Predicting remaining useful life (RUL) becomes significant to implement prognostics and health management of industrial systems. The relevant studies have contributed to creating RUL prediction models and validating their acceptable performance; however, they are confined to drive reasonable preventive maintenance strategies derived from and connected with such predictive models. This paper proposes a data-driven preventive maintenance method that predicts RUL of industrial systems and determines the optimal replacement time intervals to lead to cost minimization in preventive maintenance. The proposed method comprises: (1) generating RUL prediction models through learning historical process data by using machine learning techniques including random forest and extreme gradient boosting, and (2) applying the system failure time derived from the RUL prediction models to the Weibull distribution-based minimum-repair block replacement model for finding the cost-optimal block replacement time. The paper includes a case study to demonstrate the feasibility of the proposed method using an open dataset, wherein sensor data are generated and recorded from turbofan engine systems.

연구대상판결은 크게 두 부분으로 구성되어 있다. 첫째, 민법 제663조 제2항과 제3항에 의해 도급인의 ‘하자보수청구권’과 ‘하자 보수에 갈음하는 손해배상채권’은 특별한 사정이 없는 한 수급인의 도급인에 대한 ‘공사대금채권’과 동시이행의 관계에 있고, 이로 인해 도급인이 하자보수나 이에 갈음하는 손해배상청구권을 보유하고 이를 행사하는 한 도급인의 공사비 지급채무는 이행지체에 빠지지 않는다. 둘째, 수급인의 공사비채권의 변제기는 건물의 준공, 인도일이고, 도급인의 하자 보수에 갈음하는 손해배상채권의 변제기는 도급인이 그 권리를 행사한 때인데, 도급인이 하자보수에 갈음하는 손해배상채권을 자동채권으로 하고, 수급인의 공사비잔대금채권을 수동채권으로 하여 상계의 의사표시를 한 경우, 상계적상일 다음날이 아니라 “상계의 의사표시를 한 다음날”부터 이행지체에 빠진다. 연구대상판결은 동시이행의 범위에서 전부거절설에 기초하고 있다. 그러나 전부 거절설을 취한 이유에 대해서는 밝히지 않고 있다. 그러나 연구대상판결에서 동시이행의 항변권에 기해 전부거절설을 취한 것은 i) 하자보수에 갈음한 손해배상채권과 보수채권 사이의 동시이행의 항변권은 비쌍무계약상 동시이행의 항변권에 해당하므로, ii) 제667조 제3항에서 제536조 를 준용한 취지를 살펴 그 동시이행의 항변권에 기한 이행거절의 범위를 결정할 필요가 있는데, iii) 그 준용의 취지가 하자보수에 갈음하는 손해배상채권에 기한 상계권을 대금감액적으로 행사할 수 있도록 특별히 동시이행관계를 설정한 것 이라고 보는 것이 가장 적절한 설명이 될 수 있을 것으로 보인다. 또한 상계적상일 다음날이 아니라 상계의 의사표시 다음날부터 잔여보수채무의 이행지체책임을 지도록 한 것은 i) 하자보수에 갈음한 손해배상청구에서 하자 보수비용의 확정이 현실적으로 용이하지 않다는 현실적인 문제를 고려하여 그 하자보수비용 확정 전에 보수채무의 변제기가 도래하는 상황에서 도급인이 하자보수에 갈음하는 손해배상채권에 기한 상계권을 대금감액을 위해 행사할 수 있도록 제667조 제3항에서 제536조를 준용하여 하자보수에 갈음하는 손해 배상채권에 기한 동시이행의 항변권의 행사로 보수채무 전부를 거절할 수 있다는 현실적 관점과 ii) 상계의 소급효가 전부거절설에 의한 이행지체책임의 면제이익을 뒤집을 수 없다는 이론적 관점에서 정당화될 수 있다고 본다.

Asphalt concrete(Ascon) is used to repair potholes and cracks. Special truck-mounted cargo boxes transport 200℃ asphalt concrete to repair potholes and cracks. However, long working and transportation hours to repair wide roads decrease the temperature of the asphalt concrete inside the cargo boxes. If the asphalt concrete temperature drops below 170℃, the adhesion with roads that need repair decreases. Therefore, the temperature of the asphalt concrete needs to be maintained for a long time. Conventional asphalt concrete cargo boxes are mostly burner-type models using hot air to prevent the temperature of the asphalt concrete from dropping. However, there are significant temperature differences between the asphalt concrete near and far away from the hot air, so the temperature decreases over time and leads to the disposal of large amounts of asphalt concrete. This causes waste of resources and environmental pollution. Therefore, this study proposed a heat dissipation cut-off type cargo box model to solve this problem and demonstrated its performance over conventional burner-type models through tests and analysis.

This study was described with a focus on the maintenance and management of Local Confucian School(Hyanggyo) architecture, centering around cases investigated through official documents written in the 1910s. In 1910, by the Japanese imperial rule, the regulations on Local Confucian School(Hyanggyo) property were enacted, and the income was paid solely to elementary school education expenses and ancestral rites. Through this process, many Local Confucian School(Hyanggyo) buildings were destroyed while only the space for ritual sacrifices remained by the Japanese colonial rule. In particular, as the land, which was the basis of Local Confucian School's property, was sold for various reasons, the finances gradually deteriorated. In addition, as the architectural acts that Local Confucian School preserves itself are restricted, it loses its original character. This study was of great significance that identified the intention to dispose of Local Confucian School(Hyanggyo) property by Japanese imperialism in the 1910s and clarified the purpose of its disposal.

Predictive maintenance has been one of important applications of data science technology that creates a predictive model by collecting numerous data related to management targeted equipment. It does not predict equipment failure with just one or two signs, but quantifies and models numerous symptoms and historical data of actual failure. Statistical methods were used a lot in the past as this predictive maintenance method, but recently, many machine learning-based methods have been proposed. Such proposed machine learning-based methods are preferable in that they show more accurate prediction performance. However, with the exception of some learning models such as decision tree-based models, it is very difficult to explicitly know the structure of learning models (Black-Box Model) and to explain to what extent certain attributes (features or variables) of the learning model affected the prediction results. To overcome this problem, a recently proposed study is an explainable artificial intelligence (AI). It is a methodology that makes it easy for users to understand and trust the results of machine learning-based learning models. In this paper, we propose an explainable AI method to further enhance the explanatory power of the existing learning model by targeting the previously proposedpredictive model [5] that learned data from a core facility (Hyper Compressor) of a domestic chemical plant that produces polyethylene. The ensemble prediction model, which is a black box model, wasconverted to a white box model using the Explainable AI. The proposed methodology explains the direction of control for the major features in the failure prediction results through the Explainable AI. Through this methodology, it is possible to flexibly replace the timing of maintenance of the machine and supply and demand of parts, and to improve the efficiency of the facility operation through proper pre-control.

Considering the features of body repair for automotive body where same damage and repair conditions does not exist in car accident, it is essential to acquire know-how and continuously approach new materials and new technologies on the site of maintenance where the theoretical instruction of textbook cannot react accurately minute by minute. Especially, in case of car repair from unexpected accidents such as body repair or dent repair, it is difficult to satisfy vehicle owners despite their request. Accordingly, this study researched the better maintenance technology to restore to its original state with more improved technology as vehicle owners wish. This study made time to repair reduced by 98% and the cost reduced by 79.6% through the accurate diagnostic technique before repair and maintenance technologies of body crash analysis applying property of high-speed tensile. It also obtains intangible effects including prevention of environmental pollution and maximization of vehicle owners satisfaction.

During the latter part of Joseon Dynasty, Local Confucian School(Geochanghyanggyo) had served as a government school and left many official documents on the educational construction. The construction of Local Confucian School(Geochanghyanggyo), which was recorded in official documents, was diverse, and most of them were reconstructed. Construction-works recorded in an official document was drafted in two ways. One was in the same format as the accounting records and the other was written in the diary format by date. The construction cost was mainly financed by selling the land owned. Of course, with the help of the government, they could receive some of the essential timber and expenses for the construction. The management and maintenance of educational construction was entrusted by a manager called ‘Chaji(次知)’. Then there were employees called ‘Jeonjik(殿直)’ and ‘Gojik(庫直)’ and they were paid for their work.

Machines and facilities are physically or chemically degenerated by continuous usage. The representative type of the degeneration is the wearing of tools, which results in the process mean shift. According to the increasing wear level, non-conforming products cost and quality loss cost are increasing simultaneously. Therefore, a preventive maintenance is necessary at some point . The problem of determining the maintenance period (or wear limit) which minimizes the total cost is called the ‘process mean shift problem’. The total cost includes three items: maintenance cost (or adjustment cost), non-conforming cost due to the non-conforming products, and quality loss cost due to the difference between the process target value and the product characteristic value among the conforming products. In this study, we set the production volume as a decreasing function rather than a constant. Also we treat the process variance as a function to the increasing wear rather than a constant. To the quality loss function, we adopted the Cpm+, which is the left and right asymmetric process capability index based on the process target value. These can more reflect the production site. In this study, we presented a more extensive maintenance model compared to previous studies, by integrating the items mentioned above. The objective equation of this model is the total cost per unit wear. The determining variables are the wear limit and the initial process setting position that minimize the objective equation.