Newsgroups: comp.robotics
Path: brunix!uunet!usc!wupost!csus.edu!netcom.com!nagle
From: nagle@netcom.com (John Nagle)
Subject: Re: Laser Range Finder
Message-ID: <hb1nfph.nagle@netcom.com>
Date: Wed, 16 Sep 92 07:34:55 GMT
Organization: Netcom - Online Communication Services  (408 241-9760 guest) 
References: <1992Sep14.161207.22138@mail.cornell.edu>
Lines: 33

YAQX@cornella (Richard Zimmerman) writes:
>	Does anyone have any information on the theory behind a laser range
>finder?  I assume it works by sensing the phase change on the returning
>reflected beam, but I'm not sure of all the smaller details.
>	Also, does anyone have any information on constructing such a device at
>a minimal cost.  (what would a minimal cost really be?)  I'm looking for
>a device to mount on a mobile robot as a obstacle detection device.

       I've been building one, but it's not going well at the moment.
Low-noise high-gain RF amplifiers are hard to build, modulating laser
diodes without blowing them out is hard, the output from PIN photodiodes
is tiny, and the mechanics are a big pain.  But I'm having fun.

       Fundamentally, though, these things ought to be buildable for
under $1000 in modest quantities.  The parts aren't that expensive.
Building the prototype, though, is tough.  

       There are several approaches to laser rangefinding.  The usual
one is to modulate the outgoing beam with an RF carrier, receive the
return beam, extract the RF carrier, and measure the phase difference.
The optics is all vanilla.  The electronics is mostly variations on
standard radio technology.  Ranges to miles are quite possible, with
resolutions down  a few millimeters.  Commercial surveying equipment using 
this technology has been available at least since 1980.  Laser imagers
using this approach have been used by most of the major autonomous
vehicle projects, including the CMU, JPL, and Martin-Marietta machines.

       There's another, simpler approach, and someone out here has a
prototype going.  It's proprietary, though.  I've seen it work.
Range about 20-50' indoors, 5-10' in sunlight.  If anybody wants to
finance this guy, I can put him in touch with you.

       					John Nagle
