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  1. #21
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    I don't think it would be overly good for digitizing as there won't be much localization in x and y axes. Interesting item though and might well be handy as a sort of adaptable z limit switch perhaps?



  2. #22
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    Default Sharp distance sensor

    Am not sure how you define localization.

    I'm thinking that with the proper tube it might project a beam of about an eighth of an inch in diameter. Part of the sensor uses an intregal light sensor that works as a camera to triangulate the angle to the point of light and estimate distance. The offset distance from light projector to light sensor is a fraction of an inch, so distances less than a foot might be accurate enough. This would probably have to be done in a darkened room, and the object might have to be painted for the best results.

    The machine would have to do some kind of grid search pattern. The beam would hopefully be mounted perfectly perpendicular to the x and y axis. But, if not, it might not matter much. Any small angle off-perpendicular would be consistant throughout the search pattern, so it probably wouldn't be a problem. It would be the same as a slight offset in the true object location.

    Anyway, it looks like it would be a lot cheaper than a laser setup. And wouldn't require laser safety glasses either.



  3. #23
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    "flat black light absorbing tube "

    I didn't understand this to be honest unless you mean to try and remove all but the most collimated rays with a tube.

    The sensors do not respond only to the central point being scanned. If you try and make the light into a beam then if you imagine it comming down at a single angle and then lift the sample (same thing as scanning two points of different height) the beam will traverse the sample and probably move off the sensor. If you make the source vertical then you get no light back to the sensor. Also if the object is angled it will divert the beam and give a false reading.

    A laser setup (and do we know exactly how they normally work for digitizing?) might not be expensive if you base it on a laser pointer. You don't need goggles just a bit of card to put around the digitizing process, if that.

    Graham



  4. #24
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    I'm too lazy to make a drawing right now, but I think the way most laser probes work is to point the laser straight down from the spindle. Then a camera (one or more) look at the dot from an angle. The software finds the center of the projected spot - the position of the spot is used to calculate the distance from the spindle.

    There are a couple issues to work around:

    1) laser light causes speckle. The light interferes with itself and causes that "grainy" look. Normally, I find that kind of cool, but the software will have to deal with this. Adding a filter on the camera so that only the laser light reaches the sensor helps.

    2) The bigger the angle between the camera and the laser, the more accurate the system will be (up to 45 degrees). However, this makes it difficult to measure into recessed areas. Trial and error would have to determine the best compromise.

    3) Historically, laser probes have a difficult time dealing with edges. As the laser aproaches the edge the dot gets smaller and smaller. At the same time, the part of the beam that is falling over the edge has to do something... and that causes trouble.


    I'm very new to this whole CNC world. Is there anyone currently working on a DIY probe? Maybe I could offer some help...


    Henry



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