STUDIES ON OPTIMUM PREVENTIVE MAINTENANCE POLICIES FOR GENERAL REPAIR RESULT

In this paper we consider that a unit is repaired preventively after it has operated for time T. After repair, the unit is not as good as a new one, but is equivalent to one which has been used for a period of time. If we let Y indicate such a period of time, then Y is a random variable related to the time for which the unit has already operated . Hence, under the same repair condition as above, we obtain the unit's renovation degree distribution Of Y after the unit is repaired preventively at time kT (k = 2, 3, . . . ). Further, using the method of leading variables, we obtain the mean number of times the unit has broken down from time (k - 1)T to time kT (k = 1, 2, . . . ). Finally, considering an objective function with a bound condition and using the Lagrange multipliers method, we obtain an optimal preventive maintenance time T, for which the minimum total repair cost is achieved.