Siemens Sinumerik 840D sl Programming Manual page 534

Axis couplings
9.3 Axial leading value coupling (LEADON, LEADOF)
Actual value and setpoint coupling
Setpoint coupling provides better synchronization of the leading and following axis than actual
value coupling and is therefore set by default.
Setpoint coupling is only possible if the leading and following axis are interpolated by the
same NCU. With an external leading axis, the following axis can only be coupled to the
leading axis via the actual values.
A switchover can be programmed via setting data $SA_LEAD_TYPE
You must always switch between the actual-value and setpoint coupling when the following
axis stops. It is only possible to resynchronize after switchover when the axis is motionless.
Application
You cannot read the actual values without error during large machine vibrations. If you use
master value coupling in press transfer, it might be necessary to switchover from actual-value
coupling to setpoint coupling in the work steps with the greatest vibrations.
Master value simulation with setpoint coupling
Via machine data, you can disconnect the interpolator for the leading axis from the servo. In
this way you can generate setpoints for setpoint coupling without actually moving the leading
axis.
Master values generated from a setpoint link can be read from the following variables so that
they can be used, for example, in synchronized actions:
- $AA_LEAD_P
- $AA_LEAD_V
534
Master value position
Master value velocity
Programming Manual, 02/2011, 6FC5398-2BP40-1BA0
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