Siemens Sinamics S120 Function Manual page 367

The velocity override set is only effective during the search for the reference cam (step 1).
This ensures that the "cam end" and "zero mark" positions are always overrun at the same
speed. If signal propagation delays arise during switching processes, this ensures that the
offset caused during establishment of position is the same in each referencing process.
Axes that only have one zero mark over their complete traversing or modulo range are
designated with parameter p2607 = 0 (no reference cam present). After starting the
referencing process, synchronization to the reference zero marks is started straight away
(see step 2) for these axes.
Step 1: travel to reference cam
If there is no reference cam present (p2607 = 0), go to step 2.
When the referencing process is started, the drive accelerates at maximum acceleration
(p2572) to the reference cam approach velocity (p2605). The direction of the approach is
determined by the signal of binector input p2604 (search for reference start direction).
When the reference cam is reached, this is communicated to the drive using the signal at
binector input p2612 (reference cam); the drive then brakes down to standstill with the
maximum deceleration (p2573).
If a signal at binector input p2613 (reversing cam, MINUS) or at binector input p2614
(reversing cam, PLUS) is detected during reference point approach, the search direction is
reversed.
If the minus reversing cam is approached in the positive direction of travel or the plus
reversing cam in the negative direction of travel, fault F07499 (EPOS: reversing cam
approached with the incorrect traversing direction) is output. In this case, the wiring of the
reversing cams (BI: p2613, BI: p2614) or the direction of approach to the reversing cam must
be checked.
The reversing cams are low active. If both reversing cams are active (p2613 = "0" and p2614
= "0"), the drive remains stationary. As soon as the reference cam is found, then
synchronization to the reference zero mark is immediately started (refer to step 2).
If the axis leaves its start position and travels the distance defined in parameter p2606 (max.
distance to reference cam) heading towards the reference cam without actually reaching the
reference cam, the drive remains stationary and fault F07458 (reference cam not found) is
issued.
Drive functions
Function Manual, (FH1), 01/2012, 6SL3097-4AB00-0BP2
Function modules
7.8 Basic positioner
365