Author Topic: Galvo/Ilda Basics  (Read 20584 times)

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Offline bruce.bushby

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Galvo/Ilda Basics
« on: June 10, 2015, 11:12:36 am »
Greetings from London!!

Just found laserboy while searching google for a "dxf to ilda" converter…..big thanks to James for Laserboy, I downloaded and compiled (on Fedora 20) in 5 min, couldn't ask for an easier "blooding". I did have to "yum install" some boost but otherwise it all just worked, very cool.

I'm starting out with arguably the worlds cheapest setup:
http://www.ebay.co.uk/itm/301170779843
and a standard $15 green laser "pen stick" I bought from some guy who was selling them on a pavement in Turkey.

So now I need some help understanding some fundamental basics about galvo scanners, perhaps a member could correct the little I've learned so far
 
 1. Galvo scanner receives a linear signal to drive a coil...similar to a speaker
 2. The amplifier boards simply amplifi the linear signal to drive various sized glavos
 3. Laserboy software can convert a DXF file (lets say a tooth path) in a linear signal and write it as a wav file
 4. To control the galvo, connect your sound out to amplifier boards and write your wav file to your sound card


...how do you calibrate the WAV generation to the galvo?
 
 
 ...and now I'm lost ...where does Ilda come in? In my setup, I guess I can replace the logic board with a raspberry pi connecting the audio out to the two amplifier boards I got with my starter kit?
 
 
 My focus/interest is material processing, both hobby and commercial.

 
 
 Cheers
 Bruce

Offline James

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Re: Galvo/Ilda Basics
« Reply #1 on: June 16, 2015, 06:05:54 pm »
Oh boy!

There is a lot to cover here...

Scanner amps and scanners are uaually closed loop devices. They need each other and are tuned together as a system.

The scanners are fixed coils in the stator and a magnetic shaft with no torsion spring in the rotor.

If the coils are charged one way the rotor will want to rotate in that direction. If the polarity of the juice to the coils is revered, it will want to rotate the other way.

Meanwhile, the rotor has a position sensor on it that feeds back to the amp.

So, the way it works in general is that you apply some voltage (from negative to positive relative to ground) to the input of the amp and the amp juices up the coils to accelerate the rotor to the position that corresponds to the input voltage. As the rotor is approaching that position the amp juices the coils in the opposite direction to decelerate the rotor to stop on the position.

Or to put it another way, the coils are only energized as long as the rotor is not in the position indicated by the input to the scanner amp.

So, it is possible to use a wave file to store and play a signal that moves the scanners around in a way that does not exceed the maximum rotational speed of the galvos.

ILDA is the International Laser Display Association, also a file format, or rather a set of formats that are stored in *.ild files.

It is a very brief and no-frills binary list of frames; each frame being a header and a set of consecutive elements of either 2D, 3D vertices or RGB colors for a palette or a combination of vertices and RGB values.

LaserBoy knows how to read and write all flavors of ILDA, plus DXF, waves and plain text tables. Once that data is loaded in LaserBoy it can be saved as a LaserBoy Formatted Wave.

If you look in the [Tab] menu, you will see a set of parameters; some of which are used to "optimize" wave output.

Optimization is all about controlling the timing of raw vector art such that it will work properly and look good on your scanners.

LaserBoy Formatted Waves can be opened back into LaserBoy with all of the end of frame and repeated frame information intact.

Since the waves are written according to the "legal" spec, they can be opened and played by any wave app that recognizes multi-channel waves.

By default LB waves are 6 channels:

X
Y
red
green
blue
other

Where other is your choice of RGB mixtures or possibly Z (3D)

It is worth noting that a standard sound device is almost always capacitor decoupled and thus cannot produce a DC coupled control signal.

That is why one needs to modify the sound card a bit and add a "Correction Amp".

http://laserboy.org/forum/index.php?topic=561.0

James.
« Last Edit: June 16, 2015, 06:24:18 pm by James »
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But it will never be Alpha King Done!

Offline bruce.bushby

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Re: Galvo/Ilda Basics
« Reply #2 on: June 30, 2015, 11:03:54 am »
Hi James


Thanks for the detailed explanation, absolutely fascinating stuff!!


>> As the rotor is approaching that position the amp juices the coils in the opposite direction.....  not in the position indicated by the input to the scanner amp


ahhh....position encoder feeds back to amp .... so galvo scanner amp boards are a special kind of amp? I can see I have a lot to learn, will focus on getting my pc sound card right and start playing.




Cheers
Bruce




Offline James

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Re: Galvo/Ilda Basics
« Reply #3 on: July 01, 2015, 12:11:45 pm »
Do you understand the principal of why you need to eliminate the output decoupling capacitors on the DAC and add a correction amp stage?

James.
LaserBoy is Sofa King Cool!
But it will never be Alpha King Done!

 

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