Delta RMC151 - Manual (Page 982)

RMC70/150 and RMCTools User Manual
All the gains of the axis are ratioed by the Positive Negative Velocity Feed Forwards. Once
the Positive and Negative Velocity Feed Forwards have been tuned, the gains in the
direction of the highest Velocity Feed Forward will be applied as they are. The gains in the
direction of the lowest Velocity Feed Forward will be decreased by the ratio of the Velocity
Feed Forwards. This results in very good control of the cylinder in both directions.
Note:
Ratioed gains are automatically selected by the Tuning Wizard if moves in both directions are
used.
Example
Consider a single-rod hydraulic cylinder that moves at 3 in/sec when a Control Output of
1V is applied and -2.3 in/sec when a Control Output of -1V is applied. Since it moves
faster in the positive direction, those gains need to be smaller.
The correct Positive Velocity Feed Forward for this system is 3.33. The correct Negative
Velocity Feed Forward is 4.35. By choosing Ratioed gains, the gains in the negative
direction will be applied as they are. The gains in the positive direction will be multiplied
by 3.33/4.35, which is 0.766.
The Velocity Feed Forward Term is the portion of the Control Output resulting from the
Velocity Feed Forwards, which are gains.
I-PD
In Position I-PD and Velocity I-PD control, the Velocity Feed Forwards are used, only if
the gains are set to Ratioed. In that case, the Velocity Feed Forward (Positive) and
Velocity Feed Forward (Negative) do not contribute to the Control Output. They are used
only to ratio the gains for either direction of travel.
If either Feed Forward is set to zero, or they are identical, the gain ratio will be one.
Otherwise, for the direction of the largest Feed Forward, the gains will be applied as they.
In the direction of the smallest Feed Forward, the gains will be multiplied by the ratio of
the smallest Feed Forward divided by the largest feed forward.
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 Forwards help 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.
9.2.2.4.12. Acceleration Feed Forward
Type: Axis Parameter Register
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