Siemens Sinamics S120 Function Manual page 368

Function modules
7.8 Basic positioner
If the axis is already located at the cam, when referencing is started, then traversing to the
reference cam is not executed, but synchronization to the reference zero mark is
immediately started (refer to step 2).
Note
The velocity override is effective during the search for the cam. By changing the encoder
data set, status signal r2684.11 (reference point set) is reset.
The cam switch must be able to delivery both a rising and a falling edge. For a reference
point approach with evaluation of the encoder zero mark, for increasing position actual
values the 0/1 edge is evaluated and for decreasing position actual values, the 1/0 edge.
Inversion of the edge evaluation is not possible at the sensor zero mark.
If the length measuring system has several zero marks which repeat at cyclic intervals (e.g.
incremental, rotary measuring system), you must ensure that the cam is adjusted so that the
same zero mark is always evaluated.
The following factors may impact the behavior of the "reference cam" control signal:
• Switching accuracy and time delay of reference cam switch
• Position controller cycle of drive
• Interpolation cycle of drive
• Temperature sensitivity of machine's mechanical system
Step 2: Synchronizing to the reference zero mark
(encoder zero mark or external zero mark)
Reference cam available (p2607 = 1):
In step 2, the drive accelerates to the velocity specified in p2608 (zero mark approach
velocity) in the direction opposite to that specified using binector input p2604 (reference point
approach start direction). The zero mark is expected at distance p2609 (max. distance to
zero mark). The search for the zero mark is active (status bit r2684.0 = "1" (search for
reference active)) as soon as the drive leaves the cam (p2612 = "0") and is within the
tolerance band for evaluation (p2609 - p2610). If the position of the zero mark is known
(encoder evaluation), the actual position of the drive can be synchronized using the zero
mark. The drive starts the search for reference (see step 3). The distance moved between
the end of the cam and the zero mark is displayed in diagnostics parameter r2680
(difference between the cam - zero mark).
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Function Manual, (FH1), 01/2012, 6SL3097-4AB00-0BP2
Drive functions