Siemens SIMATIC FM 453 Manual page 268

Description of Functions
9.6.4 Synchronization
Overview
When using incremental encoders, or stepper motors without encoders, at
switch-on there is an offset, which cannot 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.
Zero Reference
This signals the synchronization point of the axis, in some cases, with refer-
Mark
ence to the reference point switch (see Figure 5-5 "Zero reference mark
selection").
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 zero marker on the tra-
Switch (RPS)
versing path of the axis.
9-68
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 or stepper motors without
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 453.
FM 453 Servo Drive / Step Drive Positioning Module
C79000-G7076-C453-01