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Autonomous Multi-Robot Exploration inCommunication-Limited Environments

Stephen Cameron, Julian de Hoog and Arnoud Visser

University of Oxford

University of Amsterdam

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Mobile Robots Today

• reconnaissance, surveillance

• mapping, exploration

• search and rescue

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• using the

RoboCup Rescue scenario asinspiration

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Typical Challenges

• Engineering

• Localisation and Mapping

• Team Coordination

•Communication

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The Exploration Problem

• Team of robots exploring unknown environment

• Assume reasonable SLAM (particle filters / scan matching)

• Central base station

• Possibly communication drop-out or failure

• How to:

• explore as quickly as possible

• relay as often and as efficiently as possible

• currently assuming paths are easily found and stay found!

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Existing Approaches

• Line of sight

• Frontiers / Utilities

• Robot packs

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- information gain- path cost- communication likelihood

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Role-based Exploration

Relays Explorers

Ferry information back andforth between teammates

Explore far reachesof the environment

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Hierarchy

• control commands

• new information

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Both centralisedand distributed

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Demo

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Where to Rendezvous? 

• open space

•  junctions

• large comm range

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Path Edges and Nodes

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More Examples

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Dynamic Environments

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A problem

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Swap roles?

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Another Common Scenario:

Loops

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The “Role Swap” Rule

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• Two robots, A and B

• A wants to go to DA, B to DB

• Let  γ(u,v) be path cost from u to v

• If  max{ γ(A,DA), γ(B,DB)} > max{ γ(A,DB), γ(B,DA)}...

• ... then let A and B swap(role, state, location in hierarchy, everything)

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The “Role Swap” Rule

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Demo

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Which is better?

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Opportunistic exploration Dynamic role-based exploration

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Knowledge at BaseStation

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Opportunistic exploration Dynamic role-based exploration

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Control over team

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Opportunistic exploration Dynamic role-based exploration

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Dynamic Role-based Exploration

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• Simple, easy to implement

• Not dependent on communication

• Speed of exploration is equivalent toopportunistic frontier / utility based exploration

• Information is returned to the BaseStation muchfaster and more frequently 

• Greater control over the team

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Another Example(showing hierarchy and role changes)

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The Same Example(showing comm links)

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Dynamic Role-based Exploration

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• Simple, easy to implement

• Not dependent on communication

• Speed of exploration is equivalent toopportunistic frontier / utility based exploration

• Information is returned to the BaseStation muchfaster and more frequently 

• Greater control over the team

• Dynamic adjustment to various environmenttypes

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Realistic?

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Future Work 

•Theoretical Description of the Role SwapRule

• Extensive testing of emergent behaviour

• Additional roles: static relays?

• Testing on real robots / third partysimulation platform

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Credits

• UAV video: microdrone GmbH (http://www.youtube.com/watch?v=Y4jtguSF0n4)

• Mapping robot: Tsubouchi Laboratory, University of Tsukuba

• Search and rescue Kenaf robot: Tadokoro Laboratory, Tohoku University

• Search and rescue robot on rubble: NIST, http://www.nist.gov/public_affairs/techbeat/tb2007_0608.htm

• Rescue robot entry hole: researchchannel.org, http://www.researchchannel.org/

prog/displayevent.aspx?rID=3820

• Thinning example: Danielle Azar, http://cgm.cs.mcgill.ca/~godfried/teaching/projects97/azar/skeleton.html

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