Rockwell Automation 1771-QC , D17716.5.25 SER/B SERVO POS - Manual (Page 18)

Positioning Concepts
Chapter 3
3Ć5
Feed forwarding requires an additional summing point and an amplifier.
The axis feedrate is multiplied by the feed-forward gain (K2) to produce
the feed-forward value. The feed-forward value is added to the following
error multiplied by the gain to generate the velocity command.
Without feed forward, the axis will not begin to move until the axis
feedrate builds up enough following error to generate a sufficiently large
velocity command to overcome friction and inertia to move the axis.
However, the feed-forward value could generate a velocity command to
move the axis almost immediately. This immediate response keeps the
actual position closer to the position command, thereby reducing the
following error.