Velocity based extrusion
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I recently ran across a concept from 2014 that seems to have been implemented in LinuxCNC and MachineKit, but none of the main printer firmwares around: Velocity based extrusion.
In short, the extruder is not an axis controlled by the GCode directly, but the firmware is instructed about target line width and height and controls extrusion speed according to nozzle movement. This is similar to volumetric extrusion but different (extruder is still an axis) and should basically result in pressure equalization similar to Pressure Advance, but based on nozzle movement velocity rather than as a heuristic adjusting the extruder movement.
Further reading:
https://basdebruijn.com/2014/05/machinekit-and-additive-manufacturing/
https://basdebruijn.com/2014/09/velocity-extruding-revisited/
Post processing script for slic3r:
https://github.com/machinekoder/Machinekit-Slic3r-postprocess/blob/master/velocity-extrusion.py
