
4. SERVO FUNCTION DETAILS B-65150E/04
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4.17.10 Notes on Tandem Control
(1) Tandem control and synchronous control selection criteria
Two control methods are supported to enable the control of one axis
using two motors: tandem control and synchronous control. The
synchronous control method controls the position of the master axis
and slave axis by using the same command. If a position feedback
difference occurs between the two motors, control is applied by
correcting the slave axis. The servo system applies position control
separately to the master and slave axes.
The tandem control method exercises position control over the main
axis only; this method exercises torque control over the sub-axis only.
(For clarity, the terms master and slave are used for synchronous
control, while main and sub are used for tandem control.)
When building a machine system, select a suitable control method,
paying careful attention to the differences between the control
methods.
In general, apply the following guideline:
When the machine system is rigid or supports back-feed, select
tandem control.
When the machine system exhibits effects such as twisting, or
does not support back-feed, select synchronous control (for
example, when a gantry type machine or worm wheel is used).
Machine system rigid?
Yes
No
Back-feed possible?
Yes
No
Synchronous control Tandem control
Main
motor
Reducer
Sub-
motor
Reducer
Flow of selection
Fig. 4.17.10 (a) Flow of selection Fig. 4.17.10 (c) Example of tandem control
(machine system supporting back-feed)
Sub-
motor
Main
motor
Sub-
motor
Main
motor
Fig. 4.17.10 (b) Example of synchronous control Fig. 4.17.10 (d) Example of tandem control
(machine system not supporting back-feed) (rigid machine system)