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Multi Robot System

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Title: Multi Robot System


1
?? ??? ???
  • Multi Robot System
  • Mehrdad bibak

2
(No Transcript)
3
Multi-Robot Systems
4
Multi-Robot Systems
5
Multi-Robot Systems
6
Multi-Robot Systems
  • Biological Inspirations
  • Communication
  • Architectures, task allocation, and control
  • Localization, mapping, and exploration
  • Object transport and manipulation
  • Motion coordination
  • Reconfigurable robots

7
Multi-Robot Systems
  • Biological Inspirations
  • The most common application of this knowledge is
    in the use of the simple local control rules of
    various biological societies ? particularly ants,
    bees, and birds? to the development of similar
    behaviors in cooperative robot systems.
  • Nearly all of the work in cooperative mobile
    robotics began after the introduction of the new
    robotics paradigm of behavior based control
  • Competition in multi-robot systems, such as that
    found in higher animals including humans, is
    being studied in domains such as multi-robot
    soccer.

8
Multi-Robot Systems
  • Communication
  • implicit and explicit
  • implicit communication occurs as a side-effect of
    other actions.
  • explicit communication is a specific act designed
    solely to convey information to other robots on
    the team.
  • More recent work in multi-robot communication has
    focused on representations of languages and the
    grounding of these representations in the
    physical world

9
Multi-Robot Systems
  • Architectures, task allocation, and control
  • A great deal of research in distributed robotics
    has focused on the development of architectures,
    task planning capabilities , and control.
  • Three architectures (for Example)
  • Linear
  • Parallel of linear
  • Tree structured

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Multi-Robot Systems
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Multi-Robot Systems
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Multi-Robot Systems
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Multi-Robot Systems
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Multi-Robot Systems
  • Localization, mapping, and exploration
  • Almost all of the work has been aimed at 2D
    environments.
  • most of this research took an existing algorithm
    developed for single robot mapping ,localization,
    or exploration, and extended it to multiple
    robots.
  • Object transport and manipulation
  • Enabling multiple robots to cooperatively carry,
    push, or manipulate common objects has been a
    long-standing, yet difficult, goal of multi-robot
    systems.
  • Motion coordination
  • An advancement in the analysis of motion
    coordination in multi-robot teams is the
    development of provable theorems that
    characterize the cooperative performance of team
    formations under certain conditions.
  • Reconfigurable robots

15
Multi-Robot Systems
16
Multi-Robot Systems
  • Cooperation situation in which several robots
    operate together to perform some global task that
    either cannot be achieved by a single robot , or
    whose execution can be improved by using more
    than one robot, thus obtaining higher
    performances.
  • Awareness the property of a robot in the MRS to
    have knowledge of the existence of the other
    members of the system.
  • Coordination cooperation in which the actions
    performed by each robotic robot take into account
    the actions executed by the other robotic robots
    in such a way that the whole ends up being a
    coherent and high-performance operation.

17
Multi-Robot Systems
  • Centralization the organization of a system
    having a robotic agent (a leader) that is in
    charge of organizing the work of the other
    robots the leader is involved in the decisional
    process for the whole team, while the other
    members act according to the directions of the
    leader.
  • Distribution the organization of a system
    composed by robotic agents which are completely
    autonomous in the decisional process with respect
    to each other in this class of systems a leader
    does not exist.
  • Strong centralization centralization in which
    decisions are taken by a leader that remains the
    same during the entire mission duration.

18
Multi-Robot Systems
19
Multi-Robot Systems
  • Weak centralization centralization in which more
    then one robot is allowed to become a leader
    during the mission.
  • Direct communication communication that makes
    use of some hard-ware on board dedicated device
    to signal something that the other team members
    can understand..
  • Indirect communication
  • MRS social deliberation a system behavior that
    allows the team to cope with the environmental
    changes by providing a strategy that can be
    adopted to reorganize the team members' tasks, so
    as to use all the resources available to the
    system itself to effectively achieve the global
    goal.
  • MRS reactivity a system behavior in which every
    single robot in the team copes with the
    environmental changes by providing a specific
    solution to reorganize its own task in order to
    fulfill the accomplishment of its originally
    assigned goal.

20
Multi-Robot Systems
21
Task Decomposition Methods
  • 1

22
Task Analysis
Task Decomposition Methods
  • A technique for analyzing existing tasks by
    observation.
  • Doesnt require understanding of Users goals,
    just what they do.
  • But because of that its harder to apply to the
    design of a newsystem.
  • Good for training materials anddocumentation

23
Task Analysis 3 Approaches
Task Decomposition Methods
  • Tasks decomposition looks at how a task is split
    into subtasks and the order in which these are
    performed.
  • Knowledge-based techniques what do users need to
    know about the objects and actions involved in a
    task? How is that knowledge organized?
  • Entity-relation-based analysis an object-based
    approach, identify objects, relationships and
    actions.

24
Task Decomposition
Task Decomposition Methods
  • Break the task into subtasks
  • Hierarchical Task Analysis (HTA)
  • Organize tasks into a hierarchy
  • Include ordering constraints
  • Looks something like logic programming (PROLOG)

Clean house
Get vacuumcleaner
Cleanrooms
Emptydust bag
Put everythingaway
Cleanhall
Cleanliving room
Cleanbedrooms
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Task Decomposition
Task Decomposition Methods
  • 0. In order to clean house
  • Get vacuum cleaner out
  • Fix attachment
  • Clean the rooms
  • 3.1 Clean the hall
  • 3.2 Clean the living rooms
  • 3.3 Clean the bedrooms
  • Empty the dust bag
  • Put the vacuum cleaner away
  • Plan 0 Do 1-2-3-5 in that order
  • Plan 3 Do any of 3.1, 3.2, and 3.3 in any
    order depending on which rooms need cleaning

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Task Decomposition Methods
  • 2

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Task Decomposition
Task Decomposition Methods
  • A divide-and-conquer approach can reduce the
    complexity of a task smaller subtasks require
    less capable agents and fewer resources
  • The system must decide among alternative
    decompositions, if available
  • Successful task decomposition depends greatly on
    a designers choice of operators
  • The decomposition process must consider the
    resources and capabilities of the robots. Also,
    there might be interactions among the subtasks
    and conflicts among the robots

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Task Decomposition Methods
Task Decomposition Methods
  • Inherent (free!) the representation of the
    problem contains its decomposition, as in an
    AND-OR graph
  • System designer (human does it) decomposition is
    programmed during implementation. (There are few
    principles for automatically decomposing tasks)
  • Hierarchical planning (robots do it)
    decomposition again depends heavily on task and
    operator representation

29
Task Decomposition Examples
Task Decomposition Methods
  • Spatial decomposition by information source or
    decision point
  • Functional decomposition by expertise

Agent 1
Agent 3
Agent 2
Pediatrician
Internist
Neurologist
Psychologist
Cardiologist
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Task Distribution Criteria
Task Decomposition Methods
  • Avoid overloading critical resources
  • Assign tasks to robots with matching capabilities
  • Make an robot with a wide view assign tasks to
    other robots
  • Assign overlapping responsibilities to robots to
    achieve coherence
  • Assign highly interdependent tasks to robots in
    spatial or semantic proximity. This minimizes
    communication and synchronization costs
  • Reassign tasks if necessary for completing urgent
    tasks

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Task Distribution Mechanisms
Task Decomposition Methods
  • Market mechanisms tasks are matched to robots by
    generalized agreement or mutual selection
    (analogous to pricing commodities)
  • Contract net announce, bid, and award cycles
  • Multiagent planning planning robots have the
    responsibility for task assignment
  • Organizational structure robots have fixed
    responsibilities for particular tasks
  • Recursive allocation responsible agent may
    further decompose task and allocate the resultant
    subtasks

32
Task Decomposition Methods
  • 3

33
Task Decomposition Methods
Task Sharing and Result Sharing
  • Three stages
  • Problem decomposition
  • Sub-problem solution
  • Solution synthesis

Problem decomposition
  • Iteratively hierarchically decompose overall
    problem into smaller subproblems until robot can
    solve them
  • Different decomposition levels ?? different
    levels of abstraction

34
Task Decomposition Methods
Task Sharing and Result Sharing
Problem decomposition
  • Important Decomposition granularity.decomposed
    problem until sub-problems are at the level of
    programming language commands ? too fine grained.
    ? problems with synthesis, management overhead
    etc. outweigh decomposition advantages

Sub-problem solution
  • Sharing of information during sub-problem
    solution

Solution synthesis
  • may also be hierarchical (respecting different
    levels of abstraction)

35
Coordination
  • Coordination Managing inter-dependencies
    between the activities of robots
  • Examples of inter dependencies
  • 2 people want to go through the same door
  • I cannot proceed with my work until you have
    given your ok
  • I make you a copy of an interesting paper
    without being asked to do so
  • Inter dependencies can be positive or negative
  • Positive relationships (benefits for at least
    one of the robots while leaving others at least
    as happy (? pareto-optimality) may be requested
    or non requested

36
Coordination
consumable resource
resource
non-consumable resource
negative
inter-dependencies
incompatibility
requested (explicit)
positive
non-requested (implicit)
37
Coordination
  • Three types of non-requested interdependencies
  • Action-equality-interdependence Both robots
    need to have action a done ? one of them can do
    it
  • Consequence-interdependence Actions of one
    robots plan have side effect of achieving other
    robots goal
  • Favour-interdependence Actions of one robots
    plan have side effect of partially achieving
    other robots goal (positively contributing to
    it)
  • 3 iterated stages
  • each robot decides about his goals, creates
    local plan
  • robots exchange plans to determine
    interdependencies\\
  • robots alter local plans to achieve better
    coordination

38
communication Methods
  • Black boarding (Strong centralized system)
  • Knowledge sharing (Weak centralized system)
  • Communicative language (Distributed system)
  • Same language
  • Different language
  • language
  • Structure of language
  • Type of language

39
communication Methods
  • Message
  • direct exchange
  • common language
  • conversation - sequences of messages
  • Blackboard
  • information available for all
  • no direct communication
  • simple architecture

robot
robot
Blackboard
robot A (Sender)
robot B (Receiver)
Message
robot
robot
robot
robot
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communication Methods
  • Consider
  • performative requestcontent the door is
    closedspeech act please close the door
  • performative informcontent the door is
    closedspeech act the door is closed!
  • performative inquirecontent the door is
    closedspeech act is the door closed?

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communication Methods
  • (Request
  • Sender sender1
  • Receiver receiver1
  • Language KIF/FIPA
  • Ontology Ontology1
  • Reply-With 1
  • Content content1

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communication Methods
  • We now consider robot communication languages
    (ACLs) standard formats for the exchange of
    messages
  • The best known ACL is KQML, developed by the ARPA
    knowledge sharing initiativeKQML is comprised of
    two parts
  • the knowledge query and manipulation language
    (KQML)
  • the knowledge interchange format (KIF)

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communication Methods
  • KQML is an outer language, that defines various
    acceptable communicative verbs, or
    performativesExample performatives
  • ask-if (is it true that. . . )
  • perform (please perform the following action. .
    . )
  • tell (it is true that. . . )
  • reply (the answer is . . . )
  • KIF is a language for expressing message
  • content

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communication Methods
  • The temperature of m1 is 83 Celsius(
    (temperature m1) (scalar 83 Celsius))
  • An object is a bachelor if the object is a man
    and is not married(defrelation bachelor (?x)
    (and (man ?x) (not (married ?x))))
  • Any individual with the property of being a
    person also has the property of being a
    mammal(defrelation person (?x) gt (mammal ?x))

45
communication Methods
  • In order to be able to communicate, robots must
    have agreed on a common set of terms
  • A formal specification of a set of terms is known
    as an ontology
  • The knowledge sharing effort has associated with
    it a large effort at defining common ontologies
    software tools like monolingual for this purpose
  • Example KQML/KIF dialogueA to B (ask-if (gt
    (size chip1) (size chip2)))B to A (reply
    true)B to A (inform ( (size chip1) 20))B to
    A (inform ( (size chip2) 18))

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