Laser projector displays trapezium rectangular instad of square

[trojek]

Hi.

I changed galvo (to PT-A40) in my laser projector. When I want to display square shape it looks like a right angle trapezium laser_image.png.

Vertical lines are parallel to each other but right one is shorter then left one.
Horizontal lines aren't parallel to each other.
On the other words most right-up point of displayed image isn't in the place where I expect it to be.

I try to figure out what this happens. Does anybody have some idea?

[mixedgas]

Oh, You have what is called Horizontal Keystoning. Is your projector exactly parallel to the screen? If its not Keystone from projecting off axis, and your DAC is adjusted to produce perfect waveforms, then you have a small crosstalk or leakage of signal from one scanner amp to another.
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Three main possible causes....
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1. Off Axis projection, projector not at or near normal 90' angle to the screen.
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2. Dac OR software error. What are you using to control the Galvos?
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3. Signal Crosstalk (Leakage) between analog input portion of scanner amplifiers and scan signal, can be bad signal wiring, bad grounding, or in rare cases too small a power supply for the scanners.
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Check your wiring against this:
http://www.pangolin.com/resguide12.htm
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What is your hardware and software setup? Can we see pictures?
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Does this only occur at very large scan angles?
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If you connect the vertical signal to the horizontal amplifier, and connect the horizontal signal to the vertical amplifier by swapping/exchanging the input signal connectors, does the distortion remain?
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Steve

[trojek]

I have one more observation. When I move horizontal line from it's top position (on Y axis) to the bottom position it became more parallel to the ground.

I answer below:

Oh, You have what is called Horizontal Keystoning. Is your projector exactly parallel to the screen?

Yes, it is parallel to the screen.

If its not Keystone from projecting off axis, and your DAC is adjusted to produce perfect waveforms, then you have a small crosstalk or leakage of signal from one scanner amp to another.

I tried to display images on two different DACs, so I think that they work properly.

1. Off Axis projection, projector not at or near normal 90' angle to the screen.

It is.

2. Dac OR software error. What are you using to control the Galvos?

I don't think that it is DAC or software error. As I mentions I tried to DACs with different software, one is mine (very simple) and some scripts from the Internet(in different languages).

3. Signal Crosstalk (Leakage) between analog input portion of scanner amplifiers and scan signal, can be bad signal wiring, bad grounding, or in rare cases too small a power supply for the scanners.

I tried to change cables. I have "home made" cables and I connect them directly to the ILDA port on board. I attach pictures of my setup.

Does this only occur at very large scan angles?

It occurs on each scan angle but if the horizontal line is closer to the bottom of the screen it looks much better.

If you connect the vertical signal to the horizontal amplifier, and connect the horizontal signal to the vertical amplifier by swapping/exchanging the input signal connectors, does the distortion remain?

No, the distortion still occurs. The image(ilda test pattern) is turned but the boarders still looks the same - the upper right corner is displayed to low.


ildA_connect.jpggalvo_connect.jpgpower_supply.jpg

[mixedgas]

How many volts and amps are your galvo power supplies?

Steve

[trojek]

How many volts and amps are your galvo power supplies?

Steve

+24V 1A, -24V 1A - this is information from label on my power supply (Ryan RSH-50D-2H). I got it with galvo scanners as a set.

Tomek

[mixedgas]

+24V 1A, -24V 1A - this is information from label on my power supply (Ryan RSH-50D-2H). I got it with galvo scanners as a set.

Tomek

Factor of five or more two small. Will work for very small angles, but not full field, my guess right now is your scanning full field, and pulling the PSUs downs... Galvos draw 5-6 amps peak for a few hundred microseconds when jumping large angle and 5 amps per rail is the minimum PSU size I would use. You still need 24 volts, too... Often I place electrolytic capacitors across the PSU rails to help with the peak current.
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Steve

[trojek]

What can I say.... Chines galvo set.
That explains a lot. Could you recommend me a electrolytic capacitor or PSU?
What does it mean that PSU is -xV +xV? Isn't it just xV?

[mixedgas]

Two pieces of Mean Well RS-150-24 is a typical setup... Cheaper then buying a split supply capable of +/- 24 Volts at same time..

Galvo amps need Minus 24 volts, ground, and Plus 24 volts, three wire power supply...

Measure with your voltmeter and you will see what I mean...

Steve

[trojek]

Do I need to split voltage rail?
If I understand that I have two options: first is to buy two PSU and the second is to buy one PSU + split supply?
Does PSU dedicated to Galvoscanners has build in split supply?

Tomek

[aricha]

Make sure that your beam is coming straight in to the scanners.

If the mirrors are not exactly where the old ones where, than the beam will not be in a right angel to the X scanner or Y scanner or both.