Search

The three-dimensional(3D) measurement technology based on structured light fringe projection has the advantages of high efficiency, simplicity and non-contact acquisition. However, its measurement quality is heavily dependent on the reflective properties of the target surface. For a highly reflective surface, overexposure may be caused in some areas of the image, bringing decoding errors and causing the degradation of accuracy or even measurement failure. In recent years, a lot of researches have been done on this problem and many methods have been proposed. However, a systematic survey of these methods is still lacking. In this work, a review of the structured light 3D measurement techniques for highly reflective surfaces is presented. Firstly, the challenges posed by surface reflectivity to structured light 3D measurement are analyzed. Secondly, recent methods, which are classified into two categories, are reviewed. Finally, the accuracy and efficiency of these methods are discussed, and the trends of future researches are summarized. [ABSTRACT FROM AUTHOR]

Full-field three-dimensional (3D) measurement technology based on phase information has become an indispensable part of geometric dimension measurement in modern scientific research and engineering applications. This field has been developing and evolving for the study of highly reflective phenomena, diffuse reflections, and specular surfaces, and many novel methods have emerged to increase the speed of measurements, enhance data accuracy, and broaden the robustness of the system. Herein, we will discuss the latest research progress in full-field 3D shape measurement based on phase information systematically and comprehensively. First, the fundamentals of 3D shape measurement based on phase information are introduced, namely, phase-shifting and transform-based methods. Second, recent technological innovations are highlighted, including increases in measurement speed and automation and improvements in robustness in complex environments. In particular, the challenges faced by these technological advances in solving highly dynamic, composite surface measurement problems are presented, i.e., with multiexposure techniques proposed for high dynamics that extend the dynamic range of the camera to reduce the effects of overexposure but increase the cost of time and have high hardware requirements, fringe adaptive techniques that overcome light variations but are computationally complex, and multipolarized camera techniques that reduce the effects of light variations but are sensitive to the light source. Third, the phase-shifting method combined with coding is proposed to improve the measurement speed, but the accuracy is slightly reduced. Deep learning techniques are proposed to cope with measurements in complex environments, but the dataset computation process is cumbersome. Finally, future research directions are suggested, and the challenges are presented. Overall, this work provides a reference for researchers and engineers. Highlights: This paper reviews advancements in technology aimed at the high precision and high speed of measurements, ensuring more efficient and reliable full-field 3D shape measurements. The challenges related to the advancement of error compensation for phase calculations are outlined and discussed in various techniques with their advantages and trade-offs. The examination of future research directions and challenges in the field of full-field 3D measurements based on phase information culminates by providing insightful perspectives. [ABSTRACT FROM AUTHOR]

Due to color object surface interference, the distortion of captured sinusoidal fringe patterns in a colorful object measurement using fringe projection profilometry causes significant phase error and therefore shape measurement error. To address the problem, an intensity correction method is proposed to correct the acquired nonsinusoidal fringe of color object and aim to improve three-dimensional (3D) reconstruction accuracy. In this paper, first, the look-up tables (LUTs) and multi-fusion matrices (MFM) are established; secondly, finding the optimal indexing value to correct the color fringe pattern for improving recognition rates and sine; finally, the corrected pattern is separated into three phase-shifting fringe patterns, which can obtain demodulation phase by the three-step phase-shifting algorithm and then recover unwrapping phase. The simulation and experimental results demonstrate that the proposed method effectively reduces the phase error of color objects and achieves complete measurement of different color regions. [ABSTRACT FROM AUTHOR]

Fringe projection profilometry is widely used for the 3D measurement of real-world objects; however, quickly obtaining high-precision 3D measurements is an issue that needs to be resolved. Therefore, a novel fast 3D measurement method based on phase coding is proposed in this paper. It involves an unconstrained fast phase unwrapped method that can solve the absolute phase with only four fringe patterns and does not require any pre-acquired object information. This method uses the special relationship between one coded fringe pattern and the three other phase-shifting fringe patterns to achieve an unwrapped phase. To ensure higher measurement accuracy, a special coding sequence is designed to improve the projection frequency in the coding stage (0 , π) , which not only increases the number of code words, but also effectively improves the decoding accuracy. The high-speed and high-accuracy performance of the proposed method is successfully verified through simulations and experimentation, verifying its future applicability in the field of rapid measurement. [ABSTRACT FROM AUTHOR]

We demonstrate a single-shot uniaxial 3D profilometry system that illuminates a sample with a structured polarization pattern and measures the reflected full-Stokes polarimetric image. Some non-contact 3D measurements require evaluating samples located in a protected environment. For example, this may be a sample under the lid of an acrylic Petri dish, a sample that has a protective film overlay, or products housed inside a plastic container. To deal with these cases, we adapt our measurement system to capture the complete polarization state using a single-shot full-Stokes imaging system consisting of two polarization cameras. This system cannot only measure the dynamic 3D shape at video rate, but can also compensate for any birefringent layers between the illumination arm and the sample under measurement. We present the measurement principles of the system and show the results of a real-time 3D profilometry experiment in which a sample was measured under the lid of an acrylic Petri dish. [ABSTRACT FROM AUTHOR]

There are many optical methods for extracting the geometric information of an object from an image. The structured light method based on digital fringe projection is widely employed. Sometimes the fringe patterns have some undesired invalid areas due to drastic surface profile changes of the tested object, or geometric discontinuities. In addition, a large projection angle affects the quality of the acquired data. These invalid areas may introduce difficulties for further processing. We propose to combine image fusion methods and a typical structured light system to alleviate the shadow problems created by a single projector. [ABSTRACT FROM AUTHOR]

In this work, we present experimental results that show the feasibility of measuring three-dimensional displacement in models of dry granular avalanches. For this purpose, we have used a technique that is capable to measure simultaneously the three involved mutually perpendicular components of displacement on the free surface of the granular flow. The approach comprises two simultaneously used optical techniques: fringe projection, FP, and digital image correlation, DIC; the first technique yields the out-of-plane component of displacement, and the second one, the two in-plane components. Combination of both techniques is achieved by color encoding, which consists in using different color illumination sources for the two optical techniques, in conjunction with a camera recording in RGB. The resulting combination is robust since the illumination sources are non-coherent between them, avoiding any optical interference. This contribution shows the potentiality of the method to analyze dynamic events, by presenting temporal full-field sequences of displacement of small-scale granular flows down an inclined plane, at camera speeds up to 2000 fps. These types of measurements are valuable for validation of physical and numerical models related with the analysis of the dynamic behavior of granular flows in the earth. Because these phenomena, which include rock avalanches, debris avalanches, debris flows, and pyroclastic density currents, are among the most dangerous natural hazards in mountainous and volcanic areas, the possibility to foresee their behavior in a more precise way is extremely important in order to elaborate more rigorous physical models and improve the predictive capacity of the simulation software. [ABSTRACT FROM AUTHOR]

Fringe projection is a versatile method for mapping the topography of surfaces. In this paper, it is used to measure the defects on the head of railroad rails while the rails are moving. Railroad rails are made by hot rolling. The quality of the finished product is generally good, but surface texture will deteriorate with increasing temperature. A method for online inspection therefore is very desirable. In the present experiment, dimensional inspection of the railroad rails was made online while moving at a speed of 1–2 m/s. Therefore, it is important to minimize the registration time. To achieve this, we apply a method of fringe location with sub-pixel accuracy that requires only a single exposure for each registration. [ABSTRACT FROM AUTHOR]

Fast 3D optical sensing of complex shapes remains challenging. While in the passive techniques, there is the correspondence problem, in the active techniques based on fringe projection, there is the challenge of phase recovery and disambiguation. We propose a stereo system that combines active and passive approaches in a complete 3D measurement system. A modified version of the Fourier transform profilometry technique is combined with the beating technique for absolute phase estimation. Stereo correspondence is performed using the obtained phase images. The results demonstrate that one or two frames are enough to estimate the 3D shape of complex objects, and therefore, the proposed approach can be applied for fast shape characterization. [ABSTRACT FROM AUTHOR]

In order to reduce nonlinear phase error in fringe projection based on phase-shifting algorithm, a novel phase retrieval method is proposed. Firstly, on the basis of expression for wrapped phase and corresponding phase in N-step phase-shifting algorithm, the nonlinear phase error and its simple expression is deduced. Secondly, based on the four-step phase-shifting algorithm, the wrapped phase expression of actual measured object is obtained. The corresponding nonlinear phase error is derived in a simple form, and then the new phase error value is obtained by offsetting π/4 from the nonlinear phase value. The mean of the new and original phase error values yields the final phase error; hence, the nonlinear phase errors are significantly reduced. Finally, the results of numerical simulations and experiments show that the proposed method is effective to reduce the nonlinear phase error due to system gamma nonlinearity in phase-shifting algorithm. [ABSTRACT FROM AUTHOR]

Corrosion detection and monitoring is a relevant task in many different fields including automotive, naval, civil etc. In the case of artifacts, corrosion is a relevant topic because this process can introduce huge damages on really ancient objects so that preventive procedures and long term monitoring are required. In this specific field the monitoring task presents, in addition, some extra requirements. In fact, monitoring the surface condition without contact, without sampling the object and, possibly, without diminishing the fruition of the handwork is preferable. Optical techniques, in general, are successfully used in many fields where non-contact, high accuracy measurements are required. In particular, an approach based on fringe projection will be explored in this paper. This method mainly consists in projecting a given intensity pattern on the object and in observing the fringe modulation introduced by the object itself; modulation contains information about the contour of the object itself. In this study corrosion tests on bronze alloy were performed both under salt spray and acid rain condition. A sinusoidal fringe pattern was projected on the analyzed samples before starting the measurement and at each advancement step of the corrosion test. Fringe patterns were analyzed using two approaches. Fast Fourier Transform of the recorded patterns was studied to detect if formation of corrosion patina can be related to some variation in the frequency spectrum. Moreover, continuous wavelet analysis was performed to detect where corrosive patina forms. [ABSTRACT FROM AUTHOR]

A model to predict and characterize the impact of out-of-focus blurring on the range uncertainty associated with the measurement by a phase-shift 3D scanner is presented. First, the reduction of the sine wave magnitude introduced by the projector lenses and the camera lenses is considered. Then, the noise reduction effects related to the camera image blurring introduced by the camera lenses are also included in the model. The main results of this study indicate that the uncertainty for a high-resolution system varies and exhibits a slanted 'W' shape, which significantly differs from the inverse square of the range expected from the triangulation equation or the slanted 'U' shape, which may be intuitively expected when combining blurring caused by a limited depth of field and the triangulation equation. We provide a comprehensive experimental characterization of a purposely constructed 3D scanner designed to isolate the performance degradation caused by out-of-focus projection and acquisition lenses. This scanner is designed to mimic the characteristics of a high-resolution scanner that can be employed for demanding quality control applications. In the tested configurations, the predicted depth-of-fields were within 16.3% of the corresponding measured values. This concordance between the theoretical results and experimental results suggests that the proposed model can be used to assist the design of phase-shift scanners. [ABSTRACT FROM AUTHOR]

This paper studies application of the method of projected fringes on measurement of the surface topography of double-curved propeller blades, produced in liquid metal, i.e. NiAl-bronze, with surface areas of about one square meter. The measurements are performed inside a grinding hall of a propeller factory. To meet the challenges encountered in such a demanding environment, it is important to keep the equipment as simple and robust as possible. Therefore, a method is developed for locating the fringe positions with sub-pixel accuracy. To avoid the need for a physical reference plane of sufficient area, a method of extrapolating the fringes projected on a small reference plane is applied. The method has been tested on a grinded propeller blade and the results agree very well compared to a standard manual measurement method. [ABSTRACT FROM AUTHOR]

Processes of the new production technology sheet-bulk metal forming allow a fast and efficient near-net-shape forming of highly complex parts. Thus the need of energy and raw material as well as the production cycle time can be reduced. In order to guarantee these advantages by avoiding scrap and moreover to ensure the parts' geometrical requirements, production-related metrological solutions for an adapted inspection of parts and tools of sheet-bulk forming processes have to be developed. To fulfill the demands of the differing measuring tasks two prototypical measurement solutions are under development: a multi-scale multi-sensor fringe projection system allows for holistic inspections in feature adapted resolutions, whereas a fiberscopic fringe projection system captures the forming tool partly between forming steps. For the purpose of evaluating the metrological solutions' capabilities of capturing the geometry of filigree structures a comparison of both systems is presented in this work. To guarantee realistic results, the performed measuring tasks have to be comparable to the areas of applications both systems were designed for. During the development of the measuring systems the emphasis was put on the inspection of small complex geometries. These are most challenging for fast and reliable optical inspection under production-related conditions. By considering measurements of calibrated standards on the one side as well as of measuring tasks resulting out of real sheet-bulk metal forming processes on the other side a realistic comparison is assured. Next to the measuring systems' performances also an approach for combining the measurement data of both metrological solutions is shown. By combining the advantages of both measuring systems, highly detailed information for further interpretations of the forming processes can be provided. [ABSTRACT FROM AUTHOR]

Shape reconstruction using structured light has become one of the most widely used optical 3D scanning methods, especially in the field of reverse engineering. Longitudinal resolution is a main parameter in a shape reconstruction technique. An experimental assessment technique is proposed to evaluate the longitudinal resolution of a structured light measurement system. The proposed approach is based on incrementally moving a flat board, and reconstructing its shape at each position. The phase shift between the board wavefront at each position and the reference position wavefront is evaluated. The unwrapped phase is then used to evaluate the smallest board movement detectable by the measurement system. Taguchi method and ANOVA test are used to investigate the effect of various measurement system parameters on the estimated resolution. [ABSTRACT FROM AUTHOR]

Fringe projection is a versatile method for mapping the surface topography. In this paper, it is used to measure the deformation of steel plates under static penetration. Here, the surface shape changes continuously. Therefore, it is important to minimize the registration time. To achieve this, we apply a method of fringe location with subpixel accuracy that requires only a single exposure for each registration. This is in contrast to phase shifting techniques that require at least three separate exposures. [ABSTRACT FROM AUTHOR]

An experimental setup has been built and instrumented with non intrusive measurement methods aiming at measuring temperature fields and deformations of a soda-lime-silica glass piece during thermoforming process. A real scale furnace has been used and a realistic thermal load case applied. Infrared measurements based on the Christiansen effect have been performed on the present glass sample, providing the temperature distribution on the sample surface through IR images at 7.8 μm. Piece deformation has been registered simultaneously, using a DIC (Digital Image Correlation) technique combined with a fringe projection method. Results have been analysed in a combined manner, showing a non symmetrical deformation despite a quite homogeneous thermal field, which could be explained by mould/glass contact problems. The non intrusive measurement technique has been proven to be relevant for a possible control of the thermal environment of the piece during the thermoforming process. Further tests should be carried out on a wide range of shapes and glass types. [ABSTRACT FROM AUTHOR]

A solder bump is regarded as a specular-dominant shiny component that distorts the height profile and causes poor repeatability during the bump height measurement. In this paper, we analyze the relationship between the projection angle and other factors based on the general reflectance mechanism of the specular surface. An optimum projection angle exists, such that can produce the best repeatability of the bump height measurement; therefore, we propose a convenient experimental system with a circular motion guide that can evaluate the optimum projection angle experimentally. The experimental results show that best repeatability is obtained with the optimum projection angle. The proposed method to find the optimum projection angle in this paper can therefore be applied to the many cases of measurement for ball grid array samples having specular-dominant shiny component. [ABSTRACT FROM AUTHOR]

Three-dimensional (3-D) surface imaging has gained clinical acceptance, especially in the field of cranio-maxillo-facial and plastic, reconstructive, and aesthetic surgery. Six scanners based on different scanning principles (Minolta Vivid 910®, Polhemus FastSCAN™, GFM PRIMOS®, GFM TopoCAM®, Steinbichler Comet® Vario Zoom 250, 3dMD DSP 400®) were used to measure five sheep skulls of different sizes. In three areas with varying anatomical complexity (areas, 1 = high; 2 = moderate; 3 = low), 56 distances between 20 landmarks are defined on each skull. Manual measurement (MM), coordinate machine measurements (CMM) and computer tomography (CT) measurements were used to define a reference method for further precision and accuracy evaluation of different 3-D scanning systems. MM showed high correlation to CMM and CT measurements (both r = 0.987; p < 0.001) and served as the reference method. TopoCAM®, Comet® and Vivid 910® showed highest measurement precision over all areas of complexity; Vivid 910®, the Comet® and the DSP 400® demonstrated highest accuracy over all areas with Vivid 910® being most accurate in areas 1 and 3, and the DSP 400® most accurate in area 2. In accordance to the measured distance length, most 3-D devices present higher measurement precision and accuracy for large distances and lower degrees of precision and accuracy for short distances. In general, higher degrees of complexity are associated with lower 3-D assessment accuracy, suggesting that for optimal results, different types of scanners should be applied to specific clinical applications and medical problems according to their special construction designs and characteristics. [ABSTRACT FROM AUTHOR]

The tilt angles of peripheral component interconnect (PCI) connectors on a printed circuit board assembly (PCBA) were measured using the phase-shift fringe projection method. The inspection system developed consists of a personal computer, digital camera, a standard projector and a mirror. The projector was used for projecting a sinusoidal fringe pattern onto the connectors. Phase-shifting was achieved by using a mirror mounted on a rotary stage in the path of the projected fringes. Since the light source used is non-collimated, calibration was performed to obtain an equation for the incident angle of the beam along the length of the object surface for different object heights. Glass blocks of known dimensions were used to test and verify the measurement system. The phase-shifting technique was applied to determine the tilt angles on the glass blocks and later applied to actual connectors. The vision-based inspection system developed using phase-shifting technique demonstrates successful tilt angle measurement on a PCBA. [ABSTRACT FROM AUTHOR]

This paper discusses current research and development of fringe projection-based techniques. A system based on Fourier transform profilometry (FTP) is proposed for three-dimensional (3D) shape recovery. The system improves the method of phase unwrapping to gain accurate 3D shapes of objects. The method uses a region-growing algorithm for the path prediction guided by the quality map to increase the recovering accuracy and provides a fast and simple tool for 3D shape recovery. The shape measurement and data recovery are integrated to offer a new method of 3D modelling. Examples are presented to verify the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

Acquisition of physical data with high precision is a key step in reverse engineering (RE). It is an important stimulative for the progress of reverse engineering with which various digitizing devices are invented, developed and made applicable. This paper introduces a three dimensional optical measurement method based on digital fringe projection technique in RE to improve the technique through its application. A practical example is presented and the result demonstrates the applicability and feasibility of the measurement system as well as the reliability and validity of relevant methods and algorithms. [ABSTRACT FROM AUTHOR]

Ball-Grid-Array (BGA) has become one of the most popular packaging techniques in the electronics industry. Coplanarity inspection of BGA solder balls is critical for process and quality control in BGA manufacturing. Currently, the 3D measurement systems for BGA coplanarity inspection are mainly based on laser scanning techniques. However, they suffer from low inspection speed due to the physical line-scanning process. In this paper, a fast and cost-effective 3D measurement system for coplanarity inspection of BGA solder balls is proposed. The proposed system uses an LCD-based phase measuring technique to perform full-field 3D measurement of BGA solder balls with high accuracy. Experiments have shown that the coplanarity measurement of BGA solder balls is very efficient and effective with the proposed system. The measurement repeatability is in the micrometer range. The processing time of the proposed 3D measurement system for an image of 640×480 pixels is less than 2 s on a typical personal computer. [ABSTRACT FROM AUTHOR]

Measuring impact‐induced contact force history is critically important to understanding the nature of impact events and the associated damage processes of materials/structures involved in the impact. In order to investigate the impact‐induced contact force history involved in free impacts, such as ballistic impact and high‐speed crash, this study developed an innovative instrumented projectile. Both instrumented projectiles with and without an innovative geometry were constructed, tested, and compared. An independent optical method was also used to justify the measurements from the innovative instrumented projectile. Experimental results confirmed the effectiveness and the accuracy of the innovative instrumented projectile in measuring impact‐induced force history. [ABSTRACT FROM AUTHOR]