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전파속도를 알수 없는 재료에서의 AE 발생위치 온라인 측정
장경영,이원흠,김달중,Jhang, Kyung-Young,Lee, Weon-Heum,Kim, Dal-jung 대한기계학회 1998 大韓機械學會論文集A Vol.22 No.3
The ability to locate the defects in materials is one of the major attrations of the acoustic emission(AE) technique. The most conventional method for planar AE source localization is to place three or more AE sensors on the plate and to determine the source position by measuring the differences in the arrival times of the AE wave at the sensors, which is called as triangulation method. But this method can not be applied in the material of which elastic wave propagtion velocity is not known. In this paper, we propose two methods, vector method and error minimization method, for AE source location on the material with unknown AE wave velocity. In this method, it is not needed to know the propagation velocity previously, that is, we can apply this method to arbitrary material of which properties are not known exactly. Also, in this paper, the robustness to the error in the measurement of time differences are discussed for both methods. Finally, in order to evaluate the actual performances, experiments using a pencil lead break as the AE source were carried out on the aluminum plate.
머신비젼을 이용한 SMD VR의 중심위치와 홈방향 정밀계측
장경영,김병엽,한창수,박종현,감도영,Jhang, Kyung-Young,Kim, Byung-Yup,Han, Chang-Su,Park, Jong-Hyun,Gam, Do-Young 대한기계학회 1997 大韓機械學會論文集A Vol.21 No.8
The automation of final inspection and tuning process in the manufacturing of electric products is hot issue now, because it is the only part that has not been wholey automized yet, mainly due to the difficulties to handle so small size of VR which is the final tuning point in the most of electric products. For the automation of this process, at first the accurate measurement of position and orientation of SMD VR on PCB in real time is strongly needed. In this paper, a new image processing algorithm to detect the center position and orientation of target VR by using machine vision is proposed for automatic final tuning of the 8mm camcoder's performance. In the method, the outline feature of object is used actively. The usefulness of the proposed methods were tested by several experiments, and the results showed enough accuracy for both of position and orientation. Additatively, we discussed about the total visual system construction and preprocessing of image.
장경영(Kyung Young Jhang),박종웅(Jong Woung Park) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.2
So far, various technologies have been researched for the car safety. Among these researches, the studies about the active safety vehicle (ASV) connecting the intelligent vehicle are most popular. The ASV must cope effectively with the change of the outside world. The sensors for these skills are CCD camera, infrared camera, ultrasonic waves, laser radar, and millimeter-wave radar. In this paper, we investigate the features and classes, and applying technologies for these sensors.
장경영(Kyung-young Jhang),김주철(Joo-chul Kim),김홍준(Hong-jun Kim),황원호(Won-ho Hwang) Korean Society for Precision Engineering 2004 한국정밀공학회지 Vol.21 No.10
The particle amount monitoring technique using ultrasound is proposed to determine the proper maintenance time of the filter in the supply process of pure gas in the unit of oxygen plant. There are advantages that it is adaptable in high temperature and high pressure, and it is not disturbed by being exposed in the gas flow, and it can be implemented very economical1y. The applicability of the ultrasonic technique is pre-studied through the theoretical analysis for the dependency of attenuation of ultrasonic wave on the particles in the gas flow. For the purpose, absorption, scattering and dispersion models are considered, and the attenuation by absorption and the change rate of the propagation speed are calculated for the specific range of particle size and the ultrasonic wave frequency. It was expected by simulation that the absorptive attenuation by particles was the most sensitive to the change of particle amount. The experimental result showed high correspondence with the theoretical expectation so that this ultrasound attenuation measurement was proved to be highly effective for monitoring the amount of floating particles in the gas flow.
레이저와 공기결합 트랜스듀서를 이용한 비접촉식 초음파 비파괴 평가/검사
장경영(Kyung Young Jhang),김홍준(Hong Joon Kim),Donatella Cerniglia,Boro Djordjevic 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.3
Ultrasonic NDE/I methods have been demonstrated as very effective tool in characterization of cracks and structural defects such as bond-line failures. Most of the ultrasonic testing is performed using conventional contact ultrasonic transducers that cannot be readily adapted to automation and field application. Also for large area inspection contact type is time consuming and as a result, it is important to develop a rapid and more efficient ultrasonic technique. in this paper, laser generation and air-coupled detection of ultrasound is proposed as a solution of non-contact method with no requirement of a coupling medium, and the bond quality of adhesively bonded and riveted aluminum lap splice joints is investigated as an application. A Q-switched Nd:YAG laser and a periodic transmission mask are used to generate a selected Lamb mode. The experimental show that multi-line laser source produces significant directed ultrasound and that the presence of defects can be detected. reliably from the attenuation of signal amplitude. These results demonstrate that the proposed technique is well suitable and flexible for non-contact NDE/I applications.
선배열 슬릿마스크를 이용한 협대역 레이저 여기 표면파의 음향 비선형성
장경영(Kyung-Young Jhang),고광철(Kwang-Cheol Ko),김정석(Chung Seok Kim),남태형(Taehyung Nam),최성호(Sungho Choi),이태훈(Taehun Lee) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.6
본 연구의 목적은 선배열 슬릿 마스크를 이용한 레이저에 의해 발생된 협대역 표면파에 존재하는 본질적인 음향 비선형성을 이론적 및 실험적으로 연구하는 것이다. 레이저 여기 표면파의 주파수 특성을 이론적으로 분석하여 고조파 발생 기구를 규명하고 알루미늄 6061-T6 시험편을 대상으로 단일 슬릿과 선배열 슬릿에 대한 슬릿 열림폭, 레이저 세기의 영향을 분석하였다. 고조파 성분은 슬릿 열림폭, 공진형 수신기에 크게 의존하는 것으로 나타났으며 레이저 세기에 따라서 A₁²과 A₂간에는 선형의 관계가 나타났다. The objective of this study is to investigate theoretically and experimentally intrinsic acoustic nonlinearity that exists in narrow band surface wave generated by laser beam with line arrayed slit masks. The generation of higher harmonic was examined by theoretical analyzing the frequency characteristic of surface wave generated by laser beam, and also the effects of slit width and laser intensity on the acoustic nonlinearity of aluminum 6061 alloy using single slit and line arrayed slit mask were analysed. The higher harmonic component was shown that it defends dominantly on the slit width and resonance-type transducer. It also shows the linear relationship between A₁² and A₂ with the laser intensity.