Siemens SINUMERIK 840D Function Manual page 884

S3: Synchronous spindle
19.4 Special features
Read offsets of following spindle
The current offset always changes when a differential speed is programmed. The current offset
can be read at the setpoint end with $AA_COUP_OFFS[Sn] and at the actual value end with
$VA_COUP_OFFS[Sn].
The last offset programmed returns the variable $P_COUP_OFFS[Sn].
Display differential speed
The programmed difference component is displayed as the speed setpoint for the programmed
differential speed (in our example, corresponds to 100 rpm).
The actual speed refers to the motor speed. In the example, the actual speed is 500 rev/min *
(-1) + 100 rpm = -400 rev/min.
IS, NC to the PLC
Following spindle in speed-controlled operation
The IS "Spindle in setpoint range" (DB31, ... DBX83.5) is set for the following spindle by the NC
if the programmed speed difference (see previous example, N26 with M2=3 S2=100) is
reached. If a differential speed is programmed and not enabled by the PLC, this VDI interface
signal is not set.
Even if a differential speed has been programmed, the following spindle remains under position
control if this is required by the coupling.
Note
The axial VDI interface signal NC → PLC IS "Superimposed motion" (DB31, ... DBX98.4) is set
when the differential speed programming creates setpoints in addition to the coupling
setpoints.
Actual direction of rotation clockwise (DB31, ... DBX83.7)
IS "Actual direction of rotation clockwise" (DB31, ... DBX83.7) refers to the resulting motor
direction.
IS PLC to the NC
Influence on following spindle via PLC interface
The effect of the axial VDI interface signals on the following spindle with differential speed in
speed control mode is described below:
Delete distance to go / Spindle Reset (DB31, ... DBX2.2)
The programmed differential speed and direction can be terminated by IS "Delete distance-to-
go / Spindle Reset" (DB31, ... DBX2.2). To delete the programmed speed only, it is possible to
set IS "Delete S value" (DB31, ... DBX16.7).
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Axes and spindles
Function Manual, 06/2019, A5E47437747B AA