Siemens SINUMERIK 840D sl Function Manual page 409

5.5.4 Torque feedforward control
In the case of torque feedforward control, an additional current setpoint proportional to the
torque is applied directly to the current controller input. This value is formed using the
acceleration and moment of inertia.
The equivalent time constant of the current control loop must be determined accurately and
input as machine data to adjust the torque type of feedforward control correctly, refer to:
MD32800 $MA_EQUIV_CURRCTRL_TIME
Because of the direct current setpoint injection, torque feedforward control is only possible
on digital drives (SIMODRIVE 611D).
Figure 5-18
Application
Torque feedforward control is required to achieve high contour accuracy where the demands
on the dynamics are great. If set correctly, the following error can almost be completely
compensated even during high acceleration.
Parameter
The following axis-specific parameters must be defined during commissioning for torque
feedforward control:
SIMODRIVE 611D machine data MD1004 $MD_CTRL_CONFIG (configuration structure)
The torque feedforward control is activated in the SIMODRIVE 611D with bit 0 = 1.
MD32800 $MA_EQUIV_CURRCTRL_TIME
(equivalent time constant of closed current control loop)
The equivalent time constant of the closed current control loop is determined by measuring
the step response of the current control loop. With the SIMODRIVE 611D, the settling
process can be displayed using the commissioning tool.
Extended Functions
Function Manual, 03/2009, 6FC5397-1BP10-4BA0
Dynamic feedforward control (following error compensation)
Torque feedforward control
Compensations (K3)
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