Simulation of Manufacturing and Material Handling Systems

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Simulation of Manufacturing and Material Handling
Systems

• Jerry Banks
• Atlanta, GA

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Definition of Simulation

• Simulation is the operation of a real-world
  process or system over time.
• Simulation involves the generation of an
  artificial history of the system, and the
  observation of that artificial history to draw
  inferences concerning the operating
  characteristics of the real system that is
  represented.

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Definition of Simulation

• One of the top 3 technologies
• Simulation is no longer the technique of last
  resort
• It is an indispensable problem-solving methodology

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Definition of Simulation

• We use simulation to
• Describe and analyze the behavior of a system
• Ask what if questions about the real system
• Aid in the design of real systems
• Existing and conceptual systems
• We model both kinds

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Ad Hoc Simulation

• Customers arrive for service between one and ten
  minutes apart in time
• Customers are served in a time between one and
  six minutes
• Integer values
• Simulate for twenty customers
• Idle and empty

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Ad Hoc Simulation Table
Customer Time Arrival Service Service Time Time I
dle Time between Time Time begins Service in Time
in Arrivals Ends System Queue ______________
__________________________________________________
__________________________________________________
_________1 - 0 2 0 2 2 0 0 2 5 5 2 5 7 2 3 0 3 1 6
6 7 13 7 0 1 20 7 98 1 98 99 1 4 0 72
34 7
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Performance Measures

• Avg time in system 72/20 3.6 minutes
• idle time (34/99)100 34
• Avg waiting time/customer 7/20 0.35 minutes
• Fraction having to wait 3/20 0.15
• Avg waiting time of those that waited 7/3
  2.33 minutes

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Mfg and MH systems

• Competition requires automation
• Major design blunders can result
• Mismatches in machine capacity
• Insufficient buffer space
• AGVs that pile up in traffic
• Bottlenecks
• Traditional methods are inadequate to the task

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Mfg and MH systems

• Simulation is the technique of choice
• Calculates movement of parts and interaction of
  system components
• Evaluates flow of parts through the system
• Examines conflicting demand for resources
• Examines contemplated changes before their
  introduction

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Typical questions

• What will be the throughput?
• How can we change it?
• Where are the bottlenecks?
• Which is the best design?
• What is the reliability of the system?
• What is the impact of breakdowns?

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Level of detail

• Proper level of detail is required
• Level of detail is limited by
• Availability of input data
• Knowledge of how system components work

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Example questions about detail

• Should the model simulate each conveyor section,
  or can some be replaced by a simple time delay?
• Should the model simulate manufacture of
  purchased parts, or should we assume that they
  are always available at the right location?

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Example questions about detail

• At what level of detail do control systems need
  to be simulated?
• Distribution centers and other facilities are
  operated by control software
• The algorithms play a key role
• Simulation is used to compare the effectiveness
  of competing control schemes

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Material handling models

• 85 of time is in MH or waiting for MH
• Vast investment in WIP

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Material handling models

• Possible MH systems include
• Conveyors
• Pathmovers
• Bridge cranes
• Power free
• Storage systems
• Kinematics
• Tanks pipes

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Conveyors

• Accumulating
• Non-accumulating
• Indexing (form slugs)

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Pathmovers

• Unconstrained (FLTs)
• Automated Guided Vehicles
• Automated
• Person aboard
• Wire guided
• Chemical path
• Rail guided

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Storage Systems

• Pallet storage
• Case storage
• Small part storage (totes)
• Oversize items/Rack storage
• Automated storage and retrieval systems with
  storage-retrieval machines (AS/RS with SRM)

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Goals and performance measures

• Purpose is understanding, not numbers or
  animations
• Will the system meet throughput requirements?
• What happens to response time at peak periods?

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Goals and performance measures

• What is the recovery time when short-term surges
  cause congestion and queueing?
• What is the system capacity?
• If problems occur, what is their cause?

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Conveyor system/basic
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Non-accumulating
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Fixed interval
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Conveyor system/graphics added
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AGVsystem
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Front compartment sub assembly/VR graphics
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Engine plant/VR graphics
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Questions