Rockwell Automation 1784-PM16SE SoftLogix Motion Card Setup and Configuration Manual - Manual (Page 138)

Publication 1784-UM003A-EN-P – June 2003
130 Naming & Configuring Your Motion Axis
Note: The parameters on this tab become read-only and cannot be
edited when the controller is online if the controller is set to Hard Run
mode, or if a Feedback On condition exists.
When RSLogix 5000 is offline, the following parameters can be edited and the
program saved to disk using either the Save command or by clicking on the
Apply button. You must re-download the edited program to the controller
before it can be run.
Velocity Feedforward
Velocity Feedforward Gain scales the current Command Velocity by the
Velocity Feedforward Gain and adds it as an offset to the Velocity Command.
Hence, the Velocity Feedforward Gain allows the following error of the servo
system to be reduced to nearly zero when running at a constant speed. This is
important in applications such as electronic gearing, position camming, and
synchronization applications, where it is necessary that the actual axis position
not significantly lag behind the commanded position at any time. The optimal
value for Velocity Feedforward Gain is 100%, theoretically. In reality, however,
the value may need to be tweaked to accommodate velocity loops with
non-infinite loop gain and other application considerations.
Acceleration Feedforward
Acceleration Feedforward Gain scales the current Command Acceleration by
the Acceleration Feedforward Gain and adds it as an offset to the Servo
Output generated by the servo loop. With this done, the servo loops do not
need to generate much of a contribution to the Servo Output, hence the
Position and/or Velocity Error values are significantly reduced. Hence, when
used in conjunction with the Velocity Feedforward Gain, the Acceleration
Feedforward Gain allows the following error of the servo system during the
acceleration and deceleration phases of motion to be reduced to nearly zero.
This is important in applications such as electronic gearing, position camming,
and synchronization applications, where it is necessary that the actual axis
position not significantly lag behind the commanded position at any time. The
optimal value for Acceleration Feedforward is 100%, theoretically. In reality,
however, the value may need to be tweaked to accommodate velocity loops
with non-infinite loop gain and other application considerations.
Note: Acceleration Feedforward Gain is not applicable for applications
employing velocity loop servo drives. Such systems would require the
acceleration feedforward functionality to be located in the drive itself.