rescheduling manufacturing sytsems: a framework of strategies, policies, and methods rescheduling...

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)