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Experimental setup with the depth of field (DOF), width of equispaced fringes (WEF), and depth of equispaced fringes (DEF).
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A method is presented that allows real-time three-dimensional displacement maps to be obtained for deformable objects using a single color camera and a color fringe projector. The acquired images have speckle and fringe information embedded in them, which are separated using the R, G, and B color signals from a color CCD camera to permit the indepe...
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Citations
... The DIC technology expects the obvious reflectivity difference with fabricating speckle patterns on the tested surface to ensure accurate image matching and deformation calculation, while the FPP technology requires the reflectivity of the measured surface to be uniform for high-accuracy shape measurement. To tackle this contraction, Philip Siegmann et al. employed red speckles along with projected blue and white fringe and demodulated fringes and speckles in various color channels [32,33]. However, the encountered color crosstalk problem caused the incomplete information separation. ...
Multi-dimensional and high-resolution information sensing of complex surface profiles is critical for investigating various structures and analyzing their mechanical properties. This information is currently accessed separately through different technologies and devices. Fringe projection profilometry (FPP) has been widely applied in shape measurement of complex surfaces. Since structured light information is projected instead of being attached onto the surface, it holds back accurately tracking corresponding points and fails to further analyze deformation and strain. To address this issue, we propose a multi-dimensional information sensing method based on digital image correction (DIC)-assisted FPP. Firstly, colorful fluorescent markers are introduced to produce modulated information with both high-intensity reflectivity and color difference. And then, the general information separation method is presented to simultaneously acquire speckle-free texture, fringe patterns and high-contrast speckle patterns for multi-dimensional information sensing. To the best of our knowledge, this proposed method, for the first time, simultaneously realizes accurate and high-resolution 2D texture (T), 4D shape (x, y, z, t) and analytical dimensional mechanical parameters (deformation (d), strain (s)) information sensing based on the FPP system. Experimental results demonstrate the proposed method can measure and analyze 3D geometry and mechanical state of complex surfaces, expanding the measuring dimension of the off-the-shelf FPP system without any extra hardware cost.
... A sampling moiré method has been proposed for out-of-plane displacement estimation, but the method estimates single-directional displacement, and requires an additional artificial target [24,25]. There have been a few attempts at vision-based three-dimensional (3D) displacement estimation, but they require either a projector [26,27] or a binocular camera [28,29], and may have limited performance for long-distance displacement estimation. ...
Structural displacements play an important role in the health monitoring of civil structures; however, the accurate measurement of structural displacements remains a difficult task. Previous efforts have combined a monocular camera and an accelerometer to estimate structural displacement, but only in-plane displacements could be estimated in this way. In this study, the fusion of a monocular camera and an accelerometer was further extended for out-of-plane or three-dimensional displacement estimation. A computer vision algorithm and an adaptive multi-rate Kalman filter were integrated to efficiently estimate high-sampled displacements from low-sampled vision images and high-sampled acceleration measurements. All parameters associated with the computer vision algorithm were automatically calibrated without using any user-defined thresholds. Experimental validation was performed on two building structures and a 10-m-long bridge structure, and the proposed method accurately estimated the displacement for all three structures with a root mean square error of less than 1 mm.
... To overcome respective limitations of two techniques mentioned, some combining techniques of FPP and DIC were proposed [22][23][24], which can be mainly categorized into two types: Fourier transform profilometry (FTP) plus DIC method and phase measuring profilometry (PMP) plus DIC. Both of them utilized FPP to restore specimens' shape and out-ofplane displacement and applied DIC to analyze in-plane displacement, so errors will emerge in in-plane displacement 2 > TIM-23-00206R1< when out-of-plane displacement exists [25]. ...
... In the existing methods, median filtering [19] is used to remove speckle from captured fringe patterns, but it only works for speckle with discrete impulse distribution. Besides, RGB color components can be extracted from the projected blue fringes and printed red speckle [22,28], but there are still some fringes information remaining in the speckle patterns because of color crosstalk. And comparison of the above-mentioned shape and deformation measurement methods is shown in Tabl. ...
... To demonstrate the superiority of the proposed CDICassisted FPP, comparative experiments of reconstructing braided composite structure were performed using classic filtering separation [19], RGB separation [22] and the proposed method. A single-camera FPP system was established with a camera (Baumer VCXU-23M, resolution: 2448×2048 pixels) and a DLP projector (Lightcrafter DLP4500, resolution: 912×1140 pixels). ...
The recently emerging digital image correlation (DIC)-assisted fringe projection profilometry (FPP) has been demonstrated to be superior in shape and deformation measurement on complex structure. But the contradictory demands on reflectivity of tested surface between FPP and DIC extremely limit its measuring accuracy. In this work, chromatic DIC-assisted FPP is proposed to achieve accurate 3D shape, deformation measurement and strain analysis. Firstly, colorful fluorescent pigment is introduced to fabricate speckle patterns and the optimal fluorescent color is solved to simultaneously ensure high fringes intensity modulation and speckles’ chroma difference. And then, intensity-chroma space analysis method is presented to modulate and demodulate the projected fringe and fabricated speckle information in intensity and chroma space without interference. High-quality fringe and speckle patterns can be simultaneously obtained for accurate shape, deformation and strain measurement. To the best of our knowledge, it for the first time essentially overcomes inherent contradictions between FPP and DIC on requirement of surface reflectivity. Finally, chain rule is introduced to further complete strain analysis with less computational cost. Experimental results demonstrated that the proposed method can simultaneously guarantee shape and deformation measurement accuracy. Meanwhile, both complete and fine surface geometry and its strain distributions can be obtained with simple convolution and algebraic operations, which can provide an alternative method for bridging 3D geometric structures and mechanical state of complex specimens.
... (a) Encoding and decoding process for 8 -period fringes; (b) schematic of tripartite phase unwrapping method [21] 研究论文 第 43 卷 第 11 期/2023 年 6 月/光学学报 Fig. 4 Calculation process of conversion coefficients Fig. 8 Comparison of three FPP combined DIC methods. (a) Filtering method [33] ; (b) color channel separation method [32] ...
... FP + 2D-DIC requires a red speckle pattern on the specimen surface and a blue fringe pattern projected on the same surface. Both patterns can be separated using Color Encoding [17] and can be analyzed independently using FP and 2D-DIC algorithms. However, this separation usually leads to some pattern crosstalk. ...
Recently, the combination of Fringe Projection (FP) and 2D Digital Image Correlation (2D-DIC) has become a low-cost alternative for measuring deformations even in dynamic events such as vibration testing. FP and DIC are displacement measurement techniques, so high frequency vibration tests associated with low levels of displacement suppose a challenge. By means of Phase-Based Motion Magnification algorithm (PBMM), the periodic displacement observed in an image sequence can be magnified. This makes it possible to measure clear displacement maps by FP + 2D-DIC even when subtle displacement occurs. This methodology allows a better interpretation of the vibration behavior of mechanical components. In this work, the behavior of a beam excited at its natural frequencies has been studied, showing the potential of PBMM and FP + 2D-DIC
... Therefore, Siegmann et. al used a color camera and a color fringe projector to separate the artificial speckle and fringe pattern from different color channels [17] , and based on this work, Felipe-Sese et al implemented a robust integrated method [18] and employed this technique to complete validation of numerical models [19] , study of vibration analysis [20] , prelaminar dynamic tests [21] , and high-speed impact test [22] . This kind of singleshot method has the highest reconstructed efficiency and is unaffected by the interframe motion, but color crosstalk of different channels and filtering on the fringe pattern limit its measurement accuracy. ...
High-speed three-dimensional (3D) shape measurement techniques based on fringe projection profilometry (FPP) have undergone huge advances over the past two decades. However, accurate 3D displacement mapping and deformation analysis of dynamic scenes using FPP remains an unsolved problem. Because fringe patterns are projected rather than attached on the tested surfaces, the full-field point-to-point correspondence cannot be accurately established between any two 3D shape results. To deal with this challenge, a DIC-assisted FPP for high-speed 3D shape, displacement and deformation measurement of textured surfaces is proposed. Firstly, a high-speed 3D shape measurement system is adopted using our recently proposed robust and efficient Gray-coded coding strategy, which can accurately reconstruct full-field shape of discontinuous surfaces with rich texture information. Then, the modulation-based method is proposed to retrieve high-quality texture map from three phase-shifting fringe patterns, which can eliminate the adverse influence of the nonuniform and time-varying ambient light. By matching the retrieved surface texture images at difference states using DIC, accurate point tracking between the measured 3D shape data can be fulfilled, leading to precise 3D displacement and deformation measurement. Experiments have verified that the proposed method can achieve 3D shape, displacement and deformation measurement of dynamic scenes at a frame rate of 542 fps without any extra expense of hardware or calibration for the FPP system. The presented method is reliable and promising for further 3D displacement mapping and deformation analysis of dynamic scenes using FPP.
... Therefore, Siegmann et. al used a color camera and a color fringe projector to separate the artificial speckle and fringe pattern from different color channels [17], and based on this work, Felipe-Sese et al implemented a robust integrated method [18] and employed this technique to complete validation of numerical models [19], study of vibration analysis [20], prelaminar dynamic tests [21], and high-speed impact test [22]. This kind of single-shot method has the highest reconstructed efficiency and is unaffected by the interframe motion, but color crosstalk of different channels and filtering on the fringe pattern limit its measurement accuracy. ...
High-speed three-dimensional (3D) shape measurement techniques based on fringe projection profilometry (FPP) have undergone huge advances over the past two decades. However, accurate 3D displacement mapping and deformation analysis of dynamic scenes using FPP remains an unsolved problem. Because fringe patterns are projected rather than attached on the tested surfaces, the full-field point-to-point correspondence cannot be accurately established between any two 3D shape results. To deal with this challenge, a DIC-assisted FPP for high-speed 3D shape, displacement and deformation measurement of textured surfaces is proposed. Firstly, a high-speed 3D shape measurement system is adopted using our recently proposed robust and efficient Gray-coded coding strategy, which can accurately reconstruct full-field shape of discontinuous surfaces with rich texture information. Then, the modulation-based method is proposed to retrieve high-quality texture map from three phase-shifting fringe patterns, which can eliminate the adverse influence of the nonuniform and time-varying ambient light. By matching the retrieved surface texture images at difference states using DIC, accurate point tracking between the measured 3D shape data can be fulfilled, leading to precise 3D displacement and deformation measurement. Experiments have verified that the proposed method can achieve 3D shape, displacement and deformation measurement of dynamic scenes at a frame rate of 542 fps without any extra expense of hardware or calibration for the FPP system. The presented method is reliable and promising for further 3D displacement mapping and deformation analysis of dynamic scenes using FPP.
... This approach, however, has the drawback of synchronization of two/multiple cameras, long calculation time, and the difficulty of finding the same corresponding point. Further, several researchers have reported some unique approaches to measure the out-ofplane displacement using a single camera by DIC [9][10][11] or a combination of DIC and fringe projection [12]. Since the SM method can analyze the phase distribution with a single fringe pattern, it can be applied to the measurement of inplane displacement (deflection) of the bridge [13], vibration testing [14], and the measurement of strain at micro-scale for newly developed materials [15]. ...
... where k = − 2πpd 2 af is a constant according to the measurement set-up of the grating, camera and lens used in the experiment. This result suggests that the telescope lens is more challenging to measure than the wide-angle lens, and longer distances make it more difficult to measure the out-of-plane displacement with high accuracy, as indicated in equation (12). ...
Out-of-plane displacement measurement is an important task not only to analyze the microelectronic device’s behavior at the micro-scale but also to evaluate the structural health monitoring (SHM) of infrastructures at the meter-scale. In this study, an accurate and fast out-of-plane displacement measurement method with a single camera is presented, including the theoretical equations, and calibration of phase-gradient to out-of-plane displacement. Since the proposed method requires only a single grating image before and after deformation and analyzes by the sampling moiré method, it yields high accuracy and speed. An experiment of out-of-plane displacement with three different focal length lenses has been conducted to verify the validity of this method. Experimental results indicated that both small and large out-of-plane displacement measurements could be performed accurately. This optical measurement technique will be of high value for SHM of various infrastructures under digital camera or video/cinema camera recording.
... We highlight that a projector has already been adopted in DIC systems [20][21][22] . In 2D-DIC, a laser projector was used to generate optical strip for error compensation, which can be classified into the first category described above [20] . ...
Although the 3D-DIC method has matured both theoretically and technically, the 2D-DIC method still plays an important role in in-plane deformation measurements. However, the accuracy of 2D-DIC is affected by out-of-plane motion (including out-of-plane translation and out-of-plane rotation) and non-perpendicular alignment. To tackle this problem, we propose to directly measure these unfavorable error sources by cross-shaped structured light (CSSL) and the optical triangulation method. Subsequently, pseudo-strains are calculated and compensated using an integrated mathematical model developed in this paper. To avoid mutual interference between the structured light strips and the speckle image, color coding is also proposed to use different color information for 2D-DIC processing and error compensation. Experiments with controlled out-of-the-plane motions show that the mean error after compensation can be as small as 50με. Uniaxial tension tests were also conducted to verify the feasibility of the proposed method in the real material parameter estimation experiment.
... Regarding the displacement measurement sensor, the various method has been proposed based on POF [35]. The prescribed method are able to detect static measurement [36], dynamic response [37], and some of them used for plane-in-out measurement [38]. Teng et.al [39] proposed the displacement sensor using POF whereas the achieved range was 22 mm. ...
... The parameters of the developed sensor shown in Table 1 and comparison with other developed displacement sensor based on POF shown in Table 2. An extensive range of 150 mm has accomplished through this design which is better than prior reported work [35][36][37][38][39][40]. The sensor structure is simple and easy to manufacture and cost-effective. ...
In this paper, a displacement sensor is proposed based on the coupling of scattering loss during the bending of fiber. We adopted a twisted structure of two fiber to couple the scattered loss which caused by bending. Two polymer optical fiber were used in the experiment and the fibers were twisted and bent. When the fiber draft then the bent radius becomes shorter. The scattered-bend loss was arisen from illuminating fiber and being coupled in receiving fiber. The proposed sensor has range about 150 mm and the sensor used for static, dynamic and plane-in-out measurement. The sensor has good linearity between 0 mm to 80 mm, having the sensitivity of 1.26 nW\mm, resolution of 0.79 mm, and repeatability error of 1.26%. The design structure of the sensor is simple, holistic and cost-effective and has potential advantages on industrial application.
