Yaskawa SGDS Sigma III Servo Amplifier - Manual (Page 71)

3 SERVOPACK Specifications and Dimensional Drawings
3.5.3 Load Moment of Inertia
3-14
Calculate the torque from the motor current using servomotor torque constant × motor current (effective value).
The following figure shows the motor torque and motor speed timing chart.
3.5.3 Load Moment of Inertia
The size of the load moment of inertia (J
L
) allowable when using a servomotor depends on motor capacity and is
limited to within 5 to 30 times the moment of inertia of each servomotor (J
M
). This value is provided strictly as a
guideline and results may vary depending on servomotor drive conditions.
An overvoltage alarm is likely to occur during deceleration if the load moment of inertia exceeds the allowable
load moment of inertia. SERVOPACKs with a built-in regenerative resistor may generate a regeneration overload
alarm. Take one of the following steps if this occurs.
• Reduce the torque limit.
• Reduce the deceleration rate.
• Reduce the maximum motor speed.
• Install an externally mounted regenerative resistor if the alarm cannot be cleared. Contact your Yaskawa
Application Engineering Department.
Regenerative resistors are not built into 200 V SERVOPACKs for 50 W to 400 W or 100 V SERVOPACKs for
50 W to 400 W. The following figures show the tentative relationship between the load moment of inertia and
motor speed using an example with a load moment of inertia 10 to 30 times the load moment of inertia at the
motor shaft.
External regenerative resistors are required when this condition is exceeded or if the allowable loss capacity (W)
of the built-in regenerative resistor is exceeded due to regenerative drive conditions when a regenerative resistor
is already built in.
Motor torque
(current amplitude)
Motor speed
tr tf
N
M
T PM
TL
Time
Time
T
PM