Siemens SINUMERIK 840D sl Function Manual page 410

Compensations (K3)
Dynamic feedforward control (following error compensation)
In addition, the current setpoint of the 1st drive of each module on the 1st DA converter of
the module is output so that it can also be observed with an oscilloscope.
The equivalent time constant must be determined as exactly as possible.
References:
/FB1/ Function Manual, Basic Functions; Velocities, Setpoint-Actual Value Systems, Closed-
Loop Control (G2), Chapter "Optimization of Control"
MD32650 $MA_AX_INERTIA
(total moment of inertia of axis)
The total moment of inertia (moment of inertia of drive + load referred to the motor shaft) of
the axis must be determined and entered in the MD for torque feedforward control.
The recommended initial value corresponds to 1 to 2 times the setting in the SIMODRIVE
611D machine data
MD1117 $MD_MOTOR_INERTIA
(motor moment of inertia)
for entry in the following machine data:
MD32650 $MA_AX_INERTIA
Fine adjustment
By making minor adjustments (fine tuning) to the values set in
MD32800 and MD32650
it is possible to set the desired response for the relevant axis/spindle. Owing to the very high
speed of acceleration processes, it is not possible to use the service display to fine tune the
parameters. In the case of the SIMODRIVE 611D, for example, changes made to the
machine data should be checked by recording the following error from an analog setpoint
output (this can only be done with the commissioning tool).
In addition to the response at constant traversal, it is particularly important to monitor the
following error which occurs which the axis/spindle is accelerating. The adjustment criterion
for the torque feedforward control is:
Following error ≈ 0
● Case 1:
● Case 2:
410
When the axis is traveling in a positive direction, the recorded following error has a
positive value.
→ the values entered for the equivalent time constant of the current control loop or for the
moment of inertia of the axis are too low.
When the axis is traveling in a positive direction, the recorded following error has a
negative value.
→ the values entered for the equivalent time constant of the current control loop or for the
moment of inertia of the axis are too high.
Function Manual, 03/2009, 6FC5397-1BP10-4BA0
Extended Functions