Turning, Milling, Nibbling
Function Manual, 11/2012, 6FC5397-1CP10-5BA0
59
Continuous Path Mode, Exact Stop and LookAhead
(B1)
3
3.1 Brief description
For continuous path control, the CNC processes a part program block by block. Only when
the functions of the current block have been completed is the next block processed. Various
requirements with respect to machining or positioning require different block change criteria.
There are two ways that the path axes can behave at block boundaries.
The first way is called "exact stop" and means that all path axes must have reached the set
target position depending on an exact-stop criterion before the next block change is initiated.
To be able to fulfill the criterion, the path axes must reduce the path velocity at every block
change which, however, delays the block change.
The second way is called "continuouspath mode" and it attempts to avoid deceleration of the
path velocity at the block boundary in order to change to the next block with as little change
of path velocity as possible.
"LookAhead" is a procedure in continuous path mode that achieves velocity control with
LookAhead over several NC part program blocks.
3.2 General
Machine axes that are related interpolatively must have the same dynamic response, i.e. the
same following error at any given velocity.
The term path axes refers to all machining axes which are controlled by the interpolator
calculating the path points in such a manner that:
● All the axes involved start at the same time
● All the axes involved travel with the correct velocity ratios
● All the axes reach the programmed target position at the same time
The acceleration rates of the individual axes may vary depending on the path, e.g. circular
path.
Path axes can be geometry axes and special axes (e.g. workpiece turning axes that are
involved in the workpiece machining process).
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