Development And Assessment Of Fringe Projection Method For Accurate Surface Shape Measurements
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Development And Assessment Of Fringe Projection Method For Accurate Surface Shape Measurements
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Author : Wenzhong Zhao
language : en
Publisher:
Release Date : 2002
Development And Assessment Of Fringe Projection Method For Accurate Surface Shape Measurements written by Wenzhong Zhao and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2002 with categories.
Real Time 3d Surface Shape Measurement Using Fringe Projection And System Geometry Constraints
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Author : Xinran Liu
language : en
Publisher:
Release Date : 2019
Real Time 3d Surface Shape Measurement Using Fringe Projection And System Geometry Constraints written by Xinran Liu and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2019 with Three-dimensional imaging categories.
Optical three-dimensional (3D) surface-shape measurement has diverse applications in engineering, computer vision and medical science. Fringe projection profilometry (FPP), uses a camera-projector system to permit high-accuracy full-field 3D surface-shape measurement by projecting fringe patterns onto an object surface, capturing images of the deformed patterns, and computing the 3D surface geometry. A wrapped phase map can be computed from the camera images by phase analysis techniques. Phase-unwrapping can solve the phase ambiguity of the wrapped phase map and permit determination of camera-projector correspondences. The object surface geometry can then be reconstructed by stereovision techniques after system calibration. For real-time 3D measurement, geometry-constraint based methods may be a preferred technique over other phase-unwrapping methods, since geometry-constraint methods can handle surface discontinuities, which are problematic for spatial phase unwrapping, and they do not require additional patterns, which are needed in temporal phase unwrapping. However, the fringe patterns used in geometry-constraint based methods are usually designed with a low frequency in order to maximize the reliability of correspondence determination. Although using high-frequency fringe patterns have proven to be effective in increasing the measurement accuracy by suppressing the phase error, high-frequency fringe patterns may reduce the reliability and thus are not commonly used. To address the limitations of current geometry-constraint based methods, a new fringe projection method for surface-shape measurement was developed using modulation of background and amplitude intensities of the fringe patterns to permit identification of the fringe order, and thus unwrap the phase, for high-frequency fringe patterns. Another method was developed with background modulation only, using four high-frequency phase-shifted fringe patterns. The pattern frequency is determined using a new fringe-wavelength geometry-constraint model that allows only two point candidates in the measurement volume. The correct corresponding point is selected with high reliability using a binary pattern computed from the background intensity. Equations of geometry-constraint parameters permit parameter calculation prior to measurement, thus reducing computational cost during measurement. In a further development, a new real-time 3D measurement method was devised using new background-modulated modified Fourier transform profilometry (FTP) fringe patterns and geometry constraints. The new method reduced the number of fringe patterns required for 3D surface reconstruction to two. A short camera-projector baseline allows reliable corresponding-point selection, even with high-frequency fringe patterns, and a new calibration approach reduces error induced by the short baseline. Experiments demonstrated the ability of the methods to perform real-time 3D measurement for a surface with geometric discontinuity, and for spatially isolated objects. Although multi-image FPP techniques can achieve higher accuracy than single-image methods, they suffer from motion artifacts when measuring dynamic object surfaces that are either moving or deforming. To reduce the motion-induced measurement error for multi-image FPP techniques, a new method was developed to first estimate the motion-induced phase shift errors by computing the differences between phase maps over a multiple measurement sequence. Then, a phase map with reduced motion-induced error is computed using the estimated phase shift errors. This motion-induced error compensation is computed pixel-wise for non-homogeneous surface motion. Experiments demonstrated the ability of the method to reduce motion-induced error in real-time, for real-time shape measurement of surfaces with high depth variation, and moving and deforming surfaces.
Adaptive Fringe Projection And Error Compensated Calibration For Compact Three Dimensional Shape Measurement Systems
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Author : Dong Li
language : en
Publisher:
Release Date : 2014
Adaptive Fringe Projection And Error Compensated Calibration For Compact Three Dimensional Shape Measurement Systems written by Dong Li and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2014 with categories.
Measurement of the three-dimensional (3-D) shape of an object is needed for both industrial and consumer applications. In industrial applications, compact measurement systems are needed to accomplish certain tasks such as measuring an interior surface in a confined space. In consumer applications, compact measurement systems are also needed for common consumers to conveniently get access to 3D data for a wide range of everyday uses. Fringe-projection techniques have been increasingly used for 3D shape measurement due to the advantage of dense full-field measurement. For a camera-projector measurement system, system geometry (the relative camera-projector position and angle) determine the system compactness. Analysis of the relation of system geometry to measurement accuracy is challenging owing to the effect of the various factors that vary with system geometry on measurement accuracy. It is thus necessary to experimentally determine how measurement accuracy varies with system geometry, in order to determine the most compact design that satisfies a desired measurement accuracy. This has been achieved in a compactness study, in which the measurement accuracy is evaluated at different relative camera-projector positions and angles. Measurement results in the compactness study have shown that there is a tradeoff in loss of accuracy for increased compactness and loss of compactness for increased accuracy. The smallest camera-projector angle (for an industrial system) or the smallest physical distance between the camera and projector (for a consumer system) that satisfies the desired accuracy would provide the most compact design. Several new methods including 1) an improved heterodyne phase-unwrapping method, 2) an adaptive fringe-pattern projection (AFPP) method for surfaces of high variation in reflectivity and illumination, and 3) a pixel-wise adaptive fringe-pattern projection (PWAFPP) method for such surfaces, have been developed in this research to improve measurement accuracy, thus contributing to enable a more compact system design to achieve a desired measurement accuracy. First, the new improved heterodyne phase-unwrapping method detects and compensates for the spike-like errors in absolute phase maps. The method has demonstrated improved projector calibration accuracy from 18.2 to 0.2 pixels, thus ensuring usable camera-projector stereovision system calibration for 3D measurement. Second, the new AFPP method adapts the projector maximum input gray levels (MIGLs) to local surface reflectivity using only two prior fringe-pattern projection and image-capture rounds. The method demonstrated greatly improved 3D measurement accuracy by avoiding image saturation in highly-reflective surface regions while maintaining high intensity modulation of captured fringe patterns across the entire surface with large range in reflectivity. Third, the new PWAFPP method projects a MIGL adapted to the surface reflectivity and illuminance for each pixel. The method has demonstrated a 34% root-mean-square (RMS) error reduction in 3D measurement for pixels that remained saturated after applying the AFPP method. The new method can thus be used to measure surfaces with more complex variation in surface reflectivity.
Development Of A High Speed Robust System For Full Field Of View 3d Shape Measurements
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Author : Michael Jay Zervas
language : en
Publisher:
Release Date : 2011
Development Of A High Speed Robust System For Full Field Of View 3d Shape Measurements written by Michael Jay Zervas and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with categories.
Abstract: 3D shape measurements are critical in a range of fields, from manufacturing for quality measurements to art conservation for the everlasting archival of ancient sculptures. The most important factor is to gather quantitative 3D information from measurement devices. Currently, there are limitations of existing systems. Many of the techniques are contact methods, proving to be time consuming and invasive to materials. While non-contact methods provide opportunities, many of the current systems are limited in versatility. This project focuses on the development of a fringe projection based system for 3D shape measurements. The critical advantage of the fringe projection optical technique is the ability to provide full field-of-view (FOV) information on the order from several square millimeters to several square meters. In the past, limitations in speed and difficulties achieving sinusoidal projection patterns have restricted the development of this particular type of system and limited its potential applications. For this reason, direct coding techniques have been incorporated to the developed system that modulate the intensity of each pixel to form a sinusoidal pattern using a 624 nm wavelength MEMS based spatial light modulator. Recovered phase data containing shape information is obtained using varying algorithms that range from a single image FFT analysis to a sixteen image, phase stepping algorithm. Reconstruction of 3D information is achievable through several image unwrapping techniques. The first is a spatial unwrapping technique for high speed applications. Additionally, the system uses an optimized Temporal Phase Unwrapping (TPU) algorithm that utilizes varying fringe frequencies ranging from 4 to 512 pixels per fringe to recover shape information in the time domain. This algorithm was chosen based on its robustness and accuracy for high resolution applications [Burke et al., 2002]. Also, unwrapping errors are minimized by approximately 90% as the number of images used is increased from the minimum to maximum fringe density. Contrary to other systems, the 3D shape measurement system developed in the CHSLT laboratories has unprecedented versatility to accommodate a variety of applications with the z-depth resolution of up to 25.4 [mu]m (0.001 inches) and speeds close to 200 frames per second. Hardware systems are integrated into user-friendly software that has been customized for fringe projection. The system has been tested in two extreme environments. The first is for quantification of cracks and potholes in the surface of roads under dynamic conditions. The second application was digitization of an art sculpture under static conditions. The system shows promising results and the potential for high quality images via algorithm optimization. Most importantly, there is potential to present real time 3D information at video speeds.
Journal Of Rehabilitation Research Development
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Author :
language : en
Publisher:
Release Date : 2001
Journal Of Rehabilitation Research Development written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2001 with Disabled veterans categories.
Construction And Error Analysis Of A Fringe Projection System
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Author : Daryl Purcell
language : en
Publisher:
Release Date : 2005
Construction And Error Analysis Of A Fringe Projection System written by Daryl Purcell and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2005 with categories.
Moiré fringe projection techniques are gaining popularity due to their non-contact nature and high accuracy in measuring the surface shape of many objects. All such instruments use phase algorithms to reconstruct the surface, with the accuracy dependent on many factors. In an effort to better understand the limitations of moiré fringe projection techniques, a detailed uncertainty analysis is investigated on a constructed moiré fringe projection system for static objects. In addition, a calibration process is presented which produces an equivalent wavelength map, which takes into account the variation of the equivalent wavelength over the field of view for a divergent system. This includes the use of a calibration artifact to check the calibration process for a detailed analysis of the systematic biases. Lastly, the moiré fringe projection system was adapted to measure the vibrational amplitude of a thin-walled part while it was being machined. The system utilizes an inexpensive super-bright LED as a light source, which allows the system to strobe a dynamic object to measure the surface shape at an arbitrary phase of the vibration cycle.
Precision Dimensional Measurements
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Author : Kuang-Chao Fan
language : en
Publisher: MDPI
Release Date : 2019-10-21
Precision Dimensional Measurements written by Kuang-Chao Fan and has been published by MDPI this book supported file pdf, txt, epub, kindle and other format this book has been release on 2019-10-21 with Science categories.
This collection represents successful invited submissions from the papers presented at the 8th Annual Conference of Energy Economics and Management held in Beijing, China, 22–24 September 2017. With over 500 participants, the conference was co-hosted by the Management Science Department of National Natural Science Foundation of China, the Chinese Society of Energy Economics and Management, and Renmin University of China on the subject area of “Energy Transition of China: Opportunities and Challenges”. The major strategies to transform the energy system of China to a sustainable model include energy/economic structure adjustment, resource conservation, and technology innovation. Accordingly, the conference and its associated publications encourage research to address the major issues faced in supporting the energy transition of China. Papers published in this collection cover the broad spectrum of energy economics issues, including building energy efficiency, industrial energy demand, public policies to promote new energy technologies, power system control technology, emission reduction policies in energy-intensive industries, emission measurements of cities, energy price movement, and the impact of new energy vehicle.
Advancement Of Optical Methods In Experimental Mechanics Volume 3
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Author : Helena Jin
language : en
Publisher: Springer Science & Business Media
Release Date : 2013-08-30
Advancement Of Optical Methods In Experimental Mechanics Volume 3 written by Helena Jin and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013-08-30 with Technology & Engineering categories.
Advancement of Optical Methods in Experimental Mechanics: Proceedings of the 2013 Annual Conference on Experimental and Applied Mechanics, the third volume of eight from the Conference, brings together contributions to this important area of research and engineering. The collection presents early findings and case studies on a wide range of optical methods ranging from traditional photoelasticity and interferometry to more recent DIC and DVC techniques, and includes papers in the following general technical research areas: Optical metrology and displacement measurements at different scales Digital holography and experimental mechanics Optical measurement systems using polarized light Surface topology Digital image correlation Optical methods for MEMS and NEMS Three-dimensional imaging and volumetric correlation Imaging methods for thermomechanics applications 3D volumetric flow measurement Applied photoelasticity Optical residual stress measurement techniques Advances in imaging technologies
High Speed 3d Imaging With Digital Fringe Projection Techniques
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Author : Song Zhang
language : en
Publisher: CRC Press
Release Date : 2018-09-03
High Speed 3d Imaging With Digital Fringe Projection Techniques written by Song Zhang and has been published by CRC Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-09-03 with Computers categories.
Digital fringe projection (DFP) techniques are used for non-contact shape measurement of 3D images. In the rapidly expanding field of 3D high-speed imaging, the demand for DFP continues to grow due to the technology’s fast speed, flexibility, low cost, and high accuracy. High-Speed 3D Imaging with Digital Fringe Projection Techniques discusses the generation of digital fringe with digital video projection devices, covering a variety of core technical aspects. The book begins by establishing the theoretical foundations of fringe pattern analysis, reviewing various 3D imaging techniques while highlighting the advantages of DFP. The author then: Describes the differences between digital light processing (DLP), liquid crystal display (LCD), and liquid crystal on silicon (LCoS) Explains how to unwrap phase maps temporally and spatially Shows how to generate fringe patterns with video projectors Demonstrates how to convert phase to coordinates through system calibrations Provides a detailed example of a built-from-scratch 3D imaging system Incorporating valuable insights gained during the author’s 15+ years of 3D imaging research, High-Speed 3D Imaging with Digital Fringe Projection Techniques illuminates the pathway to advancement in high-speed 3D optical imaging using DFP.
Adaptive Fringe Pattern Projection Techniques For Imgae Saturation Avoidance In 3d Surface Measurement
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Author : Christopher Waddington
language : en
Publisher:
Release Date : 2010
Adaptive Fringe Pattern Projection Techniques For Imgae Saturation Avoidance In 3d Surface Measurement written by Christopher Waddington and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.
Fringe-pattern projection (FPP) techniques are commonly used for surface-shape measurement in a wide range of applications including object and scene modeling, part inspection, and reverse engineering. Periodic intensity fringe patterns with a specific amplitude are projected by the projector onto an object and a camera captures images of the fringe patterns, which appear distorted by the object surface from the perspective of the camera. The images are then used to compute the height or depth of the object at each pixel. One of the problems with FPP is that camera sensor saturation may occur if there is a large change in ambient lighting or a large range in surface reflectivity when measuring object surfaces. Camera sensor saturation occurs when the reflected intensity exceeds the maximum quantization level of the camera. A low SNR occurs when there is a low intensity modulation of the fringe pattern compared to the amount of noise in the image. Camera sensor saturation and low SNR can result in significant measurement error. Careful selection of the camera aperture or exposure time can reduce the error due to camera sensor saturation or low SNR. However, this is difficult to perform automatically, which may be necessary when measuring objects in uncontrolled environments where the lighting may change and objects have different surface reflectivity. This research presents three methods to avoid camera sensor saturation when measuring surfaces subject to changes in ambient lighting and objects with a large range in reflectivity. All these methods use the same novel approach of lowering the maximum input gray level (MIGL) to the projector for saturation avoidance. This approach avoids saturation by lowering the reflected intensity so that formerly saturated intensities can be captured by the camera. The first method of saturation avoidance seeks a trade-off between robustness to intensity saturation and low SNR. Measurements of a flat white plate at different MIGL resulted in a trade-off MIGL that yielded the highest accuracy for a single adjustment of MIGL that is uniform within and across the projected images. The second method used several sets of images, taken at constant steps of MIGL, and combined the images pixel-by-pixel into a single set of composite images, by selecting the highest unsaturated intensities at each pixel. White plate measurements using this method had comparable accuracy to the first method but required more images to form the composite image. Measurement of a checkerboard showed a higher accuracy than the first method since the second method maintains a higher SNR when the object has a large range of reflectivity. The last method also used composite images where the step size was determined dynamically, based on the estimated percentage of pixels that would become unsaturated at the next step. In measurements of a flat white plate and a checkerboard the dynamic step size was found to add flexibility to the measurement system compared to the constant steps using the second method. Using dynamic steps, the measurement system was able to measure objects with either a low or high range of reflectivity with high accuracy and without manually adjusting the step size. This permits fully automated measurement of unknown objects with variable reflectivity in unstructured environments with changing lighting conditions. The methods can be used for measurement in uncontrolled environments, for specular surfaces, and those with a large range of reflectivity or luminance. This would allow a wider range of measurement applications using FPP techniques.