Delta RMC151 - Manual (Page 979)

9 Register Reference
Gain Set #2: %MDn.132, where n = 24 + the axis number
System Tag: Gain Set #1: _Axis[n].VelFFwd
Gain Set #2: _Axis[n].VelFFwd_2
where n is the axis number
How to Find: Axes Parameters Pane, Tune tab: Position/Velocity Gains
Data Type: REAL
Units: %/(pu/s)
Range: ≥ 0
Default Value: 0
Description
The Velocity Feed Forward is one of the gains used in Position PID and Velocity PID
control. It causes the controller to give an amount of Control Output proportional to the
speed of the velocity of the axis. The Velocity Feed Forward is only applied when the axis
is in Closed Loop control. It helps the axis maintain the Target Position while the axis is
moving at constant velocity.
The Velocity Feed Forward is available on position or velocity axes with symmetrical
gains. Position or velocity axes with ratioed gains have a Velocity Feed Forward (Positive)
and a Velocity Feed Forward (Negative).
The Feed Forward Adjust (69) command can be used to set the Velocity Feed Forward
during machine operation to adjust the system for changing system dynamics.
The Velocity Feed Forward Term is the portion of the Control Output resulting from the
Velocity Feed Forward, which is a gain.
I-PD
In Position I-PD and Velocity I-PD control, the Velocity Feed Forward is not used. If the
gains are set to Ratioed, the Velocity Feed Forward (Positive) and Velocity Feed Forward
(Negative) are used, but they do not contribute any Control Output. They are used only
to ratio the gains for either direction of travel.
Definition
The Velocity Feed Forward units are: percent of the maximum Control Output per
position-units per second (pu/sec). The maximum Control Output is 10V, but can be
changed using the Output Scale parameter.
The Velocity Feed Forward Term is calculated from the Velocity Feed Forward as follows:
D
VFF
n = K
VFF
V
Target
n
where
D
VFF
n = Velocity Feed Forward Term at sample n [% of maximum Control
Output]
K
VFF
= Velocity Feed Forward [%/(pu/s)]
V
Target
n = Target Velocity at sample n [pu/s]
Tuning
The Velocity Feed Forward helps the axis maintain the Target Position while the axis is
moving. This makes it "easier" for the other gains to control the position of the axis. See
the Tuning topic for details on how to properly adjust the Velocity Feed Forward.
The Feed Forward Adjust (69) command can also be used to set the Velocity Feed
Forward.
9.2.2.4.10. Velocity Feed Forward (Positive)
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