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3D Multi-Robot Patrolling with a Two-Level Coordination 
Strategy


Teams of robots patrolling harsh and complex environments can experience interference and spatial conflicts one another, which crucially affect their activity. Neglecting the occurrence of these events hinders both soundness and reliability of a patrolling process. In this work, we present a distributed multi-robot patrolling technique, which uses a two-level coordination strategy that minimizes and explicitly manages the occurrence of conflict and interference. The first level guides the agents to single out exclusive target nodes on a topological map. This selection relies on a shared heuristic criterion and a coordination mechanism preventing topological conflicts. The second level hosts strategies based on a metric representation of space and it is supported by a laser-based SLAM system. Here, each robot path planner negotiates spatial conflicts by applying a multi-robot traversability function. Continuous interactions between these two levels ensure coordination and conflict resolution. The presented method is fully distributed and inherently fault-tolerant. Both simulations and experiments presented validate the good performances of the proposed patrolling two-level coordination strategy, showing that it is a promising solution for spatial conflicts.


  



Documents 

Luigi Freda · Mario Gianni · Fiora Pirri
Abel Gawel · Renaud Dubé · Roland Siegwart · Cesar Cadena
"3D Multi-Robot Patrolling with a Two-Level Coordination Strategy - Simulations and Experiments"   
submitted to Autonomous Robots Journal



Simulations 

The following simulations are realized within V-REP. The environment is represented by using a point cloud map. The built map is segmented in traversable regions (green) and obstacle regions (red).


Path planning with multi-robot traversability 
The following two simulations show how our path planner succeeds in managing metric conflicts by using the multi-robot traversability. Each robot moves back and forth between its two assigned waypoints. Planned paths are emanated from each robot.
  • path planning and multi-robot traversability with 2 robots - video
  • path planning and multi-robot traversability with 3 robots - video

Patrolling 
The following simulations show our full patrolling strategy with a team of robots. Here, the CC (Coordination Plus Cooperation) strategy is used in order to guide the robot team. Each node of the patrolling graph is represented by a disc whose radius is proportional to the node idleness.
  • 3 robots in the small-crossroad scenario - video 
  • 4 robots in the crossroad scenario - video 
  • 4 robots in the corridor scenario  - video 
  • 4 robots in the fork scenario - video 
  • 4 robots in the multi-floor ramp scenario - video 
  • 4 robots in the two-floor ring scenario - video 
N.B.video speed can be increased by using the media player interface


Experiments

In the following experiments, the environment is represented by using a point cloud map. The built map is segmented in traversable regions (green) and obstacle regions (red). Each node of the patrolling graph is represented by a disc whose radius is proportional to the node idleness. Planned paths are emanated from each robot.


The following patrolling experiments aim at showing the applicability and portability of the developed software in the real world. The CC (Coordination Plus Cooperation) strategy was tested on the TRADR robots.
  • exp1: 2 robots in DIAG corridor with CC strategy - video (2X speed)
  • exp2: 2 robots in DIAG corridor: this experiment highlights the dynamic mapping capability of our system - video (2X speed)
  • exp3: 2 robots in DIAG court with CC strategy - video (2X speed)
Experiments with 3 UGVs:
  • exp4: 3 robots in DIAG corridor (big graph) with CC strategy - video (2X speed)
  • exp5: 3 robots in DIAG ramp with CC strategy - video (2X speed)
N.B.
 video speed can be further increased on the media player interface
 in the above videos, the visualized data in RVIZ may sometimes appear delayed: this is due to the transfer and visualization of the point cloud maps on the central user interface; the use of such a GUI is an option and is not necessary to the patrolling system

     




TRADR EU Project

On March 8th, we successfully showed two robots patrolling in a rescue scenario during the third year review of the TRADR EU Project. The review was held in Montelibretti at the "Scuola di Formazione Operativa di Montelibretti" of Vigili del Fuoco (the Italian Firefighters).
 

Here you are some video shots of the demo:
  • two robots patrolling in the gallery - video
  • patrolling around a wrecked car - video
  • patrolling in the dark - video






Authors

Luigi Freda · Mario Gianni · Fiora Pirri   (Alcor Lab - University of Rome "La Sapienza")
Abel Gawel · Renaud Dubé · Roland Siegwart · Cesar Cadena  (ASL ETHZ)


Credits 

We would like to thank Indro Spinelli for his great help in performing patrolling experiments with the robots. 




website maintained by Luigi Freda
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