Variable laser power

[Joakim]

The lens is the original 2" (50.8mm) focal length with the the curved side up. ZnSe type properly not high quality.
Mirrors are original, except for one I replaced as it got scratched.

[ArtF]

>>17mA therefore I choose 15mA as maximum to save the tube.

  Smart move, and about all you need to do.

>>To me it looks like there are a linear relationship between thickness and power for a given current and material.

Absolutely. The relationship to speed is also linear. Its all about energy/mm so power and speed are both linear to each other
for the most part. A cut at 100% at 12mm/s second is equal to a cut at 50% at 6mm/sec. on both of mine.

  It allows us to use either a pwm power correction for distance, or to change the feedrate to suit. I almost never use lower
power than near max, as their is no benefit other than burning certain materials. I will reduce power to stop scorching,
but when it comes to cutting or engraving I prefer to vary speed, as the job gets done in maximum time with no other
real effect that Ive been able to notice. (Though corners can burn differently at various speeds due to accel in the corners.).
(Auggie deals with that by providing a set power per distance moved. This keep accel from influencing the burn .. though
likely not perfectly and may require a calibration curve to be done on linearity to requested power.. thats the thing
that is most nonlinear I suspect. Just as mine wont fire until 27% request.. and yours fires at a different ma than anothers..

  All good information,
Thx
Art

[Joakim]

Art:
You're right that must be the relationship between power and cutting. Energy per cubic mm removed material - It makes sense as the laser has to evaporate the material from the cut.

Would be nice to set the laser current with the S parameter from GCode. Like 0 to 100 (0% to 100%) given a current from 0mA to 15mA in my case. Easier to change between light engraving and deep cutting in same job.

Blueyonder:
This is the type of laser I have.
http://www.ebay.com/itm/High-Precise-40 ... 0825065645

Is your the same type?

[Blueyonder]

Yes, looks the same as mine.

[Blueyonder]

I'm cutting some 2mm MDF at the moment using 3mA @ 6mm/s and cutting fine with those settings so thought i would try the linear theory. I doubled the power to 6mA and doubled the speed to 12mm/s cut it needed two passes to cut through the material. Is this what you would expect?

[ArtF]

Hi:

>>I doubled the power to 6mA and doubled the speed to 12mm/s cut it needed two passes to cut through the material.

  There are some related losses so its not quite linear, there is a temperature climb rate to allow a material to burn,
so Id expect to be able to double it, and lower that by 10% or so. SO from 6mm/ssec to maybe 10mm/sec, its about what I usually
do.

    Easy enough to allow an S word to control power, as Ill be making the max and min PWM settable, I suggest a usage of
0 - 100% as the power no matter what kind of laser, we'll just have different PWM settings.. as to max and min...

Art

[Blueyonder]

Just ran a test while cutting 2mm MDF at 6mA and 3mA power settings at speeds from 20mm/s down to 5mm/s. I have attached a photo of the results as seen from the backside of the material. The 6mA is not a great improvement over the 3mA?

[ArtF]

Seems to indicate a nonlinearity in power..
I would imagine that varies from system to system and power supply to power supply..
It will be interesting to see similar tests over various systems. I could be all wrong as to
how they react generally, I have only 2 that Ive cut with.. but they seem more linear that
that. 6ma still seems low though, what does it do at 15ma? do things get more linear as
power goes up?

Thx for the examples, interesting results.

Art

[ArtF]

Makes me want to add an ma meter to mine, I select only 0 - 100% and who knows what that means to ma..
it could be ma isnt linear to pwm command.. but then, I typically use 99% and vary feedrate.. still, interesting..

Art

[Richard Cullin]

I read in one of arts  posts that the  beam pwm output is not continuous when lasing  to allow the laser tube to recover  , i'm thinking this is not a good thing for a laser diode in that it limits the power unnecessarily  .  when viewed on the oscilloscope the beam pwm output  in indeed in bursts  at 50/50 mark space
is a  diode pwm mode possible ?
am I only getting 50% laser power ?

[ArtF]

Hi Richard:

  Well, that's dependent on a few things. There are two settings in the config that help control that,
Max Laser and MinLaser. They set the maximum and minimum laser power for any given situation.
So lets say you set them to 0 and 100. Your PWM now has the capability of 0 - 100 PWM, so it means you
can use Maximum 100% power. Auggie decides that based on Feedrate. Lets say you command a feedrate of
2000 mm/min , when you get to 1000, your PWM will be 50%, as you approach 2000 your PWM will
approach 100%.
  The normal trouble one has is you command 1000 inches per minute on a job where your machine
can ( due to accel or jerk limits on that job) only do 500 most of the time, the PWM will not exceed
50% in that case. Lowering the commanded feedrate will allow you to hit 100% of the feedrate,
and therefore hit 100% of the power.
  By doing this Auggie keeps you from burning so easily in corners or shallow curves where it must slow down.
Its all more about power/distance rather than just raw power if one wants a good engraving. It is possible
to turn off the power to feed-rate correlation and simply have the power you selected, 0-100%, but unless
its a cutting operation,. I dont recommend it. The DistCorrection mode button  can be turned off and power
will always be the selected power if one wishes. You may not have the laser control panel with a distance correction
button on it, Ill check I put it on the released screen.

Art

[Richard Cullin]

whats confused the situation is the test fire  button timing .  if I set  time to 100mS  then that's what I get
if I set the time to 200ms&nbsp; I get&nbsp; 139ms if I set it to 500ms I get < 250ms

[Richard Cullin]

screen shot of salea logic analyser measuring &nbsp;fire pulse &nbsp;
bottom trace is zoome in a bit to show duty cycle better

fire time set to 200mS power 72%&nbsp; &nbsp; &nbsp; result 139mS&nbsp; of pwm @72%

[ArtF]

Richard:

Hmm, that one is new. I just used testfireing this week to retest power, it did a good 38 second run at 38000 in the timer.
Im trying to think what could make that variable.. its hard to imagine as its coded to the tick timer..

&nbsp;I did have trouble last week with a system that hadnt been booted in quite a while so the tick timer went negative, I wasnt
checking for the upper bit to toggle. Can you reboot and see if the fire test works properly. When the time runs out, does the led go off as well or does the laser just stop firing? ( Like if you do a 10 second test, does the led stay on for 10 seconds on the firing panel?)

Art

[ArtF]

Richard:

Was that a 2 second test fire at 72% power?

Art