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The Hierarchical Paradigm

The Hierarchical Paradigm. Describe the Hierarchical Paradigm in terms of the 3 robot primitives and its organization of sensing

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The Hierarchical Paradigm

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  1. The Hierarchical Paradigm • Describe the Hierarchical Paradigm in terms of the 3 robot primitives and its organization of sensing • Name and evaluate one representative Hierarchical architecture in terms of: support for modularity, niche targetability, ease of portability to other domains, robustness • Solve a simple navigation problem using STRIPS (hint: work through Sec. 2.2.2) • Understand precondition, closed world assumption, open world, frame problem • List two advantages and disadvantages of the Hierarchical Paradigm Organization -SPA -global Strips -Shakey Rep. Arch. -evaluation -NHC -RCA Summary Chapter 2: The Hierarchical Paradigm

  2. World model: • A priori rep • Sensed info • Cognitive SENSE PLAN ACT Organization Organization -SPA -global Strips -Shakey Rep. Arch. -evaluation -NHC -RCA Summary Chapter 2: The Hierarchical Paradigm

  3. Shakey • First AI robot • Built by SRI (Stanford Research Institute) for DARPA 1967-9 • Used Strips as main algorithm for controlling what to do Organization -SPA -global Strips -Shakey Rep. Arch. -evaluation -NHC -RCA Summary Chapter 2: The Hierarchical Paradigm

  4. Strips: Means-ends analysis “Go to Stanford AI Lab” Organization -SPA -global Strips -Shakey Rep. Arch. -evaluation -NHC -RCA Summary INITIAL STATE: Tampa, Florida (0,0) GOAL STATE: Stanford, California (1000,200) Difference: 1020 miles Chapter 2: The Hierarchical Paradigm

  5. Distance (difference) mode of transportation (OPERATOR) d<1 WALK Difference Table d>=200 miles FLY Organization -SPA -global Strips -Shakey Rep. Arch. -evaluation -NHC -RCA Summary 100<d<200 TRAIN d<=100 DRIVE mode=difference_table(INITIAL STATE, GOAL STATE, difference) • Look up what to do: FLY • Not at SAIL, so repeat • Look up what to do: DRIVE Chapter 2: The Hierarchical Paradigm

  6. difference OPERATOR PRECONDITIONS at airport d<1 WALK at home Preconditions Organization -SPA -global Strips -Shakey Rep. Arch. -evaluation -NHC -RCA Summary d>=200 miles FLY 100<d<200 TRAIN d<=100 DRIVE (rental) DRIVE (personal car) How do I know if I’m at the airport or at home? Now must keep up with the state of the world Chapter 2: The Hierarchical Paradigm

  7. distance OPERATOR PRE-CONDITIONS ADD-LIST DELETE-LIST at city Y at airport at city X at city Y at train station at city X d<1 WALK Maintaining State of the World:Add and Delete Lists Organization -SPA -global Strips -Shakey Rep. Arch. -evaluation -NHC -RCA Summary d>=200 miles FLY 100<d<200 TRAIN d<=100 DRIVE (rental) at airport DRIVE (personal) at home Chapter 2: The Hierarchical Paradigm

  8. distance OPERATOR PRE-CONDITIONS ADD-LIST DELETE-LIST d<=200 miles FLY at city Y at airport at city X at city Y at train station 100<d<200 TRAIN at city X d<=100 DRIVE (rental) at airport d<1 WALK DRIVE (personal) at home Class Exercise • Write down the world model, the operator applied, the change in world state, etc. to go from Tampa to Stanford Organization -SPA -global Strips -Shakey Rep. Arch. -evaluation -NHC -RCA Summary Chapter 2: The Hierarchical Paradigm

  9. Strips Summary • Designer must set up • World model representation • Difference table with operators, preconditions, add & delete lists • Difference evaluator • Strips assumes closed world • Closed world: world model contains everything needed for robot (implication is that it doesn’t change) • Open world: world is dynamic and world model may not be complete • Strips suffers from frame problem • Frame problem: representation grows too large to reasonably operate over Organization -SPA -global Strips -Shakey Rep. Arch. -evaluation -NHC -RCA Summary Chapter 2: The Hierarchical Paradigm

  10. Architecture • provides a principled way of organizing a control system. However, in addition to providing structure, it imposes constraints on the way the control problem can be solved [Mataric] • describes a set of architectural components and how they interact [Dean & Wellman] • Types of architectures [Levis, George Mason University] • operational architecture: describes what the systems does, not how it does it • systems architecture: describes how a system works in terms on major subsystems • technical architecture:implementation details Organization -SPA -global Strips -Shakey Rep. Arch. -evaluation -NHC -RCA Summary Chapter 2: The Hierarchical Paradigm

  11. Evaluating an Architecture • support for modularity: does it show good software engineering principles? • niche targetability: how well does it work for the intended application? • ease ofportability to other domains: how well would it work for other applications or other robots? • robustness: where is the system vulnerable, and how does it try to reduce that vulnerability? Organization -SPA -global Strips -Shakey Rep. Arch. -evaluation -NHC -RCA Summary Chapter 2: The Hierarchical Paradigm

  12. Hierarchical Paradigm… • Top-down: • Plan, plan, plan • Control-theoretic: • must measure error in order to control device • Planning means: • dependence on world models Chapter 2: The Hierarchical Paradigm

  13. Nested Hierarchical Controller(Meystel) Organization -SPA -global Strips -Shakey Rep. Arch. -evaluation -NHC -RCA Summary Chapter 2: The Hierarchical Paradigm

  14. NHC Planner Organization -SPA -global Strips -Shakey Rep. Arch. -evaluation -NHC -RCA Summary Chapter 2: The Hierarchical Paradigm

  15. RCS (Albus) • the hierarchy • how the hierarchy works for navigation • how it is implemented • nodes and modules • planning time periods Chapter 2: The Hierarchical Paradigm

  16. Examples of RCS Apps Organization -SPA -global Strips -Shakey Rep. Arch. -evaluation -NHC -RCA Summary Chapter 2: The Hierarchical Paradigm

  17. RCS-4 Levels Chapter 2: The Hierarchical Paradigm

  18. Each Level has a RCS Node Engineering of Mind, Albus & Mystel, 2001 Sensory Processing, World Modeling, Behavior Generation, Value Judgment Chapter 2: The Hierarchical Paradigm

  19. Implementation View:Nodes are Recursive Chapter 2: The Hierarchical Paradigm

  20. Demo III XUV http://museum.nist.gov/exhibits/timeline/item.cfm?itemId=38 Experimental Unmanned Vehicle in action at Ft. Indiantown Gap. Photo courtesy of the Army Research Labs. Nov. 2001 Chapter 2: The Hierarchical Paradigm

  21. Demo III Control Hierarchy PLANNER vehicle1 vehicle2 Section 10m Vehicle 1m VEHICLE PLANNER communications plan AM plan RSTA plan Subsystem 5s COMMS PLANNER message list AM PLANNER Driver Plan Gaze plan RSTA PLANNER gaze plan Primitive 500ms DRIVER PLANNER Velocity Plan GAZE PLANNER Stereo Gaze Plan LADAR Gaze Plan VELOCITY PLANNER F Wheels R Wheels F Steer R Steer Servo 50ms F Wheel R Wheel F Steer F Steer Chapter 2: The Hierarchical Paradigm

  22. RCS XUV Example Vehicle Level: AM Plan (A1…A10) Primitive Level: Driver Plan (D1…D10) Chapter 2: The Hierarchical Paradigm

  23. t=0.5 Primitive Level: Driver Plan extends to A2 Chapter 2: The Hierarchical Paradigm

  24. t=1 s Obstacle Detected Primitive Level: Driver Plan new waypoints Vehicle Level: detects too large a variation Chapter 2: The Hierarchical Paradigm

  25. t=1 s Vehicle Level Planner Opt 1 Vehicle Level: new AM Plan Primitive Level: new Driver Plan Chapter 2: The Hierarchical Paradigm

  26. t=3 More obstacle is seen… fail upwards again Vehicle Level: new AM Plan Primitive Level: new Driver Plan Chapter 2: The Hierarchical Paradigm

  27. t=4.5s Vehicle Level: new AM Plan skip A1, go to A2 Primitive Level: new Driver Plan Chapter 2: The Hierarchical Paradigm

  28. t=6 s Vehicle Level: new AM Plan skip old A2 Primitive Level: new Driver Plan Chapter 2: The Hierarchical Paradigm

  29. Exercise: Adapt to Rescue Robots? PLANNER vehicle1 vehicle2 Section 10m Vehicle 1m VEHICLE PLANNER communications plan AM plan RSTA plan Subsystem 5s COMMS PLANNER message list AM PLANNER Driver Plan Gaze plan RSTA PLANNER gaze plan Primitive 500ms DRIVER PLANNER Velocity Plan GAZE PLANNER Stereo Gaze Plan LADAR Gaze Plan VELOCITY PLANNER F Wheels R Wheels F Steer R Steer Servo 50ms F Wheel R Wheel F Steer F Steer Chapter 2: The Hierarchical Paradigm

  30. Nodes are made from Modules xd is from “above” G is feedback actions sensors transform into x* uff applies rule (transition rules) u=uff+G(xd-x*) u is control action x* is predicted world state xd is desired world state uff is the feedforward control plan Chapter 2: The Hierarchical Paradigm

  31. Nodes are made from Modules xd is from “above” G is feedback actions sensors transform into x* uff applies rule (transition rules) if BALL, move toward centroid if NOT BALL, turn clockwise (feedback determines how fast) Chapter 2: The Hierarchical Paradigm

  32. Nodes are made from Modules xd is from “above” G is feedback actions sensors transform into x* uff applies rule (transition rules) when to stop? how far is far enough? what about noise/fuzzy ball? … sensor noise, actuator error, rigid models if BALL, move toward centroid if NOT BALL, turn clockwise (feedback determines how fast) Chapter 2: The Hierarchical Paradigm

  33. Advantages of Hierarchies Albus and Mystel 01: • Natural way to organize • Not intrinsically rigid • Not intrinsically inefficient • not the same as centralized planning • priorities and goals are clear, therefore efficient Chapter 2: The Hierarchical Paradigm

  34. Summary RCS • hierarchy with node structure at each level • have operator interface (in theory) • nodes consist of • Sensory Processing • World Model • Behavior Generation • Value Judgment • top-down, plan for a particular horizon • control theoretic Chapter 2: The Hierarchical Paradigm

  35. Evaluating the Two Architectures • support for modularity: • decomposition by functionality • niche targetability: • good, both have been used for apps like vehicle guidance, mining equipment • ease ofportability to other domains: • unclear, not sure if code could be reused—lots of rewriting on previous apps • robustness: • RCA simulates plans in advance, but not sure what it would do with sensor or mechanical failures, etc. Organization -SPA -global Strips -Shakey Rep. Arch. -evaluation -NHC -RCA Summary Chapter 2: The Hierarchical Paradigm

  36. Hierarchical Review • Describe the hierarchical paradigm in terms of the three robot primitives • Describe sensing in the hierarchical paradigm • What is STRIPS? • What is the closed world assumption? • What are preconditions? • What is the frame problem? • What are two representative architectures? • What is the NHC decomposition? Organization -SPA -global Strips -Shakey Rep. Arch. -evaluation -NHC -RCA Summary Chapter 2: The Hierarchical Paradigm

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