Three-dimensional defect detection method and system based on multi-color stripe projection

Abstract

The invention relates to the technical field of photoelectric detection, and particularly discloses a three-dimensional defect detection method and system based on compound color stripe projection, and the method comprises an upper computer control and processing module which is used for generating a compound color stripe pattern coded with phase difference information, and coordinating and controlling the synchronous operation of the whole system; the structured light projection module is used for receiving the composite color stripe pattern and projecting the composite color stripe pattern to the surface of a measured object at one time; the imaging module is used for receiving the composite colored light reflected after being modulated by the surface of the measured object and separating the composite colored light into monochromatic light signals with different colors for synchronous acquisition; the imaging module further comprises an active highlight suppression unit which is used for dynamically adjusting the polarization direction according to an instruction of the upper computer control and processing module so as to suppress highlight caused by specular reflection. Multiple groups of sine fringes with fixed phase differences are projected to the surface of a measured object at one time. And a plurality of deformed fringe patterns with phase displacement can be synchronously acquired under single exposure.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photoelectric detection, and in particular to a three-dimensional defect detection method and system based on complex color stripe projection. BACKGROUND

[0002] Traditional structured light three-dimensional measurement technology faces severe challenges in the online detection of rapidly moving targets such as automobile sheet metal parts with high light reflection characteristics. On the one hand, the traditional phase shift method requires multiple time-sharing projection and collection, which cannot be applied to high-speed moving workpieces on the production line, and the defect detection efficiency is low. On the other hand, the surface varnish of the sheet metal part causes strong specular reflection, which forms a highlight overexposure at a specific viewing angle, resulting in the loss of local stripe information and the inability to detect subtle defects.

[0003] Existing highlight suppression methods mostly use orthogonal polarizers, but their polarization direction is fixed and cannot adapt to the dynamic changes in the polarization state of the highlight caused by the continuous change of the surface normal of the moving curved workpiece, and the suppression effect is limited. Although high dynamic range (HDR) imaging technology can be used, multiple exposures are still required, which still cannot meet the real-time requirements of dynamic detection.

[0004] Therefore, there is an urgent need for a three-dimensional detection system that can simultaneously complete multi-phase shift stripe collection within a single exposure and dynamically suppress the highlight that changes with angle and color. SUMMARY

[0005] The present application aims to provide a three-dimensional defect detection method and system based on complex color stripe projection to solve the problems raised in the background art.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solution: a three-dimensional defect detection system based on complex color stripe projection, comprising: a host computer control and processing module, a structured light projection module, and an imaging module; The host computer control and processing module is used to generate a complex color stripe pattern encoded with phase difference information and to coordinate and control the synchronous operation of the entire system. The structured light projection module is used to receive the complex color stripe pattern and project it onto the surface of the measured object at one time. The imaging module is used to receive the reflected complex color light modulated by the surface of the measured object and separate it into different color monochromatic light signals for synchronous collection. The imaging module further comprises an active highlight suppression unit for dynamically adjusting the polarization direction according to the instructions of the host computer control and processing module to suppress the highlight caused by specular reflection.

[0007] As a further scheme of the present application, the composite color fringe pattern is synthesized by encoding three sinusoidal fringe patterns with preset phase differences into red, green and blue color channels of a frame of color image respectively.

[0008] As a further scheme of the present application, the phase differences of the three sinusoidal fringe patterns are 0°, 120° and 240° respectively.

[0009] As a further scheme of the present application, the structured light projection module is a 3LCD projector, which includes liquid crystal panels corresponding to red, green and blue color channels respectively, for independently modulating light intensity of each channel and combining into a color fringe pattern for projection.

[0010] As a further scheme of the present application, the imaging module comprises: a dichroic mirror color separation group for separating the reflected composite color light into red, green and blue monochromatic light; three photoelectric detectors for receiving monochromatic light of corresponding color and performing image acquisition respectively; The three photoelectric detectors are synchronously exposed by hardware triggering.

[0011] As a further scheme of the present application, the dichroic mirror color separation group comprises two-stage dichroic mirrors: a first-stage dichroic mirror for reflecting red light and transmitting green and blue light; a second-stage dichroic mirror for reflecting green light and transmitting blue light.

[0012] As a further scheme of the present application, the active high light suppression unit comprises: an electric rotating table; a linear polarization analyzer mounted on the electric rotating table; The host computer control and processing module controls the electric rotating table to rotate, so as to adjust the polarization axis angle of the polarization analyzer.

[0013] As a further scheme of the present application, the host computer control and processing module performs a prediction-tracking gradient descent algorithm to dynamically search and track the optimal polarization angle for suppressing high light.

[0014] As a further scheme of the present application, the prediction-tracking gradient descent algorithm comprises: a coarse positioning stage: quickly locking the angle range with the lowest high light brightness by sparse sampling; a fine positioning stage: performing gradient descent method in the angle range to find the optimal suppression angle in a step-by-step manner; a tracking stage: using the continuity of polarization angles at adjacent time instants, taking the optimal angle at the last time instant as the starting point of the current search.

[0015] The application also provides a three-dimensional defect detection method based on the system, comprising the following steps: Fusing three sinusoidal fringe patterns with preset phase differences into a composite color fringe pattern and projecting the composite color fringe pattern onto the surface of the measured object; Receiving the monochromatic channel deformed fringe image after light splitting and highlight suppression, and determining the optimal polarization angle for suppressing highlights based on a prediction-tracking gradient descent algorithm in the highlight suppression step; Calculating absolute phase by a phase unwrapping algorithm; Reconstructing three-dimensional topography according to the absolute phase and performing defect detection.

[0016] Compared with the prior art, the application has the beneficial effects that: by projecting a plurality of sets of sinusoidal fringes with fixed phase differences onto the surface of the measured object at one time, at the imaging end, the reflected composite color light after being modulated by the surface of the object is separated in real time and the corresponding color light is received, so that a plurality of deformed fringe patterns with phase shifts are synchronously collected at one time. This design converts the three-step phase shift operation in the traditional time sequence into one-time concurrent processing in the color space, greatly improves the data acquisition speed, and enables the application to be effectively applied to the detection of fast-moving targets.

[0017] An active and dynamic highlight suppression scheme is proposed, which upgrades the "passive fixed extinction" to "active dynamic suppression", can match the changing polarization direction of highlights on the moving workpiece in real time, ensures that the best highlight suppression effect is always maintained during dynamic detection, and thus complete and accurate three-dimensional data of the surface is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only some embodiments of the application.

[0019] Figure 1 A structure diagram of a three-dimensional defect detection system based on composite color fringe projection provided by the embodiment of the application.

[0020] Figure 2 A full flowchart of a three-dimensional defect detection system based on composite color fringe projection provided by the embodiment of the application.

[0021] Figure 3 A fringe generation and projection flowchart provided by the embodiment of the application.

[0022] Figure 4 An active highlight suppression control flowchart provided by the embodiment of the application.

[0023] Figure 5 The red 0° phase sinusoidal stripe light provided for the embodiment of the present application.

[0024] Figure 6 The green 120° phase sinusoidal stripe light provided for the embodiment of the present application.

[0025] Figure 7 The blue 240° phase sinusoidal stripe light provided for the embodiment of the present application.

[0026] Figure 8 The synthesized stripe light projected onto the sheet metal part provided for the embodiment of the present application.

[0027] Figure 9 The high light effect diagram provided for the embodiment of the present application.

[0028] Figure 10 The effect diagram after eliminating the high light provided for the embodiment of the present application.

[0029] Wherein, 1, host computer control and processing module; 2, structured light projection module; 3, measured object; 4, convex lens; 5, first electrically controlled rotating polarizer; 6, red filter; 7, first photodetector; 8, dichroic mirror dichroic piece group; 9, second electrically controlled rotating polarizer; 10, green filter; 11, second photodetector; 12, third electrically controlled rotating polarizer; 13, blue filter; 14, third photodetector. DETAILED DESCRIPTION

[0030] In order to make the technical problems to be solved by the present application, the technical solutions and beneficial effects more clearly and clearly, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0031] As Figures 1 to 10 In the embodiment of the present application, a three-dimensional defect detection system based on complex color stripe projection comprises: Host computer control and processing module 1, structured light projection module 2, imaging module; The host computer control and processing module 1 is used to generate a complex color stripe pattern encoded with phase difference information, and to coordinate and control the synchronous operation of the whole system; The structured light projection module 2 is used to receive the complex color stripe pattern and project it onto the surface of the measured object 3 at one time; The imaging module is used to receive the reflected complex color light modulated by the surface of the measured object 3, and separate it into different color monochromatic light signals for synchronous collection; The imaging module further comprises an active highlight suppression unit for dynamically adjusting the polarization direction according to the instruction of the host computer control and processing module 1 to suppress the highlight caused by the specular reflection.

[0032] In the embodiment, the structured light projection module 2 comprises a projector, and the measured object 3 is a car sheet metal part.

[0033] The workflow of the whole system starts from the host computer. The host computer control and processing module 1, which comprises the host computer, firstly generates three sinusoidal fringe patterns with preset phase differences, encodes them into the red, green and blue color channels of a frame of color image respectively, and combines them into a single frame of composite fringe pattern, and is responsible for coordinating the synchronous operation of all hardware modules. Subsequently, the 3LCD projector receives the composite pattern and projects it onto the surface of the measured object 3 at one time. The topography of the object surface will modulate the fringe and cause its deformation. The reflected back composite color deformed fringe light is received by the dichroic mirror beam splitter group in real time, and is separated into three independent monochromatic lights of red, green and blue, which are guided to three photodetectors respectively for collection, so as to simultaneously acquire three deformed fringe images of single color channels. In this imaging process, the high-performance polarizer driven by the high-precision motorized rotary stage as an active highlight suppression unit will adjust the polarization axis angle in real time according to the instruction of the host computer, optimize the light of different wavelengths independently, and actively suppress the changing highlight caused by the movement of the object through a specially designed predictive-tracking gradient descent optimal angle search algorithm, so as to guarantee the image acquisition quality. Finally, all image data are returned to the host computer, which executes the phase unwrapping and three-dimensional reconstruction algorithm to finally complete the reconstruction of the three-dimensional topography of the object surface, and thus realizes the scratch detection on the surface of the car sheet metal part.

[0034] As Figures 5 to 10 , as a preferred embodiment of the present application, the composite color fringe pattern is obtained by combining three sinusoidal fringe patterns with preset phase differences into the red, green and blue color channels of a frame of color image respectively.

[0035] The phase differences of the three sinusoidal fringe patterns are 0°, 120° and 240° respectively.

[0036] In the embodiment, the host computer firstly generates three gray-scale sinusoidal fringe patterns with fixed phase differences of 0°, 120° and 240°, and inserts them into the red, green and blue channels of a frame of color image respectively to combine them into a single frame of composite color fringe pattern. The composite pattern is completely transmitted to the 3LCD projector through the video interface (HDMI).

[0037] As Figure 3As shown, in a preferred embodiment of the present invention, the structured light projection module 2 is a 3LCD projector, which includes liquid crystal panels corresponding to the red, green and blue channels respectively, for independently modulating the light intensity of each channel and combining them into a colored striped pattern for projection.

[0038] In this embodiment, after the projector receives the frame signal, its internal image processing circuit routes the brightness data of the three channels R, G, and B to the driving circuits of the corresponding red, green, and blue liquid crystal panels (LCDs) in parallel.

[0039] The high-intensity white light emitted by the projector's light source is separated into three primary color beams—red, green, and blue—by a beam splitter system, and each beam illuminates its corresponding LCD panel. The image on each LCD panel is independently modulated by the intensity of the primary color light passing through it—specifically, the red LCD panel is driven by the R channel data of the composite pattern, modulating the red light intensity and carrying 0° phase information; the green panel is driven by the G channel data, modulating the green light intensity and carrying 120° phase information; and the blue panel is driven by the B channel data, modulating the blue light intensity and carrying 240° phase information.

[0040] The modulated beams of the three primary colors of light are precisely recombined in the color combining prism of the projector, thereby projecting a composite color stripe pattern simultaneously from a projection lens. This pattern physically contains red, green, and blue sinusoidal stripes with different phase shifts.

[0041] Changes in the object's height modulate the fringe phase. The intensity distribution of the three fringes using the three-step phase-shifting method is as follows: ; in, , , These are the light intensity values ​​collected from the red, green, and blue channels, respectively. , , These represent the background light intensity of each channel, indicating the influence of ambient light and the reflectivity of the object's surface. , , These represent the stripe contrast for each channel; The absolute phase, modulated by the height of the object, is the solution to be obtained.

[0042] like Figure 1 As shown, in a preferred embodiment of the present invention, the imaging module includes: Dichroic mirror dichroic filter group 8 is used to separate the reflected composite light into three monochromatic lights: red, green, and blue. Three photodetectors are used to receive monochromatic light of the corresponding color and to acquire images. The three photodetectors achieve synchronous exposure through hardware triggering.

[0043] In this embodiment, the three photodetectors include a first photodetector 7, a second photodetector 11, and a third photodetector 14. The active high-light suppression unit includes a first electrically controlled rotating polarizer 5, a second electrically controlled rotating polarizer 9, and a third electrically controlled rotating polarizer 12. A convex lens 4 is also provided on the reflected light path.

[0044] A red filter 6 is provided between the first electrically controlled rotating polarizer 5 and the first photodetector 7, a green filter 10 is provided between the second electrically controlled rotating polarizer 9 and the second photodetector 11, and a blue filter 13 is provided between the third electrically controlled rotating polarizer 12 and the third photodetector 14.

[0045] like Figure 1 As shown, in a preferred embodiment of the present invention, the dichroic mirror separation group 8 includes two-stage dichroic mirrors: The first-order dichroic mirror is used to reflect red light and transmit green and blue light. The second-order dichroic mirror is used to reflect green light and transmit blue light.

[0046] In this embodiment, the reflected light, which is deformed after being modulated by the surface height of the sheet metal part, is first collected and collimated by a main imaging system, namely convex lens 4.

[0047] The collimated polychromatic beam enters the dichroic mirror beam splitter group. This group consists of two-stage dichroic mirrors: The first-order dichroic mirror is designed to reflect long-wavelength light (red light with wavelengths > 630nm) while transmitting medium- and short-wavelength green and blue light. The reflected red light stripe image is received by the first photodetector 7.

[0048] The second-stage dichroic mirror receives the transmitted green / blue mixed light. Its film is designed to reflect mid-wavelength light (green light with wavelengths between 500nm and 560nm) while transmitting short-wavelength blue light. The reflected green stripe image is received by the second photodetector 11.

[0049] The remaining blue light (wavelength <480nm) is transmitted directly and received by the third photodetector 14.

[0050] The three photodetectors are connected by a hardware trigger cable and are controlled by a host computer to ensure that they are exposed and acquire images synchronously at exactly the same time, so that pure red, green and blue deformed stripe patterns can be obtained in a single exposure.

[0051] In a preferred embodiment of the present invention, the active specular suppression unit includes: A motorized rotary stage; A linear polarizer mounted on the motorized rotary stage; The host computer control and processing module 1 adjusts the polarization axis angle of the polarizer by controlling the rotation of the motorized rotary stage.

[0052] In this embodiment, the linear polarizer mounted on the motorized rotary stage includes a first electrically controlled rotating polarizer 5, a second electrically controlled rotating polarizer 9, and a third electrically controlled rotating polarizer 12.

[0053] The host computer control and processing module 1 performs a prediction-tracking gradient descent algorithm to dynamically search and track the optimal polarization angle for suppressing highlights.

[0054] The prediction-tracking gradient descent algorithm includes: Coarse positioning stage: quickly lock the angle interval with the lowest highlight brightness through sparse sampling; Fine positioning stage: perform gradient descent method within the angle interval to find the optimal suppression angle in a step-by-step manner; Tracking stage: use the continuity of the polarization angle at adjacent time points, and use the optimal angle at the previous time as the starting point for the current search.

[0055] In this embodiment, before entering each photodetector, a high-precision motorized rotary stage (such as Thorlabs PRM1Z8) and a visible light broadband high-performance linear polarizer (such as Thorlabs LPVIZ series) mounted thereon are arranged in the optical path to form an active highlight suppression unit.

[0056] The selection of the mechanical rotation scheme is based on the pursuit of extreme measurement accuracy. Compared with liquid crystal devices, high-quality linear polarizers (polarimeters) can provide ultra-high extinction ratios far higher than 100000:1, but require different wavelength selection for high-transmittance polarizers, and their polarization performance is very stable with changes in wavelength and temperature. This provides the most reliable physical basis for eliminating highlights and subsequent accurate colorimetric response correction. PRM1Z8 type DC servo motor rotary stage provides positioning accuracy and repeatability better than 0.1°, ensuring accurate and error-free angle control.

[0057] According to Malus' law, the light intensity after the linear polarizer can be represented as: ; Where, is the incident light intensity, is the angle between the polarizer axis and the incident light polarization direction.

[0058] For multi-color light (such as R / G / B), the optimal polarization angle for high light suppression may be slightly different for different color channels due to the differences in polarization characteristics of different wavelengths, especially the wavelength-dependent phase delay introduced by the reflection of metal surfaces. The present application further improves the suppression effect by optimizing the polarization control of R, G, and B light channels independently.

[0059] Traditional Malus law describes the intensity attenuation of linearly polarized light passing through an analyzer, but it does not consider the wavelength λ factor. For specular reflection (high light) on a metal surface, the polarization state of the reflected light is related to the wavelength and the incident angle.

[0060] Therefore, we can propose a multi-wavelength-dependent Malus law correction model: For each color channel c (c ∈ {R, G, B}), the light intensity after passing through the analyzer is: ; where is the final output light intensity of channel c (red / green / blue), is the original high light incident light intensity of channel c. is the wavelength and angle-dependent transmittance coefficient, is the preset analyzer rotation angle for channel c, which is the system control variable. is the optimal suppression polarization angle of the incident light of channel c.

[0061] Predictive-tracking gradient descent optimal angle search algorithm: First, the system performs a default angle pre-collection, and quickly locates the high light area by brightness threshold method. If it is the first detection or the target has changed dramatically, the system performs a fast sparse scan as a global coarse positioning. Command the rotation table to collect the brightness of the high light area every 30°, only a few sampling points are needed to lock a rough angle interval with the lowest brightness .

[0062] Then the system immediately performs fine positioning with as the center using the gradient descent method. Specifically, the controller commands the rotation table to fine-tune the sampling at both sides of with a small angle (±5°), determines the gradient direction (i.e. the direction with the fastest brightness decrease) according to the brightness change, and then continues to iterate the search with a smaller step (1°) along the direction until the optimal suppression angle is found at which the brightness of the high light area no longer decreases. This process only needs a few steps to converge and takes very short time.

[0063] The mathematical description of this process is: Define the brightness function as the angle The high-brightness intensity of the workpiece at the kth step is denoted as Lk. ; wherein, is the angle of the kth step, is the step size (1°), is the gradient of the brightness function, indicating the rate of change of brightness.

[0064] Since the measured workpiece is continuously moving, the polarization direction of the surface highlight will also change continuously. Therefore, the optimal angle at the next time must be located in the neighborhood of the optimal angle at the current time. The algorithm uses this prior knowledge to skip the global coarse positioning step from the second measurement and directly use the at the last time as the starting point of the local gradient fine positioning this time, thereby realizing real-time and efficient tracking of the target polarization direction.

[0065] The mathematical model of this process can be represented by the following formula: ; wherein, is the change in polarization direction at adjacent times, which is estimated by the brightness difference between adjacent two images.

[0066] This active suppression process converts a high-precision but limited-speed mechanical system into a dynamic system that can intelligently predict and accurately match the changing polarization direction of the highlight on the moving workpiece, ensuring the best highlight suppression effect at all times. The algorithm flowchart for the highlight suppression part is shown in Figure 4 .

[0067] The photoelectric detector detects the deformed fringe after the object is modulated. The height of the same object point is different, and the fringe phase shift is also different. According to the phase shift, the phase calculation part can be entered to reconstruct the 3D model of the automobile sheet metal part.

[0068] When the phase difference caused by the change in the height of the object surface exceeds 2π, the light intensity distribution will repeat, and it is not possible to directly distinguish the phase of different periods, so the phase calculation result naturally presents a wrapped state ([-π, π]). The principal value of the phase is solved by eliminating the background and contrast from the light intensity information of three fringes.

[0069] Three-step phase shift method phase calculation: ; wherein, is the four-quadrant arctangent, and the output range is [-π, π]. It can be converted to the [0, 2π] range by adding 2π operation.

[0070] ​Due to the nature of the arctangent function, the directly calculated phase is wrapped, discontinuous. In order to obtain the real phase corresponding to the object height, phase unwrapping must be performed to obtain the real phase .

[0071] The core of phase unwrapping is to detect and compensate for the 2π integer multiple jumps in the wrapped phase map. The basic principle can be expressed as: along the spatial path of the phase data, when the phase difference value of adjacent pixels exceeds the jump threshold of π, the jump is eliminated by adding or subtracting 2kπ (k is an integer) to restore the continuity of the phase. The mathematical expression is: ; Where is the number of integer jumps (i.e. order) required for each pixel. In practical applications, robust algorithms such as quality map guided path, least squares or multi-frequency heterodyne can be used to complete this process to ensure that it can still be correctly unwrapped when there is noise and occlusion.

[0072] Finally, through the pre-calibrated system parameters, the continuous absolute phase obtained after unwrapping is converted into the real height information of the object , the three-dimensional topography is reconstructed, and finally the three-dimensional point cloud generated is combined with the upper computer software processing to realize the surface detection of the automobile sheet metal part.

[0073] The present application also provides a three-dimensional defect detection method of the system, characterized by comprising the following steps: fuse three sinusoidal fringe patterns with a predetermined phase difference into a composite color fringe pattern and project it onto the surface of the measured object 3; receive the monochrome channel deformed fringe image after light splitting and highlight suppression, and determine the optimal polarization angle for suppressing highlights based on the prediction-tracking gradient descent algorithm in the highlight suppression step; calculate the absolute phase by phase unwrapping and phase unwrapping algorithms; reconstruct the three-dimensional topography according to the absolute phase and perform defect detection.

[0074] The present application proposes a high-efficiency single-shot three-dimensional measurement method, which solves the problem of low detection efficiency caused by multiple projections to ensure accuracy in traditional structured light technology.

[0075] Three groups of red (R), green (G), and blue (B) sinusoidal fringes with fixed phase difference (0°, 120°, 240°) are projected onto the surface of the measured object 3 by a 3LCD projector at one time. At the imaging end, an optical splitting system composed of a dichroic mirror is used to separate the composite color light reflected after being modulated by the surface of the object into independent red, green, and blue light in real time. Three photodetectors are used to receive the corresponding color light, so that three deformed fringe patterns with phase shifts are synchronously collected under single exposure.

[0076] This design converts the three-step phase shift operation in the traditional time sequence into one-time concurrent processing in the color space, greatly improves the data acquisition speed, and enables it to be effectively applied to the detection of fast-moving targets.

[0077] The present application proposes an active and dynamic high light suppression scheme for the strong reflection (high light) interference problem of metal surfaces such as automobile sheet metal parts, overcoming the limitations of traditional fixed polarizers.

[0078] Traditional fixed-angle polarizers cannot cope with the simultaneous changes in high light position and polarization direction caused by the movement or curvature changes of the workpiece, resulting in reduced or ineffective suppression efficiency.

[0079] The present application uses an electrically controlled rotating polarizer to quickly adjust the polarization direction of the polarizer through a dynamic polarization matching algorithm that tracks the polarization angle of the high light in real time. This process upgrades the "passive fixed extinction" to "active dynamic suppression".

[0080] This technology can match the constantly changing polarization direction of the high light on the moving workpiece in real time, ensuring that the best high light suppression effect is maintained during dynamic detection, thereby obtaining complete and accurate surface three-dimensional data.

[0081] The above only describes the preferred embodiments of the present application and does not limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A three-dimensional defect detection system based on polychromatic fringe projection, characterized in that, include: The system comprises a host computer control and processing module, a structured light projection module, and an imaging module. The host computer control and processing module is used to generate composite color stripe patterns encoded with phase difference information and to coordinate and control the synchronous operation of the entire system. The structured light projection module is used to receive the composite color stripe pattern and project it onto the surface of the object being measured in one go; The imaging module is used to receive composite color light reflected after being modulated by the surface of the object under test, and to separate it into monochromatic light signals of different colors for synchronous acquisition. The imaging module also includes an active specular highlight suppression unit, which dynamically adjusts the polarization direction according to the instructions of the host computer control and processing module to suppress specular highlights caused by specular reflection.

2. The three-dimensional defect detection system based on polychromatic fringe projection according to claim 1, characterized in that, The composite color stripe pattern is obtained by encoding three sinusoidal stripe patterns with a preset phase difference into the red, green, and blue color channels of a color image frame, respectively.

3. The three-dimensional defect detection system based on polychromatic fringe projection according to claim 2, characterized in that, The phase differences of the three sinusoidal fringe patterns are 0°, 120°, and 240°, respectively.

4. The three-dimensional defect detection system based on polychromatic fringe projection according to claim 1, characterized in that, The structured light projection module is a 3LCD projector, which includes liquid crystal panels corresponding to the red, green, and blue channels respectively. These panels are used to independently modulate the light intensity of each channel and combine them into a colored striped pattern for projection.

5. A three-dimensional defect detection system based on polychromatic fringe projection according to claim 1, characterized in that, The imaging module includes: Dichroic mirrors are used to separate the reflected composite light into three monochromatic lights: red, green, and blue. Three photodetectors are used to receive monochromatic light of the corresponding color and to acquire images. The three photodetectors achieve synchronous exposure through hardware triggering.

6. A three-dimensional defect detection system based on polychromatic fringe projection according to claim 5, characterized in that, The dichroic mirror separation group includes two levels of dichroic mirrors: The first-order dichroic mirror is used to reflect red light and transmit green and blue light. The second-order dichroic mirror is used to reflect green light and transmit blue light.

7. A three-dimensional defect detection system based on polychromatic fringe projection according to claim 1 or 5, characterized in that, The active specular suppression unit includes: Electric rotary table; Linear polarization analyzer installed on the electric rotary table; The host computer control and processing module controls the rotation of the electric rotary table to adjust the polarization axis angle of the analyzer.

8. A three-dimensional defect detection system based on polychromatic fringe projection according to claim 7, characterized in that, The host computer control and processing module executes a predictive-tracking gradient descent algorithm to dynamically search for and track the optimal polarization angle for suppressing specular highlights.

9. A three-dimensional defect detection system based on polychromatic fringe projection according to claim 8, characterized in that, The predictive-tracking gradient descent algorithm includes: Coarse localization stage: Quickly locate the angle range with the lowest highlight brightness through sparse sampling; Fine positioning stage: Gradient descent is performed within the specified angle range to find the optimal suppression angle in a step-by-step manner; Tracking phase: Utilizing the continuity of polarization angles between adjacent time moments, the optimal angle of the previous time moment is used as the starting point for the current search.

10. A three-dimensional defect detection method based on the three-dimensional defect detection system based on polychromatic fringe projection as described in any one of claims 1-9, characterized in that, Includes the following steps: Three sinusoidal fringe patterns with a preset phase difference are fused into a composite color fringe pattern and projected onto the surface of the object being measured. The image of the monochrome channel deformed stripes after beam splitting and highlight suppression is received. In the highlight suppression step, the optimal polarization angle for suppressing highlights is determined based on a prediction-tracking gradient descent algorithm. The absolute phase is calculated using phase solution and phase expansion algorithms; The three-dimensional shape is reconstructed based on the absolute phase, and defects are detected.

Images