INSPECTION POLICIES FOR REPAIRABLE SYSTEMS

The usual practice of monitoring a production process is to inspect th e process at a uniform rate. For processes involving failure mechanism that obey a Markovian model, the practice of inspecting uniformly ove r time is, usually, optimum. For non-Markovian systems, however, this practice of inspection at a uniform rate is generally not optimum. It is believed that the frequency of inspections should be increased with time for increasing-failure-rate models. In this article we address t his issue of an appropriate inspection policy for non-Markovian system s. Further, associated with a non-Markovian system is the usual practi ce of repairing the machine to bring it back to an 'in-control' state. We assume that, at a moderate cost, the system can be repaired and th at the residual life on this system will depend upon its current age. The replacement costs are high and a decision to replace this machine is undertaken only when a repair at this stage is not expected to yiel d positive economic benefits. The objective is to determine an optimum inspection and replacement policy so as to minimize the expected prod uction cost per unit time.