Re: Location Detection

Hello All

I noticed on a previous post by Aleksandar the use of RFID for 
recalibration of a positioning solution based on accelerometers.
I do not have experience with RFIDs and i do not know the "distance 
resolution" that the AGC stage of an RFID receiver can offer 
(pressumably the fine tuning of location is done by measuring the signal 
strength from at least 3 tags). If one is interested in rough 
positioning of the kind "I know that my robot is now in room 117C" it 
seems OK, BUT if one is interested in laying down RFIDs in known 
positions (probably obtained with GPS) and then having the robot to 
recalibrate itself once it meets one of the tags (to account for "swell" 
or any other accumulative errors of an inertial navigation system) then 
this solution is not a serious candidate. I suspect that the RFID tag 
can be sensed (as a hard decision like YES / NO) within a circle of 
radius R which introduces a serious error when positioning is performed 
in small spaces.

As far as accelerometers are concerned, i found a very nice (although a 
bit bulky) project that uses 6 accelerometers for a strapdown inertial 
navigation system. You can find it here:
http://www.electronic-engineering.ch/study/ins/ins.html
With sources about the sensors as well.

Also, STMicroelectronics is manufacturing three axis accelerometers in a 
single chip (2g-6g range) with analog and digital outputs that are 
capable of detecting even static gravitational fields (like earths 
gravitational field for example). More about it here:
http://www.st.com/stonline/prodpres/dedicate/mems/products/lis3l02.htm

So theoritically, 6 DOF sensing can be done with two ST accelerometers 
(one for sensing linear acceleration and one 3 axis linear accelerometer 
for sensing tilt) tightly packed together and mounted on the robot...Any 
chance of having these on an AcceliStix? :-)

All the best.
thanOS


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