Siemens SINUMERIK 840D sl Function Manual page 1191

2.12.19 FC 15: POS_AX positioning of linear and rotary axes
Description of Functions
(Do not use for new applications, function is integrated in FC 18 in SW 3.6 and higher.)
FC POS_AX can be used to traverse axes in any operating mode, also from the PLC.
References:
/FB2/ Function Manual, Extended Functions; Positioning Axes (P2)
In order to traverse the NC axes via the PLC, the traversing check must be activated for the
PLC. This can be achieved, for example, by calling FC "POS_AX" with activation of the
"Start" parameter. FC "POS_AX" then requests an axis check by the NC. The NC feeds back
the status of this axis in byte 68 in the associated axis interface DB 31, ... see lists/ (Book 2),
Interface signals power line.
Once the axis check has been completed ("InPos" is True, "Start" changes to zero), it is
switched to a neutral state by FC POS AX. Alternatively, the PLC user program can also
request the check for the PLC prior to calling FC "POS_AX".
By calling this function several times in succession, a better response reaction by the axes
can be obtained as the changeover process in the FC can be omitted.
Activation through the PLC user program is executed in the corresponding axis interface in
byte 8.
After return of the check, the axis can again be programmed by the NC program.
Note
Rotary axes can be positioned by the shortest possible route through the programming of a
negative feed value in absolute programming mode. In incremental mode (parameter "IC" :=
TRUE), the traversing direction can be defined by means of the parameter "Pos" sign:
Positive sign indicates travel in a positive direction
Negative sign indicates travel in a negative direction
After the FC has been called, ACCU1 contains an error statement by the NCK (but not if the
output parameters are assigned to a data block). This is generally the value 0 (signifies: No
error has occurred). The interpretation of other numerical values is shown in the following
table.
FC 15 must be called cyclically until the "Active" signal produces an edge transition from 1 to
0. Only when the "Active" signal has a 0 state can the axis concerned be restarted (the next
start must be delayed by at least one PLC cycle). This also applies when the assignment in
data byte 8 has changed.
The function cannot be aborted by means of parameter "Start", but only by means of the
axial interface signals (e.g., delete distancetogo). The axial interface also returns status
signals of the axis that may need to be evaluated (e.g., exact stop, traverse command).
Basic logic functions: PLC Basic program powerline (P3 pl)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0
Detailed description
2.12 Block descriptions
207