CO2 laser driving

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CO2 laser driving

Postby 3d0g » Sat Apr 14, 2018 3:54 am

So I'm making the switch from parallel / LinuxCNC to UC400ETH / UCCNC on my home-built 80W CO2 laser cutter. There's nothing out of the ordinary with the setup but I want to make sure I'm understanding how UCCNC operates. With LinuxCNC, I used M62/M63 for PPI based laser modulation, and set power output of the supply via a 20kHz PWM signal.

From what I've gleaned from posts here, UCCNC's M10/M11 are instantaneous, like M62/M63, but an M3 spindle speed must be set first? Using the spindle speed to set the laser supply output will work great - I see where I can set the supplies required 20kHz PWM freq and max/min duty % (which is very nice). What about modulation of the laser output, however? The manual says M10 takes a parameter of 0..255 for 0 to 100% PWM duty cycles, but where can I set the frequency? A typical CO2 tube cannot be excited faster than 3-5kHz.

Apologies in advance if this has already been covered - the search tool here finds terms like "laser" "M10", etc too vague.

Cheers.
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Re: CO2 laser driving

Postby dezsoe » Mon Apr 16, 2018 12:35 pm

M3 is required to enable the M10 output. The S spindle speed is not needed, as the PWM output is controlled by the Q parameter of M10, not the spindle speed. (The M3 has to be on before the M10, it is a safety function for the laser output.) The laser output PWM frequency is fixed, you cannot change it, and is independent from the PWM settings of the spindle. The UC400ETH (and all other ethernet UCs) work on about 3.5 kHz.
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Re: CO2 laser driving

Postby 3d0g » Mon Apr 16, 2018 12:54 pm

dezsoe wrote:M3 is required to enable the M10 output. The S spindle speed is not needed, as the PWM output is controlled by the Q parameter of M10, not the spindle speed. (The M3 has to be on before the M10, it is a safety function for the laser output.) The laser output PWM frequency is fixed, you cannot change it, and is independent from the PWM settings of the spindle. The UC400ETH (and all other ethernet UCs) work on about 3.5 kHz.


Thanks dezsoe. Ideally, a CO2 laser will have two PWM inputs - one that sets the power supply output, and one that pulses the actual laser output. Using the spindle speed for the power supply is perfect. Are you saying the laser output PWM is fixed at 3.5kHz? If so, that would be ideal...
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Re: CO2 laser driving

Postby dezsoe » Mon Apr 16, 2018 1:42 pm

Yes, it's 3.5kHz.
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Re: CO2 laser driving

Postby 3d0g » Tue Apr 17, 2018 8:49 pm

So, dusted off the old scope and ran some tests. Sure enough, the UC400ETH runs a ~ 3.2kHz frequency on M10. PWM control of laser output worked beautifully. PWM control of the power supply hit a snag though as the max spindle PWM freq is 5kHz. Power supply requires 20kHz min so I improvised and built a second-order low pass filter to convert the M3 PWM back to a 0-5V analog value to feed the supply. All good. Really liking UCCNC so far.
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