#linuxcnc-devel Logs

Sep 26 2017

#linuxcnc-devel Calendar

11:35 AM Roguish_ is now known as Roguish
01:44 PM stustev: I just bought a Xenetech XLT 1325 laser engraver w/o the control computer. Has there been some rastering development in LinuxCNC?
01:50 PM KimK: I looked at the wiki (updated 2010) http://wiki.linuxcnc.org/cgi-bin/wiki.pl?Rastering_With_A_Laser There's a broken link to the Toronto Hacklab, I'm writing them now.
01:54 PM KimK: OK, got a good link, fixing the wiki now...
02:09 PM skunkworks: currently the rastering would have to be done with the printer port.
02:09 PM skunkworks: no one has integreated the rastering into say a mesa card
02:09 PM skunkworks: spelling!
02:09 PM skunkworks: jepler, is this a known problem? https://forum.linuxcnc.org/9-installing-linuxcnc/32941-linuxcnc-on-debian-stretch?start=40#99428
02:10 PM jepler: pcw_home has expressed interest in adding mesa rastering, but needs a developer for the parts of the code that would go in LinuxCNC. It is not a small project.
02:11 PM jepler: skunkworks: I don't follow glade, they change it all the time and I hate it.
02:11 PM skunkworks: heh - ok
02:11 PM jepler: skunkworks: but yeah probably
02:11 PM skunkworks: I don't glade.. yet
02:11 PM jepler: .. depends what "known" means
02:12 PM skunkworks: I guess it means that using glade to make screens and side panels is broken
02:19 PM KimK: I'm back, rastering wiki done.
02:23 PM Roguish_ is now known as Roguish
02:23 PM KimK: jepler: Maybe sometime when PCW is not busy (??) I can chat with him by phone about Mesa rastering and development of same. Thanks for the tip.
03:10 PM stustev: How fast can the printer port pulse a laser?
03:19 PM jepler: stustev: just like any parport pin, it can turn the pin on or off each BASE_PERIOD
03:26 PM stustev: jepler: thanks - this thing moves at max 150inches/second. The encoder is 2000 pulses per rev and 1 encoder rev is 2 inches X travel. sounds doable to me.
03:28 PM stustev: now for the laser power adjustment - am I looking at gcode or some other method? I don't know if LinuxCNC can process the gcode file to keep up laser pulses t a resonable resolution and 9000 inches/minute feed rate
03:31 PM stustev: an example video https://www.youtube.com/watch?v=XXgR-Am_Tk8
03:31 PM jepler: I don't know exactly how that "graster" software works. trying to manipulate the laser power from gcode is not going to give good rastering, that's limited to somewhat under 1 per servo cycle
03:31 PM jepler: that's part of why graster has two files, the gcode file and the other file, just based on skimming it
03:32 PM stustev: that is the kind of answer I am looking for - I skimmed it also and then asked the questions as I was not liking the feeling I got about graster
04:25 PM skunkphone: stustev: KimK http://www.buildlog.net/forum/viewtopic.php?f=16&t=557&start=110
04:26 PM skunkphone: Good read on rastering
04:26 PM KimK: Thanks, Sam, will look.
04:28 PM skunkphone: I think he takes the raster stuff and improves it
04:30 PM skunkphone: In the end I think he buys a commercial laser ; )
06:19 PM pcw_mesa: I dont think the FPGA firmware to do rastering (or general data painting for arbitrary paths) is terribly difficult
06:19 PM pcw_mesa: but some clean way for linuxCNC to handle the data (buffered and synced with motion) is needed
06:55 PM KimK: pcw_mesa: What do you imagine the block diagram of your proposed Mesa hardware would look like? It seems like it would take some kind of prepared-image-file transferred little-by-little to a Mesa bidirectional wide and fast shift-register, hardware synced with the rastering axis (probably X).
06:55 PM KimK: Is there a simpler way? How wide can you go, and what would the daugter cards be like? Does your scheme allow for combining the shift registers in layers, so that 4 layers would give 16 intensities to the output (in cases where the laser is variable)?
06:57 PM KimK: s/How wide can you go/How wide can you go (in shift register bit count width)/
07:02 PM pcw_mesa: I would probably have a byte mode and a bit mode (and syncing to axis is done ins hal so it could be X or a length vector calculated in hal)
07:04 PM KimK: These would be new daughter boards, I presume? Or can you re-use another daughter board in some way?
07:04 PM pcw_mesa: so its general (not just rastering but general data painting/heat treatment apps)
07:04 PM pcw_mesa: No, just firmware (and a lot of driver/LinuxCNC work)
07:06 PM pcw_mesa: its just data out, either bitstream or PWM so any daughtercard with a fast output would do
07:06 PM KimK: I guess I'm not seeing how to get those speeds without some kind of external shift register or something?
07:06 PM pcw_mesa: shift register +FIFO in FPGA
07:08 PM pcw_mesa: +clock logic and position trigger setpoints
07:09 PM KimK: And you think 1us pixels are easily obtainable, on a more-or-less continuous basis, once started?
07:10 PM KimK: We were doing some "back of the envelope" calculations earlier.
07:13 PM pcw_mesa: Yes
07:17 PM KimK: OK, great! Is there a good "video output" daughter board that you have in mind?
07:18 PM KimK: Or does this have to come right off of the FPGA?
07:19 PM pcw_mesa: any with fast output should do (like a step/dir card)
07:21 PM KimK: OK. How about the layers (video DAC) business? Any chance of variable intensities? Or just on/off?
07:24 PM pcw_mesa: I can do about 1 MHz 8 bit PWM so if you dont need extreme data rate it should be OK
07:25 PM pcw_mesa: AFAIK only diode lasers can be modulated at MHz rates
07:31 PM KimK: I think we had guesstimated around 600-700kHz(?), so 1MHz should work. The intensity is a just-in-case, I don't expect to need it on this laser. And there's always pre-processing in halftone.