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Topics - iggy

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Hi, I am trying to set up a laser cutting/engraving system with Mach3, for engraving I want to use Art's plugin, but I have experienced some problems and I have some queries.

First of all, the 5us (or optional 40us) pulses are too short for my PWM CO2 laser, so I use the digital trigger pulses as a trigger for a variable pulse width pulse generator, which I connect to the gate input of a homebuilt CO2 laser controller (basically a gated 20kHz PWM oscillator with manual pulsewidth control via front panel knob).

When I first tried this, all I got was a mess - after a lot of fiddling around, I realised that unless the image is exactly square, it seems to produce multiple, superimposed images along the x-axis. As I don't really understand how the plugin works, I can't work out what I'm doing, or doing wrong.

The settings in the plugin do not really make sense to me - in particular, why does changing the "width (x axis)" affect the "size of the Y pixel (in steps)". Is this a simple labelling error? Can anybody out there help? Art?

Thanks,
Ilya

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Forum suggestions and report forum problems. / PWM for laser control issues
« on: December 23, 2007, 07:34:51 AM »
Hi, I know this topic has come up a couple of times, but I have not been able to resolve my problem with previously posted information, hence this post.

It's a bit long-winded, but I wanted to explain all the background so that the issue makes sense - please bear with me...

Basically, I am trying to control the power output of a CO2 laser using the PWM capabilities of Mach3.
In the ideal case, S commands embedded in the G code would enable me to directly modulate the laser power (e.g. to select between acrylic engrave and acrylic cut in the same job).

I have set Mach3 up based on the information given by Art and others (spindle output enabled, PWM frequency and minimum set, PWM output on step pin of spindle motor output, pulley speeds set up correctly). I have intentionally not enabled the laser option, as this generates a continuous pulse output - my system does not require a constant tickle input.

Now, when I look at the voltage on the spindle motor step output usin an oscilloscope, I do NOT see a smooth PWM signal as I enter Sxx to change the spindle speed. In fact, I only get four discrete states - off, about 30% PWM, about 45%, and about 55%. I know why this is - the manual explains the compromise between kernel speed (100k in this case), PWM base frequency (20kHz input, gets reduced to 16666Hz by Mach on input) and number of possible PWM steps.

I cannot reduce the PWM base frequency, as this directly affects the laser power output and pulse frequency, giving rise to visible discrete spots on the workpiece, which is not acceptable. I also don't want to slow down the x/y speeds (increased processing time).

My problem: I would be very happy with 3 different PWM settings (off, engrave, cut), as long as it is possible to preset the available PWM pulse widths (e.g. 10%, 50%). Is this possible? If so, how?

Thank you very much for any suggestions, and Season's Greetings to all of you out there in MachLand!
Ilya

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