
B-63782EN/01 NC FUNCTIONS 20.AXIS CONTROL FUNCTIONS
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20.7 SYNCHRONOUS CONTROL
When one axis is driven by two servo motors as in the case of a large
gantry machine, a command for one axis can drive two motors
synchronously. Moreover, for synchronization error compensation,
feedback information from each motor allows a positional difference
(synchronization error) between the two motors to be detected. If a
synchronization error beyond a set value occurs, an alarm is issued to
stop movement along the axes.
If synchronization error compensation is not applied, the synchronous
control function can be used to apply automatic compensation that will
eliminate any displacement in the machine coordinates, such as that
which occurs when an emergency stop is canceled.
An external signal can also be used to turn synchronization on and off.
In this case, however, neither synchronization error compensation nor
synchronization error check can be performed.
20.8 TANDEM CONTROL
When enough torque for driving a large table cannot be produced by
only one motor, two motors can be used for movement along a single
axis.
Positioning is performed by the main motor only. The sub-motor is
used only to produce torque. With this tandem control function, the
torque produced can be doubled.
Table
Ball screw
Main motor
Sub-motor
In general, the NC regards tandem control as being performed for one
axis. However, for servo parameter management and servo alarm
monitoring, tandem control is regarded as being performed for two
axes.