Commercially available laser controllers

Electronics related to CNC

Re: Commercially available laser controllers

Postby bdring » Fri Feb 12, 2010 12:08 am

Yes, a PWM can be slow to change, but only over a large range. A well filtered high speed PWM is as quick as you want. The slow change can be good for gray scale, but detrimental for hard on off like engraving text on a white background.

One problem with the dithering is that it takes a lot of resolution to get a gray. It takes a lot of on/off dots when a single gray dot does it all at once. With that said, you are more in a position to check all this out.
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Re: Commercially available laser controllers

Postby lasersafe1 » Fri Feb 12, 2010 12:17 am

The controller offers many modes of raster scanning. It can do:
1. Bi-directional raster of X. Laser fires on forward sweep and return sweep.
2. Uni-directional raster of X. Laser fires only during forward sweep.
3. Bi-dir Y
4. Uni-dir Y

At first I didn't understand why I would ever want uni-directional. After doing a couple of test engravings with bi-directional I noticed that the image looked muddy. I looked closely at a thin line and noticed a double image. At first I thought that perhaps the laser was turning on at a different time, but the DSP manufacturer told me that it is the very slight play in the drive belt of the X sweep. Even though it feels as if the belt is tight, the belt is always shorter on one side than the other (with respect to the motor). I think there is a correction value I can enter for this somewhere, but I haven't found it yet.

When I switched to uni-directional drive it cleared up completely and I get clean edges.

Pictures coming.
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Re: Commercially available laser controllers

Postby bdring » Fri Feb 12, 2010 12:42 am

Cool..a wealth of useful information...keep it coming.
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Re: Commercially available laser controllers

Postby lasersafe1 » Fri Feb 12, 2010 3:00 am

Here are a few outputs from the machine. I am testing the DSP controller and learning about appropriate speed and power setting. I have recorded a video of these tests and I will attach it in a future entry

DSC02025.JPG
Fast raster of anodized aluminum to remove anodization layer. Laser was set too strong.


DSC02017.JPG
US Navy EOD Crab before cleaning
100mm/sec 30% power (12 Watt)


DSC02021.JPG
EOD Crab after cleaning. Perhaps I should have only cleaned the crab and not the background. 100mm/sec raster. 12 Watts


DSC02019.JPG
300mm/sec 70% power (28 Watts)


DSC02022.JPG
Black Walnut 500mm/sec 40 watts. This would have been beautiful at a lower speed!
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Re: Commercially available laser controllers

Postby lasersafe1 » Fri Feb 12, 2010 4:45 am

Here is the complete review of the DSP. I forgot to mention a few things, but you get the idea. There were a few bumps in the road to get this running, but now I am quite pleased with it.

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Re: Commercially available laser controllers

Postby lasersafe1 » Fri Feb 12, 2010 5:01 am

Now if I can only engrave metal plates....
DSC02031.JPG


ONLY A JOKE. But I suppose it is possible.
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Re: Commercially available laser controllers

Postby pixpop » Fri Feb 12, 2010 7:22 am

I have a friend who makes etchings. He's interested in trying (once my machine is working) to make plates using a laser. It's pretty simple.. you have a metal plate covered in lacquer. Normally, you use a sharp instrument to scrape away the lacquer so the metal shows through. Then you etch it with acid. Then you remove all the lacquer, apply ink, and print. You get ink wherever you scraped away the lacquer; it makes very fine lines.

The laser would replace the sharp instrument, cutting through the lacquer to expose the metal underneath. The rest of the steps would be the same.
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Re: Commercially available laser controllers

Postby lasersafe1 » Sat Feb 13, 2010 3:12 am

pixpop wrote:I have a friend who makes etchings. He's interested in trying (once my machine is working) to make plates using a laser. It's pretty simple.. you have a metal plate covered in lacquer. Normally, you use a sharp instrument to scrape away the lacquer so the metal shows through. Then you etch it with acid. Then you remove all the lacquer, apply ink, and print. You get ink wherever you scraped away the lacquer; it makes very fine lines.

The laser would replace the sharp instrument, cutting through the lacquer to expose the metal underneath. The rest of the steps would be the same.



The really fine stuff is actually done with a photographic process and photo-resist polymer. An actual bill like the 20 might start out as a 4 foot wide drawing, but it can be imaged on to a small plate with the photo-resist. After exposure and developing comes the acid etch. The same principle is used to make IC chips on silicon with nano-meter line widths.
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Re: Commercially available laser controllers

Postby lasersafe1 » Sat Feb 13, 2010 3:13 am

So now I have the definitive answer for the PWM question.. as far as this controller is concerned during a raster engrave.

1. All of the ON-OFF bit banging occurs on the TTL line to the laser power supply.
2. The PWM frequency is fixed at 20 KHz. (this is adjustable within the DSP setup for a different base frequency)
3. The PWM output rests high (3.3 volts) when the scan is not running. This is full power ON, but the TTL line is keeping the laser off.
4. If I tell the controller to put out 50% power, I see a 50% duty cycle at the 20KHz base frequency.
5. If I tell the controller to put out 98% power, I see a 98% high duty factor at 20KHz. (98% high, 2% low)
6. If I tell the controller to put out 2% power, I see a 2% duty factor at 20KHz. (mostly low, but 2% high)

I did a fast raster (500mm/sec) of that EOD crab and looked at the TTL. I was seeing pulses high and low as short as 15 microseconds each.
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Re: Commercially available laser controllers

Postby bdring » Sat Feb 13, 2010 2:16 pm

Do you have to do that 2 color dithering yourself or do you just supply a gray scale image?
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