Flexible calibration method for telecentric fringe projection profilometry systems

Rao, Li; Da, Feipeng; Kong, Weiqi; Huang, Heming

doi:10.1364/oe.24.001222

Cited by 54 publications

(17 citation statements)

References 14 publications

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“…Chen et al [13] proposed raising the calibration plate for three-dimensional space calibration; however, increasing the calibration plate will introduce errors, and the operation is inconvenient [22]. Because we need to measure the height of objects in three-dimensional space, a two-dimensional calibration plate or calibration cube should be used to obtain the M matrix [23].…”

Section: ) Calibration Of the Telecentric Vision Systemmentioning

confidence: 99%

High-Precision Measurement of Binocular Telecentric Vision System With Novel Calibration and Matching Methods

Sheng-fu

Ren

et al. 2019

IEEE Access

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In stereo vision-based three-dimensional measurements, calibration, and stereo matching are the most challenging tasks for accurate three-dimensional reconstruction. The traditional binocular vision algorithm has low precision, and we propose a binocular vision system using a telecentric lens. In this paper, we propose a calibration and matching algorithm for the telecentric binocular vision system, which collects only two pictures of the calibration plate to complete the system calibration. The algorithm is a special application of 3D reconstruction. In this paper, if the measurement points are selected as points on the grid, the appropriate extension can be used for high-precision 3D reconstruction, which will be explained in detail in the experiments. In order to reduce the calibration error and obtain high maneuverability, the binocular vision system is only calibrated once with a two-dimensional calibration board, and the depth information is obtained through the parallax of the detection process, so as to effectively simplify the calibration process and reduce the errors introduced in the calibration process. For the matching of images in the right and left cameras, the polar theory of telecentric binocular vision system is constructed according to the characteristics of telecentric lens imaging model based on the traditional binocular vision system theory. The matching algorithm only needs to apply the two-dimensional calibration information and then calculates the results according to the parallax combined with the polar line matching algorithm, which simplifies the algorithm flow and reduces the error. In this paper, experiments show that the algorithm proposed is simple and has high precision, good stability, and high-practical value. INDEX TERMSBinocular vision, image matching, machine vision, three-dimensional sensing, calibration, image matching. BO LI received the Ph.D. degree, in 2009. He is currently an Associate Professor with the School of Electronic Science and Engineering, Nanjing University, where he is currently the Deputy Director of the Network Video Information Technology Research and Development Center, Zhenjiang High-Tech Research Institute. His research interests include broadband network communication, artificial intelligence, and image recognition. FUJI REN received the Ph.D. degree from the

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Section: ) Calibration Of the Telecentric Vision Systemmentioning

confidence: 99%

High-Precision Measurement of Binocular Telecentric Vision System With Novel Calibration and Matching Methods

Sheng-fu

Ren

et al. 2019

IEEE Access

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“…For example, the HP 3D SLS Pro [9] (the benchmark scanner in this work) and EinScan-Pro+ [10] are professional-grade commercial scanners, but can only achieve 50 µm spatial resolution. Rao et al [11] achieved 15 µm spatial resolution, and Liu et al [12] have achieved 10 µm but it is still not precise enough for EBM melt pool monitoring. Challenges exist in 3D scanner system design and calibration procedure, which motivated the research work reported in this paper.…”

Section: Introduction 11 Backgroundmentioning

confidence: 99%

Development of structured light 3D-scanner with high spatial resolution and its applications for additive manufacturing quality assurance

Wang

Law

García

et al. 2021

Int J Adv Manuf Technol

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Digital three-dimensional (3D) scanning is a cutting-edge metrology method that can digitally reconstruct surface topography with high precision and accuracy. Such metrology can help traditional manufacturing processes evolve into a smart manufacturing paradigm, which can ensure product quality by automated sensing and control. However, due to limitations with the spatial resolution, scanning speed, and size of the focusing area, commercially available systems cannot be directly used for in-process monitoring in smart manufacturing. For example, a metal 3D printer requires a scanner with second-level sensing, micron-level spatial resolution, and a centimeter-scale scanning region.Among the 3D scanning technologies, structured light 3D scanning can meet the scanning speed criteria but not the spatial resolution and scanning region criteria. This work addresses these challenges by reducing the eld of view of a structured light scanner system while increasing the image sensor pixel resolution. Improvements to spatial resolution and accuracy are achieved by establishing hardware selection criteria, integrating the proper hardware, designing a scale-appropriate calibration target, and developing noise reduction procedures during calibration. An additively manufactured Ti-6Al-4V part was used to validate the effectiveness of the proposed 3D scanner. The scanning result shows that both melt pool geometry and overall shape can be clearly captured. In the end, the scanning accuracies of the proposed scanner and a professional-grade commercial scanner are validated with a nanometer-level accuracy white light interferometer using high-density point cloud data. Compared to the commercial scanner, the proposed scanner improves the spatial resolution from 48 µm to 5 µm and the accuracy from 108.5 µm to 0.5 µm.

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“…Fringe projection profilometry is a state-of-the-art method in order to characterize the geometry information of three-dimensional (3-D) objects, as it allows a noncontact, fast, and areal data acquisition in the micrometer range. [1][2][3] If a measurement setup with a small field-of-view (FOV) is required, telecentric lenses can be employed either in stereo vision (with 4,5 or without additional projector 6,7 ) or in single camera-projector configurations (with entocentric [8][9][10] or telecentric projector 11,12 ) or telecentric Scheimpflug approaches. 13,14 The calibration of a telecentric structured light sensor is not as straightforward as in the entocentric case, as a telecentric camera cannot be modeled by the pinhole camera but requires the introduction of the so-called affine camera model instead.…”

Section: Introductionmentioning

confidence: 99%

Calibration routine for a telecentric stereo vision system considering affine mirror ambiguity

et al. 2020

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A robust calibration approach for a telecentric stereo camera system for threedimensional (3-D) surface measurements is presented, considering the effect of affine mirror ambiguity. By optimizing the parameters of a rigid body transformation between two marker planes and transforming the two-dimensional (2-D) data into one coordinate frame, a 3-D calibration object is obtained, avoiding high manufacturing costs. Based on the recent contributions in the literature, the calibration routine consists of an initial parameter estimation by affine reconstruction to provide good start values for a subsequent nonlinear stereo refinement based on a Levenberg-Marquardt optimization. To this end, the coordinates of the calibration target are reconstructed in 3-D using the Tomasi-Kanade factorization algorithm for affine cameras with Euclidean upgrade. The reconstructed result is not properly scaled and not unique due to affine ambiguity. In order to correct the erroneous scaling, the similarity transformation between one of the 2-D calibration plane points and the corresponding 3-D points is estimated. The resulting scaling factor is used to rescale the 3-D point data, which then allows in combination with the 2-D calibration plane data for a determination of the start values for the subsequent nonlinear stereo refinement. As the rigid body transformation between the 2-D calibration planes is also obtained, a possible affine mirror ambiguity in the affine reconstruction result can be robustly corrected. The calibration routine is validated by an experimental calibration and various plausibility tests. Due to the usage of a calibration object with metric information, the determined camera projection matrices allow for a triangulation of correctly scaled metric 3-D points without the need for an individual camera magnification determination.

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Flexible calibration method for telecentric fringe projection profilometry systems

Cited by 54 publications

References 14 publications

High-Precision Measurement of Binocular Telecentric Vision System With Novel Calibration and Matching Methods

High-Precision Measurement of Binocular Telecentric Vision System With Novel Calibration and Matching Methods

Development of structured light 3D-scanner with high spatial resolution and its applications for additive manufacturing quality assurance

Calibration routine for a telecentric stereo vision system considering affine mirror ambiguity

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