An Availability-Constrained Integrated Maintenance–Monitoring Model for a System With Failures Following an NHPP

This article presents an integrated model for production equipment maintenance and online process monitoring when the assignable causes and the equipment failures come from a nonhomogeneous Poisson process. To this end, six possible scenarios within a production cycle are described. These scenarios are defined based on equipment failures and control chart signals (true or false) within a production cycle and process condition at the end of cycle. Then, the occurrence probability and the expected time and cost of each scenario are calculated. The proposed model is characterized by five decision parameters, including number of inspections until planned maintenance, time interval between consecutive inspections, sample size, control limit coefficient, and optimal planned maintenance time. Moreover, the long-run expected cost rate is used as the objective function of the optimization problem, and two sets of constraints have been considered. The former set stands for statistical design of control chart, and the latter is related to equipment availability. Finally, a comprehensive numerical analysis is conducted to assess the sensitivity of the model and to compare the performance of the proposed integrated model to a stand-alone planned maintenance model. The results of the comparative study show that the integrated model outperforms the corresponding stand-alone planned maintenance model. The proposed policy is illustrated using a case study in a food production process.