摘 要

本研究在探討兩階層可完全維修零件庫存系統之批次存貨政策問題，系統中上層僅含一個維修站，負責系統內所有損壞零件之維修和提供所有下層維修點所需之備品，而下層則含有數個平行且不相同之維修點，負責提供顧客即時之零件替換服務，但不進行損壞零件之維修。下層的各維修點會依據其批次存貨政策決定何時應將其累積之損壞零件送回上層之維修站進行維修，並取回相同數量之備品，而上層之維修站則會依據其批量政策，決定何時開始進行損壞零件的維修。

本研究之目的為決定上層維修站與所有下層各維修點中，最佳的訂貨維修批量與最佳之再訂購點，使得系統內之庫存相關總成本最小。本問題中，存貨相關總成本包含了下層維修點之訂購成本、良好備品和損壞零件之存貨持有成本及缺貨成本，及上層維修站之維修固定成本、良好備品與損壞零件之存貨成本及缺貨成本。本研究中將使重新報酬理論、條件機構和條件期望值求得系統之單位時間期望總相關成本函數，並發展一有效之搜尋方法，在合理計算時間內求得最佳或近似最佳之訂購批量和再訂購點。

本系統在運作上十分複雜，故特用近似分配來描述系統內上游維修站之存貨周期與需求分配，並使用二維加速搜尋之演算法，先求得上游維修站之再維修點與固定維修批量，並在固定此上游維修站決策變數下，找到可以最小化系統內單位總相關成本的各下游維修點固定訂購批量和再訂購點，並回到上一層迴圈重覆運算至收歛為止。依據32個部分因子演算實驗的結果可以發現，近似模式表現良好，且總成本模式對再訂購點可能存在凸性質。下游維修點的缺貨成本會隨因子的改變而大幅變動，為總成本波動的主要來源。部分因子實驗結果亦發現縮減兩階層可維修零件系統本之主要方式為良好的物流政策規劃(階層備品的配置)，亦即降低階層存貨價值的增加與縮減前置時間。

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