Cutting Laser CNC

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05 Jul 2012 14:27 #21610 by diegoroman17
Hi guys,

I have a cnc laser machine. I need control it with 5i25 and 7i78 mesa cards. The x-y move is not problem but the control of laser power is a conflict. The source laser power is controled for PWM pulses but this pulses should be synchronized with the velocity x-y to avoid discontinuity in the cutting or engraver. Exist any G code for this? My cnc laser have stepper motor to x-y move without encoder, resolver or any feedback. Thanks to help me.

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05 Jul 2012 16:49 #21620 by andypugh
Replied by andypugh on topic Re:Cutting Laser CNC
diegoroman17 wrote:

I have a cnc laser machine. I need control it with 5i25 and 7i78 mesa cards.

Dual 7i78s seems an odd choice for a 2-axis machine. You seem to have a lot more step/dir outputs than you need, but no general-purpose IO.
I would have thought that a single 7i76 would have been a better choice?

The source laser power is controled for PWM pulses but this pulses should be synchronized with the velocity x-y to avoid discontinuity in the cutting or engraver. Exist any G code for this?

Someone has come up with a solution which varies the PWM output to be a constant number of "dots per inch" but I couldn't really understand the system they used.
wiki.linuxcnc.org/cgi-bin/wiki.pl?Rastering_With_A_Laser

It ought to be possible to use the HAL "hypot" function to calculate the current travel velocity and scale the PWM intensity.

Are you using raster or vector artwork?

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05 Jul 2012 19:32 #21630 by diegoroman17
Replied by diegoroman17 on topic Re:Cutting Laser CNC
Thanks for answering me my friend. I have only single 7i78. You have reason a 7i76 is better choice but I choiced 7i78 for cost and the IO of general purpouse to obtain of second connector of 5i25 with a expansion card designed for me.

My source power laser can be controlled for PWM or Analog voltage. I read that 7i78 have analog output to spindle. can I to connect my source power laser to this output?can I do that the output voltage is proportional to the x-y feed?

I read that is posible connect the power laser to the control axis z but dont understand how I can do it? because if I configure z axis with pwm output pncconf say that I forgot to specificate encoder and I have not any enconder for my system.

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05 Jul 2012 19:45 #21631 by andypugh
Replied by andypugh on topic Re:Cutting Laser CNC
diegoroman17 wrote:

My source power laser can be controlled for PWM or Analog voltage. I read that 7i78 have analog output to spindle. can I to connect my source power laser to this output?

I see no reason why not, it ought to work well.

can I do that the output voltage is proportional to the x-y feed?

I think that should be possible. You would feed the X and Y axis velocity pins into a hypot HAL function, then use that as an input to a HAL scale function to modify the spindle speed command prior to passing it to the 7i78.

I read that is posible connect the power laser to the control axis z but dont understand how I can do it?

I don't like that approach, it means that the XY motion stutters every time the Z axis "moves" as LinuxCNC tries to keep a steady velocity in space (it doesn't know that the Z isn't a real axis)

A bit of background reading:
www.linuxcnc.org/docs/html/hal/intro.html
www.linuxcnc.org/docs/html/man/man9/motion.9.html
www.linuxcnc.org/docs/html/man/man9/hypot.9.html
www.linuxcnc.org/docs/html/man/man9/scale.9.html

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05 Jul 2012 21:11 #21638 by diegoroman17
Replied by diegoroman17 on topic Re:Cutting Laser CNC
Ok thank you my friend. you help me a lot

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