Exact Stop - Siemens SINUMERIK 802D sl Function Manual

Continuous Path Mode, Exact Stop and LookAhead (B1)

3.3 Exact stop

Velocity for zero cycle blocks
The term zero cycle is applied to blocks whose path length is shorter than the distance that
can be traveled on the basis of the programmed set feedrate and the interpolator cycle
(time). For reasons of precision the velocity is reduced until at least one interpolator cycle is
required for the distance. The velocity is then equal to or less than the quotient of the path
length of the block and the IPO cycle.
Stop for synchronization
Regardless of whether exact stop or continuous path mode is selected, the block change
can be delayed by synchronization processes which can stop the path axes. In exact stop
mode, the path axes are stopped at the end of the current block. In continuous path mode,
the path axes are stopped at the next block end point at which they can be decelerated
without violating their deceleration limits. The following synchronization processes cause
axes to stop.
● PLC acknowledgment
● Missing following blocks
● Emptying of the buffer
Stopping because of synchronization does not cause contour violations. However, stopping
is undesirable, especially in continuous path mode because it can cause backing off.
3.3 Exact stop
With the exact stop function (G60, G9), all the path axes must reach the programmed block
end point. Only when all path axes have reached the exact stop criterion is the block change
performed. The velocity at the block transition is practically zero.
That is:
● The path axes at the block end point are decelerated almost to rest without overshoot.
● The delay for fulfilling the exact stop criterion prolongs the machining time.
● The delay for fulfilling the exact stop criterion can cause backing off.
60
If acknowledgment by the PLC is required for an auxiliary function that is output before or
after the end of motion, the axes stop at the end of the block.
If following blocks are conditioned too slowly (e.g. "External processing") the axes stop at
that last possible block boundary.
If the NC part program requests that the run-in be synchronized with the main run (empty
the buffer, e.g. STOPRE), this involves an implicit blockrelated velocity reduction or exact
stop.
Turning, Milling, Nibbling
Function Manual, 11/2012, 6FC5397-1CP10-5BA0