• Journal of the Korean Society for Precision Engineering
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• v.26 no.6
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• pp.68-73
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• 2009

One of the traditional optical methods to monitor a tool is a CCD sensor-based vision system which captures an aspect of the tool in real time. In the case using the CCD sensor, specific lens-modules are necessary to monitor the tool with higher resolution than its pixel size, and a microprocessor is required to attain desired data from captured images. Thus theses additional devices make the entire measurement system complex. Another method is to use a pair of an optical source and a detector per measuring axis. Since the method is based on the intensity modulation, the structure of the measurement system is simper than the CCD sensor-based vision system. However, in the case measuring the three dimensional position of the tool, it is difficult to apply to micro machine-tools because there may not be space to integrate three pairs of an optical source and a detector. In this paper, in order to develop a tool-origin measurement system which is employed in micro machine-tools, the improved method to measure a tool origin in x, y and z axes is introduced. The method is based on the intensity modulation and employs one pair of an optical source radiating divergent beams and a quadrant photodiode to detect a three dimensional position of the tool. This paper presents the measurement models of the proposed tool-origin sensor. The models were verified experimentally The verification results show that the proposed method is possible and the induced models are available for design.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.1
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• pp.16-24
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• 1999

Residual stress is one of the causes which make defects in engineering components and materials. And interest in the measurement of residual stress exists in many industries. There are commonly used methods by which residual stresses are currently measured. But these methods have a little demerits. time consumption and other problems. Therefore we devised a new experimental technique to measure residual stress in materials with a combination of laser speckle pattern interferometry, finite element method and spot heating. The speckle pattern interferometer measures in-plane deformations while the heating provides for very localized stress relief. FEM is used for determining heat temperature and other parameters. The residual stresses are determined by the amount of strain that is measured subsequent to the heating and cool-down of the region being interrogated. A simple model is presented to provide a description of the method. In this paper, the ambiguity problem for the fringe patterns has solved by a phase shifting method.

• School Mathematics
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• v.10 no.2
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• pp.297-317
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• 2008

This study was designed to gain insight to adopt CAS into secondary level algebra education in Korea. Most inactive usage of calculators in math and most negative effects of calculators on their achievements of Korean students were shown in International studies such as TIMSS-R. A comparative study was carried out with consideration of mathematical backgrounds and technological environments. 8 Korean students and 26 US students in Grade 11 were participated in this study. Subjects' Problem solving process and their strategies of CAS usage in classical Box-problem with CAS were analyzed. CAS helped modeling by providing symbolic manipulation commands and graphs with students' mathematical knowledge. Results indicates that CAS requires shifts focus in algebraic contents: recognition of decimal & algebraic presentations of numbers; linking various presentations, etc. The extent of instrumentation effects on the selection of problem solving strategies among Korea and US students. Instrumentation

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.136-136
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• 2011

AlSb는 광전자 소자응용에 매우 유용한 재료이며 이를 이용한 반도체소자 설계 및 밴드갭 엔지니어링을 위해서는 화합물 반도체의 전자밴드구조를 포함한 광학적 특성이 반드시 요구된다. 본 연구는 이러한 요구의 해결방안으로서 AlSb 화합물의 유전함수 온도의존성을 0.7~5.0 eV의 에너지 영역에서 타원편광분석법을 이용하여 분석하였다. AlSb는 산소와 급격히 반응하기 때문에, 대기 중에서 물질 고유의 광특성이 유지되기 어려울 뿐만 아니라, 박막 위에 생성되는 산화막 때문에 순수한 AlSb의 유전함수 측정이 불가능하다. 따라서 박막의 산화 효과를 최소화하기 위하여 초고진공 상태의 molecular beam epitaxy 챔버 안에서 800 K의 온도로 성장한 1.5 ${\mu}m$ 두께의 AlSb 박막을 상온 300 K 까지 온도를 단계적으로 변화시켜가며 타원편광분석기를 이용하여 실시간으로 측정하였다. 각 온도에서 측정된 AlSb의 유전함수를 2차 미분하여 전이점(critical point)을 분석한 결과 $E_0$, $E_0+{\Delta}_0$, $E_1$, $E_1+{\Delta}_1$, $E_0'$, $E_0'+{\Delta}_0'$, $E_2$, $E_2+{\Delta}_2$에 해당하는 각 전이점들의 온도 의존성을 확인할 수 있었다. 실험에서 측정된 특정 온도를 포함하여 임의의 온도에서의 AlSb의 유전함수를 유도하기 위하여 변수화모델을 사용하였고 이를 통하여 각 변수들의 온도 의존 궤적을 분석하였다. 2차 미분법을 이용한 전이점들의 온도의존성 분석결과를 기준으로 변수화 모델링을 진행하였으며 그 결과 각 온도에서 실제 유전함수와 근소한 차이를 갖는 AlSb의 유전함수 모델을 만들 수 있었다. 따라서 본 연구결과는 반도체 물성에 대한 학술적 측면뿐 아니라 고온에서의 소자공정 실시간 모니터링 및 반도체 소자 설계 등의 산업적 측면에서 매우 유용하게 사용될 것으로 기대된다.

• Journal of the Korean Institute of Intelligent Systems
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• v.21 no.5
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• pp.555-563
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• 2011

The goal of image calibration is to find a relation between image and world coordinates. Conventional image calibration uses physical camera model that is able to reflect camera's optical properties between image and world coordinates. In this paper, we try to calibrate images distortion using performance criterion-based polynomial model which assumes that the relation between image and world coordinates can be identified by polynomial equation and its order and parameters are able to be estimated with image and object coordinate values and performance criterion. In order to overcome existing limitations of the conventional image calibration model, namely, over-fitting feature, the performance criterion-based polynomial model is proposed. The efficiency of proposed method can be verified with 2D images that were taken by laser scan camera.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.76-76
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• 2019

최근 기후변화로 인해 퇴적 및 세굴이 심화되었고, 4대강 사업으로 인해 급격한 하천 지형 변화가 발생하였다. 특히, 4대강 사업 이후 하상변동 모니터링에 대한 지속적인 수요가 증가하고 있다. 이에 따라 개정된 하천법에 따르면 하상변동조사를 기본 10년 주기로 정기적으로 실시하되, 퇴적 및 세굴 발생 구간에 대해서는 기본 2년을 기준으로 하상변동이 큰 곳에 대해서는 1년 주기로, 하상변동이 작은 곳에 대해서는 5년 주기로 실시해야 한다. 하지만 기술 및 예산의 한계로 인해 하상변동조사의 경우 현장 유사량 및 하상토 입도 측정과 유량-총유사량 관계식을 활용하여 모델링을 통해 하상변동을 예측하고 있는 실정이다. 하상변동은 기본적으로 하천 수심을 기본으로 하고 있으며, 사람이 직접 투입하여 임의의 지점에 대한 수심 계측을 실시하고 있다. 하지만 직접 수심 계측의 경우 낮은 자료의 밀도로 인해 많은 인력과 예산, 시간이 소요되며 무엇보다도 관측 대상인 물이라는 작업환경에서는 인명피해가 발생할 수 있는 문제점을 가지고 있다. 최근에는 이러한 한계를 극복하기 위해 초음파 센서가 탑재된 이동식 보트를 활용하여 경로형 수심 계측을 실시하고 있으나, 초음파 센서가 가지는 기기적 한계로 인해 약 50cm 이하에 대한 수심은 측정이 어려운 실정이다. 특히, 국내 하천의 경우는 홍수기를 제외하면 수심이 얕기 때문에 얕은 수심에 대한 자료 확보가 어려워 공간적 정밀도 확보가 어려운 실정이다. 따라서 기존의 하천계측의 패러다임을 지점, 선형 계측이 아닌 면 측량을 실시를 통해 높은 밀도의 자료를 확보해야 한다. 이러한 측량이 가능한 기술로 하천원격탐사가 대안으로 제시되고 있다. 하천원격탐사는 직접 접촉하지 않고, 대상체의 광학적 특성을 통해 물리적 특성을 파악하는 기술로서 적은 시간에 높은 밀도의 자료의 확보와 저예산의 고효율 방법으로 알려져 있다. 본 연구에서는 기존의 하천원격탐사에서 활용한 고비용, 저해상도의 시공간 스케일에 해당하는 위성 및 유인항공기가 아닌 하천의 흐름방향으로 비행이 가능하고 상대적으로 저비용, 고해상도의 시공간 스케일의 측정이 가능한 드론을 활용하여 하천원격탐사를 수행하는 방법에 대해 논하고자 한다. 특히, 기술적 한계가 존재하는 청색, 녹색, 적색에 해당하는 RGB 영상을 활용한 하천원격탐사를 극복하기 위한 대안으로 초분광 영상을 수집하고 활용하는 방법을 제시하고자 한다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.30 no.3
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• pp.243-251
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• 2019

Recently, several studies were conducted on the micro-Doppler(MD) phenomenon to identify a warhead from decoys. Both, the warhead and decoy, can be modeled as various shapes and maneuver with their own micro-motion. Their MD phenomenon can be demonstrated by amplitude modulation and phase modulation. Most studies have utilized approximate solutions to express the amplitude modulation regardless of various warhead and decoy shapes. However, the exact solution of the amplitude modulation is required for more effective warhead identification. In this study, we proposed a new modeling method of receiving radar signals from warheads and decoys based on physical optics. The proposed solution was evaluated using an electromagnetic prediction technique and computer-aided design models.

• Korean Journal of Remote Sensing
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• v.40 no.3
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• pp.285-293
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• 2024

This study explores the use of Sentinel-1 Synthetic Aperture Radar (SAR), processed through Google Earth Engine (GEE), to monitor changes in the areas of Antarctic ice shelves. Focusing on the Campbell Glacier Tongue (CGT) and Drygalski Ice Tongue (DIT),the research utilizes GEE's cloud computing capabilities to handle and analyze large datasets. The study employs Otsu's method for image binarization to distinguish ice shelves from the ocean and mitigates detection errors by averaging monthly images and extracting main regions. Results indicate that the CGT area decreased by approximately 26% from January 2016 to January 2024, primarily due to calving events,while DIT showed a slight increase overall,with notable reduction in recent years. Validation against Sentinel-2 optical images demonstrates high accuracy,underscoring the effectiveness of SAR and GEE for continuous, long-term monitoring of Antarctic ice shelves.

• Journal of Biomedical Engineering Research
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• v.22 no.5
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• pp.459-468
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• 2001

The Average Coordinate Referenee System (ACRS) method is developed to reduce experimental errors in human locomotion analysis. Experimentally measured kinematic data is used to conduct analysis in human modeling, and the model accuracy is directly related to the accuracy of the data. However. the accuracy is questionable due to skin movement. deformation of skeletal structure while in motion and limitations of commercial motion analysis system . In this study. the ACRS method is applied to an optically-tracked segment marker system. although it can be applied to many of the others as well. In the ACRS method, each marker can be treated independently. as the origin of a local coordinate system for its body segment. Errors, inherent in the experimental process. result in different values for the recovered Euler angles at each origin. By employing knowledge of an initial, calibrated segment reference frame, the Euler angles at each marker location can be averaged. minimizing the effect of the skin extension and rotation. Using the developed ACRS methodology the error is reduced when compared to the general Euler angle method commonly applied in motion analysis. If there is no error exist in the experimental gait data. the separation and Penetration distance of the femoraltibial joint using absolute coordinate system is supposed to be zero during one gait cycle. The separation and Penetration distance was ranged up to 18 mm using general Euler angle method and 12 mm using the developed ACRS.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.6
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• pp.78-86
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• 2014

In this paper, a novel intensity-based fiber optic vibration sensor using a mass-spring structure, which consists of four serpentine flexure springs and a rectangular aperture within a proof mass, is proposed and its feasibility test is given by the simulation and experiment. An optical collimator is used to broaden the beam which is modulated by the displacement of the rectangular aperture within the proof mass. The proposed fiber optic vibration sensor has been analyzed and designed in terms of the optical and mechanical parts. A mechanical structure has been designed using theoretical analysis, mathematical modeling, and 3D FEM (Finite Element Method) simulation. The relative aperture displacement according to the base vibration is given using FEM simulation, while the output beam power according to the relative displacement is measured by experiment. The simulated sensor sensitivity of $15.731{\mu}W/G$ and detection range of ${\pm}6.087G$ are given. By using reference signal, the output signal with 0.75% relative error shows a good stability. The proposed vibration sensor structure has the advantages of a simple structure, low cost, and multi-point sensing characteristic. It also has the potential to be made by MEMS (Micro-Electro-Mechanical System) technology.