A Robust Layered Control System for a Mobile Robot

1
A Robust Layered Control System for a Mobile Robot

• Rodney A. Brooks
• Presenter Michael Vidal

2
Requirements

• Multiple Goals
• Multiple Sensors
• Robustness
• Extensibility

3
Starting Assumptions

1. Complex behavior need not be reflected by a
   complex control system
2. Things should be simple
3. Map making is of critical importance
4. A robot must model in 3 dimensions
5. Relational maps are more useful
6. Build no artificial environment for the robot

4
Starting Assumptions

1. Visual data allows for intelligent interaction
   with the world
2. Processing steps should be self-calibrating
3. Robots should be self-sustaining

5
Levels of Competence

• Typical composition of robotic functions includes
  5 sections
• Sensing
• Mapping
• Planning
• Task execution
• Motor Control
• This division represents a solution based on the
  internal functionality of the robot

6
Levels of Competence

• Proposed approach creates levels based on
  expected external functionality
• Avoid contact with objects
• Wander around aimlessly (without hitting things)
• Explore the world
• Build a map of the world to plan routes
• Notice changes in the static environment
• Reason about the world and perform tasks
• Formulate and execute plans to change the world
• Reason about the behavior of objects and modify
  plans accordingly

7
Layers of Control

• Layers of control directly map to layers of
  confidence
• Subsumption architecture
• Build and debug a control layer with level 0
  confidence
• Level 0 layer should never be altered
• Add one layer of control at a time to previous
  layers
• A layer may examine the data of the layer below
  it
• A layer may interfere with the layer below it

8
Layers of Control

• This approach naturally lends itself to meeting
  the stated requirements
• Multiple Goals Individual layers may work on
  individual goals concurrently
• Multiple Sensors Sensors need not feed data into
  some central representation
• Robustness Lower layers continue to function
  when higher layers fail
• Extensibility Each layer can run on its own
  processor

9
Layer Structure

• Each layer (module) an individual processor
• Each module has some number of inputs and outputs
• Modules connected by wires
• Wires generally connect a layers output to the
  input of the layer below
• Messages passed are unreliable

10
Implementation

• 0-Level Layer Avoid
• Ensures that the robot does not come in contact
  with other objects
• Will avoid stationary objects
• Will flee from moving obstacles
• Consists of a number of mini-modules, including
  sonar, collide, feelforce, runaway,
  turn, and forward
• The latter two interact directly with the robot

11
Implementation

• Level 1 Layer Wander
• Creates a new destination for the robot every few
  seconds
• Relies on 0-level functionality to avoid
  obstacles
• Adds two mini-modules to the system Wander,
  and Avoid

12
Implementation

• Level 3 Layer Explore
• Allows the robot to seek out interesting places
  to visit
• Adds the mini-modules Stereo, Look,
  Pathplan, Integrate, and Whenlook
• Impedes output of level 1 layer to reach its goal