Siemens SINUMERIK 840Di Function Manual page 23

Fig. 2-3
Drives with analog setpoint interface
A drive with an analog setpoint interface is capable of traversing the machine axis with an
external setpoint. If "follow-up mode" is set for the machine axis, the actual position
continues to be acquired. Once follow-up mode has been cancelled, homing is not required.
The following procedure is recommended:
1. Activate follow-up mode:
2. Deactivate external servo enable and external speed setpoint
3. Deactivate external servo enable and cancel external speed setpoint
4. Cancel follow-up mode
Various NC/PLC Interface Signals and Functions (A2)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0
Trajectory for clamping and "follow-up"
DB31, ... DBX2.1 = 0 (servo enable)
DB31, ... DBX1.4 = 1 (follow-up mode) (in the same or previous OB1 cycle)
=> Axis/spindle is in follow-up mode
=> Axis/spindle moves with external setpoint
=> NC continues to detect the actual position and corrects the setpoint position to the
actual position
=> Axis/spindle stops
DB31, ... DBX2.1 = 1 (servo enable)
DB31, ... DBX1.4 = 0 (follow-up mode)
=> NC synchronizes to current actual position. The next traversing movement begins at
this position.
Note
"Follow-up mode" does not have to be canceled because it only has an effect in
combination with "servo enable".
Detailed Description
2.1 NC/PLC interface signals
2-11