Siemens SINUMERIK 840Di sl Programming Manual page 214

Path Action
5.3 Continuous-path mode (G64, G641, G642, G643, G644)
Look Ahead speed control
In continuous-path mode with G64 or G641, the control automatically detects the velocity
control in advance for several NC blocks. This enables acceleration and deceleration across
multiple blocks with almost tangential transitions.
Look Ahead is particularly suitable for the machining of movement sequences comprising
short traverse paths with high path feedrates.
The number of NC blocks included in the Look Ahead calculation can be defined in machine
data.
Note
Look Ahead across more than one block is an option.
Continuous-path mode in rapid traverse G0
One of the functions G60/G9 or G64/G641 must also be specified for rapid traverse.
Otherwise, the default in the machine data is used.
By setting MD 20490: IGNORE_OVL_FACTOR_FOR_ADIS results in block transitions being
smoothed irrespective of the programmed overload factor.
214
Programming Manual, 11/2006, 6FC5398-1BP10-2BA0
Fundamentals