This section faces the three fundamental problems, or phases, in MS corresponding to planning, scheduling, and control from an integrated perspective. As mentioned earlier, the three problems are strictly interconnected. On the one hand, planning and scheduling (P&S) differ for the aggregate vs. detailed way, respectively, in coping with production decisions and influence each other by imposing constraints (planning over scheduling) or by revealing inconsistency or actual infeasibility (scheduling over planning). Scheduling and control (S&C), on the other hand, may share the same temporal scope as the first one may be responsible for optimizing performance with on-line decisions; the second one, moreover, forces the shop floor devices to follow such decisions while respecting the correct production requirements. However, it should also be clear that planning, scheduling, and control deal with the same problem (obviously, from different, but contiguous, standpoints). Consider the block diagram of Figure 3.1 in which the basic manufacturing activities relevant to production management are reported in a three-layered hierarchy that evinces the three conventional planning, scheduling, and control decision levels.

Figure 3.1: Main Activity Flow in Manufacturing Production

In the figure, the typical flow of information, in particular related to decisions characterizing the production process in manufacturing, clearly highlights the strong link between the activities (blocks in the figure) devoted to planning and those devoted to scheduling. The lowest block in the diagram reflects the presence of the real-time control system, which is able to make things...