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Old 12-02-2011, 12:17 AM #1
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Default Help me reapair a laser based museum exhibit

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.



Last edited by madsci1016; 12-02-2011 at 12:30 AM.
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Old 12-02-2011, 12:51 AM #2
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Default Re: Help me reapair a laser based museum exhibit

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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Old 12-02-2011, 01:35 AM #3
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Default Re: Help me reapair a laser based museum exhibit

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/spec..._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.
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Old 12-02-2011, 03:02 AM #4
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Default Re: Help me reapair a laser based museum exhibit

Quote:
Originally Posted by madsci1016 View Post
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/spec..._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)
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Old 12-02-2011, 03:36 AM #5
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Default Re: Help me reapair a laser based museum exhibit

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.
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Old 12-04-2011, 06:13 AM #6
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Default Re: Help me reapair a laser based museum exhibit

I've emailed Cambridge, which seems to have taken over General Scanning.

In the mean time can anyone give me guidance on if this kits would/wouldn't work?

20Kpps HightSpeed galvo scanner for laser lighting NEW (Without Show Card) | eBay

My guess is they just want an analog signal for mirror position.

Is ILDA just DMX signalling by another name?
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Old 12-04-2011, 06:32 AM #7
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Default Re: Help me reapair a laser based museum exhibit

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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Old 02-20-2012, 03:06 PM #8
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Default Re: Help me reapair a laser based museum exhibit

Well, I got the exhibit going again. See

Repairing and Upgrading Laser Spirograph The Mind of Bill Porter

Thanks for the help guys.
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