Welcome to LinuxCNC.org

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.

diegoroman17 wrote: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?
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?

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.

diegoroman17 wrote:I see no reason why not, it ought to work well.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 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

Ok thank you my friend. you help me a lot