Siemens sinumerik 840D sl Function Manual page 787

Detailed description
2.1 Functional description
Freely programmable threshold value
A freely programmable velocity threshold value is used to define the setpoint velocity
programmed in the part program block at and above which the switching signal is
activated/deactivated.
If the setpoint velocity programmed in the part program is higher than the programmed
threshold value, the switching signal is deactivated. If the setpoint velocity is at or below the
threshold value, the switching signal is activated. The edge change marks the programmed
end of block position of the previous block as the switching position.
For example the positions X30 when changing edge from N10 to N20 and X70 when
changing edge from N20 to N30 in the following figure:
Figure 2-2
Note
G0 always deactivates the switching signal, regardless of the threshold value.
Calculating switching instants
In order for the switching to be as precise as possible at the switching positions calculated,
the control calculates the positional difference between the actual position of the geometry
axes involved and the switching difference in every position controller cycle.
If the positional difference is less than 1.5 position controller cycles, you convert it into a
temporal difference taking into account the current path velocity and acceleration rate of the
geometry axes.
With the temporal difference specified, a hardware timer is started, which triggers the
switching signal at exactly the instant calculated in advance regardless of the position
controller cycle.
8
Switching signal states with freely programmable threshold value
Special functions: Cycle-Independent Path-Synchronous Signal Output (TE8)
Function Manual, 11/2006, 6FC5397-2BP10-2BA0