Delta RMC151 - Manual (Page 990)

RMC70/150 and RMCTools User Manual
9.2.2.4.19. Symmetrical/Ratioed
Type: Axis Parameter Register
RMC70 Address: %MDn.60/4, where n = 12 + the axis number
RMC150 Address: %MDn.60/4, where n = 24 + the axis number
System Tag: _Axis[n].PriControlBits.Symm, where n is the axis number
How to Find: Axes Parameters Pane, Tune tab: Position/Velocity Gains
Data Type: Bits
Range: Ratioed (0), Symmetrical (1)
Default Value: Ratioed (0)
Description
This parameter specifies whether to use ratioed or symmetrical gains. Ratioed gains are
usually necessary on systems that behave differently in each direction of motion, such as
hydraulic cylinders. Many systems, such as electric motors, usually do not require ratioed
gains.
When this parameter is set to Symmetrical, the position or velocity gains are applied the
same in both directions of motion. With the Symmetrical option, only one Velocity Feed
Forward is available.
When this parameter is set to Ratioed, the position or velocity gains are applied
differently in each direction of motion. With the Ratioed option, two Velocity Feed
Forwards are available: Velocity Feed Forward (Positive) and Velocity Feed Forward
(Negative). 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.
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.
If the Symmetrical/Ratioed parameter is set to Ratioed and any of the Velocity Feed
Forwards are set to zero, the gains will have a ratio of 1:1, and the Velocity Feed
Forwards will be applied as they are.
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.
Format Details
This section is primarily for addressing this parameter when communicating with the RMC
from an external device. This information is not necessary when configuring this
parameter in RMCTools.
970 Delta Computer Systems, Inc.