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of specific factory activities, control of the activities and the operation of machines on the shop floor, and mechanisms for providing rapid feedback that becomes the basis for near-real-time adjustments in various production activities. Table 4.1 summarizes information technology (IT)-related research needed to advance shop floor and production systems.

Scheduling Factory Activities

Centralized Control

The dominant issues in production planning today are achieving major reductions in manufacturing lead time and major improvements in honoring promised completion times. Better scheduling and planning might well help to reduce the total time required for converting raw materials and parts to finished products.

Today's dominant scheduling paradigms are based on material requirements planning (MRP) and manufacturing resources planning (MRP-II), although other approaches are used from time to time. MRP and MRP-II were developed in the 1970s and 1980s. Originally developed to handle planning purchases of parts required for the products to be manufactured, MRP assumes a plant of infinite capacity. MRP-II goes beyond MRP to take into account inventory, labor, actual machine availability and capacity, routing capabilities, shipping, and purchasing. MRP-II generates a master production schedule that serves as the driver or trigger of shop floor activities.

By design, the characteristic time scale of scheduling (in MRP jargon, the "bucket") based on MRP and MRP-II is days or weeks, perhaps even months; depending on the implementation, MRP and MRP-II may or may not be the basis for "to-the-minute" or "work-to" timetables for equipment use and material flows. Under any circumstances, however, arranging for the moment-to-moment control of factory operations is the job of the shift supervisor. For the shift supervisor, situational awareness is at a premium. He or she must draw on information provided by workers on the previous shift (reflecting matters to which he or she must attend on this shift) and sensors and worker reports of what is happening on the shop floor during this shift (e.g., the condition of various tools, how various processes are operating, who has reported for work, what materials are available), as well as directives from senior management concerning overall objectives. From these sources, the shift supervisor must develop a local plan of operation for the next 8 hours.

In principle, the real-time factory controllers of today operate by periodically receiving a list of jobs that must be completed if the MRP-based scheduling plan is to be followed. For each production job, a process plan is retrieved from a database. Such a plan involves the identification of routings of particular work in progress to specific process cells, scheduling of all activities at both the cell and workstation levels, coordinating those activities across the equipment, monitoring



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