• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.6
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• pp.357-365
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• 2022

Refrigerant mischarging is one of the most frequently occurring failure modes in air conditioners, and both undercharging and overcharging degrade cooling performance. Therefore, it is important to accurately determine the amount of charged refrigerant. In this study, a support vector machine (SVM) model was developed to multi-classify the refrigerant mischarge through steady-state identification via fuzzy clustering techniques. For steady-state identification, a fuzzy clustering algorithm was applied to the air conditioner operation data using the difference between moving averages. The identification results using the proposed method were compared with those using existing steady-state determination techniques studied through the inversed Fisher's discriminant ratio (IFDR). Subsequently, the main features were selected using minimum redundancy maximum relevance (mRMR) considering the correlation among candidate features, and an SVM multi-classification model was devised using the derived features. The proposed method achieves satisfactory accuracy and robustness from test data collected in the new domain.

• 한국ITS학회:학술대회논문집
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• 2008.11a
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• pp.581-584
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• 2008

무선 센서 네트워크는 최근 대두되고 있는 유비쿼터스 컴퓨팅의 연구에 힘입어, 광범위하게 설치되어 있는 유무선 네트워크 인프라에 상황인지를 위한 다양한 센서 디바이스를 결합하여 감지된 환경 데이터를 응용서비스와 연동하는 기술이다. 기본적으로 홈/빌딩 시큐리티, 사회기반 안전시설, 기계의 고장 진단, 의료 분야 등의 실세계의 다양한 분야에 응용될 수 있다. 본 논문에서 다루고자하는 실종 아동에 대한 문제는 어제 오늘의 이야기가 아니다. 미아 발생률은 꾸준히 증가하고 있으며 장기 미아의 발생 역시 증가하고 있다. 따라서 미아 방지를 위해 새로운 서비스들이 소개되었으나 이용자의 경제적 비용 부담 증가와 같은 문제점을 안고 있다. 본 논문에서 제안하는 미아 찾기 시스템은 무선 센서 네트워크 기술 응용 중의 하나로서 미아가 발생 시에 아동이 장기 미아가 되지 않도록 효율적이면서도 빠르게 미아를 찾을 수 있도록 하기 위해서 개발되었다. RFID 리더기가 장착된 고정형 센서 노드와 이동형 센서노드가 RFID 태그를 지닌 아동의 정보를 얻어서 중앙 제어 서버로 데이터를 넘기면 태그 정보와 전송한 센서 노드의 위치, 전송 시간을 바탕으로 아동의 위치를 파악할 수가 있다. 미아 찾기 시스템은 이용자가 태그만을 지니면 되기 때문에 경제적 부담은 줄어 들 수 있다. 또한 상기 시스템으로 미아 찾기만이 아니라 주변 환경 감시등의 여러 응용에도 적용 시킬 수가 있다.

• Journal of Biosystems Engineering
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• v.32 no.3
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• pp.190-196
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• 2007

The purpose of this study is to develop a measurement system of cutter conditions for combine header diagnosis during rice harvesting. A load cell was installed at the locker-arm to measure load fluctuation and an acceleration senor was used to monitor vibration signal of cutter bar. The data were collected from a paddy field during harvesting. The tests were conducted with a normal cutter, a loosened cutter, a broken cutter, and a worn-out connecter pin at the field. The vibration signals converted by FFT (Fast Fourier Transformation), filtered, and normalized. The load data and peak values of vibration signals in four different frequency ranges were used to determine the cutting operation and the cutter conditions of combine. The multiple comparison tests showed that the load data and peak values of vibration signals were important to monitor the cutting operation and cutter conditions of combine header.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.798-801
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• 2009

소각로를 포함한 다양한 산업설비의 배폐열은 열병합 등의 다양한 방법을 통해 재활용되고 있으나 에너지의 효율적 사용과 편의성을 고려할 때, 단순한 온수공급 등의 방법보다는 전력으로서의 재활용이 매우 필요하다. 특히 재활용이 어려운 $400^{\circ}C$이내의 중저온급 폐열원을 발전할 수 있는 유력한 방안으로 열전발전기술이 최근 부각되고 있다. 열전발전은 발전모듈의 변환효율이 7~10%이고, 시스템 효율은 5%내외로 증기발전에 비해서는 낮지만 기계적 가동부분이 없어 고장발생이 적고 기동정지가 용이하며 열이 있으면 바로 발전이 가능한 차세대 친환경 발전기술이다. 본 연구에서는 현재까지 시도, 개발되지 못한 $100^{\circ}C$에서 $400^{\circ}C$내외 온도영역인 중저온급 소각폐열 회수를 위한 목적으로 중온용 열전발전소재 및 모듈과 저온과 중온에 각기 대응하여 폐열발전의 효용성을 높인 복식열전발전시스템을 개발 중에 있다. 본 고에서는 현재까지 진행된 일부 연구내용들을 소개하고자 하였다.

• Journal of Biosystems Engineering
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• v.11 no.1
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• pp.76-85
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• 1986

This study was intended to examine the failure characteristics and breakdowns of the head-fed type combines generally used on farms. The failure distribution was assumed to follow Weibull distribution function and the Weibull parameters of the major parts, units and combine as whole were estimated by using the data collected in a survey. A computer program for the estimation of the Weibull parameter was developed. Monte Carlo method was used in predicting the time between failures. The results of study may be summarized as follows: 1. The number of failures per combine was 4.83 times per year and 0.3 times per hectare of combines of different ages. 2. According to the Kolmogorov-Smirnov test method, it was proved that the Weibull distribution function is well fitted to the characteristics of the failure and breakdowns of combines. 3. Weibull parameters of failure distribution of the combine as a whole were estimated to give the shape parameter ${\beta}$=1.3089 and the scale parameter ${\alpha}$=105.2409. The combining area with 80% reliability was 1.1 ha, and the probability of operating the combine without any failure for a year, was $2.76{\times}10^{-4}$. 4. The mean time between failures (MTBF) of the combines was predicted to be 3.2 ha of operation, which corresponds to 32 hours of operation.

• Journal of Biosystems Engineering
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• v.32 no.5
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• pp.324-331
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• 2007

The purpose of this study is to analysis effects of defect factors of combine header for cutting speed of combine header, feeding depth of straw, and cylinder speed of thresher. Measurement system for defect factors was consists of sensors to monitor the combine operation and I/O interface to convert the signals. Cutting speed of combine header, feeding depth of straw, cylinder speed of thresher were measured and analyzed. The data were collected from three paddy field during rice harvesting. The tests were conducted at different grounding speeds, lug troubles, and cutter condition. The one way ANOVA and the multiple comparison tests were performed. The results showed that the measured data were useful to monitor the defect factors of combine during harvesting. The faults conditions of grounding speeds, lug troubles, and cutter conditions affected cutting speeds, feeding depths and cylinder speeds of the combine. The data seem to be useful to analysis the faults conditions of combine header.

• Journal of Korea Multimedia Society
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• v.22 no.11
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• pp.1233-1241
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• 2019

The goal of the sound-based mechanical fault diagnosis technique is to automatically find abnormal signals in the machine using acoustic emission. Conventional methods of using mathematical models have been found to be inaccurate due to the complexity of industrial mechanical systems and the existence of nonlinear factors such as noise. Therefore, any fault diagnosis issue can be treated as a pattern recognition problem. We propose an automatic fault diagnosis method using discrete wavelet transform and power spectrum density using multi pattern recognition. First, we perform DWT-based filtering analysis for noise cancelling and effective feature extraction. Next, the power spectral density(PSD) is performed on each subband of the DWT in order to effectively extract feature vectors of sound. Finally, each PSD data is extracted with the features of the classifier using multi pattern recognition. The results show that the proposed method can not only be used effectively to detect faults as well as apply to various automatic diagnosis system based on sound.

• Journal of Welding and Joining
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• v.27 no.2
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• pp.76-81
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• 2009

Tandem GMAW is one of the high performance welding process and used in many industries to increase the productivity. An evaluation is presented of the mechanical properties and microstructural characteristics of the Tandem GMAW and conventional Single GMAW welds in 30mm thickness 490MPa grade steel by comparison method. Welding sequence and bead with and hight was kept, avoiding the effect of the bead shape and welding sequence. Tension, bending, hardness and Charpy impact test results of Tandem GMAW met the requirement of specification and showed similar distribution with conventional Single GMAW. Volume fraction of ferrite phase in weld metal showed little difference between Tandem GMAW and Single GMAW

• Journal of Drive and Control
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• v.16 no.4
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• pp.93-100
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• 2019

Nuclear and thermal power plants must provide the turbines with an appropriate degree of high temperature and high pressure steam, to produce the optimum electricity. Additionally, in the event of system and power system failure during electrical production, the steam is immediately disabled, to protect the turbines and generators rotating at high speed. The plant thus uses a special steam control valve system for turbine control, which is opened by force of the hydraulic servo actuator and closed by a large steel spring force. In this study, the causes of failure of the turbine control valve system, a key device of the power plants, were analyzed, and the causes of failure were improved relative to reliability of the equipment.

• Journal of Bio-Environment Control
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• v.12 no.2
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• pp.63-67
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• 2003

Cucumber fruits requires a lot of labor to harvest in time in Korea, since the fruits are cut and grabbed by hand. In this study, we developed an end-effector for robotic harvester of cucumber fruits. Its development involved the integration of an end-effector system with a PC compatible, DC motors, and a motor controller board. Software, written in Pic-basic, combined the functions of motor control with various circumstances. Cucumber's properties were measured and analyzed for precision of the end-effector. The results were similar to those of other vegetables. Properties including hardness of cucumber fruits were used as basic data for development of a harvester.