3D Surface Measurement Research Articles

3D surface measurements with isogeometric stereocorrelation—Application to complex shapes

The aim of the present study is to measure complex shapes of tested objects by using a priori information given by their CAD model via stereocorrelation. To follow a 3D object during its deformation and to determine 3D surface displacement fields, a first measurement of the object shape is necessary. It is achieved by updating the CAD reference via a global approach to stereocorrelation. Once the 3D shape has been determined, the next step is to measure 3D displacement fields during loading. The kinematics of the deformed shape is assumed to be written within the same isogeometric framework. Isogeometric stereocorrelation is applied to analyze a compression test on a ribbed cylinder in two different configurations of the stereo rig.

A mobile sensing system for real-time 3D weld pool surface measurement in manual GTAW

An innovative mobile sensing system has been developed to non-intrusively monitor the manual pipe gas tungsten arc welding (GTAW) process. The system consists of a projective torch held by a welder, and a sensory helmet on the welder’s head. The three-dimensional (3D) weld pool surface is effectively measured in real-time as the welder performs the weld despite the movements of the torch and the helmet. In this study, the sensing system is first analyzed by numerical simulations in which the adjustment boundaries of the torch and helmet, i.e. their translation and orientation ranges, for effective sensing have been determined. Then, the sensing system is further evaluated using a simulation platform in which the movements of the helmet/welder’s head is mimicked by a tripod head with 6 degree-of-freedom (DOF), and a convex spherical mirror with a comparable size of a typical weld pool in a GTAW process is applied as a weld pool substitute. The effectiveness of the proposed system is validated by successfully capturing laser reflections from the mirror without great constraints on the welder’s movements of the torch and the helmet. Based on the analysis of the spatial relations among the torch, the helmet and the weld pool, an innovative real-time algorithm is proposed to reconstruct the 3D weld pool surface. The effectiveness and robustness of the algorithm have been verified by accurately reconstructing the convex spherical mirror surface despite the movements of the torch and the helmet in the simulation platform.

Reconstruction of baseline time-trace under changing environmental and operational conditions

Compensation of changing environmental and operational conditions (EOC) is often necessary when using guided-wave based techniques for structural health monitoring in real-world applications. Many studies have demonstrated that the effect of changing EOC can mask damage to a degree that a critical defect might not be detected. Several effective strategies, specifically for compensating the temperature variations, have been developed in recent years. However, many other factors, such as changing humidity and boundary conditions or degradation of material properties, have not received much attention. This paper describes a practical method for reconstruction of the baseline time-trace corresponding to the current EOC. Thus, there is no need for differentiation or compensation procedures when using this method for damage diagnosis. It is based on 3D surface measurements of the velocity field near the actuator using laser vibrometry, in conjunction with high-fidelity finite element simulations of guided wave propagation in free from defects structure. To demonstrate the feasibility and efficiency of the proposed method we provide several examples of the reconstruction and damage detection.

Precision hole making on laminate composite: a tool wear analysis and comparison between drilling and punching

Hole precision is highly critical for accurate and strong fastener assembly. This factor is considerably important for structural materials, such as composite materials. Drilling is the most commonly used process for producing holes on composites. However, drilling causes excessive tool wear, which may affect the quality of holes and result in damage, such as delamination. The main objective of this study is to compare the drilling and punching processes in terms of tool wear by using the focus variation technique. The scanned images of both the puncher and drill bits are obtained by using a 3D optical surface measurement device called Alicona IFM. Tool wear patterns from both drilling and punching are analysed and compared, and the effects of the processes on the quality of the produced holes are observed.

Underwater 3D Surface Measurement Using Fringe Projection Based Scanning Devices.

In this work we show the principle of optical 3D surface measurements based on the fringe projection technique for underwater applications. The challenges of underwater use of this technique are shown and discussed in comparison with the classical application. We describe an extended camera model which takes refraction effects into account as well as a proposal of an effective, low-effort calibration procedure for underwater optical stereo scanners. This calibration technique combines a classical air calibration based on the pinhole model with ray-based modeling and requires only a few underwater recordings of an object of known length and a planar surface. We demonstrate a new underwater 3D scanning device based on the fringe projection technique. It has a weight of about 10 kg and the maximal water depth for application of the scanner is 40 m. It covers an underwater measurement volume of 250 mm × 200 mm × 120 mm. The surface of the measurement objects is captured with a lateral resolution of 150 μm in a third of a second. Calibration evaluation results are presented and examples of first underwater measurements are given.

Axial alignment for high-precision interferometric measurements of steeply-curved spheres

Incorrect positioning of a steeply-curved sphere along the optical axis of a laser Fizeau interferometer introduces a measurement error that is proportional to the cosine of the inclination angle of the ray trace within the cavity, and directly proportional to the misalignment. The standard metrology solution is to subtract a fitted parabola from the 3D image, which corrects for most of the error, but neglects higher terms. As a consequence, measurements of steeply curved parts may have residual errors resembling spherical aberration. Here we calculate the magnitude of the error and present it in a graphical format that allows for straightforward quantification of the residual error as a function of the measured quadratic or power term in the measured 3D surface form. While our recommendation is to employ automated alignment for best results, we also consider options for higher-order software corrections for geometric misalignments.

3D Surface Roughness Parameters of Nanostructured Coatings with Application in the Aerospace Industry

This paper presents a study of 3D surface texture measurements and analysis of several surface texture parameters. A stylus measuring instrument was used to measure 3D surface topographies. In experimental part of this study, two coated gas turbine blades used in aerospace industry were chosen to examine surface of the coatings in nano-scale. Surface texture parameters of Ti-Al coating and Ti-Al-N coating were measured and compared to each other. The aim of the research is to analyze the surface of these coatings in an areal (3D) manner. The results indicate slight differences between these two surface textures despite the fact that both are Titanium-based coatings, and the surface of base material for both samples was prepared in the same way before deposition. Further study with repeated measurements of surface texture for deposed coatings has to be made after erosion tests.

A reference material for establishing uncertainties in full-field displacement measurements

A simple reference material for establishing the minimum measurement uncertainty of optical systems for measuring 3D surface displacement fields in deforming objects is described and its use demonstrated by employing 3D digital image correlation as an exemplar technique. The reference material consists of a stepped bar, whose dimensions can be scaled to suit the application, and that can be clamped rigidly at its thick end to create an idealized cantilever. The cantilever was excited at resonance to generate out-of-plane displacements and, in a separate experiment, loaded statically in-plane to provide in-plane displacement fields. The displacements were measured using 3D digital image correlation and compared to the predicted displacement fields derived from tip deflections obtained using a calibrated transducer that provided traceability to the national standard for length. The minimum measurement uncertainties were evaluated by comparing the measured and predicted displacement fields, taking account of the uncertainties in the input parameters for the predictions. It was found that the minimum measurement uncertainties were less than 3% for the Cartesian components of displacement present during static in-plane bending and less than 3 µm for out-of-plane displacements during dynamic loading. It was concluded that this reference material was more straightforward to use, more versatile and yielded comparable results relative to an earlier design.

Improved differential 3D shape retrieval

Phase unwrapping is a complex step in three-dimensional (3D) surface measurement. To simplify the computation process, Martino et al. proposed a differential algorithm. However, it will result in large error when the orthogonal fringes are not in horizontal or vertical direction. To solve this problem, the relationship between projector׳s and camera׳s coordinate systems is introduced. With the data obtained from coordinate transformation, the improved differential algorithm can be used for orthogonal fringes in any direction. Besides that, taking advantage of Fourier differentiation theorem makes operation and calculation simpler. By contrast, the results of experiments show that the proposed method is applicable to the patterns with orthogonal fringes in every direction. In addition, Fourier differentiation theorem effectively increases the speed of differential process.

The 3D Surface Measurement and Simulation for Turbine Blade Surface Based on Color Encoding Structural Light

This paper proposes a color encoding structural light approach for the three-dimensional measurement of turbine blade surface. It adopts RGB color mode design coding scheme, by using the six basic colors, red, green, blue, yellow, magenta, and cyan for color-coded stripes. Every three stripes are grouped together, while the color combinations for each group are different. The coding pattern based on these color stripes is projected to the blade. A CCD camera then captures the image modulated by the blade. We then decode this image to obtain the three-dimensional coordinates of the measured points on blade surface. According to the structure light measurement principle, we designed and determined the parameters of the three-dimensional measurement. This paper established a mathematical model of a turbine blade through simulation by using 3ds max software. We designed a threedimensional measurement system for the simulation, and obtained the three-dimensional coordinates of the blade surface by measuring the turbine blade. Finally, the threedimensional blade model reconstructed by the measured data is established.

Roundness error evaluation of cold embossed hole based on profile measurement technique

Roundness is one of the main features to ensure the perfect mating of assembled parts. A coordinate measurement machine is commonly utilized for measurement, but the use of this machine is limited because of the small size and characteristics of the hole. This study aims to evaluate the quality of an AA6061 cold embossing hole. A simple approach based on profile deviation is proposed to evaluate the roundness of the hole. The profile is obtained with the use of InfiniteFocus Alicona system, a commercially available 3D surface measurement technique. Several specimens with various depths and diameters are prepared for measurement. Results are validated with the commercial Mitutoyo roundtest machine.

Quantification of roping in aluminium sheet alloys for car body applications by combining 3D surface measurements with Fourier analysis

Abstract The present study introduces a new method to characterise and evaluate the roping behaviour of aluminium sheet alloys of the AA 6xxx series for car body applications. The new approach combines two known methods into a novel powerful tool, (i) the measurement of a 3D surface topography with a white-light interferometer and (ii) the subsequent data analysis by means of Fourier analysis. Use of the white-light interferometer allows analysing roping of deformed samples without the need of additional surface preparation steps, e.g. inking, stoning, etc., which may falsify the surface appearance. The use of data analysis by means of fast Fourier transform allows differentiating between different surface phenomena, e.g. unidirectional component versus isotropic components. It was found that the new approach is capable of giving reliable and reproducible data, which qualifies this method to study roping in aluminium car body sheets in an objective manner.

Snapshot phase shift fringe projection 3D surface measurement.

We propose a novel snapshot phase shift fringe projection three-dimensional (3D) surface measurement method using polarization-coded light illumination and polarization camera. The light from the light source is split into two beams, one is left circularly polarized and the other is right circularly polarized, to illuminate the object simultaneously. A four-channel division of focal plane (DoFP) polarization camera is employed to capture the light reflected from the object surface. Four images with a phase shift of π/2 are extracted from the snapshot image and then analyzed to reconstruct a 3D object surface. The proposed method is the first snapshot phase shift fringe projection approach for 3D surface imaging. It is insensitive to motion and has the potential for ultrafast 3D surface imaging.

3D Overhead Modeling Using Depth Sensor

Purpose This paper was purposed to suggest the method to produce the supportive helmet (head correction) for the infants who are suffering from plagiocephaly and to evaluate the level of transformation through 3D model. Method Either of CT or X-ray restored images has been used in making the supportive helmet (Head correction) in general, but these methods of measuring have problems in cost and safety. 3D surface measurement technology was suggested to solve such matters. Results It was to design the transformed model of the head within 0.7cm in average by scanning the surface of head and performing 3D restoration with marching cube and the changing rate of the head was compared in numerical data with 3D model. Conclusion The suggested methods displayed the better performance than the conventional method in respect of the speed and cost.

An improved stair phase encoding method for absolute phase retrieval

An improved phase unwrapping method is proposed to reduce the projection fringes in three-dimensional (3D) surface measurement. Color fringe patterns are generated by encoding with sinusoidal fringe and stair phase fringe patterns in red and blue channels. These color fringe patterns are projected onto the tested objects and then captured by a color CCD camera. The recorded fringe patterns are separated into their RGB components. Two groups of four-step phase-shifting fringe patterns are obtained. One group of the stripes are four sinusoidal patterns, which are used to determine the wrapped phase. The other group of stripes are four sinusoidal patterns with the codeword embedded into stair phase, whose stair changes are perfectly aligned with the 2π discontinuities of sinusoidal fringe phase, which are used to determine the fringe order for the phase unwrapping. The experimental results are analyzed and compared with those of the method in Zheng and Da (2012. Opt Express 20(22):24139–24150). The results show that the proposed method needs only four fringe patterns while having less error. It can effectively reduce the number of projection fringes and improve the measuring speed.

On-line surface inspection using cylindrical lens-based spectral domain low-coherence interferometry.

We present a spectral domain low-coherence interferometry (SD-LCI) method that is effective for applications in on-line surface inspection because it can obtain a surface profile in a single shot. It has an advantage over existing spectral interferometry techniques by using cylindrical lenses as the objective lenses in a Michelson interferometric configuration to enable the measurement of long profiles. Combined with a modern high-speed CCD camera, general-purpose graphics processing unit, and multicore processors computing technology, fast measurement can be achieved. By translating the tested sample during the measurement procedure, real-time surface inspection was implemented, which is proved by the large-scale 3D surface measurement in this paper. ZEMAX software is used to simulate the SD-LCI system and analyze the alignment errors. Two step height surfaces were measured, and the captured interferograms were analyzed using a fast Fourier transform algorithm. Both 2D profile results and 3D surface maps closely align with the calibrated specifications given by the manufacturer.

Automatic tracking of intraoperative brain surface displacements in brain tumor surgery.

In brain tumor surgery, soft-tissue deformation, known as brain shift, introduces inaccuracies in the application of the preoperative surgical plan and impedes the advancement of image-guided surgical (IGS) systems. Considerable progress in using patient-specific biomechanical models to update the preoperative images intraoperatively has been made. These model-update methods rely on accurate intraoperative 3D brain surface displacements. In this work, we investigate and develop a fully automatic method to compute these 3D displacements for lengthy (~15 minutes) stereo-pair video sequences acquired during neurosurgery. The first part of the method finds homologous points temporally in the video and the second part computes the nonrigid transformation between these homologous points. Our results, based on parts of 2 clinical cases, show that this speedy and promising method can robustly provide 3D brain surface measurements for use with model-based updating frameworks.

Erosion-Corrosion Rates of Corrosion-Resistant Alloys Under High-Velocity Multiphase Conditions

The erosion-corrosion behavior of two corrosion-resistant alloys (UNS S42000 and UNS N08028) has been assessed under gaseous-liquid-solid impingement conditions. Erosion-corrosion impingement tests were conducted at three different impact angles and at three different impact velocities up to 60 m/s, and furthermore, pure erosion and pure corrosion impingement tests were run for UNS S42000, and carbon dioxide (CO2) at a pressure of 1,500 kPa was used as the gas phase. The sand content, with grain size below 150 μm, was 2.7 g/L brine. Artificial brine with a sodium chloride (NaCl) content of 2.7% was used as liquid phase. The damaged surfaces of samples exposed to the high-velocity multiphase flow were investigated using scanning electron microscopy (SEM) and an optical device for 3D surface measurements to assess the depth of attack. Electrochemical investigations according to ASTM G61 were performed to determine electrochemical behavior of tested materials including critical pitting potentials (Epit) and ...

Accurate 3D surface measurement of mountain slopes through a fully automated image-based technique

In this paper an automated procedure for surface reconstruction that can be used for surveying and monitoring rock and ground slopes is presented. This method has been developed for geological and engineering applications, where accuracy and completeness are factors of primary importance for the final 3D model, which must provide a detailed metric survey and not only a visual reconstruction of the scene. The proposed procedure integrates two image matching techniques. The first one is used to automatically extract a set of tie points that are needed for computing the exterior orientation parameters of all images through a photogrammetric bundle adjustment. Such tie oints are also exploited to obtain a preliminary seed model that is then enriched based on Multi-photo Least Squares Matching. During this second stage, the surface model is improved in terms of point density and accuracy. Different strategies were implemented to successfully combine both techniques, along with some new improvements. The presented procedure has been tested in two different applications: geometric modelling of rock cliffs and evaluation of weathering of a ground slope. In both cases the obtained results presented accuracy sufficient for geological investigation. Moreover, outcomes were comparable to the ones from laser scanning surveying and other photogrammetric implementations.

Quantitative phenotyping of leaf margins in three dimensions, demonstrated on KNOTTED and TCP trangenics in Arabidopsis

The geometry of leaf margins is an important shape characteristic that distinguishes among different leaf phenotypes. Current definitions of leaf shape are qualitative and do not allow quantification of differences in shape between phenotypes. This is especially true for leaves with some non-trivial three-dimensional (3D) configurations. Here we present a novel geometrical method novel geometrical methods to define, measure, and quantify waviness and lobiness of leaves. The method is based on obtaining the curve of the leaf rim from a 3D surface measurement and decomposing its local curvature vector into the normal and geodesic components. We suggest that leaf waviness is associated with oscillating normal curvature along the margins, while lobiness is associated with oscillating geodesic curvature. We provide a way to integrate these local measures into global waviness and lobiness quantities. Using these novel definitions, we analysed the changes in leaf shape of two Arabidopsis genotypes, either as a function of gene mis-expression induction level or as a function of time. These definitions and experimental methods open the way for a more quantitative study of the shape of leaves and other growing slender organs.