• 대한기계학회논문집B
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• 제27권1호
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• pp.25-31
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• 2003

Airborne contaminant particles are intruded into optical disk drives(ODD) due to the flow caused by disk rotation and can be adhered to lens or disk surfaces, which causes decrease of laser power and increase of read/write errors. Such a phenomenon can be more serious as the space between the disk and the lens is reduced fur high-density storage devices. The purpose of this paper is to understand design parameters to reduce the particle intrusion into an ODD. Suggestions are made to prevent the particle intrusion that can decrease the stability of an ODD and also prevent the potential heat build-up problem. The sealing effect of drive and the forced injection of clean air (using HEPA filter) into the drive minimizes intrusion of the outside air and dusts in an ODD remarkably. Moreover it is proved by experiments that the installation of a heatproof pad to isolate heat generation part (PCB) from information read/write sections and the forced injection of dust-free air reduce the gas temperature inside the drive as well as the amount of particles intruded.

• 한국생산제조학회지
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• 제8권5호
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• pp.115-120
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• 1999

This research is a described result of experimental for the parameter's effecting the microhole machining by Nd-Yag laser, The parameters are energy, pulse interval time a kin of assisting gas and its pressure. The result reveals that parameter value of energy 0.08J, pulse 20Hz, interval time of 300 microseconds could be a good machining condition to make upper microhoel that is the diameter range of 50-70${\mu}{\textrm}{m}$. At tat time the assistant gas such air, $O_2$, Ar $N_2$, was appelied. Assistant gas of air makes heat affected zone enlarge due to burning of material surface. Also it makes microhole irregular and damageable. Because of refusion caused by chemical reaction with $Al_2O_3$ ceramic material . The $O_2$(99.9%) has good characteristics to get good drilling and smooth surface on pressure of 0.2kgf/$\textrm{cm}^2$ but it is expensive. Ar, $N_2$ make material crack and burnning and proved that to be unappropriate but, Ar was a better than $N_2$.

• 한국측량학회지
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• 제36권5호
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• pp.355-369
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• 2018

LiDAR (Light Detection And Ranging) strip adjustment is process to improve geo-referencing of the ALS (Airborne Laser Scanner) strips that leads to seamless LiDAR data. Multiple strips are required to collect data over the large areas, thus the strips are overlapped in order to ensure data continuity. The LSA (LiDAR Strip Adjustment) consists of identifying corresponding features and minimizing discrepancies in the overlapping strips. The corresponding features are utilized as control features to estimate transformation parameters. This paper applied SURF (Speeded Up Robust Feature) to identify corresponding features. To improve determination of the corresponding feature, false matching points were removed by applying three schemes: (1) minimizing distance of the SURF feature vectors, (2) selecting reliable matching feature with high cross-correlation, and (3) reflecting geometric characteristics of the matching pattern. In the strip adjustment procedure, corresponding points having large residuals were removed iteratively that could achieve improvement of accuracy of the LSA eventually. Only a few iterations were required to reach reasonably high accuracy. The experiments with simulated and real data show that the proposed method is practical and effective to airborne LSA. At least 80 % accuracy improvement was achieved in terms of RMSE (Root Mean Square Error) after applying the proposed schemes.

• 한국정밀공학회지
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• 제23권3호
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• pp.156-162
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• 2006

Direct fabrication of nano patterns has been studied employing a nano-stereolithography (NSL) process. The needs of nano patterning techniques have been intensively increased for diverse applications for nano/micro-devices; micro-fluidic channels, micro-molds. and other novel micro-objects. For fabrication of high-aspect-ratio (HAR) patterns, a thick spin coating of SU-8 process is generally used in the conventional photolithography, however, additional processes such as pre- and post-baking processes and expansive precise photomasks are inevitably required. In this work, direct fabrication of HAR patterns with a high spatial resolution is tried employing two-photon polymerization in the NSL process. The precision and aspect ratio of patterns can be controlled using process parameters of laser power, exposure time, and numerical aperture of objective lens. It is also feasible to control the aspect ratio of patterns by truncation amounts of patterns, and a layer-by-layer piling up technique is attempted to achieve HAR patterns. Through the fabrication of several patterns using the NSL process, the possibility of effective patterning technique fer various N/MEMS applications has been demonstrated.

• 한국응용과학기술학회지
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• 제28권1호
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• pp.102-108
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• 2011

The study of wave propagation and scattering in biological media has become increasingly important in recent years. The propagation of light within tissues is an important problem that confronts the dosimetry of therapeutic laser delivery and the development of diagnostic spectroscopy. In the clinical application of photodynamic therapy(PDT) and in photobiology, the photon deposition within a tissue determines the spatial distribution of photochemical reactions. Scattered light is measured as a function of the distance (r) between the axis of the incident beam and the detection spot. Consequently, knowledge of the photosensitizer(Chlorophyll-a) function that characterizes a phantom is measured. To obtain the results of scattering coefficients(${\mu}s$) of a turbid material from diffusion described by experimental approach. It was measured the energy fluency of photon radiation at the position of penetration depth. From fluorescence experimental method obtained the analytical expression for the scattered light as the values of $(I/I_o)_{wavelength}$ vs the distance between the center of the incident beam and optical fiber in terms of the condition of "in situ spectroscopy(optically thick)" and real time by fluorometric measurements. The result was compromised with transport of intensities though a random distribution of scatters.

• 한국정밀공학회지
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• 제17권6호
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• pp.162-168
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• 2000

The automatic die polishing machine by liquid honing has been developed and experimented on the surface of machined die. The goal of development in the automatic die polishing machine by liquid honing is to increase the accuracy and the productivity in die polishing. To reach this goal, the polishing machine consists of the automatic measuring device for contour of die, the nozzle and pumping system to spray the powder mixed with liquid, and the 3-axis guides. Before polishing, the measuring device with a semiconductor laser scans the surface of mould to get the data of contour. The data store a PC and use to control the nozzle head to move above a couple of centimeters on the machined surface of die. The experimental parameters are the spraying time, the pressure, the size of abrasive grain and the mixing ratio between abrasive grain and liquid. The surface roughness is measured on the polished die which are SKDl 1 and Al7075 machined by NC. The surface roughness indicates the values of Rmax 0.5${\mu}{\textrm}{m}$ for Al7075 and Rmax 1.4${\mu}{\textrm}{m}$ for SKDl 1. It reduces the polishing time significantly and reduces the monotonous work for labors. As the results, the liquid honing system is useful method to apply for the die polishing and the automatic die polishing machine using liquid honing shows that it's very effective processing ability.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.1279_1280
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• 2009

Vanadium dioxide(VO2) has been reported to be the most attractive material for thermochromic windows due to its semiconductor-metal phase transition at around $68^{\circ}C$. However, our previous experiment showed it is difficult to grow VO2 thin films directly on glass substrate, whereas thermochromic VO2 thin films were successfully grown on R-cut sapphire substrate. Properties of VO2 thin films on different orientations of sapphire substrates were already reported. Furthermore, VO2 thin films were successfully grown heteroepitaxially on (001) preferred oriented ZnO coated glass. We deposited VO2 thin films using V2O5 targets on substrates with various lattice parameters with same orientation(SrTiO3, MgO, and Sapphire substrate of (001) orientation) by pulsed laser deposition. In this work, we will discuss the effects of lattice misfit, substrate-induced stress and grain size on the properties of VO2 thin films deposited on various substrate materials.

• 한국생산제조학회지
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• 제26권4호
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• pp.410-417
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• 2017

Hydro-forming is being employed increasingly to realize lightweight vehicular parts. The bumper beam produced by this process weighs 30% less than the conventional products with equal stiffness. However, hydro-forming involves complex parameters to obtain the target geometry and low residual stress. Parametric studies are conducted using finite element analysis to obtain optimized process conditions. Through these numerical approaches, the internal and holding pressures and feeder forward stroke along the extruded direction are optimized to achieve low residual stress and to minimize springback. The numerical results are verified by experimental observations made by employing a three-dimensional laser scanner. The numerical and experimental results are compared in terms of the springback. Both results show similar tendencies.

• Design & Manufacturing
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• 제11권1호
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• pp.30-33
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• 2017

In this study, the mold technology for manufacturing of porous implant was investigated. Firstly, we considered the concept of insert molding technology with 3D printing of porous inert part. The part on implant was designed in the end region of the implant. And then main implant bodies were manufactured using conventional machining method. The other porous parts were designed and optimized with molding simulation. As the feature size of porous implant was so small that perfect feature of it using 3D printing technology could not be obtained. So, we proposed another scheme for manufacturing of the porous implant in the replace of the former approach. Polymer mold cores with 3D printing technology were considered. The effects of addictive manufacturing process parameters on the properties of mechanical and dimensional accuracy were investigated. Direct 3D printed polymer mold cores were designed and manufactured under the simulation of thermal and molding analysis. It was shown that 3D printed mold core with polymer could be adapted to the injection molding for porous implant.

• Smart Structures and Systems
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• 제19권6호
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• pp.679-694
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• 2017

The complexity, enlargement and irregularity of structures and multi-directional dynamic loads acting on the structures can lead to unexpected structural behavior, such as torsion. Continuous torsion of the structure causes unexpected changes in the structure's stress distribution, reduces the performance of the structural members, and shortens the structure's lifespan. Therefore, a method of monitoring the torsional behavior is required to ensure structural safety. Structural torsion typically occurs accompanied by displacement, but no model has yet been developed to measure this type of structural response. This research proposes a model for measuring dynamic torsional response of structure accompanied by displacement and for identifying the torsional modal parameter using vision-based displacement measurement equipment, a motion capture system (MCS). In the present model, dynamic torsional responses including pure rotation and translation displacements are measured and used to calculate the torsional angle and displacements. To apply the proposed model, vibration tests for a shear-type structure were performed. The torsional responses were obtained from measured dynamic displacements. The torsional angle and displacements obtained by the proposed model using MCS were compared with the torsional response measured using laser displacement sensors (LDSs), which have been widely used for displacement measurement. In addition, torsional modal parameters were obtained using the dynamic torsional angle and displacements obtained from the tests.