Siemens SIMATIC S5 Manual page 107

IP 266
Actual-value display following a reference point approach
The reference point is set when the position encoder's zero mark signal goes from
0 to 1. At the same time, the drive is decelerated. The drive moves a distance of X
away from the reference point, the value of X depending on the specified
deceleration rate and on reference speed 2. The distance X varies in dependence
on the specified deceleration rates. If the drive is to come to rest exactly at the
reference point, it must be set to this position with the "Increment mode
absolute" following termination of the reference point approach.
V
V
2
a
1
x
Figure 5-18. Deceleration at Different Deceleration Rates
Reproducibility of a reference point
In order to be able to use the traversing programs without any modifications
even after an IP 266 power failure, it must be possible to reproduce the
coordinate zero point exactly. This can be done when you make the next
reference point approach from the same direction.
A change in the direction of reference point approach shifts the coordinate zero
point. You can thus define two different zero points. The distance between them
depends on the "width" of the reference point switch (see Figure 5-19).
Note:
If you replace an encoder, the old reference point cannot be reproduced
because of a change in the position of the zero mark.
EWA 4NEB 812 6057-02
Machine Data, Modes and Traversing Programs
a
3
a , a , a
1 2
a
V :
2
2
Encoder's zero mark
: Deceleration values
3
Reference point approach speed 2
5-35