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Thread: Will this burn up galvos?

  1. #11
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    Hmmmm yea, i see your point.

  2. #12
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    AOM, nice idea, you can enlarge the whole thing with a lens later. So long as you don't have a lot of overlap between lines or excessive aspect ratio error, correction is doable, even easy. Although people who have tried might tell me different.

    I suggested the sawtooth on vertical because it's easy, but mostly because that way the division of 1 by the frame rate is observed for all parts of the frame so any 'point' in the frame gets updated at equal rate and step at all times. With triangle in horizontal that's not entirely true but the time difference is very small, while a bigger problem gets solved, no instant transitions full scale on the X axis at high speed. Even an AOM might benefit from that given the extreme speed of that transition if sawtooth is used, especially if by doing it, you can push an AOM into wider deflections.

    Main problem with triangle X axis scan is the scanned lines aren't parallel, which might be annoying.

  3. #13
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    mixedgas is offline Creaky Old Award Winning Bastard Technologist
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    I have a resonant galvo in my desk drawer, it resonates at 1/2 15570 khz, go figgure, so you scan in BOTH directions, and voila, you have laser video. You need to do some linerizing cause its a sinusoid, but its much easier then syncing a spinning polygon with 32 faucets or trying to get wide angles using lenses for a AOBD.

    and yes, you can raster with regular galvos, it flickers somewhat.

    heck for 7 kilobucks you can buy the whole laser video AO system from intraaction, seen it at a conference with a 100 mW yag running daffy duck cartoons off a vcr.

    Steve Roberts

  4. #14
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    Would it be possible to use two spinning wheels that were geared together so that one spins a lot faster than the other? One wheel would give X and the other Y.

  5. #15
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    The only issue with gearing is any time you add mechanics into a system, you are going to get slop (especially with Gearing)...The whole system will bog down greatly.

  6. #16
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    Cool

    Not to mention the fact that the scan frequency for Y is very low. Even at broadcast quality video you're only talking about 60 frames per second, so that's 60 hz on the vertical. No problem doing that with a galvo, so there's no reason to go with a clunky mechanical system.

    On the other hand, the horizontal is running at 14.7 Khz for NTSC video. (31.4 Khz for VGA). That's a couple orders of magnitude faster than what most galvos can handle, which is why the spinning polygonal mirror becomes viable. It's a kludge for sure, but it *will* get the job done, whereas a galvo won't.

    However, from a purely theoretical point, you *could* do it with two sets of polygonal mirrors that were geared together. It would be sloppy, but it would work.

    BTW, one thing about the spinning mirror trick. If you have a mirror failure, it's pretty destructive. I had a grocery-store scanning mirror wheel fail on me a few years ago, and it was amazing (and scary) to watch. The mirror cracked, flew off it's mount (thus destabalizing the balance of the rotor), and in a matter of seconds the rotor tore itself completely apart - sending mirror fragments and rotor pieces flying in all directions. Lucky for me I didn't get hit by anything sharp, but I had to extract glass fragments from the sheet rock in the room after it was all over...

    Adam

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