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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
Abstract
● Describes robots developed at JPL (Jet Describes robots developed at JPL (Jet Propulsion Laboratory)Propulsion Laboratory)
● Demonstrate using behavior-control Demonstrate using behavior-control approach to control small robots on approach to control small robots on planetary surfacesplanetary surfaces
● Behavior-Control uses very little Behavior-Control uses very little computation.computation.
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
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
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
ALFA – Code Sample
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
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
Tooth Control Structure
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
Tooth - Results
● No way of searching out objects, just finds them while wandering around
● Very Robust● Could not handle wires, holes or bright lights
Rocky III - Overview
● Demonstrate behavior control could be used in a realistic planetary mission
● Infrared beacon detector● 10 kBytes of RAM● Weighs 18kg
Rocky III – Control Structure
● 3 Layers nearly identical to Tooth– Speed and Direction– Obstacle Avoidance– Sequencer
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
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
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)
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
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
Questions?