Laser Advice and Guidance - Mesa Card

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20 Jun 2021 18:49 #212507 by Project_Hopeless
With my primary project/mission complete in large part to the help I've received on this forum I'm now looking at adding a laser etch/engraver head to my CNC router.

With a Mesa 7i96e card or similar, can I etch in grey scale?

I've read some posts from circa 2013 and the method was to use G67 plus a phantom Z motion to control the laser. Is there a more refined method today?

I use Fusion 360 as a one stop shop for CAM and generating g-code. Is there a better work flow and software option for laser engraving?

I currently use the Axis GUI as it does everything I need it to do as a beginner/novice. Is there a better suited interface/GUI for lasers?

Any advice is appreciated.

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20 Jun 2021 21:22 #212516 by PCW
You could certainly use the Z axis for setting a PWM value

You would want to set very high accel/velocity values for Z or alternatively
set a very high z scale number so that the range of numbers used for PWM control
were a small fraction of the (imaginary) Z axis position range

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21 Jun 2021 12:15 #212552 by andypugh

You could certainly use the Z axis for setting a PWM value


Which is possibly inelegant, but does mean that image2gcode can be configured so that you can simply open a bitmap file in the Axis UI and it will "just work"
www.linuxcnc.org/docs/html/gui/image-to-gcode.html

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21 Jun 2021 21:52 - 21 Jun 2021 21:52 #212602 by Project_Hopeless

You would want to set very high accel/velocity values for Z or alternatively
set a very high z scale number so that the range of numbers used for PWM control
were a small fraction of the (imaginary) Z axis position range

What if my Z axis can't achieve fast enough accel values? Will the motor just stall and hum? And wouldn't the heat build up be bad?

Can I leave the Z axis as is and use a phantom A axis set to a high value or does LinuxCNC need to see hardware (stepper motor)?
Last edit: 21 Jun 2021 21:52 by Project_Hopeless.

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21 Jun 2021 22:14 #212604 by PCW
I assumed Z was driving the laser PWM value so there are no velocity
or accel limits

Not sure A is a good choice for modulation due to blending/lookahead
limitations of the standard TP

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22 Jun 2021 00:41 #212627 by Project_Hopeless

I assumed Z was driving the laser PWM value so there are no velocity
or accel limits

I'm still trying to wrap my head around this implementation.

I read through this wiki Rastering_With_A_Laser probably need to read it a couple more times. Know of any other examples?

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23 Jun 2021 13:09 #212736 by andypugh

Can I leave the Z axis as is and use a phantom A axis set to a high value or does LinuxCNC need to see hardware (stepper motor)?


If you have an actual height adjustment axis then I would suggest configuring that as W and using a "phantom Z" to control PWM. Also set the Z so it moves a _tiny_ virtual amount between 0 and 100% PWM to minimise the effect on the trajectory.

M67 ought to be the correct way, but rumours are circulating here that it slows the motion (though it shouldn't)

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29 Jun 2021 16:43 - 29 Jun 2021 16:50 #213248 by chris@cnc
I like the idea of ​​controlling laser power via Z-axis.
But I'm not sure how to connect it.
Maybe you can help me.

For the test, I loaded the PWM bitfile onto my 7i76e simulator.
The following lines are written in the hal.

setp hm2_7i76e.0.pwmgen.pwm_frequency 20000
setp hm2_7i76e.0.pwmgen.pdm_frequency 6000000
net z-enable => hm2_7i76e.0.pwmgen.00.enable
net z-pos-fb => hm2_7i76e.0.pwmgen.00.value
I have now loaded a picture in linuxcnc and started the program.
I think I can get a finer structure on the lasered picture, which there is still to try.
On TB3 pin 2 and 3 I now measure 20Khz and a nicely fluctuating voltage between 0-12V depending on the height of the Z-axis.
So I can easily adjust the power of the laser with the engraving depth.
Now two questions.
Why 12V? I thought PWM was only 5V. Background: the Borad once had a short circuit. Are that 5V on a healthy board? Because laser has only  5V PWM connection.

And how can I connect the laser to the board? I only have 3 cables on the laser. PWM, GND and 12V 
Attachments:
Last edit: 29 Jun 2021 16:50 by chris@cnc.

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29 Jun 2021 17:37 - 29 Jun 2021 17:37 #213251 by PCW
The step/dir outputs (being used for PWM now) on a 7I76e are 5V signals
I suspect a measurement error
Last edit: 29 Jun 2021 17:37 by PCW.

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29 Jun 2021 18:52 #213258 by chris@cnc

The step/dir outputs (being used for PWM now) on a 7I76e are 5V signals
I suspect a measurement error

Okay i measure now TB3 Pin 1 an 2 and got 5V max. I would wired laser this way but have fear to share thre ground.
Laser PWM -> TB3 Pin 2
Laser GND -> -12V Powersupply
Laser 12V -> +12V Powersupply
Or should  i better use  a level converter between Laser PWM and TB3 on mesa board to not share the ground?
 

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