Siemens SINUMERIK 828D Function Manual page 1225

R1: Reference point approach
15.6 Referencing with distance­coded reference marks
Phase 1: Sequence
Sequence without touching a reference cam
Once reference point approach is started, the machine axis accelerates to the assigned reference point creep
velocity:
MD34040 $MA_REFP_VELO_SEARCH_MARKER (reference point creep velocity)
Once the parameterized number of reference marks 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 parameterized number of reference marks 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 reference point approach is started, the machine axis accelerates to the assigned reference point creep
velocity:
MD34040 $MA_REFP_VELO_SEARCH_MARKER (reference point creep velocity)
Before the machine axis travels over the parameterized number of reference marks, it touches the reference
cam. It is then reversed and reference mark search is restarted in the opposite direction.
Once the parameterized number of reference marks 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").
Basic Functions
1225
Function Manual, 09/2011, 6FC5397-0BP40-2BA0