• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.10a
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• pp.387-392
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• 2001

Fused deposition(FD) modeling by Stratasys Inc., is one of the material deposition subfamilies of solid freeform fabrication(SFF) technologies. In this process, build material in the form of a flexible filament, is heated to a semi-liquid state and extruded from a robotically controlled deposition head onto a fixtureless table in a temperature controlled environment. The position of nozzle is computer controlled relative to the base, which allows geometric complex models to be made to precise dimensions. FDM provide what the part was directly tested by the worker. It provide believable data. This study is experiment on surface roughness of part at FDM

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.233-234
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• 2006

For the machining of freeform surface, fly cutting is one of the key technology to meet profile accuracy and surface roughness simultaneously. Fly cutting can be applied to manufacturing of optical components with complex profile. In this study aluminum alloy was machined in the process of ultra precision fly cutting and investigated optimum machining conditions in terms of feed-rate, pitch per cycle and depth of cut.

• Journal of the Korea Computer Graphics Society
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• v.16 no.4
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• pp.11-16
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• 2010

We present an efficient algorithm for rendering sweep surfaces using programmable graphics hardware. A sweep surface can be represented by a cross-section curve undergoing a spline motion. This representation has a simple matrix-vector multiplication structure that can easily be adapted to programmable graphics hardware. The data for the motion and cross-section curves are stored in texture memory. The vertex processor considers a pair of surface parameters as a vertex and evaluates its coordinates and normal vector with a single matrix multiplication. Using the GPU in this way is between 10 and 40 times as fast as CPU-based rendering.

• Current Optics and Photonics
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• v.2 no.3
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• pp.280-285
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• 2018

A new method to design a see-through off-axis head-mounted-display (OA-HMD) optical system with an ellipsoidal surface is proposed, in which a tilted ellipsoidal surface is used as the combiner, which yields the benefits of easier fabrication and testing compared to a freeform surface. Moreover, we realize a coaxial structure in the relay lens group, which is simple and has looser tolerance requirements, thus making assembly easier. The OA-HMD optical system we realize has a simple structure and consists of a combiner and 7 pieces of coaxial relay lenses. It has a $48^{\circ}{\times}36^{\circ}$ field of view (FOV) and 12-mm exit pupil diameter.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.2
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• pp.41-48
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• 2014

Direct writing(DW) is a method of patterning materials to a substrate directly, without a mask. It can use a variety of materials and be applied to various fields. Among DW systems, the flow-based type, using a syringe pump and nozzle, is simpler than other types. Furthermore, the range of materials is exceptionally wide. In additive processes, a three dimensional structure is made of stacking layer. Each layer is made of several lines. In this regard, good surface roughness of fabricated layers is essential to three dimensional fabrication. The surface roughness of any fabricated layer tends to change with the dispensing pattern. When multiple layers fabricated by a nozzle dispensing system are stacked, control of the nozzle position from the substrate is important in order to avoid interference between the nozzle and the fabricated layer. In this study, a fluid direct writing system for three dimensional structure fabrication was developed. Experimentsto control the position of the nozzle from substrate were conducted in order to examine the characteristics of the material used in this system.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.134.1-134.1
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• 2017

In this study, we propose a new scaffold fabrication method, "direct electro-hydrodynamic jet process," using the initial jet of an electrospinning process and ethanol media as a target. The fabricated threedimensional (3D) fibrous structure was configured with multilayered microsized struts consisting of randomly entangled micro/nanofibrous architecture, similar to that of native extracellular matrixes. The fabrication of the structure was highly dependent on various processing parameters, such as the surface tension of the target media, and the flow rate and weight fraction of the polymer solution. As a tissue regenerative material, the 3D fibrous scaffold was cultured with preosteoblasts to observe the initial cellular activities in comparison with a solid-freeform fabricated 3D scaffold sharing a similar structural geometry. The cell-culture results showed that the newly developed scaffold provided outstanding microcellular environmental conditions to the seeded cells (about 3.5-fold better initial cell attachment and 2.1-fold better cell proliferation).

• Polymer(Korea)
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• v.38 no.6
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• pp.815-819
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• 2014

Scaffolds of tissue engineering should be biocompatible and biodegradable for cell attachment, proliferation and differentiation. In the various scaffold fabrication, 3D printing technique can make the three dimensional scaffold with interconnected pores for cell ingrowth. Polycaprolactone (PCL) is biodegradable polyester with a low melting temperature and has been approved by the Food and Drug Administration (FDA). In this study, PCL scaffold was fabricated by 3D bioprinting system and surface modification of PCL scaffold was controlled by NaOH treatment. Morphological change and wetability of NaOH-treated scaffold were observed by SEM and contact angle measurement system. The remnant of PCL treated with NaOH was measured by ATR-FTIR. In vitro study of scaffolds was evaluated with WST-1 and ALP activity assay. NaOH treatment of PCL scaffolds increased surface roughness, hydrophilicity, cell proliferation and osteogenic differentiation. These results indicate that NaOH-treated PCL scaffold made by 3D bioprinting has tissue engineered potential for the development of biocompatible material.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.134-139
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• 2001

Laser scanners are widely used for reverse engineering and inspection of freeform parts in industry such as motors, electronic products, dies and molds. Due to the lack of measuring software and positioning device, the laser scanning processes have been erroneous and inconsistent. In order to automate measuring processes, an automated scan plan generation software and a proprietary hardware are developed. In this paper, an automated laser scanning system using a 3-axis motorized stage is proposed. In the scan planning step, scan directions, paths, and the number of scans are generated considering optical and mechanical parameters. In the scanning step, the generated scan plan is downloaded into the laser scanner and the motorized stage and the points on the surface are captured automatically. Finally, the point data set is analyzed to evaluate the performance of the system.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.8
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• pp.29-34
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• 2009

• Korean Journal of Computational Design and Engineering
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• v.11 no.6
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• pp.455-463
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• 2006

Hidden line removal(HLR) algorithms can be devised either in the image space or in the object space. This paper describes a hidden line removal algorithm in the object space specifically for the CAD viewer data. The approach is based on the Appel's 'Quantitative Invisibility' algorithm and fundamental concept of 'back face culling'. Input data considered in this algorithm can be distinguished from those considered for HLR algorithm in general. The original QI algorithm can be applied for the polyhedron models. During preprocessing step of our proposed algorithm, the self intersecting surfaces in the view direction are divided along the silhouette curves so that the QI algorithm can be applied. By this way the algorithm can be used for any triangulated freeform surfaces. A major advantage of this algorithm is the applicability to general CAD models and surface-based visualization data.