CN109781033B - Deep ultraviolet structured light precision detection device for transparent material three-dimensional contour reconstruction - Google Patents
Deep ultraviolet structured light precision detection device for transparent material three-dimensional contour reconstruction Download PDFInfo
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Abstract
The invention discloses a deep ultraviolet structured light precision detection device for three-dimensional contour reconstruction of a transparent material. The deep ultraviolet stripe projection system comprises a wide-spectrum deep ultraviolet LED light source, a narrow-band ultraviolet band filter, a collimation beam expanding system, a one-dimensional deep ultraviolet transverse shearing grating and a beam expanding lens group, wherein the wide-spectrum deep ultraviolet LED light source and the narrow-band ultraviolet band filter form an ultraviolet light source unit; the deep ultraviolet imaging system consists of an imaging lens and a deep ultraviolet CCD. The invention realizes high-precision deformation detection on the three-dimensional profile of the surface of the curved glass made of the transparent material, overcomes the defect that the deformation of the upper surface and the lower surface is confused when the traditional visible structured light source penetrates through the transparent material, avoids the error caused by the sawtooth-shaped stripes generated by the digital exposure sinusoidal grating, and realizes the accurate reconstruction of the three-dimensional profile of the large-size curved glass.
Description
Technical Field
The invention belongs to the technical field of machine vision structured light precision detection, and particularly relates to a deep ultraviolet structured light detection imaging system applied to measuring a three-dimensional profile of a transparent material.
Background
Transparent materials are used in various categories in national defense, industrialization and daily life: small to transparent optical elements in various lenses, large to protective glass of aircraft and automobile cabins, various display screens and the like. Free-form surface elements made of various transparent materials such as those mentioned above have been widely used in daily research and daily life, and with the development of technology and industrialization, the requirements for detecting surface deformation of protective glass of aircraft and automobile cabins have been increasing. However, these glass profiles are basically free-form surfaces and have large areas, and the deformation amount cannot be obtained by a method of detecting a spherical surface by optical interference. At present, the similar complex contour detection and the multi-purpose structured light projection are performed at home and abroad, stripe structured light with alternate brightness and darkness can be generated by a projector, and the method is realized by combining monocular or binocular vision methods, but the methods are generally used for various non-transparent diffuse reflection materials, and the deformation information can be acquired by adopting scattering imaging. For the optical detection of the surface deformation structure of the transparent material, two key difficulties exist in the acquisition of surface shape information: firstly, the large-area transparent material is smooth and can only be subjected to reflection imaging, the deformation of the upper surface and the deformation of the lower surface can be mixed together by the reflection imaging of the upper surface and the lower surface, single information of the upper surface cannot be obtained, and meanwhile, the reflectivity of the transparent material is very low, so that the CCD obtains weak information mixed with the upper surface and the lower surface, and the contrast of stripes is very poor, as shown in FIG. 2; and secondly, the form of generating light with alternate bright and dark stripe-shaped structures is provided with a projector or a grating, the projector basically generates visible light structural light, and the deformation of the upper surface and the deformation of the lower surface are mixed together by the reflection imaging of the upper surface and the lower surface, so that the information of the upper surface and the lower surface cannot be distinguished. Furthermore, the grating lithography technology is implemented by using a digital technology, so that structured light irradiated on an object to be detected can present a grid saw-toothed structure, and high-precision detection cannot be achieved, as shown in fig. 3 (a). These are bottlenecks in deformation detection of transparent materials, so that research on high-precision optical three-dimensional contour detection of transparent materials at home and abroad is still blank, and the application limitation of the transparent materials in the fields of scientific research and industrialization is greatly limited. Therefore, the invention provides a deep ultraviolet structured light precision detection method for transparent material three-dimensional contour reconstruction.
Disclosure of Invention
The invention aims to provide a deep ultraviolet structured light precision detection device for three-dimensional contour reconstruction of a transparent material aiming at the blank of the prior art. The method provides a method for realizing high-precision deformation detection on the three-dimensional profile of the surface of the curved glass made of the transparent material by using a deep ultraviolet waveband structured light detection system for the first time.
The technical scheme adopted by the invention for solving the technical problems is as follows:
the deep ultraviolet stripe projection system comprises a wide-spectrum deep ultraviolet LED light source (S0), a narrow-band ultraviolet band filter (S1), a collimation beam expanding system (S2), a one-dimensional deep ultraviolet transverse shear grating (S3) and a beam expander set (S5), wherein the wide-spectrum deep ultraviolet LED light source (S0) and the narrow-band ultraviolet band filter (S1) form an ultraviolet light source unit; the deep ultraviolet imaging system consists of an imaging lens (S7) and a deep ultraviolet CCD (S8);
broadband light emitted by a deep ultraviolet LED light source (S0) is incident into a narrow band ultraviolet band filter plate (S1) to obtain narrow band deep ultraviolet light, the narrow band deep ultraviolet light passes through a collimation beam expanding system (S2) and then is incident on a one-dimensional transverse shear grating (S3) as parallel light, two replication wavefronts with the same wavefront and a certain inclination angle are formed by diffraction, interference fringes are formed in the overlapping area of the two replication wavefronts and serve as stripe structure light, and the stripe structure light forms the deep ultraviolet band structure light with a stable period through a beam expanding lens group (S5); the deep ultraviolet waveband structured light is projected on a reference platform (S6) which is provided with a measured object (S9) made of transparent materials, and a deep ultraviolet imaging system is used for receiving a deformed stripe image modulated by the height of an object.
The one-dimensional transverse shearing grating (S3) is provided with a grating phase shift device (S4), so that the rotation and phase shift operation of the deep ultraviolet waveband structured light is realized.
Since the diffraction field formed by diffraction is only diffraction light of +1 and-1 diffraction orders, the overlapped area of the two copied wavefronts forms interference fringes as fringe structure light.
The one-dimensional transverse shear grating (S3) comprises a one-dimensional amplitude grating (G1) and a one-dimensional phase grating (G2); the one-dimensional amplitude grating (G1) adopts a series of random coding modes to enable the transmittance to meet the distribution of | cos (π x/d) |, wherein d is the grating period of the one-dimensional transverse shearing light (G3); the one-dimensional phase grating (G2) is etched in a rect (2x/d) × comb (x/d) area to a depth h ═ λ/2(n-1), so that the phase difference between an etched area light wave and an unetched area is π, wherein λ is the light source wavelength, and n is the refractive index of fused silica.
The one-dimensional transverse shearing grating (S3) has a grating period ranging from 100 micrometers to 500 micrometers, and the line logarithm per millimeter of the corresponding interference fringe ranges from 4lp/mm to 20 lp/mm.
The center wavelength of the broadband light emitted by the deep ultraviolet LED light source (S0) is 280nm, and the bandwidth is +/-10 nm.
The invention has the following beneficial effects:
in order to obtain the deformation information of the upper surface of the large-area transparent material, the invention innovatively provides that the LED deep ultraviolet waveband light is utilized, the waveband light can be transmitted only through quartz glass, and the light cannot be transmitted when passing through other transparent materials, and the reflection phenomenon of the upper surface is mainly shown to the outside, so that the upper surface reflected light of the transparent material can be obtained, and the upper surface deformation information can be obtained. Meanwhile, structured light is generated by utilizing a one-dimensional deep ultraviolet transverse shear grating interference technology, the x direction in a diffraction light field of the structured light is only two diffraction orders of +1 and-1, interference is formed in the overlapping area of two diffraction wavefronts, and interference strip-shaped structured light with alternate brightness and darkness meeting a trigonometric function such as a sine wave can be generated, as shown in fig. 3 (b). The structured light is interference fringes formed by an interference technology, so that the structured light has no sawtooth shape and can realize high-precision deformation detection.
In conclusion, the development of the high-precision three-dimensional contour detection technology for the transparent material has important historical significance for the development of precision glass manufacturing industry and the improvement of structured light technology, and will generate great technical leap in the detection field at home and abroad.
The invention provides the method for realizing the accurate three-dimensional contour detection of the transparent object to be detected, thereby breaking through the bottleneck that the traditional visible structured light can not accurately reconstruct the transparent object, and having important significance for completing the research of related scientific problems and solving the fundamental problems required by the development of detection instruments.
Drawings
FIG. 1 is a top view of a deep ultraviolet band structured light three-dimensional profile detection optical path system mechanism;
FIG. 2 is a CCD (charge coupled device) collected visible light stripe projection view of transparent glass
FIG. 3(a) is a fringe pattern formed by conventional sinusoidal grating digital lithography;
FIG. 3(b) is a diagram of interference fringes produced by a one-dimensional transverse shearing grating;
FIG. 4 is a perspective view of a one-dimensional transverse shear grating based on light flux constraints;
FIG. 5(a) is a graph of amplitude grating transmittance distribution in a one-dimensional transversal shear grating with a pitch of 120 um;
FIG. 5(b) is a phase grating phase delay distribution diagram in a one-dimensional transversal shearing grating with a grating pitch of 120 um;
FIG. 6 is a measurement schematic of a deep ultraviolet band structured light detection system;
FIG. 7 is a quality map acquisition flow chart;
FIG. 8 is a flow chart of a three-dimensional reconstruction algorithm;
FIG. 9 shows a measurement procedure for transparent material profile reconstruction based on deep ultraviolet band structured light;
FIG. 10 is a phase shift diagram of the reference platform (S6) distributed along the vertical direction;
FIG. 11 is a phase shift diagram of the reference platform (S6) distributed along the horizontal direction;
FIG. 12 is a graph of modulation phase shift distributed along the vertical direction;
FIG. 13 is a graph of modulation phase shift distributed along the horizontal direction;
fig. 14 is a diagram showing a three-dimensional reconstruction result of deep ultraviolet structured light on a transparent convex curved object.
Detailed Description
The invention is further illustrated by the following figures and examples.
According to the invention, high-precision detection of the three-dimensional profile of the surface of the curved glass made of the transparent material is realized by converting the traditional visible structure light into a deep ultraviolet light source which cannot penetrate through the transparent glass, combining with a traditional phase solving method and adopting an optimized phase unfolding mode.
1. As shown in fig. 1, the system comprises a deep ultraviolet stripe projection system and a deep ultraviolet imaging system, wherein the deep ultraviolet stripe projection system comprises a wide-spectrum deep ultraviolet LED light source (S0), a narrow-band ultraviolet band filter (S1), a collimation beam expanding system (S2), a one-dimensional deep ultraviolet transverse shear grating (S3) and a beam expander set (S5), and the wide-spectrum deep ultraviolet LED light source (S0) and the narrow-band ultraviolet band filter (S1) form an ultraviolet light source unit; the deep ultraviolet imaging system consists of an imaging lens (S7) and a deep ultraviolet CCD (S8);
according to the light source emitting sequence, firstly, broadband light emitted by a deep ultraviolet LED light source (S0) with the central wavelength of 280nm and the bandwidth of +/-10 nm is emitted into a narrow band ultraviolet band filter (S1) to obtain narrow band deep ultraviolet light with the wavelength of 280nm, the narrow band deep ultraviolet light passes through a collimation and beam expansion system (S2), then the narrow band deep ultraviolet light is emitted to a one-dimensional transverse shearing grating (S3) with the grating pitch of 200 microns as parallel light, two replication wave fronts which are completely the same but have a certain inclination angle are formed through diffraction, and interference fringes are formed in the overlapping area of the two replication wave fronts to serve as the fringe structure light of a detection system, as shown in fig. 3 (. And forming deep ultraviolet waveband structured light with a stable period and a proper size through a beam expander set (S5), projecting the light onto a reference platform (S6) on which a transparent object to be detected (S9) is placed, and receiving a deformed stripe image subjected to height modulation of the object by using a deep ultraviolet imaging system consisting of an imaging lens (S7) and a deep ultraviolet CCD (S8). Meanwhile, the grating phase shift device (S4) is added on the one-dimensional transverse shearing grating (S3) to realize the rotation and phase shift operation of the deep ultraviolet waveband structured light.
Wherein, as shown in fig. 4, the one-dimensional transverse shear grating (S3) is composed of a one-dimensional amplitude grating (G1) and a one-dimensional phase grating (G2). The one-dimensional amplitude grating (G1) adopts a series of tiny pixels to enable the transmittance to meet the distribution of | cos (π x/d) | in a random coding mode, wherein d is the grating period of the one-dimensional transverse shearing light (G3); the one-dimensional phase grating (G2) is etched in a region of a transparent fused silica substrate rect (2x/d) × comb (x/d) to a depth h ═ lambda/2 (n-1), so that the phase difference between an etched region light wave and an unetched region is pi, wherein lambda is the wavelength of a light source, and n is the refractive index of the fused silica.
The one-dimensional transverse shearing grating (S3) has a grating period ranging from 100 micrometers to 500 micrometers, and the line logarithm per millimeter of the corresponding interference fringe ranges from 4lp/mm to 20 lp/mm.
Fig. 6 is a schematic diagram of two-dimensional measurement of deep ultraviolet band structured light. The deep ultraviolet stripe projection system consists of an ultraviolet light source system consisting of the wide-spectrum deep ultraviolet LED light source (S0) and a narrow-band ultraviolet band filter (S1), a collimation and beam expansion system (S2), a one-dimensional deep ultraviolet transverse shear grating (S3) and a beam expander set (S5); the deep ultraviolet imaging system is composed of an imaging lens (S7) and a deep ultraviolet CCD (S8). In FIG. 6, C1And C2The optical centers of the deep ultraviolet stripe projection system and the deep ultraviolet imaging system respectively, and the reference platform (S6) is a diffuse reflection surface. The deep ultraviolet stripe projection system projects deep ultraviolet grating stripes to a reference platform (S6) to form a grating stripe image; assuming that when the transparent object to be measured is not placed (S9), the light beam projected at the point a of the reference platform (S6) is reflected and imaged at a certain point P on the image plane of the deep ultraviolet imaging system, and the corresponding light intensity is:
I(x,y)＝A(x,y)+B(x,y)cos[φ(x,y)](1)
wherein, A (x),y) For background intensity, B (x, y) is the fringe contrast, and φ (x, y) is the initial phase distribution. After the transparent object to be measured (S9) is placed on the reference platform (S6), the light beam imaged at the point P on the camera image plane becomes a light beam reflected at the point M on the object surface, and when the transparent object to be measured (S9) is not placed, the light beam is projected at the point B on the reference platform (S6), and the corresponding light intensity becomes:
where Δ φ (x, y) is the phase difference caused after the object is placed on the reference platform (S6).
The phase of the stripe obtained at the point is modulated into the phase at the point B by the transparent object to be measured (S9) from the phase at the point A on the original reference platform (S6), and the relationship between the phase and the height of the transparent object to be measured (S9) can be established according to the change of the phase. In fig. 6, it is assumed that the optical centers of the deep ultraviolet fringe projection system and the deep ultraviolet imaging system are respectively at a vertical distance h from the reference platform (S6)1And h2. The relationship between the height of the transparent object to be measured (S9) at the M point and the phase difference between the two points AB and AB is shown as follows:
wherein phi isA(x, y) is the phase value of a certain image point of the imaging plane when the transparent object to be measured (S9) is not placed; phi is aB(x, y) is the phase value at the same image point after the transparent object to be measured is placed (S9); theta1And theta2The included angles of the point A and the optical center of the deep ultraviolet stripe projection system and the included angles of the point A and the optical center of the deep ultraviolet imaging system can be obtained through system calibration calculation; f is the propagation frequency of the grating stripe; alpha is an included angle between the normal of the surface of the transparent object to be detected (S9) and the normal of the reference platform (S6), tan alpha can represent the gradient of the transparent object to be detected (S9) at the point, and for a curved object, the gradient distribution exists in the x direction and the y direction.
As can be seen from equation (3), in order to obtain the true height of the transparent object to be measured (S9), first, phase demodulation is performed to solve the size of the phase value modulated by the grating stripe. Because the curved object has gradient distribution in both x and y directions, it is necessary to collect fringes distributed in vertical and horizontal directions. Taking the vertical direction as an example, by adopting a four-step phase shifting method, the deep ultraviolet CCD respectively collects 4 reference platforms (S6) with different phases, which are not provided with the transparent object to be measured (S9) and 4 grating fringe images with different phases, which are provided with the transparent object to be measured (S9), and the fringe light intensity distribution can be expressed as:
wherein, i is 0, and 1 represents that the transparent object to be tested is not put on the reference platform (S6) (S9) and the transparent object to be tested is put on the reference platform (S9);
j is 1,2,3,4, which represents four phase shifts respectively, and the corresponding phase value is
Phi (x, y) is the absolute phase value.
Thereby calculating the phase values of the transparent object to be measured (S9) and the transparent object to be measured (S9) which are not put on the reference platform (S6) respectively as follows:
wherein phi is0(x, y) and phi1(x, y) respectively represent the phase values of the transparent object to be measured (S9) and the transparent object to be measured (S9) which are not put on the reference platform (S6). Because the solution of the arctan function is utilized, the phases are all wrapped phases, the curves jump, and the phase wrapping graph is obtained.
And after the wrapped image is obtained, unwrapping operation is carried out to obtain an accurate and continuous phase value. The invention adopts a quality guide algorithm, the acquisition process is shown in figure 7, pixels with higher quality values in the parcel image are firstly unfolded according to the reliability sequence of the pixel points, and then pixels with lower quality are unfolded, so that the phase unfolding error is limited in a low-quality area, and the accumulation and transmission of the error are effectively avoided.
And then, calibrating external parameters and internal parameters of the deep ultraviolet imaging system by using a pinhole model of the camera. The relationship between the deep ultraviolet CCD pixel points and the corresponding points of the world coordinate system is as follows:
wherein
I.e., the camera's internal reference, [ R T ]]Is an external parameter of the camera (x)w,yw,zw) World coordinates of spatial points, (x)c,yc,zc) The coordinates of the space point in the camera coordinate system, (u, v) the image pixel coordinates of the space point on the CCD camera imaging plane, (u0,v0) As principal point coordinates, fx、fyThe pixel values are respectively corresponding to the focal length in the u-axis direction and the v-axis direction on the image pixel coordinate. In addition, the distortion coefficient of the camera should be calibrated to correct the image to eliminate the nonlinear effect of the actual camera.
In the formula (3), the system parameter to be determined is θ1And theta2. Calculating the vertical distance h between the optical center of the deep ultraviolet fringe projection system and the optical center of the deep ultraviolet imaging system by calibrating the positions of the optical centers of the deep ultraviolet fringe projection system and the deep ultraviolet imaging system and the reference platform (S6)1And h2And coordinates of point A, to obtain the calculated tan theta from the tangent function1And tan θ2。
In equation (3), the unknown parameters are z (x, y) and α. α represents a first partial differential relationship between the gradient tan α and the height z (x, y):
wherein, gx(x, y) and gy(x, y) denotes the gradient in the x-direction and y-direction, respectively, corresponding to the components of tan α in the x-and y-directions. Therefore, by integrating the gradient, the height of the transparent object to be measured (S9) can be obtained. As shown in fig. 8, an iterative strategy is adopted, the initial height is assumed to be 0, the first group of gradient data is calculated by substituting the initial height into formula (3), then, a new height is obtained by reconstruction by using an integration method, and the second group of gradient data is calculated by substituting the new height into formula (3). And repeating the steps until the height difference between two adjacent reconstructions is smaller than a threshold value condition, thereby obtaining the final surface shape to be measured.
In the iterative process, a Southwell area wavefront reconstruction method is adopted by an integral algorithm of gradient recovery height, and the calculation formula of the algorithm is as follows:
wherein x ism,n，ym,n，zm,nAnd
respectively, the corresponding three-dimensional coordinates and corresponding gradients at point (m, n). The Southwell area wavefront reconstruction algorithm has strong noise suppression capability, and can better avoid noise accumulation in the integration process, so that the three-dimensional shape of the object is recovered with higher precision.
So far, according to the real phase information and the system calibration parameters obtained in the above steps, the two-dimensional coordinates of the image shot by the deep ultraviolet CCD can be converted into the two-dimensional real world coordinates of the actual transparent object to be measured (S9) on the reference platform (S6), and the real height value corresponding to the transparent object to be measured (S9) is calculated according to the absolute phase and the relation between the gradient and the height, so that the three-dimensional reconstruction of the transparent object is completed.
Examples
The surface of the transparent object to be measured (S9) of the embodiment is a convex curved surface having a diameter of 30 mm. The deep ultraviolet LED light source (S0) emits broadband light with the central wavelength of 280nm and the bandwidth of +/-10 nm, narrow-band deep ultraviolet light with the wavelength of 280nm is obtained through a deep ultraviolet band filter (S1), parallel light is formed through a collimation and beam expansion system (S2), the parallel light is incident on a one-dimensional transverse shearing grating (S3) with the grating pitch of 200 microns, interference fringes are generated to serve as detection system fringe structure light, the deep ultraviolet band structure light with the stable period and the proper size is formed through a beam expansion mirror group (S5) and is projected onto a reference platform (S6) where a transparent object to be detected (S9) is placed, and a deep ultraviolet imaging system composed of an imaging lens (S7) and a deep ultraviolet CCD (S8) is used for receiving a deformation fringe image after the height of the object is modulated. Meanwhile, a grating phase shift device (S4) is added on the grating structure to realize the rotation and phase shift operation of the structured light.
Based on the above detection device, according to the flow shown in fig. 9, the specific operation steps for detecting the three-dimensional profile of the transparent convex curved surface object are as follows:
step 1: sequentially adjusting the grating phase shift devices (S4) in the light detection system with the deep ultraviolet waveband structure shown in the figure 1 to ensure that grating fringe images are distributed along the vertical direction and move by phases of 0, pi/2, pi and 3 pi/2 along the vertical direction, and acquiring 4 reference platform (S6) fringe images I with different phases and phase shifts of 0, pi/2, pi and 3 pi/2 respectively by using a deep ultraviolet imaging systemp01、Ip02、Ip03、Ip04As shown in fig. 10.
Step 2: adjusting the rotation of the grating phase shift device (S4) by 90 degrees to ensure that grating fringe images are distributed along the horizontal direction, and respectively acquiring 4 reference platform (S6) fringe patterns I with the phase shifts of 0, pi/2, pi and 3 pi/2 distributed along the horizontal direction according to the phase shift method of the step 1s01、Is02、Is03、Is04As shown in fig. 11.
And step 3: putting a transparent object to be measured on a reference platform (S6), adjusting a grating phase shift device (S4) according to the methods of the step 1 and the step 2, so that grating fringe images are distributed along the vertical direction and the horizontal direction respectively, and acquiring a modulation phase diagram I with corresponding phase shifts of 0, pi/2, pi and 3 pi/2p11、Ip12、Ip13、Ip14And Is11、Is12、Is13、Is14As shown in fig. 12 and 13.
And 4, step 4: and (5) solving the phase. According to the formula (5) and the formula (6), respectively carrying out phase solution on the acquired reference platform fringe images distributed along the vertical direction and the horizontal direction and the fringe images of the transparent object to be detected placed on the reference platform to obtain corresponding wrapping phases distributed along the vertical direction and the horizontal direction and having jump.
And 5: and (5) phase unwrapping. According to the quality map acquisition flow shown in fig. 8, the algorithm of quality map guided phase unwrapping is adopted to sequentially and preferentially unwrapp the phases of the high-quality pixels, and the wrapped phases obtained in step 3 are unwrapped to obtain continuously-changing real phases distributed in the vertical and horizontal directions, respectively.
Step 6: and (5) calibrating the system.
Firstly, shooting a plurality of checkerboard calibration images with different poses by using a deep ultraviolet CCD (S8), calibrating the deep ultraviolet CCD (S8), and determining an internal reference A of the deep ultraviolet CCD (S8)cAnd (c) external reference kcSolving two-dimensional point coordinates (X, Y) of the transparent object (S9) to be detected on the reference platform by a formula (7) and correcting the image by using the calibrated distortion coefficient;
secondly, calibrating the physical positions of the optical center of the deep ultraviolet stripe projection system, the optical center of the deep ultraviolet imaging system, the reference platform (S6) and the world coordinate position of the point A, and calculating the vertical distance between the optical center of the deep ultraviolet stripe projection system and the optical center of the deep ultraviolet imaging system and the reference platform (S6) so as to calculate tan theta1And tan θ2；
And 7: assuming that the initial height z (x, y) is 0, the first set of gradient data is calculated according to equation (3). Then, the Southwell area wavefront reconstruction method is used for integration, and the new height is obtained through reconstruction according to the formula (9). And analogizing in sequence until the height difference between two adjacent reconstructions is smaller than a threshold value condition, thereby obtaining the final surface shape to be measured. The result is shown in fig. 14, where the reconstructed root mean square error is about 0.1157 mm.
And 8: and (6) finally solving the accurate three-dimensional contour information (X, Y, Z) of the transparent object to be measured in the world coordinate system by combining the height information Z of the transparent object to be measured in the image coordinate system obtained by the reconstruction algorithm in the step (7) and the system calibration result in the step (6).
Claims (3)
1. A deep ultraviolet structured light precision detection method for transparent material three-dimensional contour reconstruction is characterized by comprising the following steps:
step 1: sequentially adjusting a grating phase shift device (S4) in the deep ultraviolet fringe projection system to ensure that grating fringes are distributed along the vertical direction and move by phases of 0, pi/2, pi and 3 pi/2 along the vertical direction, and acquiring 4 reference platform fringe patterns I with different phases and phase shifts of 0, pi/2, pi and 3 pi/2 respectively by using a deep ultraviolet imaging systemp01、Ip02、Ip03、Ip04；
Step 2: adjusting the grating phase shift device (S4) to rotate 90 degrees, so that the grating stripes are distributed along the horizontal direction, and move the phases of 0, pi/2, pi and 3 pi/2 along the horizontal direction, and acquiring 4 reference platform stripe patterns I with different phases and phase shifts of 0, pi/2, pi and 3 pi/2 respectively by using a deep ultraviolet imaging systems01、Is02、Is03、Is04；
And step 3: putting a transparent object to be measured (S9) on a reference platform (S6), adjusting a grating phase shift device (S4) according to the steps 1 and 2 to ensure that grating fringe images are distributed in the vertical direction and the horizontal direction respectively, and acquiring a modulation phase diagram I with corresponding phase shifts of 0, pi/2, pi and 3 pi/2p11、Ip12、Ip13、Ip14And Is11、Is12、Is13、Is14；
And 4, step 4: solving the phase; respectively carrying out phase solution on the acquired reference platform fringe patterns distributed along the vertical direction and the horizontal direction and the fringe patterns of the transparent object (S9) to be tested placed on the reference platform according to a formula (1) and a formula (2) to obtain corresponding wrapping phases distributed along the vertical direction and the horizontal direction and having jump;
wherein phi is0(x, y) and phi1(x, y) respectively represent phase values of the transparent object to be measured (S9) and the transparent object to be measured (S9) on the reference plane;
and 5: phase unwrapping;
adopting an algorithm of guiding phase unwrapping by a quality map, preferentially unwrapping the phases of the high-quality pixels in sequence, unwrapping the wrapped phases obtained in the step 3, and respectively obtaining continuously-changed real phases distributed along the vertical direction and the horizontal direction;
step 6: calibrating a system;
firstly, shooting a plurality of checkerboard calibration images with different poses by using a deep ultraviolet CCD (S8), calibrating the deep ultraviolet CCD (S8), determining internal reference, external reference and distortion coefficients of the deep ultraviolet CCD (S8), solving two-dimensional point coordinates (X, Y) of a transparent object (S9) to be detected on a reference platform by using a formula (3), and correcting the images by using the calibrated distortion coefficients;
secondly, calibrating the physical positions of the optical center of the deep ultraviolet stripe projection system, the optical center of the deep ultraviolet imaging system, the reference platform (S6) and the world coordinate position of the point A, and calculating the vertical distance between the optical center of the deep ultraviolet stripe projection system and the optical center of the deep ultraviolet imaging system and the reference platform (S6) so as to calculate tan theta1And tan θ2；
The point A refers to a point projected on the reference platform (S6) by the deep ultraviolet stripe projection system when the transparent object to be detected (S9) is not placed;
theta is1And theta2Respectively forming included angles between the point A and the optical center of the deep ultraviolet fringe projection system and the optical center of the deep ultraviolet imaging system;
said
I.e., the camera's internal reference, [ R T ]]Is an external parameter of the camera (x)w,yw,zw) World coordinates of spatial points, (x)c,yc,zc) The coordinates of the space point in the camera coordinate system, (u, v) the image pixel coordinates of the space point on the CCD camera imaging plane, (u0,v0) As principal point coordinates, fx、fyPixel values corresponding to focal distances in the u-axis direction and the v-axis direction on the image pixel coordinate respectively;
and 7: assuming that the initial height z (x, y) is 0, calculating a first set of gradient data according to equation (4); then, carrying out integral reconstruction by utilizing a Southwell area wavefront reconstruction method to obtain a new height; analogizing in sequence until the height difference between two adjacent reconstructions is smaller than a threshold value condition, thereby obtaining the final surface shape to be measured;
wherein phi isA(x, y) is the phase value of a certain image point of the imaging plane of the transparent object (S9) not placed with the object to be measured; phi is aB(x, y) is the phase value at the same image point where the transparent object to be measured is placed (S9); f is the propagation frequency of the grating stripe; alpha is an included angle between the surface normal of the transparent object to be measured (S9) and the surface normal of the reference platform (S6), tan alpha can represent the gradient of the measured object at the point, and for a curved object, the gradient distribution exists in the x direction and the y direction;
and 8: according to the height information Z of the transparent object to be detected (S9) under the image coordinate system obtained by the reconstruction algorithm in the step 7, and the result of the system calibration in the step 6, the accurate three-dimensional contour information (X, Y, Z) of the transparent object to be detected under the world coordinate system is finally solved;
the detection device used by the detection method comprises a deep ultraviolet stripe projection system and a deep ultraviolet imaging system, wherein the deep ultraviolet stripe projection system comprises a wide-spectrum deep ultraviolet LED light source (S0), a narrow-band ultraviolet band filter (S1), a collimation beam expanding system (S2), a one-dimensional deep ultraviolet transverse shear grating (S3) and a beam expander set (S5), and the wide-spectrum deep ultraviolet LED light source (S0) and the narrow-band ultraviolet band filter (S1) form an ultraviolet light source unit; the deep ultraviolet imaging system consists of an imaging lens (S7) and a deep ultraviolet CCD (S8);
broadband light emitted by a deep ultraviolet LED light source (S0) is incident into a narrow band ultraviolet band filter plate (S1) to obtain narrow band deep ultraviolet light, the narrow band deep ultraviolet light passes through a collimation beam expanding system (S2) and then is incident on a one-dimensional transverse shear grating (S3) as parallel light, two replication wavefronts with the same wavefront and a certain inclination angle are formed by diffraction, interference fringes are formed in the overlapping area of the two replication wavefronts and serve as stripe structure light, and the stripe structure light forms the deep ultraviolet band structure light with a stable period through a beam expanding lens group (S5); projecting the deep ultraviolet waveband structured light onto a reference platform (S6) on which a transparent material object to be measured (S9) is placed, and receiving a deformed stripe image modulated by the height of an object by using a deep ultraviolet imaging system;
a grating phase shift device (S4) is arranged on the one-dimensional transverse shearing grating (S3), so that the rotation and phase shift operation of the deep ultraviolet waveband structured light is realized;
the one-dimensional transverse shear grating (S3) comprises a one-dimensional amplitude grating (G1) and a one-dimensional phase grating (G2); the one-dimensional amplitude grating (G1) adopts a series of tiny pixels to enable the transmittance to meet the distribution of | cos (π x/d) | in a random coding mode, wherein d is the grating period of the one-dimensional transverse shearing light (G3); the one-dimensional phase grating (G2) is etched in a region of a transparent fused quartz substrate rect (2x/d) × comb (x/d) to a depth h ═ lambda/2 (n-1), so that the phase difference between an etched region light wave and an unetched region is pi, wherein lambda is the wavelength of a deep ultraviolet light source, and n is the refractive index of the fused quartz.
2. The deep ultraviolet structured light precision detection method for transparent material three-dimensional contour reconstruction as claimed in claim 1, characterized in that the grating period range of the one-dimensional transverse shearing grating (S3) is 100 microns to 500 microns, and the corresponding interference fringe logarithm per millimeter is 4lp/mm to 20 lp/mm.
3. The deep ultraviolet structured light precision detection method for transparent material three-dimensional contour reconstruction according to claim 2, characterized in that the center wavelength of the broadband light emitted by the deep ultraviolet LED light source (S0) is 280nm, and the bandwidth is ± 10 nm.
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