TABLE OF CONTENTS Until now, we have dealt primarily with the basic maintenance models and their combined models. This chapter introduces modified and extended maintenance models proposed mainly by the author and our co-workers. These models further reflect the real world and present more interesting topics to theoretical researchers.
In Section 9.1, we convert the continuous models of age, periodic, and block replacements and inspection to discrete ones [1]. These would be useful for the cases where: (i) an operating unit sometimes cannot be maintained at the exact optimum time for some reason such as shortage of spare units, lack of money or workers, or inconvenience of time required to complete the maintenance, and (ii) a unit is usually maintained in idle times. We have already discussed the optimum inspection policies for a finite interval in Section 8.6. In Section 9.2, we propose the models of periodic and block replacements for a finite interval because the working times of most units would be finite in the actual field. It is shown that the optimum policies are easily given by the partition method obtained in Section 8.6, using the results of optimum policies for basic models [2], [3].
In Section 9.3, we suggest the extended models of age, periodic, and block replacements in which a unit is replaced at either a planned or random time. Furthermore, we consider the random inspection policy in which a unit is checked at both periodic and random times. These random maintenance policies would be...
