Siemens SIMATIC S7-300 Manual page 243

9.6.3 Synchronizing the encoders
Overview
When using incremental encoders, at switch-on there is an offset, which can-
not be determined in advance, between the internal position value in
the FM and the mechanical position of the axis. To establish the position ref-
erence, the value internal to the FM must be synchronized with the real posi-
tion value of the axis. Synchronization is performed by taking over a position
value at a known point of the axis.
When using absolute encoders (SSI), at switch-on there is already a defined
relationship between the position value internal to the FM and the mechani-
cal position of the axis. This reference can be adjusted by setting an absolute
encoder alignment value (see Section 9.3.9, Setting the reference point).
Absolute encoder is the compensation value for numerical alignment of the internal FM posi-
alignment tion value.
Reference point
is an operating mode used to position the axis at the reference point.
approach
Reference point is a fixed point on the axis. It is:
Reference point
Difference in distance between the synchronization point and the reference
offset
point.
The reference-point shift serves:
Reference point The reference point switch selects the synchronizing (encoder) zero marker
switch (RPS) on the traversing path of the axis.
Synchronization is a defined point on the traversing path of the axis. It is defined by the me-
point chanical position of a reference-point switch or in association with a cyclic
zero mark of an incremental encoder.
FM 354 Servo Drive Positioning Module
The target coordinate in the Reference-Point Approach mode
Removed from the synchronization point by the amount of the reference-
point shift, in axes with incremental encoders.
for numerical measuring-system readjustment when an encoder is
changed
as a displacement reserve to brake the drive if the synchronization point is
overshot.
It is also the signal encoder for a speed reduction before the synchroniza-
tion point is reached.
It is connected to a digital input of the FM 354.
Description of Functions
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