• Title/Summary/Keyword: Non-contact Mode

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Non-contact Ultrasonic Technique for the Thin Defect Evaluation by the Lamb-EMAT (비접촉 Lamb-EMAT를 이용한 두께감육 평가에 관한 연구)

  • Kim, Tae-Hyeong;Park, Ik-Geun;Lee, Cheol-Gu;Kim, Yong-Gwon;Kim, Hyeon-Muk;Jo, Yong-Sang
    • Proceedings of the KWS Conference
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    • 2005.06a
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    • pp.194-196
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    • 2005
  • Ultrasonic guided waves are gaining increasing attention for the inspection of platelike and rodlike structures. At the same time, inspection methods that do not require contact with the test piece are being developed for advanced applications. This paper capitalizes on recent advances in the areas of guided wave ultrasonics and noncontact ultrasonics to demonstrate a superior method for the nondestructive detection of thinning defects simulating hidden corrosion in thin aluminum plates. The proposed approach uses EMAT(electro-magnetic acoustic transducer) for the noncontact generation and detection of guided plate waves. Interesting features in the dispersive behavior of selected guided modes are used for the detection of plate thinning. It is shown that mode cutoff measurements provide a qualitative detection of thinning defects. Measurement of the mode group velocity can be also used to quantify of thinning depth.

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The Therapeutic Effects of a Pulsed Nd:YAG Laser on Oral Lesions (구강병소에 대한 펄스형 Nd: YAG 레이저의 치료효과)

  • 신금백
    • Journal of Oral Medicine and Pain
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    • v.22 no.2
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    • pp.309-325
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    • 1997
  • In order to set the lasing variables and evaluate, clinically, the therapeutic effects of a pulsed Nd:YAG laser on oral lesion, the author applied the laser energy from a fiberoptic delivered, free running, pulsed Nd:YAG laser (wavelength 1064nm, Pulse duration 120$\mu$sec, fiber diameter 200$\mu$m/320$\mu$m) to 22 cases of oral soft tissue lesions and 6 cases of oral hard tissue lesions. The obtained results were as follows : 1. The effective excision with contact mode and the effective hemostasis of accompanied bleeding with noncontact mode were occurred by lasing on oral soft tissue lesions with fiber diameter of 320$\mu$m under the variables of 2.0~4.0W and 20~50Hz which were controlled into high power/low pulses for excision, low power/high pulses for hemostasis, low power in granulation tissue and high power in fibrous tissue according to therapeutic goals and tissue conditions. 2. About 50% of decreasing effect on hypersensitivity was occurred by lasing with non-contact and contact mode on cervical abrasion which caused dentinal hypersensitivity with fiber diameter of 320$\mu$m under the variables of 0.7 - 1.0W and 10Hz which were applied 2~3 times with 1 week interval. 3. The effective sterilization of infected root canal and lesion of periapical abscess was occurred by lasing with contact and spiral modes on wall of root canal and periapical abscess with fiber diameter of 200$\mu$m of which the tip was placed about 1mm shorter than root canal length under the variables of 1.OW and 10Hz.

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Displacement Measurement of Multi-Point Using a Pattern Recognition from Video Signal (영상 신호에서 패턴인식을 이용한 다중 포인트 변위측정)

  • Jeon, Hyeong-Seop;Choi, Young-Chul;Park, Jong-Won
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2008.11a
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    • pp.675-680
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    • 2008
  • This paper proposes a way to measure the displacement of a multi-point by using a pattern recognition from video signal. Generally in measuring displacement, gab sensor, which is a displacement sensor, is used. However, it is difficult to measure displacement by using a common sensor in places where it is unsuitable to attach a sensor, such as high-temperature areas or radioactive places. In this kind of places, non-contact methods should be used to measure displacement and in this study, images of CCD camera were used. When displacement is measure by using camera images, it is possible to measure displacement with a non-contact method. It is simple to install and multi-point displacement measuring device so that it is advantageous to solve problems of spatial constraints.

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The Study of Non-contact Thickness Measurement of Thin Transparent Object (비접촉 얇은 투명체의 두께 측정에 관한 기초연구)

  • Hong, Jun-Hee;Jeong, Seok-Kyu;Park, Simon S.
    • Journal of the Korean Society for Precision Engineering
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    • v.26 no.12
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    • pp.62-68
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    • 2009
  • In this paper, we investigate a new method to measure the thickness of thin transparent objects utilizing a step index multi-mode optical fiber sensor. The method mainly depends on the refraction rate of transparent target, the diameter of optical fibers and the distance to reflector. We confirmed the effects of these parameters through the experimental verification tests. The comparison between the theoretical vs. analytical results shows good agreements with each other. The proposed model also enables users to measure the thickness of thin transparent objects without considering the reflection from the target. This approach provides simple, cost-effective and non-contact solutions to measure the thickness.

Displacement Measurement of Multi-point Using a Pattern Recognition from Video Signal (영상 신호에서 패턴인식을 이용한 다중 포인트 변위측정)

  • Jeon, Hyeong-Seop;Choi, Young-Chul;Park, Jong-Won
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.18 no.12
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    • pp.1256-1261
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    • 2008
  • This paper proposes a way to measure the displacement of a multi-point by using a pattern recognition from video signal. Generally in measuring displacement, gab sensor, which is a displacement sensor, is used. However, it is difficult to measure displacement by using a common sensor in places where it is unsuitable to attach a sensor, such as high-temperature areas or radioactive places. In this kind of places, non-contact methods should be used to measure displacement and in this study, images of CCD camera were used. When multi-point is measure by using a pattern recognition, it is possible to measure displacement with a non-contact method. It is simple to install and multi-point displacement measuring device so that it is advantageous to solve problems of spatial constraints.

The Origin and Effect of Hot Spot Phenomena on Judder Vibration in Automotive Disk Brake (디스크 브레이크에서 열섬 현상이 발생되는 원인과 저더 진동에 미치는 영향)

  • Cho, Ho-Joon;Cho, Chong-Du;Kim, Myoung-Gu;Maeng, Ju-Won;Lee, Jae-Han
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2006.05a
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    • pp.213-218
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    • 2006
  • Hot spot phenomenon is caused by non-uniform contact area between brake pad and disk frequent braking. Brake disk deformed by locally concentrated heat increases magnitude of frictional vibration. And this deformation can highly influence the judder vibration. In this experimental study, vibration and hot spot was measured in accordance with rotation of disk and pressure of master cylinder for finding the factors that causes hot spot phenomena. For comparing hot spot aspects with mode shapes of disk, mode shapes were measured by conducting modal test, and analyzed by using finite element analysis. Relation between hot spot phenomenon, and mode shape, pressure of master cylinder and rotation speed of disk respectively, was achieved by hot spot measurement and frequency analysis.

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Sliding Mode Control based on Disturbance Observer for Magnetic Levitation Positioning Stage

  • Zhang, Shansi;Ma, Shuyuan;Wang, Weiming
    • Journal of Electrical Engineering and Technology
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    • v.13 no.5
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    • pp.2116-2124
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    • 2018
  • Magnetic levitation system with the advantages of non-contact, no friction and no wear can satisfy the requirement of high precision and high speed positioning. In this paper, magnetic levitation positioning stage which mainly consists of planar coil and HALBACH permanent magnet array and its control and driving system are designed. Magnetic levitation system is a highly nonlinear and strongly coupled complex system and its control performance can be influenced by the uncertainty and external disturbance. So exact feedback linearization method is used to realize exact linearization and decoupling, and a strategy of sliding mode control based on disturbance observer is proposed to compensate the uncertainty and external disturbance. Detailed proofs of observer's convergence property and system stability are derived. Both the simulation and experiment results verify the effectiveness of sliding mode control algorithm based on disturbance observer.

The Origin and Effect of Hot Spot Phenomena on Judder Vibration in Automotive Disk Brake (디스코 브레이크에서 열섬 현상이 발생되는 원인과 저더진동에 미치는 영향)

  • Cho, Chong-Du;Kim, Myoung-Gu;Cho, Ho-Joon
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.16 no.8 s.113
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    • pp.886-892
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    • 2006
  • Hot spot phenomenon is caused by non-uniform contact area between brake pad and disk frequent braking. Brake disk deformed by locally concentrated heat increases magnitude of frictional vibration. And this deformation can highly influence the judder vibration. In this experimental study, vibration and hot spot was measured in accordance with rotation of disk and pressure of master cylinder for finding the factors that causes hot spot phenomena. For comparing hot spot aspects with mode shapes of disk, mode shapes were measured by conducting modal test, and analyzed by using finite element analysis. Relation between hot spot phenomenon, and mode shape, pressure of master cylinder and rotation speed of disk respectively, was achieved by hot spot measurement and frequency analysis.

Non-Contact Ultrasonic Testing of Aircraft Joints using Laser Generated Lamb Wave (레이저 여기 램파를 이용한 항공기 판재 접합부의 비접촉식 초음파 검사)

  • Jhang, Kyoung-Young;Kim, Hong-Joon;Ceringlia, Donatella;Djordjevic, Boro
    • Journal of the Korean Society for Nondestructive Testing
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    • v.21 no.2
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    • pp.163-168
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    • 2001
  • Due to aging, adhesively bonded and riveted aircraft lap joints can contain distends, cracks around rivet holes, fatigue induced flaws, and corrosion. It is required for the safety of aircraft to inspect these defects through the whole region of mint in rapid speed. Bond quality or adhesively bonded and riveted aluminum lap splice joints is investigated using non-contact remote ultrasonic nondestructive evaluation (NDE). Non-contact ultrasonic tests are performed using laser generation and air-coupled transducer detection. A Q-switched Nd:YAG laser and a periodic transmission mask are used to generate a selected Lamb mode. The Lamb wave is generated on one side of the lap splice joint, propagates along the plate, interacts with the joint and is detected on the other side by a micromachined air-coupled capacitance transducer. Analysis of recorded signals allows to evaluate the condition of the bond.

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Alumina Ceramics Reinforced by Ni-coated Chopped Alumina Fiber

  • Kim, Hai-Doo;Lee, Kyu-Hwan
    • The Korean Journal of Ceramics
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    • v.7 no.2
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    • pp.74-79
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    • 2001
  • Alumina composite reinforced by chopped alumina fiber was fabricated by filter-pressing the fiber slurry followed by the infiltration of alumina slurry. The chopped fiber was coated with nickel by electroless plating method. The green samples were densified by hot-pressing. Microstructures were studied by SEM and the mechanical properties such as bending strength and fracture toughness were measured. The resulting mechanical properties were analyzed in relation with processing parameters such as preform density and resulting microstructures. The load-displacement curve of the specimen with Ni interlayer but without Ni inclusion showed brittle fracture mode due to the direct contact between matrix and fiber. The load-displacement curve of the specimen with Ni interlayer and Ni inclusion in the matrix which is introduced by high applied pressure during specimen preparation showed non-brittle fracture mode due to the fiber pull-out and dutile phases in the matrix.

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