Siemens SINUMERIK 840D sl Function Manual page 431

05.08
Note
The error at a reference point approach is no more than one revolution of the
motor (difference between two zero marks). This offset is usually not critical for the
mechanical parts of the machine. If problems arise with the traversing limits
because of the type of reference point approach, then for example, set the offset
values in MD 34080 /34090 to non–critical values.
Alarms 27000/C01797 "Axis not safely referenced" are still present and indicate
that the functions "safe limit positions" and "safe cams" are not active in this state.
For example, if "safe limit positions" is being used as a substitute for
hardware limit switches, then it is important to note that at this time, the
safe limit positions are not functional!
After completion of the reference point approach, the axis goes into the
"referenced" status. However, because of the zero mark offset between the
encoders, the reference position still has to be calibrated, i.e. the position
reference with respect to the mechanical system must be re–established. The
system is calibrated after measuring the difference – usually in MD 34080
REFP_MOVE_DIST or 34090 REFP_MOVE_DIST_CORR.
4. After the reference point has been re–calibrated, the reference point approach
must be re–initiated. The axis changes over into the "referenced'" state. At this
time, the reference point value is taken over as the safe actual value for the
axis and drive.
5. Finally, with the JOG/REF machine mode active, on the HMI the "user agree-
ment" softkey must be pressed and the user agreement for the axis involved
must be reset. Alarms 27000/C01797 disappear and the functions "safe limit
position" and "safe cams" are safely active again.
Comments about 2–encoder systems
Case A
1st measuring system: Incremental motor measuring system
2nd measuring system: Absolute direct measuring system
The 2nd position measuring system (DBAx 1.5 = 0, DBAx 1.6 =1) is selected via
the axis interface as the active measuring system.
In this case, motor replacement is straightforward because the NC reference point
position is only supplied with values from the 2nd measuring system (DMS).
Case B
1st measuring system: Absolute motor measuring system
2nd measuring system: Incremental direct measuring system
The 1st position measuring system (DBAx1.5 = 1, DBX 1.6 =0) is selected as the
active measuring system via the axis interface when the system boots. This is for
monitoring purposes. A changeover is then made to the 2nd position measuring
system (DBAx 1.5 = 0, DBX 1.6 =1).
© Siemens AG 2008 All Rights Reserved
SINUMERIK 840D sl/SINAMICS S120 SINUMERIK Safety Integrated (FBSI sl) – 05.2008 Edition
Commissioning
9.6 Replacing a motor or encoder
9-431