Rockwell Automation 8520-ARM2 9/Series CNC AMP Reference Manual Documentation Set - Manual (Page 221)

Servo Parameters
Chapter 7
7-75
Function
This parameter is available on all digital systems version 12.xx and earlier,
except 9/260 or 9/290 systems that use the three axis 8520 Digital servo
cards. Analog systems only use this parameter when the loop type is
configured as position/velocity.
During steady state the VE (Velocity Error) integrator compensates for
external forces working on the motor (such as increase or decrease in
loads). The VE integrator also plays a role in Acceleration/Deceleration
compensating for any error during the velocity transition.
When the axis is accelerating or decelerating, the velocity error integrator
compensates for any non-linear response of the servo. Any lag or lead in
the servo response is accumulated by the VE integrator and returned in the
form of an increased (or decreased) acceleration command.
Typically this accumulated error is returned to the system towards the end
of the velocity ramp with little chance of positioning error. However, in
some cases, (such as when the servo is coming to a stop while under a
heavy load) the integrator may not discharge itself completely before the
end of the velocity transition. When this happens, the VE integrator forces
a velocity overshoot, and possibly a position overshoot. (This is even
more likely when the type of position loop is chosen as “ZFE
Closed Loop.”)
This parameter sets the rate at which the VE integrator discharges. A value
of 1 indicates that the integrator cancels the error at the same rate it is
accumulated. Setting this parameter to a value larger than 1 causes the
integrator to cancel the accumulated error faster than it was accumulated.
This can improve the performance of the integrator during velocity
transitions, though having little to no effect on steady state behavior.
Important: Before adjusting this parameter, both the Velocity
Proportional Gain and the Velocity Integral Gain should have been
adjusted to attain the best possible servo performance. This should be
done with the default value of one set for the VE integrator discharge
rate. Once the servo is running properly, test for improved performance
by adjusting this parameter.
To adjust this parameter, a small part program should be made using
a series of:
G01 moves making at least two noticeable velocity transitions
Note that the G01 moves should take place at cutting feedrates.
G00 moves making at least two noticeable velocity transitions
7.3.9
VE Integrator Discharge
Rate