Support separate jerk values for extrusion and travel moves



  • To avoid a print quality issue, I have been setting the x/y jerk to a low value during travel moves. It has been suggested that changing the jerk "on the fly" is not a good idea so my wish is to have some means of setting the x/y jerk to be used for travel moves independently from the x/y jerk used for moves that involve the extruder. It would then be possible to set the x/y jerk values once at the start of the print.
    The simplest solution I guess would be to have an option that forces the x/y jerk to be 0 for travel moves. A more complex scheme would be to be able to specify independent jerk values for the travel and non-travel scenarios.



  • May I ask you why you had to set a low jerk during travel moves? What was the printing issue? Travel moves are supposed to be straight lines, so I don't understand where jerk applies… Am I missing something?



  • I could see there being some merit in having different settings for printing and travel, much of which is handled in the slicer except jerk. However I can't see why you want 0 jerk for travel. I could see the case for 0 jerk extrduing small details.


  • administrators

    I think the issue is when a printing move is preceded or followed by a travel move. Depending on the relative directions of the two moves, jerk may be applied, so that the printing move does end at zero speed if it is followed by a travel move, or does not start at zero speed if it is preceded by a travel move. I've made an experimental change to the firmware that should prevent jerk being applied between printing and non-printing moves.



  • I see; thanks for the explanation!



  • @fma:

    May I ask you why you had to set a low jerk during travel moves? What was the printing issue? Travel moves are supposed to be straight lines, so I don't understand where jerk applies… Am I missing something?

    What I was seeing was faint vertical banding on an outside wall caused by the machine (a delta) wobbling following rapid deceleration at the end of the travel move that immediately preceded the wall. By reducing both the acceleration and jerk used for travel, I could reduce the magnitude of the banding. In this case the travel move was normal to the direction of the wall and so the velocity had to become 0 and I wanted that to occur at the rate set by M204 and not with a big step at the end.


  • administrators

    @burtoogle, please try the 1.19+5 firmware, it no longer uses jerk between printing and non-printing moves. It also includes what I hope is a fix for the short move/retraction move issue you reported.


 

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