• 한국광학회:학술대회논문집
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• 한국광학회 2008년도 동계학술발표회 논문집
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• pp.109-110
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• 2008

• 한국광학회:학술대회논문집
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• 한국광학회 2006년도 하계학술발표회 논문집
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• pp.157-158
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• 2006

• 한국정밀공학회지
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• 제18권6호
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• pp.159-165
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• 2001

Recently Moire and PMP(Phase Measuring Profilometry) are adopted as a practical methodology for non-contact 3-D measurement of free surface. These methods extract the 3-D informations from the images of the object projected with stripe-pattern light. This paper presents a simple projector generating stripe-pattern light using expensive polygon mirror. In this projector, slit-beam is generated with a Laser diode and a rod lens and the laser diode is switched on/off synchronizing with the rotation of the polygon mirror. So its structure is very simple and light-weighted compared to the existent projection methods using several lenses and it is also easy to change the pitch and the phase of the stripe pattern. Experimental results show that the intensity profile of the stripe pattern can be approximated with sinusoidal curve by reducing the pitch of the stripe pattern.

• 한국정밀공학회지
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• 제19권5호
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• pp.36-42
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• 2002

This paper presents the way of building an occupancy grid map which a mobile robot needs to autonomously navigate in the unknown environment. A disparity map resulting from stereo matching can be converted into the 2D distance information. If the stereo matching has some errors, however, the subsequent map becomes unreliable. In this paper, a new morphological filter is proposed to reject 'spikes' of the disparity map due to stereo mismatch by considering the fact that these spikes occur locally. The new method has advantages that it is simpler and more easily realized than existing similar algorithms. Several occupancy grid maps based on stereo vision using the proposed algorithm have been built and compared with the actual distance information to verify the validity of the proposed method.

• 한국정밀공학회지
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• 제27권3호
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• pp.18-26
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• 2010

Diffraction gratings with precise spatial periods of 2 ${\mu}m$ and 5 ${\mu}m$ have been fabricated by using a femtosecond laser which does not have limits on materials of micromachining and small thermal effects due to high peak power. Diffraction angle and diffraction efficiency of those were measured. Simulation results of diffraction angle and diffraction efficiency of the diffraction grating calculated with the parameters such as line width, depth, and spatial period of the fabricated gratings were compared with experimental results measured with a He-Ne laser. Besides these, Fresnel Zone Plates (FZPs) with focal distances of 50 mm and 25 mm were fabricated and focal distances of fabricated FZP were measured. Those experimental results for diffraction gratings and FZPs match well with experimental results.

• 한국광학회지
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• 제12권5호
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• pp.371-375
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• 2001

온도 변화에 민감한 1480 nm LD로 펌핑되는 erbium doped fiber와 단일 광섬유 브래그 격자를 사용하여 스트레인과 온도를 동시에 측정할 수 있는 센서 헤드를 구성하였고 optical spectrum analyzer (OSA) 대신에 마하젠더 간섭계를 demodulator 로 사용하여 측정 정밀도와 속도를 향상 시켰다. 출력 신호의 진폭 변화로 측정한 온도의 최소 측정 단위는 0.05$^{\circ}C$이고 위상 변화로 측정한 스트레인의 경우는 0.1$\mu$strain으로서 0.07 nm의 측정 해상도를 가지는 OSA를 demodulator로 사용하는 경우보다 측정 정밀도가 각각 140배 이상과 700배 이상 향상되었음을 볼 수 있었다.

• 한국정밀공학회지
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• 제12권5호
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• pp.126-135
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• 1995

An exhaust muffler is one of the simple and effective means to meet the demand for a quiet vehicle, and it deserves a close attention to effectively reduce the engine noise. The transfer function technique is one of the tools that have been used to analyze the noise characteristics of the exhaust muffler. In this paper we obtained a transfer function using the forward-going and backward-going components of sound pressure in the exhaust muffler, which is compatible wiht lattice filter algorithm. This form of transfer function is obtained for the basic elements of a muffler, such as uniform tube, open termin- ation, closed termination, anechoic termination, expansion, contraction, extended-tube resonator, hole, Helmholtz resonator, and concentric hole-cavity resonator. The results are combined to produce the transfer function of various types of mufflers. With this transfer function we calculate the transmission and insertion losses of mufflers, and examined the effects of various design parameters. Comparisons were made between the calculation and experimental results, which showed a good agreement, and we conclude that the transfer function of lattice form can be used to analyze the noise characteristics of the exhaust mufflers.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.607-610
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• 2005

A remeshing algorithm using tetrahedral elements has been developed, which is adapted to the mesh density map constructed by a posteriori error estimation. In the finite element analyses of metal forging processes, numerical error increases as deformation proceeds due to severe distortion of elements. In order to reduce the numerical error, the desired mesh sizes in each region of the workpiece are calculated by a posteriori error estimation and the density map is constructed. Piecewise density functions are then constructed with the radial basis function in order to interpolate the discrete data of the density map. The sample mesh is constructed based on the point insertion technique which is adapted to the density function and the mesh size is controlled by moving and deleting nodes to obtain optimal distribution according to the mesh density function and the quality optimization function as well. After finishing the redistribution process of nodes, a tetrahedral mesh is constructed with the redistributed nodes, which is adapted to the density map and resulting in good mesh quality. A goodness and adaptability of the constructed mesh is verified with a testing measure. The proposed remeshing technique is applied to the finite element analyses of forging processes.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.844-847
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• 2005

A seamless analysis of complex geometry is one of greatly interesting topic. However, there are still gaps between the industrial applications and fundamental academic studies owing to time consuming modeling process. To resolve this problem, an auto mesh generation program based on grid-based approach has been developed for IT-product in the present study. At first, base mesh and skin mesh are generated using the information of entities which extracted from IGES file. Secondly the provisional core mesh with rugged boundary geometry is constructed by superimposing the skin mesh as well as the base mesh generated from the CAD model. Finally, the positions of boundary nodes are adjusted to make a qualified mesh by adapting node modification and smoothing techniques. Also, for the sake of verification of mesh quality, the hexahedral auto mesh constructed by the program is compared with the corresponding tetrahedral free mesh and hexahedral mapped mesh through static finite element analyses. Thereby, it is anticipated that the grid-based approach can be used as a promising pre-processor for integrity evaluation of various IT-products.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.149-152
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• 2008

광섬유센서 계측시스템의 대표적인 방식인 광섬유격자센서(FBG센서)는 포인트 센서 개념의 센서로써 측정하고자 하는 지점에 설치되는 반영구적이며, 분해능이 우수한 센서이다. 광섬유센서는 유리섬유의 코어(Core)/클래딩(Cladding)부분과 유리섬유를 보호하기 위한 코팅(Coating)으로 구분된다. 이와 같이 구성된 광섬유에 외력이 작용할 경우 유리섬유부분과 코팅부분 사이에서 미끄러짐(Slip)현상이 쉽게 발생하는 단점이 있어 패키징을 한 후 데이터에 오류가 생기는 경우가 있었다. 두 재료 간에 발생하는 미끄러짐(Slip)현상을 방지하기 위해서 광섬유의 코팅을 부분적으로 박피한 후 유리섬유부분을 직접 특정한 고정구로 고정하는 방식을 적용하고 프리스트레인을 부가하여 외력에 의한 변형을 정밀하게 측정할 수 있게 하였다. 콘크리트의 변형률을 측정하기 위하여 1미터의 게이지길이를 갖는 광섬유격자센서를 고정하고 프리스트레인을 부가함으로서 광섬유센서의 장점을 더욱 높여 콘크리트구조물의 인장 및 압축 거동을 정밀하고도 장기간 지속적으로 측정할 수 있게 하였으며, 이를 이용하여 인근의 전력구 공사 기간 동안 지하철 콘크리트 라이닝구조물의 안전을 감시하였다.