More information regarding 'jerk policy'
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I been using my Duet board for my high speed FFF printer. It can be a bit heavy on the Y axis and I always had a problem with very specific move types missing steps. Today I think I found the answer, by initiating "jerk policy" to 1. I was able to stop a move that consistently causes a Y axis stepper skip. It always seemed to be a spot that went from a print move to a very short travel and print again.
I want to know more about what "jerk policy 1" is doing as the information that is readily available is a bit vague. From what I can gather some moves do not obey the jerk setting? I can't understand, or something is missing.
I am still testing to make sure its not some fluke, but either way I would like to know. Thank you!
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That would be quite the fluke. If anything, one would expect jerk policy 1 to illicit a stall more than the other way around.
Jerk policy 0 will bring the X/Y axes and the extruder to zero speed when the next move is a travel only move (ie an XY or Z move without E values in the line).
Jerk policy 1 will never bring the X/Y axes down to zero speed, even if the next move is a travel move. The jerk speed is always the start and stop speed for every move (unless commanded at less than jerk speed).
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The default jerk policy (0) anly allows XY jerk to be used between one printing move and another. So travel moves will always come to a complete stop, a printing move after a travel move will start from standstill, and a printing move that is followed by a travel move will end at standstill. This means that jerk (i.e. a commanded instantaneous speed change) is only used where it is needed to allow curves to be printed at a constant speed, where the curve is made up of short straight line segments.
Jerk policy 1 allows XY jerk to be used between any pair of moves.
