Siemens SINUMERIK 828D Function Manual page 175

Example:
Limiting velocity characteristics, whereby:
- Override = 50 %, 100 % or 150 %
- Number of LookAhead blocks = 4
- MD20430 $MC_LOOKAH_NUM_OVR_POINTS = 2
- MD20440 $MC_LOOKAH_OVR_POINTS = 1.5, 0.5
- 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, 09/2011, 6FC5397-0BP40-2BA0
B1: Continuous­path Mode, Exact Stop, LookAhead
3.3 Continuous-path mode
175