商品失效與衰退通常都不會只受單一因素的影響，廠商在制定相關之保固政策時，常用雙構面的保固模式，例如以使用時間及使用程度作為衡量的工具。近年來買賣雙方皆越來越重視商品可靠度與品質的維持，而預防保養的導入可以有效達到此目的，因此過去有許多學者致力於制訂定期性預防保養保固政策之研究，發展許多最佳化的成本及利潤模式。然而，隨著使用時間的增加，商品故障與失效的次數會比一開始來的頻繁，若採用定期性的保養方式，可能到後期時商品仍頻繁地發生失效或故障，使預防保養失去其應有的功效。本研究以非週期的預防保養方式，取代定期性的預防保養，利用持續監控商品可靠度，並且制定可靠度門檻，做為保養間隔週期的規劃依據，以廠商的角度，做相同的模式推導與計算，在廠商利潤最大化的目的下，發展出最適之保養排程及商品保固使用期限。最後經由模式的驗證，發現在加入非週期預防保養於保固中，廠商可提供相較於現有定期預防保養之保固政策更長之保固期限。而保固期的延長，一方面使得消費者權益保障提升，另ㄧ方面也成為廠商刺激顧客需求，提高利潤的重要行銷工具。

In dealing with the problem of maintaining a critical reliability level for products subject to degradation, it may not be satisfactory to consider only one effect of time or usage, since both of them usually affect the product reliability at the same time. Therefore, two-dimensional warranty with consideration of both time and usage for deteriorating products would be more suitable for both manufacturers and customers. In general, the manufactures would undertake periodic preventive maintenance program during product warranty term. However, the increase of product degradation, a product may still breakdown very often even the latter preventive maintenance action have been performed. In this paper, the concept of a two-dimensional warranty was integrated with the deliberation of non-periodic preventive maintenance to determine the optimal warranty policy that maximizes the manufacturers’ profits, with lower warranty cost, and an extended warranty period. A numerical application is provided to demonstrate the effectiveness of the proposed approach, with sensitivity analyses being conducted to investigate the robustness of the derived optimal warranty policy.

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