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Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 1
5 Designing a Reactive Implementation
• List the steps involved in designing a reactive behavioral system.
• Use schema theory to program behaviors using object-oriented programming principles.
• Design a complete behavioral system, including coordinating and controlling multiple concurrent behaviors.
• Describe the two methods for assembling primitive behaviors into abstract behaviors: finite state machines and scripts.
Design-Beh. Table-StepsCase StudyCoordination-FSA-ScriptsSummary
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 2
5 Steps in Designing a Reactive Behavioral System
Describe the task
Describe the robot
Describe the environment
Specification& Analysis:ecologicalniche
Implement & refine each behavior
Test each behavior independently
Implementation& unit testing
Test behaviors together SystemTesting
Describe how the robot should act in response to its environment
Design
Design-Beh. Table-StepsCase StudyCoordination-FSA-ScriptsSummary
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 3
5 CSM 1994 UGV Competition
• Fully autonomous vehicle, all on-board, navigate a course 10ft wide, about 800ft long
• Obstacles
• Carry a 20 pound payload
(this is from1996, but it’sa way betterpicture)
Design-Beh. Table-StepsCase StudyCoordination-FSA-ScriptsSummary
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 4
5 1-3. Describe the Task, Robot, Environment
• Have to use computer vision… black &white, slow processor speeds (didn’t get to design the robot)
– White (bright) should be in the center of the image– Reflections on grass are white, but random so average out
• If stay in middle, never encounter an obstacle!• 150ms update rate needed for steering to stay in control at ~1.5mph
Camcorder on aPanning mast, going toA framegrabber
Sonar on a panningmast
33MHz 486 PC runningLynx (commercial unix)Design
-Beh. Table-StepsCase StudyCoordination-FSA-ScriptsSummary
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 5
5 4. Describe how robot should act
• Follow the line and stay in the middle– Follow-line
– Only need the Camcorder!Design-Beh. Table-StepsCase StudyCoordination-FSA-ScriptsSummary
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 6
5 5-6 Refine and test each behavior
• Follow-line– Worked with toilet paper (indoors),
– Worked with athletic line tape (outdoor)Design-Beh. Table-StepsCase StudyCoordination-FSA-ScriptsSummary
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 7
5 7 Test with other behaviors
• “Full dress rehearsal”– Oops, bales of hay are bright compared to grass, change the
centroid to cause collision
• Go back to step 4:– Follow line until “see” an obstacle, then just go straight until
things return to normal• Hard to do visually in real time
• Sonar! Look to the side and when something is close, it’s a bale, so go straight
Design-Beh. Table-StepsCase StudyCoordination-FSA-ScriptsSummary
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 8
5 Final System• Round 1
– OOPS: sonar connection off so it hit the bale
• Round 2– White shoes and
dandelions, plus Killer Bale
• Demo round– Hill vs. implicit flat earth
assumption
• Round 3– Trapped by sand, but
$5K richer!
Design-Beh. Table-StepsCase StudyCoordination-FSA-ScriptsSummary
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 9
5 Main Points
• Let the WORLD BE ITS OWN BEST REPRESENTATION and CONTROL STRUCTURE– “line” wasn’t a “line” just centroid of brightest pixels in the
image
– Pick up trash: if can is in gripper, then go to the recycle bin
• Design process was iterative; rarely get a workable emergent behavior on the first try
• There is no single right answer
• Could have been done with subsumption, pfields, rules, whatever
Design-Beh. Table-StepsCase StudyCoordination-FSA-ScriptsSummary
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 10
5 Other Lessons Learned
• Don’t count on getting much work done in the field!
“A river runs through it…”
Design-Beh. Table-StepsCase StudyCoordination-FSA-ScriptsSummary
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 11
5 Case Study and Field Trip:Polar Robotics
• Existing robots– DANTE, DANTE II
– Nomad
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 12
5 DANTE• Task
– explore volcanoes in Antarctica (reduce risk to vulcanologists)
• Environment– steep, rocky slopes
• Robot– legged “framewalker”
• Behaviors– rappel down
• Refine and test
• Test with other behaviors– 1997 South America, failed
– 1998 Antarctica, med. success
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 13
5 Lessons to Be Learned
• A robot is part of a system, must design system– example tether breaking
• Testing and evaluation really does take ~30% of the time allocated (just like software engineering)– and more to fix the problem
• NASA technical readiness levels– Level 1: just an idea
– Level 6: demonstrated on a realistic test bed
– Level 9: has flown, fully operational
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 14
5 Nomad• Task
– search for and analyze meteorities
• Environment– Antarctica
• Robot– hybrid mobility, LADAR,
omnivision, sample sensors
• Behaviors– search an area using GPS, avoid
obstacles, stop at possible meteorities and alert user. Can be controlled by human
• Refine and Test• Test with other behaviors
– 1999 – 2000 success
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 15
5 Nomad Omnivision
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 16
5 Hyperion (really about Mars)• Task
– navigate Arctic
• Environment– Arctic
• Robot– wheeled, uses solar
• Behaviors
• Refine and test
• Test with other behaviors– 2002 success
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 17
5 NASA HMP / Mars Society Flashline Project Robotics Support
• Confined space inspection of Mars habitat• Marsupial deployment for fault identification• Human robot team for collaborative exploration of •hazardous areas & narrow fissures in search of micro-organisms
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 18
5 Case Study in Pfields:Docking
• Needed for marsupial robots
• Note– use of reactivity
– simple perception
– pfields
– improvement over human
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 19
5 Daughter-centric Docking Behavior
Potential field methodology:
orientation, Xbar=
tangent vectoroverall size=
attraction vector(Arkin, Murphy 90)
Silver Bullet:AMD K-6 400MHz
clearance=+/-2cm+/-5 degrees
Bujold: Inuktun mVGTVPan only, color camera,optics at about 2ms,skid steering,no on-board processor
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 20
5 Docking Behavior Results
Pfields weren’tintended to workbehind thegate
Optics dictated 120 deg, 2mApproach Zone
• 48 data points (3 per 16 stations) on time to completion– by angle
– by radial position
• Larger angles, the slower, and farther away the slower
• 2 failures: 3, 7
• Fastest: 26 sec.
• Slowest: 81 sec.
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 21
5 Docking Behavior Results: teleoperation
Performance comparison:- 66 data points, 22 teleoperators- paired sample t-test (conf>95%)Communications data:-36 data points, 6 teleoperators
Autonomous vs. Teleoperated Performance
01020304050607080
time
collisions
commands/meter
commands/min
autonomous
teleoperated
Teleoperators did better only at 1,3 where the robot wasn’tsupposed to be able to dock from. Noticed that teleoperators used a different strategy; opportunity for improvement
17% faster 17% faster
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 22
5 Docking Vision
• Spherical Coordinate Transform space instead of HSV, RGB
• Biomimetic vision: gradient, looming
• O(m x n) lighting insensitive color segmentation
• 8-10 frames/sec on commercial hardware vs. 30 frames/sec for Cognachrome hardware
• Robust algorithm– 2-colored landmark to prevent confusion
– imprinting and time of day look up tables (LUT)
– if time-out, mother moves
a color is a circle on the plane
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 23
5
Initialvalues
Computeregion
statistics
new values for region
Light insensitive color segmentation
Imprint AdaptExtractregions
Performconnected
components
>15 tries
LUT(time of day,
weather)
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 24
5 Indoor Data Collection and Demonstrations
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 25
5 Outdoor Demonstrations
Imprint at dawn (light mist), return 6 hours later
As expected, mediocre performance from dusk to night (~50%) due to headlight reflection
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 26
5 Additional Case Studies:Commercial Products
• Robomow– cutting grass in residential areas
• My Real Baby– toy dolls
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 27
5 Robomow
• Behaviors?
• Random
• Avoid– Avoid(bump=obstacle)
– Avoid(wire=boundary)
• Stop– Stop(tilt=ON)
• All active www.friendlymachines.com
OverviewHistoryReactive USARSummary
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 28
5 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
OverviewHistoryReactive USARSummary
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 29
5 Commercial Case Studies
• Purely reactive
• May not need subsumption or pfields, very straightforward
• State of practice is much less complicated than state of the art!
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 30
5 Design Tool: Behavior Table
An agent is attracted to light. If it sees light, it heads in that direction. If it encounters an obstacle, it turns either left or right, favoring the direction of the light. If there is no light, it sits and waits. But if an obstacle appears, the agent runs away.
1. photropism
2. Obstacle avoidance
Design-Beh. Table-StepsCase StudyCoordination-FSA-ScriptsSummary
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 31
5 Behavior Table
Releaser Behavior Motor Schema
Percept Perceptual Schema
Light phototropism move2Light():Attraction
Light: direction & strength
Brightest(dir), atLight()
Range
<tasked level>
Obstacle avoidance
avoid(): turn left or right;
runaway()
proximity Obstacle()
An agent is attracted to light. If it sees light, it heads in that direction. If it encounters an obstacle, it turns either left or right, favoring the direction of the light. If there is no light, it sits and waits. But if an obstacle appears, the agent runs away.
Design-Beh. Table-StepsCase StudyCoordination-FSA-ScriptsSummary
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 32
5 Assemblages of Behaviors• What to do if you have a SEQUENCE of behaviors as
well as CONCURRENCY?• Two equivalent methods
– Finite state automata (FSA)– Scripts– (other ways too)
• Two approaches:– Stuff the coordination mechanism into a separate controlling
program (like a main())• Hurts portability, adding new behaviors “on top”
– Stuff the coordination mechanism into a meta-behavior or abstract behavior using recursive-ness of schemas
• Coordination mechanism is the coordinated control program part of the behavioral schema
Design-Beh. Table-StepsCase StudyCoordination-FSA-ScriptsSummary
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 33
5 Example of a Sequence:Catch Suzy!
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 34
5 Example Continued
• “Tracking Phase”– move to goal
– avoid obstacle
• “Pick up Phase”– fine position
– pick up
• “Return Home Phase”– move to goal
– avoid obstacle
same behaviors, just DIFFERENT
INSTANTIATION OF GOAL
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 35
5 FSA: M={K,,,s,F}
• K: all the states, each is “q”- behaviors : transition function, (q,)= new behavior : inputs that agent can “see”, each is –
stimulus/affordances• q0: Start state(s)- part of K• F: Terminating state(s)- part of K
Design-Beh. Table-StepsCase StudyCoordination-FSA-ScriptsSummary
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 36
5 FSA Summary
• “State” doesn’t mean “state of world” (bad); it means more “where the innate releasing mechanism is currently at”
• Advantages– Formal mechanism
– Have to fill in the table, so a way of spotting unforseen effects
• Disadvantages– Hard to keep up with implicit behaviors
• Ex. Avoid obstacle is often running throughout ALL states, gets tedious to express it formally
– Tend to add explicit variable for transitions, rather than rely on emergent behavior from environment
Design-Beh. Table-StepsCase StudyCoordination-FSA-ScriptsSummary
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 37
5 Scripts
• UGV competition really didn’t have a sequence of behaviors, just toggling back and forth
• USAR victim detection has more of a typical sequence or order of behaviors (like digger wasps mating)
• Imagine trying to do an FSA for the USAR task
• Scripts are equivalent to FSA but may be more natural or readable for sequences
Design-Beh. Table-StepsCase StudyCoordination-FSA-ScriptsSummary
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 38
5 ScriptsScript Behavior Analog Examples
Goal Task Find victims in rubble
Places Environment, applicability or
“taskability” for new tasks
Collapsed buildings
Actors Behaviors explore(), dance(), avoid(), crawl, move2void, move2victim
Props, cues Percepts Voids: Dark, concave
Victims: heat, motion, color
Causal Chain
Sequence of behavior Explore, dance, move2void, crawl, move2victim, dropRadio
Subscripts Exception handling If lose communications, return home
Design-Beh. Table-StepsCase StudyCoordination-FSA-ScriptsSummary
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 39
5 Scripts Summary
• Advantages– A more storyboard like way of thinking about the behaviors
– If-then, switch style of programming like FSA
– Since a Script is “in” a behavior, other behaviors such as avoid can be running concurrently without having to appear “in” the script
– Exception handling is a big plus in Real Life
• Disadvantages– Can be a bit of overkill for simple sequences, especially with
C++
Design-Beh. Table-StepsCase StudyCoordination-FSA-ScriptsSummary
Introduction to AI Robotics (MIT Press) Chapter 5: Designing a Reactive Implementation 40
5 Summary• Design of reactive systems is similar to design of
object-oriented software systems– Highly modular, can test behaviors independently
• Follows the basic steps in the Waterfall Lifecycle– Describe task, robot, environment, how robot should act, refine
behaviors, test independently, test together. – Except lots more iteration, making it more like Spiral
• Behavior tables can help keep track of what’s a behavior and its releasers and percepts
• Sequences of behaviors, rather than combinations, can be controlled by a separate routine or by adding a routine to the coordinated control program in the behavioral schema– FSA and Scripts are two main methods
Design-Beh. Table-StepsCase StudyCoordination-FSA-ScriptsSummary