Rockwell Automation 1784-PM16SE SoftLogix Motion Card Setup and Configuration Manual - Manual (Page 416)

Publication 1784-UM003A-EN-P – June 2003
408 Motion Object Attributes
There are practical limitations to the maximum Velocity Servo Bandwidth for
the velocity servo loop based on the drive system and 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:
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.
Position Servo Bandwidth The value for the Position 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 position servo is unable to provide any significant
position disturbance correction. In general, within the constraints of a stable
servo system, the higher the Position Servo Bandwidth the better the dynamic
performance of the system. A maximum value for the Position 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 Position Servo Bandwidth before
executing the MAAT instruction.
There are limitations to the maximum bandwidth that can be achieved for the
position loop based on the dynamics of the inner velocity and current loops of
the servo system and the desired damping of the system, Z. Exceeding these
limits could result in an unstable system. These bandwidth limitations may be
expressed as follows:
Max Position Bandwidth (Hz) = 0.25 * 1/Z 2 * Velocity Bandwidth (Hz)
For example, if the maximum bandwidth of the velocity servo loop is 40 Hz
and the damping factor, Z, is 0.8, the maximum the maximum position
bandwidth is 16 Hz. Based on these numbers the corresponding proportional
gains for the loops can be computed.
GSV/SSV Access Attribute Name Data Type Values
SSV/GSV Position Servo Bandwidth REAL
Hertz