RESCHEDULING MANUFACTURING SYSTEMS: A FRAMEWORK OF STRATEGIES, POLICIES, AND METHODS G.Vieira, J. He

1
RESCHEDULING MANUFACTURING SYSTEMS A
FRAMEWORK OF STRATEGIES, POLICIES, AND
METHODSG.Vieira, J. Herrmann E.LinJournal
of Scheduling, 2003

• Presented by
• Banu KARAKAYA

2
OUTLINE

• Definition of Rescheduling in Manufacturing
  Systems
• Terminology Framework
• Rescheduling Environments Performance Measures
• Rescheduling Strategies
• Rescheduling Policies
• Rescheduling Methods
• Theory and Practice
• Conclusion

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RESCHEDULING MANUFACTURING SYSTEMS

• Generate and update production schedules
• Schedules are plans stating when controllable
  activities should take place
• Schedules enable better coordination to
• -increase productivity
• -reduce operating costs
• -control the release of jobs to the shop
• -to determine whether delivery promises
  can be met
• -give a statement of what should be done
  by shoop floor
• personel

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RESCHEDULING MANUFACTURING SYSTEMS

• Dynamic, stochastic environments
• Unexpected events or disruptions occur so that
  both the initial
• production schedule and system performance is
  affected
• Rescheduling must be done in order to minimize
  the effect of
• disturbances in the performance of the system

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DEFINITION OF RESCHEDULING

• Rescheduling is the process of updating an
  existing production schedule in response to
  disruptions or other changes
• Unexpected events(disruptions)are called
  rescheduling factors (Dutta, 1990 Dhingra,
  Musser and Blankenship,1992)
• -machine failure
• -urgent(rush or hot)job arrival
• -job cancellation
• -due date change
• -change in job priority
• -rework or quality problems
• -over or underestimation of process time

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TERMINOLOGY FRAMEWORK

• Scope of research on rescheduling varies widely
• No standard classification scheme in the
  rescheduling literature
• 3 primary types of studies
• -methods for repairing a schedule that has
  been disrupted
• -methods for creating a schedule that is
  robust with
• respect to disruptions
• -how rescheduling policies affect the
  performance of the
• dynamic manufacturing system

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TERMINOLOGY FRAMEWORK

• The paper presents a framework to understand
  rescheduling
• Some common terms are defined throughout the
  paper
• Manufacturing system organizes equipment, people
  and information to fabricate and assemble
  finished goods shipped to the customers
• Order release controls a manufacturing systems
  input by determining which orders should be moved
  into production (like order release, input
  control)

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TERMINOLOGY FRAMEWORK

• Shop floor control determines which operation
  each person and piece of equipment should do and
  when they should do it
• Production schedule specifies the planned start
  time and end time of each job assigned to the
  resource
• Scheduling is the process of creating a
  production schedule for a given set of jobs and
  resources
• Rescheduling is the process of updating an
  existing schedule in response to disruptions or
  other changes

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TERMINOLOGY FRAMEWORK

• Framework for understanding rescheduling includes
  
• -Rescheduling Environments
• -Rescheduling Strategies
• -Rescheduling Policies
• -Rescheduling Methods

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RESCHEDULING ENVIRONMENTS

• identify the set of jobs that need to be
  scheduled

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RESCHEDULING ENVIRONMENTS

• Static rescheduling finite set of jobs
• For deterministic, static rescheduling the
  specified schedule can be followed without any
  modifications
• Stochastic, static rescheduling
• -when task processing times are modeled as
  random
• variables, the actual start and end
  times will not match the expected ones
  a rule or policy is needed for
• 
  reconciling the error
• -or uncertainty is not modeled as probability
  distribution
• worst-case performance is the key
  objective

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RESCHEDULING ENVIRONMENTS

• Dynamic rescheduling infinite set of jobs, i.e.
  jobs continue to arrive over an infinite time
  horizon
• a) No uncertainty or variability in the job
  arrival
• -jobs to be processed are known in advance
• -production schedule is continuously
  repeated cyclic
  scheduling
• b) Arrival variability in a flow shop
• -there may exist some uncertainty in job
  arrivals
• -but all jobs follow the same route through
  the manufacturing
• system
• -arrival rate is steady

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RESCHEDULING ENVIRONMENTS

• c) Process flow variability often occurs in a
  job shop
• -many products, but a limited subset of them
  are to be produced at any given time
  products arrival process varies greatly
• -in some situations, no advance information is
  available about jobs until they arrive
• -some info. about future arrivals may be
  known, but it is subject to change because of the
  disruptions

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PERFORMANCE MEASURES

• A rescheduling point is the point in time when a
  schedule is created or revised
• The rescheduling period is the time between the
  consecutive scheduling points
• Rescheduling frequency is the inverse of the
  rescheduling period and it measures how often
  rescheduling is performed
• It can significantly affect the system
  performance
• A lower frequency (longer rescheduling periods)
  lowers the
• number of setups, but increases manufacturing
  cycle time and WIP

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PERFORMANCE MEASURES

• (Re)Scheduling stability measures the number of
  revisions or
• changes that a schedule undergoes during the
  execution
• (Re)Scheduling nervousness is defined as
  significant changes in
• MRP plans or instability opposite
  of scheduling stability
• (Re)Scheduling robustness measures how much
  disruptions
• would degrade the performance of the system
  when executing
• the production schedule

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PERFORMANCE MEASURES

• Measures can be divided into 3 groups
• a) Measures of Schedule Efficiency
• -time-based measures (makespan, mean
  tardiness, mean flow-
• time, average resource utilization
  etc.)
• b) Measures of Schedule Stability
• -impact of schedule change is a nonregular
  performance
• measure
• -deviation between the revised and initial
  schedule(such as
• starting time deviations, sequence
  difference)
• -for ex when searching for more stable and
  robust schedules,
• the impact of machine failure is the
  major concern
• -as the level of uncertainty ,
  frequent rescheduling becomes
• more effective to improve the
  robustness

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PERFORMANCE MEASURES

• c) Cost (economic performance measure for
  rescheduling)
• -objective is to minimize the cost of
  starting jobs too early,
• WIP inventory and tardiness
• Computational costs
• -costs of computational burden on the computer
• -costs of investments in the necessary
  information systems
• Setup costs
• -occur when tooling and fixtures are created
  or allocated in
• advance to the schedule
• Transportation costs
• -costs of material handling work to transport
  jobs
• -costs of delivering materials earlier than
  required

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THE FRAMEWORK

• Framework for understanding rescheduling includes
  
• -Rescheduling Environments
• -Rescheduling Strategies
• -Rescheduling Policies
• -Rescheduling Methods

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RESCHEDULING STRATEGIES

• For dynamic rescheduling environments with
  uncertain job arrivals
• 1) Dynamic Scheduling
• -does not create production schedules
• -dispatching rules(SPT or EDD) and pull
  mechanisms(such as
• Kanban cards) are used to control the
  production
• -it can be defined as online scheduling or
  reactive scheduling
• -it is related to real-time control
  because of the decisions made
• based on the current state of the
  manufacturing system

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RESCHEDULING STRATEGIES

• 2) Predictive-reactive scheduling
• -common strategy to rescheduling dynamic
  manufacturing systems
• -It has two primary steps
• generating a production schedule
• updating the schedule in response to a disruption
  to minimize its impact on system performance
• -It can also be described as an iterative
  process of three steps
• (Wu and Li, 1995)
• Evaluation step considers the impact that a
  disruption causes
• Solution step determines the rescheduling
  solutions
• Revision step updates the existing schedules or
  generates a new one

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RESCHEDULING POLICIES

• A rescheduling policy is needed to implement a
  predictive-reactive scheduling strategy
• Three types of policies have been studied
• a) Periodic Policy
• -reschedules the facility periodically and
  implements the schedules on a rolling time
  horizon basis
• -it yields more schedule stability and less
  nervousness than
• constant rescheduling
• -determining the optimal rescheduling period is
  a difficult
• task when using this type of policy

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RESCHEDULING POLICIES

• b) Event-Driven Policy
• -rescheduling can be performed repeatedly
  in dynamic
• manufacturing environments or it can be
  a single event for
• revising the schedule in a static sytem
• -for static environments, it is mostly
  used to reschedule the system
• when m/c failures occur
• -for dynamic systems, rescheduling is
  triggered when the total
• number of job arrivals reaches a
  threshold
• -In the extreme, a new schedule is
  created every time an event
• changing the system status occurs

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RESCHEDULING POLICIES

• c) Hybrid Policy
• -reschedules the system periodically and
  also when
• special (or major) events take place
• -major events m/c breakdowns, arrival of
  urgent jobs, job
• cancellation or job piority changes
• Determining the impact of rescheduling
  policies on dynamic environments requires careful
  study, modeling and analysis of the manufacturing
  system

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THE FRAMEWORK

• Framework for understanding rescheduling includes
  
• -Rescheduling Environments
• -Rescheduling Strategies
• -Rescheduling Policies
• -Rescheduling Methods

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RESCHEDULING METHODS

• Methods to create or update schedules as part of
  predictive-reactive scheduling strategy (a most
  commonly used in practice)
• a) Generating robust schedules
• -attempt to maintain good system
  performance with simple
• schedule adjustments
• -number of papers have proposed methods for
  creating
• schedules that are robust with respect
  to disruptions
• b)Repairing schedules
• -larger deviations occur when unexpected
  events disrupt the
• initial schedule schedule
  repair occurs to react to the
• 
  disruptions

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RESCHEDULING METHODS

• There are 3 common methods used to repair(update)
  the schedule
• Right Shift Rescheduling postpones each remaining
  operation by the amount of time needed to make
  the schedule feasible
• Partial Rescheduling reschedules only the
  operations affected directly or indirectly by the
  disruption
• It preserves the initial schedule as much as
  possible to maintain schedule stability with less
  nervousness
• For example, match-up scheduling
• Regeneration reschedules the entire set of
  operations not processed before the rescheduling
  point, including jobs not affected by the
  disruption
• It is also known as complete rescheduling

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THEORY AND PRACTICE

• Rescheduling points out that there is a gap
  between theory and practice of production
  scheduling
• Most scheduling results do not consider important
  characteristics of the environment in which
  scheduling occurs
• Researchers do not consider fully the dynamic
  aspects of the manufacturing system
• (Re)Scheduling is actually part of a dynamic
  process

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CONCLUSION AND FUTURE RESEARCH

• Since there are no standard definitions of the
  strategies, policies and methods in the
  rescheduling literature, this paper aims to
  describe a framework for understanding
  rescheduling concept
• More research is needed
• -to compare the performance of manufacturing
  systems under different rescheduling policies and
  
• -to understand how interactions between
  rescheduling policies and other production
  planning functions(capacity planning, MRP) affect
  system performance

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• THANK YOU
• presented by Banu Karakaya

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RESCHEDULING MANUFACTURING SYSTEMS A
FRAMEWORK OF STRATEGIES, POLICIES, AND
METHODSG.Vieira, J. Herrmann E.LinJournal
of Scheduling, 2003

• Presented by
• Banu KARAKAYA