Reactive Systems Design 159'734

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Reactive Systems Design 159.734

• 01257358
• H Dayal S Ranadewa

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The Components of Reactive Architecture

• Behaviours and Mechanism for merging the output
  of the concurrent behaviours.
• Many applications have a series of behaviours
  operating in a sequence.
• Ex Picking up and disposing an empty soft drink
  can.
• Behaviours include search for a can, move toward
  the can, pick up the can, search for the recycle
  bin, move toward the bin, drop the can.

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Behaviours as Objects in OOP
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Primitive Move-To-Goal Behaviour

• Ex Pick up the Trash
• Robot must move to the Red Coke Can and pick it
  up and then move to the Blue Bin and drop it
• Single generic behaviour would be move-to goal
  (colour)
• move-to-goal (goal-colour)

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Where do releasers go in OOP?

• Perception serves two purposes
• 1) To Release a behaviour
• 2) Guide the behaviour
• The Releaser it self is a perceptual schema
  and can execute independently and is not bound to
  a motor schema
• It is common to have the releaser be part
  of the behaviour. This requires a Coordinated
  Control Program. Although the behaviour is always
  active if the releaser is not satisfied the
  coordinated control program short circuits
  processing.

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Design Methodology
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Case Study Unmanned Vehicle to Autonomously
Navigate around an outdoor course of white lines
painted on grass

• Step 1 Describe the Task
• Robot must follow a path with turns,
  obstacles and a sand pit.
• Step 2 Describe the Robot
• Determine the basic physical abilities of
  the robot and limitations and consider the fixed
  constraints.
• Step 3 Describe the Environment
• This step is a key factor in determining the
  situatedness of the robot and identifies the
  perceptual opportunities for the behaviours

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Case Study Unmanned Vehicle to Autonomously
Navigate around an outdoor course of white lines
painted on grass

• Step 4 Describe how the robot should act in
  response to its environment
• Identify one or more behaviours. Identify
  what the Robot should do?
• Ex follow_line behaviour
• Perceptual Schema Use the white lines to
  compute the centroid.
• Motor Schema Convert the percept to a
  command to steer the motor.
  
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  Behaviour Table

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Case Study Unmanned Vehicle to Autonomously
Navigate around an outdoor course of white lines
painted on grass

• Step 5 Refine each behaviour
• Concentrate on the design of each individual
  behaviour
• Step 6 Test each behaviour independently
• The only way to verify the perceptual schema
  is to try in the real world.

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Case Study Unmanned Vehicle to Autonomously
Navigate around an outdoor course of white lines
painted on grass

• Step 7 Test with other behaviours
• Perform integration testing with the
  behaviours combined in the actual environment
• Ex follow_line did not work well with visual
  distractions! In the presence of distractions the
  robot needed to ignore vision and deploy
  move_ahead. Use the sonar as a releaser for
  move_ahead. Sonar releaser for move_ahead
  inhibited the follow_line and the lack of a sonar
  releaser inhibited move_ahead.
• New Behaviour Table

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Representing a Sequence of Behaviours

• 1 Finite State Automata
• Provides a set of popular mechanisms for
  specifying what
• a program should be doing at a given time.
  FSA can be
• written as a table or a state diagram.
• 2 Scripts
• Abstract behaviours often use scripts or
  related construct called skills to provide a
  different way of generating logic for a seqence
  of behaviours. Encourages the designer to think
  of the robot ad task in terms of a screenplay.
• 3 Skills
• Skills collect behaviour like primitives
  called Reaction-Action-Packages (RAPs) into a
  sketchy plan which is filled in as the robot
  executes.

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Finite State Automata

• States
• current state q element of set of states K
• Initial State
• s or q0, starting state
• Transition Function
• ? a function that specifies the next state when
  the stimulus ? is encountered. ? is the set of
  stimuli
• Final State the terminating states (F)

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FSA example
Range far
Time remaining
Time elapsed
Move ahead
Follow line
Range near
MK Follow line, Move ahead, ? Range
near, Range far, Time remaining, Time elapsed s
Follow line, F Follow line, Move ahead
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FSA example for Pick Up the Trash Behaviour
Table
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Contd. FSA example for Pick Up the Trash
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FSA for picking up and recycling Coke Cans
State Transitions
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Scripts

• Abstract Behaviours use scripts/skills to create
  a generic template.
• Scripts encourage the designer to think of the
  robot and the tasks.
• The use of scripts in robots can be thought of as
  a screenplay where the actors are robots reading
  the scripts.
• Scripts allow improvisation and when an
  exception is encountered the robot will follow
  the subscript.

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Robot Script of Pick Up the Trash
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Scripts

• Skills
• sets of behaviours
• Props, Cues
• percepts, sensor inputs
• Sub-script
• exception handling
• Causal Chain
• Sequence of behaviours
• Focussing of attention

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Summary

• Reactive implementation consists of one or more
  behaviours and a mechanism for combining the
  output of concurrent behaviour.
• Designer must develop individual behaviours and
  assemble them into a sequence or abstract
  behaviour
• Finite State Automata offer a method of
  representing the coordination logic needed to
  control a sequence of behaviours
• Scripts are an equivalent with a more natural
  story like flow of control.
• A Behaviour Table represents the releasers, motor
  perceptual schemas for each behaviour.
• Must fully specify the ecological niche of the
  robot in order to design useful behaviours.
• The control should rely on the world to inform
  the robot as to what to do next rather than rely
  on the program to remember and maintain state.