Siemens sinumerik 840D sl Function Manual page 238

Detailed description
2.1 Coupled motion
Figure 2-1
Multiple couplings
Up to two leading axes can be assigned to one coupled motion axis. The traversing
movement of the coupled motion axis then results from the sum of the traversing movements
of the leading axes.
Dependent coupled motion axis
A coupled motion axis is a "dependent coupled motion axis" when it traverses as a result of
a leading axis movement.
Independent coupled motion axis
A coupled motion axis is an "independent coupled motion axis" when it traverses as a result
of a direct traverse instruction. The traversing movement resulting from the coupled motion
axis is then the sum total of the traversing movements as a "dependent" and an
"independent" coupled motion axis.
Coupled motion axis as leading axis
A coupled motion axis can at the same time be the leading axis of a further coupled axis
grouping.
Coordinate system
Coupled axis motion is always executed in the base coordinate system (BCS).
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Application Example: Two-sided machining
Special functions: Axis Couplings and ESR (M3)
Function Manual, 11/2006, 6FC5397-2BP10-2BA0