Delta RMC151 - Manual (Page 980)

RMC70/150 and RMCTools User Manual
Type: Axis Parameter Register
RMC70 Address: Gain Set #1: %MDn.65, where n = 12 + the axis number
Gain Set #2: %MDn.132, where n = 12 + the axis number
RMC150 Address: Gain Set #1: %MDn.65, where n = 24 + the axis number
Gain Set #2: %MDn.132, where n = 24 + the axis number
System Tag: Gain Set #1: _Axis[n].VelFFwdP
Gain Set #2: _Axis[n].VelFFwdP_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 Positive Velocity Feed Forward is one of the gains. It causes the controller to give an
amount of Control Output proportional to the speed of the velocity of the axis.
The Positive Velocity Feed Forward applies when the Control Output is positive. The
Negative Velocity Feed Forward applies when the Control Output is negative. The Velocity
Feed Forwards are only applied when the axis is in Closed Loop control. They help the
axis maintain the Target Position while the axis is moving at constant velocity.
The Positive and Negative Velocity Feed Forwards are available only on position or
velocity axes with ratioed gains. Position or velocity axes with symmetrical gains have
only one Velocity Feed Forward.
All the gains of the axis are ratioed by the Positive and 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.
960 Delta Computer Systems, Inc.