Siemens SINUMERIK 840D sl Function Manual page 196

Detailed description
2.4 LookAhead
2.4 LookAhead
Function
LookAhead is a procedure in continuouspath mode (G64, G641) that achieves velocity
control with LookAhead over several NC part program blocks beyond the current block.
If the program blocks only contain very small paths, a velocity per block is achieved that
permits deceleration of the axes at the block end point without violating acceleration limits.
This means that the programmed velocity was not actually reached although a sufficient
number of prepared blocks with virtually tangential path transitions was available.
With the LookAhead function it is possible to plan the acceleration and deceleration phase
with approximately tangential path transitions in order to achieve a higher feedrate with
shorter distances. Deceleration to velocity limits is possible with LookAhead such that
violation of the acceleration and velocity limit is prevented.
Figure 2-12
LookAhead takes plannable velocity limits into consideration such as:
• Exact stop at block end
• Velocity limit in the block
• Acceleration limit in the block
• Velocity limit on block transition
• Synchronization with block change at block transition.
44
Comparison of velocity response with exact stop G60 and continuouspath mode G64
with LookAhead with short traversing paths.
Basic logic functions: Continuouspath Mode, Exact Stop, LookAhead (B1)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0