rescheduling manufacturing sytsems: a framework of strategies, policies, and methods rescheduling...
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Rescheduling Rescheduling Manufacturing Sytsems:Manufacturing Sytsems:
A framework of strategies, A framework of strategies, policies, and methodspolicies, and methods
G. Vieira, J.W. Herrmann, E. Lin
Salih ÖZTOP20202801
03.03.2003
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Context
1) Introduction
2) Some Definitions
3) Rescheduling Environment
4) Performance Measures
5) Rescheduling Strategies
6) Rescheduling Methods
7) Results of papers
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1. Introduction
Aim of the paper• A survey type article to summarize and
group the articles about rescheduling and combine the definitions in each paper into the same structure.
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Rescheduling
• The process of updating an existing production schedule in response to disruptions or other changes.
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Disruptions/Changes
• Arrival of new/urgent jobs• Machine failers/repairs• Cancellation of jobs• Due date change (to an earlier or a later date)• Delay in the arrival of materials• Shortage of materials• Absent operator• Change in job priority• Rework • Over or underestimateion of process time
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2.Some Definitions
• Manufacturing System: organizes equipment, people and information to fabricate and assemble finished goods for customers. It includes order release, shop floor control and material handling.
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2.Some Definitions
• Order Release: Which jobs should be moved into production.
• Shop Floor Control: Which operation each worker and equipment should do and when they should do.
• Production Schedule: planned start and end time of each job
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2.Some Definitions
• Rescheduling Environment: set of jobs that need to be scheduled.
• Rescheduling Strategy: whether or not to genarate production schedules.
• Rescheduling Policy: when and how rescheduling is done.
• Rescheduling Methods: generate and update production schedules
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3.Rescheduling Environment
1-Static (finite set of jobs)
2-Dynamic (infinite set of jobs) (continue to arrive)
-Deterministic(no uncertainty about future)-Stochastic(some information uncertain)
-No Arrival Variability (cyclic production)-Arrival Variability (flow shop)-Proces Flow Variability(job shop)
(set of jobs that need to be scheduled).
(schedule is repetead)
(uncertainty in arrival, but same route)
(uncertainty in arrival and route)
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4.Performance Measures
• Scheduling Point: point in time when a scheduling decision is made.
• Rescheduling Period: time betweentwo consecutive scheduling points.
• Scheduling Stability: number of revisions or changes of a schedule
• Scheduling Nervousness: Opposite of scheduling stability
• Scheduling Robustness: measure changes to system-level performance.
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4.Performance Measures
• Schedule Efficiency:– Time based measures: makespan,mean
tardiness, mean flowtime,max latenss...
• Schedule Stability– Starting time deviance– Sequence difference
• Cost– Economic performance measure
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4.Performance Measures
• Cost of rescheduling:– Computational Effort (human & computer)
– Disruption of existing plans (nervousness)
• Setup costs• Transportation costs
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5.Rescheduling Strategies
1-Dynamic (does not create schedule)
2-Predictive-reactive(generate&update)
(whether or not to genarate production schedules)
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5.Rescheduling Strategies
1-Dynamic (does not create schedule)-Dispatching rules (prioritize jobs)
ex. SPT,EDD-Control-theoretic:Used to develop rules for which action to take and when to response the disruptions
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5.Rescheduling Strategies
2-Predictive-reactive(generate&update)
Rescheduling Policies-Periodic(periodically schedule on a rolling time horizon)
-Event-driven(reschedule after machine breakdown)
-Hybrid(reschedule periodically and after an event)
Iterative process:i) Evaluation/Planningii) Solution/Controlii) Revision/Rescheduling
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6.Rescheduling Methods
1-Schedule Generation
2-Schedule Repair
-Nominal schedules-Robust schedules
-Right-shift rescheduling-Partial rescheduling-Complete rescheduling
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6.Rescheduling Methods
1-Schedule Generation-Nominal schedules-Robust schedules
(To maintain good system performance with simple schedule adjustments)
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6.Rescheduling Methods
2-Schedule Repair-Right-shift rescheduling (postpone each remainig operation with delay time amount)-Partial rescheduling (reschedule only the operations affected by the disruption)-Complete(Regeneration)rescheduling(reschedule all the jobs not processed before, including those not affected by disruption.)
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7.Results of papers
Rescheduling periods:Longer: less number of setups but more WIPShorter: react more quickly to disruptions,
but increase number of setups
Rescheduling periods affects system performance more when there is a greater uncertainty. In other words frequent rescheduling becomes more effective as the level of uncertainty is high.
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7.Results of papers
• A robust,partial schedule leads to better system performance than dispatching rules
• As processing time variability increases,dispatching rules give better performance
•Too long and too frequent monitoring periodsresulted in worse system performance
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7.Results of papers
• Under loose due date condition, performance is not sensitive to changes in rescheduling interval.At tight due date conditions,it has a much more significant effect on performance.
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References
• Rescheduling manufacturing systems: a fremawork of strategies, policies, and methods. G. Vieira, J.W. Herrmann, E. Lin
• Using real time information for effecive dynamic scheduling- P. Cowling, M. JohansonEuropean Journal of Operational Research 139 (2002)