Siemens SIMATIC FM 351 - Page 19

Basics of Positioning
2-3
FM 351 Positioning Module
C79000-G7076-C351-02
Figure 2-1 shows a possible arrangement of the switching points and differences
for a positioning operation. To simplify the illustration, it is assumed that the change
in actual speed is linear over the distance traveled. The ramps that result, are due
to mechanical inertia or due to the parameter settings for the power unit.
v
rapid
v
creep
Travel
Start
Switchover point
Switch-off point
Switchover
difference
Sw-off
diff.
Target
Actual speed
Figure 2-1 Switching Points and Differences
Figure 2-2 illustrates how the switching ranges can be arranged around the target.
Target
Software end limit switch
0
Switchover difference in travel direction plus
Switch-off difference in travel direction plus
Working range
Target range
Stationary range
1
2
3
4
5
6
7
1
2
3
4
5
6
Switch-off difference in travel direction minus
Switchover difference in travel direction minus
Software start limit switch
7
Figure 2-2 Switching Ranges Around a Target