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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. Behavior Control for Robotic Exploration of Planetary Surfaces. Abstract. Describes robots developed at JPL (Jet Propulsion Laboratory)

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Behavior Control for Robotic Exploration of Planetary Surfaces

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  1. Written by Erann Gat, Rajiv Desai, Robert Ivlev, John Loch and David P Miller Presented By Tony Morelli 9/30/2004 Behavior Control for Robotic Exploration of Planetary Surfaces

  2. 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.

  3. 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

  4. 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

  5. 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

  6. ALFA – Code Sample

  7. 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

  8. 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

  9. Tooth Control Structure

  10. 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

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

  12. Rocky III - Overview • Demonstrate behavior control could be used in a realistic planetary mission • Infrared beacon detector • 10 kBytes of RAM • Weighs 18kg

  13. Rocky III – Control Structure • 3 Layers nearly identical to Tooth • Speed and Direction • Obstacle Avoidance • Sequencer

  14. 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

  15. 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

  16. 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)

  17. 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

  18. 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

  19. Questions?

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