Siemens SINUMERIK 840Di Function Manual page 355

C-axis operation
The control system has to switch the spindle into C-axis mode before the "Travel to fixed
stop" function is selected. The PLC does this by activating one of the programmable
terminals E1-D9 (e.g. terminal E1) of the drive actuator.
Selection
The NC detects that the function "travel to fixed stop" is selected via the command
FXS[x]=1 and signals the PLC via the IS "Activate travel to fixed stop" (DB31, ... DBX62.4)
that the function has been selected.
As a result, the PLC activates the unassigned gear stage, in which the torque limitation is
effective, by means of programmable terminals E1 - E9 of the drive actuator. It then switches
the speed controller monitor off (one terminal (E1-E9) to deactivate error F11 of drive
actuator).
If the machine paramete:
MD37060 FIXED_STOP_ACKN_MASK
is set accordingly, then the IS waits for acknowledgment by the PLC in the form of IS
"Activate travel to fixed stop" (DB31, ... DBX3.1) and then the function is started.
Note
This acknowledgment should always be programmed for analog drives for safety reasons,
i.e. so that the motion is not started before the torque has been limited.
The NC then internally sets the torque limit to the value specified via the machine parameter:
MD37070 FIXED_STOP_ANA_TORQUE
(torque limit on fixed stop approach for analog drives).
This value must correspond to the torque limit value set in the actuator.
In addition, the acceleration is automatically reduced in the NC according to the value in the
machine parameter:
MD37070 FIXED_STOP_ANA_TORQUE.
The rotary axis now traverses to the target position at the programmed velocity.
Fixed stop reached
As soon as the Caxis reaches the fixed stop, the axial contour deviation increases.
If the recorded threshold in the machine parameter:
MD37030 FIXED_STOP_THRESHOLD
is exceeded or the IS signal
"Sensor fixed stop" (DB31, ... DBX1.2) is set,
the controller recognizes that the fixed stop has been reached.
The position controller then responds by outputting a speed setpoint corresponding to the
value set in the machine parameter:
MD37070 FIXED_STOP_ANA_TORQUE.
Travel to Fixed Stop (F1)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0
Detailed Description
2.3 Travel to fixed stop with analog drives
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