K3: Compensations
4.5 Dynamic feedforward control (following error compensation)
Extended Functions
282 Function Manual, 03/2013, 6FC5397-1BP40-3BA1
4.5.3 Torque feedforward control
Function
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.
Application
Torque feedforward control is required to achieve high contour accuracy where the demands
on the dynamic response are very high. If set correctly, the following error can almost be
completely compensated even during high acceleration.
Commissioning
The following axis-specific parameters must be defined during commissioning for torque
feedforward control:
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Equivalent time constant of the current control loop (MD32800)
The equivalent time constant of the current control loop must be determined accurately (e.g.
graphically from the step response of the current control loop) and entered in the following
machine data in order to correctly set the torque feedforward control:
MD32800 $MA_EQUIV_CURRCTRL_TIME (equivalent time constant current control loop for
feedforward control)
Total moment of inertia of axis (MD32650)
The total moment of inertia (moment of inertia of drive plus load referred to the motor shaft)
of the axis must be determined and entered in the following machine data:
MD32650 $MA_AX_INERTIA (inertia for torque feedforward control)
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