laser raster engraving

25 Jul 2017 15:10 - 25 Jul 2017 15:22 #96396 by vre
vre replied the topic: laser raster engraving
Chinese DC power supply for glass tubes have response rate <= 1ms according to the datasheet
and has 2 input ports one for turning on/off the laser beam (this is the only needed port for raster engraving)
and one analog input port that accepts 0v to 5v for specifying the power of the laser,
in this port you can put a potentiometer and tune the power of the laser manually
because the raster engraving implemented with 1bit black/white dithered images at constant power/speed.
The only thing controller need to do is to turn on the laser when read black pixel and turn off the laser when it reads white pixel in image.
Engraving must be at constant speed about 300mm/sec to 500mm/sec
the problem with parport is that can not achieve speeds like 300mm/sec because stepper drivers for this application have very high microstepping to avoid resonance (in my machine drivers set up with 5000 microstepping/step).
Wincnc controller that i think had same codebase with linuxcnc supports raster laser engraving but costs 2000usd with all hardware.

this is the power supply for laser
Last Edit: 25 Jul 2017 15:22 by vre.
25 Jul 2017 17:40 #96403 by Todd Zuercher
Todd Zuercher replied the topic: laser raster engraving
I am pretty sure Wincnc does not share any code base with Linuxcnc. (We do have one machine running their hardware/software) Their older software based systems were Dos based and had more in common with Turbocnc.
25 Jul 2017 21:42 #96425 by rodw
rodw replied the topic: laser raster engraving
Thanks for explaining things a bit more. There is no reason why you can't run a separate faster thread with Mesa hardware to trigger the laser. Using the Z axis was a convenience to pulse the laser but surely there are other ways to do that provided you have an output under control of the laser thread, not the Mesa servo thread. I guess the problem then might be that you only get velocity updates every millisecond but would that be a deal breaker? Having sufficient overtravel to allow the axis to get up to speed before it started rasterising would almost eliminate the need to monitor velocity if it was accepted the commanded axis velocity was obeyed accurately during the run.

I had a look at the code in Github. I can't see anything in it that would mean its not compatible with the current version of LCNC except possibly the need to include Joint Axis code if you are running a dual motor gantry somewhere. This would require some simple changes to the ini file.

So I think the question becomes "Is the so called Magic Z the right way to trigger the laser with Mesa Hardware or is there a better way?"

And "What other hardware could be used to trigger the laser on and off if its not tied to Mesa?"
25 Jul 2017 23:02 #96433 by PCW
PCW replied the topic: laser raster engraving
The problem with doing laser rastering with Mesa Ethernet card is the you cannot use a base thread so you are limited to a maximum raster data update rate of the servo thread period

At 500 mm/sec this means that the shortest pixel is 0.5 mm long at a 1 KHz servo thread.
You can run Mesa Ethernet cards at up to 4 KHz with the correct fast CPU but that's rather limiting.

Ideally there would be some clean way to include the raster data in the gcode file or external file and have "data painting"
firmware in the FPGA card.

I can make firmware that buffers raster data and synchronizes it with motion
(either a single axis or a length vector for data painting on curved surfaces) but this also
requires LinuxCNC driver support and possibly changes in the interpreter, though a lot could be done
in hal with gstreamer.
26 Jul 2017 13:08 #96465 by rodw
rodw replied the topic: laser raster engraving
Peter, thanks for your input. How would Linuxcnc send raster data to the FGPA? 0.5mm long dots is about 50 dots per inch (dpi). If you could transfer a 32bit unsigned long per servo period, you would have about 1600 dpi resolution, if you could send 2 unsigned longs per period, you'd have 3200 dpi which is right up there with resolution along with film and laser platesetters and the like used in the printing industry (although they are not often driven past 2400 dpi).
26 Jul 2017 14:16 #96471 by PCW
PCW replied the topic: laser raster engraving
I would not use a fixed data per servo cycle system but rather send a variable amount of data
to keep a motion synced FIFO full. The FIFO data-out clock would effectively be phase locked to the
desired axis position or a hal synthesized length vector for data painting on complex surfaces.
This allows for very high resolutions (Diode lasers can be modulated to the MHz region
and beyond) and greyscale data
30 Jul 2017 21:14 - 31 Jul 2017 00:13 #96702 by vre
vre replied the topic: laser raster engraving
PCW how difficult is to implement this?
What changes need linuxcnc driver?
This with support of diode lasers is awesome.
Last Edit: 31 Jul 2017 00:13 by vre.
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