Re: Balance between theory and practice




The PatrolBot relies mainly on a laser range-finder
to build floor plans, navigate, avoid obstacles
and monitor movement.


Sounds cool. 



And a laser range-finder sounds expensive?



Actually, you could integrate it into your vision system. (if youll have one) and it wont cost any more than a pocket laser pointer!

Use a webcam for your vision system...a good one 50-100 dollars.

Get yourself a green laser pointer (you can use red, but green not only looks cooler, it's more intense and the beam is usually more coherent for a given amount of power).

Mount the laser point underneath (or above) the webcam perfectly in line with the webcam so that the centerline of the lense is on the same plane and parallel with the laser.

Angle the laser upwards (or downwards if mounted above) so that the minimum distance you want to be able to measure just makes it into the field of view of the webcam. I.E.- if you want to start measuring at a minimum distance of 4 feet, place the apparatus 4 feet away from a flat wall, and adjust the laser so it's barely into the FOV of the webcam.

Then in your software, take a picture and scan it for the brightest pixel in the color your looking for (or the brightest pixel period, green lasers are WAYYY bright and often swamp the detector unless it's very well filtered).

The higher up the pixel is on the picture, the farther away the object is. You could even get fancy and use the shape and intensity of the resultant beam reflection to determine alot of information about the object it's reflecting off of.


I've done this with a logitech webcam (I've got a logitech 3000 pro I think, but anything "should" work) using the logitech SDK which is free to download, and has samples for C and VB. I used VB cause basic is the only language I REALLY know (ok, commence the picking on of me! :-) ).

I wish I could claim this idea for my own but I believe it was developed by a student at MIT or carnegie melon. I found it on the web, dont remember where, and my bookmarks for it are long gone (mozilla has a tendancy to eat my goddamned bookmarks). A google search should turn up good info.

I used it to augment my sonar, and used it sparingly due to the power consumption of the laser and the danger of a super bright green laser whipping around and possibly hitting people in the eye (bad juju). The chip in my webcam is particularly sensitive to IR, so an IR laser would have been cool and a hell of alot more eye safe, but man are they $$$.

You could even externally adjust the position of the laser with steppers o servos to give a good scan, and come up with a 3d model in the 'bots "brain" of what's going on around it to a very fine extent. Alot more difficult for sure, but still possible.


Anywhoo, just an idea (since you'll have a vision system anyways!)

---Andy P
.

Relevant Pages

  • Re: Balance between theory and practice
    ... > Get yourself a green laser pointer (you can use red, ... it's more intense and the beam is usually more coherent ... > Mount the laser point underneath the webcam perfectly in line ...
    (comp.robotics.misc)
  • Re: Balance between theory and practice
    ... > one) and it wont cost any more than a pocket laser pointer! ... > Use a webcam for your vision system...a good one 50-100 dollars. ... > Get yourself a green laser pointer (you can use red, ... > I've done this with a logitech webcam (I've got a logitech 3000 pro I ...
    (comp.robotics.misc)
  • Re: Balance between theory and practice
    ... >> Get yourself a green laser pointer (you can use red, ... >> Mount the laser point underneath the webcam perfectly in line ... >> pixel in the color your looking for (or the brightest pixel period, ...
    (comp.robotics.misc)
  • Re: Balance between theory and practice
    ... If you have jsut a point source, it's not that difficult to pick out which pixel is the one your looking for, even if there are multiple reflections, because you know, generally, where the laser is pointed. ... If you had a wide continuous beam, youll get alot of reflected shapes, not just points, and the software to find your "line" would have to be alot more complex and intensive. ... An idea better than a wide beam would be to set the webcam to a very high frame rate. ... This will make the contrast horrible for the bulk of the picture, but the laser is a very bright and intense source of light and it's entirely possible it would be the only thing left in the frame visible to the camera. ...
    (comp.robotics.misc)
  • Re: Red or green laser?
    ... I and many others have been using red lasers at night for years _ ... CL> <5mW red laser makes an effective pointer to celestial objects! ... CL> the green laser is hard to see for anyone more than a few feet from the source. ... star viewings at Jones Beach, ...
    (sci.astro.amateur)