Siemens SINUMERIK 840D sl Function Manual page 360

Compensations (K3)
Backlash compensation
5.3 Backlash compensation
Mechanical backlash
During power transmission between a moving machine part and its drive (e.g. ball screw),
there is normally a small amount of backlash because setting mechanical parts so that they
are completely free of backlash would result in too much wear and tear on the machine.
Thus, backlash (play) can occur between the machine component and the measuring
system.
Effect
In the case of axes/spindles with indirect measuring systems, mechanical backlash results in
corruption of the traverse path, causing an axis, for example, to travel too much or too little
by the amount of the backlash when the direction of movement is reversed (see the following
2 diagrams).
Compensation
To compensate for backlash, the axis-specific actual value is corrected by the amount of
backlash every time the axis/spindle changes direction.
This quantity can be entered for each axis/spindle at the commissioning phase in the
following machine data:
MD32450 $MA_BACKLASH
If a second measuring system is available, the relevant backlash values must be entered for
each of the two measuring systems.
The backlash can be weighted by a factor as a parameter set function.
This weighting factor is set to between 0.01 and 100.0 in the following machine data:
MD32452 $MA_BACKLASH_FACTOR (backlash weighting factor)
The factor default setting is 1.0.
Application: e.g. compensation of gear-stage-dependent backlash.
Activation
Backlash compensation is always active in all operating modes after reference point
approach.
Position display
The normal actual-value and setpoint position displays ignore the compensation values and
show the position values of an ideal machine.
Display the compensation values
The compensation value applying to the current actual position is output as the total
compensation calculated from "LEC" and "backlash compensation" in the "Service axes"
display in the "Diagnosis" operating area.
360
Function Manual, 03/2009, 6FC5397-1BP10-4BA0
Extended Functions