Siemens SIMATIC FM 453 Manual page 183

7.3.12 Activation of Software Limit Switches
Overview
Move the axis carefully to the end positions defined for normal machining.
Enter these position actual values into the machine data MD21/MD22 as soft-
ware limit switches, and activate them.
Note
If you change the reference-point coordinate later or use Set reference point
for the absolute encoder, you must redefine the positioning values of the
software limit switches.
If you do not need the software limit switches, the input limits –10
MSR must be entered in MD21/MD22 (for default values, see Table 5-5).
7.3.13 Activation of Drift Compensation
Overview If you want to use the drift compensation function in addition to the offset
compensation already described in Section 7.3.2, activate it in the machine
data (please see the function description in Section 9.7, position control).
7.3.14 Activation of Backlash Compensation
Overview
With indirect position measurement (for example, with an encoder on the
motor) the free play of mechanical transmission elements during positioning
may cause a position deviation of a machine part (such as a lathe saddle) that
is to be positioned but does not lie in the measured-value feedback loop. As a
rule, a piece of the distance will be "missing" after a reversal of direction.
This backlash amount can be determined as a mean at various axis positions,
and entered in the machine data MD30 and MD31.
You can use the following flow chart to determine backlash and activate
backlash compensation.
FM 453 Servo Drive / Step Drive Positioning Module
C79000-G7076-C453-01
Starting up the FM 453
9 9
and 10
7-41