Non-contact Scanning System Research Articles

Fast and high-resolution laser-ultrasonic imaging for visualizing subsurface defects in additive manufacturing components

Additive manufacturing (AM) is an emerging technique for efficient fabrication of individually tailored and complex geometry parts. The fabrication process is prone to induce various defects that can have detrimental effects on the AM components. Therefore, a reliable technique that enables monitoring the integrity of AM components and in return helping to optimize the fabrication parameters in mission-critical structures is highly demanded. This work presents a fast and high-resolution damage visualization method using laser-ultrasonic (LU) imaging technique for accurately detecting and quantifying the subsurface defects in printed AM components. Specifically, a fully noncontact LU scanning system is implemented to generate and detect high signal-to-noise ratio laser ultrasonic waves using a pulsed laser and laser Doppler vibrometer, respectively. A strategy for fast defect localization using Rayleigh waves with circular scans is firstly proposed. The high-resolution 3D synthetic aperture focusing technique (SAFT) imaging with raster scans is subsequently performed focusing around the located damage areas to stereoscopically visualize and quantify the subsurface defects. The reconstructed images are further processed and improved using Gaussian filter algorithm to obtain accurate defect shapes, sizes, and positions. The feasibility of the proposed method is eventually verified on AlSi10Mg and stainless steel (316L) components containing subsurface defects with various types and dimensions. The measured sizes are well consistent with the designed values, suggesting that it is a reliable inspection method for AM parts to ensure quality control and feedback.

Ultrasonic Tomography Study of Metal Defect Detection in Lithium-Ion Battery

Lithium-ion batteries are widely used in electric vehicles and energy storage systems. Sudden fire accident is one of the most serious issue, which is mainly caused by unpredicted internal short circuit. Metal particle defect is a key factor in internal short circuit it will not show an obvious abnormal change in battery external characteristic just like mechanical and thermal abuse. So, a non-destructive testing of battery internal metal defect is very necessary. This study is first time to scan and analyze different types of defects inside a battery by using ultrasonic technology, and it shows the detection capability boundary of this methodology. A non-contact ultrasonic scanning system with multi-channel was built to scan the battery sample with aluminum foil, copper foil and copper powder defects. The position and shape of those defects were clearly shown by using tomography methodology. It was found that the acoustic properties difference between metal defects and battery active materials has a strong influence on detection sensitivity. Compared with aluminum foil, copper foil and copper powder are easier to be detected and change the ultrasonic signal greatly, they will produce an obvious shadowing artifacts and speed displacement phenomena in tomography images. Ultrasonic tomography technology is an effective method for non-destructive testing of lithium-ion batteries.

A 3D Scanning System for Inverse Analysis of Moist Biological Samples: Design and Validation Using Tendon Fascicle Bundles.

In this article, we present the design and validation of a non-contact scanning system for the development of a three-dimensional (3D) model of moist biological samples. Due to the irregular shapes and low stiffness of soft tissue samples, the use of a non-contact, reliable geometry scanning system with good accuracy and repeatability is required. We propose a reliable 3D scanning system consisting of a blue light profile sensor, stationary and rotating frames with stepper motors, gears and a five-phase stepping motor unit, single-axis robot, control system, and replaceable sample grips, which once mounted onto the sample, are used for both scanning and mechanical tests. The proposed system was validated by comparison of the cross-sectional areas calculated based on 3D models, digital caliper, and vision-based methods. Validation was done on regularly-shaped samples, a wooden twig, as well as tendon fascicle bundles. The 3D profiles were used for the development of the 3D computational model of the sample, including surface concavities. Our system allowed for 3D model development of samples with a relative error of less than 1.2% and high repeatability in approximately three minutes. This was crucial for the extraction of the mechanical properties and subsequent inverse analysis, enabling the calibration of complex material models.

Robust non-destructive inspection of composite aerospace structures by extraction of ultrasonic guided-wave transfer function in single-input dual-output scanning systems

Ultrasonic guided-wave testing is widely utilized for damage detection in plate-like structural components, including composite aircraft fuselage and wing panels. Many guided-wave tests involve transducer scanning to cover finite areas, a task that is most effectively performed by non-contact wave transduction means. The most common guided-wave test implementation consists of a “single-input single-output” scheme. The single-input single-output scheme leads to a transfer function that is convolved with the particular frequency response of the transducers and that of the transducer-to-structure paths (in both excitation and detection). These responses can be unknown or generally variable, especially in non-contact scanning systems and impact excitations. This article proposes a “single-input dual-output” scheme for ultrasonic guided-wave testing in scanning systems that is based on a deconvolution operation. The single-input dual-output scheme better isolates the structural transfer function that is the only property affected by the presence of possible damage. The single-input dual-output scheme was applied to two guided-wave scanning systems under development to detect impact-type damage in stiffened skin-to-stringer panels representative of modern composite aircraft construction. The results demonstrate the dual-output technique and also shed some light on the role of the different frequency bands for the detection of damage at different locations of the skin-to-stringer assembly.

Inspection of delamination defect in first wall with a flexible EMAT-scanning system

In-vessel inspection of delamination defects in first wall (FW) is one of the major maintenance challenges for ITER and future fusion reactors. In this paper, a noncontact and flexible ultrasonic scanning system with combining an electromagnetic acoustic transducer (EMAT) and a robotic inspection manipulator is proposed and investigated for the delamination defects inspection in the FW. Instead of using pulse echo method in conventional ultrasonic method for delamination inspection, a new method based on measuring the ultrasonic resonance signal at the delamination area is applied here. The use of resonant ultrasonic signals and signal processing with power spectrum analysis can significantly enhance signal amplitude of the EMAT and its ability to resist electromagnetic interference from the servo motors of the robotic manipulator. Finally, ultrasonic C-scan images of the delamination defects in an Aluminum-Copper welding specimen are obtained to demonstrate the capability of this technique.

Performance verification of a photogrammetric scanning system for micro-parts using a three-dimensional artifact: adjustment and calibration

Performance verification is a fundamental issue to assure the traceability of a measurement instrument. This issue is very important for non-contact 3D scanning systems, also for the limited number of existing standards. There are many factors affecting the process in a photogrammetric scanning system, and they have to be considered during a performance verification. In this context, it is crucial to completely define the camera model and its spatial locations and orientations during the scan, estimating the intrinsic and extrinsic parameters. There are two main proposals in this paper. Firstly, authors investigated on how the reliability of the adjustment procedure could be improved, adopting a more complex geometry of the reference object, using a three-dimensional one instead of a bi-dimensional pattern of targets. Secondly, an approach to a calibration procedure for photogrammetric scanning system has been drawn up and applied, using the same artifact used for the adjustment. The ISO 15530-3 2011 standard was adopted for the uncertainty assessment of the results.

A morphometric study of the middle and lower cervical vertebral endplates and their components.

Cervical disc arthroplasty is a common method of treating cervical degenerative disease. However, the footprints of most prosthesis dimensions are obtained from data of Caucasian individuals. Besides, there is a large discrepancy between footprints of currently available cervical disc prostheses and anatomic dimensions of cervical endplates. We aimed to detail the three-dimensional (3D) anatomic morphology of the subaxial cervical vertebral endplate, utilizing high-precision, high-resolution scanning equipment, and provide a theoretical basis for designing appropriate disc prostheses for Chinese patients.A total of 138 cervical vertebral endplates were studied. Each endplate was digitized using a non-contact optical 3D range scanning system and then reconstructed to quantify diameters and surface area for the whole endplate and its components (central endplate and epiphyseal rim). The whole endplate and mid-plane concavity depth were measured.There is marked morphologic asymmetry, in that the cranial endplate is more concave than the corresponding caudal endplate, with endplate concavity depths of 2.04 and 0.69 mm, respectively. For the caudal endplates, the endplate concavity apex locations were always located in the posterior portion (81.42%), while in cranial endplates relatively even. The central endplate was approximately 60% of the area of the whole endplate and the anterior section of the ring was the widest. From C3/4 down to C6/7 discs, the vertebral endplate gradually became more elliptical. Chinese cervical endplate anatomic sizes are generally smaller than that of Caucasians. Although Korean and Chinese individuals both belong to the Asian population subgroup, the majority of anatomic dimensions differ. Singaporean cervical endplate morphology is very similar to that of Chinese patients.We performed a comprehensive and accurate quantitative description of the cervical endplate, which provide references to shape and profile an artificial cervical disc without sacrificing valuable bone stock. To design a device with footprint as large as possible to distribute the axial load, we suggest that additional attention should be paid to the marginal rim. It is essential to specifically design appropriate disc prosthesis for Chinese patients. To fit the morphologic and biomechanical variations, we also propose that the disc prostheses for different vertebral segments should be separately designed.

The Laser Rotating of Non-contact Body Scanning System

This paper focus on the requiring of Made To Measure apparel production mode according to individual types and make calibration about body measurement and production in a line. In this paper, based on the measurement principle of structured light, a laser rotating body scanning of non-contact measurement system is introduced. Firstly, the key part of this system, such as digital motor, CCD, lens, etc, is introduced and discussed. Secondly, the principle of the whole system is brought up by analyzing the theory and realization of the structured light measurement, and a 3D reconstruction mathematical model is built based on the characteristic parameter of digital motor. Lastly, some important factors related to the accuracy of this system are discussed. The point cloud data of 3D body contour is acquired successfully via data processing and data piecing together. The further processing can be done according to the raw data. The validity of the principle of this system and the feasibility of arithmetic are veried by experiments.

Modelowanie kształtu struktur tkankowych z wykorzystaniem skanerów laserowych mobilnych i systemów fringe optic

The aim was to compare the accuracy of mapping the shape of the bone structures using the following non-contact scanning systems: the mobile laser scanner and two fringe optic systems with structured light. The procedure enabled the creation of anatomical models of the femur and osteochondral defects in the articular surfaces and the analysis of their mapping errors. The accuracy of the measurements depend on the degree of differentiation shape and reflectance of the surface of the test object. (Modeling the shape of the tissue structures using a mobile laser scanners and fringe optic systems).

Complete noncontact laser ultrasonic imaging for automated crack visualization in a plate

This paper presents an automated crack visualization technique using ultrasonic wavefield images obtained by a complete noncontact laser scanning system. First, the complete noncontact laser scanning system is built by integrating and synchronizing a Q-switched Nd:YAG laser for ultrasonic generation, a laser Doppler vibrometer for ultrasonic measurement and galvanometers for scanning. Then, four different laser scanning schemes are compared to find the most effective and practical ultrasonic scanning strategy for the presented application. Second, a novel image processing technique is developed to isolate and visualize crack-induced standing wave energy from the constructed ultrasonic propagation images. Finally, the effectiveness of the proposed laser ultrasonic scanning system and imaging processing technique is experimentally verified using ultrasonic scanning images obtained from an aluminum plate. The test results confirmed that a hidden notch invisible from the scanned surface was successfully detected and visualized, while no false positive alarm was triggered for an intact specimen.

Three-dimensional analyses of facial soft tissue configuration of Japanese females with jaw deformity – A trial of polygonal view of facial soft tissue deformity in orthognathic patients

In this study, we evaluated the three-dimensional (3D) soft tissue configuration of Japanese females with/without jaw deformity in order to establish the polygonal view of facial soft tissue deformity three-dimensionally. A polygonal chart was applied to assess the outcomes of orthognathic surgery for patients with mandibular hyperplasia with/without deviation.The study included 20 Japanese females with mandibular hyperplasia with/without deviation. All patients received mandibular setback surgery, and 3D measurements were carried out pre-operation, and at 1, 3 and 6 months postoperatively using a non-contact laser scanning system. Eighteen soft tissue landmarks were set on each 3D image and used to calculate a set of selected parameters. As controls, 20 Japanese females with class I occlusion were included.A polygonal chart was constructed based on the mean and S.D. of the control group. Patients with mandibular protrusion characteristically demonstrated significant variances in the items around the lower face. In asymmetric patients, deviation in the mental area disappeared postoperatively, but a small deviation remained when compared to the controls.The method used in this study seems to be a useful index for diagnosis and as a treatment plan for patients with mandibular hyperplasia with/without deviation.

Optical scanning system for light-absorption measurement of deep biological tissue

A noncontact near-infrared scanning system for multi-distance absorption measurement of deep biological tissue was developed. An 808-nm laser, whose focal point on the surface of biological tissue is controlled by a galvano scanner, is used as a light source. A phosphor is placed at a detection focal point on the tissue surface. The light that propagates through tissue and exits from the tissue surface beneath the phosphor excites the phosphor. The fluorescence emitted from the phosphor is detected by an avalanche photodiode. The system is used to measure 20 points on tissue surface at which source-detector (S-D) distances are 7-45 mm (with 2-mm intervals). Neither the light source nor the detector contacts the tissue surface. The system was validated by using it to measure the absorption change of an absorber (which is embedded in a deep layer of a tissue-simulating phantom) while the surface-layer thickness of the phantom was changed from 1 to 12 mm. It was demonstrated that both the relative absorption change of the absorber and the absolute thickness of the surface layer can be estimated from the measured optical-density change (ΔOD) and the dependence of ΔOD on S-D distance, respectively.

Analysis of laser scanning and strategies for dimensional and geometrical control

Noncontact scanning systems are becoming more present in the industry every day. These systems allow a significant reduction in manufacturing costs, mainly due to the important decrement in the inspection time. They enable obtaining a great amount of data that provides very good levels of quality in results. In spite of the well-known advantages that these systems offer, there are also some difficulties, such as the undefined and nonstandardized accuracy when compared with traditional inspection systems based on touch-trigger probes. That is one of the reasons for the practical absence of scanning systems in metrological applications: they have not been adequately tested in terms of accuracy for geometric and dimensional tolerance control. In fact, these systems are mainly used in reverse engineering or multimedia applications. The goal pursued in this research is to analyze the applicability of scanning systems for measuring and control of tolerances. Two different scanning systems were analyzed: a laser triangulation sensor and a touch-trigger probe, both mounted on a coordinate measuring machine. Several test parts were designed, which include different canonical features: planes, spheres, cylinders, holes (outer and inner), and conical surfaces. A common alignment method was defined in order to compare the geometry generated for both scanning systems. Different scanning orientation strategies were defined for laser scanning. Besides this, features were reconstructed with several computer-aided design systems, and the correlation between the contact and noncontact geometries was analyzed to study the convergence of results among them. Finally, an analysis was carried out to compare them in terms of geometrical and dimensional tolerances, considering the contact measurements as datum. As a result, some advises are given with respect to the best strategies for scanning, estimating the deviations.

DEVELOPMENT OF FRASTA SIMULATION SOFTWARE

Fracture-surface topography analysis (FRASTA) was successfully used to simulate the process of crack and calculate parameters of crack such as the crack opening angle (COA) and crack-tip opening angle (CTOA). But because the amount of calculation is large, errors are often made during the course of calculation. FRASTA simulation software, namely fracture surface analyst (FSA) is developed and a series of center-cracked tension (CCT) and double edge notched (DEN) specimens of different materials with different sizes are tested, their fracture surfaces are scanned by non-contact 3D scanning system and the elevation data of the fracture surfaces is recorded. FSA used the recorded elevation data of fracture surfaces to simulate the process of crack based on the principle of FRASTA. Results show that FSA can accurately simulate the process and calculate the parameters of crack.

Fabric Surface Roughness Evaluation Using Wavelet-Fractal Method

A wavelet-fractal method to calculate the fractal dimension is proposed to objectively evaluate the surface roughness of fabric wrinkle, smoothness appearance and seam pucker. The proposed method was validated using the fractal surfaces produced from the mathematical functions and compared with the box and cube counting methods. The more accurate three-dimensional mesh grid data points of wrinkle replicas, smoothness appearance replicas and seam pucker samples were obtained using a three-dimensional, noncontact scanning system. As a supplementary reference the standard roughness parameters, which differentiate the degree of fabric surface roughness, were also investigated. The results show that the fractal dimension measured by the wavelet-fractal method as well as the surface average mean curvature show the power to clearly discern the grades of wrinkle, smoothness appearance as well as seam pucker, and thus can evaluate the fabric surface roughness objectively and quantitatively

The error analysis of the NC machined free form surfaces in reverse engineering

In this paper a feasible methodology that deals with the issues in reverse engineering is reported. It starts by introducing the cubic polynomial to construct the CAD model in accordance with the points measured from the original object by using the optical non-contact scanning system. The needed control points for reconstruction are sifted from the tight squeezed scanned point cloud. Next, based on the control point, the interference-free algorithm connected with the developed CAM system is used to generate the fine-cutting tool paths for NC machining to avoid over-cut. When carrying out the error analysis, points scanned from the machined replica are compared to the reconstructed CAD model to investigate the error distribution. The test-point is sampled statistically from the scanned points due to analyzing the large number of points. The suitable sample size can stand for the entire population with sufficient confidence and accuracy. Meanwhile, a datum is needed to unify both the coordinate systems of the test-point and the reconstructed CAD model to make sense of the aftermath of error detection. For fulfilling the tasks of coordinate alignment and error detection, the test-point is transformed iteratively by means of the rigid-body transformation matrix, so as to minimize the sum of squares distance. The Nelder–Meade simplex method is used in resolving the parameters of the rigid-body transformation matrix in an optimal fashion, where the trouble that arises from resolving the derivates of non-linear equation can be prevented. Once the sum of squares distance in the normal direction converges to a preset value, the coordinate system of the reconstructed CAD model and that of the test-point are treated as consistent. As a result, the margin of error and the error distribution are evaluated. An example for system implementation was also demonstrated to show the validity of the proposed methodology .

Optimal shape error analysis of the matching image for a free-form surface

When using an optical non-contact scanning system to measure an object that has a large surface, large curvature, or a full 360° profile, one can acquire only one set of sectional measurement points each time. For reconstructing the entire object, every set of sectional measurement points acquired at different positions must match. Therefore, the optimal shape error analysis for the matching image of two or more sets of sectional measurement points is desired. This paper presents a measurement system that combines two CCD cameras, one line laser and a three-axis motion stage. It forms an optical non-contact scanning system in association with the mathematical method of direct shape error analysis for the use in reverse engineering. This analysis and measurement system can be used for the profile measurements of free-form objects. It analyzes the matching image of a free-form surface with high efficiency and accuracy. The validity and applicability of this system are demonstrated by two practical examples.

Automatic Measurement of Dimensional Change of Grinding Wheel by Noncontact Scaning-Type Radial Difference Comparison Methods.

The thermal expansion and wear of the grinding wheel are measured during cylindrical grinding by a new experimental method called the scanning-type radial difference comparison system. This method is developed from the previous automated difference comparison method, and a new noncontact scanning system is introduced instead of the blade method. A laser optical displacement sensor supported on the positioning table is scanned on the grinding surface of the wheel by means of computer control, and a surface profile of the grinding surface is constructed from the output of the laser displacement meter. By using this method, the measuring procedure is eliminated and time interval between measurements can easily be shortened.

A non-contact scanning system for laser ultrasonic defect imaging

A non-contact scanning system is described which is capable of producing two-dimensional ultrasonic images of defects in opaque materials. Lasers are used both for generation and detection of ultrasound. Short-duration high-power ( approximately 2 MW) laser pulses are used to generate ultrasound on the surface of a sample. Such ultrasound in the form of steps or pulses propagates through the sample and after interaction with defects are monitored by a 50 cm confocal Fabry-Perot interferometer. The interferometer uses back-scattered laser light from the sample's surface, which can be diffuse in nature. System sensitivity is sufficient for applications on optically rough surfaces. Two-dimensional scans have been performed, leading to computer-generated images of artificial defects in aluminium.