Siemens SINUMERIK 840D Function Manual page 269

Instead, the actual position of the leading axis is specified as the target position and is
approached in the uncoupled state.
Note
For the leading axis, automatic synchronization can be locked using the following NC/PLC
interface signal:
DB31, ... DBX29.5 = 1 (no automatic synchronization process)
This always makes sense if no axis enabling signal has yet been issued for the axes. In this
case, the synchronization process should also be started explicitly with the NC/PLC interface
signal:
DB31, ... DBX29.4 = 1 (start gantry synchronization process)
Loss of synchronization
The gantry grouping becomes desynchronized as a result of:
● "Tracking" the gantry axes
● Loss of the reference position of a gantry axis, e.g. by "Parking" (no measuring system
active)
● Re-referencing of gantry axis
● The gantry grouping is opened (dissolved) by:
MD37140 $MA_GANTRY_BREAK_UP = 0 (invalidate gantry axis grouping)
The corresponding NC/PLC interface signal is reset:
● DB31, ... DBX60.4 or DBX60.5 == 0 (referenced/synchronized 1 or 2 respectively)
● DB31, ... DBX 101.5 == 0 (gantry grouping is synchronized)
If, in operation, gantry grouping synchronization is lost due to a fault, then synchronization can
be restarted using the NC/PLC interface signal:
DB31, ... DBX29.4 == 1 (start gantry synchronization process)
Requirement is that the following applies to all axes of the gantry grouping:
DB31, ... DBX60.4 or DBX60.5 = 1 (referenced/synchronized 1 or 2 respectively)
In this case, the synchronizing axes traverse the current actual position of the leading axis in
the decoupled state.
If, when the gantry grouping is traversing, the signal "Emergency Stop" (DB10, DBX56.2) is set
and again reset, and the gantry axes have drifted apart less than the standstill tolerance of the
synchronous axes, then these are automatically resynchronized. Automatic synchronization
can be suppressed using the NC/PLC interface signal for the leading axis:
DB31, ... DBX29.5 = 1 (no automatic synchronization process)
Axes and spindles
Function Manual, 06/2019, A5E47437747B AA
9.3 Referencing and synchronization of gantry axes
G1: Gantry axes
269