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Robot Formations Using Only Local Sensing And

Control

Jakob Fredslund, Maja J Mataric {jakobf, maja}@robotics.usc.edu

Interaction Lab, University of Southern California, USA /

Dept. of Computer Science, Aarhus University, Denmark

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Related Work

• Flocking - local info; Mataric ’95

• Simulated formations – global info; Chen, Luh ’94 – local info; Desai, Ostrowski, Kumar

’01• Real robot formations – global info; Balch, Arkin ’98 – local info; Alur et al. ’00

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Goals

• Moving in formation, local info & control• Arbitrary formations• Formation switching• Suitable for real robots (robust wrt. noise)

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Approach

• Detectable, unique IDs• ID broadcast regularly (heartbeat)• The conductor also broadcasts f

Each robot knows: group size, IDs of all robots & the desired formation.

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Approach

• Each robot follows a friend at a certain angle and distance

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Approach

• Each robot follows a friend at a certain angle and distance

• Each robot has only one follower -> chain of friendships, sorted by ID.

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Approach

• Each robot follows a friend at a certain angle and distance

• Each robot has only one follower -> chain of friendships, sorted by ID.

• Median or lowest ID is conductor (centered/non-centered formations)

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Finding The Right Position

By group size, IDs, and f, each robot knows its position in the formation ~ its friend andthe angle to keep to it.

• N = 8, f = diamond:• Self-organization gives heading

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The Friend-Sensor

• Gives friend’s ID, angle, distance• Assume 180 field of view• Can be panned

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Three Levels Of Abstraction

Pan sensor

Center friend in field of view

Avoid collisions

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Implementation of Algorithm

• ID: color-blob detection

• Angle: camera pan• Distance: laser

Friend-sensor: camera + laser scanner

Simulation/real robots (CIRA paper/tech report)

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Collision Avoidance

• Buffered bounding-box obstacle detection

• If robot in front: long ahead-buffer

Real robot data, units are meters

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Pan Camera, Center Friend

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Experimental Evaluation

Formal evaluation criteria:

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Properties Tested

• Stability of established formations

• Robustness to failure of group members

• Switching between any two formations

• Obstacle Avoidance ~ maintain or re-establish formation

Evaluation criteria used in all experiments –

results in paper.

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Stability

Line Diamond

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Robustness (1)

Principle: Incomplete 6-diamond to complete 4-diamond.

Simulation:hexagon to pentagon.

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Robustness (2)

Real robots:

4-wedge,

3-wedge,

4-wedge.

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Switching

Real robots:

Diamond to line.

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Obstacle Avoidance

Real robots: two robots maintain a line while negotiating an obstacle.

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Conclusions• Global formations from local

information + minimal communication

• Formation guarantee (by ID)• Layered algorithm -> simple rules,

same for all friendship angles

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More Information

Simulator, robot interface:http://robotics.usc.edu/player

More videos & papers:http://robotics.usc.edu/~agents/projects/formations.html

Thanks to Richard Vaughan, Andrew Howard, Brian Gerkey, Boyoon Jung, Esben Østergaard, & everyone in the Robotics

Labs at University of Southern California, Los Angeles.