User manual

Rockwell Automation Publication MOTION-UM003F-EN-P - March 2015 277
Program Appendix C
Corrective Action
If you want the axis to accelerate right away, use a trapezoidal profile.
Why does my axis reverse direction when I stop and start it?
While an axis is jogging at its target speed, you stop the axis. Before the axis stops
completely, you restart the jog. The axis continues to slow down and then
reverses direction. Eventually the axis changes direction again and moves in the
programmed direction.
Example
You use a Motion Axis Stop (MAS) instruction to stop a jog. While the axis is
slowing down, you use a Motion Axis Jog (MAJ) instruction to start the axis
again. The axis continues to slow down and then moves in the opposite direction.
Eventually it returns to its programmed direction.
Look For
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 speed up
again.
• If you reduce the acceleration, it takes longer to get acceleration to 0.
• In the meantime, the axis continues past 0 speed and moves in the opposite
direction.