Siemens SIMATIC S5 Manual page 103

IP 266
6. An edge change from 1 to 0 in the signal from the reference point switch sets
an internal Enable signal. When this signal is set, the IP 266 waits (while the
drive is moving at reference speed 2) for the next zero mark pulse from the
encoder. This signal is present only once during each encoder revolution. A
change of the zero mark signal from 0 to 1 sets the reference point. The
reference point coordinate specified in the machine data is assigned to this
position. At the same time, the IP 266 decelerates the drive until it reaches
zero speed. The actual value is detected and displayed.
When the drive is at zero speed, the actual value is lower (i. e. more negative)
than the reference point coordinate.
A
N H
A A
V
for
Start
V
rev
Encoder's zero mark
H /H : Hardware limit switches start/end
A E
V : Reference speed 1
1
V : Reference speed 2
2
Figure 5-14. Principle of the Reference Point Approach in Example A
EWA 4NEB 812 6057-02
Machine Data, Modes and Traversing Programs
B
REF
R
V 1
V 2
R: Reference point
Position of the drive:
A: Prior to the reference point approach
B: After the reference point approach
Forward
H N
E E
s
5-31