B1: Continuous­path Mode, Exact Stop, Lookahead; Brief Description - Siemens SINUMERIK 828D Function Manual

B1: Continuous­path Mode, Exact Stop, LookAhead
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Brief Description

Exact stop or 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.
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.
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 the traversing block immediately following the current traversing block into consideration when determining
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 a configurable number of traversing blocks following the current traversing
block, a much higher path velocity can be attained under certain circumstances because the NC now has
considerably more traversing 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
Smoothing the path velocity
"Smoothing the path velocity" is a function especially for applications (such as high speed milling in mold and die
production) that require an extremely steady path velocity. Deceleration and acceleration processes that would
cause high-frequency excitations of machine resonances are avoided with the "Smoothing the path velocity"
function.
This results in the following advantages:
• Improved surface quality and machining time by avoiding excitation of machine resonances.
• Constant profile of path velocity and cutting rates by avoiding "unnecessary" acceleration processes, i.e.
acceleration processes that do not greatly improve the program run time.
Basic Functions
Function Manual 09/2011, 6FC5397-0BP40-2BA0
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