Siemens SINUMERIK 840D sl Function Manual page 465

Setting the equivalent time constant of the current control loop
MD32800 torque feedforward control for each additional option
The same rules and recommendations apply to setting the time constant of the current
control loop as to the speed feedforward control.
However, as previously, activation of the torque feedforward control filter via:
MD32620 $MA_FFW_MODE = 4
must be enabled both in the drive and via the optionin order to set the time constant via:
MD32800 $MA_EQUIV_CURRCTRL_TIME
.
As with activating the previous filter via:
MD32620 $MA_FFW_MODE = 2,
all other machine data are set in consideration of the corresponding elasticity limits of the
machine.
Limitation to stiff machines
Experience has shown that this expenditure is only worthwhile in the case of very stiff
machines, and requires appropriate experience. The elasticities of the machine are often
excited due to the injection of the torque so strongly that the existing vibrations neutralize the
gain in contour accuracy.
In this case, it would be worth trialing the use of dynamic stiffness control as an alternative:
MD32640 $MA_STIFFNESS_CONTROL_ENABLE.
Example of torque feedforward control
Programming sample of a selection of the torque feedforward control with new balancing and
default setting: FFWON and FFWOF are active.
MD32620 $MA_FFW_MODE[X1] = 4
MD32630 $MA_FFW_ACTIVATION_MODE[X1] = 1
FFWON now enables the torque feedforward control in the program
(with all axes of the channel with the same settings as X1);
FFWOF will disable them again.
Machine data:
MD20150 $MC_GCODE_RESET_VALUES[23] (G group initial setting)
can be used to set a default value for FFWON for every program.
MD32620 $MA_FFW_MODE[X1] = 4
MD32630 $MA_FFW_ACTIVATION_MODE[X1] = 0
In this case, the torque feedforward control with X1 is enabled continuously, also in JOG
mode. MD20150 $MC_GCODE_RESET_VALUES[ ], FFWON and FFWOF have no effect on
X1. This can be practical if the machine is only permitted to run with feedforward control,
e.g., for reasons of accuracy, or if you also want to test the feedforward control without a
program during startup.
Basic logic functions: Velocities, Setpoint/Actual Value Systems, Closed-Loop Control (G2)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0
Detailed description
2.5 Optimization of the control
; New mode for torque feedforward control
; FFWON and FFWOF are active.
; New mode for torque feedforward control
; FFWON and FFWOF are active.
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