a decentralized architecture for multi-robot systems based ... · gianluca antonelli università...
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Alessandro Marino Università degli Studi di Cassino
Gianluca Antonelli Università degli Studi di Cassino
Fabrizio Caccavale Università degli Studi della Basilicata
Lynne E. Parker University of Tennessee, Knoxville
A decentralized architecture for multi-robot systems based on the Null-Space-Behavioral control with
application to multi-robot border patrolling
Automatica.it 2011 Pisa, 7 Settembre 2011
Outline
• The border patrolling mission • Null-Space-based (NSB) behavioral approach • Centralized NSB approach to multi-robot border patrolling • Decentralized NSB approach to multi-robot border patrolling
• Simulation and experimental results
• Area patrolling (cenni) • Conclusions
Automatica.it 2011 Pisa, 7 Settembre 2011
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Simulation example
The Border Patrolling Mission
Patrol a border by means of one or more (semi)autonomous agents
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Automatica.it 2011 Pisa, 7 Settembre 2011
Task function
Inverse solution
NSB 1/2 A Null-space Based Behavioral ApproachTo Multi-Robot Patrolling
Automatica.it 2011 Pisa, 7 Settembre 2011
Task velocity
with
with
Handling two behaviors
Any number of tasks can be handled. In the case of three tasks:
NSB 2/2 A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Automatica.it 2011 Pisa, 7 Settembre 2011
Centralized NSB approach
Primary Task Secondary Task
Output velocities (NSB)
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Automatica.it 2011 Pisa, 7 Settembre 2011
Decentralized Border Patrolling
Desired Goals Development and testing of a decentralized control architecture
for border patrolling such that:
Requirements
The solution has to be fully decentralized: each robot acts based only on its own sensory information The solution has to be robust vs changes in the number of teammates Collisions among robots must be avoided also in very critical conditions (high density) The algorithm has to be computationally efficient
Main Assumptions Each robot can localize itself in the environment Each robot knows the geometric description of the border Each robot has a visibility range in which it detects the presence of other agents (teammates, friends, others) Each robot has a safety range (collisions)
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Automatica.it 2011 Pisa, 7 Settembre 2011
The same for each robotic agent
Supervisor
behaviors actions NSB
sensors actuators
Elementary behaviors Behaviors combined in more complex actions in the NSB framework The Supervisor, on the basis of sensory information, selects the action to be executed (velocity commands)
Architecture A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Automatica.it 2011 Pisa, 7 Settembre 2011
Reach Frontier
This behavior allows the robot to reach the border along the shortest path Null space tangent to the border
Behaviors 1/3
Supervisor
behaviors actions NSB
sensors actuators
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Automatica.it 2011 Pisa, 7 Settembre 2011
Clockwise (Counterclockwise) Patrol
They define the motion direction along the border Null space normal to the border
Behaviors 2/3
Supervisor
behaviors actions NSB
sensors actuators
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Automatica.it 2011 Pisa, 7 Settembre 2011
Avoid (Teammate or Friend)
As a robot (blue) enters the safety area of another robot (red), a velocity command (radially directed) is generated, forcing the robot to stay on the border of the safety area The Null-space direction is tangent to the circle
Behaviors 3/3
Supervisor
behaviors actions NSB
sensors actuators
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Automatica.it 2011 Pisa, 7 Settembre 2011
Action Reach Frontier
Coincides with the elementary behavior Reach Frontier Activated when the robot is far from the border: in this case, the only objective is to reach the border as soon as possible
Actions 1/4
Supervisor
behaviors actions NSB
sensors actuators
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Automatica.it 2011 Pisa, 7 Settembre 2011
Action Patrol Clockwise (or Counterclockwise)
They are composed by two behaviors fully compatible in the NSB sense Forces the robot to stay on the border while moving in the clockwise or counterclockwise direction Activated to change the motion direction, when, e.g., a robot is met along the path
Actions 2/4
Supervisor
behaviors actions NSB
sensors actuators
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Automatica.it 2011 Pisa, 7 Settembre 2011
Action Keep Going
Actions 3/4
Composed by two behaviors fully compatible in the NSB sense Activated to confer some unpredictability to agents patrolling behavior: based on a random variable, every T seconds the robot changes its patrolling direction
F(t,
r)
F(t,
r)
Supervisor
behaviors actions NSB
sensors actuators
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Automatica.it 2011 Pisa, 7 Settembre 2011
Action Friend (or Teammate) Avoidance
Resulting path
Actions 4/4
Composed by two behaviors in general not fully compatible in the NSB sense Forces the robot (blue) to reach the frontier while avoiding another agent (black): motion along the circular border of the safety area of the agent
Supervisor
behaviors actions NSB
sensors actuators
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Automatica.it 2011 Pisa, 7 Settembre 2011
Supervisor
behaviors actions NSB
sensors actuators
Two Supervisors: Finite State Automata: simple design (with a small number of states) Fuzzy Logic Inference System: linguistic rules to define the action selection mechanism
Supervisor 1/2
FSA FLIS
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Automatica.it 2011 Pisa, 7 Settembre 2011
Supervisor
behaviors actions NSB
sensors actuators
3 macro-state {MS1, MS2, MS3} Each state associated with an action C1: border out from visibility area C2: distance from border less than a given threshold
c1: teammate in safety area c2: teammate on the left c3: teammate on the right c4: !c2 & !c3
C1
MS1: border not in the visibility area
C2
Action Reach Frontier
Action Avoid Teammate
Action Keep Going
Action Avoid Teammate
MS1: border in the visibility area
Action Patrol CW
Action Patrol CCW
Action Keep Going
MS3: robot patrolling
c1
!c1
c1
!c1
!c2
c2 !c3
c3
!C1
!C2
c4
Supervisor 2/2
Corso di Dottorato in Ingegneria Industriale e dell’Innovazione, Ciclo XXII
Finite State Automata
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Simulations A large number of patrolling robots is present (green); their visibility and safety areas are assumed to be equal; friends (red) enter the border; sudden faults
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Experiments and Simulations 1/7
Automatica.it 2011 Pisa, 7 Settembre 2011
Distance between robots
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Coverage Index
Simulation without friend vehicles Simulation with friend vehicles
Distance between robots and friends
Coverage Index
Experiments and Simulations 2/7
Automatica.it 2011 Pisa, 7 Settembre 2011
Situation immediately after faults
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Coverage Index
Robot Redistribution
Experiments and Simulations 3/7
Automatica.it 2011 Pisa, 7 Settembre 2011
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Experiments and Simulations 5/7
Instantaneous Segment Idleness (ISI) = time elapsed since a border segment has been visited last time Instantaneous Border Idleness (IBI) = average over all the segments of ISI Border Idleness (BI) = average of IBI over the mission duration
IBI BI vs number of robots
Automatica.it 2011 Pisa, 7 Settembre 2011
The Experimental Setup
Three Pioneers 2-DX Localization achieved by means of LRF (particle filter algorithm)
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Experiments and Simulations 5/7
Automatica.it 2011 Pisa, 7 Settembre 2011
Experiments
Open Border
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Experiments and Simulations 6/7
Automatica.it 2011 Pisa, 7 Settembre 2011
Experiments
Closed Border
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Experiments and Simulations 6/7
Automatica.it 2011 Pisa, 7 Settembre 2011
Distance from the border over time
faults
Distance between consecutive robots along the border
Experiments and Simulations 7/7 A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Automatica.it 2011 Pisa, 7 Settembre 2011
Ongoing Work
Area Patrolling
A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Automatica.it 2011 Pisa, 7 Settembre 2011
Probabilistic approach Voronoi-based Map-based Communication required only to exchange maps key data Motion computed to increase information Handle
Spatial variability (patrol more often gates) Time-dependency (come back to visited places) Asynchronous spot visiting demand
Ongoing Work A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Automatica.it 2011 Pisa, 7 Settembre 2011
Voronoi partitions (tessellations/diagrams): subdivisions of a set S characterized by a metric with respect to a finite number of points belonging to the set
The cells union gives back the set The cells intersections is null Computation of the cells is a decentralized algorithm
Ongoing Work A Null-space Based Behavioral Approach To Multi-Robot Patrolling
Automatica.it 2011 Pisa, 7 Settembre 2011
Area patrolling - experimental validation At the Laboratory of Robotics and Systems in Engineering and
Science IST, Technical University of Lisbon 3 Medusas ASVs Virtual obstacles
Greetings
Grazie e buon appetito
Fabrizio CACCAVALE Area Lab
Dipartimento di Ingegneria e Fisica dell’Ambiente
Università degli Studi della Basilicata, Italy [email protected]
www.unibas.it
A Null-space Based Behavioral Approach To Multi-Robot Patrolling