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주사 레이저 광집게를 위한 압전 구동기 주파수 특성 분석과 주사 경로 추적 및 보상
황선욱,이송우,이용구,Hwang, Sun-Uk,Lee, Song-Woo,Lee, Yong-Gu 한국광학회 2008 한국광학회지 Vol.19 No.2
주사 레이저 광집게에서 대물렌즈에 의해 집속된 레이저 초점을 제어하기 위해 사용되는 고속 구동기는 입력 신호의 주파수가 증가함에 따라 출력이 감소한다. 이러한 입출력의 괴리는 CCD 카메라를 통해 관찰이 어려우며 사용자는 희미하게 보이는 레이저 주사 형상을 보고 물체를 조작하여 물체를 포획할 수 없거나 포획하더라도 안정된 제어를 할 수 없다. 본 연구에서는 이러한 문제를 해결하기 위해 사용된 고속 구동기의 주파수 특성을 분석하고, 이를 바탕으로 입력 주파수에 따른 실제 주사 경로를 측정하여 시각화해주는 방법과 입출력 데이터의 차이를 계산하여 입력 데이터를 보상하는 방법을 제안한다. In scanning laser optical tweezers, high speed scanning stages are used to manipulate a laser beam spot. Due to the inertia of the stage, the output scanning signal decreases with increased frequency of the input signal. This discrepancy in the signals is difficult to observe since most of the energy from the laser beam is blocked out to avoid CCD damage. In this paper, we propose two methods to alleviate these problems. Firstly, frequency responses of piezo stages are measured to analyze the signal drops and the input signal is compensated accordingly. Secondly, an overlay of the scanning path is drawn on the live monitoring screen to enhance the visibility of the scanning path. The result is a drop-compensated scanning with clear path view.
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 tweezers use a tightly focused laser beam to hold and manipulate microscopic particles immersed in aqueous media. Due to the unique ability to easily grab and release objects, this technique is recently being used as a tool for micro-assembly. However, since not all micro-parts are symmetric in shape, simple single-beam trap geometry cannot always be used. In this paper, we present a method to manipulate ring-shaped micro-objects using holographic optical tweezers. To enable optical trapping of ring-shaped micro-objects (micro-rings), proposed method evenly distributes multiple traps produced by digital holography on the ring-shaped micro-object. By the ring-shaped trap pattern, micro-rings are trapped because the gradient force that attracts a mass towards focal spot with highest intensity is acting on the annular mass distribution of the object.
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.
김정대(Jung-Dae Kim),황선욱(Sun-Uk Hwang),신현근(Hyun-Geun Shin),이용구(Yong-Gu Lee) (사)한국CDE학회 2011 한국 CAD/CAM 학회 학술발표회 논문집 Vol.2011 No.1
Two-photon photopolymerization has recently been used for the fabrication of micro parts for microassembly. In order to increase assembly success rate, fabrication errors need to be reduced at a certain tolerance level. However, such a research for fabrication accuracy of micro part in two-photon photopolymerization is very rare. Generally, there exist several causes: reflecting mirror rotated off-axis, position error of laser scanner induced by incorrect arrangement of optical setup, laser pointing instability, laser power irregularity and mechanical stage movement errors. This paper aims at reduction of both length and angle errors within respectively, 10 percents and 5 degrees. A 10 micro-meter rod and 10 micro-meters cross shape are used for the length and angle error.
마이크로 부품의 성형 정밀도 향상을 위한 레이저 초점 경로 교정
신현근(Hyun-Geun Shin),황선욱(Sun-Uk Hwang),이용구(Yong-Gu Lee) (사)한국CDE학회 2011 한국 CAD/CAM 학회 학술발표회 논문집 Vol.2011 No.1
Two-photon photopolymerization is a technique that fabricates micro-parts through solidification of photosensitive resin at the focal spot of laser. It needs to control the laser spot in calculated path to fabricate the micro-parts of required shape. For controlling laser spot, galvanometric or tilt mirror is usually used. These devices have errors when controlling laser focal spot such as reflection surface being off-axis, optical rotational difference between two axes. In addition, the alignment of optical system can never be perfect. Such problems lead to the degradation of fabrication quality. In this paper, a correction algorithm for distorted laser spot is presented. The algorithm represents the relationship between distorted laser spot position and reference position. The more sections the whole area is subdivided into, the better the accuracy of laser spot path will be. The algorithm is tested with tilt mirror.
황성택(Sung-Tack Hwang),김정대(Jun-Dae Kim),황선욱(Sun-Uk Hwang),이용구(Yong-Gu Lee) (사)한국CDE학회 2011 한국 CAD/CAM 학회 학술발표회 논문집 Vol.2011 No.1
Two-Photon Photopolymerization (2PP) is one of the effective microfabrication techniques to manufacture microparts. By utilizing tightly focused ultra-short pulse laser beam, this method can solidify a liquid photoresist at the laser focal spot. When fabricating small microparts with complex shape using this technique, it is important to have high surface quality. The surface quality is closely related to the voxel size, which is a unit polymerized volume that single laser pulse can produce. Generally the voxel size varies with several experimental parameters, i.e., laser power, laser exposure time, wavelength and characterization of voxel size by varying these parameters is an important step in 2PP microfabrication. In this paper, we investigate the optimal condition for minimum voxel size by varying the laser power and exposure time.