• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.779-782
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• 2000

An internal finishing process by the application of magnetic abrasive machining has been developed as a new technology to obtain a fine inner surface of pipe. In this paper, the finishing process of a non-ferromagnetic pipe by a static magnetic field method is introduced and its finishing characteristics is discussed with effective factors by various experiments. From these experimental results, it is found that the proper suppling quantity of magnetic abrasives per diameter of pipe is important, and the inner surface roughness of pipe is not changed much after certain critical finishing time. As a result of this investigation the 3.2$\mu$m Rmax in inner surface roughness of stainless steel pipe is improved to 0.7$\mu$m Rmax after 6 minutes finishing.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.915-918
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• 1997

An internal finishing process by the application of magnetic abrasive machining has been developed as a new technology to obtain a fine inner surface of pipe. In this paper, an abrasive circulation system was designed and manufactured. As a result, it was found that a fine inner surface abrasive of pipe was available by the use of this machining methods. The basic machining characteristics of pin-type magnetic tools were analyzed experimentally. In addition, the experimental results show that we can realize that pin-type magnetic tools have more machining efficiency than iron particles as magnetic tools.

• 한국정밀공학회지
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• 제30권9호
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• pp.951-959
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• 2013

In order to improve the speed performance of the direct drive mechanical systems, a comprehensive analysis of the velocity ripples of blushless DC motors should be required. Every motor has a certain level of torque ripples when it generates power, and the generated torque ripple also makes the velocity ripples in the final output stage in speed control system. In this paper, a novel algorithm for reducing velocity ripples is proposed based on the modeling of torque ripples for BLDC motors. Various algorithms have been made for torque ripples, but usually they should be installed inside the amplifier logic, result in the difficulties of flexibility for various kinds of torque ripples. The proposed algorithm was developed for being ported in the controller not the amplifier, and it has the capability of the automatic compensation adjustment. The performance of the proposed algorithm was verified by effective simulations and experiments.

• 한국정밀공학회지
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• 제30권8호
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• pp.831-838
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• 2013

This paper focused on the design of an efficient temperature controller for a plant with a wide range of operating temperatures. The greater the temperature difference a plant has, the larger the nonlinearity it is exposed to in terms of heat transfer. For this reason, we divided the temperature range into five sections, and each was modeled using ARMAX(auto regressive moving average exogenous). The movement of the dominant poles of the sliced system was analyzed and, based on the variation in the system parameters with temperature, optimal control parameters were obtained through simulation and experiments. From the configurations for each section of the temperature range, a temperature-based gain-scheduled controller (TBGSC) was designed for parameter variation of the plant. Experiments showed that the TBGSC resulted in improved performance compared with an existing proportional integral derivative (PID) controller.

• KSTLE International Journal
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• 제10권1_2호
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• pp.1-5
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• 2009

This paper reports an investigation on nanotribological properties of silicon nanochannels coated by a diamond-like carbon (DLC) film. The nanochannels were fabricated on Si (100) wafers by using photolithography and reactive ion etching (RIE) techniques. The channeled surfaces (Si channels) were then further modified by coating thin DLC film. Water contact angle of the modified and unmodified Si surfaces was examined by an anglemeter using the sessile-drop method. Nanotribological properties, namely friction and adhesion forces, of the Si channels coated with DLC (DLC-coated Si channels) were investigated in comparison with those of the flat Si, DLC-coated flat Si (flat DLC), and Si channels, using an atomic force microscope (AFM). Results showed that the DLC-coated Si channels greatly increased hydrophobicity of silicon surfaces. The DLC coating and Si channels themselves individually reduced adhesion and friction forces of the flat Si. Further, the DLC-coated Si channels exhibited the lowest values of these forces, owing to the combined effect of reduced contact area through the channeling and low surface energy of the DLC. This combined modification could prove a promising method for tribological applications at small scales.

• Journal of Power Electronics
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• 제11권1호
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• pp.97-104
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• 2011

This paper proposes a new alternating current driving method for highly capacitive loads such as plasma display panels or piezoelectric actuators, etc. In the proposed scheme, a current balance transformer, which has two windings with the same turn-ratio, provides not only a resonance inductance for energy recovery but also a current balance among all of the switching devices of the driver for current stress reduction. The smaller conduction loss than conventional circuits occurs due to the dual conduction paths which are parallel each other in the current balance transformer. Also, the leakage inductances of the transformer are utilized as resonant inductors for energy recovery by the series resonance to the capacitive load. Furthermore, the resonance contributes to the small switching losses of the switching devices by soft-switching operation. To confirm the validity of the proposed circuit, prototype hardware with a 12-inch mercury-free flat fluorescent lamp is implemented. The experimental results are compared with a conventional energy-recovery circuit from the perspective of luminance performances.

• 한국소음진동공학회논문집
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• 제26권3호
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• pp.248-257
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• 2016

Recently, researches on the free-piston Stirling engines(FPSEs) are actively investigated. FPSEs have merits in its light weight, simple structure, and little need for maintenance, thus becoming a promising solution for the power conversion of renewable energy and waste heat recycle. This paper presents the methodology that estimates damping coefficients using analytical models of linear and nonlinear dynamics for FPSEs, and validates the methodology by comparing with existing experimental results. The analysis model predicts an operable range of linear damping coefficients forming limit cycles by using the root locus, and time responses obtained by numerical integration determines nonlinear damping coefficients. The model predictions are compared with experimental results of the well-known FPSE B-10B. We also investigate the damping characteristics regarding heater temperatures and power piston motions.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.61-61
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• 2009

This paper has been performed in order to figure out the reason of failure in T23 weldments used for boiler tube at 550 $^{\circ}C$. Defects such as cracks and cavities occurred in CGHAZ (coarse grain heat-affected-zone) and multi pass of weld metal, and these crack propagated along grain boundary. Microstructure evolution such as grain growth and carbide precipitation was investigated by optical microscope (OM), transmission electron microscope(TEM). Moreover, Auger electron spectroscope (AES) was employed in order to examine segregation along the grain boundaries. There is significant difference in grain size and precipitation distribution in the region where cracking took place. In addition, sulfur segregation was observed. Based on the results of this investigation, it has been possible to establish that this type of cracks were consistent with reheat cracking and creep damage. Selection of optimal filler metal, heat input, and PWHT temperature is required for prevention in order to avoid this type of cracking.

• 한국산업정보학회:학술대회논문집
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• 한국산업정보학회 2007년도 춘계학술대회
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• pp.213-223
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• 2007

E-Business Platform for SMEs in GMS Countries(GMSEB) is a E-business service portal which based on Yunnan, face to ASEAN, connect with China's mainland. lt is established by Kunming Dongxun Sic&Tech Co.,Ltd and E-Business Centre of Yunnan University of Financial & Economics, who get supports from UNESCAP, Science and Technology Department of Yunnan Provincial and Yunnan SMEs Bureau. The portal will bulid a B2B & B2C E-business and. ASP portal to provide service of e-business and enterprise management informatization according with the different languages and situation to China and GMS countries. The paper starts with analysis of the policy in China of promoting GMS cooperation and exchanges, importance of Yunnan and cultural universality in GMS countries. It expounds the necessity of establishing such a regional e-commerce platform. The project explores how to develop the model of e-business and enterprise management informationization for SMEs under the condition of weak economic strength and scarcity of Information Technology talents. To promote the SMEs in GMS countries participate in the integration with the global economy through the international SMEs'E-business Platform, make a fairly rapid progress by full play to its advantages.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 영호남 합동 학술대회 및 춘계학술대회 논문집 센서 박막 기술교육
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• pp.27-30
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• 2006

In this paper, the undoped and Co-doped $Zn_4SnSe_6$ single crystals grown by the chemical transporting reaction(CTR) method using iodine as a transporting agent are investigated. For the crystal growth, the temperature gradient of the CTR furnace was kept at $680^{\circ}C$ for the source zone and at $780^{\circ}C$ for the growth zone for 7days. It was found from the analysis of x-ray diffraction that the $Zn_4SnSe_6$ and $Zn_4SnSe_6Co^{2+}$ compounds have a monoclinic structure. The direct optical energy band gap of the $Zn_4SnSe_6$ and $Zn_4SnSe_6Co^{2+}$ single crystals at 300K were found to be 2.146eV and 2.042eV.