Reference Manual

PMAC 2 Software Reference
PMAC I-Variable Specification 87
If Ix30 is set to a negative value, this has the effect of inverting the command output
polarity for motors not commutated by PMAC, when compared to a positive value of the
same magnitude. This can eliminate the need to exchange wires to get the desired polarity.
On a motor that is commutated by PMAC, changing the sign of Ix30 has the effect of
changing the commutation phase angle by 180
o
. Negative values of Ix30 cannot be used
with the auto-tuning programs in the PMAC Executive program.
This parameter is usually set initially using the Tuning utility in the PMAC Executive
Program. It may be changed on the fly at any time to create types of adaptive control.
Note:
The default value of 2000 for this parameter is exceedingly weak
for most systems (all but the highest resolution velocity-loop
systems), causing sluggish motion and/or following error failure.
Most users will immediately want to raise this parameter
significantly even before starting serious tuning.
If the servo update time is changed, Ix30 will have the same effect for the same numerical
value. However, smaller update times (faster update rates) should permit higher values of
Ix30 (stiffer systems) without instability problems.
See Also
PID Servo Filter (Closing the Servo Loop)
I-variables Ix31-Ix39
Tuning Instructions (PMAC Executive Program manual)
Ix31 Motor x PID Derivative Gain
Range
-8,388,608 .. 8,388,607
Units
(Ix30*Ix09)/2
26
DAC bits/(Counts/cycle)
Default
1280
Remarks
Ix31 subtracts an amount from the control output proportional to the measured velocity of
Motor x. It acts effectively as an electronic damper. The higher Ix31 is, the heavier the
damping effect is.
If the motor is driving a properly tuned tachometer-loop (velocity) amplifier, the amplifier
will provide sufficient damping, and Ix31 should be set to zero. If the motor is driving a
current-loop (torque) amplifier, or if PMAC is commutating the motor, the amplifier will
provide no damping, and Ix31 must be greater than zero to provide damping for stability.
On a typical system with a current-loop amplifier and PMAC’s default servo update time
(~440 µsec), an Ix31 value of 2000 to 3000 will provide a critically damped step response.
If the servo update time is changed, Ix31 must be changed proportionately in the opposite
direction to keep the same damping effect. For instance, if the servo update time is cut in
half, from 440 µsec to 220 µsec, Ix31 must be doubled to keep the same effect.
This parameter is usually set initially using the Tuning utility in the PMAC Executive
Program. It may be changed on the fly at any time to create types of adaptive control.
See Also
I-variables Ix30, Ix32-Ix39
PID Servo Filter (Closing the Servo Loop)
Tuning Instructions (PMAC Executive Program manual)