عنوان مقاله [English]
The primary goal of condition-based maintenance (CBM) is to extend system lifetime based on the information collected through periodic inspections. There have been many attempts to include economic considerations in the process of decision making in CBM. A well-known approach is called the control limit policy. In this approach, using historical data of the equipment and the values of condition monitoring covariates, the hazard rate function is first
estimated. It is assumed that the inspections are performed at fixed and given intervals of time. The equipment is replaced whenever it fails. Also, after each inspection and based on the inspection results, if the cost-related
failure rate reaches or exceeds a pre-determined limit, a preventive replacement is scheduled. The limit is, then, determined such that the expected average maintenance costs per unit time, due to preventive and failure replacements over a long time horizon, is minimized. However, it is assumed that the failure cost is constant, no matter when or at which state the failure occurs.
Using the main principals of the control limit policy, this paper extends the approach assuming that the failure cost depends on both the age of the system and the value of the covariates observed. This assumption is more practical, as equipment usually incurs more failure cost as it deteriorates. However, determination of the function that can represent the variable failure cost is often difficult. In this paper, we consider a hypothetical non-decreasing
failure cost function. This does not limit the scope of the application of the proposed method, as its relaxation only entails replacing the failure cost function with the one determined in a given application. The derivation of the
required mathematical formulation to obtain the optimal control limit is presented in detail. A numerical example is also given to illustrate the proposed approach.