User manual

272 Rockwell Automation Publication MOTION-UM003F-EN-P - March 2015
Appendix C Program
Cause
When you use an S-curve profile, jerk determines the acceleration and
deceleration time of the axis:
• An S-curve profile has to get acceleration to 0 before the axis can slow
down.
• The time it takes depends on the acceleration and speed.
• In the meantime, the axis continues to speed up.
The following trends show how the axis stops with a trapezoidal profile and an
S-curve profile.
Corrective Action
If you want the axis to slow down right away, use a trapezoidal profile.
Why does my axis overshoot its target speed?
While an axis is accelerating, you try to stop the axis or change its speed. The axis
keeps accelerating and goes past its initial target speed. Eventually it starts to
decelerate.
Example
You start a Motion Axis Jog (MAJ) instruction. Before the axis gets to its target
speed, you try to stop it with another MAJ instruction. The speed of the second
instruction is set to 0. The axis continues to speed up and overshoots its initial
target speed. Eventually it slows to a stop.
Stop while accelerating
Trapezoidal S-curve
The axis slows down as soon as you start the stopping instruction. The axis continues to speed up until the S-curve profile brings the acceleration rate
to 0.