Issues in Specifying Planning Horizons for Production Planning within CIM Environments
The development of production plans for the CIM hierarchy directs the firm’s manufacturing activities over an extended time horizon. All of the subordinate CIM functions (e.g. production scheduling, material and capacity requirements planning, purchasing, and others) are impacted by this plan. The first step in the development of a production plan is the specification of an appropriate planning horizon--a complex task that is plagued with numerous uncertainties. To address this task, this paper views the production planning problem as a two-point boundary value problem where boundary conditions must be specified at both the beginning and at the end of the planning horizon. A difficulty arises in the specification of the ending boundary conditions since they are generally unknown. Furthermore, an incorrect specification can have a significant, perhaps detrimental, effect upon the quality of the developed plan. An additional requirement for the planning horizon is that it be of suitable duration to permit an effective integration of production planning with the other CIM functions.
The reported research addresses the uncertainties in specifying the boundary conditions. An integrated solution approach that employs both Monte Carlo simulation and mathematical programming is used to consider the inherent uncertainties associated with the production planning problem. For the considered computational examples, it is shown that the specification of boundary conditions do effect the quality of the derived production plan. Furthermore, the results also suggest that planning epochs exist. The observation of planning epochs implies that a variable length planning horizon, rather than a constant length horizon, should be employed within the context of a rolling horizon implementation of production planning. Using this approach, the planning would be performed to the end of the current epoch where boundary conditions can be specified with greater accuracy. Finally, the issue of establishing the length of an epoch is discussed.
KeywordsTransportation Haas Plague
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