Siemens SINUMERIK 840D sl Function Manual page 525

Traversal close to pole
If a tool center point traverses past the pole, the control system automatically reduces the
feedrate and path acceleration rate such that the settings of the machine axes (MD32000
$MA_MAX_AX_VELO[AX*] and MD32300 $MA_ MAX_AX_ACCEL[AX*]) are not exceeded.
The closer the path is to the pole, the greater the reduction in the feedrate.
Tool center point path with corner in pole
A tool center point path which includes a corner in the pole will not only cause a step change
in axis velocities, but also a step change in the rotary axis position. These cannot be reduced
by decelerating.
Figure 7-7
Requirements:
AUTOMATIC mode,
MD24911 $MC_TRANSMIT_POLE_SIDE_FIX_1 = 0
or
MD24951 $MC_TRANSMIT_POLE_SIDE_FIX_2 = 0
The control system inserts a traversing block at the step change point. This block generates
the smallest possible rotation to allow machining of the contour to continue.
Extended Functions
Function Manual, 03/2009, 6FC5397-1BP10-4BA0
Pole traversal
Kinematic Transformation (M1)
TRANSMIT
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