Siemens Sinumerik 840D sl Programming Manual page 202

Motion commands
10.8 Involute interpolation (INVCW, INVCCW)
Supplementary conditions
● Both the starting point and the end point must be outside the area of the basic circle of the
involute (circle with radius CR around the center point specified by I, J, K). If this condition
is not satisfied, an alarm is generated and the program processing is aborted.
● The two options for the programming of the end point (directly via Cartesian coordinates
or indirectly via the specification of an opening angle) are mutually exclusive. Consequently,
only one of the two programming options may be used in a block.
● If the programmed end point does not lie exactly on the involute defined by the starting
point and basic circle, interpolation takes place between the two involutes defined by the
starting and end points (see following figure).
The maximum deviation of the end point is determined by a machine data (→ machine
manufacturer). If the deviation of the programmed end point in the radial direction is greater
than that by the MD, then an alarm is generated and the program processing aborted.
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Programming Manual, 01/2015, 6FC5398-1BP40-5BA2
Fundamentals