Siemens SINUMERIK 840D sl Function Manual page 125

System variables
In the case of online tool length offset, the following system variables are available to the
user:
System variables
$AA_TOFF[ ]
$AA_TOFF_VAL[ ]
$AA_TOFF_LIMIT[ ]
$AA_TOFF_PREP_DIFF[ ]
References: /PGA1/ LHB System Variables
Boundary conditions
The online tool length offset function is an option and is available during "generic 5-axis
transformation" by default and for "orientable tool holders".
If the tool is not perpendicular to the workpiece surface during machining or the contour
contains curvatures whose radius is smaller than the compensation dimension, deviations
compared to the actual offset surface are produced. It is not possible to produce exact offset
surfaces with one tool length compensation alone.
Special Functions
Function Manual, 09/2011, 6FC5397-2BP40-2BA0
Meaning for online tool length offset
Position offset in the tool coordinate system
Integrated position offset in the WCS
Query whether the tool length offset value is close to the limit
Magnitude of the difference between the currently active value of
$AA_TOFF[ ] and the value prepared as the current motion block.
F2: Multi-axis transformations
1.12 Online tool length offset
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