1. Coordinated exploration of labyrinthine environments with application to the “pursuit- evasion” problem Leibniz Laboratory Magma team Damien Pellier – Humbert Fiorino {Pellier, Fiorino}@imag.fr

2. 1 Plan  Problems tackled  Principle of surveillance algorithms  A cooperative approach  Discussion and future prospects  Demonstration

3. 1 Problems tackled  « pursuit evasion » problem for mobile robots by a multi robot cooperation approach  Distributed decision  Sharing robots knowledge  Computing motion strategies  Deliberation protocol

4. 1 Principle of surveillance algorithms  Build a motion strategy that guarantees an intruder will be discovered by the pursuers [Suzuki 92]  Constraints on the environment  known [Yamashita 00]  unknown [Rajko 01] 1. Constraints on the robot perception  omnidirectional perception [Lavalle 97]  flash light perception [Simov 01] 1. Limits  complexity  management of robots resources

5. 1 A cooperative approach Principle  Algorithm for one pursuer  Assumptions - the environment is known - the robots have an infinite omnidirectional perception - the intruder can have an infinite speed >> robots speed

6. 1 A cooperative approach Construction of the trajectory  1st step : the critical points must be found (a critical point is an obstacle vertex that has an internal angle < 180°)  2nd step: from the critical vertices list, build the visibility graph of the environment 1 2 3 4 5 4 2 1 3 5

7. 1 A cooperative approach Construction of the trajectory  3td step: the surveillance graph construction gathers all surveillance trajectories in the environment Example from the critical point 1:  4th step: choice of the best motion strategy based upon the Dijkstra algorithm so as to compute the shortest surveillance path 1 2 3 4 5 N: Cleared C: Contaminated

8. 1 Cooperation implementation A cooperative approach Cooperation implementation   Detection of the « delegation points »  Assistance computation  The stuck robot tries to split the environment that can be monitored by independent robots

9. 1 Cooperation implementation A cooperative approach Cooperation implementation  Tasks delegation: the deliberation protocol  A robot can play 4 different roles:  Explorer  Guard  Idle robot  Stuck robot  The robot’s role changes during the exploration  The deliberation protocol is based on « contracts » between the team robots

10. 1 Cooperation implementation A cooperative approach Cooperation implementation   Deliberation protocol

11. 1 A cooperative approach Discussion and future prospects   Number of robots minimization by making them work as a team   Deliberation protocol allows an efficient use of the robots resources  C  Computation distribution  Fault tolerance  Robustness   Limitation of the critical points representation   Adaptation of the deliberation protocol for unknown environments

12. 1 Demonstration