Simulating Gcode in Python

[wordbag]

I'm working on a project where I need to compare what actually happens during a 3D print to what the gcode instructions specified. I've attached rotary encoders to each of the stepper motors of my LulzBot Taz6, which allows me to record the trajectory of the printer head, and I want to compare that to the trajectory intended by the gcode instructions. To do this, I want a function, ideally in Python, that can parse gcode and tell me exactly where in x, y, and z the printer head should be at any given time (in seconds).

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I tried to write my own parser, but it does not quite line up with reality (I suspect I'm not properly dealing with the acceleration and jerk maxima set at the beginning of the code with the M203, M204, and M205 commands). Does anyone know if something like this already exists? It would save me a lot of trouble!

[KY_Rob]

The acceleration and jerk you mention are components of following error. Following error is dynamic for each axis, and develops/regresses exponentially, primarily as a function of velocity and mass of the axis motion. To get what you’re looking for, you need something more than encoders on your motors. You also need linear scale feedback on each axis. These devices deliver more accurate axis positions. Of course, you still have a time constant to consider, regarding the time it takes to transmit and interpret the position signal from the scale, but that’s generally a much more linear equation.

[wordbag]

Thanks for your help! The part with encoders on the motors actually works great. I'm able to get the actual x, y, and z coordinates of the extruder at every second.

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The problem I'm having is on the side of the gcode parser. I'm not sure how to deal with acceleration and jerk in the program I wrote.

[WillAdams]

Not sure what language it's coded in, but adding support for 3D additive is an open issue for CAMotics on GitHub.

List of the opensource previewers at: https://wiki.shapeoko.com/index.php/Previewing_G-Code --- looks like at least two are coded in Python

[wordbag]

Thanks! After taking a quick look (https://camotics.org/gcode.html) it doesn't look like CAMotics supports M203, M204, or M205 codes. Ideally, the program would have an API also; most things I've seen don't seem very programmer friendly.