Enhancing Robot Team Performance Through Collaboration and Coordination

1. Multi-Robot Collaboration and Coordination Han Xu, Fall 2002 CS8803L, Georgia Tech

2. Contents • “Protocols for Collaboration, Coordination and Dynamic Role Assignment in a Robot Team” -- Emery, Sikorski and Balch, ICRA-2002 • “Coordination of Heterogeneous Robots for Large-Scale Assembly” -- Hershberger, et al, Textbook chapter 13 CS8803L Fall 2002

3. Part One • “Protocols for Collaboration, Coordination and Dynamic Role Assignment in a Robot Team” -- Emery, Sikorski and Balch, ICRA-2002 • Main idea: use collaboration and coordination to improve team performance CS8803L Fall 2002

4. Introduction • Robotic Soccer • RoboCup • CMU Hammerheads 2001 Team • Collaboration and Coordination • Definition and differences • Application in robotic soccer • Related work • other teams: CS Freiburg 2000, ART 2000, RMIT United 2000, Italian Golem. CS8803L Fall 2002

5. Research Platform • Digital camera • Wireless Ethernet communication • Control systems on laptop • Using Clay Java library • Behavior-based control • Message-based approach • Commercially available hardware (cye) CS8803L Fall 2002

6. Individual Behaviors • Four players, four roles • Goalie, halfback, floater and forward • Common behaviors: • Search and track ball • Ball acquiring • Return to homebase • Different behaviors: • After obtaining ball • Moving Speed CS8803L Fall 2002

7. Collaborative Behaviors • Teammate avoidance • Linear repulsion • Swirl motor-schema • Homebase selection • Minimize interference • Take advantage of game rules CS8803L Fall 2002

8. Coordination strategies (I) • Hierarchical Teammate Avoidance • Give precedence to defensive robots • Dynamically adjustment • Ball claiming • High-ranked player has priority to claim • Have-ball robot should be avoided • Support the have-ball robot CS8803L Fall 2002

9. Coordination strategies (II) • Teammate Support • Goalie support (goalie messages) • Offensive support (have-ball messages) • See a short video Offensive support CS8803L Fall 2002

10. Dynamic Role Assignment (I) • Motivation • High-level role swap protocol • Inspired by multi-threaded programming • Process: • LOCK • ACKLOCK • SWAP • ACKSWAP • Sequence identifier CS8803L Fall 2002

11. Dynamic Role Assignment (II) • Flow charts: • Right: Initiator • Left: Receiver • Implementation • TeamBots • Case-based reasoning • Assignment roll-back • Further refinement CS8803L Fall 2002

12. Limitations • Dependence on communications • Quality of localization • Solution: visual detection (coloring) CS8803L Fall 2002

13. Conclusions • Robotic soccer team needs collaboration and coordination. • 3 key points with benefits: • Hierarchical teammate avoidance • Teammate support • Dynamic role assignment • Comments. CS8803L Fall 2002

14. Part Two • “Coordination of Heterogeneous Robots for Large-Scale Assembly” -- Hershberger, et al, Textbook chapter 13 • Main idea: Utilize heterogeneous nature of robots in coordination, and achieve the goal. CS8803L Fall 2002

15. Motivation • Sometimes multi-robots are required (why) • Sometimes explicit coordination is required (why) • Application: Large-scale assembly • Research focus: distributed coordination between heterogeneous robots • Related approaches CS8803L Fall 2002

16. Layered Architecture • 3 layers in each robot control system • Interactions between layers and peers CS8803L Fall 2002

17. Testbed • Mission: Emplace an 8-foot beam to a fixed point • Crane -- Robocrane • Mobile manipulator – Bullwinkle • Roving eye – Xavier (stereo vision) • Communicating using wireless ethernet CS8803L Fall 2002

18. Distributed Coordination (I) • Execute plans by dynamically constructing task trees • Distribute the task tree over robots • Tasks have synchronization temporal constraints • TDL (Task Description Language) • www.cs.cmu.edu/~tdl/ CS8803L Fall 2002

19. Distributed Coordination (II) • Dynamic team forming and role assignment • Choose “foreman” • Choose team members and assign roles • Current implementation: fixed roles • Foreman leads and monitors the procedure CS8803L Fall 2002

20. Distributed Visual Servoing (I) • Runs as a set of distributed behaviors • Roving eye robot tracking the fiducials • Sending messages out CS8803L Fall 2002

21. Distributed Visual Servoing (II) • Relative localization • The control procedure: • Feedback for crane’s motion • Indicate when “close enough” • Servo the arm to grasp the beam • Servo the arm to dock the beam • Coordinative distributed behaviors CS8803L Fall 2002

22. Roving Eye Motion • Panning to keep the fiducials centered • Forward/backward to keep closed • Lateral motion • To face directly CS8803L Fall 2002

23. Conclusions & Assessment • Mission accomplished • Accurate visual feedback is key • Mobile manipulator is essential • 46% success without manipulator • 90% success with it, 100% after retry • Let’s see a short movie • Comments CS8803L Fall 2002

24. Questions ? CS8803L Fall 2002