S-Curve acceleration? Why not "Plastic-Flow-Curve" acceleration with Pressure Advance?

Maybe (probably) somebody else already had the idea, but I haven’t read about it anywhere.

When looking at the graph under the Pressure Advance section of the documentation:

I’m wondering: Pressure Advance helps to match the extrusion of plastic to the movement of the head.

However, it’s not really possible to match that perfectly because plastic likes to flow as it does (as shown in the graph).

Wouldn’t it be much better if pressure advance would also match the head movement to the plastic-flow? After all, head-movement can be controlled precisely, implementing the “actual filament” curve as head velocity curve shouldn’t be a problem, or?

Well, basically this is exactly what Pressure Advance ¶ does:

  • During constant speed movement there is not much to control: You have a constant flow that is determined by the capability of your hotend, the speed, extrusion factor, material etc
  • During acceleration and deceleration PA comes into play allowing you to empirically (test print / tuning tower) optimize the flow so that you neither have too much nor too less extruded filament at the start, respectively end of these phases

Note that adjusting the acceleration profile to match the filament flow (instead of PA) will typically reduce the attainable acceleration, and potentially considerably slow down the prints. Moreover, during deceleration the filament flow exponentially decays but never truly stops, so some form of PA to pull back the filament is still required to stop the filament oozing due to back pressure in the hotend.

Yes, maybe I wasn’t clear, “Plastic-Flow-Curve” should not replace pressure advance, it should work together with it. PA ofcourse still needs to be active, otherwise you’d need way longer slopes which indeed would affect print time a lot I guess.

But with PA active, it won’t make such a big difference in overall print time, as acceleration/decelaration needs to happen anyway and it’s usually just a few percent of the whole line length that is slowed-down in comparsion to the default trapezoid head movement curve.

I’ve used the “coasting” setting in Cura slicer (it allows to stop the extrusion earlier, i.e. no extrusion for the last few millimeters as well as reduce the speed for those last milimeters, but only as a fixed percentage, no slope) and it doesn’t really make a difference time-wise.

Just as reminder: Coasting and PA are not compatible.

Yes, I know. What’s your point?