1/22 robot formations using only local sensing and control jakob fredslund, maja j mataric {jakobf,...
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1/22
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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2/22
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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3/22
Goals
• Moving in formation, local info & control• Arbitrary formations• Formation switching• Suitable for real robots (robust wrt. noise)
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4/22
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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5/22
Approach
• Each robot follows a friend at a certain angle and distance
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6/22
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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7/22
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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8/22
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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9/22
The Friend-Sensor
• Gives friend’s ID, angle, distance• Assume 180 field of view• Can be panned
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10/22
Three Levels Of Abstraction
Pan sensor
Center friend in field of view
Avoid collisions
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11/22
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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12/22
Collision Avoidance
• Buffered bounding-box obstacle detection
• If robot in front: long ahead-buffer
Real robot data, units are meters
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13/22
Pan Camera, Center Friend
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14/22
Experimental Evaluation
Formal evaluation criteria:
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15/22
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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16/22
Stability
Line Diamond
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17/22
Robustness (1)
Principle: Incomplete 6-diamond to complete 4-diamond.
Simulation:hexagon to pentagon.
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18/22
Robustness (2)
Real robots:
4-wedge,
3-wedge,
4-wedge.
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19/22
Switching
Real robots:
Diamond to line.
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20/22
Obstacle Avoidance
Real robots: two robots maintain a line while negotiating an obstacle.
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21/22
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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22/22
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.