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Thread: Small oscillations in my scanner

  1. #1
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    Default Small oscillations in my scanner

    I am getting some tiny oscillations in my images from my galvos. (30K chinese scanner) It doesn't happen all of the time. It depends on the image I am scanning and what my scan rate is. I can post a picture late I think. But in the meantime, does anyone know what would cause them? I mostly see it when drawing vertical lines. Which I guess means that the oscillations are in my X-axis. Any ideas?

  2. #2
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    OK I have attached a picture to look at. The large sine wave is thing is what it is supposed to look like. The tiny little waves should not be there at all! Look at the small oscillations on the left side and how they seem to only oscillate on the X-axis. Also notice that they are worse on the left side for some reason.
    Attached Thumbnails Attached Thumbnails DSCN0097.JPG  


  3. #3

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    carmangary,

    i am thinking you should start checking out the X axis scanner, it seems from your picture that it is the X axis...

    Try swapping the scanner driver card outputs, to see if the problem shifts to the Y axis, if not, then it is probebly the galvo itself that is starting to fail...

    I am assuming that you have checked that all your connections are good and all wires running up and down are in good order, no break in insulation or so...

    Nothing worse than equipment fooling around, enough to cause sleepless nights

    werner

  4. #4
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    Good check. I swapped X and Y galvo connections and the image and oscillations turned sideways so that the oscillations were then in the Y direction. I guess this means that the galvo is fine and the problem is with the X scan amp or somewhere up stream.

  5. #5
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    Thats pretty strange, i have never seen anything link that before..
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  6. #6
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    Default

    Now swap the x and y inputs of your drivers physically.

  7. #7
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    When I swap the inputs from the DAC the problem stays on the same axis. So, it appears that it is the X scan amp that is producing the oscillations. If I drop the scan speed down to around 15K or less they aren't very visible.

  8. #8

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    Dave says he hasn't seen that before so I'm wary of my own suggestion, but here it is anyway: tuning too high. If that amp is getting fast positional control by too much gain fighting too much damping, it might try to oscillate at a high frequency and low amplitude like that. This is bad, I've read, it can cause strain even under light input conditions, if the gain/damping are set too strong. In this case it could allow the resonance in the system to decay when there isn't much to excite it, which might acount for lower scan speeds not making it happen so much. That effect should be something familiar to people here so I guess it's something else...

    So look at the scan boards closely, see if there are differences involving small capacitances on sensitive inputs. That effect looks like a small parasitic oscillation in the amp.
    Last edited by The_Doctor; 07-22-2007 at 02:00.

  9. #9
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    I think you may be right, Doc. I followed the tuning instructions on the LaserFX page and I had to lower the damping and servo gain quite a bit in order to get overshoot and circle size correct. After I did that I did the sine pattern again and the oscillations are all but gone. It also made the galvos a bit quieter... or maybe it is my imagination.

  10. #10

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    carmangary,

    ok, here's another one to try:
    try swapping the power supply to the x and y board, as you said, it might be further upstreem...

    werner

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