Siemens SINUMERIK 840D sl Function Manual page 433

Supplementary conditions
If the encoder to be used for position control is connected directly at the tool, the gear stage
change only affects the physical quantities at the speed interface between the NC and the
drive of the motor/load gear. The internal parameter sets are not changed.
Reference point and position reference
In the case of gear changes, it is not possible to make a statement about the effect of the
reference point or machine position reference on the encoder scaling. In such cases, the
control partially cancels the status "Axis referenced/synchronized".
If the position reference to the machine, tool, etc., has been lost, it must first be restored
through appropriate adjustment or referencing of the lost reference point. This is especially
important for the functions Travel to fixed stop, Referencing to Bero, Cam and Zero marker.
Caution
The control cannot detect all possible situations that can lead to loss of the machine position
reference. Therefore, it is the responsibility of the commissioning engineer or user to initiate
explicit referencing of zero marker synchronization in such cases.
Note
To facilitate re-referencing without a disruptive RESET,
machine data:
MD34080 $MA_REFP_MOVE_DIST
and
MD34090 $MA_REFP_MOVE_DIST_CORR
should be reset to NewConfig efficacy.
For more information about referencing, please see:
References:
/FB1/ Function Manual, Basic Functions; Reference Point Approach (R1)
Basic logic functions: Velocities, Setpoint/Actual Value Systems, Closed-Loop Control (G2)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0
Detailed description
2.3 Setpoint /actual-value system
45