Spock Kirks real TPN Planner

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SpockKirks real TPN Planner

• Jonathan Kennell

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Traditional Model-based Programming
New Model-based Programming
Mission Planning Spock
Mission Planning Ex. Europa
Scientist
Model-based Executive Kirk
Model-based Executive Ex. Titan
Robot
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Planner Requirements

• Optimal
• Robots are expensive non-optimal technology
  cannot be trusted
• Flexible Time-bounds
• Planners that use an idealized representation of
  time are not robust when applied to real-world
  problems
• Rich Activity Representation
• Vehicle models require expressive language

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Existing Technology

• Task-decomposition Planners
• i.e. SHOP2, present-day Kirk
• Not optimal
• (dont actually solve planning problem)
• Plan-graph-based Planners
• i.e. Graphplan, LPGP
• Not optimal over metrics other than makespan
• Cant handle flexible time-bounds
• Local-search Planners
• i.e. LPG
• Not optimal

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Our Solution - Spock

• Representation - Complete
• Based on Temporal Plan Networks
• Inherits from
• Constraint programming
• i.e. TCC, HCC
• Simple temporal networks
• Supports optimality, temporal flexibility, and
  rich activities
• Algorithm Work Ongoing
• Needs to be fast
• Could be a challenge, since optimality and
  expressiveness usually come at a cost of speed
• Needs to be optimal (systematic)
• Future work
• Incorporate relaxed plan cost heuristic
• Use conflicts to focus search
• Adapt for solving via SAT-solver (i.e. Blackbox)

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The Big Idea

• Plan by building a TPN
• The TPN satisfies the control program by adding
  in primitive activities
• Key issues
• TPN should be consistent
• Should explore systematically

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What is a TPN?
0,?
0,?
450,540
1
2
Group Traverse
Group Wait
Ask(PATH1OK)
Ask(PROCEED)
4
5
9
10
405,486
0,54
Science Target
3
8
13
Group Traverse
Group Transmit
Ask(PATH2OK)
0,?
6
7
11
12
405,486
0,2
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Enforcing Consistency

• Temporal Consistency
• Structure based on STN
• Use STN temporal consistency checks between
  iterations
• Incremental temporal consistency checker would be
  useful thanks I-hsiang

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Enforcing Consistency

• Symbolic Consistency
• Objective
• Want to make sure all Asks are supported
• Want to make sure no Tells conflict
• Solution
• Only insert asks when satisfying tell exists
• When inserting ask, add ordering arcs that ensure
  support
• Only insert Tells when existing tells do not
  conflict
• Add ordering arcs between mutex tells

Inserted
Enabled
Tell F true
Not Enabled
Tell F false
Ask F true
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Enablement

• A node is enabled when
• All predecessors have been inserted
• Any Asks that follow this node can be matched
  with active Tells
• Any Tells that follow this node are consistent
  with the active Tells

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Enforcing Systematic Search
(A V B V C)
C
A
B
B
B
A
C
A
C
Repeated States
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Enforcing Systematic Search
(A V B V C)
Not A
A
Thats Search-tastic!
B
Not B
B
Not B
C
C
Not C
Not C
Not C
Not C
C
C
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Spocks Systematic Search

• Same idea
• Each node is either inserted, or blocked
• Blocked nodes can never be inserted via the
  blocked enabling set

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Example Problem
main start A 0 INF (tell A true) start B 0
INF B C 0 INF (ask B true) activity
1 start mid1 0 10 (ask A true) mid1 mid2 0 0
mid2 end 2 4 (tell B true) (tell A false)
Control Program
Tell A true
A
0,INF
start
Ask B true
C
B
0,INF
0,INF
Primitive Activity
Tell B true Tell A false
Ask A true
start
mid1
mid2
end
0,10
0,0
2,4
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Initialization
Control Program
Tell A true
A
start
0,INF
Ask B true
C
B
0,INF
0,INF
Primitive Activity
Ask A true
start
mid1
0,10
0,0
Tell B true Tell A false
mid2
end
2,4
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Step 1
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Step 2
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Step 3
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Step 4
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Step 5
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Step 6
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Step 7
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Step 8
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Complete Plan
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Rich Activities

• Spocks TPN Control Program and Primitive
  Activities are super-flexible
• PDDL Operators can be mapped in their entirety
  into TPNs

Tell B
PDDL Start preconditions AStart effects
BInvariant conditions CInvariant effects DEnd
preconditions EEnd effects FDuration G
0,INF
Ask E
Tell D
Ask A
Ask C
0,0
0,0
G,G
Tell F
0,INF
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Future Work

• Make Fast Algorithm
• Incorporate relaxed plan cost heuristic
• Use conflicts to focus search
• Adapt for solving via SAT-solver (i.e. Blackbox)
• Problem
• Detecting symmetry
• Detecting no progress

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The End