Non-contact Inspection System Research Articles

The Design of a Non-Contact Inspection System Integrated With the Time of Flight-Based Flaw Detection (TOFFD) Criterion to Investigate the Structural Integrity of the Rail Track

The Design of a Non-Contact Inspection System Integrated With the Time of Flight-Based Flaw Detection (TOFFD) Criterion to Investigate the Structural Integrity of the Rail Track

Method and Installation for Efficient Automatic Defect Inspection of Manufactured Paper Bowls

Various techniques were combined to optimize an optical inspection system designed to automatically inspect defects in manufactured paper bowls. A self-assembled system was utilized to capture images of defects on the bowls. The system employed an image sensor with a multi-pixel array that combined a complementary metal-oxide semiconductor and a photo detector. A combined ring light served as the light source, while an infrared (IR) LED matrix panel was used to provide constant IR light to highlight the outer edges of the objects being inspected. The techniques employed in this study to enhance defect inspections on produced paper bowls included Gaussian filtering, Sobel operators, binarization, and connected components. Captured images were processed using these technologies. Once the non-contact inspection system’s machine vision method was completed, defects on the produced paper bowls were inspected using the system developed in this study. Three inspection methods were used in this study: internal inspection, external inspection, and bottom inspection. All three methods were able to inspect surface features of produced paper bowls, including dirt, burrs, holes, and uneven thickness. The results of our study showed that the average time required for machine vision inspections of each paper bowl was significantly less than the time required for manual inspection. Therefore, the investigated machine vision system is an efficient method for inspecting defects in fabricated paper bowls.

A high-accuracy hollowness inspection system with sensor fusion of ultra-wide-band radar and depth camera

AbstractWith the dangerous and troublesome nature of hollow defects inside building structures, hollowness inspection has always been a challenge in the field of construction quality assessment. Several methods have been proposed for inspecting hollowness inside concrete structures. These methods have shown great advantages compared to manual inspection but still lack autonomy and have several limitations. In this paper, we propose a range-point migration-based non-contact hollowness inspection system with sensor fusion of ultra-wide-band radar and laser-based depth camera to extract both outer surface and inner hollowness information accurately and efficiently. The simulation result evaluates the performance of the system based on the original range-point migration algorithm, and our proposed one and the result of our system show great competitiveness. Several simulation experiments of structures that are very common in reality are carried out to draw more convincing conclusions about the system. At the same time, a set of laboratory-made concrete components were used as experimental objects for the robotic system. Although still accompanied by some problems, these experiments demonstrate the availability of an automated hollow-core detection system.

Non-Contact Inspection of Railhead via Laser-Generated Rayleigh Waves and an Enhanced Matching Pursuit to Assist Detection of Surface and Subsurface Defects.

Laser ultrasonic technology can provide a non-contact, reliable and efficient inspection of train rails. However, the laser-generated signals measured at the railhead are usually contaminated with a high level of noise and unwanted wave components that complicate the identification of defect echoes in the signal. This study explores the possibility of combining laser ultrasonic technology (LUT) and an enhanced matching pursuit (MP) to achieve a fully non-contact inspection of the rail track. A completely non-contact laser-based inspection system was used to generate and sense Rayleigh waves to detect artificial surface horizontal, surface edge, subsurface horizontal and subsurface vertical defects created at railheads of different dimensions. MP was enhanced by developing two novel dictionaries, which include a finite element method (FEM) simulation dictionary and an experimental dictionary. The enhanced MP was used to analyze the experimentally obtained laser-generated Rayleigh wave signals. The results show that the enhanced MP is highly effective in detecting defects by suppressing noise, and, further, it could also overcome the deficiency in the low repeatability of the laser-generated signals. The comparative analysis of MP with both the FEM simulation and experimental dictionaries shows that the enhanced MP with the FEM simulation dictionary is highly efficient in both noise removal and defect detection from the experimental signals captured by a laser-generated ultrasonic inspection system. The major novelty contributed by this research work is the enhanced MP method with the developments of, first, an FEM simulation dictionary and, second, an experimental dictionary that is especially suited for Rayleigh wave signals. Third, the enhanced MP dictionaries are created to process the Rayleigh wave signals generated by laser excitation and received using a 3D laser scanner. Fourth, we introduce a pioneer application of such laser-generated Rayleigh waves for inspecting surface and subsurface detects occurring in train rails.

DEVELOPMENT OF A STRAIGHTNESS INSPECTION SYSTEM OF THE RIFLED GUNS CHANNELS

The article discusses the development of a non-contact straightness inspection system of the rifled guns channels based on the structured light method. A compact optical probe has been developed, in which a diffractive optical element (DOE) is used to illuminate the bore. Algorithms for processing a series of images obtained by scanning a bore are proposed and developed. In the issue of image processing 3D form of the controlled product is reconstructed. The test results of the straightness inspection system on real samples are presented. As a result of the tests, the error of measurements of straightness deviations at the level of ± 4 microns was obtained.

Surface Topography Measurement of Mirror-Finished Surfaces Using Fringe-Patterned Illumination

Mirror-finished surface products have a wide range of applications in different engineering industries, such as power generation, aerospace, semiconductors and optics. The surface topography of mirror-finished products is typically measured in a metrology laboratory, which is typically time consuming and cannot be integrated into the manufacturing process. To allow for in-situ product quality assurance and automatic tool change for manufacturing processes, a more accurate and responsive surface-measurement method is needed. For highly polished surfaces, a sub-micron surface fluctuation makes it possible to use light-scattering effects and image processing for surface texture analysis. A non-contact surface inspection system using a fringe-patterned illumination method is proposed in this paper. A predesigned pattern was projected onto the target surface, and its reflected image was captured by a camera. It was found that the surface parameters Sa and Sq, which are widely used to evaluate surface quality, are significantly correlated with luminous-intensity distribution. Another parameter, Str, which quantifies the uniformity of surface-texture directions due to polishing or grinding marks, was traditionally quantified after a complete-surface topographic measurement. In this research, a new approach is proposed to determine surface isotropy through a luminance-intensity distribution analysis. By rotating the test coupon, the variation of specular reflection showed correlation with the significance of surface-texture direction. The experimental results demonstrate that mirror-finished surfaces with a large deviation in luminance intensity across the pattern possess low Str values, which indicates low uniformity in surface texture.

Lamb wave-based subwavelength damage imaging using the DORT-MUSIC technique in metallic plates

A Lamb wave-based, subwavelength imaging algorithm is developed for damage imaging in a metallic plate based on a decomposition of the time-reversal operator method together with a multiple signal classification imaging condition in the space-frequency domain. In this study, a hybrid non-contact inspection system was proposed to image damage in an aluminum plate using a piezoelectric linear array for actuation and a laser Doppler vibrometer line-scan perpendicular to the piezoelectric array for sensing. The physics of incident waves, reflection, and reflected waves that underlie the transfer matrix in the decomposition of the time-reversal operator method is mathematically formulated in the context of guided waves based on the first-order Born approximation. Singular value decomposition is then employed to decompose the experimentally measured transfer matrix into three matrices, detailing the incident wave propagation from the linear actuator array, reflection from the damage, and followed by reflected waves toward the linear sensing array for each small damage. The singular value decomposition and multiple signal classification imaging condition enable providing insight on both the damage “reflectivity” and detecting damage smaller than a wavelength (subwavelength). With the flexibility of this inspection system, a considerably large area can be imaged using lower frequency Lamb waves with rapid line-scans. The experimental results showed that the hardware system with a signal processing tools such as the decomposition of the time-reversal operator with multiple signal classification (time-reversal with multiple signal classification) imaging technique can provide robust, highly accurate imaging results as well as providing damage reflectivity estimation with unknown material properties.

Guided ultrasonic wave testing of an immersed plate with hidden defects

This paper presents the results of an experimental study in which guided ultrasonic waves are used for the contactless nondestructive testing of a plate immersed in water. In the experiment, narrowband leaky Lamb waves are generated using a focused transducer and are detected with an array of five immersion sensors arranged in a semicircle. The ultrasonic signals are processed to extract a few damage-sensitive features from the time and frequency domains. These features are then fed to an artificial neural network to identify the presence of hidden defects, i.e., defects devised on the surface of the plate not facing the probing system. We find that the noncontact inspection system and the signal processing technique enable the classification of the plate health with a success rate >75%.

Errors in non-contact sensor measurements due to misalignment and scanning methodology

Non-contact sensors are becoming an increasingly popular tool for use in dimensional measurement, inspection and quality control. However, there exist a number of challenges associated with the use of these non-contact sensors in dimensional inspection systems. One important challenge is to understand the associated measurement errors and determine the objective accuracy of such an inspection system. This paper examines the effect of misalignment and scanning methodology on the measurement accuracy of a non-contact dimensional inspection system. It is important to understand this topic since the majority of optical sensor manufacturers do not supply information about the alignment between the optical line of sight and the mechanical interface of the sensor or measurement system. We prove the evidence of this measurement error through both experimental results and simulation. Finally, by using a constant standoff measurement method we succeeded to show that the majority of inherent misalignment error can be eliminated.

윙립 두께 측정용 비접촉식 검사 시스템에 관한 실험적 연구

ABSTRACT This paper presents a non-contact inspection system for automatically measuring the thickness of an aircraft wing rip product. In order to conduct the inspection of the wing rib thickness automatically, a non-contact laser displacement sensor, end-effector, and a robot were selected for use. The non-contact type inspection system was evaluated by measuring the measurement deviation of the rotation direction of a C-type yoke end-effector and the transfer direction of a V-slim end-effector. In addition, the non-contact inspection system for wing rib thickness measurements was validated through thickness measurements of a web, flange, and stiffener. Key Words : Wing Rib(윙립), Non-contact Inspection System(비접촉 검사 시스템), Thickness Measurement(두께 측정), End-Effector(엔드 이펙터) * School of Automotive Engineering, Gyeongnam NationalUniversity of Science and Technology** Korea Aerospace Industries, LTD.# Corresponding Author : Dept, of Automotive Engineering, Gyeongnam National University of Science and Technology E-mail : khji@gntech.ac.kr

Inspection of Packaged Integrated Circuits using Terahertz Radiation

Abstract A non-destructive, non-contact inspection system for packaged integrated circuits using terahertz (THz) radiation is tested. Our results show that we are able to reconstruct the internal structure of the IC, like the microelectronic chip and the interconnections. Due to the limitation of the system and the wavelength of THz radiation the fine bonding wires could not be detected. However, we show that the THz technology will be a valuable tool for the automatic online inspection of packaged integrated circuits.

Application of infrared thermography for predictive/preventive maintenance of thermal defect in electrical equipment

Internal heat of electrical equipment rises due to various reasons such as contact problems, unbalance loading, cracks in insulation, defective relays or terminal blocks, etc until eventual failure which can cause unplanned outages and possible injuries. Therefore, early prevention of thermal abnormalities in electrical equipment is necessary to avoid failure. Nowadays a fast, reliable, non-contact and cost effective infrared thermographic inspection system is being utilized widely for detecting where and how internal and external defects occur in equipment. The system collects data for investigating thermal condition through the analysis of thermal image of equipment. The image is captured by infrared camera without interrupting the running operation of system. Both preventive and predictive maintenance programs are adopted for defect diagnosis. Actually, the frequency and sequence of thermographic inspection depend on various factors including thermal condition, expense of a failure, type of production and age of equipment, etc. The objectives of this article are to discuss about preventive and predictive maintenance, thermal defects in electrical equipment and also an intelligent thermal defect identification system for accelerating the predictive defect diagnosis technique. The intelligent system proposes the application of artificial neural network and statistical features to detect the existence of defect within equipment by monitoring its thermal condition. Using discriminant analysis, the optimum features were chosen as the inputs of the neural network. The performances of the neural network were compared with the performances of discriminant analysis classifier. The comparison results showed that discriminant analysis classifier produced better performance with accuracy 82.40%.

3D surface profile measurement of unsymmetrical microstructure using Fizeau interferometric microscope

In this paper, an automatic optical inspection system for the 3D surface profile of an unsymmetrical microstructure using Fizeau interferometer was proposed. This non-contact optical inspection system is suitable for measuring the lens sag and 3D surface profile of symmetrical and unsymmetrical microlenses. Referring to the unsymmetrical microlenses as an example, the distribution of the interference fringes is partly dense and partly rare, and is completely different from the equally dense distribution of symmetrical microlenses. Thus, a novel algorithm is proposed to solve the above mentioned problem in this paper, namely, individually determining the darkest points of the dark fringes and the brightest points of the bright fringes, and fitting these discrete points as close curves through the Bezier curve theory. As the contour lines of an unsymmetrical microlens are obtained, the 3D surface profile of the unsymmetrical microlens can be plotted correspondingly. Furthermore, the proposed system has the following advantages due to its non-contact structure. This system is specifically designed for in-line measurements according to the rapid inspection speed; it has no need to coat a reflective layer on the inspected microstructure, thus avoiding damaging the surface structure of the sample.

Solar Cell Defects Detection Using Lock-In Amplifier

In this research we present a Lock-In amplifier photoluminescence image (PLI) detection system. Using a commercially available CCD camera, combined with a modulated excitation light source system, Lock-In amplifier technique is employed to enhance the sensitivity and signal-to-noise ratio of the image. Using a high resolution camera, we developed a high spatial resolution non-contact inspection system for solar cell. Each solar cell can be examined within 2s relevant for inline processing control.

Development on Inspection System for Gear’s Dimension Based on Machine Vision

A noncontact inspection system for gear based on machine vision is developed in this work, according to the mathematical model of lens distortion; the calibration of the camera was realized by the MATLAB calibration toolbox, obtained the distortion coefficients, by which the pixel is proofread. After then the key parameters of gear could be automatically acquired with proposed algorithm. In this work, the algorithm is applied to a practical case of a standard spur gear; the experimental results reported here confirm the effectiveness of the approach.

Non-Contact Vision Inspection System of Geometric Dimension Based on LabVIEW and IMAQ Vision

This paper researched on the characteristic of circle, line and area of 2-D mechanical parts. The non-contact vision inspection system is based on labVIEW and IMAQ Vision, and the main hardware include GIGE camera, image acquisition and the NI PXI-1042 platform. The system uses image processing and analysis technology, such as image filtering, smoothing processing, local enhancement and edge detection to complete the work of size measurement. According to the contrast testing results, this system has characteristics of less time-consuming, quick inspection speed and high measurement accuracy, which completely satisfies the requirements.

Design and development of automatic visual inspection system for PCB manufacturing

Inspection of solder joints has been a critical process in the electronic manufacturing industry to reduce manufacturing cost, improve yield, and ensure product quality and reliability. This paper proposes two inspection modules for an automatic solder joint classification system. The ''front-end'' inspection system includes illumination normalisation, localisation and segmentation. The ''back-end'' inspection involves the classification of solder joints using the Log-Gabor filter and classifier fusion. Five different levels of solder quality with respect to the amount of solder paste have been defined. The Log-Gabor filter has been demonstrated to achieve high recognition rates and is resistant to misalignment. This proposed system does not need any special illumination system, and the images are acquired by an ordinary digital camera. This system could contribute to the development of automated non-contact, non-destructive and low cost solder joint quality inspection systems.

Dynamic Error Characterization for Non-Contact Dimensional Inspection Systems

High-precision non-contact dimensional inspection systems typically utilize high-precision motion stages to manipulate the sensor. Such motion stages are susceptible to position errors, which need to be characterized. While geometric and thermal errors can be characterized and compensated, compensation of dynamic errors is a challenging task. This paper presents a method for dynamic error characterization that is significantly different from dynamic error characterization on contact-based systems. A mathematical model to translate the vibrations on the sensor to the measurement errors on the part is presented. Through experiments on a four-axis system, a relationship between sensor motion speed, sampling frequency, and measurement accuracy is derived. The results of the experiments are used to describe the selection of optimal operating parameters for best accuracy and least uncertainty.

Automatic Noncontact Quality Inspection System for Industrial Parabolic Trough Assembly

The construction of solar thermal power plants with several thousand m2 of collector area requires quality control measures for components, subsystems, and the entire collector rows. While quality control has a significant potential to increase the solar field efficiency, the main objective is to assure high-quality standards for the whole solar field. Quality control, assembly documentation, and performance measurements are required by the investors. Based on previous R&D work in collector development and prototype qualification, measurement systems have been developed for use in solar field construction and operation supervision. In particular, close-range photogrammetry can be used to measure the geometry of collector steel structures. The measurement system consists of a digital camera, which moves around the structure automatically while shooting photos of the concentrator structure from various positions. The photos are evaluated with photogrammetry software to check the assembly quality. The whole measurement and evaluation procedure is computer controlled and is fast enough to be integrated in a solar collector production line. This paper deals with the required measurement accuracy and shows ways to reach, maintain, and control this accuracy in the rough environment of an on-site production line.

Non-contact inspection system for large concrete structures

A method and apparatus are provided for performing non-contact inspection of large concrete structures such as dams. A phrased array acoustic source transmits an acoustic wave onto the concrete structure. A laser transmitter-receiver unit transmits a laser beam onto the surface of the structure such that the beam is modulated by the acoustic wave and reflected back to the receiver portion of the unit. The acoustic wave will be distorted by defects or anomalies in the concrete structure and this will affect the signal content of the received laser beam. The laser beam is ultimately converted into a two-dimensional image or a three-dimensional tomographic image for further processing.