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MIT2_854F10_control - Multi-Stage Control and Scheduling...

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Multi-Stage Control and Scheduling Lecturer: Stanley B. Gershwin
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Definitions Events may be controllable or not, and predictable or not. controllable uncontrollable predictable loading a part lunch unpredictable ??? machine failure
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Definitions Scheduling is the selection of times for future controllable events. Ideally, scheduling systems should deal with all controllable events, and not just production. That is, they should select times for operations, set-up changes, preventive maintenance, etc. They should at least be aware of set-up changes, preventive maintenance, etc.when they select times for operations.
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Definitions Because of recurring random events, scheduling is an on-going process, and not a one-time calculation. Scheduling, or shop floor control, is the bottom of the scheduling/planning hierarchy. It translates plans into events.
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Control Paradigm Definitions Control Actuation Noise System State Observations This is the general paradigm for control theory and engineering.
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Control Paradigm Definitions In a factory, State: distribution of inventory, repair/failure states of machines, etc. Control: move a part to a machine and start operation; begin preventive maintenance, etc. Noise: machine failures, change in demand, etc.
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Release and Dispatch Definitions Release: Authorizing a job for production, or allowing a raw part onto the factory floor. Dispatch: Moving a part into a workstation or machine. Release is more important than dispatch. That is, improving release has more impact than improving dispatch, if both are reasonable.
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Requirements Definitions Scheduling systems or methods should ... deliver good factory performance. compute decisions quickly, in response to changing conditions.
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Performance Goals To minimize inventory and backlog. To maximize probability that customers are satisfied. To maximize predictability (ie, minimize performance variability).
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Performance Goals For MTO (Make to Order) To meet delivery promises. To make delivery promises that are both soon and reliable . For MTS (Make to Stock) to have FG (finished goods) available when customers arrive; and to have minimal FG inventory.
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Performance Objective of Scheduling Goals Cumulative t Production and Demand earliness production P(t) demand D(t) surplus/backlog x(t) Objective is to keep cumulative production close to cumulative demand.
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Performance Difficulties Goals Complex factories Unpredictable demand (ie D uncertainty) Factory unreliability (ie P uncontrollability)
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Basic approaches Simple rules heuristics Dangers: Too simple may ignore important features. Rule proliferation. Detailed calculations Dangers: Too complex impossible to develop intuition.
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