Siemens SINAMICS S120 Function Manual page 242

Function modules
7.8 Closed-loop position control
parameters p2504 and p2505. Position tracking can be activated with rotary axes (modulo)
and linear axes.
For linear axes, the virtual multiturn resolution (p2721) is preset with p0421 and extended by
6 bits for multiturn information (max. overflows 31 positive/negative)
Position tracking for the load gearing can only be activated once for each motor data set
MDS.
The load position actual value in r2723 (must be requested via GnSTW.13) is limited to 2
places. When position tracking (p2720.0 = 1) is switched on, the load position actual value
r2723 comprises the following position information:
● Encoder pulses per revolution (p0408)
● Fine resolution per revolution (p0419)
● Virtual number of stored revolutions of a rotary absolute encoder (p2721)
● Load gear ratio (p2504/p2505)
● Measuring gearbox ratio (p0433/p0432), if p0411.0 = 1
Example: Absolute encoder can count 8 encoder revolutions (p0421 = 8)
Note
Load gear problems and solutions, see example in chapter Position tracking -> Measuring
gearbox.
Example of position area extension
With absolute encoders without position tracking, it must be ensured that the traversing
range is 0 smaller than half the encoder range, because beyond this range, no unique
reference remains after switching on and off (see description on parameter p2507). This
traversing range can be extended using the virtual multiturn (p2721).
For reasons of presentation, an absolute encoder was selected in the figure below that can
represent 8 encoder revolutions (p412 = 8). The parameter p2721 is pre-assigned a value of
512. To simplify the presentation, p2721=24 as well as a setting of p2504 = p2505 =1 (gear
factor = 1) were selected.
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Function Manual, (FH1), 07/2007 Edition, 6SL3097-2AB00-0BP4
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Drive Functions