• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2017년도 추계 학술논문 발표대회
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• pp.52-53
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• 2017

Through the case study, we surveyed an applicability of digital fabrication in irregular-shaped building construction project. By digital fabrication, we mean is a precision manufacturing method has been used in aircraft, ship and car manufacturing industry. We collected construction-completed "LotteWorld Tower Podium" project data and analyzed its process in terms of construction quality andduration. The result shows that digital fabrication is considered a competitive technology that enabled to complete the project in seven months within 3mm surface curvature threshold. The digitalfabrication is expected to apply on a number of irregular-shaped building construction project.

• Current Optics and Photonics
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• 제4권4호
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• pp.277-285
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• 2020

Computer-generated holograms (CGH) are the core devices to solve the problem of freeform surface measurement. In view of the overlay error introduced in the manufacturing process of CGH, this paper proposes an evaluation model for analyzing the overlay error of CGH. The detection method of extracting CGH profile information by an ultra-depth of field micro-measurement system is presented. Furthermore, based on the detection method and technical scheme, the effect of overlay error on the wavefront accuracy of CGH can be evaluated.

• 천문학회보
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• 제46권2호
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• pp.56.1-56.1
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• 2021

표준우주모형이 예측하는 천체의 성장 역사를 추적하기 위해서는 보통의 밤하늘 밝기보다 약 1000배 어두운 낮은 표면밝기(Low Surface Brightness, LSB) 우주 탐사가 필요하지만, 관측기술의 한계로 아직 LSB 우주는 거의 미지의 세계에 있다고 할 수 있다. 한국천문연구원에서는 LSB 천체 관측에 최적화된 직경 300 mm K-DRIFT Pathfinder 망원경을 개발하였다. LSB 천체는 ~28 mag/arcsec2 보다 어두운 천체로 표면밝기가 매우 낮기 때문에 망원경 내부의 미광(stray light)을 최소화하는 것이 중요하다. 이를 구현하기 위해 K-DRIFT Pathfinder 망원경에는 선형 비점수차가 제거된 비축 자유곡면 삼 반사경 형태를 적용하였다. 본 연구를 통해 가시광 영역에서 선형 비점수차가 제거된 비축 자유곡면 삼 반사 망원경의 설계, 제작 및 측정 가능성을 검증하였다. 본 발표에서는 K-DRIFT Pathfinder 망원경에 적용된 비축 자유곡면 광학면의 가공, 삼 반사 망원경의 조립 및 정렬 결과를 소개한다.

• 한국정밀공학회지
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• 제29권8호
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• pp.845-852
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• 2012

The diaphragm-type stylus probe was developed for ultra-precision on-machine measurement (OMM) application. This probe is equipped with two diaphragms which are parallel and one capacitive sensor is used for detecting the vertical motion of end tip in the stylus when it is contacted to the optical freeform surface. For better performance of proposed probes, several design parameters such as axial stiffness and the lateral deformations were investigated with finite element analysis techniques. To verify the feasibility, the profiles of the master sphere ball were measured on the ultra-precision milling machine. The measurement results show that the proposed probe can calculate the radius of the circle within the accuracy of 0.1 ${\mu}m$ for the ultraprecision optical surface.

• 대한기계학회논문집A
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• 제24권8호
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• pp.1958-1967
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• 2000

Rapid Prototyping( RP ) has been increasingly applied in the process of design and development of new products. RP can shrink the time and expense required to bring a new product from initial concept to production. However, the necessity of using RP for short-run manufacturing is continuously driving a development of a cost-effective technique that will produce completely-finished quality parts in a very short time. To meet these demands, the improvements in production speed, accuracy materials, and cost are crucial. Thus, a new hybrid-RP system performing both deposition and machining in a station is proposed in this paper. It incorporates both material deposition in layers and material removal from the outer surface of the layer to produce the required surface finish. The new hybrid-RP system can dramatically reduce the total build time and fabricate largo-sized and freeform objects because it uses very thick layers, i.e.

• 천문학회보
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• 제46권1호
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• pp.38.3-38.3
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• 2021

We are developing an optomechanical design of infrared telescope for the CubeSat and Unmanned Aerial Vehicle (UAV) which adapts the Linear Astigmatism Free- Three Mirror System in the confocal off-axis condition. The small entrance pupil (diameter of 40 mm) and the fast telescope (f-number of 1.9) can survey large areas. The telescope structure consists of three mirror modules and a sensor module, which are assembled on the base frame. The mirror structure has duplex layers to minimize a surface deformation and physical size of a mirror mount. All the optomechanical parts and three freeform mirrors are made from the same material, i.e., aluminum 6061-T6. The Coefficient of Thermal Expansion matching single material structure makes the imaging performance to be independent of the thermal expansion. We investigated structural characteristics against external loads through Finite Element Analysis. We confirmed the mirror surface distortion by the gravity and screw tightening, and the overall contraction/expansion following the external temperature environment change (from -30℃ to +30℃).

• 천문학회보
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• 제45권1호
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• pp.68.2-68.2
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• 2020

UVO-Multiband Polarizing Imager System (UVOMPIS) is an ultraviolet to visible light multi-wavelength polarization/imaging system for Compact Advanced Satellite. We developed Linear Astigmatism Free-Three Mirror System (LAF-TMS) D200F2 as an optical system of UVOMPIS which has an entrance pupil diameter of 200 mm, a focal ratio of 2, a field of view of 2° × 4°. LAF-TMS is a confocal off-axis reflecting telescope system that removes linear astigmatism, and its all mirrors (M1, M2, M3) are optimized with the freeform surface to reduce high-order aberrations. Through the sensitivity analysis and Monte-Carlo simulation as the tolerance analysis, we can confirm the feasibility of the system, relatively sensitive parameters (tilt, decenter, despace, surface RMS error), and considerations for optomechanical design. From the sensitivity analysis, we can discover the relatively sensitive optical alignment parameters to a single perturbation. Further more, in the monte-carlo simulation, we investigate the minimum tolerance budget satisfying the required optical performance and whether the tolerance range is satisfied within manufacturing error.

• 전자공학회논문지SC
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• 제42권1호
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• pp.1-11
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• 2005

본 연구에서는 다양한 재료의 시트(Sheet)를 각각 절단하여 적층하는 방법으로 기존 적층조형법과는 다른 쾌속 임의형상제작 시스템인 CAFL/sup VM/(Computer Aided Fabrication of Lamination for Various Material)을 제안한다. 이러한 조형 방법은 가공 속도를 빠르게 하며 복잡한 후처리 과정을윽 대폭 줄일 수 있고, 여러 가지 재료가 사용 가능한 장점을 지니고 있다. 이러한 목적으로 개발된 2자유도의 X-Y테이블 형태의 CAFL/sup VM/은 레이저빔으로 시트(Sheet)를 절단, 적층하여 조형물을 완성하는 새로운 고속적층 시스템으로 가능성을 검증하였다. 하지만 2자유도 시스템은 X-Y 평면을 이동하는 작업공간에 수직으로 레이저 가공이 이루어지는 방법으로, 조형된 사물의 표면에 계단 형상이 나타나는 표면정밀도상의 문제점을 드러낸다. 이러한 문제점을 해결하고자 2자유도에 3자유도를 추가한 5자유도 시스템을 제안하여 레이저의 경사절단이 가능하게 함으로서 조형된 사물의 표면 정밀도를 높이고, 일정한 패턴의 모양을 갖는 조형물 가공의 경우 여러 시트(Sheet)가 적층되는 부분을 한번에 가공할 수 있도록 하여 보다 빠르고 정밀한 5자유도 매니퓰레이터 CAFL/sup VM/ 시스템을 설계한다. 즉, 정속경로제어와 경사각절단제어를 구현하고 그 외에 수반된 자동화 CAFL/sup VM/ 시스템을 구현하는 것이 본 논문의 목적이다.

• Macromolecular Research
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• 제17권3호
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• pp.197-202
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• 2009

Solution-based, direct-write patterning by an automated, computer-controlled, inkjet technique is of particular interest in a wide variety of industrial fields. We report the construction of three-dimensional (3D), micro-patterned structures by polymer inkjet printing. A piezoelectric, drop-on-demand (DOD) inkjet printing system and a common polymer, PVA (poly(vinyl alcohol)), were explored for 3D construction. After a systematic preliminary study with different solvent systems, a mixture of water and DMSO was chosen as an appropriate solvent for PVA inks. The use of water as a single solvent resulted in frequent PVA clogging when the nozzles were undisturbed. Among the tested polymer ink compositions, the PVA inks in a water/DMSO mixture (4/1 v/v) with concentrations of 3 to 5 g/dL proved to be appropriate for piezoelectric DOD inkjet printing because they were well within the proper viscosity and surface tension range. When a dot was printed, the so-called 'coffee-ring effect' was significant, but its appearance was not prominent in line printing. The optimal polymer inkjet printing process was repeated slice after slice up to 200 times, which produced a well-defined, 3 D micro-patterned surface. The overall results implied that piezoelectric DOD polymer inkjet printing could be a powerful, solid-freeform, fabrication technology to create a controlled 3D architecture.

• International Journal of CAD/CAM
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• 제5권1호
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• pp.1-10
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• 2005

A new approach based on vector field clustering for tool path optimization of 5-axis CNC machining is presented in this paper. The strategy of the approach is to produce an efficient tool path with respect to the optimal cutting direction vector field. The optimal cutting direction maximizes the machining strip width. We use the normalized cut clustering technique to partition the vector field into clusters. The spiral and the zigzag patterns are then applied to generate tool path on the clusters. The iso-scallop method is used for calculating the tool path. Finally, our numerical examples and real cutting experiment show that the tool path generated by the proposed method is more efficient than the tool path generated by the traditional iso-parametric method.