Siemens SINUMERIK 840D Description Of Functions page 175

11.03
3.11 Encoder mounting arrangements
3.11.4 Actual value synchronization (slip for 2-encoder systems with
SW 5.2 and higher)
If a 2-encoder system is used, SI actual values from the NC and the drive drift
Description of function
apart for systems subject to slip because the drive evaluates the motor
measuring system and the NC evaluates the direct measuring system after the
gearbox.
This offset is detected by the crosswise data comparison and a stop response
is triggered. In the case of axis drives with variable coupling factors (slip or belt
drive) until now it was necessary to use a 1-encoder system to prevent the SI
actual values of the NC and drive from drifting apart.
If a direct measuring system was required for position control up until now it
was necessary to use an additional 611digital module for actual value sensing.
To avoid this, a solution using a 2-encoder system with slip has now been
implemented in the software.
In order to define the slip tolerance, the maximum input value is set in
Slip tolerance
MD 36949 $MA_SAFE_SLIP_VELO_TOL. As a result of an action, such as
e.g. maximum acceleration, gear stage change with oscillation, a situation is
created where the actual values drift apart. This value can be taken as nominal
value from the diagnostics display (maximum speed difference), multiplied by a
factor of 1.5 and then entered into MD 36949.
Actual value synchronization is performed in two channels. Machine data
$MA_/$MD_SAFE_SLIP_VELO_TOL is introduced to both channels and the
maximum offset between the NCK and drive actual value entered in it as a
speed. This machine data is converted to an internal format and is used as the
actual value tolerance for the crosswise data comparison. The tolerance value
entered in MD 36949: $MA_SAFE_SLIP_VELO_TOL is not relevant as only the
"new" tolerance value is taken into account in the crosswise data comparison.
For the actual value synchronization, both channels correct their SI actual
position to half the derived actual value difference. Please note that the two SI
actual positions no longer display the correct absolute position. The NC actual
position and the two SI actual positions are different.
Both the load-side actual value and the motor-side actual position are
corrected. This ensures that the corrected actual value remains active in
subsequent monitoring cycles until the next synchronization.
Actual value synchronization is performed in the crosswise data comparison
cycle. Actual value synchronization is also performed when a crosswise data
comparison of the SI actual position outputs an error. The advantage here is
that Alarms 27001/300911 can be acknowledged and do not re-appear
immediately.
Actual value synchronization is also performed after "referencing" and with
"parking axis".
The latest calculated and maximum SI speed difference since the last reset is
displayed in the axis-specific service display for diagnostics purposes.
© Siemens AG 2003 All Rights Reserved
SINUMERIK 840D/SIMODRIVE 611 digital SINUMERIK Safety Integrated (FBSI) - Edition 11.03
Note
Actual value synchronization is not performed until an actual value difference
between the two channels of 2 µ m or 2 millidegrees is detected per SI
monitoring cycle.
3 Safety-Related Functions
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