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 #2 Base #3 Base #1

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/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