• The Transactions of the Korean Institute of Power Electronics
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• v.13 no.3
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• pp.179-185
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• 2008

In this paper, an advanced torque control scheme of SRM using DITC(Direct Instantaneous Torque Control) and PWM(pulse width modulation) is presented. Different from conventional DITC method, proposed method uses one or two switching modes at every sampling time, instead of only one switching mode. The duty ratio of the phase switch is regulated according to the torque error and simple control rules of DITC. Moreover the sampling time of control can be extended, which allows implementation on low cost micro-controllers. A simple calculation of PWM can assure a constant switching frequency with an excellent control performance. The proposed control method is verified by the simulations and experimental results.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.51 no.7
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• pp.387-398
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• 2002

In this paper, a new Three-Phase Lead-Lag Random Pulse Position PWM(LL-RPWM) scheme is proposed and implemented for decreasing audible acoustic noise of motor drives. In the proposed RPWM(Random PWM), each of three phase pulses is located randomly in each switching interval. Based on the space vector modulation technique, the duty ratio of the pulses is calculated. Along with the randomization of the PWM pulses, we can obtain the effects of spread spectra of voltage, current as in the case of randomly changed switching frequency. To verify the validity of the proposed LL-RPWM, the simulation and experimental study was tried. Along with the randomization PWM pulses, the space vector modulation is also executed in the C167 micro-controller. The simulation and experimental results show that the voltage and current harmonics are spread to a wide band area and that the audible acoustic noise is reduced by the proposed RPWM method.

• Transactions of Materials Processing
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• v.24 no.6
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• pp.411-417
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• 2015

The piston engine is an essential component in automobiles. Since the piston is used in a high temperature and high pressure environment, the piston needs to be manufactured to achieve high strength and high durability. In addition, cost reduction is also an important consideration. In conventional forging, an additional heat treatment after hot forging is necessary to ensure proper mechanical properties for heavy-duty engine pistons. The newly developed manufacturing method lowers production costs by saving manufacturing time and reduces energy consumption. The current paper describes the hot forging of an engine piston made from 38MnSiVS5 micro-alloyed steel using controlled cooling. The finite element analysis was used to check for possible problems and suitable press capacity. Hot forging experiments were then conducted on a 2500tons crank press to evaluate feasibility of the proposed material and process. To check the mechanical properties after hot forging, the forged specimens were tensile tested, and the microstructures were examined in order to compare the results with the conventionally forged material. The skirt region of the as-forged 38MnSiVS5 piston showed better material properties compared to the conventional material. In addition, the total production time was reduced by about 80% as compared to conventional forging.

• The Journal of Korean Academic Society of Nursing Education
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• v.4 no.1
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• pp.107-119
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• 1998

This study tried to answer the question : 'How does the human communication happen at the oriental medicine hospital between nurse and patient?' To answer that, a micro-ethnographic research method was used. Researcher visited T university hospital of oriental medicine and observed nurse-patient communication from September 1997 to December 1997. The data was obtained through participant observation, interview, audio-tape recording, home video camera, field note-taking, and related documents. After reviewing the whole data and deliberate analysis, first, I learned that most oriental medicine nurses communicate with their patients for their routine nursing job like recording, hand-over to the next duty, report to doctor, etc. I named this type of communication as 'ritual communication'. Second, I can define major argument as follow : Human communication of oriental medicine between nurse and patient is performed more frequently and variously when nurse contacts the patient for the routine nursing activities than for the incidental activities. As a result of these understandings, I suggest that oriental nursing need to develop the body of knowledge and expand its role and independent nursing activity. Also the bureaucratic hospital management centered doctors must be changed reasonalbly.

• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.2
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• pp.178-186
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• 2004

This paper proposes a two-phase RCD-PWM scheme which is much better than a three-phase RCD-PWM scheme from the standpoint of the broadening and linearizing effect of the power spectrum. To implement the proposed scheme and conventional scheme, the experiment based on the SAB-Cl67 micro-controller was executed. Based on the space vector modulation technique, the duty ratio of the pulses is calculated using the SAB-Cl67 and each of PWM pulses is located randomly in each switching interval. The power spectrum of the output voltage, output current, the d.c link current and the acoustic noise radiated from inverter drives are experimentally investigated. 1'hen, the performance of the proposed scheme was compared and discussed with the conventional scheme.

• Proceedings of the KIEE Conference
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• 2002.04a
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• pp.106-111
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• 2002

In this paper, a new three phase RPWM(Random PWM)with fixed switching frequency is proposed. In the proposed RPWM, each of three phase pulses is located randomly in each switching interval. Based on the space vector modulation technique, the duty ratio of the pulses is calculated. Along with the the randomization of the PWM pulses, we can obtain the effects of spread spectra of voltage, current as in the case of randomly changed switching frequency. To verify the validity of the proposed RPWM, the experimental study was tried. Along with the randomization of PWM pulses, the space vector modulation is also executed in the C167 micro-controller. The experimental results show that the voltage and current harmonics are spread to a wide band area and that the audible acoustic noise is reduced by the proposed RPWM method.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.8
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• pp.9-15
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• 1999

Die-sinking electrical discharge machining(EDM) for conductive ceramic matrix composite(CMC) of Tic/$Al_2O_3$ was experienced with addition of ultrasonic emission, and the results were compared with ones obtained by the EDM only. From this experimental study, the values of material removal rate(MRR) and surface roughness($R_{max}$), scanning electron microscope(SEM) micrographs, and weibull probability distribution of bending strength for the specimens were obtained and compared. The trend of MRR was found to be increased slightly with the current and the duty factor for both EDM only and EDM with ultrasonic emission. The MRR values were found to be increased for EDM with ultrasonic emission. The SEM micrographs of EDMed surface by under various operating conditions showed less micro cracks in various places. Although smaller bending strength value was obtained by EDMed surface with ultrasonic emission by weibull probability distribution analysis of bending strength.

• Journal of Mechanical Science and Technology
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• v.20 no.11
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• pp.1914-1919
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• 2006

Recently, the microrobots powered by biological muscle actuators were proposed. Among the biological muscle actuators, frog muscle is well known as a good muscle actuator and has a large displacement, actuation forces and piezoelectric properties. Therefore, for the application of the biomimetic microrobot, this paper reports the electromechanical properties of frog muscle. First of all, the experimental setup has been established for measuring generative force of the frog muscle. Through the various electrical stimulating inputs to the frog muscle, we measured the contractile force of the frog muscle. From the measuring results, we found that the actuating contractile force responses of the frog muscle are determined by the amplitude, frequency, duty ratio, and wave form of the stimulation signal. This study will be beneficial for the development of the microrobot actuated by frog muscle.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.169-169
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• 2016

크롬산 용액에 황산을 촉매로 하여 Sargent에 의해 개발된 크롬도금은 경도, 내식성, 내마모성 등의 특성이 우수하다. 이로 인해 장식용 박막 도금뿐만 아니라 경질의 후막 도금층을 형성이 가능함으로써 기계 부품류를 비롯한 산업 전반에 걸쳐 폭넓게 적용되고 있다. 이러한 크롬도금이 적용된 소재부품에 대해 장수명화와 더불어 가혹한 환경에서의 사용요구가 점차 증가하고 있으며, 이를 위해서는 보다 더 우수한 내식성과 기계적 물성을 확보해야할 필요성이 높다. 한편 경질 크롬 도금의 내식성과 관련해 도금 과정에서 발생하는 마이크로 크랙에 의해 제품의 내식성의 한계를 나타내게 된다. 본 연구에서는 내식성이 우수할 뿐만 아니라 표면 경도가 우수한 도금층을 얻기 위해 도금 전류 조건으로 펄스 전류를 적용하는 방안을 시도한 것으로 펄스전류를 적용하여 경질크롬도금 시 크랙 발생에 미치는 영향을 조사하였다. 도금욕은 일반적인 경질크롬도금에 사용되는 Sargent 욕을 이용하였고, duty ratio를 조절하여 전류 조건 변화에 따른 단면 내 크랙의 수 변화를 관찰하여 최적의 전류 조건을 도출하였다. 그리고 도출된 전류 조건을 이용해 도금 두께에 따른 크랙 수 변화를 관찰하였고, 이때의 경도를 측정하였다. 또한 XRD 분석을 통해 도금 전류 조건 및 시간 변화에 따른 결정구조 변화를 확인하였다. 실험결과 펄스 전류를 적용하는 경우, 기존 직류 적용 시에 비해 크랙 발생을 현저하게 감소시킬 수 있었으며, 사실상 크랙프리(Crack free) 도금이 가능하였다. 또한 크랙의 감소와 함께 경도 저하가 나타나게 되나 펄스 전류 인자의 최적화에 따라 이러한 경도 저하 현상의 최소화가 가능하였다.

• Transactions of The Korea Fluid Power Systems Society
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• v.8 no.1
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• pp.19-25
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• 2011

This study presents the design of digital amplifier.controller for a proportional control valve and the development of PID discrete control scheme by using RCP(Rapid Controller Prototyping) system. RCP system is the device to embed the control code developed in PC into the microcontroller on-site. Ramp input test using the digital amplifier.controller developed in this study was carried out for the proportional control valve of domestic production and Bosch Rexroth respectively. The instability problem occurred around maximum displacement of localized valve spool at ramp input test was solved by supplementing offset current to the duty ratio of PWM(Pulse Width Modulation) driving signal to the solenoid. The comparison of test results between localized proportional control valve and Bosch Rexroth's product shows that the characteristics obtained by ramp input test and static flow gains are alike each other. Two valves are about the same in dead bands and hysteresis characteristics.