model-based programming of cooperating explorers brian c. williams csail dept. aeronautics and...
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Model-based Programming of Cooperating Explorers
Brian C. WilliamsCSAIL
Dept. Aeronautics and AstronauticsMassachusetts Institute of
Technology
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Programming Long-lived Embedded Systems
Large collections of devices must work in concert to achieve goals• Devices indirectly observed and controlled• Need quick, robust response to anomalies throughout life• Must manage large levels of redundancy
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Coordination Recapitulated At TheLevel of Cooperating Explorers
(Courtesy of Jonathan How. Used with permission.)
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Coordination Issues Increase For Dexterous Explorers
(Courtesy of Frank Kirchner. Used with permission.)
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Outline• Model-based Programming
• Autonomous Engineering Operations – An Example – Model based Execution – Fast Reasoning using Conflicts
• Cooperating Mobile Vehicles – Predictive Strategy Selection – Planning Out The Strategy
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Approach
Elevate programming and operation to system-level coaching.
Model-based Programming– State Aware: Coordinates behavior at the level of intended state.
Model-based Execution– Fault Aware: Uses models to achieve intended behavior under normal and faulty conditions.
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Why Model-based Programming?
Polar Lander Leading Diagnosis:
• Legs deployed during descent.• Noise spike on leg sensors latched by software monitors.
• Laser altimeter registers 40m.• Begins polling leg monitors to determine touch down.
• Read latched noise spike as touchdown.
• Engine shutdown at ~40m.
Programmers often make commonsense mistakes when reasoning about hidden state.
Objective: Support programmers with embedded languages that avoid these mistakes, by reasoning about hidden state automatically.
Reactive Model-based Programming Language (RMPL)
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Model-based ProgramsInteract Directly with State
Embedded programs interact with Model-based programs plant sensors and actuators: interact with plant state:
• Read sensors • Read state• Set actuators • Write state
Embedded ProgramModel-based
Embedded Program
Obs Cntrl
SPlant
Obs Cntrl
SPlant
S’Model-based Executive
Programmer must map between Model-based executive maps
state and sensors/actuators. between state and sensors/actuators.
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RMPL Model-based Program Titan Model-based Executive
Control Program
• Executes concurrently• Preempts• Queries (hidden) states• Asserts (hidden) state
Generates target goal states conditioned on state
estimates
State estimates
Tracks likely plant states
State goals
Tracks least cost goal states
Observations
CommandsPlan
t
System Model
OpenStuck open
Open Close
0. 01
Closed
Stuck closedinflow = outflow =
0
0.01
0. 01
0. 01
Valve
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Outline• Model-based Programming
• Autonomous Engineering Operations – An Example – Model based Execution – Fast Reasoning using Conflicts
• Cooperating Mobile Vehicles – Predictive Strategy Selection – Planning Out The Strategy
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Motivation
(Courtesy of Mitch Ingham. Used with permission.)
Mission-critical sequences:
• Launch & deployment
• Planetary fly-by
• Orbital insertion
• Entry, descent & landing
images courtesy of NASA
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Mars Entry Example
(Courtesy of Mitch Ingham. Used with permission.)
engine to standbyplanetary approach
separate lander
switch toinertial nav rotate to entry-orient
& hold attitude
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Mars Entry Example
(Courtesy of Mitch Ingham. Used with permission.)
engine to standbyplanetary approach
separate lander
switch toinertial nav rotate to entry-orient
& hold attitude
Descent engine to “standby”:
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Mars Entry Example
(Courtesy of Mitch Ingham. Used with permission.)
engine to standbyplanetary approach
separate lander
switch toinertial nav rotate to entry-orient
& hold attitude
Spacecraft approach:• 270 mins delay• relative position wrt Mars not observable• based on ground computations of cruise trajectory
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Mars Entry Example
(Courtesy of Mitch Ingham. Used with permission.)
engine to standbyplanetary approach
separate lander
switch toinertial nav rotate to entry-orient
& hold attitude
Switch navigation mode:
“Inertial” = IMU only
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Mars Entry Example
(Courtesy of Mitch Ingham. Used with permission.)
engine to standbyplanetary approach
separate lander
switch toinertial nav rotate to entry-orient
& hold attitude
Rotate spacecraft:• command ACS to entry orientation
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Mars Entry Example
(Courtesy of Mitch Ingham. Used with permission.)
engine to standbyplanetary approach
separate lander
switch toinertial nav rotate to entry-orient
& hold attitude
Rotate spacecraft:• once entry orientation achieved, ACS holds attitude
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Mars Entry Example
(Courtesy of Mitch Ingham. Used with permission.)
engine to standbyplanetary approach
separate lander
switch toinertial nav rotate to entry-orient
& hold attitude
Separate lander from cruise stage:
cruise stage
pyro latches
lander stage
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Mars Entry Example
(Courtesy of Mitch Ingham. Used with permission.)
engine to standbyplanetary approach
separate lander
switch toinertial nav rotate to entry-orient
& hold attitude
Separate lander from cruise stage:• when entry orientation achieved, fire primary pyro latch
cruise stage
pyro latches
lander stage
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Mars Entry Example
(Courtesy of Mitch Ingham. Used with permission.)
engine to standbyplanetary approach
separate lander
switch toinertial nav rotate to entry-orient
& hold attitude
Separate lander from cruise stage:• when entry orientation achieved, fire primary pyro latch
cruise stage
lander stage
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Mars Entry Example
(Courtesy of Mitch Ingham. Used with permission.)
engine to standbyplanetary approach
separate lander
switch toinertial nav rotate to entry-orient
& hold attitude
Separate lander from cruise stage:• in case of failure of primary latch, fire backup pyro latch
cruise stage
lander stage
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Mars Entry Example
(Courtesy of Mitch Ingham. Used with permission.)
engine to standbyplanetary approach
separate lander
switch toinertial nav rotate to entry-orient
& hold attitude
Separate lander from cruise stage:• in case of failure of primary latch, fire backup pyro latch
cruise stage
lander stage
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Mars Entry Example
(Courtesy of Mitch Ingham. Used with permission.)
engine to standbyplanetary approach
separate lander
switch toinertial nav rotate to entry-orient
& hold attitude • simple state-based control specifications• models are writable/inspectable by systems engineers
• handle timed plant & control behavior• automated reasoning through low- level plant interactions• fault-aware (in-the-loop recoveries)
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Descent Example
Turn camera off and engine on
EngineA EngineB EngineA EngineB
Science Camer Science Camera
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Model-based Program
Control program specifies state trajectories:
OrbitInsert()::
(do-watching ((EngineA = Thrusting) OR (EngineB = Thrusting))
• fires one of two engines
• sets both engines to ‘standby’
• prior to firing engine, camera must be turned off to avoid plume contamination
• in case of primary engine failure, fire backup engine instead
Plant Model describes behavior of each component:– Nominal and Off nominal
– qualitative constraints
– likelihoods and costs
(parallel (EngineA = Standby) (EngineB = Standby) (Camera = Off)
(do-watching (EngineA = Failed) (when-donext ( (EngineA = Standby) AND
(Camera = Off) )
(EngineA = Thrusting)))
(when-donext ( (EngineA = Failed) AND (EngineB = Standby) AND (Camera = Off) )
(EngineB = Thrusting))))
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Plant Modelcomponent modes…
described by finite domain constraints on variables…
deterministic and probabilistic transitions
cost/reward
one per component … operating concurrently
Engine Model
(thrust = zero) AND
(power_in = zero)
(thrust = full) AND (power_in = nominal)
(thrust = zero) AND(power_in = nominal)
(power_in = zero) AND(shutter = closed)
(power_in = nominal) AND(shutter = open)
Off
Standby
Firing
standby-cmd
Failed
Off
On
off-cmd
standby- cmd
fire-cmd
turnoff –cmd
turnoff –
cmd
Camera Model
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Example: The model-based program sets engine = thrusting, and the deductive controller . . . .
Mode ReconfigurationMode EstimationOxidizer tank Fuel tank
Deduces thatthrust is off, and
the engine is healthy Deduces that a valvefailed - stuck closed
Determines valves on backup engine that will achieve thrust, and plans needed actions
Selects valveconfiguration;plans actions
to opensix valves
Mode Reconfiguration Mode Estimation
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Outline
• Model-based Programming
• Autonomous Engineering Operations– An Example– Model based Execution– Fast Reasoning using Conflicts
• Cooperating Mobile Vehicles– Predictive Strategy Selection– Planning Out The Strategy
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Engine Model
(thrust = zero) AND
(power_in = zero)
(thrust = full) AND (power_in = nominal)(thrust = zero) AND
(power_in = nominal)
(power_in = zero) AND(shutter = closed)
(power_in = nominal) AND(shutter = open)
Off
Standby
Firing
standby-cmd
Failed
Off
On
off-cmd
standby- cmd
fire-cmd
turnoff –cmd
turnoff –
cmd
Camera Model
Modeling Plant Dynamics using ProbabilisticConcurrent, Constraint Automata (PCCA)
Compact Encoding:– Concurrent probabilistic transitions– State constraints between variables
Typical Example (DS1 spacecraft):– 80 Automata, 5 modes on average– 3000 propositional variables, 12,000 propositional clauses
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•Assigns a value to each variable (e.g.,3,000 vars).•Consistent with all state constraints (e.g., 12,000).
• A set of concurrent transitions, one per automata (e.g., 80).•Previous & Next states consistent with source & target of transitions
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RMPL Model-based Program Titan Model-based Executive
Control Program
Executes concurrentlyPreemptsAsserts and queries states Chooses based on reward
Control Sequencer:
Generates goal states conditioned on state estimates
State estimates State goals
Mode Estimation:
Tracks likely States
Observations
Plant
Orbitlnsert():(do-watching((EngineA=Firing)OR (EngineB=Firing)) (parallel (EngineA=Standby) (EngineB=Standby) (Camera=Off) (do-watching(EngineA=Failed) (when-donext((EngineA=Standby)AND (Camera=Off)) (EngineA=Firing))) (when-donext((EngineA=Failed)AND (EngineB=Standby)AND (Camera=Off)) (EngineB=Firing))))
MAINTAIN(EAR OR EBR)
EAS
EBS
CO
LEGENO:EAS (EngineA=Standby)EAF (EngineA=Failed)EAR (EngineA=Firing)EBS (EngineB=Standby)EBF (EngineB=Failed)EBR (EngineB=Firing)CO (Camera=Off)
hierarchical constraint automata on state s
MAINTAIN(EAF)(EAS AND CO)
EAS AND COEAR
(EAF AND EBS AND CO)
EBREAF AND EBS AND CO
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X0 X1XN-1XN
X0 X1XN-1XN
S T
RMPL Model-based Program Titan Model-based Executive
Control Program
Executes concurrentlyPreemptsAsserts and queries states Chooses based on reward
Control Sequencer:
Generates goal states conditioned on state estimates
State estimates State goals
Mode Estimation:
Tracks likely States
Observations
Plant
Mode Reconfiguration:Tracks least-cost
state goals
Commands
Valve fails stuck closed
Current Belief State
Fire backup engine
First Action
least cost reachable goal state
X0 X1 XN-1 XN X0 X1 XN-1 XN
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Mod
e
XN XN
S T
State estimates State goals
Mode Estimation:
Tracks likely States
Observations
Plant
Mode Reconfiguration:Tracks least-cost
state goals
Commands
Valve fails stuck closed
Current Belief State
Fire backup engine
First Action
least cost reachable goal state
X0 X1 XN-1 XN X0 X1 XN-1 XN
arg max PT(m')s.t. M(m')^O(m') is satisfiable
OpSat:arg min f(x)s.t. C(x) is satisfiable D(x) is unsatisfiable
arg min RT*(m')s.t. M(m') entails G(m')s.t. M(m') is satisfiable
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Outline
• Model-based Programming• Autonomous Engineering Operations
– An Example – Model based Execution – Fast Reasoning using Conflicts
• Cooperating Mobile Vehicles – Predictive Strategy Selection – Planning Out The Strategy
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Diagnosis Formulation
Consistency-based Diagnosis: Given symptoms, find diagnoses that are consistent with symptoms.
Handle Novel Failures by Suspending Constraints: Make no presumptions about faulty component behavior.
1
1
1
1
0
A
B
C
D
E
X
Y
Z
F
G
1
1
1
0
1
Or1
Or2
Or3
AND1
AND2
Symptom
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Diagnosis FormulationConsistency-based Diagnosis: Given symptoms,
find diagnoses that are consistent with symptoms. Handle Novel Failures by Suspending
Constraints: Make no presumptions about faulty component
behavior.
1
1
1
1
0
A
B
C
D
E
X
Y
Z
F
G
1
1
1
0
1Or2
Or3
AND1
AND2
Symptom
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Fast Reasoning Through Conflict
• When you have eliminated the impossible, whatever remains, however improbable, must be the truth.
-Sherlock Holmes. The Sign of the Four.
1. Test Hypothesis
2. If inconsistent, learn reason for inconsistency (a Conflict).
3. Use conflicts to leap over similarly infeasible options to next best hypothesis.
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Compare Most Likely Hypothesis to Observations
Helium tank
Oxidizer tank Fuel tankFlow1 = zero
Pressure1 = nominalPressure2 = nominal
Acceleration = zero
Main Engines
It is most likely that all components are okay.
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Isolate Conflicting Information
Helium
tank
Oxidizer
tank
Fuel
tankFlow1= zero
Main
Engines
The red component modes conflict with the model and observations.
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Leap to the Next Most Likely Hypothesis that Resolves the Conflict
Helium tank
Oxidizer tank
Fuel tank
Flow1= zero
Main
Engines
The next hypothesis must remove the conflict
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New Hypothesis Exposes Additional Conflicts
Helium tank
Oxidizer tank
Fuel tank
Main
Engines
Another conflict, try removing both
Pressure1 = nominal Pressure2 = nominal
Acceleration = zero
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Final Hypothesis Resolves all Conflicts
Helium tank
Oxidizer tank
Fuel tank
Main
Engines
Pressure1 = nominal Flow1 = zero
Pressure2= nominal Flow2 = positive
Acceleration = zero
Implementation: Conflict-directed A* search.
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A*
IncreasingCost
Infeasible
Feasible
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Conflict-directed A*
IncreasingCost
Infeasible
Feasible
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Conflict-directed A*
IncreasingCost
Feasible
Conflict 1
Infeasible
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Conflict-directed A*
IncreasingCost
Feasible
• Conflicts are mapped tofeasible regions as implicants(Kernel Assignments)
•Want kernel assignmentcontaining the best cost state.
Conflict 1
Infeasible Conflict 2
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Outline
• Model-based Programming
• Autonomous Engineering Operations– An Example– Model based Execution– Fast Reasoning using Conflicts
• Cooperating Mobile Vehicles– Predictive Strategy Selection– Planning Out The Strategy
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Coordination is Recapitulated at theLevel of Cooperating Explorers
(Courtesy of Jonathan How. Used with permission.)
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Traditional Robot Architectures
• Explicit human guidance is at the lowest levels
Goals Action descriptions
Goal-directed Programs
Planning and Scheduling
Goal-directed Execution
Reactive Behaviors
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RMPL for Robotics
What types of reasoning should the programmer/operator guide?
•State/mode inference•Machine control•Scheduling
•Method selection•Roadmap path planning•Optimal trajectory planning•Generative temporal planning
Reactive Model-based Programming Language(P
MPL)Model-based Executive
Control Programs
Plant Models
Goal-directed Execution
Deductive Controllers
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HOME
T W O
O N E
Landing Site: ABC
COLLECTION POINT RENDEZVOUSCOLLECTION POINT
Enroute
Landing Site: XYZ
SCIENCE AREA 3
SCIENCE AREA 1SCIENCE AREA 1
DivergeSCIENCE AREA 1’
RMPL Model-based Program Kirk Model-based Executive
Control Programz Executes concurrently
z Preemptsz non-deterministic choicez A[l,u] timingz A at l location
Control Sequencer Predictive Strategy Selection Dynamic
Scheduling
Ensures Safe ExecutionEnvironmentModel
location estimates
location goals
DeductiveControllerAchieves State via Path
PlanningEstimates using LocalizationObservations Commands
Plant
COLLECTION POINTCOLLECTION POINT
HOME
Landing Site: ABC
Landing Site: XYZ
EnrouteRENDEZVOUSRENDEZVOUS
SCIENCE AREA 1SCIENCE AREA 1
SCIENCE AREA 3
DivergeDiverge
SCIENCE AREA 1’SCIENCE AREA 1’
TVO
ONE
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Example Scenario
Properties:• Mars rover operators have been leery of generative planners.• z Are more comfortable with specifying contingencies.• z Want strong guarantees of safety and robust to uncertainty.• z Global path planning is on the edge
Extend RMPL with planner-like capabilities ..except planning
ONE
TWO
HOME
Landing Site: ABC COLLECTION POINT Enroute RENDEZVOUS
Landing Site: XYZ
SCIENCE AREA 1
DivergeSCIENCE AREA 1’
SCIENCE AREA 3
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Reactive Model-based Programming
Idea: To describe group behaviors, start with concurrent language:
• p • Primitive activities
• If c next A • Conditional execution
• Unless c next A • Preemption
• A, B • Full concurrency
• Always A • Iteration
•Add temporal constraints:
• A [l,u] • Timing
•Add choice (non-deterministic or decision-theoretic):
• Choose {A, B} • Contingency
•Parameterize by location:
• A at [l]
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Example Enroute Activity:
Enroute
Corridor 2
Rendezvous
Corridor 1
Rescue Area
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RMPL for Group-EnrouteTemporal Constraints:
Group-Enroute()[l,u] = { choose { do { Group-Fly- Path(PATH1_1,PATH1_2,PATH1_3,RE_POS)[l*90%,u*90%]; } maintaining PATH1_OK, do { Group-Fly- Path(PATH2_1,PATH2_2,PATH2_3,RE_POS)[l*90%,u*90%]; } maintaining PATH2_OK }; { Group-Transmit(OPS,ARRIVED)[0,2], do { Group-Wait(HOLD1,HOLD2)[0,u*10%] } watching PROCEED } at RE_POS}
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RMPL for Group-EnrouteGroup-Enroute()[l,u] = { choose { do { Group-Fly- Path(PATH1_1,PATH1_2,PATH1_3,RE_POS)[l*90%,u*90%]; } maintaining PATH1_OK, do { Group-Fly- Path(PATH2_1,PATH2_2,PATH2_3,RE_POS)[l*90%,u*90%]; } maintaining PATH2_OK }; { Group-Transmit(OPS,ARRIVED)[0,2], do { Group-Wait(HOLD1,HOLD2)[0,u*10%] } watching PROCEED } at RE_POS}
Location Constraints:
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RMPL for Group-EnrouteGroup-Enroute()[l,u] = { choose { do { Group-Fly- Path(PATH1_1,PATH1_2,PATH1_3,RE_POS)[l*90%,u*90%]; } maintaining PATH1_OK, do { Group-Fly- Path(PATH2_1,PATH2_2,PATH2_3,RE_POS)[l*90%,u*90%]; } maintaining PATH2_OK }; { Group-Transmit(OPS,ARRIVED)[0,2], do { Group-Wait(HOLD1,HOLD2)[0,u*10%] } watching PROCEED } at RE_POS}
Non-deterministic choice:
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Outline
• Model-based Programming
• Autonomous Engineering Operations– An Example – Model based Execution– Fast Reasoning using Conflicts
• Cooperating Mobile Vehicles– Predictive Strategy Selection– Planning Out The Strategy
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HOME
T W O
O N E
Landing Site: ABC
COLLECTION POINT RENDEZVOUSCOLLECTION POINT
Enroute
Landing Site: XYZ
SCIENCE AREA 3
SCIENCE AREA 1SCIENCE AREA 1
DivergeSCIENCE AREA 1’
RMPL Model-based Program Kirk Model-based Executive
Control Programz Executes concurrently
z Preemptsz non-deterministic choicez A[l,u] timingz A at l location
EnvironmentModel
location estimates location goals
Observations Commands
Plant
COLLECTION POINTCOLLECTION POINT
HOME
Landing Site: ABC
Landing Site: XYZ
EnrouteRENDEZVOUSRENDEZVOUS
SCIENCE AREA 1SCIENCE AREA 1
SCIENCE AREA 3
DivergeDiverge
SCIENCE AREA 1’SCIENCE AREA 1’
TVO
ONE
Selects consistent threads of activity from redundant methods
Tracks
Finds leastlocatio
ncost paths
Executive • pre-plans activities • pre-plans paths • dynamically schedules [Tsmardinos et al.]
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Enroute Activity Encoded as a Temporal Plan Network• Start with flexible plan representation
Activity (or sub-activity)
Duration (temporal constraint)
Enroute [450,540]
Group Traverse Group Wait
Group Transmit
Science Target
[0, 0]
[405, 486][0, 0] [0, 0]
[0, 54]
[0, 0]
[0, ][0, 0]
[0, 2]
[0, 0]
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Activity (or sub-activity)
Duration (temporal constraint)
Conditional node
Enroute Activity Encoded as a Temporal Plan Network• Add conditional nodes
Enroute [450,540]
Group Traverse Group Wait
Group Transmit
Science Target
[0, 0]
[405, 486][0, 0] [0, 0]
[0, 54]
[0, 0]
[0, ][0, 0]
[0, 2]
[0, 0]
3
[0, 0] [0, 0]Group Traverse
[405, 486]
8
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Enroute Activity Encoded as a Temporal Plan Network
•Add temporally extended, symbolic constraints
Activity (or sub-activity)
Duration (temporal constraint)
Conditional node
Symbolic constraint (Ask,Tell)
Enroute [450,540]
Group Traverse Group Wait
Group Transmit
Science Target
[0, 0]
[405, 486][0, 0] [0, 0]
[0, 54]
[0, 0]
[0, ][0, 0]
[0, 2]
[0, 0]
3
[0, 0][0, 0]Group Traverse
[405, 486]
8
Ask( PATH1 = OK)
Ask( PATH2 = OK)
Ask( EXPLORE = OK)
6 7 11 12
13
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Instantiated Enroute Activity•Add environmental constraints
Activity (or sub-activity)
Duration (temporal constraint)
Conditional node
Symbolic constraint (Ask,Tell) External constraints
Group-Enroute [500,800]
Group Traverse Group Wait
Group Transmit
Science Target
[405, 486] [0, 54]
[0, 2]
3
Group Traverse
[405, 486]
8
Ask( PATH1 = OK)
Ask( PATH2 = OK)
Ask( EXPLORE = OK)
6 7 11 12
1
5
14 15 16 17
[450,540]
[0,∞][0,∞]
[0,∞]
[200,200][450,450]
[10,10]Tell(PATH1=OK)
Tell( PROCEED)
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Generates Schedulable Plan
To Plan, . . . perform the following hierarchically: • Trace trajectories • Check schedulability • Supporting and protecting goals (Asks)
Group-Enroute[500,800]
[450,540]
[0,∞] [0,∞]
Group Traverse Group Wait
Ask(PATH1=OK) Ask(PROCEED)
[0,54][405,486]Science Target
Group TraverseAsk(PATH2=OK)
Group Transmit
[0,∞]
[405,486] [0,2]
3 8
6 7 11 12
1
5
14 15 16 17
Tell(PATH1=OK) Tell(PROCEED)
[450,450] [200,200]
[10,10] [0,∞]
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Supporting and Protecting Goals
Resolving Unsupported Subgoals:
• Scan plan graph,identifying activities that support open sub-goals; force to co-occur.
Resolving Threatened Subgoals:
• Search for inconsistent activities that co-occur, and impose ordering.
Key computation is bound time of occurrence:
• Used Floyd-Warshall APSP algorithm O(V3).
Unsupported Subgoal Threatened Activities
Goal: any UCAV at TargetActivity: UAV1 at Base
Activity: UCAV1 at Target
Activities can’t co-occurClose open goals
Activity:UAVI at Targer
1 2
3 4
1 2
3 4
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Randomized Experiments for Assessing Scaling and Robustness
Randomized Experiments:
• Randomly generated range of scenarios with 1-50 vehicles.• Each vehicle has two scenario options, each with five actions and 2
waypoints: 1. Go to waypoint 12. Observe science 3. Go to waypoint 24. Observe science 5. Return to collection point
• Waypoints generated randomly from environment with uniform distribution.
Strategy Selection:• TPN planner chooses one option per vehicle.• Combined choices must be consistent with timing constraints and vehicle
paths.
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Kirk Strategy Selection:Scaling and Robustness
Performance Improvement Through• Incremental temporal consistency• Conflict-directed Search (in progress)
Planning Time vs. Number of UAVs
Each vehicle visits 2 science sites and returns
to collection point
35
30
25
20
15
10
5
00 505 2520 35301510 4540
Pla
nn
ing
Tim
e (
min
)
Number of UAVs
Kirk Oct. ’02
Kirk April ’03
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HOME
T W O
O N E
Landing Site: ABC
COLLECTION POINT RENDEZVOUSCOLLECTION POINT
Enroute
Landing Site: XYZ
SCIENCE AREA 3
SCIENCE AREA 1SCIENCE AREA 1
DivergeSCIENCE AREA 1’
RMPL Model-based Program Kirk Model-based Executive
Control Programz Executes concurrently
z Preemptsz non-deterministic choicez A[l,u] timingz A at l location
EnvironmentModel
location estimates location goals
Observations Commands
Plant
COLLECTION POINTCOLLECTION POINT
HOME
Landing Site: ABC
Landing Site: XYZ
EnrouteRENDEZVOUSRENDEZVOUS
SCIENCE AREA 1SCIENCE AREA 1
SCIENCE AREA 3
DivergeDiverge
SCIENCE AREA 1’SCIENCE AREA 1’
TVO
ONE
Selects consistent threads of activity from redundant methods
Tracks
Finds leastlocatio
ncost paths
Executive • pre-plans activities • pre-plans paths • dynamically schedules [Tsmardinos et al.]
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Achieving Program States CombinesLogical Decisions and Trajectory Planning
Vehicle
WaypointObstacle
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Explorers Will Need to Be Dexterous
(Courtesy of Frank Kirchner. Used with permission.)
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Outline
• Model-based Programming
• Autonomous Engineering Operations– An Example– Model based Execution– Fast Reasoning using Conflicts
• Cooperating Mobile Vehicles– Predictive Strategy Selection– Planning Out The Strategy
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Example:Coaching Heterogeneous Teams
• Search and Rescue• Ocean Exploration
• A dozen vehicles is too many to micro manage→ Act as a coach:
• Specify evolution of state and location.
(Courtesy of Jonathan How. Used with permission.)
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Forest Fire Rescue
• Goal: retrieve family from fire.
• Rescue cannot take place until the local fire is suppressed.
• Retrofit one rescue vehicle for fire suppression
Fire Line
Ambulance
Rescue Point
Fire
Forest
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Kirk Model-based Execution System Overview
• Strategy Selectiondetermines the optimal rules / strategies to accomplish mission goals.
• Activity Planning figures out within how to achieve mission goals within strategic framework using available low-level actions.
Mission Controller
Mission Developer
state configuration goals
environment and action data
schedulable plan with rationale
PMPL control
programStrategy macro decomposition
Strategy Selection
TPN Planner
Activity PlanningVisibility Graph
Generative Activity Planner
Strategy Macro Library
Operators, Tactics,
Scenario Model
Human / Computer Interface
MILP Path-Planning
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RMPL Control Program• (defclass rescue-team
(execute () (sequence (parallel [l1,u1] (tell-start(at family RescuePoint)) (tell-start(at uav1 Ambulance)) (tell-start(at uav2 Ambulance)) ) (parallel [l2,u2] (tell-atart(at family RescuePoint)) (ask-end(rescued family)) (ask-end(at uav1 Ambulance)) (ask-end(at uav2 Ambulance)) ) ) ))
Initial State
Intermediate State
Goal State
Phase 1
Phase 2
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Environment Model• Terrain Map
• Object instantiations: – UAV uav1– UAV uav2– RESCU-READY uav1– RESCUE-READY uav2– IN-DISTRESS family– LOCATION Ambulance– LOCATION Fire– LOCATION RescuePoint
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Vehicle Specifications
• Vehicle linearized dynamics• Vehicle primitive operators:
– Fly(V,A,B)• move UAV “V” from location “A” to location “B”
– Refit(V) • Prepare UAV “V” to drop fire retardant
– Drop(V,A) • Drop fire retardant at location “A” with UAV “V”
– Rescue(V,P,A) • Rescue people “P” in distress with UAV “V” at location “A”
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Kirk Model-based Execution System Overview
• Strategy Selectiondetermines the optimal rules / strategies to accomplish mission goals.
• Activity Planning figures out within how to achieve mission goals within strategic framework using available low-level actions.
Mission Controller
Mission Developer
state configuration goals
environment and action data
schedulable plan with rationale
PMPL control
programStrategy macro decomposition
Strategy Selection
TPN Planner
Activity PlanningVisibility Graph
Generative Activity Planner
Strategy Macro Library
Operators, Tactics,
Scenario Model
Human / Computer Interface
MILP Path-Planning
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Kirk Constructs Vehicle Activity PlanUsing a Generative Temporal Planner
Approach: • Encode Goal Plan using an LPGP-style encoding• Prototype using LPGP [Fox/Long, CP03]
Mission Goal State Plan
Vehicle Operator Definitions
Vehicle Activity Plan
Translate to Planning Problem with Atomic Operators
Use Atomic Generative Planner (GraphPlan-Blum & Furst)
To Generate Operators and Precedence
Extract Temporal Plan and Check Schedulability
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Generated Activity Plan
Fire
Kirk extracts a least commitment plan and generates a rationale
Refit-StartRefit-Inv[10,+lNF] Refit-End
Fly-lnv[20,+lNF]
[20,+lNF][20,+lNF]Fly-Start
Fire
CP-Start CP-lnv-1[0,100]
CP-lnv-1[0,100]
CP-lnv-1[0,100]
Fly-End
CP-lnv-1[0,100]
CP-lnv-1[0,100]
CP-lnv-1[0,100]
CP-lnv-1[0,100][0,100][0,100]
Fly-StartFly-Inv
[20,+lNF]Fly-Inv
[20,+lNF]
Suppress-Start Suppress-lnv[10,20] Suppress-End
[10,20][10,20]
CP-Midpoint
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Kirk Model-based Execution System Overview
• Strategy Selectiondetermines the optimal rules / strategies to accomplish mission goals.
• Activity Planning figures out within how to achieve mission goals within strategic framework using available low-level actions.
Mission Controller
Mission Developer
state configuration goals
environment and action data
schedulable plan with rationale
PMPL control
programStrategy macro decomposition
Strategy Selection
TPN Planner
Activity PlanningVisibility Graph
Generative Activity Planner
Strategy Macro Library
Operators, Tactics,
Scenario Model
Human / Computer Interface
MILP Path-Planning
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Output: Least Commitment Planwith Rationale
Plan layered with rationale Rescue(UAV1,Troops,RSQ)
Fly(UAV1,RSQ,Base)Fly(UAV1,Base,RSQ)Refit(UAV1)
Control Program Phase I
Fly(UAV2,Base,Radar)
Control Program Phase II
Attack(UAV2,Radar) Fly(UAV2,Radar,Base)
[10,+INF] [20,+INF] [30,60] [20,+INF]
[20,+INF]
[0,100]
[10,20]
[0,100]
[20,+INF]
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Kirk Ensures Plan Completeness, Consistency and Minimality
• Complete Plan • A plan is complete IFF every precondition of every activity is achieved. • An activity’s precondition is achieved IFF: • The precondition is the effect of a preceding activity (support), and • No intervening step conflicts with the precondition (mutex).
• Consistent Plan • The plan is consistent IFF the temporal constraints of its activities are co
nsistent (the associated distance graph has no negative cycles), and • no conflicting (mutex) activities can co-occur.
• Minimal Plan • The plan is minimal IFF every constraint serves a purpose, i.e., • If we remove any temporal or symbolic constraint from a minimal
plan, the new plan is not equivalent to the original plan
fact-J
Start
fact-K
[l1,u1][l3,u3]
fact-O
fact-M
[l2,u2] fact-N [l4,u4]fact-P
End
Activity-A Activity-C
Activity-B Activity-D
fact-L
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Plan-based HCI Proof of Concept:Coaching through Coordinated Views
WAYPOINT1
UCAV2
BASE1
SAM1UCAV1
RADAR1
HVT1
Action: FLY-TOActor: UCAV2Objects: WAYPOINT1
Action: FLY-TOActor UCAV1Objects: SAM1
Action: FLY-TOActor: UCAV2Objects: HVT1
Action: ATTACKActor UCAV1Objects: SAM1
Action: ATTACKActor: UCAV2Objects: HVT1[10, 10]
Action: FLY-TOActor UCAV1
Action: FLY-TOActor: UCAV2Objects: BASE1[5, NA]
Set Current Plan Revert Clear Screen
(Courtesy of Howard Shrobe, Principal Research Scientist, MIT CSAIL. Used with permission.)
Action: FLY-TOActor: UCAV2Objects: BASE1[5,NA]
Action: FLY-TOActor: UCAV1Objects: BASE1
Action: FLY-TOActor: UCAV1Objects: SAM1[5,NA]
Action: FLY-TOActor: UCAV2Objects: WAYPOINT1
Action: ATTACKActor: UCAV1Objects: SAM1[10, 10]
Action: FLY-TOActor: UCAV2Objects: HVT1
Action: ATTACKActor: UCAV2Objects: HVT1[10, 10]
PlanTop Level
Activity UCAV2-FLY-TO-WAYPOINT beginning UCAV2-FLY-TO-WAYPOINT Establishes the following prerequisites: UCAV2-FLY-TO-WAYPOINT helps establish (AT UCAV2 WAYPOINT) a prerequisite of UCAV2-FLY-TO-TARGET UCAV2-FLY-TO-WAYPOINT establishes (AT UCAV2 WAYPOINT)
UCAV2 executes a FLY-TO operation on WAYPOINT1Activity UCAV1-FLY-TO-SAM beginning UCAV1-FLY-TO-SAM Establishes the following prerequisites: UCAV1-FLY-TO-SAM helps establish (AT UCAV1 SAM1) a prerequisite of UCAV1-FLY-TO-SAM UCAV1-FLY-TO-SAM establishes (AT UCAV1 SAM1) UCAV1 executes a FLY-TO operation on SAM1UCAV1-FLY-TO-SAM finished, go on? [default Yes]: ▌
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Plan & Geography View
WAYPOINT1
UCAV2
BASE1
SAM1
RADAR1
HVT1
UCAV1
(Courtesy of Howard Shrobe, Principal Research Scientist, MIT CSAIL. Used with permission.)
Sequencing: Action: FLY-TOActor: UCAV2Objects: WAYPOINT1
Action: FLY-TOActor UCAV1Objects: SAM1[5, NA]
Action: FLY-TOActor: UCAV2Objects: HVT1
Action: ATTACKActor UCAV1Objects: SAM1[10, 10]
Action: ATTACKActor: UCAV2Objects: HVT1[10, 10]
Action: FLY-TOActor UCAV1Objects: BASE1
Action: FLY-TOActor: UCAV2Objects: BASE1[5, NA]
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Causal ViewCausality
Explanation
Action: FLY-TOActor: UCAV2Objects: BASE1[5,NA]
Action: FLY-TOActor: UCAV1Objects: BASE1
Action: FLY-TOActor: UCAV1Objects: SAM1[5,NA]
Action: FLY-TOActor: UCAV2Objects: WAYPOINT1
Action: ATTACKActor: UCAV1Objects: SAM1[10, 10]
Action: FLY-TOActor: UCAV2Objects: HVT1
Action: ATTACKActor: UCAV2Objects: HVT1[10, 10]
PlanTop Level
UCAV2-ATTACK-TO-TARGET Has the following prerequisites: UCAV2-ATTACK-TO-TARGET requires (AT UCAV2 HVT1) This was established by Activity UCAV2-FLY-TO=TARGET achieving (AT UCAV2 HVT1)
UCAV2-ATTACK-TO-TARGET Establishes the following prerequisites: UCAV2-ATTACK-TO-TARGET helps establish (DESTROYED HVT1) prerequisite of NEW UCAV2-ATTACK-TO-TARGET establishes (DESTROYED HVT1)
(Courtesy of Howard Shrobe, Principal Research Scientist, MIT CSAIL. Used with permission.)
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Model-based Programmingof Robust Robotic Networks
• Long-lived systems achieve robustness by coordinating a complex network of internal devices.
• Programmers make a myriad of mistakes when programming these autonomic processes.
• Model-based programming simplifies this task by elevating the programmer to the level of a coach: – Makes hidden states directly accessible to the programmer. – Automatically mapping between states, observables and control
variables.• Model-based executives reasoning quickly and extensively by
exploiting conflicts.• Mission-level executives combine activity planning, logical
decision making and control into a single hybrid decision problem.