# The dynamics of the extruder

Posted by Calendar
 The dynamics of the extruder February 02, 2014 11:12AM Registered: 5 years ago Posts: 1
Is there firmware out there that takes into account the dynamics of the extruder when extrusion speed is coordinated with head movement speed?

A while back i searched around, all i found was an attempted at a implementation of something like this in marlin that didn’t quite work in practise.
I know that a very good aproximate model for the extruders is.

G(s)=e^-(d*s)*K/(1+Ts)

Research article: "liquefier dynamics in fused deposition modeling" gives this model, the article is based on a bigger thesis with loots of information on what happens to the plastic in the extruder.

e^(-d*s) = timedelay, Usualy so small it can be ignored

K = gain constant
T = timeconstant

u(s) = comanded flow rate
y(s) = ActualFlowrate

ActualFlowrate=G(s)*U

I am under the impresion that extruison of plastic is done in a speed as constant as possible(with as little aceleration as possible in the path direction) to avoid problems with over fill, is this corect?

Is this is the best place to post this topic?

Edited 1 time(s). Last edit at 02/02/2014 01:26PM by Calendar.
 Re: The dynamics of the extruder March 04, 2014 08:36PM Registered: 8 years ago Posts: 1,761
all that math. in the real world, it is about keeping nozzle pressurized. it does not need to be exact. with the tiny orifice, and the small space for filament to extrude, it really is self regulated as long as back pressure exists. the only area i see this math being use is for setting adhesion layers bond strength of witch you want a set amount of material and pressure on nozzle on base layer.

so i will just come out and say it. it is not needed, except perhaps for first layer.

Edited 1 time(s). Last edit at 03/04/2014 08:37PM by jamesdanielv.
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