Scheduling Imperfect Inspections in Preventive Maintenance of Systems with Increasing Failure Rates

摘要

Periodic inspections are usually carried out at regular intervals to detect and correct hidden failures that generate a loss per unit of time undetected. The periodic inspections specified by the guidelines of governments or companies can accurately detect hidden failures. They are called perfect but are usually costly. The periods of perfect inspections (PI) cannot be changed easily because of regulations and management problems. With the improvement of monitoring technology," many devices for remote sensing are available with costs reasonable when compared with those for perfect inspections. They are called imperfect in that they can detect hidden failures with probability less than 100%. The periods of imperfect inspections (IPI) can be adjusted easily. In this paper, we propose an integrated inspection policy that combines PI and IPI, which is flexible in that the frequency of IPI need not be common for all PI periods. The inspection frequencies of IPIs are determined to minimize the expected total cost of inspection and operation, which includes loss due to undetected failures. The property of the objective function of this optimization problem is investigated and is used to implement the optimization algorithm. Numerical examples are provided to compare the expected costs of the proposed policy with optimal IPI frequencies and of that with the common IPI frequency. These examples indicate that the proposed policy can reduce the total costs for systems with increasing failure rate and so can enhance the effectiveness of the inspection plan.