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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

Wireless Positioning System

Compiled by Austin Stoker

ECE 5320 Spring 2012

Dr. Chen



GPS What sensor could I use?

  • 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


Corrected gps
Corrected GPS What sensor could I use?

  • Expensive

  • Requires base station.

  • Note: By 2020 (probably sooner) new GPS satellites will make 10cm GPS as cheap as 10m GPS is today.


Video sensors
Video Sensors What sensor could I use?

  • Complex to implement

  • Not highly reliable


Acoustic gps
Acoustic GPS What sensor could I use?

  • Accurate. (~1 inch)

  • Fairly easy to implement

  • Cheap

  • Only works within setup area

  • Requires programming

  • Requires assembly


How aps works
How What sensor could I use?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


How aps works cont
How APS works (cont.) What sensor could I use?

  • 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.


How aps works cont1
How APS works (cont.) What sensor could I use?

  • The robot times the response time of each signal. Calculates the distance to each base and triangulates it’s position.


Parts
Parts What sensor could I use?

  • Acoustic sensor/transmitters

    • Murata MA40S4S/R

    • $10 each

Prices from www.mouser.com/


Parts1
Parts What sensor could I use?

  • Computation board

    • Microchip dsPIC 30F401

    • $7

Prices from www.mouser.com


Parts2
Parts What sensor could I use?

  • RF transmitters/reciever

    • EasyRadio ~$20-$40

www.active-robots.com/


How to use
How to use What sensor could I 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.


How to use1
How to use What sensor could I use?

  • Avoid interference noise of 40kHz


How to use2
How to use What sensor could I use?

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


Calculations
Calculations What sensor could I use?

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


Details
Details What sensor could I use?

  • 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


Details1
Details What sensor could I use?

Make sure the

beacons respond

without

overlapping

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


How accurate
How accurate? What sensor could I use?

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


Z accuracy in 3d
Z accuracy in 3D What sensor could I use?

  • Z axis accuracy


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