Constructing Janus, by Dirk

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Progress video #2

Postby dirktheeng » Sun Jun 26, 2011 9:33 pm

I had some time this weekend to work on the laser and made a video of the progress. Here it is:



What you will see is the homing setup I have in the LCGCi code in githup and all 3 axis moving as well as my connection setup.
Last edited by dirktheeng on Sun Jun 26, 2011 9:57 pm, edited 3 times in total.
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Re: Constructing Janus, by Dirk

Postby dirktheeng » Sun Jun 26, 2011 9:44 pm

bdring wrote:Well, my original response was to Ben's engraving with G-code question. There is more going on than just G-Code. You should profile the read time for the SD card. You may need to adjust the code around that timing.

The XMOS is a better chip for the problem if being a popular open source platform is not part of the problem. That is why I stopped working on the project. There was no collaboration interest.


Maybe I should take a second look at the XMOS if this doesn't work. I think there should be plenty of time to read a the file lines necessary to execute a raster line inbetween the raster lines (I hope). I can make it pause for the time needed at the ends if it doesn't. I can also set an interrupt when the laser needs to fire and do it throughout the process. I agree, however, this timing may end up being critical.

during vector cutting, this won't be an issue as readign the file and keeping the slave buffer full is all it has to do.
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Re: Constructing Janus, by Dirk

Postby bdring » Sun Jun 26, 2011 9:55 pm

I would continue with the Arduino. Even if it is vector only, I think it would be a nice option. If you switch to the Maple or XMOS, I would be glad to sponsor you with some hardware.
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Re: Constructing Janus, by Dirk

Postby tylerv » Sun Jun 26, 2011 10:01 pm

If all else fails for raster engraving, you could have a switch, transistor array, or something similar that moves the physical connection between the Arduino/GRBL connection and an external parallel port, XMOS, or Maple.
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Re: Constructing Janus, by Dirk

Postby dirktheeng » Sun Jun 26, 2011 10:31 pm

bdring wrote:I would continue with the Arduino. Even if it is vector only, I think it would be a nice option. If you switch to the Maple or XMOS, I would be glad to sponsor you with some hardware.



Bart, do you think there would be any interest in a traditional galvanometer based stereo lithography system? After I finish this project, I plan on developing that next. I will use the laser to cut all the parts I need to build that. I will use a uv laser or blue ray laser with a UV set epoxy like solarez (used for surf boards). It's not too expensive, about $20/gallon or so if you buy a 5 gallon bucket. You can also add fibers and fillers to make it stretch. The galvanometer can devflect the beam about 40 degrees to either side and isnt too expensive (a few hundred dolars wth controller for a closed loop version) I think this would be better than a 3D printer like the reprap (much more accurate) and potentially faster. It may end up being faster than using a projector as well and waste less resin. the UV source from a regular projector isn't very strong and the bleed through on dark pixels can be somewhat significant which can cause resin to go bad faster (starts to polymerize the rezin over time). It's an idea I've been kicking around anyhow. The only place it would potentially use use the maker slide would be in the z axis tray.
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Re: Constructing Janus, by Dirk

Postby BenJackson » Sun Jun 26, 2011 10:36 pm

Bart & Dirk,

I'm definitely interested in driver collaboration. My goals would be:
  • Ethernet connected
  • Acts as network print server, accepting PostScript
  • Automatically handles raster and vector operations based on color and possibly other in-band information
  • Configurable via webpage for out-of-band settings
  • Perhaps also accepts gcode on a separate port
I can get a Mini-ITX motherboard, a stick of RAM (1G or more) and a USB flash drive to boot off of for about $100. In terms of enabling Ethernet, a PostScript interpreter and having tons of memory, this combo is impossible to beat with any kind of "dev board" solution. I could run something like EMC2 and have a known-working motion control system good to at least 1000mm/s on the 2.x setup. What it lacks is any GPIO more sophisticated than a parallel port.

That leaves laser PWM. Back-of-the-envelope math says 500mm/s at 600dpi would take about 115.2k bps, so the serial port bandwidth is probably enough. Perhaps a small board that accepts serial bytes and clocks them out (as PWM) based on strobes from the parallel port (to sync). That would be something Bart could even add to his control interface.
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Re: Constructing Janus, by Dirk

Postby bdring » Sun Jun 26, 2011 10:40 pm

I don't know much about galvo based systems. The two issues you need to get comfortable with are the focal length problem. The distance the beam travels after the lens is always changing. A fiber laser or diode laser might help there, and the beam angle issue, where the beam is always hitting the surface at a different angle.
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Re: Constructing Janus, by Dirk

Postby dirktheeng » Tue Jun 28, 2011 11:38 pm

BenJackson wrote:Bart & Dirk,

I'm definitely interested in driver collaboration. My goals would be:
  • Ethernet connected
  • Acts as network print server, accepting PostScript
  • Automatically handles raster and vector operations based on color and possibly other in-band information
  • Configurable via webpage for out-of-band settings
  • Perhaps also accepts gcode on a separate port
I can get a Mini-ITX motherboard, a stick of RAM (1G or more) and a USB flash drive to boot off of for about $100. In terms of enabling Ethernet, a PostScript interpreter and having tons of memory, this combo is impossible to beat with any kind of "dev board" solution. I could run something like EMC2 and have a known-working motion control system good to at least 1000mm/s on the 2.x setup. What it lacks is any GPIO more sophisticated than a parallel port.

That leaves laser PWM. Back-of-the-envelope math says 500mm/s at 600dpi would take about 115.2k bps, so the serial port bandwidth is probably enough. Perhaps a small board that accepts serial bytes and clocks them out (as PWM) based on strobes from the parallel port (to sync). That would be something Bart could even add to his control interface.


Ben,

Im interested in doing this. GRBL has a lot of bugs in the motion control system as I am finding out and it isn't very stable. I started streaming code over my USB and it didn't really perform well, not nearly like mach 3. I was fairly disappointed in how it ran. How do you plan on controlling the pulses and doing all the calcs for motion planning?
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Re: Constructing Janus, by Dirk

Postby BenJackson » Wed Jun 29, 2011 3:22 am

I started to draw some block diagrams but for now I'll keep it simple:

The software stack is something like:

windows/OSX/linux generic PostScript driver -> samba -> CUPS? -> pstoedit w/plugin -> gcode -> EMC

  • samba is the Windows File/Print server component
  • CUPS is a print spooling system which may or may not be useful (OSX and linux can also print to it directly without samba)
  • pstoedit is the swiss army knife of vector file formats and will do the heavy lifting of accepting PostScript. It already has a gcode plugin but it is not very sophisticated
  • EMC is a machine controller. There are pre-built realtime Linux distributions with EMC installed which would be the base platform. You can download a bootable CD of one and try it on any PC that you could run Mach3 on.

EMC already handles all the motion planning and low-level parallel-port based stepper control (it can also drive servos and all manner of things like robots driven with inverse kinematics). The idea would be to build a small board to sit in-line with the EMC "laser on" pin on the parallel port and use that to clock out PWM (or even analog) output samples to the PSU. EMC would emit the raster data (or repeating stipple patterns or whatever is required) over a very simple serial port protocol and then pulse the power pin to step through the pattern. Some EMC extension would be used to load the raster data and then regular gcode motion commands would handle the positioning.
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Re: Constructing Janus, by Dirk

Postby onlyjus » Fri Jul 01, 2011 3:13 am

I have been running EMC with Ubuntu for a three axis CNC and it works well: http://onlyjus-cnc.blogspot.com/. If I end up dropping steps or running into "real time errors" I might look into grbl.

On a side note: there is an open cam library being developed: http://code.google.com/p/opencamlib/
in which a CAD/CAM program was developed on called HeeksCAD: http://heeks.net/
I have not played around with it enough but for an open-source program, it seems pretty powerful. Maybe useful for creating you gcode.
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