Siemens SINUMERIK 840D sl Programming Manual page 299

Corners are also traversed at a constant velocity. In order to minimize the contour error, the
velocity is reduced according to an acceleration limit and an overload factor.
Note
The extent of smoothing the contour transitions depends on the feedrate and the overload
factor. The overload factor can be set in MD32310 $MA_MAX_ACCEL_OVL_FACTOR.
Setting MD20490 $MC_IGNORE_OVL_FACTOR_FOR_ADIS means that block transitions will
always be rounded irrespective of the set overload factor.
The following points should be noted in order to prevent an undesired stop in path motion (relief
cutting):
● Auxiliary functions, which are enabled after the end of the motion or before the next motion,
interrupt the continuous path mode (exception: fast auxiliary functions).
● Positioning axes always traverse according to the exact stop principle, positioning window
fine (as for G601). If an NC block has to wait for positioning axes, continuous-path mode is
interrupted on the path axes.
However, intermediate blocks containing only comments, calculation blocks or subprogram
calls do not affect continuous-path mode.
Note
If FGROUP does not contain all the path axes, there is often a step change in the velocity at
block transitions for those axes excluded from FGROUP; the control limits this change in
velocity to the permissible values set in MD32300 $MA_MAX_AX_ACCEL and
MD32310 $MA_MAX_ACCEL_OVL_FACTOR. This braking operation can be avoided through
the application of a smoothing function, which smooths the specific positional interrelationship
between the path axes.
LookAhead predictive velocity control
In continuous-path mode, the control automatically determines the velocity control for several
NC blocks in advance. This enables acceleration and deceleration across multiple blocks with
almost tangential transitions.
Look Ahead is particularly suitable for the machining of motion 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.
NC programming
Programming Manual, 12/2019, 6FC5398-2EP40-0BA0
Fundamentals
2.11 Path action
299