Siemens Sinumerik 840D sl Programming Manual page 468

Path traversing behavior
8.1 Tangential control (TANG, TANGON, TANGOF, TLIFT, TANGDEL)
Limit angle using the working area limitation
For path movements, which oscillate back and forth, the tangent jumps through 180° at the
turning point on the path and the orientation of the following axis changes accordingly. This
behavior is generally inappropriate: The return movement should be traversed at the same
negative offset angle as the approach movement:
To do this, limit the working area of the following axis (G25, G26). The working area limit must
be active at the instant of path reversal (WALIMON). If the offset angle lies outside the working
area limit, an attempt is made to return to the permissible working area with the negative
offset angle.
Insert intermediate block at contour corners (TLIFT)
At one corner of the contour the tangent changes and thus the setpoint position of the
following axis. The axis normally tries to compensate this step change at its maximum
possible velocity. However, this causes a deviation from the desired tangential position over a
certain distance on the contour after the corner. If such a deviation is unacceptable for
technological reasons, the instruction TLIFT can be used to force the control to stop at the
corner and to rotate the following axis to the new tangent direction in an automatically
generated intermediate block.
The path axis is used for turning if the following axis has been used once as the path axis. A
maximum axis velocity of the following axis can be achieved with function
TFGREF[<axis>]=0.001.
If the follow-up axis was not previously traversed as a path axis it is now traversed as a
positioning axis. The velocity is then dependent on the positioning velocity in the machine
data.
The axis is rotated at its maximum possible velocity.
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Programming Manual, 02/2011, 6FC5398-2BP40-1BA0
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