A Prescriptive Maintenance Policy in the Presence of Imperfect Maintenance

The objective of this paper is to provide preliminary insights to support maintenance decision-making in a context imperfect maintenance is present and "prescriptive actions" (i.e., actions which suppose that the performances of the system can be voluntarily altered to obtain a desired outcome) can be integrated.
The policy consists in performing an inspection at a predetermined time and, based on its outcome, deciding whether to immediately replace (i.e., perfect replacement) the unit or to postpone its replacement. If the replacement is postponed, an imperfect maintenance may be concurrently performed which reduces the degradation level and modifies (stochastically) the degradation behavior of the unit. After the first inspection, the imperfectly maintained systems are then inspected again and, based on the outcome of this second inspection, it is decided whether to immediately replace the unit or to further postpone its replacement to a future time where no inspection is performed and the unit is replaced systematically. In case of this second postponement, the degradation information gathered at the inspection times is also used to (possibly) adjust the usage rate of the unit. The idea here is to use the degradation measurements to quantify the uncertainty brought about by the imperfect action and intervene accordingly with the usage rate. Any change in the usage rate is assumed to affect both the future evolution of the degradation of the system and its operational costs. The driving idea behind the conception of this policy is to investigate if and how prescriptive maintenance actions (i.e., changing the usage rate) can assist in reducing the uncertainty brought about by the imperfect maintenance action. Failure is defined by the first passage time of the degradation process to a predefined threshold. It is also supposed to be not self-announcing and that failed units keep operating, albeit with reduced performances/additional costs.

Keywords: Prescriptive maintenance, Imperfect maintenance, Usage rate, Uncertainty.