Siemens sinumerik 840D sl Function Manual page 66

Detailed description
2.7 Restrictions for kinematics and interpolation
Figure 2-15
End point within the circle
If the end point is within the circle, the first axis comes to a standstill and the second axis
moves until the difference between target and actual orientation is minimal. However, since
the first rotary axis does not move, the orientation will generally deviate from the
programmed value (see previous Figure). However, the programmed orientation can at least
be reached exactly if the first rotary axis happens to be positioned correctly.
Note
In the previous Figure the resulting path is a straight line because the position of the first
rotary axis is constant on that path. This representation is always correct, irrespective of the
angle between the two rotary axes. The orientation vector only moves in a plane, however, if
the two rotary axes and the basic orientation are all mutually perpendicular. In all other
cases, the orientation vector describes the outside of a cone.
End point outside the circle
If the orientation interpolation describes a path through the circle, while the end point is
outside the circle, the end point is approached with axis interpolation. This applies in
particular if the interpolation starting point is located inside the circle. Path deviations from
the programmed setpoint orientation are thus unavoidable.
60
Generic 5-axis transformation; end point of orientation inside tolerance circle.
Special functions: 3-Axis to 5-Axis Transformation (F2)
Function Manual, 11/2006, 6FC5397-2BP10-2BA0