A heuristic for machine scheduling at general mail facilities

In most major population centers mail collected during the day and mail arriving from outside the area are centrally processed at a general mail facility (GMF). This paper addresses the problem faced by the tour supervisor who must schedule machines at a GMF to handle the hourly fluctuations in workload without violating critical dispath times and service standards. The problem is complicated by the fact that decisions made upstream often have unpredictable consequences on downstream operations and inter-process storage. Machine scheduling in GMFs involves managing up to 200 different mail streams over a 24-hour period. Arriving mail must be separated according to major categories, stored, and assembled into suitable batches prior to sorting. During the distribution operations, a given mail piece may follow any one of a dozen routes through the system. The purpose of this paper is to present an efficient heuristic for generating operational machine schedules that are both smooth with respect to their utilization profiles, and consistent with the goal of batch processing. An example, based on data obtained from the Northern Virginia GMF, is given to demonstrate the computations.