本論文針對雙零件串聯及並聯系統，探討系統零件具韋伯壽命分配之個別與群體置換策略的比較，進一步分析相關的停機成本對雙零件的個別與群體置換策略在串聯與並聯結構下之差異。對於雙零件以串聯或並聯方式組成之系統，當零件失效時，則以小修方式處理，小修後零件恢復正常運作，但零件的失效率維持不變。一般來說，零件的失效次數會隨著使用的時間或零件壽命而增加，為了有效降低失效次數，零件將在一個特定時程執行預防性置換。在串聯系統中，任一零件的失效將導致整個系統無法運作；在並聯系統中，因零件的運作彼此互相獨立，因此任一零件的失效並不會影響整體系統運作。考量到串聯及並聯的系統特性，當相關的停機成本高昂時，對系統零件同時執行預防性置換將有利於個別置換處理。依據以上的維修置換策略，本論文將分別建構出串聯與並聯系統個別與群體置換的成本模式，並進一步求得串聯與並聯系統的個別與群體置換的最佳置換時程並比較其優劣，同時分別推導出串聯與並聯系統零件選擇個別與群體置換的準則，以達到成本為最低之目的。

This paper investigates the comparisons of optimal replacement policies for two-component repairable systems with Weibull lifetime distributions and analyzes the influence of the related downtime cost for individual and group replacement policies under series and parallel systems. The system consists of two components by series and parallel. When any component fails in the operation time, the failed component is rectified by a minimal repair. Due to the inevitable deterioration of the component, it may fail more frequently as its age increases. To minimize the number of failures, a preventive replacement action should be carried out at a pre-specified time. For series system, the system fails whenever one of the components fails and a minimal repair is carried out to rectify the failed component. For parallel system, the operation of each component is independent, that is, any failure of component will not affect the normal operation of the system. When the related downtime cost is high, it might be worthwhile to replace both components at the same time instead of replacing them separately. Under these maintenance schemes, this paper will construct cost models of series and parallel systems with individual replacement and group replacement. Furthermore, the optimal individual and group replacement policies are obtained and compared. Simultaneously, some criterions are derived to choose individual or group replacement policies for components of parallel and series systems.

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