Not Needed - (Separate pressure advance and retard)



  • How much of a pain would it be to have a (say) R parameter as well as an S parameter for pressure advance? One being used to advance the extruder at the start of a move, and the other being used to retard the extruder at the end of the move - in a similar fashion to how firmware retract/unretract can be made to work.

    I've been mulling over nozzle pressure compensation and can't help thinking that the amount of positive compensation that needs to be applied at the start of a print move may well be less than the amount of negative compensation that is required at the end of a print move. Of course, until we actually fit a pressure transducer inside a hot end, close to the nozzle tip, we'll never know for sure but my gut feel is that this would be the case. My reasoning goes like this.

    Ignoring current thinking as to why and how pressure builds up, at the end of a move, even with pressure advance (actually retardation) being applied as it stands at the moment, there is still a need for retraction (albeit a reduced amount). This would indicate that there is still some latent pressure in the nozzle at the end of a print move. That being the case, then logically it would seem that there is less need to advance the pressure at the start of the next print move than there is to retard it at the end of a print move.

    Anyway, would it be possible to implement even as an experimental test branch in order to evaluate, or would it be a real PITA?


  • administrators

    The problem with doing that is that using different values would give over or under extrusion. But I have thought of a variation on that idea that might work.



  • I guess I'm thinking along the lines of an extension to "coasting" that some slicers allow. It gets applied at the end of a print move but the opposite is not applied at the start of a print move.



  • As an update, some recent testing that I've done shows that my hunch was ill founded and that I was wrong. My latest tests show that there is no need for asymmetric pressure advance.



  • What brought you to this conclusion? Please share your findings.



  • @bot:

    What brought you to this conclusion? Please share your findings.

    https://www.duet3d.com/forum/thread.php?pid=35801#p35801


 

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