失效模式與效應分析(Failure mode and effect analysis; FMEA)是一種被廣泛地運用於各種產業的可靠度與風險評估手法，可用來辨別產品或流程中的潛在失效模式，依該失效所造成的效應來排定進行矯正作業或預防措施的優先順序，並進一步降低該失效發生的機會。此手法透過風險優先數(Risk Priority Number; RPN)的評估，將該失效的重要性加以量化，依其重要性來決定預防措施或矯正作業的優先順序，其中風險優先數為該失效的嚴重度、發生頻率、檢出性的三種等級之乘積。但是，實施失效模式與效應分析時，通常會發現以下幾種缺點: (1)失效模式與效應分析中的資訊通常是以主觀的語言來表示，以致於不客觀與不明確；(2)三種參數之間的相對重要性未必相同；(3)相同的風險優先數，未必代表具有相同的風險；(4)分析小組組員之間的專業知識不容易分享與傳承。為了改善這些缺失，本篇論文將提出一種以模糊理論為基礎的重要性評估手法，並進一步以一座污水處理廠為例，分別以傳統的失效模式與效應分析與以模糊理論為基礎的失效模式與效應分析來進行該污水處理系統的可靠度分析。

Failure mode and effect analysis (FMEA) is a widely used reliability analysis and risk assessment tool in various industries. This risk assessment tool is used to identify the potential failure modes of a product or a process, rank the priority for corrective action according to the respective effects of the failures, and eliminate the chance of the failures occurring. In traditional FMEA method, the risk priority number (RPN) is utilized to rank the failure modes in system, and is determined by finding the multiplication of severity, occurrence, and detection ratings of each failure mode. However, during performing FMEA, FMEA teams usually suffer from several problems: (1) the subjective and qualitative description in natural language; (2) the relative importance among the three parameter ratings; (3) the difference of risk representation between the same RPN; and (4) the knowledge share among FMEA team members. Thus, a new risk assessment system based on the fuzzy set theory and fuzzy rule base theory will be proposed to deal with these drawbacks in this thesis. Furthermore, an analysis of a sewage treatment plant will be presented to demonstrate the traditional FMEA and the proposed FMEA.

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