Siemens SINUMERIK 840D sl Function Manual page 205

– MD20400 $MC_LOOKAH_USE_VELO_NEXT_BLOCK = 1
A combination of both procedures (determination of following block velocity and determination
of override points) can be used to calculate the velocity profiles and is generally advisable
because the preset machine data for these functions already takes the widest range of override-
dependent velocity limits into account.
Note
If neither of the procedures has been activated, the setpoint velocity is always applied in the
current block.
Note
Plannable velocity limits restrict override-specific velocity limits.
Relief factor with block cycle problems
Block cycle problems are encountered in cases where the traversing distances of the NC
blocks to be processed are so short that the LookAhead function has to reduce the machine
velocity to provide enough time for block processing. In this situation, constant braking and
acceleration of path motion may occur.
Velocity fluctuations of this type can be dampened by specifying a relief factor:
MD20450 $MC_LOOKAH_RELIEVE_BLOCK_CYCLE (relieving factor for the block cycle
time)
Basic Functions
Function Manual, 01/2015, 6FC5397-0BP40-5BA2
B1: Continuous-path mode, Exact stop, Look Ahead
4.3 Continuous-path mode
205