
4.SERVO FUNCTION DETAILS B-65270EN/05
- 332 -
Required
torque
+preload
−preload
Torque command
Required torque =
(drive torque)/2
+preload
Torque limit
Sub-motor
Main motor
(Drive torque)/2 = (main + sub)/2
− Torque limit
Fig. 4.18.1 (b) Relationship between required torque and torque
command for each motor
1980 (FS15i)
Preload value (PRLOAD)
2087 (FS30i, 16i)
Set this parameter for the main- and sub-axes.
CAUTION
Set a value that is as small as possible but greater
than the static friction torque. A set preload torque
is applied to each motor at all times. So, set a
value that does not exceed the rated static torque
of each motor. As a guideline, specify a value
equal to one-third of the rated static torque.
As shown in Fig. 4.18.11 (a) in Subsec. 4.18.11, a
preload torque is added in any case. So, set the
preload torque directions as follows:
• When the rotation directions of the main axis
and sub-axis are the same: Different signs
• When the rotation directions of the main axis
and sub-axis are different: Same sign
Example of setting For the αiF4/4000 (Servo amplifier αi SV 40)
When a preload torque of 1 N⋅m is to be applied, the torque constant is
0.52 N⋅m/Arms according to the specifications of the servo motor.
So, the peak value is 0.368 N⋅m/Ap. The torque is converted to a
current value as follows:
1/0.368 = 2.72 Ap.
The amplifier limit is 40 Ap, so that the value to be set is:
2.72/40 × 7282 = 495
So, set 495 for the main axis, and -495 for the sub-axis (when the
directions of rotation of the two motors are the same).