Siemens SINUMERIK 840D sl Function Manual page 157

Brief Description
Continuous-path mode
In continuous-path mode, the NC attempts to keep the programmed path velocity as
constant as possible. In particular, deceleration of the path axes at the block limits of the part
program is to be avoided.
Exact stop mode
In exact stop traversing mode, all axes involved in the traversing motion (except axes of
modal traversing modes) are decelerated at the end of each block until they come to a
standstill. The transition to the next block occurs only when all axes involved in the traversing
motion have reached their programmed target position with subject to the selected exact
stop criterion.
Exact stop
Exact stop is a state of a machine axis that refers to the position difference relative to its
setpoint position at the end of the traversing motion. The machine axis reaches the "exact
stop" state, as soon as its following error is less than the specified position difference (exact
stop limit).
LookAhead
"LookAhead" is a function for optimizing the continuous path mode.
Smooth machining of workpieces is necessary to ensure a high-quality surface finish. For
this reason, path velocity variations should be avoided during machining whenever possible.
Without "LookAhead", the NC only takes into consideration the block immediately following
the current block to determine the possible path velocity. If the following block contains only
a short path, the NC must reduce the path velocity (decelerate in the current block) to be
able to stop in time at the end of the next block, if necessary.
When the NC "looks ahead" over an parameterizable number of blocks following the current
block, a much higher path velocity can be attained under certain circumstances because the
NC now has more blocks and more path available for calculation.
This results in the following advantages:
• Machining with higher path velocities on average
• Improved surface quality by avoiding deceleration and acceleration processes
Basic logic functions: Continuouspath Mode, Exact Stop, LookAhead (B1)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0
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