Siemens SINUMERIK 840D sl Function Manual page 203

unnecessarily. For this reason, the required number of blocks is derived from the velocity which
is calculated from the following multiplication:
● Programmed velocity * MD12100 $MN_OVR_FACTOR_LIMIT_BIN
(when using a binary-coded feedrate override switch)
● Programmed velocity * MD12030 $MN_OVR_FACTOR_FEEDRATE[30]
(when using a gray-coded feedrate override switch)
The value for MD12100 or the 31st override value for MD12030 defines the dynamic response
reserves which the velocity control provides for when the path feed is overshot.
Note
The 31st override value for MD12030 should correspond to the highest override factor which
is actually used.
Note
The number of blocks considered by the LookAhead function is limited by the possible number
of NC blocks in the IPO buffer.
Velocity profiles
In addition to the fixed, plannable velocity limitations, LookAhead can also take account of the
programmed velocity. This makes it possible to achieve a lower velocity by applying
LookAhead beyond the current block.
● Determination of the following block velocity
One possible velocity profile contains the determination of the following block velocity.
Using information from the current and the following NC block, a velocity profile is calculated
from which, in turn, the required velocity reduction for the current override is derived.
The calculated maximum value of the velocity profile is limited by the maximum path velocity.
With this function it is possible to initiate a speed reduction in the current block taking
override into account such that the lower velocity of the following block can be achieved. If
the reduction in velocity takes longer than the travel time of the current block, the velocity
is further reduced in the following block. Velocity control is only ever considered for the
following block.
The function is activated via the machine data:
MD20400 $MC_LOOKAH_USE_VELO_NEXT_BLOCK
Value
TRUE
FALSE
Basic Functions
Function Manual, 01/2015, 6FC5397-0BP40-5BA2
Meaning
Function active
Function not active
B1: Continuous-path mode, Exact stop, Look Ahead
4.3 Continuous-path mode
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