Rockwell Automation 1784-PM16SE SoftLogix Motion Card Setup and Configuration Manual - Manual (Page 355)

Publication 1784-UM003A-EN-P – June 2003
Motion Object Attributes 347
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 is 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.
Tuning Configuration Bits
Tuning Direction Reverse
The Tune Direction Reverse bit attribute determines the direction of the
tuning motion profile initiated by the MRAT (Motion Run Axis Tune)
instruction. If this bit is set (true), motion is initiated in the reverse (or
negative) direction.
GSV/SSV Access Attribute Name Data Type Values
SSV/GSV Position Servo Bandwidth REAL
Hertz
GSV/SSV Access Attribute Name Data Type Values
SSV/GSV Tuning Configuration Bits DINT 0: Tuning Direction Reverse
1: Tune Position Error Integrator
2: Tune Velocity Error Integrator
3: Tune Velocity Feedforward
4: Tune Acceleration Feedforward
5: Tune Output Low-Pass Filter
6-31: Reserved