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[DPRG] Placement and interpretation of ultrasonic
Subject: [DPRG] Placement and interpretation of ultrasonic
From: Triffid Hunter
triffid_hunter at funkmunch.net
Date: Tue Jun 5 23:42:41 CDT 2007
On Tue, 5 Jun 2007, Ed Paradis wrote:
> On the Tankbot, we had mounted a small array of Maxbotix sensors.
> While they _are_ very narrow beam width sensors, they will still cross
> talk.
>
> The simple solution used on the Tankbot was to poll each sensor one at
> a time. We used the pulse width output, and simply waited the full
> 255ms time period for each sensor, regardless of when the pulse came
> back. This gave us a constant known sensor rate (all four sensors
> return each second.
Simple, effective, but takes a relatively long time to build a map.
An excellent starting point, but improvements are possible :)
> You could also simply wait till one sensor returns its data, and then
> pulse the other. For two sensors, this would allow for a high refresh
> rate from the sensors. This usually means you can detect objects and
> the associated collision faster, and therefore your robot can drive
> faster.
Only problem with this method is that it can be difficult to tell the
difference between the reflections from each pulse. Pulses return via
multiple paths from everything in front of the sensor, not just the
nearest object.
Some of the more complex robots (and ground radar) exploit the multiple
return pulses to build their map faster, and I've read a paper
( http://www-personal.umich.edu/~johannb/Papers/paper32.pdf ) that
'scatter-fires' the sonar units in a pseudo-random fashion, then applies a
best-fit algorithm to the results in order to differentiate between
reflections from the associated tx and other txs with an overlapping field
of view or multiple reflection paths around the robot.
Johann Borenstein has written heaps of very interesting papers including
"Where am I?" - Systems and Methods for Mobile Robot Positioning, and
University of Michigan Benchmark (UMBmark) test and calibration procedure
for measuring and improving odometric accuracy in mobile robots.
Check them all out at http://www-personal.umich.edu/~johannb/
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