Rockwell Automation 1784-PM16SE SoftLogix Motion Card Setup and Configuration Manual - Manual (Page 354)

Publication 1784-UM003A-EN-P – June 2003
346 Motion Object Attributes
Velocity Servo Bandwidth The value for the Velocity Servo Bandwidth represents the unity gain
bandwidth that is to be used to calculate the gains for a subsequent MAAT
(Motion Apply Axis Tune) instruction. The unity gain bandwidth is the
frequency beyond which the velocity servo is unable to provide any significant
position disturbance correction. In general, within the constraints of a stable
servo system, the higher the Velocity Servo Bandwidth is the better the
dynamic performance of the system. A maximum value for the Velocity Servo
Bandwidth is generated by the MRAT (Motion Run Axis Tune) instruction.
Computing gains based on this maximum value via the MAAT instruction will
result in dynamic response in keeping with the current value of the Damping
Factor described above. Alternatively, the responsiveness of the system can be
“softened” by reducing the value of the Velocity Servo Bandwidth before
executing the MAAT instruction.
There are practical limitations to the maximum Velocity Servo Bandwidth for
the velocity servo loop based on the drive system and, in some cases, the
desired damping factor of the system, Z. Exceeding these limits could result in
an unstable servo operation. These bandwidth limitations may be expressed as
follows:
For an external velocity loop servo drive,
Max Velocity Servo Bandwidth (Hz) = 0.159 * 2/Tune Rise Time
For an external torque loop servo drive,
Max Velocity Servo Bandwidth (Hz) = 0.159 * 0.25 * 1/Z
2
* 1/Drive
Model Time Constant
The factor of 0.159 represents the 1/2PI factor required to convert Radians
per Second units to Hertz.
GSV/SSV Access Attribute Name Data Type Values
SSV/GSV Velocity Servo Bandwidth REAL Hertz