Rockwell Automation Publication MOTION-UM003K-EN-P - January 2019 311
Out of Box Configuration for PowerFlex Drives Appendix B
For Decel Jerk:
Jerk Programming in Units/Sec
3
If you want to specify the jerk in 'Units/sec
3
' instead of '% of time', adjust your
jerk value as follows so that you get the value that you programmed.
Unique Program Considerations
If you program a move by using the % of Time units, the programming
software computes an Accel Jerk = a
2
/v where a = the programmed Accel
Rate and v = programmed Speed.
Therefore, the higher the programmed speed, the lower the computed Jerk.
The system has a Jerk priority planner. In other words, Jerk always takes
priority over acceleration and velocity.
Therefore, you always get the programmed Jerk. If a move is velocity-limited,
the move does not reach the programmed acceleration and/or velocity. Once
you reach the velocity limit for the length of the move, as the velocity is
increased, the move takes longer and longer to complete.
Decel Jerk is computed similarly to the Accel Jerk described previously. The
only difference is that instead of a
2
/v, Decel Jerk = d
2
/v, where d = the
programmed Decel Rate.
j
d
[% of Time] =
1 +
100
2
j
d
[EU/s
3
] v
max
[EU/s]
d
max
[EU/s
2
]
Temporary Speed =
Desired Decel Jerk value in Units/Sec
3
Programmed Decel Rate
2
k =
Max (Programmed Speed, Temporary Speed)
Start Speed - Programmed Speed
if (k < 1)
•Instruction Faceplate Decel Jerk in Units/Sec
3
= Desired Decel Jerk in Units/Sec
3
else
•Instruction Faceplate Decel Jerk in Units/Sec
3
= Desired Decel Jerk in Units/Sec
3
* k
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