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For Regular Seminar Robot Software Dec. 23, 2003 Jaesoo Lee RTOS Lab., SoEECS, SNU Contents Requirements of Robot Software History of Robot Software Architecture SPA (Sense-Plan-Act) Subsumption Hybrid Our Robot Software Architecture

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Robot software l.jpg

For Regular Seminar

Robot Software

Dec. 23, 2003

Jaesoo Lee


Contents l.jpg

  • Requirements of Robot Software

  • History of Robot Software Architecture

    • SPA (Sense-Plan-Act)

    • Subsumption

    • Hybrid

  • Our Robot Software Architecture

  • Unexplored Issues Requiring Further Research

  • Remarks on Robot Research

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Robot Software - Requirements

  • Basic capabilities: deliberation + reactivity

  • Requirements

    • Programmability – easiness of introducing new goals

    • Autonomy and adaptability – aware current goal, execution context

    • Consistent behavior – reactions guided by objectives

    • Robustness – fault tolerance

    • Extensibility – pluggable, reusable, and reconfigurable components

    • Coordination – multiple goals, multiple (redundant) sensors

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SPA (Sense-Plan-Act)

  • Features

    • Unidirectional and linear flow of control

    • Easy execution of a plan (task execution)

      • Partial orderings, conditionals, and loops

  • Shortcomings

    • Planning and world modeling are very hard problems

    • Open-loop plan execution is inadequate in uncertain and unpredictable environment

    • Very slow !!

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  • Vertical (hierarchical) decomposition of tasks

    • Behaviors in higher layer implement more complex, specified task

    • Each behavior still follows SPA architecture

  • “The World is its own best model”

    • No internal models, sense the surroundings on need instead

    • Direct, ego-centric, and distributed perception

  • Lisp-like languages to describe behaviors (Augmented Finite State Machine and connecting wires)

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Level 2: explore

Level 1: wander

every 10sec

Level 0: avoid objects


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  • Advantages

    • Good reactiveness, inherent concurrency

    • The lower levels have no awareness of higher levels

    • Competitive coordination with inhibition and suppression mechanisms

    • Provides a development architecture to incrementally build and test a complex system

  • Shortcomings

    • Bad modularity

      • Upper layers interfere-with/depend-on the internal functions of lower-level behaviors

      • Increasingly complex

    • Bad runtime flexibility

      • Priorities are hardwired

    • No support for reverse suppression

    • No global planning

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Hybrid Architecture

  • Goal: reactive planning

    • Slow planning (SPA, vulnerable to stale decision)

    • + fast reactivity (Subsumption, subject to fail on sensor errors)

  • Approach: reintroducing/separating planning

  • Organization: Plan, (“Sequencing”), Sense-Act

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Hybrid Architecture

  • 3 layer architecture

    • Deliberate/planning/deliberator

      • State reflecting predictions about the future

      • Reasoning, deliberation, planning, world modeling

    • Task-execution/sequencing/sequencer

      • State reflecting memories about the past

      • Coordination of multiple tasks

    • Reactive/skill/controller/behavior

      • No state, relying on current knowledge

      • Tight feedback control loops

Ex. NASA 3T Architecture

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Huddles and The Trends

  • Planning, world modeling and increasing complexity of autonomous mobile robot system are turned out to be huddles very hard to solve.

  • Among these, AI and robot people are trying to solve the complexity problem by eliminating direct communications between modules

    • TCA by Reid Simmons at CMU

      • Central Control Module, one of framework component, routes messages, manages resources, and executes task sequences

    • CORBA is getting used for telerobotics

Our approach l.jpg
Our Approach

  • Applications in our view point

    • Implements task to achieve specific goals

    • By concatenating behaviors using partial orderings, parallel executions, conditionals and loops

    • Has activation conditions, parameter lists, and affinity

Our approach12 l.jpg

Robot software component architecture


Modularity, reusability

ORB middleware & component model



Robot software component communication architecture

Deployment, implementation

Transparency, efficiency, reusability, retargetability, time-to-market

UML-based development tool

Integrated robot simulator

Design, implementation, simulation, packaging

Our Approach

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Unexplored Issues

  • Middleware issues on QoS

    • End-to-end QoS (deadline, delay, jitter, throughput)

      • Global priority

      • Reservation-based vs. priority-based communication

      • Collocated optimization

      • Schedulability analysis based on constraints annotation

    • Control quality

      • Clock synchronization

      • Real-time event, time-triggered event

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Unexplored Issues

  • Architectural issues

    • Robot software component communication architecture

      • Prioritized suppression/inhibition

      • Subscription/Un-subscription of sensor data

      • Application affinities

    • Sequencer service

    • Reconfiguration on-the-fly and permanent storage

      • Accustom the robot

      • Affinities and default parameters for applications

      • Learning results, acquired landmarks, constructed maps

  • Requires corresponding supports of underlying ORB, OS, and hardware

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Remarks on Robot Research

  • We can do constructing framework better than them, but how about planning and controls ?

  • Even though our approach seems to be on the right way, our potential contributions would be small compared to the paid efforts