
B-65270EN/05 4.SERVO FUNCTION DETAILS
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4.18.9 Cautions for Controlling One Axis with Two Motors
(1) Tandem control and synchronous control (position tandem control)
selection criteria
Two control methods are supported to enable the control of one axis
using two motors: tandem control and synchronous control. The
(simple) synchronous control method controls the position of the
master axis and slave axis by using the same command. Position
control is exercised separately on each of the master axis and slave
axis. Control exercised when the master axis and slave axis are
allocated on the same DSP is particularly referred to as position
tandem control.
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. Tandem control is used in the following cases and when
back-feed is enabled:
• Two motors are used because sufficient torque cannot be
produced by one motor alone.
• Two small motors have an advantage over one large motor in
terms of inertia.
• The full preload function is used to suppress backlash.
In other cases, position tandem control (synchronous control) is
usually used.
Position tandem control is also used when two motors are used to
improve the precision degraded by a machine position difference.
Sub-
motor
Reducer
Main
motor
Reducer
Fig. 4.18.9 (a) Example of tandem control (machine system supporting back-feed)
Sub-
motor
Main
motor
Sub-
motor
Main
motor
Fig. 4.18.9 (b) Example of synchronous control Fig. 4.18.9 (c) Example of tandem control
(to suppress the effect of a position difference) (when a torque two times greater is required)