FormationBased MultiRobot Coverage

1
Formation-Based Multi-Robot Coverage

• DeWitt T. Latimer IV, Siddhartha Srinivasa,
  Vincent Lee-Shue, Samuel Sonne, Aaron Hurst,
  Howie Choset
• Carnegie Mellon University

Coverage Determine a path that passes the robot
over all points in a target region
2
Multi-Robot Coverage

• Assumptions
• Unknown space
• Homogenous circular robot
• No marking capability
• Common coordinate frame

• Goals
• Complete coverage of space
• Coordinated, yet decentralized, among multiple
  robots
• Minimize repeat coverage

3
Final (current) Demonstration
4
Cell Decomposition and Critical Point Sensing
At a critical point x,
5
Sensor-based Complete Coverage
Goal Complete coverage of an unknown
environment Cell decomposition Incremental
construction
Time-exposure photo of a coverage experiment
6
Cover Interior of Cell (one corridor at a time)

• Two motions
• Lapping
• Wall follow

Wall follow
Lap
7
Characterize Critical Points
8
Critical Point Sensing
Look for parallel vectors during forward wall
following, but after a reverse wall follow,
lap, and then the forward
Look for anti-parallel vectors during reverse
wall following
Look for parallel vectors during forward wall
following
Look for parallel vectors during reverse wall
following
9
Action at Critical Points
Team divides into two separate teams, each
covering a new cell
VIRTUAL FRONTIER (Butler)
Team finishes cell and then looks for a new cell
to cover
10
Virtual Frontier
As an attempt to minimize repeat coverage, we
use the virtual frontier believing that another
team will be coming from the other cell
associated with the forward critical point
11
Team Rejoining (work in progress)

• Types of encounters
• Two teams covering in opposite slice directions
• Both teams finish the current corridor
• Two teams covering in same slice direction
• Both teams finish the current corridor
• One team covering and the other traversing
• Since robots only traverse through known space,
  the covering team stops covering and joins
  traversing team
• Two teams encountering each other on the border
  of two cells (very hard case)
• Combine adjacency graphs

12
Example
13
Acknowledgements

• Dave Conner
• Ercan Acar
• Tucker Balch
• Matt Mason and Mike Erdmann

14
Distributed Localization and Mapping
15
Challenges

• Guaranteeing completeness
• Single robot Hert Lumelsky, Choset Acar, Cao
• Multi-robot Butler, Hollis, and Rizzi
• Minimize repeat coverage
• Planning in a multi-dimensional configuration
  space
• Balch and Arkin, each robot acts independently
• Retract methods, Yap, Choset and Burdick, Rao,
  Kuipers, etc. etc.
• Space not known a priori
• Single robot Hert Lumelsky, Choset Acar, Cao
• Multi-robot Butler, Hollis, and Rizzi
• Scalability

16
Why do the robots jerk back and forth during wall
following?Encountering All Critical Points

• Conventional back and forth motions are not
  sufficient
• (Cao et al.88, Hert et al.97, Lumelsky et
  al.90)

17
Incremental Complete Coverage

• NOT Occupancy Grid Less memory, More meaningful,
  Minimize turns, Completeness