The uncertainty of preventive maintenance cycle time of machinery based on cost — Revenue ratio model

Determining the optimal preventive maintenance cycle time is one of the problems in maintenance task because there are many factors to be considered such as continuous operation, equipment conditions or the necessity of delivery date. Theoretically, preventive maintenance (PM) cycle time is inconsistent and it is assumed as normal distribution or N(MTTF,σ²). The assumption in this paper considers the relationship between the cost of monitoring and the extra revenue when the machine operation is still in good conditions during the PM interval. On the other hand, if the machine operation fails before PM interval, there are the opportunity lost costs due to lack of manufactured parts and cost of failure to be considered. This paper presents the developed model for the relationship between the uncertainty of PM interval and cost - revenue ratio. The mathematical model in this paper is φ(δ*/σ)/Φ(δ*/σ)=C_Mσ/R-(L+C_F). At the conclusion, the developed model is validated by using published data from previous research.