On a recent discussion I was on about the Roomba vacuum, several laser-scanner methods were discussed. Here is one paper on the subject;
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He said, "In all our experiments we used the commercially available Acuity AccuRange4000LR. The Acuity sensor is a compromise between building a laser range finder by one's own and devices like the scanners of SICK (e.g. PLS100, LMS200)."
Another paper mentioned;
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this laser; scanner;
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I've also looked a bit into Microwave radar, having read about it in popular science many years ago. Of course, they are known for touting a technology well before it is viable. I did find some university stuff, but not commercial units for sale. The ones I came across, that seemed to have enough resolution for a mobile robot, had antennas that were way too large for anything less than a human-scale vehicle. Google the .edu domain for "microwave radar" or "MM Wave Radar".
Joe Dunfee