4 Review Organization SA beh specific Subsumption Philosophy

4 Review Organization -SA -beh. specific Subsumption -Philosophy -Level 0 -Level 1 -Level 2 Summary The Reactive Paradigm • Describe the Reactive Paradigm in terms of the 3 robot primitives and its organization of sensing • List the characteristics of a reactive robotic system, and discuss the connotations of surrounding the reactive paradigm • Describe the two dominant methods for combining behaviors in a reactive architecture: subsumption and potential field summation • Be able to program a behavior using pfields • Be able to construct a new potential field from primitive pfields and sum pfields to generate an emergent behavior Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 1

4 Review Organization -SA -beh. specific Subsumption -Philosophy -Level 0 -Level 1 -Level 2 Summary Review: Lessons from Biology • Programs should decompose complex actions into behaviors. Complexity emerges from concurrent behaviors acting independently • Agents should rely on straightforward activation mechanisms such as IRM • Perception filters sensing and considers only what is relevant to the task (action-oriented perception) • Behaviors are independent but the output may be used in many ways including: combined with others to produce a resultant output or to inhibit others Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 2

4 Hierarchical Organization is “Horizontal” Review Organization -SA -beh. specific Subsumption -Philosophy -Level 0 -Level 1 -Level 2 Summary Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 3

4 More Biological is “Vertical” Review Organization -SA -beh. specific Subsumption -Philosophy -Level 0 -Level 1 -Level 2 Summary Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 4

4 Sensing is Behavior-Specific or Local Review Organization -SA -beh. specific Subsumption -Philosophy -Level 0 -Level 1 -Level 2 Summary Behaviors can “share” perception without knowing it This is behavioral sensor fusion Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 5

4 Reactive Robots RELEASER Overview History Reactive USAR Summary SENSE behavior ACT • Most apps are programmed with this paradigm • Biologically based: – Behaviors (independent processes), released by perceptual or internal events (state) – No world models or long term memory – Highly modular, generic – Overall behavior emerges Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 6

4 Overview History Reactive USAR Summary Example 1: Robomow • Behaviors? • Random • Avoid – Avoid(bump=obstacle) – Avoid(wire=boundary) • Stop – Stop(tilt=ON) • All active Introduction to AI Robotics (MIT Press) www. friendlymachines. com Chapter 4: The Reactive Paradigm 7

4 Overview History Reactive USAR Summary Example 2: My Real Baby • • • Behaviors? Touch-> Awake Upside down & Awake-> Cry Awake & Hungry -> Cry Awake & Lonely -> Cry www. irobot. com • Note can get crying from multiple behaviors • Note internal state (countdown timer on Lonely) Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 8

4 Reactive • Historically, there are two main styles of creating a reactive system – Subsumption architecture • Layers of behavioral competence • How to control relationships – Potential fields • Concurrent behaviors • How to navigate • They are equivalent in power • In practice, see a mixture of both layers and concurrency Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 9

4 Review Organization -SA -beh. specific Subsumption -Philosophy -Level 0 -Level 1 -Level 2 Summary Introduction to AI Robotics (MIT Press) Subsumption: Rodney Brooks From http: //www. spe. sony. com/classics/fastcheap/index. html Chapter 4: The Reactive Paradigm 10

4 Subsumption Philosophy • Review • Organization -SA -beh. specific Subsumption -Philosophy -Level 0 -Level 1 • -Level 2 Summary • Modules should be grouped into layers of competence Modules in a higher lever can override or subsume behaviors in the next lower level – Suppression: substitute input going to a module – Inhibit: turn off output from a module No internal state in the sense of a local, persistent representation similar to a world model. Architecture should be taskable: accomplished by a higher level turning on/off lower layers Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 11

4 Level 0: Runaway follow-corridor 2 wander 1 runaway 0 Review Organization -SA -beh. specific Subsumption -Philosophy -Level 0 -Level 1 -Level 2 Summary RUN AWAY PS MS HALT COLLIDE Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 12

4 Review Organization -SA -beh. specific Subsumption -Philosophy -Level 0 -Level 1 -Level 2 Summary Example Perception: Polar Plot if sensing is ego-centric, can often eliminate need for memory, representation • Plot is ego-centric • Plot is distributed (available to whatever wants to use it) • Although it is a representation in the sense of being a data structure, there is no memory (contains latest information) and no reasoning (2 -3 means a “wall”) Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 13

4 Level 1: Wander follow-corridor 2 wander 1 runaway 0 Review Organization -SA -beh. specific Subsumption -Philosophy -Level 0 -Level 1 -Level 2 Summary WANDER PS MS AVOID MS encoders What would Inhibition do? PS Note sharing of Perception, fusion Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 14

4 Class Exercise move 2 light 2 wander 1 Review Organization -SA -beh. specific Subsumption -Philosophy -Level 0 -Level 1 -Level 2 Summary runaway 0 LIGHT PHOTOTROPHISM Introduction to AI Robotics (MIT Press) S Chapter 4: The Reactive Paradigm 15

4 Level 2: Follow-Corridors STAY-IN-MIDDLE PS follow-corridor 2 wander 1 runaway 0 MS Review Organization -SA -beh. specific Subsumption -Philosophy -Level 0 -Level 1 -Level 2 Summary Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 16

4 Class Exercise • Design the roomba with subsumption Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 17

4 Review Organization -SA -beh. specific Subsumption -Philosophy -Level 0 -Level 1 -Level 2 Summary Subsumption Review • What is the Reactive Paradigm in terms of primitives? • What is the Reactive Paradigm in terms of sensing? • Does the Reactive Paradigm solve the Open World problem? • How does the Reactive Paradigm eliminate the frame problem? • What is the difference between a behavior and a level of competence? • What is the difference between suppression and inhibition in subsumption? Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 18

4 Potential Fields: Ron Arkin From http: //www. cc. gatech. edu/aimosaic/faculty/arkin From http: //www. cc. gatech. edu/aimosaic/robot-lab/MRLhome. html Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 19

4 Potential Fields Philosophy • The motor schema component of a behavior can be expressed with a potential fields methodology – A potential field can be a “primitive” or constructed from primitives which are summed together – The output of behaviors are combined using vector summation • From each behavior, the robot “feels” a vector or force – Magnitude = force, strength of stimulus, or velocity – Direction • But we visualize the “force” as a field, where every point in space represents the vector that it would feel if it were at that point Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 20

4 Example: Run Away via Repulsion Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 21

4 5 Primitive Potential Fields Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 22

4 Draw These Now! Common fields in behaviors • Uniform – Move in a particular direction, corridor following • Repulsion – Runaway (obstacle avoidance) • Attraction – Move to goal • Perpendicular – Corridor following • Tangential – Move through door, docking (in combination with other fields) • random – do you think this is a potential field? what would it look like? Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 23

4 Class Exercise • Name the field you’d use for – Moving towards a light – Avoiding obstacles Attractive Repulsive Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 24

4 Combining Fields for Emergent Behavior goal obstacle If robot were dropped anywhere on this grid, it would want to move to goal and avoid obstacle: Behavior 1: MOVE 2 GOAL Behavior 2: RUNAWAY The output of each independent behavior is a vector, the 2 vectors is summed to produce emergent behavior Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 25

4 Fields and Their Combination Note: inrepulsive this example, robot canforsense the Note: In this example, field only extends 2 meters; from meterswithin away the robot runsgoal away only 10 if obstacle 2 meters Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 26

4 Robot only feels vectors for this point when it (if) reaches that point Path Taken • If robot started at this location, it would take the following path • It would only “feel”the vector for the location, then move accordingly, “feel” the next vector, move, etc. • Pfield visualization allows us to see the vectors at all points, but robot never computes the “field of vectors” just the local vector Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 27

4 Discussion • Could you represent the Arctic Tern feeding behavior with potential fields? – what happens with multiple red dots? – can you inhibit with potential fields? Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 28

4 Example: follow-corridor or follow -sidewalk Note use of Magnitude profiles: Perpendicular decreases Perpendicular Uniform Combined Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 29

4 Class Exercise: Draw Fields for Wall-Following (assume that robot stands still if no wall) Just half of a follow-corridor, but… Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 30

4 But how does the robot see a wall without reasoning or intermediate representations? • Perceptual schema “connects the dots”, returns relative orientation Sonars PS: Find-wall Introduction to AI Robotics (MIT Press) orientation MS: Perp. MS: Uniform Chapter 4: The Reactive Paradigm S 31

4 OK, But why isn’t that a representation of a wall? • It’s not really reasoning that it’s a wall, rather it is reacting to the stimulus which happens to be smoothed (common in neighboring neurons) Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 32

4 Level 0: Runaway Note: multiple instances of a behavior vs. 1: Could just have 1 Instance of RUN AWAY, Which picks nearest reading; Doesn’t matter, but this Allows addition of another Sonar without changing the RUN AWAY behavior Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 33

4 Level 1: Wander is Uniform, but Changes direction aperiodically Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 34

4 Level 2: Follow Corridor Follow-corridor Should we Leave Run Away In? Do we Need it? Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 35

4 Pfields • Advantages – – Easy to visualize Easy to build up software libraries Fields can be parameterized Combination mechanism is fixed, tweaked with gains • Disadvantages – Local minima problem (sum to magnitude=0) • Box canyon problem – Jerky motion Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 36

4 Example: Docking Behavior Orientation, ratio of pixel counts tangent vector Total count attraction vector Introduction to AI Robotics (MIT Press) • Arkin and Murphy, 1990, Questa, Grossmann, Sandini, 1995, Tse and Luo, 1998, Vandorpe, Xu, Van Brussel, 1995. Roth, Schilling, 1998, Chapter 4: The Reactive Paradigm 37 Santos-Victor, Sandini, 1997

4 Docking Behavior Video Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 38

4 Class Discussion: When Does a Field End? • Imagine the case of a “Soda. Pup” robot (MIT) – task: find and pick up a Coca-Cola can – environment: red cans are only red object in world – behavior: ? ? Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 39

4 Pfields Summary • Reactive Paradigm: SA, sensing is local – Solves the Open World problem by emulating biology – Eliminates the frame problem by not using any global or persistent representation – Perception is direct, ego-centric, and distributed • Two architectural styles are: subsumption and pfields • Behaviors in pfield methodologies are a tight coupling of sensing to acting; modules are mapped to schemas conceptually • Potential fields and subsumption are logically equivalent but different implementations • Pfield problems include – local minima (ways around this) – jerky motion – bit of an art Introduction to AI Robotics (MIT Press) Chapter 4: The Reactive Paradigm 40