Siemens SINUMERIK 840C - Manual (Page 1080)

09.95 12 Functional Descriptions
12.30.2 Difference to synchronous spindle/GI
12.30.2 Difference to synchronous spindle/GI
Unlike the synchronous spindle or GI, master/slave operation is no substitute for a mechanical
link but can only support torque distribution where a mechanical coupling exists. Master/slave
operation is not advisable where there is no fixed mechanical coupling because then there can
be no torque distribution over a common mechanical link.
While master/slave operation can provide a speed and/or torque coupling of several drives, GI
and synchronous spindle operation are used to implement positional coupling of several drives.
The functions GI and synchronous spindle provide a position reference between the leading
and the following drives and monitor it. Without compensation controllers, the leading and
following axes involved are each responsible for executing motions that do not violate the
contour.
If master/slave operation is activated (leading axis LA = master, following axis FA = slave),
the position reference between the leading and the following axes is lost if they are not
mechanically coupled.
There is no position difference control, only coupling at the speed/torque level.
12.30.3 Function description
The control structure of master/slave operation is shown in the following diagram: the speed
setpoint N
set
of the master is output directly to the slave. For clarity's sake, only one slave is
shown. If there are several slave drives they all receive the speed setpoint of the master.
Cascading (where a master in speed setpoint coupling is itself a slave) is not permissible. Any
existing position control of the slaves is automatically deactivated. When the speed setpoint of
the master is transferred, internal normalization to the same load speed is performed. This
makes different motor speeds of master and slave possible.
In addition, it is possible to use a torque compensation controller for better torque distribution
(especially during acceleration). However, this requires a SIMODRIVE 611D because with
analog drives, the torque setpoints are not available in the position control.
The outputs and inputs of the torque compensation controller can be connected as required. In
the simplest case, as shown in the diagram, the torque setpoints of the master and slave are
used as input variables (if there are several slaves: star-shaped configuration) and the output is
injected with reversed polarity as an additional speed setpoint to the master and to the slave.
If there are several slave drives it is possible to use the torque setpoint of a further slave as
an input instead of the master torque setpoint. This slave is then the master of the torque
compensation control (chain structure).
© Siemens AG 1992 All Rights Reserved 6FC5197- AA50 12–305
SINUMERIK 840C (IA)