• 품질경영학회지
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• 제22권3호
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• pp.119-123
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• 1994

A frequently recurring question posed by researchers concerns a test of a constant failure rate against the alternative of a failure rate involving a single chang-point. Park (1988) has presented a new test procedure for testing constant failure rate against a bathtub shaped (upside-down bathtub shaped) failure rate. assuming that the proportion of population that fails at or before the change point of failure rate is known. Jeong (1992) has extended Park's test to randomly censored data under the same assumption. In this paper, we have investigated efficiency loss to the presence of censoring.

• 한국신뢰성학회:학술대회논문집
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• 한국신뢰성학회 2005년도 학술발표대회 논문집
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• pp.115-120
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• 2005

This paper introduces models for preventive maintenance policies and considers periodic preventive maintenance policy with minimal repair when the failure of system occurs. It is assumed that minimal repairs do not change the failure rate of the system. The failure rate under prevention maintenance received an effect by a previously prevention maintenance and the slope of failure rate increases the model where it considered. Also the start point of failure rate under prevention maintenance considers the degradation of system and that it increases quotient, it assumed. Per unit time it bought an expectation cost from under this prevention maintenance policy. We obtain the optimal period time and the number for the periodic preventive maintenance by using Nakagawa's Algorithm, which minimizes the expected cost rate per unit time. Finally, it suppose that the failure time of a system has a Weibull distribution as an example and we obtain an expected cost rate per unit time the optimal period time and the number when cost of replacement and cost of minimal repair change.

• Journal of Biosystems Engineering
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• 제42권2호
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• pp.75-79
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• 2017

The use of tractors to carry out agricultural work has played an important role in mechanizing the agricultural sector. A repairable mechanical system (such as an agricultural tractor) is subject to deterioration or failure. In this study, a regression model was used to predict the failure rate of a John Deere 3140 tractor. The machine failure pattern was carefully studied, and key factors affecting the failure rate were identified in five regions of the Khouzestan province. Through a questionnaire, data was obtained from farm records. This data was grouped into six sub-groups, according to the annual use hours (AUH) and the manner in which the tractors were stored. Results showed that AUH and storage policies affected failure rate slightly. With an increase in the age of the tractors, the failure rate in the tractors used for 1050-2000 hours annually and stored outdoors was higher than those used for 200-1000 hours annually and stored in sheds. When the tractors were of the same age, the slope of the curve in the 200-1000 annual use hours increased gradually and then rapidly, but failure rate in the 1050-2000 annual use hours was high from the beginning, and subsequent increase in this value was almost uniform. As a result, it can be said that with an increase in the annual use hours, the failure and breakdown rate in John Deere 3140 tractors rapidly increases, but maintenance conditions only slightly affect the failure and breakdown rate.

• 한국항공우주학회지
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• 제49권9호
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• pp.781-789
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• 2021

본 연구에서는 소형무인기(≤25kg)가 도심 지역에서 비행하고자 할 때 요구되는 고장 빈도를 무인기 추락 시 발생할 수 있는 지상 인명 피해를 기반으로 정량적으로 분석하였다. 도심 지역의 인구 밀도, 차량 교통량, 건폐율, 건물 층수 데이터 및 무인기 추락 궤적 모델링을 이용하여 특정 위치에서 무인기 추락 시 인명 피해를 계산하였고 이를 바탕으로 각 무인기 추락 위치에서 안전성 목표값을 만족하기 위한 최대 허용 가능 무인기 고장 빈도를 계산하였다. 이를 통해 각 무인기 추락 위치별 고장 빈도 요구사항을 맵 형태로 도출할 수 있었다. 최종적으로 최대 허용 가능 무인기 고장 빈도를 몇 구간으로 구분하여 각 구간별 도심 지역 비행 가능 영역을 분석하였다. 영월 지역을 대상으로 했을 때 인구 주거 지역 접근을 위해서는 최소 10^-4 (failure/flight hour) 이하의 무인기 고장 빈도가 요구됨을 확인하였다.

• 대한산업공학회지
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• 제36권1호
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• pp.69-77
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• 2010

The failure rate model of External Environment Maintenance(EEM) for a system under severe environment is investigated. EEM, which is recently introduced concept, is a maintenance activity controlling external environment factors that potentially cause system failure such as cleaning equipment, controlling temperature (humidity) and removing dust inside of electronic appliances. EEM can not have any influence on the inherent failure rate of a system but reduce the severity of the external environment causing failure since it deals with only external environment factors. Therefore, we propose two failure rate models to express the improvement effect of EEM: The intensity reduction model and age reduction model. The intensity and age reduction models of EEM are developed assuming the quality of improvement effect is proportioned to an extra intensity or age respectively. The validation of proposed failure rate models is performed in order of data generation, parameter estimation and test for goodness-of-fit.

• 한국산학기술학회논문지
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• 제10권6호
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• pp.1346-1352
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• 2009

자동차 부품의 품질보증 비용은 각 시장의 품질보증 영역(warranty region) 내에서 부품이 고장 날 확률에 따라 달라진다. 부품이 고장 날 확률은 각 시장의 다른 스트레스 조건이 비슷하다고 가정할 때 사용비율(usage-rate)에 영향을 크게 받는다. 그러므로 품질보증 비용은 사용비율을 반영한 고장모형을 수립하고 이를 이용한 확률과정 (stochastic process)을 통하여 예측할 수 있다. 본 논문에서는 사용비율을 선형으로 가정한 후 가속실험 모형을 적용하여 2차원 고장모형을 1차원으로 축소시킨다. 이렇게 1차원으로 축소된 고장모형은 사용비율의 함수로 표현될 수 있으므로 사용비율의 변동에 따른 부품의 고장확률 변동을 설명할 수 있다. 이를 통해 새로운 시장의 사용비율을 알면 실측 데이터가 없다고 하더라도 고장확률 분포를 추정할 수 있고 교체되어야 하는 부품일 경우 재생과정(renewal process)으로 비용을 예측할 수 있다. 응용사례에서 실제 두 시장의 품질보증 데이터를 이용하여 이를 분석해 보았다.

• Smart Structures and Systems
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• 제22권2호
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• pp.151-159
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• 2018

Maintenance activities are regarded as a key part of the repairable deteriorating system because they maintain the equipment in good condition. In practice, many maintenance policies are used in engineering fields to reduce unexpected failures and slow down the deterioration of the system. However, in traditional maintenance policies, maintenance activities have often been assumed to be performed at the same time interval, which may result in higher operational costs and more system failures. Thus, this study presents two non-periodic preventive maintenance (PM) policies for repairable deteriorating systems, employing the failure rate of the system as a conditional variable. In the proposed PM models, the failure rate of the system was restored via the failure rate reduction factors after imperfect PM activities. Operational costs were also considered, which increased along with the operating time of the system and the frequency of PM activities to reflect the deterioration process of the system. A numerical example was provided to illustrate the proposed PM policy. The results showed that PM activities performed at a low failure rate threshold slowed down the degradation of the system and thus extended the system lifetime. Moreover, when the operational cost was considered in the proposed maintenance scheme, the system replacement was more cost-effective than frequent PM activities in the severely degraded system.

• Industrial Engineering and Management Systems
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• 제16권1호
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• pp.52-63
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• 2017

The inventory level of concurrent spare parts (CSP) has a significant impact on the availability of a weapon system. A failure rate function might be of particular importance in deciding the CSP inventory level. We developed a CSP optimization model which provides a compromise between purchase costs and shortage costs on the basis of the Weibull and the exponential failure rate functions, assuming that a failure occurs according to the (non-) homogeneous Poisson process. Computational experiments using the data obtained from the Korean Navy identified that, throughout the initial provisioning period, the optimization model using the exponential failure rate tended to overestimate the optimal CSP level, leading to higher purchase costs than the one using the Weibull failure rate. A Pareto optimality was conducted to find an optimal combination of these two failure rate functions as input parameters to the model, and this provides a practical solution for logistics managers.

• 한국신뢰성학회지:신뢰성응용연구
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• 제11권2호
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• pp.167-176
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• 2011

This paper introduces models for preventive maintenance policies and considers periodic preventive maintenance policy with minimal repair when the failure of system occurs. It is assumed that minimal repairs do not change the failure rate of the system. The failure rate under prevention maintenance received an effect by a previously prevention maintenance and the slope of failure rate increases the model where it considered. Also the start point of failure rate under prevention maintenance considers the degradation of system and that it increases quotient, it assumed. Per unit time it bought an expectation cost from under this prevention maintenance policy. We obtain the optimal periodic time and the number for the periodic preventive maintenance by using Nakagawa's Algorithm, which minimizes the expected cost per unit time.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2004년도 춘계학술대회 논문집
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• pp.370-373
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• 2004

The inside and outside of the country utilities considered that they focused energy and economic aspect for short-term in new environment change of restructure. but it need service reliability preservation and improvement countermeasure, that is no to use existent estimation method for reliability preservation. therefore, analyze the equipment failure rate for suitable reliability preservation through equipment failure rate analysis of power distribution r system and evaluated equipment that is composing power distribution system by the failure rate. This paper estimated failure causes and the TVFR(Time Varying Failure Rate) for main equipment that is composing power distribution system using Weibull distribution.