Siemens SINUMERIK 840D sl Programming Manual page 591

Software limit switches and transformations
With CALCPOSI(), the positions of the machine axes (MCS) cannot always be uniquely
determined from the positions of the geometry axes (WCS) during various kinematic
transformations (e.g. TRANSMIT) because of ambiguities at certain positions of the traversing
distance. In normal traversing operation, the uniqueness generally results from the history and
the condition that a continuous motion in the WCS must correspond to a continuous motion in
the MCS. Therefore, when monitoring the software limit switches, the machine position at the
time when CALCPOSI() is executed is used to resolve the ambiguity in such cases.
Note
Preprocessing stop
When using CALCPOSI() in conjunction with transformations, it is the sole responsibility of the
user to program a preprocessing stop (STOPRE) with the preprocessing before CALCPOSI()
for the synchronization of the machine axis positions.
Protection zone clearance and conventional protection zones
With conventional protection zones, there is no guarantee that the safety clearance set in
parameter <Limit>[3] is maintained for all protection zones during a traversing movement
on the specified path. It is only guaranteed that no protection zone will be violated when the end
point returned in <Dist> is extended by the safety clearance in the traversing direction.
However, the straight line can pass very close to a protection zone.
Protection zone clearance and collision avoidance protection zones
With collision avoidance protection zones, there is a guarantee that the safety clearance set in
parameter <Limit>[3] is maintained for all protection zones during a traversing movement
on the specified traversing path.
The safety clearance specified in parameter <Limit>[3] only takes effect when the following
applies:
<Limit>[3] > (MD10619 $MN_COLLISION_TOLERANCE)
If bit 4 is set in parameter <TestLim> (calculation of the ongoing traversing direction), then the
direction vector received in <DIST> is only valid when the hundred thousands digit is set in the
function return value (<status>). If a direction such as this cannot be determined, either
because protection zones were violated, or because a transformation is active, then the input
value in <DIST> remains unchanged. An additional error message is not output.
NC programming
Programming Manual, 12/2019, 6FC5398-2EP40-0BA0
Work preparation
3.6 Protection zones
591