Siemens SINUMERIK 840D Description Of Functions page 472

8 Application examples
8.7 Replacing a motor or encoder
4.
5.
Comments about Case A
2-encoder systems
In this case, motor replacement is straightforward because the NC reference
point position is supplied with values exclusively from the 2nd measuring
system (DMS). This means that the measuring system does not have to be re-
calibrated.
Case B
In this case, the motor must be replaced carefully observing the Description,
motor with absolute value encoder. This is because it is necessary to re-
calibrate the absolute value encoder. When re-calibrating the system, we
recommend to permanently select the 1st positioning measuring system and to
only traverse the axis using the motor measuring system.
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SINUMERIK 840D/SIMODRIVE 611 digital SINUMERIK Safety Integrated (FBSI) - Edition 11.03
Note
The error at a reference point approach is no more then one motor
rotation (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 27000/300950 "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 to substitute 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.
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.
Finally, if the JOG/REF machine mode is active on the MMC, the "user
agreement" softkey must be pressed and the user agreement for the axis
involved must be reset. Alarms 27000/300950 disappear and the functions
"Safe limit positions" and "Safe cams" are safely active again
1st measuring system: Incremental motor measuring system
2nd measuring system: Absolute direct measuring system
The 2nd position measuring system ( (DBX 1.5 = 0, DBX 1.6 =1)
is selected as the active measuring system via the axis interface
1st measuring system: Absolute motor measuring system
2nd measuring system: Incremental direct measuring system
The 1st position measuring system (DBX 1.5 = 1, DBX 1.6 =0)
is selected as the active measuring system via the
axis interface when the system runs-up. This is for monitoring
purposes. A changeover is then made to the 2nd position
measuring system (DBX 1.5 = 0, DBX 1.6 =1) .
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11.03