The Reactive Par-adigm

Embedded System Lab Kim Jong Hwi

Chonbuk National University

Introduction to Intelligent Robots

Chonbuk National University

Chapter Objectives

• Define what the reactive paradigm • List the characteristics of a reactive robotic

system• Describe the two dominant methods for com-

bining behaviors in a reactive architecture: subsumption and potential field summation

• Be able to program a behavior using a poten-tial field methodology

• Be able to construct a new potential field form primitive potential fields, and sum potential fields to generate an emergent behavior

Contents

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Reactive Paradigm - Overview Subsumption Architecture Potential Field Methodologies Pros and cons Summary

Reactive Paradigm

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The Reactive Paradigm• emerged in the late 1980’s• grew out of dissatisfaction with the hier-

archical paradigm -summarized by Roney Brooks

Reactive Paradigm

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The Reactive Paradigm• layered in a vertical decomposition• access to sensors and actuators indepen-

dently

Reactive Paradigm

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Attributes of Reactive Paradigm• all actions are accomplished through

behaviors

• motor schema : algorithm for generating the pattern of action in physical actuator

• perceptual schema : algorithm for ex-tracting the percept and its strength

Reactive Paradigm

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S-A organization

Reactive Paradigm

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Behavior-specific sensing orga-nization in the Reactive Para-digm

Reactive Paradigm

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Connotations of reactive behav-iors

• executes rapidly• have no memory

Reactive Paradigm

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5 Characteristics of reactive be-haviors• Robots are situated agents operating in an

ecological niche• Behaviors serve as the basic building

blocks for robotic actions, and the overall behavior of the robot is emergent

• Only local, behavior-specific sensing is permitted

• These systems inherently follow good software design principle

• Animal models of behavior are often cited as a basis for these systems or a particu-lar behavior

Reactive Paradigm

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Representative architectures

• Subsumption – how behaviors are com-bined

• Potential Field Methodologies – require behaviors to be implemented as potential fields and the behaviors are combined by summation of the fields

• Rule encoding, fuzzy methods, winner-take-all voting …

Subsumption Architecture

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Subsumption architecture Rodney Brooks’s architecture the most influential of the purely Reactive Paradigm

systems

Subsumption Architecture

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Subsumption architecture

• Modules are grouped into layers of com-petence

(low layer ~ high layer)• Modules in a higher layer can override, or

subsume, the output from behaviors in the next lower layer

• The use of internal state is avoided• A task is accomplished by activating the

appropriate layer

Subsumption Architecture

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Example

Subsumption Architecture

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Level 0 recast as primitive behav-iors

Subsumption Architecture

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Level 1 : wander

Subsumption Architecture

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Level 1 recast as primitive behav-iors

Subsumption Architecture

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Level 2 : follow corridors

Potential Fields Methodologies

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Potential Field• force field on the surrounding space

exerted from perceivable objects Vector

– Magnitude; real number between 0.0 and 1– Direction

Potential Fields Methodologies

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Potential Field

Potential Fields Methodologies

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Potential Field

Potential Fields Methodologies

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Programming a single potential Field

Potential Fields Methodologies

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Programming a single potential Field

Potential Fields Methodologies

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Programming a single potential Field

Potential Fields Methodologies

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Programming a single potential Field

Potential Fields Methodologies

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Programming a single potential Field

Potential Fields Methodologies

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Programming a single potential Field

Potential Fields Methodologies

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Programming a single potential Field

Potential Fields Methodologies

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Programming a single potential Field

Potential Fields Methodologies

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Programming a single potential Field

Pros and cons

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Advantages and disadvantages• Advantages

– easy to visualize over a large region of space– easier for the designer to visualize the robot’s overall

behavior– easy to combine fields, and languages such as C++– well works behaviors developed for 2D in 3D inviro-

ment• Disadvantages

– Local minima (vector with 0 magnitude)» producing vectors with a small magnitude

from random noise» NaTs (navigation templates)

Summary

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Summary• subsumption and potential fields

appear to be largely equivalent in practice

• The ease of portability to other domains is relative to the complexity of the changes in the task and enviroment

• Neither style of architecture explicitly addresses robustness

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Thank you for listening!