Understanding Laser Power Output

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swpax
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Understanding Laser Power Output

Post by swpax »

Hi Guys,

I am having some trouble sorting out laser power settings.

My PWM maxes out at 400Hz.  So if I test the laser output using the FIRE button in Auggie and set the laser to 100%, I get 400Hz.  I also get 14V power output to the laser.

If I set the laser power to 50% using the slider and hit the FIRE button I get 50% power at 200 Hz and 7V.  So all good there.

However if I run this test script "g1 x100"  with the Laser Power 100% on the slider in the GUI I get 400Hz.  Additionally if I set the power output to 50% on the slider I get ~250 Hz.  Obviously not linear but pretty close. 

I am generating the GCode file to burn an image using AUGS.  Since I can't see all of the commands in the GCode file (only X and Y moves) it's hard to track what's going on.  I can hover over each line and see more detail but that doesn't seem to provide much more info.

@Art I know you tried to explain how it works before, but I'm not yet grasping the concept.  Based on the .tap file produced by AUGS, how is the power being regulated to the laser?  At first, what I am trying to understand, for a given image what is the max. and min. power output for the laser based on pixel greyscale?

Setting MaxPWM in the configuration doesn't seem to make any difference.  I guess I would like to understand the relationship between the PWM setting in the config and how the laser is driven by the .tap file.

I have the feedrate set at 100% and the feedrate is constant at the set value of 2400mm/min during the GCode test.

Thanks,

Scott
BobbyW
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Re: Understanding Laser Power Output

Post by BobbyW »

Hi
Well ...first of all , i think you laser source have 0-5V input .
I use channel 2 if i remember well and i convert to 0-5V from 0-3.3V
how much pokeys delivery. If you power source are good , i mean high impedance you can
do it with 2 transistors to convert to 0-5V . In that case you should have at 50% PWM 2.5V
ideal case or close to. Until you don't get that any test with engrave is pointless.
Second . Art can explain more detailed how Auggie works.
What i figure out is :
the .TAP file are line by line coordonates to engrave , nothing special
but Auggie generate a second file .AUG who store entire photo information like
all pixels " depends of size of you pic to engrave" and also  the value of that pixel
in 8 bit " i think" . In time of laser travel , on each pixel the laser will fire
with the power equal with that pixel value. I assume Art limit the pixel value at 100
or made the conversion 1*100/256 because pokeys will know only 0 to 100  . He know how is programmed.
If you will see , on any pic the .AUG file will have different size in close relation
with the pic size.
I can not tell how .AUG file are encoded , only Art know that and can be any language , even one
invented by him.
But the principle i think is not different . Art can correct me where i'm wrong . I'm a user like you are  :)
You first step should be to get the PWM output value between 0-5V . And after you can start testing.
Maybe you lucky , my laser source was a mess , on 0 input the laser fire at 30% power , residual input voltage was
1.22V and the source has very very low impedance something at 300R. I was forced to build a complex circuit
to solve that . And still like that i have some trouble sometime.
I wish you good luck .
Thanks
Bobby

Attachments
aug and tap file.jpg
swpax
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Re: Understanding Laser Power Output

Post by swpax »

Thanks Bobby.  The big clue here is the output.  More research!  :o
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ArtF
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Re: Understanding Laser Power Output

Post by ArtF »

All True. And good explanation. Auggie has a pixel data for each pixel and scales it from 0 -100.

Then a formula is applied.  Output = (PixelValue * ( current feedrate / commanded feedrate))) * (power/100);

  If the current coordinate is not over a pixel, the PixelValue is zero.

Your PWM gets a command from 0 - 100, which gives you a PWM output. The voltage is actually always 5 volts during
on time and the frequency is always 400hz if set for that. But the average voltage is then 5vdc * ( OUTPUT/100);
  So if 50% is commanded, you should have 2.5volts.

  Most laser are full power on the PWM input when its 5vdc and go from there to zero. Many , like my sinrad need 1% as a tickle
voltage. It turns the laser on for 1-4us at 2khz which is my base PWM frequency.

Art
BobbyW
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Re: Understanding Laser Power Output

Post by BobbyW »

ArtF wrote:  
If the current coordinate is not over a pixel, the PixelValue is zero.

Art
You can explain please . Become interesting .
So basicaly can be way acurate result if i convert my photo before to generate with AUGS
on 100 pixels/cm asuming the min step is 0.1 to detect pixel value.
Or the detect is dependent of my setting . As example if i set like is default
0.2 step , that mean on 1cm of photo the aug will take 50 pixel informations?
That info should very useful , because can be developed a standard formula for any photo size with
perfect scan and maybe result.

Usualy i use low frequency for engrave , below 300Hz.
Thanks
Bobby
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ArtF
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Re: Understanding Laser Power Output

Post by ArtF »

Bobby:


  Yes, that is correct. The system uses the # of motor steps as compared to photo size.
So the pixel to be burned is  (((currentpositionSteps - startofimageSteps) / length of image in Steps) * #ofpixelsinline)
as to what pixel will be used for power.
  Power will then be  (Current1msspeed / FullFeedrate1msStepRate)  * (powerslider% or spindleRate%) = PWM%

This is done every 1ms as to position and power. You can literally make sine waves over an image
and only the image will burn , and in a sinewave raster.

Art
BobbyW
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Re: Understanding Laser Power Output

Post by BobbyW »

ArtF wrote: Bobby:

This is done every 1ms as to position and power. You can literally make sine waves over an image
and only the image will burn , and in a sinewave raster.

Art
Hi Art.
This is done every 1ms as to position and power.
So in that case the PWM should be strict in 1000 multiple otherwise can search the info of pixel between
and will ignore probably. I dont think i folow you with .....
And about sine waves you mean , white sine waves over a photo , right?
Thanks
Bobby
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ArtF
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Re: Understanding Laser Power Output

Post by ArtF »

Bobby:

  By sine waves I only meant one could do graphs of x,y sine waves as a raster and the image would appear.
It doesnt matter how the motion occurs, as long as the head is moving in G1, and inside the bounds of the
image the laser will at pixel burn rate.
  As to the 1ms rate of update, thats simply how the Pokeys works, I send it the motion for the next 1ms
and the power for the next 1ms. If you cross 10 pixels in 1ms, you will get the average power of those
10 pixels.

Art
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