As an adition, are you only switching the axis to AB without first commanding a stop command? Did you check suggested procedure in this post?
Start velocity command (with position mode)
Switch of drive surveillance of position command value (C1300)
Wait to your purposes (screwing finished)
Use stop command
Use command to set actual drive position to motion interpolator (axsSetIpoPosFromActPos)
Switch on drive surveillance of position command value
Switch drive to AB (or leave it in AF and open clamp)
Continue with your application
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