Design of Discrete-Event Systems Using Templates

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Design of Discrete-Event Systems Using Templates

• Lenko Grigorov1, José Eduardo Ribeiro Cury2 and
  Karen Rudie1
• 1 Queens University, Kingston, Canada
• 2 Federal University of Santa Catarina, Brazil

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Discrete Event Systems

• Ramadge and Wonham '86
• Model as FSAs

events
System
Supervisor
control decisions
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System
Robotic arm
Press
4
Requirements
Process
Collision prevention
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Problem 1 synchronization
Process
Collision prevention
Press
6
Problem 2 explicit specs
Process
Collision prevention
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Supervisors
Trivial example
Real system
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Problem 3 implementation
Programmable Logic Controller (PLC) code for real
system
Abstract supervisor
?
(50 states, 200 transitions)
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Conceptual design framework

• What we really talk about is
• Event generators
• Protocols

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Conceptual design framework

• What we really talk about is
• Event generators
• Protocols
• Santos et al. '01
• Active components
• Passive components
• Connections between them
• Simultaneous structural functional design

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Example diagram
Process control
Avoid collision
Transport belt
Press
Arm
Welder
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Example diagram
Event synchronization
Process control
Avoid collision
Transport belt
Press
Arm
Welder
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Templates (abstract)

• Abstract common behavior

template
abstract
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Templates (instantiate)

• Instantiate existing templates

template
instantiate
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Templates

• Faster
• No need to remodel similar behavior
• More robust
• Can be thoroughly tested
• Easier
• Graphical conceptual designs

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Process

• Model templates as FSAs
• Instantiate graphically the templates
• Link graphically the events to synchronize the
  template instances
• Enter custom PLC code for events
• Click GO to automatically
• Make implicit specifications explicit
• Compute modular supervisors
• Obtain PLC code for download to controller

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Process

• Model templates as FSAs
• Instantiate graphically the templates
• Link graphically the events to synchronize the
  template instances
• Enter custom PLC code for events
• Click GO to automatically
• Make implicit specifications explicit
• Compute modular supervisors
• Obtain PLC code for download to controller

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Process
Control engineer
Programmer

• Model templates as FSAs
• Instantiate graphically the templates
• Link graphically the events to synchronize the
  template instances
• Enter custom PLC code for events
• Click GO to automatically
• Make implicit specifications explicit
• Compute modular supervisors
• Obtain PLC code for download to controller

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Example application

• Methodology used to design controllers for a
  robotic testbed at DAS, UFSC

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Benefits of thetemplate design methodology

• Operates in the standard DES framework
• Saves time and testing effort
• Reduces likelihood of errors
• Facilitates integration of expertise
• Focuses on conceptual design
• Supports quick prototyping

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Future work

• Improve user interface
• Focus on fast design prototyping
• Conceptual designs with placeholder components
• Parametrization
• Scaling of templates
• Two-way real-time interaction between DES model
  and PLC

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