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Help me reapair a laser based museum exhibit

madsci1016

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Hi guys, new here. Found this site via google and spent a few hours lurking for help. I'm an Electrical Engineer, but have no experience with lasers.

I'm trying to repair a laser based exhibit for my local non-profit science museum. It's basically an old gas laser, shot into an x-y galvanometer rig and displayed on an opaque screen. A dual channel frequency generator (adjustable by the museum guest via big pots on the outside of the box) feeds the galvo driver board. A picture of the inards: (click for larger)



The exhibit is well over a decade old, run 6 days a week/8 hours a day. The symptom was the pattern on the screen was 1/8 the size it should have been.

I'm in the process reverse engineering it to start to troubleshoot it. The first thing I noticed was the galvos (General Scanning G124) were only measuring a coil resistance of 2 Ohms, when the spec sheet shows they should be 7 ohms. Is this expected with laser galvos, or a sign of bad ones?

And if yes, suggestions on where I could buy suitable replacements? Ebay only seems to have expensive closed loop galvo kits, I'd only need open loop glavos sans driver, or with drivers if it was cheap enough.
 
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ARG

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Well, I have no idea what the problem is, but for cheap galvos you can get a pair of 10Kpss ones for around 80$, but I have no idea what scan speeds you need for the purpose of this exhibit.

Plus, I assume with running this exhibit so often that reliability is needed so there isn't constant maintenance which may mean you need a pair of brand name galvo's....
 
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madsci1016

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Haven't figured out what Kpss means, but from what I gather from googling, the G124's are the bottom of the barrel cheap, slow, open loop galvos. I wouldn't need anything better then their specs.

Here's the spec sheet I found: http://www.camtech.com/products/specialty/open_loop_datasheet_736-49506.pdf

All they will do is scan sine waves. I will scope the frequency generators tomorrow to find out the max frequency driving the galvos.
 

Jacob32123

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Haven't figured out what Kpss means, but from what I gather from googling, the G124's are the bottom of the barrel cheap, slow, open loop galvos. I wouldn't need anything better then their specs.

Here's the spec sheet I found: http://www.camtech.com/products/specialty/open_loop_datasheet_736-49506.pdf

All they will do is scan sine waves. I will scope the frequency generators tomorrow to find out the max frequency driving the galvos.

KPPS = Points per second. The more KPPS (sometimes refereed to as K), the more complex images you can draw, without flickering (ex: 10k galvos = 10,000 points per second)
 

bobhaha

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I would suggest getting them from general scanning. That's the only company that I can think of, that carry open loop galvos.

The reason you can't run the normal galvos we use in our laser scanners are they are ILDA interfaced (unless you mod the driver boards). With an open loop galvo, you can connect it straight to the sine wave generator to get output to the motor. Its a much cheaper and direct way of what you are trying to accomplish.
 

MarioMaster

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It's just a signal generator so I see no reason why a pair of modern closed loop galvos wouldn't work.

ILDA is pure analog signals, and has nothing to do with DMX
 




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