July 2013 7.11 Commissioning linear and torque motors 1139
Finding the
feedforward values
Automatic adjustment of feedforward values in TNCopt often fails for linear
motors. The reason is the often extreme ripple of the nominal current due to
the pronounced torque ripple. But even if the automatic adjustment does not
work, TNCopt can still be used for manual adjustment.
The proposed curves are sometimes not the optimum for linear motors. It can
therefore be better for manual adjustment if you increase the traverse paths
and the feed rate (by approximately doubling it, for example) and adjust the
acceleration in MP1060 to about 1 m/s
2
to 2 m/s
2
.
If the integral current should approach the nominal current only very slowly,
reduce the k
V
factor and increase the I factor. However, these changes should
be undone after determining the feedforward values.
The image below shows an adjustment of a highly critical linear motor with a
distinctly inhomogeneous magnetic field. This can be seen from the nominal
current, which fluctuates very strongly depending on the position:
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