Maintenance strategies have been studied extensively and applied successfully to reduce the operation costs of industrial assets. However, the study for heterogeneous two-unit systems is rarely based on the usage and condition information of units, simultaneously. This paper originally proposes a novel imperfect opportunistic maintenance model for a two-unit series system considering random repair time and two types of failures, where unit 1 and unit 2 are respectively subject to soft failure and hard failure. The system maintenance actions are performed not only based on the deterioration level of unit 1 but also on the usage of unit 2. To utilize the economic dependence between the two units, the opportunistic maintenance policy is adopted in the series system. When a unit fails or is being repaired, the other unit has an opportunity to be simultaneously maintained once it meets the requirement of opportunistic maintenance. Herein, opportunistic maintenance action is imperfect maintenance, which means that the deterioration level of unit 1 and the usage of unit 2 restore to a lower level than the as-good-as new status after repair. Nonetheless, once both units meet the requirement of replacement actions, they will be perfectly replaced by new ones. The objective is to minimize the system average maintenance cost by optimizing the thresholds of opportunistic maintenance and perfect replacement of two units. Finally, an illustrative example is presented to demonstrate the superiority of the proposed maintenance model.

维护策略已被广泛研究并成功应用于降低工业资产的运营成本。然而，对异构二单元系统的研究很少同时基于单元的使用和状态信息。本文最初提出了一种考虑随机维修时间和两种故障类型的两机组串联系统的新的不完美机会主义维修模型，其中机组1和机组2分别遭受软故障和硬故障。系统维护动作不仅基于1号机组的老化程度，还基于2号机组的使用情况。为了利用两台机组之间的经济依赖性，串联系统采用机会主义维护策略。当设备出现故障或正在维修时，另一个单位一旦满足机会维修的要求，就有机会同时维修。这里的机会性维修行为是不完全维修，是指1号机组的劣化程度和2号机组的使用率在维修后恢复到低于原样的水平。尽管如此，一旦两个单元都满足更换动作的要求，它们将被新的完美替换。目标是通过优化机会维修和两台机组完美更换的阈值来最小化系统平均维修成本。最后，给出了一个说明性的例子来证明所提出的维护模型的优越性。机会性维修行为是不完全维修，即1号机组的劣化程度和2号机组的使用率在维修后恢复到低于原样的水平。尽管如此，一旦两个单元都满足更换动作的要求，它们将被新的完美替换。目标是通过优化机会维修和两台机组完美更换的阈值来最小化系统平均维修成本。最后，给出了一个说明性的例子来证明所提出的维护模型的优越性。机会性维修行为是不完全维修，即1号机组的劣化程度和2号机组的使用率在维修后恢复到低于原样的水平。尽管如此，一旦两个单元都满足更换动作的要求，它们将被新的完美替换。目标是通过优化机会维修和两台机组完美更换的阈值来最小化系统平均维修成本。最后，给出了一个说明性的例子来证明所提出的维护模型的优越性。它们将被新的完全取代。目标是通过优化机会维修和两台机组完美更换的阈值来最小化系统平均维修成本。最后，给出了一个说明性的例子来证明所提出的维护模型的优越性。它们将被新的完全取代。目标是通过优化机会维修和两台机组完美更换的阈值来最小化系统平均维修成本。最后，给出了一个说明性的例子来证明所提出的维护模型的优越性。