K3: Compensations
4.5 Dynamic feedforward control (following error compensation)
Extended Functions
286 Function Manual, 03/2013, 6FC5397-1BP40-3BA1
4.5.6 Secondary conditions
Axes that are interpolating axes with one another
Also for axes that interpolate with one another, the feedforward control parameter should be
optimally set for each axis, i.e. also several axes that are interpolating with one another can
have different feedforward control parameters.
Check contour monitoring
As the two equivalent time constants:
● MD32810 $MA_EQUIV_SPEEDCTRL_TIME (equivalent time constant speed control loop
for feedforward control)
and
● MD32800 $MA_EQUIV_CURRCTRL_TIME) (equivalent time constant current control
loop for feedforward control)
also influence the contour monitoring, this should be subsequently checked.
Reference:
Function Manual, Basic Functions; Axis Monitoring, Protection Zones (A3)
Effect on servo gain factor
When the feedforward control is set correctly, the response to setpoint changes in the
controlled system under speed feedforward control is as dynamic as that of the speed
control loop or, under torque feedforward control, as that of the current control loop, i.e. the
servo gain factor entered into MD32200 $MA_POS_CTRLGAIN hardly has any effect on the
control behavior (e.g. corner errors, overshoots, circle/radius errors).
On the other hand, feedforward control does not affect the response to disturbances
(synchronism). In this case, the servo gain factor entered in MD32200 is the active factor.
Service display "Servo gain factor"
When a feedforward control is active, the servo gain of the axis (corresponds to servo gain
factor active as response to setpoint changes) shown in the service display "axis/spindle" is
very high.
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