Siemens SINUMERIK 840Di Function Manual page 1894

Detailed Description
2.1 Various interface signals and functions (A2)
DB31, ...
DBX1.4 Follow-up mode
Signal state 0 Follow-up mode is not selected (hold).
When "controller enable" is removed the previous position setpoint is kept in the control.
If the axis/spindle is moved out of position during this time a following error occurs between the
position setpoint and the position actual value. This position difference is reduced to zero
immediately by issuing "controller enable" so that the previous setpoint position is restored. Then,
all the other axis movements start from the setpoint position valid before "controller enable" was
removed.
When the position control is switched in again the axis may make a speed setpoint jump.
Zero speed monitoring or clamping monitoring is still active.
In order to disable (switch-out) the zero speed
monitoring, when clamping an axis, the interface signal:
DB31, ... DBX2.3 (clamping operation running)
should be set.
In the "holding state", the interface signal:
DB31, ... DBX61.3 (follow-up mode active)
is set to a 0 signal.
Special cases, If the drive controller enable is withdrawn inside the control due to faults, then the following
errors, .... should be carefully observed:
Before an NC start, after the queued alarms have been successfully deleted
(i.e. inside the control, the controller enable is re-issued), then "holding" should be activated:
DB31, ... DBX1.4 (follow-up mode) = 0
Otherwise, for an NC start and selected follow-up mode, the traversing distance of the previous NC
block would not be executed due to the internal delete distance to go.
Notice:
When changing over from the "follow-up" state to the "hold" state and in the control mode (a
controller enable is issued), a delete distance-to-go command is activated in the control. As a
consequence, for example, an NC block - in which only this axis is traversed - is ended directly.
Corresponding to .... DB31, ... DBX2.1 (controller enable)
DB31, ... DBX2.3 (clamping in progress)
DB31, ... DBX61.3 (follow-up mode active)
2-30
NC/PLC Interface Signals (Z1)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0