Detailed description
2.5 Optimization of the control
Basic logic functions: Velocities, Setpoint/Actual Value Systems, Closed-Loop Control (G2)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0
71
2.5.2 Position controller position setpoint filter: New balancing filter
For speed and torque feedforward control
Application
With feedforward control active, the position setpoint is sent through a socalled balancing
filter before it reaches the controller itself. It is thus possible to feedforward control the speed
setpoint at 100%, without resulting in overshoots when positioning.
Functionality
Until now, it was possible to compensate the negative effects of the balancing filter (a low
pass with settable time constant), which has remained unchanged since SW 1 and which
has admitted instead of an overshoot also undesired undershoots of some 10 micrometers,
as follows:
• Setting a compromise of overshoots and undershoots
• Setting the positioning slightly overshooting and reducing the amplitude of these
overshoots by way of position setpoint signal smoothing and jerk limitation
• Setting a speed controller with reference model instead of PI behavior
(only possible with 840D)
• Setting the filter time to zero and setting the feedforward control factor to a value less
than 100%
• Sacrificing the feedforward control and bringing the machine to a very high position
controller gain using dynamic stiffness control.
This measure requires a stiff machine.
With SW 5 and higher, a second, improved balancing filter is therefore available.
The existing filter is still installed and is active with the same function when transferring
existing archives (e.g., in the case of upgrades).
Advantages
The new balancing filter provides the following improvements:
• An axis with feedforward control has a considerably lower inclination to undershoots
when positioning.
• Achieves a higher accuracy at bent contours (can be measured, e.g., using the circularity
test) and can be set more easily.
• A part of the setting is carried out by the control system automatically.
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