近年來由於工業技術的精進，市場對於產品品質的要求逐漸提升，因此廠商必須在品質與成本間取得最佳的權衡，雖然製造技術已經快速進步且具有一定水準，但產品仍然免不了會隨著時間而逐漸衰退，甚至因為外在大環境等未知干擾因素，而使失效的機會增加並產生重大損失，有鑒於此，許多廠商紛紛以預防性保養政策來避免產品失效，藉此規避失效所產生之龐大成本。
過去針對預防保養或多重失效模式議題，已有許多學者探討，但卻鮮少討論失效模式間之相依關係，因此本研究探討相依多重競爭失效模式，產品除了會隨著時間而一般退化外，還有無法預測之隨機損害會直接造成失效或使退化程度劇烈增加，並以條件式預防保養(Condition-based maintenance)的概念，當產品或系統的退化程度與某些物理性變數(例如：金屬材料磨損程度)或系統性能量測變數(例如：生產產品之不良率)，便可依據退化程度，在期望單位時間成本最小化的條件下，擬定預防保養的實施條件，制定最適預防保養門檻值以及預防保養總次數，以避免過度頻繁的預防保養，規劃出最適預防保養策略。本研究建構模式幫助廠商分析可靠度以及失效時間，以最小化期望單位時間成本為目標，擬定最適預防保養門檻值與預防保養總次數，進而推算預防保養間隔時間與排程，提供廠商一非週期性預防保養策略，最後透過實例來說明本研究所提出之最適預防保養模型的實際應用，並探討穩定程度不同之系統模型的條件式預防保養策略，結果顯示較不穩定模型需要較多次的預防保養且期望單位時間成本也相對提高，最後對失效門檻值、隨機損害頻率以及預防保養成本三方面進行參數分析。本研究考量相依多重競爭失效模式並研擬條件式預防保養策略，以更貼近實際情形與更有效率的預防保養，提供廠商進行預防保養策略制定相關的決策。

A failure often occurs in a complex system due to deterioration or other external factors. For complex systems, two failure processes are often considered as Multiple Dependent Competing Failure Processes (MDCFP): catastrophic failure which are caused by a sudden stress from a random shock process, and soft failures which are caused jointly by continuous degradation and the additional damage due to the same shock process. Condition-based maintenance is carried out through monitoring system state to keep the system functioning in a good state. In this study, a condition-based maintenance policy is considered through monitoring the degrees of deterioration (e.g., material wear) . The expected total cost per unit time is minimized to determine the optimal maintenance threshold, and then the optimal non-periodic preventive maintenance schedules are derived. Numerical examples are given to demonstrate the effectiveness of the proposed model, and how the optimal condition-based maintenance policy can be applied to the complex system subject to MDCFP. A sensitivity analysis is performed and the discussion on the optimal policy are also presented. The proposed model provides decision makers with an effective method in determining the appropriate maintenance policy.

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