Behavior Control for Robotic Exploration of Planetary Surfaces

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Behavior Control for Robotic Exploration of
Planetary Surfaces

• Written by Erann Gat, Rajiv Desai, Robert Ivlev,
  John Loch and David P Miller
• Presented By Tony Morelli
• 9/30/2004

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Abstract

• Describes robots developed at JPL (Jet Propulsion
  Laboratory)
• Demonstrate using behavior-control approach to
  control small robots on planetary surfaces
• Behavior-Control uses very little computation.

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Introduction

• Cannot remote control robots from Earth because
  of the delay
• Size is limited by power, not physical size
• 3 ways to power a robot
• Radioisotope Thermal Generators (decay of
  Plutonium)
• Photovoltaic cells Require heavy batteries
• Non-Rechargable batteries Short life

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Behavior control

• (Rod) Brooks Decompose the problem by task
  rather than function Subsumption
• Advantages of Behavior Based Control
• Fast behaviors are not slowed down by slow
  behaviors (act independent of each other)
• Task Specific so designers can simplify the
  behavior

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ALFA A Language For Action

• Programming Language to describe reactive
  behavior-control mechanisms for
  autonomous robots
• Consists of Modules connected by Channels
• Module Converts inputs to a set of outputs
• Channel Dataflow Data from Modules or sensors
• Similar to Subsumption
• No Wires
• Easier to add modules
• Provide layers of computational abstraction
  rather than layers of functionality

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ALFA Code Sample

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Tooth - Overview

• 30 cm X 20 cm Indoor Robot
• 1 Bit Sensors
• Grippers and rear bumper
• Infrared Proximity Sensors
• Analog Sensors
• Photo Cells (Find Light Beacon)
• Tachometer on the drive motors
• Used 3.5kBytes of EEPROM and 100 bytes of RAM

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Tooth Control Structure

• Drive Processor/Grasp Processor
• Bottom Up Design
• Cooridinating the Drive and Steering Motors
• Backing up and getting out of endless loops
• Picking up/Dropping objects Head to beacon

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Tooth Control Structure
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Tooth Getting Out of Loops and Dead Ends

• Unthrash Module
• Lower priority than obstacle avoidance
• Counts the number of times the robot changes
  direction in a certain amount of time and tunrs
  at a random direction if it thinks it's stuck
• Dead ends If the Robot hits a dead end it will
  back up, then try to go forward. If it hits a
  wall again, it will back up more the next time.
• Grasp Module If it tries too many times to pick
  up something, it will give up
• Forward turning radius is different than backwards

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Tooth - Results

• No way of searching out objects, just finds them
  while wandering around
• Very Robust
• Could not handle wires, holes or bright lights

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Rocky III - Overview

• Demonstrate behavior control could be used in a
  realistic planetary mission
• Infrared beacon detector
• 10 kBytes of RAM
• Weighs 18kg

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Rocky III Control Structure

• 3 Layers nearly identical to Tooth
• Speed and Direction
• Obstacle Avoidance
• Sequencer

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Rocky III - Results

• Very Reliable
• 90 of the time completes its mission
• First example of an autonomous that operates in
  outdoor natural terrain that performs both
  navigation and manipulation

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Rocky IV - Overview

• Chasis is virtually identical to Rocky III
• Weighs 7.5kg
• Construction Materials were modified to work in
  the climate on mars.
• 1 Master Processor and 3 slave processors

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Rocky IV - Status

• Not yet complete
• Every aspect of a Mars mission has been
  demonstrated
• Hardware Issues Activating the rock chipper
  caused the computer to crash (Obviously not
  software related)

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Discussion

• Behavior control succeeds because action
  selection is not a difficult problem.
• ALFA code is easy to write, debug, and re-use
• Other robots were larger because they were
  required to scale a 1 meter tall objects
• Few simple sensors work as well as a lot of
  complex sensors

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Summary and Conclusion

• Low power consumption is a necessity
• Low CPU usage to save power
• Used a modified version of subsumption
• ALFA seperates data flow computations from state
  machine computations
• As complex as other State of the Art robots

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Questions?