CS 415 – A.I.

Slide Set 10

Controlling Multiple Robots• Different considerations for multiple robots– Inherently dynamic environment–Complex local and global interaction– Increased (Compounded) Uncertainty• My uncertainty about myself• My uncertainty about you• Your uncertainty about yourself

–Need for Coordination• identity, intention, communication, plans• Working as a “team”

–Need for Communication

Team Work

• Coordination – arranging things in some kind of order

• Cooperation – joint actions with a mutual benefit

• Large area of active research– group robotics– social robotics– team robotics– swarm robotics–multi-robot systems

Benefits of Teamwork

• Some Tasks Require 2+ Robots–Transporting objects• Construction/building• Clearing barriers (disaster relief)• Moving wounded people

• Some Tasks are Better with 2+–Cheaper, faster, more efficient• Foraging

– land mines, crops, laying cables

• Surveillance• Mapping?

Benefits of Teamwork

• Robustness and Redundancy–Robustness – ability to resist failure–Redundancy – replication of abilities on the team• Not all teams are redundant

– Some teams are made up of specialist robots– Not very robust then

Challenges of Teamwork

• Interference → enemy number 1–The more robots, the worse it is• Physical Interference

1 robot undoes the work of another

• Communication Interference Uncertainty

The more robots, the worse it is Compounding Expenses

Always costlier for more hardware Always more to break down/not work

Types of Teams

• How program a team of robots to play soccer?–Everyone tries to get the ball and score• Is this a good idea?

– Instead Division of Labor

• Homogenous Teams–Pros? Cons?

• Heterogenous Teams– require active cooperation to get coordinated

behaviour

Types of Teams

• Merely coexisting–Multiple robot with shared task–No communications or maybe even recognize one

another–Treat each other as obstacles

• Loosely coupled–Recognize one another / simple coord.–Don't depend on one another• Members of groups can be removed• Precise tasks are hard to complete

Types of Teams

• Tightly Coupled– Focus on a precise task• Use communication, turn-taking, etc.

–Removing robots hurts performance

Communication

• Many times members of a team need to communicate information to each other– Improve perception– Synchronize actions– Enabling coord. and negotiation

• What get communicated– Task-related states– Individual states– Environment states– Goal(s)– Intentions

The How of Communication

• Explicit Comm. → send a preformed message–Broadcast Comm.–P2P Comm.

• Publish-subscribe Comm.–Player/Stage

• Inherent cost to explicit comm.

The How of Communication

• Implicit Comm. → individual leaves info. In the environment– Stigmergy – comm. through intentionally changing

the environment• Ant trails• Positive feedback → the stronger the “change” (i.e.

pheromones) the more it happens

Kin Recognition

• Kin recognition – recognizing members of my team in a dynamic multi-faceted environment

• Kin recognition is no simpler than object recognition–Already know object recognition is hard

• Dominance Hierarchy–Who's in charge–How do you identify that robot?

Team Control

• Centralized Control– “I'm the boss”• The boss doesn't even necessarily have to be a robot →

not exactly autonomous control then

–Cons? Pros?

• Distributed Control–No central store of information– Immanently scalable (add robots)–Hard to plan for this kind of control

The Next Assignment

• Groups (again, 2-3 people)• Team Robotics Project–Do you use a map?–What kind of team organization?• Anything but merely coexisting will be fine

–What kind of control• Totally up to you