6 – 126 HEIDENHAIN Technical Manual TNC 426, TNC 430
Feedback control
with velocity
semifeedforward
MP1396.x allows the operator to switch to velocity semifeedforward control.
Normally, work will be carried out using velocity feedforward. For example,
velocity semifeedforward is activated by an OEM cycle before roughing, in
order to permit a higher following error and thereby a higher velocity,
combined with a lowered accuracy, in order to traverse corners.
Before finishing, another OEM cycle can be used to switch back to velocity
feedforward, in order to finish with the highest accuracy possible.
In order to use velocity semifeedforward, a factor must be entered for every
axis in MP1396.x, where values toward 0 control the following error more, and
values toward 1 control the velocity feedforward more. The factor can be
overwritten with FN17: SYSWRITE ID600. However, the factor from
MP1396.x becomes valid again at the end of a program (MP7300 = 1) and
whenever a new NC program is selected.
As soon as a factor between 0.001 and 0.999 has been entered in MP1396.x,
the k
V
factor from MP1516.x becomes effective.
The values for position monitoring are interpolated according to the factor in
MP1396.x between the values for servo lag (MP1710.x, MP1720.x) and the
values for velocity feedforward control (MP1410.x, MP1420.x).
Note
For axes that are interpolated with each other, the k
v
factors must be equal.
In this case the smaller k
V
factor determines the input value for these axes.
Feedback control with
following error (servo lag)
Feedback control with velocity
semifeedforward
Feedback control with
velocity feedforward
MP1391 bit x = 0
MP1392 bit x = 0
MP1396.x = nonfunctional
MP1391 bit x = 1
MP1392 bit x = 1
MP1396.x = 0.001 MP1396.x = 0.999
MP1391 bit x = 1
MP1392 bit x = 1
MP1396.x = 1
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