• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.2
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• pp.642-648
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• 2016

As 3D solid modeling prevails, a range of applications have become possible and intensive research on the integration of CAD/CAM has been conducted. As a consequence, methods to recognize the machining features from CAD models have been developed. On the other hand, generating a machining sequence using the machining features is still a problem due to a combinatorial problem with a large number of machining features. This paper proposes a new method that utilizes the precedence constraints through which the number of the combinations is reduced drastically. This method can automatically generate machining sequences requiring the lowest amount of machining time. An airplane part was used to test the usefulness of the proposed method.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.6
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• pp.2624-2630
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• 2013

In LED chip packaging, die bonding is a very important process which fixes the LED chip on the lead flame to provide enough strength for the next process. During the process, inspection processes are very important to detect exact locations of dispensed epoxy dots and to determine bonding status of dies whether they are lies at exact positions with sufficient bonding strength. In this study, a useful machine vision based inspection system is proposed for the LED die bonder. In the proposed system, 2 cameras are used for epoxy dot position detection and 2 cameras are sued for die attaching status determination. New vision processing algorithm is proposed, and its efficiency is verified through required field experiments. Measured position error is less than $X:-29{\mu}m$, $Y:-32{\mu}m$ and rotation error:$3^{\circ}$ using proposed vision algorithm. It is concluded that the proposed machine vision based inspection system can be successfully implemented on the developed die bonding system.

• Composites Research
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• v.17 no.3
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• pp.29-37
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• 2004

The aeroelastic stability analysis of composite bearingless rotors is investigated using a large deflection beam theory in hover. The bearingless rotor configuration consists of a single flexbeam with a wrap-around type torque tube and the pitch links located at the leading edge and trailing edge of the torque tube. The outboard main blade, flexbeam and torque tube are all assumed to be an elastic beam undergoing flap bending, lead-lag bending, elastic twist and axial deflections, which are discretized into beam finite elements. For the analysis of composite bearingless rotors, flexbeam is assumed to be a rectangular section made of laminate. Two-dimensional quasi-steady strip theory is used for aerodynamic computation. The finite element equations of motion for beams are obtained from Hamilton's principle. The p-k method is used to determine aeroelastic stability boundary. Numerical results are presented for selected bearingless rotor configurations based on the lay-up of laminae in the flexbeam and pitch links location. A systematic study is made to identify the importance of the stiffness coupling terms on aeroelastic stability for various fiber orientation and for different configuration.

• The Journal of the Korea Contents Association
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• v.6 no.12
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• pp.128-135
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• 2006

RTLS(Real Time Location System) is the system to provide information and real-time location of tagged objects by using RTLS tag. In this paper, in order to enhance the performance of the port operation system, and efficient operation method of yard is suggested by applying RFID(Radio Frequency Identification)-based RTLS that provides real-time accurate positions of containers. In the group-based loading sequence system, the containers in the same group should have the similar characteristics such as POD(Port of Destination), size, weight, etc. In order to run this system, we propose the scheme using the parameters to the unspecified N bytes of RFID tag specified in ISO 18000-7. According to simulation result, the group-based system reduces the re-handling ratio of TC(Transfer Crane) in yard. It will reduce the whole lead-time in the process of port pogistics.

• Journal of the Korean Applied Science and Technology
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• v.22 no.4
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• pp.362-370
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• 2005

Copolymers (HSA-98-20, HSA-98-0, HSA-98+20) which are acrylic resin containing 80% solid content were synthesized by the reaction of monomers, including methyl methacrylate, n-butyl acrylate, and 2-hydroxyethyl acrylate with a functional monomer, such as acetoacetoxyethyl methacrylate (AAEM), which may improve in cross-linking density and physical properties of films. The physical properties of prepared acrylic resins, containing AAEM, are as follows : viscosity, $1420{\sim}5760cps$ ; number average molecular weight, $2080{\sim}2300$ ; polydispersity index, $2.07{\sim}2.19$ ; conversions, $88{\sim}93%$, respectively. To prepare acryl resins, four kinds of initiators including ${\alpha},{\alpha}'-azobisisobutyronitirile$ (AIBN), di-tert-butyl peroxide (DTBP), t-amylperoxy-2-ethyl hexanoate (APEH), benzoyl peroxide (BPO) were used. The viscosity of the acrylic resins prepared with these initiators was increased in the order of DTBP>APEH>AIBN>BPO. APEH was proved as a suitable initiator in this study. Shear rates of acrylic resins were constant in respect to viscosity. From these results, it would appear that the resins have Newtonian flow characteristics and good workability.

• Journal of the Korean Applied Science and Technology
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• v.20 no.1
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• pp.8-19
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• 2003

Environmental friendly acrylics/urea high-solid paints (BEHCU) were prepared through the curing reaction of acrylics resin(BEHC) containing 70wt% of solids content and butylated urea curing agent. BEHC was synthesized by addition copolymerization of caprolactone acrylate(CLA), 2-hydroxypropyl methacrylate(2-HPMA), ethyl methacrylate, and n-butyl acrylate. The addition polymerization of these monomers, especially including flexible CLA monomer and 2-HPMA monomer with OH funtional group, under appropriate reaction conditions resulted in polymers with controlled glass transition temperature($T_g$) and crosslinking density. The molecular weight($M_w$) of these polymers(BEHCs) was 2940${\sim}$3240 and polydispersity ($M_w/M_n$) was in the range of 1.61${\sim}$1.72. The viscosity and the molecular weight of these acrylic resins increased with increasing $T_g$. The coated films were prepared using curing reaction between BEHC resin and butylated urea curing agent at 100$^{\circ}C$ for 30 minutes. Our experimental resulted showed that enhancement of the coating properties such as adhesion, flexibility, impact resistance, water resistance, and abrasion resistance could be expected through introducing CLA component in acrylic resin for the high-solid content acrylics/urea coatings.

• Journal of the Korean Applied Science and Technology
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• v.25 no.3
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• pp.322-331
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• 2008

In order to synthesize high-solid coatings, acrylic resins (HSAs) containing 90% solid content were first synthesized, then the synthesized HSAs were cured with a curing agent, isocyanate, at room temperature to obtain high-solid coatings. In the HSAs synthesis, conversion was in a range of $82{\sim}87%$, and viscosities and number-averaged molecular weight ($M_n$) of the HSAs were in a range of $4380{\sim}8010$ cP and $1540{\sim}1660$, respectively. From the correlation between $T_g$ value, viscosity and $M_n$, it was found that, with increasing $T_g$ value, viscosity increases rapidly and molecular weight increases slowly. From the visco-elasity measured by the pendulum method, it was found that the curing time decreased with increasing $T_g$ values. From the tests of physical properties of the coatings' film, $60^{\circ}$ specular gloss, impact resistance and heat resistance were proved to be good and pencil hardness, drying time and pot-life were proved to be poor.

• Information Systems Review
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• v.13 no.1
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• pp.61-74
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• 2011

Software industry still has many deep-seated problems. As a natural consequence, it may have to learn from best practices in more mature industry like manufacturing. An example is 'lean' software development which is defined as translation of 'lean manufacturing' principles to the software development domain. The principles include 'eliminate waste' and 'amplify learning.' It was much asserted that these principles are worth applying. Not much study, however, was done on how to practically implement these principles into software development practice. In this study we attempt to present a method in which project lead time and software defects are regarded as major targets of management and are visualized using Cumulative Flow Diagram. We further applied this method on actual projects. The result confirms that agile is positively effective on reducing wastes.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.24-24
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• 2009

현재 조선소를 비롯하여 각종 산업 전반적으로 기존의 SCR 용접기를 대체하여 용접품질이 우수한 인버터 용접기가 널리 사용되고 있는 실정이다. 그러나 기존 인버터 용접기의 전원은 Mono 타입으로 이루어져 있어 대용량 인버터 용접기의 경우 대용량 스위칭 소자가 요구되어 제조원가가 높다. 그리고 문제 발생 시 용접기의 사용이 불가능하게 된다. 개발된 단위모듈을 병렬로 연결하여 대용량 용접기를 구성하게 되면 제조원가를 절감할 수 있으며 병렬로 연결되어 단위 모듈에 문제가 발생하여도 계속적인 사용이 가능하고, 주 회로를 작은 용량으로 분산시켜 전력을 제어하므로 높은 에너지 효율을 가지게 된다. 또한 인버터 용접기의 가장 중요한 성능인 스위칭 주파수에 있어서도 기존의 인버터 용접기는 20kHz의 스위칭 주파수를 가지지만 본 기술은 낮은 전력을 병렬로 연결하여 대용량을 동시에 제어가능 하므로 약 70kHz의 고속제어가 가능하다. 본 연구에서는 개발된 용량 170A단위모듈을 병렬로 연결하여 단위모듈 집적형 인버터 아크용접기 510A, 680A급의 부하테스트 실시 및 기본출력특성에 대하여 실험하였으며, GMAW에서 ${\Phi}1.6$ 솔리드 와이어를 이용하여 두께 20t의 후판 맞대기 용접에 적용실험을 실시하였다. 그 결과 모든 전류영역에서의 부하특성 및 출력특성이 양호하게 나타났으며, 후판 맞대기 용접에서는 SAW에 버금가는 생산성과 용접특성을 얻을 수 있었다.

• Journal of Educational Research in Mathematics
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• v.20 no.4
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• pp.445-458
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• 2010

This study intends to investigate the process of the development of quantity concept and how to deal with the quantity calculus in elementary school, and to find out the implication for improving the curriculum and mathematics textbooks of Korea. There had been the binary Greek categories of discrete number and continuous magnitude in quantity concept, but by the Stevin's introduction of decimal, the unification of these notions became complete. As a result of analyzing of the curriculum and mathematics textbooks of Korea, there is a tendency to disregard the teaching of quantity and its calculus compared to the other countries. Especially multiplication and division of quantity is seldom treated in elementary mathematics textbooks. So these should be reconsidered in order to seek the direction for improvement of mathematic teaching. And Korea's textbooks need the emphasis on the quantity calculus and on constructing quantity concept.