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ArcticMyst Security by Avery

Galvo alignment

Joined
Mar 5, 2013
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Hi,

My projector has a strange issue, the projected image is kind of rotated / skewed.
I had this with Mamba, and now that i have pangolin i got the same issue.

Pictures:
md09bc.jpg

(Projecting a straight line)

vipfk6.jpg

(Projecting a square box)

e6sob5.jpg

(Projecting a test patern, should be square)

If it is of any help, i replaced the mirrors on the galvos, because they both broke.
I can kind of fix the output within quickshow, but i prefer to fix the hardware.

If anyone has experienced the same, or knows a solution, please let me know!
 





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Dec 31, 2012
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What does a circle look like? Is it elliptical?

My guess is your scanners need some tuning. I bought a used REKE RGB projector, and was seeing similar problems until I took the scanners through the tuning and calibration process.

http://www.skywise711.com/lasers/scanner/scanner.html

The scanner manual, linked above, describes the calibration procedure. When one changes a mirror on a scanner, the mass of the new mirror may be minutely different than the old one. As such, the scanner must be tuned to the mass of the new mirror.

Even crummy 12K scanners perform admirably when properly tuned.
 

DJZ

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You may want to check your wiring. What kind of cable are you using between your DAC and the projector? Is it wired pin for pin? Did you wire the inside of the projector? I can simulate the exact skewing by wiring +X to +X, -X to -Y, +Y to +Y and -Y to nothing.
 
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Im using a standard 10M ilda cable that came with my pangolin dongle and software, so that should be OK.
I think my wiring on the inside is indeed wrong, could you post a picture of your wiring?

Mine is like this:

1: X+ (red)
2: Y+ (white)
5: R+
6: G+
7: B+
14: X- (white and ground)
15: Y- (red and ground)
18: R-
19: G-
20: B-


I dont got pin 25 connected (ground) but i guess i should do that?
 
Joined
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Messages
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Your X- and Y- inputs should be independent signals, not tied to ground, and not tied to other signals. They're not ground reference points, but rather X+/X- are differential inputs. See if that helps.
 
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Thanks for the fast reply, i'll try it immediatly!
And should the ground reference of the galvo inputs be tied to pin 25 or not?
 

DJZ

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The elliptical question still stands. It may also be that your two scanners are not centered in relation to one another.

Loosen the locking screw holding the scanners to the block (the block that holds them at 90 degrees to one another) just enough so you can rotate them in place.

Then, try projecting the square image, again. While projecting on the wall, rotate the X and Y scanners, one at a time, and see if you can correct the skewing that way. If you cannot, you may need to recalibrate them.

The fact that your square displays as a diamond suggests to me you are almost there. And being almost there tells me it isn't your wiring. It is hard to imagine incorrect wiring would display an image that is close. I would expect the image to be way, way off if the scanners were connected incorrectly.

Another point: Your first image showing the line at a 30 degree angle. If it is your expectation that line is supposed to be horizontal, and if that is true, again, you may need to rotate your scanners within the scanner block to correct.

Bear in mind, the placement of those scanners within the scanner block is not some super-accurate setting you need to be afraid of screwing up. On one of my Chinese projectors, the center point of the projection was skewed upward and to the left of the projector by 15 degrees. I adjusted the center point of the projected image, so it was exactly in front of the output point of the projector by rotating the scanners within the block.
 
Last edited:
Joined
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Messages
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Thanks for the fast reply, i'll try it immediatly!
And should the ground reference of the galvo inputs be tied to pin 25 or not?

I wouldn't tie the ground signal pin of the galvos to anything; that is the general practice with galvos because they rely on differential inputs. Just leave the ground disconnected. The power supply may have a ground, but don't bother connecting that to anything else besides the galvo it is supplying. Remember: you don't need a ground reference with galvos.

Oh yeah, and watch out what you're projecting at. Those drawer handles can reflect light into your eyes.
 
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Once i connected the galvo inputs the right way (like bionic badger suggested) everything works perfectly!
The scan angle is also a lot higher now, can't believe i was using my projector like this for almost a month :whistle:
The galvo's still need some alignment though, when i project text, some straight angles are a bit round. But im sure i will figure that out with the tutorial that pschlosser posted :)
 
Joined
Oct 26, 2007
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Good to hear it fixed your problems!

For the sharper straight angles, it might just be that those corners need more points in the vector file in order to slow down the galvo around them and make sharper angle transitions. Think of it like slowing down your car to make a right-hand-turn at a stop-light.
 




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