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Cao, B.X.,Hoang, P.,Ahn, S.,Kim, J.o.,Sohn, H.,Noh, J. Applied Science Publishers 2016 Optics and lasers in engineering Vol.86 No.-
The real-time fabrication of microgrooves on a curved surface using a laser beam, without preprogramming their shapes into the machining instructions, is a major challenge in laser processing owing to limitations associated with the real-time detection of the focal position. A new approach using a sampled fraction of the beam from a diffractive beam sampler (DBS) is therefore presented in order to overcome this limitation. By considering the sampled fraction of the beam an analysis of the results allows for precise positioning of the specimen for focal-point identification. This allows for the determination of the focus for a broad variety of laser types and laser powers, thereby providing stringent focusing conditions with high numerical apertures. This approach is easy to implement, inexpensive, independent of the roughness or granularity of the workpieces, and more importantly does not require auxiliary lasers and displacement sensors for real-time measurement during the fabrication process.
High-precision detection of focal position on a curved surface for laser processing
Cao, B.X.,Hoang, P.L.,Ahn, S.,Kim, J.o.,Noh, J. Butterworths [etc.] 2017 Precision engineering Vol.50 No.-
A new technique for detecting the focal position of a curved surface provides several advantages both in research and industrial applications. The quality of patterns lasered on a roll surface is determined by the precision of the focus detection, and surfaces of the massive rolls used in laser fabrication can be difficult to adjust properly using conventional technologies. Here, a unique method for detecting the focal position of a curved surface based on the reflected profile of a laser beam is presented. The versatility of the proposed technique results from being able to adjust the laser beam based on changes in the shape and diameter of the beam spot when the specimen surface deviates from the focal plane. A theoretical model based on three-axis movement is proposed, and experimental setups are developed based on the model. Analysis of the obtained results enables high precision positioning of the specimen and identification of the focal point. Furthermore, the presented technique can be used to locate the focal point on any curved surface. Therefore, the theoretical model, analysis results, and focal detection method can be combined in an algorithm for a novel auto-focusing system that can be applied to laser processing of curved surfaces, such as fabricating microgrooves, or engraving roll surfaces in printed electronics.
소설(小說) 읽기 교육(敎育)에서 초점화(焦點化) 리론(理論)의 수행적(遂行的) 관점(觀點)
정래필 ( Jeong Rae-pil ) 한국어문교육연구회 2018 어문연구(語文硏究) Vol.46 No.1
本 論文은 焦點化 理論에 대한 小說敎育의 현황을 확인하고, 遂行的 관점에서 초점화 이론의 가능성을 탐구했다. '遂行'은 초점화의 疏通 脈絡과 讀者의 解釋 過程을 결합한 소설 읽기의 실제적인 방법을 가리킨다. 讀者의 초점화는 장면의 역동성과 연속성을 파악함으로써 작품 해석의 통합성에 기여하며, 主體와 對象의 이분법적 관계를 초월해 脈絡에 따라 인물 관계를 통합적으로 이해하도록 이끈다. 또한 독자의 초점화는 텍스트 해석의 근거를 제공한다. 이처럼 독자의 초점화 활동은 작품 해석의 경로로 활용될 수 있다. 이 논문은 독자 초점화의 작동 양상과 역할을 검토한 후 '焦點化 主體의 位置 定하기', '脈絡을 考慮하여 知覺하기', '對象에 대한 觀點 形成하기' 등을 焦點化의 遂行 戰略으로 제시했다. 이러한 논의를 바탕으로 독자 초점화 활동과 관련된 小說 읽기 敎育의 成就基準과 內容要素를 제시했다. 본 논문은 소설교육에서 초점화 이론의 受容 過程을 제시한 후 작품 해석과 연계할 수 있는 초점화 이론의 遂行的 次元을 탐구했다는 점에서 의미가 있다. This paper examines the current state of novel education on focalization theory and explores the possibility of focalization from a performance perspective. 'Performance' refers to the practical method of novel reading that combines the communication context of focus and the reader's interpretation process. The recent focalization theory shifts from the analysis aspect of narrative aspect to the method center of text interpretation. Based on this trend, this paper also identifies the reader' focalization and suggests a strategy for focusing on the performance level. The reader' focalization focuses on the dynamics and continuity of the scene, contributing to the integration of the interpretation of the work, and transcending the dichotomy between the subject and the object, leading to a comprehensive understanding of the person's relationship according to the context. The reader's focalization also provides the basis for interpreting the text. Thus, the reader's focalization activities can be used as a path of interpreting the work. In this paper, after reviewing the role and function of the independent focus, the focus of this study is focused on 'positioning the focalizor', 'perceiving by considering the context', and 'evaluating through the formation of perspective.' Based on these discussions, I presented the achievement standard and content elements of novel reading education related to independent focalization activities.
COMPARISON OF SMALLEST EIGENVALUES FOR RIGHT FOCAL ATICI-ELOE FRACTIONAL DIFFERENCE EQUATIONS
AijunYang,Li Zhang,Johnny Henderson 한국수학교육학회 2017 純粹 및 應用數學 Vol.24 No.4
The theory of u0-positive operators is applied to obtain smallest eigen- value comparison results for right focal boundary value problems of Atici-Eloe frac- tional difference equations.
이광자 중합 광조형을 이용한 마이크로 부품 성형을 위한 복셀 기반 레이저 초점 이동 경로 제어
황선욱(Sun-Uk Hwang),이용구(Yong-Gu Lee) (사)한국CDE학회 2010 한국 CAD/CAM 학회 학술발표회 논문집 Vol.2010 No.1
Two-photon photopolymerization via two-photon absorption is a promising three-dimensional microfabrication technique that has a considerable attraction. This method uses tightly focused ultra-short laser pulses to apply high energy in small volume of photo-sensitive polymer resin for subsequent photopolymerization. Because of nonlinear nature of this process, a resolution beyond diffraction limit can be realized by carefully controlling the laser pulse energy and exposure time. In this paper, we present the voxel based laser focal point positioning method for fabrication of micro-parts using two-photon photopolymerization. The proposed method can locate the laser focal point layer by layer using voxel position and exposure time can be controlled using gray level voxel value.
레이저의 산란 패턴을 이용한 마이크로 로드의 변위 및 회전 측정
신현근(Hyun-Geun Shin),황선욱(Sun-Uk Hwang),김정대(Jun-Dae Kim),이용구(Yong-Gu Lee) (사)한국CDE학회 2011 한국 CAD/CAM 학회 학술발표회 논문집 Vol.2011 No.1
Optical trapping is very useful to assemble micro-parts. Assembly of micro-parts requires one to control their positions and postures precisely. For the precise control, information related to positions and postures should be obtained through accurate measurement. In this paper, the measurement experiments are conducted by means of QPD (Quadrant Photodiode) using laser scattering pattern that happens when laser hit the micro-rods. To obtain the reference data of the displacement and rotation of micro-rods, micro-rods are fabricated stuck on a substrate. The displacement reference is measured by moving laser along with micro-rods in length and thickness. The rotation reference is measured by locating laser at a fixed point of micro-rods that are fabricated with some angles.
김 용(Yong Kim),박기영(Ki-Young Park),이경돈(Kyoung-Don Lee) 한국레이저가공학회 2009 한국레이저가공학회지 Vol.12 No.3
The laser welding was performed for the flange joint of two overlapped coaxial circular pipes which serve as the inlet and connector pipes of STS 316L. The laser welding test finally resulted in a good penetration depth of 1.8 to 2.0mm. On the way to get the good welding quality, two important parameters were found to be optimized. One is the focal positioning which is the offset of the laser beam focus to the exact welding seam line, which is more critical in the inner flange laser welding. When the beam spot size was deviated more than 200㎛ from the seam line, welding of two pipes is failed. The other is a gap size since a certain amount of gap is inevitable due to fabrication tolerance, or artificial allowances for smooth insertion of a pipe. However, it is required to restrict the gap allowance within 0.2mm to avoid undesirable undercut on a welding bead.
오스테나이트계 304 스테인레스강의 Nd:YAG 레이저 초점크기와 용접특성
유영태,오용석,노경보 조선대학교 에너지.자원신기술연구소 2002 에너지·자원신기술연구소 논문지 Vol.24 No.2
Laser beam welding is increasingly being used in welding of structural steels. The laser welding process is one of the most advanced manufacturing technologies owing to its high speed and penetration. The thermal cycles associated with laser welding are generally much faster than those involved in conventional arc welding processes, leading to a rather small weld zone. The experiments are performed for 304 stainless steel plate applying variation of : laser power(1500~2000W), welding speed (3~5m/min), shielding gas flow rate, presence of surface pollution, with fixed or variable gap and misalignment between the similar and dissimilar and plates, etc. The follow conclusions can be drawen that unlikely laser power, welding speed has a pronounced effect on size and shape of the fusion zone. Increase in welding speed resulted inan increase in weld depth/ welding ratio and hence a decrease in the fusion zone size. The penetration depth increased with the increase in laser power.