عنوان مقاله [English]
Condition-based maintenance (CBM) is a maintenance strategy that recommends maintenance actions based on information collected through condition monitoring (periodic inspections). The primary goal of CBM is to extend the lifetime of systems, to avoid unnecessary preventive maintenance, and to improve equipment reliability.There has been much research, attempting to include economic considerations, into the process of decision making in CBM. A well-known approach is called the; control limit policy. In this approach, it is assumed that the inspections are performed at fixed and given intervals of times. The equipment is replaced whenever it fails. Also, after each inspection, and based on inspection results, if the cost-related failure rate reaches or exceeds a pre-determined limit, a preventive replacement is scheduled. The limit is determined, such that the expected average aintenance costs per unit time, due to preventive and failure replacements over a long time horizon, are minimized.Clearly, a higher frequency of inspection may provide more information about the condition of the equipment and, thus, maintenance actions are performed more effectively. Consequently, the cost associated with failure and preventive replacements is decreased. But, in many real cases, inspection requires labour, specific test devices and, sometimes, suspension of operations. Thus, when the inspection and analysis of observations are costly, performing inspections at short intervals incur large inspection costs. In contrast, if inspections are carried out over long intervals, the cost of failure replacements may significantly increase. Therefore, it is necessary to consider not only the preventive and failure replacement costs, but also inspection costs in CBM. This paper extends the control limit policy to include inspection costs for optimization of inspection intervals and control limits, simultaneously. For different alternative inspection intervals, the optimal control limit is determined and, then, the associated costs are compared to identify the optimal inspection interval and the optimal control limit. A numerical example is given to illustrate the proposed approach.