Delta RMC151 - Manual (Page 106)

RMC70/150 and RMCTools User Manual
Gain Set#2 applies when the Current Control Mode is Velocity PID or
Velocity I-PD.
PID, I-PD
Automatically chooses a gain set based on PID or I-PD control.
Gain Set#1 applies when the Current Control Mode is Position PID or
Velocity PID.
Gain Set#2 applies when the Current Control Mode is Position I-PD or
Velocity I-PD.
Choosing a Gain Set Option
To set the Gain Set option, use the Gain Sets parameter. This parameter is located in the
Axis Tools, Axis Parameters pane, on the All tab, in the Position/Velocity Control
section.
3.5.7. Ratioed Gains
Position or velocity control axes that behave differently in either direction of motion are called
asymmetric systems. Such systems require different gains in each direction. The RMC can
ratio the gains such that the system controls identically in both directions. A single-rod
hydraulic cylinder is an asymmetrical system. A motor with the same load in both directions is
typically symmetrical.
A related concept is using different gains for different control types. See the Gain Sets
Overview topic for details.
To apply different directional gains to an asymmetrical system, the RMC ratios the gains. To
ratio the gains, set the Symmetrical/Ratioed parameter to Ratioed. This creates two Velocity
Feed Forwards, one for each direction. Once the 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 matches the PID output to the system dynamics in each
direction, resulting in very good control of the cylinder.
The RMC uses the Target Velocity and Position Error to determine whether to use the forward
or reverse gains. If there is a non-zero Target Velocity, then its sign determines which
directional gains to use. If the Target Velocity is zero, then the Position Error (or Velocity Error
for Velocity Control) determines the intended direction of movement.
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 (1 / 3). The correct
Negative Velocity Feed Forward is 4.35 (1 / 2.3). 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.
Choosing Ratioed Gains
Use the Symmetrical/Ratioed parameter to choose ratioed gains. This parameter is
located in the Axis Tools, Axis Parameters pane, on the Tune tab.
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