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Wireless Positioning System

Wireless Positioning System. Compiled by Austin Stoker ECE 5320 Spring 2012 Dr. Chen. I want a robot lawn mower but I don’t want to bury a wire. What sensor could I use?. GPS. Only accurate to a few meters . Small (1cmx1cmx.2cm) Cheap ($3-$30). Image from Wikipedia /GPS

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Wireless Positioning System

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  1. Wireless Positioning System Compiled by Austin Stoker ECE 5320 Spring 2012 Dr. Chen

  2. I want a robot lawn mower but I don’t want to bury a wire. What sensor could I use?

  3. GPS • Only accurate to a few meters. • Small (1cmx1cmx.2cm) • Cheap ($3-$30) Image from Wikipedia/GPS Dimensions and prices http://www.semiconductorstore.com/cart/pc/viewprd.asp?idProduct=42046

  4. Corrected GPS • Expensive • Requires base station. • Note: By 2020 (probably sooner) new GPS satellites will make 10cm GPS as cheap as 10m GPS is today.

  5. Video Sensors • Complex to implement • Not highly reliable

  6. Acoustic GPS • Accurate. (~1 inch) • Fairly easy to implement • Cheap • Only works within setup area • Requires programming • Requires assembly

  7. How APS works Measuring the time in takes to receive a sound signal from 3 different beacons with known locations the sensor can triangulate it’s location. With only 2 bases the position can be found if the robot is supposed to be within the bounds of the bases. Base #1 Base #2 Base #3

  8. How APS works (cont.) • The robot sends a request via RF transmitter. • The RF request is encoded for a specific base. The base responds with a uniquely modulated audio transmission. This is repeated for each base.

  9. How APS works (cont.) • The robot times the response time of each signal. Calculates the distance to each base and triangulates it’s position.

  10. Parts • Acoustic sensor/transmitters • Murata MA40S4S/R • $10 each Prices from www.mouser.com/

  11. Parts • Computation board • Microchip dsPIC 30F401 • $7 Prices from www.mouser.com

  12. Parts • RF transmitters/reciever • EasyRadio ~$20-$40 www.active-robots.com/

  13. How to use • Accuracy of 1cm or less has been shown. Plenty good for a lawn mower if it is equipped with touch sensors for curbing and such.

  14. How to use • Avoid interference noise of 40kHz

  15. How to use • Allow enough time between requesting from station 1 and station 2. At least 30ms per meter of diameter of lawn.

  16. Calculations http://www.ias.uwe.ac.uk/~a-winfie/Bjerknes_etal_TAROS07.pdf

  17. Details • Since the beacons positions are known S is known • It is simple from the knowledge of the position of the beacons to calculate the h and y and thus pinpoint the location of the robot. http://www.ias.uwe.ac.uk/~a-winfie/Bjerknes_etal_TAROS07.pdf

  18. Details Make sure the beacons respond without overlapping http://www.ias.uwe.ac.uk/~a-winfie/Bjerknes_etal_TAROS07.pdf

  19. How accurate? http://www.ias.uwe.ac.uk/~a-winfie/Bjerknes_etal_TAROS07.pdf

  20. Z accuracy in 3D • Z axis accuracy

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