E motion letter support for 3D printers

[revarbat]

This is a beautiful library for parsing CNC subtractive process GCode. However, 3D printing, an additive process, uses a slight variant on GCode.

Almost all cheap 3D printers use the E letter to denote extruder motion, such that X, Y, Z and E are motion axes. Yes, it would have been smarter to use the A, B, C, U, V, or W codes instead. Unfortunately E became the standard, and it's too late to do much about that.

In addition:

• M82 sets E axis (and only E axis) motion to absolute mode.
• M82 sets E axis (and only E axis) motion to relative mode.
• G29 does a homing similar to G28, with the addition of multiple Z height tests at various XY positions to test how level the bed is.
• There are also various other G and M codes it would be nice to get info from in parsing, that don't affect motion. You can find more info at http://reprap.org/wiki/G-code though it includes info on obsolete and obscure codes for older or unusual printers as well. Info specific for the Marlin firmware, which I am most interested in, is at http://marlinfw.org/meta/gcode/

If there is a way you could at least enable the E motion axis in this library, that'd let me use this library to write a program to visually preview GCode files with PyOpenGL.

[fragmuffin]

Thanks for the lesson!,
I don't have a 3d printer, but this library is intended to be useful for both additive and subtractive processes.

The issue is being able to support multiple conflicting variants of the gcode language.

Modifying Base G-Code set
I could provide a function to add and modify the LinuxCNC defined gcodes, but that would mean you couldn't parse subtractive and additive gcode in the same script.
(and it's messy and hard to trace what each GCode class actually contains)

Registering Language Variants
I could have the LinuxCNC defined codes as the base set, then modifications as languages.
So to change the language you could...

import pygcode
pygcode.set_lang('reprap')
# or
pygcode.set_lang('marlin')

That's a bit more work, but I like it.

Workaround
But for now... in 0.2.1 you can write:

import pygcode

# Add 'E' parameter to all motion commands
for cls in pygcode.gcodes._subclasses(pygcode.GCodeMotion):
    cls.param_letters.add('E')

# Add G29 gcode
class GCodeAutomaticBedLevel(pygcode.GCode):
    word_key = pygcode.Word('G', 29)

# Cannot create duplicate codes, so G82 and G83 will be broken

Then the code

lines = [
    'G1 X1 Y2 E3',
    'G82',
    'G83',
    'G29',
]
for line in lines:
    print(pygcode.text2gcodes(line))

will give

[<GCodeLinearMove: G01{E3, X1, Y2}>]
[<GCodeDrillingCycleDwell: G82>]
[<GCodeDrillingCyclePeck: G83>]
[<GCodeAutomaticBedLevel: G29>]

I doubt passing these into a virtual Machine will do what you expect.

[fragmuffin]

Thanks for raising this issue @revarbat !
this really helps me make this library useful.

[revarbat]

The variants plan in #9 sounds excellent. One correction, though, is the E axis relative/absolute mode codes are M82 and M83, not G-codes. So, no conflicts with standard GCode, I think. But how does the parser return them?

[fragmuffin]

oh!, of course, my mistake.
then there's no conflict.

# Add M82 / M83 gcodes
class GCodeExtruderAbsoluteMotion(pygcode.GCode):
    word_key = pygcode.Word('M', 82)

class GCodeExtruderRelativeMotion(pygcode.GCode):
    word_key = pygcode.Word('M', 83)

but still, they won't be modal until I've done #9.

@revarbat: do you have a pressing need to have this done soon?

[IanCarr-deAvelon]

A further problem with 3d printer gcode is that S has other uses and pygcode takes them all as spindle speed changes. Eg
M420 S1 = retrieve bed leveling from memory
M106 S255 = set cooling fan power to $FF ie. max
Probably all Ms should be dealt with separately.
Yours
Ian

[petaflot]

see https://github.com/petaflot/pygcode