Fast Inspection Research Articles

A rigorous fastener inspection approach for high-speed railway from structured light sensors

Rail fasteners are critical components in high-speed railway. Therefore, they are inspected periodically to ensure the safety of high-speed trains. Manual inspection and two-dimensional visual inspection are the commonly used methods. However, both of them have drawbacks. In this paper, a rigorous high-speed railway fastener inspection approach from structured light sensors is proposed to detect damaged and loose fasteners. Firstly, precise and extremely dense point cloud of fasteners are obtained from commercial structured light sensors. With a decision tree classifier, the defects of the fasteners are classified in detail. Furthermore, a normal vector based center extraction method for complex cylindrical surface is proposed to extract the centerline of the metal clip of normal fasteners. Lastly, the looseness of the fastener is evaluated based on the extracted centerline of the metal clip. Experiments were conducted on high-speed railways to evaluate the accuracy, effectiveness, and the influence of the parameters of the proposed method. The overall precision of the decision tree classifier is over 99.8% and the root-mean-square error of looseness check is 0.15 mm, demonstrating a reliable and effective solution for high-speed railway fastener maintenance.

Study on rail fastener failure testing based on fractal theory

The residual vibration of steel rail is rich in the mechanical properties, which include the constraint, that was, the degree of tightness of the fastener. The aim of this research is to characterize the tightness of rail fastener. A fractal analysis procedure based on 1-D curve length calculation is proposed, which applies a length unit to cover fastening the behavior of fasteners. Using the rail vibration data under periodic pulse excitation measured by a track fastener inspection vehicle, this method can derive the fractal dimension of fastener tightness directly (D∈ [1, 2)). Furthermore, 1-D curve length method is also introduced into multi-fractal spectrum analysis for investigating fine scale information. The statistical analysis demonstrates that, fractal dimension Dl, Dr, and multi-fractal parameters αfmax, ∆α can reflect the change process of the tightness of rail fasteners effectively. Therefore, it shows potential to use the fractal parameters of the rail vibration signal to characterize the tightness of the fastener.

Information and communication architecture for transmission power line inspections using unmanned aircraft system

The inspection of the transmission lines in the Brazilian electrical system, given the continental dimensions of the country, is a task of a high complexity. The search for technological alternatives that satisfy the need for fast, safe and reliable transmission lines inspection is something that has been sought by the entire sector. This study presents the architecture of a management system using unmanned aircrafts for transmission lines inspection. The proposed architecture in the scope of a project for Celesc Distribuição – Brazil shows the sub-systems integration such as mission planning and execution, data transmission, image processing and flight control. The architecture was verified by the main project stakeholders and simulation systems in the aeronautics area showing to be strong and safe for the execution of transmission lines inspection.

Detection of creep degradation during pressure vessel testing using electromagnetic sensor technology

9%Cr steels have been in use in power generation for over 20 years. Over this time, there have been a number of incidents of failure by Type IV cracking at welds initiating sub-surface, making surface inspection procedures unsuitable for crack detection. Replication to identify creep cavitation damage can potentially give an early warning of imminent cracking, but has proved unsuccessful in high Cr martensitic steels. Electromagnetic (EM) inspection can provide fast inspection of welded components with minimal surface preparation and some increase in inspection depth. This paper shows the results of accelerated creep tests carried out on a P91 pressure vessel, with EM inspections during regular test interruptions. The results show that EM inspection gave indications of damage in the latter stages of creep cavitation. EM is considered to have the potential for quick assessment of component through thickness damage, flagging up locations of potential problems for more detailed investigation.

Line-scanning laser scattering system for fast defect inspection of a large aperture surface.

Inspection of defects with micrometer level on large aperture surfaces with hundreds of millimeters is one of the challenges in surface quality evaluation. Various microscopic imaging methods have been applied to inspecting the surface defects, while they are time-consuming for the small field of view and the sub-aperture stitching. To tackle this problem, a high-speed line scanning system based on the dark-field laser scattering method is proposed. The laser beam is scanned by the rotating polygon mirror to a laser line for high throughput and then the telecentric F-theta lens converges each incoming laser beam to a focused spot that creates a high intensity to enhance the signal-to-noise ratio. The scattered light from surface defect is collected by the designed integrating sphere for low background noise and the scattering signal is detected for each focused spot at a proper acquisition rate by a photomultiplier (PMT) detector with extremely short response time. In the meanwhile, the tested surface is moving perpendicular to the laser line to realize high-speed large area inspection. The defect inspection system is confirmed experimentally with laser line length of 60mm, minimum detectable size less than 0.5μm, and figure of merit of 9.6 cm2 s-1 μm-1. The work put forward an effective method for automatic discovery of surface defects such as scratches, digs, and contaminants on large aperture surfaces.

RuleScope: Inspecting Forwarding Faults for Software-Defined Networking

Software-defined networking (SDN) promises unprecedentedly flexible network management but it is susceptible to forwarding faults. Such faults originate from data-plane rules with missing faults and priority faults. Yet existing fault detection ignores priority faults, because they are not discovered on commercial switches until recently. In this paper, we present RuleScope, a more comprehensive solution for inspecting SDN forwarding. RuleScope offers a series of accurate and efficient algorithms for detecting and troubleshooting rule faults. They inspect forwarding behavior using customized probe packets to exercise data-plane rules. The detection algorithm exposes not only missing faults but also priority faults and the troubleshooting algorithm uncover actual forwarding states of data-plane flow tables. Both of them help track real-time forwarding status and benefit reliable network monitoring. Furthermore, toward fast inspection of dynamic networks, we propose incremental algorithms for rapidly evolving network policies to amortize detection and troubleshooting overhead without sacrificing accuracy. Experiments with our prototype on the Ryu SDN controller and Pica8 P-3297 switch show that the RuleScope achieves accurate fault detection on 320-entry flow tables with a cost of 1500+ probe packets within 16 s.

Designing Pattern Recognition-Based Method for Fast Visual Inspection of the Bucket Wheel Excavator Lattice Structure

The proposed paper shows some experimental results of a research in metallic structures inspection by using a high definition camera controller by high processing capabilities. The dedicated ARM Cortex-M4 initializes the ARM Cortex-M0 system for image acquiring. Then, by programming options, we are action for patterns (abnormal situations like metal cracks, or discontinuities) types and tuning, for enabling overexposure highlighting and adjusting camera brightness/exposure, to adjust minimum brightness, and to adjust the pattern’s teach threshold. The proposed system has been tested in normal lighting conditions from the typical site.

Computer vision detection of surface defect on oranges by means of a sliding comparison window local segmentation algorithm

Automatic detection of defective oranges by computer vision system is not easy because of the uneven lightness distribution on the surface of oranges. It means that the methods onlydirectly using global segmentation provide unsatisfactory results when orange images present faint defect characters or inhomogeneous surface. The contrast between sound and defective regions can be used to produce more accurate segmentation results, which is more capable of detecting pixels lying around the defect boundary on orange surface based on the local segmentation method. In this paper, we study and propose a sliding comparison window local segmentation algorithm and also presents the detailed image processing procedure including removal of background pixels, image binarization using local segmentation, image subtraction, image morphological modification, removal of stem end pixels for detecting surface defect in an orange gray-level image. This method is an original contribution that allows successful segmentation of various types of surface defects (e.g., insect injury, wind scarring, thrips scarring, scale infestation, canker spot, dehiscent fruit, copper burn, phytotoxicity).The image segmentation algorithm was tested with 1191 samples of oranges. The proposed algorithm was able to correctly detect 97% of the defective orange. Future work will be focused on whole surface and fast on-line inspection.

Application of the magnetic induction technique for the non-destructive assessment of salt gain after the salting process of Parma ham

The fast and non-destructive inspection of salt uptake after the salting phase of dry-cured ham process still remains a goal to allow the optimization of the salting process.This work aims to show the capability of a single frequency, magnetic induction (MI) system, to predict salt (NaCl) content of whole hams after the salting stage. MI system is based on the measurement of the perturbation caused by an alternating excitation magnetic field on a conductive sample; the perturbation is typically detected by measuring the current induced in a suitable receiver coil. One hundred and fifty-nine hams were scanned by the MI scanner before and after the salting phase. Hams were dissected, separated into muscle and fat parts, and analysed for salt content (potentiometric method). Predictive models (multi-linear regression analysis) of the salt gain in hams were developed, based on output signals generated by the MI system. The model including independent variables given by scanning ham when raw and after the salting, achieved the best accuracy (R2 = 0.89; RMSEC = 0.19%). It was concluded that variations in electrical conductivity originated by different salt content and revealed by magnetic induction have potential application to predict the salt content inside entire bone-in hams after salting process.

Application of golay complementary coded excitation schemes for non-destructive testing of sandwich structures

In recent years, InfraRed Thermography (IRT) has become a widely accepted non-destructive testing technique to evaluate the structural integrity of composite sandwich structures due to its full-field, remote, fast and in-service inspection capabilities. This paper presents a novel infrared thermographic approach named as Golay complementary coded thermal wave imaging is presented to detect disbonds in a sandwich structure having face sheets from Glass/Carbon Fibre Reinforced (GFR/CFR) laminates and core of the wooden block.

Comparative analysis of nanometric inspection methods in fringeless speckle pattern interferometry.

In digital speckle pattern interferometry, fringeless speckle pattern interferograms are obtained when the object field deformation is insufficient to produce local phase variations higher than 2π. Therefore, the use of the well-known phase recovery algorithms based on fringe processing is not adequate. In this work, distinct algorithms based on the application of a straightforward arccosine function to a filtered interferogram and the correlation of intensity images and implicit smoothing splines are proposed, analyzed, and compared for the fast inspection of nanometric displacement fields, avoiding the acquisition of several images. In addition, three different methods for the normalization of fringeless speckle pattern interferograms are proposed. The Structural Similarity Index is used to assess the performance of the tested methods by means of numerical simulations under different illuminations, signal-to-noise ratios, phase excursions, and mean speckle size conditions. The analysis shows that the phase recovered by the methods based on the arccosine function and correlation are appropriate for a fast inspection solution. The implicit smoothing spline outperforms other methods in almost all conditions.

Finding faint HI structure in and around galaxies: Scraping the barrel

Soon to be operational HI survey instruments such as APERTIF and ASKAP will produce large datasets. These surveys will provide information about the HI in and around hundreds of galaxies with a typical signal-to-noise ratio of $\sim$ 10 in the inner regions and $\sim$ 1 in the outer regions. In addition, such surveys will make it possible to probe faint HI structures, typically located in the vicinity of galaxies, such as extra-planar-gas, tails and filaments. These structures are crucial for understanding galaxy evolution, particularly when they are studied in relation to the local environment. Our aim is to find optimized kernels for the discovery of faint and morphologically complex HI structures. Therefore, using HI data from a variety of galaxies, we explore state-of-the-art filtering algorithms. We show that the intensity-driven gradient filter, due to its adaptive characteristics, is the optimal choice. In fact, this filter requires only minimal tuning of the input parameters to enhance the signal-to-noise ratio of faint components. In addition, it does not degrade the resolution of the high signal-to-noise component of a source. The filtering process must be fast and be embedded in an interactive visualization tool in order to support fast inspection of a large number of sources. To achieve such interactive exploration, we implemented a multi-core CPU (OpenMP) and a GPU (OpenGL) version of this filter in a 3D visualization environment ($\tt{SlicerAstro}$).

Fast Industrial Inspection of Optical Thin Film Using Optical Coherence Tomography.

An application of spectral domain optical coherence tomography (SD-OCT) was demonstrated for a fast industrial inspection of an optical thin film panel. An optical thin film sample similar to a liquid crystal display (LCD) panel was examined. Two identical SD-OCT systems were utilized for parallel scanning of a complete sample in half time. Dual OCT inspection heads were utilized for transverse (fast) scanning, while a stable linear motorized translational stage was used for lateral (slow) scanning. The cross-sectional and volumetric images of an optical thin film sample were acquired to detect the defects in glass and other layers that are difficult to observe using visual inspection methods. The rapid inspection enabled by this setup led to the early detection of product defects on the manufacturing line, resulting in a significant improvement in the quality assurance of industrial products.

Carbon fiber composites inspection and defect characterization using active infrared thermography: numerical simulations and experimental results.

Composite materials are widely used in the aeronautic industry. One of the reasons is because they have strength and stiffness comparable to metals, with the added advantage of significant weight reduction. Infrared thermography (IT) is a safe nondestructive testing technique that has a fast inspection rate. In active IT, an external heat source is used to stimulate the material being inspected in order to generate a thermal contrast between the feature of interest and the background. In this paper, carbon-fiber-reinforced polymers are inspected using IT. More specifically, carbon/PEEK (polyether ether ketone) laminates with square Kapton inserts of different sizes and at different depths are tested with three different IT techniques: pulsed thermography, vibrothermography, and line scan thermography. The finite element method is used to simulate the pulsed thermography experiment. Numerical results displayed a very good agreement with experimental results.

Multiscale measurement of air foils with data fusion of three optical inspection systems

Measuring the geometry of machine parts with complex geometries creates new challenges towards measurement systems. Due to cost, fast inspection is nevertheless desirable. Additionally the characterization of a parts health and functionality requires geometric information in different scales. We have developed a set of optical measurement systems which together meet those requirements: A borescopic fringe projection system, a macroscopic fringe projection system using newly developed algorithms for fast inspection of turbine blades and a low coherence Michelson interferometer (LCI). The first can detect geometric variances in hard to reach areas, e.g. inside machines or in between parts with highly complex geometries like blade integrated discs (blisks). Using fully adaptable fringe patters, the second system can locate geometric variances with a single fringe pattern. These patterns lead to high sensitivity and high measurement speed. Afterwards the LCI further inspects the micro structure of defects and characterizes the surface structure of the air foil. The presented algorithms provide fast 3D reconstruction with a nanometer resolution and, compared to other systems, a large measurement range. Together, these three inspection systems are capable to detect and quantify defects or geometric variances of industrial parts in different scales. This information improves the prediction of the reliability of a part and helps extending its lifetime to reduce the maintenance costs of machines. As an example a turbine blade was measured with all three systems and the results are visualized in one dataset. Means to merge the measurements are discussed.

(Invited) Non-Visual Defect Monitoring with Surface Photovoltage Mapping

Non-Visual Defects (NVD) is a category of semiconductor material and process induced defects that cause electrical failures, but are not detected with visual wafer inspection tools. This paper gives an overview of our non-contact electrical NVD metrology that uses fast whole wafer inspection with standard mm resolution Kelvin probe surface voltage mapping. In an advanced approach the detected NVD regions are imaged in high resolution (mm range) using Force Kelvin Probe Microscopy. In depth NVD characterization is done with the corona-Kelvin method that quantifies dielectric and interfacial properties in the defect sites. This characterization is performed in a non-invasive fluence range of corona charging and all measurements are non-contact, and do not require fabrication of test devices. Principles of non-contact surface voltage are explained for whole wafer mapping using a high throughput dual Kelvin-probe approach, and for high-resolution micro-Kelvin Force Probe mapping of defect sites. Application examples are discussed in chronological order of the metrology development, starting with monitoring of plasma damage first introduced about 20 years ago. Further examples include surface voltage mapping of surface alkali-metals including novel high resolution micro-Kelvin Force Probe results. Recent trends in monitoring are illustrated with patterned wafer mapping and micro-scale intra die NVD’s. Finally an extension of the technique to defect mapping in SiC is presented together with in-depth corona-Kelvin characterization of defect sites. A broad application range is demonstrated with examples relevant to silicon IC, silicon photovoltaics and to wide bandgap epitaxial SiC.

X-ray computed tomography for fast and non-destructive multiple pearl inspection

X-ray computed tomography displays a highly valuable nondestructive testing tool in various fields. A major disadvantage of this method comprises its high operating costs. Therefore, the reduction of the scanning times would be highly beneficial. Here, we demonstrate exemplarily for the testing of pearls the possibility to decrease the scanning times. The great diversity of pearls on the market, often of unclear origin, especially used for jewelry, demands non-destructive test methods for the fast and reliable classification and validation. We discuss the use of a nano-focus X-ray computed tomography (nf-XCT) system for fast three-dimensional characterization to distinguish between natural and cultured pearls. We test the approach not on individual pearls but for a more demanding task namely for a pearl necklace, that is multiple pearls on a strand. We show that with just one scan the 3D image data of the individual pearls within the whole necklace, which is composed of about 200 pearls can be scanned and reconstructed in only about 24 minutes. That is, we illustrate that nf-XCT as a inspection method is highly competitive to conventional radiography or radioscopy. The presented work also reveals possibilities for other fields like microelectronics etc.

(Invited) Non-Visual Defect Monitoring with Surface Photovoltage Mapping

Non-Visual Defects (NVD) is a category of semiconductor material and process induced defects that cause electrical failures, but are not detected with visual wafer inspection tools. This paper gives an overview of our non-contact electrical NVD metrology that uses fast whole wafer inspection with standard mm resolution Kelvin probe surface voltage mapping. In an advanced approach the detected NVD regions are imaged in high resolution (mm range) using Force Kelvin Probe Microscopy. In depth NVD characterization is done with the corona-Kelvin method that quantifies dielectric and interfacial properties in the defect sites. This characterization is performed in a non-invasive fluence range of corona charging and all measurements are non-contact, and do not require fabrication of test devices. Principles of non-contact surface voltage are explained for whole wafer mapping using a high throughput dual Kelvin-probe approach, and for high-resolution micro-Kelvin Force Probe mapping of defect sites. Application examples are discussed in chronological order of the metrology development, starting with monitoring of plasma damage first introduced about 20 years ago. Further examples include surface voltage mapping of surface alkali-metals including novel high resolution micro-Kelvin Force Probe results. Recent trends in monitoring are illustrated with patterned wafer mapping and micro-scale intra die NVD’s. Finally an extension of the technique to defect mapping in SiC is presented together with in-depth corona-Kelvin characterization of defect sites. A broad application range is demonstrated with examples relevant to silicon IC, silicon photovoltaics and to wide bandgap epitaxial SiC.

Quantitative Phase Contrast Imaging of Microinjection Molded Parts Using Computational Shear Interferometry

Microinjection molding is an effective mass production technology to replicate microcomponents. However, compared with conventional injection molding, microinjection molding requires an adapted processing due to larger surface-area-to-volume ratios, as well as higher shear and cooling rates. Since the functionality of the final parts depends on their defect-free fabrication, a fast, robust, and reliable quality inspection of the final part is mandatory. Here, we demonstrate the applicability of computational shear interferometry (CoSI) for the quality inspection of microinjection molding parts. An analytic model based on the Jones matrix is developed to predict what information of the light field generated behind the inspected part is measured using CoSI technique. A microinjection molding part having spiral shape is inspected indicating areas with manufacturing defects, such as air bubbles, scratches, and internal stresses.

Longitudinal guided waves confined in radius filler regions of composite joints.

This paper studies the feasibility of using ultrasonic guided waves for fast inspection of conformal deltoid radius filler or "Noodle" regions of joints in stringer composite structures. Semi-analytical finite element simulations, supported by experiments and three-dimensional finite element models, are used to demonstrate the existence of a longitudinal guided ultrasonic mode confined or trapped in the Noodle regions. Studies reveal that this mode has attractive properties for rapid screening of Noodle joints, including strong energy concentration, low dispersion, and attenuation. Discussing the physics of mode confinement in light of material differences and geometry, the phenomenon is shown to be related to feature-guiding effects noted in literature recently.