behavior-based control - georgia institute of technology · behavior-based control frank dellaert...
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Behavior-Based Control
Frank DellaertMost slides adapted from Tucker Balch or Robin Murphy’s publiclyavailable slides (http://www.cse.usf.edu/~murphy/book/)
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Timeline of Influences
1980 19901970
Braitenberg’sVehicles
Arbib’sSchemas
Tinbergen &Lorenz & von Frisch
Marr’s ComputationalTheory
J.J. Gibson
Neisser
Middlestat
Arkin’s Schemas
Brook’s Insects
Payton
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Behavior Definition (graphical)
BEHAVIOR
SensoryInput
Patternof MotorActions
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Types of Behaviors
• Reflexive– stimulus-response, often abbreviated S-R
• Reactive– learned or “muscle memory”
• Conscious– deliberately stringing together
WARNING Overloaded terms:Roboticists often use “reactive behavior” to mean purely reflexive,
And refer to reactive behaviors as “skills”
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Ethology: Coordination and Controlof Behaviors
Nobel 1973 inphysiology ormedicine•von Frisch•Lorenz•Tinbergen www.nobel.se
INNATE RELEASING MECHANISMS
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Arctic Terns• Arctic terns live in Arctic (black, white, gray
environment, some grass) but adults have a redspot on beak
• When hungry, baby pecks at parent’s beak, whoregurgitates food for baby to eat
• How does it know its parent?– It doesn’t, it just goes for the largest red spot in its field of
view (e.g., ethology grad student with construction paper)– Only red thing should be an adult tern– Closer = large red
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Example: Cockroach Hide• light goes on, the cockroach turns and runs
• when it gets to a wall, it follows it
• when it finds a hiding place (thigmotrophic),goes in and faces outward
• waits until not scared, then comes out
• even if the lights are turned back off earlier
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Gibson’s Ecological Approach• Acting and sensing co-evolved as agent survived in a
particular environment. The environment affords theagent what it needs to survive.
• The perception needed to release or guide the “rightaction” is directly in the environment, not inferred ormemorized– Ex. Red on Artic Terns== food– Ex. Sound of filling container==full
• Percepts are called affordances or said to be obtainedthrough direct perception
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Gibsonian Affordances• How do you know you’re going fast in a car? Or in a
space movie?
• How do animals know when to mate?
• How do mosquitoes know to bite in the most tenderareas?
• What should you do when you think you’re being stalkedby a mountain lion?
• What’s your favorite fishing lure?
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Motor Schemas
• Multiple independent processes each generate avector combined by weighted summation
• Computationally simple and fast• Enables design by composition. Related to
artificial potential fields– Khatib, Krogh, Payton, Singh
Behavior-Based Architectures: Motor Schemas
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Definition 1: Reactive
“A reactive robotic system tightly couplesperception to action without the use ofintervening abstract representations or timehistory.” --Ron Arkin
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Definitions: Behavior-Based
A behavior-based robotic system generallyrelies on a tight stimulus-response framework,but may utilize minimal state information aswell. --Tucker Balch
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Example 1: Robomow
• Behaviors?• Random• Avoid
– Avoid(bump=obstacle)– Avoid(wire=boundary)
• Stop– Stop(tilt=ON)
• All active
www.friendlymachines.com
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Example 2: My Real Baby• Behaviors?• Touch-> Awake• Upside down & Awake-> Cry• Awake & Hungry -> Cry• Awake & Lonely -> Cry
• Note can get crying from multiple behaviors• Note internal state (countdown timer on Lonely)
www.irobot.com
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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
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Influential Architectures
• Subsumption -- Brooks, 1986• Motor schemas -- Arkin, 1987• Distributed Architecture for Mobile Navigation
(DAMN) -- Rosenblatt, 1989• Colony Architecture -- Connell, 1989• Reactive Action Packages (RAPs) -- Firby, 1989
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Subsumption:Rodney Brooks
From http://www.spe.sony.com/classics/fastcheap/index.html
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Subsumption Philosophy• Modules should be grouped into layers
of competence
• Modules in a higher lever can overrideor subsume behaviors in the nextlower level– Suppression: substitute input going to a
module– Inhibit: turn off output from a module
• No internal state in the sense of alocal, persistent representation similarto a world model.
• Architecture should be taskable:accomplished by a higher level turningon/off lower layers
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Level 0: Runaway
HALT
COLLIDE
PS MS
RUN AWAYPS MS
runaway 0wander 1
follow-corridor 2
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Example Perception: Polar Plot
• 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”)
if sensing is ego-centric, canoften eliminate need formemory, representation
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Level 1: Wander runaway 0wander 1
follow-corridor 2
encoders
AVOID
PS
MSWANDER
PS MS
Note sharing ofPerception, fusion
What wouldInhibition do?
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Moving to Light
runaway 0wander 1
move2light 2
LIGHT PHOTO-TROPHISM
S
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Follow-Corridors runaway 0wander 1
follow-corridor 2
STAY-IN-MIDDLEPS MS
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Potential Fields:Ron Arkin
From http://www.cc.gatech.edu/aimosaic/faculty/arkin
From http://www.cc.gatech.edu/aimosaic/robot-lab/MRLhome.html
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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 pointin space represents the vector that it would feel if it wereat that point
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Primitive: Move to GoalBehavior-Based Architectures: Motor Schemas
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Primitive: Avoid Obstacle
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Combining Fields forEmergent Behavior
obstacleobstacle
goal
If robot were dropped anywhere on this grid,it would want to move to goal and avoid obstacle:
Behavior 1: MOVE2GOALBehavior 2: RUNAWAY
The output of each independent behavior is a vector,the 2 vectors is summed to produce emergent behavior
obstacle
goal
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Avoid Obstacle + Move to Goal
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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
Robot only feels vectors for this
point when it (if) reaches that point
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5 Primitive Potential Fields
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Example: follow-corridor orfollow-sidewalk
Perpendicular Uniform
Combined
Note use of Magnitude profiles:Perpendicular decreases
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More Complex Problem: PushingBehavior-Based Architectures: Motor Schemas
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Approach: Specialized SchemasBehavior-Based Architectures: Motor Schemas
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Video: PushingBehavior-Based Architectures: Motor Schemas
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Level 0: Runaway
Note: multiple instances ofa behavior vs. 1:Could just have 1 Instance of RUN AWAY,Which picks nearest reading;Doesn’t matter, but thisAllows addition of anotherSonar without changing theRUN AWAY behavior
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Level 1: WanderWander is
Uniform, but Changes direction
aperiodically
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Level 2: Follow Corridor
Follow-corridorShould weLeaveRun AwayIn? Do weNeed it?
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Potential fields
• 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
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Example: Docking Behavior
•Arkin and Murphy, 1990, Questa,Grossmann, Sandini, 1995, Tse andLuo, 1998, Vandorpe, Xu, VanBrussel, 1995. Roth, Schilling, 1998,Santos-Victor, Sandini, 1997
Orientation, ratio ofpixel counts → tangent vectorTotal count → attraction vector
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Docking Behavior Video
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Docking Behavior Video 2
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Behavior-Based Summary• Reactive Paradigm: SA, sensing is local
– Solves the Open World problem by emulating biology– 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 schemasconceptually
• Potential fields and subsumption are logically equivalentbut different implementations