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Chapter 2 Installation and Storage
2-12
Revision June 2010
(2) With Load
When there is an external load torque, servo motor is in reverse rotation when external
load greater than motor torque. Servo motor is usually in forward rotation and the motor
torque output direction is the same as the rotation direction. However, there is still some
special condition. If the motor output torque is in the reverse direction of rotation, the
servo motor is also in the reverse direction of rotation. The external power is input into
the servo drive through servo motor. The figure below is an example. The users can see
the motor is in forward rotation at constant speed when a sudden external load torque
change and great power is transmitted to regenerative resistor rapidly.
Motor Rotation Speed
External Load Torque
Motor Output Torque
Reverse
Rotation
Reverse
Rotation
Forward
Rotation
Forward
Rotation
External load torque in reverse direction: TL x Wr TL : External load torque
For the safety, we strongly recommend the users should select the proper resistance value
according to the load.
For example:
When external load torque is a +70% rated torque and rotation speed reaches 3000r/min,
if using 400W servo drive (rated torque: 1.27Nt-m), then the users need to connect a
external regenerative resistor which power is 2 x (0.7 x 1.27) x (3000 x 2 x
π / 60) = 560W,
40 Ω .