifting comprises the following steps:

[0007] 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;

[0008] After calibrating the system parameters and solving the corresponding formula between phase and height, move the sample to be tested; project a fixed structured light image onto the surface of the sample to be tested through a projector, collect several pictures of the stripe structured light intensity distribution on the surface of the sample to be tested when it is moving through a camera, and use the structured light phase solution algorithm based on natural phase shift to solve the corresponding phase distribution; according to the corresponding formula between phase and height, convert the solved phase distribution into a height value, thereby extracting the three-dimensional morphology information of the object.

[0009] Furthermore, the process of calibrating the system parameters and solving the phase-to-height corresponding formula is as follows:

[0010] A projector and a camera are set above the object plane, and the system parameters of the projector and the camera are calibrated; the 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 change of background light intensity with spatial position.

[0011] Furthermore, the system parameter calibration process of the projector and camera is specifically as follows:

[0012] 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;

[0013] 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.

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

[0015] 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.

[0016] Furthermore, the transformation expression of Fourier transform of the one-dimensional signal is:

[0017]

[0018] 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;

[0019] The solution expression of the stripe structure light period is:

[0020]

[0021]

[0022] 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;

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

[0024]

[0025] 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.

[0026] Furthermore, 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:

[0027] Change the phase of the generated stripe structured light image to 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.

[0028] Furthermore, the method adopts a structured light phase solution algorithm based on natural phase shifting, solves the phase according to several stripe structured light intensity distribution images of the surface of the sample to be tested when it moves, 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.

[0029] Furthermore, the structured light phase solution algorithm based on natural phase shift is specifically:

[0030] 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;

[0031] 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.

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

[0033]

[0034] 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;

[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 tested in pixel coordinates, and p is the stripe width;

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

[0039]

[0040] In the formula, Modulate the phase of the object obtained by solving;

[0041] The expression for calculating the harmonic coefficients in combination with Fourier transform is:

[0042]

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

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

[0045] p i ←p i +Wrap(Δδ i ')*p

[0046] In the formula, Δδ i ' is the phase difference of the stripe structured light before and after the update.

[0047] The present invention also provides a structured light three-dimensional shape measurement device that implements the above-mentioned structured light three-dimensional shape measurement method based on natural phase shift, which is used to reconstruct the three-dimensional shape of a sample to be measured, including: a camera, a projector and a loading platform; the sample to be measured is placed on the loading platform; the projector projects a stripe structured light image vertically downward, the loading platform is placed horizontally, the sample to be measured can be movably placed on the loading platform, and the camera is tilted to collect imaging results.

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

[0049] (1) Compared with the traditional structured light active phase shifting method, the structured light three-dimensional shape measurement method based on natural phase shifting proposed in the present invention captures the natural phase shifting process of the object under specific lighting conditions, and uses the phase difference between the frame and the frame to solve the real phase based on the natural phase shifting algorithm, and converts the phase value into the height value according to the pre-calculated corresponding formula between the phase and the height, so as to reconstruct the three-dimensional shape of the naturally moving object, allowing the sample to move freely during the measurement process without the need for a fixed position, thereby realizing true in-situ measurement, improving the real-time and versatility of the method, breaking through the technical bottleneck of the traditional structured light method that requires the projection stripes to be transformed, and broadening the application scope of three-dimensional shape measurement. On the other hand, it eliminates the need for complex control devices and mechanical structures, reducing the complexity and cost of the system.

[0050] (2) The Fourier transform fitting algorithm proposed in the present invention realizes the resolution of high-order harmonics and solves the problem of inaccurate object modulation phase resolution caused by factors such as nonlinearity of light intensity, position estimation deviation of the object, and axial jitter of the measurement plane during the measurement process, thereby further improving the accuracy and reliability of the structured light three-dimensional morphology measurement method. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 A schematic diagram of the structure of a structured light three-dimensional shape measurement device based on natural phase shift provided in an embodiment of the present invention;

[0052] Figure 2 A schematic diagram of the composition of a structured light three-dimensional shape measurement device based on natural phase shift provided in an embodiment of the present invention;

[0053] Figure 3 A schematic flow chart of a structured light three-dimensional shape measurement method based on natural phase shifting provided in an embodiment of the present invention;

[0054] Figure 4 A schematic diagram of a state of measuring a sphere under measurement by a structured light three-dimensional shape measurement device based on natural phase shift provided in an embodiment of the present invention;

[0055] Figure 5 A comparison chart of experimental results of using the structured light three-dimensional topography measurement method based on natural phase shift of the present invention and using the traditional structured light three-dimensional topography measurement method based on active phase shift under Matlab simulation provided in an embodiment of the present invention;

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

[0057] Figure 7 A comparison diagram of simulation effects of using the structured light three-dimensional topography measurement method based on natural phase shifting of the present invention and using the traditional structured light three-dimensional topography measurement method based on active phase shifting under Matlab simulation is provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0058] In order to make the purpose, 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 in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here 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 accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0060] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0061] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, or are the directions or positional relationships in which the inventive product is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0062] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0063] In addition, the terms "horizontal", "vertical" and the like do not mean that the components are required to be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0064] Example 1

[0065] like Figure 3 As shown, this embodiment provides a structured light three-dimensional shape measurement method based on natural phase shift, comprising the following steps:

[0066] 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;

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

[0068] The 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 by combining the system parameters; the phase of the projected stripe structured light image is changed to solve the change of background light intensity with spatial position.

[0069] Equivalently, the above method comprises 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, 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 camera is set to collect actual light intensity information and stripe structured light distribution, the camera may be a monocular camera, 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;

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

[0073] Place a checkerboard calibration plate on the loading platform, and project complementary Gray code images onto the checkerboard calibration plate through a projector. The number of Gray code images must be sufficient to fully encode each point on the projector imaging surface. Change the position of the checkerboard calibration plate multiple times, and take pictures of the imaging results projected onto the checkerboard calibration plate each time.

[0074] The imaging model of the projector and camera is established as a pinhole camera imaging model. The corner points of the chessboard captured in each photo are identified and the corresponding complete Gray code sequence is solved. The local homology matrix corresponding to each corner point is calculated, and the coordinates of each corner point on the camera imaging plane are converted into coordinates on the projector imaging plane through the local homology matrix, thereby realizing the calibration of the internal and external parameters of the projector and camera pinhole imaging model.

[0075] S2: Projecting a stripe structured light image on the surface of the object plane through a projector, collecting light intensity information and stripe distribution on the surface of the object plane through a camera, and obtaining stripe light intensity, i.e., stripe structured light image;

[0076] S3: Use Fourier transform to solve the light period of the stripe structure, and combine the system parameters of the projector and 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 image signal of the fringed structured light, it compresses the image signal into a one-dimensional signal and obtains the fringing period through Fourier transform. Based on the system parameters and geometric relationship, the calculation formula between the phase and height of the object is obtained.

[0079] The expression of the stripe 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 image frame number, δ is the projection fringe phase;

[0082] The fringe structured light image signal captured by the camera is compressed into a one-dimensional signal, and the image transformation formula of the fringe period is obtained by Fourier transform:

[0083]

[0084] Where W is the image width, img is the captured background stripe image;

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

[0086]

[0087] 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 signal (i.e. the height of the image), and f is the frequency;

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

[0089]

[0090]

[0091] Where P1(f) is the single-side amplitude, T is the fringe signal period;

[0092] The calculation formula between the phase and height of an object 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 object plane, p is the fringe period, and φ is the object modulation phase. φ and h can be approximately regarded as a linear relationship.

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

[0096] The fringes can be phase-shifted in four steps to solve the variation of background light intensity with spatial position. The specific process is:

[0097] The phases of the cosine fringe images generated by changing are The light is projected onto the stage 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.

[0098] S5: placing the sample to be tested on the loading plane and moving it; projecting a stripe structured light image onto the surface of the sample to be tested by a projector;

[0099] S6: Collect the stripe light intensity distribution on the surface of the sample to be tested when it moves through the camera;

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

[0101] A structured light phase solution algorithm based on natural phase shifting is adopted to solve the phase according to the stripe light intensity distribution on the surface of the sample to be tested when it moves, and the change of background light intensity with spatial position. Then, the unwrapping algorithm is used to obtain the unfolded phase and the phase distribution.

[0102] The structured light phase solution algorithm based on natural phase shift is as follows:

[0103] Solution steps: Divide the stripe light intensity distribution 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 the fringe phase and the initial position of the object are further updated by solving the updated fringe light intensity distribution and the object modulation phase;

[0104] Iteration step: Repeat the solution step for multiple rounds to calculate the object modulation phase, fringe phase and harmonic coefficients until the object modulation phase converges to the preset ideal accuracy.

[0105] This is equivalent to the natural phase shifting algorithm solving the phase through iteration. First, I i Divide it by the background light intensity to compensate for the influence of uneven light intensity, and determine the initial position p of the object in pixel coordinates by optical flow method or marking. i , so as to translate the object to be tested in each frame image to the same spatial position, regard the background light intensity and contrast as constant between frames, estimate the fringe phase, use the least square solution formula combined with Fourier transform to iteratively solve the object modulation phase and update the fringe light intensity, and then further update the fringe phase and the initial position of the object through the updated light intensity and object modulation phase solution, repeat the above steps for multiple rounds of calculation of the physical modulation phase, fringe phase, and harmonic terms until they converge to the ideal accuracy, and finally obtain the object modulation phase with 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 projection fringe phase;

[0109] The expression of the fringe phase estimate is:

[0110]

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

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

[0113]

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

[0115] The Fourier transform formula for calculating harmonic coefficients 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] Where F{} is the Fourier transform, (x m ,y m ) is the coordinate of the spectrum peak point;

[0118] The formula for updating the fringe intensity using the calculated harmonic coefficient is:

[0119]

[0120] The further position calculation update expression is:

[0121] p i ←p i +Wrap(Δδ i ')*p

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

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

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

[0125] Example 2

[0126] like Figure 1 and Figure 2 As shown, this embodiment provides a three-dimensional morphology measurement device that implements a structured light three-dimensional morphology measurement method based on natural phase shift as in Embodiment 1, which is used to perform three-dimensional morphology measurement on a sample to be measured, and includes a camera 1, a projector 2 and a loading platform 4; the sample to be measured 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 measured 3 is placed on the loading platform 4, and moves freely on the loading platform 4, and the camera 1 is tilted to collect imaging results.

[0127] like Figure 4As shown, the three-dimensional shape measurement device based on natural phase shift structured light three-dimensional shape measurement of this embodiment measures a regular geometric body, specifically a sphere. The measurement process is as follows: the system parameters of the monocular camera and the projector in the device are calibrated, and a fixed stripe structured light image is projected onto the background by the projector. The camera captures the stripe light intensity on the background, and solves the stripe period by Fourier transform, and obtains the corresponding formula between phase and height in combination with the system parameters, and then performs four-step phase shift on the stripes to solve the change of background light intensity with spatial position; then, the object to be measured is mounted on the loading platform and placed in the initial position, and the projector projects a stripe structured light image of fixed stripes onto the surface of the object to be measured. During the movement of the object on the loading platform, the camera is used to record the light intensity of the object when it moves on the loading plane, and the phase is solved by the natural phase shift solution algorithm, and the unfolded phase is further obtained by the unwrapping algorithm, so that the phase value is converted into a height value according to the corresponding formula between phase and height, and finally the three-dimensional reconstruction of the surface of the sample to be measured is realized.

[0128] like Figure 5 As shown in the figure, it is a comparison diagram of the effects of using the structured light three-dimensional topography measurement method based on natural phase shift of the present invention and the traditional structured light three-dimensional topography measurement method based on active phase shift in an actual experimental environment. The measurement effect of the natural phase shift method of the present invention is close to that of the traditional method, and meets the high-precision dynamic measurement requirements.

[0129] Example 3

[0130] like Figure 6 As shown, this embodiment is substantially the same as Embodiment 2, except that this embodiment is performed in a Matlab simulation environment, and the fringe projection of the projector on the object to be measured and the imaging of the camera are realized by 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 solution effect of the traditional active phase shifting method and the solution effect of the passive phase shifting method involved in the present invention.

[0131] like Figure 7 As shown in FIG. 1 , a comparison diagram of the effects of the structured light three-dimensional topography measurement method based on natural phase shift of the present invention and the traditional structured light three-dimensional topography measurement method based on active phase shift under Matlab simulation is shown. The measurement effect of the natural phase shift method of the present invention on complex surface shapes is also close to that of the traditional method, and the high-precision dynamic measurement requirements are achieved.

[0132] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection 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 process of calibrating the system parameters and solving the phase and height corresponding formula 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 3, 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 structured light three-dimensional shape measurement method based on natural phase shift according to 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 the update.

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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