Siemens SINUMERIK 840D Function Manual page 313

Phase 1: Sequence
Sequence without contact witha reference cam
Once the reference point approaching process is started, the machine axis accelerates to the
reference point shutdown speed set by means of parameter assignment:
MD34040 $MA_REFP_VELO_SEARCH_MARKER (reference point creep velocity)
Once the number of reference marks set by means of parameter assignment has been
crossed, the machine axis is stopped again and the actual value system of the machine axis is
synchronized to the absolute position calculated by the NC.
Sequence when starting from the reference cam
If the machine axis is at the reference cam at the start of the reference point traversing, it
accelerates to the parameterized reference point creep velocity against the parameterized
reference point approach direction:
MD34040 $MA_REFP_VELO_SEARCH_MARKER (reference point creep velocity)
MD34010 $MA_CAM_DIR_IS_MINUS (reference point approach in minus direction)
That ensures that the machine axis does not reach the travel range limit before it has crossed
the parameterized number of reference marks.
Once the number of reference marks set by means of parameter assignment has been
crossed, the machine axis is stopped again and the actual value system of the machine axis is
synchronized to the absolute position calculated by the NC.
Sequence when contact is made with reference cam during referencing
Once the reference point approaching process is started, the machine axis accelerates to the
reference point shutdown speed set by means of parameter assignment:
MD34040 $MA_REFP_VELO_SEARCH_MARKER (reference point creep velocity)
Before the machine axis travels over the parameterized number of reference marks, it makes
contact with the reference cam. It is then reversed and reference mark search is restarted in the
opposite direction.
Once the number of reference marks set by means of parameter assignment has been
crossed, the machine axis is stopped again and the actual value system of the machine axis is
synchronized to the absolute position calculated by the NC.
Plausiblity check of the reference mark distance
An error occurs if, during reference point traversing for two subsequent reference marks, the
NC determines a distance greater than twice the parameterized reference mark distance.
MD34300 $MA_ENC_REFP_MARKER_DIST (reference mark distance)
The machine axis will then traverse in opposite direction at half the parameterized reference
point creep velocity (MD34040) and the search for reference mark is restarted.
If a faulty reference mark distance is detected again, the machine axis is stopped and the
reference point traversing is aborted (alarm 20003 "fault in the measuring system").
Axes and spindles
Function Manual, 06/2019, A5E47437747B AA
10.6 Referencing with distance-coded reference marks
R1: Referencing
313